The patella fracture is under tension and distracted apart by the pull of the quadriceps muscle group. Acute patella fractures can be reduced. Chronic patella fractures may not be reducible. The fixation method must resist the large tension forces constantly acting on the patella. A longitudinal K-wire and figure of 8 wire can be an effective method to counteract the tension on the patella.
An arthroscopic assisted minimally invasive approach can be used for some fractures.
The proximal fragment migrates proximally under the tension of the quadriceps muscles. It can be repositioned distally by extending the leg and by using pointed reduction forceps.
The stifle is fully extended, and traction is applied to the proximal fragment to reduce it.
The fragments are anatomically reduced and stabilized using small pointed reduction forceps.
Note: Attention should be paid to preserve the patellar ligament fibers.
A K-wire is introduced centrally from the smaller fragment, cranial to the articular cartilage. A power drill is used at low speed (less than 300 rpm), using irrigation to minimize heat generation. As a guideline, the dimension of the K-wire for a German shepherd is 0.062'' (1.55 mm). Smaller K-wires are used in medium and small breeds. For example, 0.045'' (1.15 mm) is used in a border collie, and a 0.032'' (0.8 mm) is used in a miniature poodle or a cat.
Both ends of the K-wire should be accessible. 5 cm of K-wire should be accessible to facilitate wire placement and K-wire bending.
Orthopedic wire is wrapped in a figure of 8 pattern over the ends of the K-wire and twisted. As a guideline, the dimensions of the wire for a German shepherd breed is 18 gauge (1.25 mm). Smaller wires are used in medium and small breeds. For example, 20 gauge wire (1.0 mm) is used in a border collie, and a 22 gauge wire (0.8 mm) is used in a miniature poodle or a cat.
Note: The K-wire is directed perpendicular to the main fracture line, making sure to avoid the articular surface. The K-wire should be as caudal as possible, to minimize distraction of the articular surface.
The articular surface is evaluated to make sure that it is anatomically reduced.
The K-wire ends are cut and bent away from the articular surface and the patellar ligament.
The ends of the K-wire should not interfere with the patellar ligament.
The stifle joint is sutured using monofilament absorbable suture material. The wound is closed in layers.
Limb disuse after the repair of a patellar fracture is unusual. Most dogs start weight bearing within 3 days of surgery.
The focus of physical rehabilitation is to:
Avoid loss of stifle joint motion, particularly loss of extension
Avoid excessive stress on the surgical repair during the healing period
The stifle joint is protected and partially immobilized if deemed necessary for approximately 14 days.
Cryotherapy and passive range of motion are indicated but not possible if immobilization is used.
Activity is limited to leash walks until bone healing is radiographically evident.
Phase 1: 1-3 days after surgery
The aim is to reduce the edema, inflammation and pain using cryotherapy anti-inflammatory and analgesic medications.
Gentle passive range of motion of the hip and stifle joint can be initiated to promote mobility and joint health.
Phase 2: 4-14 days after surgery
The aim is to resolve the hematoma, edema, control pain and prevent muscle contracture.
Anti-inflammatory and analgesic medications may still be needed.
If the dog is not starting to use the limb within a few days after surgery, re-evaluation is recommended.
Phase 3: 14 days-8 weeks after surgery
Rehabilitation therapy is continued.
10-14 days after surgery the sutures are removed.
Radiographic assessment is performed every 4-8 weeks until bone healing is confirmed.
If the implants interfere with soft tissues, they should be removed after the fracture is healed.
7. Case example: German shepherd dog
This 5-year-old female spayed German shepherd dog sustained a patellar fracture 1 year after TPLO, leading to a mild and constant lameness.
Intraoperative fluoroscopic image showing the patellar fragments after reduction, showing the placement of a K-wire through the patella.
16 weeks follow-up
Evidence of bone healing is observed at the 16-week radiographic recheck. A small gap remained at the articular side of the patella. New bone formation is visible on the cranial aspect of the patella, proximal to the fracture site.
8. Case example: Skeletally immature cat
Craniocaudal and mediolateral views of the left femur of a skeletally immature cat showing patellar fracture and severe proximal displacement.
The fracture has been repaired using the K-wire and figure of 8 technique. A gap remains visible at the fracture site, on the lateral aspect of the patella.