Extensor mechanism ruptures

Overview

This instructional lecture, published in EFORT Open Reviews in 2022, reviews disruptions of the knee extensor mechanism. These serious injuries occur in three main settings: primary tendon ruptures, disruptions in patients with a knee replacement, and patellar tendon tears as part of multi-ligament knee injuries. Early surgical repair is advised, because delayed treatment leads to worse outcomes and more complex reconstruction.

Patellar and quadriceps tendon ruptures

Patellar tendon ruptures tend to affect younger patients, while quadriceps tendon tears occur mainly in older adults. A substantial share of patients have local risk factors, such as prior tendinopathy or steroid injections, or systemic ones, including obesity, diabetes, chronic kidney disease, hyperparathyroidism and certain medications; these are more common in bilateral injuries. The hallmark of both injuries is loss of active knee extension, which can be hard to detect in a painful, swollen knee. Plain radiographs may show a change in patellar height or a bony avulsion, ultrasound is useful but operator-dependent, and MRI is the gold standard.

Treatment and recovery

Partial tears can often be managed without surgery. Complete tears should be repaired surgically, ideally within the first weeks after injury. Transosseous sutures and suture anchors give similar clinical results. Isolated repair works well in younger patients with acute tears and good tendon quality, while augmentation with autograft, allograft or synthetic material should be considered for poor tissue, chronic tears or tendon defects. Rehabilitation usually combines protected weight-bearing with a gradual increase in range of motion. Most patients return to work and sport and re-rupture is rare, although fewer regain their pre-injury level of play.

Extensor mechanism disruption after knee arthroplasty

After total knee arthroplasty these injuries are harder to treat, because patients are older, have more comorbidities and often have poor soft tissue and bone quality. Outcomes are inferior to those in native knees, and some form of augmentation is advisable in all cases, as primary repair alone has a high failure rate. Options include hamstring autograft, Achilles tendon or bone-patellar tendon-bone allografts and synthetic mesh. Whole extensor mechanism allografts and mesh reconstruction are salvage procedures for knees with extensive bone and soft-tissue loss; their results are similar, and mesh is cheaper and carries no risk of disease transmission. Dehiscence of the arthrotomy after a fall can usually be repaired directly.