Off-the-shelf femoral components consistently understuff the anterior compartment in kinematically aligned total knee arthroplasty: A prospective observational analysis from the FP-UCBM knee study group.

Abstract

To assess the postoperative restoration of native anterior femoral offset (AFO) in kinematically aligned (KA) total knee arthroplasty (TKA) with the hypothesis that current off-the-shelf femoral components inadequately address the anterior compartment native anatomy. A prospective analysis was performed on 93 knees undergoing TKA with KA using GMK Sphere (Medacta) femoral components, excluding patients with posttraumatic osteoarthritis, radiographic signs of trochlear dysplasia ≥ type A of the Dejour classification, anterior femoral cortex notching or femoral component flexion >5° on postoperative lateral radiographs. After performing the anterior chamfer cut, the resected bone was measured with a caliper at the most prominent point of the trochlear groove, as well as the lateral and medial trochlear facets. After compensating for cartilage wear and saw blade thickness, the adjusted values were recorded as the native AFO. The thickness of the GMK Sphere femoral component at the trochlear surface corresponding to the middle of the anterior chamfer-specific to each implant size-defined the prosthetic AFO. AFO difference (AFOd) was defined as the difference between prosthetic and native AFO. <i>T</i>-test and equivalence testing were performed to compare prosthetic and native AFO. Statistical significance was defined as <i>p</i> < 0.05. AFO was consistently reduced across all regions, with a mean AFOd of -5.40 ± 2.40 mm at the medial trochlear facet, -2.32 ± 1.46 mm at the lateral facet, and -2.49 ± 1.11 mm at the trochlear sulcus (<i>p</i> < 0.001). The AFO was preserved in only 11.8% of cases at the medial trochlear facet, 29.0% at the lateral facet, and 18.3% at the sulcus. In none of the cases was the AFO increased. KA using off-the-shelf femoral components does not allow a full resurfacing of the trochlea, resulting in consistent offset reduction of the anterior compartment. Level IV, prospective observational study.