Background/Purpose:   Osteoarthritis (OA) is characterized by increased subchondral bone mineral density at affected joints.  In the knee, proximal tibial bone mineral density (BMD) is associated with dynamic joint loading (Thorp et al, Bone, 2006), and thereby serves as a marker for structural consequences of sustained altered joint loading.  Biomechanical interventions such as specialized footwear (the mobility shoe) have been shown to reduce joint load in knee OA.  We hypothesized that load reduction with use of the mobility shoe would yield appreciable reductions in proximal tibial BMD over 48 weeks.

Methods: Subjects with mild to moderate medial compartment radiographic knee OA were randomized to wear either the mobility shoe or “non-flexible” control shoe.  All participants and investigators were blind to treatment group allocation.  Participants were asked to wear the shoes 6 hours per day at least 6 days per week.  Subjects underwent DXA scanning of bilateral knees at baseline and at 24 and 48 weeks after starting the intervention.  These scans were evaluated in a blinded manner by a trained investigator using a previously validated method. The BMD of the medial and lateral regions of the tibial plateau were measured in each knee.  Repeated measures ANOVA (rm-ANOVA) was used to evaluate changes in BMD over time in each group.

Results: Nine subjects in the mobility shoe group and 13 subjects in the control group had BMD data available at all three time points (0, 24, and 48 weeks).  The mobility shoe group demonstrated a significant reduction in the medial proximal tibial BMD of the affected knee from 0 to 24 to 48 weeks (p=0.01, see Table).  The control shoe group did not demonstrate a statistically significant reduction in medial proximal tibial BMD over this time (see Table).   There were no significant changes in lateral tibial BMD in either group from 0 to 24 to 48 weeks (see Table).

Conclusion: The mobility shoe yielded a significant reduction in medial tibial BMD over 48 weeks of use.  A control walking shoe did not yield similar BMD changes.   These results suggest that use of the mobility shoe can lead to potentially beneficial structural changes in subchondral bone as the result of a dynamic load reducing intervention.

*Values are the mean ± SD unless otherwise indicated; BMD, bone mineral density; rm-ANOVA, repeated measures ANOVA.