37Specific Issues in Surgical Techniquesfor Unicompartmental Knees 37

(1)

37 Specific Issues in Surgical Techniques for Unicompartmental Knees

L. Pinczewski, D. Kader, C. Connolly

Summary

The concept of unicompartmental knee arthroplasty (UKA) is not new. Although it was introduced in the 1960s, it did not gain popularity till the early 1990s. The new interest in UKA was attributed largely to the technological advances in biomaterial science, a refined surgical technique, and patient selection criteria with the intro- duction of a minimally invasive approach. UKA is per- formed using either resurfacing, resection, or mobile- bearing designs. The three designs share a common theme, which involves achieving ligament balance through bony resection.A novel technique was developed to pre-balance the knee joint and restore ligament tension prior to bony resection. This alternative approach mini- mizes bony resection and takes into consideration the fundamental differences between the basic principles of total knee arthroplasty and unicompartmental knee arthroplasty.

History and Development of

Unicompartmental Knee Arthroplasty

The concept of unicompartmental knee replacement or resurfacing is not new. McKeever, in 1960 [28], and Mac- Intosh and Hunter, in 1972 [23], reported on the insertion of metallic spacers onto the worn-out tibial plateau. In the early 1970s, Gunston reported the use of polycentric femoral and tibial resurfacing for osteoarthritic knee joints which retained the cruciate ligaments and simulated normal joint kinematics [10-12]. Inspired by the work of Gunston and McKenzie, Engelbrecht designed the St.

George sledge prosthesis in 1969 [8]. In 1972, Marmor introduced a modular unconstrained unicondylar device designed to provide different plateau thickness and to resurface single or both arthritic femorotibial compart- ments [24-27]. At the same time bicondylar designs such as the Geometric knee emerged [6], which consisted of two linked unicompartmental components. The bicom- partmental design was later transformed into a tricom- partmental design by adding an anterior femoral flange for the femoropatellar articulation.These procedures sac-

rificed the anterior cruciate ligament and retained or sub- stituted for excision of the posterior cruciate ligament.

Therefore, a certain degree of ligament balancing was required, which resulted in the development of instrumentation and surgical techniques for total knee arthroplasty.

Although selected authors initially reported positive results with unicompartmental knee arthroplasty (UKA) [17-19, 26, 35], high failure rates began to appear in the lit- erature [15,16,20].In highly specialized units,excellent results were achieved due to the combination of a high degree of surgical skill and experience. This translated into strict patient selection criteria and an intuitive understanding of ligament balance. However, Insall and co- workers reported their disappointment with medial UKA. Nevertheless, they advocated the procedure for the lateral compartment,which did not do well after tibial os- teotomy [15, 16]. In retrospect, it appeared that the lateral compartment was more suited to the available prosthetic designs and contemporary implantation techniques.As a result of Insall’s studies, the use of UKA fell out of favor in the USA.

The demise in popularity of the UKA can be attributed to many factors [26].The most significant factor was the use of a surgical approach similar to that for total knee arthroplasty (TKA).The surgical approach for UKA therefore demanded results equal to those with total knee arthroplasty. Furthermore, the retention of the major ligaments of the knee joint, combined with the lack of instrumentation to align components and guide resections, led to a high margin of error and a difficult and prolonged learning curve.

The Resurgence of Interest in

Unicompartmental Knee Arthroplasty

The technological advances in material science during the 1980s have led to specific improvements in polyethylene quality and in the abrasive properties of metallic components. At the few centers that persevered with UKA, results were seen to improve with modification of prosthetic design to remove edge loading and thin polyethylene,with the use of a decreased constraint in the sur-

(2)

Chapter 37 · Specific Issues in Surgical Techniques for Unicompartmental Knees – L. Pinczewski et al.

gical design of components, but most importantly with better patient selection. It became clear that unicompartmental replacement was contraindicated for patients with inflammatory synovitis, multicompartment disease, and severe deformity with or without subluxation. It also became clear that UKA was an intra-articular procedure that could not be used to correct a significant nonarticu- lar deformity such as tibia vara. Relative contraindica- tions included anterior cruciate ligament degeneration, chondrocalcinosis, lateral meniscectomy, osteonecrosis, combined obesity and small bone size as may be seen in a subgroup of osteoarthritic women.

The renewed interest in UKA in the 1990s can be attributed to John Repicci,who pioneered the minimally invasive approach,without dislocating the patella or violat- ing the suprapatellar pouch [33]. The aim was to offer the patient a lesser procedure than a TKA. Repicci’s recogni- tion of this in 1992 led to his concept of minimally invasive UKA being a restoration procedure supplementary to future TKA.This concept is valid,as the Repicci technique does not sacrifice significant tibial bone stock.

The minimally invasive approach to UKA has led to a reduction in postoperative morbidity, a decrease in reha- bilitation time, excellent subjective results, and a good long-term outcome [3, 13]. In addition to better cost-ben- efit ratios for patients and health systems, these factors have driven orthopedic surgeons to reconsider UKA as a real option for their patients with unicompartmental knee osteoarthritis.Given that the most common cause of UKA failure is tibial loosening, resulting from polyethylene wear and component malposition,however,a re-evaluation of the surgical technique was required.

Current Surgical Options

There are currently three systems with different surgical techniques for the implantation of UKA.

Resurfacing Designs. Resurfacing designs such as the Repicci II Unicondylar Knee System (Biomet Inc.Warsaw, IN) use a free-hand resurfacing technique in which alignment is achieved without the use of instrumentation guides. The major advantage of this system is minimal bone resection, preserving the tibial buttress. This free- hand technique has been criticized, however, by many authors who believe that proper alignment often cannot be obtained without the use of instruments [2, 21, 34].

Resection Designs. Resection design systems integrate modular saw-cut components and jig-type guide instrumentation to help in making the correct bony resection.

The use of intramedullary instrumentation systems allows for a more standard method of placing unicompartmental prosthetic components and ensures precise

anatomical cuts and component fit [2]. It is a technique familiar to TKA surgeons. Although this type of guide instrumentation produces accurate resections,it does not deal with ligamentous balance, which is crucial to ensure a successful outcome regardless of design. The main dis- advantage of resection designs is the considerable amount of bone loss, particularly from the medial tibial plateau. Combined with the use of pegs, screws, and fixation methods, this further compromises medial tibial bone stock, which may be a significant factor during later revision.

Berger reported excellent results with resection UKA utilizing a patellar dislocating approach [1].

However, the results of combining resection arthroplasty with a minimally invasive approach may increase the complexity of the procedure, requiring a higher degree of surgical skills and experience, with greater understanding of the basic principles of the technique, to achieve a successful outcome [9]. This may not be available to the multi-disciplinary orthopedic surgeon.

Mobile-bearing Designs.The Oxford Meniscal Prosthesis, a mobile-bearing design, has produced excellent long- term survivorship with low wear characteristics in expe- rienced hands and with a patella dislocating approach [30-32,37].It is acknowledged that in order to obtain these excellent results,adherence to strict selection criteria and a high degree of surgical precision are required. Early experience with this technique illustrated the difficulty in achieving precise ligament balancing due to the small margin of error [22].Another main drawback of the technique is the significant femoral and tibial resection required to accommodate even the thinnest mobile bearing.

The common theme of these apparently differing surgical techniques is that restoration of ligament balance is essential.Also,these three surgical techniques share a fea- ture common to TKR, i.e., that bony resection precedes ligament balancing,which is achieved by comparing flexion and extension gaps as well as trial components. The algorithm for obtaining ligament balance in TKA by pre- liminary bony resection followed by sequential ligament release [29, 40, 41] is not suitable for UKA. As one of the pioneers of unicompartmental arthroplasty asserts,

“A unicompartmental knee replacement is not half a total knee” [9].

An alternative approach is to restore the joint line and ligament tension as well as lower limb alignment prior to making any bony resection of the femur and tibia. This has the added advantage of minimizing bony resection and restoring the joint line with respect to the unaffected compartment and aligning components through the complete flexion and extension arc. This technique is compatible with a minimally invasive approach, as the patella should not be dislocated, since otherwise abnormal joint kinematics would occur.

(3)

Novel Technique

A novel technique was developed by the senior author (Accuris, Smith & Nephew Inc, Memphis, TN). This technique determines the appropriate joint line using an articular spacer (or ‘shim’), prior to making any femorotibial resection. The articular spacer is designed to closely match the femorotibial anatomy (similar to a tibial joint spacer). Osteophytes are removed first to achieve normal ligament tension. When the spacer remains stable through a full range of knee motion, the proper joint line is defined.Thus it is possible to pre-balance the knee joint prior to bony resection. With the shim in situ, the tibial cut can be set to minimize the resection level from the restored joint line. An extramedullary tibial guide then allows a cutting block to be positioned accurately in all planes.The cutting jig will guide the resection of both the proximal tibia and posterior femur, providing a parallel flexion space. This technique results in minimal tibial resection and joint line restoration.

An important principle is resection of the proximal tibia at an appropriate varus/valgus angle. Cartier has shown that a tibial resection made at right angles to the mechanical axis of the tibia, similar to that of total knee arthroplasty, is rarely suitable for UKA due to the intra- articular obliquities of the medial compartment (⊡ Fig.

37-1) [4]. UKA differs from TKA in that alignment can be corrected only to the normal tension of the knee ligaments. Thus the UKA surgical procedure can correct alignment only within the joint. Attempts to correct low-

er limb alignment by exceeding normal ligamentous length have resulted in failure. Thus the proximal tibia must be resected along its epiphyseal plane.This has to be assessed individually for each joint but generally dictates a varus alignment of components in the sagittal plane and a 3°-5° posterior slope. This can be assessed intraop- eratively using the jig as a guide. If the resected proximal tibial “biscuit” is uniform in both anterior/posterior and medial/lateral directions, then component stability should be maintained throughout a full range of motion.

The femoral instrumentation consists of a device that resects the femoral surface by reaming 3-4 mm of bone proximal to the restored joint line through full range of motion. The system utilizes a femoral reamer that locks into a tibial base plate.The reamer is firmly planted on the resected tibial plateau and the distal femur is reamed through its range of motion while normal ligamentous tension is maintained.Thus the joint’s own ligaments and anatomy guide the bony resection (⊡ Fig. 37-2). This min- imizes femoral bony resection and, given that the replacement femoral component does not exceed 4 mm in thickness from the resected surface when applied, abnormal forces at the joint line are minimized (⊡ Fig. 37-3).

Also,over-correction,a known cause of UKA failure,is al- most impossible. Conversely, slight under-correction of the angular deformity is known to protect the opposite compartment from excessive loading [5, 14, 38].

Prosthetic design has been modified to avoid the known causes of prosthetic failure.A tapered anterior as- pect and rounded edges of the femoral component minimize the risk of patella impingement and abnormal polyethylene edge loading, respectively. Fixed-bearing UKA designs must be unconstrained to minimize shear stress at the cement-bone interface of the component. A poten- tial significant improvement is the use of a ceramic femoral surface such as oxinium with a lower coefficient

37

⊡ Fig. 37-1.Resection guide for tibia and femur ⊡ Fig. 37-2. Femoral reamer

(4)

Chapter 37 · Specific Issues in Surgical Techniques for Unicompartmental Knees – L. Pinczewski et al.

of friction; this has variably been reported to decrease wear rates in biomechanical simulators by a factor of 2-10 [36,39].Debate exists regarding the use of a metal-backed tibial component versus an all-polyethylene component.

It is accepted that a minimum polyethylene thickness of 6 mm must be implanted [7, 13, 26, 27]. The advantage of an all-poly tibial component is that a minimum 8 mm polyethylene thickness is implanted, and due to the lack of screws, pins, or pegs, any future revision is conserva- tive regarding medial tibial bony loss [5, 13]. These technological advances should improve the wear characteristics of current designs and may significantly improve long-term survivorship.

However, these issues in surgical technique can be verified only by a prospective randomized study. Re- search should initially aim to verify the reproducibility of any technique utilizing the current minimally invasive approaches, and then be followed by a long-term study to confirm the place of unicompartmental arthroplasty in the management of osteoarthritis.

In summary, the principles of TKA are fundamental- ly different from those of UKA. TKA could be considered primarily a lower limb realignment procedure, UKA as a periarticular ligamentous balancing procedure.

References

1. Berger RA, Nedeff DD, Barden RM, Sheinkop MM, Jacobs JJ, Rosenberg AG, Galante JO (1999) Unicompartmental knee arthroplasty. Clinical experience at 6- to 10-year follow-up. Clin Orthop Rel Res 367:50-60 2. Bert JM (1991) Universal intramedullary instrumentation for unicom-

partmental total knee arthroplasty. Clin Orthop Rel Res 271:79-87 3. Cameron HU, Jung YB (1988) A comparison of unicompartmental knee

replacement with total knee replacement. Orthop Rev 17:983-988 4. Cartier P (2000) Unicompartmental prosthetic replacement. In: Surgical

techniques in orthopaedics and traumatology, pp 570-A-10. Editions Scientifiques et Medicales Elsevier SAS, Paris

5. Cartier P Sanouiller JL, Grelsamer RP (1996) Unicompartmental knee arthroplasty surgery: 10-year minimum follow-up period. J Arthroplasty 11:782-788

6. Coventry MB, Upshaw JE, Riley LH, Finerman GA, Turner RH (1973) Geometric total knee arthroplasty. I: Conception, design, indications, and surgical technic. Clin Orthop Rel Res 94:171-184

7. Deshmukh RV, Scott RD (2001) Unicompartmental knee arthroplasty:

long-term results. [Review] [29 refs]. Clin Orthop Rel Res 392:272-278 8. Engelbrecht E (1971) Sliding prosthesis, a partial prosthesis in destructive

processes of the knee joint [in German]. Chirurg 42:510-514

9. Grelsamer RP, Cartier P (1992) A unicompartmental knee replacement is not “half a total knee”: five major differences. Orthop Rev 21:1350-1356 10. Gunston FH (1971) Polycentric knee arthroplasty. Prosthetic simulation of

normal knee movement. J Bone Joint Surg [Br] 53:272-277

11. Gunston FH (1973) Polycentric knee arthroplasty. Prosthetic simulation of normal knee movement: interim report. Clin Orthop Rel Res 94:128-135 12. Gunston FH, MacKenzie RI (1976) Complications of polycentric knee

arthroplasty. Clin Orthop Rel Res 120:11-17

13. Heck DA, Marmor L, Gibson A, Rougraff B (1993)T Unicompartmental knee arthroplasty. A multicenter investigation with long-term follow-up evaluation. Clin Orthop Rel Res 286:154-159

14. Hernigou P, Deschamps G (2004) Alignment influences wear in the knee after medial unicompartmental arthroplasty. Clin Orthop 432:161-165 15. Insall J, Aglietti P (1980) A five- to seven-year follow-up of unicondylar

arthroplasty. J Bone Joint Surg [Am] 62:1329-1337

16. Insall J, Walker P (1976) Unicondylar knee replacement. Clin Orthop Rel Res 120:83-85

17. Johnell O, Sernbo I, Gentz CF (1985) Unicompartmental knee replacement in osteoarthritis: an 8-year follow-up. Arch Orthop Trauma Surg 103:371-374

18. Kozinn SC, Marx C, Scott RD (1989) Unicompartmental knee arthroplasty. A 4.5- to 6-year follow-up study with a metal-backed tibial component.

J Arthroplasty 4 [Suppl]:S1-10

19. Kozinn SC, Scott R (1989) Unicondylar knee arthroplasty. [Review] [24 refs]. J Bone Joint Surg [Am] 71:145-150

20. Laskin RS (1978) Unicompartmental tibiofemoral resurfacing arthroplasty. J Bone & Joint Surg [Am] 60:182-185

21. Laskin RS (2001) Unicompartmental knee replacement: some unan- swered questions. [Review] [21 refs]. Clin Orthop Rel Res 392:267-271 22. Lewold S, Goodman S, Knutson K, Robertsson O, Lidgren L (1995) Oxford

meniscal bearing knee versus the Marmor knee in unicompartmental arthroplasty for arthrosis. A Swedish multicenter survival study. J Arthro- plasty 10:722-731

23. MacIntosh DL, Hunter GA (1972) The use of the hemiarthroplasty prosthesis for advanced osteoarthritis and rheumatoid arthritis of the knee.

J Bone Joint Surg [Br] 54:244-255

24. Marmor L (1973) The modular knee. Clin Orthop Rel Res 94:242-248 25. Marmor L (1977) Results of single compartment arthroplasty with acrylic

cement fixation. A minimum follow-up of two years. Clin Orthop Rel Res 122:181-188

26. Marmor L (1988) Unicompartmental arthroplasty of the knee with a minimum ten-year follow-up period. Clin Orthop Rel Res 228:171-177 27. Marmor L (1988) Unicompartmental knee arthroplasty. Ten- to 13-year

follow-up study. Clin Orthop Rel Res 226:14-20

28. McKeever DC (1960) Tibial plateau prosthesis. Clin Orthop 18:86-95 29. Mihalko WM, Whiteside LA, Krackow KA (2003) Comparison of ligament-

balancing techniques during total knee arthroplasty. J Bone Joint Surg [Am] 85 [Suppl 4]:132-135

30. Murray DW (2000) Unicompartmental knee replacement: now or never?

Orthopedics 23:979-980

31. Murray DW, Goodfellow JW, O’Connor JJ (1998) The Oxford medial unicompartmental arthroplasty: a ten-year survival study. J Bone Joint Surg [Br] 80:983-989

32. Psychoyios V, Crawford RW, O’Connor JJ, Murray DW (1998) Wear of congruent meniscal bearings in unicompartmental knee arthroplasty: a retrieval study of 16 specimens. J Bone Joint Surg [Br] 80:976-982 33. Repicci JA, Eberle RW (1999) Minimally invasive surgical technique for

unicondylar knee arthroplasty. J South Orthop Assoc 8:20-27 34. Ridgeway SR, McAuley JP, Ammeen DJ, Engh GA (2002) The effect of

alignment of the knee on the outcome of unicompartmental knee

⊡ Fig. 37-3. Radiograph of unicompartmental knee replacement

(5)

Joint Surg [Br] 84:351-355

35. Scott RD, Santore RF (1981) Unicondylar unicompartmental replacement for osteoarthritis of the knee. J Bone Joint Surg [Am] 63:536-544 36. Spector BM, Ries MD, Bourne RB, Sauer WS, Long M, Hunter G (2001) Wear

performance of ultra-high molecular weight polyethylene on oxidized zirconium total knee femoral components. J Bone Joint Surg [Am] 83 [Suppl 2, Pt 2]:80-86

37. Svard UC, Price AJ (2001) Oxford medial unicompartmental knee arthroplasty. A survival analysis of an independent series. J Bone Joint Surg [Br]

83:191-194

five years after unicompartmental knee replacement. J Bone Joint Surg [Br] 82:996-1000

39. White SE, Whiteside LA, McCarthy DS, Anthony M, Poggie RA (1994) Simulated knee wear with cobalt chromium and oxidized zirconium knee femoral components. Clin Orthop Rel Res 309:176-184

40. Whiteside LA (1999) Selective ligament release in total knee arthroplasty of the knee in valgus. Clin Orthop Rel Res 367:130-140

41. Whiteside LA (2002) Soft tissue balancing: the knee. J Arthroplasty 17:23- 27

37

(6)

38 Computer-Assisted Surgery: Principles – 241

J. B. Stiehl, W. H. Konermann, R. G. Haaker

39 Computer-Assisted Surgery: Coronal and Sagittal Alignment – 247

J. Victor

40 Computer-Assisted Surgery and

Rotational Alignment of Total Knee Arthroplasty – 254

G. M. Sikorski

41 Imageless Computer-Assisted Total Knee Arthroplasty – 258

J.-Y. Jenny

42 Robotics – 264

J. Bellemans

43 The Unicompartmental Knee: Minimally Invasive Approach – 270

T. V. Swanson

44 Minimally Invasive: Total Knee Arthroplasty – 276

S. Haas, A. Lehman

45 The Electronic Knee – 282

C. W. Colwell, Jr., D. D. D’Lima