Aim

In Total Knee Arthroplasty (TKA), knee phenotype including joint line obliquity are of interest regarding surgical realignment strategies. This study aims to assess the effect of restoring knee phenotype on clinical outcomes.

Methods

A retrospective analysis was performed on prospective data, including 1078 primary osteoarthritic knees in 936 patients. International Knee Society Scores and standardized long-leg radiographs were collected preoperatively and two years postoperatively. Patients were categorized using the Coronal Plane Alignment of the Knee (CPAK) classification including the Lateral-Distal-Femoral-Angle (LDFA) and Medial-Proximal-Tibial-Angle (MPTA), allowing knee phenotypes to be categorized considering the arithmetic Hip-Knee-Ankle (aHKA) angle (MPTA-LDFA) as measure of constitutional alignment, and Joint Line Obliquity (JLO) (MPTA+LDFA). Patients with surgically restored preoperative constitutional knee phenotype were compared with patients without restored constitutional knee phenotypes.

Results

33.4% of patients had constitutional knee varus with apex distal JLO. 63.5% of patients had preoperative apex distal JLO. Postoperatively, 57.8% of patients had a neutral HKA (-2° to 2°) and a neutral JLO (-3° and 3°), with only 18% of patients with restored constitutional knee phenotype. Of these patients, less postoperative pain was observed in patients where apex distal JLO was restored compared to non-restored apex distal JLO (pain score 46.7 vs. 44.6; p=0.02). Other categories of restored JLO or HKA angle were not associated with improved outcomes.

Conclusion

Restoring constitutional apex distal joint line obliquity resulted in improved outcomes with less postoperative pain. This emphasizes the need for a personalized TKA surgical realignment strategy that considers joint line obliquity and not only the HKA angle.