Dynamic hydraulic flow stimulation on mitigation of trabecular bone loss in a rat functional disuse model

Bone fluid flow (BFF) has been demonstrated as a critical regulator in mechanotransductive signaling and bone adaptation. Intramedullary pressure (ImP) and matrix strain have been identified as potential generators to regulate BFF. To elevate in vivo oscillatory BFF using ImP, a dynamic hydraulic stimulation (DHS) approach was developed. The objective of this study was to evaluate the effects of DHS on mitigation of bone loss and structural alteration in a rat hindlimb suspension (HLS) functional disuse model. Sixty-one 5-month old female Sprague-Dawley rats were divided into five groups: 1) baseline control, 2) age-matched control, 3) HLS, 4) HLS+static loading, and 5) HLS+DHS. Hydraulic flow stimulation was carried out daily on a "10 min on-5 min off-10 min on" loading regime, 5 days/week, for a total of 4 weeks in the tibial region. The metaphyseal trabecular regions of the proximal tibiae were analyzed using μCT and histomorphometry. Four weeks of HLS resulted in a significant loss of trabecular bone, leading to structural deterioration. HLS with static loading alone was not sufficient to attenuate the bone loss. Bone quantity and microarchitecture were significantly improved by applying DHS loading, resulting increase of 83% in bone volume fraction, 25% in trabecular number and mitigation of 26% in trabecular separation compared to HLS control. Histomorphometry analysis on trabecular mineralization coincided with the μCT analysis, in which DHS loading yielded increases of 34% in histomorphometric BV/TV, 121% in MS/BS, 190% in BFR/BS and 146% in BFR/BV, compared to the HLS control. Overall, the data demonstrated that dynamic hydraulic flow loading has potentials to provide regulatory signals for mitigating bone loss induced by functional disuse. This approach may provide a new alternative mechanical intervention for future clinical treatment for osteoporosis.