A Closer Look At The Use Of Interference Screws For Lateral Ankle Stabilization
Feldman compared the strength of interference screw fixation to suture-button fixation and staple fixation.15 The failure load was 62.8 N for interference screws, 13.9 N for staple fixation and 23.9 N for suture-button fixation. Weiler and colleagues researched the pull-out strength of six different biodegradable interference screws in comparison to a titanium screw.16 The titanium screw had an 8 mm thread diameter and was 25 mm in length. Researchers found that the absorbable interference screws achieved initial pull-out forces comparable with those of a conventional titanium interference screw.
In a more recent study, surgeons performed a biomechanical evaluation for ankle stabilization, comparing interference screws to bone anchors.17 They tested two devices: the Mitek GII anchor with Ethibond (DePuy) and the 5.5 mm Bio-Tenodesis Screw with FiberWire (Arthrex). The study authors performed a separate group of tests that involved a secured anchor and use of the FiberWire suture to determine the effect of the suture on the construct. Completely gripped screws produced a mean load of approximately double that of the bone anchors.
Researchers also found that the suture material has little effect on the screws.17 Load to failure for the single pull anchor and Ethibond group was significantly lower than the failure load required to rupture the anterior talofibular and calcaneofibular ligaments. The failure load of the single pull screw group was significantly greater than that of the anterior talofibular ligament and not significantly different from the failure load of the calcaneofibular ligament.
The fully gripped interference screw group showed significant biomechanical advantages over the partially gripped screw and anchor when reconstructing the anterior talofibular and calcaneofibular ligaments.17 The authors also concluded that patients in the bone anchor group may not be suitable for reconstruction of either the anterior talofibular or calcaneofibular ligaments.
Barber measured the load to failure for each anchor test (anchor pullout, eyelet wire or suture cut out, or wire or suture breakage).18 In order of strongest to weakest suture in terms of failure load were Fiberwire no. 5, Ethibond no. 5 (Ethicon), Fiberwire no. 2, Panacryl no. 2, Ethibond no. 2 and Fiberwire no. 2-0. The most likely mode of repair failure is the suture cutting through the tissue rather than suture anchor failure.
According to the study, the Ultrasorb was the weakest in load to failure and the TwinFix Ti 5.0 (Smith and Nephew) was the strongest.18 In order from weakest to strongest in terms of failure load were UltraSorb, BioCorkscrew 6.5 (Arthrex), BioCorkscrew 5.0, AlloAnchor RC (Regeneration Technologies), Duet (Bionix Implants), TwinFix Ti 3.5 (Smith & Nephew), Super Revo (Linvatec), TwinFix AB (Smith and Nephew), Opus Magnum (Opus Medical) and TwinFix Ti 5.0.