KNEE INJURIES

Because of the bleeding within the joint, the knee becomes painful, swollen and often tense within an hour or so of injury. This differentiates it from a synovial effusion which comes on more slowly and tends to suggest a less serious injury although there may still be meniscal or chondral damage that will require surgery. An x-ray usually shows no bony injury.

A normal x-ray does not rule out a serious injury. All too often at this point the patient may leave the Accident Department/Clinic with no diagnosis and no clear instructions.

Immediate treatment

Injuries of this type are frequently sustained while skiing. The local clinic usually provides an x-ray, pain relief and a splint although countries vary greatly in provision of medical services. Rarely is this injury an emergency.

Treatment advice after immediate injury

• Unless there are very specific reasons for immediate surgery it is safe to return home

• If a splint is used to protect the joint it should be removed and ice applied to the knee to limit unnecessary swelling (apply for 10 minutes every two hours)

• Reduce walking and standing to a minimum • Elevate the knee where possible to reduce swelling • A stick or crutches can be used to give comfort and reduce the load on the knee

• It is inadvisable to try and drive immediately after injury

Aspiration Aspiration of the haemarthrosis both confirms there is blood in the knee and can relieve pressure in the knee, but it does carry a very small risk of infection and should always be performed in sterile conditions.

Figure 2: The Lachmann test

Aspiration of the knee Arthroscopy

There is no consensus regarding immediate arthroscopic surgery. The benefits are:

• Washing out the blood • Relieving pain • Diagnosing the extent of injuries • Identifying associated injuries

Some countries carry out immediate direct repair of the ACL but this has not been found useful in Britain. Immediate or early reconstruction of the ACL, even if you can be sure that it will definitely be required, carries a small but significant risk of arthrofibrosis (joint stiffness). Most surgeons feel that the earliest time for reconstruction is when the knee is biologically quiet, ie. has no swelling and full movement. This occurs three to six weeks after injury.

The laxity can also be documented by knee “laxiometers”. Rotational tests such as the pivot shift test are more difficult to perform and more painful but are probably more important as lack of rotational control leads to feelings of instability. It is better carried out in the post-acute phase. The therapist will notice lack of progress of rehabilitation when early rotational work is introduced.

The Lachmann test remains the mainstay of diagnosis of ACL injury. To reduce the protective effect of the muscles, the patient must be lying as comfortably and relaxed as possible.

X-ray

This will rule out haemarthrosis caused by fracture but does NOT rule out serious injury.

Magnetic resonance imaging (MRI)

MRI can be quite sensitive in diagnosing an ACL injury but while showing the anatomical damage it does not give information about the joint stability and is a relatively expensive option compared to careful examination.

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Blood is an excellent culture medium and septic arthritis is a disaster so sterility is critical. Aspiration in some less developed countries can be hazardous.

Instead, common management is to promote early supervised rehabilitation concentrating on reducing the swelling and regaining movement and muscle control. Surgical intervention is then only necessary if this rehabilitation fails or if there is obvious laxity.

Methods of diagnosis of ACL injury

Joint laxity tests The presence of a haemarthrosis makes ACL injury likely but laxity of the knee may be difficult to assess in the early days because of protective muscle spasm. Nevertheless clinical awareness and examination remains the mainstay of diagnosis.

The Lachmann and anterior draw tests (of the knee) will reveal laxity in a front to back plane. Both reveal abnormal anterior movement of the tibia on the femur. The Lachmann test (Fig.2) is more sensitive and easier to do in the acute phase. It is performed at about 25-30 degrees of knee flexion. If the knee moves forward on the lower end of the femur with no firm end point then it is almost certain the ACL is damaged.

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