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    Coracoacromial Ligament: A Comparative Arthroscopic

    and Anatomic Study

    Mario Gallino, M.D., Bruno Battiston, M.D., Giovanni Annaratone, M.D.,

    and Flavio Terragnoli, M.D.

    Summary:

    An anatomic study of the coracoacromial ligament was conducted.

    The data collected from 20 anatomical preparations and the arthroscopic findings

    in 40 cases were compared. The shape and the tension of the ligament were

    evaluated, as well as the thickness. Anatomic tradition describes the ligament as

    a fibrous triangular lamina inserted with its apex on the acromial tip and its base

    on the lateral edge of the coracoid. It s imply closes the coracoacromial arch and

    has no mechanical role. However, our observations suggest that the ligament has

    a trapezoidal shape and is situated below the acromion with a wide reflex portion.

    Its thickness varies from 2 to 5.6 mm. Given that structure, the ligament appears

    like a robust suspension structure of the coracoid, which contrasts the action of

    the muscles that connect to it. From these observations, a pathogenic hypothesis

    of the subacromial impingement proposes itself.

    Key Words:

    Shoulder-Anat-

    omy-Coracoacromial ligament-Subacromial impingement.

    T

    he subacromial impingement syndrome derives

    from an anomalous friction of the tendons of the

    rotator cuff with the undersurface of the coracoacro-

    mial arch that overhangs them. Neer clearly described

    it and defined its staging. Later Nee? and Apoil et a1.3

    identified the two principal areas of conflict with the

    areas of acromial and coracoid connections of the cora-

    coacromial ligament. In the literature,4-6 the ligament

    is described as a fibrous triangular lamina whose point

    is connected to the apex of the acromion while its base

    is connected to the whole lateral edge of the coracoid.

    This would have meant the closure of the coracoacro-

    mial arch with no mechanical role.

    The arthroscopic observations of Johnson7 and of

    Ellmann allow us to hypothesize a differing configu-

    ration of the ligament that extends right under the acro-

    mion. Our arthroscopic observations confirmed this

    view and encouraged the following arthroscopic and

    anatomic study that aimed to better evaluate its struc-

    ture and function.

    MATERIALS AND METHODS

    From the Division e di Ortopedia , Presidio Sanitaria Gradenigo,

    Torino, Italy (M. G., G. A.); I I I Divisione Ortopedica, C.T.O ., To-

    r ino, Italy (B. B.); and Clinica Ortopedica dell lJniversit& Brescia,

    Italy (F. T.) .

    Address correspondence and reprint requests to Mario Gallino,

    M.D ., Via Boves IO, 10099 San Mauro (Torino), Italy.

    0 I995 by the Arthroscopy Association of North America

    0749-8063/95/I 105-1126 3.00/O

    We analyzed the arthroscopic findings of 40 pa-

    tients, 27 women and 13 men, with an average age of

    35 (30 to 52) years, affected by subacromial impinge-

    ment who underwent arthroscopic surgery with sub-

    acromial debridement. Each patient had local ized

    shoulder pain and experienced increased pain during

    the arc of forward elevation. The diagnosis of impinge-

    ment was made following Neers criteria. We describe

    that part of arthroscopic diagnosis that regards the ana-

    tomic description of the coracoacromial ligament. Un-

    der general anesthesia, the patient is positioned in lat-

    eral decubitus on the healthy side with the limb to be

    examined abducted 30, flexed by 15 and under axial

    traction of 3 to 4 kg.

    The arthroscope is placed through a posterior portal

    situated l- to 2-cm below and l-cm medial to the

    564 Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol II, No 5 (October), 1995: pp 564-567

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    ANATOMY OF CORACOACROMIAL LIGAMENT 56.5

    FIG 1. A natomic dissection of left shoulder. A distal overturn of

    the deltoid muscle has been made to expose acromion, coracoid,

    and coracoacromial ligamen t. The dotting on the acromion shows

    the projection of the insertion of the ligame nt at its undersurface.

    posterior apex of the acromion. An anterior portal is

    defined under direct view by inserting a needle from

    outside the joint into the triangle formed by the sub-

    scapularis, the glenoid, and the tendon of the long head

    of the biceps. The procedure is divided into two parts:

    the arthroscopy of the glenohumeral joint and that of

    the subacromial space. No additional portal for irriga-

    tion was used. No local injection of epinephrine or

    other vessel constr ictors was carried out so as not to

    alter the anatomic view of the structures. Nor was a

    bursectomy performed before observation. The liga-

    ment was observed through the subacromial bursa, thus

    visualizing it for the whole of its acromial insertion

    and its anterior portion, as well as after a removal of

    the bursa by shaving. Through the anterior portal, a

    FIG 2. Anatomic dissection of left shoulder. After vertical osteot-

    omy of the acromion, the whole extension of the ligament , with its

    wide insertion on the acriomal undersurface, is visible.

    CA4

    FIG 3. (A) Arthroscopic view of the insertion of the ligame nt

    under the acromion in the subacromial space in a left shoulder. (B)

    Drawing of the latter view. A, acromion; SST, supraspinatus tendon;

    CAL, coracoacromial ligamen t.

    hook-shaped probe was inserted to verify its extent

    and consistency. A transcutaneous needle was placed

    to correspond to the anterior apex of the acromion to

    arthroscopically verify where this projected out and

    how great a portion of the ligament carried on under

    the acromial arch. A 5-mm diameter cannula was intro-

    duced via the anterior portal along the supraspinatus

    outlet to verify where a stenosis might be, which would

    make it imposs ible for the cannula to proceed. We

    chose this technique because it is simple, quick, and

    reliable. We observed an easy progression of the can-

    nula in patients with no impingement who underwent

    arthroscopic surgery for other reasons (e.g., shoulder

    instability).

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    566

    M. GALLINO ET AL.

    An anatomic comparison with 20 autopsy prepara-

    tions (from fresh bodies) was made.g The dissection

    of the subacromial space was carried out with removal

    of the acromial insert ions of the deltoid muscle and its

    distal overturn. Besides showing the morphological

    and course characteristics of the coracoacromial liga-

    ment, measurements were also taken (length, width,

    and thickness of the subacromial portion). Measure-

    ments were always

    a precision caliper.

    taken by the same surgeon using

    RESULTS

    Al l observed cases, both arthroscopic and fresh ana-

    tomic specimens, showed a different structure of the

    coracoacromial ligament from that described in the

    class ic literature. Its form appears to be a trapezoidal

    ribbon with the greater base inserted at the undersur-

    face of the acromion and poster iorly originated from

    the dorsal edge of the acromion. The ligament is mod-

    erately twisted into a hel ix downwards and to the exte-

    rior as far as the insertion on the coracoid apophysis

    (Figs l-3). In particular, the subacromial portion of

    the ligament is variable in thickness; in the anatomic

    preparations, it varies from 2 mm to a real curtain

    of 5.6 mm (average, 3.9 mm). Nine cases out of 20

    (45 ) presented a subacromial portion above 4 mm

    measured at the level of the anterior acromial edge.

    The ligament has a close relationship with the rotator

    cuff. In some cases, this is presented on a level almost

    perpendicular to the anterior portion of the supraspi-

    FIG 4. Palpat ion and traction with a probe of the ligame nt during

    subacromial arthroscopy of a right shoulder.

    natus tendon from above, with the subdeltoid bursa

    interposed. An arterial vessel is constantly available

    on the posterior surface of the ligament, coming from

    the coracoid and circulating upwards, a branch of the

    suprascapular artery. In the arthroscopic observations,

    the palpation through a probe revealed a constant ten-

    sion of the ligament (Fig 4). The 5-mm cannula always

    stopped at the level of the subacromial portion of the

    ligament, confirming the site of the stenosis.

    DISCUSSION

    Despite valid theses that describe a local area of

    relative avascularity,l the mechanical pathogenesis of

    impingement against the coracoacromial arch is gener-

    ally accepted as determining the degenerative lesions

    of the rotator cuff.

    Anatomic variants of the acromion, defined as

    curved and hooked, have been associated with

    the impingement syndrome by Bigliani et al., as well

    as Fu et al. Nonetheless, based on recent anthropo-

    metric studies by Edelson and Taitz,13 a true hook

    appears to be quite rare in incidence representing an

    unusual development of preacromial epiphysis being

    the influence of the hook determined mainly by the

    slope of the acromion to which it is attached.

    In 1970, Pujadas14 emphasized how the confl ict in

    subacromial pathology was not so much between hu-

    merus and acromion, as between greater tuberosity and

    the free edge of the coracoacromial ligament. He noted

    that patients with impingement position their arm ante-

    riorly and with internal rotation. Our findings that the

    coracoacromial ligament inserts beyond the tip and

    extends onto the undersurface of the acromion is of

    clinical significance, and the surgeon has to consider

    potential variations in origin and size (thickness) of

    the ligament.

    Two orders of consideration emerge from the pres-

    ent study. Firs t of all, the constant presence of a wide

    portion of the ligament

    below the

    acromion, variable

    in size and thickness, makes a stenosis of the supraspi-

    natus outlet possible, not only because of protruding

    bones, (as in the case of spurs as well as in the anatomic

    variants of the acromion already mentioned) but also,

    and above all, because of the fibrous structures. The

    variabili ty of size of this ligament portion would offer

    an explanation of the origin of primi tive impingement

    syndromes that have arisen in young patients, and that

    are linked neither to bone alterations nor articular insta-

    bility nor muscular imbalance.

    Furthermore, some reflect ions can be made on the

    biomechanical role of the ligament on the basis of the

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    ANATOMY OF CORACOACROMIAL LIGAMENT

    567

    pathogenesis of the impingement syndrome. According

    to Tillmanns biomechanical studies,15 the acromion

    and the coracoid are under opposite directional forces

    exerted by the muscles attached to them. The coraco-

    acromial ligament acts as a tension band within the

    humeral fossa, and this reduces the bending movement

    of the coracoid process and of the acromion, counter-

    acting the action of the pectoralis minor and of the

    coracobrachialis and the short head of the caput brevis

    biceps. From this viewpoint, the coracoacromial liga-

    ment takes on the signif icant role of the transmitter of

    forces from the pectoralis minor to the acromion, and

    its more or less ample extension may be consistent

    with more or less tension.

    Should there be muscular imbalances with an in-

    creased tone of the pectoralis minor compared with

    the external rotators of the upper arm, this would lead

    to the behavior of anterior positioning and internal

    rotation of the scapula as described by Pujadas,14 and

    the ligament tension wil l also increase. An increase of

    its thickness is possible, leading to a further increased

    friction. The development of an anterior spur from the

    acromial edge that takes place within the substance of

    the coracoacromial ligament probably resul ts from the

    transmission of tensile forces through it and is a possi-

    ble expression of the passage from a dysfunctional

    syndrome to an organic stenosis.16

    Acknowledgment: The Authors thank Julian Hoskins,

    Ph.D., English lecturer at the University of Turin, for

    translating and reviewing the manuscript.

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