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How is Osteoarthritis Diagnosed?

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The diagnosis of Osteoarthritis is generally and relatively simple.  The characteristic symptom of the disease is pain.  The pain related to Osteoarthritis has certain features that differentiate it from inflammatory causes of joint disease, such as Rheumatoid arthritis.  The pain is generally localized to the joint and is usually precipitated by activity that stressors/loads the joint.  That is, movement that strains the affected cartilage and (more importantly) the underlying bone.  Often rest relieves the pain, although in the latter stages of the disease the patient may experience pain at night that can disturb their sleep.  However, generally, when this occurs the affected is able to return to sleep once the joint has been placed into a comfortable position.  A common phenomenon is the increase in pain that is felt upon movement after a period of immobility.  This generally is of short duration, improving to the baseline level after a few moments.  This is termed the ‘gelling’ phenomenon and when it occurs at the knees after a period of sitting has been referred to as ‘movie-goers’ knee.

These features of the pain contrasts to what is experienced with joint disease related to an inflammatory arthritis, such as Rheumatoid arthritis, in which the pain is usually aggravated by rest and improved with activity.  However, even in these conditions the pain can be more marked with activity, albeit this is usually the case after a period of rest.  The greater challenge is in differentiating the pain of Osteoarthritis from other specific mechanical causes, such as ligament sprains, tendon and muscle strains, or injury to other joint structures such as the menisci.  In these structural injuries the pain is usually exacerbated only by activity/movements that specifically strain those particular tissues, whereas other movements at that joint do not cause symptoms.   Furthermore, in these conditions the pain is most commonly localized to the affected structure rather than being felt diffusely throughout the joint.  Furthermore, injury to the tendons and muscles is suggested when pain occurs upon contraction of these structures in the absence of joint movement.

In addition to pain, Osteoarthritis is also associated with a number of other clinical features including stiffness, swelling, and deformity.  The stiffness in Osteoarthritis is generally of short duration as described above, lasting most commonly for a few minutes and rarely less than 30 minutes.  In comparison, stiffness is a characteristic symptom of the inflammatory joint diseases, commonly being present for longer than 30 minutes.  Swelling in Osteoarthritis can be variable in severity but is usually only present in the later stages of the disease, whereas in the conditions such as Rheumatoid arthritis it is present from the onset of the disease.  Deformity occurs in both categories of joint disease, although in Osteoarthritis these are usually firm/hard and nodular, resulting in restriction in the range of motion and impairment of function.

A careful approach to obtaining the clinical history of the patients’ symptoms followed by a thorough examination is generally successful in arriving at the diagnosis of Osteoarthritis.  On the examination, the supportive findings often include the presence of a characteristic deformity (such as Heberden’s nodes at the joint of the fingers), crepitus, painful limitation of movement, swelling (termed a joint effusion), and tenderness to palpation/pressure along the joint line.  Crepitus is a medical term used to describe  the abnormal sensation felt by the clinician during movement of a joint that has been compared to grating, cracking, and/or popping.  In the latter stages of Osteoarthritis, there may develop laxity/looseness of the ligaments resulting in a degree of instability.

Although these clinical features are often sufficient to arrive at the diagnosis of Osteoarthritis, radiological investigations are often obtained to confirm the presence of disease.  The simple x-ray is often all that is needed.  The characteristic findings on an x-ray that imply Osteoarthritis include narrowing of the joint space, thickening of the bone underlying the joint line (termed subchondral sclerosis), and extra bone formation at the edges that are known as Osteophytes.  Not all of these features are needed to make the diagnosis of Osteoarthritis, with the earliest of these being the loss of joint space.  This finding relates to thinning of the articular cartilage.  The appearance of Osteoarthritis is simple to determine when the disease is relatively advanced, however, in the early stages of the disease the x-ray abnormalities are subtle and can be considered normal.

In that context, more sensitive options at detecting the features of Osteoarthritis mentioned above include investigations such as Computed Tomography (CT), Ultrasound (US) and Magnetic Resonance Imaging (MRI).  The latter of these is the most accurate test as it is best able to visualize the cartilage.  Recent techniques in the acquisition of MRI even allow for the total volume of cartilage to be calculated.  What has become apparent with MRI imaging is the presence of swelling within the subchondral bone, which cannot be seen by the other anatomical imaging modalities.  This finding, termed bone marrow oedema, has certain implications regarding symptoms, prognosis, and management.

Bone scan imaging is not able to define the presence the cartilage and bone changes but it does provide information regarding the location and severity of disease.  The activity seen on the bone scan has similar implication to the bone marrow oedema seen on the MRI scan.  The evolution of MRI technology has resulted in a reduction in the need to perform diagnostic arthroscopic operations.  There are no blood tests that are useful in the diagnosis of Osteoarthritis, however, these are often useful in excluding the possibility of other types of joint disease as well as ensuring there are no health conditions that may alter the treatment approach adopted.

Therefore in summary, the clinician will consider the clinical history and examination in the context of the imaging findings in order to develop a comprehensive assessment that details the location and severity of the disease upon which they will base their management decisions.  The next section will expand upon the approach to managing the disease, considering non-pharmacological, pharmacological, and surgical options.