Arthroscopic Instability Repair with Knotless Suture Anchors

Chapter 5


Arthroscopic Instability Repair with Knotless Suture Anchors








Of the numerous surgical techniques introduced for performance of successful arthroscopic Bankart repair, fixation of the avulsed labrum with suture anchors has most consistently shown results comparable with those of open repair.1,2 This has often been attributed to the ability of suture anchors to achieve an anatomically reduced labrum and capsule while also providing a more secure construct when compared with other techniques such as bioabsorbable tacks. Traditional suture anchors, however, require proficiency with technically demanding knot designs and techniques, which are time-consuming and provide the surgeon little room for error. Furthermore, the completed knot may be bulky, and this has been reported to pose a threat to the glenohumeral cartilage via knot abrasion.3 In an attempt to simplify suture anchor placement, in 2001 Thal introduced the Mitek Knotless Suture Anchor (Mitek, Norwood, MA) and presented its use in the repair of Bankart lesions.4 The proposed advantages of this suture anchor were faster anchor placement and use, elimination of the arthroscopic knot as a source of failure, technical ease, and superior capsular shift compared with traditional anchors. Since its development, a number of other knotless anchors have been developed that offer the surgeon different options with regard to size, material, and method of fixation. In this chapter we discuss the functional characteristics of knotless anchors, the results of studies that have used such anchors for traumatic Bankart repair (Table 5-1), and the risks and benefits of use of such anchors versus traditional designs.




Knotless Anchor Design and Biomechanical Studies


Since introduction of the Mitek Knotless Suture Anchor, many anchor designs have been introduced that differ in material, method of fixation, and technique of application. Knotless anchors have been demonstrated to similarly restore labral height when compared with traditional suture anchors,5 but fundamental to their clinical performance is how the anchors will resist displacement once placed, because displacement of the anchor will result in displacement of the labrum and captured tissue from its appropriate position on the glenoid.6 Broadly, knotless anchors can be grouped based on their method of fixation into bone as either form-fit or force-fit. Form-fit anchors function by changing their original shape once deployed in such a way that they become wedged within the bone. The original Knotless Suture Anchor is an example of this, where nitinol arcs spread after insertion to increase resistance to pull-out. Force-fit anchors rely on the friction of the anchor-to-bone interface created by the anchor’s design to resist pull-out; screw-type anchors are an example of this.


Initial biomechanical testing of the Mitek Knotless Anchor was done by Thal, who compared maximal pull-out strength of the Knotless Anchor with that of the Mitek GII anchor, on which its design was based.7 Results from these studies were encouraging—failure by suture breakage occurred at considerably higher loads in the Knotless Anchor group (55.6 pounds vs. 24.3 pounds with use of No. 1 Ethibond), and there was no significant difference in bone pull-out strength. As other designs have been introduced they have also undergone biomechanical and in vitro testing. Nho and colleagues compared the force-fit type knotless PushLock anchor with the SutureTak anchor (both from Arthrex, Naples, FL) with regard to both noncyclic load-to-failure testing and cyclic load-to-failure testing with use of simple, horizontal mattress, and double-loaded simple stitch patterns.8 This anchor has the proposed advantage of making final tissue tension independent of anchor depth, which would allow the anchor to be wedged more consistently in subchondral bone. Ultimate load-to-failure and methods of failure were not significantly different between the two suture anchor constructs. Overall, knotless suture anchors have provided good results in both clinical and biomechanical studies.



Preoperative Considerations




Physical Examination


Patients typically demonstrate preserved strength and range of motion at the shoulder joint despite their history of instability; absence of these should raise flags for the presence of alternative or additional pathology contributing to the symptoms. A sense of apprehension and discomfort can be elicited by placing the patient in a position of instability, classically at 90 degrees of abduction and external rotation (the apprehension test). Conversely, a sense of relief and stability are achieved by placement of a counterforce on the humeral head in the position of instability (the Jobe relocation test). Patients may also exhibit a sulcus sign in association with inferior instability, in which downward traction on the arm produces a depression between the acromion and humeral head that is greater on the affected side than on the unaffected side.




Surgical Indications and Contraindications


Indications for arthroscopic Bankart repair include a history of traumatic subluxation or dislocation with recurring instability that is refractory to conservative treatment such as physical therapy. Examination should reveal apprehension when the arm is placed in a position of instability, and relief of symptoms when a counteracting force is applied. Patients should retain full range of motion and strength to both the deltoid and rotator cuff. Preoperative imaging should demonstrate either a bony or soft tissue Bankart lesion; associated pathology, such as rotator cuff tears, capsular tears, or superior labral anterior-posterior (SLAP) tears, can also be addressed at the time of surgical repair if necessary. In addition, as with any surgery, patients must be willing and able to comply with the surgeon’s postoperative rehabilitation protocol to ensure a successful outcome. Contraindications to surgery include degenerative joint disease of the glenohumeral joint, glenoid bone loss (which may be more amenable to bone-restoring reconstructions such as the Latarjet procedure), and atraumatic multidirectional instability.

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Sep 11, 2016 | Posted by in SPORT MEDICINE | Comments Off on Arthroscopic Instability Repair with Knotless Suture Anchors

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