By: 25 October 2011

William E. Bylund, BS, and Kevin de Weber, MD.
In Sports Health. September/October 2010. Vol. 2. No. 5. Pp. 380-384.

The authors of this article bring to our attention the possible causes of posteromedial knee pain. In particular, the focus is on one that is infrequent but should be considered: semimembranosus ten­dinopathy.

Overuse of this muscle from sports activities or degeneration from overuse with age is the underlying cause in two age groups: young endurance athletes and middle-aged (and older) adults. The diagnosis can be elusive.

In older adults, there are often many changes in the knee going on at the same time. They could have semimembranosus tendinopathy and bursitis or a meniscal tear or bone spurs rubbing against various tendons. Sometimes they have combinations of pathologies.

No matter the age of the affected individual, the symptoms are the same. Pain is localised right to the posteromedial aspect of the knee. The pain gets worse with activities that involve using the hamstring muscle to bend the knee.

For athletes, pain may come on after increasing their training (e.g., running or cycling). For older adults, it could be associated with going down stairs, walking, or any activity that requires full knee flexion. A careful examination is necessary to pinpoint and isolate the problem to the semimembranosus tendon. The examiner will look at the overall posture to see what biomechanical problems might be contributing to the problem. Besides palpation (feeling where the pain is located), there are a few clinical tests that can be performed to help make the diagnosis.

The use of imaging studies may help. X-rays don’t usually show anything to suggest a problem with the muscles so the physician must rely on MRIs or even better, bone scans and ultrasound. It’s a tough little area of the knee to really get a view of what’s going on — even with arthroscopy, the problem isn’t easily visible.

When the surgeon can see evidence of a problem, it’s usually the presence of fluid around the bursa in that area of the knee or a thickening of the tendon. Sometimes breakdown of the tissue or scarring called fibrosis can be seen on the ultrasound test.

In some cases, the most accurate diagnostic test and the treatment are the same: local anesthetic injection. The surgeon injects a numbing agent around the semimembranosus tendon where it attaches to the bone. Immediate relief of pain confirms the site of the problem.

What next? The patient is sent to physical therapy where he or she will be instructed in proper use of ice, activity modification, stretching, and strengthening exercises. Posture and alignment will be assessed and corrected with exercises and/or shoe modifications. Sometimes a heel lift is all that’s needed. In other cases, a specific shoe might be recommended.

Medications such as anti-inflammatories may be prescribed. For cases that don’t improve with conservative care, up to three injections can be done. Surgery is a final option for those who have bone spurs that need to be removed or when it is necessary to re-route the tendon.

The surgeon is careful to look for other contributing causes to the problem and treat those as well. Semimembranosus tendinopathy should be suspected when posteromedial pain just never quite goes away. Pain that is pinpointed to the insertion site of this tendon is a pretty good indicator, too.

Results are good when the problem is identified properly early on. Conservative care is all that’s needed for nine out of 10 patients. But a delay in diagnosis because there’s more than one problem or the semimembranosus tendon isn’t considered as a possible cause is all too common.

The authors hope this article will alert physicians to remember to investigate semimembranosus tendinopathy as a potential part of the differential diagnosis when posteromedial knee pain develops in patients of all ages.