Examination - Supine

Examination supine involves a combination of look, feel and move. In order to look properly we need to feel the knee aiming to detect and confirm specific appearances and problems.

General inspection: This takes into account evaluating alignment, position of the knee, skin problems, scars, muscle wasting, bruising for site of trauma, and the manner in which the knee is held.

Presence of effusion: This may be obvious due to loss of the usual divot or dent on the medial aspect of the patella or it may need to be detected by the bulge test. In this test the flat palm of the examiners hand milks fluid from the medial side via the suprapatella pouch into the lateral gutter. This collection of fluid is then sharply pushed back to the medial side by stroking the lateral gutter with the back of the hand eliciting a bulge on the medial side. Squeezing the suprapatella pouch with one hand and balloting the patella may elicit the patella tap sign.

Patella tap sign, bouncing the patella off the trochlea to demonstrate effusion

Fixed flexion deformity: The patient may be holding the knee in a flexed posture indicating true locking or pseudo locking due to pain. The knee can be gently straightened to full hyperextension looking for any loss compared to the other side. Full passive extension is determined by holding the knee flat and lifting the foot and heel off the couch – quantifying any difference between the two knees by number of fingerbreadths heel height difference. An alternative measure is heel height difference in cm on prone lying with the distal thigh supported by the couch.

Measuring heel height difference in prone lying to record loss of knee extension

Assessing extension in the acutely injured knee: In the acute phase initially resting the knee over a pillow to encourage the muscles to relax and then gradually lifting the heel off the couch can allow detection of any true loss of extension. Pain felt over the medial aspect while achieving full extension indicates MCL injury rather than meniscal locking. Simply holding the legs by the heels may also detect a difference in knee height.

Range of movement (ROM): After trying to detect loss of extension it is useful at this stage to examine for flexion, partly because the patient is expecting the knee to be moved but mainly because this will elicit how painful the knee is and therefore guide the remainder of the examination. In the obviously arthritic knee, range of movement is the most important sign and palpation of tender points less so. By convention ROM is expressed by three numbers: hyperextension or recurvatum, active extension and flexion eg 5/0/135.