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Ligamentous anatomy of the distal clavicle
Ligamentous anatomy of the distal clavicle Kevin J. Renfree, MD,a Michael K. Riley, MD,b Donna Wheeler, PhD,c Joseph G. Hentz, MS,d and Thomas W. Wright, MD,c Scottsdale, AZ, and Ocala and Gainesville, FL
We describe the insertional variations of supporting ligaments of the acromioclavicular joint, especially with respect to gender. We analyzed 41 cadaveric clavicles (22 female and 19 male) with attached ligaments. The distance between the insertion of the trapezoid ligament and the distal end of the clavicle was not significantly different between sexes, although that of the conoid ligament and the mean anteroposterior width of the distal clavicle was significantly greater in men. Although there are significant sex-related differences in the insertional distances of the CC ligaments, resection of less than 11.0 mm should not violate the trapezoid ligament and less than 24.0 mm should not violate the conoid ligament in either sex in 98% of the general population. Resection of more than 7.6 mm of the distal clavicle in men and 5.2 mm in women, performed by an arthroscopic approach, may violate the superior acromioclavicular ligament. (J Shoulder Elbow Surg 2003;12:355-9.)
T
he acromioclavicular (AC) joint is a common site of pain, most often from primary or posttraumatic arthritis. This articulation may also be involved in the pathogenesis of shoulder impingement and rotator cuff tears from attrition of inferiorly projecting osteophytes from the distal clavicle. Treatment typically includes excision of the terminal portion of the distal clavicle. However, the recommended amount of bone that should be excised varies among reports in the literature. The coracoclavicular (CC) (trapezoid and conoid) ligaments may be at risk for injury through excessive bone excision, subperiosteal dissection, or aggressive placement of retractors medially, which could result in instability of the remaining distal clavicular stump. We are not aware of any studies that provide data on the insertional distances of these ligaments from the lateral end of the clavicle. First, we From the Sections of aHand Surgery and bBiostatistics, Mayo Clinic, Scottsdale; bPrivate Practice, Ocala; and cDepartment of Orthopaedic Surgery, University of Florida, Gainesville. Reprint requests: Kevin J. Renfree, MD, Section of Hand Surgery, Mayo Clinic, 13400 E Shea Blvd, Scottsdale, AZ 85259. Copyright © 2003 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2003/$35.00 ⫹ 0 doi:10.1016/S1058-2746(03)00029-6
sought to determine these distances and whether there is side-to-side variability of the insertional distances of these ligaments within the same patient. We evaluated variability between persons with respect to gender because women and men often differ in habitus. Our goal was to provide guidelines from an anatomic study that will allow surgeons to resect the distal clavicle adequately in all patients, regardless of size or sex, without disrupting the biomechanically important CC ligaments. Arthroscopic resection of the distal clavicle has been described more recently, and the proposed advantages of this procedure include reduction of morbidity from an open incision and preservation of the deltotrapezial fascia and superior AC ligament. Accelerated rehabilitation and better preservation of rotational and horizontal stability of the remaining distal clavicle are potentially seen. Therefore, for the second part of the study, we examined histologically the insertional distances of the superior AC ligament on both the distal clavicle and adjacent medial acromion. MATERIALS AND METHODS We evaluated 41 clavicles (22 female and 19 male) from 23 cadavers. Five clavicles were excluded because they were inadequate. The mean age was 79 years (range, 64-101 years); the mean age was 79 years (SD, 10 years) for women and 79 years (SD, 12 years) for men. Nineteen clavicles were from the left side and twenty-two were from the right. Of these, there were 19 matched (right and left) pairs (38 clavicles). Nine of the matched pairs were from men, and ten were from women. Measurements were made with a handheld caliper-type micrometer with 3.5⫻ loupe magnification before the tissue was digested in a household bleach solution. All clavicles were number-coded, thereby blinding the examiners to the sex and matched-pair status of the clavicles.
CC ligament insertions The following measurements were obtained (Figure 1): the maximum anteroposterior (AP) width of the metaphyseal portion of the distal clavicle medial to the articular surface (a) and the distance from the center (b) of the articular surface of the distal clavicle to the anterior lateral (c) and mid-medial (d) origin of the trapezoid ligament (TL) and to the lateral (e) and medial (f) origin of the conoid ligament (CL). Soft tissue was digested by submerging clavicles in
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Figure 1 Inferior surface of distal clavicle. Shaded trapezoidal area represents TL insertion, and diamond-shaped area represents CL insertion. a, AP width of distal clavicle; b, center of articular surface of distal clavicle; c, lateral edge of TL insertion; d, medial edge of TL insertion; e, lateral edge of CL insertion; f, medial edge of CL insertion.
J Shoulder Elbow Surg July/August 2003
Figure 3 Histologic AC joint section.
Superior AC ligament insertions
Figure 2 TL and CL insertions stained with methylene blue after digestion in bleach.
individual containers of bleach, and measurements were confirmed after the ligament footprint was stained with methylene blue (Figure 2). Statistical analysis of the measurements was performed with the 2-sample t test, which allowed a comparison of the sex-related difference in insertional distances of the TL and CL insertions from the articular surface of the distal clavicle. Measurements of 12 clavicles from women and 10 from men were compared; this comparison was, therefore, independent of matched-pair status (ie, 3 unmatched clavicles from women and 1 from a man). Confidence intervals (CIs) were calculated for the difference between group means to show how precisely the difference has been quantified and to show whether the sample was large enough to conclude reliably that the groups were equivalent. The Pearson correlation coefficient was used to determine the correlation of measurements between clavicles from the right and left sides within the same cadaver. Partial correlation was used to control for differences between sexes and to assess the relationship between the distance of insertion of the TL or CL from the articular surface of the distal clavicle and the size of the clavicle (AP width).
Three fresh-frozen human cadaveric clavicles, acromions, and intact AC joints were resected from 1 man and 2 women. Muscle tissue was removed from bone with care to preserve the AC joint ligaments. The clavicle and acromion were transected approximately 4 cm from the joint surface to facilitate histologic processing. Clavicles were prepared for undecalcified histologic processing by standard techniques.1 In brief, the clavicles were fixed in an alcoholformalin solution (9 parts 80% ethanol and 1 part 37% formaldehyde), dehydrated in a sequence of graded ethanol solutions (70%, 85%, 95%, 100%, and 100%), cleared with histologic-grade xylene (Fisher Scientific, Suwanee, GA), and infiltrated and embedded under a vacuum with graded resin mixtures of methyl methacrylate (Fisher Scientific), dibutyl phthalate (Sigma Chemical Company, St Louis, MO), and benzoyl peroxide (Aldrich Chemical Company, Inc, Milwaukee, WI). Serial macrosections of the AC joint, including the AC ligament, were made in the coronal plane by use of an EXAKT 310 Band Systems Macro diamond saw (EXAKT Technologies, Inc, Oklahoma City, OK). Approximately twelve 200-m-thick sections were cut from the anterior to posterior aspect of the joint. Sections were ground to 50 m with an EXAKT 420 CL Precision Grinding System (EXAKT Technologies, Inc). The ground sections were stained with Sanderson’s Rapid Bone Stain (Surgipath Medical Industries, Inc, Richmond, IL) and picrosirius red, a 1% aqueous solution of Direct Red 80, Color Index 35780 (Aldrich Chemical Company, Inc), in a 1:9 ratio with saturated aqueous picric acid (Lab Chem Inc, Pittsburgh, PA).14 These stains provided optimal contrast among the bone, ligament, and transitional Sharpey’s fibers. High-resolution calibrated digital images were acquired for each serial section from the anterior to the posterior aspect of the AC joint with the use of an Axiophot 2 microscope (Carl Zeiss, Inc, Thornwood, NY) and a SPOT digital camera (Diagnostic Instruments, Inc, Sterling Heights, MI) (Figure 3). These images were transferred to an IBM computer with a Pentium processor with expanded
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Figure 4 Drawing of AC joint. a, Distance from articular surface of distal clavicle to lateral insertion point of superior AC ligament; b, distance from articular surface of distal clavicle to medial insertion point of superior AC ligament; c, distance from articular surface of acromion to medial insertion point of superior AC ligament; d, distance from articular surface of acromion to lateral insertion point of superior AC ligament.
memory capabilities (Dell Computer Corporation, Round Rock, TX). Morphometric measurements were manually digitized with an Image-Pro Plus imaging system (version 4.0; Media Cybernetics, LP, Baltimore, MD). Joint surfaces of the acromion and clavicle were identified and marked with lines drawn perpendicular to the long axes of these bones at the joint surface. The insertion footprint of the superior AC ligament was identified on both the acromion and clavicle by microscopic observation of the Sharpey’s fibers penetrating into the periosteum (Figure 3). The most proximal and distal insertion points of the AC ligament were marked on both the acromion and clavicle. Measurements perpendicular to the joint surface markers and parallel to the bone axis were made by manual digitization. The mean distance of the insertion points of the superior AC ligament on both the distal clavicle (a and b) and the acromion (c and d) was determined from the distances measured on each of the 12 sections of each bone from the individual clavicles (Figure 4).
RESULTS CC ligament insertions
The results are listed in Table I, and the mean distances (⫾ SD) reported (in millimeters) reflect those between the points illustrated in Figure 1 (ie, between the center of the articular surface of the clavicle and the medial and lateral extents of the TL and CL insertions) for both sexes. Mean b-e and b-f distances (lateral and medial extent of clavicular insertions for CL and TL, respectively) were significantly greater in men than in women. The 95% CIs show that the mean b-c distance for the general population of men is unlikely to be more than 2.3 mm greater than that for women. The mean b-d distance among the general population of men is unlikely to be more than 6.5 mm greater than that for women. Although the lateral insertion point (e) of the CL was significantly (P ⫽ .027) further from the articular surface of the distal clavicle in men, there was greater variability between sexes (difference unlikely to be greater from 8.6 mm per 95% CI) compared with the variability of the lateral insertion of the TL.
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The mean AP width of the distal clavicle was 26.7 ⫾ 2.7 mm in the clavicles from men and 21.5 ⫾ 2.7 mm in those from women (P ⬍ .001). Within each sex, however, there was no strong correlation between insertional distances of the TL and CL and AP width of the distal clavicle. The partial correlations between distance and AP width, in a linear model including a term for sex, were only ⫺0.12, 0.43, ⫺0.01, and 0.12 (P ⫽ .59, .050, .97, and .60, respectively) for TL lateral insertion (Figure 1, c), TL medial insertion (Figure 1, d), conoid lateral insertion (Figure 1, e), and conoid medial insertion (Figure 1, f), respectively. Significant correlations were noted between measurements from the left and right sides of the same cadaver with use of the Pearson correlation coefficient test. Superior AC ligament insertions
The termination of the superior AC ligament was noted to be confluent with the periosteum of the clavicle and acromion, so there was not an abrupt transition to facilitate the measurements of ligament insertion. Therefore, measurements (in millimeters, ⫾ SD) were made at the point where there were no more clearly identifiable Sharpey’s fibers inserting into bone. The results are listed in Table II (mean [range]) and reflect those measurements illustrated in Figure 4. DISCUSSION Anatomic and biomechanical studies of the AC joint have been presented by other authors. Salter et al16 provided a detailed anatomic description from cadaveric specimens. With respect to the AC ligaments, they found that the superior AC ligament was more substantial and thicker (2-5 mm) than the inferior AC ligament and had a better-defined insertion into the distal clavicle. The superior AC ligament was also noted to insert into the clavicle and essentially merge with the musculotendinous aponeurosis of the deltotrapezial fascia. The authors did not, however, specify the mean distance of insertion of this ligament on the medial acromion or distal clavicle from their articular surfaces. The CC ligaments were noted to course from the clavicle to the coracoid process and consist of 2 components, the CL and TL. The mean length of these structures was 1.3 cm. They did not, however, report the mean distance of insertion of either of these CC ligaments from the articular surface of the distal end of the clavicle. Branch et al5 performed selective ligament sectioning combined with distal clavicle excision in cadaveric samples. They reported that resection of 5 mm of distal clavicle was adequate to ensure that no boneto-bone contact occurred postoperatively. They also
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Table I Measured distances of CL (trapezoid and conoid) insertions from articular surface of distal clavicle Distance of insertion (mm)
Insertion point
Men
b-c b-d b-e b-f
16.7 28.2 33.5 49.7
⫾ ⫾ ⫾ ⫾
Women
2.4 5.7 4.4 5.4
16.1 26.6 28.9 44.4
⫾ ⫾ ⫾ ⫾
1.4 5.2 2.5 4.4
P .44 .44 .027 .018
95% CI –1.1 –3.2 0.6 1.0
to to to to
2.3 6.5 8.6 9.7
See Figure 1 for locations of insertion points a, b, c, and d.
Table II Measured distances of superior AC ligament insertions from the articular surface of distal clavicle and acromion Mean distance (mm) (range)
Insertion point a* b* c† d†
Men 1.4 5.5 1.1 8.1
⫾ ⫾ ⫾ ⫾
0.33 (0.8-1.8) 1.7 (2.6-7.6) 0.37 (0.6-1.79) 0.75 (7.4-9.84)
Women 0.7 3.6 2.0 4.7
⫾ ⫾ ⫾ ⫾
0.63 (0-2.0) 0.78 (2.3-5.2) 0.5 (1.0-2.9) 0.98 (3.0-6.7)
See Figure 4 for locations of insertion points a, b, c, and d. *Articular surface of distal clavicle. †Articular surface of acromion.
found that the rotational stability of the distal clavicle was strongly influenced by the superior AC ligament. Fukuda et al7 also performed selective ligament sectioning in cadaveric samples and reported that the CL had a primary role in constraining anterior and superior translation and anterior and superior displacement of the clavicle, especially under high loading conditions. The TL was found to contribute less constraint to horizontal and vertical displacement, except under axial compressive loading conditions. The AC ligaments were noted to contribute approximately two thirds of the constraining force to superior displacement, with lesser amounts of displacement and induced loads. The operative management of AC pain has been well described in the literature. Open distal clavicle excision is probably the most widely accepted method based on descriptions by Gurd9 and Mumford.11 It is unclear which of these 2 authors actually performed the procedure first because they reported their experiences independently in 1941. Gurd recommended excision of the “distal third of clavicle,” and Mumford recommended excision of “1/2 to 1 inch” of the distal clavicle. Their descriptions, however, contained only case reports and subjective results. Other authors have also reported their results with open excision of the distal clavicle, yet the recommended amount of excision is quite variable. Neer12 reported that a minimum resection of 2 cm was needed. Rockwood and Matsen13 concurred with this opinion and also recommended a minimum
resection of 2 cm. Blazar et al4 reported that 1.5 to 2.0 cm was necessary. Conversely, Rowe15 indicated that less than 1 cm was ideal. Eskola et al6 presented convincing data for resecting less than 1 cm, because they noted a significant increase in postoperative pain in patients who had resection of greater than 1 cm. The precise rationale for the recommended amount of distal clavicle resection in these studies is unclear, however. The available reports describing arthroscopic distal clavicle resection are not consistent with regard to the amount of distal clavicle to excise and the precise rationale for this amount. Gartsman et al8 reported 1.5 cm as an appropriate amount of distal clavicle to excise. Bell2 indicated that slightly less, 10 to 15 mm, was adequate. Tolin and Snyder17 resected 1.5 cm and reported that the results were excellent in 39% of patients, good in 48%, and fair in 13%. Kay et al10 resected 1 cm in 10 patients, all of whom reported satisfactory results. Bigliani et al3 resected only 5 to 6 mm in 42 shoulders, and 91% of these patients had a resolution of symptoms and returned to full activity at a mean follow-up of 21 months. Our data point to a significant sex-related difference in the insertional distance of the CL, which originates farther from the distal or lateral end of the clavicle in men. No significant difference was seen between the clavicles from men and those from women for the insertion of the TL. The mean AP width of the distal clavicle was significantly greater in clavicles from men than in those from women. However, in both sexes the AP width of the distal clavicle did not correlate directly with the insertional distances of either the TL or CL. Therefore, it is difficult to explain the reason for a significant difference in the distance of insertion of the CL from the articular surface of the distal clavicles among men and women. Intuitively, one might assume that this is because of a generalized larger habitus in men than in women. Unfortunately, this could not be proven in this study because the maximal antimortem height and body weight of these cadavers were not available. Although it appears that there might be a sex-related difference in the insertion of the superior AC ligament on the distal clavicle as well, only 3 clavicles were evaluated in
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Table III Normal range based on mean ⫾ 2 SDs (central 95%) Left
Right
Men Insertion point a b-c b-d b-e b-f
Women
Men
Women
No.
Normal range (mm)
No.
Normal range (mm)
No.
Normal range (mm)
No.
Normal range (mm)
9 9 9 7 9
21-31 11-22 15-41 24-45 36-64
10 10 9 4 8
14-28 13-19 20-28 24-36 36-51
10 10 9 8 9
21-35 13-22 20-40 24-42 41-59
12 12 11 6 11
17-26 11-20 17-39 24-34 35-54
See Figure 1 for locations of insertion points a, b, c, and d.
this costly and time-consuming portion of the study; therefore, statistical analysis was not possible. On the basis of these data, it is difficult to provide clinical recommendations regarding a definitive amount of distal clavicle or medial acromion removal for optimal preservation of superior AC ligament attachments. Our data provide information for surgeons who perform excision of the distal clavicle. In a normally distributed population, 95% of the subjects fall within the mean ⫾ 2 SDs. Our best estimates of the normal ranges are from the means and SDs of our sample. If the distance is measured from the center of the articular surface of the distal clavicle, resection of less than 11.0 mm should never violate any portion of the TL in 98% of adult men or women, and resection of less than 24.0 mm should never violate any of the CL in either group (Table III). Although a theoretical advantage of arthroscopic resection of the distal clavicle is preservation of the superior AC ligament, this may not be easily realized. Our limited data suggest that this structure could be disrupted if resection of the distal clavicle is greater than 5.2 mm in women and 7.6 mm in men, and resection of the medial acromion is greater than 4.7 mm in women and 8.0 mm in men. One may, therefore, wish to consider only a few millimeters of resection from both the distal clavicle and medial acromion when performing arthroscopic decompression of the AC joint, rather than excising bone from the distal clavicle alone, to preserve the superior AC ligament. We thank Joan Yonchek and Liza Eschbach (Department of Orthopaedic Surgery, Section of Orthopaedic Research, University of Florida, Gainesville, FL) for technical assistance.
REFERENCES
1. Baron R, Vignery A, Neff L, Silverglate A, Maria Santa A. Processing of undecalcified bone specimens for bone histomorphometry. In: Recker RR, editor. Bone histomorphometry: techniques and interpretation. Boca Raton: CRC Press; 1983. p. 13-35. 2. Bell RH. Arthroscopic distal clavicle resection. Instr Course Lect 1998;47:35-41. 3. Bigliani LU, Nicholson GP, Flatow EL. Arthroscopic resection of the distal clavicle. Orthop Clin North Am 1993;24:133-41. 4. Blazar PE, Iannotti JP, Williams GR. Anteroposterior instability of the distal clavicle after distal clavicle resection. Clin Orthop 1998;348:114-20. 5. Branch TP, Burdette HL, Shahriari AS, Carter FM II, Hutton WC. The role of the acromioclavicular ligaments and the effect of distal clavicle resection. Am J Sports Med 1996;24:293-7. 6. Eskola A, Santavirta S, Viljakka HT, et al. The results of operative resection of the lateral end of the clavicle. J Bone Joint Surg Am 1996;78:584-7. 7. Fukuda K, Craig EV, An KN, Cofield RH, Chao EY. Biomechanical study of the ligamentous system of the acromioclavicular joint. J Bone Joint Surg Am 1986;68:434-40. 8. Gartsman GM, Combs AH, Davis PF, Tullos HS. Arthroscopic acromioclavicular joint resection. An anatomical study. Am J Sports Med 1991;19:2-5. 9. Gurd FB. The treatment of complete dislocation of the outer end of the clavicle: an hitherto undescribed operation. Ann Surg 1941;113:1094-8. 10. Kay SP, Ellman H, Harris E. Arthroscopic distal clavicle excision. Technique and early results. Clin Orthop 1994;301:181-4. 11. Mumford EB. Acromioclavicular dislocation. A new operative treatment. J Bone Joint Surg Am 1941;23:799-802. 12. Neer CS II. Impingement lesions. Clin Orthop 1993;173:70-7. 13. Rockwood CA Jr, Matsen FA III, editors. The shoulder. Philadelphia: Saunders; 1990. p 42-3, 210-1. 14. Rousch JK, Breur GJ, Wilson JW. Picrosirius red staining of dental structures. Stain Technol 1988;63:363-7. 15. Rowe CR. Trends in treatment of complete acromioclavicular dislocations. In: Bateman JE, Welsh RP, editors. Surgery of the shoulder. Philadelphia: BC Decker; 1984. p 73-8. 16. Salter EG Jr, Nasca RJ, Shelley BS. Anatomical observations on the acromioclavicular joint and supporting ligaments. Am J Sports Med 1987;15:199-206. 17. Tolin BS, Snyder SJ. Our technique for the arthroscopic Mumford procedure. Orthop Clin North Am 1993;24:143-51.
We describe the insertional variations of supporting ligaments of the acromioclavicular joint, especially with respect to gender. We analyzed 41 cadaveric clavicles (22 female and 19 male) with attached ligaments. The distance between the insertion of the trapezoid ligament and the distal end of the clavicle was not significantly different between sexes, although that of the conoid ligament and the mean anteroposterior width of the distal clavicle was significantly greater in men. Although there are significant sex-related differences in the insertional distances of the CC ligaments, resection of less than 11.0 mm should not violate the trapezoid ligament and less than 24.0 mm should not violate the conoid ligament in either sex in 98% of the general population. Resection of more than 7.6 mm of the distal clavicle in men and 5.2 mm in women, performed by an arthroscopic approach, may violate the superior acromioclavicular ligament. (J Shoulder Elbow Surg 2003;12:355-9.)
T
he acromioclavicular (AC) joint is a common site of pain, most often from primary or posttraumatic arthritis. This articulation may also be involved in the pathogenesis of shoulder impingement and rotator cuff tears from attrition of inferiorly projecting osteophytes from the distal clavicle. Treatment typically includes excision of the terminal portion of the distal clavicle. However, the recommended amount of bone that should be excised varies among reports in the literature. The coracoclavicular (CC) (trapezoid and conoid) ligaments may be at risk for injury through excessive bone excision, subperiosteal dissection, or aggressive placement of retractors medially, which could result in instability of the remaining distal clavicular stump. We are not aware of any studies that provide data on the insertional distances of these ligaments from the lateral end of the clavicle. First, we From the Sections of aHand Surgery and bBiostatistics, Mayo Clinic, Scottsdale; bPrivate Practice, Ocala; and cDepartment of Orthopaedic Surgery, University of Florida, Gainesville. Reprint requests: Kevin J. Renfree, MD, Section of Hand Surgery, Mayo Clinic, 13400 E Shea Blvd, Scottsdale, AZ 85259. Copyright © 2003 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2003/$35.00 ⫹ 0 doi:10.1016/S1058-2746(03)00029-6
sought to determine these distances and whether there is side-to-side variability of the insertional distances of these ligaments within the same patient. We evaluated variability between persons with respect to gender because women and men often differ in habitus. Our goal was to provide guidelines from an anatomic study that will allow surgeons to resect the distal clavicle adequately in all patients, regardless of size or sex, without disrupting the biomechanically important CC ligaments. Arthroscopic resection of the distal clavicle has been described more recently, and the proposed advantages of this procedure include reduction of morbidity from an open incision and preservation of the deltotrapezial fascia and superior AC ligament. Accelerated rehabilitation and better preservation of rotational and horizontal stability of the remaining distal clavicle are potentially seen. Therefore, for the second part of the study, we examined histologically the insertional distances of the superior AC ligament on both the distal clavicle and adjacent medial acromion. MATERIALS AND METHODS We evaluated 41 clavicles (22 female and 19 male) from 23 cadavers. Five clavicles were excluded because they were inadequate. The mean age was 79 years (range, 64-101 years); the mean age was 79 years (SD, 10 years) for women and 79 years (SD, 12 years) for men. Nineteen clavicles were from the left side and twenty-two were from the right. Of these, there were 19 matched (right and left) pairs (38 clavicles). Nine of the matched pairs were from men, and ten were from women. Measurements were made with a handheld caliper-type micrometer with 3.5⫻ loupe magnification before the tissue was digested in a household bleach solution. All clavicles were number-coded, thereby blinding the examiners to the sex and matched-pair status of the clavicles.
CC ligament insertions The following measurements were obtained (Figure 1): the maximum anteroposterior (AP) width of the metaphyseal portion of the distal clavicle medial to the articular surface (a) and the distance from the center (b) of the articular surface of the distal clavicle to the anterior lateral (c) and mid-medial (d) origin of the trapezoid ligament (TL) and to the lateral (e) and medial (f) origin of the conoid ligament (CL). Soft tissue was digested by submerging clavicles in
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Figure 1 Inferior surface of distal clavicle. Shaded trapezoidal area represents TL insertion, and diamond-shaped area represents CL insertion. a, AP width of distal clavicle; b, center of articular surface of distal clavicle; c, lateral edge of TL insertion; d, medial edge of TL insertion; e, lateral edge of CL insertion; f, medial edge of CL insertion.
J Shoulder Elbow Surg July/August 2003
Figure 3 Histologic AC joint section.
Superior AC ligament insertions
Figure 2 TL and CL insertions stained with methylene blue after digestion in bleach.
individual containers of bleach, and measurements were confirmed after the ligament footprint was stained with methylene blue (Figure 2). Statistical analysis of the measurements was performed with the 2-sample t test, which allowed a comparison of the sex-related difference in insertional distances of the TL and CL insertions from the articular surface of the distal clavicle. Measurements of 12 clavicles from women and 10 from men were compared; this comparison was, therefore, independent of matched-pair status (ie, 3 unmatched clavicles from women and 1 from a man). Confidence intervals (CIs) were calculated for the difference between group means to show how precisely the difference has been quantified and to show whether the sample was large enough to conclude reliably that the groups were equivalent. The Pearson correlation coefficient was used to determine the correlation of measurements between clavicles from the right and left sides within the same cadaver. Partial correlation was used to control for differences between sexes and to assess the relationship between the distance of insertion of the TL or CL from the articular surface of the distal clavicle and the size of the clavicle (AP width).
Three fresh-frozen human cadaveric clavicles, acromions, and intact AC joints were resected from 1 man and 2 women. Muscle tissue was removed from bone with care to preserve the AC joint ligaments. The clavicle and acromion were transected approximately 4 cm from the joint surface to facilitate histologic processing. Clavicles were prepared for undecalcified histologic processing by standard techniques.1 In brief, the clavicles were fixed in an alcoholformalin solution (9 parts 80% ethanol and 1 part 37% formaldehyde), dehydrated in a sequence of graded ethanol solutions (70%, 85%, 95%, 100%, and 100%), cleared with histologic-grade xylene (Fisher Scientific, Suwanee, GA), and infiltrated and embedded under a vacuum with graded resin mixtures of methyl methacrylate (Fisher Scientific), dibutyl phthalate (Sigma Chemical Company, St Louis, MO), and benzoyl peroxide (Aldrich Chemical Company, Inc, Milwaukee, WI). Serial macrosections of the AC joint, including the AC ligament, were made in the coronal plane by use of an EXAKT 310 Band Systems Macro diamond saw (EXAKT Technologies, Inc, Oklahoma City, OK). Approximately twelve 200-m-thick sections were cut from the anterior to posterior aspect of the joint. Sections were ground to 50 m with an EXAKT 420 CL Precision Grinding System (EXAKT Technologies, Inc). The ground sections were stained with Sanderson’s Rapid Bone Stain (Surgipath Medical Industries, Inc, Richmond, IL) and picrosirius red, a 1% aqueous solution of Direct Red 80, Color Index 35780 (Aldrich Chemical Company, Inc), in a 1:9 ratio with saturated aqueous picric acid (Lab Chem Inc, Pittsburgh, PA).14 These stains provided optimal contrast among the bone, ligament, and transitional Sharpey’s fibers. High-resolution calibrated digital images were acquired for each serial section from the anterior to the posterior aspect of the AC joint with the use of an Axiophot 2 microscope (Carl Zeiss, Inc, Thornwood, NY) and a SPOT digital camera (Diagnostic Instruments, Inc, Sterling Heights, MI) (Figure 3). These images were transferred to an IBM computer with a Pentium processor with expanded
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Figure 4 Drawing of AC joint. a, Distance from articular surface of distal clavicle to lateral insertion point of superior AC ligament; b, distance from articular surface of distal clavicle to medial insertion point of superior AC ligament; c, distance from articular surface of acromion to medial insertion point of superior AC ligament; d, distance from articular surface of acromion to lateral insertion point of superior AC ligament.
memory capabilities (Dell Computer Corporation, Round Rock, TX). Morphometric measurements were manually digitized with an Image-Pro Plus imaging system (version 4.0; Media Cybernetics, LP, Baltimore, MD). Joint surfaces of the acromion and clavicle were identified and marked with lines drawn perpendicular to the long axes of these bones at the joint surface. The insertion footprint of the superior AC ligament was identified on both the acromion and clavicle by microscopic observation of the Sharpey’s fibers penetrating into the periosteum (Figure 3). The most proximal and distal insertion points of the AC ligament were marked on both the acromion and clavicle. Measurements perpendicular to the joint surface markers and parallel to the bone axis were made by manual digitization. The mean distance of the insertion points of the superior AC ligament on both the distal clavicle (a and b) and the acromion (c and d) was determined from the distances measured on each of the 12 sections of each bone from the individual clavicles (Figure 4).
RESULTS CC ligament insertions
The results are listed in Table I, and the mean distances (⫾ SD) reported (in millimeters) reflect those between the points illustrated in Figure 1 (ie, between the center of the articular surface of the clavicle and the medial and lateral extents of the TL and CL insertions) for both sexes. Mean b-e and b-f distances (lateral and medial extent of clavicular insertions for CL and TL, respectively) were significantly greater in men than in women. The 95% CIs show that the mean b-c distance for the general population of men is unlikely to be more than 2.3 mm greater than that for women. The mean b-d distance among the general population of men is unlikely to be more than 6.5 mm greater than that for women. Although the lateral insertion point (e) of the CL was significantly (P ⫽ .027) further from the articular surface of the distal clavicle in men, there was greater variability between sexes (difference unlikely to be greater from 8.6 mm per 95% CI) compared with the variability of the lateral insertion of the TL.
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The mean AP width of the distal clavicle was 26.7 ⫾ 2.7 mm in the clavicles from men and 21.5 ⫾ 2.7 mm in those from women (P ⬍ .001). Within each sex, however, there was no strong correlation between insertional distances of the TL and CL and AP width of the distal clavicle. The partial correlations between distance and AP width, in a linear model including a term for sex, were only ⫺0.12, 0.43, ⫺0.01, and 0.12 (P ⫽ .59, .050, .97, and .60, respectively) for TL lateral insertion (Figure 1, c), TL medial insertion (Figure 1, d), conoid lateral insertion (Figure 1, e), and conoid medial insertion (Figure 1, f), respectively. Significant correlations were noted between measurements from the left and right sides of the same cadaver with use of the Pearson correlation coefficient test. Superior AC ligament insertions
The termination of the superior AC ligament was noted to be confluent with the periosteum of the clavicle and acromion, so there was not an abrupt transition to facilitate the measurements of ligament insertion. Therefore, measurements (in millimeters, ⫾ SD) were made at the point where there were no more clearly identifiable Sharpey’s fibers inserting into bone. The results are listed in Table II (mean [range]) and reflect those measurements illustrated in Figure 4. DISCUSSION Anatomic and biomechanical studies of the AC joint have been presented by other authors. Salter et al16 provided a detailed anatomic description from cadaveric specimens. With respect to the AC ligaments, they found that the superior AC ligament was more substantial and thicker (2-5 mm) than the inferior AC ligament and had a better-defined insertion into the distal clavicle. The superior AC ligament was also noted to insert into the clavicle and essentially merge with the musculotendinous aponeurosis of the deltotrapezial fascia. The authors did not, however, specify the mean distance of insertion of this ligament on the medial acromion or distal clavicle from their articular surfaces. The CC ligaments were noted to course from the clavicle to the coracoid process and consist of 2 components, the CL and TL. The mean length of these structures was 1.3 cm. They did not, however, report the mean distance of insertion of either of these CC ligaments from the articular surface of the distal end of the clavicle. Branch et al5 performed selective ligament sectioning combined with distal clavicle excision in cadaveric samples. They reported that resection of 5 mm of distal clavicle was adequate to ensure that no boneto-bone contact occurred postoperatively. They also
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J Shoulder Elbow Surg July/August 2003
Table I Measured distances of CL (trapezoid and conoid) insertions from articular surface of distal clavicle Distance of insertion (mm)
Insertion point
Men
b-c b-d b-e b-f
16.7 28.2 33.5 49.7
⫾ ⫾ ⫾ ⫾
Women
2.4 5.7 4.4 5.4
16.1 26.6 28.9 44.4
⫾ ⫾ ⫾ ⫾
1.4 5.2 2.5 4.4
P .44 .44 .027 .018
95% CI –1.1 –3.2 0.6 1.0
to to to to
2.3 6.5 8.6 9.7
See Figure 1 for locations of insertion points a, b, c, and d.
Table II Measured distances of superior AC ligament insertions from the articular surface of distal clavicle and acromion Mean distance (mm) (range)
Insertion point a* b* c† d†
Men 1.4 5.5 1.1 8.1
⫾ ⫾ ⫾ ⫾
0.33 (0.8-1.8) 1.7 (2.6-7.6) 0.37 (0.6-1.79) 0.75 (7.4-9.84)
Women 0.7 3.6 2.0 4.7
⫾ ⫾ ⫾ ⫾
0.63 (0-2.0) 0.78 (2.3-5.2) 0.5 (1.0-2.9) 0.98 (3.0-6.7)
See Figure 4 for locations of insertion points a, b, c, and d. *Articular surface of distal clavicle. †Articular surface of acromion.
found that the rotational stability of the distal clavicle was strongly influenced by the superior AC ligament. Fukuda et al7 also performed selective ligament sectioning in cadaveric samples and reported that the CL had a primary role in constraining anterior and superior translation and anterior and superior displacement of the clavicle, especially under high loading conditions. The TL was found to contribute less constraint to horizontal and vertical displacement, except under axial compressive loading conditions. The AC ligaments were noted to contribute approximately two thirds of the constraining force to superior displacement, with lesser amounts of displacement and induced loads. The operative management of AC pain has been well described in the literature. Open distal clavicle excision is probably the most widely accepted method based on descriptions by Gurd9 and Mumford.11 It is unclear which of these 2 authors actually performed the procedure first because they reported their experiences independently in 1941. Gurd recommended excision of the “distal third of clavicle,” and Mumford recommended excision of “1/2 to 1 inch” of the distal clavicle. Their descriptions, however, contained only case reports and subjective results. Other authors have also reported their results with open excision of the distal clavicle, yet the recommended amount of excision is quite variable. Neer12 reported that a minimum resection of 2 cm was needed. Rockwood and Matsen13 concurred with this opinion and also recommended a minimum
resection of 2 cm. Blazar et al4 reported that 1.5 to 2.0 cm was necessary. Conversely, Rowe15 indicated that less than 1 cm was ideal. Eskola et al6 presented convincing data for resecting less than 1 cm, because they noted a significant increase in postoperative pain in patients who had resection of greater than 1 cm. The precise rationale for the recommended amount of distal clavicle resection in these studies is unclear, however. The available reports describing arthroscopic distal clavicle resection are not consistent with regard to the amount of distal clavicle to excise and the precise rationale for this amount. Gartsman et al8 reported 1.5 cm as an appropriate amount of distal clavicle to excise. Bell2 indicated that slightly less, 10 to 15 mm, was adequate. Tolin and Snyder17 resected 1.5 cm and reported that the results were excellent in 39% of patients, good in 48%, and fair in 13%. Kay et al10 resected 1 cm in 10 patients, all of whom reported satisfactory results. Bigliani et al3 resected only 5 to 6 mm in 42 shoulders, and 91% of these patients had a resolution of symptoms and returned to full activity at a mean follow-up of 21 months. Our data point to a significant sex-related difference in the insertional distance of the CL, which originates farther from the distal or lateral end of the clavicle in men. No significant difference was seen between the clavicles from men and those from women for the insertion of the TL. The mean AP width of the distal clavicle was significantly greater in clavicles from men than in those from women. However, in both sexes the AP width of the distal clavicle did not correlate directly with the insertional distances of either the TL or CL. Therefore, it is difficult to explain the reason for a significant difference in the distance of insertion of the CL from the articular surface of the distal clavicles among men and women. Intuitively, one might assume that this is because of a generalized larger habitus in men than in women. Unfortunately, this could not be proven in this study because the maximal antimortem height and body weight of these cadavers were not available. Although it appears that there might be a sex-related difference in the insertion of the superior AC ligament on the distal clavicle as well, only 3 clavicles were evaluated in
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Table III Normal range based on mean ⫾ 2 SDs (central 95%) Left
Right
Men Insertion point a b-c b-d b-e b-f
Women
Men
Women
No.
Normal range (mm)
No.
Normal range (mm)
No.
Normal range (mm)
No.
Normal range (mm)
9 9 9 7 9
21-31 11-22 15-41 24-45 36-64
10 10 9 4 8
14-28 13-19 20-28 24-36 36-51
10 10 9 8 9
21-35 13-22 20-40 24-42 41-59
12 12 11 6 11
17-26 11-20 17-39 24-34 35-54
See Figure 1 for locations of insertion points a, b, c, and d.
this costly and time-consuming portion of the study; therefore, statistical analysis was not possible. On the basis of these data, it is difficult to provide clinical recommendations regarding a definitive amount of distal clavicle or medial acromion removal for optimal preservation of superior AC ligament attachments. Our data provide information for surgeons who perform excision of the distal clavicle. In a normally distributed population, 95% of the subjects fall within the mean ⫾ 2 SDs. Our best estimates of the normal ranges are from the means and SDs of our sample. If the distance is measured from the center of the articular surface of the distal clavicle, resection of less than 11.0 mm should never violate any portion of the TL in 98% of adult men or women, and resection of less than 24.0 mm should never violate any of the CL in either group (Table III). Although a theoretical advantage of arthroscopic resection of the distal clavicle is preservation of the superior AC ligament, this may not be easily realized. Our limited data suggest that this structure could be disrupted if resection of the distal clavicle is greater than 5.2 mm in women and 7.6 mm in men, and resection of the medial acromion is greater than 4.7 mm in women and 8.0 mm in men. One may, therefore, wish to consider only a few millimeters of resection from both the distal clavicle and medial acromion when performing arthroscopic decompression of the AC joint, rather than excising bone from the distal clavicle alone, to preserve the superior AC ligament. We thank Joan Yonchek and Liza Eschbach (Department of Orthopaedic Surgery, Section of Orthopaedic Research, University of Florida, Gainesville, FL) for technical assistance.
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