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. Longitudinal K-wires and tension bands 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.
Non-reconstructible avulsed fragments are removed using forceps.
The stifle is fully extended and traction is applied to the proximal fragment to reduce it.
The reconstructible fragments are anatomically reduced and stabilized using small pointed reduction forceps.
Note: Attention should be paid to preserve the patellar ligament fibers.
A hole is drilled transversally in the extra-articular portion of the patella.
Orthopedic wire is pre-placed in the hole. 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.
Two K-wires are introduced from the proximal or distal aspect of the patella, based on fracture configuration. K-wires are placed:
From the smaller to the larger fragment
At the medial and lateral edges of the patellar ligament
Cranial to the articular surface
The K-wires are directed along the long axis of the patella, making sure to avoid the articular surface.
The K-wires are placed using a power drill, 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.
In small dogs and cats, placing two K-wires may not be feasible due to the small patellar size and a single K-wire may be sufficient.
A second orthopedic wire is slid under the K-wires. This wire should be placed in close contact with the K-wires and remain cranial to the articular surface.
Note: Be sure the K-wire is placed in close contact to the patella.
The two wires are tightened using two twists, in a figure of 8 pattern.
The excess length of the twist is trimmed. Care must be taken to avoid interference between the remaining twists and the articular surface.
The K-wires are cut and bent on the near end away from the articular surface. Far ends may also be bent, if accessible.
Note: The end of the K-wires should not interfere with the patellar ligament or the trochlear ridges.
Alternative: single orthopedic wire as tension band
A single longer piece of orthopedic wire can be used to create the tension band.
The wire is threaded through the patella; one end is wrapped cranial to the patella under the K-wires and twisted onto the other end of the wire.
Note: This technique may cause uneven tension and displacement of the fragment. The benefit of having one twist knot is minimized tissues interference.
The excess length of the twist is trimmed.
The articular surface is evaluated to make sure that it is anatomically reduced.
The K-wires are cut and bent on the near end, away from the articular surface. Far ends may also be bent, if accessible.
The end of the K-wires 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