The Journal of Bone and Joint Surgery 80:1622-5 (1998)
© 1998 The Journal of Bone and Joint Surgery, Inc.
Anatomy and Histological Characteristics of the Spinoglenoid Ligament*
CRAIG A. CUMMINS, M.D. ,
KYLE ANDERSON, M.D.,
MARK BOWEN, M.D.,
GORDON NUBER, M.D. and
SANFORD I. ROTH, M.D., CHICAGO, ILLINOIS
Investigation performed at the Department of Orthopaedic Surgery, Northwestern University Medical School, Chicago
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Abstract
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The spinoglenoid (inferior transverse scapular) ligament, when present, is located at the spinoglenoid notch. The ligament originates on the spine of the scapula and inserts on the superior margin of the glenoid neck. Because of discrepancies in the literature, we sought to determine its prevalence and to define its histological characteristics. We dissected 112 shoulders of seventy-six cadavera and classified the ligament as absent or an insubstantial structure, a thin fibrous band (type I), or a distinct ligament (type II). We found no distinct ligamentous structure in twenty-two shoulders (20 percent), a type-I ligament in sixty-eight shoulders (20 percent), a type-I ligament in sixty-eight shoulders (61 percent), and a type-II ligament in twenty-two shoulders (20 percent). Overall, ninety (80 percent) of the shoulders had a fibrous band of tissue that, together with the spine of the scapula, formed a narrow fibro-osseous tunnel through which the suprascapular nerve traveled.
The bone-spinoglenoid ligament-bone complexes from three specimens were analyzed histologically. There were two type-I ligaments and one type-II ligament; all three ligaments were composed of collagen fibers. One type-I ligament and the type-II ligament demonstrated Sharpey fibers at their origin on the spine of the scapula. The other type-I ligament attached to the spine of the scapula through the periosteum. All three ligaments inserted into the periosteum of the glenoid neck.
CLINICAL RELEVANCE: The spinoglenoid ligament may be clinically relevant in two respects. First, the ligament may limit mobilization and advancement of the infraspinatus tendon during repair of a massive tear of the rotator cuff, placing the distal part of the suprascapular nerve at risk. Second, the spinoglenoid ligament represents a potential site for nerve entrapment, particularly with the added stress of traction that can occur with overhead athletic activities.
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Introduction
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The spinoglenoid ligament, also known as the inferior transverse scapular ligament, has been identified as a site of entrapment of the suprascapular nerve resulting in isolated weakness of the infraspinatus muscle1. The ligament travels from the spine of the scapula to the superior margin of the glenoid. Together with the spine of the scapula, the spinoglenoid ligament forms a fibro-osseous tunnel through which the suprascapular nerve courses (Fig. 1). Previous anatomical studies have been inconsistent regarding the prevalence of this ligament3-5. In addition, to our knowledge, the histological characteristics of the spinoglenoid ligament have not been described. The purpose of the present study was to determine the prevalence of the spinoglenoid ligament and to define its anatomy and histological characteristics.
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Fig. 1 Illustration of the posterior part of the scapula and the proximal aspect of the humerus. The suprascapular nerve travels through a fibro-osseous tunnel formed by the scapular spine and the spinoglenoid ligament.
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Materials and Methods
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One hundred and twelve shoulders of seventy-six cadavera were dissected. Fifty-four of the cadavera were male and fifty-eight were female. The mean age of the individuals at the time of death was seventy-six years (range, eighteen to ninety-seven years). The cadavera were preserved in a water-soluble, alcohol-based solution. A posterior approach was used for all dissections. The infraspinatus muscle was elevated inferiorly out of the infraspinatus fossa from medial to lateral to expose the suprascapular nerve and the spinoglenoid ligament, if present. We classified the ligament as absent or insubstantial, as a thin fibrous band (type I), or as a distinct ligament (type II). Type-I and type-II ligaments differed from each other only in terms of thickness.
Three cadaveric bone-spinoglenoid ligament-bone complexes were obtained for histological analysis. Two of the ligaments were type I, and one was type II. The specimens were decalcified and were stained with hematoxylin and eosin as well as Masson trichrome. The slides were examined under direct and polarized light microscopy by an orthopaedic pathologist at our institution.
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Results
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Twenty-two shoulders (20 percent) had no spinoglenoid ligament or an insubstantial one, sixty-eight (61 percent) had a type-I ligament (Fig. 2-A), and twenty-two (20 percent) had a type-II ligament (Fig. 2-B). Overall, ninety shoulders (80 percent) had a fibrous band of tissue extending from the spine of the scapula to the superior margin of the glenoid.
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Figs. 2-A and 2-B: Photographs of the scapula. The infraspinatus muscle has been reflected inferiorly. The suprascapular nerve (black arrow) can be identified coursing through the foramen formed by the scapular spine and the spinoglenoid ligament (white arrow).
Fig. 2-A: A type-I ligament, which has a thin, membranous quality.
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Histologically, the findings in the type-I and type-II ligaments were similar. All three specimens were composed of collagen fibers. One type-I ligament and the type-II ligament had evidence of Sharpey fibers at their origin on the spine of the scapula (Fig. 3). The other type-I ligament originated from the periosteum at the scapular spine. All three ligaments attached to the periosteum of the glenoid neck.
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Fig. 3 Low-power photomicrograph of a specimen from a type-I ligament originating from the spine of the scapula. The ligament has dense collagen and is attached directly to the scapular spine (hematoxylin and eosin, x 4).
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An attempt was made to evaluate the suprascapular nerve and its relationship to the spinoglenoid ligament with the arm in various positions. However, the study design and the viscoelastic properties of the preserved cadavera did not allow accurate observation of the dynamics of the suprascapular nerve with respect to the spinoglenoid ligament.
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Discussion
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The anatomy of the suprascapular nerve has been well described2,5,6. It is derived from the distal portion of the fifth cervical nerve root or from the superior trunk of the brachial plexus, and it initially courses along the superior aspect of the scapula. The nerve then enters the suprascapular foramen through the suprascapular notch and travels underneath the superior transverse scapular ligament. The suprascapular artery and vein pass superior to the ligament but can occasionally send branches through the suprascapular notch with the nerve. After innervating the supraspinatus muscle and supplying sensory fibers to the acromioclavicular joint, glenohumeral joint, and subacromial bursa, the nerve courses around the spine of the scapula at the spinoglenoid notch. After passing around the spinoglenoid notch, the suprascapular nerve terminates in three or four branches that supply motor function to the infraspinatus muscle2,6.
At the spinoglenoid notch, the nerve may be enclosed by a fibro-osseous tunnel formed by the spine of the scapula and the spinoglenoid ligament. The reported prevalence of the spinoglenoid ligament has varied widely. Mestdagh et al. identified the spinoglenoid ligament in ten of twenty cadavera and described it as "an aponeurotic band which separates the supra and infraspinatus muscles."5 Kaspi et al. found the ligament in five of ten female cadavera and thirteen of fifteen male cadavera in their study; overall, they identified the ligament in eighteen (72 percent) of the twenty-five cadavera4. Demaio et al. found the ligament in only two of seventy-five shoulders3. An aponeurosis, described as "a condensation of fascia distinct from surrounding tissues," was identified in ten other shoulders. The aponeurosis did not extend to the glenoid neck.
Our anatomical dissections demonstrated a distinct ligament (type II) in 20 percent of the 112 shoulders and a thin fascial band (type I) in 61 percent. All of these ligaments extended from the spine of the scapula to the glenoid neck. These ligaments differed in thickness, but they were all identifiable structures that contributed to the formation of a fibro-osseous tunnel through which the suprascapular nerve traveled. Although this fibro-osseous tunnel is a potential site of nerve impingement, the nerve was not compressed by the spinoglenoid ligament in any of the cadavera that we studied. However, a traction injury of the suprascapular nerve may occur at the site of the spinoglenoid ligament. Unfortunately, we were not able to identify the positions of the arm during which the suprascapular nerve was stretched over the spinoglenoid ligament.
Our histological findings were consistent with our anatomical observations, confirming the ligamentous nature of this structure. Both the type-I and the type-II ligaments were composed of collagen fibers, and both inserted on the spine of the scapula and the glenoid neck.
The presence of the spinoglenoid ligament is of potential clinical importance for two reasons. First, the ligament may limit the advancement of the infraspinatus tendon during repair of a massive tear of the rotator cuff, placing the distal part of the suprascapular nerve at risk. Second, the spinoglenoid ligament represents a potential site for entrapment of the suprascapular nerve, particularly with the added stress of traction that can occur with overhead athletic activities. If other possible causes of weakness of the infraspinatus muscle have been excluded and nonoperative treatment has failed, exploration and operative release of the spinoglenoid ligament may be indicated.
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Footnotes
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*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. no funds were received in support of this study.
Department of Orthopaedic Surgery, Northwestern University Medical School, 645 North Michigan Avenue, Room 1058 B, Chicago, Illinois 60611. E-mail address for Dr. Cummins: cac357@nwu.edu.
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References
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Bigliani, L. U.; Dalsey, R. M.; McCann, P. D.; and April, E. W.: An anatomical study of the suprascapular nerve. Arthroscopy, 6: 301-305, 1990.[Medline]
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Demaio, M.; Drez, D., Jr.; and Mullins, R. C.: The inferior transverse scapular ligament as a possible cause of entrapment neuropathy of the nerve to the infraspinatus. A brief note. J. Bone and Joint Surg., 73-A: 1061-1063, Aug. 1991.[Free Full Text]
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Kaspi, A.; Yanai, J.; Pick, C. G.; and Mann, G.: Entrapment of the distal suprascapular nerve. An anatomical study. Internat. Orthop., 12: 273-275, 1988.[Medline]
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Mestdagh, H.; Drizenko, A.; and Ghestem, P.: Anatomical bases of suprascapular nerve syndrome. Anat. Clin., 3: 67-71, 1981.
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Abstract
Introduction