3 CT and CT Arthrography
S. Bianchi, A. Keller, J. Fasel, J. Garcia
CONTENTS
3.1 Introduction 25 3.2 CT 25
3.2.1 Technique 25 3.2.2 Results 26
3.3 CT Arthrography 30 3.3.1 Technique 30 3.3.2 Results 31
References 33
3.1 Introduction
In recent years the advent of MR imaging has reduced the utilisation of computed tomography (CT) in the assessment of shoulder diseases. Magnetic reso- nance imaging (MRI) has multiplanar capability and excellent tissue contrast that are helpful in the assessment of complex anatomic areas such as the shoulder region. CT, however, still remains useful in the evaluation of a variety of shoulder disorders.
In trauma, standard radiography is the fi rst modality to be performed, but often superimposi- tion of different bone structures compromises ability to evaluate the anatomic details. Although specialised projections can be obtained to accurately assess frac- tures and dislocations, these views can be diffi cult to achieve in traumatised patients due to movement lim- itation and pain. CT can be performed on patients in
almost every clinical condition and enables an accu- rate evaluation of fracture fragments, subluxations, dislocations and loose bodies. Moreover, coronal and sagittal reformatted images as well as three-dimen- sional (3D) reconstructions ease interpretation of the CT images, especially to the referring clinicians.
As a general rule, shoulder arthropathies, tumours and infections are best evaluated with MRI. Possible exceptions are osteoid osteoma, in which thin-slice thickness is necessary to demonstrate the nidus, and the assessment of sequestra in osteomyelitis. With the advent of spiral equipment, shoulder CT arthrog- raphy has regained popularity as a valuable and accurate modality to investigate rotator cuff tendons, joint capsule, ligaments and glenoid labrum as well as intraarticular loose bodies. Reformatted images can be obtained in any required plane and allow accurate evaluation of size and location of tendon tears as well as dislocation of biceps tendon. The use of thin col- limation thickness yields an assessment of the details of capsuloligamentous lesions secondary to shoulder instability.
The aim of this chapter is to present the technical aspects and normal fi ndings of CT and CT arthrog- raphy of the shoulder.
3.2 CT
3.2.1 Technique
The patient is examined in the supine position with the shoulder as close to the gantry centre as possible.
The upper arm is positioned closely to the body and immobilised in neutral rotation by an elastic bandage.
A small pad placed below the elbow and a pillow placed beneath the knees afford a more comfortable position for the patient. To minimise artefacts the opposite arm is abducted and rests above the patient’s head.
Anteroposterior scanning radiograph is used to plan S. Bianchi, MD
Department of Radiology, Hopital Cantonal Universitaire, 24 rue Micheli-du-Crest, 1211, Geneva 4, Switzerland A. Keller, MD
Department of Radiology, Hopital Cantonal Universitaire, 24 rue Micheli-du-Crest, 1211, Geneva 4, Switzerland J. Garcia, MD
Department of Radiology, Hopital Cantonal Universitaire, 24 rue Micheli-du-Crest, 1211, Geneva 4, Switzerland J. Fasel, MD
Division of Anatomy, Department of Morphology, University Medical Center, Rue M. Servet 1, 1211 Geneva 4, Switzerland
the level of axial slices. In most patients a traditional acquisition is performed. Depending on the clini- cal history and on the goal of the examination, slice thickness can vary from 1 to 6 mm. For most patients 2–4 mm thick, contiguous sections reconstructed with bone or soft tissue algorithms are appropriate. If two- dimensional (2D) and 3D reconstructions are needed, a spiral acquisition with small thickness acquisition (1–2 mm), pitch of 1, and reconstruction thickness permitting overlapping is performed. Slices from the acromioclavicular joint to 1 cm below the glenoid are obtained. A 25-cm fi eld of view can usually image the scapula, proximal humerus and the lateral two thirds of the clavicle and permits satisfactory image resolu- tion. Routine comparison images of the contra-lateral shoulder are not obtained.
For the evaluation of the sternoclavicular joint the patient is supine with both arms resting at the side of the trunk. Care must be taken to correctly position the patient inside the gantry to allow symmetrical images of the joints. On an anteroposterior scout view 1 mm axial slices are centred from 1 cm cranial to 1 cm caudal to the medial epiphysis of the clavicle. A 15 cm fi eld of view centred on the midline allows good evaluation of both joints. Coronal reconstructions are obtained to show displacements in the frontal plane.
3.2.2 Results
CT can demonstrate the normal bone anatomy of the shoulder region. Cranially the lateral portion of the clavicle and anterior portion of the scapular spine, the acromion, constitute the AC joint. CT can readily diagnose an os acromiale, that results from a non-union of the distal ossifi cation centre of the acromion with the posterior main centre, and evalu- ate its size. When present the os acromiale articulates with both the clavicle and the acromion and can be implicated in the pathogenesis of anterior impinge- ment syndrome (Granieri and Bacarini 1998).
More caudally the spine of the scapula and the coracoid process, respectively anterior and posterior to the glenohumeral joint, are imaged. The round surface of the humeral head and the oval and slightly concave glenoid cavity form the joint surfaces of the glenohumeral joint. The humeral surface is about twice the glenoid surface. The humeral head presents two lateral projections, the anteromedial lesser tuber- osity (LT) and the posterolateral greater tuberosity (GT). Humeral torsion can be measured with CT by comparing an image obtained just below the coracoid
process with an image obtained about 2.5 cm proxi- mal to the interepicondylar line. Increased humeral torsion may predispose to recurrent glenohumeral joint dislocation (Dias et al. 1993). Between the two tuberosities the biceps groove or sulcus is found.
The glenoid cavity is perpendicular to the body of the scapula. Glenoid retroversion can be associated with recurrent posterior glenohumeral instability.
CT demonstration of retroversion can be useful in operative treatment (Wirth et al. 1994). The poste- rior glenoid rim appears rounded while the anterior one is pointed and thinner. Intraarticular structures can be hardly imaged by CT. The lax and redundant fi brous capsule is reinforced by the glenohumeral ligaments which insert into the humerus and into the fi brocartilaginous glenoid labrum. The labrum, which is attached at the edge of the glenoid fossa, is thought to increase joint stability. The anatomy of muscles and tendons surrounding the shoulder are easily assessed by CT. The rotator cuff is composed of four muscles which surround the glenohumeral joint. Anteriorly the subscapularis muscle is found between the anterior face of the scapula and the chest wall. Its tendon inserts into the internal aspect of the LT. The main function of the subscapularis muscle is adduction and internal rotation of the arm. The supraspinatus muscle, the main abductor of the arm, is located in the homologous bone fossa, delimited posteriorly by the spine of the scapula and anteriorly by the upper third of the body. The muscle continues in a tendon which inserts into the anterior portion of the GT. Posteriorly, inside the infraspinatus fossa, the infraspinatus and teres minor muscles are found.
Both allow external rotation of the humerus. Their tendons insert into the middle and posterior facets of the GT respectively. Muscle fatty degeneration can be assessed by CT in the preoperative evaluation of rotator cuff tears. Five degrees of fatty degeneration were described depending on the amount of adipose infi ltration of the muscle (Goutallier et al. 1994).
A better patient outcome can be expected if surgical treatment of wide tears is made before irreversible muscular damage takes place. Although the degree of fatty degeneration was signifi cantly related to the amount of atrophy of the respective muscles, CT degree of fatty degeneration correlate poorly with MRI fi ndings (Fuchs et al. 1999). The long head of the biceps tendon originates from the muscle in the anterior aspect of the arm, lies inside the biceps groove and enters into the joint between the supra- spinatus and subscapularis tendons (interval of the rotator cuff) to insert into the superior edge of the glenoid fossa. The deltoid muscle is separated from
the rotator cuff by the subacromial subdeltoid bursa.
In normal conditions only the peribursal fat can be imaged at CT while the bursa itself cannot be visu- alised. Full thickness tears of rotator cuff tendons allow communication between the joint and the bursa. Additional periarticular muscles imaged at CT
include the short head of the biceps, which inserts into the tip of the coracoid process together with the coracobrachialis and pectoralis minor muscle, the pectoralis major and triceps muscle.
Normal shoulder axial anatomy and the corre- sponding CT-anatomy are shown in Fig. 3.1.
Fig. 3.1a–i. Normal shoulder anatomy revealed by axial sec- tions of a cadaveric preparation and cor- responding computed tomography anatomy.
a S, skin; S. Fat, subcu- taneous fat; LS, leva- tor scapulae. b Clav, clavicle; V, vessels; LS, levator scapulae. c Clav, clavicle; Acr, acromion;
Dap, deltoid anterior portion; Dmp, deltoid middle portion. ...
a
b
c
d CP, coracoid process; HH, humeral head; Dap, deltoid muscle anterior portion; Dmp, deltoid muscle middle portion; Dpp, deltoid muscle posterior portion; Ss, supraspinatus muscle. e CP, coracoid process; HH, humeral head; G, glenoid; Dap, deltoid muscle ante- rior portion; Dmp, deltoid muscle middle portion; Dpp, deltoid muscle posterior portion; Is, infraspinatus muscle; asterisks, rotator cuff tendons; arrows, peribursal fat. f CP, coracoid process; HH, humeral head; G, glenoid; Dap, deltoid muscle anterior portion;
Dmp, deltoid muscle middle portion; Dpp, deltoid muscle posterior portion; Is, infraspinatus muscle; IsT, infraspinatus tendon; SS, subscapularis muscle, SST, subscapularis tendon; asterisks, glenoid labrum; arrow, peribursal fat; long white arrow, glenoid notch;
PM, pectoralis major; SA, serratus anterior. g HH, humeral head; G, glenoid; Dap, deltoid muscle anterior portion; Dmp, deltoid muscle middle portion; Dpp, deltoid muscle posterior portion; Is, infraspinatus muscle; Tm, teres minor; SS, subscapularis muscle;
e d
f
BT, long head biceps tendon; CB, coracobrachialis muscle; SB, short head biceps muscle; Pm, pectorals minor; asterisks, glenoid labrum; white arrow, glenoid notch; PM, pectoralis mayor; SA, serratus anterior; V, vessels. h HH, humeral head; G, glenoid; Dap, deltoid muscle anterior portion; Dmp, deltoid muscle middle portion; Dpp, deltoid muscle posterior portion; Is, infraspinatus muscle; Tm, teres minor; SS, subscapularis muscle; BT, long head biceps tendon; CB, coracobrachialis muscle; SB, short head biceps muscle; Pm, pectorals minor; asterisks, glenoid labrum; PM, pectoralis mayor; SA, serratus anterior; V, vessels. i HH, humeral head;
G, glenoid; Dap, deltoid muscle anterior portion; Dmp, deltoid muscle middle portion; Dpp, deltoid muscle posterior portion; Is, infraspinatus muscle; Tm, teres minor; SS subscapularis muscle; BT, long head biceps tendon; CB, coracobrachialis muscle; SB, short head biceps; Pm, pectorals minor; asterisks, glenoid labrum; PM, pectoralis mayor; SA, serratus anterior; V, vessels
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3.3 CT Arthrography
3.3.1 Technique
CT arthrography includes two steps: arthrography and CT.
Arthrography is usually performed in a radiologi- cal room under fl uoroscopic control. The patient is asked to lie supine with the arm in slight external rotation and the elbow close to the trunk. No rota- tion of the patient is necessary. Usually both the right and the left shoulder can be injected by the right-handed examiner, positioned at the right of the patient. After careful skin asepsis, under fl uoroscopic control, a spinal needle (7 cm - 21 gauge), connected with an extension tube to a 20-ml syringe is inserted by an anterior approach into the glenohumeral joint.
The extension tube should be used to avoid exposure of the radiologist’s hands during contrast injection (Obermann 1996) The site of the puncture is at the union between the middle and the lower third of the glenoid cavity. Usually no local anaesthesia is needed.
If an accurate evaluation of the anterior structures is desired, attention must be paid to careful positioning of the needle. Inadvertent contrast injection inside the subscapularis tendon can signifi cantly affect the assessment of the tendon as well as of the anterior capsulolabral complex. In this setting a posterior approach to joint puncture can be useful and can be performed under fl uoroscopic control (patient prone) or utilising a US-guided technique (patient seated). Confi rmation of the correct intraarticular positioning of the needle is obtained by injection of a small quantity of contrast. If the needle position is correct, the injected dye fl ows quickly away from the needle tip. If the contrast remains around the needle tip the needle is usually located inside the subscapu- laris tendon. Repositioning of the needle in a deeper position allows intraarticular injection. A single or double contrast technique can be used. We routinely utilise the single contrast technique since we believe that it allows better quality CT arthrography images.
Serial plain fi lms are usually obtained during slow injection of 10–15 cc of contrast. The quantity of contrast injected depends on the capacity of the joint that is easily judged at fl uoroscopy. In adhesive cap- sulitis no more then 7 ml can be introduced inside the joint. Adrenaline (0.1–0.3 ml of a 1:1000 solution) is added only if the CT cannot be performed within 30 min. After removal of the needle gentle passive movements of the humerus are performed to obtain
homogeneous intraarticular diffusion of the dye. In cases of rotator cuff tears a complete elevation of the arm over the head is suitable, since this can allow the dye to penetrate in small tears. Radiographs are then obtained in the AP view (neutral, internal and external rotation). The patient is then asked to hold the arm close to the trunk in order to avoid shoulder movements and prevent extraarticular contrast leak- age.
CT examination is performed with the patient examined in the same position described for the standard CT. Care must be taken to place the glenoid surface perpendicular to the plane of CT sections to allow good evaluation of intraarticular structures.
The arm is routinely maintained in a neutral rotation.
In patients evaluated for anterior instability, internal rotation of the upper arm can better display tears of the anterior glenoid labrum and fi lling of the anterior camera. In contrast, if an evaluation of the posterior labrum is needed external rotation of the arm allows optimal imaging since the labrum may be not coated by the contrast in internal rotation. If a double con- trast technique is used, a change in the patient pos- ture (prone vs. supine) can induce displacement of the injected air and a more detailed evaluation of the posterior and anterior structures can be obtained. In subjects with a clinical suspicion of medial instabil- ity of the biceps tendon, after the standard examina- tion, some images obtained at the level of the biceps groove in forced external rotation can show tendon subluxation or dislocation. Anteroposterior scanning radiograph is used to plan the level of axial slices.
Slices from above the acromioclavicular joint to the axillary recess are obtained. A 15 cm fi eld of view can usually image the lateral aspect of the scapula, the humeral head and the rotator cuff muscle. If a traditional acquisition is performed, 3 mm thick, contiguous sections are obtained reconstructed with a bone algorithm. If 2D and 3D reconstructions are required, a spiral acquisition with a collimation of 2 mm, reconstruction at 1 mm, pitch of 1 is per- formed in order to obtain the maximum amount of information. Comparison images of the contralateral shoulder are obtained if a dysplastic appearance is evident. Because of utilisation of intraarticular con- trast, images must be recorded on fi lms by utilising a wide window width (2500–3000) and a window level of 400–600.
Evaluation of the rotator cuff with direct sagittal CT arthrography has been described (Beltran et al.
1986). The technique was successful in diagnosing complete and incomplete rotator cuff tears although axial CT scanning was better for diagnosis of Bankart
lesions. Direct coronal view of the shoulder, obtained after CT axial sections, has been proposed and was an effective way to improve arthrographic CT (Blum et al. 1993). The utilisation of a spiral equipment which allows optimal reconstructions in any desired plane has considerably reduced the need for direct coronal and sagittal sections.
3.3.2 Results
Intraarticular injection of contrast greatly enhances the appreciation of internal structures of the glenohumeral joint.
The hyaline cartilages covering the articular sur- faces of the glenoid fossa and of the humeral head are demonstrated. The glenoid labrum is imaged in cross section as a triangular structure. The base is attached to the peripheral edge of the glenoid fossa and hya- line cartilage while the apex projects laterally. Usu- ally the anterior labrum is thinner and more pointed than the more rounded posterior labrum. For proper interpretation of CT arthrography images, however, awareness that the normal glenoid labrum presents a wide variety of shapes and sizes is essential. More- over, considerable variations of labrum attachment can be found in normal subjects (McNiesch and Callaghan 1987). At the superior labrum a slight, normal separation between the hyaline cartilage and the labrum (cleaved appearance) is a normal varia- tion and must not be interpreted as a posttraumatic lesion. Occasionally the separation can be complete allowing communication between the joint cavity and the subcoracoid recess (foramen infralabrum).
The joint capsule is loose and redundant to allow wide range of movement of the joint.
The anterior glenohumeral ligaments, superior glenohumeral ligament (SGHL), middle glenohu- meral ligament (MGHL) and inferior glenohumeral ligament (IGHL), are fi brous bands which strengthen the lax anterior capsule. A wide range of normal shapes of these structures can be found. The SGHL is the one most commonly identifi ed. The MGHL inserts into the upper portion of the anterior labrum and directs laterally and caudally to reach the ante- rior region of the anatomic neck of the humerus.
The MGHL can be absent or appears as a cordon like structure. In the Buford complex a cord-like MGHL is associated with the absence of the anterosuperior labrum. The IGHL is the ligament that is most fre- quently torn in anterior dislocation of the shoulder. It is composed of an anterior and a posterior portion.
Variations in the anterior capsule attachment into the neck of the scapula are found. In type 1 the capsule inserts into the glenoid labrum. In type 3 the capsule attaches more medially, into the scapular neck. Type 2 shows an intermediate insertion.
Two synovial recesses are found. The anterior subcoracoid recess and the inferior axillary recess.
The subcoracoid recess communicates with the main joint cavity through an opening found between the superior and middle anterior glenohumeral ligaments (the Weitbrecht–Broca foramen) and/or between the middle and inferior ligaments (the Rou- vière foramen).
Normal shoulder axial anatomy as visualised by CT arthrography is shown in Fig. 3.2.
In summary, CT arthrography is an accurate and easily performed technique to evaluate intraarticular shoulder structures. An accurate technique for joint puncture and CT examination is required. Awareness of normal variations of glenoid labrum (absence, cleaved appearance, different shape in different loca- tions), as well as of glenohumeral ligaments (absence, Buford complex), is essential for correct interpreta- tion of CT-arthrography images and to avoid false positive results.
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References
Beltran J, Gray LA, Bools JC et al (1986) Rotator cuff lesions of the shoulder: evaluation by direct sagittal CT arthrography.
Radiology 160:161–165
Blum A, Boyer B, Regent D et al (1993) Direct coronal view of the shoulder with arthrographic CT. Radiology 188:
677–681
Dias JJ, Mody BS, Finlay DB (1993) Recurrent anterior gle- nohumeral joint dislocation and torsion of the humerus.
Injury 24:329–332
Fuchs B, Weishaupt D, Zanetti M et al (1999) Fatty degenera- tion of the muscles of the rotator cuff: assessment by com- puted tomography versus magnetic resonance imaging. J Shoulder Elbow Surg 8:599–605
Goutallier D, Postel JM, Bernageau Jet al (1994) Fatty muscle degeneration in cuff ruptures. Pre- and postoperative evaluation by CT scan. Clin Orthop 304:78–83
Granieri GF, Bacarini L A (1998) A little-known cause of pain- ful shoulder: os acromiale. Eur Radiol 8:130–133
McNiesch LM, Callaghan JJ (1987) CT arthrography of the shoul- der: variations of the glenoid labrum. AJR 149:963–966 Obermann WR (1996) Optimizing joint-imaging: (CT)-
arthrography Eur Radiol 6:275–283
Wirth MA, Seltzer DG, Rockwood CA Jr (1994) Recurrent pos- terior glenohumeral dislocation associated with increased retroversion of the glenoid. A case report. Clin Orthop 308:
98–101
Fig. 3.2a–h. Normal shoulder CT arthrography anatomy revealed by axial images from cranial to caudal. SL, superior labrum;
AL, anterior labrum; PL, posterior labrum; IL, inferior labrum; SGHL, superior glenohumeral ligament; MGHL, middle glenohu- meral ligament; IGHL, inferior glenohumeral ligament; BT, long head biceps tendon; SST, subscapularis tendon; SR, subcoracoid recess; AR, axillary recess
