The American Academy of Orthopaedic Surgeons reports that in 2003, 19.4 million Americans visited a physician because of a knee problem.1 An increasing older population and a greater number of persons who participate in recreational activities are making knee pain and injuries more common among the general population. All health care providers should be able to perform a physical examination of the knee, accurately determine a differential diagnosis, and decide whether to treat or refer the patient.
As with any clinical evaluation, begin by taking a complete history of the patient's problem, including the date of the injury, the mechanism of injury, and any treatment the patient has already received. Table 1 lists key questions that will provide critical information about the nature of the injury, the onset of symptoms, and any prior problems the patient has had with the involved knee. The answers to these basic questions can go a long way toward developing the differential diagnosis. A young, athletic person who sustains an acute knee injury while participating in a sport will generate a different list of potential diagnoses than will a middle-aged sedentary person with atraumatic insidious pain. In many cases, the differential can be narrowed down simply by talking to the patient.
THE PHYSICAL EXAMINATION
A systematic approach is vital when examining the knee. This prevents the examiner from missing pathology and allows him or her to recognize which signs indicate a possible abnormality. Observation, range of motion (ROM), palpation, special tests, and a neurovascular examination are the components of a comprehensive examination. The uninvolved knee is examined first to establish normalcy for that patient. Pain felt in the knee may be referred from the back or the hip, so examining both of those areas is important as well. A systematic examination may seem time-consuming; however, a PA who performs it consistently can become quite proficient very quickly.
Observation and inspection The examination begins by inspecting the knee and observing the patient walk. The patient's gait can provide information about the location of the pain and its effect on activities of daily living. Knee alignment is evaluated both while the patient is standing and lying supine; signs to look for are genu varum (also known as bowleg), genu valgum (or knock knee), and genu recurvatum (a hyperextension of the knee or back knee). In addition, the PA should note the details about any signs of muscle atrophy, ecchymosis, scars, abrasions, lacerations, or rashes.
Range of motion Musculoskeletal joint examinations must include an assessment of ROM. Active and passive ROM are assessed. ROM is recorded as the degree of hyperextension (if any), neutral position, and degree of flexion (ie, 5/0/135 indicates 5° of hyperextension, neutral position is at 0, and 135° of flexion). If the patient does not have full ROM, determine what is preventing full motion. Is pain and/or swelling limiting ROM?
The examiner must determine if the patient has an isolated area of swelling or a knee effusion. Swelling is defined as a localized area of edema on one part of the knee and is caused by an extra-articular injury. An effusion is a symmetrical area of inflammation around the knee that manifests hours after a traumatic event; it is a common sign of an intra-articular injury. To differentiate between swelling and an effusion, place your hand on the patient's thigh and apply gentle pressure, sliding your hand down toward the suprapatellar area, and palpate the knee with your other hand. A ballotable patella indicates presence of a knee effusion. The most common causes of an acute effusion resulting from hemarthrosis are peripheral meniscal tears, anterior cruciate ligament (ACL) rupture, intraarticular fracture, extensor tendon rupture, patella dislocation, and knee dislocation.2-6
Palpation The soft tissue and bony landmarks of the knee are evaluated (see Figure 1). The most painful areas should be palpated last. Starting above the knee, palpate along the quadriceps and patella tendons with the knee straight; any defects or gaps indicate an extensor tendon rupture. Next, palpate along the medial collateral ligament (MCL), lateral collateral ligament (LCL), iliotibial band, biceps femoris, pes anserine, and hamstring tendons. Flex the knee to 90°, and palpate along the medial and lateral joint lines (see Figure 2). The assessment continues with the bony landmarks, including the medial and lateral femoral condyles, the patella, the tibial tubercle, and the fibular head. As each of these structures is palpated, determine if the patient's pain is reproduced.
