The history of suture anchors in orthopaedic surgery

The invention of the suture anchor has revolutionised orthopaedic surgery, allowing the rapid and efficient fixation of soft tissue to bone in both open and arthroscopic surgery. The evolution in anchor design to meet new demands and overcome demonstrated biomechanical shortfalls is a good example of evidence driven innovation. Anchors have found predominant application around the shoulder but are also commonly used in the hand, wrist and joints in the lower limb.

Whilst the applications of suture anchors are numerous and the surgical repairs can be quite complex, the sole function of a suture anchor is simple; to form a strong and stable point of bony fixation. Multiple advances in anchor design have occurred in the aim of maximising this function with variations in both form and material properties to optimise performance. Modern operative demands have seen the development of contemporary anchors with smaller design for use in more peripheral locations, and the use of biodegradable materials to combat perceived issues with persisting metal anchors, as well as the ability to use advanced anchors in arthroscopic procedures.

In view of the varying design features, the assessment of anchor efficacy remains simple, with suitability categorised into three overarching principals 1) maximise pull out strength, 2) minimise acute iatrogenic damage, and 3) minimise long term pro-arthritic potential.

The pull out force is the primary measure of an anchors performance. It is commonly measured by inline tensional loading often performed by a materials testing machine (Instron, Norwood, USA) and gives a value for the maximum load the anchor can withstand before it fails and is extracted from the bone (US Food and Drug Administration, 2017). The inline testing gives a pull out force representative of the worst-case scenario, with any angle less than 90° to the bone reducing the resultant contribution force to extraction. The minimisation of iatrogenic damage is a secondary performance criterion; however, size is the primary way to select one anchor over the other for a specific surgical purpose.

The purpose of this narrative review is to report the history of anchor design, the performance of both legacy and contemporary implants and consider their suitability for different applications. Further, comments are made on the lessons learnt from previous design changes, in view of creating a firm foundation to allow better surgical selection of anchors and ongoing design innovation.

Section snippets

The original suture anchors

The first five suture anchors designed demonstrated varying mechanisms for bone fixation. A few early faults were rapidly corrected but many of the evident themes were carried through to future products. The first suture anchor was patented by Goble and Somers in 1985 and marketed as Statak (formerly Zimmer, Warsaw, USA). They described the bonding of a No.2 braided polyester to a self-drilling and tapping headless hex screw, allowing for the versatility of suture and the strength and ease of a

Material choice

Early fears of metal anchors migrating over time, interfering with diagnostic imaging and consideration of suitability for the paediatric age group lead to the development of biodegradable suture anchors (Barber and Deck, 1995). Published evidence of these feared complications did not emerge for another decade suggesting that the incidence rate was very low, but nevertheless degradable anchors provided peace of mind and were therefore attractive to the surgeon.

Chain failure at the suture

As rate of failure of the anchor construct decreased and mean force to pull out of bone increased, the failure point consistently became at the suture itself. In response companies began to provide anchors loaded with multiple sutures, two then three strands (Barber et al., 2003). However, strength was still limited with no.2 braided polyester sutures failing at around 90?N. The introduction of ultrahigh molecular weight polyethylene (UHMWP) sutures (branded as Dyeema Purity, DSM, Heerlen.

The anchor-suture interface

The majority of testing for suture anchors utilised a similar method to Barber, testing for the direct pull out strength in an axial direction which was thought to be the weakest direction. In 1997 Burkhart recognised that for rotator cuff repairs cyclical loading might be more accurate method of simulating physiological loading conditions whereas all previous experiments had tested single pull to failure (Barber et al., 1997a). In two separate experiments but utilising the same experimental

Knotless anchors

Whilst arthroscopic repairs were acknowledged as improving patient outcomes, the complexity and steep learning curve for consistent results in arthroscopic knot tying was recognised as a significant obstacle (Barber et al., 1997b). In 2001 Thal published an article describing the first knotless suture anchor, called the Mitek Knotless (Mitek Inc.). Similar to the Mitek GII design with a titanium body and nitinol arcs 11?mm in length and 2.8?mm in width, it had the additional feature of a distal

Conclusion

Both the design and use of suture anchors has changed dramatically since their inception in 1985. With increased expectations from a device that originally had only the role of resisting pull out, anchors now must match the structural performance of their predecessors whilst being smaller in size, made of safer radiolucent materials, being self-tensioning and knotless.

Through a process of evidence driven innovation, extensive changes have occurred in the form of bony fixation, eyelet placement...