Summary

After cruciate-retaining total knee arthroplasty, dynamic joint line orientation angle (JLOA) during the stance phase in gait was affected by mechanical lateral distal femoral angle and static JLOA. The more lateral tilt of dynamic JLOA at terminal stance was associated with the higher patient-reported outcome measures.

Abstract

Background

The optimal alignment in total knee arthroplasty (TKA) is controversial, and the joint line orientation angle (JLOA), i.e., the mediolateral tilt of the tibial articular surface to the ground under weight-bearing condition, is one of interest. Static JLOA in the standing position is often discussed, but its relationship with dynamic JLOA during gait remains unclear. The purposes of this study were to investigate the effect of alignment-related parameters including static JLOA in the standing position on dynamic JLOA during gait in the coronal plane after cruciate-retaining (CR) TKA, and to assess the relationship between JLOA and postoperative patient-reported outcome measures (PROMs).

Methods

Thirty-five conventional mechanically aligned CR-TKAs (27 patients) were prospectively examined at a mean follow-up of 72.4 months. Alignment-related parameters in the coronal plane including hip-knee-ankle angle (HKAA), mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA) as well as JLOA were measured using a postoperative long-leg weight-bearing radiograph. The JLOA was defined as the angle between the tibial component and the line parallel to the ground in the coronal plane, with medial tilt defined as positive values. Using a fluoroscopy, dynamic JLOA during the stance phase of gait were analyzed at four time points: initial contact, mid stance (the first half of single limb support), terminal stance (the second half of single limb support), and toe off. Linear regression analyses were performed to detect the alignment-related parameters affecting static and dynamic JLOAs, and to assess the effect of static JLOA on dynamic JLOA. In addition, correlations between static and dynamic JLOAs and 2011 Knee Society Score (KSS) were evaluated by Spearman’s rank correlation test.

Results

The HKAA, mLDFA, and MPTA averaged 0.8° varus, 90.4°, and 89.2°, respectively. The mean static JLOA was -1.6°, and dynamic JLOA at initial contact, mid stance, terminal stance, and toe off averaged 3.1°, -1.3°, -2.4°, and 0.3°, respectively. Static JLOA was significantly associated with mLDFA (regression coefficient (ß) = -0.73; p < 0.001) and MPTA (ß = -0.39; p = 0.018) by multiple linear regression, whereas only mLDFA had a significant influence on dynamic JLOA at terminal stance (ß = -0.45; p = 0.010). Static JLOA was significantly associated with dynamic JLOA at mid stance (ß = 0.47; p = 0.008) and at terminal stance (ß = 0.44; p = 0.005). Dynamic JLOA at terminal stance was significantly correlated with patient expectations (correlation coefficient [?] = -0.47; p = 0.005) and standard activities score of 2011 KSS (? = -0.41; p = 0.017). Medial tilt of the joint line during gait was negatively correlated with postoperative patient expectation and knee function.

Conclusion

After CR-TKA, dynamic JLOA during the stance phase in gait was affected by mLDFA and static JLOA. The more lateral tilt of dynamic JLOA at terminal stance was associated with the higher PROMs.