Abstract
This report describes the successful management of a carpal hyperextension injury in a cat using combined temporary transarticular internal and external skeletal fixation, without performing an arthrodesis. To our knowledge, there have been no previous reports of management of feline carpal hyperextension injuries in this fashion.
Case Report
A 4-year-old male neutered Maine Coone cat was presented with a 5 day history of partial palmigrade stance of the right thoracic limb and weight-bearing lameness.
On physical examination, the right carpus was swollen and painful. Hyperextension and mild varus deformation of the right carpus were evident.
Orthogonal radiographs of both carpi were obtained under sedation with intravenous (IV) dexmedetomidine 2 μg/kg (Dexdomitor; Elanco) and butorphanol 0.1 mg/kg (Alvergesic; Dechra Veterinary Products). Radiographs showed periarticular soft tissue swelling affecting the right carpus (Figure 1). Dorsal subluxation of the second carpal bone was evident on stressed radiographs (Figure 2).
Craniocaudal radiograph of the right carpus demonstrating mild periarticular swelling
Lateral stressed radiograph of the right carpus showing dorsal luxation of the second carpal bone and hyperextension of the carpus at the carpometacarpal joint level
For surgical management of the carpus, premedication was performed with 0.2 mg/kg methadone (Comfortan; Eurovet) by intramuscular injection. Anaesthesia was induced by IV infusion to effect using alfaxalone (Alfaxan; Jurox) and maintained using isoflurane (IsoFlo; Abbot Animal Health) in 100% oxygen delivered by an endotracheal tube. Cefuroxime (Zinacef; GlaxoSmithKline) was given intravenously at 20 mg/kg 30 mins before surgery and at 90 min intervals.
Using a dorsal approach to the right carpus, the subluxated second carpal bone was reduced and held in place with bone reduction forceps. The metacarpophalangeal joints were flexed to allow insertion of 1.1 mm Kirschner wires proximally into the distal epiphyses of metacarpal bones II, III and IV. Fluoroscopic guidance was used to ensure accurate placement of the Kirschner wires, which were driven proximally through the intramedullary canal of each metacarpal bone and through their proximal articular surfaces crossing the carpo-metacarpal joint, passing through each respective distal carpal bone. The first Kirschner wire was placed through metacarpal bone III, through the third carpal bone and into the radial carpal bone. After reduction and fixation of the second carpal bone, carpal hyperextension was still evident, indicating injury to the palmar carpal support structures. Kirschner wires were then similarly driven through metacarpal bones II and IV. Kirschner wire advancement was stopped prior to penetration of the proximal articular surface of the radial carpal bone. The distal ends of the Kirschner wires were bent dorsally at their exit from the metacarpophalangeal joints, enabling their incorporation into a modified type IIb transarticular external skeletal fixator (TESF) (Figures 3 and 4). Two 2 mm centrally threaded full pins and a 2 mm negative thread half pin were placed in the radius. The distal ends of the metacarpal intramedullary wires were fixed to external skeletal fixator clamps on a connecting bar placed mediolaterally, dorsal to the metacarpal arcade. No attempt was made to arthrodese the antebrachiocarpal, intercarpal or carpometacarpal joints. Postoperative radiographs confirmed satisfactory limb alignment, reduction of the second carpal bone and placement of the implants (Figures 3 and 4).
Postoperative craniocaudal radiograph showing type IIb tied-in external skeletal fixator and Kirschner wires crossing intercarpal and carpometacarpal joint spaces
Postoperative mediolateral oblique radiograph showing satisfactory implant placement
Buprenorphine (Vetergesic; Alstoe Animal Health) was given at a dose rate of 0.02 mg/kg as needed during hospitalisation. For 7 days, cephalexin (Ceporex; Merck Sharp and Dohme) was administered orally at a dose rate of 20 mg/kg twice daily. Three days after surgery the cat was 3/10 lame, comfortable and discharged with instructions to the owner to restrict the cat to a cage for 6 weeks. A 5 day postoperative course of meloxicam (Metacam; Boehringer Ingelheim) was given orally once daily at a rate of 0.05 mg/kg.
Six weeks postoperatively, the cat had a 1/10 weight-bearing lameness of the right thoracic limb. The right metacarpophalangeal joints were painful on manipulation. Radiographs of the right thoracic limb were obtained using sedation with dexmedetomidine 2 μg/kg (Dexdomitor; Elanco) and butorphanol 0.1 mg/kg (Alvergesic; Dechra Veterinary Products) administered intravenously, as previously described. Radiological examination of the right thoracic limb showed an area of lucency in the radius surrounding the proximal TESF pin (Figure 5). The TESF clamps were loosened, and the carpus was stressed for hyperextension and for valgus/varus instability. No hyperextension was evident and varus/valgus stability was good; therefore, the implants were removed (Figure 6). Following recovery from sedation, the cat was able to bear weight and limb alignment was good. The cat was discharged with meloxicam (Metacam; Boehringer Ingelheim) at a dose rate of 0.05 mg/kg once daily for 5 days; cage restriction was instructed for a further 2 weeks prior to return to unrestricted activity. The cat was re-examined 10 weeks after surgery, at which time there was no lameness and no pain on manipulation of the right carpus or paw, and carpal range of motion was normal, without hyperextension. Re-examination 1 year postoperatively revealed that the cat was able to jump and climb normally. On clinical examination there was no lameness. Limb posture, and function and range of motion of the carpus and carpometacarpal joints were normal.
Craniocaudal radiograph of the right carpus 6 weeks postoperatively after removal of the mediolateral connecting bar and clamps connected to the metacarpal pins, showing lucency around proximal transarticular external skeletal fixator pin
Craniocaudal radiograph of the right distal limb after removal of the transarticular external skeletal fixator. There is slight irregularity of the joint surfaces of the carpometacarpal joints
This is, to our knowledge, the first report of successful management of a carpal hyperextension injury with concurrent luxation of the second carpal bone in a cat without performing either partial or pancarpal arthrodesis. Successful management of traumatic luxation of the radial carpal bone using a TESF to immobilise the joint has been previously described in a cat; 1 however, in this report, no damage to the support structures of the carpus was reported. In cats, immobilisation of the carpus in flexion has been described as a management approach for hyperextension injury, but the success of this technique has not been reported. 2 Carpal hyperextension injuries occur most commonly after falls or jumps.2–7 Patients generally present with a palmigrade stance and carpal extension of at least 20–30°.1,5 According to the level of injury within the carpus, partial3–7 or pancarpal arthrodesis has been recommended for treatment of carpal hyperextension injury.5,7–9 The successful outcome reported for our case suggests that arthrodesis may not be necessary for successful return to normal function for cats with carpal hyperextension injury.
Only minor complications were encountered during the management of the cat in this report, including mild ongoing lameness, lucency around the most proximal TESF pin and pain in the paw, presumed to be due to penetration of the metacarpophalangeal joints by the implants. Complications, including bandage-related morbidities, osteomyelitis, implant migration and aseptic loosening occur in 30–40% of dogs and cats managed with carpal arthrodesis.6,10 Loosening of the TESF full pin in the proximal radius, as observed 6 weeks postoperatively in this case, is not uncommon and may have occurred as a result of pin overload. This problem may have been prevented by the assembly of a more rigid TESF construction in the radius. The 6 week duration of immobilisation of the carpus used in the management of this case compares favourably with the time generally required to achieve radiographically evident bone fusion when arthrodesis is performed.6,10 Hence, the recovery period for this novel management technique for carpal extension injury in the cat is acceptable. Furthermore, there was no radiological evidence of ankylosis as a result of temporary internal fixation of the luxated carpal bone 6 weeks postoperatively.
The ongoing lameness during the period of TESF application in this cat was most likely due to the placement of the Kirschner wires through the metacarapal phalangeal joints and the resultant enforced flexion of these joints. Although causing some morbidity, the degree of lameness was considered to be acceptable, and limb function was deemed to be adequate during the period in which the TESF was in place.
Postoperative pain and morbidity from the intramedullary/transfixing Kirschner wires would have been reduced by inserting these wires through slots created in the dorsum of the metacarpal bones, as has been previously described. 5 We elected not to use this ‘slot insertion’ technique because, invariably, use of the slot technique results in the necessary selection of an intramedullary implant of smaller size and less stiffness than can be used by insertion through the distal epiphysis of the metacarpal bone. Furthermore, the ‘slot insertion’ technique tends to result in a foreshortening of the working length of metacarpal bone supported by implant and this, in turn, would be expected to reduce the stiffness of this transarticular fixation method. The use of Kirschner wires inserted into the intramedullary cavity of the metacarpal bones precluded the necessity to insert TESF pins mediolaterally into the metacarpal bones to create the transarticular external skeletal fixator. Following standard TESF application principles, 5 the largest implant that would have been safely inserted mediolaterally would have been of the order of 0.9 mm. It is likely that multiple pins of this size would have been required in the metacarpal arcade in order to achieve comparable stability to that achieved with the three 1.1 mm intramedullary Kirschner wires used.
Arthrodesis results in obliteration of the range of motion of the carpal joint, and reduced jumping climbing and grooming is reported by owners of cats in which pancarpal arthrodesis has been performed. 10 That carpal function and the carpal range of motion returned to normal in the cat described in this report, and that the cat returned to normal function and behaviour further indicates the value of this approach to the management of carpal hyperextension injury in cats.
Conclusions
Treatment in this case was successful, suggesting that combined internal fixation and transarticular immobilisation using a TESF may offer a useful alternative treatment option to partial or pancarpal arthrodesis in cats with hyperextension injuries to the carpus. Further studies are warranted.
Footnotes
Conflict of interest
The authors do not have any potential conflicts of interest to declare.
Funding
The authors received no specific grant from any funding agency in the public, commercial or not-for-profit sectors for the preparation of this case report.