CONTROVERSIES IN KNEE ARTHROPLASTY
Neutral mechanical alignment IS IT NECESSARY?
M. M. Allen, M. W. Pagnano From Mayo Clinic, Minnesota, United States
The cause of dissatisfaction following total knee arthroplasty (TKA) remains elusive. Much attention has been focused on static mechanical alignment as a basis for surgical success and optimising outcomes. More recently, research on both normal and osteoarthritic knees, as well as kinematically aligned TKAs, has suggested that other specific and dynamic factors may be more important than a generic target of 0 ± 3º of a neutral axis. Consideration of these other variables is necessary to understand ideal targets and move beyond generic results. Cite this article: Bone Joint J 2016;98-B(1 Suppl A):81–3.
M. M. Allen, MD, MSCR, Orthopaedic Surgery Resident, M. W. Pagnano, MD, Orthopaedic Surgeon, Department Chair, Department of Orthopedic Surgery Mayo Clinic, 200 1st St SW, Rochester, Minnesota 55905, USA. Correspondence should be sent to Dr M. M. Allen; e-mail: [email protected]
©2016 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.98B1. 36403 $2.00 Bone Joint J 2016;98-B(1 Suppl A):81–3.
Historically, the orthopaedic community has looked at alignment in total knee arthroplasty (TKA) as a dichotomous variable that is either aligned within 0 ± 3° of a neutral axis or malaligned. As a consequence of this focus on malalignment our knowledge about the ideal alignment is little better today than it was in the 1970s when knee arthroplasties were first introduced. The question remains whether the ideal target is really broad and generic such as 0 ± 3º range or might actually be narrow and specific for each patient, with a penalty to pay with deviations of even one degree. It is important to choose the right target in order to maximise both durability of the implant and function of the TKA in the patient. While one target value might maximise both durability and function, it might be that there are two different targets, for example one that maximises durability, recognising the biomaterial limitations of metal, plastic and bone cement, and another target that maximises function, recognising the biological limitations of ligaments and soft tissues. Furthermore, it is debatable whether a single two-dimensional value such as varus or valgus on a plain radiograph can describe the ideal alignment.1,2 In contrast to the high patient satisfaction rate following total hip arthroplasty, up to 20% of patients remain dissatisfied after TKA for reasons that are not clear.3 The limitations of most outcome measures, which primarily consider pain relief and the patient’s ability to perform activities of daily living, confound accurate understanding. A recent multicentre questionnaire aimed at quantifying patient satisfaction and residual symptoms following
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TKA found that only 436 of 661 patients (66%) felt their knee was 'normal' while 357 of 661 (54%) had residual symptoms.4 The current accepted practice of achieving postoperative mechanical neutral alignment is based largely on studies with some fundamental flaws. Two of the more problematic flaws are the reliance on post-operative short knee radiographs, which do not allow for accurate calculation of the mechanical axis, and that the original more elementary TKA designs that have been studied which have few similarities to modern condylar TKA.5 The reason for reconsidering the principle of neutral mechanical alignment is based on both the gap between current methodology and patient satisfaction, as well as evidence regarding normal and osteoarthritic joint anatomy and mechanics. In addition, the inconsistent correlation between achieving mechanical alignment needs examining, especially the key outcomes such as implant survival and optimal function and then these need to be compared with the favourable outcomes in the literature of kinematically aligned TKA. Substantial resources have been dedicated to the use of computer-assisted navigation, robotics and patient specific instrumentation under the hypothesis that achieving precisely the generic target of a mechanical axis will promote durability or improve function. In a randomised controlled trial (RCT), Gøthesen et al6 found that computer-assisted surgery was more predictable than conventional surgery for achieving mechanical alignment but functional results were marginally improved. Kim et al7 similarly found that there was little 81
M. M. ALLEN, M. W. PAGNANO
functional benefit to computer-assisted navigation versus conventional TKA, although the alignment and survivorship were not statistically different. In conventional TKA studies, small deviations from 0 +/- 3° also have had a small effect on durability.8 We have reviewed modern cemented TKA in 398 patients in order to evaluate whether achieving a mechanical axis of 0 ± 3° conferred a 15-year survivorship advantage when looking at revision for all causes and revision for mechanical failure.9 This group of patients had implants that are similar to contemporary knee arthroplasties and were all performed by one experienced surgeon (JR). The results showed a revision rate of 45 in 292 knees (15.4%) in the mechanically aligned group versus 14 in 106 knees (13%) for all causes. Thus, attaining the mechanical axis or being an outlier within relatively narrow limits did not have a major impact on the 15-year survivorship. The findings of this study are that factors other than alignment at 0 ± 3º are more important in determining the survival of modern implants. In other words, perfect mechanical alignment is not a ‘safe harbour’ when it comes to implant durability and high patient satisfaction. In primary osteoarthritis research, the factors other than alignment that may be important have been studied extensively. These include gait dynamics10 and the influence of neurological, muscular, or skeletal issues,11 and the dynamic loading that goes across the knee joint.12 The conclusions from these studies are that two patients with very different body shapes or comorbidities should not be expected to achieve the same result from one generic target. However, little research has addressed these same issues following TKA. In our own gait laboratory, we studied the relationship between mechanical alignment and dynamic loading after modern knee arthroplasties.13 In total 15 patients went through the gait laboratory pre-operatively and again after two years. Despite 13 of 15 patients (87%) having static mechanical alignment of 0 ± 3°, only seven of the 15 patients (47%) had balanced dynamic loading of their knee joint. The substantial variation found between static and dynamic alignment showed that mechanical alignment does not predict dynamic loading after modern knee arthroplasty. This data may provide insight as to why some well-aligned knees fail and some outliers prove durable at 15 and 20 years. Similar inconsistencies between static mechanical alignment and dynamic kinetics have also been identified.14,15 In parallel to the research demonstrating some of mechanical alignment’s shortcomings, there has been evidence in support of so-called kinematic alignment. The principle of this technique is to restore the patient’s own pre-arthritic anatomy and maintain the normal axes of rotation about the knee.16 The traditional mechanical alignment protocol is to cut the tibia at 0° and minimise the thickness of cuts. After cutting the tibia at 0° in the typical varus knee, the lateral side is relatively over resected. The femur must then be over-resected medially with possible
medial collateral ligament release and then externally rotated to balance the flexion gap.17 If changes are not made on the femur, then in most knees, the lateral side will be relatively lax and have varus tilt in extension, flexion, or both. A minimal tibial cut also causes relatively tight extension and flexion gaps, thus more of the distal femur must be cut, which raises the joint line, or it is necessary to cut more of the posterior femur, leading to a smaller femoral component and decreased posterior offset. When the femoral component is smaller, more external rotation is needed to achieve a balanced flexion gap to artificially fill the loose lateral side,18 but the distal femoral condyle is normally internally rotated to the patellar tendon at 90° of flexion.19 All of these factors are potential contributors to poor final outcome. Several clinical studies have recently been published in support of kinematically aligned TKA. In a RCT, Dossett et al20 compared the outcomes of patients undergoing either kinematically or mechanically aligned TKA. In this study of 88 patients, those allocated to the kinematically aligned cohort had better improvement in Western Ontario and McMaster Universities Arthritis Index (WOMAC), Oxford, and Knee Society scores as well as higher mean flexion and superior pain relief at two years. Howell et al21 reported on the function of 198 patients (214 knees) with kinematically aligned knees during a minimum follow-up of 31 months in order to assess the relationship with alignment and mechanical failure. Patients with alignment classified as either in range or a varus/valgus outlier according to their tibial component, knee and limb, all had similar Oxford knee and WOMAC scores and no patient went on to be revised for loosening, instability, or wear. In a separate study, Howell et al22 investigated contact kinematics in kinematically aligned TKA and were able to demonstrate a reduction in detrimental contact forces during both standing and kneeling. Finally, in the questionnaire administered by Nam et al,4 patients who had a kinematically aligned TKA were three-times more likely than those with a mechanically aligned TKA to report that their knee felt normal. A final question that arises is whether it is safe to explore alternatives to the mechanical axis. Certainly, the mechanically aligned TKA has a history of safety and should be the basis of comparison. In our study we showed no difference at 15 years in survivorship and no predictive ability for dynamic loading with a static mechanical axis target and hence along with reports from other institutions, it does seem reasonable to explore an alternative strategy.9. However, until more data is available, staying within the boundaries of an overall alignment 2° to 7° valgus23 and tibial component alignment less than 3° varus24 remains a useful target range. Most surgeons today would agree that alignment plays an important role in TKA function and survival, but certainly factors other than alignment are also important in determining the survival of modern TKAs.25,26 The evidence suggests that ideal alignment after knee arthroplasty CCJR SUPPLEMENT TO THE BONE & JOINT JOURNAL
NEUTRAL MECHANICAL ALIGNMENT
is probably very specific for any given patient and influenced by individual differences. There is a complex interplay between limb alignment, component rotation, sizing, ligament balance and gait dynamics. Moving forward, more attention needs to be devoted to function in knee arthroplasty in order to improve patient satisfaction. While the mechanical axis has been useful, future improvements are dependent on achieving better targets. The historical focus on radiographical outliers to explain total knee failures has been shown to be inadequate and has possibly constrained our intellectual curiosity. Author contributions: M. M. Allen: Background research, Writing the paper. M. W. Pagnano: Primary content, concepts, opinion, edited paper. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. This article was primary edited by S. P. F. Hughes. This paper is based on a study which was presented at the 31st Annual Winter 2014 Current Concepts in Joint Replacement® meeting held in Orlando, Florida, 10th-13th December.
References 1. Miller MC, Berger RA, Petrella AJ, Karmas A, Rubash HE. Optimizing femoral component rotation in total knee arthroplasty. Clin Orthop Relat Res 2001;392:38–45. 2. D’Lima DD, Chen PC, Colwell CW Jr. Polyethylene contact stresses, articular congruity, and knee alignment. Clin Orthop Relat Res 2001;392:232–238. 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 2012;470:45–53. 4. Nam D, Nunley RM, Barrack RL. Patient dissatisfaction following total knee replacement: a growing concern? Bone Joint J 2014;96-B(supplA):96–100. 5. Abdel MP, Oussedik S, Parratte S, Lustig S, Haddad FS. Coronal alignment in total knee replacement: historical review, contemporary analysis, and future direction. Bone Joint J 2014;96-B:857–862. 6. Gøthesen O, Espehaug B, Havelin LI, et al. Functional outcome and alignment in computer-assisted and conventionally operated total knee replacements: a multicentre parallel-group randomised controlled trial. Bone Joint J 2014;96-B:609–618. 7. Kim YH, Park JW, Kim JS. Computer-navigated versus conventional total knee arthroplasty a prospective randomized trial. J Bone Joint Surg [Am] 2012;94-A:2017– 2024. 8. Bonner TJ, Eardley WG, Patterson P, Gregg PJ. The effect of post-operative mechanical axis alignment on the survival of primary total knee replacements after a follow-up of 15 years. J Bone Joint Surg [Br] 2011;93-B:1217–1222. 9. Parratte S, Pagnano MW, Trousdale RT, Berry DJ. Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg [Am] 2010;92-A:2143–2149.
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10. Hurwitz DE, Ryals AB, Case JP, Block JA, Andriacchi TP. The knee adduction moment during gait in subjects with knee osteoarthritis is more closely correlated with static alignment than radiographic disease severity, toe out angle and pain. J Orthop Res 2002;20:101–107. 11. Hunt MA, Birmingham TB, Bryant D, et al. Lateral trunk lean explains variation in dynamic knee joint load in patients with medial compartment knee osteoarthritis. Osteoarthritis Cartilage 2008;16:591–599. 12. Kumar D, Manal KT, Rudolph KS. Knee joint loading during gait in healthy controls and individuals with knee osteoarthritis. Osteoarthritis Cartilage 2013;21:298–305. 13. Miller EJ, Pagnano MW, Kaufman KR. Tibiofemoral alignment in posterior stabilized total knee arthroplasty: static alignment does not predict dynamic tibial plateau loading. J Orthop Res 2014;32:1068–1074. 14. Specogna AV, Birmingham TB, Hunt MA, et al. Radiographic measures of knee alignment in patients with varus gonarthrosis: effect of weight bearing status and associations with dynamic joint load. Am J Sports Med 2007;35:65–70. 15. Deep K, Eachempati KK, Apsingi S. The dynamic nature of alignment and variations in normal knees. Bone Joint J 2015;97-B:498–502. 16. Park A, Duncan ST, Nunley RM, et al. Relationship of the posterior femoral axis of the “kinematically aligned” total knee arthroplasty to the posterior condylar, transepicondylar, and anteroposterior femoral axes. Knee 2014;21:1120–1123. 17. Daines BK, Dennis DA. Gap balancing vs. measured resection technique in total knee arthroplasty. Clin Orthop Surg 2014;6:1–8. 18. Chon JG, Sun DH, Jung JY, Kim TI, Jang SW. Rotational alignment of femoral component for minimal medial collateral ligament release in total knee arthroplasty. Knee Surg Relat Res 2011;23:153–158. 19. Kawahara S, Okazaki K, Matsuda S, et al. Distal femoral condyle is more internally rotated to the patellar tendon at 90° of flexion in normal knees. J Orthop Surg Res 2015;10:54. 20. Dossett HG, Estrada NA, Swartz GJ, LeFevre GW, Kwasman BG. A randomised controlled trial of kinematically and mechanically aligned total knee replacements: two-year clinical results. Bone Joint J 2014;96-B:907–913. 21. Howell SM, Howell SJ, Kuznik KT, Cohen J, Hull ML. Does a kinematically aligned total knee arthroplasty restore function without failure regardless of alignment category? Clin Orthop Relat Res 2013;471:1000–1007. 22. Howell SM, Hodapp EE, Vernace JV, Hull ML, Meade TD. Are undesirable contact kinematics minimized after kinematically aligned total knee arthroplasty? An intersurgeon analysis of consecutive patients. Knee Surg Sports Traumatol Arthrosc 2013;21:2281–2287. 23. Fang DM, Ritter MA, Davis KE. Coronal alignment in total knee arthroplasty: just how important is it? J Arthroplasty 2009;24(suppl):39–43. 24. Berend ME, Ritter MA, Meding JB, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res 2004;(428):26–34. 25. Bankes MJK, Back DL, Cannon SR, Briggs TWR. The effect of component malalignment on the clinical and radiological outcome of the Kinemax total knee replacement. Knee 2003;10:55–60. 26. Harvey IA, Manning MP, Sampath SA, Johnson R, Elloy MA. Alignment of total knee arthroplasty: the relationship to radiolucency around the tibial component. Med Eng Phys 1995;17:182–187.