Rupture of the Quadriceps Tendon
It is not common for the quadriceps tendon to rupture and when it does it mostly presents in those older than 40 years. Certain diseases and previously existing degeneration in the knee extensor apparatus makes this condition more likely to occur. A rupture on one side is the most common occurrence and bilateral ruptures indicate there are very likely to be underlying causative factors. Patellar tendon ruptures are less frequent than ruptures of the quads tendon and present in younger people under 40. It is important to make an early diagnosis of this problem and operate as soon as possible afterwards as delay makes the outcomes poorer.
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.
Rupture of the quadriceps tendon usually occurs through abnormal tissue in the first two centimetres just above the patella. Medical conditions can damage the blood supply to the tendon or alter the structure of the tendon. Diabetes can cause changes in blood vessels and obesity leads to increased tendon forces and degeneration within the tendon by replacement with fatty tissues. In the microscopic examination of ruptured tendons the vast majority were suffering from degenerative changes without inflammatory changes and commonly showing abnormalities of blood vessels and supply. Decreased blood flow leading to poor nutrition and low oxygen levels may be crucial factors in 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.
In diagnosis of this condition it is important to determine the patient's ability to effect knee straightening against the force of gravity. A rupture can be indicated by the patient being unable to straighten their knee joint under their own power and this is known as an extension lag. Ruptures which are partial are more difficult to recognise and the patient's ability to knee straighten will vary with the level of quadriceps tendon damage. Misdiagnosis can be quite common and this can lead to the wrong treatment and inadequate follow up.
As time passes patients may regain the ability to walk and the ability to use their quadriceps to some extent as the pain and swelling settles. As the knee can routinely give way patients hip hitch to carry the leg through and hyperextend the knee to attain weight bearing stability. Without this the knee gives way frequently and in most cases climbing hills or stairs is problematical. Acute and complete ruptures are treated by primary and early surgical repair although chronic ruptures can be successfully repaired. Plaster cast immobilisation can be used for partial tendon ruptures with the knee kept in extension for three to six weeks followed by physiotherapy rehab.
Typical post-operative management is to place the knee in full extension in a plaster of Paris cylinder for a period of four to six weeks, allowing the patient to bear weight with a walking aid. Removal of the plaster is followed by application of a hinged brace which can be adjusted to allow progressively more flexion as healing progresses. Patients attend physiotherapy to regain the knee range of motion and strength until their knee is as good as the unaffected one.