The Knee 21 S1 (2014) S1–S2

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The Knee

Editorial

Unicompartmental knee arthroplasty: function versus survivorship, do we have a clue? Emmanuel Thienpont, Andrea Baldini

The optimum surgical management of unicompartmental femorotibial or patellofemoral end-stage arthritis of the knee is still a controversial topic. Surgeons confronted with partial disease face the dilemma of resurfacing the involved compartment or replacing the entire joint. Total knee arthroplasty (TKA) has for many years seemed the option of choice because of its high success rates compared to partial knee arthroplasty, especially if revision is taken as an endpoint [1]. However with the current evolution in knee arthroplasty surgery many parameters in the equation have changed. With a better understanding of knee anatomy and its biomechanics, more accurate instrumentation leading to better surgical technique, improved tribology increasing longevity and, finally, improved patient selection, the results of unicompartmental knee arthroplasty (UKA) have improved over time. Improved longevity of the ‘baby boom’ generation that wants to remain more active yet with a higher incidence of obesity has resulted in a change in the demographics of the patients who need TKA [2]. Furthermore, there is evidence that the TKA patients of today, especially younger males, have poorer outcomes that fail to satisfy patient expectations [3-6]. This has prompted the surgical community to consider different surgical options. When considering survival as an endpoint, TKA is still sustainable for 90% of patients at 10 years [7]. However, only 70% of patients are satisfied with the outcome after knee arthroplasty [3,5]. Typical TKA complaints from patients include some residual pain in 33% of cases, stiffness in 41%, grinding or noise in 33%, swelling in 33% and around 40% still have patellofemoral symptoms [6,8]. The observation that these symptoms are more frequent in young male patients who are more active presents a topic for discussion. Many of the above complaints could be explained by the absence of anterior and posterior cruciate ligaments and the subsequent sagittal plane instability or by a lack of proprioception [6]. This may explain why higher forgotten joint scores (FJS-12) were found in younger males in UKA compared to TKA [9,10]. Higher patient satisfaction has been observed in young patients undergoing UKA compared with TKA [11]. An option would be of course to retain both cruciate ligaments with the prosthesis. However, the easiest and most obvious way to guarantee better biomechanics and function for patients is not to replace undamaged tissues and therefore to apply partial replacement to the affected parts of the osteoarthritic joint. The biomechanics of bicompartmental knee arthroplasty was discussed by Heyse et al. [12] in this supplement. One of the questions that remains unanswered by resurfacing surgeons is to decide what is normal aging for the patient and what is arthritic wear leading to pain and dysfunction [13]. Thienpont et al. [14] observed that progressive wear in the osteoarthritic 0968-0160/© 2014 Elsevier B.V. All rights reserved.

knee is related to the varus alignment of the limb. In medial compartment osteoarthritis with more varus the medial facet of the patella will be involved in the arthritic process and in over 170° hip knee ankle-angle deformity impingement on the lateral side is observed. Realigning, at least partially, this predominant varus axis with a partial knee replacement can therefore prevent further disease progression. Selective resurfacing of the patellofemoral joint is, if possible, even more controversial. Borus et al. [15] in their review article described the problems of the past with first and second generation patellofemoral arthroplasty (PFA). Third generation implants with accurate instrumentation and adapted designs have reduced these problems dramatically; however, Thienpont et al. [16] showed in their paper how new technical challenges appear. They found that Whiteside’s line (antero-posterior (AP) axis) can be used not only as an axial reference line for femoral rotation but also as a reference line to find back the mechanical axis of the femur. The AP axis represents the mechanical axis of the femur in the coronal plane, from the center of the knee to the center of the hip. The native trochlea has been observed to follow this mechanical axis [17]. So aligning a PFA with Whiteside’s line in the coronal plane could be a new anatomical landmark to improve the accuracy of implant positioning. This supplement was dedicated to papers on UKA to promote science and the dissemination of knowledge on this topic. If, over time, quality papers can show that the function and the level of satisfaction of partial knee replacements is superior for patients, without early failure or higher revision rates, then surgeons facing the decision of whether partial replacement is indicated would no longer have to doubt they are making the right choice for their patient [18]. Conflict of interest statement E. Thienpont reports: royalties: Biomet, Convatec, Zimmer, and Jaypee Brothers; speaker fees: Biomet, Convatec, Medacta. Board member of European Knee Society. A. Baldini reports: royalties: SAMO; Consultant: Zimmer, Biomet, S&N; Reviewer: KSSTA, CORR; Board member of SIGASCOT (Italian Knee Society), European Knee Society. References [1] Price A, Beard D, Thienpont E. Uncertainties surrounding the choice of surgical treatment for ‘bone on bone’ medial compartment osteoarthritis of the knee. Knee 2013;20(Suppl 1):S16–20. [2] Klit J, Jacobsen S, Rosenlund S, Sonne-Holm S, Troelsen A. Total knee arthroplasty in younger patients evaluated by alternative outcome measures. J Arthroplasty 2014;29:912–7.

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E. Thienpont, A. Baldini / The Knee 21 S1 (2014) S1–S2

[3] Bourne RB, Chesworth BM, Davis AM, Mahomed NN, Charron KD. Patient satisfaction after total knee arthroplasty: who is satisfied and who is not? Clin Orthop Relat Res 2010;468:57–63. [4] Noble PC, Conditt MA, Cook KF, Mathis KB. The John Insall Award. Patient expectations affect satisfaction with total knee arthroplasty. Clin Orthop Relat Res 2006;452:35–43. [5] Scott CE, Howie CR, MacDonald D, Biant LC. Predicting dissatisfaction following total knee replacement: a prospective study of 1217 patients. J Bone Joint Surg Br 2010;92:1253–8. [6] Parvizi J, Nunley RM, Berend KR, Lombardi AV Jr, Rush EL, Clohisy JC, Hamilton WG, Della Valle CJ, Barrack RL. High level of residual symptoms in young patients after total knee arthroplasty. Clin Orthop Relat Res 2014;472:133–7. [7] Robertsson O, Knutson K, Lewold S, Lidgren L. The Swedish Knee Arthroplasty Register 1975-1997: an update with special emphasis on 41,223 knees operated on in 1988-1997. Acta Orthopaedica 2001;72:503. [8] Du H, Gu Jian-Ming, Yi-Xin Zhou. Patient satisfaction after posteriorstabilized total knee arthroplasty: A functional specific analysis. Knee 2014;21:866–70. [9] Thienpont E, Opsomer G., Koninckx A., Houssiau F. Joint awareness in different types of knee arthroplasty evaluated with the forgotten joint score. J Arthroplasty 2014;29:48–51. [10] Williams DP, O’Brien S, Doran E, Price AJ, Beard DJ, Murray DW, Beverland

DE. Early postoperative predictors of satisfaction following total knee arthroplasty. Knee 2013;20:442–6. [11] Von Keudell A, Sodha S, Collins J, Minas T, Fitz W, Gomoll AH. Patient satisfaction after primary total and unicompartmental knee arthroplasty: An age-dependent analysis. Knee 2014;21:180–4. [12] Heyse TJ, El-Zayat BF, De Corte R, Scheys L, Chevalier Y, Fuchs-Winkelmann S, Labey L. Biomechanics of medial unicondylar in combination with patellofemoral knee arthroplasty. Knee 2014;21(Suppl 1):S3–9. [13] Cobb JP. Patient safety after partial and total knee replacement. Lancet doi:10.1016/S0140-673(14)60885-0 [14] Thienpont T, Schwab PE, Omoumi P. Wear patterns in anteromedial osteoarthritis of the knee evaluated with CT‑arthrography. Knee 2014;21(Suppl 1):S15–9. [15] Borus T, Brilhault J, Confalonieri N, Johnson D, Thienpont E. Patellofemoral joint replacement, an evolving concept. Knee 2014;21(Suppl 1):S47–50 [16] Thienpont E, Lonner JH. Coronal alignment of patellofemoral arthroplasty. Knee 2014;21(Suppl 1):S51–7. [17] Iranpour F, Merican AM, Dandachii W, Amis AA, Cobb JP. The geometry of the trochlear groove. Clin Orthop Relat Res 2010;468:782–8. [18] Liddle AD, Judge A, Pandit H, Murray DW. Adverse outcomes after total and unicompartmental knee replacement in 101 330 matched patients: a study of data from the National Joint Registry for England and Wales. Lancet 2014 doi:10.1016/s0140-6736(14)60419-0