Pancarpal Arthrodesis Using Bone Graft From Proximal Humerus

Clinical History
Max was presented unable to weightbear on the right foreleg, having jumped over a wall. The right carpus was swollen and painful on palpation. Radiographs were taken the following day, under general anaesthesia. Nothing abnormal was detected on the radiographs (see right) but on palpation it was found that the right carpus was unstable.

A dressing with gutter splints was applied for a total of 8 weeks. This proved to be unsuccessful and the dog still had a severe plantigrade stance at the end of this period. The options were discussed with the owners and it was decided that a pancarpal arthrodesis would be the best course of action. The owner was warned of the risks associated with general anaesthesia..

On 13/5/98 the dog was admitted for surgery, having been starved overnight with access to water until 3 hours prior to surgery. A pre-anaesthetic clinical examination revealed no cardiovascular or thoracic abnormalities. Temperature was 38.1 C, pulse 127, respiration 27 per minute.

The owner signed a consent form and premedication was given with 1mg acepromazine (ACP, C Vet) by subcutaneous route 35 minutes prior to general anaesthesia. Analgesia and antibiotics were also given at this time, with 4mg morphine sulphate (Evans) by intra- muscular route, 100mg carprofen (Zenecarp, C Vet) and 450mg ampicillin (Duphacillin, Solvay Duphar Vet) by subcutaneous route. A 19 gauge intra-venous catheter was placed aseptically into the left cephalic vein and a slow infusion of 1 litre of compound sodium lactate (Hartmann's, Intraven) was started.

Anaesthesia was induced using 300 mg thiopentone sodium 2.5% (Intraval Sodium, Rhone Merieux) by intra-venous route, followed by intubation with a 12 cuffed endotracheal tube. A parallel semi-closed Lack circuit with 4L nitrous oxide, 2L oxygen and halothane was used to maintain anaesthesia.

Pre-surgical preparation
The dog was placed in left lateral recumbency and the whole of the right foreleg, including shoulder, right of sternum and brisket was clipped as in the first paragraph of Appendix 1. The dog was moved to theatre and placed in left lateral recumbency, where preparation of the skin around the right proximal humerus was completed, as in the second paragraph of Appendix 1. Four drapes were applied in a quadrant, leaving access to the right lateral proximal humerus only, the rest of the dog being covered by the drapes.

A standard kit, as listed in Appendix 2, was laid out with additional instruments as listed in Appendix 3.

Surgical procedure - harvest of the bone graft
An incision was made across the lateral approach to the greater tubercle of the right humerus through the skin and fascia. The deltoideus muscle was retracted to expose the area of bone just distal to the greater tubercle. An electric drill, fitted with a 4.5 mm bit, was used to drill a hole into the cancellous bone. A Volkmann scoop was used to harvest the graft bone. A total of ten scoops were put onto a saline soaked swab, which was carefully wrapped and put to one side in a sterile bowl.

The wound was closed using 3.5m chromic catgut (Ethicon) in a simple continuous suture pattern for both the muscle and subcutaneous tissue, and the skin was closed with simple interrupted sutures using 3m multifilament polyamide (Supramid, BK Vet Products).

The dog was then placed in ventral recumbency with a large cradle supporting the thorax. The right leg was tied, by the digits, to a drip stand and the skin from the bandage on the digits to the proximal radius and ulna was prepared as in Appendix 1. The surgeon and assistant changed surgical gloves. A new size 10 scalpel blade and new swabs were exchanged for the contaminated ones. A nurse released the leg from the drip stand (only holding the bandaged digits) and then held the leg proximal to the elbow to allow the surgeon to wrap the digits with a sterile bandage.

A large drape was placed under the right leg covering all parts of the dog caudal to the right axilla, including all of the left leg. A second drape was placed overlapping the first on the left side and laying over the dorsal aspect of the proximal radius and ulna on the right side. A third drape was laid to overlap both the other drapes on the right side, forming a triangle through which the right leg protruded. The last drape was laid approaching from the cranial direction and wrapping round the proximal radius and ulna. All drapes were secured with towel clips. The only part of the dog left exposed was the right leg (distal to the proximal radius and ulna), which lay, dorsal aspect uppermost, on the drapes covering the ventral abdomen. This was followed by a fenestrated barrier drape through which the limb was passed. See Figure 1.

The surgeon instructed the theatre nurse to apply a tourniquet to the distal humerus and the time was noted, as the surgeon requested that the tourniquet should only remain in place for 20 minutes.

Surgical procedure - pancarpal arthrodesis
An incision through the skin and fascia was made on the mid-dorsal surface from the distal third of the radius, across the carpus to the distal third of metacarpal III. The incision was made lateral to the accessory vein, following the vein. Gelpi retractors were used to retract the accessory vein and the common digital extensor tendon. The joint was then exposed by incising through the deep fascia. At this time a scalpel was used to sever the proximal insertions of the tendons of the extensor carpi radialis at metacarpals II and III, and the tendon of the abductor pollicis longus muscle. The joint capsule was then cut using a scalpel. The carpus was then held in the flexed position to locate the joint spaces between the radiocarpal joint; middle carpal joint and the carpometacarpal joints. An osteotome was used to debride the articular cartilages in order to provide space for the bone graft material to be inserted. Holes were then drilled in the distal radius to promote vascularisation of the area.

The plate was placed in position for a trial fitting. The fifth hole (of the nine holes) was located over the radial carpal bone. The carpus joint was proud and therefore only the end of the plate was in contact with the metacarpal. Plate benders were used to bend the plate midway along it's length. Rongeurs were also used to debride tissue from the dorsal carpus. On a second fitting the plate made contact with bone along the entire length of the plate. NOTE - at this time the tourniquet was removed.

The plate was positioned and the first hole to be drilled was into the radial carpal bone as this was the smallest bone. A 2.7 mm bit was used and 3.5 mm x15 mm Sherman screws were used for holding the plate in place. The order in which the screws were fitted is as shown in Diagram 1. After the first three screws had been placed the bone graft material was packed in the joint spaces.

The ninth hole was left unscrewed, as it appeared that it was aligned over the carpo- metacarpal joint space. The incision was then closed using 3m Supramid with simple interrupted sutures. Post-operative radiographs were then taken to check the alignment of the plate, (see radiograph pictured left). These were satisfactory - See discussion.

Post-operative management.
A short palmar moulded cast was applied to the leg. This was achieved by applying a sterile, nonadherent dressing to the wound, followed by a layer of conforming bandage, a layer of cotton wool and a further layer of conforming bandage. Delta-lite 7.5 cm casting tape was used to form a cast from the mid radius/ulna to claws. The cast had set after 8 minutes and was then split medially and laterally with an oscillating saw. The dressing was then re-applied with cotton wool padding in between all the toes, (including dew claw), using the caudal half of the cast as a splint. Care was taken to ensure adequate padding was in place under all edges of the cast to avoid tissue damage.

Recovery from anaesthesia was uneventful. The dog seemed uncomfortable during the post-operative period and the morphine was repeated after four hours. The dog went home the following day with Zenecarp 50mg tablets, to be given one twice daily with food.

The tubercle graft site wound healed well after initial swelling and a small amount of serous discharge. The dressing on the carpus was changed every 3 days initially, followed by weekly changes and was taken off after four weeks due to the skin around the dew claw being sore, despite padding.

Five weeks after surgery some swelling appeared over the carpus and the dog appeared to be in pain. A subsequent radiograph showed osteolysis around the proximal screw. See radiograph no. 3 pictured right.

A five week course of clindamycin 150mg (Antirobe, Upjohn), one twice daily, resolved the infection and the dog was walking well. The plate was expected to stay in place for approximately one year, until complete fusion of the joint had taken place. Ten months after surgery the dog became lame again and was admitted for radiography, followed by removal of the plate. Radiography showed complete fusion of the carpometacarpal joint and partial fusion of the radiocarpal joint. See Radiograph no. 4 pictured above. On removal of the plate it was noted that the distal 5 screws were loose. A post-operative Robert Jones support dressing was applied for 3 weeks. The dog is walking well now and the carpus has remained stable.

Discussion
In this case, after failure to respond to conservative treatment, surgery was indicated to restore the dog's mobility and to alleviate pain. This was achieved and can therefore be considered as successful surgery.

Hamish R Denny FRCVS (JSAP 32:329, 1991) suggests that the skin incision should be made down the medial side of the leg, curving laterally over the distal metacarpals. This ensures that the skin closure does not occur over the plate. However, in this case healing of the wound did not appear to be compromised despite being located directly over the plate. He also stated that the tourniquet could be left in place for one hour.

Packing of the joint spaces with graft material, after placement of the plate, proved difficult as the plate obstructed access. Hamish Denny recommends packing the joint spaces before fitting of the plate, while the carpus is partially flexed. This would have enabled more material to be inserted throughout all the joint spaces, and could account for incomplete fusion of the joint. A barrier drape is essential during orthopaedic surgery to prevent bacterial strike through ocurring, due to wet drapes.

An attempt could possibly have been made to drill and screw the last hole as the post-operative radiograph showed that the hole was, in fact, aligned over the proximal end of the metatarsal, although this could have resulted in the screw working loose if there wasn't adequate bone present. External post-operative support is essential to protect the plate from excessive bending forces until fusion has begun, and the gutter splint dressing should have ideally stayed on for 6 - 8 weeks.

When the post-operative infection round the proximal screw was diagnosed, ideally a swab could have been taken for a bacterial culture and sensitivity test to ensure that an effective antibiotic was prescribed. However, Antirobe was selected and did prove to be effective in eliminating the infection.

The combination of Zenecarp and morphine was an adequate choice of analgesia for this procedure, as orthopaedic surgery is extremely painful. Morphine is an opiate and therefore a potent analgesic, especially useful during anaesthesia to reduce the amount of halothane used. It also provides good analgesia in the immediate post-operative period, which is very important when using thiopentone as it has an ant-analgesic effect for up to 7 hours (the elimination half-life of the drug in the dog). Morphine lasts only 4 hours and therefore had to be repeated. Zenecarp is a non steroidal anti-inflammatory drug (NSAID), and therefore not as potent as morphine, but is considered to be the most potent of the NSAID's and a good choice as a post-operative analgesic for the following reasons: Zenecarp injectionable lasts for 24 hours, is the only NSAID considered safe to be given peri-operatively as it does not reduce the body's production of prostaglandins (which play a part in the protection of the GI tract and inadequate perfusion within the kidneys), and Zenecarp tablets enable the owner to continue administering analgesia at home.

Post-operative nursing of this case involved 8 dressing changes, management of the leg to avoid sores, initial wound management to avoid infection, observation of the leg, checking temperature and general health of the dog and advice to the client on restriction of exercise, care of the dressing and suitable post-operative diet.

The role of the owner is extremely important in a case where long-term post-operative management is needed and this commitment must be fully understood by the client before this type of surgery is carried out. In this case, despite our best efforts, the owner did not follow our advice and during the first eight weeks after the initial injury the dog was presented every 3 to 4 days with a broken gutter splint due to the dog being allowed to run free with no restriction of exercise. Had the owner followed our repeated advice surgery may not have been necessary. Unfortunately, this attitude continued into the post-operative period and the consequence of this could well have been amputation. However, despite not presenting the dog at the correct time for dressing changes and not restricting exercise the leg eventually healed.

References:
Brinker, Piermattei; Small Animal Orthopedics & Fracture Treatment, W B Saunders & Co, 2nd Ed, p 530 - 535, 1990.
Journal Small Animal Practice, 32:329, 1991.
BSAVA Manual of Anaesthesia, 3rd Rev Ed, p 53, 1992.
Small Animal Surgery, Fossum, Mosby, p938 - 942, 1997.