Extensor Mechanism Rupture and Total Knee Replacement

Orthopaedic & Spine Center
Dr. Carlson in the OR

Jeffrey R. Carlson, MD

All surgeons and their patients hope for perfect surgeries and recoveries, like a scene out of Marcus Welby, MD, where the patient has a heart transplant and lives happily ever after with her adoring family and friends all around her.  Fortunately, that surgical scenario tends to play out in real life most of the time, at least in the United States, where we are blessed with great surgeons, superb hospitals, advanced technology, and wonderful care teams.  Even so, occasionally during surgery or after surgery, something can go wrong.  In this article, I’m going to discuss a rare complication that can happen during or after knee replacement surgery – an extensor mechanism rupture – and discuss how it is treated when it occurs.

First, let’s start with the parts of the anatomy that comprise the extensor mechanism of the knee.  That includes the patella (kneecap), the patellar tendon, patellar ligaments, medial and lateral retinaculum (a band of fascia that supports and holds a tendon in place), the quadriceps muscles and tendon and the tibial tubercle (this is a bump right below the kneecap on the larger bone in the lower leg).  All these muscles, ligaments, tendons, and fascia connect to each other and to bone in the knee.  This complex system provides stability for the knee joint and allows for extension of the knee in a variety of daily and sports activities. 

Usually, most of these anatomic components are quite strong on their own.  You may be surprised to know that some bones will break before a tendon ruptures.  However, there are some reasons for these tissues to degrade, which are typically age, disease and injury related. There are some known risk factors as well, which are:

  • Multiple surgeries on the knee
  • Obesity
  • Hyperthyroidism
  • Chronic renal failure
  • Diabetes
  • Rheumatoid Arthritis/Connective Tissue Disorders
  • High dosage glucocorticoid or fluoroquinolone
  • Repeated intra-articular injections of glucocorticoids
  • Prior knee joint infections

Although Orthopaedic surgeons take every precaution and do contingency planning based on a patient’s medical history, during a knee replacement surgery, one of these components can rupture.  Though this complication is quite rare, it tends to be either the patellar tendon or the quadriceps tendon that fails.  If it happens while the knee is being replaced, the surgeon can effectively address the tendon rupture and perform tendon reconstruction at the same time as the knee arthroplasty. 

A more likely scenario would be that some time after the patient has their knee replacement (it could be months or years), they suffer a fall going downstairs, or have some sort of trivial incident which causes the extensor mechanism rupture or injury.  As there are many components to the extensor mechanism, various injuries are possible. For example, the kneecap may fracture or dislocate and/or tendon rupture may also be included in the injury.   The symptoms of extensor mechanism rupture are mild to severe pain, swelling, inability to partially or fully extend the injured leg, inability to walk unaided or without an assistive device, palpable disruption or space in the patellar tendon and patella, extensor lag (the inability to extend the leg to its passive limit without undue force). A physical exam, asking the patient to perform a supine straight leg raise, x-rays, ultrasound or an MR scan will assist with confirming the diagnosis.

Partial tendon tears and stable kneecap fractures can be treated conservatively with rest, bracing, physical therapy and time. Unfortunately, other extensor mechanism injuries will have to be treated surgically. Because the surgeon is working with tissue that has already been traumatized during the knee replacement surgery, reconstruction and healing is made all the more difficult.  Repairs and reconstruction must be reinforced with tissue grafts and wires, augmented with mesh and other supportive materials to give the patient’s body the best chance at healing without reinjury.  As your surgeon, I would recommend the surgical approach for optimal recovery and longevity for your replaced knee, so that we don’t have to go back in surgically for a long time, the good Lord willing. 

Patients who undergo extensor mechanism rupture repair surgery after knee replacement will also need to be prepared for a long and careful rehabilitation period, which will include lots of slow, gentle Physical Therapy for months to build strength and stamina, while allowing the repaired/reconstructed tendons and bones to heal. Depending on the severity of injury, patients may be non-weight bearing and use crutches or other assistive devices for a period of their recovery after reconstructive surgery.


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