1 LITHUANIAN UNIVERSITY OF HEALTH SCIENCES
MEDICAL ACADEMY
Final Master Tesis Armando Márquez Gómez
ALIGNMENT ANALYSIS OF TKA
Department of traumatology and orthopaedics2
CONTENTS
Abstract……….…..3 Acknowledgements………....3 Conflict of interest………..3 Abbreviations……….4 Introduction………51. Aim and objectives of the study………...7
2. Literature review………..8
2.1 Anatomy of the femur………..8
2.2 Anatomy of the knee………..10
2.3 Alignment of the lower extremity………..12
2.4 Total knee arthroplasty………..14
2.5 Total knee arthroplasty surgery……….15
2.6 Total knee arthroplasty accuracy………...16
2.7 Influence of anatomical femoral angles on TKA………...17
2.8 Effect of malalignment after TKA……….18
3. Methods………..21
3.1 Patients and methods………..21
3.2 Study population………21
3.3 Inclusion criteria………21
3.4 Exclusion criteria………...21
3.5 Allocation of the groups……….22
3.6 Patients’ characteristics………..23
3.7 Radiological assessment………23
3.8 I study part (Investigation of component and anatomical angles alignment on the coronal plane after TKA)………...23
3.9 II Study part (Evaluation of the effect of component alignment, FBA, CCD angles on overall mechanical axis alignment)………...24
3.10 Statistical analysis………24
4. Results………25
4.1 Investigation of component and anatomical angles alignment on the coronal plane after TKA………...25
4.2 Evaluation of the effect of component alignment, FBA, CCD angles on overall mechanical axis alignment……….28
5. Discussion………..30
6. Conclusions………33
3 ABSTRACT
Knee arthroplasties are becoming one of the most common surgical procedures on the last decades. Many researches have been made in order to understand why postoperative alignment after a total knee arthroplasty is important and which factors are the ones affecting such alignment. Postoperative neutral mechanical axis alignment has been shown to affect the implant survival, the revision rate and the function of knee arthroplasties. Many factors have been suggested to affect the mechanical axis, from which the most important are the individual component alignment. In our study we wanted to check these factors, their distribution among the patients undergoing TKA and how each of them was related with the MA alignment. We included tibial and femoral component and two femoral anatomical angles which are known to have wide variations among population: the femoral bowing angle (FBA) and the Caput-Collum-Diaphyseal angle (CCD). For our study we retrospectively evaluated radiographs from 255 consecutive patients undergoing TKA. From those patients 123 would pass our inclusion and exclusion criteria and form part of our research population. We evaluated the distribution of the different factors (MA, TC, FC, FBA and CCD) and distributed them into normally aligned or outliers and the correlation they had with one another. The most common operative failure we found was the femoral component positioning which had an outlier rate of 22.8% and a big correlation with the MA alignment (p=0.000). Similar findings were found regarding the tibial component. With a decreased outlier rate (14.6%) and a high correlation with the MA alignment (p=0.002). The femoral anatomical angles didn’t show any correlation with any of the other factors, although FBA was slightly different among genders with the female average of 3.3° and 1.5° for males (p=0.33). We concluded that surgeons should have a greater concern on the proper alignment of the femoral component, for it is the most common operative failure in TKA surgeries. We found that age plays a small role in MA alignment, although is not statistically significant. Femoral and tibial component proper alignment are crucial for good results after TKA, and femoral anatomical angles do not play a role in the overall MA alignment.
AKNOWLEDGEMENTS
We acknowledge with gratitude the department of orthopaedics and traumatology for providing the means and in particular Dr. Justinas Stučinskas and Prof. Šarūnas Tarasevičius for their time and help.
CONFLICT OF INTEREST
4 ABBREVIATIONS
BMI – Body mass index
CCD – Caput-Collum-Diaphyseal (angle) FBA – Femoral Bowing Angle
FVA – Femoral valgus angle KKL – Kauno klinikos ligonine KSS – Knee society score
LDFA – Lateral distal femoral angle MA – Mechanical axis alignment MPTA – Medial proximal tibial angle
NSAIDs – Non-steroidal anti-inflammatory drugs OA – Osteoarthritis
PCL – Posterior cruciate ligament SF-12 – Short-Form 12 score
5 Introduction
Osteoarthritis (OA) is one of the most common causes of disabilities in our era. A research from 1999 in the USA reported that from all interviewed adults with disabilities (44 million, 22%), 2 million (17.5%) had arthritis and rheumatism [60]. The estimated lifetime risk of developing symptomatic OA in the United States was 13.83%, ranging from 9.60% for non-obese males to 23.87% in obese females. About 9.29% of the US population is diagnosed with symptomatic knee OA by age 60, with highest incidence among adults aged 55 to 64 [64]. OA in a degenerative joint disease that worsens with age, thus incidence and demand for surgery are increasing in the last years due to an ageing population and increased life expectancy [58]. Racial and gender disparities have been reported with a significantly higher incidence in African-American population and in women [18]. Between 1990 and 2002 a research showed that both the number and the rate of total hip and knee arthroplasties (TKA) increased steadily. Over the evaluated period of time, the rate of primary total knee arthroplasties almost tripled. The rate of revision TKA increased by 5.4 procedures per 100,000 persons per decade [54]. The same authors estimated an unprecedented increase in the number of TKA equivalent to 673% respect of actual numbers by the year 2030 [55]. In an international survey published in 2011 was stated that from the surveyed countries the country with highest rate of TKA per inhabitant was USA (213.3/100.000 inh.) and the country with the lowest rate was Romania (8.6/100.000) [56]. Thus, an ageing population and an increased number of indications for TKA in both young and senior patients are increasing the number of TKA worldwide and will continue doing so in the future. The concept of surgical repair of knee began in the XIX century, with attempts of substituting the soft tissue of the damaged knee. It wasn’t until the 1930s that a metal prosthesis was initially used, although the results were not completely satisfactory. On the 1950, Walldius finally developed a hinge prosthesis that replaced the articular surfaced of femur and tibia [22]. The modern knee replacement surgeries were introduced in the early 1970s in United States and overseas. Then raised the concept of replacement the articular surfaces of the tibiofemoral joint, with, with time, has been evolving, producing many variables such as posterior-cruciate ligament retaining/sacrificing surgeries or cemented/non-cemented fixation [75]. Nowadays, TKA is one of the most common surgical procedures in the western civilization, increasing evermore with the ageing population.
The primary indication for TKA is relief of significant, disabling pain caused by severe arthritis which conservative therapy has failed to treat [6]. Is a primarily bony procedure with modification of soft-tissue of the knee joint. Its major technical goal is to achieve a proper alignment of the prosthetic components to form a neutral mechanical axis, which is considered to be 180±3º [1, 7, 24, 25, 31, 77, 78, 93]. Neutral component alignment after TKA has been widely studied and many results have shown a positive correlation
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with longer component survival rates and better functional outcomes [13, 39, 63] while other studies didn’t show a decreased postoperative performance related with malalignment of components after TKA [37, 68, 85]. This correlation between a neutral alignment and better therapeutic results has led an “arms race” in generic (standard) and patient-specific surgical techniques, tools, prosthesis and measuring methods. Computer-assisted techniques and navigation techniques are beginning to be more common, but there are other techniques, such as preoperative patient-specific radiological assessment, that show good results in achieving a neutral mechanical axis and component alignment after TKA [17]. Intraoperative achievement of neutral positioning of the components is performed by using intra and/or extramedullar guides with standard or patient-specific radiologically assessed angulation for bony cuts.
Some preoperative factors have been suggested to affect the postoperative alignment after TKA: the severity of preoperative valgus or varus deformation, femoral and tibial pathological or traumatic deformities, femoral and tibial shaft bowing, CCD angle or condition musculature of the lower limb [52, 72, 87, 95].
7 1. AIM AND OBJECTIVES OF THE STUDY
The aim of the study: to investigate the distribution and values of femoral anatomical
angles and component alignment angles on patients following TKA and the relation of these factors with the overall mechanical axis alignment.
Objectives of the study:
1. To investigate which factors must be thought of before performing TKA to avoid malalignment
2. To investigate the possible correlation between age and MA alignment in patients undergoing TKA
3. To investigate the influence of femoral and tibial component alignment on overall MA alignment in TKA
8 2. LITERATURE REVIEW
2.1 Anatomy of femur
The femur is the longest and strongest bone in the human skeleton. It articulates with the acetabulum at its proximal part of the lower extremity forming the hip joint and with the tibia and patella at its distal part to form the knee joint.
It is divided in 5 major parts: head, neck, trochanters, shaft and lower extremity.
The femoral head (caput femoris) is a hemispherical structure at the proximal end of the femoral bone which articulates with the acetabulum to create the hip joint. The femoral head is pointing medially, upwards and slightly forward. It is coated with a smooth articular cartilage to prevent it from damage in the whole of the articular surface except from the fovea capitis femoris which serves as attachment to the ligamentum teres.
Fig.2.1.1. Upper extremity of right femur viewed from behind and above. [30]
The femoral neck (collum femoris) is a pyramidal structure connecting the femoral head and the femoral shaft, forming an angle known as neck-shaft angle or Caput-Collum-Diaphyseal (CCD) angle. This angle can vary depending on factors as age, gender, height or weight, being widest in infancy and narrowing during the growth period. The average CCD angle for adult population is about 125° widely varying between individuals. The femoral neck is pointing medially, upwards and forward. The proximal part of the femoral neck and the femoral head are covered by the synovial capsule of the hip, and the whole of the neck and the head are covered by the articular capsule.
The trochanters, greater and lesser trochanter (trochanter major, trochanter minor), are prominent processes which provide anchorage for the muscles that rotate the lower extremity. They are on the line that delimitates the end of the femoral neck and beginning of the femoral shaft.
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The femoral shaft or body (corpus femoris) is an almost-cylindrical structure between the proximal and distal femur. It is broader in the extremes and narrow in the middle and along the posterior surface lays the linea aspera, a longitudinal ridge which strengthens it. It isn’t a completely straight structure, it has a slight curvature which varies between individuals but that is mostly curved posterolaterally.
Fig.2.1.2. Right femur: Anterior surface. Right femur: Posterior surface. [30]
The femoral lower extremity is broader than the proximal femur and serves as an articular structure to form the knee joint. In the distal end there are the lateral and medial femoral condyles separated by the intercondyloid fossa. The femoral condyles are covered by articular cartilage to improve the motion of the knee joint.
10 2.2 Anatomy of the knee
The knee joint is one of the most important articulations in the human body, allowing movement of the lower leg relative to the femur. It is the largest joint on our species and it allows movements necessary for the daily life such as walking, running, jumping, standing siting and climbing up or down. The particular structure of the human knee joint allows the characteristic upright position of our species reducing the effort of the muscles by increasing the load on the bones perpendicularly placed to the ground [53, 69].
Fig. 2.2.1. Right knee-joint. Posterior view. Right knee-joint. Anterior view. [30]
Knee joint is basically composed of three bones: femur, tibia and patella. As the rest of vertebrates, human knees are asymmetrical three dimensional structures formed by the surfaces of the three mentioned bones. The distal femur forms two convex condyles, which fit in the two concave condyles of the proximal tibia. The position of the knees compared with that of the hips is closer to each other, aiding for a better balance and walking efficiency, producing a slight valgus angulation. This mild natural valgus angulation is demonstrated by the anatomical differences of medial and lateral condyles of both bones, being both medial condyles bigger in size and positioned lower the femoral and higher the tibial compared to the lateral condyles of both bones. All the four condyles are covered by layers of cartilaginous tissue and between the both contact surfaces are situated the medial and lateral menisci, all protecting the surface of bones from trauma and aiding for a better movement.
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The third bone, the patella, is situated ventrally in relation with the other two, and acts as the mechanical lever of the joint. The patella is held in place by the medial and lateral patellar retinaculum and some fibres of vastus lateralis and vastus medialis muscles. The inner surface of the patella (the articulate surface) is characterized by a medial and lateral articular facet, two concave structures on each side for a better gliding along the middle region between femoral condyles (intercondylar groove) during flexion. Patella serves as an anchor for the quadriceps muscle group tendon, the largest muscle group on the body, superiorly, to the tibial tuberosity inferior by means of the patellar ligament. The quadriceps’ main function is to extend the knee, with a secondary function to flex de hip, and a tertiary to decelerate flexion of the knee during the early stance phase of gait [44]. The quadriceps group is formed by: rectus femoris, vastus medialis, vastus lateralis and vastus intermedius.
Fig.2.2.2. Right knee-joint, from the front, showing interior ligaments. Left knee-joint from behind, showing interior ligaments [30]
On the inner aspect of the knee is located the Sartorius muscle tendon, followed on a more dorsal position by tendons of semimembranosus and semitendinosus muscles, lying the semitendinosus on the surface of the semimembranosus. The medial collateral ligament bends anteriorly with the medial patellar retinaculum and vastus medialis, being the deepest structure the capsule along with the medial collateral ligament. In the posterior part of the knee the soleus, plantaris, popliteal and medial and lateral heads of gastrocnemius muscles and the posterior capsule are found superficially covering the popliteal fossa. On the lateral surface of the knee joint lays superficially the iliotibial tract, a structure of great importance in knee stability, in which gluteus maximus and tensor of the fascia latta muscles attach. Right underneath and posterior of the ileotibial band, lays biceps femoris muscle. Beneath this muscles is the quadriceps retinaculum and two patellofemoral ligaments, and again, the deepest layer is the capsule along with the lateral collateral ligament.
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The main function of the muscles situated on the lateral and medial parts of the knee is to aid the collateral ligaments to provide stability of both, hip and knee joints. The group of muscles situated on the posterior part of the femur is known as the hamstrings, further divided into lateral hamstring (biceps femoris), attaching to the fibular head, and medial hamstrings (semimembranosus, semitendinosus, gracilis and sartorius), attaching to the medial aspect of the tibia.
Fig.2.2.3. The muscles of the knee (anterior and posterior view)[15]
Inside the knee joint are the anterior and posterior cruciate ligaments, which have a critically important function in providing anteroposterior stability of the knee joint and allow it to perform the screw lock mechanism that locks the joint at about 20° of flexion to terminal extension, in which the femur rotates medially to the tibia.
2.3 Alignment of the lower extremity
The lower extremity is a complex group of structures with particular anatomical characteristics.
The femoral Caput-Collum-Diaphyseal angle (CCD) is the angle formed between the femoral head and neck with its shaft, and it is described as an age-related angle, getting smaller with age, ranging from an average of 140° in young children down to 115° on senior population. An exceedingly narrow angle in called coxa vara (<120° in senior adults) and an exceedingly wide angle is called coxa valga (>135° in senior adults). However, a research by Gilligan et al. [29] showed that CCD shows a high variability between different regions, races and lifestyles, and that the age-related changes are minimal in adult population.
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Fig.2.3.1 A)Coxa valga, B)Normal CCD, C)coxa vara angle[42]
Femoral bowing angle (FBA) is described as the angle formed by the curvature of the femoral shaft in the coronal plane. The mechanical axis of the knee joint is formed by centre of the femoral head, centre of the knee and centre of the tallus. The mechanical axis alignment (MAA) angle is determined by the medial angle formed by the three structures. The lateral distal femoral angle (LDFA) is formed by the mechanical femoral axis and the line formed by the femoral condyles. The medial proximal tibial angle is formed by the mechanical tibial axis and the line formed by the tibial condyles. The angle formed by mechanical and anatomical axes of the femur is called femoral valgus angle (FVA) [87].
Fig. 2.3.2 (left) Anteroposterior standing long-leg radiograph showing the method of
calculating the orientation angles (LDFA, lateral distal femoral angle; MPTA, medial proximal tibial angle; LDTA, lateral distal tibial angle) [59].
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Some investigations in healthy individuals have reported a normal mean MAA of 179±2° [70]. Another research not only showed a similar angulation but a difference between genders, in which the males mean MAA was 178±2° and the female mean was 179±2° [4]. In this study they suggested that Hueter-Volkmann’s law (growth is slowed in regions of increased compression and accelerated in regions of decreased compression) was responsible for that and the difference in the percentage of individuals with constitutional varus angulation with a MAA of ≤3° (32% of males, 17.2% of females) [4, 21, 86, 94]. A greater varus angulation is associated with
increasing structural damage in the knee and is a significant predictor in patients with knee osteoarthritis [40, 41]. The same authors found that the mean LDFA was 88±2°
and MPTA 87±2° [4, 70]
2.4 Total knee arthroplasty
Primary treatment of OA is conservative, consisting primarily on lifestyle changes (including weight loss, exercise activity, physical therapy, massage therapy, knee braces and thermal therapy for management of pain and movement) and drug therapy (including pain management with Paracetamol, NSAIDS, COX-2 inhibitors, opioids and intraarticular hydrocortisone injections) [11, 19, 26, 34, 48, 80].
When conservative treatment fails in the treatment of symptomatic knee OA, surgery is, in most cases indicated, being TKA the treatment of choice, although surgery to transfer articular cartilage from a non-weight-bearing area to the damaged area is one possible procedure. The goal of TKA is to replace damaged bone cartilage with a prosthetic implant, which will vary depending on the site and extent of articular damage. The various implant options are: unicondylar, total, femoropatellar, unifemoropatellar or hinge. The most commonly used implant is the total knee prosthesis, implanted either by the gap balancing technique or the measured surgical technique. Total knee prosthesis mainly consist of metal femoral and tibial components (The metal parts of the implant are made of titanium or cobalt-chromium based alloys) and a polyethylene component in between. The surgery can be further classified as posterior cruciate retaining and or posterior stabilised (in which the polyethylene component acts as the PCL). The metal components of TKA are fixed by the uncemented technique or using a polymethylmethacrylate bone cement.
TKA has become a very common procedure in the last years, being one of the most common surgeries nowadays not only in orthopaedic surgery but in the general medical field. It is demonstrated to improve function, reduce pain and thus increasing the quality of life of patients with knee OA undergoing the operation [23, 46, 47]. The evolution of the implants has led to a major improvement in their survival reaching a near 95% 10-year survival for most implants [28, 61, 74]. Even though this numbers are positive, around 10-25% of the patients undergoing TKA are not satisfied with the outcome [2, 10, 19, 79, 82]. It has been reported that the outcome of the surgery correlates with patient specific factors [27, 50, 92], implant type and surgical technique [13, 39, 63].
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Fig.2.4.1. The individual components used in total knee replacement. B. The implants and joint liner assembled in place, minus the patellar implant.[89]
2.5 TKA Surgery
The main goals of TKA are to reduce joint pain, improve function of the joint and to restore a neutral mechanical axis with a stable knee prosthesis [88]. To achieve these goals, surgeon must perform a proper preoperative planning, understand the surgical technique, and choose the right instruments and implant.
TKA exposure may vary, being the most used the medial parapatellar surgical approach (others include midvastus, subvastus, trivector, quadriceps snip and others) [81]. This approach ensures proper exposure of underlying tissues reducing the damage to them and allows the patella to be everted or laterally subluxaed. After superficial incision a deeper incision is made to enter the capsule. After proper positioning of the patella, osteophytes and anterior cruciate ligament are removed. After the preparation and clearance of the area are finished, follows the bone cuts, of the distal femur and the proximal tibia, with no major importance in the order of them. The bone cuts are performed using intramedullary and/or extramedullary guides with standard or preoperatively pre-set angles. These bone cuts will be crucial for a proper postoperative alignment, which is generally accepted to be within 3° of a neutral mechanical axis [9, 14]. The femoral and tibial components are fixed in a perpendicular line to the mechanical axis in the coronal plane. In the sagittal plane, the posterior tibial slope must be restored; either determined by bone cut or by the implant.
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Fig.2.5.1. Main steps of knee replacement surgery [36]
The femoral component must be position taking into account the femoral bowing in order to avoid anterior femoral cortex notching and to restore the posterior offset. The proper election of bone cuts and component size provide a good patellar tracking and an appropriate height of the joint and ligament balance. Once the bone cuts are performed, the stability and function are tested with trial components, which can be changed according to the surgeon’s judgement. Once the components have been chosen, the final prostheses are positioned either with or without cement depending on the prosthesis. When cement is used, time must be provided for it to harden, and once it’s hard, the remains of it must be removed. Once everything is finished, an intraarticular catheter may be placed and wound suturing is made.
2.6 TKA Accuracy
The accuracy of the procedure should be evaluated in short and long term. Short term evaluation of TKA accuracy is performed by radiographic measurement of the alignment of mechanical axis and individual components in the coronal, sagittal and transverse plains, being the most important the coronal evaluation. Long term evaluation of the results is performed by measuring range of motion, function, patient subjective feedback and recording of the prosthetic survival.
Neutral mechanical alignment is achieved by performing femoral and tibial bone cuts and component positioning at 90° of the femoral and tibial mechanical axes respectively. Human error plays a crucial role in postoperative mechanical and component malalignment [1]. There are some studies that estimate the rate of malalignment (a deviation greater than 3° from the neutral position) using conventional
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instruments can range from 2% to 72% [9, 33]. A good performance in TKA neutral alignment has been described to be about 75%.
There have been developed several techniques aimed to improve the accuracy of TKA such as patient specific instrumentation and computer assisted TKA. From the studies about computer assisted technique there are some that state an improvement in component orientation and mechanical axis [3, 67] while others have shown no improvement compared to conventional TKA [12]. Patient specific instrumentation technique has shown a similar result, demonstrating no significant improvement in comparison to conventional technique.
Fig.3.5.2. Postoperative long-standing lower extremity radiographs: A – normal alignment: straight mechanical axis alignment (MAA) with perpendicular femoral component (FCA) and
tibial component (TCA) angles; B – malaligned mechanical axis alignment and femoral component and tibial component position [87].
2.7 The influence of anatomical femoral angles on TKA
Among the researches regarding influencing factors on TKA alignment, the ones regarding femoral bowing angle (FBA) and Caput-Collum-Diaphyseal (CCD) angle are a minority. Most of the studies are focused on preoperative varus/valgus angulation of the knee. Nonetheless, there are some reference publications on the matter. The standard TKA technic has a recommended fixed femoral cutting angle of 5-7°, which depending on the individual features of femoral anatomy of each patient may cause femoral component malalignment.
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Lasam et al. studied the influence of preoperative anatomical femoral and tibial angles, including FBA, femoral condylar orientation and severe tibial plateau inclination in Korean females. Their results showed that FBA and varus femoral condylar orientation had a correlation with postoperative alignments and that several clinical outcome scales were inferior in the outlier group. The prevalence of femoral lateral bowing was 88% in the TKA group whereas in the control group was 77% [57]. In a study published by Nam et al. similar variability in the relationship between distal femoral anatomic and mechanical axes in patients undergoing primary TKA was found. The reason was believed to be that 28.6% of patients were outside the range of 5 ± 2°, which fall out of the recommended fixed angle of standard technic [72]. Similar results were found by Mullaji et al. who found that 18.8% of the patients in the research had a femoral mechanical-anatomical axis greater than 9°. One of the most influencing publications on the influence of anatomical femoral angles on femoral cuts during TKA was published by Kim et al. [52]. They studied the influence of FBA, CCD and FVA on each other and their influence on distal femoral cutting angle. The FBA was the factor that showed the strongest correlation with this angle, while the CCD showed no correlation. Apparent femoral bowing (>3°) was found in 13.3% of the patients, whose femoral cutting angle was 8.6° ± 2.2° relative to the femoral intramedullary guide.
The apparent influence of FBA and CCD on femoral valgus angle is something that surgeons should consider for the femoral distal cut during TKA, for apparent and severe FBA may have considerable influence on the postoperative mechanical axis alignment if not taken into account.
2.8 Effect of malalignment after TKA
In 2012 a research was published by Halder et al. in which was demonstrated that an increase of varus-valgus angle on 1° would increase de medial-lateral load by 5% [35]. This demonstrated the importance of properly aligned prosthesis after TKA to increase the implant survival and functional outcomes.
It is generally accepted that a knee after TKA is perfectly aligned when mechanical axis is at 180° in the coronal plane [1, 32, 45, 77]. Most of these publications accept as normal a deviation of ≤3° from the neutral alignment to accomplish good long-term results [13, 39, 62]. The correct component, and thus, mechanical axis alignment provides an even distribution load on the knee, spreading the weight evenly on the polyethylene component, tibial component, knee ligaments and lower extremity osseous structures, which altogether provide a better functional outcome; while a malalignment of the hip-knee-ankle axis along with patient specific factors, such as obesity, can produce instability of the knee, damage to the soft tissues of the knee, tibial bone collapse, decreased functional outcomes and a reduced component survival [5, 7,83]. Some cadaver studies demonstrated during biomechanical investigations that more than 3° of tibial component varus or valgus alignment increases the strain received by lateral or medial compartments of the proximal tibia [31, 38, 92].
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Several other publications concluded that a malalignment superior than 3° will increase the rate of polyethylene wear off, thus destabilizing the knee and leading to increased revision rate [16, 45]. Ritter et al. demonstrated that not only tibial component malalignment gad repercussion in the long term survival, but femoral component malpositioning also has influence on the TKA revision rate [77]. The same authors concluded that varus malalignment had a higher revision rate in comparison with normally or valgus aligned TKA.
The long term functional results after TKA have been widely studied in the past, leaving an unclear set of results regarding the matter. Some studies like the one conducted by Hoppe et al. [37] stated that there was no correlation between coronal alignment and knee function at a 5-year follow-up while others like that of Huang et al. [39] suggests that on the same follow-up period there was a correlation between these two factors, with the correctly aligned TKA having a higher Knee Society Score (KSS) and Short-Form 12 physical scores (SF-12). Longstaff et al. published an article in which patients with correct postoperative TKA alignment had a faster rehabilitation and better function than the outliers [63]. This discordance of results has been reported by many authors in the last years, with some results of significant correlation between alignment and functional outcome [13, 39, 63] and some results of no correlation between them [66, 68, 91]
As well as the mechanical axis alignment and its correlation with functional outcomes, the influence of individual component alignment and its influence in postoperative long-term function of the knee joint have been widely studied, and, as well, contradictory results have appeared. Again Longstaff et al. [63] reported a better KSS in patients with femoral components within 2° of neutral alignment in comparison to outliers. On the other hand, Dossett et al. found that at 6 months postoperatively, the Western Ontario and McMaster Universities Osteoarthritis Index, Oxford score, KSS scores and flexion was better in kinematically aligned knees with the femoral component 2.4° more valgus and the tibial component 2.3° more varus.
Rienmüller et al. studied the influence of femoral component rotation on TKA outcome. There is a large given natural variability in optimal rotational orientation, in this study between 6° external rotation and 15° internal rotation, with no difference with regard to subjective and objective outcome in a 5-year follow-up [76].
Kim et al. studied the influence of postoperative coronal, sagittal and rotational alignment of TKA components on component survival in a long-term follow-up research. Their conclusions stated that a surgeon should look up to keep femoral component alignment at 0-3° in the sagittal plane and a rotational angle within 2-5° of external rotation and the tibial component alignment between 0-7° on the sagittal plane and a rotational angle within 2-5° on external rotation. [51]. Kelly et al. showed an association between femoral and tibial component malrotation and patellofemoral complications, such as patellar dislocation and subluxation, patellar mal -tracking, lateral patellar tilt and lateral patellar overhang [49]. Two studies demonstrated that
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too much or too little resection of the tibial slope could affect flexion function by increasing or decreasing flexion gap tightness and instability [43, 74]. One study showed increased knee functional flexion in a group of patients when the femoral component was placed in a flexed angle (mean 5.3°) compared to a control group who had the component neutrally placed (mean 1.6° [71], while another study reported that a femoral component placed at more than 3.5° from the mechanical axis was related with an increased flexion contracture at one-year follow-up [65].
21 3. METHODS
3.1 Patients and methods:
The research was performed in the hospital of Lithuanian University of Health Sciences, Kauno Klinikos, at the department of Orthopaedics and Traumatology. We evaluated 123 OA patients treated with TKA in the first halve of the year 2016.
The research was divided in two parts according to the objectives of our research plan. In the I part we investigated the component and anatomical alignment angles on the coronal plane after TKA. In II part we evaluated the effect of component alignment, FBA, CCD angles on overall mechanical axis alignment.
3.2 Study Population:
We included 123 consecutive OA patients treated at Kauno Klinikos Ligonine (KKL) from 01/01/2016 till 30/06/2016.
3.3 Inclusion Criteria
-Patients diagnosed with OA and treated with TKA in selected time. -Patients on the age of 50-90 years.
-Patients with present frontal postoperative long standing radiographs of the lower extremity.
3.4 Exclusion Criteria
-Patients treated with TKA from other disorder different from OA. -Patients being <50-90> years of age.
-Patients with previous knee bone surgeries (e.g. Osteosynthesis, osteotomy).
-Patients without frontal postoperative long standing radiographs of the lower extremity. -Patients with defective radiological images (absence of femoral head or talus on X-ray; lower limb rotation).
-Patients with fixed-angle TKA implants. -Patients with hip arthroplasty.
22 3.5 Allocation of the groups
In the first part of our research anatomical angles (CCD, FBA) and prosthetic component angulation (femoral and tibial) were postoperatively evaluated and classified as outliers or within standard range according to literature. Coxa vara and coxa valga were defined as a CCD angle of <120° and >135° respectively. Apparent femoral bowing was defined as a medial or lateral FBA greater than 3° from the neutral femoral shaft line. Normal component alignment was defined as TKA in which position of femoral and tibial components were within 3° from the neutral mechanical axis and abnormal component alignment was defined as a radiological deviation greater than 3° from neutral mechanical axis.
In the second part of our research we evaluated the effect of component alignment, FBA and CCD angles on overall mechanical axis alignment after TKA. Neutral mechanical axis alignment was defined as an angulation within 3º of neutral mechanical axis (180°) and abnormal alignment was defined as a radiological deviation greater than 3º from neutral mechanical axis.
23 3.6 Patients’ characteristics
Out of 123 patients fitting in the research criteria, 92 were females and 31 were males. The mean age was 67 years. From all TKA patients 55 had it on the left side and 68 on the right side.
3.7 Radiological assessment
Days after the operation long-standing radiographs were performed by assistants of the Department of Radiology using Siemens MULTIX PRO system (Siemens Medical System Inc.). The plain radiographs were performed on the phosphor plates (Regius model RC-110T, Konica Minola medical & Graphic Inc.) and digitalized (Direct Digitalizer Regius model 210, Konika Minolta Inc.). The measurements were performed on the digitalized radiographs using Cedara I-Reach™ radiology viewer (Cedara Sofware corp. Merge OEM).
Long-standing lower extremity anterior-posterior radiographs (120x30) were performed at a focal distance of 2.5m. With the patients standing on both legs parallel to each other and the patella facing forward. Long-standing hip-knee-ankle radiographs are the standard method for lower limb alignment evaluation.
Postoperative radiological evaluations were performed. In the research Caput-Collum-Diaphyseal angle (CCD) was defined as the projection of the angle between diaphysis and the femoral neck; Femoral Bowing angle (FBA) was defined as femoral shaft curvature deformity on the coronal plane, and the Mechanical Axis alignment (MA) was defined as the medial Hip-Knee-Ankle angle with reference points: the centre of the femoral head, the centre of the knee (as the midpoint between the intercondylar femoral component sulcus and the centre of the tibial component) and the centre of the ankle (centre of the superior facet of the talus).
3.8 I study part (Investigation of component and anatomical angles alignment on the coronal plane after TKA)
255 consecutive OA patients treated with TKA were evaluated radiologically. From those patients, 123 were included in the study. Femoral CCD angle, FBA and femoral and tibial component alignment were studied. The patients were divided depending on the individual results on each of the different categories as outliers or within normal range of each one of the studied factors, according to the appropriate literature.
From the 123 patients, 12 had coxa valga of the hip (>135°) and 38 had coxa vara (<120°); 64 patients had apparent bowing of the femoral shaft, of which 5 were medial (<-3°) and 59 were lateral (>3°); 94 patients had a femoral component alignment within 3° from neutral alignment while 28 were placed on the outlier group, 17 from which were <87° and 11 were >93°; 105 patients had a tibial component alignment within 3° from neutral alignment while 15 were <87° and 3 were >93°.
24 3.9 II Study part (Evaluation of the effect of component alignment, FBA, CCD angles on overall mechanical axis alignment).
From the 255 included in the study only were evaluated those 123 patients fitting our criteria. In this part of the study we evaluated the correlation between the results of the first part of our study and the overall mechanical alignment of the lower extremity. The mechanical-axis alignment was measured and from the 123 evaluated cases, 81 had an alignment within 3° of neutral alignment while 42 were placed on the outlier group. From those 42, 35 were varus knees (<187°) and 7 were valgus knees (>193°).
3.10 Statistical analysis
Data are presented as means ± standard deviations (SD). To determine whether the data were normally distributed we performed a Shapiro-Wilk normality test. As part of the data was not normally distributed we used both parametric and non-parametric tests. As the calculated p-values were similar in terms of significance independent of the method used, the non-parametric tests were chosen to report the data. We used non parametric Mann-Whitney test for independent samples. Fisher’s exact test was used when comparing proportions between the groups. Spearman’s rank correlation coefficient was used to investigate the relation between MA and age, TC, FC, FBA, CCD. Multiple linear regression analysis (backward method) was used to evaluate the relationship between the MA grouping and potential risk factors (gender, age, TC, FC, FBA, CCD). A p-value of < 0.05 was considered significant. SPSS software (SPSS, Chicago, Ill) was used for the calculations.
25 RESULTS
The 123 patients who met the inclusion criteria were radiologically evaluated. These patients mean age was 68±8 years old with a minimal and maximal age of 51 and 90 respectively. The mean Mechanical Axis (MA) was 179±3° with minimal and maximal values of 169.6° and 187° respectively. The mean Tibial Component (TC) was 89±2° with minimal and maximal values of 83.5° and 93.5° respectively. The mean Femoral Component (FC) was 89±3° with minimal and maximal values of 83.3° and 96.3° respectively. The mean Femoral Bowing Angle (FBA) was 3±3° with minimal and maximal values of -5.3° and 15.2° respectively. The mean Caput-Collum-Diaphyseal angle was 124±8° with minimal and maximal values of 101.1° and 141.6° respectively.
I study part (Investigation of component and anatomical alignment angles on the coronal plane after TKA)
N Minimum Maximum Mean
Std. Deviation age 123 51,0 90,0 67,870 8,2571 MA 123 169,6 187,0 178,724 3,1613 TC 123 83,5 93,5 89,154 1,9393 FC 123 83,3 96,3 89,498 2,5629 FBA 123 -5,3 15,2 2,904 3,4048 CCD 123 101,1 141,6 124,402 7,9296
We evaluated the influence of gender in the different parameters studied and there was no correlation. There was though, a difference of FBA among the two sexes having the females a mean FBA of 3.3° and the males of 1.57° from the neutral femoral shaft line (p=0.33)
26
Age didn’t have any statistically significant influence on any of the factors evaluated, although the MA had a tendency to decrease with increasing age (p=0.120)
Graf. 4.1.2. Influence of age on MAA
On the evaluation regarding distribution of TC alignment we found that 105 patients (85.4%) had a normally aligned TC (average 89.5°) and that 18 (14.6%) were out of that range (average 86.9°). From the outlier group 15 (12.2%) patients had a varus
angulation (average 85.6°) and 3 (2.4%) showed a valgus angulation (average 93.4°). Regarding the femoral component alignment we didn’t find any statistically significant data. From the 123 patients 95 patients (77.2%) had a normally aligned FC (average 89.6°) and that 28 (22.8%) were out of that range (average 89.0°). From the outlier group 17 (13.8%) patients had a varus angulation (average 85.5°) and 11 (8.9%) showed a valgus angulation (average 94.5°).
27
On the evaluation regarding distribution of FBA was found that 59 patients (48%) had a non-apparent FBA (average 0.7°) and that 64 (52%) were out of that range (average 4.9), from which 5 (4.1%) patients had an apparent bowing towards the medial surface
(average -4.2°) and 59 (48%) showed an apparent bowing towards the lateral surface (average 5.6°).
Graf. 4.1.4. Distribution of the different angles of FBA
On the evaluation regarding distribution of CCD angulation in the given population was found that 73 patients (59.3%) had a CCD angle within normal range (average 127.1°) and that 50 (40.7%) were out of that range(average 120.3°). From this outlier group, 38 (30.9%) patients had a coxa vara angulation (average 115°) and 12 (9.8%) showed a coxa valga angulation (average 137.3°). We evaluated the possible correlation between CCD and age to find that no correlation lies between these two factors (p=0.232).
28 II Study part (Evaluation of the effect of component alignment, FBA, CCD angles on
overall mechanical axis alignment)
On the evaluation regarding distribution of Mechanical Axis (MA) alignment in the given population was found that 81 patients (65.9%) had a normally aligned MA (average 179.8°) and that 42 (34.1%) were out of that range (average 176.4°). From the outlier group 35 (28.5%) patients had a varus angulation (average 174.8°) and 7 (5.7%) showed a valgus angulation (average 184.7°).
Graf. 4.2.1. Distribution of MAA
In relation to the correctly aligned MA, the TC was properly aligned in 77 (62.6%) patients and malaligned in 4 (3.3%), whereas in the malaligned group of MA the TC was properly aligned in 28 (22.8%) patients and malaligned in 14 (11.4%). (p=0.002). Similar to the TC, FC was evaluated in relation to MA. The FC was properly aligned in 73 (59.3%) patients and malaligned in 8 (6.5%) on the neutrally aligned MA group, whereas in the malaligned group of MA the FC was properly aligned in 22 (17.9%) patients and malaligned in 20 (16.3%)(p=0.000). In the study of MA and its relation with the component alignment, three patients had both components at varus, thus having an overall varus MA, and one patient had the tibial component in varus and the femoral in valgus which annulled them, leaving a neutrally aligned MA.
29 In relation to the correctly aligned MA, the FBA was not apparent in 38 (30.9%) patients and apparent in 43 (35.0%), whereas in the malaligned group of MA the non-apparent FBA was found in 21 (17.1%) patients and apparent FBA was found in 21 (17.1%). (p=0.849)
Graf. 4.2.3 Relation between MA and FBA angulation
Among the correctly aligned MA, the CCD was within the standard range in 48 (39%) patients and coxa vara/valga in 33 (26.8 %), whereas in the malaligned group of MA the CCD was in range in 25 (20.3%) patients and coxa vara/valga in 17 (13.8%) (p=1.00).
30 5. DISCUSSION
There are many publications regarding the influence of femoral and tibial component alignment in the overall mechanical axis alignment to this day. Nonetheless, studies regarding the influence of anatomical femoral angles, as Caput-Collum-Diaphyseal angle and Femoral Bowing angle, on the mechanical axis are not as common, with very few examples about it.
Among the orthopaedic surgeons, it is widely accepted that a postoperative neutral mechanical angle alignment after a total knee replacement brings better outcomes and longer survival, as it has been demonstrated in several studies [1, 7, 16, 24, 25, 31, 45, 77, 78, 93]. This goal is achieved by a proper technique and planning. Whereas tibial positioning is usually achieved by performing a perpendicular cut of the tibial head (because of its particular anatomical straight perpendicular structure), achieving a proper femoral component positioning has been a matter of discussion among orthopaedic surgeons because of the variability of the femoral anatomical structure among individuals. It has been studied in many cases the different results between a standard (fixed-angle) femoral cut technique and the individualized measure of femoral angles and proper planning for the femoral cut [17, 87].
In our research we studied the component alignment distribution among those osteoarthritic patients treated with total knee arthroplasty who met our criteria. We got 123 patients and we evaluated the distribution of the different factors, falling into one of two categories: properly aligned and malaligned components. Regarding the tibial component, we found out that from the 123 evaluated patients 105 (85.4%) had a component alignment within <3° from the neutral alignment, whereas regarding the femoral component we encountered 95 (77.2%) patients with a neutral alignment, leaving 18 (14.6%) and 28 (22.8%) patients with malaligned tibial and femoral component respectively. Furthermore, we evaluated the distribution of those malaligned tibial and femoral components, to find out that from the tibial outliers 15 (12.2%) patients had a varus angulation and 3 (2.4%) showed a valgus angulation and from the femoral outliers 17 (13.8%) patients had a varus angulation and 11 (8.9%) showed a valgus angulation. Our results do not coincide with those of Magnussen et al., whose results on tibial component distribution showed that from 553 patients, 514 (93%) were neutrally aligned, 35 (6.3%) had a varus angulation and 4 (0.7%) had a valgus angulation of the component [66]. The same author evaluated the distribution of femoral component angulation after TKA, and these results, as well as those of the tibial component, differ from ours. In his study, 554 patients were evaluated, from which 513 (92.5%) were neutrally aligned, 25 (4.5%) showed a varus alignment and 16 (3%) fell into the valgus component angulation group.
31
Regarding the femoral angles distribution fewer researches have been conducted in comparison with those focussing on component alignment, and those who have been conducted focus on the influence of these on the distal femoral cut and in turn on the overall mechanical axis. The distribution of FBA in our group was 59 patients (48%) had a non-apparent FBA (<3° from the neutral anatomical femoral line) and that 64 (52%) were out of that range. Lasam et al studied the prevalence of femoral lateral bowing on TKA patient, and that of lateral femoral bowing was 88% [57], although this studied considered lateral FBA as any bowing lateral to the femoral anatomical line, instead of our criteria of >3° for an apparent FBA. Kim et al. studied FBA, CCD and FVA in one of the most influencing researches on the matter. They found a distribution of apparent FBA of 13.3% on the studied group.
Regarding the distribution of CCD angle in TKA we found one study regarding the distribution of CCD angle but it was a cohort study evaluating full body trauma CT of non TKA patients. The distribution of the CCD angle corresponding to an age group similar to that of our own study had a mean CCD of 143.4° with a maximum of 164.6° and a minimum of 124° [8], which differs from our own mean, maximal and minimal values, which are 124±8° 101.1° and 141.6° respectively.
On the evaluation of mechanical alignment of the knees after TKA, we found that 81 patients (65.9%) had a normally aligned MA and that 42 (34.1%) were out of that range and that from those 42 outliers 35 (28.5%) patients had a varus angulation and 7 (5.7%) showed a valgus angulation. Our results are not far from other studies like those by Chong et al. or Huang et al. whose percentage of neutrally aligned MA was 74.7% and 74.6% respectively. Our results are even more similar to those from other studies like the one by Magnussen et al., whose outlier rate was 34% [66].
Our main finding was on the evaluation of the correlation between component malalignment and mechanical axis changes. We found that the percentage of tibial component malalignment was greater on the malaligned MA group (33%) than in the neutrally aligned group (4.9%) (p=0.002), which are relatively similar to those results of femoral component within the same groups (44.6% in the malaligned MA group and 9.9% in the neutrally aligned group) (p=0.000). These results coincide somehow with those by Stucinskas et al. who showed that, from their results, the 29 patients from the outlier group 8 (27.5%) had a TC malalignment and 11 (38%) had a FC malalignment compared to the 11% malalignment rate of both components in the neutrally aligned MA group [87]. The reason for this correlation is the direct effect of femoral and tibial component alignment on the overall MA, for the sum of the angulations of both components should result in the MA angulation (with exception of minimal variations due to knee ligament laxity individual to each patient)
On the investigations regarding the femoral anatomical angles, Kim et al. studied the variations of several factors (CCD, FBA among them) among Korean population and how these factors were affecting the preoperative distal valgus cutting angle referenced off the femoral intramedullary guide. They found the biggest correlation between FBA
32
and the FVA, greatly influencing on the femoral cutting angle (p=<0.001), thus suggesting an influence in overall MA alignment [52]. In our research the results differ from those of Kim et al. in that no correlation was found between FBA and overall MA alignment (p=1.00). This discordance may result from the different approaches in evaluating the correlation. While they evaluated the direct influence on the distal femoral cut for the use of particular femoral component angulation, we evaluated the direct relation between the FBA and MA after TKA. The influence of FBA on a the perpendicular cut may be greater than in the overall MA alignment. Our results regarding CCD evaluation and its correlation with MA alignment do coincide with those from Kim et al. showing no correlation at all with either the femoral component or the mechanical axis alignment [52] whilst other studies as the one conducted by Nam et al. showed that an increased CCD angle strongly correlates with a decreased FVA, thus influencing in the femoral cutting angle and in turn its alignment.
A drawback of our study is that the was not possible to measure the preoperative FVA, which could have given a different perspective on how femoral anatomical angles were distributed and how they could affect the distal femoral cut and in turn the overall mechanical axis as it has been suggested in other publications [84]. Another drawback faced in our investigation was the impossibility to add other personal factors such as BMI (which has been demonstrated to affect postoperative lower limb alignment after TKA [77]) or intraoperative evaluable factors such as ligament instability (demonstrated by Sharkey et al. in 2002 [83]).
33 6. CONCLUSIONS
1. On the preoperative planning regarding TKA more attention should be paid to the varus malalignment of the femoral component, for it is the most common component malalignment present on TKA surgeries.
2. Age does not affect postoperative MA alignment on TKA
3. Tibial and femoral components proper alignment is crucial to achieve a neutrally aligned MA on TKA.
4. FBA and CCD do not have statistical correlation with the overall MA alignment on TKA.
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