Which Investigation for the Painful Knee ?

Dr Christopher Vertullo MBBS FRACS

It is always difficult knowing which investigation to order when a patient presents with a painful knee. Often the most expensive test is not the best, and in many situations some radiological modalities have no place at all. A 70-year-old male patient presents to you with increasing right medial knee pain and aching. It had an atraumatic onset, and is worse with activity.  He had pain which was 1-3 / 10 previously , but since helping his daughter move house 3 weeks ago it has become much worse, and is interfering with his sleep. You examine him and notice he walks with a limp, has a reduced range of motion to 5- 100 degrees with no effusion. His hip is not stiff to rotation and he has a good distal vascular perfusion to his feet.  He then asks for an MRI, “like all the footballers get”.   

Investigation of atraumatic  onset knee pain should always start with a plain radiograph. A series of four XRs, is the Gold Standard. These include an Erect Antero-Posterior (AP) Radiograph, a Lateral, a Patellofemoral view and an erect flexion AP, known as a Rosenberg. Oblique X-Rays are rarely useful. 

What about the MRI ? Well in these situations, middle-aged or older patients with atraumatic onset of their pain, MRI is only a secondary investigation as the diagnosis is an exacerbation of osteoarthritis and degeneration . In fact, often the XR is all that is needed. The only reason to get an MRI is if the XR shows very little osteoarthritis and the patient fails to settle with a few weeks of rest. In these situations, a stress fracture can present with a similar history but fails to settle with rest. 

The Australian Knee Society recently combined with the Australian MusculoSkeletal Imaging Group to produce a position statement for the investigation of the degenerative knee. It is a handy reference for all musculoskeletal primary care practitioners.