Skeletal Radiology

, Volume 42, Issue 3, pp 353–362

Sublabral clefts and recesses in the anterior, inferior, and posterior glenoid labrum at MR arthrography

Authors

    • Department of RadiologyUniversity of Wisconsin School of Medicine and Public Health
  • Jonathan W. Currie
    • Department of RadiologyUniversity of Wisconsin School of Medicine and Public Health
  • John F. Orwin
    • Department of Orthopedics and RehabilitationUniversity of Wisconsin School of Medicine and Public Health
  • Geoffrey S. Baer
    • Department of Orthopedics and RehabilitationUniversity of Wisconsin School of Medicine and Public Health
  • Alejandro Munoz del Rio
    • Department of RadiologyUniversity of Wisconsin School of Medicine and Public Health
Scientific Article

DOI: 10.1007/s00256-012-1496-0

Cite this article as:
Tuite, M.J., Currie, J.W., Orwin, J.F. et al. Skeletal Radiol (2013) 42: 353. doi:10.1007/s00256-012-1496-0

Abstract

Purpose

To determine the prevalence of a normal variant cleft/recess at the labral–chondral junction in the anterior, inferior, and posterior portions of the shoulder joint.

Materials and methods

One hundred and three consecutive patients (106 shoulders) who had a direct MR arthrogram followed by arthroscopic surgery were enrolled in this IRB-approved study. Scans were carried out on a 1.5-T scanner with an eight-channel shoulder coil. The glenoid rim was divided into eight segments and the labrum in all but the superior and anterosuperior segments was evaluated by two radiologists for the presence of contrast between the labrum and articular cartilage. We measured the depth of any cleft/recess and correlated the MR findings with surgical results. Generalized estimating equation models were used to correlate patient age and gender with the presence and depth of a cleft/recess, and Cohen’s kappa values were calculated for interobserver variability.

Results

For segments that were normal at surgery, a cleft/recess was present within a segment on MR arthrogram images in as few as 7 % of patients (within the posteroinferior segment by observer 1), and in up to 61 % of patients (within the posterosuperior segment by observer 1). 55–83 % of these were only 1 mm deep. A 2- to 3-mm recess was seen within 0–37 % of the labral segments, most commonly in the anterior, anteroinferior, and posterosuperior segments. Age and gender did not correlate with the presence of a cleft/recess, although there was an association between males and a 2- to 3-mm deep recess (p = 0.03). The interobserver variability for each segment ranged between 0.15 and 0.49, indicating slight to moderate agreement.

Conclusion

One-mm labral–chondral clefts are not uncommon throughout the labrum. A 2- to 3-mm deep smooth, medially curved recess in the anterior, anteroinferior or posterosuperior labrum can rarely be seen, typically as a continuation of a superior recess or anterosuperior labral variant.

Keywords

ShoulderMR arthrographyLabrumNormal variants

Multiple articles have been published describing normal labral variants of the shoulder on MR imaging [112]. These normal variants are portions of the labrum that are not completely attached to the articular cartilage, and have been described mainly in three regions of the glenoid rim. The first is in the superior portion of the glenoid rim where the caudal aspect of the labrum is partially unattached from the 11-o’clock to 1-o’clock position, and is known as a “superior recess” [3, 5]. The second occurs in the anterosuperior labrum where there are three subtypes. One is the sublabral foramen where the labrum is focally unattached to the glenoid rim [13]. The second is the Buford complex where the anterosuperior portion of the labrum is absent and there is a thick, cord-like middle glenohumeral ligament [4]. The third is an anterosuperior sublabral recess, similar to the superior recess [14]. Finally, there is a study describing a sublabral cleft in the 7- to 8-o’clock region of the posteroinferior labrum [2].

Other than the regions of the normal variants, the labrum is usually described as firmly adherent to, or a rounded extension of the articular cartilage [1517]. This feature has been recommended to help correctly diagnose on MR those labral tears that appear as a somewhat smoothly margined labral–chondral detachment [5, 7, 11].

We have occasionally noticed a labral–chondral junction groove in other regions of the labrum on published anatomy photographs of normal shoulder joints [15, 1820]. We have also sometimes seen on arthroscopic images at our institution similar grooves with a smooth margin without vascular “injection.” Our surgeons have stated that they have probed the groove, and if it is stable they consider it a variable of the appearance of the normal labrum (Fig. 1). We have noted a similar cleft/recess on MR arthrogram images in some patients.
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Fig. 1

Twenty-one-year-old man with internal impingement and no history of dislocation or instability, presented at our MR–arthroscopy correlation conference. a Video still image during arthroscopic inspection of the anterior labrum from a posterior portal, with the superior labrum and biceps tendon (asterisk) to the right. There is a superior recess (curved arrow) that continues as a labral–chondral groove extending down into the anterior labrum (straight arrow). The labrum was stable to probing and called normal. b Arthroscopic image of the posterior labrum from an anterior portal with the superior labrum (asterisk) and superior recess (curved yellow arrow) in the lower left. There is superficial tearing of the free edge of the posterosuperior labrum (curved black arrow), and a labral–chondral groove extending into the posterior segment (straight arrows) that was also stable to probing. Note the size of the groove relative to a 5-mm cannula (dagger). c Oblique axial fat-suppressed intermediate-weighted (left), and straight axial T1-weighted (right) images show the small labral–chondral clefts in the anterior (straight arrow) and posterior labrum (curved arrow)

Our purpose was to determine the prevalence of a labral–chondral junction cleft/recess in regions other than the superior and anterosuperior labrum on MR arthrogram images.

Subjects and methods

This study was approved by our Institutional Review Board. Our study plan was to retrospectively review MR arthrogram images and identify areas where we saw a cleft/recess. We would then look back at operative reports to identify areas where no labral tear, synovitis, or fraying was seen at arthroscopy. Finally, we would compare the MR-identified clefts/recesses with these normal areas of labrum to determine how often this normal variant MR finding is seen.

Patient characteristics

The study group consisted of 103 consecutive patients who had not had prior labral surgery and who underwent shoulder MR arthrography between June 2010 and June 2011 followed by arthroscopic surgery. Three patients had an MR arthrogram and surgery on both shoulders within the study period to make a total of 106 shoulders. The arthroscopic surgeries were performed by one of five Sports Medicine fellowship-trained orthopedic surgeons who have primarily a experience in shoulder surgery. There were 71 men and 32 women, with an average age of 36 years (range, 14–76 years). The primary postoperative diagnosis was impingement/rotator cuff tear in 35 shoulders, Bankart labral tear in 28, SLAP tear in 9, Bankart/SLAP in 8, posterior Bankart in 8, multidirectional instability in 5, a 360° labral tear in 5, internal impingement in 4, Bankart/posterior Bankart in 3, and a chondral lesion in 1 shoulder.

MR imaging technique

All patients received an intra-articular injection of 12–15 ml of 1:200 dilute gadolinium using a 22-gauge needle and an anterior interval approach. The MR arthrogram images were obtained on a 1.5-T scanner (GE Healthcare, Milwaukee, WI, USA) with an eight-channel shoulder coil (NeoCoil, Pewaukee, WI, USA). The humerus was positioned in comfortable external rotation. The MR arthrogram pulse sequences are listed in Table 1. The oblique axial images were prescribed from an oblique sagittal image through the glenoid fossa, and were perpendicular to the long axis of the glenoid fossa defined as extending from the biceps anchor superiorly to the origin of the long head of the triceps tendon inferiorly. The field of view was 14 cm for all sequences. Abduction–external rotation images were also obtained, but not used for this study.
Table 1

MR arthrogram pulse sequences

Image plane

Pulse sequence

Fat suppression

TR/TE eff (ms)

Slice thickness/gap

Echo train

Matrix

Signals averaged

Oblique coronal

FSE IntermediateT2-weighted

Yes

2,200/52–58

4/1 mm

11

288 × 256

4

Oblique sagittal

FSE Intermediate T2-weighted

Yes

2,700/52–58

4/1 mm

11

288 × 256

4

Oblique coronal

FSE T1-weighted

Yes

650/18–20

4/1 mm

3

288 × 256

2

Axial

FSE T1-weighted

No

835/18–20

3/1 mm

3

288 × 256

1

Oblique axial

FSE Intermediate

Yes

2,200/31–34

4/0.4 mm

7

288 × 224

4

FSE fast spin echo

MR image analysis

The studies were randomly mixed and the labrum evaluated separately by two radiologists, one a musculoskeletal fellow and the other a musculoskeletal radiologist with 19 years’ experience, who were blinded to patient history and arthroscopic results. We first identified the oblique sagittal image through the glenoid fossa and drew a line down the long axis of the glenoid fossa extending from the center of the biceps anchor superiorly (defined as 12 o’clock) to the origin of the long head of the triceps tendon inferiorly (6 o’clock) (Fig. 2). We determined the midpoint of this line and drew a perpendicular line from 9:00 posteriorly to 3:00 anteriorly. The glenoid rim in each quadrant was then bisected with an additional line radiating from the intersection of the long and short axis lines. The point where these eight lines met the labrum was defined as the center of eight labral segments: superior, anterosuperior, anterior, anteroinferior, inferior, posteroinferior, posterior, and posterosuperior.
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Fig. 2

Oblique sagittal fat-suppressed T2-weighted image shows eight thin gray lines intersecting the labrum at the center of eight labral segments. The thicker white dashes are the borders of the eight segments. S superior, AS anterosuperior, A anterior, AI anteroinferior, I inferior, PI posteroinferior, P posterior, and PS posterosuperior

The superior and anterosuperior segments were not evaluated further because the normal labral variants in these regions are well described. We evaluated the other six segments for fluid-signal or gadolinium-signal intensity extending to the surface of the labrum, including at the labral–chondral junction, on T1- or intermediate-weighted images. If there was no high signal either at the labral–chondral junction or through the labrum, the labrum was graded as “MR normal.” If there was irregular high signal at the labral–chondral junction, or high signal extending to the surface of the labrum more peripherally, the labrum was graded as “torn.” If there was smooth, medially curved high signal at the labral–chondral junction, the depth of the linear high signal was measured to the nearest millimeter using the measurement tool on our PACs system (McKesson, San Francisco, CA, USA). The depth measurement was obtained by magnifying the image ×2 and drawing a line from the surface of the hyaline cartilage to the adjacent outer surface of the labrum, and measuring the distance from that line to the deepest extent of the cleft (Fig. 3). If the high signal measured 1 mm deep the labrum was graded as a “1-mm cleft,” if ≥2 mm deep it was graded as a “recess.”
https://static-content.springer.com/image/art%3A10.1007%2Fs00256-012-1496-0/MediaObjects/256_2012_1496_Fig3_HTML.gif
Fig. 3

Seventeen-year-old male patient with a posterior subluxation injury sustained during football, and a posterior Bankart-type labral tear and chondral lesion, but normal anterior labrum at arthroscopy. a Oblique axial fat-suppressed intermediate-weighted image through the anterosuperior labrum with the corresponding oblique sagittal T2-weighted localizer image (lower right) shows a normal variant anterosuperior recess (arrow). b Four consecutive oblique axial fat-suppressed intermediate-weighted images are shown through the anterior and anteroinferior labrum. The partially unattached anterior labral–chondral junction was smooth and a continuation of the anterosuperior labral variant. Both observers graded the anterior and anteroinferior segments as a 2-mm labral–chondral recess (arrow). Also seen is the posterior Bankart-type tear, chondral lesion (curved arrow) and an intra-articular loose body. c A scanned arthroscopic image of the anterior labrum from a posterior portal with the superior labrum and biceps tendon (asterisk) to the right shows a superior and anterosuperior normal labral variant (curved arrows), and an anterior labral–chondral groove (straight arrow). d A screen capture from the PACS shows a measured depth of 2 mm for the anterior recess

We also drew a curved line following the concave surface of the glenoid fossa articular cartilage and continued the same degree of curvature of the line out beyond the glenoid rim (Fig. 4). If the labrum was lateral to this line the cleft was subclassified as resulting at least partially from folding of the labrum into the joint toward the center of the glenoid fossa.
https://static-content.springer.com/image/art%3A10.1007%2Fs00256-012-1496-0/MediaObjects/256_2012_1496_Fig4_HTML.gif
Fig. 4

Fifty-two-year-old man with a humeral head chondral lesion and normal anterior labrum at arthroscopy. a Oblique axial fat-suppressed intermediate-weighted image shows a labral–chondral recess graded as 1 mm by one observer and 2 mm by the 2nd observer. Both observers also thought the labrum (arrow) extended lateral to the concavecurved dotted line along the surface of the articular cartilage, and subclassified it as at least partially due to a fold. b A scanned arthroscopic image of the anterior labrum from a posterior portal shows an anterior labral-–chondral groove (straight arrows)

Clefts and tears had to be identified and confirmed on more than one image. Depth measurements were performed on the image plane most orthogonal to the particular segment.

Surgical correlation

The average time between the MR arthrogram and surgery was 75 days (range, 3–281 days). The surgeons were not blinded to the MR images or the original MR report. All the surgeons use a clock face to describe the extent of labral tears in their surgical reports, and these were used as the reference standard. At surgery, at least a portion of the 106 anterior labral segments (2:15–3:45 clock face portion) was abnormal (torn, frayed or affected by synovitis) in 51 shoulders, anteroinferior in 51, inferior in 34, posteroinferior in 28, posterior in 34, and posterosuperior in 62 shoulders. We determined the prevalence of a labral–chondral cleft/recess in the segments that were not found to be torn, frayed or synovitic. For the statistical analysis, the segments with a recess of at least 2 mm were all scored as ≥2 mm.

Because the surgeons may not have been exact in determining the clock face extent of tears, we also analyzed our data excluding the segments adjacent to torn labral segments. For example, 8 of the anterior segments were normal at surgery, but adjacent to a torn segment, so only 47 (106 minus 51 + 8) were considered in our more stringent analysis of normal anterior segments.

We also determined our MR arthrogram sensitivity for a labral tear, using the surgical finding of a tear (not including fraying or synovitis) as the reference standard.

Statistical analysis

Generalized estimating equation (GEE) models were used to assess whether clefts and ≥2-mm recesses were associated with age and gender using the combined grading of both readers. A logit link with independent correlation working structure was used, and odds ratios and 95 % confidence intervals were obtained based on the robust sandwich variance estimator. Inter-reader agreement was assessed with Cohen’s kappa (unweighted), for which 95 % confidence intervals were obtained [21]. p < 0.05 (two-sided) was the criterion for statistical significance. All statistical graphics and computations were obtained in R 2.12.1 [22]; the “gee package” was used for GEE models [23].

Results

Normal segment labral–chondral clefts/recesses

Ninety of the 103 shoulders had at least one arthroscopically normal labral segment. Of these 90 shoulders, a cleft/recess was seen in at least one normal segment in 46 of the 90 shoulders (51 %) by Observer 1 and 60 (67 %) by Observer 2. The maximum depth of a recess was 3 mm for both observers. The prevalence of a cleft/recess in all arthroscopically normal segments is shown in Table 2.
Table 2

Prevalence of a labral–chondral cleft in all arthroscopically normal segments

Segment (n)

Reader 1

Reader 2

No cleft

1 mma

≥2 mm

No cleft

1 mm

≥2 mm

Anterior (55)

26 (47 %)

17 (31 %)

12 (22 %)

24 (44 %)

18 (33 %)

13 (24 %)

Anteroinferior (55)

32 (58 %)

8 (14 %)

15 (27 %)

25 (45 %)

18 (33 %)

12 (22 %)

Inferior (72)

64 (89 %)

5 (7 %)

3 (4 %)

43 (60 %)

22 (31 %)

7 (10 %)

Posteroinferior (78)

71 (91 %)

5 (6 %)

2 (3 %)

64 (82 %)

13 (17 %)

1 (1 %)

Posterior (72)

54 (75 %)

16 (22 %)

2 (3 %)

51 (71 %)

17 (24 %)

4 (6 %)

Posterosuperior (44)

17 (39 %)

10 (23 %)

17 (39 %)

25 (57 %)

16 (36 %)

3 (7 %)

aDepth of cleft/recess

The prevalence of a cleft/recess excluding normal segments adjacent to a segment with a torn labrum is shown in Table 3. Using the data excluding the segments adjacent to torn labral segments, a cleft/recess was present in 7–61 % of the six arthroscopically normal labral segments analyzed, with a 1-mm cleft comprising 47 out of 86 (55 %) of these for Observer 1, and 85 out of 102 (83 %) for Observer 2. For Observer 1, the arthroscopically normal segment where a cleft/recess was most commonly seen on MR arthrography was the posterosuperior segment (61 %), followed by the anterior segment (49 %). For Observer 2, a cleft/recess was most common in the anterior segment (51 %). A cleft/recess was least common for both readers in the posteroinferior segment (7 % and 12 % respectively). A 2- to 3-mm deep recess was most common for Observer 1 in the posterosuperior segment (37 %), followed by the anteroinferior (25 %) segment. For Observer 2, a 2- to 3-mm recess was most common in the anteroinferior segment (17 %) followed by the anterior segment (13 %).
Table 3

Prevalence of the labral–chondral cleft or recess excluding normal segments adjacent to the torn segment

Segment (n)

Observer 1

Observer 2

No cleft (%)

1 mm (%)a

2–3 mm (%)

No cleft (%)

1 mm (%)

2–3 mm (%)

Anterior (47)

24 (51)

15 (32)

8 (17)

23 (49)

18 (38)

6 (13)

Anteroinferior (48)

30 (62)

6 (12)

12 (25)

25 (52)

15 (31)

8 (17)

Inferior (61)

56 (92)

3 (5)

2 (3)

42 (69)

19 (31)

0 (0)

Posteroinferior (72)

67 (93)

4 (6)

1 (3)

63 (88)

9 (12)

0 (0)

Posterior (57)

47 (83)

9 (16)

1 (2)

47 (82)

9 (16)

1 (2)

Posterosuperior (41)

16 (39)

10 (24)

15 (37)

24 (58)

15 (37)

2 (5)

aDepth of cleft/recess

A 2- to 3-mm recess not due at least partially to a fold was most common for Observer 1 in the posterosuperior segment, where it was seen in 15 (37 %) of the 41 normal segments (Table 4). For Observer 2, a non-fold recess was most common in the anterior (4 out of 47, 8 %) segment.
Table 4

Cleft or recess not from a labral folda

Segment

Observer 1

Observer 2

1 mmb

2–3 mm

1 mm

2–3 mm

Anterior

6/15

3/8

11/18

4/6

Anteroinferior

3/6

3/12

8/15

2/8

Inferior

1/3

2/2

11/19

0/0

Posteroinferior

4/4

1/1

8/9

0/0

Posterior

8/9

1/1

8/9

1/1

Posterosuperior

7/10

15/15

13/15

2/2

aDenominator = total normal shoulders with the measured depth

bDepth of the cleft/recess

Labral tear

Of the 43 torn (out of 51 arthroscopically abnormal) anterior labral segments, Observer 1 graded 39 out of 43 as torn for a sensitivity of 0.91. The sensitivity was 38 out of 47 (0.81) for the anteroinferior segment, 21 out of 32 (0.66) for the inferior segment, 21 out of 24 (0.88) for the posteroinferior segment, 26 out of 28 (0.93) for the posterior segment, and 44 out of 46 (0.96) for the posterosuperior segment. For Observer 2, the sensitivity was 39 out of 43 (0.91) for the anterior labral segment, 43 out of 47 (0.92) for the anteroinferior segment, 24 out of 32 (0.75) for the inferior segment, 15 out of 24 (0.62) for the posteroinferior segment, 18 out of 28 (0.64) for the posterior segment, and 29 out of 46 (0.63) for the posterosuperior segment.

Statistics results

There was no association between age (p = 0.42) or gender (p = 0.25) and the presence of a cleft/recess. There was an association between a 2- to 3-mm-deep recess and male gender (p = 0.03), but not age (p = 0.11). The Interobserver variability for each segment ranged between 0.15 and 0.49, indicating slight to moderate agreement. The Cohen’s kappa values for the six segments were: posterosuperior 0.15, posterior 0.46, posteroinferior 0.35, inferior 0.34, anteroinferior 0.49, anterior 0.47.

Discussion

Our findings show that the articular surface of the anterior, inferior, and posterior labrum is not always flush and continuous with the surface of the adjacent articular cartilage. The most common variant at the labral–chondral junction is a 1-mm cleft, a finding seen in about 40 % of the arthroscopically normal labral segments that we analyzed, mostly the anterior, anteroinferior, and posterosuperior segments. Our study confirms that these clefts are within the normal range of appearances of the glenoid labrum and do not need to be mentioned in MR reports.

A 2- to 3-mm deep, non-fold recess considered normal at surgery was seen by both observers in all but the inferior (5:15–6:45) and posteroinferior (6:45–8:15) segments of the labrum. A 2- to 3-mm recess was seen in 3–8 % of the labral segments that we analyzed. Our results show that a normal variant labral–chondral recess is rare in the six segments analyzed in our study, but they do occur at these additional sites around the glenoid rim.

Several previous articles have described labral–chondral junction clefts/recesses in some of these six segments of the labrum. Lee et al. described a cleft in the posterior labrum in 16–19 % of 127 shoulders [2]. Although the authors stressed that 67–71 % of the clefts occurred at either the 7- or 8-o’clock position, they reported clefts at all hourly clock face positions from 6-o’clock up posteriorly to 12-o’clock. The depth of the posterior labral “clefts” in their study ranged from 0.8 to 3.3 mm, with a mean of 1.5 mm. We found a lower 7–12 % prevalence of clefts/recesses in our posteroinferior segment (6:45–8:15 portion), and had a similar low prevalence of clefts/recesses in our inferior (5:15–6:45), posterior (8:15–9:45), and posterosuperior (9:45–11:15) segments. We had a higher prevalence of clefts/recesses in the posterosuperior segment than Lee et al.; however, where they reported only a 2–4 % prevalence of clefts at the 10- and 11-o’clock positions. A superior recess has been identified in up to 73 % of shoulders on MR arthrography [3, 7, 24], and has been classically described as deep to the biceps anchor and extending posteriorly to the 11-o’clock position (just within our posterosuperior segment). More recent papers, however, have described the recess as extending posterior to the biceps anchor in 10–91 % of subjects on MR arthrography [7, 2527], which would be well into our posterosuperior segment. Our 5–37 % prevalence of 2- to 3-mm recesses in the posterosuperior segment appears to be mainly from posterior extension of a superior recess (Fig. 5).
https://static-content.springer.com/image/art%3A10.1007%2Fs00256-012-1496-0/MediaObjects/256_2012_1496_Fig5_HTML.gif
Fig. 5

Forty-four-year-old woman with a partial thickness rotator cuff tear and normal variant superior recess with stable biceps anchor at surgery. a Oblique coronal fat-suppressed T1-weighted image shows the partial thickness rotator cuff tear (arrowhead), and a superior recess (curved arrow). b Three consecutive oblique axial fat-suppressed intermediate-weighted images, with a small oblique sagittal T2-weighted localizer image for the far-right image. Both observers graded the posterosuperior segment as a 2-mm labral–chondral recess (arrows), which appeared contiguous with the superior recess

Several papers have described the anterosuperior labral variants as occurring between the origins of the middle and inferior glenohumeral ligaments, and therefore extending as far inferior as the 3:30 o’clock position [11, 28], which would lie within our anterior segment (2:15–3:45 portion). We also had several shoulders with a recess in the anterior segment that were mainly due to inferior extension of an anterosuperior labral variant, and would not expect these to be confused with a tear (Fig. 3).

We identified a 2- to 3-mm non-fold recess in the anteroinferior segment (3:45–5:15 portion) in 6–8 % of normal segments in our patients. These may represent a far inferior extent of an anterosuperior labral variant in patients with a particularly caudal origin of the inferior glenohumeral ligament. If this recess is seen in patients without instability or a Hill–Sachs lesion, the attachment of the anterior labrum should be followed up to the anterosuperior portion to confirm an associated anterosuperior labral variant (Fig. 3). Recesses in the anteroinferior segment might be particularly confusing on MR because they can mimic partial labral detachment tears that occur after an anterior dislocation/subluxation. Previous papers have reported a specificity as low as 0.55–0.64 for direct MR arthrography of anterior inferior labral lesions [29], although most papers have reported specificities in the 0.86–0.98 range [3034]. A labral–chondral recess may have contributed to some of the false-positive cases in these studies.

We found that 39–92 % of segments did not contain a labral–chondral cleft/recess at least 1 mm deep on MR arthrography. We had limited arthroscopic images of some of these segments, but in most the labrum was flush and continuous with the surface of the adjacent articular cartilage. Some shoulders graded as “MR normal” had a tiny groove on the arthroscopic images, but the groove was small and shallow relative to the 5-mm arthroscopy cannula and might have been obscured by partial averaging artifact on our MR images that had pixel dimensions up to 0.49 by 0.62 mm.

We were concerned that some apparent clefts and recesses could have simply represented a labral–chondral junction “kink” or “fold” if those patients’ labrum was bent into the joint toward the center of the glenoid fossa (e.g., the anterior labrum bent back posteriorly into the joint). We therefore drew a concave line along the surface of the articular cartilage and extended it out past the glenoid rim, and recorded if the labrum extended lateral to this line (Fig. 4). This feature was present in 33–37 % of the clefts/recesses in our study, and may have accentuated the depth of some clefts/recesses. Partial labral tears, such as an anterior labrum periosteal sleeve avulsion (ALPSA) lesion, usually displace medially toward the glenoid neck [34]; thus, this is another feature that can help distinguish a recess from a partial tear.

There is controversy whether some of the normal labral variants, especially the superior recess, constitute an anatomical variant or a developmental partial detachment. De Palma found that the superior recess becomes more prevalent with age and believed that it was an acquired lesion, possibly due to chronic repetitive traction [35, 36]. Tena-Arregui et al. found that a superior recess was not present in still-born fetal specimens [37]. Lee et al., however, looked at a population with an average age of 45 years, and found that 46 % of the labral–chondral clefts in the posterior half of the labrum were in patients <30 years old [2]. Deutsch et al. reported on CT arthrography that “air or contrast may normally track between the base of the labrum and the cartilage,” but didn’t say if this was only in certain portions of the labrum [38]. We found that a 2- to 3-mm deep recess in the six regions of the labrum that we analyzed was more common in men, but there was no association with increasing age. Articles on multiple arthroscopy have stressed that a superior recess or an anterosuperior labral variant is an asymptomatic incidental finding at surgery and if “repaired” will only worsen symptoms [14, 39, 40]. Our surgeons do not repair or debride smooth, nonhemorrhagic labral–chondral junction recesses, and consider these a normal variant.

We also decided to carry out an analysis after excluding data from segments adjacent to arthroscopically abnormal segments. Although this reduced the total number of normal segments available for analysis, we did not have adequate arthroscopic images of some of our patients to confirm the accuracy of the extent of the labral tears described in the surgical reports. We therefore felt it was prudent to include an analysis of only segments that were clearly separate from abnormal segments.

The lack of arthroscopic images for all our clefts/recesses is one of the main limitations of our study because we could not correlate every one with a groove at arthroscopy, or confirm that there was not a pathological partial labral detachment. We attempted to determine indirectly if we might be overcalling clefts/recesses by calculating our sensitivity for labral tears. Our sensitivity for labral tears ranged from 0.62 to 0.96 for the different segments around the glenoid rim, which is within the range of most MR arthrogram articles that also report high specificity [30, 34, 41]. We also only called clefts or recesses with gadolinium or fluid signal, not just increased signal intensity, on the MR arthrogram images.

There are several additional limitations of our study. The surgeons were not blinded to the clinical history or the original MR arthrogram report so may have been biased in their arthroscopic assessment. Although we graded the labrum as either torn or a cleft/recess, we did not perform an in-depth analysis of the criteria for distinguishing a tear from a recess. We had a relatively small number of subjects with a 2- to 3-mm deep recess; thus, our prevalence may not be accurate. Our imaging criterion for calling a labral fold was only modestly objective. Finally, we had only slight to moderate interobserver agreement for identifying clefts in each segment. This may have been due to variability in grading the clefts, as well as whether a given slice was on one side or the other of the border between adjacent labral segments.

In summary, a cleft or recess at the labral–chondral junction is fairly common in the anterior, anteroinferior, and posterosuperior labrum, seen in 38–61 % of arthroscopically normal segments. 55–83 % of these are only 1 mm deep, and 33–37 % are at least partially due to a fold at the labral–chondral junction. Smooth, medially curved high signal at the labral–chondral junction on MR arthrogram images that appears to be a continuation of a the superior recess or anterosuperior labral variant should not be interpreted as a labral tear, particularly in the absence of a history of instability or additional findings such as a Hills–Sachs lesion.

Acknowledgement

Conflict of interest

The authors have nothing to disclose.

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