Altered bone density and stress distribution patterns in long-standing cubitus varus deformity and their effect during early osteoarthritis of the elbow.

ABSTRACT

OBJECTIVE: To quantify the bone density and stress distribution patterns in long-standing cubitus varus and clarify the effects of the deformity on bone density. DESIGN: We created three-dimensional computed tomography (CT) elbow models from 21 patients with long-standing cubitus varus deformities without advanced osteoarthritis (OA) and assessed the deformity by superimposing the affected humerus onto a mirror-image of the contralateral normal. Elbows were divided into 13 regions before measuring the bone density of each region and comparing the percentage of high-density volume (%HDV) between affected and normal sides. We constructed finite element models and quantitatively analyzed stress distribution. RESULTS: Average degrees of deformities were 20.1° of varus, 6.4° of extension, and 12.7° of internal rotation. The medial side of the affected humerus and ulna, Anteromedial trochlea (P < 0.001), Medial coronoid (P = 0.004), and Medial olecranon (P = 0.049) had significantly higher %HDVs than their normal counterparts. Conversely, %HDVs on the affected lateral side, Capitellum (P < 0.001), Anterolateral trochlea (P = 0.010), Posterolateral trochlea (P < 0.001), Lateral coronoid (P = 0.007), and Lateral olecranon (P < 0.001) were significantly lower than the normal side. The affected radial head %HDVs at Anterolateral and Posteromedial quadrants were high (P = 0.007) and low (P = 0.007), respectively. The bone density distribution coincided with stress distribution patterns revealed by finite element analysis (FEA), except in the lateral region influenced by forearm rotation. CONCLUSIONS: Repetitive stress on the medial elbow may alter bone density distribution patterns, probably presenting from early stage of OA.