INVESTIGADORES
COINTRY Gustavo Roberto
congresos y reuniones científicas
Título:
Human tibia bone strength is unaffected following long term spinal cord injury or bed rest.
Autor/es:
ALEX IRELAND; RICARDO FRANCISCO CAPOZZA; GUSTAVO ROBERTO COINTRY; JOSÉ LUIS FERRETTI; JOERN RITTWEGER
Reunión:
Congreso; XXXVI ANNUAL MEETING, AMERICAL SOCIETY FOR BONE & MINERAL RESEARCH (ASBMR).; 2014
Resumen:
The tibia bears over 80% of compressive loading in the shank in humans (Wang et al, Clin Orthop Rel Res, 1996). Given this high level of habitual loading, it is unsurprisingly highly responsive to disuse.  Long-term spinal cord injury is associated with a 60% reduction in tibial bone mass (Eser et al, Bone, 2004), and 90 days? bed rest results in up to 4.4% loss of bone mass dependent on site (Rittweger et al, Bone, 2005).  Conversely the fibula contributes to only -6 to +19% of shank compressive force transmission, with greater contributions observed during pronounced foot eversion and plantar flexion (Goh et al, Clin Orthop Rel Res, 1992) and as absolute load increases. However, the influence of disuse on the human fibula has not previously been explored. To investigate fibular response to disuse, re-analysis of two previous pQCT datasets were completed. First, serial scans at 5% increments from 5% to 95% distal-proximal tibia length in 9 long-term spinal cord injury (SCI) patients aged 39.2±6.2y taken 9-32 years post-injury, and in 9 age, height and mass-matched controls were compared. Also, scans taken in 25 young male volunteers aged 33.7±3.7y prior to and 14 days after 90 days of 6° head-down tilt bed rest were examined.   No significant differences or group-site interactions in total & cortical BMC, and bone area, cortical vBMD, periosteal and endocortical circumferences and cortical thickness of the fibula were found between SCI patients and controls (P > 0.16 for all parameters). In contrast, tibial BMC was 22-51% lower in SCI patients with group-site interactions revealing more pronounced differences in distal and proximal sites as opposed to shaft measures (both P < 0.001).  There was no effect of bed rest on tibial bone mass, with only fibular trabecular BMD differing significantly (-1.4%, P = 0.04) from baseline measures. Tibial analysis revealed significant 0.9%-4.4% lower tibia bone mass following bed rest (all P < 0.01). Results suggest that the fibula is affected little by disuse, with diaphyseal sites in particular displaying no effects of reduced physical activity in either SCI or bed rest data. This may be a result of the fibula?s comparatively small contribution to load-bearing in the shank.  Exercise models involving high compressive shank loads and pronounced eversion and /or plantarflexion may be effective in elucidating substantial exercise response in the fibula.