Association between Coronal Mechanical Axis Correction and Early Functional Outcomes after Primary Total Knee...

Restoration of the mechanical axis is an important objective of primary total knee arthroplasty (TKA), although the relationship between the magnitude and pattern of post-operative alignment and early functional recovery remains incompletely defined. This study evaluated post-operative mechanical-axis restoration and its association with early functional outcomes following primary TKA.

This retrospective study included 60 patients (85 knees) undergoing primary TKA. Pre-operative and post-operative full-length radiographs were assessed for femorotibial mechanical axis (FTMA) and mechanical axis deviation (MAD). Post-operative FTMA was classified as valgus, neutral, mild varus, or severe varus. Functional outcomes were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Oxford Knee Score (OKS) preoperatively and at 6 weeks, 3 months, and 6 months. Patient-clustered analyses accounted for bilateral knees.

Mean FTMA improved from -10.13 ± 4.82° preoperatively to -1.49 ± 3.95° postoperatively (P < 0.001), while MAD decreased from 4.85 ± 2.17 to 1.61 ± 1.24 cm (P < 0.001). WOMAC improved from 76.21 ± 5.75 to 11.58 ± 4.35, and OKS increased from 10.98 ± 2.55 to 41.95 ± 3.35 at 6 months (both P < 0.001). Neutral alignment was associated with the best 6-month outcomes (WOMAC, 8.33 ± 2.13; OKS, 44.80 ± 1.65). Correction magnitude was not associated with WOMAC (P = 0.168) but was associated with OKS (P = 0.009). Correction of 5-10° resulted in higher OKS than correction >10° (P = 0.044).

Primary TKA significantly improved mechanical alignment and functional outcomes. Neutral post-operative alignment was associated with better early function, while correction beyond 10° did not provide additional functional benefit.