Introduction: Cement augmentation of osteoporotic vertebral fractures by vertebroplasty can alleviate pain, although the mechanism remains unknown. We hypothesise that vertebral fracture reduces loading by the vertebral body, and that vertebroplasty reverses this effect.

Methods: Nineteen thoracolumbar motion segments (64 – 90 yrs) were used. Specimens were compressed at 1.5kN in moderate flexion and extension while intradis-cal stress profiles were obtained by pulling a miniature pressure transducer along the mid-sagittal diameter of the disc (1). Vertebral fracture was induced by compressive overload in moderate flexion. Vertebroplasty was then performed by injecting polymethylmethacry-late cement into the anterior vertebral body. Stress profiles were repeated after fracture, and after vertebroplasty.

Stress concentration in the annulus was calculated by subtracting the nuclear pressure from the maximum stress in the annulus. Neural arch compressive load was obtained by subtracting the disc compressive force, calculated by integrating intradiscal stress over area, from the applied 1.5kN (1).

Results: Fracture increased the stress concentration in the annulus from 0.21 to 0.58MPa in flexion (p< 0.01) and from 0.02 to 0.20MPa in extension (p< 0.05). It also increased neural arch load bearing from 9% to 27% of the applied load in flexion (p< 0.01), and from 53% to 70% in extension (p< 0.01). Following vertebroplasty, these changes were largely reversed: in flexion, stress concentrations in the annulus decreased to 0.36MPa and neural arch load-bearing fell to 5% (p< 0.01). Similar, non-significant trends were observed in extension.

Discussion: Vertebral fracture reduces load-bearing by the vertebral body, and increased compressive loading of the neural arch. Vertebroplasty goes some way to reversing these effects, and significantly decreased stress concentration in the annulus and loading of the neural arch in flexion. This could contribute to pain relief in patients undergoing this procedure.

We reviewed 31 patients at a mean of five years after mallet deformity of the finger had been treated with a thermoplastic splint. Intra-articular fractures were present in 35% of patients. Osteoarthritic changes had developed in 48%, most in association with fracture, and 29% had a swan-neck deformity. There was a loss of extension greater than 10° in 35%; the average deficit at the interphalangeal joint was 8.3° and the average flexion arc was 48.5°.

Despite these findings, patient satisfaction was generally high, with little evidence of functional impairment.