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8/9/2019 Pie analisis
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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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