Resorbable fillers reduce stress risers from empty screw holes

Background: Empty screw holes after hardware removal are stress risers that weaken bone and can lead to refracture in an active individual. We sought to reduce these stress risers. We hypothesize that resorbable screws used as hole fillers would (1) provide immediate strength and (2) maintain this strength during resorption. Methods: Randomized, prospective controlled animal laboratory study with 75 live New Zealand white rabbits' paired femurs. Single mid-diaphyseal holes were filled with a metal or resorbable screw; contralateral femurs were paired empty hole controls. Main outcome measurements included histologic analysis, torsion to failure, peak torque, energy to failure, and stiffness at baseline, 1 week, and 13 weeks postimplantation. Results: At time baseline, resorbable fillers produced an immediate 30% increase in the peak torque (p = 0.01) and 73% increase in peak energy (p = 0.006). Metal screws produced a 17% increase in peak torque (p = 0.038), and a 58% increase in the amount of energy to failure (p = 0.009). At 1 week, although the resorbable (p = 0.01) but not the metal (p = 0.82) screws increased the peak torque, both metal (p = 0.003) and resorbable (p = 0.050) screws increased the peak energy compared with contralateral empty controls. At 13 weeks, metal and resorbable screw-filled bones were as strong as the healed contralateral femurs. Partial screw resorption and new bone formation without lysis was demonstrated histologically. Resorbable screw hole fillers immediately increase the strength of bones without weakening during early resorption. Conclusions: Placing resorbable fillers in bone defects after hardware removal could reduce the likelihood of refracture.