Allograft Strut Fixation to Humeral Bone: A Biomechanical Comparison of Suture-Tape Cerclage, Wire Cerclage, and Screws.

BACKGROUND: Shoulder arthroplasty is increasingly utilized to treat shoulder arthritis, cuff tear arthropathy and proximal humerus fractures. Onlay allograft cortical strut augmentation is a common technique used in the management of humeral bone loss, periprosthetic fractures, and during revision surgeries to enhance stability and potentially reconstitute bone. This study investigated the biomechanical performance of three commonly used strut fixation methods used to secure an allograft strut to host diaphyseal bone: suture-tape cerclage, wire cerclage and lag screw fixation.

METHODS: Eight unique onlay cortical tibial allograft struts were affixed to cadaveric humeral diaphyseal specimens using suture-tape cerclage, wire cerclage and lag screw fixation. Static testing measured the mean compressive force and contact area between the strut and the humeral shaft. Dynamic testing involved cyclical shear loading applied to the strut up to 150 N. Statically tested fixation configurations were three and five-point fixation constructs for suture-tape and wire cerclage, and three bi-cortically and tri-cortically engaging lag screws. Dynamically tested fixation configurations were five-point constructs for suture-tape and wire cerclage, and three bi-cortically engaging lag screws.

RESULTS: In static testing, 3-lag screw bi-cortical and tri-cortical fixation and three and 5-wire cerclage fixation demonstrated a significantly greater mean compressive force and contact area compared to both three and 5-suture-tape cerclage configurations (P < 0.004) and (P ≤ 0.003). Five-wire cerclage technique exhibited a greater mean compressive force (P= 0.003) and contact area (P= 0.008) than the 3-wire fixation technique. Additionally, 3-lag screw tri-cortical fixation produced a significantly greater mean compressive force (P = 0.040) and contact area (P = 0.026) compared to the 3-wire cerclage fixation technique. In dynamic testing, the 5-suture-tape cerclage technique exhibited a significantly lower mean compressive force and contact area compared to both the 3-lag screw bi-cortical (P < 0.001) and (P < 0.001) and 5-wire cerclage (P < 0.001) and (P ≤ 0.002) fixation techniques. Five suture-tape cerclage fixation exhibited significantly greater strut translation beyond 50 N of cyclical loading (P <0.033).

CONCLUSION: Bi- and tri-cortical lag screw and wire cerclage fixation techniques are biomechanically superior to suture-tape cerclage for the fixation of tibial allograft struts to humeral shafts. Wire cerclage requires greater fixation density than lag screw fixation in order to generate a comparable contact force and area. Additionally, lag screw fixation lessens the need for circumferential exposure for safe wire and suture passage, potentially mitigating the risk of a radial nerve injury.

LEVEL OF EVIDENCE: Basic Science Study, Biomechanics.