Injuries reported in the literature, often referred to as ‘tennis leg’, involve tears of the gastrocnemius muscle rather than the tendon.1–4
The case we now present demonstrated an interstitial partial tear of the tendon and partial avulsion form its insertion site. This case shows a different type and appearance of a partial tear of the medial head of gastrocnemius tendon compared to the case we previously reported,5
which showed a longitudinal split in the distal gastrocnemius tendon at the musculotendinous junction. It had presented as a painless lump with no clear history of trauma. The current case also had an unclear history of trauma and presented with symptoms suggestive of medial meniscus tear. It was shown at imaging to be a proximal tear of the tendon close to the insertion site into the posterior aspect of the femoral condyle. The tear was interstitial rather than a discreet split in the tendon. The two different patterns of tear and different sites suggest therefore that isolated tears of the medial head of the gastrocnemius tendon may take on various forms and are likely to be underreported. Other injuries to consider in the differential of posterior medial knee pathology include avulsion fractures of the medial head of gastrocnemius muscle.
Machara et al
reported the first recorded case of avulsion fracture of the medial head of gastrocnemius muscle.6
This followed an acute skiing injury. Plain radiographs revealed a bone fragment in the popliteal fossa. MRI revealed no tear to the gastrocnemius muscle, but it had avulsed from its insertion along with a bone fracture avulsion fragment.6
Unlike the case reported by Machara et al
, the abnormality in our case was confined only to the tendon which demonstrated partial tear proximally. The muscle was normal. As the patient did not present with a clear history of trauma, the other differential diagnosis we should have considered is calcifying tendonitis of the gastrocnemius tendon. Iguchi et al7
reported three cases of isolated non-traumatic calcifying tendonitis of the medial head of gastrocnemius tendon presenting with pain in the posterior medial aspect of the knee.
Of important consideration also, and highlighted by our two cases, is the role of imaging. During assessment of the tendon with ultrasound in the case we present here, we encountered difficulties due to anisotropy. Anisotropy in ultrasound happens when the structure being imaged is at an angle other than 90° to the incident ultrasound beam emitted from the probe. Anisotropy occurred because the tendon to the medial head of the gastrocnemius takes a curvilinear direction as it courses from the muscle to the medial femoral condylar attachment. It therefore depends on the skill of the ultrasound operator to be aware of this and take corrective measures such as angling the probe to be able to see the tendon. The appearance of anechoic sections of the tendon as a result of anisotropy were an artefact that suggested complete tendon disruption. MRI did not suffer from this artefact and was therefore the imaging modality of choice in this case. In the previous case,5
however, the tear being in the straight (distal, musculotendinous) portion of the tendon, anisotropic artefact did not occur and was therefore not an issue. Hence ultrasound was an excellent imaging tool for the assessment of that portion of the tendon. The case we present here also had bone abnormalities which would not have been seen if ultrasound alone had been done. MRI demonstrated the subchondral bone oedema.
To conclude, isolated medial head of gastrocnemius tendon tears may present in various forms and are likely to be under-reported. In order to identify these injuries, diagnostic imaging modalities should be carefully considered and appropriately selected in order to show all relevant abnormalities. Both MRI and ultrasound have advantages and disadvantages depending on the specific abnormalities to be demonstrated.
- A tear of the medial head of gastrocnemius tendon should be considered in patients presenting with signs suggestive of medial meniscus tear or pain behind the medial aspect of the knee joint.
- MRI is the investigation of choice, particularly in suspected proximal tendon injury or avulsion. It demonstrates bone contusion and oedema at the site of tendon traction injury. It is essential therefore that the field of view of the MRI includes the tendon insertion site which lies proximal and superior to the knee joint at the level of the femoral metaphysis and just above the medial femoral condyle.
- During assessment of the tendon with ultrasound, the appearance of anechoic sections of the tendon as a result of anisotropy were an artefact that suggested complete tendon disruption. Anisotropy occurred because the tendon to the medial head of the gastrocnemius takes a curvilinear direction as it courses from the muscle to the medial femoral condylar attachment. Anisotropy in ultrasound happens when the structure being imaged is at an angle other than 90° to the incident ultrasound beam emitted from the probe. It therefore depends on the skill of the ultrasound operator to be aware of this and take corrective measures such as angling the probe to be able to see the tendon.