Undercoverage of lateral trochlear resection is correlated with the tibiofemoral alignment parameters in kinematically aligned TKA: a retrospective clinical study

Abstract

Background A mismatch between the femoral component and trochlear resection surface is observed in kinematically aligned total knee arthroplasty (KA-TKA) when conventional prostheses are employed. This mismatch is mainly manifested in the undercoverage of the lateral trochlear resection surface. The aim of the present study was to assess the relationship between the mismatch and the alignment parameters of the tibiofemoral joint. Methods Forty-five patients (52 knees) who underwent KA-TKA in our hospital were included. Patient-specific instrumentation was used in 16 patients (16 knees), and conventional instruments with calipers and other special tools were employed in the other 29 patients (36 knees). The widths of the exposed resection bone surface at the middle (MIDexposure) and distal (DISexposure) levels on the lateral trochlea were measured as dependent variables, whereas the hip-knee-ankle angle (HKAA), mechanical lateral distal femoral angle (mLDFA), joint line convergence angle (JLCA), medial proximal tibial angle (MPTA) and transepicondylar axis angle (TEAA) were measured as independent variables. Correlation analysis and subsequent linear regression were conducted among the dependent variables and various alignment parameters of the tibiofemoral joint. Results The incidence of undercoverage of the lateral trochlear resection surface was 86.5 % with MIDexposure and DISexposure values of 2.3 (0–6 mm) and 2.0 (0–5 mm), respectively. The widths of the two levels of exposed bone resection were significantly correlated with mLDFA and HKAA but were not related to TEAA. Conclusions The undercoverage of the trochlear resection surface in KA-TKA is mainly correlated with the degree of valgus of the distal femoral joint line. The current study suggests that this correlation should be considered in the development of KA-specific prostheses.

The Trochlear Groove of a Femoral Component Designed for Kinematic Alignment Is Lateral to the Quadriceps Line of Force and Better Laterally Covers the Anterior Femoral Resection Than a Mechanical Alignment Design

“…One case series of 52 KA TKAs with a MA d -FC reported a 3 mm mean lateral undercoverage of the anterior femoral resection, which increased as the femoral phenotype became more valgus. The three of 52 KA TKA’s with the most valgus femoral phenotype had 5–6 mm of lateral undercoverage [ 2 ]. The present study’s 2 mm and 4.4 mm mean lateral undercoverage of the anterior femoral resection’s for the KA d - and MA d -FC was comparable to the 3 mm mean lateral undercoverage in the case series.…”

“…A concern about performing total knee arthroplasty (TKA) with kinematic alignment (KA) is that it uses femoral components (FC) designed for mechanical alignment (MA d -FC) that might not be optimal for patellofemoral tracking [ 1 , 2 , 3 ]. Whereas MA of the femoral component changes most distal joint lines and Q-angles and rotates the posterior joint line externally from the native knee, KA restores the patient’s pre-arthritic distal and posterior femoral joint lines and Q-angle [ 4 , 5 , 6 , 7 ].…”

“…Although KA does not set the MA d -FC to its intended target, a registry study comparing 7-year follow-up of KA and MA reported little difference in the incidence and type of patellofemoral complications, while some case series reported a small number cases with patella maltracking [ 8 , 9 ]. Hence, there is an interest in evaluating a femoral component explicitly designed for KA (i.e., KA d -FC) with the intent of restoring radiographic characteristics that promote patellofemoral kinematics [ 1 , 2 , 10 ].…”

“…A second newly described radiographic measurement that could assess the effectiveness of a KA d -FC is the extent of lateral coverage of the anterior femoral resection ( Figure 4 ) [ 2 ].…”

“…A study of a MA d -FC aligned in KA showed greater lateral undercoverage of the anterior femoral resection in those patients with the valgus femoral phenotype because of a medial shift of the proximal extension of the trochlear groove orientation relative to those with varus femoral phenotypes. Therefore, the authors suggested a better lateral coverage between the KA d -FC and femoral trochlea resection could reduce the risk of unfavorable patellar kinematics [ 2 ].…”