دانلود رایگان مقاله تخمین استحکام استخوان نسبت به نیروی عکس العمل زمین

Abstract

Purpose: To determine differences in bone geometry, estimates of bone strength, muscle size and bone strength relative to load, in women runners with and without a history of stress fracture. Methods: We recruited 32 competitive distance runners aged 18–35, with (SFX, n = 16) or without (NSFX, n = 16) a history of stress fracture for this case-control study. Peripheral quantitative computed tomography (pQCT) was used to assess volumetric bone mineral density (vBMD, mg/mm3 ), total (ToA) and cortical (CtA) bone areas (mm2 ), and estimated compressive bone strength (bone strength index; BSI, mg/mm4 ) at the distal tibia. ToA, CtA, cortical vBMD, and estimated strength (section modulus; Zp, mm3 and strength strain index; SSIp, mm3 ) were measured at six cortical sites along the tibia. Mean active peak vertical (pkZ) ground reaction forces (GRFs), assessed from a fatigue run on an instrumented treadmill, were used in conjunction with pQCT measurements to estimate bone strength relative to load (mm2 /N ∗ kg−1 ) at all cortical sites. Results: SSIp and Zp were 9–11% lower in the SFX group at mid-shaft of the tibia, while ToA and vBMD did not differ between groups at any measurement site. The SFX group had 11–17% lower bone strength relative to mean pkZ GRFs (p b 0.05). Conclusion: These findings indicate that estimated bone strength at the mid-tibia and mean pkZ GRFs are lower in runners with a history of stress fracture. Bone strength relative to load is also lower in this same region suggesting that strength deficits in the middle 1/3 of the tibia and altered gait biomechanics may predispose an individual to stress fracture.

5. Conclusion

In conclusion, our data reveal that women runners with a history of stress fracture have lower bone strength in the middle third of the tibia and smaller muscle cross-sectional area. The difference in bone strength is not significant after adjusting for muscle size, suggesting a welladapted muscle-bone relationship in both groups. However, women runners with a history of stress fracture have significantly lower bone strength relative to the loads they encounter during running, suggesting that suboptimal bone geometry and lower bone strength relative to load during running may predispose an individual to stress fracture. Further research is needed to determine whether altering biomechanics to decrease pkZ GRFs is a viable solution to reduce injury risk in women with a history of stress fracture.