Knee

Ligament injuries of the knee

The four major ligaments of the knee (anterior and posterior cruciate, medial and lateral collateral) maintain its stability and guide its motion. The anterior cruciate ligament (ACL) provides the major restraint to anterior translation of the tibia on the femur, and the posterior cruciate ligament (PCL) to posterior translation. The medial collateral ligament (MCL) resists valgus deformation but the lateral collateral ligament (LCL) is the weakest of the four and does little to prevent varus deformity, the majority of restraint coming from the dynamic input of the iliotibial band. All four ligaments work in close harmony and injury to one affects the function of the others. The following combination of injuries is roughly in their frequency of occurrence:

MCL;

ACL;

ACL and MCL;

PCL;

PCL and posterolateral structures;

ACL, MCL, PCL (knee dislocation, rare).

 

MCL injury

These occur after a valgus injury, commonly during snow skiing. There is pain and tenderness localised to the site of injury, usually the midsubstance or proximal insertion and valgus instability may be elicited. Grade I injuries may be treated symptomatically; grade Il—Ill should be braced with knee motion restricted from 10degree to 90degree for 3—4 weeks. Athletes should be warned of ‘tweaking’ pains that persist for up to a year following MCL injury.

ACL and ACL-MCL injury

The history of a noncontact injury when the athlete was run­ning and tried to change direction, felt the knee ‘jump’, heard a pop and developed immediate swelling is almost diagnostic of ACL injury. If the knee took 2—3 weeks to settle down and the athlete is left with a feeling of, or experiences, instability then any lingering doubts over the diagnosis can be dispelled. Clinical confirmation comes from increased anterior tibial translation with the knee held in 300 of flexion (positive Lachmann test) and abnormal anterior subluxation of the lateral tibial plateau (positive Pivot shift test). The main indication for surgery is the recurrent episodes of instability that patients experience when changing direction or landing from a jump.

ACL rupture is commonly associated with injury to other structures in the knee. Meniscal tears are present 80 per cent of the time and unstable meniscal tears should be repaired at the time of ACL reconstruction. ‘Bone bruises’ visible on MRI scans represent subchondral oedema and are evidence of impact damage sustained at the time of injury.

All patients with ACL injury should undergo an intensive rehabilitation programme, with special emphasis on hamstring proprioception. The decision making concerning the need for, and technique of, surgical reconstruction is not straight­forward. There is a massive body of literature, but very little science. At present, the major determining factors are the degree of knee laxity and the level of sport to which the athlete wishes to return. The decision is relatively easy at each end of the spectrum; the high-demand athlete with a loose knee probably (but still by no means certainly) requires reconstruction, whereas the nonsporting office worker with a fairly stable knee does not need a reconstruction. With patients in the middle ground, who may or may not wish to adapt their sporting lifestyle to accommodate their knee, it is reasonable to adopt a wait-and-see policy, and if functional instability develops then reconstruction can be offered at a later date.

Surgery should be delayed until the swelling and range of motion have improved in order to avoid a painful stiff knee postoperatively (arthrofibrosis). Combination ACL—MCL injuries should be braced for 3—6 weeks to allow the MCL to heal and then have the ACL reconstructed.

Techniques of ACL reconstruction

The child’s ACL usually avulses with a fragment of bone from the tibia. It is relatively simple to fix this fragment back into the tibia either with a bone screw or with sutures passed through to the front of the tibia. The adult ACL tears midsubstance or at the femoral insertion but rarely heals.

Extra-articular reconstructions

These prevent the abnormal anterior subluxation of the lateral tibial plateau by re-routing the iliotibial band around the LCL. Whilst they abolish the pivot shift phenomenon they do not restore normal knee kinematics and the majority of surgeons no longer uses them routinely.

lntra-articular reconstruction

Suturing the ends of the ACL back together is only possible in the acute injury, but the long-term stability of the knee is poor and the technique has largely been abandoned. The ACL is therefore replaced with a graft placed through bone tunnels which enter the joint at the sites of attachment. Graft positioning is critical to the success of ACL reconstruction, and ideally the graft should not lengthen or shorten by more than 2 mm when the knee is put through its full range of motion, i.e. it is isometric. Prosthetic grafts are very attractive because of the lack of donor morbidity and their high initial strength. However, the early optimism with their use has been dampened as problems have developed due to particulate debris when the grafts fail. They are usually only used if a viable alternative is not available.

Allografts have no donor morbidity but all methods of sterilisation (to prevent disease transmission) significantly reduce the biomechanical properties and delay the revascularisation of the graft.

Autografts are the most widely employed at present, the two most common ones being the middle third of the patellar tendon with patellar and tibial bone blocks at either end, and the quadrupled semitendinosus and gracilis tendon graft. These may be secured with interference screws within the bone tunnels or via sutures to screws/posts on the external cortex (Fig. 29.7). The surgery may be performed open or with the arthroscope, drilling the tunnels from within the joint. The modern trend for accelerated rehabilitation permits early weight-bearing without braces, and athletes can return to contact sport 6 months after reconstructions

PCL injury

Commonly sustained during road traffic accidents from a direct blow to the front of the tibia, PCL injuries are much less common than ACL injuries (occurring in a ratio of about 1:10). Examine the patient with both knees flexed to 900 and you will see the tibia sagging back on the side of PCL injury. The knee of patients who have a femoral shaft fracture should always be examined to exclude injury to the PCL.

Isolated PCL injuries probably do very well if rehabilitated and, as the surgery to reconstruct them is not as well developed as ACL surgery, nonoperative treatment is recommended.

PCL and posterolateral structures

 These are significant injuries but diagnosis is often difficult, and the loss of posterolateral structures (posterior capsule, popliteus tendon and the popliteofibular ligaments) in addition to the PCL can render the knee unstable. In an athletic individual acute reconstruction is probably to be recommended, but the surgery is complex and the results are not yet convincing.

  Knee dislocation (combination of three or more ligament injuries)

  Thankfully rare and a result of high-energy trauma, knee dislocation is a surgical emergency. Neurovascular injury may occur in 50 per cent of cases despite a normal-looking radio­graph, and vigilance must be maintained at all times with these injuries to avoid catastrophe. Reconstruction of all of the damaged structures is difficult surgery but in experienced hands can lead to a reasonable outcome.