Pullout strength of knotless suture anchors

Suture anchors are used consistently for repairs of soft tissues, especially around the glenohumeral joint. These anchors can be used either arthroscopically or in an open procedure to anatomically restore the labrum and capsular tissues to the glenoid after avulsion injuries (Bankart lesion). The purpose of this study was to analyze the pullout strength of a new knotless suture anchor (Mitek Knotless Suture Anchor; Mitek, Norwood, MA) compared with 2 commercially available suture anchors that require knots to be tied (Mitek Panalok 3.5-mm Anchor and Mitek GII Quick Anchor).

Randomized cadaveric study.

Three groups of 10 anchors were tested on 15 fresh-frozen cadaveric glenoids. Two anchors were affixed to the anterior glenoid in subchondral bone, 1 each from 2 groups. In this way, the variance of bone density among groups was minimized. The anchors requiring knots were fixed to the glenoid and tied to a ring using a Duncan knot with 3 half-hitches alternating posts. The Knotless Anchor was looped through the ring and anchored into the glenoid as described by the manufacturer. All constructs were then tested for tensile strength on an Instron machine (Canton, MA) using a crosshead speed of 200 mm/min. Ultimate failure was defined as complete failure of the construct (either suture breakage or anchor pullout). Data were then analyzed for statistical significance using analysis of variance analysis among the 3 groups, and a 2-tailed t test for statistical significance among groups.

The average failure under tensile load for the GII, Panalok, and Knotless Anchors were 471.5 N, 432.8 N, and 650.0 N, respectively. Statistical analysis showed a statistical difference between the Knotless Anchor and the GII and Panalok sutures ( P = .02). Two-tailed t tests between the Knotless Anchor and the GII or Panalok Anchors were also significant (P = .02 and P = .02, respectively). Observations included a large standard deviation within groups. This is thought to result from the variation in bone density because markedly lower tensile loads were recorded for those anchors that pulled out from the bone before suture failure.

The Knotless Suture Anchor is a statistically stronger construct with respect to tensile loads. It appears to be a viable option for any type of soft-tissue repair around the glenoid.

Because the knot in suture repair is consistently the weakest point in the construct and because of the difficulty in tying knots arthroscopically, the Knotless Suture Anchor appears to be a stronger and easier method for both arthroscopic and open Bankart repair, with or without capsular shift.