A 15 kg, 4-year-old female Arabian Tahr from the Omani Mammals Breeding Center had its left hind leg at the distal tibia amputated 5 months before the prosthesis operation.
The initial injury was a left distal tibia extra-articular multi-fragmented open fracture with severe contamination and soft tissue loss. It was treated by a circular external fixator. Within 5 days ischemic necrosis and infection developed and amputation of the distal tibia was performed.
Post-amputation the animal showed severe problems in ambulation. Different custom-made exoprostheses were tested without positive results. The negative outcomes were caused primarily by attachment failure, stump irritation, and infection. Considering the animal's welfare, an attempt to restore normal movement by the implantation of ITAP was undertaken.
Preoperative assessment of limb length and diameter of the medullary canal was based on radiographic projections with Kirschner wire that was 5 mm in diameter, 100 and 200 mm in length, as well as photographs of the animal.
CT scanning and 3D image reconstruction of the affected leg were unavailable.
The custom-designed prosthesis was manufactured by the IWET Company in Kleosin, Poland by engineers Marek Lubak and Michal Sujeta.
The prostheses elements are pictured in Figure 1. The prostheses are comprised of a titanium alloy (Ti6Al4V) stem for intramedullary placement with dorsal and medial locking plates for additional secure fixation, a perforated umbrella-shaped flange for skin in-growth and a distal extra cutaneous pin for exoprosthesis attachment. The exoprosthesis consisted of an adjustable locking hinge made from stainless steel attached to a carbon fiber leg with the hoof. All elements of the designed prosthesis were subjected to structural analysis by finite element methods (FEM). Due to the patient's very active nature, triple weight (45 kg) was assumed for calculations. The titanium prosthesis was made by combining techniques of computer numerical control milling and 3D printing. Elements of the prosthesis were adjustable with the possibility of regulating the length (+/- 40 mm) and a flexion angle for the best fit for the animal.
The 15 kg Tahr was sedated with 1 mg medetomidine at a dose of 0.06 mg/kg (Domitor 1 mg/ml Orion Pharma) and 1.5 mg butorphanol at a dose of 0.1 mg/kg (Butomidor 10 mg/ml Orion Pharma), followed with 750 mg ceftriaxone at a dose of 50 mg/kg (Rocephin 1 g Roche) and 7.5 mg meloxicam at a dose of 0.5 mg/kg (Meloxicam 5 mg/ml Troy Laboratories) by intravenous injection. After sedation, the leg was prepared for aseptic surgery in the standard manner.
Anesthesia was induced by 30 mg propofol at a dose of 2 mg/kg (Propofol 1% 10 mg/ml Fresenius), then an endotracheal tube that was 5 mm ID, 7.3 mm OD x 20 cm (Mila International) was inserted, cuff inflated, and anesthesia was maintained with 2-5% isoflurane in 100% oxygen.
The patient underwent an electrocardiogram, capnography, pulse oximetry, and indirect blood pressure for monitoring anesthesia. Ringer lactate as a supportive fluid therapy was maintained at a dose of 10 ml/kg/h during the surgical procedure. The patient was placed in the right lateral position with the affected limb facing in the uppermost direction.
A circumferential transverse incision of skin was made 1 cm proximal from the stump and extended 4 cm proximally at the dorsal aspect of the tibia. Dissection of the soft tissue from the shaft of the tibia allowed for a 20 mm osteotomy of the distal tibia using an oscillating saw. The medullary canal of the tibia was broached using a curette and a 6 mm drill. The ITAP implant was inserted and pushed into position with a slap-hammer and secured by one 3.5 mm and two 2.7 mm locking screws both at the dorsal and medial plate. Intraoperative radiographs were taken to assess the implant position and its alignment before the final tightening of locking screws (Figure 2).
The remaining muscles and tendons were attached to a perforated umbrella-shaped flange with 2-0 polyglactin 910 (VICRYL Plus, Ethicon). The skin was closed with 2-0 polyamide (Ethilon, Ethicon) simple interrupted sutures. Recovery from the anesthesia was uneventful. Postoperative medications included antibiotic therapy with 135 mg combination of amoxicillin, clavulanic acid at a dose of 9 mg/kg (Synulox RTU Zoetis), and pain control with 7.5 mg meloxicam at a dose of 0.5 mg/kg (Meloxicam 5 mg/ml Troy Laboratories) every 24 h for 10 days. The wound dressing was changed every 2 days. The skin seal around the distal flange was achieved after 30 days. A radiographic examination at 8 weeks revealed thickening and bone remodeling around the distal end of the bone (Figure 3).
An exoprosthesis was attached 2 weeks after surgery. After the initial adjustment, including length, and hinge flexion, the animal immediately started bearing its own weight. Initially, lameness was not ideal at a level of 2/5 on the AAEP scale. Within a 3-week period, however, this improved to a 1/5 on the AAEP scale.
Three months post-implantation a complication occurred. Larvae of the Old-World screwworm fly (Chrysomya bezziana), which feeds on living tissue, were found in the junction between the skin and the implant. It was observed that the subsequent infection with sanguine-purulent discharge affected the skin and subcutaneous tissue around the prosthesis (Figure 4). Treatment for the screwworm fly consisted of aggressive tissue debridement, antibiotic therapy, pain management, and wound care. Under general anesthesia, with the same protocol as described previously, surgical debridement, and maggot removal was performed.
Following the removal of the screwworm larvae and maggots, systemic antibiotic treatment with 33 mg of ceftiofur at a dose of 2.2 mg/kg every 24 h (EXCENEL RTU, Zoetis) and 300 mg of amikacin at dose of 20 mg/kg IV every 24 h (Amikin inj 100 mg/ml Bristol-Myers) was administered for 7 days, with a 135 mg combination of amoxicillin and clavulanic acid at a dose of 9 mg/kg (Synulox RTU Zoetis), and pain control with 7.5 mg meloxicam at a dose of 0.5 mg/kg (Meloxicam 5 mg/ml Troy Laboratories) every 24 h for the next 10 days. This combination of medicine administered post-treatment of the infection proved effective.
To promote healing and reduce the risk of implant-bone infection for the first 4 days, interactive moist dressings with the addition of 200 mg amikacine (Tenderwet active 24, Hartmann) combined with silver mesh (Atrauman Ag, Hartmann) were applied and changed daily. After 4 days, the remaining skin defect was treated with hydrocolloid dressing (Hydrocoll, Hartmann) combined with silver mesh (Atrauman Ag, Hartmann) and wound healing cream, containing Sh-Polypeptide-1- acidic Fibroblast Growth Factor (Regen Gel, VET STEM CELL Poland), applied daily. The skin defect completely healed in 18 days. Radiography examination revealed bone remodeling around the distal end of the tibia without any signs of osteolysis. During the treatment, the animal was kept indoors for close observation. Post-treatment the Tahr was released from a safe enclosure into its herd.
The distal part of the tibia was constantly protected with soft dressing (Softban) and secured by an adhesive bandage (Tensoplast) all the time and changed every 7-10 days. The patient tolerated the situation very well; the dressing was changed without sedation and no more skin-implant complications have been observed.
With time, it was found that an S-shape design of the "hoof" in the prosthesis is not optimal, as it hooks on long grass or even might cause leg entrapment with wire mesh fences. The gap on the distal end of the prosthesis was closed by silver duct tape (Scotch).
After 6 months post-surgery, the animal was successfully returned to the herd, where it was accepted and now walks and runs using the prosthetic. Although a shortening of stride was noticeable throughout the rehabilitation process, the restoration of lameness from 2/5 to 1/5 (on the AAEP scale) within 3 weeks was a positive indicator of functional restoration success.