Lag screws
1. General considerations
The fixation method must resist the large tension forces constantly acting on the patella.
Lag screws use is limited to large avulsed fragments.
2. Preparation and approach
The patient is positioned in dorsal recumbency. The pelvic limb is extended.
A lateral parapatellar or medial parapatellar approach is performed along the patellar ligament and patella proximally to the quadriceps muscle.
An arthroscopic assisted minimally invasive approach can be used for some fractures.
3. Reduction
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 reconstructible fragments are anatomically reduced and stabilized using small pointed reduction forceps.
4. Fixation
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.
In case of a transverse fracture, screw diameter should be approximately 25% of the width of the patella. For example, a 3.5 mm screw may be used in a German shepherd.
In small dogs and in cats, a K-wire and tension band procedure may be a more appropriate choice of fixation.
5. Closure
6. Aftercare
General considerations
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
- Promote low-impact weight bearing pelvic limb exercise
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.
