Knee pain is a common problem among the young and old alike. From athletes to middle-aged adults to seniors, knee pain can develop suddenly. There are many potential causes owing to the fact that there can be ligament involvement, cartilage tears, muscle strains, cysts, arthritis, and more.
Most of the time, knee pain is felt in the front of the knee or along either side. Posteromedial pain (inside back corner) is less common and more puzzling -- especially when it lasts a long time.
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.
The semimembranosus muscle is part of what you might know otherwise as the hamstring muscle. It is made up of three separate but conjoined parts. This portion starts at the base of your sit bone (called the ischial tuberosity).
It travels down from the pelvis to the knee and inserts right along the posteromedial corner. The job of the semimembranosus is to flex or bend the knee. If you feel under the knee while in the sitting position you'll be able to feel the tendon easily.
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 localized 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.