Tutorial Article Imaging of the Shoulder W

EQUINE VETERINARY EDUCATION / AE / april 2010 199

Tutorial Article Imaging of the shoulder W. R. Redding* and A. P. Pease† Department of Clinical Sciences; and †Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough Street, Raleigh, North Carolina

27606, USA.eve_55 199..209

Keywords: horse; lameness; shoulder; ultrasonography; radiology

Summary be performed before intra-articular anaesthesia to determine if effusion is present in the joint and to assist with Diagnosis of lameness associated with the shoulder region directing the placement of the needle into the shoulder requires a careful clinical examination, the use of joint. specifically placed intra-articular analgesia and a This paper discusses the normal anatomy as well as the combination of some common imaging techniques to radiographic and ultrasonographic examination of the accurately define the source of pain. Most equine shoulder area. In addition, reference to the use of nuclear practices performing lameness examinations in the horse scintigraphy and the benefits to help localise lesions to the have the radiographic and ultrasonographic equipment shoulder is discussed. necessary to accurately image the shoulder. This article presents a description of the unique anatomy of the Normal anatomy of the shoulder region shoulder and the specific application of radiographic and ultrasonographic techniques to provide a complete set of The most proximal joint in the appendicular skeleton of the diagnostic images of the shoulder region. A brief discussion forelimb is the scapulohumeral joint. It is composed of 2 of nuclear scintigraphy of this region is also included. bones, the distal end of the scapula and the proximal humerus (Sisson 1975). The large amount of musculature Introduction covering the scapula along with their corresponding tendons act as collateral ligaments supporting the Front limb lameness referable to the proximal aspect of the scapulohumeral joint (Tnibar et al. 1999). The lateral head limb can be difficult to accurately define. Localisation of of the supraspinatus muscle and the infraspinatus muscle the lameness to the shoulder region requires a act as lateral stabilisers and insert on the caudal eminence combination of careful clinical examination followed by of the greater tubercle of the humerus. The supraspinatus radiographic, ultrasonographic and occasionally nuclear muscle also has a medial head that inserts on the lesser scintigraphic examinations. Because most injuries to the tubercle of the humerus. The subscapularis muscle which shoulder are traumatic in nature it is necessary to assess originates on the medial side of the scapula and inserts on both bony and soft tissue structures involved to the caudal eminence of the lesser tubercle of the humerus appropriately determine prognosis and most effectively acts as a stabiliser for the medial aspect of the joint. The treat the injuries of this area. Radiographic and nuclear biceps brachii tendon crosses the cranial aspect of scintigraphic examinations can be helpful in defining the scapulohumeral joint coursing distally from its origin on osseous involvement but generally requires sophisticated the supraglenoid tubercle passing between the medial imaging equipment. Even when adequate radiographic and lateral lobes of the supraspinatus tendon, to support and nuclear scintigraphic images are obtained the joint cranially as it runs in the intertubercular groove. ultrasonographic imaging is necessary to provide The long head of the triceps brachii and teres major complementary information on soft tissue injuries muscle, originating on the caudal border of the scapula associated with this area. Ultrasonographic examination is acts to support the scapulohumeral joint caudally (Figs 1, easily performed with equipment normally used for other 2, 3 and 4). musculoskeletal examinations in the horse. In addition, The bicipital bursa lies deep to the biceps tendon as it ultrasonographic examination of the shoulder should courses through the intertubercular groove. The bursa is interposed between the biceps brachii tendon and the *Author to whom correspondence should be addressed. proximal humerus. The bursa extends around the medial and

Fig 1: The normal anatomy of the shoulder region is demonstrated in this series of MRI images of a cadaver limb. The biceps tendon originates on the supraglenoid tubercle of the scapula. It appears as a crescent shape structure on cross section.

Fig 2: Coursing distally, the biceps tendon begins to appear bi-lobed and of mixed signal due to adipose tissue within the tendon and interposed between the tendon and humerus. lateral lobes of the biceps brachii tendon assuming a more bursa located between the infraspinatus tendon and the sheath-like function. Unlike the canine, the bicipital bursa caudal part of the greater tubercle. Occasionally, a bursa does not routinely communicate with the scapulohumeral can be found at the supraglenoid tubercle (Sisson 1975) that joint, but occasionally a communication does exist (Sisson protects the supraspinatus muscle as it divides into the lateral 1975; Grant et al. 1992; Dyson and Dik 1995). There is also a and medial lobes.

Fig 3: The biceps tendon is now uniquely bilobed. The bicipital bursa lies deep to the biceps tendon as it courses through the intertubercular groove. The bursa is interposed between the biceps brachii tendon and the proximal humerus.

Fig 4: In the most distal aspect of the tendon at the musculotendinous junction the signal again becomes variable due to the increased fat content as the tendon blends into the low signal muscle of the biceps brachii. The fat pad can easily be seen separating the tendon from the humerus.

Radiographic examination of the shoulder standing animal; however the quality of the radiograph can be significantly improved when the horse is positioned Good quality radiographs are best obtained with high under general anaesthesia with the affected side closest output x-ray generators with fixed or oscillating (‘Bucky’) to the radiographic plate. Portable x-ray generators have grids. Radiographs of the shoulder can be obtained in the a limited power output necessitating longer exposure times

to achieve the appropriate exposure factors. These longer exposure times decrease the detail of the radiograph due to motion artifact which can be minimised by the use of cassette stands, though patient movement is still problematic. Radiographs of the shoulder are technically difficult to achieve because of the large muscle mass covering the joint as well as the superimposition of the opposite shoulder, cervical spine, and neck musculature. Radiographic exposures are made with the patient nonweightbearing with the limb pulled cranially from the body and superimposed on the trachea to minimise overlying soft tissues to help reduce the needed exposure settings. Fast film and fast rare earth screen combinations can help reduce exposure times but are often insufficient to improve the diagnostic quality of the shoulder radiographs due to the large crystal size therefore limiting anatomic detail when using portable machines. In addition, since portable developers are not readily available, any screen-film images acquired are not available for review or interpretation until the veterinarian is able to develop the radiographs. Digital radiographic Fig 6: Craniomedial-caudolateral oblique projection of a shoulder and proximal humerus. Soft tissue swelling and bone remodelling systems are becoming more available to the equine of the deltoid tuberosity is present. practitioner and these systems provide a larger latitude to help compensate for the decreased generator power. In addition, since most systems come with portable readers, caudolateral oblique projections (Figs 5 and 6). For the the images are available for review in a more timely mediolateral projection, the affected limb should be manner. However, the lack of high kVp settings as well as pulled forward and slightly distally and the shoulder should the sharp contrast of the thick shoulder region surrounded be positioned as close as possible to the cassette. The by air can still make diagnostic images of the shoulder medial rim of the glenoid is normally projected more region challenging using portable x-ray units. At best, good proximally than the lateral rim. Frequently, the lateral rim of quality radiographs may not detect osteochondrosis the glenoid is superimposed over the cranial part of the lesions and consistently underestimate the extent and humeral head creating a radiolucent defect (Dyson 1986). severity of many of the lesions affecting the shoulder. The caudal edge of the glenoid rim is sharply pointed. The The typical radiographic examination of the shoulder subchondral bone of the caudal two-thirds of the glenoid should include mediolateral and craniomedial- cavity is uniform in thickness and quite dense. The craniomedial-caudolateral oblique view is useful to highlight the lesser tubercle, the intermediate tubercle and the deltoid tuberosity. A cranioproximal-craniodistal oblique view can be obtained when the tubercles of the humerus are thought to be involved. This projection has been especially helpful in defining osseous cyst-like lesions of the greater or intermediate tubercles. These images are technically difficult to obtain but have been rewarding when nuclear scintigraphy or ultrasonography have indicated the tubercles are involved. This view is performed by flexing the shoulder and pushing the shoulder craniodistal. Then the x- ray tube is place proximal to the shoulder and the cassette is placed as close to the craniodistal aspect of the shoulder as possible to minimise magnification and distortion. Radiographically apparent injuries to the shoulder include osteochondrosis, degenerative joint disease, and fractures. (Figs 7, 8 and 9) However, diseases of the shoulder with significant cartilage and soft tissue pathology may require contrast arthrography to better evaluate the extent of cartilage affected. Horses that have resolution of Fig 5: Mediolateral radiograph of a normal shoulder joint. clinical signs with local anaesthesia administered into the

Fig 7: Radiographic abnormalities of osteochondrosis range from Fig 9: Radiograph of a Salter-Harris type 2 physeal fracture of the subtle flattening of the humeral head to more extensive proximal humerus. irregularities of the subchondral surfaces of the glenoid cavity and proximal humeral articular surface. This radiograph demonstrates a severe case of osteochondrosis of the shoulder joint affecting the allows for the iodinated contrast medium to coat the glenoid cavity of the scapula. articular surface while the room air provides delineation of the contrast medium as well as distension of the joint to provide greater contrast detail between the contrast medium and the articular cartilage that is soft tissue opaque. The region is first clipped and aseptically prepared and the landmarks used are standard for an intra-articular injection. The acromion process of the scapula is followed distally to the greater tubercle and the needle is introduced just cranial to the deltoid tendon half way between the greater tubercle and acromion process. Room air is then injected to distend the joint followed by nonionic contrast medium. The volume of contrast medium is considered to be 10% of the injected gas volume. After the contrast medium and room air is administered, the joint is then manipulated (flexed and extended) several times to ensure adequate distribution prior to taking the radiographs. Contrast arthrographic procedures under general anaesthesia do carry the disadvantage of having to prepare and inject the affected leg when it is uppermost and then flipping the horse to obtain the radiographic study so that the affected shoulder is closest to the radiographic cassette. This procedure can be performed in a standing horse as well, but the image Fig 8: Osteoarthritis of the scapulohumeral joint occurs and is quality is less optimal due to patient motion and increased usually associated with osteochondrosis or intra-articular fractures of the joint. This image is an example of severe osteoarthritis of the radiation exposure to personnel. scapulohumeral joint. Ultrasonographic examination of shoulder joint but have little obvious pathology may need the shoulder to be anaesthetised and contrast medium introduced into the shoulder to better define osteochondrosis lesions Ultrasonographic examination of the biceps brachii (Nixon and Spencer 1990). Most contrast procedures tendon should follow an established routine. A complete involve the use of iodinated, ionic or nonionic contrast ultrasonographic examination of the shoulder area should medium as well as room air. This double contrast procedure include the biceps tendon, bicipital bursa, humeral

Fig 12: Transverse ultrasonographic image demonstrating both lobes of the biceps tendon with a more uniform appearance of the Fig 10: Transverse ultrasonographic image demonstrating the origin fibre pattern at the level of the intermediate ridge of the tubercle. of the biceps tendon on the hyperechoic crescent shaped supraglenoid tubercle of the scapula. The biceps tendon is convex in shape and has a homogenous appearance. Bicipital brachii tendon and bursa

The biceps brachii tendon should be evaluated in transverse and longitudinal sections, beginning at its origin on the supraglenoid tubercle of the scapula to its musculotendinous junction located distal to the humeral tubercles. The origin of the biceps tendon appears as a hyperechoic crescent shaped structure (Figs 10 and 11) The tendon is convex in shape and has a homogenous appearance. Superficial to the biceps brachii tendon, the muscle fibres of the supraspinatus can be seen. The supraspinatus tendon remains superficial to the biceps tendon, but may be in the far field of the image depending on the angle of ultrasound acquisition. Coursing distally, the tendon appears tri-lobed and Fig 11: Longitudinal ultrasonographic image of the origin biceps heterogeneous due to adipose tissue within the tendon tendon of the supraglenoid tubercle. The proximal aspect of the and interposed between the tendon and the humerus. biceps brachii tendon has parallel linear echoic lines originating from the hyperechoic supraglenoid tubercle. Further distal, the biceps brachii tendon becomes more homogenous and less heterogeneous in echogenicity and tubercles, infraspinatus bursa and tendons of attachment bilobed in shape (Fig 11). At this level, muscle fibres of the of the supraspinatus muscle, and infraspinatus muscle as biceps brachii appear as hypoechoic tissue present along well as the shoulder joint. When evaluating the biceps the cranial border of the tendon. The biceps tendon brachii tendon, the zoning system and reference begins to widen with the lateral lobe becoming slightly measurements previously described by Tnibar et al. (1999) larger in size. Over the point of the shoulder, the biceps and Crabill et al. (1995) should be used. The contralateral tendon becomes bilobed and is seen in the intertubercular limb should also be evaluated for comparison. A recent groove. The smaller, medial lobe is situated between the paper provides a more descriptive interpretation of the intermediate tubercle and the lesser tubercle. The larger, architecture and provides reference images of the lateral lobe is situated between the cranial eminence of longitudinal scan of the proximal tendon of the biceps the greater tubercle and the intermediate tubercle. The brachii (Pasquet et al. 2008). medial and lateral lobes are connected by an isthmus at Linear and microconvex high frequency transducers the level of the intermediate tubercle. The humeral (7.5–18 MHz) should be used at a scanning depth of greater, intermediate and lesser tubercles appear as 4–6 cm. The shoulder joint may require a lower frequency smoothly undulating hyperechoic cortical surfaces with probe to allow for a deeper scanning depth, especially if distal acoustic shadowing. In standard sized Quarter the caudal aspect of the joint is being evaluated. Clipping Horses, the bilobed biceps tendon at this level is 50–60 mm the shoulder area with a No. 40 clipper blade and wide and the lateral lobe is 15–20 mm thick and the medial scrubbing with a detergent before application of the lobe is 14–18 mm thick. It is interesting to note that the coupling gel is recommended. Saturation with alcohol lateral lobe at this level is only 14 mm from the skin surface may provide acceptable images in some cases and the medial lobe is 23 mm from the skin surface (Crabill particularly in frequently groomed, short haired horses. et al. 1995).

Fig 13: Transverse ultrasonographic image of the lateral branch of Fig 15: Ultrasonographic examination of the anatomy of the the supraspinatus tendon found lateral to the biceps brachii tendon shoulder joint is easiest when the probe is oriented longitudinally at the point of the shoulder. and in a proximodistal orientation. The caudal aspect of the humeral head is visible with an irregular subchondral surface and effusion in the joint consistent with osteochondrosis.

hypoechoic area between the lobes of the tendon. The biceps tendon fibre pattern becomes more uniform in appearance on transverse view as it curves over the intermediate ridge of the tubercle (Fig 12). In the most distal aspect of the tendon the echogenic pattern can be seen as it enters the hypoechoic muscle of the biceps brachii. The fat pad can easily be seen separating the tendon from the humerus and having an echoic appearance. Palpation of the greater tubercle of the humerus will aid with placement of the transducer for ultrasonographic evaluation of the bicipital tendon and the corresponding bursa. The bicipital bursa is a consistent anechoic Fig 14: Transverse ultrasonographic image of effusion within the appearance and expands to an echoic pouch at the infraspinatus bursa at the level that the infraspinatus tendon crosses distal aspect of the bicipital tendon (Tnibar et al. 1999). It is over the caudal part of the greater tubercle of the humerus. easily seen in transverse imaging over the point of the shoulder where it is reported to be <3 mm measured in the In mature horses, the biceps tendon is uniformly cranial to caudal direction in Quarter Horses (Crabill et al. echogenic in appearance that is superficial to the smooth 1995) at all locations. The bursa should also be evaluated in undulating cortical margin of the greater, intermediate and sagittal section. lesser tuburcles. However, the intermediate tubercle in young Evaluating the biceps brachii tendon requires horses can have a variable degree of ossification which can constantly maintain a perpendicular angle of incidence of be seen as a hypoechoic region due to the abundance of the sound beam to the tendon fibre orientation. A small cartilage rather than ossified bone (Pugh et al. 1994; change in angle will create beam angle (hypoechoic) McDiarmid 1999). There is an anechoic area between the artifact within the tendon called anisotropism (Crabill et al. biceps tendon and the humerus, which includes the bicipital 1995; Tnibar et al. 1999). Evaluation in both transverse bursa and hyaline cartilage. The most distal aspect of the section and longitudinal section will help to define biceps brachii tendon has an irregular shape and the hypoechoic areas as lesions or artifacts. However, it is hypoechoic fat pad can be seen between the tendon and important to remember that in the proximal aspect the the humerus. At the level of the proximal humerus, a biceps brachii tendon has areas of fat within the tendon tendonous band of the ascending pectoral muscle holds the seen as hypoechoic foci. biceps brachii tendon over the humerus (Sisson 1975). On longitudinal section, the proximal aspect of the Supraspinatus tendon biceps brachii tendon has parallel linear echoic lines originating at the supraglenoid tubercle (Fig 11). Distally, Evaluation of the supraspinatus tendon can be difficult the biceps brachii tendon is heterogeneous in (Tnibar et al. 1999). The tendons are small but appearance, and the fat pad can be seen as a ultrasonographic imaging is possible (Dik 1996; Tnibar et al.

1999). The supraspinatus tendon is located superficial to the humeral head can be imaged (Dik 1996; Cauvin 1998; biceps tendon. The lateral lobe attaches to the cranial part Tnibar et al. 1999). The normal ultrasonographic of the greater tubercle. The lateral lobe is homogenously appearance of the humeral head is a smoothly rounded echogenic, roughly triangular in shape and measures subchondral bone surface with a 2–3 mm covering of approximately 10–12 mm medial to lateral and 6–8 mm smooth anechoic (water equivalent) cartilage (Tnibar cranial to caudal, in average sized horses (Tnibar et al. et al. 1999) with a hyperechoic superficial margin. The 2 1999). The medial lobe is small, round in shape, attaches to echogenic lines used to measure the thickness of the the lesser tubercle and is 5–7 mm medial to lateral and articular cartilage is the joint capsule and the 3–5 mm cranial to caudal in average sized horses. To cartilage-subchondral interface. This measurement should examine the lateral supraspinatus tendon, identify the be performed as perpendicular as possible to the joint biceps brachii tendon at the point of the shoulder and surface to maximise the likelihood of an accurate move the probe laterally (Fig 13). The lateral lobe can be measurement of thickness of the cartilage. The lateral and found at its point of insertion on the cranial part of the some aspects of the caudal humeral head are the only greater tubercle. The tendon can be followed proximally areas imaged. The probe is placed between the cranial from the greater tubercle. The brachiocephalicus muscle and caudal parts of the greater tubercle and angled in a can be seen as a hypoechoic structure superficial to the caudodistal direction. When trying to examine the lateral lobe of the supraspinatus tendon throughout its short placement of a needle into the shoulder joint it is best course. Then the medial lobe of the supraspinatus tendon evaluated caudal to the infraspinatus tendon with the can be imaged by again finding the biceps tendon at the probe directed craniodistally. point of the shoulder and moving the transducer medially towards the lesser tubercle of the humerus. Nuclear scintigraphic evaluation of the shoulder Infraspinatus tendon Nuclear scintigraphy is more sensitive than radiography at Ultrasonographic examination of the infraspinatus tendon diagnosing fractures, osteomyelitis, periostitis, neoplasia has also been described by Tnibar et al. (1999). This report and joint disease; however, it is not considered to be a has a similar zoning system and gives normal reference specific modality since all it indicates is bone remodelling measurements for the infraspinatus. The infraspinatus and any of the above disease processes have a similar tendon can be palpated as it crosses over the greater appearance (Figs 16, 17 and 19). This sensitivity comes tubercle of the humerus. Proximally the infraspinatus from the mechanism of action of the radiopharmaceutical tendon is seen as a dense echoic structure rectangular in used. When technetium pertechnetate is bound to shape within the infraspinatus muscle. The superficial hypoechoic muscle is the omotrasversarius. Between the origin in the muscle and the attachment to the infraspinatus just distal to the lateral supraspinatus tendon on the greater tubercle, the infraspinatus tendon changes shape into 3 portions (Tnibar et al. 1999). The infraspinatus bursa exists between the deep portion of the infraspinatus tendon and the caudal part of the greater tubercle of the humerus (Fig 14). Just lateral to the superficial portion of the tendon is the omotransversarius muscle. The tendon begins to widen as it approaches its insertion on the greater tubercle of the humerus. In both transverse and sagittal images the infraspinatus tendon is echoic proximally but as the tendon progresses distally it becomes heterogeneous due to the lobulated structure.

Scapulohumeral joint

A limited examination of the lateral aspect of the scapulohumeral joint can be performed with ultrasonography. The author finds it best to orient the probe longitudinally in a proximodistal orientation to evaluate the Fig 16: Nuclear scintigraphy is more sensitive at diagnosing anatomy of the shoulder joint (Fig 15). The glenoid cavity is fractures and joint disease, however it is not considered to be very not accessible to the sound beam since it is surrounded by specific since all it indicates is bone remodelling. This image shows bone, however some parts of the articular cartilage of the a fracture of the deltoid tuberosity.

Fig 17: The origin of the biceps tendon has a heterogeneous appearance on transverse section which can be typical of this area. However the cross sectional area measurement demonstrated enlargement of the tendon compared to the opposite limb. More importantly there is a loss of the normal fibre alignment at the attachment to the supraglenoid tubercle apparent on the longitudinal section which corresponds to the region of IRU seen on the nuclear scintigram (insert). methylene diphosphonate (MDP) or hydroxy-methylene when compared to the other modalities such as bone diphosphonate (HDP), it acts to bind with hydroxyapatite nuclear scintigraphy, ultrasound and CT, these techniques of the bone lattice. The hydroxyapatite is only exposed are not generally used in the equine shoulder patient. during osteoblastic activity, therefore, the more the bone is Nuclear scintigraphy is a useful diagnostic tool for undergoing osteoblastic remodelling of any cause, the shoulder injuries that involve bone since changes can be more methylene diphosphonate is bound to the area, thus seen before radiographic abnormities are detected. making more technetium pertechnetate present and However, nuclear scintigraphy is expensive and time thereby causing increased activity to be detected. For soft consuming and requires very specialised equipment, tissue lesions, the main mechanism of activity is considered licensing, housing and isolation of the patient and bedding to occur through the increased vascular supply secondary due to the use of radioactive materials. to inflammation. Since this increased vascularity is generally not substantial in the authors’ opinion, as well as the lack of exposed hydroxyapatite with soft tissue injuries, Shoulder abnormalities most activity detected during the pool phase (approximately 5–20 min after injection) is considered to Injury to the shoulder area requires a systematic evaluation be early bone uptake rather than a soft tissue lesion of the entire limb to provide an accurate diagnosis and especially if the lesion persists during the bone phase. It is implementation of the most appropriate therapy. In most the absence of a radiopharmaceutical marker for soft instances, this requires using a variety of diagnostic tissue lesions that makes nuclear medicine unrewarding in imaging modalities. Clinical examination combined with the authors’ opinion. Other radiopharmaceutical products perineural anaesthesia of the distal limb must be are available for use that bind with other specific products performed to rule out other sites of lameness. Once the such as red blood cells, white blood cells or even distal limb is eliminated as the source of pain (via perineural antibiotics. The main drawback to these modalities are the blocks or through physical examination in the case limited amount of anatomic information gained during the of obvious trauma or fracture) then intra-articular scan since the labelled cells only accumulate in the areas anaesthesia of the shoulder joint and anaesthesia of the of injury and/or infection and the surrounding structures will bicipital bursa is warranted. Once the shoulder area is have no activity therefore providing no landmarks for confirmed as the site of lameness, further diagnostics localisation of the lesion. Since these techniques are including radiography, ultrasonography, and when generally labour intensive and have limited usefulness available, nuclear scintigraphy may be necessary.

of the joint. Due to the lack of conspicuity of some of the lesions, especially smaller lesions such as osteochondritis dissecans, arthrography may be necessary. Using a double contrast arthrogram, the contrast medium coats the articular service to define dissecting cartilage defects as well as helping to see tearing or fibrillation of the biceps tendon. Many clinicians feel that if general anaesthesia is necessary to perform a double contrast arthrogram, which is the current recommendation to eliminate motion and optimise image quality while minimise personnel radiation exposure, then arthroscopic exploratory surgery is chosen instead. This is because arthroscopic surgery will likely provide a more effective method to diagnose a lesion and, more importantly, managing many of the intra- articular lesions seen in the shoulder joint. Fig 18a: Ultrasonographic image of an acute biceps tendinitis of Ultrasonography has gained widespread acceptance the lateral lobe of the biceps tendon. as a superior, noninvasive imaging tool for soft tissue injuries of the musculoskeletal system of the horse. This modality should be considered when the lameness is eliminated by intra-articular or intra-bursal analgesia, when there is a history of trauma or any swelling associated with the shoulder area, when there is any radiographic abnormality, or when nuclear scintigraphy is positive for a shoulder problem (Fig 18a,b). Ultrasonographic and radiographic examination are considered complementary

Fig 18b: Gross anatomical section of the corresponding lateral lobe bicipital tendinitis.

Accurate interpretation of radiographs of the shoulder area requires a complete knowledge of the anatomy including an understanding of artifacts that are created by variations from the normal projection(s). Radiography of the shoulder remains a useful diagnostic tool and is particularly useful to image articular fractures and joint abnormalities such as osteochondrosis and osteoarthritis even though it generally underestimates the extent and severity of many lesions. Radiographic abnormalities of osteochondrosis range from subtle flattening of the humeral to head to more extensive regularities of the subchondral surfaces of the glenoid cavity and proximal humeral articular surface (see Fig 12). Subchondral bone cysts exist in the glenoid cavity and humeral head similar to many other joints in the horse and are generally seen based on the sclerosis of the surrounding bone rather than the lucent region. However, small cystic structures in the middle thd of the glenoid surface can occur in the normal Fig 19: Mediolateral radiograph and nuclear scintigam of the (nonclinical) horse (Dyson 1986). Osteoarthritis of the shoulder. There is a moderate increased radiopharmaceutical scapulohumeral joint occurs rarely and is usually uptake in the intermediate tubercle corresponding to an osseous associated with osteochondrosis or intra-articular fractures cyst-like lesion seen on radiographs at this location.

imaging modalities since radiographs allow for the Conclusion evaluation of the bony structures of the shoulder, while ultrasonography provides information about the Multiple modalities are available to evaluate the shoulder surrounding soft tissues as well as the shoulder joint itself. including radiography, ultrasonography and nuclear When used in the field, ultrasonography can effectively aid scintigraphy. Each of these modalities provide different in diagnosing a fracture of the supraglenoid tubercle and levels of information with radiographs mainly evaluating greater tubercle and is more easily performed than the bone, ultrasonography evaluates the soft tissues and shoulder radiographs using portable equipment. bone surface and nuclear scintigraphy able to image Radiographs are still necessary to delineate the fracture bone remodelling and to a limited extent increased blood configuration, but in a field situation, ultrasonography can flow from a soft tissue injury. Though all these modalities provide enough information to determine if the patient could be used individually, it is the combination of needs to be referred as well as the damage to the radiography and ultrasonography that makes the most associated soft tissues surrounding the shoulder. robust evaluation of the shoulder for the equine Ultrasonography has proven very helpful in assessing soft practitioner. Ultrasonography is, in these authors’ opinion, tissue injuries (Fig 19) as well as some bony injuries that are underused as a diagnostic modality due to the technical poorly defined by radiographs. In fact, some fractures of expertise required as well as the knowledge of anatomy. the humeral tubercles that have proven difficult to identify However, with training, supervision and practice as well as on radiographs are easily seen with ultrasonography and a good quality ultrasound machine, ultrasonography is allow a more dect radiographic examination of the considered invaluable in the evaluation of the equine affected area. shoulder lameness. Nuclear scintigraphy can also be used if available; however, this modality should be reserved for cases of vague or ill-defined lameness rather than specifically References evaluating the shoulder joint. In cases of severe soft tissue Cauvin, E.R.J. (1998) Soft tissue injuries in the shoulder region: systematic injuries of the biceps tendon, osteochondrosis lesions not approach to differential diagnosis. Equine vet. Educ. 10, 70- seen on radiographs as well as small stress fractures or 74. bone bruising, nuclear scintigraphy can provide useful Crabill, M.R., Chaffin, K.M. and Schmitz, D.G. (1995) Ultrasonographic information to help localise the lameness. The main morphology of the bicipital tendon and bursa in clinically normal Quarter horses. Am. J. vet. Res. 56, 5-10. drawback is that although sensitive for disease, as stated Dik, K.J. (1996) Ultrasonography of the equine shoulder. Equine pract. earlier, most of the diseases listed above will have the same 18, 13-18. appearance on nuclear scintigraphic images and Dyson, S. (1986) Interpreting radiographs 7: Radiology of the equine therefore the cause for the lameness is difficult to shoulder and elbow. Equine vet. J. 18, 352-361. determine, only the location. For this reason, nuclear Dyson, S. and Dik, K.J. (1995) Miscellaneous conditions of scintigraphy can localise a region of bone remodelling; tendons, tendon sheaths, and ligaments. Vet. Clin. N. Am. 11, however, ultrasonography or radiography would be 315-338. needed in conjunction with the physical examination to Grant, B.D., Peterson, P.R., Bohn, A. and Rantanen, N.W. (1992) Diagnosis and surgical treatment of traumatic bicipital bursitis in the help determine the clinical importance. In addition, due to horse. Proc. Am. Ass. equine Practnrs. 38, 349-356. the size of the horse and width of the thorax, computed McDiarmid, A.M. (1999) The equine bicipital apparatus - review of tomography (CT) and magnetic resonance imaging (MRI) anatomy, function, diagnostic investigative techniques and clinical are not able to image these regions at the present time. conditions. Equine vet. Educ. 11, 63-68. Since digital radiography is becoming more readily Nixon, A.J. and Spencer, C.P. (1990) Arthrography of the equine shoulder joint. Equine vet. J. 22, 107-113. available to the ambulatory practitioner, radiography of Pasquet, H., Coudry, V. and Denoix, J.M. (2008) Ultrasonographic the shoulder may be a readily available and rapid examination of the proximal tendon of the bicips brachii: Technique diagnostic test in the future. However, ultrasonography and reference images. Equine vet. Educ. 20, 331-336. provides a noninvasive method to evaluate the bone and Pugh, C.R., Johnson, P.J., Crawle, G. and Finn, S.T. (1994) soft tissues of the shoulder as well as the shoulder joint itself. Ultrasonography of the equine bicipital tendon region: a case Since the images are readily available and, with practice, history and review of anatomy. Vet. Radiol. 35, 183-188. rapidly acquired, it is the authors’ belief that this modality Sisson, S. (1975) Equine osteology. In: The Anatomy of Domestic Animals, 5th edn., W.B. Saunders Co., Phiadelphia. pp 273-279. will serve to complement if not surpass radiology as the Tnibar, M.A., Auer, J.A. and Bakkali, S. (1999) Ultrasonography of the primary diagnostic modality of choice for shoulder joint equine shoulder: technique and normal appearance. Vet. Radiol. evaluation. Ultrasound 40, 44-57.