Quantifying the effects of eccentrically drilled distal interlock screws in cadaveric tibias

OBJECTIVES: Intramedullary nailing (IMN) is the standard treatment for tibial shaft fractures; however, postoperative malalignment remains a relevant complication. Deviations in distal nail position can influence tibial alignment, and eccentric drilling during distal interlocking screw placement may alter fracture reduction and length. The purpose of this study was to quantify the effect of intentionally eccentric distal interlocking screw placement on tibial alignment in a controlled cadaveric model. METHODS: Ten paired, formalin-fixed, human-cadaveric tibias underwent standardized IMN via suprapatellar approach following reaming of 1.5mm over nail diameter. A simulated comminuted distal tibia-fibula fracture was created using a 2-cm defect 4-cm proximal to the plafond. A 10mm IMN was then seated and secured with a 60mm interlocking screw, placed in the medial-to-lateral proximal oblique hole. Crossing K-wires were placed in the coronal and sagittal planes to serve as markers for angular and axial displacement. Using fluoroscopic "perfect-circles" technique, three surgeons performed standardized, intentional, eccentric-drilling with proximal-to-distal trajectory. Distal screw placement was performed in the medial-lateral plane, then removed and repeated in the anterior-posterior plane. Coronal and sagittal angulation and axial length were measured by digital goniometer and calipers following screw insertion, respectively. RESULTS: For medial-lateral screws, proximal-to-distal eccentric drilling yielded a mean coronal angulation of 6.0° induced valgus (SD= 3.8°, R:1.5°min-12.2°max). While for anterior-posterior screw placement, proximal-to-distal eccentric drilling yielded a mean of 5.8° procurvatum (SD = 2.0°, R: 2.8°min-8.5°max). Translational distraction in the coronal plane was 3.0mm (SD = 2.2mm, R: 0.05mmmin-7.8mmmax), and distraction in the sagittal plane was 3.9mm (SD = 3.0mm, R: 1.1mmmin,-9.8mmmax). CONCLUSION: Eccentric distal interlocking screw placement produced radiographically appreciable angular and axial changes in distal tibial IMN constructs. Deviations during the "perfect-circles" technique can generate malalignment, or alternatively, be used to fine tune reduction in theory. Precise distal screw trajectory and strategies to minimize drilling eccentricity may reduce postoperative malalignment, particularly in distal tibial fractures. LEVEL OF EVIDENCE: Level V.