Lag Screw Fixation of Medial Malleolar Fractures: A Biomechanical, Radiographic and Clinical Comparison of Unicortical Partially Threaded Lag Screws and Bicortical Fully Threaded Lag Screws
Reference: Ricci WM, Tornetta P, Borrelli JJ. Lag Screw Fixation of Medial Malleolar Fractures: A Biomechanical, Radiographic, and Clinical Comparison of Unicortical Partially Threaded Lag Screws and Bicortical Fully Threaded Lag Screws. Journal of Orthopedic Trauma, 26(10);2012: 602-606.
Scientific Literature Review
Reviewed by: Lauren Karger, DPM
Residency Program: UMDNJ- University Hospital, Newark NJ
Transverse medial malleolar fractures often require internal fixation, and the use of partially threaded (PT) lag screws (by design) are a standard and common method for treating this type of injury. Although outcomes are usually good, there are shortcomings such as the lack of purchase within the distal tibial metaphysis cancellous bone due to screw length. Screw loosening and back-out are additional concerns. An alternative to PT lag screw fixation are fully threaded (FT) lag screw fixation, to lag by “method.”
A biomechanical evaluation was performed with three human cadavers with recreated transverse medial malleolar fractures bilaterally, which were used to determine maximum screw insertion torque generation. A radiographic and clinical retrospective cohort study design with control used 141 patients with closed medial malleolar fracture fixation, 46 in PT cohort, and 46 in FT cohort. The patients’ demographic data was analyzed, and the fracture type was classified according to the Orthopaedic Trauma Association. The average follow-up for the PT group was 56 weeks and 40 week for those in the FT group.
Biomechanically, the FT lag screw group showed an average maximum torque generation of 14.4 in-lbf and the PT lag screw group of 4.0 in-lbf. Radiographic and clinical results showed that the use of FT lag screws was associated with significantly lower rate of screw loosening (1 of 46) compared with the use of PT lag screws (11 of 46). Two of the PT group with loose screws required reoperation for hardware removal. All of those in FT group healed after the index procedure, two of the PT group developed non-unions.
Fixation of the medial malleolus is commonly performed with a unicortical PT lag screw, but incorrect length can lead to suboptimal fixation. It is believed that FT lag screw by method has not been popularized due to the required length of screw, which may not be readily available in small fragment sets. The authors believe that based on biomechanical, radiographic and clinical evidence, bicortical FT lag screw fixation provided improved outcomes as compared to the PT lag screw.