Safety of Superior Labrum Anterior and Posterior (SLAP) Repair Posterior to Biceps Tendon Is Improved With a Percutaneous Approach

Results

In the ASL portal group, 8 (66.7%) of 12 anchors (4/6 at 11 o’clock, 4/6 at 10 o’clock) penetrated the medial glenoid vault.

In the 8 penetration cases, mean distance to SSN was 6.8 mm (range, 0-14 mm) for 11 o’clock anchors and 4.8 mm (range, 0-14 mm) for 10 o’clock anchors (Table).

In the PW portal group, 2 (16.7%) of 12 anchors (1/6 at 11 o’clock, 1/6 at 10 o’clock, both from a single specimen) penetrated the medial glenoid vault. Actually, in each case the eyelet and not the anchor penetrated the vault. In the penetration cases, distance to SSN was 20 mm for the 11 o’clock anchor and 8 mm for the 10 o’clock anchor (Table). Of the 6 portals, 3 passed through the supraspinatus muscle, 2 through the infraspinatus musculotendinous junction, and 1 through the infraspinatus muscle.

Discussion

Our study findings support the hypothesis that SLAP repair anchors placed posterior to the biceps tendon are more likely to remain in bone with use of a percutaneous approach relative to an ASL approach. Our findings also support the growing body of evidence that such anchors placed with an anterior approach increase the risk for SSN injury.

Three other cadaveric studies have evaluated anchor placement for SLAP repair. Chan and colleagues⁷ evaluated drill penetration during bone socket preparation for SLAP repair in 21 matched pairs of formalin-embalmed cadavers. A 20-mm drill was used for correspondence to a 14.5-mm anchor, though no anchors were inserted, and sockets were created in an open manner. Through a mimicked ASL portal, 1 socket was made anterior to the biceps tendon, at 1 o’clock; then, through a mimicked PW portal, 2 sockets were made posterior to the tendon, at 11 o’clock and 9 to 10 o’clock. Glenoid vault penetration occurred in 29% of the 42 anterior sockets, but only 1 anchor (2.4%) touched the SSN. Penetration did not occur with the 11 o’clock anchors. The 9 to 10 o’clock anchor was at highest risk for SSN injury (9.5%, 4 cases). The study was limited by lack of anchor placement and open creation of bone sockets in embalmed cadavers.

Koh and colleagues⁸ evaluated arthroscopic placement of anterior SLAP anchors in 6 matched pairs of fresh-frozen cadavers. Through an ASL portal, each 14.5-mm knotted anchor was placed anterior to the biceps tendon, at 1 o’clock. As in the study by Chan and colleagues,⁷ drill depth was 20 mm. Notably, anchors were seated 2 mm beyond manufacturer recommendations, and the cadavers were of Asian origin, likely indicating smaller glenoids compared to specimens from North America or Europe. All 12 anchors penetrated the glenoid vault; mean distance to SSN was 3.1 mm.

Morgan and colleagues⁹ compared anterior and ASL portals created for SLAP repairs in 10 matched-pair cadavers. Anchors were placed at 1 o’clock, 11 o’clock, and 10 o’clock. As in the studies by Chan and colleagues⁷ and Koh and colleagues,⁸ 14.5-mm knotted anchors were used. One anterior anchor (10%) placed through an ASL portal penetrated the cortex by 1 mm, and 2 anterior anchors (20%) placed through anterior portals penetrated the cortex (1 was completely out of the bone). Overall, 65% of 11 o’clock anchors and 100% of 10 o’clock anchors violated the glenoid vault. With the 11 o’clock anchors, mean distance to SSN was 6 mm for ASL portals and 4.2 mm for anterior portals; with the 10 o’clock anchors, mean distance to SSN was 8 mm for ASL portals and 2.1 mm for anterior portals.

Overall, the results of these 3 studies suggest that, with use of ASL portals, placement of SLAP anchors anterior to the biceps tendon is safe. Using the same portals, however, anchors placed posterior to the tendon are at higher risk for glenoid vault penetration. Supporting these findings are our study’s penetration rates: 66.7% for anchors placed through ASL portals and 16.7% for anchors placed through percutaneous PW portals. The different rates are not surprising given that the coracoid process projects anterior to the glenoid and provides additional bone stock for placement of anchors anteriorly vs posteriorly. Therefore, with percutaneous PW portals, the approach angle directs the anchor toward the bone of the coracoid base. Furthermore, the SSN passes nearest the posterior aspect of the glenoid. In a study by Shishido and Kikuchi,¹² the distance from the posterior rim of the glenoid to the SSN was 18 mm, and from the superior rim was 29 mm. Therefore, anchors placed with an anterior approach naturally are directed toward the SSN.

Given these findings, we think surgeons who repair posterior SLAP tears should place anchors through percutaneous PW portals, not ASL portals, in order to minimize the risks for glenoid vault penetration and SSN injury (Figures 3, 4A-4B).

In addition to portal placement and approach angle, anchor length likely affects the risks for glenoid vault penetration and SSN injury.

Koh and colleagues⁸ found a mean distance of 14.2 mm from the glenoid rim to the medial cortex for anchors placed anterior to the biceps tendon and a mean distance of 20.7 mm from the glenoid rim to the SSN. Morgan and colleagues⁹ also evaluated the shortest distance from the glenoid rim to the SSN. Mean distance was 17.9 mm for 10 o’clock anchors and 20.9 mm for 11 o’clock anchors. Whereas the 3 cadaveric studies discussed earlier^7-9 examined 14.5-mm knotted anchors with drill depths of 20 mm, we examined 12.5-mm knotless anchors with drill depths of 18 mm. Even with the 1 anchor penetration that occurred with a percutaneous portal in our study, the SSN was 20 mm from the 11 o’clock portal and 8 mm from the 10 o’clock portal. It is important to note that, for SLAP repair, the biomechanical characteristics of knotless anchors are equivalent to those of knotted anchors.¹³ In addition, knotless anchors offer the advantage of avoiding knot impingement and migration.¹⁴ On that basis, and given the anatomy mentioned, we primarily use short knotless anchors for SLAP repair and think that, as long as biomechanically supported, the trend should be to use shorter anchors for SLAP repair in order to minimize the risks for glenoid vault penetration and SSN injury.

One limitation of this study was the small number of cadavers, all of which were male. Female cadavers and cadavers of other ethnic origins likely have smaller glenoid vaults, and thus their inclusion would have altered our results. This issue was well described in studies mentioned in this article, and our goal was simply to compare ASL portals with percutaneous PW portals, so we think it does not change the fact that the risks for glenoid vault penetration and SSN injury are reduced with use of PW portals for anchors placed posterior to the biceps tendon.