The skin incision is performed along the cranial edge of the scapula and extended over the glenoid tubercle distally to the level of the mid humerus.
After splitting the brachiocephalicus muscle longitudinally parallel to its fibers, the biceps muscle is identified.
The joint is exposed; the suprascapular nerve is identified and marked with a Penrose drain to facilitate its manipulation.
The origin of the biceps brachii tendon at the supraglenoid tubercle is transected with a scalpel and reflected. This allows access to the shoulder joint.
Removal of the intermediate tubercle
The intermediate tubercle is removed with the help of an oscillating saw to facilitate a solid interface for the plate.
After opening of the joint the articular cartilage of the humeral and scapular joint surfaces is removed with a curette or an oscillating saw blade.
3. Reduction and fixation
The joint is bridged with a long plate and as many transarticular screws as possible are placed through the plate.
Because the screws in the middle of the plate cross each other, care has to be taken to avoid contact with the other screws. Therefore they cannot be inserted all in the same plane.
The plate is either carefully placed underneath the suprascapular nerve (this is shown in this reference) or it is contoured to facilitate passing of the nerve along the bone surface and underneath the plate without touching it (this will not be discussed in this reference).
The plate to be used should engage the proximal half of the humerus and a third of the scapular length. In a Minishetty, usually a broad 3.5 mm DCP, LC-DCP or LCP is selected. In most cases a 14-18 hole plate is used.
The LCP is preferred by most surgeons nowadays.
The joint is realigned in a physiological position. The suprascapular nerve is carefully elevated from the cranial edge of the scapula to allow placement of the aluminum template. The template is then pressed onto the cranial aspect of the scapula and the proximal half of the humerus.
The long 3.5 mm template allows determination of the number of screw holes in the plate that are needed for the arthrodesis.
With the help of the plate-bending press the plate is contoured to match the template.
The plate is carefully placed onto the cranial aspect of the scapula giving special attention to the suprascapular nerve, which crosses over the plate.
Subsequently the plate is attached to the scapula with the help of a 3.5 mm cortex screw using routine technique.
It is preferred to select a screw hole towards the proximal end of the plate to assure that the plate is located along the narrow cranial edge of the scapula.
The plate is aligned over the intermediate tubercle and the proximal humerus. Once correct alignment is achieved it is attached to the humerus with two 3.5 mm cortex screws. Application of axial compression is optional, especially if a LCP is used.
Insertion of hypodermic needles
Hypodermic needles marking the direction of the transarticular screws are placed in the soft tissues overlaying the scapulohumeral joint.
The position and direction of the hypodermic needles is verified with the help of radiography. Any potential adjustment is implemented and if needed verified with additional radiographs.
Insertion of transarticular screws
After preparing the glide hole for the first transarticular cortex screw across the proximal humerus, the thread hole is drilled across the distal scapula.
The first transarticular cortex screw is inserted followed by the preparation of the hole for the second transarticular screw from the cranial aspect of the distal scapula into the proximal humerus.
The transarticular cortex screws provide effective fixation of the caudal aspect of the joint and together with the cranial plate compress the entire articular surface. This effectively fixes the angle of the scapulohumeral joint.
The cortex screws in the joint region are now inserted avoiding contact with each other through deviating the insertion plane away from each other. In some holes, shorter screws may have to be inserted.
At this point of time, should a LCP be used, at least 2 locking head screws are subsequently inserted into the scapula and the proximal humerus.
Note: if a DCP or LC-DCP is used, all remaining empty plate holes are filled with cortex screws.
The remaining empty plate hole is filled with a cortex screw entering the respective bone.
Note: In the clinical example two plate holes were left without a screw because of lack of space to introduce an effective screw.
After verifying proper placement of all screws radiographically, a Garamycin® sponge is placed or antibiotic-impregnated polymethylmetacrylate (PMMA) beads are inserted along the plate.
The subcutaneous tissues are closed in a simple continuous suture pattern using 2-0 monofilament suture material.
The skin is closed with simple continuous and horizontal mattress sutures. On either side of the skin suture line loose single sutures are placed at approximately 1cm distance to fix the cross sutures for the stent bandage.
Because this region cannot be effectively covered with a bandage, a stent bandage is sutured over the incision for protection and left in place for 10 days. The sent bandage is covered with an adhesive surgical drape for added protection, especially during recovery from anesthesia.
Postoperative images are taken while the animal is still anesthetized allowing immediate correction of potential technical inadequacies.
Note: This lateromedial radiographic image depicts the arthrodesis in a different animal.
The animal is kept in a box stall for one month. The stent bandage is removed 10 days postoperatively together with the skin staples. Hand-walking is started 2 weeks postoperatively. A mechanical unevenness at the walk may be present for some time.
Follow up radiographs are taken 3 months postoperatively.
3 year follow up radiographs show complete fusion of the scapulohumeral joint.
The pony was walking pain free on the right shoulder but showed some pain in the feet because of a recent bout of laminitis.