The subcoracoid space an anatomic study

The Subcoracoid Space An Anatomic Study

CHRISTIAN GERBER, M.D.,* FRANCOIS TERRIER, M.D.,** ROLF ZEHNDER PH.D.,~ AND REINHOLD GANZ, M.D.$

Soft tissue impingement under the coracoid process has recently been identified as a cause of painful

shoulder disability. In this study the normal space between the humeral head and the coracoid process in two functional positions of the arm was measured in an attempt to delineate anatomic risk factors pre- disposing to subcoracoid impingement. Forty-seven normal shoulders were studied by computerized to- mography (CT) in adduction, 20 additionally in for-

ward flexion/internal rotation, which is the position most frequently causing subcoracoid impingement. The distance between the humeral head and the coracoid tip averaged 8.7 mm for the adducted arm

and 6.8 mm for the flexed arm. Modifications of the coracohumeral relationship were found to affect the subcoracoid clearance roughly 1.5 times more in flexion than with the arm at the side. Subcoracoid impingement appeared particularly likely during forward flexion of a shoulder with a coracoid tip close to the scapular neck and projecting far lat- erally.

Impingement of the tendinous cuff beneath the coracoacromial arch is an established cause

acromioclavicular joint are recognized sites of impingement.6-9," Not only congenital ana- tomic variation^,',^,^ but also traumatic skeletal

change^,^ and surgical can lead

to symptomatic impingement on the coracoid process. The skeletal configurations that pre- dispose to impingement of the cuff between the tip of the coracoid process and the humeral head are unknown. Furthermore, the effects of advertent or inadvertent surgical modifi- cations of the subcoracoid space4 have not been studied. This computed tomography (CT) study was done to define the normal space between the tip of the coracoid process and .the humeral head (termed the subcoracoid space) in vivo and to assess the significance of individual skeletal variations as predisposing factors for subcoracoid impingement.

MATERIALS AND METHODS of chronic shoulder disability.8 The anteroin- SCAPULAR AND

CoRACoHUMERAL

romial ligament and the undersurface of the ferior surface of the acromion, the coracoac- RELATIONSHIP IN INTERNAL, NEUTRAL, AND

EXTERNAL ROTATION

From the University of Bern and the AO/ASIF Docu- * Department of Orthopaedic Surgery, University of

** Department of Diagnostic Radiology, University of

t AO/ASIF Documentation Center, Bern, Switzerland.

$ Professor and Chairman, Department of Orthopaedic Surgery, University of Bern, Switzerland. Reprint requests to Christian Gerber, M.D., Department of Orthopaedic Surgery, University of Bern, Inselspital, 3010 Bern, Switzerland.

mentation Center, Bern, Switzerland. Bern, Switzerland. Bern, Switzerland.

Received: August 26,

1985.

Nineteen male (28 shoulders) and 15 female (19 shoulders) volunteers participated in the study (age range, 24-59 years; average, 32.9 years). None of the individuals had any history of previous pain, dysfunction, or injury to the shouldefls). Clinical

examination revealed normal range of motion, no atrophy or overt weakness, a negative impingement

sign," a negative modified impingement test: and

the absence of (atraumatic) uni- or multidirectional

instability.' True anteroposterior (AP) and axillary roentgenograms were normal. The individuals were studied in the supine po- sition in a Siemens SOTATOM CT Scanner (Sie-

132 Number 215

February, 1987 The Subcoracoid Space 133

FIG. 1. Computer tomogram through the tip of the coracoids of two shoulders, as used for measurements. The right shoulder is normal; an anatomic variant of the coracoid accounts for the idiopathic subcoracoid impingement syndrome of the left shoulder. Note the left/right difference of the distances between the

humeral head and the coracoid tip (c = coracoid tip; s = subscapularis).

mens, Erlangen, Germany). Both shoulders were flat on the examining table. With the humerus at the side, 4-mm CT cuts of both shoulders were taken from the top of the humeral head to the inferior glenoid rim. The cuts were initially taken in neutral rotation (elbows flexed to go”, forearms perpendic- ular to the examining table), and full external and internal rotation (elbows at the side, forearms under lumbar spine). In the first 18 shoulders studied, the distance between the humeral head and the tip of the coracoid was consistently smallest in internal rotation. The coracohumeral relationship was con- sequently evaluated in additional patients but only in internal rotation. Computerized tomography cuts through the tip of the coracoid process were used for all measurements (Fig. 1). All metric and angular measurements were repeated three times and the mean value was recorded. Unilateral recording was due to absence of an internal rotation film depicting exactly the tip of the coracoid in eight patients and to an abnormal opposite shoulder in 13 others. The following variables were defined and measured on adequate computertomograms (Fig. 2): The scapuloglenoid angle (a). A reference line “a” was drawn through the anterior and posterior glenoid rim representing the plane of the glenoid fossa. A second reference line “b” ran from the middle of the glenoid through the medial rim of the scapular blade. This line was approximately parallel to the dorsal contour of the scapula and represented the plane of the scapular body. The an- gle formed between “a” and a perpendicular line to “b” represented the anterior or posterior glenoid tilt and was called the scapuloglenoid angle “a ”.