Introduction: Historically, blocking screws have been used to assist in acute reduction of fractures during intramedullary (IM) nailing. The reverse-rule-of-thumbs (RROT) for blocking screws was introduced to facilitate internal lengthening nail use in deformity correction and limb lengthening. Our study investigated the ability of blocking screws, using same principle, to accurately correct long-bone deformity with and without lengthening and to prevent lengthening-induced deformity. Materials and methods: This is an institutional review board (IRB)-approved retrospective study on 86 patients who had IM nail-assisted limb reconstruction of femur or tibia with blocking screws. Surgeries were performed for deformity correction, limb lengthening, or deformity correction and limb lengthening. Data on the following variables were collected: number of blocking screws, distance of each blocking screw to osteotomy, distance of osteotomy from joint line, and amount of lengthening. Mechanical axis deviation (MAD) and joint alignment parameters were measured preoperatively and at the final postoperative follow-up. The primary outcome was the ability to obtain desired MAD and joint orientation angles. Accuracies were reported as postoperative measurements relative to goal. Association for the Study and Applications of the Methods of Ilizarov (ASAMI) scores were collected. Results: The accuracy of deformity correction was within 6 mm from goal, while joint orientation was corrected to within 1.5° of goal. Number of blocking screws did not significantly impact accuracy. Distance of blocking screw to osteotomy and amount of lengthening did not affect accuracy. In femurs, osteotomies greater than 10 cm from the joint line were more accurate in MAD goal (p = 0.017). This result was not replicated in tibias. ASAMI scores were excellent or good. Conclusion: Using RROT configuration, blocking screws were effective in correcting deformities of lower extremity long bones and in preventing deformity during limb lengthening. If positioned correctly, number of screws and their distance to osteotomy did not affect accuracy. Amount of lengthening did not impact accuracy. Distal femoral osteotomy less than 10 cm from knee joint may be challenging even with using blocking screws.
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