Symmetric vs. Asymmetric Mediolateral Gaps in Total Knee Arthroplasty

Background: Historically, total knee arthroplasty (TKA) used resection and balancing techniques to target symmetric medial and lateral gaps throughout range of motion (ROM). With modern awareness on alternate alignment concepts, one area of ongoing debate is whether asymmetric medial and lateral compartment gaps improve outcomes. Proponents of an asymmetric looser lateral compartment gap philosophy postulate that this phenotype recreates native knee kinematics with lateral femoral condylar rollback pivoting through a tighter medial compartment during knee flexion. The purpose of this study was to compare patient-reported outcomes (PROs) and ROM with respect to symmetric or asymmetric gaps. Methods: We performed a systematic review and random-effects meta-analysis of prospective and retrospective studies. We compiled all comparative studies reporting symmetric and asymmetric gaps, irrespective of directional or nondirectional gap asymmetry. However, we performed a meta-analysis only between a cohort of directional asymmetric gaps (looser lateral than medial gap) and symmetric gaps (equal medial and lateral gaps). Gaps were compared in flexion and extension. ROM and PROs were evaluated through standardized mean difference (SMD), with statistical significance defined by 95% confidence interval (CI). Results: A total of 17 studies with 3,319 knees were included. Four studies reported nondirectional gap asymmetry, whereas 13 studies reported directional gap asymmetry, of which 8 shared common outcome variables and were therefore included in the meta-analysis. Analysis of gaps in flexion revealed significantly increased ROM favoring asymmetric looser lateral gaps over symmetric gaps (SMD −0.19, 95% CI −0.29 to −0.09). Analysis of gaps in extension also revealed increased ROM favoring asymmetric looser lateral gaps (SMD −0.10, 95% CI −0.36 to 0.16). Finally, the Forgotten Joint Score (FJS) favored looser lateral gaps in flexion over symmetric gaps (SMD −0.13, 95% CI −0.41 to 0.15). However, differences in the latter 2 were nonsignificant. Conclusion: This is the first meta-analysis evaluating the postoperative outcomes as a function of symmetric vs. asymmetric mediolateral gaps. We report improved FJS and ROM favoring asymmetric looser lateral gaps in flexion. Level of Evidence: Therapeutic Level II , systematic review of Level II and III and IV studies. See Instructions for Authors for a complete description of levels of evidence.