External femoral rotation of 2 degrees is associated with the lowest stuffing rates around the femur in functionally aligned TKA.
Maslaris A., Kenanidis E., Mylonakis N., Gamie Z., Alvand A., Jackson WF., Price AJ., Tsiridis E.
PURPOSE: Modifying femoral morphology after total knee arthroplasty (TKA) poses a potential risk for ligament-imbalances and patella mal-tracking. The purpose of this study was primarily to quantify TKA-induced stuffing around the femur and secondarily assess the effect of femoral rotation (FR) on trochlear and condylar anatomy-changes. METHODS: Knee anatomy-modification was quantified in 69 robotic-assisted TKAs utilising tibia-based functional alignment (FA). Caliper-measurements were performed on the medial (Med), central (Ctr), and lateral (Lat) sides of the following resection planes: anterior trochlea (AT), oblique trochlea (OT), distal condyles (DC), posterior condyles (PC) and tibia (TIB). The same caliper-measurements were performed on the femoral components used to calculate bone-implant differences and analyse possible patterns of postoperative trochlear anatomy-modifications (TAM) and condylar anatomy-modifications (CAM). Over- or understuffing analysis for different FRs and regression analysis were conducted to assess the effect of FR on CAM and TAM. RESULTS: TAM results were Lat-AT -3.2 mm ([95% confidence interval [CI]: -3.71 to -2.63], p 2 mm in 60.9%, 39.1%, and 39.1%, respectively. CAM results were Med-DC -3.6 mm ([95%CI: -4.14 to -3.05], p 0.001) with stuffing > 2 mm in 78.3% and 63.8%. FR (3.8 ± 2.6°, range: -1.6° to 8.5°) affected mostly the anterior (r = -0.40, p 2 mm and ≥ 4 mm. CONCLUSIONS: FA-typical modification-pattern was a TAM with lateral facet understuffing, and CAM with medial distal understuffing and lateral posterior overstuffing. Trochlear groove height was non-significantly affected by FR. FA with the current off-the-shelf implant induces the lowest stuffing rates when set in 2° external femoral rotation. LEVEL OF EVIDENCE: Level II.