Lag screw fixation

This injury represents an avulsion of the anterior cruciate ligament.

This intraarticular avulsion fracture is most often seen in the younger patient.

The anterior horn of one or both menisci may be entrapped beneath the avulsed fragment.

Depending on the size of the fragment one or two antegrade lag screws are used. Unless the physis is open the screws should engage the posterior cortex.

This procedure is normally performed with the patient in a supine position. The leg should be free-draped to allow varying degrees of knee flexion.

• Supine position

An arthroscopic approach may be used but advanced experience in arthroscopic surgery is essential.

• Arthroscopic approach

Depending on the fracture fragment size and location a small anteromedial or anterolateral parapatellar approach is used.

• Medial/posteromedial approach
• Anterolateral/extended anterolateral approach

The fracture is visualized, and reduction is attempted with a hook, or another instrument inserted through another portal.

In open procedures, the avulsed bony fragment of the intercondylar eminence is visualized directly and may be reduced with the help of a clamp or a ball-spiked pusher.

Fixation should be performed while ensuring that the screws do not compromise the articular cartilage or ligament insertion sites. Conventional or cannulated screws are acceptable.

If two screws appear to be inadequate, augmentation with suture fixation is indicated.

In case of a solid avulsion fragment retrograde fixation with a small cancellous screw can be performed. Antegrade lag screws are usually left in place whereas these retrograde lag screws can be easily removed after fracture healing.

If the screw appears to be inadequate, augmentation with sutures is indicated.

Close monitoring of the tibial compartments should be carried out, especially during the first 48 hours after injury and again after surgery to rule out compartment syndrome. More information is provided here:

• Compartment syndrome

The neurovascular status of the extremity must be carefully monitored. Impaired blood supply or developing neurological loss must be investigated as an emergency and dealt with expediently.

Oral or subcutaneous administration of DVT prophylaxis for six weeks should be strongly considered.

Optimal stability should be achieved at the time of surgery, in order to allow early range of motion exercises. Unless there are other injuries or complications, mobilization may be performed on post OP day 1. If available, continuous passive motion (CPM) splints can be very helpful in the early phase of rehabilitation. Static quadriceps exercises with passive range of motion of the knee should be encouraged. Afterwards special emphasis should be given to active knee and ankle movement.

The goal is to achieve as full range of motion as possible within the first 4–6 weeks.

Weight-of-leg weight bearing is initiated depending on patient comfort. Depending on the severity of the articular displacement, weight bearing can begin as early as 6 weeks postoperatively. In situations where articular displacement was significant weight bearing should be delayed for 10–12 weeks.

Wound healing should be assessed within the first two weeks. Subsequently, a 6- and 12-week follow-up with radiographic assessment is usually performed. If a delayed union is recognized, further surgical care may be necessary and should be carried out as soon as possible. Residual knee instability may require delayed reconstruction.

Implant removal is not mandatory and should be discussed with the patient.

AP and lateral x-rays demonstrating avulsion of the tibial spine with slight displacement.

CT scan in coronal image showing the displacement.

Medial parapatellar incision is used.

The medial parapatellar retinaculum is opened and the joint capsule is incised, revealing a hemarthrosis.

By elevating the patella with the knee extended, the avulsed tibial spine can be seen. This image shows a pair of forceps in the fracture gap below the tibial spine.

The hematoma has been removed from beneath the avulsed tibial spine and it has been reduced and held with a K-wire.

A small fragment cancellous lag screw is inserted.

A second lag screw is inserted.

Final intraoperative view of the tibial plateau.

Intraoperative check x-rays in two views.

The medial parapatellar retinaculum and capsule are carefully repaired.

Four-week X-ray showing reduction of the spine.

One-year images showing maintenance of flexion and full extension of the knee.