Ischaemia of the index finger and thumb secondary to thrombosis of the radial artery in the anatomical snuffbox.

We report on nine patients who presented with spontaneous ischaemia of the index finger and thumb over an 11 year period. Arteriography revealed thrombosis of the radial artery in the region of the anatomical snuffbox with evidence of digital artery embolization in each. None had suffered direct trauma to the area or had a demonstrable proximal source for thrombus. While the cause of radial artery thrombosis in our patients in not entirely clear, local inflammation and/or systemic disease may predispose to this entity.

A comparison of fixation screws for the scaphoid during application of cyclical bending loads.

UNLABELLED: Matched pairs of scaphoids from cadavera were stressed with ramped intensity cyclical bending loads after osteotomy and fixation of one scaphoid with a Herbert screw and fixation of the other with an AO 3.5-millimeter cannulated screw, a Herbert-Whipple screw, an Acutrak cannulated screw, or a Universal Compression screw. The AO screw, Acutrak screw, and Herbert-Whipple screw demonstrated superior resistance to cyclical bending loads compared with the Herbert screw. The Universal Compression screw did not provide better fixation than the Herbert screw because of fractures that occurred at the time of insertion. The AO screw and the Herbert screw were then tested in a separate setup in which a segment of volar cortex had been removed in addition to the simple osteotomy. The loss of volar cortex greatly diminished the quality of the fixation provided by both of the screws during application of ramped intensity cyclical bending loads. CLINICAL RELEVANCE: A fixation device in the scaphoid must be able to withstand the stresses that are placed on the scaphoid as a result of its position spanning the proximal and distal carpal rows. Also, because of the prolonged time required for healing of fractures or non-unions of the scaphoid, the device must be able to withstand many such cycles of stress. The present study demonstrates that commonly used screws for fixation of the scaphoid vary significantly (p < 0.005) in their ability to resist cyclical bending loads.

The strength and stiffness of thoracic implant anchors in osteoporotic spines.

OBJECTIVE: To gain a better understanding of factors affecting dorsal implant pull-out strength and stiffness so thoracic spinal implant fixation can be improved. METHODS: Posterior pull-out testing of six thoracic implant anchor types was performed on 54 osteoporotic human vertebra, T2-10, with an average bone mineral density of 0.67 g/cm2. RESULTS: The mean loads at neural arch failure were similar (296 to 382 N). Pedicle strength was greatest at T2 and least at T3. Hook claws were stiffer than sublaminar wires (121 N/mm and 180 N/mm versus 42 N/mm and 52 N/mm, respectively). Facet hook and pedicle hook claws were comparable, as were subpars wires. Bone mineral density of the vertebral bodies correlated with the stiffness of the sublaminar wire anchors only. CONCLUSION: To optimize the strength and stiffness of implant constructs designed to resist forward flexion, this study supports using hook-claws rather than sublaminar wires and extension of fixation to T2 when clinically realistic.