Risk of avulsion of the Achilles tendon after partial excision for treatment of insertional tendonitis and Haglund's deformity: a biomechanical study.

Surgical treatment of posterior heel pain caused by insertional (calcific) Achilles tendonitis or retrocalcaneal bursitis includes resection of diseased tendon or exostectomy. Currently, no guidelines exist to determine how much tendon may be excised without risking rupture of the Achilles tendon. Anatomic dissections revealed the average height of the insertion measured 19.8 mm (range, 13-25 mm). Average width at the proximal aspect of the insertion measured 23.8 mm (range, 17-30 mm) and distally measured 31.2 (range, 25-38 mm). To assess the risk of avulsion, the tendon insertion was partially released in 25% increments of its measured height or width by one of the four methods: (1) from superior to inferior, (2) from the central portion outward, (3) from medial to lateral, and (4) from lateral to medial. Repeated cyclic loading of body weight x 3 was applied, and, if the tendon remained intact, the next 25% increment was released. This process was repeated until failure occurred. Failure occurred in all specimens by an oblique intratendonous separation or shear between the intact portion remaining on the calcaneus and the resected fibers remaining in the clamp. Fibers inserting into the bone did not avulse. Superior-to-inferior resection was found to be superior to the other three methods with eight of nine specimens remaining intact after 75% resection. We therefore conclude that superior-to-inferior offers the greatest margin of safety when performing partial resections of the Achilles insertion, and as much as 50% of the tendon may be resected safely.