Acute Deltoid Injury in Ankle Fractures: A Biomechanical Analysis of Different Repair Constructs.

BACKGROUND: The importance of the deltoid ligament in the congruency and coupling of the tibiotalar joint is well known. The current trend is to repair it in cases of acute injuries in the context of ankle fractures; however, there is limited information on how it should be reconstructed. The objective of this study was to compare different deltoid ligament repair types in an ankle fracture cadaveric model. METHODS: Sixteen cadaveric foot-ankle-distal tibia specimens were used. All samples were prepared as a supination external rotation ankle fracture model. Axial load and cyclic axial rotations were applied on every specimen using a specifically designed frame. This test was performed without deltoid injury, with deltoid injury, and after repair. The reconstruction was performed in 4 different ways (anterior, posterior, middle, and combined). Medial clear space (MCS) was measured for each condition on simulated weightbearing (WB) and gravity stress (GS) radiographs. Reflective markers were used in tibia and talus, registering the kinematics through a motion analysis system to record the tibiotalar uncoupling. RESULTS: After deltoid damage, in all cases the MCS increased significantly on GS radiographs, but there was no increase in the MCS on WB radiographs. After repair, in all cases, the MCS was normalized. Kinematically, after deltoid damage, the tibiotalar uncoupling increased significantly. All isolated repairs achieved a similar tibiotalar uncoupling value as its baseline condition. The combined repair resulted in a significant decrease in tibiotalar uncoupling. CONCLUSION: Our results show that deltoid repair recovers the tibiotalar coupling mechanism in an ankle fracture model. Isolated deltoid repairs recovered baseline MCS and tibiotalar uncoupling values. Combined repairs may lead to overconstraint, which could lead to postoperative stiffness. Clinical studies are needed to prove these results and show clinically improved outcomes. CLINICAL RELEVANCE: This study helps in finding the optimum deltoid repair to use in an acute trauma setting.

Biomechanical Cadaveric Evaluation of the Role of Medial Column Instability in Hallux Valgus Deformity.

BACKGROUND: Medial column instability is a frequent finding in patients with flatfeet and hallux valgus, within others. The etiology of hallux valgus is multifactorial, and medial ray axial rotation has been mentioned as having an individual role. Our objective was to design a novel cadaveric foot model where we could re-create through progressive medial column ligament damage some components of a hallux valgus deformity. METHODS: Ten fresh-frozen lower leg specimens were used, and fluorescent markers were attached in a multisegment foot model. Constant axial load and cyclic tibial rotation (to simulate foot pronation) were applied, including pull on the flexor hallucis longus tendon (FHL). We first damaged the intercuneiform (C1-C2) ligaments, second the naviculocuneiform (NC) ligaments, and third the first tarsometatarsal ligaments, leaving the plantar ligaments unharmed. Bony axial and coronal alignment was measured after each ligament damage. Statistical analysis was performed. RESULTS: A significant increase in pronation of multiple segments was observed after sectioning the NC ligaments. Damaging the tarsometatarsal ligament generated small supination and varus changes mainly in the medial ray. No significant change was observed in axial or frontal plane alignment after damaging the C1-C2 ligaments. The FHL pull exerted a small valgus change in segments of the first ray. DISCUSSION: In this biomechanical cadaveric model, the naviculocuneiform joint was the most important one responsible for pronation of the medial column. Bone pronation occurs along the whole medial column, not isolated to a certain joint. Flexor hallucis longus pull appears to play some role in frontal plane alignment, but not in bone rotation. This model will be of great help to further study medial column instability as one of the factors influencing medial column pronation and its relevance in pathologies like hallux valgus. CLINICAL RELEVANCE: This cadaveric model suggests a possible influence of medial column instability in first metatarsal pronation. With a thorough understanding of a condition's origin, better treatment strategies can be developed.