Effects of Fibular Plate Fixation on Ankle Stability in a Weber B Fracture Model With Partial Deltoid Ligament Sectioning.

BACKGROUND: Weber B fractures with concomitant deltoid ligament injury have traditionally been operated with open reduction and internal fixation of the fibular fracture. More recently, clinical studies have suggested that some fractures have concomitant partial deltoid ligament injury with the deep posterior tibiotalar ligament intact (SER4a), allowing for nonoperative treatment in this subgroup. This study explores whether plate fixation of the fibula improves ankle stability in an SER4a injury model. And if so, does it restore native ankle stability? METHODS: Fifteen cadaver ankle specimens were tested in 3 states using an industrial robot: intact joint, SER4a models without plate fixation of the fibula, and SER4a models with plate fixation of the fibula. The robot measured ankle stability in lateral translation, valgus, and internal and external rotation in 3 talocrural joint positions: 10 degrees dorsiflexion, neutral, and 20 degrees plantar flexion. Furthermore, fluoroscopic mortise view radiographs were taken to measure isolated talar shift and talar tilt. RESULTS: The talar shift and tilt tests showed no differences between the SER4a injury model with and without fibular plate fixation at neutral ankle position with a mean difference of -0.16 mm (95% CI -0.33 to 0.01 mm, P = .071) for talar shift and -0.15 degrees (95% CI -0.01 to 0.30 degrees, P = .068) for talar tilt. However, plate fixation increased external rotation stability, with mean improvements ranging from -7.43 to -9.52 degrees (P < .001 for all comparisons), but did not restore intact ankle stability. For internal rotation, plate fixation resulted in minor differences. CONCLUSION: The results of this suggest that plate fixation of the fibular fracture primarily improves external rotation stability but does not substantially improve lateral translation, valgus, or internal rotation stability in SER4a injury models. In this robotic cadaver model, fibular plate fixation did not fully restore intact ankle stability after simulated SER4a injury. CLINICAL RELEVANCE: This study offers insights into the effects of fibular plate fixation on Weber B/SER4a injury models and may assist informed decisions when selecting treatments for these types of fractures.

Effects of Progressive Deltoid Ligament Sectioning on Weber B Ankle Fracture Stability.

BACKGROUND: Conventionally, transsyndesmotic fibula fractures with concomitant signs of deltoid ligament injury have been considered unstable and thus treated operatively. Recent studies have indicated that partial deltoid ligament rupture is common and may allow for nonoperative treatment of stress-unstable ankles if normal tibiotalar alignment is obtained in the weightbearing position. Biomechanical support for this principle is scarce. The purpose of this study was to evaluate the biomechanical effects of gradually increasing deltoid ligament injury in transsyndesmotic fibula fractures. METHODS: Fifteen cadaveric ankle specimens were tested using an industrial robot. All specimens were tested in 4 states: native, SER2, SER4a, and SER4b models. Ankle stability was measured in lateral translation, valgus, and internal and external rotation stress in 3 talocrural joint positions: 20 degrees plantarflexion, neutral, and 10 degrees dorsiflexion. Talar shift and talar valgus tilt in the talocrural joint was measured using fluoroscopy. RESULTS: In most tests, SER2 and SER4a models resulted in a small instability increase compared to native joints and thus were deemed stable according to our predefined margins. However, SER4a models were unstable when tested in the plantarflexed position and for external rotation in all positions. In contrast, SER4b models had large-magnitude instability in all directions and all tested positions and were thus deemed unstable. CONCLUSION: This study demonstrated substantial increases in instability between the SER4a and SER4b states. This controlled cadaveric simulation suggests a significant ankle-stabilizing role of the deep posterior deltoid after oblique transsyndesmotic fibular fracture and transection of the superficial and anterior deep deltoid ligaments. CLINICAL RELEVANCE: The study provides new insights into how the heterogenicity of deltoid ligament injuries can affect the natural stability of the ankle after Weber B fractures. These findings may be useful in developing more targeted and better treatment strategies.