A retrospective comparison of mechanically vs. kinematically aligned unicompartmental knee arthroplasties.

BACKGROUND: Unicompartmental Knee Arthroplasties (UKAs) treat unicompartmental arthritic degeneration. Traditionally, they are placed in a mechanical alignment with bone cuts perpendicular to the leg's mechanical axis. Kinematic alignment, an alternative, considers the patient's pre-arthritic alignment.

METHODS: A retrospective study at Medstar Washington Hospital Center from 2015 to 2022 identified 72 UKA patients. Among them, 53 had mechanical alignments, and 20 had kinematic alignments. Using the Forgotten Joint Score (FJS) and Oxford Knee Score (OKS), Patient Reported Outcome Measures for these surgeries were recorded. Individuals were additionally analyzed post-surgically for Coronal Plane Alignment of the Knee (CPAK). Analysis was performed within the post-operative joint imaging, where mechanical medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were measured. The arithmetic hip knee ankle angle (aHKA) and joint line obliquity (JLO) were calculated according to the results of MPTA-LDFA and MPTA + LDFA respectively and grouped in accordance with the CPAK classification.

RESULTS: Overall, there was a statistically significant response rate of 51% (>50%). According to the FJS, the mechanical cohort averaged a score of 39.1 (±33.8), while the kinematical cohort averaged 56.5 (±35.2). A two-sample t -test of this data demonstrated a statistically insignificant p-value of 0.1537. According to the OKS, the mechanical cohort averaged a score of 29.1 (±10) and the kinematical cohort averaged 38.4 (±8). A two-sample t -test of this data demonstrated a statistically significant p-value of <0.001. Of note, 7 patients had to undergo revisions in the mechanical alignment cohort compared to 0 in the kinematic alignment cohort due to aseptic loosening.

CONCLUSION: This study demonstrates the potential benefit in patient outcomes for individuals who undergo a kinematic rather than mechanical alignment of their UKAs. The results of the CPAK data with the significance of LDFA are consistent with the goals of the mechanical and kinematic alignment respectively.