Patellofemoral instability after total knee arthroplasty

 

Patellofemoral instability after total knee arthroplasty (TKA) is a serious complication that has significant impact on knee function. The underlying causes are usually related to the surgical technique. Most often, patellar instability results from component malposition, limb malalignment, improper patellar preparation, or soft-tissue imbalance. Understanding the root causes helps to prevent these complications as well as to manage them successfully.

Factors determining patellofemoral stability

Patellofemoral (PF) instability after TKA has been reported in up to 20% of TKAs [1]. Most often, it is caused by technical errors during surgery [1, 2]. Given the complexity of TKA biomechanics, many technical parameters are susceptible to error. Therefore, in most cases, PF instability cannot be traced back to a single cause. More likely, there are multiple contributors.

As a general rule, any manipulation of the normal anatomical and kinematic relationships of knee structures that increases tension in the lateral retinaculum or increases the quadriceps angle, or Q-angle (Figure 1), will produce an abnormal, laterally-directed muscle vector and thus cause lateral maltracking of the patella, instability of the PF joint, and more serious patellar complications if left untreated [3, 4].

Figure 1. The Q-angle is the angle between a line from the ASIS to the midpoint of the patella (dotted line) and the line from the tibial tubercle to the midpoint of the patella. By moving the patella laterally (b), the CQ-angle decreases to zero, whereas the RFQ-angle becomes negative. When the patella is moved medially (c) both CQ and RFQ become larger (more positive). Abbreviations: ASIS: anterior superior iliac spine; CQ: clinical Q-angle; PA: patella; RF: rectus femoris; RFQ: RF-Q-angle; TT: tibial tubercle.

Redrawn from source: Freedman BR, Brindle TJ, Sheehan FT. Re-evaluating the functional implications of the Q-angle and its relationship to in-vivo patellofemoral kinematics. Clin Biomech (Bristol, Avon). 2014;29(10):1139–1145.

Guillermo Bonilla, clinical professor for orthopedic surgery at the Universidad de los Andes in Bogota, Colombia, emphasizes: “In order to adequately treat problems arising from patellar instability, it is essential to understand the underlying biomechanical mechanisms.” So, let us consider and analyze the major factors that may lead to patellar instability.

Guillermo Bonilla, MD

Hospital Universitario Fundación Santa Fe de Bogotá
Universidad de los Andes Bogotá, Colombia


First and foremost, excessive valgus alignment is an important risk factor, since it leads to a mismatch of the trochlear groove and the extensor vector [4]. This encumbers proper patellar tracking and may cause the patella to tilt, subluxate, or even dislocate. A similar mechanism takes effect when a normal Q-angle is not restored. Especially patients with severe preoperative valgus or external rotational deformity, preoperative maltracking [5], and loss of bone stock in the distal lateral condyle are at risk [3]. In patients with pronounced preoperative valgus, the main culprit for this predisposition is usually the retraction of the lateral retinaculum.

Beyond the overall leg alignment, individual component positioning is the most important contributor. Internal rotation of the femoral or the tibial component [5-10] as well as medialization of the femoral component and incorrect placement of the patellar component [10, 11] appear the most obvious.

An internally rotated femoral component shifts the trochlear groove medially, thus increasing the distance to the patella, which tracks laterally relative to the femur. Through the tension exerted by the lateral retinaculum, the patella is pulled sideways. This may lead to patellar tilt, subluxation, or even dislocation [4].

On the other hand, an internally rotated tibial component causes the tibia to rotate externally during knee flexion (Figure 2). This drives the tibial tubercle laterally, which increases the Q-angle and thus leads to lateral tracking. Depending on the severity, this may again lead to patellar tilt, subluxation, or dislocation.

Figure 2. Internal rotation of the tibial component forces the tibia into external rotation during knee flexion, increasing the Q-angle and leading to lateral patellar tracking and subluxation. Diagram on the right showing that rotating the implant (sagittal axis dotted line) internally (medially) relative to the tibia (sagittal axis continuous line) displaces the tibial tubercle laterally and consequently the patella as well. Adapted from: Malo M, Vince KG. The unstable patella after total knee arthroplasty: etiology, prevention, and management. J Am Acad Orthop Surg. 2003;11(5):364–371.

Did you know?

When rotational platforms were introduced, there were high hopes that through the inherent self-alignment, a certain degree of malrotation could be corrected for. Unfortunately, this was not the case. Biomechanical studies analyzing the effect of rotational platforms on patellar tracking in the presence of malrotated femoral components did not find a significant compensatory effect [6, 7], and neither did a large randomized clinical study [12].


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  • Placement of the prosthetic patella
  • Medialization of the femoral component
  • Soft-tissue imbalance
  • Other risk factors
  • Diagnostic workup in PF instability
  • The clinical workup
  • The radiological workup
  • Management algorithm
  • Outcome and conclusion
Additional Resources

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Contributing experts

This series of articles was created with the support of the following specialists (in alphabetical order):


Guillermo Bonilla, MD

Hospital Universitario Fundación Santa Fe de Bogotá
Universidad de los Andes Bogotá, Colombia

Clemens Gwinner, MD

Center for Musculoskeletal Surgery (CMSC),
Charité—Universitätsmedizin
Berlin, Germany

Yixin Zhou, MD, PhD

Department of Joint Surgery
Beijing Jishuitan Hospital
The Fourth Clinical College of Peking University
Beijing, China



This issue was  written by Elke Rometsch, AO Innovation Translation Center, Clinical Science, Switzerland.

References 

  1. Assiotis A, To K, Morgan-Jones R, et al. Patellar complications following total knee arthroplasty: a review of the current literature. Eur J Orthop Surg Traumatol. 2019 Dec;29(8):1605–1615.
  2. Lee GC, Cushner FD, Scuderi GR, et al. Optimizing patellofemoral tracking during total knee arthroplasty. J Knee Surg. 2004 Jul;17(3):144–149; discussion 149–150.
  3. Eisenhuth SA, Saleh KJ, Cui Q, et al. Patellofemoral instability after total knee arthroplasty. Clin Orthop Relat Res. 2006 May;446:149–160.
  4. Malo M, Vince KG. The unstable patella after total knee arthroplasty: etiology, prevention, and management. J Am Acad Orthop Surg. 2003 Sep-Oct;11(5):364–371.
  5. Wheeless CR. Wheeless' Textbook of Orthopaedics Data Trace; 2020 [cited 2021 January].
  6. Colwell CW, Jr, Chen PC, D'Lima D. Extensor malalignment arising from femoral component malrotation in knee arthroplasty: effect of rotating-bearing. Clin Biomech (Bristol, Avon). 2011 Jan;26(1):52–57.
  7. Kessler O, Patil S, Colwell CW, Jr, et al. The effect of femoral component malrotation on patellar biomechanics. J Biomech. 2008 Dec 5;41(16):3332–3339.
  8. Putman S, Boureau F, Girard J, et al. Patellar complications after total knee arthroplasty. Orthop Traumatol Surg Res. 2019 Feb;105(1s):S43–s51.
  9. Warschawski Y, Garceau S, Frenkel Rutenberg T, et al. Revision total knee arthroplasty for patellar dislocation in patients with malrotated TKA components. Arch Orthop Trauma Surg. 2020 Jun;140(6):777–783.
  10. Saito H, Saito K, Shimada Y, et al. Successful treatment of a habitual patellar dislocation after a total knee arthroplasty with a closing-wedge distal femoral varus osteotomy and medial patello-femoral ligament reconstruction. J Exp Orthop. 2020 Sep 1;7(1):63.
  11. Assi C, Kheir N, Samaha C, et al. Optimizing patellar positioning during total knee arthroplasty: an anatomical and clinical study. Int Orthop. 2017 Dec;41(12):2509–2515.
  12. Pagnano MW, Trousdale RT, Stuart MJ, et al. Rotating platform knees did not improve patellar tracking: a prospective, randomized study of 240 primary total knee arthroplasties. Clin Orthop Relat Res. 2004 Nov(428):221–227.
  13. Lamotte A, Neri T, Kawaye A, et al. Medial patellofemoral ligament reconstruction for patellar instability following total knee arthroplasty: A review of 6 cases. Orthop Traumatol Surg Res. 2016 Sep;102(5):607–610.
  14. Bracey DN, Brown ML, Beard HR, et al. Effects of patellofemoral overstuffing on knee flexion and patellar kinematics following total knee arthroplasty: a cadaveric study. Int Orthop. 2015 Sep;39(9):1715–1722.
  15. Keshmiri A, Maderbacher G, Baier C, et al. The influence of component alignment on patellar kinematics in total knee arthroplasty. Acta Orthop. 2015;86(4):444–450.
  16. Nedopil AJ, Howell SM, Hull ML. What clinical characteristics and radiographic parameters are associated with patellofemoral instability after kinematically aligned total knee arthroplasty? Int Orthop. 2017 Feb;41(2):283–291.
  17. Nakamura S, Shima K, Kuriyama S, et al. Tibial Tubercle-Trochlear Groove Distance Influences Patellar Tilt After Total Knee Arthroplasty. J Arthroplasty. 2019 Dec;34(12):3080–3087.
  18. Scott RD. Prosthetic replacement of the patellofemoral joint. Orthop Clin North Am. 1979 Jan;10(1):129–137.
  19. Gasparini G, Familiari F, Ranuccio F. Patellar malalignment treatment in total knee arthroplasty. Joints. 2013 Mar;1(1):10–17.
  20. Donell S. Patellar tracking in primary total knee arthroplasty. EFORT Open Rev. 2018 Apr;3(4):106–113.
  21. Chalidis BE, Tsiridis E, Tragas AA, et al. Management of periprosthetic patellar fractures. A systematic review of literature. Injury. 2007 Jun;38(6):714–724.
  22. Motsis EK, Paschos N, Pakos EE, et al. Review article: Patellar instability after total knee arthroplasty. J Orthop Surg (Hong Kong). 2009 Dec;17(3):351–357.
  23. Saffarini M, Demey G, Nover L, et al. Evolution of trochlear compartment geometry in total knee arthroplasty. Ann Transl Med. 2016 Jan;4(1):7.
  24. Saffarini M, Ntagiopoulos PG, Demey G, et al. Evidence of trochlear dysplasia in patellofemoral arthroplasty designs. Knee Surg Sports Traumatol Arthrosc. 2014 Oct;22(10):2574–2581.
  25. Clavé A, Le Henaff G, Roger T, et al. Joint line level in revision total knee replacement: assessment and functional results with an average of seven years follow-up. Int Orthop. 2016 Aug;40(8):1655–1662.
  26. Jazrawi LM, Birdzell L, Kummer FJ, et al. The accuracy of computed tomography for determining femoral and tibial total knee arthroplasty component rotation. J Arthroplasty. 2000 Sep;15(6):761–766.
  27. Kanekasu K, Kondo M, Kadoya Y. Axial radiography of the distal femur to assess rotational alignment in total knee arthroplasty. Clin Orthop Relat Res. 2005 May(434):193–197.
  28. Takai S, Yoshino N, Isshiki T, et al. Kneeling view: a new roentgenographic technique to assess rotational deformity and alignment of the distal femur. J Arthroplasty. 2003 Jun;18(4):478–483.
  29. Berger RA, Rubash HE, Seel MJ, et al. Determining the rotational alignment of the femoral component in total knee arthroplasty using the epicondylar axis. Clin Orthop Relat Res. 1993 Jan(286):40–47.
  30. Watanabe H, Gejo R, Matsuda Y, et al. Femoral anterior tangent line of the osteoarthritic knee for determining rotational alignment of the femoral component in total knee arthroplasty. J Arthroplasty. 2011 Feb;26(2):268–273.
  31. Melloni P, Valls R, Veintemillas M. Imaging patellar complications after knee arthroplasty. Eur J Radiol. 2008 Mar;65(3):478–482.
  32. Goto T, Hamada D, Iwame T, et al. Medial patellofemoral ligament reconstruction for patellar dislocation due to rupture of the medial structures after total knee arthroplasty: a case report and review of the literature. J Med Invest. 2014;61(3-4):409–412.
  33. van Gennip S, Schimmel JJ, van Hellemondt GG, et al. Medial patellofemoral ligament reconstruction for patellar maltracking following total knee arthroplasty is effective. Knee Surg Sports Traumatol Arthrosc. 2014 Oct;22(10):2569–2573.
  34. Whiteside LA, Ohl MD. Tibial Tubercle Osteotomy for Exposure of the Difficult Total Knee Arthroplasty. Clinical Orthopaedics and Related Research®. 1990;260:6–9.
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