Biomechanical Analysis of a Novel Double-Point Fixation Method for Displaced Intra-Articular Calcaneal Fractures.

The development of minimally invasive procedures and implant materials has improved the fixation strength of implants and is less traumatic in surgery. The purpose of this study was to propose a novel "double-point fixation" for calcaneal fractures and compare its biomechanical stability with the traditional "three-point fixation." A three-dimensional finite element foot model with a Sanders type IIIAB calcaneal fracture was developed based on clinical images comprising bones, plantar fascia, ligaments, and encapsulated soft tissue. Double-point and three-point fixation resembled the surgical procedure with a volar distal radius plate and calcaneal locking plate, respectively. The stress distribution, fracture displacement, and change of the Böhler angle and Gissane's angle were estimated by a walking simulation using the model, and the predictions between the double-point and three-point fixation were compared at heel-strike, midstance, and push-off instants. Double-point fixation demonstrated lower bone stress (103.3 vs. 199.4 MPa), but higher implant stress (1,084.0 vs. 577.9 MPa). The model displacement of double-point fixation was higher than that of three-point fixation (3.68 vs. 2.53 mm). The displacement of the posterior joint facet (0.127 vs. 0.150 mm) and the changes of the Böhler angle (0.9° vs. 1.4°) and Gissane's angle (0.7° vs. 0.9°) in double-point fixation were comparably lower. Double-point fixation by volar distal radius plates demonstrated sufficient and favorable fixation stability and a lower risk of postoperative stress fracture, which may potentially serve as a new fixation modality for the treatment of displaced intra-articular calcaneal fractures.

Fracture mapping of complex intra-articular calcaneal fractures.

BACKGROUND: Intra-articular calcaneal fracture remains challenging to manage. Computed tomography and fracture mapping are useful for the diagnosis and treatment of calcaneal fractures. The aim of the present study was to characterize calcaneal fracture patterns using fracture mapping. METHODS: Sixty-two calcaneal fractures were retrospectively included in the study. For each case, the fracture was simulated reduction manually. The fracture lines and zones of comminution were graphically superimposed onto an intact calcaneal template to identify fracture patterns. Major fracture lines and comminution were assessed by focusing on the posterior joint facet, medial wall, lateral wall, sustentaculum tali, and anterior process. RESULTS: The fracture lines were mostly concentrated on the area anterior to the posterior joint facet and extended medially. The longitudinal lines ran posteriorly from the angle of Gissane, and separated the sustentaculum tali and medial wall from the calcaneal tuberosity. In the lateral wall, the fracture lines extended posteriorly with some branches to the bottom of the calcaneus. No fracture lines passed through the sustentaculum tali. Fracture lines of the posterior tuberosity and anterior process were rare. CONCLUSIONS: Calcaneal fracture lines follow characteristic patterns, which are closely related to the bone structure and fracture mechanism. These fracture patterns will aid clinicians choose surgical approach and fixations in the treatment of calcaneal fractures.

Finite element method based parametric study of Gastrocnemius-soleus recession: implications to the treatment of midfoot-forefoot overload syndrome.

Gastrocnemius-soleus recession has been used to treat midfoot-forefoot overload syndrome and plantar fasciitis induced by equinus of the ankle joint. A controlled and selective amount of recession is imperative to maintain muscle strength and stability. The objective of this study was to conduct a parametric study to quantify the relationship between the level of recession and plantar fascia stress. A finite element model of the foot-ankle-shank complex was reconstructed from magnetic resonance and computed tomography images of a 63-year-old normal female. The model was validated by comparing modeled stresses to the measured plantar pressure distribution of the model participant during balanced standing. The midstance and push-off instants of walking stance were simulated with different levels and combinations of gastrocnemius-soleus recession resembled by different amounts of muscle forces. Halving the muscle forces at midstance reduced the average plantar fascia stress by a quarter while reducing two-third of the muscle forces at push-off reduced the average fascia stress by 18.2%. While the first ray of the plantar fascia experienced the largest stress among the five fasciae, the stress was reduced by 77.8% and 16.9% when the load was halved and reduced by two-third at midstance and push-off instants, respectively. Reduction in fascia stress implicates a lower risk of plantar fasciitis and other midfoot-forefoot overload syndromes. The outcome of this study can aid physicians to determine the amount of gastrocnemius-soleus recession towards patients with vdifferent levels of plantar fascia overstress. A detailed three-dimensional modelling on the plantar fascia is warranted in future study.

Biomechanical analysis of minimally invasive crossing screw fixation for calcaneal fractures: Implications to early weight-bearing rehabilitation.

BACKGROUND: Minimally invasive fixation using crossing screws was believed to produce satisfactory clinical outcome whereas its stability in early weight-bearing remained controversial. This study aimed to analyze the biomechanical stability of minimally invasive fixation during balanced standing and walking stance, and provide evidence for early rehabilitation. METHODS: A finite element model of foot-ankle-shank complex was reconstructed based on computed tomography and magnetic resonance images, and validated by plantar pressure of the model participant. A Sanders III calcaneal fracture was created on the model, and then fixed using crossing screws. The predicted stress distribution, fracture displacement, Bohler's angle and Gissane's angle were compared between the intact calcaneus and fracture model with the fixation. FINDINGS: Postoperatively, the concentrated stress appeared at the junction of the calcaneus and its surrounding tissues (especially Achilles tendon, plantar fascia and ligaments) during standing and walking stances, and the stress exceeded the yield strength of trabecular bone. The longitudinal screws sustained the highest stresses and concentrated at the tips and the calcaneal tuberosity junction. The displacement of posterior joint facet, Bohler's angle, and Gissane's angle were within the acceptable range either standing or walking after the fixation. INTERPRETATION: Early weight-bearing standing and walking after minimally invasive fixation may cause high stress concentration thereby induce calcaneus stress fractures and other complications like plantar fasciitis and heel pain, so it should not be supported. The peri-calcaneus tendons, i.e., Achilles tendon and plantar fascia, play key roles in the stabilization of the calcaneal fracture after operation.