Predictors of Lower Limb Coronal Malalignment after Conventional Total Knee Arthroplasty Using a Mechanical Alignment Strategy.

OBJECTIVES

The primary goal of total knee arthroplasty (TKA) is to restore the neutral mechanical axis of the lower limb using mechanical alignment. However, no studies to date have investigated the risk factors of coronal malalignment (CM) following conventional TKA. In this study, we aimed to determine the incidence of post-TKA CM and identify its potential risk factors.

METHODS

We retrospectively reviewed all conventional primary TKAs utilizing cemented posterior-stabilized prostheses in our institute from January 2019 to 2022. The following variables were extracted from the Joint Reconstruction Research Center (JRRC) Knee Registry Database: demographics, varus classification, flexion contracture, femoral and tibial bowing, pre- and postoperative Hip-knee-ankle angle (HKAA), mechanical lateral distal femoral angle (LDFA), mechanical medial proximal tibial angle (MPTA), joint-line congruency angle (JLCA), and caput-collum-diaphyseal (CCD) angle. Multiple logistic regression was used to develop a predictive model for post-TKA CM.

RESULTS

Among the 402 TKAs analyzed after exclusions, 172 (42.79%) fell outside the acceptable postoperative HKAA range (180° ± 3°). Of the 17 factors studied, the following were associated with an increased risk of postoperative CM: flexion contracture > 10° (OR = 2.95, P < 0.001), femoral bowing > 4.9° (OR= 1.89, P= 0.006), tibial bowing > 2.2° (OR= 2.00, P= 0.002), preoperative MPTA≤ 85° (OR= 1.68, P= 0.037) or HKAA ≥ 20° varus (OR= 5.07, P= 0.017), preoperative JLCA 4°-10° (OR= 2.49, P= 0.023), and CCD ≤ 131° (OR= 1.62, P= 0.044). The results remained almost consistent even after excluding the extreme HKAA outliers (> ±6° varus and valgus).

CONCLUSION

In mechanically aligned TKAs, the risk of post-TKA CM can be estimated preoperatively based on specific risk factors (e.g., a 40.5% risk for patients with ≥ 3 risk factors). Identifying higher risks can warn the surgeon to address these factors and perform the TKA with greater precision.