Acute Knee Assessment

Assessment of Acute Knee Injuries

History: Determine the exact mechanism of injury to help predict the possible extent of damage to the knee. It is important to know the position of the knee at the time of injury, the magnitude of the forces and direction applied to the knee.

An RTA or fall from a height is likely to generate massive forces capable of rupturing ligaments and fracturing bone. Football is a knee disease with a high frequency of ligamentous injury. Skiing can apply great force to the knees if the skis get crossed or stuck and the body continues with considerable stored momentum! Patients and bystanders often report an audible crack/pop/snap indicating a sudden release of energy as something fails under load.

A history of prodromal symptoms in the knee suggests wear which may have been exacerbated by the current injury. Progressive aching and joint-line tenderness before developing a locked knee is usually due to a degenerative meniscal tear. Repeated episodes true-locking suggests a large meniscal fragment or a loose body in the knee.

Disability: Inability to bear any weight on the leg immediately after an injury suggests some serious pathology. A gradual onset of swelling and discomfort leading to limping and reduced weight bearing suggests swelling is limiting activity, rather than a mechanical failure in the knee.

Patients unable to walk/drive/work benefit from early treatment either by referral to physiotherapy or to the knee clinic.

Examination:

LOOK - Compare the two sides and note malalignment, swelling, bruising and any wounds. Intra-articular swelling will be limited by the capsule of the knee (unless the capsule has been ruptured, for example in a knee dislocation). A haemarthrosis may be very tense and limit any movement. Only structures with a good blood supply can cause an acute haemarthrosis (e.g. ACL Rupture, PCL Rupture, Peripheral Meniscal Detachment and Intra-articular fractures such as Tibial Plateau Fractures )

Do not confuse intra-articular swelling due to injury, with pre-patella bursitis which is usually inflammatory and occasionally infective: -

FEEL - Look through the skin to understand what you are palpating. Note tenderness of the bones, ligaments and meniscii.

MOVE - Compare the two sides for passive range, active movement and ligamentous stability.

Patients satisfying departmental guidelines for x-rays should have these done before stress testing the ligaments.
Loss of terminal passive extension (locked knee) is a cardinal sign of a large interposed meniscal tear. However this situation can be mimicked by hamstring spasm secondary to pain or swelling.
Loss of active extension, in a knee that will passively extend, is a sign of extensor mechanism rupture .
Abnormal movement on stressing the joint is a sign of ligament rupture. Again compare the sides to determine what is normal for each individual patient.

Valgus force tests the MCL
Varus force tests to LCL / Proximal Tibiofibular Joint / ITB
AP force test the ACL ("Lachman's test", "Anterior draw test")
PA force test the PCL ("Posterior sag sign", "Posterior draw test", "Quads Active test")
IR subluxation/reduction tests ACL ("Pivot shift test")
ER subluxation/reduction tests PCL ("Reverse pivot shift test")
ER instability tests the PLC and PCL ("ER Recurvatum Test", "Dial Test")

Imaging:

As with all investigations imaging should only be used to aid decision making:-

Confirm a diagnosis: Only where there is doubt.
Exclude a diagnosis: Only where there is a significant probability.
Assess the severity of injury: To direct treatment.

For high energy knee joint injuries plain x-rays must be undertaken before referral to the knee clinic. MRI scanning is not always necessary and patients should not be told this "will be required".