Screw fixation

Complete moderately to severely displaced fractures are indications for surgery.
In these cases the patellar fascia is disrupted, the horse cannot fix the stifle and is therefore non weight bearing. The severity of lameness will cause angular deformities in young horses and laminitis in older horses of the weight bearing limb. Surgical fixation with bone screws reestablishes the stay-apparatus of the hind limb to allow comfortable weight bearing and prevent secondary complications of the intact limb.

A thorough understanding of the geometry of the patella is necessary prior to applying internal fixation techniques.
Care should be taken to avoid perforation of the articular surface of the patella by instruments or implants.
Drill holes made perpendicular to the patellar surface are likely to enter the joint. Instruments and drill should be placed parallel to the articular surface to avoid this complication (see illustrations…).

This procedure is performed with the patient placed in dorsal recumbency through the skin incision for patellar fractures.

The fracture is reduced and held in reduction with bone-holding forceps.

Articular reduction can be confirmed arthroscopically if elected.

4.5 mm or 5.5 mm cortex screws placed in lag fashion can be used to repair sagittal displaced fractures of the patella.
At least 2 screws should be used to provide rotational stability.

Pearl: Radiographic control and/or retrograde drilling of the glide holes will ensure that the implants are placed parallel to the joint surface and reduce the risk of perforating the articular surface with instruments or implants.

Pitfall: The patella is softer than typical equine bone and it is possible that the heads of the cortex screws may penetrate the surface of the patella during tightening. In such circumstances washers placed under the screw heads are used to prevent this complication.

Closure is performed carefully to apply suture lines in all layers separately. Tension-relieving sutures in the skin are recommended.

A stent-bandage is typically applied to the surgical wound and a full-limb bandage used in the immediate postoperative period (10-14 days) to limit stifle flexion.
Pool or sling recovery systems are indicated to protect the surgical incision.
Complete stall confinement is recommended and varies based on the age of the animal. Foals typically are confined in a stall for 6-8 weeks and adult horses may be confined for as long as 4 months.

Follow-up radiographs are recommended 6-8 weeks postoperatively to assess healing and provide further exercise instructions.