Efficacy of bone staples for fixation

The pull-out strength of two types of bone staples (A, Techmedica; B, Richards) was evaluated in a canine model and compared with a control of 6.5 mm cancellous bone screw (Synthes). Fifteen adult mongrel dogs were divided into three groups of five animals each. The implants were placed in the lateral femoral condyle and proximal humerus on the right side at time zero, and on the left side 3 weeks later. The dogs were killed at 6 weeks. In addition a third site, the tibial tubercle, was used to examine the effectiveness of each device for patellar tendon reattachment. The strength of the reattached patellar tendon was measured and compared with a control intact patellar tendon insertion. The pull-out loads from bone of the two staple types are not statistically different. The displacement to failure, however, was found to be 71% greater (p less than 0.007), and the work to failure 128% greater (p less than 0.010) for staple A as compared with staple B. This may be of clinical relevance in avoiding staple back-out. Both staples were inferior to the screw for pull-out load displacement and work to failure (p less than 0.0001). All reattached tendons were significantly weaker (mean 202 N) than the intact tendon (mean 1,448 N) regardless of implant type. The dissected specimens uniformly showed necrosis of the tendon under the implant. Healing was by massive scar formation surrounding the implant.