Quadriceps tendon ruptures are not common and mostly occur in people who are older than forty years of age. It is much more common in patients with various diseases and who have had degenerative changes in the extensor mechanism of the knee. Ruptures typically occur on one side only and if they occur in both knees there are very likely to be significant predisposing factors. Ruptures of the patellar tendon are not as common as quadriceps tendon ruptures and occur more often in younger patients under forty years old. Early diagnosis and surgical repair of the ruptured tendon is essential as later repairs are much more difficult with poorer results.

The typical mechanism of injury is for the damage to occur during a rapid contraction of the quadriceps whilst it is lengthening and with the foot on the ground. Falls, direct blows to the knee, cuts and lacerations are all possible causes. Since normal tendons have been shown not to typically rupture and that the quadriceps can rupture after relatively minor trauma, it follows that rupture most likely occurs through an abnormal area in the tendon. Many medical conditions can increase the likelihood of tendon rupture including immobilisation, long term steroid use, infections, rheumatological conditions and obesity. Steroid injections in the knee can weaken tendons and rupture can occur secondary to various knee operations.

Tendon rupture of the quadriceps occurs mainly through pathological tissues just above the upper pole of the kneecap. Alteration to the tendon blood supply or changes in the tendon structure can occur with various medical illnesses. Blood vessel changes can occur in diabetes, with raised forces applied to the tendons and replacement of tendon tissues with fatty tissues in obese persons. Microscopically, ruptured tendons have shown to exhibit changes which are degenerative and not inflammatory. Since under the microscope abnormal blood supply and blood vessels have been shown, important factors in degeneration of tendons may be poor oxygen levels and poor nutrition.

On presentation patients show a loss of the ability to use the knee functionally, swelling in the suprapatellar region and severe knee pain after a traumatic event such as a fall or stumble, or after the knee giving way without falling. There can be a clearly audible pop at the time and the patient may never have complained of knee pain before. Walking will be difficult due to pain and knee instability and a physical exam will show bruising, tenderness and the suprapatellar swelling. On manual examination a tissue gap may be found above the patella and the patella itself may lie rather lower than is normal.

The ability to extend the knee actively against gravity is the key aspect of the determination of the diagnosis. If there is a rupture then there should be an extension lag, an inability to straighten the knee up on its own. This will be of varied severity depending on the degree of rupture, with partial ruptures needing more careful assessment to discover them. It’s more difficult to diagnose this condition if there is a delay in assessing the patient and many inaccurate diagnoses are given, with simple knee strains a common diagnosis with the consequent incorrect treatment and follow-up.

Improvement should occur in the knee swelling and pain with time, with the patient regaining walking ability and some quadriceps function. Walking can be difficult with the knee having the tendency to give way regularly and going up stairs being difficult, the patient hip hitching to bring their leg through in gait and then bracing the knee back to prevent instability. Typical management for complete, acute ruptures is to operate early and surgical repair can be effective also in chronic ruptures. Immobilisation in a plaster cast may be used for partial tears, with 3-6 weeks in the cast followed by extensive physiotherapy to regain function.

4-6 weeks in a cylinder plaster in full knee extension is the common management after this operation and weight bearing is usually permitted early with a frame or crutches. After the plaster is taken off then a hinged knee brace can be applied which can be adjusted to limit flexion range which can be gradually increased to allow greater and greater knee bend. Patients are then referred to physiotherapy to work at gradual increases in knee strength and ranges of motion until the knee is rehabilitated close to the function of the other knee.