SLR - January 2024 - Stawicki
Title: Is just one screw really enough? Single- versus double-screw in the medial malleolus in supination-external rotation ankle fractures: A comparative biomechanical study using partially threaded cancellous screwsReference: Giordano V, Rodrigues A, Voelcker L, Alves G, Pires RE, Freitas A, Mariolani JR, Belangero WD. Is just one screw really enough? Single- versus double-screw in the medial malleolus in supination-external rotation ankle fractures: A comparative biomechanical study using partially threaded cancellous screws. Injury. 2023 Nov 2:111175. doi: 10.1016/j.injury.2023.111175. Epub ahead of print. PMID: 37926664.
Level of Evidence: Biomechanical, Level V
Scientific Literature Review
Reviewed by: Christie Stawicki DPM
Residency program: University Hospital, Newark, New Jersey
Podiatric Relevance: In displaced oblique fractures of the medial malleolus, anatomic reduction and rigid internal fixation are critical in providing optimal outcomes. Currently, the most common method for fixation of this injury type include two 4.0 mm partially threaded cancellous screws placed perpendicular to the fracture line. Recent literature, including a randomized clinical trial assessing long term functional outcomes of single and two screw fixation, has demonstrated that single screw fixation is equally safe and effective. However, a biomechanical analysis comparing single to double cancellous screw fixation for medial malleolar fractures in supination external rotation ankle fractures has not been conducted. The authors hypothesize that single screw fixation provides similar stiffness when compared with double- screw fixation.
Methods: Twelve composite polyurethane synthetic right distal tibias from a single manufacturing site were used to create the oblique medial malleolus fractures. The osteotomy was done with a band saw using a custom guide. Bone models were separated into two randomized groups and corrected with one or two 4.0 mm cancellous screws. Biomechanical stiffness testing was conducted on an MTS 810 material testing system with a maximum force capacity of 100kN. Specimens were then tested using offset axial tension at 10mm/ minute up to maximum load displacement. Student T tests were used to compare stiffness and maximum load to failure between experimental groups.
Results: There was no significant difference in stiffness and maximum load among the two fixation constructs (p=0.290 and p=0.191). Mean stiffness was 62.26 N/mm for double-screw fixation group and 48.24 N/mm for single-screw fixation group. Mean maximum load was 387.83 N for double screw fixation group and 306.64 N for single screw fixation.
Conclusions: From a biomechanical standpoint, this study demonstrates that there is no significant difference in stiffness and maximum load to failure with a single partially threaded cancellous screw for oblique medial malleolus fractures in supination-external rotation ankle pathology. Historically, the ideal fixation method has remained controversial for oblique medial malleolar fractures. Recent randomized control studies have demonstrated no increase in risk of postoperative fragment displacement with single screw fixation for medial malleolar fractures. This study supports this hypothesis and demonstrates biomechanically that there is not a signification difference in fixation constructs with reproducible results. Although axial stability was addressed in this study, rotational stability was not. From a biomechanical standpoint, two points of fixation are required to prevent a medial malleolar fracture from rotating on a single axis. Further, rotational stress was not evaluated or discussed in this study despite the importance of this factor on overall function of the ankle. The surgical decision to select a single screw for treatment can assist in reducing the number of implant complications including irritation, cartilage damage, and intra-articular hardware penetration while providing the most cost-effective option for the patient.