Fri., 10/19/07 Foot & Ankle, Paper #35, 3:33 pm OTA-2007
Why Not Use Long Bicortical Lag Screws for Medial Malleolar Fracture Fixation?
A Biomechanical, Radiographic, and Clinical Comparison of Long Bicortical Lag Screws to Traditional Partially Threaded Unicortical Lag Screws
William M. Ricci, MD1 (a-Synthes, AONA; a,c,e-Smith+Nephew; e-OrthoVita);
Erica Jantho1 (n); Paul Tornetta, III, MD2 (a,c,e-Smith+Nephew);
Joseph Borrelli, Jr, MD3 (a-Synthes, AONA; e-Wright Medical, Medtronics);
1Washington University School of Medicine, St. Louis, Missouri, USA;
2Boston Medical Center, Boston, Massachusetts, USA;
3University of Texas–Southwestern, Dallas, Texas, USA
Introduction: Traditional medial malleolar screw fixation with partially threaded unicortical lag screws (lag by screw design) was compared to long bicortical lag screws biomechanically and in a clinical cohort series.
Methods:
Biomechanics: Human cadavers (n = 3) had bilateral transverse medial malleolar fractures (n = 6) created with an osteotome. Fixation of each side was randomly allocated to either two unicortical lag screws (traditional 4.0-mm partially threaded screws, length 45 mm) or two long bicortical lag screws that engaged the lateral cortex of the distal tibial metaphysis (3.5-mm cortical screws, near cortex overdrilled). Fixation strength was evaluated by measuring the peak insertion torque generated during screw insertion (proportional to fracture-site compression).
Radiographic and clinical evaluation (IRB-approved): A retrospective cohort design with control was utilized. Between January 1, 2004 and December 31, 2006, 100 patients with closed ankle fractures (OTA 44) and lag screw fixation of associated medial malleolus fractures were identified from a prospective orthopaedic trauma database. 11 patients were lost to follow-up, leaving 89: 64 fixed with partially threaded unicortical screws (average age 45 years, range 17-80; average follow-up 33 weeks, range 12-130) and 25 fixed with long bicortical screws (average age 42 years, range 18-86; average follow-up 20 weeks, range 12-45).
Results:
Biomechanics: Bicortical screw fixation showed an average maximum torque generation of 14.4 in-lbf (range 8.0-20.1, standard deviation [SD] = 4.4) that was over three times greater than that seen with traditional unicortical fixation (average maximum torque generation 3.9 in-lbf, range 2.5-6.6, SD = 1.4) (P <.0002).
Radiographic and clinical evaluation: Screw loosening was evident in 1 of the 25 patients (4%) in the bicortical screw cohort and in 12 of the 64 patients (19%) in the unicortical screw cohort. All patients in the bicortical cohort healed after the index procedure, while two in the unicortical cohort had nonunions.
Conclusions: Bicortical lag screws have superior biomechanical, radiographic, and clinical outcomes compared to traditional unicortical lag screws for the fixation of medial malleolar fractures.
If noted, the author indicates something of value received. The codes are identified as a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts disclosed, and *disclosure not available at time of printing.
• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing.