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Shoulder arthroscopy, anatomy and variants – part 2
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Shoulder arthroscopy, anatomy and variants e part 2
structure that exhibits restraint but also permits the great mobility we see in the shoulder joint. The volume of the joint, as dictated by the capsule, varies significantly and the extremes include the small restrictive volume found in adhesive capsulitis, to the capacious capsule in those patients with connective tissue disorders or multidirectional laxity. From an anatomical perspective, the rotator cuff tendons fuse with the capsule near their insertions. Supraspinatus and infraspinatus merge with the capsule about 15 mm proximal to their insertions on the humerus and cannot be separated from the capsule by blunt dissection. The capsule importantly contains several localised areas where there are definable thickenings representing the glenohumeral ligaments. It is also necessary to remember that the capsule is lined by synovium and is therefore subject to inflammatory disorders, malignancy and tumour-like conditions.
Simon Boyle Manuel Haag David Limb Laurent Lafosse
Abstract In part 1 of this article we have described the history of shoulder arthroscopy and its current indications. We introduced concepts useful in the execution and interpretation of shoulder arthroscopy and introduced some technical tips to help those starting out, or developing their expertise, in this surgical skill. In part 2 we will focus on the range of findings that arthroscopy can yield, which can at first be daunting and confusing. The spectrum of normal findings is quite wide and substantial experience is needed simply to recognise what is within this spectrum and what should be considered pathological. Furthermore some pathological findings can be subtle or obscure, and easily missed if the arthroscopy is not complete and correlated carefully with the examination under anaesthesia.
Superior gleno-humeral ligament (SGHL) This structure is found to be present in 40e94% of shoulders1,2 and, when present, tends have the most consistent anatomy of the three anterior ligaments. It arises from the 12 o’clock position at the supra glenoid tubercle but can also take origin from the biceps anchor and labrum. It travels parallel to the biceps tendon to insert on the medial edge of the bicipital groove and the fovea capitus (just superior to the lesser tuberosity). Laterally, at its insertion, the SGHL joins the coracohumeral ligament,3 contributes to the biceps pulley and forms part of the rotator interval. The lateral insertion of the SGHL means that this structure plays a crucial role in the stabilisation of the biceps tendon against anterior shearing stress as part of the pulley system. Arthroscopically it is best seen from the A portal and can be made more visible by bringing the shoulder into adduction (Figure 1).
Keywords arthroscopy; patient positioning; portals; shoulder anatomy
Gleno-humeral joint arthroscopy Once intra-articular access has been gained with the arthroscope, as described in part 1 of this article, it is important to conduct a systematic and thorough examination of the shoulder. This usually, but not always, starts with the gleno-humeral joint. Fundamental to any surgical procedure is a good knowledge of anatomy and its variants to ensure that all abnormalities are recognised, and just as importantly, that variants are not misdiagnosed as being pathological. Shoulder capsule The use of arthroscopy has led to a better appreciation of the structure and function of the capsule and its definable anatomic components. The capsule can be considered as a watertight
Simon Boyle MSc FRCS(Tr&Orth) Shoulder Fellow, Alps Surgery Institute, Clinique Generale, Annecy, France. Manuel Haag MD Shoulder Fellow, Alps Surgery Institute, Clinique Generale, Annecy, France. David Limb BSc FRCSEd(Orth) Consultant Orthopaedic Surgeon, Department of Orthopaedics and Trauma, Leeds General Infirmary, Leeds, UK. Figure 1 HH e humeral head, SSc Subscapularis, SGHL Superior glenohumeral ligament, MGHL Middle glenohumeral ligament, BT Biceps tendon.
Laurent Lafosse MD Shoulder Surgeon, Alps Surgery Institute, Clinique Generale, Annecy, France.
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Middle gleno-humeral ligament (MGHL) This ligament is present in 84e92% of shoulders1,2,4 and arises variably from the upper part of the glenoid, the labrum, or with the SGHL. It then runs diagonally downward and across the subscapularis tendon at 45 to insert into the inferior part of the lesser tuberosity. Its superior border is usually easily identifiable as it courses away from the SGHL. The interval between the two ligaments forms the entrance to the subscapular bursa through the foramen of Weitbrecht. The appearance of the MGHL is also subject to common variations a cord like MGHL (17e22%1,2) Buford complex19 which comprises cord like MGHL arising from the superior labrum with an absent anterior superior labrum between the MGHL origin and the mid-glenoid notch an absent or thin MGHL The importance of the morphology of the MGHL may well affect the stress that certain anatomical variations put on the biceps anchor, potentially predisposing to SLAP tears. Arthroscopically, the MGHL can be seen through the A or D portals (Figure 2). Special care should be taken to ensure it is carefully assessed at its humeral insertion to avoid missing a humeral avulsion of the gleno-humeral ligaments (HAGL) lesion at this level.
Figure 3 IGHLa. The prominent anterior edge of the IGHLa can be seen easily in some shoulders.
Arthroscopically the anterior band of the IGHL is best seen through the A portal and occasionally a thickened anterior edge can be discerned7 (Figure 3). Improved visualisation of this band may require abduction and external rotation of the arm to bring it under tension and into view. Further dynamic testing of these ligaments involves performing translational movements of the humeral head and observing the structures and their tension (Figure 4). Disruption of the IGHL should be carefully looked for due to its important role in shoulder stability. The glenoid or humeral attachment may be disrupted on either band predisposing to instability (Figure 5). The ability to pass the arthroscope between the humeral head and the glenoid at the level of the IGHLa is known as the drive through sign. This was originally considered to be a sign of shoulder instability but more recent work suggests that it is associated with shoulder laxity and is not specific for instability.8
Inferior gleno-humeral ligament (IGHL) Cadaveric studies have revealed that this structure is found in 75e93% of shoulders.4,6 The IGHL has an anterior band (IGHLa) which takes origin from the glenoid between the 2 and 5 o’clock positions and a posterior band (IGHLp) which takes origin from the 7e9 o’clock position. These converge to form a sling which inserts onto the humerus in the 4e8 o’clock position. This anatomical arrangement dictates that the IGHL acts as the main static stabiliser of the GHJ in abduction. The intervening capsular tissue between the two bands represents the axillary pouch.
Figure 4 IGHLa. These fibres can be seen forming a sling around the humeral head as they descend into the axillary pouch.
Figure 2 Cord like MGHL. SSc subscapularis, HH humeral head.
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Figure 7 Sagittal schematic of subscapularis recess.24
bursa when present. This is a useful area to park sutures when performing intra-articular procedures such as subscapularis repairs and biceps tenodeses. A final bursa may be found between the coracobrachialis anteriorly and subscapularis posteriorly corresponding to our previously described sub-coracoid space. This is generally approached from the subacromial region after identifying the coracoid via the CAL. Occasionally this communicates with the subscapular bursa. These areas can be sites of loose body settling and should therefore always be examined.
Figure 5 Inferior HAGL lesion.
Gleno-humeral joint recesses and bursae Between the gleno-humeral ligaments exist a variable number of recesses in the anterior capsule. Their existence is dependant on the presence of the gleno-humeral ligaments and their variation has been classified by DePalma into six different types.9 The synovial recess seen above the MGHL is known as the superior subscapular recess or foramen of Weitbrecht, and in most cases this opens into the subscapular bursa (Figure 6). This bursa lies between the subscapularis tendon and the glenoid neck and saddlebags the top of the subscapularis tendon10 (Figure 7). It can be followed along the superior border of the subscapularis tendon and reaches further medially between the subscapularis muscle and the coracoid process for several centimetres. This space is utilised arthroscopically to perform subscapularis releases and to approach the brachial plexus and subscapular nerves when needed. The synovial recess below the MGHL is known as the inferior subscapular recess and corresponds to the sub-coracoid foramen of Rouvie`re. This communicates with an inferior subscapular
Labrum This ring of fibrous tissue produces a circumferential lip on the glenoid. It would be convenient to compare the labrum to the menisci of the knee but in actual fact, there is very little fibrocartilaginous tissue in the labrum.11 Its fibres are arranged in a predominantly circumferential pattern although a superficial randomly arranged layer and a deep layer organised into dense insertional fibre bundles can be discerned on electron microscopy.12,13 The labrum, as well as forming an origin for the glenohumeral ligaments and biceps anchor, also provides a static role in gleno-humeral stability. It deepens the socket by up to 50% leading some authors to attribute to it a ‘‘chock block’’ function, limiting humeral translation. It also aids in the concavity compression role of the rotator cuff. Anatomical variations are seen most commonly in the anterosuperior segment of the labrum. A sub-labral foramen (Figure 8) has been reported in 12e19% of shoulders2,5 and a Buford complex (Figure 9) reported in up to 1.5% of shoulders.1,5 These areas should be carefully assessed and probed so as not to be confused with a traumatic anterior labral injury (Bankart lesion). As these lesions are not pathological, an unwarranted repair can lead to a poor outcome. A non-pathological meniscal variant has also been described in up to 15% of shoulders giving the appearance of a free edge.14 Again this should be probed to prevent unnecessary treatment. Below its equator, the labrum attaches to the glenoid in a consistent manner with good fixation to bone. The labrum is best viewed initially through the A portal and probed through the D or E portal to assess its integrity. The view of the posterior labrum can be improved by either displacing the
Figure 6 Foramen of Weitbrecht.
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The function of the RI and its components is to restrict inferior and posterior translation of the humeral head via the SGHL and CHL as well as limiting external rotation. A second, more subtle, role for the RI is to maintain a negative intra-articular pressure. Its lateral components are essential to maintain the stability of the biceps tendon. Arthroscopy has promulgated the study of the function of the RI and its disorders. Lesions of the RI have been classified by Nobuhara and Ikeda16 into two types. Type I lesions are those leading to a contracture of the RI eg. adhesive capsulitis and type II lesions lead to RI laxity. Alternative methods of classification include naming the lesion according to the individual structure involved and newer entities such as coracoid impingement and biceps instability are described. The normal dimensions of the RI have been reported at the level of the glenoid, and these define a normal RI of 21.6 mm without joint distension and 27.8 mm with fluid distension. These measurements serve as guidelines for assessing laxity during arthroscopic procedures although practically this is difficult to measure. The RI can be viewed intra-articularly through the A portal or extra-articularly through the C or D portals, where it also serves to provide access to the GHJ.
Figure 8 Sublabral hole.
humeral head anteriorly or changing the viewing portal to the D portal. The rotator interval The rotator interval (RI) remains an area of great fascination, debate and confusion. It is located in the anterior shoulder and continues to be implicated in various pathologies, particularly with regard to instability and stiffness. It is triangular in shape with its base at the coracoid process, its apex is the inter-tubercular groove, the inferior margin is the superior border of the subscapularis tendon and its superior margin is the inferior border of the supraspinatus tendon. The contents of the RI are the SGHL, biceps tendon, the coracohumeral ligament and the gleno-humeral joint capsule. The organisation of the layers of the rotator interval has been studied, and these differ from the medial part of the interval, where two layers can be defined, to the lateral part where four layers can be identified.15
The coracohumeral ligament (CHL) This irregular trapezoidal structure is located in the rotator interval. It originates from an extra-articular location via two roots; a ventral root arising from the anterior part of the dorsolateral coracoid and the dorsal root arising from the base of the coracoid. Both of these roots lie beneath the CA ligament, after which the CHL takes a course parallel to the long head of biceps tendon, through the interval, although its insertion laterally is subject to enormous variation. The most common variant is insertion into the interval itself, and less commonly the CHL inserts into supraspinatus tendon, subscapularis tendon or occasionally both17 (Figure 10). The CHL is thought to represent a phylogenetic remnant of a redundant pectoralis minor tendon.32 However debate
Figure 9 Buford complex.
Figure 10 CHL running parallel to the biceps in the RI.
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continues as to whether the CHL truly represents a distinct anatomical entity or whether it is a further capsular thickening. Its function is considered to be one of limiting external rotation with the arm in adduction29,33 but it also has a role in providing resistance to inferior translation of the humeral head.20,29,34 The CHL as a structure is particularly important to shoulder arthroscopists for several reasons. The first is that it is considered to be the primary structure affected by adhesive capsulitis21 and therefore any arthroscopic surgical release should address this. Secondly, it acts as an anatomic landmark to guide the arthroscopist towards the coracoid process and therefore the conjoint tendon, plexus etc. Finally, its ablation or transgression provides a route of entry to the glenohumeral joint through anterior portals. The biceps tendon The long head of biceps tendon (LHBT) is an intra-articular shoulder structure but remains extra-synovial. The tendon is enveloped in a synovial sheath which terminates in a blind pouch at the distal end of the bicipital groove. The LHBT is important to the arthroscopist both in terms of its landmark function but also as a source of pathology and symptoms. It can be considered to have three different sections: the biceps anchor, the intra-articular tendinous portion and the pulley system.
Figure 12 Intra-articular biceps tendon (BT). RI Rotator interval.
exiting through the pulley system. This intra-articular part of the tendon is on average 100 mm in length. Its cross section changes from an oval shape near the glenoid after which it becomes more tapered as it approaches the bicipital groove to finally become more rounded.
The biceps anchor (Figure 11): 40e60% of the LHBT fibres arise from the supra-glenoid tubercle, and this lies 5 mm medial to the superior rim of the glenoid.22 The remaining fibres arise from the glenoid labrum. The anchor is the site of the Superior Labral Anterior Posterior lesion (SLAP) as coined by Snyder in 1990,23 commonly seen in overhead throwing athletes and after traction injuries. Arthroscopically, SLAP lesions can be assessed using the Peel back test,24 whereby the anchor is visualised whilst the arm is placed in abduction and external rotation. The integrity of the anchor can be seen and graded.
The pulley system (Figures 13 and 14): The LHBT is stabilised as it exits the shoulder via the pulley system prior to entering the bicipital groove. The pulley has four components, these being the supraspinatus and subscapularis tendons, the CHL and the SGHL. Floor e this is formed largely by fibres from subscapularis, intermingled with the other three components of the pulley and becomes fibrocartilaginous in the groove. Medial Sling e the SGHL parallels the LHBT in the RI but as it enters the pulley, it forms a U shaped sling inserting just above subscapularis on the lesser tuberosity.
Intra-articular tendinous portion (Figure 12): From its site of attachment, the LHBT then passes obliquely along the RI before
Figure 11 Biceps anchor. BT Biceps tendon.
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Figure 13 Medial sling of pulley.
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Figure 15 Anterior 3D representation of Type II subscapularis tear. Figure 14 Lateral sling of pulley.
Subscapularis tears can be classified as follows.29 I e partial lesion only involving the upper 1/3 of subscap II e complete lesion of the upper 1/3 (see Figures 15 and 16) III e complete lesion of the upper 2/3 IV e complete lesion of the tendon but the head remains centred and Goutallier 3 V e complete lesion with an eccentric head position and coracoid impingement and Goutallier 4 (Goutallier grades refer to fatty degeneration of the muscle belly) In retracted tears, the subscapularis can be traced medially and may require the use of a supplementary portal to effect a release eg. portal C for viewing with an instrument such as a shaver or radiofrequency probe in D or E.(Figure 17).
Roof and Lateral wall e this is formed by the fibres of the CHL crossing the groove and also from a tendinous slip from supraspinatus extending to join subscapularis.25 These intimate relations dictate that the arthroscopist should carefully evaluate the tendons of supraspinatus and subscapularis in cases of biceps tendon instability.26,27 After probing the anchor and pulley, the LHBT can be dynamically tested by performing internal and external rotation manoeuvres. Dislocation is manifested by the tendon moving completely out of the groove. The intra-tubercular potion of the tendon can be visualised by pulling it into the joint using a probe. The macrostructure of the LHBT can be graded as follows with treatment recommendations for each of these.28 0 e normal I e <50% of tendon affected (localised lesion or fibre rupture) II e >50% of tendon affected (erosion/partial rupture) III e tendon rupture
Supraspinatus: This muscle arises from the supraspinous fossa via 2 muscle bellies to insert onto the greater tuberosity. From the anterior fusiform belly arises a central tendon which migrates
The rotator cuff The rotator cuff tendons lie beneath the deltoid and are vital in enabling movement and providing stability to the shoulder joint. The cuff comprises of 4 muscles e subscapularis, supraspinatus, infraspinatus and teres minor. Subscapularis: This is the largest and most powerful of the rotator cuff muscles. Its large origin from the upper 2/3 of the anterior surface of the scapula condenses laterally to pass under the coracoid. The upper 2/3 has a tendinous morphology whilst the fibres of the lower 1/3 remain muscular. It attaches to the lesser tubercle adjacent to the biceps groove. The upper 1/3 of the subscapularis tendon can be viewed intra-articularly through the A portal and its integrity can be assessed by probing. To improve the view of the subscapularis insertion, internal rotation should be applied to the arm. There should be a high index of suspicion for a subscapularis tear in the presence of an anterior pulley rupture.
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Figure 16 Intra-articular view of type II subscapularis tear seen through the posterior A portal.
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Infraspinatus: This thick, triangular, multipennate muscle arises from the infraspinous fossa after which its fibres converge into a tendon that passes across the posterior aspect of the glenohumeral joint. The tendon overlaps the posterior border of the supraspinatus tendon, where it is almost impossible to distinguish the two. Footprint e the tendon inserts via a trapezoidal footprint onto the middle facet of the greater tuberosity with average dimensions of 29 19 mm33 (Figure 18). As with the supraspinatus tendon, this area provides a good base for tendon to bone healing. The infraspinatus insertion lies immediately adjacent to the articular cartilage at its superior aspect but a gap of 16 mm develops inferiorly. This gap between the superior and inferior insertions represents the bare area (Figure 19). Teres minor: This muscle takes origin from the dorsal surface of the lateral border of the scapula and the dense fascia of infraspinatus. It then passes laterally, across the back of the shoulder joint, to form a tendon which inserts onto the inferior facet of the greater tuberosity. As the tendon passes over the capsule, its fibres become adherent and impossible to separate with blunt dissection. The inferior border of the teres minor tendon forms the superior boundary of the quadrilateral space which transmits the posterior circumflex humeral artery and axillary nerve.
Figure 17 Cable and crescent configuration in Supraspinatus.
anteriorly, thickens and forms an external extra-muscular tendon comprising 40% of the overall width of the tendon. The posterior 60% is flatter and arises from a unipennate muscle belly. These differences in muscle belly sizes and tendon dimensions results in a 2.88 times greater stress in the anterior supraspinatus tendon which may be a risk factor for this common site of tearing.18 The supraspinatus tendon has been divided into four structurally independent subunits based on histological and biomechanical studies30 as follows: 1. Tendon proper e extends from the musculotendinous junction to 2 cm medial to the greater tuberosity. The collagen fibres in this region are parallel. 2. Rotator Cable (Figure 13) e this band of densely packed unidirectional collagen fibres extends from the CHL anteriorly to the inferior border of infraspinatus posteriorly. The rotator cable surrounds the thinner crescent where the cable here is thought to act as a stress shield to protect the weaker crescent. Because of this effect, a tear of the rotator crescent may have no discernable functional deficit in the shoulder when the integrity of the rotator crescent is maintained. A suspension bridge analogy has been drawn here by Burkhart31 to explain this phenomenon where the cuff can be anatomically deficient but biomechanically intact. In these situations, the cable ensures that a balance of the force couples is maintained. 3. Fibrocartilage attachment e extends from the tendon proper to the greater tuberosity 4. Capsule e composed of thin collagen sheets with a uniform fibre alignment. The supraspinatus tendon inserts into the superior and middle facets of the greater tuberosity. Normally, a margin of 0.9 mm (0e4 mm) exists between the articular cartilage and the supraspinatus insertion, extending from the top of the bicipital groove to the top of the bare area. From this initial insertion, the tendon extends w16 mm laterally onto the tuberosity forming the footprint. This gives a wide zone of tendon to bone contact and recreating this forms the basis of the double row technique of rotator cuff repair (see Figure 18).
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Bones and cartilage The glenoid: The glenoid concavity has three components; bone, articular cartilage and the soft tissue labrum. It is shaped like an inverted comma with a broader inferior portion and a thinner superior tail. The average vertical dimension is 35 mm and average horizontal dimension is 25 mm. 75% of glenoids are retroverted overall with regard to the plane of the scapula with an average superior tilt of 15 , though the situation in reality is more complex than this and the version alters as one moves from superior to inferior parts.34 It is formed from two ossification centres that can be roughly separated by a transverse line between the two regions of the glenoid (Figure 20).
Figure 18 Anatomical model showing the footprint of the supraspinatus tendon (green), infraspinatus (red), teres minor (black) and subscapularis (blue).46
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Figure 19 Bare area.
Figure 21 Glenoid bare spot.
The glenoid fossa is covered by hyaline cartilage, which is thicker at the periphery than in the centre. This serves to deepen the concavity of the glenoid. The thin area of discolouration in the centre corresponds to the bare spot of the glenoid (Figure 21). This represents an area of cartilage thinning with underlying subchondral bone thickening35 probably due to the increased loads experienced in this region. The geometry of the glenoid bone and cartilage contributes 50% of the depth of the glenoid concavity, with the remaining 50% coming from the labrum. Arthroscopically the glenoid should be inspected in its entirety with regard to shape, size, fractures, cartilage defects and the course of the labrum. Probing of these structures may be necessary the extent and depth of any cartilage lesions. The glenoid is best visualised initially through the A portal and
a probe introduced through the D portal. For ease of description and communication of cartilage lesions we prefer to use the classification introduced by Outerbridge.36 We also use a system of letters (AeF) representing six segments of the glenoid to describe the location of any pathology. The A segment represents the superior segment and these progress to the postero-superior F segment (see Figure 22). The three division lines for these are a transverse line through the equator and a two further lines passing at 60 to this passing through the centre. Humeral head: The humeral head articular surface forms 1/3 of a near true sphere37 which is retroverted a mean of 25e3538 and has a superior inclination of 130 . The anterior border is limited by the lesser tuberosity and the lateral border by the greater tuberosity. The inter-tubercular groove lies between the two. A bare area exists on the posterolateral humeral head, adjacent to the infraspinatus tendon. This contains osseous pits
Figure 20 Glenoid ossification centres.
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Figure 22 Sectors of the glenoid.
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Figure 23 Humeral head with anterior translation in hyperlaxity. Figure 24 Traumatic Hill-Sachs lesion. Note the area of cartilage lateral to the Hill-Sachs (HS) lesion.
which represent previous sites of vessel penetration. The bone here should be assessed carefully and not confused with a traumatic Hill-Sachs lesion. The humerus is best examined through the A portal and probed through an anterior portal for any suspected fractures or cartilage defects. Cartilage lesions are classified by the Outerbridge system and, like the glenoid, the humerus can be divided into 6 segments for ease of description in a similar fashion to the glenoid. These are based on a line passing through the equator, and two further lines at 60 to this. The segments are named as follows: I e antero-superior III e centro-superior V e postero-superior II e antero-inferior IV e centro-inferior VI e postero-inferior Arthroscopy of the humeral head is very much a dynamic process, with rotation, translation, abduction and adduction movements all essential to enable an adequate inspection. It is also important to inspect for any soft tissue or bony avulsions of the gleno-humeral ligaments (HAGL lesions) especially in cases where instability is suspected. Stability can also be dynamically assessed by repeating translational movements (Figure 23). The size depth and position of engagement of a Hill-Sachs lesion can be assessed at this point (see Figure 24).
The scope is best directed towards the antero-lateral corner of the acromion when performing bursoscopy through the A portal to ensure successful entry. Not infrequently, the SA bursa extends laterally into the sub-deltoid bursa. Where adhesions are present from inflammation or previous surgery, a bursectomy is needed to improve visualisation. During bursoscopy, the bursal side of the rotator cuff can be seen, although the overlying bursal tissue may need to be removed with a shaver. The bursal side of the cuff is then inspected for tears, their shape, the tendon involved, its reducibility and the quality of the tendon involved. Calcific deposits can be probed for and evacuated on this side of the cuff. The C portal is the best portal for assessing antero-superior cuff tears in the SA space after an initial view has be obtained from the A portal. Extra-articular subscapularis tendon evaluation can be performed by moving anteriorly and inferiorly from the subacromial space back down to the ground floor. This is best performed through the C or D portal. Acromion: The acromion is one of the most studied parts of the shoulder largely due to its presumed role in impingement and rotator cuff pathology. The main role of the acromion in bipeds is to provide a lever arm and a strong arched origin for the powerful deltoid muscle. The acromion forms from three ossification centres, which usually fuse by the age of 25,40 and failure of any of these centres to unite can lead to an os acromiale. This has a mean incidence of 8% and most commonly it is an incidental finding. These lesions can be defined as a pre-acromion, meso-acromion (most common), met-acromion and basi-acromion. The morphology of the intact acromion has been described and classified by Bigliani into three different types. I e Flat II e Curved III e Hooked
Sub-acromial space Sub-acromial bursa: The subacromial bursa lies between the anterior rotator cuff and the acromion and provides an excellent bloodless field for the initial visualisation of the first floor of the house.39 It is a synovial-lined sac that acts to reduce friction and improve gliding between the rotator cuff and the coraco-acromial arch. The SA bursa lies more anteriorly than many surgeons appreciate, which may explain the difficulty that some arthroscopists have in gaining access to the bursa first time. As a guide, the mean distance to the posterior aspect of the bursa from the antero-lateral edge of the acromion is 2.8 cm or 55% of the AP acromial length. The degree to which the bursa crosses the ACJ is variable and in some cases it does not cross not at all.
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Numerous authors have associated the type III hooked acromion with rotator cuff tears. A convex41 and a keeled42 acromion have also been described. The acromion also takes the attachment of the coraco-acromial ligament and forms an articulation with the clavicle, both of which are discussed below.The acromion is visualised through the A portal and C portals, both of which can be used for instrumented resections. The undersurface of the acromion should normally be seen to be covered with the CAL and periosteum. The shape of the tip and the presence of an os acromiale should also be checked. Dissection of the anterior aspect of the acromion and ACJ often leads to bleeding due to the inadvertent division of the acromial branch of the thoracoacromial trunk.
A third centre at the tip ossifies later although occasionally this fails. The coracoid forms the site of attachment for several tendons and ligaments and can almost be considered to have a starfish type appearance when viewed from the front. Superiorly are the coraco-clavicular ligaments (conoid and trapezoid), inferiorly lies the conjoint tendon, laterally emanates the CHL and CAL and infero-medially courses the pectoralis minor tendon. Inferomedial to the coracoid lie the neurovascular structures of the plexus and axillary vessels and passing directly beneath the coracoid is the tendon of subscapularis. Arthroscopically the coracoid is a vital landmark which serves to orientate the surgeon prior to commencing several procedures eg. the origin of the CHL for an extra-articular arthroscopic arthrolysis in adhesive capsulitis, and the graft site for the arthroscopic Latarjet procedure. The coracoid is best visualised through the C portal with instrumented dissection through the D portal (Figure 26).
Coraco-acromial ligament (CAL): This strong triangular ligament forms the anterior part of the coracoacromial arch. It is separated from the rotator cuff by the subacromial bursa and is strongly implicated in impingement syndrome. Its origin is from a broad area on the lateral aspect of the coracoid. Its apex inserts onto the antero-medial and anteroinferior surfaces of the acromion. Commonly, distinct bands can be found e antero-lateral and postero-medial e although this is subject to variation.43 Spurs of the ligament occur preferentially in the antero-lateral band so it is important to completely visualise the antero-lateral corner of the acromion when examining this ligament with regard to a subacromial decompression.33 The CAL is best viewed through the A and the C portals (Figure 25). When viewed through the A portal, the fibres can be seen on the undersurface of the acromion passing obliquely to the coracoid. In its degenerate state, the normal white fibres can be seen to be frayed. Coracoid: The coracoid is found at the base of the neck of the glenoid and projects anteriorly before hooking antero-laterally and flattening. It has two and occasionally three ossification centres, the second of which appears at around 10 years of age and contributes to the formation of the upper part of the glenoid.
Acromio-clavicular joint (ACJ) This articulation between the clavicle and the acromion is often the ‘site of degeneration associated with pain, osteophyte formation or traumatic separation, hence its importance in arthroscopic surgery. It is a diarthrodial joint with the articular surfaces being separated by an intra-articular disc of varying size and shape. The angle of the joint is variable, but in most cases it is orientated supero-lateral to infero-medial. The lateral end of the clavicle has a convex articular surface whereas that of the acromion is concave. The joint capsule is thickest on is anterior, medial and superior surfaces although dissection of this area is required to identify this joint fully. Further aids to identification include applying pressure to the clavicle and observing its movement and the placement of a needle directly in the joint. The ACJ can be viewed through the A portal (Figure 27) and the lateral C portal and it is instrumented through the C and E portal most easily.
Figure 25 Coracoacromial ligament.
Figure 26 Coracoid process (CP) and Conjoint tendon (CT) post dissection.
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8 McFarland EG, Neira CA, Gutierrez MI, Cosgarea AJ, Magee M. Clinical significance of the arthroscopic drive-through sign in shoulder surgery. Arthroscopy 2001; 17: 38e43. 9 DePalma AF. In: Regional, variational and surgical anatomy. Surgery of the shoulder. 3rd edn. Philadelphia: JB Lippincott, 1983. 10 Grainger AJ, Tirman PF, Elliott JM, Kingzett-Taylor A, Steinbach LS, Genant HK. MR anatomy of the subcoracoid bursa and the association of subcoracoid effusion with tears of the anterior rotator cuff and the rotator interval. AJR Am J Roentgenol 2000; 174: 1377e80. 11 Moseley HF, Overgaard B. The anterior capsular mechanism in recurrent anterior dislocation of the shoulder. Journal of Bone and Joint Surgery Br 1962; 44: 913e27. 12 Nishida K, Hashizume H, Toda K, Inoue H. Histologic and scanning electron microscopic study of the glenoid labrum. J Shoulder Elbow Surg 1996; 5: 132e8. 13 Tamai K, Higashi A, Tanabe T, Hamada J. Recurrences after the open Bankart repair: a potential risk with use of suture anchors. J Shoulder Elbow Surg 1999; 8: 37e41. 14 Snyder SJ. Shoulder arthroscopy. Philadelphia: Lippincott Williams and Wilkins, 2003. 15 Jost B, Koch PP, Gerber C. Anatomy and functional aspects of the rotator interval. J Shoulder Elbow Surg 2000; 9: 336e41. 16 Nobuhara K, Ikeda H. Rotator interval lesion. Clin Orthop Relat Res 1987; 223: 44e50. 17 Yang HF, Tang KL, Chen W, et al. An anatomic and histologic study of the coracohumeral ligament. J Shoulder Elbow Surg 2009; 18: 305e10. 18 Di Giacomo G, Pouliart N, Costantini A, De Vita A. Atlas of functional shoulder anatomy. Milan: Springer-Verlag Italia, 2008. 19 Ferrari DA. Capsular ligaments of the shoulder. Anatomical and functional study of the anterior superior capsule. Am J Sports Med 1990; 18: 20e4. 20 Ovesen J, Nielsen S. Experimental distal subluxation in the glenohumeral joint. Arch Orthop Trauma Surg 1985; 104: 78e81. 21 Bunker TD, Anthony PP. The pathology of frozen shoulder. A Dupuytren-like disease. J Bone Joint Surg Br 1995; 77: 677e83. 22 Vangsness Jr CT, Jorgenson SS, Watson T, Johnson DL. The origin of the long head of the biceps from the scapula and glenoid labrum. An anatomical study of 100 shoulders. J Bone Joint Surg Br 1994; 76: 951e4. 23 Snyder SJ, Karzel RP, Del Pizzo W, Ferkel RD, Friedman MJ. SLAP lesions of the shoulder. Arthroscopy 1990; 6: 274e9. 24 Burkhart SS, Morgan CD. The peel-back mechanism: its role in producing and extending posterior type II SLAP lesions and its effect on SLAP repair rehabilitation. Arthroscopy 1998; 14: 637e40. 25 Clark JM, Harryman 2nd DT. Tendons, ligaments, and capsule of the rotator cuff. Gross and microscopic anatomy. J Bone Joint Surg Am 1992; 74: 713e25. 26 Walch G, Nove-Josserand L, Boileau P, Levigne C. Subluxations and dislocations of the tendon of the long head of the biceps. J Shoulder Elbow Surg 1998; 7: 100e8. 27 Walch G, Nove-Josserand L, Levigne C, Renaud E. Tears of the supraspinatus tendon associated with ‘‘hidden’’ lesions of the rotator interval. Journal of Shoulder and Elbow Surgery 1994; 3: 353e60. 28 Lafosse L, Reiland Y, Baier GP, Toussaint B, Jost B. Anterior and posterior instability of the long head of the biceps tendon in rotator cuff tears: a new classification based on arthroscopic observations. Arthroscopy 2007; 23: 73e80. 29 Lafosse L, Jost B, Reiland Y, Audebert S, Toussaint B, Gobezie R. Structural integrity and clinical outcomes after arthroscopic repair of isolated subscapularis tears. J Bone Joint Surg Am 2007; 89: 1184e93.
Figure 27 ACJ post resection of soft tissue and bone ends.
Summary With the correct equipment, skilled anaesthesia and careful positioning shoulder arthroscopy is safe and has proved itself to be one of the most powerful investigative tools for the diagnosis of shoulder pathology. There is a significant learning curve not only because of the awkward anatomical arrangement of the joint, but also because no two shoulders are the same and there is a very wide spectrum of normal findings. However, once triangulation within the joint is mastered and the range of pathological and normal findings is understood it proves to be an excellent tool not only for establishing a diagnosis, but in also providing a minimally invasive method of treatment with success rates catching up with, or surpassing, those reported with open surgical treatment. A
REFERENCES 1 Ide J, Maeda S, Takagi K. Normal variations of the glenohumeral ligament complex: an anatomic study for arthroscopic Bankart repair. Arthroscopy 2004; 20: 164e8. 2 Ilahi OA, Labbe MR, Cosculluela P. Variants of the anterosuperior glenoid labrum and associated pathology. Arthroscopy 2002; 18: 882e6. 3 Pouliart N, Somers K, Eid S, Gagey O. Variations in the superior capsuloligamentous complex and description of a new ligament. J Shoulder Elbow Surg 2007; 16: 821e36. 4 Steinbeck J, Liljenqvist U, Jerosch J. The anatomy of the glenohumeral ligamentous complex and its contribution to anterior shoulder stability. J Shoulder Elbow Surg 1998; 7: 122e6. 5 Williams MM, Snyder SJ, Buford Jr D. The Buford complex e the ‘‘cord-like’’ middle glenohumeral ligament and absent anterosuperior labrum complex: a normal anatomic capsulolabral variant. Arthroscopy 1994; 10: 241e7. 6 De Palma AF, Callery G, Bennett GA. Shoulder joint: Variational anatomy and degenerative regions of the shoulder joint. Vol. 6, 1949. 7 Turkel SJ, Panio MW, Marshall JL, Girgis FG. Stabilizing mechanisms preventing anterior dislocation of the glenohumeral joint. J Bone Joint Surg Am 1981; 63: 1208e17.
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30 Nakajima T, Rokuuma N, Hamada K. Histological and biomechanical characteristics of the supraspinatus tendon: reference torotator cuff tearing. J Shoulder Elbow Surg 1994; 3: 79e87. 31 Burkhart SS, Esch JC, Jolson RS. The rotator crescent and rotator cable: an anatomic description of the shoulder’s ‘‘suspension bridge’’. Arthroscopy 1993; 9: 611e6. 32 Curtis AS, Burbank KM, Tierney JJ, Scheller AD, Curran AR. The insertional footprint of the rotator cuff: an anatomic study. Arthroscopy 2006; 22: 609.e1. 33 DeFranco MJ, Cole BJ. Current concepts: current perspectives on rotator cuff anatomy. Arthroscopy 2009; 25: 305e20. 34 Monk AP, Berry E, Limb D, Soames RW. Laser morphometric analysis of the glenoid fossa of the scapula. Clin Anat 2001; 14: 320e3. 35 Warner JJ, Bowen MK, Deng XH, Hannafin JA, Arnoczky SP, Warren RF. Articular contact patterns of the normal glenohumeral joint. J Shoulder Elbow Surg 1998; 7: 381e8. 36 Outerbridge RE. The etiology of chondromalacia patellae. J Bone Joint Surg Br 1961; 43-B: 752e7.
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37 Boileau P, Walch G. The three-dimensional geometry of the proximal humerus. Implications for surgical technique and prosthetic design. J Bone Joint Surg Br 1997; 79: 857e65. 38 Rockwood CA, Matsen FA, Wirth MA, Lippitt SB. The shouler. 4th edn., vol. 1. Saunders Elsevier, 2009. 39 Yepes H, Al-Hibshi A, Tang M, Morris SF, Stanish WD. Vascular anatomy of the subacromial space: a map of bleeding points for the arthroscopic surgeon. Arthroscopy 2007; 23: 978e84. 40 Liberson F. Os acromiale e a contested anomaly. J Bone Joint Surg Am 1937; 19: 683e9. 41 Vanarthos WJ, Monu JU. Type 4 acromion: a new classification. Contemp Orthop 1995; 30: 227e9. 42 Tucker TJ, Snyder SJ. The keeled acromion: an aggressive acromial variant e a series of 20 patients with associated rotator cuff tears. Arthroscopy 2004; 20: 744e53. 43 Fealy S, April EW, Khazzam M, Armengol-Barallat J, Bigliani LU. The coracoacromial ligament: morphology and study of acromial enthesopathy. J Shoulder Elbow Surg 2005; 14: 542e8.
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Shoulder arthroscopy, anatomy and variants e part 2
structure that exhibits restraint but also permits the great mobility we see in the shoulder joint. The volume of the joint, as dictated by the capsule, varies significantly and the extremes include the small restrictive volume found in adhesive capsulitis, to the capacious capsule in those patients with connective tissue disorders or multidirectional laxity. From an anatomical perspective, the rotator cuff tendons fuse with the capsule near their insertions. Supraspinatus and infraspinatus merge with the capsule about 15 mm proximal to their insertions on the humerus and cannot be separated from the capsule by blunt dissection. The capsule importantly contains several localised areas where there are definable thickenings representing the glenohumeral ligaments. It is also necessary to remember that the capsule is lined by synovium and is therefore subject to inflammatory disorders, malignancy and tumour-like conditions.
Simon Boyle Manuel Haag David Limb Laurent Lafosse
Abstract In part 1 of this article we have described the history of shoulder arthroscopy and its current indications. We introduced concepts useful in the execution and interpretation of shoulder arthroscopy and introduced some technical tips to help those starting out, or developing their expertise, in this surgical skill. In part 2 we will focus on the range of findings that arthroscopy can yield, which can at first be daunting and confusing. The spectrum of normal findings is quite wide and substantial experience is needed simply to recognise what is within this spectrum and what should be considered pathological. Furthermore some pathological findings can be subtle or obscure, and easily missed if the arthroscopy is not complete and correlated carefully with the examination under anaesthesia.
Superior gleno-humeral ligament (SGHL) This structure is found to be present in 40e94% of shoulders1,2 and, when present, tends have the most consistent anatomy of the three anterior ligaments. It arises from the 12 o’clock position at the supra glenoid tubercle but can also take origin from the biceps anchor and labrum. It travels parallel to the biceps tendon to insert on the medial edge of the bicipital groove and the fovea capitus (just superior to the lesser tuberosity). Laterally, at its insertion, the SGHL joins the coracohumeral ligament,3 contributes to the biceps pulley and forms part of the rotator interval. The lateral insertion of the SGHL means that this structure plays a crucial role in the stabilisation of the biceps tendon against anterior shearing stress as part of the pulley system. Arthroscopically it is best seen from the A portal and can be made more visible by bringing the shoulder into adduction (Figure 1).
Keywords arthroscopy; patient positioning; portals; shoulder anatomy
Gleno-humeral joint arthroscopy Once intra-articular access has been gained with the arthroscope, as described in part 1 of this article, it is important to conduct a systematic and thorough examination of the shoulder. This usually, but not always, starts with the gleno-humeral joint. Fundamental to any surgical procedure is a good knowledge of anatomy and its variants to ensure that all abnormalities are recognised, and just as importantly, that variants are not misdiagnosed as being pathological. Shoulder capsule The use of arthroscopy has led to a better appreciation of the structure and function of the capsule and its definable anatomic components. The capsule can be considered as a watertight
Simon Boyle MSc FRCS(Tr&Orth) Shoulder Fellow, Alps Surgery Institute, Clinique Generale, Annecy, France. Manuel Haag MD Shoulder Fellow, Alps Surgery Institute, Clinique Generale, Annecy, France. David Limb BSc FRCSEd(Orth) Consultant Orthopaedic Surgeon, Department of Orthopaedics and Trauma, Leeds General Infirmary, Leeds, UK. Figure 1 HH e humeral head, SSc Subscapularis, SGHL Superior glenohumeral ligament, MGHL Middle glenohumeral ligament, BT Biceps tendon.
Laurent Lafosse MD Shoulder Surgeon, Alps Surgery Institute, Clinique Generale, Annecy, France.
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Middle gleno-humeral ligament (MGHL) This ligament is present in 84e92% of shoulders1,2,4 and arises variably from the upper part of the glenoid, the labrum, or with the SGHL. It then runs diagonally downward and across the subscapularis tendon at 45 to insert into the inferior part of the lesser tuberosity. Its superior border is usually easily identifiable as it courses away from the SGHL. The interval between the two ligaments forms the entrance to the subscapular bursa through the foramen of Weitbrecht. The appearance of the MGHL is also subject to common variations a cord like MGHL (17e22%1,2) Buford complex19 which comprises cord like MGHL arising from the superior labrum with an absent anterior superior labrum between the MGHL origin and the mid-glenoid notch an absent or thin MGHL The importance of the morphology of the MGHL may well affect the stress that certain anatomical variations put on the biceps anchor, potentially predisposing to SLAP tears. Arthroscopically, the MGHL can be seen through the A or D portals (Figure 2). Special care should be taken to ensure it is carefully assessed at its humeral insertion to avoid missing a humeral avulsion of the gleno-humeral ligaments (HAGL) lesion at this level.
Figure 3 IGHLa. The prominent anterior edge of the IGHLa can be seen easily in some shoulders.
Arthroscopically the anterior band of the IGHL is best seen through the A portal and occasionally a thickened anterior edge can be discerned7 (Figure 3). Improved visualisation of this band may require abduction and external rotation of the arm to bring it under tension and into view. Further dynamic testing of these ligaments involves performing translational movements of the humeral head and observing the structures and their tension (Figure 4). Disruption of the IGHL should be carefully looked for due to its important role in shoulder stability. The glenoid or humeral attachment may be disrupted on either band predisposing to instability (Figure 5). The ability to pass the arthroscope between the humeral head and the glenoid at the level of the IGHLa is known as the drive through sign. This was originally considered to be a sign of shoulder instability but more recent work suggests that it is associated with shoulder laxity and is not specific for instability.8
Inferior gleno-humeral ligament (IGHL) Cadaveric studies have revealed that this structure is found in 75e93% of shoulders.4,6 The IGHL has an anterior band (IGHLa) which takes origin from the glenoid between the 2 and 5 o’clock positions and a posterior band (IGHLp) which takes origin from the 7e9 o’clock position. These converge to form a sling which inserts onto the humerus in the 4e8 o’clock position. This anatomical arrangement dictates that the IGHL acts as the main static stabiliser of the GHJ in abduction. The intervening capsular tissue between the two bands represents the axillary pouch.
Figure 4 IGHLa. These fibres can be seen forming a sling around the humeral head as they descend into the axillary pouch.
Figure 2 Cord like MGHL. SSc subscapularis, HH humeral head.
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Figure 7 Sagittal schematic of subscapularis recess.24
bursa when present. This is a useful area to park sutures when performing intra-articular procedures such as subscapularis repairs and biceps tenodeses. A final bursa may be found between the coracobrachialis anteriorly and subscapularis posteriorly corresponding to our previously described sub-coracoid space. This is generally approached from the subacromial region after identifying the coracoid via the CAL. Occasionally this communicates with the subscapular bursa. These areas can be sites of loose body settling and should therefore always be examined.
Figure 5 Inferior HAGL lesion.
Gleno-humeral joint recesses and bursae Between the gleno-humeral ligaments exist a variable number of recesses in the anterior capsule. Their existence is dependant on the presence of the gleno-humeral ligaments and their variation has been classified by DePalma into six different types.9 The synovial recess seen above the MGHL is known as the superior subscapular recess or foramen of Weitbrecht, and in most cases this opens into the subscapular bursa (Figure 6). This bursa lies between the subscapularis tendon and the glenoid neck and saddlebags the top of the subscapularis tendon10 (Figure 7). It can be followed along the superior border of the subscapularis tendon and reaches further medially between the subscapularis muscle and the coracoid process for several centimetres. This space is utilised arthroscopically to perform subscapularis releases and to approach the brachial plexus and subscapular nerves when needed. The synovial recess below the MGHL is known as the inferior subscapular recess and corresponds to the sub-coracoid foramen of Rouvie`re. This communicates with an inferior subscapular
Labrum This ring of fibrous tissue produces a circumferential lip on the glenoid. It would be convenient to compare the labrum to the menisci of the knee but in actual fact, there is very little fibrocartilaginous tissue in the labrum.11 Its fibres are arranged in a predominantly circumferential pattern although a superficial randomly arranged layer and a deep layer organised into dense insertional fibre bundles can be discerned on electron microscopy.12,13 The labrum, as well as forming an origin for the glenohumeral ligaments and biceps anchor, also provides a static role in gleno-humeral stability. It deepens the socket by up to 50% leading some authors to attribute to it a ‘‘chock block’’ function, limiting humeral translation. It also aids in the concavity compression role of the rotator cuff. Anatomical variations are seen most commonly in the anterosuperior segment of the labrum. A sub-labral foramen (Figure 8) has been reported in 12e19% of shoulders2,5 and a Buford complex (Figure 9) reported in up to 1.5% of shoulders.1,5 These areas should be carefully assessed and probed so as not to be confused with a traumatic anterior labral injury (Bankart lesion). As these lesions are not pathological, an unwarranted repair can lead to a poor outcome. A non-pathological meniscal variant has also been described in up to 15% of shoulders giving the appearance of a free edge.14 Again this should be probed to prevent unnecessary treatment. Below its equator, the labrum attaches to the glenoid in a consistent manner with good fixation to bone. The labrum is best viewed initially through the A portal and probed through the D or E portal to assess its integrity. The view of the posterior labrum can be improved by either displacing the
Figure 6 Foramen of Weitbrecht.
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The function of the RI and its components is to restrict inferior and posterior translation of the humeral head via the SGHL and CHL as well as limiting external rotation. A second, more subtle, role for the RI is to maintain a negative intra-articular pressure. Its lateral components are essential to maintain the stability of the biceps tendon. Arthroscopy has promulgated the study of the function of the RI and its disorders. Lesions of the RI have been classified by Nobuhara and Ikeda16 into two types. Type I lesions are those leading to a contracture of the RI eg. adhesive capsulitis and type II lesions lead to RI laxity. Alternative methods of classification include naming the lesion according to the individual structure involved and newer entities such as coracoid impingement and biceps instability are described. The normal dimensions of the RI have been reported at the level of the glenoid, and these define a normal RI of 21.6 mm without joint distension and 27.8 mm with fluid distension. These measurements serve as guidelines for assessing laxity during arthroscopic procedures although practically this is difficult to measure. The RI can be viewed intra-articularly through the A portal or extra-articularly through the C or D portals, where it also serves to provide access to the GHJ.
Figure 8 Sublabral hole.
humeral head anteriorly or changing the viewing portal to the D portal. The rotator interval The rotator interval (RI) remains an area of great fascination, debate and confusion. It is located in the anterior shoulder and continues to be implicated in various pathologies, particularly with regard to instability and stiffness. It is triangular in shape with its base at the coracoid process, its apex is the inter-tubercular groove, the inferior margin is the superior border of the subscapularis tendon and its superior margin is the inferior border of the supraspinatus tendon. The contents of the RI are the SGHL, biceps tendon, the coracohumeral ligament and the gleno-humeral joint capsule. The organisation of the layers of the rotator interval has been studied, and these differ from the medial part of the interval, where two layers can be defined, to the lateral part where four layers can be identified.15
The coracohumeral ligament (CHL) This irregular trapezoidal structure is located in the rotator interval. It originates from an extra-articular location via two roots; a ventral root arising from the anterior part of the dorsolateral coracoid and the dorsal root arising from the base of the coracoid. Both of these roots lie beneath the CA ligament, after which the CHL takes a course parallel to the long head of biceps tendon, through the interval, although its insertion laterally is subject to enormous variation. The most common variant is insertion into the interval itself, and less commonly the CHL inserts into supraspinatus tendon, subscapularis tendon or occasionally both17 (Figure 10). The CHL is thought to represent a phylogenetic remnant of a redundant pectoralis minor tendon.32 However debate
Figure 9 Buford complex.
Figure 10 CHL running parallel to the biceps in the RI.
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continues as to whether the CHL truly represents a distinct anatomical entity or whether it is a further capsular thickening. Its function is considered to be one of limiting external rotation with the arm in adduction29,33 but it also has a role in providing resistance to inferior translation of the humeral head.20,29,34 The CHL as a structure is particularly important to shoulder arthroscopists for several reasons. The first is that it is considered to be the primary structure affected by adhesive capsulitis21 and therefore any arthroscopic surgical release should address this. Secondly, it acts as an anatomic landmark to guide the arthroscopist towards the coracoid process and therefore the conjoint tendon, plexus etc. Finally, its ablation or transgression provides a route of entry to the glenohumeral joint through anterior portals. The biceps tendon The long head of biceps tendon (LHBT) is an intra-articular shoulder structure but remains extra-synovial. The tendon is enveloped in a synovial sheath which terminates in a blind pouch at the distal end of the bicipital groove. The LHBT is important to the arthroscopist both in terms of its landmark function but also as a source of pathology and symptoms. It can be considered to have three different sections: the biceps anchor, the intra-articular tendinous portion and the pulley system.
Figure 12 Intra-articular biceps tendon (BT). RI Rotator interval.
exiting through the pulley system. This intra-articular part of the tendon is on average 100 mm in length. Its cross section changes from an oval shape near the glenoid after which it becomes more tapered as it approaches the bicipital groove to finally become more rounded.
The biceps anchor (Figure 11): 40e60% of the LHBT fibres arise from the supra-glenoid tubercle, and this lies 5 mm medial to the superior rim of the glenoid.22 The remaining fibres arise from the glenoid labrum. The anchor is the site of the Superior Labral Anterior Posterior lesion (SLAP) as coined by Snyder in 1990,23 commonly seen in overhead throwing athletes and after traction injuries. Arthroscopically, SLAP lesions can be assessed using the Peel back test,24 whereby the anchor is visualised whilst the arm is placed in abduction and external rotation. The integrity of the anchor can be seen and graded.
The pulley system (Figures 13 and 14): The LHBT is stabilised as it exits the shoulder via the pulley system prior to entering the bicipital groove. The pulley has four components, these being the supraspinatus and subscapularis tendons, the CHL and the SGHL. Floor e this is formed largely by fibres from subscapularis, intermingled with the other three components of the pulley and becomes fibrocartilaginous in the groove. Medial Sling e the SGHL parallels the LHBT in the RI but as it enters the pulley, it forms a U shaped sling inserting just above subscapularis on the lesser tuberosity.
Intra-articular tendinous portion (Figure 12): From its site of attachment, the LHBT then passes obliquely along the RI before
Figure 11 Biceps anchor. BT Biceps tendon.
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Figure 13 Medial sling of pulley.
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Figure 15 Anterior 3D representation of Type II subscapularis tear. Figure 14 Lateral sling of pulley.
Subscapularis tears can be classified as follows.29 I e partial lesion only involving the upper 1/3 of subscap II e complete lesion of the upper 1/3 (see Figures 15 and 16) III e complete lesion of the upper 2/3 IV e complete lesion of the tendon but the head remains centred and Goutallier 3 V e complete lesion with an eccentric head position and coracoid impingement and Goutallier 4 (Goutallier grades refer to fatty degeneration of the muscle belly) In retracted tears, the subscapularis can be traced medially and may require the use of a supplementary portal to effect a release eg. portal C for viewing with an instrument such as a shaver or radiofrequency probe in D or E.(Figure 17).
Roof and Lateral wall e this is formed by the fibres of the CHL crossing the groove and also from a tendinous slip from supraspinatus extending to join subscapularis.25 These intimate relations dictate that the arthroscopist should carefully evaluate the tendons of supraspinatus and subscapularis in cases of biceps tendon instability.26,27 After probing the anchor and pulley, the LHBT can be dynamically tested by performing internal and external rotation manoeuvres. Dislocation is manifested by the tendon moving completely out of the groove. The intra-tubercular potion of the tendon can be visualised by pulling it into the joint using a probe. The macrostructure of the LHBT can be graded as follows with treatment recommendations for each of these.28 0 e normal I e <50% of tendon affected (localised lesion or fibre rupture) II e >50% of tendon affected (erosion/partial rupture) III e tendon rupture
Supraspinatus: This muscle arises from the supraspinous fossa via 2 muscle bellies to insert onto the greater tuberosity. From the anterior fusiform belly arises a central tendon which migrates
The rotator cuff The rotator cuff tendons lie beneath the deltoid and are vital in enabling movement and providing stability to the shoulder joint. The cuff comprises of 4 muscles e subscapularis, supraspinatus, infraspinatus and teres minor. Subscapularis: This is the largest and most powerful of the rotator cuff muscles. Its large origin from the upper 2/3 of the anterior surface of the scapula condenses laterally to pass under the coracoid. The upper 2/3 has a tendinous morphology whilst the fibres of the lower 1/3 remain muscular. It attaches to the lesser tubercle adjacent to the biceps groove. The upper 1/3 of the subscapularis tendon can be viewed intra-articularly through the A portal and its integrity can be assessed by probing. To improve the view of the subscapularis insertion, internal rotation should be applied to the arm. There should be a high index of suspicion for a subscapularis tear in the presence of an anterior pulley rupture.
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Figure 16 Intra-articular view of type II subscapularis tear seen through the posterior A portal.
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Infraspinatus: This thick, triangular, multipennate muscle arises from the infraspinous fossa after which its fibres converge into a tendon that passes across the posterior aspect of the glenohumeral joint. The tendon overlaps the posterior border of the supraspinatus tendon, where it is almost impossible to distinguish the two. Footprint e the tendon inserts via a trapezoidal footprint onto the middle facet of the greater tuberosity with average dimensions of 29 19 mm33 (Figure 18). As with the supraspinatus tendon, this area provides a good base for tendon to bone healing. The infraspinatus insertion lies immediately adjacent to the articular cartilage at its superior aspect but a gap of 16 mm develops inferiorly. This gap between the superior and inferior insertions represents the bare area (Figure 19). Teres minor: This muscle takes origin from the dorsal surface of the lateral border of the scapula and the dense fascia of infraspinatus. It then passes laterally, across the back of the shoulder joint, to form a tendon which inserts onto the inferior facet of the greater tuberosity. As the tendon passes over the capsule, its fibres become adherent and impossible to separate with blunt dissection. The inferior border of the teres minor tendon forms the superior boundary of the quadrilateral space which transmits the posterior circumflex humeral artery and axillary nerve.
Figure 17 Cable and crescent configuration in Supraspinatus.
anteriorly, thickens and forms an external extra-muscular tendon comprising 40% of the overall width of the tendon. The posterior 60% is flatter and arises from a unipennate muscle belly. These differences in muscle belly sizes and tendon dimensions results in a 2.88 times greater stress in the anterior supraspinatus tendon which may be a risk factor for this common site of tearing.18 The supraspinatus tendon has been divided into four structurally independent subunits based on histological and biomechanical studies30 as follows: 1. Tendon proper e extends from the musculotendinous junction to 2 cm medial to the greater tuberosity. The collagen fibres in this region are parallel. 2. Rotator Cable (Figure 13) e this band of densely packed unidirectional collagen fibres extends from the CHL anteriorly to the inferior border of infraspinatus posteriorly. The rotator cable surrounds the thinner crescent where the cable here is thought to act as a stress shield to protect the weaker crescent. Because of this effect, a tear of the rotator crescent may have no discernable functional deficit in the shoulder when the integrity of the rotator crescent is maintained. A suspension bridge analogy has been drawn here by Burkhart31 to explain this phenomenon where the cuff can be anatomically deficient but biomechanically intact. In these situations, the cable ensures that a balance of the force couples is maintained. 3. Fibrocartilage attachment e extends from the tendon proper to the greater tuberosity 4. Capsule e composed of thin collagen sheets with a uniform fibre alignment. The supraspinatus tendon inserts into the superior and middle facets of the greater tuberosity. Normally, a margin of 0.9 mm (0e4 mm) exists between the articular cartilage and the supraspinatus insertion, extending from the top of the bicipital groove to the top of the bare area. From this initial insertion, the tendon extends w16 mm laterally onto the tuberosity forming the footprint. This gives a wide zone of tendon to bone contact and recreating this forms the basis of the double row technique of rotator cuff repair (see Figure 18).
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Bones and cartilage The glenoid: The glenoid concavity has three components; bone, articular cartilage and the soft tissue labrum. It is shaped like an inverted comma with a broader inferior portion and a thinner superior tail. The average vertical dimension is 35 mm and average horizontal dimension is 25 mm. 75% of glenoids are retroverted overall with regard to the plane of the scapula with an average superior tilt of 15 , though the situation in reality is more complex than this and the version alters as one moves from superior to inferior parts.34 It is formed from two ossification centres that can be roughly separated by a transverse line between the two regions of the glenoid (Figure 20).
Figure 18 Anatomical model showing the footprint of the supraspinatus tendon (green), infraspinatus (red), teres minor (black) and subscapularis (blue).46
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Figure 19 Bare area.
Figure 21 Glenoid bare spot.
The glenoid fossa is covered by hyaline cartilage, which is thicker at the periphery than in the centre. This serves to deepen the concavity of the glenoid. The thin area of discolouration in the centre corresponds to the bare spot of the glenoid (Figure 21). This represents an area of cartilage thinning with underlying subchondral bone thickening35 probably due to the increased loads experienced in this region. The geometry of the glenoid bone and cartilage contributes 50% of the depth of the glenoid concavity, with the remaining 50% coming from the labrum. Arthroscopically the glenoid should be inspected in its entirety with regard to shape, size, fractures, cartilage defects and the course of the labrum. Probing of these structures may be necessary the extent and depth of any cartilage lesions. The glenoid is best visualised initially through the A portal and
a probe introduced through the D portal. For ease of description and communication of cartilage lesions we prefer to use the classification introduced by Outerbridge.36 We also use a system of letters (AeF) representing six segments of the glenoid to describe the location of any pathology. The A segment represents the superior segment and these progress to the postero-superior F segment (see Figure 22). The three division lines for these are a transverse line through the equator and a two further lines passing at 60 to this passing through the centre. Humeral head: The humeral head articular surface forms 1/3 of a near true sphere37 which is retroverted a mean of 25e3538 and has a superior inclination of 130 . The anterior border is limited by the lesser tuberosity and the lateral border by the greater tuberosity. The inter-tubercular groove lies between the two. A bare area exists on the posterolateral humeral head, adjacent to the infraspinatus tendon. This contains osseous pits
Figure 20 Glenoid ossification centres.
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Figure 22 Sectors of the glenoid.
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Figure 23 Humeral head with anterior translation in hyperlaxity. Figure 24 Traumatic Hill-Sachs lesion. Note the area of cartilage lateral to the Hill-Sachs (HS) lesion.
which represent previous sites of vessel penetration. The bone here should be assessed carefully and not confused with a traumatic Hill-Sachs lesion. The humerus is best examined through the A portal and probed through an anterior portal for any suspected fractures or cartilage defects. Cartilage lesions are classified by the Outerbridge system and, like the glenoid, the humerus can be divided into 6 segments for ease of description in a similar fashion to the glenoid. These are based on a line passing through the equator, and two further lines at 60 to this. The segments are named as follows: I e antero-superior III e centro-superior V e postero-superior II e antero-inferior IV e centro-inferior VI e postero-inferior Arthroscopy of the humeral head is very much a dynamic process, with rotation, translation, abduction and adduction movements all essential to enable an adequate inspection. It is also important to inspect for any soft tissue or bony avulsions of the gleno-humeral ligaments (HAGL lesions) especially in cases where instability is suspected. Stability can also be dynamically assessed by repeating translational movements (Figure 23). The size depth and position of engagement of a Hill-Sachs lesion can be assessed at this point (see Figure 24).
The scope is best directed towards the antero-lateral corner of the acromion when performing bursoscopy through the A portal to ensure successful entry. Not infrequently, the SA bursa extends laterally into the sub-deltoid bursa. Where adhesions are present from inflammation or previous surgery, a bursectomy is needed to improve visualisation. During bursoscopy, the bursal side of the rotator cuff can be seen, although the overlying bursal tissue may need to be removed with a shaver. The bursal side of the cuff is then inspected for tears, their shape, the tendon involved, its reducibility and the quality of the tendon involved. Calcific deposits can be probed for and evacuated on this side of the cuff. The C portal is the best portal for assessing antero-superior cuff tears in the SA space after an initial view has be obtained from the A portal. Extra-articular subscapularis tendon evaluation can be performed by moving anteriorly and inferiorly from the subacromial space back down to the ground floor. This is best performed through the C or D portal. Acromion: The acromion is one of the most studied parts of the shoulder largely due to its presumed role in impingement and rotator cuff pathology. The main role of the acromion in bipeds is to provide a lever arm and a strong arched origin for the powerful deltoid muscle. The acromion forms from three ossification centres, which usually fuse by the age of 25,40 and failure of any of these centres to unite can lead to an os acromiale. This has a mean incidence of 8% and most commonly it is an incidental finding. These lesions can be defined as a pre-acromion, meso-acromion (most common), met-acromion and basi-acromion. The morphology of the intact acromion has been described and classified by Bigliani into three different types. I e Flat II e Curved III e Hooked
Sub-acromial space Sub-acromial bursa: The subacromial bursa lies between the anterior rotator cuff and the acromion and provides an excellent bloodless field for the initial visualisation of the first floor of the house.39 It is a synovial-lined sac that acts to reduce friction and improve gliding between the rotator cuff and the coraco-acromial arch. The SA bursa lies more anteriorly than many surgeons appreciate, which may explain the difficulty that some arthroscopists have in gaining access to the bursa first time. As a guide, the mean distance to the posterior aspect of the bursa from the antero-lateral edge of the acromion is 2.8 cm or 55% of the AP acromial length. The degree to which the bursa crosses the ACJ is variable and in some cases it does not cross not at all.
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Numerous authors have associated the type III hooked acromion with rotator cuff tears. A convex41 and a keeled42 acromion have also been described. The acromion also takes the attachment of the coraco-acromial ligament and forms an articulation with the clavicle, both of which are discussed below.The acromion is visualised through the A portal and C portals, both of which can be used for instrumented resections. The undersurface of the acromion should normally be seen to be covered with the CAL and periosteum. The shape of the tip and the presence of an os acromiale should also be checked. Dissection of the anterior aspect of the acromion and ACJ often leads to bleeding due to the inadvertent division of the acromial branch of the thoracoacromial trunk.
A third centre at the tip ossifies later although occasionally this fails. The coracoid forms the site of attachment for several tendons and ligaments and can almost be considered to have a starfish type appearance when viewed from the front. Superiorly are the coraco-clavicular ligaments (conoid and trapezoid), inferiorly lies the conjoint tendon, laterally emanates the CHL and CAL and infero-medially courses the pectoralis minor tendon. Inferomedial to the coracoid lie the neurovascular structures of the plexus and axillary vessels and passing directly beneath the coracoid is the tendon of subscapularis. Arthroscopically the coracoid is a vital landmark which serves to orientate the surgeon prior to commencing several procedures eg. the origin of the CHL for an extra-articular arthroscopic arthrolysis in adhesive capsulitis, and the graft site for the arthroscopic Latarjet procedure. The coracoid is best visualised through the C portal with instrumented dissection through the D portal (Figure 26).
Coraco-acromial ligament (CAL): This strong triangular ligament forms the anterior part of the coracoacromial arch. It is separated from the rotator cuff by the subacromial bursa and is strongly implicated in impingement syndrome. Its origin is from a broad area on the lateral aspect of the coracoid. Its apex inserts onto the antero-medial and anteroinferior surfaces of the acromion. Commonly, distinct bands can be found e antero-lateral and postero-medial e although this is subject to variation.43 Spurs of the ligament occur preferentially in the antero-lateral band so it is important to completely visualise the antero-lateral corner of the acromion when examining this ligament with regard to a subacromial decompression.33 The CAL is best viewed through the A and the C portals (Figure 25). When viewed through the A portal, the fibres can be seen on the undersurface of the acromion passing obliquely to the coracoid. In its degenerate state, the normal white fibres can be seen to be frayed. Coracoid: The coracoid is found at the base of the neck of the glenoid and projects anteriorly before hooking antero-laterally and flattening. It has two and occasionally three ossification centres, the second of which appears at around 10 years of age and contributes to the formation of the upper part of the glenoid.
Acromio-clavicular joint (ACJ) This articulation between the clavicle and the acromion is often the ‘site of degeneration associated with pain, osteophyte formation or traumatic separation, hence its importance in arthroscopic surgery. It is a diarthrodial joint with the articular surfaces being separated by an intra-articular disc of varying size and shape. The angle of the joint is variable, but in most cases it is orientated supero-lateral to infero-medial. The lateral end of the clavicle has a convex articular surface whereas that of the acromion is concave. The joint capsule is thickest on is anterior, medial and superior surfaces although dissection of this area is required to identify this joint fully. Further aids to identification include applying pressure to the clavicle and observing its movement and the placement of a needle directly in the joint. The ACJ can be viewed through the A portal (Figure 27) and the lateral C portal and it is instrumented through the C and E portal most easily.
Figure 25 Coracoacromial ligament.
Figure 26 Coracoid process (CP) and Conjoint tendon (CT) post dissection.
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8 McFarland EG, Neira CA, Gutierrez MI, Cosgarea AJ, Magee M. Clinical significance of the arthroscopic drive-through sign in shoulder surgery. Arthroscopy 2001; 17: 38e43. 9 DePalma AF. In: Regional, variational and surgical anatomy. Surgery of the shoulder. 3rd edn. Philadelphia: JB Lippincott, 1983. 10 Grainger AJ, Tirman PF, Elliott JM, Kingzett-Taylor A, Steinbach LS, Genant HK. MR anatomy of the subcoracoid bursa and the association of subcoracoid effusion with tears of the anterior rotator cuff and the rotator interval. AJR Am J Roentgenol 2000; 174: 1377e80. 11 Moseley HF, Overgaard B. The anterior capsular mechanism in recurrent anterior dislocation of the shoulder. Journal of Bone and Joint Surgery Br 1962; 44: 913e27. 12 Nishida K, Hashizume H, Toda K, Inoue H. Histologic and scanning electron microscopic study of the glenoid labrum. J Shoulder Elbow Surg 1996; 5: 132e8. 13 Tamai K, Higashi A, Tanabe T, Hamada J. Recurrences after the open Bankart repair: a potential risk with use of suture anchors. J Shoulder Elbow Surg 1999; 8: 37e41. 14 Snyder SJ. Shoulder arthroscopy. Philadelphia: Lippincott Williams and Wilkins, 2003. 15 Jost B, Koch PP, Gerber C. Anatomy and functional aspects of the rotator interval. J Shoulder Elbow Surg 2000; 9: 336e41. 16 Nobuhara K, Ikeda H. Rotator interval lesion. Clin Orthop Relat Res 1987; 223: 44e50. 17 Yang HF, Tang KL, Chen W, et al. An anatomic and histologic study of the coracohumeral ligament. J Shoulder Elbow Surg 2009; 18: 305e10. 18 Di Giacomo G, Pouliart N, Costantini A, De Vita A. Atlas of functional shoulder anatomy. Milan: Springer-Verlag Italia, 2008. 19 Ferrari DA. Capsular ligaments of the shoulder. Anatomical and functional study of the anterior superior capsule. Am J Sports Med 1990; 18: 20e4. 20 Ovesen J, Nielsen S. Experimental distal subluxation in the glenohumeral joint. Arch Orthop Trauma Surg 1985; 104: 78e81. 21 Bunker TD, Anthony PP. The pathology of frozen shoulder. A Dupuytren-like disease. J Bone Joint Surg Br 1995; 77: 677e83. 22 Vangsness Jr CT, Jorgenson SS, Watson T, Johnson DL. The origin of the long head of the biceps from the scapula and glenoid labrum. An anatomical study of 100 shoulders. J Bone Joint Surg Br 1994; 76: 951e4. 23 Snyder SJ, Karzel RP, Del Pizzo W, Ferkel RD, Friedman MJ. SLAP lesions of the shoulder. Arthroscopy 1990; 6: 274e9. 24 Burkhart SS, Morgan CD. The peel-back mechanism: its role in producing and extending posterior type II SLAP lesions and its effect on SLAP repair rehabilitation. Arthroscopy 1998; 14: 637e40. 25 Clark JM, Harryman 2nd DT. Tendons, ligaments, and capsule of the rotator cuff. Gross and microscopic anatomy. J Bone Joint Surg Am 1992; 74: 713e25. 26 Walch G, Nove-Josserand L, Boileau P, Levigne C. Subluxations and dislocations of the tendon of the long head of the biceps. J Shoulder Elbow Surg 1998; 7: 100e8. 27 Walch G, Nove-Josserand L, Levigne C, Renaud E. Tears of the supraspinatus tendon associated with ‘‘hidden’’ lesions of the rotator interval. Journal of Shoulder and Elbow Surgery 1994; 3: 353e60. 28 Lafosse L, Reiland Y, Baier GP, Toussaint B, Jost B. Anterior and posterior instability of the long head of the biceps tendon in rotator cuff tears: a new classification based on arthroscopic observations. Arthroscopy 2007; 23: 73e80. 29 Lafosse L, Jost B, Reiland Y, Audebert S, Toussaint B, Gobezie R. Structural integrity and clinical outcomes after arthroscopic repair of isolated subscapularis tears. J Bone Joint Surg Am 2007; 89: 1184e93.
Figure 27 ACJ post resection of soft tissue and bone ends.
Summary With the correct equipment, skilled anaesthesia and careful positioning shoulder arthroscopy is safe and has proved itself to be one of the most powerful investigative tools for the diagnosis of shoulder pathology. There is a significant learning curve not only because of the awkward anatomical arrangement of the joint, but also because no two shoulders are the same and there is a very wide spectrum of normal findings. However, once triangulation within the joint is mastered and the range of pathological and normal findings is understood it proves to be an excellent tool not only for establishing a diagnosis, but in also providing a minimally invasive method of treatment with success rates catching up with, or surpassing, those reported with open surgical treatment. A
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30 Nakajima T, Rokuuma N, Hamada K. Histological and biomechanical characteristics of the supraspinatus tendon: reference torotator cuff tearing. J Shoulder Elbow Surg 1994; 3: 79e87. 31 Burkhart SS, Esch JC, Jolson RS. The rotator crescent and rotator cable: an anatomic description of the shoulder’s ‘‘suspension bridge’’. Arthroscopy 1993; 9: 611e6. 32 Curtis AS, Burbank KM, Tierney JJ, Scheller AD, Curran AR. The insertional footprint of the rotator cuff: an anatomic study. Arthroscopy 2006; 22: 609.e1. 33 DeFranco MJ, Cole BJ. Current concepts: current perspectives on rotator cuff anatomy. Arthroscopy 2009; 25: 305e20. 34 Monk AP, Berry E, Limb D, Soames RW. Laser morphometric analysis of the glenoid fossa of the scapula. Clin Anat 2001; 14: 320e3. 35 Warner JJ, Bowen MK, Deng XH, Hannafin JA, Arnoczky SP, Warren RF. Articular contact patterns of the normal glenohumeral joint. J Shoulder Elbow Surg 1998; 7: 381e8. 36 Outerbridge RE. The etiology of chondromalacia patellae. J Bone Joint Surg Br 1961; 43-B: 752e7.
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37 Boileau P, Walch G. The three-dimensional geometry of the proximal humerus. Implications for surgical technique and prosthetic design. J Bone Joint Surg Br 1997; 79: 857e65. 38 Rockwood CA, Matsen FA, Wirth MA, Lippitt SB. The shouler. 4th edn., vol. 1. Saunders Elsevier, 2009. 39 Yepes H, Al-Hibshi A, Tang M, Morris SF, Stanish WD. Vascular anatomy of the subacromial space: a map of bleeding points for the arthroscopic surgeon. Arthroscopy 2007; 23: 978e84. 40 Liberson F. Os acromiale e a contested anomaly. J Bone Joint Surg Am 1937; 19: 683e9. 41 Vanarthos WJ, Monu JU. Type 4 acromion: a new classification. Contemp Orthop 1995; 30: 227e9. 42 Tucker TJ, Snyder SJ. The keeled acromion: an aggressive acromial variant e a series of 20 patients with associated rotator cuff tears. Arthroscopy 2004; 20: 744e53. 43 Fealy S, April EW, Khazzam M, Armengol-Barallat J, Bigliani LU. The coracoacromial ligament: morphology and study of acromial enthesopathy. J Shoulder Elbow Surg 2005; 14: 542e8.
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