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.
Just above the upper kneecap pole is the commonest site for rupture of the tendon of the quadriceps, the rupture occurring through abnormal tissues. The structural make up of the tendon or the blood supply can be damaged by a variety of medical diseases. Changes in the blood vessels can be produced by diabetes and high body weight can produce fatty changes in the tendon structures and an increased level of forces through the tendon. Ruptured tendons have been investigated and shown microscopically to possess degenerative changes without significant inflammation. Poor supply of oxygen and insufficient nutrition are important precursors to tendon degeneration.
Typical presentation of a patient is for them to complain of acute knee pain, knee swelling and loss of functional knee ability after giving way of the knee, a fall or a stumble. They may not have had knee pain previously and the knee may have gone pop audibly at the time of the incident. Patients will have difficulty walking and examination will show swelling above the kneecap, bruising and tenderness. A gap in the tissues just above the patella may be clearly apparent to touch with the patella lying lower than normal over the knee.
Active extension or straightening of the knee against gravitational force is the important factor to assess in the patient's ability. An extension lag, where the patient cannot completely straighten their knee with their own power, is an indication of a potential rupture. The inability to straighten the knee will vary with the severity of the injury and partial ruptures are more difficult to diagnose. Any delay in assessing and diagnosing the patient is unhelpful and due to the difficulty in diagnosis it is common for this injury to be misdiagnosed with inevitably inappropriate management.
The knee pain and swelling will reduce over time and the function of the quadriceps may improve, with improved walking ability. However, patients will show a hip hitch to bring the leg through and walk on a straight knee to maintain stability. However, the knee may give way frequently and climbing stairs will be difficult. Early operation to repair the defect is the standard treatment for acute and complete ruptures of the quadriceps tendon, with chronic ones also mostly suitable for surgery. Partial tears can be immobilised in a cast in a fully extended position for three to six weeks with a gradual physiotherapy rehabilitation regime until good function is achieved.
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.
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