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. Lag screws use is limited to large avulsed fragments.
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 temporarily anatomically reduced and stabilized using small pointed reduction forceps.
Note: Attention should be paid to preserve the patellar ligament fibers.
The reduction forceps should be removed to allow distraction of the fracture site. This prevents the glide hole from being accidentally extended into the opposite fragment.
A glide hole is drilled medially or laterally in 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.
The hole should be perpendicular to the fracture line, avoiding the articular surface.
The patella is reduced again, and a thread hole is drilled through the far patellar fragment using the appropriate drill sleeve.
A depth gauge is used to determine the screw length. The far cortex is tapped.
A screw is placed and tightened, achieving interfragmentary compression.
The procedure is repeated on the opposite side of the patella. The second glide hole is drilled parallel and to the same depth as the first one. The thread hole preparation and screw insertion are identical to the first screw.
In case of avulsion or longitudinal fracture, depending on fragment size, a 2.7 mm screw may be used in a German shepherd. If the fragment is small, K-wires and tension band procedure may be a more appropriate choice of fixation.
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