Shoulder lameness in the dog- unraveling the mystery with arthroscopy S.T. Kudnig BVSc, MVS, MS, FACVSc, DACVS Melbourne Veterinary Referral Centre 70 Blackburn Road, Glen Waverley, Victoria, 3150. Lameness due to pathology within the shoulder can be one of the most difficult causes of lameness for clinicians to diagnose. The majority of lameness is secondary to soft tissue injuries and excepting shoulder OCD, radiographs are invariably non specific and frequently do not provide a diagnosis. Whilst MRI can be utilized to provide images of the soft tissue structures in the shoulder, shoulder arthroscopy provides both diagnostic information and therapy and is therefore the most expedient and cost effective means of treating shoulder lameness in dogs. Shoulder joint anatomy and biomechanics The shoulder is a very mobile, spheroidal joint capable of adduction, abduction, circumduction and rotation, with the primary motion being flexion and extension. The stability of the shoulder is provided by both passive mechanisms (do not require energy expenditure by muscle) and active mechanisms (do require energy expenditure by muscle). The normal standing angle is 135 o and the glenoid fossa is approximately? the size of the humeral articular surface. Weight bearing forces are essentially concentrated in the middle and caudal areas of the glenoid cavity. It was previously believed that cuff muscles were responsible for maintaining joint stability however it is now established that the joint capsule and glenohumeral ligaments play a significant role in joint stability. Passive mechanisms of joint stability include the medial (MGHL) and lateral (LGHL) glenohumeral ligaments, the joint capsule, the concavity of the joint enhanced by the articular cartilage and the glenoid labrum, compression between articular surfaces, and the limited synovial fluid acting to stabilize the joint with cohesion between the articular surfaces. The MGHL extends downward from the medial surface of the supraglenoid tubercle of the scapula, across the shoulder joint to attach to the joint capsule at the junction of the humeral neck and the lesser tubercle, while the LGHL extends downward from the lateral rim of the glenoid cavity to the neck of the humerus and to the caudal portion of the greater tubercle. Active mechanisms of joint stability include the biceps, subscapularis, supraspinatus, infraspinatus and the teres minor muscles ( rotator cuff in humans). The muscle insertions blend with the glenohumeral capsule and ligaments and by selective contraction of these muscles the tension in the capsule and glenohumeral ligaments can be adjusted thus producing dynamic ligaments. By contracting together, the cuff muscles press the humeral head into the glenoid fossa providing a secure scapulohumeral link. By contracting selectively, cuff muscles can resist displacing forces resulting from the contraction of the principal shoulder muscles
Shoulder lameness in dogs The most common causes of shoulder lameness in dogs include shoulder instability, OCD of the caudal aspect of the humeral head and lesions of the biceps tendon. Arthroscopy has become the diagnostic and therapeutic tool for shoulder conditions as it provides excellent visualization of intra-articular structures with a minimally invasive approach. Arthroscopy of the shoulder Indications for shoulder arthroscopy include OCD of the humeral head, shoulder instability, tenosynovitis of the biceps brachii tendon, rupture of the biceps brachii tendon, injury to the subscapularis tendon and articular fractures. Shoulder arthroscopy has allowed the diagnosis and treatment of shoulder lameness that have been previously very difficult to diagnose. The biceps tendon (Figure 1), the Y shaped medial glenohumeral ligament (MGHL) (Figure 2) and the caudal aspect of the humeral head are well visualized. a MGHL a Figure 1. The origin of the biceps tendon from the supraglenoid tubercle is well visualized with the arthroscope. The arthroscope can be directed down the bicipital groove to assess the tendon as it passes through the groove. Figure 2. The medial glenohumeral ligament (MGHL) is well visualized with the arthroscope (a) b a Figure 3. Caudal aspect of the humeral head (a) and glenoid cavity (b).
Shoulder instability Shoulder instability is a frequently under diagnosed condition causing chronic lameness in dogs. Repetitive strain injury can cause fatigue-failure of the glenohumeral ligaments and impairment of proprioceptive function of the capsule. Orthopaedic examination can produce a shoulder drawer sign and increased abduction angle. Arthroscopic evaluation can visualize the glenohumeral ligaments and the integrity can be assessed with a probe. This takes away the uncertainty of making a diagnosis of shoulder instability based on orthopaedic examination alone. Medial shoulder instability is a common disease in dogs associated with tearing of the MGHL. Diagnosis is by palpation under sedation (increased abduction of the shoulder joint) and arthroscopic visualization of a torn, incompetent MGHL. Treatment options for medial shoulder instability include arthroscopic thermal capsulorraphy (collagen shrinkage) using a radiofrequency ablation (RF) unit (See Figures 4 and 5) or placement of medial prosthetic sutures. Figure 4. Evaluation of an incompetent MGHL Figure 5. Thermal capsulorraphy using an RF probe Biceps tendon injury The biceps tendon originates at the supraglenoid tubercle and glenoid labrum, on the cranial portion of the glenoid. The tendon courses across the cranio-medial aspect of the humeral head in the inter-tubercular groove and continues down the humerus becoming musculotendinous at this point. The origin of the tendon is intra-articular but extrasynovial. The humerus moves on the tendon rather than the tendon moving within the groove. The synovial pouch extends from the shoulder joint to lie in the intertubercular groove for the greater part of its extent. Conditions affecting the biceps tendon include partial or complete rupture, avulsion of the biceps tendon from the supraglenoid tubercle, tendinitis, mid-substance tears, bipartite tendon, tendon luxation and tenosynovitis. Bicipital tenosynovitis is the inflammation of the biceps tendon of origin, its tendon sheath, and the bicipital bursa within the intertubercular groove of the humerus. The inflammation can be secondary to trauma, joint mice entrapment in the bicipital tendon sheath or secondary to intra-articular disease such as glenohumeral instability. The cause of primary trauma is unknown with proposed causes including overuse and chronic repetitive trauma. Chronic repetitive trauma results in biomechanical stress and an inflammatory response. Gross pathological changes include hyperemia of the bursa leading to joint
effusion, chronic synovitis causing synovial hyperplasia of the bursa, chondromalacia of the intertubercular groove with osteophyte formation at its margins, and metastatic calcification of the biceps tendon. Adhesions between the tendon and the tendon sheath may develop. Hypoxia of the tendon resulting from a damaged blood supply promotes chondroid metaplasia and calcification of the biceps tendon. The normal synovial space and smooth gliding surface of the intertubercular groove is typically replaced by proliferative synovium and in most instances, fibrotic adhesions. Mineralised or cartilaginous tissue develops in some joints. The disease commonly affects middle aged to older larger dogs and the chronic lameness typically improves with rest but is worse with exercise. There is limited movement of the shoulder during the swing phase of the gait as the pain originates from the tendon gliding along the bone. Diagnosis includes the identification of pain on digital pressure over tendon in intertubercular groove region while simultaneously flexing shoulder and extending the elbow, plain radiographs which may identify calcification and osteophytosis in the intertubercular groove and the skyline view of the bicipital groove. Contrast arthrography can be used to identify irregularities and filling defects along the tendon which correspond to proliferative synovium, adhesions between the tendon sheath and tendon or joint mice. Ultrasonography is a useful non invasive tool to evaluate the biceps tendon. Again arthroscopy provides the most expedient means of treating the condition as the biceps tendon can be visualized at its origin and within the groove and a tenotomy can be performed arthroscopically (See Figures 6-8). Furthermore, inflammation of the biceps tendon secondary to other intra-articular pathology can be assessed. Bicipital tenosynovitis can be treated with arthroscopic tenotomy using a scalpel blade or a radiofrequency ablater. This is a less invasive technique than biceps tenodesis with similar outcomes reported. Figure 6. Tenosnovitis of the origin of the biceps tendon with tearing of the fibres and hyperaemia of the tendon. Figure 7. Biceps tenotomy using an RF probe Figure 8. Post tenotomy, the biceps tendon slides distally in the bicipital groove.
OCD of the shoulder joint OCD lesions most commonly affect the caudal aspect of the humeral head with clinical signs frequently occurring at 6-12 months of age. The disease can be unilateral or bilateral, but dogs usually present with unilateral lameness. Clinical signs include intermittent weight bearing lameness with pain on shoulder extension and flexion and atrophy of shoulder muscle with a prominence of the scapular spine. Radiography is a commonly used diagnostic tool and the mediolateral view classically shows the deficit in the caudal aspect of the humeral head. A stressed view with external and internal rotation of the shoulder can be performed if OCD is suspected but not seen on the mediolateral view. The lesion can be off midline and a stressed view can allow visualization of the lesion. Arthrography can also be used to demonstrate the OCD lesion. Surgical arthrotomy with a caudolateral, craniolateral or a caudal arthrotomy generally provides an excellent outcome with flap removal. Shoulder arthroscopy, however has become the treatment of choice as it allows a minimally invasive approach to flap removal as well as evaluation for joint mice, particularly in the bicipital tendon sheath which are not accessible via a standard arthrotomy approach. OCD lesions can be easily visualized and the cartilage flap removed via a caudal instrument portal. An arthroscopic shaver can be used to clean out any remnant cartilage pieces and to smooth the borders of the cartilage deficit. Aggressive curettage of the cartilage bed is no longer favoured due to the damaging effect on the subchondral bone plate. Cartilage allografts are being investigated to repair the deficits left from an OCD lesion and have been a successful treatment for OCD of the stifle. References Bardet, J. F. (1998). "Diagnosis of shoulder instability in dogs and cats: a retrospective study." J Am Anim Hosp Assoc 34(1): 42-54. Bardet, J. F. (1999). "Lesions of the biceps tendon. Diagnosis and classification. A retrospective study of 25 cases in 23 dogs and one cat." Veterinary and Comparative Orthopaedics and Traumatology 12(4): 188-195. Davidson, E. B., S. M. Griffey, et al. (2000). "Histopathological, radiographic, and arthrographic comparison of the biceps tendon in normal dogs and dogs with biceps tenosynovitis." J Am Anim Hosp Assoc 36(6): 522-30. Deneuche, A. J. and E. Viguier (2002). "Reduction and stabilisation of a supraglenoid tuberosity avulsion under arthroscopic guidance in a dog." J Small Anim Pract 43(7): 308-11. Fitch RB, Breshears L, et al. (2001). "Clinical evaluation of prosthetic medial glenohumeral ligament repair in the dog (ten cases)." Vet Comp Orthop Traumatol 14: 222-228. Gilley, R. S., L. J. Wallace, et al. (2002). "Clinical and pathologic analyses of bicipital tenosynovitis in dogs." Am J Vet Res 63(3): 402-7. Holsworth IG, Schulz KS, et al. (2002). "Cadaveric evaluation of canine arthroscopic bicipital tenotomy." Vet Comp Orthop Traumatol 15: 215-222. Kramer, M., M. Gerwing, et al. (2001). "Ultrasonography for the diagnosis of diseases of the tendon and tendon sheath of the biceps brachii muscle." Vet Surg 30(1): 64-71.
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