Showing papers by "Patricia Dolan published in 2004"

Intervertebral disc degeneration can lead to "stress-shielding" of the anterior vertebral body: a cause of osteoporotic vertebral fracture?

Abstract: STUDY DESIGN Mechanical testing of cadaveric lumbar motion segments. OBJECTIVES To test the hypothesis that degenerative changes in the intervertebral discs can influence loading of the anterior vertebral body in a manner that makes it vulnerable to fracture. SUMMARY OF BACKGROUND DATA Measurements of systemic bone loss do not fully explain the patterns of osteoporotic vertebral fractures. METHODS Thirty-three cadaveric lumbar motion segments (aged 19-82 years) were subjected to 2 kN of compressive loading while positioned to simulate habitual erect standing postures and forwards bending. Intradiscal stresses were measured in each posture by pulling a miniature pressure transducer along the midsagittal diameter of the disc. "Stress profiles" were then integrated over area to calculate the force acting on the anterior and posterior halves of the vertebral body. These forces were subtracted from the applied 2 kN to determine the compressive force on the neural arch. RESULTS In motion segments with nondegenerated discs, <5% of the compressive force was resisted by the neural arch, and forces on the vertebral body were always distributed evenly, irrespective of posture. However, with severely degenerated discs, neural arch load-bearing increased to 40% in the erect posture, and the compressive force on the vertebral body was concentrated anteriorly in forwards bending, and posteriorly in erect posture. CONCLUSIONS Severe disc degeneration causes the anterior vertebral body to be stress-shielded during the usual erect posture, and yet severely loaded whenever the spine is flexed. This could help to explain why this region is frequently the site of osteoporotic fracture, and why forward bending movements often precipitate the injury.

Spinal position sense and disease progression in ankylosing spondylitis: a longitudinal study.

Abstract: STUDY DESIGN: A longitudinal study of spinal position sense in 27 patients with mild ankylosing spondylitis (AS). OBJECTIVES: To test the hypothesis that disease progression in AS is associated with deficits in spinal position sense. SUMMARY OF BACKGROUND DATA: AS is a progressive disease that frequently leads to deterioration in spinal posture. The cause of postural change is unknown. However, pathologic involvement of spinal entheses that contain proprioceptive afferents suggests that impaired pro-prioception may play a role. This study investigates whether longitudinal changes in posture and other measures of disease progression are associated with deficits in spinal position sense in patients with mild AS. METHODS: Position sense was assessed using an electromagnetic movement analysis system, the 3-Space Fastrak, to determine the absolute error in reproducing flexed and upright spinal postures. Measurements were taken from sensors at T1, T7, L1, and S2 and repeated following a mean time interval of 13.7 months. Assessments of posture, disease activity, and function were also made on both occasions. RESULTS: Patients showed a significant increase in disease activity, and losses in spinal mobility, over time. However, no significant changes in spinal posture or position sense were found. Repositioning errors in flexed postures were < or = 3.50 at the first testing session and < or = 3.77 degrees at follow-up. Corresponding values for upright postures were < or = 2.71 degrees and < or = 2.25 degrees, respectively. CONCLUSIONS: Spinal position sense appears unaffected by disease progression in patients with mild AS. Longer follow-ups may help determine any association between disease-related postural change and spinal position sense in AS.

Spinal position sense in ankylosing spondylitis

Abstract: STUDY DESIGN A cross-sectional comparison of spinal position sense in 50 patients with mild ankylosing spondylitis and 50 healthy controls. OBJECTIVES To determine if spinal position sense is impaired in patients with mild ankylosing spondylitis. SUMMARY OF BACKGROUND DATA Pathologic processes in ankylosing spondylitis target sites in the spine where joint capsules, ligaments, and tendons attach into bone. Because these sites contain receptors conveying position sense, proprioception may become impaired, and this may contribute to the spinal deformity that often develops in the more advanced stages of the disease. If deficits in proprioception are apparent then specialized exercise regimes aimed at improving proprioception in ankylosing spondylitis patients could prove beneficial. METHODS Position sense was assessed in patients and controls by determining the absolute error in reproducing upright and flexed postures in the coronal and sagittal planes using an electromagnetic tracking device, the 3-Space Fastrak (Polhemus, Colchester, VT). Measurements were taken from sensors placed on the skin overlying T1, T7, L1, and S2. In patients, the association between position sense and validated radiographic, disease activity, and functional scores was explored. RESULTS No deficits in spinal position sense were found in patients with mild ankylosing spondylitis. In these subjects, repositioning errors were < or = 3.88 degrees in flexed postures and < or = 2.76 in upright postures. Corresponding results for controls were < or = 4.86 degrees and < or = 3.42 degrees, respectively. Weak correlations were found between position sense and other ankylosing spondylitis outcome measures, which included indexes of function, disease activity, and posture and mobility, but in all cases, the overall trend was for position sense acuity to improve slightly with more advanced disease. CONCLUSION Spinal position sense is unaffected in patients with mild ankylosing spondylitis and is therefore unlikely to be a useful outcome measure in this condition.