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Anatomic variants of the coracoacromial ligament
Anatomic variants of the coracoacromial ligament E. Martin Holt, FRCS Ed, and Richard O. Alhbone, MRC Path, Liverpool and Nottingham, U.K.
Cadaveric anatomic dissections of 50 shoulders have been done with measurement and histologic analysis of the coracoacromial ligament. In subjects older than 50 years of age the coracoacromial ligament does not have a constant form. Three main types were identified: quadrangular, Y-shaped, and a broad band. A previously unreported type of coracoacromial ligament the multiple banded ligament, was found. It had the largest coracoid attachment. This ligament was similar to the Y form but with an additional band extending inferiorly and medially toward the base of the coracoid. Histologic analysis indicates the multiple banded type could be more common than this study suggests. (J SHOULDERELBOWSURG 1995;4:370-5.) | rregularity in the shape of the coracoid and the acromion was reported by Goldthwaite 7 in 1909, but more recently interest has been directed to the morphologic appearance of the coracoid and acromion in relation to the impingement syndrome.l' Although it is attached to these two structures, surprisingly little attention has been given to the variability of the coracoacromial (CA) ligament, an accepted contributor to impingement. 13' is. 2o Minimally invasive surgery is increasing, and with it an expanded knowledge of anatomic variants is required. Previous descriptions of the CA ligament have varied from a broad or triangular band to a ligament of three components, two main bands, and a third thinner intermediate section.3-5' 8-12, 17, 19 All 20 dissections in 10 subjects reported by Salter et al. 16 were found to be of a Y-shaped pattern. This study was undertaken to clarify the situation and to determine the various types of CA ligament and their incidence. We also assessed the ligaments to see whether any specific determinants existed for a particular type of ligament. MATERIAL A N D METHODS
Fifty shoulders in 25 cadavers that were preserved in a preparation of formaldehyde were From the Departments of Orthopaedics and Anatomy, Unfversib, of Liverpool; and the Department of Hislopathology, UniversilV Hospital, Queen's Medical Centre, Nottingham. Reprint requests: E. M. Holt, FRCS Ed, 14 Hillview Ave., West Kirby, Wirral, U.K. L48 5EJ. Copyright 9 1995 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/95/$5.00 + 0 3 2 / 1 / 6 5 9 9 9
370
dissected. Fourteen shoulders from seven cadavers were included in group A, and a further 36 shoulders from 18 cadavers formed group B, from which additional information was gathered. Two specimens (one a left shoulder and the other a right shoulder) were discarded because of difficulties in obtaining accurate dissections of the CA ligament. The first specimen was discarded because a malunited distal clavicular fracture with surrounding fibrosis was present, and the second was discarded because of an associated massive rotator cuff tear. The remaining 48 intact shoulders were dissected through an anterosuperior incision with reflection of the deltoid. The average age of the cadavers at death was 81 years (range 51 to 96 years). The height of the cadavers ranged from 152 cm to 185 cm, with an average of 169 cm. One body had bilateral unfused anterior acromial epiphyses of the mesoacromial type. The ligaments were found to be of one of three types: quadrangular (Figure 1), Y-shaped (Figure 2), and broad band (Figure 3). The determination of the shape was made from a superior to inferior view; this procedure was in keeping with previous descriptions. Most of the ligaments were categorized as quadrangular. The term quadrangular is used in preference to other descriptions, because all of the ligaments subtended two angles at both the coracoid and acromion, and the sides of the ligaments tended to be curved rather than straight. Ligaments were placed into the broad band category when a difference of no more than 2 mm was seen in the width between the attachments at the coracoid and the acromion. All ligaments with
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|
Aa'omion
Figure 1 Quadrangular ligament. C, Coracoid attachment; A, acromion attachment; G, minimum distance (millimeters) be~een coracoid and acromion.
a single diaphanous region between the medial and lateral bands were considered to be Y-shaped. This diaphanous tissue extended for a variable distance from the coracoid to the acromion, in some cases extending as far as the acromion. In one case the diaphanous region was an intact imperforate membrane. However, in most of the cases a defect was found adjacent to the coracoid within which vessels or fibers of the pectoralis minor muscle attachment were present with adipose tissue. One new variant of the CA ligament, a multiple banded ligament (Figure 4), was found. This ligament was composed of three bands and two diaphanous regions. In addition to the two ligament components (medial and lateral) seen in the Y-type of ligament, the multiple banded ligament had a third band arising inferomedially from the coracoid. The first diaphanous region lay between the lateral and medial bands of the ligament as in the Y-type of ligament, whereas the second diaphanous region was in between the medial and additional inferomedial band. Direct measurements of the acromial and coracoid attachments of the CA ligament were taken with calipers as shown in Figures 1 through 4. The minimum distance, G, between the coracoid and the acromion was found by dissection to extend in most of the cases from a variable point on the
Aar~mi~
Figure 2 Y-shaped ligament. C1, Lateral band attachment to coracoid; C2, medial band attachment to acromion; D, diaphanous region belween lateral and median bands. Other abbreviations as in Figure 1. C,mar,o ~
G
Figure 3 Broad band ligament. Abbreviations as in Figure 1. coracoid to the most medial aspect of attachment on the acromion. The superior to inferior thickness, T,, of the ligament was determined at the midpoint between the coracoid and the acromion with a dial micrometer. This procedure gave a maximal
372
J. Shoulder Elbow Surg. September~October 1995
Holt and Allibone
Table I Quadrangular shaped ligament (23 cases) Mean (mm) Minimum (mm) Maximum (ram) SD (mm)
C
A
T
32.8 21.0 41.0 4.6
19.4 11.0 26.0 4.3
1.3 0.7 1.8 0.3
C, Coracoid attachment; A, acromion attachment; T, thickness of ligament at midpoint between coracoid and acromion.
|
Figure 4 Multiple banded ligament. C3, Inferomedial band attachment to acromion, multiple banded ligament only; Dinf, diaphanous region between medial anainferomedial bands, multiple banded ligament only. Other abbreviations as in Figures 1 and 2.
reading of the thickness, T, at this midpoint, because any thinner section or diaphanous region was bridged by the surrounding thicker bands. Dissections were assessed for ligamentous involvement with any vessels or the tendon of pectoralis minor at the coracoid attachment. The acromial attachment of the CA ligament was not evaluated. Information was collated for each ligament and the relationship to cadaver age, sex, side, and height. The results were statistically analyzed with a combination of chi-squared analysis and t-test analysis with Bonferroni correction. The histologic condition of the ligament and the diaphanous tissue between the medial and lateral bands of the Y-shaped ligaments were examined. Longitudinal blocks of ligament, transverse blocks at the point of bifurcation, and transverse blocks between the point of bifurcation and the coracoid (to include the diaphanous section) were stained with hematoxylin-eosin and a connective tissue stain, elastic and van Gieson, and were then processed and imbedded in paraffin. RESULTS The inspection of 48 shoulders revealed 23 (48%) quadrangular, 20 (42%) Y-shaped, and four
(8%) broad band types of ligaments. In only one dissection was a multiple band-type ligament found. Tables I through IV display the results of the measurements for each type of ligament (Figures 1 through 4). In the Y-shaped ligaments with two bands of ligamentous tissue, a medial and a lateral, the lateral band had the larger attachment to the coracoid in 80% of specimens. Table II displays the results of the measured value, D, the distance of the diaphanous attachment at the coracoid, not the calculated value d = ( C - [C1 + C2]). The ligamentous attachment curves both inferomedially and inferolaterally on a coracoid of variable size and shape. The difference in D and d is a result of the ligaments having an attachment that is in an irregular arc. Table V displays the relationship of the minimum gap, G, between the coracoid and acromion for each type of ligament. The mean gap, G, for the three main types varied by only 2 mm, but the quadrangular ligament had the greatest variation. In 19 of the Y-shaped ligaments an inconsistent defect was seen in the diaphanous part of the ligament. The maximum distance the defect extended from the coracoid was 7 mm with a mean of 3.8 mm. The diaphanous membranous tissue itself extended from the margins of the defect to merge with the medial and lateral bands nearer to the acromion. The coracoid attachment of both the quadrangular and Y-shaped ligaments was longer than that of the broad band (p < 0.001 ). The broad band was significantly associated with taller people with a height more than 180 cm (p< 0.001). In the Yshaped ligaments, although a thin diaphanous region existed in the central part of the ligament, the overall thickness of these ligaments at their midpoint was no different than any of the other ligament types. No other statistical correlations were found between the three patterns of the ligament, quadran-
J. Shoulder Elbow Surg. Volume 4, Number 5
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373
Table II Y-shaped ligament (20 cases) Mean (mm) Minimum (mm) Maximum (mm) SD (mm)
C
A
T
C1
C2
D
31.2 23.0 40.0 4.5
19.4 10.0 29.0 4.5
1.3 0.8 2.3 0.4
15.0 10.0 28.0 4.5
9.8 2.0 16.0 4.0
6.8 1.0 15.0 3.7
C1, Length of lateral band attachment to coracoid; C2, length of medial band attachment to acromion; D, distance of diaphanous region between lateral and medial bands. Other abbreviations as in Table I.
Table III Broad band ligament (four cases) Mean (ram) Minimum (mm) Maximum (mm) SD (mm)
Table IV Multiple banded ligament
C
A
T
C
A
T
C1
C2
C3
D
D inf
20.0 16.0 25.0 3.4
19.0 14.0 25.0 3.9
1.2 1.0 1.5 0.2
44
21
1.3
19
10
7
3
5
C3, Length of inferomedial band altachment to coracoid; D inf, distance of diaphanous region beh,veen medial and inferomedial band. Other abbreviations as in Tables I and II.
Abbreviations as in Table II,
gular, Y-shaped, and broad band, and their respective cadaver measurements such as sex, age, height, or side. No other demographic or medical information was available for analysis. In group B dissections (35 cases) a small vessel or vessels were found in the defect region of the membrane close to the coracoid in 12 of the 13 Y-types of ligament. The pectoralis minor tendon was involved in five of the group B ligaments, four of the Y-shaped ligaments, and one of the broad band type ligaments. In only one Y-shaped ligament was no association seen with either vessel or tendon. Histologic analysis confirmed that the CA ligament was composed of true ligamentous tissue.~8 Tightly packed collagen fibers run in parallel in the longitudinal axis of the ligament with compressed fibrocytes between the collagen fibers and small numbers of fine elastic fibers. Transverse sections of Y-shaped ligaments taken at the point where the ligament divides show thinning of the middle of the ligament with separation into medial and lateral bands (Figure 5). As the medial and lateral bands diverge, the ligamentous tissue in the central part of the ligament becomes progressively thinner until in the diaphanous section, the separated medial and lateral bands are connected by an extremely fine membrane of collagenous tissue (Figure 6). As mentioned previously, most of the Y-shaped ligaments had a defect in this fine membrane close to the coracoid; such defects were also present in the multiple banded ligament.
Table V Distance, G, between acromion and coracoid for each main ligament type
Mean (mm) Minimum (mm) Maximum [mm) SD (ram)
Quadrangular
Y-shaped
Broad band
23.1 9.0 27.0 4.0
25.0 21.0 30.0 3.0
25.0 16.0 32.0 5.9
DISCUSSION This series of dissections has shown that three main forms of CA ligament exist: quadrangular, Y-shaped, and broad band. Cadaver height is associated with the presence of a broad band ligament, but we have not discovered any other variable determining a particular type of ligament. The lack of uniformity of the ligament was emphasized by the absence of statistical correlation between the type of ligament and side, sex, age, midpoint thickness, acromial attachment, or the minimum distance between the coracoid and acrotalon. In 1988 PostacchiniTM stated that the ligament found at operation was uncommonly thickened, but no dimensions were given. In this series we determined the maximum midpoint thickness of the ligament to be relatively constant but were unable to measure with accuracy the minimum thickness in diaphanous regions. In the Y-shaped ligaments we found that most of the lateral bands were broader than the medial bands supporting the findings of Brodie 2 in 1914 rather than those of Morris w2in 1879.
374
Holt and Allibone
J. Shoulder Elbow Surg. September~October 1995
Figure 5 Transverse section of Y-shaped ligament at point of bifurcation showing wider lateral band fLAT) and smaller medial band fMED) with thinning of central ligamentous tissue. (Original magnification x7; elastic and van Gieson stain.)
Figure 6 Transverse section through diaphanous part of another Y-shaped ligament (closer to coracoid attachment) showing thin membrane of collagenous tissue connecting medial and lateral bands. (Original magnification x7; elastic and van Gieson stain.) The limitation of this study based on dissection room cadavers usually with an older age range is recognized, but it is the older population rather than the younger that has shoulder problems. The macroscopic and microscopic appearances suggest the type of ligament may be determined by loss of tissue within the quadrangular type. In the same w a y in which an open oriental fan (quadrangular type) can then be closed (broad band type), the fan can also break into two or more respective segments (Y and multiple banded types). This process probably occurs during embryologic development of the joint but could be influenced by stresses related to movement in the growing joint or by degenerative changes in the adult. We thank Professor B. Wood and Dr. D. Lewis-Jones of the Department of Anatomy, University of Liverpool, for help and access to the material used, Chris McCabe for statistical assistance, and Mr. W. Brackenbury of the Department of Histopathology, Queens Medical Centre, Nottingham, for photomicrography. We are also grateful to Professor W. A. Wallace and Mr. I. G. Kelly for their guidance in the preparation of this paper.
REFERENCES 1. Bighani LU, Morrisson DS, April EW. Morphology of the acromion and its relationship to rotator cuff tears. Orthop Trans 1986;10:216.
2. Brodie CG. Note on the transverse-humeral, coraco-acromial, and coraco-humeral ligament. J Anat 1914;24:24752. 3. BrodieCG. Some observationson the ligamentsaround the shoulder. Proceedings of the Anatomical Sociely of Great Britain and Ireland 1889;March:XXI. 4. EllisGV, Ford GH. Illustrationof dissections.2nd ed. London: Smith, Elder and Co, 1867:1-12. 5. Gagey N, Ravaud E, LassauJR Anatomy of the coracoacromial arch: correlation of anatomy and magnetic reso nance imaging. Surg Radiol Anat 1993;15:63-70. 6. Gerber C, Terrier I-, Zehnder R, Ganz R. The subcoracoid space: an anatomic study. Chn Orthop 1987;215:132-8. 7. GoldthwaiteJE. An anatomic and mechanical study of the shoulder joint. Am J Orthop Surg 1909;6:579606. 8. Anderson JE, editor. Grant's atlas of anatomy. 7th ed. Baltimore: Williams & Wilkins, 1978:633. 9. Warwick R, Williams PL, editors. Grays anatomy. 35th ed. Edinburgh: Longman, 1973:424. 10. Hamilton WJ. Textbookof human anatomy. 2nd ed. London: Macmillan, 1976:87-92. 11. Hollinshead WH. Anatomy for surgeons. Vol 3. Back and limbs. 3rd ed. Philadelphia: Harper and Row, 1982:259340. 12. Morris H. Anatomy of the ioints of man. London: J&A Churchill, 1879:194-226. 13. Neer CS Ih Anterior acromioplasly for the chronic impingement syndrome n the shouder J BoneJoint Surg Am 1972 54A:41 50. 14. Postacchini F. Coracoacromial attrition syndrome: anatomy, clinical aspects and surgical treatment. Italian J Orthop Traumatd 1988;14:175-85.
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15. Pujadas GM. Coraco-acromid ligament syndrome. J Bone Joint Surg Am 1970;52A:1261-2. 16. Salter EG, Nasca RJ,Shelley BS. Anatomical observationson the acromioclavicular ioint and supporting ligaments. Am J Sports Med 1987;15:199-206. 17. Sarrafian SK. Gross and functional anatomy of the shoulden Clin Orthop 1983;173:11-9. 18. Stevens A, /_oweJ. Histology. New York: Gower Medical Publishing, 1992:247-8.
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19. Todd RB, Adams R. Cyclopaedia of anatomy and physiology; the shoulder joint. Vol 4. London: /,ongmans, Green and Co, 1852:571-621. 20. Uhthoff HK, Hammond DI, Sarker K, Hooper GJ, PapoFfWJ. The role of the coraco-acromial ligament in the impingement syndrome: a clinical and bursographic and histological study. Int Orthop 1988;12:97-104.
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Cadaveric anatomic dissections of 50 shoulders have been done with measurement and histologic analysis of the coracoacromial ligament. In subjects older than 50 years of age the coracoacromial ligament does not have a constant form. Three main types were identified: quadrangular, Y-shaped, and a broad band. A previously unreported type of coracoacromial ligament the multiple banded ligament, was found. It had the largest coracoid attachment. This ligament was similar to the Y form but with an additional band extending inferiorly and medially toward the base of the coracoid. Histologic analysis indicates the multiple banded type could be more common than this study suggests. (J SHOULDERELBOWSURG 1995;4:370-5.) | rregularity in the shape of the coracoid and the acromion was reported by Goldthwaite 7 in 1909, but more recently interest has been directed to the morphologic appearance of the coracoid and acromion in relation to the impingement syndrome.l' Although it is attached to these two structures, surprisingly little attention has been given to the variability of the coracoacromial (CA) ligament, an accepted contributor to impingement. 13' is. 2o Minimally invasive surgery is increasing, and with it an expanded knowledge of anatomic variants is required. Previous descriptions of the CA ligament have varied from a broad or triangular band to a ligament of three components, two main bands, and a third thinner intermediate section.3-5' 8-12, 17, 19 All 20 dissections in 10 subjects reported by Salter et al. 16 were found to be of a Y-shaped pattern. This study was undertaken to clarify the situation and to determine the various types of CA ligament and their incidence. We also assessed the ligaments to see whether any specific determinants existed for a particular type of ligament. MATERIAL A N D METHODS
Fifty shoulders in 25 cadavers that were preserved in a preparation of formaldehyde were From the Departments of Orthopaedics and Anatomy, Unfversib, of Liverpool; and the Department of Hislopathology, UniversilV Hospital, Queen's Medical Centre, Nottingham. Reprint requests: E. M. Holt, FRCS Ed, 14 Hillview Ave., West Kirby, Wirral, U.K. L48 5EJ. Copyright 9 1995 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/95/$5.00 + 0 3 2 / 1 / 6 5 9 9 9
370
dissected. Fourteen shoulders from seven cadavers were included in group A, and a further 36 shoulders from 18 cadavers formed group B, from which additional information was gathered. Two specimens (one a left shoulder and the other a right shoulder) were discarded because of difficulties in obtaining accurate dissections of the CA ligament. The first specimen was discarded because a malunited distal clavicular fracture with surrounding fibrosis was present, and the second was discarded because of an associated massive rotator cuff tear. The remaining 48 intact shoulders were dissected through an anterosuperior incision with reflection of the deltoid. The average age of the cadavers at death was 81 years (range 51 to 96 years). The height of the cadavers ranged from 152 cm to 185 cm, with an average of 169 cm. One body had bilateral unfused anterior acromial epiphyses of the mesoacromial type. The ligaments were found to be of one of three types: quadrangular (Figure 1), Y-shaped (Figure 2), and broad band (Figure 3). The determination of the shape was made from a superior to inferior view; this procedure was in keeping with previous descriptions. Most of the ligaments were categorized as quadrangular. The term quadrangular is used in preference to other descriptions, because all of the ligaments subtended two angles at both the coracoid and acromion, and the sides of the ligaments tended to be curved rather than straight. Ligaments were placed into the broad band category when a difference of no more than 2 mm was seen in the width between the attachments at the coracoid and the acromion. All ligaments with
J. Shoulder Elbow Surg. Volume 4, Number 5
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|
Aa'omion
Figure 1 Quadrangular ligament. C, Coracoid attachment; A, acromion attachment; G, minimum distance (millimeters) be~een coracoid and acromion.
a single diaphanous region between the medial and lateral bands were considered to be Y-shaped. This diaphanous tissue extended for a variable distance from the coracoid to the acromion, in some cases extending as far as the acromion. In one case the diaphanous region was an intact imperforate membrane. However, in most of the cases a defect was found adjacent to the coracoid within which vessels or fibers of the pectoralis minor muscle attachment were present with adipose tissue. One new variant of the CA ligament, a multiple banded ligament (Figure 4), was found. This ligament was composed of three bands and two diaphanous regions. In addition to the two ligament components (medial and lateral) seen in the Y-type of ligament, the multiple banded ligament had a third band arising inferomedially from the coracoid. The first diaphanous region lay between the lateral and medial bands of the ligament as in the Y-type of ligament, whereas the second diaphanous region was in between the medial and additional inferomedial band. Direct measurements of the acromial and coracoid attachments of the CA ligament were taken with calipers as shown in Figures 1 through 4. The minimum distance, G, between the coracoid and the acromion was found by dissection to extend in most of the cases from a variable point on the
Aar~mi~
Figure 2 Y-shaped ligament. C1, Lateral band attachment to coracoid; C2, medial band attachment to acromion; D, diaphanous region belween lateral and median bands. Other abbreviations as in Figure 1. C,mar,o ~
G
Figure 3 Broad band ligament. Abbreviations as in Figure 1. coracoid to the most medial aspect of attachment on the acromion. The superior to inferior thickness, T,, of the ligament was determined at the midpoint between the coracoid and the acromion with a dial micrometer. This procedure gave a maximal
372
J. Shoulder Elbow Surg. September~October 1995
Holt and Allibone
Table I Quadrangular shaped ligament (23 cases) Mean (mm) Minimum (mm) Maximum (ram) SD (mm)
C
A
T
32.8 21.0 41.0 4.6
19.4 11.0 26.0 4.3
1.3 0.7 1.8 0.3
C, Coracoid attachment; A, acromion attachment; T, thickness of ligament at midpoint between coracoid and acromion.
|
Figure 4 Multiple banded ligament. C3, Inferomedial band attachment to acromion, multiple banded ligament only; Dinf, diaphanous region between medial anainferomedial bands, multiple banded ligament only. Other abbreviations as in Figures 1 and 2.
reading of the thickness, T, at this midpoint, because any thinner section or diaphanous region was bridged by the surrounding thicker bands. Dissections were assessed for ligamentous involvement with any vessels or the tendon of pectoralis minor at the coracoid attachment. The acromial attachment of the CA ligament was not evaluated. Information was collated for each ligament and the relationship to cadaver age, sex, side, and height. The results were statistically analyzed with a combination of chi-squared analysis and t-test analysis with Bonferroni correction. The histologic condition of the ligament and the diaphanous tissue between the medial and lateral bands of the Y-shaped ligaments were examined. Longitudinal blocks of ligament, transverse blocks at the point of bifurcation, and transverse blocks between the point of bifurcation and the coracoid (to include the diaphanous section) were stained with hematoxylin-eosin and a connective tissue stain, elastic and van Gieson, and were then processed and imbedded in paraffin. RESULTS The inspection of 48 shoulders revealed 23 (48%) quadrangular, 20 (42%) Y-shaped, and four
(8%) broad band types of ligaments. In only one dissection was a multiple band-type ligament found. Tables I through IV display the results of the measurements for each type of ligament (Figures 1 through 4). In the Y-shaped ligaments with two bands of ligamentous tissue, a medial and a lateral, the lateral band had the larger attachment to the coracoid in 80% of specimens. Table II displays the results of the measured value, D, the distance of the diaphanous attachment at the coracoid, not the calculated value d = ( C - [C1 + C2]). The ligamentous attachment curves both inferomedially and inferolaterally on a coracoid of variable size and shape. The difference in D and d is a result of the ligaments having an attachment that is in an irregular arc. Table V displays the relationship of the minimum gap, G, between the coracoid and acromion for each type of ligament. The mean gap, G, for the three main types varied by only 2 mm, but the quadrangular ligament had the greatest variation. In 19 of the Y-shaped ligaments an inconsistent defect was seen in the diaphanous part of the ligament. The maximum distance the defect extended from the coracoid was 7 mm with a mean of 3.8 mm. The diaphanous membranous tissue itself extended from the margins of the defect to merge with the medial and lateral bands nearer to the acromion. The coracoid attachment of both the quadrangular and Y-shaped ligaments was longer than that of the broad band (p < 0.001 ). The broad band was significantly associated with taller people with a height more than 180 cm (p< 0.001). In the Yshaped ligaments, although a thin diaphanous region existed in the central part of the ligament, the overall thickness of these ligaments at their midpoint was no different than any of the other ligament types. No other statistical correlations were found between the three patterns of the ligament, quadran-
J. Shoulder Elbow Surg. Volume 4, Number 5
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373
Table II Y-shaped ligament (20 cases) Mean (mm) Minimum (mm) Maximum (mm) SD (mm)
C
A
T
C1
C2
D
31.2 23.0 40.0 4.5
19.4 10.0 29.0 4.5
1.3 0.8 2.3 0.4
15.0 10.0 28.0 4.5
9.8 2.0 16.0 4.0
6.8 1.0 15.0 3.7
C1, Length of lateral band attachment to coracoid; C2, length of medial band attachment to acromion; D, distance of diaphanous region between lateral and medial bands. Other abbreviations as in Table I.
Table III Broad band ligament (four cases) Mean (ram) Minimum (mm) Maximum (mm) SD (mm)
Table IV Multiple banded ligament
C
A
T
C
A
T
C1
C2
C3
D
D inf
20.0 16.0 25.0 3.4
19.0 14.0 25.0 3.9
1.2 1.0 1.5 0.2
44
21
1.3
19
10
7
3
5
C3, Length of inferomedial band altachment to coracoid; D inf, distance of diaphanous region beh,veen medial and inferomedial band. Other abbreviations as in Tables I and II.
Abbreviations as in Table II,
gular, Y-shaped, and broad band, and their respective cadaver measurements such as sex, age, height, or side. No other demographic or medical information was available for analysis. In group B dissections (35 cases) a small vessel or vessels were found in the defect region of the membrane close to the coracoid in 12 of the 13 Y-types of ligament. The pectoralis minor tendon was involved in five of the group B ligaments, four of the Y-shaped ligaments, and one of the broad band type ligaments. In only one Y-shaped ligament was no association seen with either vessel or tendon. Histologic analysis confirmed that the CA ligament was composed of true ligamentous tissue.~8 Tightly packed collagen fibers run in parallel in the longitudinal axis of the ligament with compressed fibrocytes between the collagen fibers and small numbers of fine elastic fibers. Transverse sections of Y-shaped ligaments taken at the point where the ligament divides show thinning of the middle of the ligament with separation into medial and lateral bands (Figure 5). As the medial and lateral bands diverge, the ligamentous tissue in the central part of the ligament becomes progressively thinner until in the diaphanous section, the separated medial and lateral bands are connected by an extremely fine membrane of collagenous tissue (Figure 6). As mentioned previously, most of the Y-shaped ligaments had a defect in this fine membrane close to the coracoid; such defects were also present in the multiple banded ligament.
Table V Distance, G, between acromion and coracoid for each main ligament type
Mean (mm) Minimum (mm) Maximum [mm) SD (ram)
Quadrangular
Y-shaped
Broad band
23.1 9.0 27.0 4.0
25.0 21.0 30.0 3.0
25.0 16.0 32.0 5.9
DISCUSSION This series of dissections has shown that three main forms of CA ligament exist: quadrangular, Y-shaped, and broad band. Cadaver height is associated with the presence of a broad band ligament, but we have not discovered any other variable determining a particular type of ligament. The lack of uniformity of the ligament was emphasized by the absence of statistical correlation between the type of ligament and side, sex, age, midpoint thickness, acromial attachment, or the minimum distance between the coracoid and acrotalon. In 1988 PostacchiniTM stated that the ligament found at operation was uncommonly thickened, but no dimensions were given. In this series we determined the maximum midpoint thickness of the ligament to be relatively constant but were unable to measure with accuracy the minimum thickness in diaphanous regions. In the Y-shaped ligaments we found that most of the lateral bands were broader than the medial bands supporting the findings of Brodie 2 in 1914 rather than those of Morris w2in 1879.
374
Holt and Allibone
J. Shoulder Elbow Surg. September~October 1995
Figure 5 Transverse section of Y-shaped ligament at point of bifurcation showing wider lateral band fLAT) and smaller medial band fMED) with thinning of central ligamentous tissue. (Original magnification x7; elastic and van Gieson stain.)
Figure 6 Transverse section through diaphanous part of another Y-shaped ligament (closer to coracoid attachment) showing thin membrane of collagenous tissue connecting medial and lateral bands. (Original magnification x7; elastic and van Gieson stain.) The limitation of this study based on dissection room cadavers usually with an older age range is recognized, but it is the older population rather than the younger that has shoulder problems. The macroscopic and microscopic appearances suggest the type of ligament may be determined by loss of tissue within the quadrangular type. In the same w a y in which an open oriental fan (quadrangular type) can then be closed (broad band type), the fan can also break into two or more respective segments (Y and multiple banded types). This process probably occurs during embryologic development of the joint but could be influenced by stresses related to movement in the growing joint or by degenerative changes in the adult. We thank Professor B. Wood and Dr. D. Lewis-Jones of the Department of Anatomy, University of Liverpool, for help and access to the material used, Chris McCabe for statistical assistance, and Mr. W. Brackenbury of the Department of Histopathology, Queens Medical Centre, Nottingham, for photomicrography. We are also grateful to Professor W. A. Wallace and Mr. I. G. Kelly for their guidance in the preparation of this paper.
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