Effect of vibratory perception on the ankle joint in patients with medial knee osteoarthritis

Abstract

Purpose: Afferent somatosensory function, including vibratory perception, has been shown to be reduced in patients with knee osteoarthritis (OA). Moreover, both dynamic knee joint loading and structural severity of disease have been shown to be associated with vibratory perception threshold (VPT) in knee OA.We hypothesized that there is a comparable association between VPT and narrowing of joint space width (JSW) in the ankle over time. Here we evaluated the effect of baseline vibratory perception on the rate of joint space narrowing in ankle joints of subjects who have medial knee OA, but no intrinsic foot disease. Methods: Participants in a previously reported prospective 36 month double blind randomized controlled study to assess lateral wedge orthoses were studied (n=109). Enrollment criteria required that they have predominant medial compartment radiographic OA (Kellgren- Lawrence grades 2-3), knee pain of at least 30mm pain of a 100 mm visual analog scale while ambulating, have essentially neutral mechanical alignment, and have no intrinsic foot disease. Image J software (US NIH, Bethesta, MD, http://rsbweb.nih.gov/ij/) was used to quantify the narrowest joint space width (JSW) of the ankles medially and laterally, according to a validated method (CORR, 467:2083, 2009). Baseline VPT was determined by timing the duration of perception using a 128Hz tuning fork placed on the bony prominence of the 1st metatarsophalangeal joint. Results: 42 patients completed the study. Of these, 35 had baseline VPT available. Baseline VPT was 13±5 seconds (mean±SD). Baseline JSW (mean±SD ankle) was 2.57±0.45 mm and 2.43±0.52 mm, medially and laterally, respectively. Mean±SD change in JSW at 36 months was -0.07±0.31 mm and -0.06±0.26mm medially and laterally, respectively (JSW at the 36th month minus baseline JSW). There was a significant relationship between baseline VPT and the magnitude of change in JSW at 36 months at the ankle joint space measured laterally (Figure 1), such that a worse VPT was associated with significantly more rapid loss of JSW of the lateral ankle joint (Pearson's r=0.37, p=0.03). No significant relationship was observed between VPT and change in medial ankle joint space width (Pearson's r=0.27, p=0.12). Conclusion: In patients with medial knee OA but no intrinsic foot disease, worse VPT at baseline is associated with more rapid narrowing of JSW in ankles laterally. This suggests that these subjects function with the foot and ankle more towards the midline of the body with the ankle/ subtalar joint complex everting to allow for foot compensation. This is consistent with current theories that those with medial knee OA have a more varus attribute to the lower leg and foot. Mechanistic studies are needed to determine whether rearfoot varus compensation is producing excessive valgus loads across the ankle joint leading to joint space narrowing. (Figure Presented).