Fibrotic Myopathy

Gracilis Contracture, Semitendinosis Myopathy

Fibrotic Myopathy is thought to be an uncommon acquired, disorder which probably occurs to some degree after any muscle contusion that heals primarily by scar tissue.  The whole muscle or part of the muscle is replaced with fibrous connective tissue within the semitendinosus and, occasionally, the quadriceps muscles of the hindleg.  When most or all of the traumatised muscle is replaced by fibrous scar tissue that contracts to an inelastic band, it is termed fibrotic myopathy or muscle contracture.

Characterized by or affected with fibrosis (the formation of fine scar-like structures that cause tissues to harden and reduces the flow of fluids through these tissues. )
Muscle Disease
Prolonged shortening of the muscle or other soft tissue around a joint, preventing movement of the joint.

Male German Shepherds with an age range from 8 months to 9 years are most commonly affected. Other affected breeds include Doberman Pinscher, Rottweiler, St. Bernard, Boxer, and Old English Sheepdog.  The cause for the disorder is unknown and  could be associated with repeated microtrauma, vascular compromise, primary neuropathy and it can even be immune mediated.  Active dogs seem to be susceptible to this disorder, and recent studies in dogs suggest that fibrotic myopathy may be related to muscle injury from excessive activity, including jumping and sprinting that can lead to muscle strain, with a suggested sequence of inflammation, edema, localized hemorrhage, and eventually fibrosis.  Most patients suffer some form of trauma weeks to months before the contracture is present.  The clinical signs include lameness, pain, weakness, decreased range of motion, a firmness noted throughout the entire muscle, and usually a characteristic gait.

1. Levator Nasolabalis muscle
2.  Jaw/nose muscle
3. Masseter muscle
4.   Parotido Auricularis
5.   Outside masseter
6.   Yoke muscle
7.   Temporal muscle
8. Chest/tongue/leg muscle
9.   Supraspinatus
10. Brachialis
11. Brachiocephalicus muscle
12. Pectoral muscle
13. Trapezius muscle
14. Supraspinatus muscle
15. Shoulder - neck muscles
16. Deltoid muscle
17. Triceps muscle
18. Extensor Carpus
19. Common Digital extensor
20. Lateral Digital extensor
21. Extensor Carpi Ulnaris
22. Flexor Carpi Ulnaris
23. Extensor carpi radialis
24. Lumbo Dorsal Fascia
25. Pectoral muscle
26. Aponeurosis muscle
27. Obliqus Abdominus Externus
28. Gluteus medius muscle
29. Tensor Fasia muscle
30. Sartorious muscle
31. Gluteus Maximus
32. Biceps Femoris muscle
33. Semitendinous muscle
34. Anterior tibial muscle
35. Long Digital Extensor
36. Tibialis
37. Flexor digitorum pedis
38. Flexor Hallicus Longus

Affected animals are usually unable to extend the hip, knee (stifle) or ankle (hock) joints very well.  So they walk short-strided and at the point that the leg should be in extension, it quickly pulls back up into flexion.  Often the paw and knee will turn in a bit when flexion occurs.  Increased angulation (flexion) at the stifle in normal German Shepherds may predispose these dogs to increased hamstring stress during physical activity. While onset in some dogs is acute (compatible with grade 2 or 3 muscle injury), the lameness appears to be insidious in most dogs (compatible with chronic or grade 1 muscle strain). Apart from semitendinosis and gracilis muscles, fibrous bands may occur in quadriceps muscles, biceps femoris, and semimembranosus in hind limbs, as well as in supraspinatus and infraspinatus muscles in dogs. A palpable band has also been found in the teres minor muscle.  Duration of signs may range from weeks or several years. 

Prognosis is guarded to poor since the condition in dogs tends to recur within several months following surgical resection, or transection, partial excision, or complete resection of the affected muscle to remove the fibrous band of tissue. Non-surgical treatment includes the managing any signs of pain and major uncoordination(e.g., the use of corticosteroids, non-steroidal inflammatory drugs, or acupuncture) but can be ineffective in many cases. Most dogs appear to have no pain once the disease process has reached its hight, but if the twist of the joint is far enough, these pets will have more trouble. Non-surgical rehabilitation, including therapeutic ultrasound and cross-fiber friction massage, may provide mild improvement in some dogs (slight increase in range of motion of the stifle and less crossing over of pelvic limbs). If fibrotic myopathy is causally related to muscle strain, appropriate preventive measures might include stretching, warm up exercises, and gradual build up to more intensive activities. Muscle contractures of the forelimb often respond better to treatment and carry a better prognosis than muscle contractures of the hindlimb.

Infraspinatus Contracture
Occurs in large active middle aged dogs, tethering of normal shoulder motion, circumduction of the limb.  There is palpable atrophy of the muscle.  Proposed to be secondary to injury causing fibrosis and functional shortening of the muscle.  Treatment is surgical - infraspinatus tenotomy.

Quadriceps Contracture
Occurs in actively growing dogs < 6months old following fracture and distal femur with voluntary or enforced immobilisation.  The result is prolonged hyperextension of stifle muscle contracture and adhesions.  It is best prevented, but if occurs, early recognition is essential as prognosis once advanced is poor.  Physiotherapy resposes have been good.

Gracilis Contracture
Occurs in active, middle aged, large dogs, secondary to injury like infraspinatus contracture.  Affected dogs can retain normal function but have a characteristic jerky gait and shortened stride.  Affected dogs tend to have guarded long-term outlook owing to recurrence after surgery.
Animal physiotherapy By Catherine M. McGowan, Lesley Goff, Narelle Stubbs

Sartorius muscle contracture
Occurs in middle aged, active, large dogs and presents as hind limb lameness.  Contracture of the sartorius muscle in dogs is seemingly rare and similar to gracilis muscle contracture with which it may be confused. Differentiation requires knowledge of muscular anatomy, careful palpation, and surgical inspection.   Sartorius muscle contracture can be treated by tenectomy or removal of contracted muscle tissue, however, long-term outcome suggests the need to develop approaches that prevent recurrence caused by scarring of transected tissues.

Muscle contractures causing varying degrees of lameness commonly occur from skeletal muscle fibrosis, the result of injury such as that caused by circulatory insufficiency, infection, autoimmune reaction, or trauma. Quadriceps contracture, whether congenital or acquired, is treated by sectioning the cordlike fibrotic muscle group by "Z" plasty, resulting in lengthening it enough to allow the knee to assume a normal standing angle. Adhesion of the muscle group to a large femoral callus (muscle tie down) may occur and require additional surgical correction. Infraspinatus contracture results in a typical foreleg deformity and change in gait. Surgical repair by tenotomy is usually followed by rapid return to normal. Gracilis contracture, though common in racing greyhounds, is not commonly reported in pet dogs. Surgical excision of the entire affected muscle mass is curative.

Fibrotic myopathy of the semitendinosus muscle is associated with a palpable thickened fibrous band that may extend from the tuber ischii to the tibia within the belly of the semitendinosus muscle. Tight fibrous cords are also palpable in affected gracilis muscles extending from the midline of the pelvis to the caudomedial aspect of the stifle. In dogs with gracilis and/or semitendinosus muscle involvement, the hind-limb gait is characterized by a shortened stride with a rapid, elastic medial rotation of the paw, external rotation of the hock, and internal rotation of the stifle during the mid-to-late swing phase of the stride. Kinematic analysis indicate that the range of motion of the stifle is reduced. The gait anomaly results from restricted abduction of the coxofemoral joint and reduced extension of the stifle and hock. Note that the lameness is best appreciated at the trot. Bilateral involvement (of the gracilis or semitendinosus muscle) is commonly encountered, with reports varying from 39% to 61% of affected dogs, while both muscles may be involved ipsilaterally or contralaterally. Histologically, the band consists of an abundance of dense collagenous connective tissue, with a distinct interface between connective tissue and muscle bundles. Morphological studies in our laboratory or in others have not identified primary muscle or peripheral nerve disease, although variable myofiber degeneration around the periphery of the fibrotic band has been seen occasionally, sometimes associated with mild mononuclear cell inflammation and focal hemorrhage. The replacement of muscle fibers with dense collagenous connective tissue results in a mechanical lameness resulting from failure to fully extend the limb. Neurological examination is usually normal; however, pressure applied to the affected muscle, abduction of the coxofemoral joints of affected limbs, and extension of stifle/talocrural joints in affected limbs may elicit pain. Serum CK levels may be normal or moderately elevated in some animals. Absence of myoelectrical activity in the band during EMG evaluation is consistent with total replacement of muscle fibers by dense connective tissue; however, spontaneous EMG activity in the vicinity of the band suggests recent muscle damage. In occasional dogs, fibrillation potentials and rare myotonic discharges have been recorded. Imaging techniques have been used to identify the intramuscular fibrous cords in people. Soft-tissue swellings associated with the myotendinous areas of affected muscles may be detected on radiographs, and two-dimensional ultrasonography in one dog revealed increased size and reduced homogeneity of the gracilis muscle, with an enlarged tendon of insertion compared to the normal muscle.

Fibrotic myopathy is a chronic, progressive, idiopathic, degenerative disorder affecting the semitendinosus, gracilis, quadriceps, infraspinatus, and supraspinatus muscles, primarily in dogs. The cause is unknown. Affected muscles are characterized by contracture and fibrosis. Normal tissues are replaced by dense collagenous connective tissue. Clinical signs include a nonpainful, mechanical lameness. Neurologic function is normal. Surgical release of affected tissues via tenotomy, myotenotomy, Z-plasty, or complete resection produces inconsistent results. Prognosis is guarded due to recurrence.

Textbook of Small Animal Surgery By Douglas H. Slatter

Gracilis Contracture in Dogs
Fibrotic Myopathy
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Fibrotic Myopathy in a German Shepherd Dog
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Physical Therapy
Infraspinatus Contracture
Sartorius Muscle Contracture in a GSD
Is Fibrotic (Gracilis) Myopathy due to Muscle Strain in Physically Active Dogs?
Eva is back to work after being treated for fibrotic myopathy

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The above information is simply informational. It's intent is not to replace the advice of a veterinarian nor to assist you in making a diagnosis of your pet. Please consult with your own veterinarian for confirmation of any diagnosis. Your pets life may depend on it.