The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 85, Issue 4

Scientific Article | April 01, 2003

Anatomical Variants in the Anterosuperior Aspect of the Glenoid Labrum : A Statistical Analysis of Seventy-three Cases

Anita G. Rao, MD; Tae Kyun Kim, MD, PhD; Efstathios Chronopoulos, MD; Edward G. McFarland, MD

Investigation performed at the Division of Sports Medicine and Shoulder Surgery, Department of Orthopaedic Surgery, Johns Hopkins University, Baltimore, Maryland

Anita G. Rao, MD
Tae Kyun Kim, MD, PhD
Efstathios Chronopoulos, MD
Edward G. McFarland, MD
Division of Sports Medicine and Shoulder Surgery, Department of Orthopaedic Surgery, Johns Hopkins University, 10753 Falls Road, Suite 215, Lutherville, MD 21093. E-mail address for E.G. McFarland: emcfarl@jhmi.edu

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

J Bone Joint Surg Am, 2003 Apr 01;85(4):653-659

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Abstract

Background: Anterosuperior labral variations of the glenohumeral joint have been previously described and are thought to represent normal anatomical variants without any known clinical importance. The goals of this study were to characterize anterosuperior labral anatomical variations and to determine their prevalence and clinical importance.

Methods: A total of 546 patients who had an arthroscopic procedure in the shoulder were prospectively evaluated for variations of the anterosuperior aspect of the labrum. Structural characteristics of the anatomical variants were noted and recorded intraoperatively. The relationships of these anterosuperior labral variations to demographic data, preoperative symptoms, findings on physical examination, and associated intra-articular abnormalities were analyzed statistically and compared with findings in patients with normal anterosuperior labral anatomy.

Results: Three distinct variations of the anterosuperior portion of the labrum were found in seventy-three patients (13.4%): a sublabral foramen only (eighteen patients; 3.3%), a sublabral foramen with a cord-like middle glenohumeral ligament (forty-seven; 8.6%), and an absence of labral tissue at the anterosuperior portion of the labrum with a cord-like middle glenohumeral ligament (eight; 1.5%). In multivariate analysis, the presence of one of these three variations revealed a significant positive association with anterosuperior labral fraying (p = 0.000), an abnormal superior glenohumeral ligament (p = 0.012), and increased passive internal rotation with the arm in 90° of abduction (p = 0.046). These lesions were negatively associated with a painful arc sign and the presence of either a partial or full-thickness supraspinatus tendon tear. Statistical analysis revealed a clinical difference between the cord-like middle glenohumeral ligament variants and the sublabral foramen variant.

Conclusions: Anterosuperior labral variants may influence glenohumeral biomechanics and may predispose the shoulder to other abnormalities. These variants are associated with increased internal rotation, which may predispose the shoulder to lesions of the superior glenohumeral ligament and anterosuperior portion of the labrum. These variations themselves do not appear to contribute to instability.

Level of Evidence: Prognostic study, Level II-1 (retrospective study). See Instructions to Authors for a complete description of levels of evidence.

Figures in this Article

Introduction

The contributions of the glenoid labrum to glenohumeral joint stability have been well described ^1-9 . The labrum is composed of a rim of fibrous tissue with a fibrocartilaginous transition zone that functions to deepen the glenoid fossa and provide a point of attachment for the soft-tissue stabilizers, such as the glenohumeral ligaments and capsule ^2,3,10 . Several different anatomic variations of the glenoid labrum have been identified ^2,3,5,11-16 .

Several studies have suggested that there is wide variability in the anatomy of the anterosuperior portion of the labrum, anteriorly between the origin of the long head of the biceps and the equator of the glenoid ^2,3,16 . Detrisac and Johnson ³ described five normal variations in labral anatomy, which were based on whether the labrum appeared wedge-shaped or meniscoid. Cooper et al. ² further investigated the anatomy of the labrum and identified additional variations, including morphologic differences between the superior and inferior aspects of the labrum. They found that the inferior part was more rounded and firmly continuous with the articular cartilage and that the superior part appeared to be more meniscoid and mobile, with loose attachments.

The presence of a sublabral foramen, which is a sulcus between the normally developed anterosuperior portion of the labrum and the glenoid articular cartilage, has been recognized as such a variant ^2,3,16 . The sublabral foramen has also been seen in association with a so-called cord-like middle glenohumeral ligament, and this combination has been previously regarded as another normal variation of anterosuperior labral anatomy ¹⁶ . While studies have shown that the middle glenohumeral ligament may vary considerably in width and thickness ³ , the normal middle glenohumeral ligament is classically described as flat, or "sheet-like," in appearance in contradistinction to the thickened, rolled appearance of the cord-like middle glenohumeral ligament ^16,17 . On the basis of a retrospective review of 200 shoulder arthroscopies, Williams et al. ¹⁶ identified a unique labral variation in three patients, which they called the "Buford complex." This complex was characterized by a cord-like middle glenohumeral ligament, which attached to the superior part of the labrum at the base of the biceps tendon, in conjunction with an absence of labral tissue at the anterosuperior portion of the labrum. On the basis of an anecdotal case report and speculation suggested by the literature, Williams et al. ¹⁶ concluded that this condition represented "another normal anatomical variant."

Despite many previous studies of anterosuperior labral anatomical variations, no study has been performed, as far as we know, to determine the clinical importance of these conditions. Most of the previous studies involved morphologic observation of anatomical structures in cadaveric shoulders. The goals of the present study were to characterize anterosuperior labral anatomical variations, to determine the prevalence of the variations, and to evaluate their clinical importance in a patient population undergoing shoulder surgery for the treatment of a variety of conditions.

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Fig. 1:: Schematic drawings demonstrating the anterosuperior labral anatomy of a right shoulder. (A) The normal shoulder. The glenoid labrum is present and attached to the rim in the anterosuperior quadrant. A normal middle glenohumeral ligament (MGHL) appears flat or "sheet like." (B) Sublabral foramen only. A sublabral foramen, a sulcus between a normally developed anterosuperior portion of the labrum and the glenoid articular rim, in the anterosuperior quadrant is shown. The middle glenohumeral ligament is normal or "sheet like." (C) Sublabral foramen with a cord-like middle glenohumeral ligament. A sublabral foramen is seen at the anterosuperior quadrant, and the middle glenohumeral ligament appears thickened and cord like in structure. (D) An absence of labral tissue at the anterosuperior portion of the labrum with a cord-like middle glenohumeral ligament. A cord-like middle glenohumeral ligament attaches to the superior part of the labrum near the base of the biceps brachii. The glenoid labrum is absent in the anterosuperior quadrant. IGHL = inferior glenohumeral ligament. (Printed, with permission, from Johns Hopkins University.)

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TABLE I: Demographic Data, History of Symptom Onset, and Primary Diagnosis

*The values are given as the number of shoulders, with the percentage in parentheses. †The values are given as the mean and the standard deviation.

Variable	Standard Anatomy Group (N = 473)	Study Group (N = 73)	P Value
Gender* (male)	275 (58)	43 (59)	1.000
Age† (yr)	45.1 ± 17.64	42.2 ± 17.16	0.185
Involvement of right arm*	284 (60)	44 (60)	1.000
Involvement of dominant arm*	300 (63)	42 (58)	0.364
High-demand occupation*	92 (19)	10 (14)	0.264
Participation in overhead sports*	102 (22)	19 (26)	0.449
High-level participation in sports*	123 (26)	17 (23)	0.668
Symptom onset with trauma history*	277 (59)	44 (60)	0.889
Primary diagnosis*
Rotator cuff disease	255 (54)	35 (48)	0.342
Glenohumeral instability	130 (27)	25 (34)	0.233
Acromioclavicular disease	53 (11)	7 (10)	0.681
Frozen shoulder	23 (5)	2 (3)	0.558
Other	12 (3)	4 (5)	0.250

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TABLE I: Demographic Data, History of Symptom Onset, and Primary Diagnosis

*The values are given as the number of shoulders, with the percentage in parentheses. †The values are given as the mean and the standard deviation.

Variable	Standard Anatomy Group (N = 473)	Study Group (N = 73)	P Value
Gender* (male)	275 (58)	43 (59)	1.000
Age† (yr)	45.1 ± 17.64	42.2 ± 17.16	0.185
Involvement of right arm*	284 (60)	44 (60)	1.000
Involvement of dominant arm*	300 (63)	42 (58)	0.364
High-demand occupation*	92 (19)	10 (14)	0.264
Participation in overhead sports*	102 (22)	19 (26)	0.449
High-level participation in sports*	123 (26)	17 (23)	0.668
Symptom onset with trauma history*	277 (59)	44 (60)	0.889
Primary diagnosis*
Rotator cuff disease	255 (54)	35 (48)	0.342
Glenohumeral instability	130 (27)	25 (34)	0.233
Acromioclavicular disease	53 (11)	7 (10)	0.681
Frozen shoulder	23 (5)	2 (3)	0.558
Other	12 (3)	4 (5)	0.250

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TABLE II: Findings on Physical Examination

*Significant differences are in bold. †The values are given as the number of shoulders with a positive finding/number of shoulders tested, with the percentage in parentheses. †The values are given as the mean and the standard deviation.

Variable	Standard Anatomy Group (N = 473)	Study Group (N = 73)	P Value*
Neer test†	284/465 (61)	38/71 (54)	0.243
Hawkins test†	299/459 (65)	47/72 (65)	1.000
Painful arc sign†	158/289 (55)	22/63 (35)	0.005
Drop-arm sign†	99/408 (24)	12/67 (18)	0.280
Relocation test†	56/243 (23)	14/59 (24)	1.000
Apprehension test†	88/441 (20)	20/71 (28)	0.119
Speed test†	136/422 (32)	19/71 (27)	0.409
Compression rotation test†	61/252 (24)	14/57 (25)	1.000
Anterior slide test†	55/354 (16)	10/66 (15)	1.000
Active compression test†	167/361 (46)	30/67 (45)	0.894
Range of motion (deg) ‡
Active flexion	137 ± 37.6	151 ± 27.3	0.003
Passive flexion	149 ± 28.0	159 ± 22.3	0.010
Active abduction	133 ± 40.2	145 ± 28.9	0.014
Passive abduction	145 ± 32.9	155 ± 25.0	0.015
Active external rotation in 90° of abduction	78 ± 25.9	85 ± 24.4	0.052
Passive external rotation in 90° of abduction	90 ± 22.8	94 ± 25.5	0.253
Active internal rotation in 90°of abduction	37 ± 30.4	51 ± 28.1	0.001
Passive internal rotation in 90° of abduction	44 ± 25.7	56 ± 27.7	0.003
Combined active rotation in 90° of abduction	118 ± 43.0	142 ± 37.6	0.054
Combined passive rotation in 90° of abduction	142 ± 40.3	153 ± 37.6	0.362

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TABLE II: Findings on Physical Examination

Variable	Standard Anatomy Group (N = 473)	Study Group (N = 73)	P Value*
Neer test†	284/465 (61)	38/71 (54)	0.243
Hawkins test†	299/459 (65)	47/72 (65)	1.000
Painful arc sign†	158/289 (55)	22/63 (35)	0.005
Drop-arm sign†	99/408 (24)	12/67 (18)	0.280
Relocation test†	56/243 (23)	14/59 (24)	1.000
Apprehension test†	88/441 (20)	20/71 (28)	0.119
Speed test†	136/422 (32)	19/71 (27)	0.409
Compression rotation test†	61/252 (24)	14/57 (25)	1.000
Anterior slide test†	55/354 (16)	10/66 (15)	1.000
Active compression test†	167/361 (46)	30/67 (45)	0.894
Range of motion (deg) ‡
Active flexion	137 ± 37.6	151 ± 27.3	0.003
Passive flexion	149 ± 28.0	159 ± 22.3	0.010
Active abduction	133 ± 40.2	145 ± 28.9	0.014
Passive abduction	145 ± 32.9	155 ± 25.0	0.015
Active external rotation in 90° of abduction	78 ± 25.9	85 ± 24.4	0.052
Passive external rotation in 90° of abduction	90 ± 22.8	94 ± 25.5	0.253
Active internal rotation in 90°of abduction	37 ± 30.4	51 ± 28.1	0.001
Passive internal rotation in 90° of abduction	44 ± 25.7	56 ± 27.7	0.003
Combined active rotation in 90° of abduction	118 ± 43.0	142 ± 37.6	0.054
Combined passive rotation in 90° of abduction	142 ± 40.3	153 ± 37.6	0.362

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TABLE III: Intra-Articular Associated Abnormalities

*The values are given as the number of shoulders, with the percentage in parentheses. †Significant differences are in bold. NA = not applicable.

Abnormality	Standard Anatomy Group* (N = 473)	Study Group* (N = 73)	P Value†
Supraspinatus tendon tear	274 (58)	29 (40)	0.005
Infraspinatus tendon tear	37 (8)	1 (1)	0.046
Subscapularis tendon tear	61 (13)	16 (22)	0.047
Biceps tendon pathologies	132 (28)	16 (22)	0.324
SLAP lesions
Type I	92 (19)	18 (25)	0.346
Type II	29 (6)	9 (12)	0.053
Types III and IV	5 (1)	0	NA
Hill-Sachs lesion	106 (22)	18 (25)	0.655
Bankart lesion	92 (19)	17 (23)	0.435
Abnormal superior glenohumeral ligament	37 (8)	10 (14)	0.114
Labral fraying
Anterosuperior labral fraying	126 (27)	40 (55)	0.000
Posterosuperior labral fraying	140 (30)	34 (47)	0.005
Anteroinferior labral fraying	70 (15)	11 (15)	1.000
Posteroinferior labral fraying	98 (21)	10 (14)	0.206
Humeral head osteoarthritis	124 (26)	19 (26)	1.000
Glenoid osteoarthritis	85 (18)	11 (15)	0.623

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TABLE III: Intra-Articular Associated Abnormalities

*The values are given as the number of shoulders, with the percentage in parentheses. †Significant differences are in bold. NA = not applicable.

Abnormality	Standard Anatomy Group* (N = 473)	Study Group* (N = 73)	P Value†
Supraspinatus tendon tear	274 (58)	29 (40)	0.005
Infraspinatus tendon tear	37 (8)	1 (1)	0.046
Subscapularis tendon tear	61 (13)	16 (22)	0.047
Biceps tendon pathologies	132 (28)	16 (22)	0.324
SLAP lesions
Type I	92 (19)	18 (25)	0.346
Type II	29 (6)	9 (12)	0.053
Types III and IV	5 (1)	0	NA
Hill-Sachs lesion	106 (22)	18 (25)	0.655
Bankart lesion	92 (19)	17 (23)	0.435
Abnormal superior glenohumeral ligament	37 (8)	10 (14)	0.114
Labral fraying
Anterosuperior labral fraying	126 (27)	40 (55)	0.000
Posterosuperior labral fraying	140 (30)	34 (47)	0.005
Anteroinferior labral fraying	70 (15)	11 (15)	1.000
Posteroinferior labral fraying	98 (21)	10 (14)	0.206
Humeral head osteoarthritis	124 (26)	19 (26)	1.000
Glenoid osteoarthritis	85 (18)	11 (15)	0.623

Materials and Methods

Between 1994 and 2000, 736 patients who underwent a shoulder procedure performed by the senior author (E.G.M.) were prospectively entered into a database. A total of 163 patients who underwent a nonarthroscopic procedure and twenty-seven who had a revision procedure were excluded, leaving 546 patients for evaluation. All patients gave informed consent prior to the procedure. The study was given approval by the Institutional Review Board.

All patients underwent a thorough preoperative history, completed a standardized questionnaire, and underwent a comprehensive physical examination performed within four weeks before surgery ¹⁸ . The examination included testing for range of motion, muscle strength, impingement signs, and apprehension as well as a complete neurological evaluation of the upper extremity. A visual analog scale with a 100-point scoring system per question was used to evaluate forty-four subjective symptoms, which included aspects of perceived pain, range of motion, weakness, stability, function, activity level, and satisfaction.

All patients were managed with general anesthesia with or without a scalene block. Examination was performed by the senior author with the patient under anesthesia and included laxity testing with use of anterior and posterior drawer tests as described by Gerber and Ganz ¹⁹ . The translation of the humeral head on the glenoid was reported with a modified Hawkins scale as previously described ²⁰ . Sulcus testing was performed and graded with use of standard criteria ^21,22 .

All shoulder arthroscopies were performed with the patient positioned on a bean bag in a lateral decubitus position and with the arm placed in an arm-holder with 10 lb (4.5 kg) of traction. The diagnostic arthroscopy was performed with use of a posterior portal, and a standardized data sheet was used in each case to record the findings. All diagnostic arthroscopy procedures were recorded with use of standard VHS video equipment.

Particular attention was given to the labrum, and anatomical variations were noted. In all patients, the labrum was probed with a nerve hook through an anterior portal. Normal anterosuperior labral anatomy was defined as depicted in Figure 1 , A . The labrum was considered normal when it was present and attached to the glenoid rim throughout. Variations in the labrum, specifically in the anterosuperior quadrant, were evaluated and recorded. Three variations were noted and included: (1) the presence of a sublabral foramen, defined as the sulcus between a well-developed anterosuperior portion of the labrum and the glenoid articular cartilage ( Fig. 1 , B ); (2) the presence of a sublabral foramen and a cord-like middle glenohumeral ligament, in which the middle glenohumeral ligament appeared as a thick cord, rolled on both the medial and lateral edges ( Fig. 1 , C ); and (3) a complete absence of labral tissue at the anterosuperior aspect of the labrum in association with a cord-like middle glenohumeral ligament, which attached to the superior part of the labrum at the base of the biceps ( Fig. 1 , D ).

Other intra-articular abnormalities were also identified and recorded. Tendon tears of the supraspinatus, infraspinatus, and subscapularis were probed and noted as partial-thickness or full-thickness tears. Degenerative changes of the articular cartilage that were higher than grade II, as described by Outerbridge ²³ , were regarded as a criterion for osteoarthritis of the humeral head and glenoid for this study. Lesions of the superior portion of the labrum, anterior and posterior (so-called SLAP lesions), were evaluated and classified as Type I through IV, as described by Snyder et al. ²⁴ . The superior glenohumeral ligament was defined as the band of tissue superior to the subscapularis tendon, which ran an oblique course to the base of the biceps attachment ^3,25,26 . The superior glenohumeral ligament was considered abnormal if there was intra-articular fraying or disruption visible at the time of arthroscopy.

A primary diagnosis was made for every patient on the basis of the history, physical examination, and arthroscopic findings ¹⁸ . The primary diagnoses in this study included rotator cuff disease, glenohumeral instability, acromioclavicular arthritis, frozen shoulder, and others (e.g., glenohumeral arthritis and paralabral cyst). Rotator cuff disease included impingement syndrome without a rotator cuff tear, impingement syndrome with a partial rotator cuff tear, and a full-thickness rotator cuff tear. Patients who had more than one diagnosis were given a final diagnosis on the basis of the primary procedure, which had been based upon the findings at surgery and the clinical impression.

For statistical analysis, initial intraoperative assessments of the anterosuperior part of the labrum were confirmed by a review of the videotapes of the shoulder arthroscopy. In order to determine whether the presence of any of these anatomical variations had clinical importance, the patients were divided into two groups: the study group, which included those who had any of these anterosuperior labral variations, or the standard anatomy group, which included those who did not have any anterosuperior labral variations. The two groups were compared with respect to demographic data, subjective symptoms, findings on physical examination, results of laxity testing, arthroscopic findings, and primary diagnoses. Subsequent comparison between the anterosuperior labral variant subtypes was performed to determine whether a specific anatomical variation had clinical importance.

For the purpose of analysis, all categorical variables were dichotomized. Univariate analysis was performed with the use of the Student t test for continuous variables, and the chi-square test was used for categorical variables. To control for potential confounding variables, stepwise logistic-regression analysis was performed. Variables with a p value of <0.20 in the univariate analysis were selected as candidates for the multivariate model. The level of significance was set at p < 0.05. Statistical analysis was performed with the SPSS software package (version 10.0; SPSS, Chicago, Illinois).

Results

Seventy-three (13.4%) of the 546 patients demonstrated one of the three different variations of the anterosuperior portion of the labrum of the glenohumeral joint and were designated as the study group. Eighteen patients (3.3%) had a sublabral foramen in association with a normal middle glenohumeral ligament, whereas forty-seven patients (8.6%) had a sublabral foramen in conjunction with a cord-like middle glenohumeral ligament. Eight patients (1.5%) demonstrated a cord-like middle glenohumeral ligament with an absence of labral tissue at the anterosuperior portion of the labrum.

No significant differences (p > 0.05) were noted between the seventy-three patients in the study group and the 473 patients in the standard anatomy group with respect to demographic factors such as age, gender, involvement of the arm in terms of side (right or left) or dominance, occupation, high-level participation in sports, symptoms associated with trauma, or primary diagnosis ( Table I ). The findings on physical examination ( Table II ) revealed that the patients in the study group had a significantly (p < 0.05) greater preoperative range of motion in active flexion, active abduction, passive abduction, active internal rotation in 90° of abduction, and passive internal rotation in 90° of shoulder abduction.

Significant differences between the groups were found with regard to associated intra-articular abnormalities at the time of arthroscopy ( Table III ). The intra-articular abnormalities, which were more prevalent in the seventy-three patients in the study group than in the 473 patients in the group with standard anatomy, included anterosuperior labral fraying (forty [55%] compared with 126 [27%], respectively, p = 0.000), posterosuperior labral fraying (thirty-four [47%] compared with 140 [30%], p = 0.005), subscapularis tendon tears (sixteen [22%] compared with sixty-one [13%], p = 0.047), and Type-II SLAP lesions (nine [12%] compared with twenty-nine [6%], p = 0.053). The study group had significantly fewer supraspinatus tendon tears (twenty-nine [40%] compared with 274 [58%], p = 0.005) and infraspinatus tears (one [1%] compared with thirty-seven [8%], p = 0.046) compared with those in the standard anatomy group. However, the prevalence of partial subscapularis tendon tears was higher in the study group (sixteen [22%] of seventy-three) than in the standard anatomy group (sixty-one [13%] of 473, p = 0.047).

Multivariate analysis revealed that three independent variables were strongly associated with anterosuperior labral variations: anterosuperior labral fraying (odds ratio, 3.58; p = 0.000), an abnormal superior glenohumeral ligament (odds ratio, 3.69; p = 0.012), and the range of passive internal rotation in 90° of shoulder abduction (odds ratio, 1.13; p = 0.046). A positive painful arc sign (odds ratio, 0.45; p = 0.000) and the presence of a supraspinatus tendon tear (odds ratio, 0.26; p = 0.022) were both negatively associated with anterosuperior labral variations.

In order to provide additional characterizations of anterosuperior labral variations and to evaluate the importance of the associated anatomy of the middle glenohumeral ligament seen with these variations, the seventy-three patients with anterosuperior labral anomalies were subdivided into two groups on the basis of the morphology of the middle glenohumeral ligament. The first group consisted of eighteen patients in whom the anatomy of the middle glenohumeral ligament was normal with a sublabral foramen only. The second group comprised fifty-five patients with a cord-like middle glenohumeral ligament, which included eight patients who had an absence of labral tissue at the anterosuperior portion of the labrum and forty-seven patients with a sublabral foramen. These two groups were compared with each other as well as with the standard anatomy group, which included 473 patients who did not have any anterosuperior labral variations (see Appendix). The group with a sublabral foramen and a normal middle glenohumeral ligament had a higher prevalence of Type-II SLAP lesions (five of eighteen) compared with the group with a cord-like middle glenohumeral ligament (four [7%] of fifty-five, p = 0.036) and with the standard anatomy group (twenty-nine [6%] of 473, p = 0.005). The cord-like group had a substantial increase in active and passive internal rotation with the shoulder in 90° of abduction compared with the group with normal anatomy of the middle glenohumeral ligament as well as with the standard anatomy group.

Discussion

We found that the overall prevalence of anterosuperior labral variation was 13.4% (seventy-three of 546 shoulders), which is very close to the prevalence of 13.5% (twenty-seven of 200 shoulders) reported by Williams et al. ¹⁶ . However, the current study showed for the first time that these anterosuperior labral variations are associated with specific intra-articular abnormalities and findings on physical examination. Although a distinct causal link was not established by this study, it is conceivable that the presence of these anatomical variations may cause biomechanical alterations leading to associated abnormalities.

One possible mechanism may involve the finding of an increased range of internal rotation in the study group compared with that in the standard anatomy group (mean, 51° compared with 37°, respectively, for the active range [p = 0.001] and 56° compared with 44° for the passive range [p = 0.003]). The increased internal rotation in patients with anterosuperior labral variations may contribute to anterosuperior or coracoid impingement. This impingement may explain the constellation of abnormal findings affecting structures lying in proximity to the anterosuperior aspect of the labrum, including the increased prevalences of anterosuperior labral fraying, abnormalities of the superior glenohumeral ligament, Type-II SLAP lesions, and subscapularis tears. Likewise, some unknown biomechanical alteration may play a protective role that results in a decreased prevalence of supraspinatus and infraspinatus tendon tears.

The finding in this study that labral variations in the anterosuperior quadrant did not appear to contribute to laxity or instability was important since the role of the labrum with respect to stability has long been recognized ^1,2,4-7,9 . As a result, this study supports the conclusions of other investigators who have suggested that these anatomical variants should not be addressed surgically as part of an operation to treat instability ^5,16,17 . The repair of these variations has been reported to produce symptoms of pain and restricted range of motion ¹⁶ , which lends support to the theory that anterosuperior labral variations may produce changes in glenohumeral biomechanics.

Several limitations of this study influenced the findings and statistical associations. First, there was an inherent selection bias since only patients who needed surgery were evaluated. Ideally, an additional control group of healthy subjects without shoulder symptoms should be used ²⁷ . However, the comparison group with standard anatomy allowed for the adjustment of multiple confounding variables, including patient demographics and intra-articular arthroscopic findings. Also, the standard anatomy group was closer to the typical patient population referred to orthopaedic surgeons for the treatment of shoulder problems. However, the findings in this patient population may be different from those in other cohorts containing a different mix of patients. The standard anatomy group was not strictly matched against the study group and, therefore, does not represent a true control group.

In addition, characterization of the anterosuperior anomalies and middle glenohumeral ligament variations was limited to our patient population, which was studied by one surgeon. While there may be disagreement among various observers, the goal of the present study was to evaluate the clinical importance of these variants, not to determine interobserver and intraobserver reproducibility. Further study of this issue is warranted. Lastly, the relationship between these anterosuperior labral variants and the multiple factors presented in this study should be seen as associations only and not as confirmation of a causal relationship. Biomechanical studies may help to elucidate how these variants are related to glenohumeral motion, mechanics, and pathological conditions.

In conclusion, this study confirms three variations of anterosuperior labral anatomy and is the first to provide clinical associations with intra-articular abnormalities and physical findings, with use of a thorough statistical evaluation. These variants may contribute to alterations in glenohumeral biomechanics, although a causal link has not been clearly delineated between these variants and associated abnormalities.

Appendix

A table showing the analysis of anterosuperior labral variants when divided into subgroups is available with the electronic versions of this article, on our web site at www.jbjs.org (go to the article citation and click on "Supplementary Material") and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM).

References

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Topics

arthroscopy ; pain ; arm ; shoulder region ; slap lesion ; biceps brachii muscle ; supraspinatus tear ; superior glenohumeral ligament ; middle glenohumeral ligament ; abduction

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Anita G. Rao, Tae Kyun Kim, Efstathios Chronopoulos, Edward G. McFarland; Anatomical Variants in the Anterosuperior Aspect of the Glenoid Labrum A Statistical Analysis of Seventy-three Cases. The Journal of Bone & Joint Surgery. 2003 Apr;85(4):653-659.

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