Pes anserinus tendinopathy

Pes anserinus tendinopathy refers to pain located on the anteromedial aspect of the knee, at the common insertion of several tendons on the inner surface of the tibia. The “pes anserinus” (literally “goose’s foot”) essentially corresponds to the junction of the tendons of three muscles: the sartorius, the gracilis and the semitendinosus.

In the immediate vicinity of this insertion lies the pes anserine bursa, a small structure that reduces friction between the different tissues. This is why the term pes anserine pain syndrome is often more accurate than “pes anserinus tendinopathy”: the pain may in fact come from the tendons themselves, from the bursa, from the interface between these structures, or more broadly from the medial tissues of the knee.

Distinguishing between bursitis and tendinopathy is sometimes clinically difficult, as the two structures are anatomically extremely close.

The pes anserinus is formed mainly by the tendons of three muscles that converge on the anteromedial aspect of the proximal tibia. The sartorius, a superficial muscle, contributes to hip flexion, abduction and external rotation as well as knee flexion. The gracilis, a medial thigh muscle, contributes to hip adduction, knee flexion and medial rotation of the leg. The semitendinosus, one of the hamstrings, contributes to hip extension, knee flexion and medial rotation of the leg.

The actual anatomy is, however, more variable than a simplified representation would suggest: recent anatomical studies show numerous variations in the configuration and tendon expansions of the pes anserinus.

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The pes anserine bursa

Beneath the pes anserinus tendons lies a synovial bursa, the pes anserine bursa, whose role is to help the different structures glide over one another. It can become painful and inflamed in certain situations — this is then referred to as anserine bursitis. This distinction is important because pain at the pes anserinus does not automatically mean that the tendon is diseased.

Function and biomechanics

The three pes anserinus muscles have different but complementary functions: they contribute to knee flexion, medial rotation of the leg, dynamic stabilisation of the knee, lower limb control and stabilisation of the pelvis and hip. The tendinous and fascial structures of this region form a genuine stabilising complex for the medial aspect of the knee.

The pes anserinus is loaded during movements that combine knee flexion, medial rotation, knee stabilisation and hip control. Stresses increase in particular during running, uphill sections, stairs, changes of direction, lateral movements, single-leg exercises and repeated knee flexion movements; overload may affect the tendons directly or increase the stresses placed on the bursa.

Pes anserine pain syndrome affects both active and non-active people: it can also appear in a context of everyday mechanical overload or associated knee disease. It is frequently found in association with knee osteoarthritis, excess weight, diabetes or older age, although these factors should not be interpreted as sole causes.

As with other tendinopathies, there is usually an imbalance between the load applied and the capacity of the tissues to withstand it. This can appear after an increase in mileage, a return to sport, an increase in elevation gain or stairs, a change in running technique, an increase in strength sessions or repeated changes of direction — often gradually, without any specific trauma.

Tendinopathy or bursitis?

In tendinopathy, the pain comes mainly from the tendon structures and is usually triggered by stretching or contracting the muscles involved. In bursitis, the pain comes mainly from the bursa and may be particularly sensitive to local pressure, to contact with certain surfaces or during certain repeated movements. In practice, the two phenomena may coexist — hence the preference for the term “pes anserine pain syndrome” — and conservative treatments are in any case largely similar in both situations.

Contributing factors

Load-related factors: sudden increase in mileage, return to running, increase in elevation gain, more hill sessions, more stairs, more strength sessions.

Biomechanical factors: poor lower limb control, hip muscle weakness, hamstring strength deficit, poor single-leg control, increased medial knee stress.

Associated factors: knee osteoarthritis, excess weight, diabetes, older age — although these should not be interpreted as sole causes.

The patient often describes pain on the inner side of the knee, a few centimetres below the joint, that has come on gradually. It is often triggered by running, stairs, uphill sections, squats or single-leg movements; in some cases, it is also present at rest or at night — although significant or atypical night pain should prompt a search for another cause.

The pain is usually medial and slightly below the joint line, often located a few centimetres below the medial joint line of the knee — a location that helps distinguish it from meniscal, ligament or patellofemoral pain, although symptoms may overlap. In runners, the pain may appear during the run, after the run, the next day, or on uphill or downhill sections: a recent change in volume or elevation gain should always be looked for. Stairs can also reproduce the pain, particularly going up, going down or after several flights.

Clinical examination

The examination should establish the precise location of the pain, tenderness on palpation and pain on contraction of the pes anserinus muscles, knee mobility, the strength of the quadriceps, hamstrings and hip muscles, lower limb control, as well as meniscal, ligament and neurological signs: the diagnosis should not rest solely on a tender spot.

Palpation looks for pain specifically at the pes anserinus insertion, comparing with the opposite side. However, the diagnostic accuracy of the clinical examination alone is imperfect: a study comparing clinical diagnosis with MRI findings found relatively low sensitivity and specificity. Contraction tests targeting the semitendinosus, gracilis and sartorius (resisted knee flexion, sometimes combined with internal rotation of the leg) may aim to reproduce the usual pain.

Examination of the hip looks for abductor weakness, poor pelvic control, pain or limited mobility — a proximal deficit can alter the stresses placed on the knee during running or single-leg movements. The squat, particularly the single-leg squat, makes it possible to assess pain, knee stability, lower limb alignment, hip control and tolerance to flexion. In runners, gait analysis mainly looks for recent changes in load (volume, speed, elevation gain, shoes, hills), which are often more decisive than looking for a biomechanical abnormality in isolation.

Surgery is very rarely necessary. It may be considered only in very specific situations, after diagnostic confirmation, prolonged conservative treatment and failure of properly conducted rehabilitation. Most patients should be managed without surgery.

Recovery time varies: a mild form may improve within a few weeks, whereas a chronic form may require several months. It depends in particular on how long the symptoms have been present, the sporting load, the presence of associated bursitis, the existence of osteoarthritis, the quality of rehabilitation and the ability to adjust loads. Persistent pain does not necessarily mean that the tendon is severely damaged.

Preventing recurrence relies mainly on a reasonable progression of load, regular strengthening, unilateral work, strengthening of the hip, hamstrings and quadriceps, and a gradual return to hills and changes of direction. Sudden changes in volume or elevation gain should be particularly avoided.