VALGUS ANGLE ASSESSMENT BEFORE TOTAL KNEE

LITHUANIAN UNIVERSITY OF HEALTH SCIENCES MEDICAL ACADEMY

Justinas Stučinskas

THE EFFECT OF LONG-STANDING RADIOGRAPHS AND FEMORAL

VALGUS ANGLE ASSESSMENT BEFORE TOTAL KNEE

ARTHROPLASTY ON IMPLANTATION ACCURACY AND KNEE FUNCTION

Doctoral Disertation Biomedical Sciences,

Medicine (06 B)

Kaunas, 2015

1

Disertation has been prepared at the Department of Orthopaedics and traumatology of Lithuanian University of Health Sciences, Medical Academy during the period of 2010–2015.

Scientific Supervisor

Prof. Dr. Šarūnas Tarasevičius (Lithuanian University of Health Scien- ces, Medical Academy, Biomedical Sciences, Medicine – 06B)

Disertation is defended at the Medical Research Council of the Lithuanian University of Health Sciences, Medical Academy.

Chairperson

Prof. Dr. Antanas Gulbinas (Lithuanian University of Health Sciences, Medical Academy, Biomedical Sciences, Medicine – 06B)

Members:

Prof. Dr. Saulius Lukoševičius (Lithuanian University of Health Scien- ces, Medical Academy, Biomedical Sciences, Medicine – 06B)

Assoc. Prof. Dr. Annette W-Dahl (Lund University (Sweden), Biome- dical Sciences, Medicine – 06B)

Prof. Dr. Jolanta Dadonienė (Vilnius University, Biomedical Sciences, Medicine – 06B)

Prof. Dr. Habil. Alfonsas Vainoras (Lithuanian University of Health Sciences, Medical Academy, Biomedical Sciences, Nursing – 10B)

Dissertation will be defended at the open session of the Medical Research Council of Lithuanian University of Health Sciences on the 3rd of July 2015 at 10 a.m. in the Great auditorium of the Hospital of Lithuanian University of Health Sciences Kauno Klinikos.

Address: Eivenių g. 2, LT-50009 Kaunas, Lithuania.

2

LIETUVOS SVEIKATOS MOKSLŲ UNIVERSITETAS MEDICINOS AKADEMIJA

Justinas Stučinskas

VISĄ KOJĄ APIMANČIŲ

RENTGENOGRAMŲ IR ŠLAUNIKAULIO VALGUS KAMPO MATAVIMO PRIEŠ KELIO SĄNARIO ENDOPROTEZAVIMĄ REIKŠMĖ IMPLANTACIJOS TIKSLUMUI

IR KELIO FUNKCIJAI

Daktaro disertacija Biomedicinos mokslai,

Medicina (06B)

Kaunas, 2015

3

Disertacija rengta 2010–2015 metais Lietuvos sveikatos mokslų universitete Medicinos akademijos Ortopedijos traumatologijos klinikoje.

Mokslinis vadovas

Prof. dr. Šarūnas Tarasevičius (Lietuvos sveikatos mokslų universitetas, Medicinos akademija, biomedicinos mokslai, medicina – 06B)

Disertacija ginama Lietuvos sveikatos mokslų universiteto Medicinos mokslo krypties taryboje:

Pirmininkas

Prof. dr. Antanas Gulbinas (Lietuvos sveikatos mokslų universitetas, Medicinos akademija, biomedicinos mokslai, medicina – 06B)

Nariai:

Prof. dr. Saulius Lukoševičius (Lietuvos sveikatos mokslų universitetas, Medicinos akademija, biomedicinos mokslai, medicina – 06B)

Doc. dr. Annette W-Dahl (Lundo universitetas (Švedija), biomedicinos mokslai, medicina – 06B)

Prof. dr. Jolanta Dadonienė (Vilniaus universitetas, biomedicinos moks- lai, medicina – 06B)

Prof. habil. dr. Alfonsas Vainoras (Lietuvos sveikatos mokslų univer- sitetas, Medicinos akademija, biomedicinos mokslai, slauga – 10B)

Disertacija ginama viešame Medicinos mokslo krypties tarybos posėdyje 2015 m. liepos 3 d. 10 val. Lietuvos sveikatos mokslų universiteto ligoninės Kauno klinikų Didžiojoje auditorijoje.

Adresas: Eivenių g. 2, LT-50009 Kaunas, Lietuva.

4

CONTENT

ABBREVIATIONS ... 7

INTRODUCTION ... 8

Scientific novelty ... 9

Practical and theoretical significance ... 10

1. THE AIM AND OBJECTIVES OF THE STUDY ... 11

2. LITERATURE REVIEW ... 12

2.1. Anatomy and biomechanics of the knee ... 12

2.2. Alignment of the lower extremity ... 14

2.3. Total knee arthroplasty ... 17

2.4. TKA surgery ... 18

2.5. Standard and measured bone cuts techniques ... 20

2.6. TKA accuracy ... 23

2.7. The effect of coronal malalignment after TKA ... 25

2.7.1. Implant survival ... 25

2.7.2. Functional outcome ... 26

2.7.3. Muscle strength ... 29

2.8. The effect of sagittal and rotational malalignment after TKA ... 30

2.9. Summary of the literature review ... 31

3. PATIENTS AND METHODS ... 33

3.1. Study population ... 33

3.1.1. Inclusion criteria ... 33

3.1.2. Exclusion criteria ... 33

3.1.3. Allocation to the groups ... 34

3.2. Patients’ characteristics ... 35

3.3. Preoperative assessment ... 35

3.3.1. Preoperative clinical examination ... 35

3.3.2. Preoperative radiological assessment ... 36

3.3.3. Preoperative muscle strength assessment ... 38

3.4. Surgery and postoperative care ... 40

3.5. Postoperative assessment ... 41

3.6. I study part (the effect of the detailed preoperative radiological assessment of the knee to the operative TKA accuracy) ... 43

3.7. II study part (TKA alignment effect on knee joint function and the muscle strength) ... 45

3.8. Statistical analysis ... 46

5

4. RESULTS ... 48

4.1. The effect of the detailed preoperative radiological assessment of the knee to the operative TKA accuracy ... 48

4.2. TKA alignment effect on knee joint function and the muscle strength ... 54

5. DISCUSSION ... 64

5.1. I study part (the effect of the detailed preoperative radiological assessment of the knee to the operative TKA accuracy) ... 64

5.2. II study part (TKA alignment effect on knee joint function and the muscle strength) ... 68

CONCLUSIONS ... 73

PRACTICAL RECOMMENDATIONS ... 74

SUMMARY IN LITHUANIAN ... 75

REFERENCES ... 87

LIST OF PUBLICATIONS ... 102

PUBLICATIONS ... 108

ACCESSORIES ... 137

ACKNOWLEDGMENTS ... 139

CURRICULUM VITAE ... 140

6

ABBREVIATIONS

OA – osteoarthritis

TKA – total knee arthroplasty

SKAR – Swedish Knee Arthroplasty Register MAA – mechanical axis alignment

LDFA – lateral distal femoral angle MPTA – medial proximal tibal angle FVA – femoral valgus angle

MRI – magnetic resonance imaging CT – computed tomography ROM – range of motion KSS – Knee Society Score OKS – Oxford Knee Score BMI – body mass index SD – standard deviation CI – confidence intervals

7

INTRODUCTION

Hip and knee osteoarthritis (OA) is among the leading causes of disability and is a major problem for health care and public health systems [91]. A lifetime risk of symptomatic knee OA was estimated 45% of the United States adults [122]. Failed conservative treatments of painful knee OA is traditionally treated with total knee arthroplasty (TKA). With increasing life expectancy and prevalence of OA, knee pain and associated disability will have an increasing demand for surgery [85]. Kurtz et al. used the United States National Hospital Discharge Survey for 1990 through 2002 to study rates of primary TKA [83]. They stated that primary TKA increased from 51 to 136 per 100,000 inhabitants. From 2000 to 2006, the TKA rate overall in the United States increased 58% [92] and further, the number of primary TKA is estimated to increase by 673% before 2030 [84].

According Swedish Knee Arthroplasty Register (SKAR) since the start of registration there has been an exponential increase in TKA [96]. In 2012 there were 140 TKA per 100,000 inhabitants in Sweden [96] as compared to much lower numbers in Lithuania: 65 TKA per 100,000 inhabitants [93, 94]. Therefore, aging of population, increasing life expectancy, broadening the indications for TKA in younger age groups will affect growing rate of TKA worldwide.

One of the pioneers of knee replacement surgery was Leslie Gordon Percival Shiers [152], who designed a stainless steel hinge prosthesis inserted in the marrow cavities of the femur ant tibiae and published his results in 1954. Modern TKA surgery began in the early 1970s [41, 42, 137]

when bone cement (polymethylmethacrylate) was use for implant fixation [47]. Over the last 40 years, the procedure has been refined but further investigated for the improvement insuring the long lasting results.

TKA is a bony and soft-tissue procedure with a great focus on the alignment of the components. It is generally accepted that postoperative alignment of the lower limb should be straight and within 3° of a neutral mechanical axis [1, 11, 27, 28, 38, 39, 45, 69, 140, 141, 173]. Clinical, simulator, finite element and cadaver studies [11, 27, 28, 38, 39, 45, 56, 62, 65, 69, 86, 140, 141, 154, 173] show that neutral mechanical axis correlates with longevity of the TKA. This affected the development of the ins- truments (patient specific instruments) or technologies (computer-assisted surgery, navigation) that should let to achieve neutral mechanical axis [170].

However, these methods are related with increased surgery costs, learning curve and methods related complications, thus is not widely used in clinical practice. Another option for achieving better TKA alignment may be a

8

detailed preoperative radiological assessment [31]. The positioning of the TKA components is determined by bone cuts, which in conventional technique are performed using intramedullary/extramedullary guides. These guides can be settled in a standardised manner for all TKA patients or adjusting individually according to the preoperative radiological assessment.

However, we were not able to find randomized studies investigating the effect of preoperative radiological measurements on postoperative mecha- nical alignment and on the positioning accuracy of femoral or tibial components.

Besides neutral TKA alignment, pain relieve and improved function are other important goals of successful TKA. However, the effect of accurate postoperative alignment on TKA function is controversial [21, 39, 53, 57, 75, 79, 99, 100, 103, 104, 107, 110, 139, 159, 169]. There are studies, which found that correct neutral TKA alignment had superior functional outcomes [21, 57, 75, 99, 100, 104, 139]. While other studies have not been able to correlate malalignment with inferior functional outcomes [53, 79, 103, 110, 159].

Besides the alignment, the muscle strength of the leg is correlated with the knee function after TKA. Patients with greater preoperative muscle strength have been reported to have faster recovery and better functional outcome after TKA [68, 115]. It is plausible that failure to restore the me- chanical axis restoration might result in inferior muscle function. This was observed in healthy males, where Sogabe et al. [157] reported the differ- rences of cross-sectional areas in quadriceps muscles with different knee alignments. They suggested that knees with varus or valgus deformation should have inferior muscle function as compared to normally aligned knees. However, we could not find studies investigating the muscle strength after TKA in relation to component alignment and mechanical axis resto- ration. Thus, it is of importance to investigate the accuracy of TKA im- plantation and its relation to postoperative function and the muscle strength.

Scientific novelty

To our knowledge, this is the first randomized study, which investigates and compares standard and detailed preoperative radiological assessment in respect to mechanical axis and TKA components alignment. We found only one study, which analysed whether the use of preoperative long-standing radiographs improved the postoperative mechanical alignment as compared to standard radiographs [112]. The authors reported that performance of preoperative long-standing radiographs did not significantly help to obtain a neutral mechanical axis. They did not analyse individual component

9

positioning. However we assume that it is important to investigate all parameters, such as accuracy of mechanical axis and individual components positioning, because malalignment of them may increases revision rates in the long-term [81, 140].

The accuracy of TKA alignment may play a role in functional outcome [21, 57, 75, 99, 100, 104, 139], but it is still unclear does it affect muscle strength postoperatively. We could not found reports in the literature investigating if the malalignment of mechanical axis and/or individual components in TKA will affect the kinematic properties of muscles surrounding the knee joint.

Practical and theoretical significance

It is plausible that detailed preoperative radiological assessment will reduce the number of alignment outliers thus prolonging TKA survival and ensure better functional results. This could provide economical efforts in reducing the number of revisions after TKA. The study will answer the scientific questions and will allow creating practical recommendations for surgeons performing TKA surgery.

10

1. THE AIM AND OBJECTIVES OF THE STUDY

The aim of the study: To investigate if the detailed preoperative radio- logical assessment of the knee will affect the operative accuracy as compared to standard and correlate the accuracy with the postoperative function and muscle strength after total knee arthroplasty.

Objectives of the study:

1. To investigate if preoperative measurements of the femoral valgus angle on the long-standing hip-knee-ankle radiographs will affect the mechanical alignment in TKA.

2. To investigate if preoperative measurements of the femoral valgus angle on the long-standing hip-knee-ankle radiographs will affect the individual component positions in TKA.

3. To investigate if coronal malalignment of mechanical axis and/or individual components will affect function one year after TKA sur- gery.

4. To investigate if coronal malalignment of the mechanical axis and/or individual components will affect the knee muscle strength one year after TKA surgery.

11

2. LITERATURE REVIEW

2.1. Anatomy and biomechanics of the knee

The knee joint is the largest and one of the most important joints in human body. It is involved in many important daily activities such as walking, running, stairs climbing, sitting and standing. It is not only a hinge, that allows flexion and extension of the joint, but also small rotational movement in flexion is possible [10, 16, 66, 162].

The knee joint is one of the most complex joints, which is formed from three bones: femur, tibia and patella (Fig. 2.1.1.).

Fig. 2.1.1. The anatomy of the knee with the everted patella [43].

Distal femur and proximal tibia are asymmetrical-three dimensional structures. Distal end of the femur has two convex, rounded condyles, which contacts two concave condyles of the proximal end of the tibia. Medial femoral condyle has greater radius and is larger thus, lies lower than lateral one. What is opposite on the tibial side – lateral tibial condyle is situated higher than medial. The bones are covered by layers of cartilage and within are surrounded by medial and lateral menisci [10, 16, 66, 162]. The patella lies on the anterior surface of the femur and acts as the mechanical lever.

The patellar ligament connects it to the tuberosity of the tibia inferiorly and superiorly quadriceps tendon bridges it to the largest human muscle quadriceps [16, 66, 162]. Although the main function of the quadriceps group is to extend the knee (with a secondary function to flex the hip),

12

another physiologic action is to decelerate flexion of the knee during the early stance phase of gait [66]. The quadriceps muscle group consists of four parts that share a common quadriceps tendon: the rectus femoris, the vastus lateralis and medialis, and the vastus intermedius (Fig. 2.1.2.).

Retinaculum and synovium attaching to the patella and its tendon pass around the knee medially and laterally to the distal femur and proximal tibia [10]. Lateral and medial patellar retinaculm with fibers from the vasti lateralis and medialis muscles holds the patella in the femoral patellar surface (intercondylar groove) [16, 66, 162]. The patellar tendon forms a septum between the anterior intercondylar notch of the femur and the fat pad [66].

Fig. 2.1.2. The muscles of the knee (anterior and posterior view)[25].

On the medial aspect, the most superficial muscular structure is the sartorius muscle. Deeper and posteriorly there are the gracilis and semi- tendinosus tendons. The semitendinosus runs distally and medially on the surface of the semimembranosus. Farther posteriorly, there are the two heads of the gastrocnemius and the structures of the popliteal fossa. In the deeper layer, superficial medial collateral ligament bends anteriorly with the medial patellar retinaculum and the vastus medialis. The deepest layer is the capsule and medial collateral ligament with superficial and deep layers. On the lateral aspect, there is the iliotibial tract, and the biceps femoris that expands posteriorly. Underneath there are the quadriceps retinaculum and

13

two patellofemoral ligaments. The deepest layer is the capsule and lateral collateral ligament. The sartorius, gracilis, and semitendinosus medially and the iliotibial tract laterally most often act for stabilizing the pelvis [66]. The muscle-tendon structures lying on the posterior aspect to the femur are referred as the hamstrings. The lateral hamstring (biceps femoris) and the medial hamstrings (sartorius, gracilis, semitendinosus, and semimembra- nosus) attach to the fibular head and medial aspect of the tibia (Fig. 2.1.2.).

Those muscles are responsible for knee flexion and rotation in relation to the femur [10]. Popliteal area of the femur is covered with the posterior capsule of the knee joint, and the popliteus muscle [66]. Above there are lateral and medial heads of the gastrocnemius muscle, the soleus and plantaris muscles [10, 16, 66, 162].

The main ligaments joining the femur and the tibia are medial and lateral collateral ligaments, and the anterior cruciate and the posterior cruciate ligaments. All of those ligaments have a significant importance on the knee stability. Because of the shape of the articulation and the ligament attachments, the femur rotates medially on the tibia between approximately 20° of flexion to terminal extension; this is the screw home mechanism that locks the joint [10, 66].

2.2. Alignment of the lower extremity

Considering the alignment of the lower extremity, various measures are used for research purposes. The mechanical axis of the leg is the line connecting the centres of the femoral head, knee and ankle. The mechanical axis alignment (MAA) is determined as the medial hip-knee-ankle angle.

The lateral distal femoral angle (LDFA) is defined as the lateral angle between the mechanical femoral axis and the line of the distal femoral condyles. The medial proximal tibial angle (MPTA) is defined as the medial angle between the mechanical tibial axis and the line of the proximal tibial condyles. The angle between mechanical and anatomical femoral axes is defined as femoral valgus angle (FVA) (Fig. 2.2.1).

14

Fig. 2.2.1. The alignment of the lower extremity:

mechanical axis alignment (MAA), femoral valgus angle (FVA).

Moreland et al. [118] investigated healthy volunteers and found that normal mean MAA was 179±2°. Similar findings were reported by Belle- mans et al. study where 500 knees were investigated in asymptomatic vo- lunteers. They found that mean MAA in males was 178±2° and in females 179±2° [9]. They found that 32% of the male knees and 17.2% of the female knees had constitutional varus alignment with an MAA of ≤3°. They believed that this might be a consequence of Hueter-Volkmann’s law, which states growth at the phases is slowed by increased compression, whereas reduced loading accelerates growth [9, 35, 161, 174]. Thus slight varus alignment of the leg is normal. Larger or increasing malalignment is associated with increasing structural damage in the knee joint and is a potent predictor of disease progression in patients with knee osteoarthritis [58, 59].

However, knee alignment is typically a consequence and not a primary cause of OA as multiple factors, including cartilage loss, meniscal degene- ration and position, bone attrition, osteophytes, and ligament damage, can contribute to knee malalignment [60].

The mean LDFA was found to be 88±2° [9] and the mean MPTA 87±2°

[9, 118].

The mean femoral valgus angle was 6±2° reported by Moreland et al.

[118] and 5±1° by Bellemans et al. [9] . However, several studies show that there is a great variation and a wide distribution (1° to 13°) of the FVA in both healthy or patients with OA and undergoing TKA (Fig. 2.2.2.).

15

Fig. 2.2.2. Diagram representing the mean± standard deviation, lowest and highest values of the FVA reported in the literature

Kharwadkar et al. found a mean FVA of 5.4±0.9°, ranging from 3.1° to 8° in a British TKA population [78]. In adults of Chinese descent, Tang et al. found the FVA to be 5.1±0.9° with a range from 2.6°–7.4° [164]. Deakin et al. investigated 174 OA knees and found that the mean FVA was 5.7±1.2°

(range 2°–9°) [29]. Several studies analysed the FVA in patients undergoing TKA: in one it averaged 5.6°±1.0° with a range of 2° to 9° [5], in the other averaged 6.9±1.0° with a range of 2.6° to 11.4° [121], in the other averaged 5.4° with a range of 1° to 10° [26], in the other averaged 6.5±1.3° with a range of 4° to 13° [82]. The major contributors to the FVA are femoral bowing [82] and the angle between the femoral neck and shat [5, 126]

(Fig. 2.2.3.).

0 2 4 6 10 8 12 14

FVA

Lowest Mean Highest

16

Fig. 2.2.3. The radiological parameters of the femur:

femoral valgus (FVA), bowing (FBA) and neck-shaft angle (FNSA).

2.3. Total knee arthroplasty

Failed conservative treatments of painful knee OA is among the leading indications for TKA. The rationale of the primary TKA is to remove damaged bone and cartilage, replacing them with the prosthesis. Depending of the damaged site and size different implant designs in primary knee arthroplasty could be used: total, unicondylar, femoropatellar, uni-femo- ropatellar or hinge. Total knee prosthesis is the most commonly used implant, which is implanted using either the gap balancing or the measured surgical technique. Total knee prosthesis consists of metal femoral and tibial components with the polyethylene insert in between (Fig. 2.3.1.). Depend- ing on posterior cruciate ligament retention during the surgery, TKA is classified as cruciate retaining or posterior stabilised. The metal components are fixed using bone cement (polymethylmethacrylate) or uncemented technique.

17

Fig. 2.3.1. Total knee prosthesis (NexGen LPS (Zimmer, Warsaw, Indiana, USA))[89].

TKA is an effective surgery of reducing pain, improving function and quality of life in patients with knee OA [37, 71, 72]. It is one of the most frequently performed orthopaedic procedures demonstrating excellent survival. 10-year survival is close to 95% for most implants [44, 95, 138].

Despite the success, it has been reported that approximately 10%–25% of patients are not satisfied with the outcome after TKA [4, 15, 32, 128, 142, 143] and the causes of dissatisfaction remain indistinct [1]. It have been reported that TKA outcome correlates with patient related factors [3, 40, 77, 172], implant type and surgical technique [21, 57, 99]. Usually the early success of TKA outcome is controlled by investigating postoperative function and the TKA alignment.

2.4. TKA surgery

The surgical goals of primary TKA are to restore the normal mechanical axis with a stable and well fixed prosthesis [165]. This is achieved by proper preoperative planning, understanding the surgical technique, instruments and choosing the right implant.

There are various surgical exposures for knee implant insertion (medial parapatellar, midvastus, subvastus and others). The most common is medial parapatellar approach that ensures extensive exposure. After midline an- terior skin incision in the middle of the patella with proximal and distal extension, medial parapatellar arthrotomy is performed. It permits the patella to be everted or subluxated laterally. After removing the osteophytes,

18

anterior cruciate ligament (if exists) bone cuts: tibia or femur first are performed. Bone cuts determine postoperative alignment of the lower limb and the components. It is generally accepted that postoperative alignment of the lower limb should be straight and within 3° of a neutral mechanical axis (14–24). To achieve a neutral alignment, both femoral and tibial compo- nents must be positioned perpendicularly to the mechanical axis. Which means that distal femoral cut must be performed at 90° to the mechanical femoral axis and proximal tibial cut at 90° to the mechanical tibial axis in the coronal plane (Fig. 2.4.1.).

Fig. 2.4.1. Neutral alignment of the TKA: straight mechanical axis, with perpendicular component position.

In the sagittal plane, the posterior slope of the natural tibia must be restored for the tibial component whether it is determined by bone cut or the implant. Femoral component must be positioned in flexion determined by femoral bowing in order to avoid anterior femoral cortex notching and restoring the posterior offset. Rotational alignment of the components affects the patellofemorall alignment and tracking. Proper bone resection and implant positioning and sizing ensure proper height of the joint line and ligament balance in extension and flexion. After the bone cuts are per- formed, the alignment, soft tissue balance, range of motion (ROM) are checked with trial implants. Soft tissue releases is performed to obtain the knee stability and adequate balance if needed. Then the final implant are implanted and wound suturing is performed.

19

2.5. Standard and measured bone cuts techniques

In conventional TKA, usually tibial bone cut is performed using the extramedullary guide as the external anatomical landmarks (tibial tubercule, tibial crest, foot and ankle) are well exposed and the mechanical tibial axis could be identified (Fig. 2.5.1.).

Fig. 2.5.1. Extramedullary tibial guide is placed parallel to the mechanical tibial axis for perpendicular bone cut [90].

Whereas on the femoral side the mechanical femoral axis (the line joining femoral head and the knee centre) is difficult to determine, thus, intramedullary guide is usually used. To perform an accurate distal femoral cut, the appropriate FVA set on the intramedullary guide should match the angle between the mechanical and anatomical axis of the femur [29] (Fig.

2.5.2.).

20

Fig. 2.5.2. Intramedullary femoral guide with adjustable angle for distal femoral cut [90].

However, there is no consensus in the orthopaedic community, at which degree the intramedullary guide should be settled in order to mimic the mechanical femoral axis and perform perpendicular distal femoral cut.

There are several techniques for performing the distal femoral cut. Standard technique uses fixed angle on the intramedullary guide for all patients, disregarding the individual FVA. Usually, short knee joint radiographs are used for standard technique. During such an assessment of standard (short) radiographs the type (varus or valgus) and severity of the knee deformity, osteophytes and bone loss are examined, but it is not possible to evaluate the individual FVA. Depended on different surgical technique manuals, recom- mended fixed angle varies from 5° to 7° [10, 66, 78, 165]. However, those are based on theoretical average of FVA but not taking in to account on FVA distribution which can be observed in the population undergoing TKA.

Kharwadkar et al reported that in a routine practice for uncomplicated TKA a fixed 5°–6° FVA on the intramedullary guide for the distal femoral cut has sufficient precision [78]. However, such standardised practice may lead to a significant number of outliers and that the mechanical axis cannot be accurately restored without preoperative measurements [5]. Thus, the use of a fixed angle intramedullary guide could result in poor alignment in some patients and subsequently increase risk of revision [140]. Based on this, several authors suggested the other, measured technique for distal femoral cut [26, 29–31, 112, 121, 151]. This modified technique requires assessment

21

and evaluation of preoperative long-standing radiographs of the lower extremity. The individual FVA is measured and this information should be considered then performing TKA. Thus, intramedullary guide is placed in the femoral canal corresponding the anatomical femoral axis and individual FVA on the guide is settled according preoperative measurements (Fig.

2.5.3.).

Fig. 2.5.3. A – preoperative FVA assessment, B – adjusting the angle on the intramedullary femoral guide according to the preoperative

FVA measurements, C – unadjusted/standard 7° angle is settled on the intramedullary femoral guide.

With this technique, distal femoral cut theoretically should be performed more accurately and perpendicularly to the mechanical axis (Fig. 2.5.3.).

However, we could find only one randomised study, which analysed if the use of preoperative long-standing radiographs improved the postoperative mechanical alignment as compared to standard radiographs [112]. They reported that it did not improve the mechanical axis alignment. However, their drawback is that they did not analysed individual component positions.

It is important to analyse individual components alignment also, as isolated malalignment the component increases revision rates in the long-term (22, 46). Two other non-randomised cohort studies were performed seeking the same aim. Deakin et al. [30] reported that measuring and adjusting the individual FVA has lower MAA outlier rate (15%) as compared to the fixed

22

FVA (31%), but they also did not analysed the effect on individual com- ponent positions. Similarly Shi et al. [151] found that the measured FVA group had significantly less MAA outliers (12.3%) as compared to the fixed FVA group (30.3%) (p<0.001). In addition, the femoral component outlier rate was lower in the measured FVA group (10.6%) as compared to the fixed FVA group (30.3%) (p<0.001). No significantly different outlier rate was observed in tibial component positioning between the groups [151].

Thus, contradictionary findings between randomised and non-randomised studies leaves uncertainty if preoperative measurements of the FVA affects the mechanical alignment and individual component positions in TKA.

2.6. TKA accuracy

TKA accuracy describes the alignment of the mechanical axis and indi- vidual components in the coronal, sagittal and transverse planes.

Straight/neutral mechanical axis in the coronal plane for TKA is achieved by bone cuts and positioning of both femoral and tibial components per- pendicular to mechanical axes of the femur and tibia respectively. However, malalignment in TKA will always exist with human error factor [1]. Using conventional instruments in TKA, malalignment greater than 3° may vary from 2% [14] to 72% of TKA’s [48]. Achievement of neutral alignment in 75% of conventional TKA has been described as the best case scenario [108].

Extraordinary healthcare resources have been designated to the develop- ment of the superior instruments or techniques, such as computer navigation and patient-specific instrumentation systems to achieve neutral mechanical alignment [1, 111, 133]. Various accuracy results are reported in the lite- rature comparing conventional and navigated TKA in terms of alignment (Table 2.6.1). There are several meta-analyses of randomised and non- randomised cohort trials, which reports that computer navigation improved component orientation and mechanical axis in TKA and reduced outlier rates [7, 17, 109]. While other meta-analysis of randomised trials, invest- tigating if computer-assisted (navigation) surgery (2268 knees) improved postoperative leg alignment and implant positioning following TKA as compared to conventional TKA found that the use navigation does not im- prove mechanical leg axis and component orientation [20]. Despite of number of advantages reported in some of the series, there are several limitations on navigated TKA use: difficult landmark registration, increased operative time, costs, risk of pin loosening or pin site infection and high learning curve [97, 170].

23

Another technique – patient-specific instrumentation system, which was recently introduced, is also aiming for better TKA implantation accuracy.

This technique uses advanced imaging (magnetic resonance imaging (MRI) or computed tomography (CT)) to assess the patient's anatomic parameters for the development of individual femoral and tibial cutting guides. Cutting guides determine the location of the bone cuts; the size and the position of the components [170]. However, a systematic review and meta-analysis of Voleti et al. [170] stated, that current data do not support routine use of patient-specific instrumentation in TKA as there was no significant differ- rence in outlier rates between conventional and patient-specific instrument- tation TKA. For those reasons, both techniques (computer navigation and patient-specific instrumentation systems) currently are not widely used in clinical practice. Thus, improvement of conventional TKA aiming for better accuracy of implantation such as preoperative radiological examination including measurements of individual FVA and subsequent intraoperative adjustments is of interest.

Table 2.6.1. Mechanical axis alignment accuracy in navigated and conventional TKA.

Author

Navigation TKA Conventional TKA Number

of TKAs Percentage

of outliers Number

of TKAs Percentage of outliers

Bonutti et al. [14] 50 6% 50 2%

Lüring et al. [101] 30 0% 60 8%

Sparmann et al. [158] 120 0% 120 13%

Anderson et al. [2] 116 5% 51 15.7%

Kim et al. [79] 160 13% 160 19%

Cip et al. [22] 92 10% 91 19%

Mullaji et al. [120] 282 9% 185 22%

Tingart et al. [166] 500 5% 500 26%

Jenny et al. [70] 235 8% 235 28%

Kim et al. [80] 100 28% 100 35%

Macule-Beneyto et al.[105] 102 52% 84 70%

Haaker et al. [48] 100 21% 100 72%

24

2.7. The effect of coronal malalignment after TKA 2.7.1. Implant survival

The occurrence of deviations from neutral mechanical axis in TKA patients should be reduced as it may affect the survival of the implant [11, 69, 140, 141]. There is a debate in the literature regarding the radiological definition of “normally” aligned TKA knees [1, 46]. The majority of reports accept that mechanical axis of 180° should be considered as perfectly aligned TKA.

Several studies have used a 3° deviation from a neutral alignment as a threshold for what it is accepted for good long-term results [11, 69, 140, 141]. Such a 3° threshold has also been chosen in numerous other studies investigating results after TKA [21, 57, 99, 133], and a deviation in alig- nment within 3° of the mechanical axis has been considered as a gold standard by many surgeons [98].

There are reported different mechanisms explaining the modes of failures in malaligned TKA knees. Neutral alignment results in even distribution of load on bone and polyethylene insert. Whereas malalignment is associated with uneven load distribution on bone, polyethylene insert and might also overload the knee joint ligaments on one side and/or result in instability on the other and those are one of the reasons of TKA failure [10, 148, 149].

Halder et al. [49] investigated TKA patients and found that any increase of the varus-valgus angle by 1° would increase or decrease the medial load share by 5%. Berend et al. [11] reported that increased loading factors such as varus tibial component alignment, relative overall varus leg alignment, and the combination of body mass index >33.7 and tibial component varus alignment were associated with medial tibial bone collapse. Similar findings were reported in biomechanical studies where they found that more than 3°

of tibial component varus alignment had a higher incidence of failure as bone collapse in increased stress areas could be indicated [55, 134]. Green et al. [45] investigated cadaver tibia with neutral or varus alignment implants and found that in neutral alignment, the strain was nearly equal medial and lateral whereas in varus alignment there was a statistically increased strain in the posteromedial quadrant. Similar findings were observed in the other cadaver study by Werner et al. [173], where they found that under static loading, a tibial malposition of 3° or more in varus or valgus can greatly alter the distribution of pressure and the load between the medial and lateral compartments. Malalignment also affects the increased stress on polyethylene insert. This was investigated using knee wear simulator by D’Lima et al. [27, 28]. They found that malaligned implants

25

generated higher polyethylene wear of the insert. Thus, malalignment may result in increased wear of the polyethylene insert and eventually loosening and revision of the TKA. Jeffery et al. [69] reported 24% loosening if deviation from neutral axis after TKA exceeded 3° as compared to 3%

loosening in normally aligned knees. Fang et al. [39] found that varus knees failed primarily by medial tibia collapse, whereas valgus knees failed from ligament instability. They also found that outliers in overall alignment had a higher rate of revision than neutrally aligned knees. Ritter et al. [141] found that varus leg alignment had a higher incidence of revisions as compared to valgus or normal alignment. Another study by Ritter et al. [140] also reported that malalignment affects the TKA survival. Isolated malposition of the femoral component increases revision rates in the long-term too [81, 140]. Regarding the isolated components positioning it was reported that correcting varus or valgus malalignment of the one component by placing the second component to attain neutral alignment is also associated with an increased failure rate [140]. Thus, aiming for neutral alignment of all mechanical axis and individual components is important for long-term TKA survival.

2.7.2. Functional outcome

A successful TKA is described as a pain free, well-functioning knee joint, but not as that with a perfect radiological alignment only. Thus, the analysis of patient related clinical/functional outcome after TKA is important. Malalignment could result in unequal joint gaps, which might be the cause of instability, pain and worse functional outcome [23, 145].

Usually clinical outcome after TKA is reported by using the patient reported outcome measures or functional scores. However, the effect of accurate postoperative alignment on TKA function is controversial [21, 39, 46, 53, 57, 75, 79, 99, 100, 103, 104, 107, 110, 139, 159, 169]. The summary of reports investigating the relation between the alignment after TKA and function is presented in Table 2.7.2.1.

Historical study of Lotke and Ecker [100] has shown positive correlation between good clinical results and well positioned implant. Also Choong et al. [21] and Huang et al. [57] reported better Knee Society Score (KSS) in TKA patients with a mechanical axis within 3° as compared to malaligned knees which remained consistent from 6 weeks to 5 year follow-up. Con- tradictory to these findings, Kamat et al. [75] compared 136 normally aligned and 15 malaligned TKA knees and found no significant differences in Oxford knee scores at 3 years follow-up. Similar results were reported by Matziolis et al. [110] who found that postoperative varus malalignment as

26

compared to neutral MAA after TKAs were not significantly different in KSS and flexion in a follow-up from 5 to 10 years. Magnussen et al. [107]

even found KSS to be slightly better in patients with residual varus as compared to those with neutral alignment. Furthermore, Vanlommel et al.

[169] reported significantly better KSS in patients with mild (3–6°) postoperative varus MAA as compared to neutral or severe postoperative varus MAA.

Other studies comparing computer assisted TKA with conventional TKA surgery have not been able to correlate malalignment of the MAA with inferior functional outcomes [53, 75, 79, 103, 159]. However, Rebal et al.

[139] performed a meta-analysis and reported that computer navigation in TKA provides superior functional outcomes at short-term follow-up. The other systemic review of Burnett et al. [18] reports opposite, that navigation TKA has limited evidence to improve function over the conventional TKA and that long-term results are needed for effective evaluation of this technique.

Concerning the femoral and tibial components alignment effect on function, Longstaff et al.[99] reported that at 1 year follow-up TKA patients with femoral alignment within ± 2° of the neutral had significantly better KSS as compared with malaligned femoral components. Similarly Magnus- sen et al. [107] found that valgus malalignment (>3°) had significantly lower KSS scores as compared to neutral (p=0.002) or varus (p=0.001) femoral component alignment. They also found that tibial components placed in varus had significantly lower KSS scores as compared to neutral (p=0.002) alignment. Contradictionary findings were reported by Dossett et al. [32], they found that alignment of the tibial component in 2.3° more varus and the femoral component placed in 2.4° more valgus resulted in better function at six months as compared to normally aligned TKA. Ho- wever, for those patients they used a different concept of surgical technique, which is called kinematically aligned TKA procedure. The philosophy of kinematically aligned TKA has arisen from the knowledge that the native knee joint line is not perpendicular to the mechanical axis and that some of the population has a constitutional varus. Thus changing it to neutral might compromise the clinical result [9, 54]. However, long-term outcome of this technique and component placement is unknown [46].

27

Table 2.7.2.1. The summary of reports investigating the relation between the alignment after TKA and function.

Author Year Site (accuracy) Number of normally

aligned TKAs/outliers Follow-up Functional score

±normal/>outliers p Choong et al.

[21] 2009 Mechanical alignment (±3°vs.>3°) 83/28 1 year KSSo 94/78 KSSf 80/60 KSS 169/135

<0.001 0.008

<0.001 Huang et al.

[57] 2012 Mechanical alignment (±3°vs.>3°) 62/21 5 years KSS 142/129 0.028

Kamat et al.

[75] 2010 Mechanical alignment (±3°vs.>3°) 136/15 3 years OKS 23/30 –

Matziolis et

al. [110] 2010 Mechanical alignment (±3°vs.>3° Largest) 154/25 5-10 years KSS 142/158

Flexion 106°/103° n.s n.s.

Vanlommel et

al. [169] 2013 Mechanical alignment (±3°/3°-6°/>6°) 75/46/22 Mean 7.2 years KSS 159/170/152 <0.02 Magnussen et

al. [107] 2011 Mechanical alignment (±3°vs.>3°) 352/181 Median 4.7 years KSS 169/173 0.12 Longstaff et

al. [99] 2009 Femoral component (±2°vs.>2°) 102/23 1 year KSSf 68/57

KSS 154/137 -

0.013 Magnussen et

al. [107] 2011 Femoral component (>3°Varus/±3°/>3°Valgus) 24/513/16 Median 4.7 years Lower KSS in valgus as compared to varus or neutral

0.001 0.002 Magnussen et

al. [107] 2011 Tibial component (>3°Varus/±3°/>3°Valgus) 35/514/4 Median 4.7 years Lower KSS in varus

as compared to neutral 0.002 KSS – Knee Society Score, KSSo – Knee Society Score objective subscale, KSSf – Knee Society Score functional subscale, OKS – Oxford Knee Score, n.s. – non significant.

28

Contradictionary findings in the studies analysing the alignment in relation to function may be affected by study design, variety of implants, surgical techniques, hospital type. Gender, age, preoperative functional status, comorbidities, depression, socioeconomic factors, and social support can also have influence on functional outcomes [40, 77, 172]. However, although clinical outcome after TKA is likely multifactorial, alignment is the most important surgeon controlled factor, which may affect the knee joint function. Thus, neutral alignment and standard bone cuts, remain the gold standard in TKA [1, 98].

2.7.3. Muscle strength

A principle of orthopaedic treatment is to restore normal musculoskeletal function as much as possible. The successful outcome of TKA is dependent on the kinematics of the knee during activities of daily living [10]. Although functional scores or patient reported outcomes are used to assess the TKA outcome, they have limitations, as are dependent on the patient’s perception.

Thus, together with patient reported outcome/functional scores it is of interest to investigate performance based measures, such as the muscle strength assessment [160]. The muscle strength is an important indicator of knee joint function in healthy older adults [12] as well as in OA patients [88, 132, 156]. Muscle weakness is a frequent finding in patients with knee OA [88, 132, 146, 150], is associated with pain, physical dysfunction and is considered to be a critical determinant of disability [50, 61, 150]. Patient’s age and gender are recognized as factors affecting muscle strength for OA patients. Ageing is associated with significant decline in neuromuscular function and performance. Age-related muscle strength decline (sarcopenia) in lower limb is typically 20–40% lower by the 7th decade and even more in older adults [12]. Similarly, muscle strength in female patients is lower as compared to males and furthermore women are recognized to be as an indicator of worse functional outcome after TKA (Petterson et al. 2007).

Also, a relation between preoperative muscle function and postoperative recovery has been reported in patients undergoing TKA [68, 115]. Mizner et al. [115], Yoshida et al. [68] found that greater preoperative quadriceps muscle strength in the operated leg correlated with superior functional performance at 6 and 12 months follow-up. However, despite positive TKA outcomes in reducing pain and improving function, full recovery of the muscle strength to a normal level after TKA is rare [13, 106, 167, 168].

Vahtrik et al. [167] found that the isometric maximal voluntary contraction of the quadriceps muscle had decreased significantly at 3 months after TKA and that although it had increased again after 6 months it was still lower

29

than preoperatively as well as compared to the non-operated leg. Muscle weakness is expected at early postoperative period, which is related to surgery. However, at later postoperative period, the reasons for muscle weakness is not well understood in TKA patient population [113]. It has been suggested that a combination of muscle atrophy and neuromuscular activation deficits contribute to residual strength impairments [113, 116].

Also, it is plausible that failure to restore the mechanical axis might result in inferior muscle function after TKA. This was observed in healthy males, where Sogabe et al. [157] reported the differences of cross-sectional areas in quadriceps muscles with different knee alignments. They suggested that knees with varus or valgus deformation should have inferior muscle func- tion as compared to normally aligned knees. Lower limb musculature is the natural brace for the knee joint and imbalance in strength between the quadriceps and the hamstrings could potentially contribute to knee symp- toms through reducing knee joint stability [24, 147]. However, we could not find studies investigating the muscle strength after TKA in relation to component alignment and mechanical axis restoration.

A shortage of information regarding muscle weakness after TKA is surprising [115], knowing that preoperative and postoperative muscle strength are important determinants of function in patients undergoing TKA [106]. Muscle weakness may be a factor that affects functional limitations after TKA [52, 116]. This is important as preoperative and postoperative muscle strengthening could optimize the benefits of TKA [113, 115, 163].

In addition, the recognition of factors affecting muscle strength such as malalignment after TKA could be an important finding for TKA patients to undergo strengthening rehabilitation program linked to weaker muscles.

2.8. The effect of sagittal and rotational malalignment after TKA The alignment of a TKA in the sagittal and transverse planes and its clinical effect on functional outcome has been studied relatively little [46].

It was recommended to implant the femoral component in 0–3° of flexion and posterior tibial slope should be 0–7° whether it is determined by tibial cut or implant design.

Murphy et al. [123] compared TKA with the femoral component placed neutrally (mean 1.6°) and in flexion (mean 5.3°). They found better knee flexion in the group where the femoral component was flexed as compared to neutral position, but they did not find quadriceps strength differences between the groups at 1 year follow-up. However, placing femoral com- ponent in great flexion may affect flexion contracture. Lustig et al. [102]

reported that sagittal placement of the femoral component of greater than

30

3.5° from the mechanical axis predicts knee flexion contracture at one-year follow-up by 2.9 times. But they failed to reveal any statistically significant differences in Oxford knee score, in self-reported pain, ability to climb stairs between the patients having flexion contracture and without.

Sagittal placement of the tibial component also affects knee joint flexion.

Insufficient tibial slope affects flexion gap tightness [63] and over resection of tibial slope may lead to excessive flexion gap and instability [131]. Tibial cut in anterior slope could be associated with dislocation of polyethylene insert, impaired posterior flexion space and possible instability [46, 171].

The femoral component should be in 2–5° of external rotation in relation to the transepicodilar femoral axis. For positioning of a tibial component, excessive internal rotation shoul be avoided and additionally combined femoral-tibial internal rotation, rotational mismatch should be avoided [46].

Malrotation, predominantly internal, of the femoral or tibial components has been correlated with pain and inferior function [6, 8, 135]. Rotational mala- lignment could lead to patella mal-tracking, lateral patellar tilt, lateral patellar overhang, subluxation, and dislocation [76] which can lead to knee pain following TKA.

However, there is a lack of information regarding the sagittal and rotational alignment effect on TKA function. The reasons for this might be that it requires CT or MRI scans, which is a logistical challenge, difficult to reproduce, as there is no gold standard technique for measurements.

Additionally, CT exposes the patient to significant radiation, which also limits scientific research on the subject [46, 51].

2.9. Summary of the literature review

TKA alignment is the most important surgeon controlled factor affecting the long-term results. Although there is a debate in the literature regarding the radiological definition of “normally” aligned TKA, it is generally accepted that neutral alignment (within 3° of the mechanical axis) and appropriate bone cuts, remain the gold standard in TKA [1, 98].

Development of the instruments or techniques (computer navigation and patient-specific instrumentation systems) that aim to achieve neutral mechanical alignment are related with additional costs and not widely used in clinical practice. Thus, improvement of conventional TKA, which attains neutral alignment in about 75% [108], is of interest. Standard technique for distal femoral cut uses a fixed FVA for intramedullary guide. However, knowing that there is a great variation and a wide distribution (1° [26] to 13°

[82]) of the native FVA the use of a fixed angle intramedullary guide will result in not always accurate alignment in some patients and subsequently

31

increased risk of revision [140]. We found only one randomized study, which investigated the effect of preoperative radiological measurements of the FVA on postoperative mechanical alignment and there was reported that it did not help to obtain a neutral mechanical axis [112]. However, they did not analyse the effect of detailed preoperative measurements on individual components positioning. This is important as isolated malalignment of the components increases revision rates in the long-term (22, 46).

The successful TKA is described as pain free, well-functioning and stable knee, but the alignment effect on postoperative function is controversial.

Numerous studies found that accurate alignment TKA had superior func- tional outcomes [21, 57, 75, 99, 100, 104, 139], while other have not been able to correlate malalignment with inferior function [53, 79, 103, 110, 159]. It seems that clinical outcome after TKA is multifactorial; however, malalignment effect on TKA function is of great importance.

When evaluating the postoperative outcome, it is important to use patient reported and performance based measures, i.e. muscle strength assessment.

Patients with greater preoperative muscle strength have been reported to have faster recovery and better functional outcome after TKA [68, 115].

However, we could not find studies investigating the muscle strength after TKA in relation to component alignment and mechanical axis restoration. It was suggested that knees with varus or valgus deformation should have inferior muscle function as compared to normally aligned knees [157] and imbalance in strength between the quadriceps and the hamstrings could potentially contribute to knee symptoms through reducing knee joint stability [24, 147].

Summarising our literature review we suggest that current knowledge cannot provide exact answers regarding the effect of preoperative measu- rements and implant alignment after TKA, also there is lack of information correlating the accuracy of TKA implantation and postoperative function including the muscle strength.

32

3. PATIENTS AND METHODS

The study was conducted in the department of Orthopaedics and traumatology of Hospital of Lithuanian University of Health Sciences Kauno Klinikos. We prospectively investigated 120 consecutive OA pa- tients, admitted for TKA in 2012. A research was conducted after approval of Kaunas regional biomedical research ethics committee, No.: BE-2-5.

The study consisted from two parts according the objectives of our research plan. In I part we investigated the effect of the detailed preo- perative radiological assessment of the knee to the operative TKA accuracy as compared to standard. In II part of the study, we evaluated the TKA alignment effect on knee joint function and the muscle strength.

3.1. Study population

We included 120 consecutive OA patients, admitted for elective TKA.

All participants were acquainted with the study and written informed consent were obtained.

3.1.1. Inclusion criteria

• The consecutive patients admitted for elective TKA and operated for OA.

• Patients having age of 50–90 years.

• ≥14 OA score according to radiographic Burnett’s atlas.

• All included patients operated with one type of prosthesis (NexGen LPS (Zimmer, Warsaw, Indiana, USA)).

• Agree to participate in the study.

3.1.2. Exclusion criteria

• The TKA patients operated for other reasons than OA

• Patients having age of <50 or >90 years

• Patients with previous knee bone surgeries, such as osteosynthesis or osteotomy

• Patients who experienced fractures of the femur or tibia after TKA

• Patients revised after primary TKA

• Patients having total hip or ankle arthroplasty

• Patients refusing to participate in the study

33

• The TKA patients who were unable to perform muscle strength assessment

3.1.3. Allocation to the groups

An identification code was assigned to all patients.

In I part of the study 120 were randomised using sealed envelope assignment and devided into two groups defining what angle of the intra- medullary femoral guide should be used during TKA (Table 3.4.1.).

Table 3.4.1. Study groups (I study part).

Groups Angle of the intramedullary femoral guide Control (n – 60) Fixed 7° angle

Measured (n – 60) Individual, according to preoperative radiological measurements

Randomisation was performed before the surgery, but after the radio- graphs were obtained. Radiological measurements (detailed radiological assessment) were performed in the measured group before the surgery and in the control the measurements postponed until after the surgery. Post- operative radiological measurements estimating the accuracy of TKA alignment and the comparison between the groups were performed in the blinded fashion without knowing in which group patients were assigned.

In II part of the study all patients were divided into normally aligned and malaligned TKA according to postoperative radiological measurements.

Normal alignment was defined as TKA in which the position of mechanical axis and/or the position of components were within 3° from the neutral mechanical axis. Radiological outliers were defined as TKA in which the position of components and/or the measured mechanical axis deviated more than 3° from the neutral mechanical axis (Table 3.4.2.). Preoperative and postoperative clinical outcome was assessed without knowing in which accuracy group the patients were assigned.

Table 3.4.2. Accuracy groups of TKA alignment (II study part).

Site Accuracy groups of TKA alignment

Mechanical axis Femoral component Tibial component Normally

aligned/malaligned ±3° >3° ±3° >3° ±3° >3°

34

3.2. Patients’ characteristics

Out of 120 included patients, 100 were female and 20 male gender. The mean age was 71±8 years, mean height 165±8 cm, weight 90±17 kg, body mass index (BMI) 33±6 kg/m ² . 62 TKA were performed on the wright and 58 on the left knee.

3.3. Preoperative assessment 3.3.1. Preoperative clinical examination

All patients were hospitalised one day before surgery. Patient’s age, gender, height, weight were recorded and BMI was calculated. Preoperative clinical examination included active range of motion (ROM) evaluation and Knee Society Score (KSS) [64] assessment.

Active ROM of the involved knee was measured according the metho- dology reported by Edwards et al. [36]. The examination was performed by experienced in knee joint examination orthopaedic surgeon. It was measured with a standard, 2-arm goniometer with 2° scale markings, while patient was in a sitting position. One arm of the goniometer was placed parallel to the shaft of the femur (axis between the greater trochanter and the lateral femoral condyle), and the other arm was placed parallel to the shaft of the tibia (axis between the lateral femoral condyle and the lateral malleolus).

KSS was assessed using both objective and functional subscales. KSS objective subscale (0–100 points) consists of pain, leg alignment, stability and joint range of motion assessment. Maximum 100 points is obtained by a well-aligned knee with no pain, 125° of motion, and negligible antero- posterior and mediolateral instability. Also pain assessment was evaluated according KSS and graded (severe/moderate continual/or occasional/mild walking/or stairs/or occasional/none). KSS functional subscale (0-100 points) consists of walking distance, stair climbing and walking aids assess- ment. The maximum function score, which is also 100, is obtained by a patient who can walk an unlimited distance and go up and down stairs normally. The maximum overall KSS (the sum of objective and functional subscales) is 200 points [64]. KSS is considered as the most popular method of tracking and reporting outcomes after total knee arthroplasty worldwide [144] and it was validated for Lithuanian population [74] (accessory no. 1).

35

3.3.2. Preoperative radiological assessment

The day before surgery, radiographs were taken by assistants of the Department of Radiology using Siemens MULTIX PRO system (Siemens Medical Systems Inc.). The radiographs were performed on the phosphor plates (Regius model RC-110T, Konica Minolta medical & Graphic Inc.) and digitised (Direct Digitizer Regius model 210, Konica Minolta Inc.). The assessment was performed on digitized radiographs using a radiology viewer Cedara I-Reach™ 4.4 (Cedara Software corp. Merge OEM).

Long-standing lower extremity (hip-knee-ankle) anterior-posterior radio- graphs (120x30 cm) were obtained at a focal distance of 2.5 m. with a consistent technique: the patients were standing on both legs with patella facing forward and the medial aspects of both feet parallel [73]. A full-limb radiograph is the gold standard method for assessing the knee alignment [58]. Additionally, the short lateral and patellar skyline radiographs were obtained. The OA grade was assessed on the preoperative radiographs according Burnett’s atlas [19]. The evaluation was based on a number of radiographical changes (i.e. narrowing, sclerosis, osteophytes) in the tibio- femoral and patellofemoral joints and graded in stages from 0 to 21, with a score ≥14 considering as severe (Fig. 3.3.2.1.).

Fig. 3.3.2.1. Radiographical OA changes (i.e. narrowing, sclerosis, osteophytes) in the knee.

Preoperative radiological measurements were performed. The mechanical axis alignment (MAA) of the lower extremity was determined as the medial hip-knee-ankle angle. Hip centre was identified by the Mose circles [119]

36

and the knee centre as the midpoint between the intercondylar femoral sulcus and the eminentia tibiae. The ankle centre was defined as the centre of the superior facet of the talus [118]. The anatomical axis alignment (AAA) (femoral shaft-knee-ankle angle) was determined as the medial angle between two lines connecting the femoral shaft-knee-ankle centres. The centre of the femoral shaft was defined as the centre of the intramedullar canal at the isthmus level where the intramedullary guide used for the distal femoral cut was to be positioned. Femoral valgus angle (FVA) was deter- mined as the angle between mechanical and anatomical axes (hip-knee- femoral shaft angle) (Fig. 3.3.2.2.).

Fig. 3.3.2.2. Preoperative long-standing lower extremity radiograph:

mechanical axis alignment (MAA), anatomical axis alignment (AAA), femoral valgus angle (FVA).

Depending on neutral mechanical alignment, all knees were categorized as “varus” (≤180°) or “valgus” (>180). Knees in ≥15° varus or valgus against the neutral mechanical alignment were classified as severe deformity (Fig. 3.3.2.3.)

37

Fig. 3.3.2.3. Long-standing lower extremity radiograph representing severe (≥15°) valgus mechanical alignment deformity.

3.3.3. Preoperative muscle strength assessment

The preoperative muscle strength was tested by a sport medicine physician using Biodex System 4 Pro dynamometer (Biodex Medical System, New York, USA) according to the instructions of the manu- facturers. To warm up, patients walked for 5 minutes after which they were seated in an adjustable electromechanical dynamometer chair with the hip in 90° of flexion and straps placed around their shoulder, waist, thigh and shin bone (proximal to medial malleoli) (Fig. 3.3.3.1.).

38

Fig. 3.3.3.1. Testing the muscle strength using Biodex System 4 Pro dynamometer.

After explaining the protocol to the patients, and allowing them to experience muscle performance, the measurements were performed. Verbal encouragement was provided during each trial during which the patients were asked to generate as much force as they felt capable of. The muscle generated torque (Nm) in 90° and 60° knee joint flexion angles was re- corded. The test protocol consisted of four isometric strength measurements of knee: 2 extensor (quadriceps) and 2 flexor (hamstring) muscle strength measurements. Each isometric contraction was held for 10 seconds with 5 seconds rest between each test or 10 seconds rest when changing the flexion angle of the knee. Each test was repeated twice and the average of the isometric peak torques was conducted and adjusted to patients body weight using Biodex System 3 software (Biodex Medical System, New York, USA) and it was done according to the manufacturer’s instructions. Further, hamstring quadriceps ratios were calculated from the isometric peak torques. Isometric muscle strength evaluation has been reported as a valid and reliable assessment in TKA patients [87].

39

3.4. Surgery and postoperative care

All patients underwent a spinal-epidural anaesthesia. Spinal anaesthesia was induced by injecting of local anaesthetic Chirocaine (levobupivacaine hydrochloride) 3 ml – 15 mg (Abbott, AbbVie Ltd) into the cerebro-spinal fluid in the lumbar spine below the level at which the spinal cord ends (L2-L3 or L3-L4). Then epidural catheter was inserted for operative and postoperative analgesia.

Patients were operated in a supine position. After appropriate preparation of the surgical field, midline anterior skin incision in the middle of the patella with proximal and distal extension was performed. A medial para- patellar arthrotomy approach was used in all cases. During the surgery, the bleeding was stopped by electrocauterization (ERBE ICC 300 (ERBE Elektromedizin GmbH)). After arthrotomy and partial synovectomy, the patella was everted. Flexion of the knee opened the tibiofemoral joint and osteophytes were removed. For proximal tibial cut an extramedullary tibial guide was used in all cases aiming for a 90° cut perpendicular to the mechanical axis and sizing of the tibial component was performed. Distal femoral cut was performed using intramedullary guide. In all patients, the entry point of the intramedullary femoral guide was placed in the centre of the patellar sulcus of the distal femur, 1 cm above the femoral intercondylar notch. The angle on the intramedullary femoral guide for distal femoral cut varied in the groups depending on the preoperative randomisation results. In the measured group, the angle on the intramedullary femoral guide was set accordingly to the individual measurements of the FVA on the preoperative radiographs, whereas in the control group it was fixed at 7°. After distal femoral cut, remaining femoral cuts were performed according the size of the femur. Posterior/anterior, as well as chamfer femoral cuts were performed using cutting block aimed for 3°external rotational alignment of the femoral component. Patellas were not replaced; they were reshaped removing the osteophytes. Bone cuts were done using a power tool Acculan 3Ti (B. Braun, Aesculap). After the bone cuts were performed, the alignment, soft tissue balance, range of motion, patella tracking were checked with trial implants. Soft tissue releases were performed to obtain the knee stability and adequate balance if needed. The bony surfaces were washed and one type of prosthesis (NexGen LPS (Zimmer, Warsaw, In- diana, USA)) were fixed with bone cement (Palamed ^® G, Heraeus Medical).

Joints were drained with a drain, which was placed subfascially and pulled through the skin laterally/proximally. The capsule and subcutaneous layers were sutured using Safil size 1 (B. Braun, Aesculap) and the skin with the

40