LAS VEGAS – Patients with medial compartment knee osteoarthritis who wore a patented flexible mobility shoe experienced a favorable reduction in medial tibial bone mineral density that directly correlated with their improved gait biomechanics and reduced peak knee adduction moment, Najia Shakoor, MD, reported at the World Congress on Osteoarthritis.
“Our results suggest that bone can be modified with sustained load reduction and that evaluation of tibial bone density may be an inexpensive tool for evaluating the consequences of load-reducing interventions,” said Dr. Shakoor, a rheumatologist at Rush University in Chicago.
Indeed, measuring changes in medial tibial bone density over time via serial dual x-ray absorptiometry is an attractive surrogate anatomic marker of a patient’s response to a biomechanical load-reducing intervention such as a special shoe or knee brace, Dr. Shakoor noted at the meeting sponsored by the Osteoarthritis Research Society International.
After all, she added, bone density measurement is simpler than sending a patient to a motion analysis laboratory for multicamera gait analysis using a force plate to evaluate changes in the peak external knee adduction moment (a validated marker of load distribution across the tibial plateau).
Studies suggest that bone, not cartilage, bears the bulk of the load burden across the knee joint. That’s why patients with knee osteoarthritis have increased proximal tibial bone mineral density. Dr. Shakoor presented evidence that sustained reduction in dynamic knee loading results in a proportionate reduction in medial tibial bone density over the course of 6 months.
She reported on 51 patients with mild to moderate radiographic and symptomatic medial compartment knee osteoarthritis who were randomized to wear a commercially available flexible mobility shoe or a similar-looking but nonflexible control shoe for 6 hours per day for at least 6 days per week for 6 months. At baseline and again at 6 months, the participants underwent knee bone density measurement and formal gait analysis.
Peak knee adduction moment decreased by 14% over the course of 6 months in the flexible shoe group, significantly greater than the 6% reduction in the controls. Moreover, Dr. Shakoor and her coinvestigators documented a significant reduction in medial tibial bone density in the flexible shoe group. The greater the improvement in knee adduction moment, the larger the reduction in bone density.
In contrast, medial tibial bone density didn’t change significantly in the controls.
Dr. Shakoor said that she had also expected to see a reduction in the ratio of medial to lateral tibial bone density in the flexible shoe group. However, there was no statistically significant change, although there was a trend in that direction.
Asked if reduction in knee adduction moment and/or medial tibial bone density correlated with improved knee pain scores, Dr. Shakoor replied that almost everyone in the study reported improvement in pain, suggesting a placebo effect for that endpoint. In any event, the relatively small study wasn’t powered to evaluate change in pain over time.
The Arthritis Foundation funded the study. Dr. Shakoor is coinventor of the flexible shoe used in the study. The patent, owned by Rush University, has been licensed to Dr. Comfort, which markets the shoe as the Dr. Comfort Flex-OA Mobility Shoe. A percentage of the proceeds from shoe sales is distributed to the university and the coinventors.