A 2-year-old, 22.6 kg castrated male Vietnamese Potbellied pig presented to the Food Animal and Camelid Hospital at Iowa State University's College of Veterinary Medicine for a 2 week history of "toe-touching" lameness. Two weeks prior, the pig was noted to have fallen while running across a wood floor and was immediately lame afterward. Other than recent lameness, the pig had an episode of suspected erythema multiformae that resolved without treatment 1 year prior.
Examination was within normal limits with exception of lameness. On presentation, the right pelvic limb was noted as Grade 4/5 lame with occasional toe-touching, but no absolute weight-bearing observed. On palpation, the patella was permanently luxated and could be manipulated in a medial fashion back into the groove (Grade 3/4). The pig was bright, alert and responsive, and had an appropriate body condition score (2/5). Radiographs taken by the referring veterinarian displayed no evidence of fracture.
Based on the confirmation of the patellar luxation and overall health of the patient, a surgical correction was planned for the next day. A single radiograph taken by the referring veterinarian showed no evidence of fracture or other orthopedic disease (Figure 1). The patient was withheld from food and water starting at midnight prior to the surgery.
The patient was classified as ASA 2 according to the American Society of Anesthesiologists. Food was withheld for 18 h and water for 10 h, respectively, prior to anesthesia. Premedication included morphine at 0.4 mg/kg, dexmedetomidine at 0.005 mg/kg and midazolam at 0.5 mg/kg administered intramuscularly (IM). An intravenous catheter was placed in the right auricular vein and the patient was induced with propofol and ketamine, each at 1.1 mg/kg intravenously. The larynx was sprayed with 2% lidocaine prior to intubation with an 8 mm internal diameter cuffed endotracheal tube. Cardiovascular and respiratory monitoring was performed with a multiparametric monitor. Oxygen saturation using pulse oximetry, continuous electrocardiography, body temperature, oscillometric blood pressure, end-tidal carbon dioxide (EtCO2) using side-stream capnography, and gas analysis were measured; cardiovascular and respiratory parameters were recorded every 5 min. Anesthesia was maintained with isoflurane in oxygen delivered via a circle system. Mechanical intermittent positive pressure ventilation was instituted soon after intubation to maintain normocapnia (EtCO2 35-45 mmHg) with a tidal volume of ~8 mL/kg and a peak inspiratory pressure of 16 cm H2O. A lumbosacral spinal epidural was performed using 0.15 mg/kg preservative free morphine and 2 mg/kg lidocaine for additional analgesia. The patient was placed in dorsal recumbency for the surgical procedure. Lactated Ringers Solution was administered at ~5 mL/kg/hr intraoperatively. Warming therapy included a forced-air warming blanket (Bair HuggerTM, 3M, Maplewood, MN, US) and warming blanket (HotDog , Augustine Surgical Inc, Eden Prairie, MN, US) to minimize intraoperative hypothermia. Tulathromycin (Draxxin, Zoetis, Parsippany, NJ, US) at 2.5 mg/kg was administered IM shortly after induction for antimicrobial prophylaxis. Intraoperative complications included hypotension which was managed with fluid boluses, an anticholinergic, and a dopamine and dobutamine constant rate infusion at 10 mcg/kg/min. Total anesthetic time was 2 h and 15 min with surgical time being 63 min. The patient recovered unremarkably.
The patient was placed in dorsal recumbency. The right pelvic limb was clipped and aseptically prepared using the hanging leg technique. A #10 scalpel blade was used to make a 20 cm craniolateral skin incision on the stifle. The incision extended from proximal to the patella to the level of the proximal third of the tibia. Metzenbaum scissors were used to incise the subcutaneous tissue. A #15 blade was used to incise the retinacular fascia on the lateral aspect of the joint and a #15 blade was used to make a stab incision into the joint capsule. Curved Mayo scissors were used to extend the arthrotomy and the patella was luxated medially (Figure 2). Hemorrhage was controlled using radiopaque gauze sponges and electrocautery throughout the procedure. The joint was inspected. Cruciate ligaments were intact and meniscal cartilages were normal. The trochlear groove was extremely shallow. The articular cartilage appeared mildly hyperemic with several streaks of reddened foci apparent.
A #15 blade was used to score the trochlear ridges of the femur for planned wedge recession. A reciprocating saw (Micro 100, Hall Surgical, Largo, Florida, US) was used to perform a wedge recession. Sufficient depth of the groove was confirmed by replacing the patella into the groove and afterwards ensuring a sufficient portion of the wedge was seated within the groove (Figure 3). The cranial tibial muscle was elevated from the lateral aspect of the tibial tuberosity and the fascia from the medial aspect of the proximal tibial was sharply reflected for planned tibial tuberosity transposition. The osteotomy was performed with the reciprocating saw. The tibial tuberosity was transposed ~0.75 cm laterally, a small K wire was placed. Two 0.0625 inch K wires were placed in the proximal tibia, and an 18 gauge tension band placed routinely (Figure 4). The stifle was reassessed for patellar luxation and no luxation in flexion or extension was noted. The joint capsule was closed with 0 polydioxanone (PDS, Ethicon inc, Somerville, NJ, US) using a horizontal mattress pattern. The lateral fascia was closed and imbricated with #0 polydioxanone in a mayo mattress pattern. The subcutaneous layer was closed with #2-0 poliglecaprone 25 suture (Monocryl, Ethicon inc) in a simple continuous pattern. The skin was closed with surgical staples. The incision was then covered with an aluminum aerosol bandage afterwards. Post-operative radiographs of the image were obtained (Figure 5).
Post-operative analgesia was administered by placing a fentanyl transdermal patch (50 mcg/kg/h) 7 h after the pre-anesthetic medications were administered. The next morning the patch was displaced by the patient. Repeated attempts to replace the patch were met with the patient removing the patches. Based on patient demeanor and attitude the patch was discontinued. Inflammation was managed postoperatively with meloxicam (0.5 mg/kg orally every 24 h).
During the first 24 h postoperative, the pig was confined to a 3 x 2 m stall divided in two, the one side bedded with hay. The other side was used to allow for the pig to defecate and urinate, as the patient was a house-trained companion animal. During recovery at the hospital the pig did not bear weight on his right pelvic limb, but was able to ambulate. The pig appeared to be otherwise doing well, not showing any obvious signs of pain or discomfort. Cryo-therapy (towel-wrapped ice pack applied for 15-20 min) was held against the incision every 6 h post-operatively. The pig was discharged 5 days post-operatively. Seven days post-operatively a second dose of tulathromycin (2.5 mg/kg, IM) was administered by the referring veterinarian. Meloxicam (generic, 0.5 mg/kg orally, q 24-48 h) was administered as needed, with the clients reporting no doses given after 3 weeks post-repair.
Initial physical restrictions involved putting the patient in a small room or crate when not being monitored as well as placing sections of carpet on the wood floor to minimize the risk of further slipping. The pig was also separated from other companion animals during this time. Physical rehabilitation therapy was performed during the first month postoperatively by focusing on massage of the limb (15 min intervals), immediately followed by 15 min of range of motion stretches. During stretching, care was taken to extend and flex the limb over a 15 s time period. The massage/stretching sessions were done three times daily for the first 4 weeks postoperatively. During this time, attempts were made to periodically and gently push the pig from the opposite rear limb in order to encourage bearing weight on the right pelvic limb. After 4 weeks the pig was reluctant to allow physical therapy for the full length of time previously described, and was also noted to be bearing more weight when walking. Approximately 5 weeks postoperatively, the pig was noted to spontaneously run around the house as he would before the incident.
At recheck examination ~7 weeks post-surgery, the pig's vital parameters were within normal limits on physical examination. Occasionally, the pig would guard the right pelvic limb while standing, however no abnormal gait or posture was noted on ambulation. The clients reported at this time that the pig had resumed normal levels of activity compared to before the injury. Post-operative radiographs were obtained and considered normal (Figure 6).