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. doi: 10.1007/s00264-016-3287-z. Epub 2016 Sep 12.


Introduction: Thirteen patients presented with patellofemoral instability out of 3212 knees treated with kinematically aligned total knee arthroplasty (KA TKA) during a nine year period. We determined the clinical characteristics and post-operative radiographic parameters associated with patellofemoral instability, and whether re-operation and patient reported outcome measures are different between patients with and without patellofemoral instability.

Methods: Patients with patellofemoral instability were matched 1:3 to a control cohort based on date of surgery (±3 months), age (±10 years), sex, pre-operative knee deformity (varus or valgus), and implant brand. We analyzed clinical characteristics and seven post-operative radiographic parameters.

Results: Patellofemoral instability presented atraumatically (12 of 13) at 5 ± 4.7 months for a 0.4 % incidence at a mean follow-up of 43 ± 36 months. No pre-operative clinical characteristics were associated with instability. Patients with patellofemoral instability had greater flexion of the femoral component (11° versus 5°; p = 0.0012), a trend toward greater external rotation of the tibial component (2° versus 0°; p = 0.2704), more reoperations (9 versus 0; p = 0.0026) and a lower Oxford Knee Score (36 versus 42; p = 0.0045) than controls.

Discussion: Patellofemoral instability after kinematically aligned TKA is infrequent, presents atraumatically, and is associated with greater flexion of the femoral component than the control group.

Conclusion: Minimizing flexion of the femoral component might reduce the risk of patellofemoral instability by promoting early engagement of the patella in the trochlear during knee flexion.

Keywords: Flexion of the femoral component; Kinematic alignment; Knee arthroplasty; Oxford knee score; Patellofemoral instability.

MeSH terms

  • Aged
  • Aged, 80 and over
  • Arthroplasty, Replacement, Knee / adverse effects*
  • Biomechanical Phenomena
  • Case-Control Studies
  • Female
  • Humans
  • Joint Instability / diagnosis*
  • Joint Instability / etiology
  • Knee Joint / surgery*
  • Knee Prosthesis / adverse effects
  • Male
  • Middle Aged
  • Range of Motion, Articular
  • Reoperation