Thursday, February 2, 2012

How To Read A Musculoskeletal X-Ray

Reading plain x-ray images of the skeleton is a basic radiology skill. A close second to reading chest x-rays, learning how to read a musculoskeletal image is an essential skill to have. Much can be said about specific diagnoses that can be made on plain imaging, but this post is more about an approach to a general MSK x-ray, whether it is a study of the fingers, hands, wrists, forearms, humeri, shoulders, pelvis, hips, femurs, knees, tibula and fibulas, ankles, or feet (gosh that's a lot!). Don't worry though: the same general approach will lead you to the right diagnosis or diagnoses on the majority of these studies.

So, the suspense has been building: what exactly does one look for on a MSK study? Well, there are five basic things to consider (of course, after you verify the patient's name and that the radiologic technologist has sent the images and labeled everything appropriately):

  1. Bone integrity - Or, in plainer terms, fractures. Many fractures will be glaringly obvious. However, a significant number may have only subtle findings. The key to identifying a fracture is to find cortical disruption. To do so, use your eyes to trace the outline of each bone. The area of increased density representing the osseous cortex should be continuous. If you see any disruption or step-off, you should be concerned for an acute fracture.
  2. Alignment - This step will help identify dislocations and subluxations when a fracture is not present. Learn the normal 'anatomic' alignment well first, and then deviations from the normal alignment will jump out at you.
  3. Mineralization - This is slightly subjective as it depends on learning a visual baseline of normal mineralization and then noticing when bones are less dense than what one would usually expect, given the patient's age and gender. For example, a patient with rheumatoid arthritis may have peri-articular demineralization, in which the portions of bone near affected joints have decreased density.
  4. Joint spaces - Learning the normal visual appearance of a joint space is key. Luckily, adjacent joint spaces (or contralateral ones) can often provide a good standard reference on any given patient (unless all the joints are affected, but this is usually obvious). Decreased joint spaces indicate loss of cartilage which can eventually lead to bone-on-bone contact. Conversely, increased joint spaces can indicate ligamentous injury or subluxation/dislocation injury.
  5. Soft tissues - Lastly, you want to assess the soft tissues for any defects that may represent soft tissue injury such as laceration. You also want to assess for calcification in the soft tissue. Depending on its configuration, this can represent a wide spectrum of diagnoses from benign post-traumatic causes to highly malignant ones. Also, on studies like a shoulder x-ray, it is important to assess the visualized portions of the lung fields. It would be poor form to miss a large lung cancer because one simply did not look. 

As an addendum to #1 above, if the patient has had prior trauma and orthopedic hardware implanted, assess the hardware to see if there are any fractured pieces (who knew metal could fracture?) or if there is lucency surrounding any of the pieces, which could suggest loosening or infection. 

That's it! Those 5 basic areas are the key things to focus on when evaluating any musculoskeletal plain xray imaging study. Of course, each specific body part will have specific areas and diagnoses to consider (for example, here's an earlier post that describes what to assess in a pelvic xray). With experience, going through these five steps will become natural and efficient.