Anterior cruciate ligament (ACL) tears occur during sports or fitness activities. The commonest injury to the ACL is associated with valgus stress and external rotation of the tibia on the femur.
This mechanism can injure the medial meniscus and medial collateral ligament.
The triad of ACL, medial meniscus and medial collateral ligament injury is known as the Triad of O'Donoghue.
The other common mechanism is forced hyperextention injury, which may be associated with rupture of the posterior cruciate ligament - a direct blow as seen in dashboard injuries.
The least common is excessive varus stress on the knee joint. These mechanisms typically occur from changing direction rapidly, slowing down when running or landing from a jump.
ACL injury should be suspected in any individual presenting to the clinic with acute haemarthrosis of the knee following trauma.
A detailed history, including the mechanism of injury and thorough examination, must be undertaken.
Individuals with an acute torn ACL often describe that their knee 'pops out', and that they feel pain and develop an immediate swelling.
Such individuals are often unable to put weight on their affected limb.
Often it is not possible to perform the special diagnostic tests in acute haemarthrosis due to pain and swelling.
The plain radiograph will not show ACL rupture, but may demonstrate bony injury if these have occurred. The diagnostic test is an MRI scan of the knee, which will confirm an ACL injury.
Management depends upon many factors, including the extent of damage to the knee, the extent of sporting activities, patient motivation to modify activities and work through rehabilitation and a patient's age and co-morbidities.
Conservative treatment is appropriate for older patients with low activity levels, no associated injuries and mild symptoms.
Conservative treatment ought to consist of rehabilitation (physiotherapy aimed at strengthening muscles around the knee conferring stability), and a knee brace to help stabilise the knee.
This approach is appropriate for children and adolescents with a torn ACL without involvement of the menisci.
Surgical treatment is suitable for patients with instability of the knee, patients who engage in high-risk activities such as football, and where there is involvement of the menisci.
Primary repair of the ACL is not recommended because it leads to persistent laxity and instability of the knee.
Instead, the ACL can be reconstructed using autografts, including bone patellar tendon bone graft, hamstring tendons, a quadriceps tendon bone graft and fascia lata.
The advantages of using autografts include minimal host reaction, decreased chances of infection and improvement of function.
A second option
Allografts offer several advantages over autografts, including decreased morbidity and the time taken in harvesting the graft, and that they come in various sizes and shapes.
However, the use of allografts is limited by agents used to sterilise the graft, such as ethylene oxide and irradiation, which can significantly weaken it and ethylene oxide can cause cystic changes in bone tunnels.
Allografts are much slower at incorporation than autografts, so they are mainly used in revision surgery and complex primary surgery.
Synthetic grafts are not used anymore because they can produce an intense foreign body reaction, infection rates are higher and they are prone to failure. Moreover, synthetic grafts are expensive. The majority of surgeons in the UK either use a patellar tendon bone graft or a hamstring tendon graft.
- Mr Dinesh Sharma is staff grade, Dr Dinendra Gill is senior house officer, Dr Idnan Yunas is house officer, and Mr James Ramos is consultant at the trauma and orthopaedics unit, Heart of England Hospital, Birmingham.
ACL INJURY DIAGNOSTIC TESTS
With the patient lying flat, stabilise the femur with one hand, flex the knee to a 20-30deg angle and gently attempt to move the tibia forward, relative to the femur. If the patient's lower leg moves forward, suspect an ACL tear.
Anterior drawer test
With the patient lying flat, flex the knee to 90deg and attempt to translate the tibia forwards using both hands.
Pivot shift test
With the patient lying flat, the tibia is rotated internally with one hand holding the foot and the other hand applying a valgus stress at the level of the knee joint. Then, with flexion in the knee of 20-30deg, a jerk is suddenly felt at the anterolaternal corner of the tibia.
This is the anterior subluxaton of the lateral tibial plateau on the femoral condyle.