Fixation of Dwyer screws for the treatment of scoliosis. A postmortem study.

The strength of fixation of Dwyer screws in seven or eight vertebral bodies in each of six fresh osteoporotic cadavera was measured under the following conditions: with fixation with only the screw; with the staple-screw combination; with each of these modes of fixation combined with polymethylmethacrylate placed in the hole prior to insertion of the screw; and with the screw reinserted after failure and filling the hole with methacrylate. The strength of fixation of the screw-staple combination was increased almost twofold by the methacrylate, and after failure followed by reinsertion of the screw embedding it in methacrylate, strong fixation was restored.

A single unit digital flexor tendon prosthesis.

Historically, the surgical repair of serious injuries to the flexor tendons of the hand have met with less than satisfactory clinical results. In an attempt to solve this problem, studies have been made on the design and testing of a Dacron polyester tendon prosthesis for complete replacement of the digital flexor tendon. The prosthesis attaches proximally at the anatomical musculotendon junction via collagen ingrowth into a fabric structure and in similar manner distally via bone ingrowth at the anatomical insertion site. These fabrics are continuous with the tendon body of the prosthesis consisting of an inextensible braided cord which is silicone rubber coated to prevent tissue adherence in the glide zone of the tendon bed. An added benefit of the prosthesis is a simple means of length adjustment which can easily be carried out on the operating table. Studies have been performed in both dogs and chickens which indicate that sufficient tissue ingrowth occurs at both the distal and proximal anastomoses for retention of full load bearing capability in these animals and that postoperative adhesions are negligible, if present at all. Full prostheses have been implanted in dogs for periods of over 1 year and chickens for 2 months. The chicken is the preferred animal model as a tendency for extensive scar tissue generation was shown in the dog. Both in vivo mechanical testing and histological characterization have been made on sacrificed animals which have received the full prostheses.