Purpose: Given the goal of achieving optimal correction and alignment after knee arthroplasty or high tibial osteotomy, literature focusing on the inter-individual variability of the native knee, tibia and femur with regards to the coronal or sagittal alignment is lacking. The aim of this study was to analyse normal angular values in the healthy middle-aged population and determine differences of angular values according to inter-individual features. The first hypothesis was that common morphological patterns may be identified in the healthy middle-aged non-osteoarthritic population. The second hypothesis was that high inter-individual variability exists with regards to gender, ethnicity and alignment phenotype.
Methods: A CT scan-based modelling and analysis system was used to examine the lower limb of 758 normal healthy patients (390 men, 368 women; mean age 58.5 ± 16.4 years) with available data concerning angular values and retrieved from the SOMA database. The hip-knee-ankle angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior distal femoral angle (PDFA), posterior proximal tibial angle (PPTA) and non weight-bearing joint line convergence angle (nwJLCA) were then measured for each patient. Results were analysed for the entire cohort and based on gender, ethnicity and phenotype.
Results: The mean HKA was 179.4° ± 2.6°, LDFA: 85.8° ± 2.0°, MPTA: 85.6° ± 2.4°, PDFA: 85.2° ± 1.5°, PPTA: 83.8° ± 2.9° and nwJLCA: 1.09° ± 0.9°. Gender was associated with higher LDFA and lower HKA for men. Ethnicity was associated with greater proximal tibial vara and distal femoral valgus for Asian patients. Patients with an overall global varus alignment had more tibia vara and less femoral valgus than patients with an overall valgus alignment.
Conclusion: Even if significant differences were found based on subgroup analysis (gender, ethnicity or phenotype), this study demonstrated that neutral alignment is the main morphological pattern in the healthy middle-aged population. This neutrality is the result from tibia vara compensated by an ipsilateral femoral valgus.
Level of clinical evidence: III, retrospective cohort study.
Keywords: Alignment; CT; HKA; HTO concepts; JLCA; Knee; LDFA; MPTA; Native; PPTA; Phenotypes.