By: William P. Rix, MD
Lower leg pain on the outside of the leg (lateral leg pain) is a common presenting complaint in the orthopedist’s office. Typically the pain is felt anywhere from the outside aspect of the knee to the lateral ankle. The patient usually gives a history of gradual onset of pain without preceding trauma. The differential diagnoses list is long and finding the exact cause can be challenging.
The spine, hip, pelvis, knee or lower leg can be the cause and within those anatomic structures the bone, joint, nerve, tendon, ligament, meniscus or muscle can be involved. When the lower leg pain is coming from an asymptomatic (painless) hip or low back we call it “referred” pain. The exact mechanism or physiology of referred pain is not completely understood.
Common Causes of Lower Leg Pain
Degenerative arthritis of the disc space or facet joints
Lumbar radiculitis (a pinched nerve)
Spinal stenosis (narrowing of the spinal column)
Degenerative changes in the hip joint
Trochanteric bursitis (inflammation of the abductor muscle tendon)
Stress or fragility fractures of the hip
Tracking problems within patellofemoral (kneecap) joint
Degenerative arthritis in the lateral (outside) joint compartment
Tear of the lateral meniscus (cartilage of the knee)
Stress or fragility fractures of the fibula, especially in people with osteoporosis.
For athletes, especially runners, the list must be expanded to include muscle compartment syndrome (swelling of a leg muscle in a restricted space), pinched nerves in the leg itself (as opposed to the low back), soft tissue (muscle, tendon, ligament or fascia) overuse syndromes, and foot and ankle malalignment problems.
Mention should be made of less common causes of lower leg pain such as peripheral vascular disease (poor blood supply to the legs) and reaction to some medications (e.g. statins).
Making the Diagnosis
The key to making the diagnosis is in the clues (the history, or what the patient tells the doctor) and the evidence (the objective findings on exam). In consultation, for example, if the patient tells the doctor the pain in the leg comes on while he/she is walking to the grocery store but goes away while leaning on the shopping cart, the orthopedist thinks immediately of lumbar stenosis; if the patient describes his/her lower leg pain as accompanied by “pins and needles” (paresthesia), then a pinched nerve is implicated, either in the low back (“referred”) or in the leg. (Note: while the absence of paresthesias does not rule out nerve involvement, its presence is a strong indicator of it.)
In physical examination, if the orthopedist can find a particular movement or maneuver that reproduces the patient’s pain, he is in luck because this narrows the diagnoses considerably. For example, if the patient experiences the lower leg pain on arching his back and tilting towards the painful leg, then painful facet joints in the lumbar spine are suspect; if stressing the hip in flexion and rotation causes the pain, then the hip joint or bone is implicated and likewise, a positive single leg squat test might point to an arthritic patellofemoral joint, while exquisite tenderness on palpation of the distal fibular bone would suggest a stress fracture.
X-rays, and to a lesser extent, MRIs are important diagnostic tools in our search for the diagnosis. X-rays detect arthritis, stress fractures, instability and malalignment. MRIs detect bone bruising, spinal stenosis, tendon/ligament injuries and meniscal tears in the knees.
Often, using any combination of clues, evidence and imaging, we can narrow the list of possible diagnoses down to two or three. At that point we will resort to diagnostic injections with local anesthetics to firm up the diagnosis. If the injection into a suspected pain generator removes or significantly reduces the lower leg pain, we have our diagnosis.
Now, specific treatment can begin.