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Background: Oblique fractures of the medial malleolus can arise from the application of axial force at various anatomic positions of the ankle, including supination-external rotation, pronation-external rotation, or pronation abduction. Although a variety of techniques exist to provide fixation of horizontal medial malleolus fractures, the optimal technique and pattern for internal fixation remains unclear. The aim of this study was to evaluate the mechanical properties of four different fixation methods for fractures of the medial malleolus., Methods: Identical oblique osteotomies were created in synthetic distal tibiae using a jig. The specimens were divided into four fixation groups: contoured 2.0 mm mini-fragment T-plate, figure-of-eight tension band wire, construct two parallel 4.0 mm cancellous screws, and two divergent 4.0 mm cancellous screws. The specimens were tested using offset axial tension at 10 mm/min until 2 mm of joint line displacement., Results: The average stiffness in tension and force at 2 mm of joint line displacement of the plate construct was significantly greater than any of the other constructs (p < 0.05), whereas the average stiffness in tension of the other three groups were not significantly different from each other (p > 0.05)., Conclusion: Using a contoured 2.0 mm mini-fragment T-plate as the method of fixation resulted in an at least 25% stiffer construct during tension and required at least 24% more force for 2 mm of joint line displacement when compared with more traditional methods of fixation in an osteotomy model of an oblique medial malleolus fracture.

Background: This study qualified and evaluated the mechanical properties of three different screw orientations used for fixation of vertical shear fractures of the medial malleolus., Methods: Identical vertical osteotomies were created in synthetic distal tibiae using a jig. The specimens were assigned to one of the three fixation groups (n = 8 per group): (1) parallel: two 40 mm length, 4.0 mm diameter screws placed parallel to each other in the transverse plane; (2) convergent: two 40 mm length, 4.0 mm diameter screws placed 25 degree convergent to each other in the transverse plane; and (3) divergent: two 40 mm length, 4.0 mm diameter screws placed 15 degree divergent to each other in the transverse plane. The specimens were tested using offset axial loading at 1 mm/s until 2 mm of displacement., Results: The average stiffness was 102 N/mm ± 51 N/mm for the parallel group, 109 N/mm ± 37 N/mm for the convergent group, and 185 N/mm ± 73 N/mm for the divergent group. The average stiffness of the divergent group was significantly greater than either the parallel (p < 0.05) or convergent (p < 0.05) groups. The divergent group was 81.4% more stiff than the parallel group and 69.7% more stiff than the convergent group. The average load at 2 mm of displacement was 324 N ± 87 N for the parallel group, 373 N ± 95 N for the convergent group, and 512 N ± 170 N for the divergent group. The average load at failure of the divergent group was significantly (p < 0.05) greater than the parallel groups. The divergent group was required 58.0% more force at 2 mm of displacement than the parallel group and 37.3% more force at 2 mm of displacement than the convergent group., Conclusion: The use of a divergent screw pattern resulted in a stiffer fixation construct that requires more force for 2 mm of displacement when used to stabilize an osteotomy model of vertical shear medial malleolus fractures.

Objective: To determine if 1) angularly stable devices created by compressing ("locking") proximal locking screws to intramedullary nails using end caps or compression screws or 2) increasing the number of proximal screws from two to three increases the stiffness of intramedullary constructs that stabilize proximal third tibia fractures in a nonosteopenic bone model., Methods: Four proximal locking screw configurations were examined in a synthetic composite tibia model with a 2-cm gap simulating a comminuted proximal third tibia fracture with no bony contact: 1) two proximal screws not compressed to the nail; 2) one of two proximal screws compressed to the nail; 3) two proximal screws compressed to the nail; and 4) three proximal screws with only the most proximal screw compressed to the nail. An 11-mm tibial nail with two distal locking screws was used. Stiffness was measured in axial and torsional loading. An analysis of variance was performed to compare results of the screw configurations for each testing mode., Results: Compressing two screws to the nail produced 22% to 39% greater (P ≤ 0.01) axial and 16% to 29% greater (P ≤ 0.03) torsional stiffness than securing neither or only one of the screws. Adding a third proximal transverse locking screw increased the axial stiffness by 28% (P = 0.005) and the torsional stiffness by 15% to 28% (P ≤ 0.04) compared with using two oblique proximal screws., Conclusions: "Locking" two proximal locking screws to the nail through compression or adding a third proximal screw increases the axial and torsional stiffness of intramedullary nails used to fix unstable proximal third tibia fractures.

Objective: In developing countries, tibial shaft fractures are frequently stabilised using Surgical Implant Generation Network (SIGN) nails. Despite widespread use throughout the world, little is known regarding their biomechanical properties. This study aimed to compare the mechanical stiffness of the SIGN tibial nail with a standard hollow tibial nail., Methods: A fracture gap model was created to simulate a comminuted mid-shaft tibia fracture (AO/OTA42-C3) using synthetic composite bones. The constructs were stabilised with either a 9 mm solid SIGN nail or a 10 mm hollow Russell-Taylor nail. Both nail systems were interlocked proximally and distally. Following fixation, the specimens were loaded in axial, torsional, and cyclical axial modes to calculate construct stiffness and irreversible (plastic) deformation., Results: The mean axial stiffness for the SIGN nail constructs was 47% higher than mean stiffness for the RT nail constructs (p<0.001). The difference in torsional stiffness was not statistically significant. However, the SIGN group demonstrated 159% more irreversible deformation than the Russell-Taylor group (p=0.006) for the loading parameters studied., Conclusion: The SIGN tibial nail, despite its slightly smaller diameter, can provide similar construct stiffness and stability, when compared to a larger hollow nail for stabilisation of tibial shaft fractures., (2010 Elsevier Ltd. All rights reserved.)

Objectives: Lateral locked plating for proximal tibial fractures with metaphyseal disruption provides a biomechanically stable and biologically favorable alternative to conventional medial/lateral plate fixation. New polyaxial screw technology incorporates expanding screw bushings, allowing variable angle screw placement, while providing angular stability. We hypothesize that polyaxial locking plates will exhibit comparable stiffness, strength to failure, and resistance to plastic deformation to conventional locking plates in a proximal tibial gap model., Methods: We stabilized extra-articular metaphyseal gap osteotomies in synthetic composite tibiae with dual medial and lateral plating, Less Invasive Stabilization System (LISS) plates, 4.5-mm proximal tibial lateral locking plates with (LP+) and without (LP-) angled screws, and 4.5-mm polyaxial locking plates with (PA+) and without (PA-) angled screws. All were tested with cyclic, ramped, and axial loading to failure., Results: No plates demonstrated screw failure before plate failure. Dual-plate constructs did not fail. All lateral plates failed at the osteotomy. LP- failed at low load. PA+ was significantly stiffer (165 +/- 17 N/mm) with greater load to failure (711 +/- 23 N) than all other constructs (PA-: 56 +/- 6 N/mm, 617 +/- 33 N; LP+: 137 +/- 23 N/mm, 488 +/- 39 N; LISS: 76 +/- 5 N/mm, 656 +/- 39 N). PA+ had significantly less plastic deformation (12.1 +/- 0.8 mm) than LP+ (13.4 +/- 3.7 mm), but more than PA- (5.8 +/- 1.2 mm) and LISS (3.9 +/- 0.6 mm). PA- did not differ significantly from LISS in any parameter., Conclusions: This study demonstrates that this unique polyaxial locking plate mechanism, when tested in various constructs, exhibits similar biomechanical performance regarding stiffness, strength to failure, and resistance to plastic deformation when compared with uniaxial locking plates. The polyaxial locking plate with an angled screw was stiffest and had the greatest load to failure. The polyaxial locking plate alone tested similar to the LISS. In addition, the benefit of the angled screw for biomechanical stability is demonstrated.