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.