AXIAL LOWER-LIMB ALIGNMENT - COMPARISON OF KNEE GEOMETRY IN NORMAL VOLUNTEERS AND OSTEOARTHRITIS PATIENTS

Osteoarthritis of the knee is associated with deformities of the lower limb and malalignment of the limb segments. Pathogenetic relationship s between the two are poorly understood. Alignment was studied by stan dardized radiography in 167 symptomatic Canadian osteoarthritis patien ts, and compared with 119 healthy adult volunteers. In healthy adults overall alignment (hip-knee-ankle angle) was principally determined by distal femoral valgus (condylar-hip angle) and proximal tibial-platea u varus (plateau-ankle angle): the angle between the joint surfaces (c ondylar-plateau) was relatively constant. In osteoarthritis, disease-a ssociated differences included condylar-plateau angles that were diver gent: accentuated medical convergence in varus osteoarthritis and late ral convergence in valgus osteoarthritis. This was interpreted as chan ge arising from focal loss of cartilage in the medial (varus osteoarth ritis) or lateral (valgus osteoarthritis) compartments of the knee. Th e changes would contribute to increasing limb malalignment during dise ase progression. But differences of limb geometry also contributed to malalignment. These were the average trends: in varus osteoarthritis t here was abnormal femoral geometry (lesser femoral condylar valgus), b ut tibial surface geometry was the same. In valgus osteoarthritis, the opposite was true: abnormal tibial geometry (less plateau varus), but normal femoral geometry. A possible explanation is that these abnorma l knee geometries pre-exist and predispose to osteoarthritis, although it is not impossible that they (like condylar-plateau angle) change a s disease progresses. Further approaches to population studies are dis cussed based on these findings, along with their implications for knee surgery.