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Anatomical variations of the anterosuperior labrum: Prevalence and association with type II superior labrum anterior-posterior (SLAP) lesions
J Shoulder Elbow Surg (2010) 19, 1199-1203
www.elsevier.com/locate/ymse
Anatomical variations of the anterosuperior labrum: Prevalence and association with type II superior labrum anterior-posterior (SLAP) lesions Ulunay Kanatli, MDa,*, Burak Y. Ozturk, MDa, Selcuk Bolukbasi, MDa a
Department of Orthopaedics and Traumatology, Gazi University Hospital, Ankara, Turkey Background: Anterosuperior labrum variations have been generally described as innocent anatomical variations without clinical significance. This study was intended to determine their prevalence and reveal their possible relationship with type II SLAP lesions. Materials and methods: A total of 713 consecutive shoulder arthroscopies were evaluated retrospectively for anterosuperior labrum variations and co-existing labral pathologies. Twenty two of these were excluded from the study due to the interobserver variability in the categorization process. The relationship of both these anatomic variants and shoulders with a normal appearing anterosuperior labrum to intra-articular pathology was analyzed statistically and compared with each other. Results: Found in 98 patients (14.18%), the anatomic variations in the anterosuperior labrum were classified into 3 groups as the sublabral recess (2.46%), the sublabral foramen (7.67%), and absent anterosuperior labrum with a cord-like middle glenohumeral ligament (4.05%). The latter 2 of these groups displayed a statistically significant relationship with type II SLAP lesions (21 of 53 and 23 of 28 patients; P ¼ .0028 and P < .0001, respectively). Discussion: Although mostly considered as simple morphological variations, the anatomic variants of the anterosuperior labrum may predispose the shoulder to labrum pathologies by altering the intra-articular biomechanics. Conclusion: As previously suggested in the literature, certain anatomic variants of the anterosuperior labrum are associated with the development of SLAP lesions. Level of evidence: Level II, Retrospective Prognosis Study. Ó 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Labrum variations; SLAP; shoulder arthroscopy; Buford; sublabral foramen; sublabral recess
The role of the glenoid labrum as one of the important static stabilizers of the glenohumeral joint has been wellemphasized in the literature.10, 18 It consists of a fibrous peripheral layer and a fibrocartilaginous transitional zone. *Reprint requests: Ulunay Kanatli, MD, Gazi University Hospital, Department of Orthopaedics and Traumatology, Ankara 06510, Turkey. E-mail address: [email protected] (U. Kanatli).
Both of these parts act as holding points for different anatomical structures. While the peripheral layer acts as an anchor for the biceps tendon and glenohumeral ligaments, the transitional zone provides a firm attachment of the peripheral layer to the deeper, central parts of the glenoid. Variations in the anatomy of glenoid labrum have been described previously.7, 8, 11, 14 In a cadaver study by Cooper et al,2 the glenoid labrum was found to have a distinct
1058-2746/$ - see front matter Ó 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2010.07.016
1200 morphology in its superior and inferior regions. While the inferior portion was seen as a rounded, elevated fibrous structure that is firmly continuous with the articular cartilage, the superior portion displayed meniscus-like features with a looser, more mobile attachment. It was also proposed that this increased mobility of the labrum proximal to the midpoint of the glenoid is a normal finding. The specific anatomy of the anterosuperior portion of the labrum has drawn attention because of its peculiar variations. The superior sublabral recess, which is located beneath the biceps tendon anchor and the anterosuperior rim of the labrum, has been described as such a variant.4 Another common variant is the sublabral foramen, which is a groove located between the normal anterosuperior labrum and the anterior cartilage border of the glenoid. Located in this particular region is another variant, characterized by a thick, cord-like middle glenohumeral ligament that attaches to the superior part of the labrum at the base of the biceps tendon in conjunction with the absence of anterosuperior labral tissue. This so-called ‘‘Buford complex’’, as described by Williams et al,19 has been recognized as another normal anatomical variant. Although there are numerous studies in the literature focused on evaluation of the anatomical variations in this location, only a few studies exist, to our knowledge, that investigated the relationship between these variants and shoulder pathologies.1,8,11 The present study was intended to delineate distinct types of anterosuperior labrum variations, to establish their true prevalence, and to clarify their possible association with type II SLAP lesions in a large population of patients scheduled for arthroscopy.
Materials and methods Data collected from 713 patients who underwent a shoulder arthroscopy for clinically diagnosed shoulder pathologies including subacromial impingement syndrome, rotator cuff or labral tears, and instability were retrospectively reviewed. All arthroscopies were performed by the senior author between 2005 and 2010, and were digitally recorded in the institutional database. All data regarding the anterosuperior labrum variants and any co-existing pathologies were collected from this database. No review board approval was required for this study. The study population consisted of 297 male (41.65%) and 416 female (58.35%) patients with a mean age of 50.5 years (range, 17-82) at the time of surgery. The dominant arm was affected in 392 patients (54.97%). All shoulder arthroscopies were performed with the patients in lateral decubitus position with the arm placed in a shoulder holder with 4.5 kg of traction. Regardless of the primary diagnosis, a routine diagnostic arthroscopy of the glenohumeral joint was performed in all patients with the use of a standard posterior portal for viewing and an anterior portal for instruments. The anterosuperior labrum was examined in all patients with a telescopic probe. Three different morphological variations of the anterosuperior labrum were observed in the digital records: 1) the superior
U. Kanatli et al. sublabral recess, which is an indentation located at 12 o’clock position, beneath the junction of the biceps tendon and the anterosuperior labral edge; 2) the sublabral foramen, which is an orifice located at 2 o’clock position, between the normally developed anterosuperior labrum and the anterior cartilage rim of the glenoid; and 3) the Buford complex, which is characterized by the absence of anterosuperior labrum in conjunction with a thick, cord-like middle glenohumeral ligament that attaches to the superior part of the labrum at the base of the biceps tendon. The labrum was considered normal when it was seen as totally attached throughout the whole anterosuperior glenoid rim. The diagnosis of a type II SLAP lesion was made with the presence of a detached labrum from the underlying glenoid and an unstable bicipitolabral complex as demonstrated with intraoperative examination.15 These findings were confirmed retrospectively from the digital video records. Of 713 arthroscopies reviewed by each author individually from the institutional database, 22 cases were excluded from the study due to the interobserver variability experienced in the categorization process. The patients were divided into 2 groups for statistical analysis. The study group included patients who had anterosuperior labrum variations and the normal anatomy group consisted of patients without labrum variations. Along with the study group, each variant group was also compared with the normal anatomy group. The categorical variables were analyzed with the chisquare test. For all comparisons, a 2-tailed value of P < .05 was considered statistically significant. Statistical analysis was performed with the SPSS software (version 16.0; SPSS Inc, Chicago, IL).
Results Out of 691 patients, a total of 98 patients (14.18%) displayed anterosuperior labrum variations and constituted the study group. Of these, 17 patients (2.46%) had a sublabral recess, 53 patients (7.67%) had a sublabral foramen, and 28 patients (4.05%) had a Buford complex (Fig). A statistically significant difference (P < .0001) was found between the study group (47 [47.95%] of 98 patients) and the normal anatomy group (123 [20.74%] of 593 patients) with regard to superior labrum lesions. To further delineate the clinical significance of this association, all variant groups were individually compared with the normal anatomy group. The sublabral foramen (21 [39.62%] of 53 patients) and Buford complex (23 [82.14%] of 28 patients) groups displayed significantly higher correlations (P ¼ .0028 and P < .0001, respectively) with a type II SLAP lesion than the normal anatomy group (Table).
Discussion The evolution of MRI techniques has given the orthopaedic surgeons a better grasp on the complex shoulder anatomy.16,17 Although our understanding of the glenohumeral joint has improved so far, recognizing the normal and anatomic variations of the labrum and differentiating
Anatomical variations of the anterosuperior labrum
Figure
Table
1201
Classificationof anterosuperior labrum variations. MGHL, middle glenohumeral ligament).
Association of anatomical variations with shoulder pathologies
Primary Pathology Rotator cuff tears Instability Subacromial impingement SLAP lesions Type Iy Type II Type III Type IV ACJ degeneration-Os acromiale Adhesive capsulitis Total
Superior sublabral recess 5 2 5 9y 3 0 0 1 1 17
Sublabral foramen 8 5 14
Buford complex 0 1 3
11y 21)(P ¼ .0028) 0 0 2 3 53
2y 23)(P < .0001) 0 0 0 1 28
Normal anatomy (reference group) 170 77 181 174y 123 2 3 16 21 593
SLAP, superior labrum anterior-posterior; ACJ, acromioclavicular joint. ) Statictically significant correlation. y SLAP type I lesion is not a primary diagnosis, it is included in the table for convenience.
them from pathological lesions may not always be an easy task.12 The anatomic variations of the labrum were first depicted in the literature by Grant.6 He illustrated the sublabral foramen and a thick middle glenohumeral ligament in an atlas half a century ago. Observational clinical studies have been performed ever since in an attempt to provide a better understanding of these variations. In 1994, Williams et al19 described the anatomic variant they referred to as the ‘‘Buford complex’’ in a retrospective study. They reported the prevalence of the sublabral foramen as 12% and the Buford complex as 1.5%. In another study by Rao et al,11 these variants were reported to have prevalence rates of 11.9% and 1.5%, respectively. In a recent clinical study, Ilahi et al8 reported somewhat higher prevalence rates as 18.3% for the sublabral foramen and 7.5% for the Buford complex. The overall prevalence of the anterosuperior labrum variations was 14.18% in this study. Our findings are parallel to previous results in the literature.
When subgroups are taken into account, we found a relatively lower prevalence rate of 7.67% for the sublabral foramen and a relatively higher prevalence rate of 4.05% for the Buford complex. This might be due to an actual difference between our patient group and distinct populations observed in the literature, as well as a possible interobserver variability. As no consensus exists on the classification of labrum variants, we comment that further investigations are warranted for their standardization and categorization processes. Although the prevalence rates of these variations were investigated in a number of studies, their clinical importance was queried only in a few studies in the literature.1,8,11 In their study, Rao et al11 found a significant correlation between the labrum variants and the superior labral fraying, as well as an increased shoulder range of motion. They asserted that this association can be explained with the fact that increased labral mobility may contribute to anterosuperior or coracoid impingement. While this
1202 claim needs objective data gathered from clinical or biomechanical studies in order to be substantiated, Gerber and Sebesta5 demonstrated that the anterosuperior impingement causes an increased contact between the biceps tendon-pulley complex and anterosuperior labrum, which possibly contributes to the pathogenesis of lesions on both contacting surfaces. Taking the labrum variations into consideration as anatomic alterations which entail the detachment of anterosuperior labrum from the glenoid rim to some degree, it is plausible to assume that they indirectly cause the bicipitolabral complex to be subjected to an increased stress. Our finding that the sublabral foramen and the Buford complex subgroups have a clinically significant correlation with a type II SLAP lesion is reinforced by this hypothesis. This mechanism for the pathogenesis of SLAP lesions in patients with labral variants was also supported by results of Ilahi et al8 and Bents and Skeete,1 who reported SLAP II lesion prevalence rates ranging from 60% to 87.8% in patients with distinct labrum variations. The glenoid labrum has a well-known role as an important stabilizer of the glenohumeral joint. Its neutralizing effect on stress distribution throughout the joint has been defined in numerous studies.9,18 Disruption of this system results in overstressed areas in the joint, leading to impaired shoulder function.10 SLAP lesions result from either compression or traction injuries, as a consequence of direct trauma or overuse.15 It was postulated in the literature that the absence of anterosuperior labrum in conjunction with a thick, cord-like middle glenohumeral ligament attaching to the base of the biceps tendon may predispose the shoulder to SLAP lesions.1,8 Our findings favor this assertion as well. Moreover, along with the Buford complex, we propose that sublabral foramen may also contribute to the pathogenesis of SLAP lesions by altering the inherent biomechanics and causing uneven bicipitolabral stress distribution in the glenohumeral joint. This may elucidate the significant correlation found between the sublabral foramen and type II SLAP lesions in this study. On the other hand, we encountered no significant correlation between the third variant, superior sublabral recess, and SLAP lesions. In light of the previous hypothesis, we may attribute this finding to the minimal alteration in the normal anterosuperior labral configuration caused by this variant. Except for a single case report,3 the presence of anterosuperior labrum variations has not been associated with other common pathologies such as instability, rotator cuff tears, and impingement syndrome in the literature.8,11,13 Our findings were also consistent with this data, and we conclude that these variants must not be surgically addressed as a cause of instability. Rather, we recommend that patients should be evaluated thoroughly for superior labral lesions whenever an anatomic variant is encountered in the anterosuperior quadrant of labrum during arthroscopy. There are some limitations that influenced the overall results of our study. This was a retrospective review
U. Kanatli et al. conducted over a population of symptomatic patients who were surgically treated for diagnosed pathologies such as instability or rotator cuff tears. The study and normal anatomy groups both originated from this pool. By taking the possible asymptomatic SLAP lesions and anterosuperior labrum variations present among the general population into account, it would have been optimal to include a control group comprised of normal individuals in such a study. There may also be issues regarding the intra and interobserver reproducibility in classification of these variations and labral lesions. Finally, the associations presented here are basically the results of a statistical analysis and should, therefore, not be considered as the scientific evidence of a cause and effect relationship between these variations and superior labral lesions. More investigations regarding this subject are needed to conclude on this matter.
Conclusion This study elaborately defines the 3 distinct anterosuperior labrum variations that may be encountered during shoulder arthroscopy and demonstrates a statistically significant correlation between 2 of these variations and the presence of SLAP lesions. Given the important role of the labrum in shoulder stability and its close relationship with other soft tissue stabilizers such as the biceps tendon and glenohumeral ligaments, a causal relationship between these variations and superior labral lesions is conceivable. Nevertheless, this warrants further investigations focused on labrum biomechanics.
Acknowledgment The authors thank Nermin Ozturk for her illustrations of glenoid labrum anatomy.
Disclaimer We hereby state that all ethical, legal, and patient rights wise considerations were fulfilled during and after this study. The authors, their immediate families, and any research foundations with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Bents RT, Skeete KD. The correlation of the Buford complex and SLAP lesions. J Shoulder Elbow Surg 2005;14:565-9. doi:10.1016/ j.jse.2005.01.002. PMID: 16337521.
Anatomical variations of the anterosuperior labrum 2. Cooper DE, Arnoczky SP, O’Brien SJ, Warren RF, DiCarlo E, Allen AA. Anatomy, histology, and vascularity of the glenoid labrum. An anatomical study. J Bone Joint Surg Am 1992;74:46-52. PMID: 1734013. 3. del Rey FC, Va´zquez DG, Lopez DN. Glenohumeral instability associated with Buford complex. Knee Surg Sports Traumatol Arthrosc 2009;17:1489-92. doi:10.1007/s00167-009-0882-1. PMID: 19629434. 4. De Maeseneer M, Van Roy F, Lenchik L, Shahabpour M, Jacobson J, Ryu KN, et al. CT and MR arthrography of the normal and pathologic anterosuperior labrum and labral-bicipital complex. Radiographics 2000;20:S67-81. PMID: 11046163. 5. Gerber C, Sebesta A. Impingement of the deep surface of the subscapularis tendon and the reflection pulley on the anterosuperior glenoid rim: a preliminary report. J Shoulder Elbow Surg 2000;9:483-90. doi:10.1067/mse.2000.109322. PMID: 11155300. 6. Grant JCB. Grant’s Atlas of Anatomy. 5th ed. Baltimore, MD: Williams and Wilkins; 1962. 7. Ide J, Maeda S, Takagi K. Normal variations of the glenohumeral ligament complex: an anatomic study for arthroscopic Bankart repair. Arthroscopy 2004;20:164-8. doi:10.1016/j.arthro.2003.11.005. PMID: 14760349. 8. Ilahi OA, Cosculluela P, Ho D. Classification of anterosuperior glenoid labrum variants and their association with shoulder pathology. Orthopedics 2008;31:226. PMID 19292248. 9. Maffet MW, Gartsman GM, Moseley B. Superior labrum-biceps tendon complex lesions of the shoulder. Am J Sports Med 1995;23: 93-8. PMID: 7726358. 10. Pagnani MJ, Deng XH, Warren RF, Torzilli PA, Altchek DW. Effect of lesions of the superior portion of the glenoid labrum on glenohumeral translation. J Bone Joint Surg Am 1995;77:1003-10. PMID: 7608221.
1203 11. Rao AG, Kim TK, Chronopoulos E, McFarland EG. Anatomical variants in the anterosuperior aspect of the glenoid labrum: A statistical analysis of seventy-three cases. J Bone Joint Surg Am 2003;85: 653-9. PMID: 12672841. 12. Rudez J, Zanetti M. Normal anatomy, variants and pitfalls on shoulder MRI. Eur J Radiol 2008;68:25-35. doi:10.1016/j.ejrad.2008.02.028. PMID: 18423935. 13. Schulz CU, Anetzberger H, Pfahler M, Refior HJ, Mueller-Gerbl M. The sublabral foramen: does it affect stress distribution on the anterior glenoid? J Shoulder Elbow Surg 2004;13:35-8. doi:10.1016/j.jse.2003. 09.007. PMID: 14735071. 14. Shortt CP, Morrison WB, Shah SH, Zoga AC, Carrino JA. Association of glenoid morphology and anterosuperior labral variation. J Comput Assist Tomogr 2009;33:584-6. doi:10.1097/RCT.0b013e31818da69d. 15. Snyder SJ, Karzel RP, Del Pizzo W, Ferkel RD, Friedman MJ. SLAP lesions of the shoulder. Arthroscopy 1990;6:274-9. PMID: 2264894. 16. Tirman PF, Feller JF, Palmer WE, Carroll KW, Steinbach LS, Cox I. The Buford complexda variation of normal shoulder anatomy: MR arthrographic imaging features. Am J Roentgenol 1996;166:869-73. PMID: 8610565. 17. Tuite MJ, Orwin JF. Anterosuperior labral variants of the shoulder: appearance on gradient-recalled-echo and fast spin-echo MR images. Radiology 1996;199:537-40. PMID: 8668808. 18. Turkel SJ, Panio MW, Marshall JL, Girgis FG. Stabilizing mechanisms preventing anterior dislocation of the glenohumeral joint. J Bone Joint Surg Am 1981;63:1208-17. PMID: 7287791. 19. Williams MM, Snyder SJ, Buford D Jr. The Buford complexdthe ‘‘cordlike’’ middle glenohumeral ligament and absent anterosuperior labrum complex: a normal anatomic capsulolabral variant. Arthroscopy 1994;10:241-7. PMID: 8086014.
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Anatomical variations of the anterosuperior labrum: Prevalence and association with type II superior labrum anterior-posterior (SLAP) lesions Ulunay Kanatli, MDa,*, Burak Y. Ozturk, MDa, Selcuk Bolukbasi, MDa a
Department of Orthopaedics and Traumatology, Gazi University Hospital, Ankara, Turkey Background: Anterosuperior labrum variations have been generally described as innocent anatomical variations without clinical significance. This study was intended to determine their prevalence and reveal their possible relationship with type II SLAP lesions. Materials and methods: A total of 713 consecutive shoulder arthroscopies were evaluated retrospectively for anterosuperior labrum variations and co-existing labral pathologies. Twenty two of these were excluded from the study due to the interobserver variability in the categorization process. The relationship of both these anatomic variants and shoulders with a normal appearing anterosuperior labrum to intra-articular pathology was analyzed statistically and compared with each other. Results: Found in 98 patients (14.18%), the anatomic variations in the anterosuperior labrum were classified into 3 groups as the sublabral recess (2.46%), the sublabral foramen (7.67%), and absent anterosuperior labrum with a cord-like middle glenohumeral ligament (4.05%). The latter 2 of these groups displayed a statistically significant relationship with type II SLAP lesions (21 of 53 and 23 of 28 patients; P ¼ .0028 and P < .0001, respectively). Discussion: Although mostly considered as simple morphological variations, the anatomic variants of the anterosuperior labrum may predispose the shoulder to labrum pathologies by altering the intra-articular biomechanics. Conclusion: As previously suggested in the literature, certain anatomic variants of the anterosuperior labrum are associated with the development of SLAP lesions. Level of evidence: Level II, Retrospective Prognosis Study. Ó 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Labrum variations; SLAP; shoulder arthroscopy; Buford; sublabral foramen; sublabral recess
The role of the glenoid labrum as one of the important static stabilizers of the glenohumeral joint has been wellemphasized in the literature.10, 18 It consists of a fibrous peripheral layer and a fibrocartilaginous transitional zone. *Reprint requests: Ulunay Kanatli, MD, Gazi University Hospital, Department of Orthopaedics and Traumatology, Ankara 06510, Turkey. E-mail address: [email protected] (U. Kanatli).
Both of these parts act as holding points for different anatomical structures. While the peripheral layer acts as an anchor for the biceps tendon and glenohumeral ligaments, the transitional zone provides a firm attachment of the peripheral layer to the deeper, central parts of the glenoid. Variations in the anatomy of glenoid labrum have been described previously.7, 8, 11, 14 In a cadaver study by Cooper et al,2 the glenoid labrum was found to have a distinct
1058-2746/$ - see front matter Ó 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2010.07.016
1200 morphology in its superior and inferior regions. While the inferior portion was seen as a rounded, elevated fibrous structure that is firmly continuous with the articular cartilage, the superior portion displayed meniscus-like features with a looser, more mobile attachment. It was also proposed that this increased mobility of the labrum proximal to the midpoint of the glenoid is a normal finding. The specific anatomy of the anterosuperior portion of the labrum has drawn attention because of its peculiar variations. The superior sublabral recess, which is located beneath the biceps tendon anchor and the anterosuperior rim of the labrum, has been described as such a variant.4 Another common variant is the sublabral foramen, which is a groove located between the normal anterosuperior labrum and the anterior cartilage border of the glenoid. Located in this particular region is another variant, characterized by a thick, cord-like middle glenohumeral ligament that attaches to the superior part of the labrum at the base of the biceps tendon in conjunction with the absence of anterosuperior labral tissue. This so-called ‘‘Buford complex’’, as described by Williams et al,19 has been recognized as another normal anatomical variant. Although there are numerous studies in the literature focused on evaluation of the anatomical variations in this location, only a few studies exist, to our knowledge, that investigated the relationship between these variants and shoulder pathologies.1,8,11 The present study was intended to delineate distinct types of anterosuperior labrum variations, to establish their true prevalence, and to clarify their possible association with type II SLAP lesions in a large population of patients scheduled for arthroscopy.
Materials and methods Data collected from 713 patients who underwent a shoulder arthroscopy for clinically diagnosed shoulder pathologies including subacromial impingement syndrome, rotator cuff or labral tears, and instability were retrospectively reviewed. All arthroscopies were performed by the senior author between 2005 and 2010, and were digitally recorded in the institutional database. All data regarding the anterosuperior labrum variants and any co-existing pathologies were collected from this database. No review board approval was required for this study. The study population consisted of 297 male (41.65%) and 416 female (58.35%) patients with a mean age of 50.5 years (range, 17-82) at the time of surgery. The dominant arm was affected in 392 patients (54.97%). All shoulder arthroscopies were performed with the patients in lateral decubitus position with the arm placed in a shoulder holder with 4.5 kg of traction. Regardless of the primary diagnosis, a routine diagnostic arthroscopy of the glenohumeral joint was performed in all patients with the use of a standard posterior portal for viewing and an anterior portal for instruments. The anterosuperior labrum was examined in all patients with a telescopic probe. Three different morphological variations of the anterosuperior labrum were observed in the digital records: 1) the superior
U. Kanatli et al. sublabral recess, which is an indentation located at 12 o’clock position, beneath the junction of the biceps tendon and the anterosuperior labral edge; 2) the sublabral foramen, which is an orifice located at 2 o’clock position, between the normally developed anterosuperior labrum and the anterior cartilage rim of the glenoid; and 3) the Buford complex, which is characterized by the absence of anterosuperior labrum in conjunction with a thick, cord-like middle glenohumeral ligament that attaches to the superior part of the labrum at the base of the biceps tendon. The labrum was considered normal when it was seen as totally attached throughout the whole anterosuperior glenoid rim. The diagnosis of a type II SLAP lesion was made with the presence of a detached labrum from the underlying glenoid and an unstable bicipitolabral complex as demonstrated with intraoperative examination.15 These findings were confirmed retrospectively from the digital video records. Of 713 arthroscopies reviewed by each author individually from the institutional database, 22 cases were excluded from the study due to the interobserver variability experienced in the categorization process. The patients were divided into 2 groups for statistical analysis. The study group included patients who had anterosuperior labrum variations and the normal anatomy group consisted of patients without labrum variations. Along with the study group, each variant group was also compared with the normal anatomy group. The categorical variables were analyzed with the chisquare test. For all comparisons, a 2-tailed value of P < .05 was considered statistically significant. Statistical analysis was performed with the SPSS software (version 16.0; SPSS Inc, Chicago, IL).
Results Out of 691 patients, a total of 98 patients (14.18%) displayed anterosuperior labrum variations and constituted the study group. Of these, 17 patients (2.46%) had a sublabral recess, 53 patients (7.67%) had a sublabral foramen, and 28 patients (4.05%) had a Buford complex (Fig). A statistically significant difference (P < .0001) was found between the study group (47 [47.95%] of 98 patients) and the normal anatomy group (123 [20.74%] of 593 patients) with regard to superior labrum lesions. To further delineate the clinical significance of this association, all variant groups were individually compared with the normal anatomy group. The sublabral foramen (21 [39.62%] of 53 patients) and Buford complex (23 [82.14%] of 28 patients) groups displayed significantly higher correlations (P ¼ .0028 and P < .0001, respectively) with a type II SLAP lesion than the normal anatomy group (Table).
Discussion The evolution of MRI techniques has given the orthopaedic surgeons a better grasp on the complex shoulder anatomy.16,17 Although our understanding of the glenohumeral joint has improved so far, recognizing the normal and anatomic variations of the labrum and differentiating
Anatomical variations of the anterosuperior labrum
Figure
Table
1201
Classificationof anterosuperior labrum variations. MGHL, middle glenohumeral ligament).
Association of anatomical variations with shoulder pathologies
Primary Pathology Rotator cuff tears Instability Subacromial impingement SLAP lesions Type Iy Type II Type III Type IV ACJ degeneration-Os acromiale Adhesive capsulitis Total
Superior sublabral recess 5 2 5 9y 3 0 0 1 1 17
Sublabral foramen 8 5 14
Buford complex 0 1 3
11y 21)(P ¼ .0028) 0 0 2 3 53
2y 23)(P < .0001) 0 0 0 1 28
Normal anatomy (reference group) 170 77 181 174y 123 2 3 16 21 593
SLAP, superior labrum anterior-posterior; ACJ, acromioclavicular joint. ) Statictically significant correlation. y SLAP type I lesion is not a primary diagnosis, it is included in the table for convenience.
them from pathological lesions may not always be an easy task.12 The anatomic variations of the labrum were first depicted in the literature by Grant.6 He illustrated the sublabral foramen and a thick middle glenohumeral ligament in an atlas half a century ago. Observational clinical studies have been performed ever since in an attempt to provide a better understanding of these variations. In 1994, Williams et al19 described the anatomic variant they referred to as the ‘‘Buford complex’’ in a retrospective study. They reported the prevalence of the sublabral foramen as 12% and the Buford complex as 1.5%. In another study by Rao et al,11 these variants were reported to have prevalence rates of 11.9% and 1.5%, respectively. In a recent clinical study, Ilahi et al8 reported somewhat higher prevalence rates as 18.3% for the sublabral foramen and 7.5% for the Buford complex. The overall prevalence of the anterosuperior labrum variations was 14.18% in this study. Our findings are parallel to previous results in the literature.
When subgroups are taken into account, we found a relatively lower prevalence rate of 7.67% for the sublabral foramen and a relatively higher prevalence rate of 4.05% for the Buford complex. This might be due to an actual difference between our patient group and distinct populations observed in the literature, as well as a possible interobserver variability. As no consensus exists on the classification of labrum variants, we comment that further investigations are warranted for their standardization and categorization processes. Although the prevalence rates of these variations were investigated in a number of studies, their clinical importance was queried only in a few studies in the literature.1,8,11 In their study, Rao et al11 found a significant correlation between the labrum variants and the superior labral fraying, as well as an increased shoulder range of motion. They asserted that this association can be explained with the fact that increased labral mobility may contribute to anterosuperior or coracoid impingement. While this
1202 claim needs objective data gathered from clinical or biomechanical studies in order to be substantiated, Gerber and Sebesta5 demonstrated that the anterosuperior impingement causes an increased contact between the biceps tendon-pulley complex and anterosuperior labrum, which possibly contributes to the pathogenesis of lesions on both contacting surfaces. Taking the labrum variations into consideration as anatomic alterations which entail the detachment of anterosuperior labrum from the glenoid rim to some degree, it is plausible to assume that they indirectly cause the bicipitolabral complex to be subjected to an increased stress. Our finding that the sublabral foramen and the Buford complex subgroups have a clinically significant correlation with a type II SLAP lesion is reinforced by this hypothesis. This mechanism for the pathogenesis of SLAP lesions in patients with labral variants was also supported by results of Ilahi et al8 and Bents and Skeete,1 who reported SLAP II lesion prevalence rates ranging from 60% to 87.8% in patients with distinct labrum variations. The glenoid labrum has a well-known role as an important stabilizer of the glenohumeral joint. Its neutralizing effect on stress distribution throughout the joint has been defined in numerous studies.9,18 Disruption of this system results in overstressed areas in the joint, leading to impaired shoulder function.10 SLAP lesions result from either compression or traction injuries, as a consequence of direct trauma or overuse.15 It was postulated in the literature that the absence of anterosuperior labrum in conjunction with a thick, cord-like middle glenohumeral ligament attaching to the base of the biceps tendon may predispose the shoulder to SLAP lesions.1,8 Our findings favor this assertion as well. Moreover, along with the Buford complex, we propose that sublabral foramen may also contribute to the pathogenesis of SLAP lesions by altering the inherent biomechanics and causing uneven bicipitolabral stress distribution in the glenohumeral joint. This may elucidate the significant correlation found between the sublabral foramen and type II SLAP lesions in this study. On the other hand, we encountered no significant correlation between the third variant, superior sublabral recess, and SLAP lesions. In light of the previous hypothesis, we may attribute this finding to the minimal alteration in the normal anterosuperior labral configuration caused by this variant. Except for a single case report,3 the presence of anterosuperior labrum variations has not been associated with other common pathologies such as instability, rotator cuff tears, and impingement syndrome in the literature.8,11,13 Our findings were also consistent with this data, and we conclude that these variants must not be surgically addressed as a cause of instability. Rather, we recommend that patients should be evaluated thoroughly for superior labral lesions whenever an anatomic variant is encountered in the anterosuperior quadrant of labrum during arthroscopy. There are some limitations that influenced the overall results of our study. This was a retrospective review
U. Kanatli et al. conducted over a population of symptomatic patients who were surgically treated for diagnosed pathologies such as instability or rotator cuff tears. The study and normal anatomy groups both originated from this pool. By taking the possible asymptomatic SLAP lesions and anterosuperior labrum variations present among the general population into account, it would have been optimal to include a control group comprised of normal individuals in such a study. There may also be issues regarding the intra and interobserver reproducibility in classification of these variations and labral lesions. Finally, the associations presented here are basically the results of a statistical analysis and should, therefore, not be considered as the scientific evidence of a cause and effect relationship between these variations and superior labral lesions. More investigations regarding this subject are needed to conclude on this matter.
Conclusion This study elaborately defines the 3 distinct anterosuperior labrum variations that may be encountered during shoulder arthroscopy and demonstrates a statistically significant correlation between 2 of these variations and the presence of SLAP lesions. Given the important role of the labrum in shoulder stability and its close relationship with other soft tissue stabilizers such as the biceps tendon and glenohumeral ligaments, a causal relationship between these variations and superior labral lesions is conceivable. Nevertheless, this warrants further investigations focused on labrum biomechanics.
Acknowledgment The authors thank Nermin Ozturk for her illustrations of glenoid labrum anatomy.
Disclaimer We hereby state that all ethical, legal, and patient rights wise considerations were fulfilled during and after this study. The authors, their immediate families, and any research foundations with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article.
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