Avulsion fractures can result from mild to moderate injury to the knee. Twisting injuries to the knee may result in major ligament disruptions of the medial collateral, or anterior or posterior cruciate ligaments (PCL). It is most commonly the medial collateral (MCL) and the anterior cruciate ligament (ACL) that are injured. Patients with an anterior cruciate ligament disruption will sometimes report a popping sensation from the knee at the time of injury. A rapid early hemarthrosis will develop with an anterior cruciate ligament injury. Anterior cruciate ligament injuries most commonly occur in young patients, who partake in sporting activities. Small avulsion fractures may represent markers or significant injuries to the knee, such as multiligamentous knee dislocation. MRI can detect significant ligament damage. Consultation and advice from specialist knee reconstructive surgeons may need to sought.
Fixation of these important ligamentous avulsion fractures is essential to knee joint stability, especially in association with intra-substance ligament injuries. Healing in displacement results in joint stiffness and laxity.
Long-term effects of avulsion of the medial collateral ligament from its femoral attachment, causing local pain and heterotopic ossification, comprise the “Pellegrini-Stieda” lesion.
Avulsion of the lateral collateral ligament from the distal femur with a small piece of bone is known as the “Segond” fracture. “Segond” fractures may accompany serious injuries to the knee. There may be peroneal nerve, or menisceal, injuries.
Similar principles apply to the fracture treatment on both the lateral and medial side of the distal femur. In the following we will show the medial avulsion injury.
Lag screw fixation
The avulsion fracture is reduced and compressed using the lag screw principle.
Use of washers to affix ligament
To secure the ligaments and small, thin fragments, a special ligament washer can be used on the screw. These washers are made of either metal, or plastic material.
2. Patient preparation and approaches
This procedure may be performed with the patient in one of the following positions:
For similar medial fractures, a direct medial approach is used, deepened cautiously to expose the medial face of the medial condyle. Care is taken to avoid the saphenous nerve and its infrapatellar branch.
Large pointed reduction forceps
Reduce the fracture with a large pointed reduction forceps. Small thin fragments may fracture if such a forceps is applied, and reduction and control with a dental pick may be preferable. The fracture is then secured with a temporary K-wire, taking care not to conflict with the proposed screw track.
Drill hole for the lag screw
The forceps are then removed, and the hole for the lag screw is drilled through the center of the avulsed fragment.
Insert a lag screw with or without a ligament washer.
A cannulated screw can be used if available.
Gently examine the knee under anesthesia to test for ligament instability. Be careful not to stress too heavily the reattached ligament.
6. Aftercare following lag screw fixation of avulsion fractures
Functional treatment Gentle range of motion in a hinged-knee brace is begun early and continued for 6 weeks.
Weight bearing Early progressive partial weight bearing (touch down, or 10-15 kg) may be performed, with the aid of crutches, or a walker.
Follow-up Wound healing should be assessed regularly within the first two weeks. Subsequently 2, 6 and 12 week follow-ups are usually made. A longer period of follow-up may be required if the fracture healing is delayed.
Implant removal Implant removal is not essential, unless there are implant-related symptoms after fracture healing.
Thrombo-embolic prophylaxis Consideration should be given to thrombo-embolic prophylaxis, according to local treatment guidelines.