The Knotless Suture Anchor
Abstract & Commentary
Synopsis: Knotless suture anchors allow secure soft tissue to bone repairs with superior suture strength compared to traditional arthroscopically tied knots.
Source: Thal R. Am J Sports Med. 2001;29:646-649.
The development of the suture anchor has allowed the orthopedic surgeon to accomplish traditionally performed open procedures using arthroscopic techniques. However, many surgeons are hesitant to use suture anchors because of the inability to tie a consistent and reliable arthroscopic knot. Arthroscopic knot tying may be technically challenging and time consuming to master. A number of novel instruments have been developed to address these concerns including the Knotless suture anchor (Mitek Products, Inc, Norwood, Mass).
The Knotless suture anchor is similar in design to the Mitek GII anchor, but there are several notable differences. There is a channel at the tip of the Knotless suture anchor and 2 linked suture loops at the tail end of the anchor. A short "anchor" loop of No.1 suture is fixed directly to the anchor, and a longer "utility" loop of No.2-0 suture is linked to the anchor loop. A 2.9-mm drill hole is created at the site of repair. The utility loop is passed through the labrum and capsule, and as it is pulled, the anchor loop follows bringing the anchor closer to the labrum. Once the anchor loop passes through the soft tissue, the anchor channel captures one strand of the loop. The anchor is inserted into the previously drilled hole with the captured suture and tapped to the desired depth in order to achieve proper tissue compression against the glenoid and capsular tension.
In this study, Knotless suture anchors with No.1 Ethibond suture (Ethicon, Inc, Somerville, NJ), GII anchors with No.1 Ethibond, GII anchors with No.2 Ethibond, and GII anchors with No.5 Ethibond were loaded to failure with an Instron testing machine (Instron, Corp, Canton, MA). All anchors were placed in a vise. The GII anchor suture was tied over a dowel pin, and the suture loop of the Knotless suture anchor was passed over the dowel pin and captured in the anchor channel. The suture strength of the Knotless suture anchor (55.95 lbs.) was significantly greater than the suture strength of all GII anchors (No.1, 24.32 lbs, No.2, 30.01 lbs, No.5, 51.29 lbs) (P < 0.0001). In addition, pull-out testing of Knotless suture anchors and GII anchors was measured in porcine distal femurs, but the difference was not statistically significant.
In this study, the Knotless suture anchor demonstrated superior suture strength and similar anchor pull-out strength to the Mitek GII suture anchor. The Knotless suture anchor can potentially provide a more reliable method of arthroscopic fixation.
Comment by Brian J. Cole, MD, MBA
Suture anchors have enabled the orthopedic surgeon to perform arthroscopic repairs for Bankart lesions and rotator cuff tears, but the ability to tie consistent quality knots is largely dependent on the surgeon’s skill and experience. The Knotless suture anchor offers a relatively easy solution because it eliminates the need to tie arthroscopic knots. Thal was able to demonstrate increased suture strength at ultimate failure and similar bone pull-out strength tested in porcine femurs. Assuming that capturing the anchor loop can be done with relative ease, the application of the Knotless suture anchor should produce clinical results that match or exceed knotted suture anchors because of its theoretical ability to tighten the capsule adjacent to the labrum during suture loop passage. More importantly, the Knotless suture anchor might permit a greater number of orthopedic surgeons the ability to perform arthroscopic repairs that require suture anchors.
Dr. Cole, Assistant Professor, Orthopaedic Surgery, Rush Presbyterian Medical Center, Midwest Orthopaedics, Chicago, IL, is Associate Editor of Sports Medicine Reports.
Acknowledgment: The reviewer would like to acknowledge Shane J. Nho, MS, for his assistance in preparation of this report.
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