Przejdź do treściPosteromedial knee pain can come from the distal semimembranosus tendon, but Baker’s cyst, meniscal disease, osteoarthritis and vascular problems can produce a similar pattern. Diagnosis depends on the exact location of pain, the clinical examination and, when appropriate, ultrasound or MRI.
Where is the semimembranosus tendon?
The semimembranosus is one of the hamstring muscles. Its tendon runs along the posteromedial aspect of the knee and inserts on the upper tibia. It contributes to knee flexion and helps control the limb during walking, running, deceleration and movement on slopes.
This area also contains bursae, the posterior horn of the medial meniscus, ligaments and vascular structures. For that reason, “pain behind the knee” is a symptom description rather than a diagnosis.
What does semimembranosus tendinopathy usually feel like?
- pain at the back and inner side of the knee that can often be localised with one finger;
- tenderness along the distal tendon or near its tibial insertion;
- worsening with running, uphill walking, acceleration or deep knee flexion;
- pain with resisted hamstring contraction or loaded hamstring lengthening;
- sometimes stiffness after rest that eases with movement but returns after heavier activity.
Chronic tendinopathy usually develops gradually. A sudden pop, bruising and clear loss of strength are more suggestive of an acute muscle-tendon injury and require a different assessment.
What else can cause pain behind the knee?
Baker’s cyst
A Baker’s cyst is a fluid-filled structure connected with the knee joint. It may cause pressure, tightness or a palpable swelling in the popliteal fossa. It is often a consequence of an intra-articular problem rather than a separate disease.
Meniscus and cartilage
A lesion of the posterior horn of the medial meniscus or degenerative joint disease can cause pain with deep squatting, twisting or rising from a chair. Locking, recurrent effusion or a clear loss of extension point the assessment towards intra-articular pathology.
Other tendons and muscles
Pain may arise from the gastrocnemius, popliteus or other hamstring structures, including after an acute injury. The clinical pattern and mechanism help separate these conditions from chronic semimembranosus tendinopathy.
Deep vein thrombosis
Unilateral calf swelling, warmth, pain or a sudden increase in calf circumference should not be attributed to a tendon problem without proper assessment. Suspected deep vein thrombosis requires urgent evaluation with an appropriate vascular pathway; this is not the same examination as routine musculoskeletal ultrasound.
What does the clinical examination involve?
The examination includes precise localisation of tenderness, range of motion, effusion, knee stability, meniscal testing and muscle strength. The clinician also checks whether symptoms can be reproduced with resisted knee flexion and other movements that load the hamstrings.
In a real-world ultrasound study of 667 adults with lower-limb pain co-authored by Tomasz Poboży, abnormalities at the semimembranosus insertion were identified in 19 patients. This was not a population prevalence study—the participants had been referred for ultrasound—but it confirms that this structure is a genuine and visible potential pain source.
When is ultrasound useful?
Ultrasound can demonstrate tendon thickening, altered echotexture, insertional changes, fluid in a neighbouring bursa and a Baker’s cyst. It also allows the imaging finding to be matched to the exact site of symptoms and compared with the opposite side. As with all tendon imaging, structural change does not automatically mean that the abnormality is the cause of pain.
Musculoskeletal ultrasound does not replace venous Doppler ultrasound when thrombosis is suspected, and it does not survey the intra-articular structures as comprehensively as MRI.
When is MRI appropriate?
MRI may be useful when the source of pain remains unclear, when a meniscal, cartilage, bone or deeper soft-tissue lesion is suspected, or when symptoms fail to improve despite appropriately managed treatment. MRI is not automatically the first investigation for every suspected tendinopathy.
How is it treated?
Treatment usually starts without surgery. The main task is to reduce the loading pattern that keeps provoking symptoms while progressively rebuilding the tendon’s capacity to tolerate work.
- temporarily reduce the movements that most strongly provoke pain without stopping all activity;
- progressively strengthen the hamstrings and the rest of the lower limb;
- work on hip, knee and trunk control;
- gradually reintroduce running, hills and changes of pace;
- choose pain treatment in the context of comorbidities and current medication.
Progress is judged by function and by the next-day response. Mild, short-lived discomfort during rehabilitation may be acceptable, whereas a clear increase in symptoms lasting into the next day usually means that the loading dose was too high.
Are injections or surgery needed?
Evidence for injections in this specific condition is limited. If the pain is shown to arise from an adjacent bursa rather than the tendon itself, a targeted ultrasound-guided procedure may be considered in selected cases. An intratendinous injection should not be performed simply because imaging describes tendon change.
Surgery is rarely required and is generally reserved for persistent symptoms with a well-supported diagnosis after a substantial course of appropriate non-operative care. The surgical literature is based largely on small case series.
Red flags
- sudden calf swelling, warmth and pain, particularly after surgery, immobilisation or a long journey;
- shortness of breath, chest pain or coughing up blood;
- a sudden pop, major bruising and loss of strength after injury;
- a hot, red knee with fever or systemic illness;
- a locked knee or inability to regain extension;
- a cold, pale or blue foot, progressive numbness or weakness.
Key point for an orthopaedic surgeon
The semimembranosus tendon is one possible cause of posterior knee pain, especially when tenderness is medial and symptoms increase with hamstring loading. The diagnosis should not be made from the location of pain alone. Intra-articular disease, Baker’s cyst and vascular causes must be considered when the clinical pattern suggests them.
References
- Poboży T, Janowski K, Domański P, Michalak K, Poboży K, Domańska-Poboża J, Konarski W, Chuść I, Kielar M. The Hidden Burden of Entheseal Pathology in Lower-Limb Pain: A Real-World Ultrasound Study of 667 Adults. Mayo Clin Proc Innov Qual Outcomes. 2026;10(4):100734. DOI: 10.1016/j.mayocpiqo.2026.100734.
- Bylund WE, de Weber K. Semimembranosus tendinopathy: one cause of chronic posteromedial knee pain. Sports Health. 2010;2(5):380–384. DOI: 10.1177/1941738109357302.
This material is educational. Identifying the cause of posterior knee pain requires the symptoms, clinical examination and appropriately selected imaging to be considered together.
Content prepared by: Tomasz Poboży - orthopaedic surgeon.