RESUMO
Vertebrae containing osteolytic and osteosclerotic bone metastases undergo pathologic vertebral fracture (PVF) when the lesioned vertebrae fail to carry daily loads. We hypothesize that task-specific spinal loading patterns amplify the risk of PVF, with a higher degree of risk in osteolytic than in osteosclerotic vertebrae. To test this hypothesis, we obtained clinical CT images of 11 cadaveric spines with bone metastases, estimated the individual vertebral strength from the CT data, and created spine-specific musculoskeletal models from the CT data. We established a musculoskeletal model for each spine to compute vertebral loading for natural standing, natural standing + weights, forward flexion + weights, and lateral bending + weights and derived the individual vertebral load-to-strength ratio (LSR). For each activity, we compared the metastatic spines' predicted LSRs with the normative LSRs generated from a population-based sample of 250 men and women of comparable ages. Bone metastases classification significantly affected the CT-estimated vertebral strength (Kruskal-Wallis, p < 0.0001). Post-test analysis showed that the estimated vertebral strength of osteosclerotic and mixed metastases vertebrae was significantly higher than that of osteolytic vertebrae (p = 0.0016 and p = 0.0003) or vertebrae without radiographic evidence of bone metastasis (p = 0.0010 and p = 0.0003). Compared with the median (50%) LSRs of the normative dataset, osteolytic vertebrae had higher median (50%) LSRs under natural standing (p = 0.0375), natural standing + weights (p = 0.0118), and lateral bending + weights (p = 0.0111). Surprisingly, vertebrae showing minimal radiographic evidence of bone metastasis presented significantly higher median (50%) LSRs under natural standing (p < 0.0001) and lateral bending + weights (p = 0.0009) than the normative dataset. Osteosclerotic vertebrae had lower median (50%) LSRs under natural standing (p < 0.0001), natural standing + weights (p = 0.0005), forward flexion + weights (p < 0.0001), and lateral bending + weights (p = 0.0002), a trend shared by vertebrae with mixed lesions. This study is the first to apply musculoskeletal modeling to estimate individual vertebral loading in pathologic spines and highlights the role of task-specific loading in augmenting PVF risk associated with specific bone metastatic types. Our finding of high LSRs in vertebrae without radiologically observed bone metastasis highlights that patients with metastatic spine disease could be at an increased risk of vertebral fractures even at levels where lesions have not been identified radiologically.
RESUMO
OBJECTIVE: To evaluate the association between thoracic kyphosis and physical function. DESIGN: Prospective cohort. SETTING: Framingham, Massachusetts. PARTICIPANTS: Framingham Heart Study Offspring and Third Generation cohort members who had computed tomography (CT) performed between 2002 and 2005 and physical function assessed a mean 3.4 years later (N = 1,100; mean age 61 ± 8, range 50-85). MEASUREMENTS: Thoracic kyphosis (Cobb angle, T4-T12) was measured in degrees using supine CT scout images. Participants were categorized according to Cobb angle to compare those in the highest quartile (Q4, most-severe kyphosis) with those in the lowest quartiles (Q1-Q3). Quick walking speed (m/s), chair-stand time (seconds), grip strength (kg), and self-reported impairments were assessed using standardized procedures. Analyses were adjusted for age, height, weight, smoking, follow-up time, vertebral fractures, and prevalent spinal degeneration. RESULTS: Thoracic kyphosis was not associated with physical function in women or men, and these results were consistent in those younger than 65 and those aged 65 and older. For example, walking speed was similar in adults younger than 65 with and without severe kyphosis (women, Q4: 1.38 m/s, Q1-Q3: 1.40 m/s, P = .69; men, Q4: 1.65 m/s, Q1-Q3: 1.60 m/s; P = .39). CONCLUSION: In healthy relatively high-functioning women and men, kyphosis severity was not associated with subsequent physical function. Individuals at risk of functional decline cannot be targeted based on supine CT thoracic curvature measures alone.