Tibia‐only planning to 3° valgus implies mechanical medial proximal tibial angle ≥94° in about two‐thirds of varus knee osteoarthritis radiographs
Xu Jiang, Yicang Wang, Xing Li, Songtao Ai, Jun Zhou, Kai Xie, Liao Wang, Mengning YanAbstract
Purpose
To estimate the proportion of radiographic records from patients with varus knee osteoarthritis in which tibia‐only planning targeting a hip–knee–ankle angle (HKA) of 183° (3° valgus) yielded a calculated mechanical medial proximal tibial angle (mMPTA) of at least 94°.
Methods
In a retrospective database, 1426 knee‐specific records were screened. Eligible records came from adults with standardised standing full‐length lower‐limb radiographs. Exclusions covered hip and foot deformities, spontaneous femoral condyle osteonecrosis, previous lower‐limb surgery, malignancy, major trauma, poor image quality and excessive rotation. Symptomatic knee osteoarthritis, numerical quality control and HKA below 176.5° defined the analytical cohort. Alignment was measured using an artificial intelligence‐assisted system. Correction was assigned entirely to the tibia. The mechanical lateral distal femoral angle and joint line convergence angle were held constant. The primary target was 3° valgus; 1°, 2°, 4°, 5° and 6° of valgus were supplementary targets. Analyses were descriptive, with two‐sided 95% Wilson confidence intervals for proportions.
Results
The analysis included 627 records from 392 patients (mean age, 67.3 ± 9.2 years; 28.6% men). At the 3° valgus target, the mean calculated mMPTA was 96.0 ± 3.7°; 424/627 records reached at least 94° (67.6%; 95% confidence interval, 63.9%–71.2%). The most frequent deformity‐source patterns were intraarticular alone (24.7%) and tibial‐side plus intraarticular (24.4%).
Conclusions
At a 3° valgus target, tibia‐only planning implied an mMPTA of at least 94° in about two‐thirds (67.6%) of records from this varus knee osteoarthritis cohort. Preoperative planning should therefore assess local tibial joint‐line orientation and deformity source alongside the whole‐limb alignment target.
Level of Evidence
Level IV, retrospective radiographic geometry study.