6-year-old male Border Collie

Radiographic Findings:

• Osteophytes were associated with the lateral fabella bilaterally, moderate on the left and marked on the right side. No joint effusion or other periarticular osteophyte formation was present.

MRI Findings:

• There is marked STIR hyperintensity and contrast enhancement of a poorly marginated area (roughly 3.8 x 2.0 x 2.3cm) at the origin of the lateral head of the gastrocnemius in the right stifle. This area shows moderate contrast enhancement. The lateral fabella is larger and more irregular than normal as was seen on the radiographs.
• Similarly, the lateral fabella in the left stifle is also larger and more irregular than normal but the lateral head of the gastrocnemius is normal on all sequences consistent with no active inflammation in this limb at this time
• All intra-articular structures are normal in both stifles. No joint effusion, cruciate or meniscal tears are present.

Chronic/active musculotendinopathy at the tendon of origin of the lateral head of the gastrocnemius.

This condition has been described recently in shepherding type dogs such as Border Collies. Indeed in a recent paper, 8 of 9 dogs were Border Collies. The musculotendinous changes are not visible on radiographs. Only the secondary mineralised changes associate with the fabellae or mineralisation within the damaged soft tissue itself are seen radiographically. MRI is used to evaluate the extent of damage to the surrounding muscle and tendon. Treatment is usually conservative with rest, pain management, massage, therapeutic ultrasound, etc.

REFERENCES

1. Avulsion of the lateral head of the gastrocnemius muscle in a working dog: Prior JE, Vet Rec 1994, 134, 382-383
2. Avulsion of the origin of the gastrocnemius muscle: Ting et al, JAVMA 2006, 228, 1497-1498
3. MRI features of gastrocnemius musculotendinopathy in herding dogs: Stahl et al, Vet Radiol Ultrasound 2010, 51, 4, 380-385