By Jonathan Davis D.O.
Board Certified Radiologist
Birmingham Radiological Group P.C.
Your at the gym enjoying the treadmill and have been progressing nicely with your workout routine and you start noticing a slight pain in your knee. You work through it and finish your work out. Over time the twinge in your knee starts to worsen and starts to affect your life style. How common is the above scenario? For quite a few of us this is common place. 65% of Americans age 18-34 are dealing with knee pain and decrease in function secondary to knee injuries. How does your primary care physician or Orthopedic surgeon work up your knee pain? First and foremost they will perform a physical exam and allow a focused diagnostic work up leading to the proper diagnosis.
The diagnostic work up for knee pain from an imaging standpoint is varied and certain imaging modalities are useful for certain structures and not necessarily other structures of the knee therefore there will be a multi-modality approach to your symptoms. One misconception of imaging is MRI will be able to diagnose all of the problems of a joint. While MRI is a key imaging component X- Ray also plays an important roll. Why you may ask. MRI ( Magnetic resonance Imaging) uses the water that is naturally in our bodies to generate the images in conjunction with Radio frequencies. Now, this allows the ligaments and tendons to be evaluated as well as the cartilage and the bone marrow. Well, that sounds like the majority of the joint for imaging one would say. We are however leaving out a very important component, the actual cortex of the bone. The hardened bony structures do not have enough water to be imaged well on MRI. To image this important portion of the joint Plain X-ray, or Computed Tomography comes into play. Finally Ultrasound can be used as well in a limited fashion to evaluate certain tendons.
Now to review a few basic and common knee injuries and problems that affect us and how we work them up from a diagnostic standpoint. First and most common is osteoarthritis. This is one the most common findings. As we age this is something we all will encounter to one degree to another. From an imaging standpoint the cartilage which acts as a “bumper” between the femur and tibia begins to wear out and thin which in turn allows the concussive force of walking or running to transfer to the adjacent bone. This causes edema (bone bruising) and pain. Now the body responds by laying down more bone in these regions caused osteophytes (bone spurs) which compounds the problem. The knee will also respond by producing more fluid in the joint due to the irritation. As one can see this is cyclical and trying to interrupt the natural body's response to the chronic changes is one way your physician will try to treat this problem. At some point your Orthopedic surgeon may recommend a joint replacement if the arthritis has progressed to the more extreme case. Plain film x ray can be used to effectively diagnose this problem.
Next we will discuss injuries to the knee. One of the more common injuries are tears of the meniscus which are small “cups” on the periphery of the tibia that the femur nestles into. These injuries can cause pain, limited range of motion and clicking/locking of the knee based on the type of tear and location. To image this portion of the knee MRI is used quite effectively. Anterior cruciate ligament tear ( ACL tear) is the next common injury seen in the knee. The anterior cruciate ligament sits in the mid portion of the knee and does not allow the tibia to translate (slide) anterior. This injury can cause pain and loss of stability of the knee and based on you activity level your orthopedic surgeon may repair this injury. Next there are collateral ligaments of the knee which can be strained or torn. These structures reside along the medial (inside) and lateral ( outside ) of the knee and stabilize the knee from abduction/ adduction motion of the lower extremity. MRI is well suited for diagnosing these injuries. Stress fractures from repetitive micro trauma can cause pain and limited range of motion. This can be diagnosed with MRI as well. There multiple tendons that insert at the knee from the proximal thigh and tendons that arise from the knee extending to the lower extremity. The tendons can be torn or strained and MRI can pick up changes in these tendons allowing your physician to tailor a treatment plan to your injury.
So as you can see the multi-modality approach of the work up of knee pain is used to quickly and accurately diagnose the problem and to structure a treatment plan using first and foremost the physical exam augmented with plain film and MRI. The diagnostic imaging used by your physician will be tailored to your symptoms and physical exam findings to get you back in the game and enjoying life.