Mechanical alignment may change both knee phenotype and join
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The hypothesis of this study is that better clinical results, including decreased postoperative knee pain, will be observed for patients with a restored knee phenotype. In total knee arthroplasty (TKA), knee phenotypes including joint line obliquity are of interest regarding surgical realignment strategies.

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 (LLR) were collected preoperatively and at 2 years follow-up after TKA.

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) measured on LLR by a single observer, 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).

Descriptive data analysis such as means, standard deviations and ranges were performed. T tests for independent samples were performed to compare group differences.

--A third 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, statistically 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) without clinical relevance.

--Other categories of restored JLO or arithmetic HKA angle were not associated with improved outcomes.

Conclusively, this study showed that performing mechanical alignment for primary TKA resulted in most cases in a change of the preoperative knee phenotype. These results emphasize the relevance of considering joint line obliquity to better understand preoperative knee deformity and better restore knee phenotypes with a more personalized realignment strategy to potentially improve TKA postoperative results.