Shoulder Disorders
Introduction
Shoulder conditions are common causes of canine sports-related issues in both dogs and people. Although both species have a complex shoulder musculoskeletal system, a recent study showed that the structural and biomechanical characteristics of the joints of quadruped animals are too different to be useful as a model for human shoulder injury (Sager et al., 2009). Therefore, we cannot extrapolate from the human literature regarding the pathophysiology, biomechanics or treatment options for sports related shoulder injury in the canine.
With the coordinated action of over 25 muscles required for shoulder motion, the ensuing action is complex, with the limb undergoing flexion, extension, rotation, abduction, and adduction (Marcellin-Little et al., 2007). The potential for muscle and tendon injuries causing performance issues and lameness is significant when all muscular contributions to the joint are considered (Figure 12.1). The author’s (SC) case database reveals the most common muscle and tendon sports related injuries in the canine include subscapularis tendinopathy (a component of medial shoulder syndrome), supraspinatus tendinopathy, biceps tendinopathy (BT), and infraspinatus myopathy, respectively.
Figure 12.1 Golden Retriever performing the weave poles demonstrating significant shoulder abduction, biomechanically stressing the medial compartment.
Supraspinatus Tendinopathy
Several degenerative disorders of the human and canine supraspinatus tendon have been identified, including rotator cuff tears, calcifying tendonitis or tendinosis (microtears), and tendinosis as a result of overuse (Fransson et al., 2005). Tendinopathy has been adopted as a generic descriptive term for the clinical conditions in and around tendons arising from overuse (Sharma & Maffulli, 2005).
Degeneration of the supraspinatus tendon is thought to be a factor in the development of rotator cuff tears in humans (Danova & Muir, 2003). That overuse is likely an important factor in this disorder has been supported in animal models. In these models of repetitive activity, the mechanical properties of supraspinatus tendons deteriorated as noted by a decreased modulus of elasticity and decreased maximum stress of failure in the tendon (Carpenter et al., 1998; Soslowsky et al., 2000). Supraspinatus tendinopathies can be difficult to treat and often require lengthy management (Carpenter et al., 1998; Soslowsky et al., 2000).
Affected tendons contain discontinuous, disorganized fibers, and typically, no acute inflammation is detected, explaining the often-noted lack of response to NSAIDs. Affected tendons that contain discontinuous, disorganized fiber patterns as noted on musculoskeletal diagnostic ultrasound are seen as hypoechoic foci or core lesions (Schramme et al., 2010). This term is now used for similar canine tendon lesions seen on diagnostic musculoskeletal ultrasound. A rapidly growing nodule develops within the supraspinatus tendon in chronic cases, compressing the biceps tendon and causing pain (Lafuente et al., 2009).
Cause
It appears that repeated strain injury is an underlying cause of this condition. In performance dogs, repeated strain can result from hitting the ground or agility contacts on an outstretched forelimb, quick turns and repetitive eccentric contractions as well as concentric contractions with the muscle in a lengthened state. Slipping, overstretching and overuse of the muscle can also contribute.
Diagnosis
Patients with supraspinatus tendinopathies present with varying degrees of lameness, from a shortened stride length to a significant weight-bearing lameness. The lameness worsens with activity and is resistant to treatment with rest and NSAIDs. Atrophy of the supraspinatus muscle may be noted as well as pain on direct palpation over the tendon during flexion of the shoulder. Concurrent biceps tendinopathy or medial shoulder syndrome (MSS) may also be present.
Mineralization within the tendon or bony remodeling on the point of insertion on the greater tubercle or along the region of the scapular notch to the supraglenoid tubercle may be noted radiographically in chronic cases (Figure 12.2). Although MRI is an excellent diagnostic modality for acute and chronic cases (Figure 12.3), musculoskeletal ultrasound can be a rapid, inexpensive means of diagnosis in the hands of experienced operators (Figure 12.4). Musculoskeletal ultrasound allows for a definitive diagnosis as well as serial evaluations to assess response to treatment.
Figure 12.2 Lateral shoulder radiograph showing mineralization within the supraspinatus tendon (arrow).
Figure 12.3 Short T1 inversion recovery (STIR) transverse image revealing a proliferative inflammatory nodule of the supraspinatus tendon (top arrow) causing flattening of the biceps tendon (bottom arrow).
Arthroscopic exploration is often performed to evaluate the shoulder for concurrent conditions. MSS is frequently noted and although the supraspinatus tendon is extracapsular and cannot be directly evaluated via arthroscopy, a supraspinatus bulge causing biceps tendon contact/compression and a biceps tendon kissing lesion is commonly found (Figure 12.5).
Figure 12.5 Arthroscopic view of a compressed biceps tendon (asterisk) secondary to a supraspinatus bulge (diamond).
Treatment
Acute cases can be treated with conservative medical management consisting of NSAIDs, controlled activity and rehabilitation therapy (manual therapy, modalities, ROM with progression to stretching and strengthening exercises). However, these cases rarely present in the acute phase. Treatment for subacute and chronic cases is dictated by the findings of advanced diagnostics (ultrasound or MRI).
An inflammatory response is needed to jump-start the healing process. Reinitiating the inflammatory process increases circulation to the tendon. For this reason, NSAIDs and intra-articular corticosteroids are contraindicated. Rehabilitation therapies include STM, heat, ultrasound therapy and pain-free ROM/stretching. Shock wave therapy may also be considered (Danova & Muir, 2003). Further details are provided in Chapter 13.
Regenerative medicine or surgical intervention may be considered for dogs that do not respond to rehabilitation therapy. The author (SC) has had good results using ultrasound-guided injections of platelet rich plasma (PRP) and cultured adipose derived progenitor cells into core lesions (Canapp, 2011). Surgically excising or debulking the supraspinatus nodule has been reported as a treatment option (Lafuente et al., 2009). Surgical treatment should include arthroscopic exploration to evaluate and treat concurrent MSS if indicated.
Infraspinatus Myopathy
Contracture of the infraspinatus muscle is uncommon. However, it is one of the two most frequently reported contractures in the dog along with quadriceps contracture (Fossum, 2002; Harasen, 2005). Unilateral contracture of the infraspinatus muscle is most common; however, bilateral contractures have been reported (Leighton, 1977; Slatter, 1985; Dillon et al., 1989). It is most commonly seen in large-breed dogs, particularly working (i.e., hunting and herding) dogs and other very active dogs (Pettit, 1980). Most present with an acute onset of shoulder lameness with work or exercise (Leighton, 1977; Slatter, 1985; Carberry & Gilmore, 1986; Dillon et al., 1989; Denny, 1993; Siems et al., 1998; Fossum, 2002).
Cause
Repetitive micro trauma, blunt trauma, and osteofascial compartment syndrome have been reported to cause this problem (Pettit et al., 1978; Matava et al., 1994). Early treatment is focused on surgical decompression by fasciotomy; however, if contraction has already occurred, tenectomy or myectomy may be necessary (Roe, 1998).
The hypothesis that an acute traumatic event with an incomplete rupture of the infraspinatus muscle leads to fibrosis and contracture is supported by the histological findings of degeneration and atrophy of skeletal muscle with fibrous tissue replacement (Roe, 1998).
Diagnosis
The patient may present with a painful, non-weight-bearing shoulder lameness. The shoulder may be swollen. The initial pain and lameness usually resolve with rest and/or supportive treatment over a period of 1–4 weeks; however, signs of contracture may appear within several days to weeks after the initial trauma (Carberry & Gilmore, 1986). The initial injury to the infraspinatus muscle is not commonly recognized.
Affected patients typically present with no signs of systemic illness. With a mature contracture, adhesion of the tendon of insertion of the infraspinatus muscle to the adjacent joint capsule occurs. Patients have a weight bearing lameness with circumduction of the affected forelimb and a characteristic flip-like action of the paw when placing the foot (Slatter, 1985; Carberry & Gilmore, 1986; Dillon et al., 1989; Denny, 1993; Siems et al., 1998). The affected forelimb is held with the shoulder externally rotated and the elbow in adduction against the thoracic wall (Siems et al., 1998). The distal forelimb and carpus is externally rotated and held in abduction (Slatter, 1985; Carberry & Gilmore, 1986). The patient is typically not painful on palpation and manipulation of the limb (Carberry & Gilmore, 1986; Siems et al., 1998). The remaining shoulder muscles, primarily supraspinatus and deltoid muscles, display disuse atrophy or may be contracted (Carberry & Gilmore, 1986; Dillon et al., 1989; Denny, 1993; Fossum, 2002). A significantly decreased range of motion (ROM) will be noted in the shoulder (Carberry & Gilmore, 1986). When the patient is placed in lateral recumbency with the affected limb up, a true infraspinatus contracture will cause the distal forelimb to remain in an abducted and externally rotated position off the floor (Leighton, 1994) (Figure 12.6).
Siems et al. reported a series of ultrasonographic findings of two traumatized infraspinatus muscles in the same dog at the same time, one of which resolved without any complications, while the other progressed to contracture (Siems et al., 1998). The ultrasonographic description of a contracted infraspinatus muscle is increased echogenicity when compared to the normal muscle (Slatter, 1985; Denny, 1993). MRI may be useful for diagnosing the condition in both the acute and chronic phases.
Treatment
In acute and subacute infraspinatus tendinopathies, rehabilitation including therapeutic ultrasound and stretching may help prevent contracture by maintaining the length and flexibility of the affected tissues.
Surgical release is required in mature contractures. Tenotomy of the tendon of insertion with release of capsular adhesions is most commonly performed. Complete transection of the infraspinatus tendon with partial tenectomy is required to restore motion in the affected limb and most often proves curative with an immediate release of contracture and return to function of the shoulder joint (Slatter, 1985; Carberry & Gilmore, 1986; O’Neill & Innes, 2004). This treatment carries an excellent prognosis (Slatter, 1985; Carberry & Gilmore, 1986). Adhesions to the infraspinatus tendon and joint capsule are commonly found and once dissected away seldom cause further issues (Pettit et al., 1978; Carberry & Gilmore, 1986). Rehabilitation therapy is started prior to suture removal to prevent the formation of further adhesions (Carberry & Gilmore, 1986).
Biceps Tendinopathy
Biceps tendinopathy (BT) was once thought to be the most common shoulder condition seen in performance dogs. However, through the use of advanced diagnostics and improved palpation techniques, BT is often a secondary finding (i.e., impingement and compression from a supraspinatus tendon nodule or referred elbow pain at the point of insertion).
When BT is the primary diagnosis, it most often involves the biceps brachii muscle and its tendon where it crosses the shoulder joint (Figure 12.7). The actions of the biceps are elbow flexion, shoulder extension, and stabilization of the shoulder during standing and the weight-bearing phase of locomotion (Evans, 1993).
Cause
The cause of injury in performance dogs appears to be repeated strain injury, including two-on/two-off contacts in agility, landing vertically on the forelimbs following a misjudged jump, overstretching the muscle, quick turns and repetitive contractions of the muscle with the shoulder flexed and/or elbow extended. The tendon can be injured via strain from overloading, leading to degeneration, or disruption (Wernham et al., 2008). Disruption can occur from a single less-than-maximal load that injures some fibers without complete failure of the tendon. Because the blood supply to the tendon is poor, healing time is protracted (Sharma & Maffulli, 2005). Degeneration of the tendon may be initiated by repetitive strain (Sharma & Maffulli, 2005). Continuous reinjury of the biceps tendon may sufficiently weaken it such that the surrounding tendons become inflamed and/or develop microtears, ultimately leading to shoulder joint instability (Gilley et al., 2002).
Diagnosis
Complaints of difficulty with quick turns and reluctance to jump are common in performance dogs with BT. Agility dogs present with complaints regarding performing two-on/two-off contacts and knocking bars with their forelimbs.
Patients often have a shortened stride and a weight-bearing lameness that can range from subtle to severe. The lameness worsens with activity. Direct palpation over the biceps tendon may elicit a pain response. Pain and spasm may be noted when performing the biceps stretch (flexing the shoulder with the elbow in extension) (Gilley et al., 2002) (Figure 12.8). A bony avulsion may be detected radiographically. Chronic cases may reveal mineralization of the tendon or sclerosis within the bicipital grove (Gilley et al., 2002). MRI and ultrasound may be used to identify acute and chronic cases (Figure 12.9) (Gilley et al., 2002; Wernham et al., 2008). Shoulder arthroscopy is an excellent diagnostic modality as well as therapeutic tool, if indicated (Figure 12.10) (Wernham et al., 2008).
Treatment
Conservative medical management and rehabilitation therapy are recommended for acute cases. Conservative medical management should include controlled activity, nonsteroidal anti-inflammatory drugs (NSAIDs), and cryotherapy. Intra-articular injections including hyaluronic acid, cortisone, platelet rich plasma (PRP), or stem cell therapy (SCT) may also be considered (Cookson & Kent, 1979; Gilley et al., 2002; Marcellin-Little et al., 2007; Wernham et al., 2008). If a core lesion is noted, ultrasound guided regenerative medicine treatment (PRP, SCT or combination therapy) may be considered.
Surgical treatment is recommended for biceps avulsions/tears and for cases that are nonresponsive to medical management and rehabilitation therapy. Surgical treatment includes arthroscopic reattachment for bony avulsions or an arthroscopic release for severe tendinopathies or tears.
Medial Shoulder Syndrome (MSS)
One of the most common causes of forelimb gait-related issues and lameness in performance, working and active dogs is medial shoulder syndrome (MSS). This condition is similar to rotator cuff injuries in people and can include ligament disruption, tendinopathy, and labral and capsular tears or disruption. These shoulders are not unstable, instead showing evidence of sprain and strain injury leading to discomfort and dysfunction. Subscapularis tendinopathy is the most common component of MSS.
The human thrower’s shoulder must be lax enough to allow extremes of motion but secure enough to provide the stabilization of the shoulder (Slatter, 1985; Arrington & Miller, 1995). The same is true for the canine athlete, which performs many extremes of ROM and requires appropriate stabilization. Signs of MSS can range from performance-related problems such as refusing tight turns to a frank, weight-bearing lameness. MSS involves multiple components of the shoulder joint and requires a thorough evaluation to confirm. It is important to identify and treat this condition early to obtain the best long-term results, and to prevent further sprain and strain injury that can lead to shoulder instability and progression of OA.
Cause
MSS is believed to be related to chronic strain and sprain due to repetitive activity or overuse rather than simply trauma. Repetitive activities such as jump-turn combinations and weave poles are performed regularly during agility practice and at trials. These routine maneuvers place the shoulder near its end range of abduction (Figure 12.11) and stress the soft tissue of the medial shoulder complex. Mishaps on agility equipment or simply slipping on wet surfaces can also contribute to the trauma inflicted on the shoulder. The cumulative effects of the micro trauma occurring to the shoulder structures can lead to performance problems, discomfort and lameness. Overuse of the shoulder support structures can lead to degeneration of the tissues, reducing tensile strength and predisposing them to fraying, disruption and eventually complete breakdown (Maganaris et al., 2004; Marcellin-Little et al., 2007). When instability, subluxation, or luxation occurs, a diagnosis of medial shoulder instability (MSI) is made.
Figure 12.11 Maneuvers such as repeated jump turn combinations and performing the weave poles at fast speeds place stress on the soft tissues of the medial shoulder.
(Photo by Rich Knecht Photography.)
Diagnosis
Presenting history will vary from avoiding tight turns during performance to intermittent forelimb lameness that worsens with exercise and heavy activity. In some cases a severe weight-bearing lameness may be noted. A history of a lack of response to rest and NSAIDs is also common.
Patients present with a unilateral lameness ranging from a mildly shortened stride in the affected forelimb at a walk or trot to a significant weight-bearing lameness (Marcellin-Little et al., 2007). In chronic cases, atrophy may be noted with forelimb circumference decreased in the affected limb as compared to the contralateral limb (Figure 12.12). Decreased shoulder extension is common. Shoulder spasm and discomfort on abduction are consistent findings. To achieve a passive stretch of the craniomedial shoulder components, the scapula must be stabilized with the evaluator’s hand at the level of the acromion process, and the elbow and shoulder must be placed in full extension with concurrent abduction of the forelimb. In severe cases, a slight thud or subluxation may be felt when abducting the shoulder. If a concurrent supraspinatus tendinopathy is present, pain may be noted when placing the shoulder into flexion (direct stretch of the supraspinatus) or on direct palpation of its tendon and/or point of insertion.
The shoulder abduction test (Cook et al., 2005a), although originally described with patients under sedation in lateral recumbency, may be performed with similarly consistent results on awake and standing patients. A goniometer is held with the stable arm parallel to the spine of the scapula, the center of rotation over the shoulder joint, and the free arm extending over the axis of the humerus in contact with the skin. With the elbow and shoulder held in extension, the forelimb is abducted to its physiologic limit and the measurement obtained as shown in (Figure 12.13). The same technique is applied to the contralateral shoulder for comparison. Using this palpation technique, it has been reported that a normal mean shoulder abduction angle is approximately 30 degrees (Cook et al., 2005a). Although this report revealed that dogs with medial shoulder instability had abduction angles significantly larger than 30 degrees, a more recent study showed an inconsistent correlation between abduction angles and medial compartment pathology identified arthroscopically (Cook et al., 2005a; Devitt et al., 2007). Patients with MSS rarely show evidence of instability but rather show signs of dysfunction and pain associated with craniomedial pathology including varying degrees of subscapular tendinopathy, medial glenohumeral ligament (MGL) disruption, craniomedial capsular lesions, and labral tears. The contralateral shoulder usually does not show signs of dysfunction, pain or spasm on abduction.
Figure 12.13 Two different ways to measure shoulder abduction.
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