4.5. Surgical procedures
Sheep tibial defects (study III) were made under general anesthesia with 2.5 % halothane. A segmental unilateral defect 16 mm in length was created with a Gigli saw on the midshaft of the right tibia of each animal. Six defects were replaced with TCP and 6 with coral cylinders. The cylinder was secured in the defect through the plugs inserted in the proximal and distal medullary canals of the osteotomized tibia. The tibia was firmly fixed by two overlapping plates with cortical screws, and the muscles and skin were closed in layers. Procaine penicillin (Novo vet., Novo Industri A/S, Copenhagen, Denmark) at a dose of 39.5 mg/kg was administered intramuscurarly to each sheep for 4 days postoperatively to prevent infection. The animals were permitted to walk immediately after surgery.
The canine operations (studies I–II and IV–V) were made under general anesthesia using pentobarbital (Mebunat“, Orion-Farmos, Helsinki, Finland) at a dose of 15 mg/kg intravenously. Xylazine (Rompun Vet“, Bayer, Germany) at 1 mg/kg was used as premedication before the operation. A single dose of prophylactic antibiotics (1 ml/8 kg of Tribrissen Vet, Mallinckrodt Veterinary LTD) was given during the operation.
For the operation, both forelegs were prepared and draped in a sterile fashion. A rubber band was used as a tournique above the elbow joint. A lateral incision was made and the ulna exposed. Using an oscillating saw, an osteotomy through the whole bone, including the periosteum, was made in mid-ulna about 6 cm from the tip of the olecranon, and another osteotomy was made 2 cm distally from that point.
The 2 cm bulk cortico-periosteal segment was removed and used as an autograft or allograft transplant(Study I). A Kirschner wire (1.2 mm thick) was introduced into the medullary canal through the tip of the olecranon for stabilizing the implant in the defect, extending about 3 cm distally from the distal end of the implant (Fig. 1).
Figure 1. A radiograph showing the study model. An autograft transplant in the defect fixed with an intramedullary Kirschner wire.
Xenograft implants (study II) were fixed with plates, and the fixation was performed with a 10-hole stainless steel miniplate and screws (Stratec Medical, Oberdorf, Switzerland) by applying 3 screws proximally and distally to the defect, with the 4 middle holes left empty The defect of the left ulna was filled with a pure xenograft implant and that of the right ulna with a xenograft implant with BMP.
The defect of the left ulna was bridged with plain coral and that in the right ulna with an autograft implant obtained from the left side with intramedullary Kirschner wire fication. Similar fixation was used in another group of six dogs with a coral+BMP implant. The Kirschner wires were removed after 9 weeks. A 10-hole miniplate and screws (Stratec Medical, Oberdorf, Switzerland) were used to bridge the defect in three dogs with coral implants. In these dogs, a plain coral implant was used in the left ulna and coral+BMP on the right side (study IV).
In the HA group, a plain HA implant was inserted into the left ulna and a composite implant with HA and BMP on to the right side. The fixation was done with an intramedullary Kirschner wire, which was removed after 9 weeks (Study V).
Pain medication after the operation (study I–II, IV–V) consisted of buprenorfin (Temgesic©, Reckitt&Colman, Hull, U.K.) at 0.01 mg/kg intramuscularly.
The dogs tolerated the operation well, and weight bearing began on the first postoperative day.
The dogs were killed after 20 weeks with an overdose of pentobarbital (Mebunat©) 60 mg/kg intravenously. The ulnae were dissected out and the soft tissue removed.
The bones were wrapped in saline and frozen at –20°C until analysis.
4.5.1. Clinical case
In the clinical case (study VI), a 18-year-old female had sustained a forearm fracture in a traffic accident in 1984. Open reduction and internal fixation of the radius and ulna was performed. The radius fracture healed uneventfully. The reduction of the ulna was not exact, and roentenograms taken at 4 months showed loosening of the proximal screws and evident nonunion. Repeated fixation of the ulna with an 8-hole plate was performed. The atrophic bone ends of the non-union were excised, and the 2 cm bone defect hereby created was filled with corticocancellous autograft. Three years later, the plates were removed because of some discomfort at the fracture site. There was no statement of the bone union in the surgical records. After this operation, the forearm became painful, and x-rays taken 3 years postoperatively showed pseudoarthrosis of the ulna. The patient was able to manage with her arm and did not seek treatment until after 10 years. The forearm was painful, and a decision for surgery was therefore made. At surgery, the pseudoarthrosis was exposed, the atrophic bone ends were excised, and the defect was substituted by a 2 cm long coral+BMP composite implant.