Comparative mechanical testing of different geometric designs of distal first metatarsal osteotomies.

BACKGROUND

The mechanical behavior of a newly described distal metatarsal osteotomy design in the shape of a reversed "L" was compared with the modified chevron and scarf osteotomies.

METHODS

Experiments were performed using full-sized Sawbone models (Sawbones Europe AB, Malmö, Sweden) of the first ray. Three groups consisting of 10 scarf, 10 modified chevron, and 10 reversed L osteotomies were investigated. All distal fragments were displaced 5 mm laterally without angulation. The proximal fragment of each specimen was embedded in an epoxy resin cylinder and positioned at 15 degrees inclination to the ground. The distal fragment was loaded by a dorsally directed vertical force which was applied at the sesamoid location under the metatarsal head. Load and displacement at failure, work to failure, site of failure and contact areas were recorded for each osteotomy.

RESULTS

Similar testing results were obtained in the reversed "L" and chevron osteotomies, while the scarf osteotomy needed almost 5 times less work to failure. In nine of 10 reversed "L" osteotomies and in all scarf osteotomies, the site of failure was at the proximal screw insertion site. The contact areas averaged 163 mm(2) for the reversed "L," 116 mm(2) for the chevron, and 270 mm(2) for the scarf osteotomy.

CONCLUSIONS

The reversed L osteotomy is a promising design combining the advantages of both the chevron and scarf osteotomies. Further investigations need to be performed to confirm its clinical utility.