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As veterinarians, animal physical therapists, veterinary technicians, and rehabilitation professionals, we often encounter complex musculoskeletal conditions in our canine patients. One such condition, fibrotic myopathy of the hamstring muscles, is a rare but debilitating disease primarily affecting young, male, working-line German Shepherds, though it can occur in other breeds like Belgian Malinois, St. Bernards, and Rottweilers. A recent study published in Frontiers in Veterinary Science (Birdwhistell et al., 2025) introduces a promising, non-invasive, and cost-effective screening method—the hamstring stretch angle measurement—that could revolutionize how we diagnose and monitor this condition. Here’s what you need to know.

What is Fibrotic Myopathy?

Fibrotic myopathy is characterized by the replacement of normal muscle tissue with fibrotic, inelastic tissue, leading to muscle contracture and reduced flexibility. In dogs, it commonly affects the hamstring muscles (gracilis, semimembranosus, or semitendinosus), which are critical for stifle flexion and hip extension—key movements for propulsion. The condition manifests as a distinctive gait abnormality, including a shortened stride, rapid medial paw rotation, external hock rotation, and internal stifle rotation during the swing phase. Palpation reveals a firm, fibrous band in the affected muscle, and while mechanical lameness is the primary complaint, pain is typically absent.

The etiology remains elusive, with potential causes including muscle trauma, fractures, compartment syndrome, neuropathy, infections, immobilization, or immune-mediated processes. Treatment options, both surgical (e.g., tenotomy or myectomy) and medical (e.g., extracorporeal shockwave therapy, stem cell injections, or rehabilitation therapies), have shown limited success, with surgical interventions often leading to persistent or recurrent lameness.

Challenges in Diagnosis

Traditionally, musculoskeletal ultrasound has been the gold standard for diagnosing fibrotic myopathy. While effective, it is expensive, often requires sedation, and demands specialized expertise. These barriers can delay diagnosis and make routine monitoring challenging, especially in busy veterinary practices or rehabilitation settings. The need for a simpler, more accessible diagnostic tool is clear.

The Hamstring Stretch Angle: A Game-Changer

The study by Birdwhistell et al. proposes using goniometry to measure the hamstring stretch angle as a fast, non-invasive, and inexpensive screening method. Goniometry, already widely used to assess joint mobility in dogs and other species, involves measuring the angle of maximum stifle extension during hip hyperflexion. The study focused on three groups: unaffected German Shepherds, unaffected retrievers (Golden and Labrador), and German Shepherds with confirmed fibrotic myopathy.

Key Findings:

•  Significant Differences in Stretch Angles: Affected German Shepherds had significantly smaller hamstring stretch angles (mean: 102° for the more affected limb, 116° for the less affected) compared to unaffected German Shepherds (mean: 147°) and retrievers (mean: 147°). The difference was approximately 37°, highlighting a clear distinction.

•  High Sensitivity and Specificity: A receiver operator characteristic (ROC) curve identified a cutoff value of 136°, with 100% sensitivity and specificity for detecting fibrotic myopathy, making it an ideal screening tool.

•  Practical Application: Measurements were taken using a standard 12-inch plastic goniometer, with dogs in lateral recumbency. The process is straightforward, requiring minimal equipment and no sedation for unaffected dogs (though some affected dogs were sedated for unrelated reasons).

Why This Matters for Veterinary Professionals

The hamstring stretch angle measurement offers several advantages for veterinarians, rehabilitation therapists, and technicians:

•  Accessibility: Unlike musculoskeletal ultrasound, goniometry requires only a basic goniometer, which is affordable and widely available in veterinary clinics and rehabilitation centers.

•  Non-Invasive: The procedure is quick and does not require sedation in most cases, reducing stress for the patient and simplifying the workflow.

•  Screening and Monitoring Potential: The study establishes reference ranges for hamstring stretch angles in unaffected German Shepherds and retrievers, providing a baseline for comparison. A stretch angle below 136° can prompt further diagnostic workup, such as ultrasound, to confirm fibrotic myopathy.

•  Rehabilitation Implications: For rehabilitation professionals, this tool could help track disease progression or response to therapies like photobiomodulation, therapeutic ultrasound, or controlled exercise, though further studies are needed to validate its use for longitudinal monitoring.

Limitations to Consider

While promising, the method has some limitations:

•  Inter-Observer Variability: The study notes that measurements for affected dogs were collected retrospectively by different clinicians, and inter- and intra-rater reliability testing is still needed.

•  Sedation Effects: Most affected dogs were sedated during measurements, which may overestimate stifle extension angles due to muscle relaxation.

•  Breed-Specific Challenges: Variations in joint mechanics and difficulty maintaining contact with bony landmarks in some breeds may affect measurement accuracy.

•  Exclusion of Hip Abduction: The study simplified the measurement by excluding hip abduction, which is typically part of hamstring stretching. This may limit the assessment of certain muscle components but improves standardization.

How to Implement in Practice

To incorporate the hamstring stretch angle measurement into your practice:

•  Equipment: Use a 12-inch plastic goniometer (e.g., Baseline goniometer, Fabrication Enterprises).

•  Positioning: Place the dog in lateral recumbency. Align the goniometer’s center on the stifle, with one arm along the greater trochanter and the other along the lateral malleolus.

•  Measurement: Extend the stifle to its maximum while maintaining maximum hip flexion (before pelvic ventroflexion). Record the angle bilaterally.

•  Interpretation: Compare the angle to the 136° cutoff. Angles below this threshold suggest fibrotic myopathy and warrant further investigation.

•  Training: Ensure staff are trained in consistent measurement techniques to minimize variability. Future studies on inter-rater reliability will help refine protocols.

Looking Ahead

This study marks a significant step toward simplifying the diagnosis of fibrotic myopathy, but more research is needed. Future studies should focus on:

•  Validating the hamstring stretch angle for long-term monitoring of disease progression or treatment outcomes.

•  Establishing inter- and intra-rater reliability to ensure consistency across clinicians.

•  Exploring its applicability in other breeds and conditions affecting hamstring flexibility.

•  Investigating the impact of sedation on measurements to refine protocols for unsedated patients.

Conclusion

The hamstring stretch angle measurement is a practical, non-invasive, and cost-effective tool that could transform how we screen for fibrotic myopathy in dogs, particularly in high-risk breeds like German Shepherds. For veterinarians, physical therapists, and rehabilitation professionals, it offers a quick way to identify potential cases, streamline diagnostics, and enhance patient care. By integrating this method into your practice, you can improve early detection and support better outcomes for dogs with this challenging condition.

For more details, refer to the full study: Birdwhistell KE, Miscioscia E, Montalbano C, Repac J (2025). The hamstring screen and the following tool for canine fibrotic myopathy. Front. Vet. Sci. 12:1600602. doi: 10.3389/fvets.2025.1600602.