Dissipation of heat during polymerization of acrylics used for external skeletal fixator connecting bars.

OBJECTIVE: To determine the amount of heat conducted by transfixation intramedullary pins (IP) and Kirschner wires (KW) during polymerization of acrylics used for external skeletal fixator (ESF) connecting bars. STUDY DESIGN: Thermal conduction was measured using thermistors applied to IP and KW surfaces during the polymerization phase of acrylics. METHODS: Type II ESF were created from IP or KW placed into wooden dowels and plastic tubing used to create connecting bars filled with one of two types of acrylic (Acrylic Pin External Fixation System or Technovit, Jorgensen Laboratories, Loveland, CO). Thermistors were positioned on the acrylic column surface and on IP or KW surfaces 5 or 10 mm from the acrylic column. Five ESF test groups were created. The maximum temperature (Tmax) of the acrylic column (Tmax-A), IP (Tmax-IP), KW (Tmax-KW), and duration that Tmax-IP or Tmax-KW remained greater than or equal to 55 degrees C were calculated. RESULTS: All IP and KW thermistors placed 5 mm from acrylic columns reached mean temperatures greater than 50 degrees C and had peak temperature ranges greater than 55 degrees C compared with all IP and KW thermistors placed 10 mm from the acrylic columns in all groups. Thermistors placed 5 mm from the acrylic column in two groups maintained temperatures greater than 55 degrees C for greater than or equal to 0.5 minute. CONCLUSIONS: Acrylic columns positioned 5 mm from a thermistor on a IP or KW had the potential to reach or exceed temperatures that have been reported to cause thermal necrosis of tissues. CLINICAL RELEVANCE: Acrylic Pin External Fixation System or Technovit acrylic connecting bars used in ESF designs have the potential to cause thermal injury to soft and bony tissue by thermal conduction along transfixation pins or wires.

Premature closure of the distal radial physis in two dogs.

Premature closure of the distal radial physis was diagnosed in two dogs. In one dog, the premature closure was symmetric; in the other, it was asymmetric. Lameness, elbow subluxation, distended elbow joint capsule, forelimb muscle atrophy, and a shortened radius and ulna had developed in each dog. Carpal valgus and outward rotation of the paw had developed in the dog with asymmetric closure. Surgical treatment resulted in marked improvement of forelimb function in both dogs.

Asynchronous growth of the canine radius and ulna: effects of retardation of longitudinal growth of the radius.

After 2,000 rads of x-radiation to the right distal radial physis of eight 70-day-old dogs, the longitudinal growth of the right radius was retarded 42.1% when compared with the growth of the nonirradiated left radius. Asynchronous growth of the right radius and ulna resulted. The gross and radiographic changes that occurred over the subsequent 75 days were described. Subluxation of the humeroradial and humeroulnar joints occurred and was first observed 31 days after irradiation. By 75 days after irradiation, the radius was puller 7.8 mm distally by the radioulnar ligament. However, subluxation of the humeroradial joint was minimized by accelerated growth from the proximal radial physis and articular cartilage. Acceleration of growth also occurred at the distal radial articular cartilage. Growth from the distal ulnar physis and styloid process was retarded. It was thus apparent that after retardation of growth from the distal radial physis, considerable adjustment occurred in the relationship between the radius and the ulna and also in growth from their other physes, which reduced the deleterious effects of the growth retardation.

Asynchronous growth of the canine radius and ulna: effects of cross pinning the radius to the ulna.

Kirschner wires were introduced into the diaphyseal region of the radius and the ulna in 4 Australian shepherd crossbred pups, and change in relationships between the bones during growth was demonstrated. The contributions to longitudinal growth of the radius from proximal and distal growth plates were also calculated. Over the period of growth, the proximal growth plate contributed approximately 40% of the length of the radius. A marked shifting of the radius in relationship with the ulna occurred. This normal shifting between radius and ulna was prevented in 6 dogs by cross pinning the radius to the ulna at 90, 111, 142, and 168 days of age. Marked change was produced in the elbow joint, where altered relationships of articular surfaces of the radius and the ulna resulted in displacement of the humeral condyle from the trochlear notch of the ulna. Changes in dogs cross pinned at 90 and 111 days of age were most severe and consisted of severe degenerative changes which were most marked on the lateral side of the distal half of the trochlear notch of the ulna.

Radiologic and gross anatomic evaluation of bone healing in the dog.

Bone healing associated with 3 techniques of midshaft femoral fracture fixation in 36 young adult Beagle-type dogs was evaluated in radiographic and gross pathoanatomic studies. A serrated transverse fracture was surgically and aseptically created on the midshaft of either the left or the right femur of each dog. The fixation devices used were intramedullary (IM) pin, IM pin and 1/2 Kirschner device, and tension bone plates. The radiographic evaluation was done in series. The first radiographs were taken during surgery. Radiographs were then taken immediately after surgery, to record the status of reduction, alignment, and fixation. Radiographs were taken at the 4th and 10th postoperative weeks, to monitor healing. All dogs were euthanatized at the 10th week. Both the normal femur and the healing femur were removed from all dogs, all soft tissue was removed from the bone, and each femur was examined grossly. Each type of fixation was associated with a distinct mode of osteogenesis. Bony union and clinical union (that stage in the healing process when fixation can be removed) were defined as a successful conclusion to each case. Malunion and nonunion were defined as unsuccessful conclusions. Delayed union was defined as neither successful nor unsuccessful. The IM pin cases had a 64.2% success rate and a 14.2% failure rate. The IM pin and 1/2 Kirschner cases had a 100% success rate. The bone plate cases were 91% successful, with 0% failure. A problem identified with IM pinning was axial rotation (6 of 14 or 42% of the cases). It was concluded that IM pins should not be used alone for the fixation of femoral fractures in adult dogs.