English
Views: 0 Author: Site Editor Publish Time: 2026-05-28 Origin: Site
Calcaneal fractures are among the most common fractures of the foot and are typically caused by high-energy trauma, including motor vehicle accidents and falls from height. As the calcaneus is the primary weight-bearing bone of the hindfoot, achieving stable fixation is critical for restoring foot function.
However, the optimal treatment strategy for calcaneal fractures remains controversial. In recent years, minimally invasive orthopedic techniques have gained increasing popularity. Among them, percutaneous screw fixation has gradually become an important option for treating calcaneal fractures due to its advantages of reduced soft tissue damage, faster recovery, and lower complication rates.
Multiple clinical studies have confirmed that percutaneous screw fixation can achieve fixation strength and clinical outcomes comparable to plate fixation. Recent meta-analyses further demonstrate that screw fixation offers additional benefits, including shorter operative time and a lower incidence of incision-related complications.
This study, published in the journal BMC Surgery, was conducted by the team from the First Affiliated Hospital of Chongqing Medical University. The research focused on identifying the optimal longitudinal screw trajectory for Sanders Type II and Type III calcaneal fractures treated with percutaneous screw fixation.
Using finite element analysis (FEA), the study explored the most biomechanically stable fixation strategy to provide theoretical guidance for clinical treatment.
Percutaneous screw fixation has become an increasingly important surgical technique for displaced intra-articular calcaneal fractures because of its minimally invasive nature and rapid postoperative recovery.
Previous clinical studies have shown that this technique provides biomechanical strength and clinical efficacy comparable to plate fixation while also reducing surgical time and soft tissue complications.
Despite these advantages, there is still no consensus regarding the optimal screw trajectory required to achieve maximum biomechanical stability. Existing studies have not fully integrated the anatomical characteristics of the calcaneus with fracture injury mechanisms.
The purpose of this study was to determine the optimal longitudinal screw trajectory for Sanders Type II (IIA, IIB, IIC) and Type III (IIIAB, IIIAC, IIIBC) calcaneal fractures using finite element analysis, thereby improving biomechanical stability after internal fixation.
Using CT data from a healthy 54-year-old male volunteer, the researchers reconstructed a three-dimensional calcaneal model with Mimics, Geomagic Wrap, and SolidWorks software.
Six joint-depression fracture models were created according to the Sanders classification system.
Four screw fixation configurations were designed and divided into two study groups and two control groups.
All groups used:
Two 3.5 mm transverse screws
Fixation from the calcaneal tuberosity to the sustentaculum tali
The major difference involved the trajectory of two 5.5 mm longitudinal screws.
▲Based on the Sanders classification system, the fracture models a–f correspond to Sanders types IIA, IIB, IIC, and types IIIAB, IIIAC, and IIIBC, respectively.
Medial longitudinal screw fixation from the calcaneal tuberosity to the sustentaculum tali
Group 1: Non-crossed screw insertion
Group 2: Crossed screw insertion
Longitudinal screws fixed from the calcaneal tuberosity to the anterior calcaneal process
Control Group 1: Parallel insertion
Control Group 2: Crossed insertion
▲Four screw orientation design diagrams, where a and e represent Study Group 1 (two longitudinal screws inserted in a non-crossed manner), b and f represent Study Group 2 (two longitudinal screws inserted in a crossed manner), c and g represent Control Group 1 (two longitudinal screws inserted parallel into the anterior calcaneal process), and d and h represent Control Group 2 (two longitudinal screws inserted in a crossed manner from the calcaneal tuberosity).
ANSYS software was used for biomechanical simulation.
Key settings included:
Mesh size finalized at 1 mm after convergence validation
Simulation of physiological standing loads
420 N and 200 N forces applied to the posterior and middle subtalar joint facets
Calcaneocuboid joint surface and posterior tuberosity fixed
Screw-fracture interfaces defined as bonded contact
Friction coefficient between fracture fragments set at 0.2
The materials were simplified as homogeneous elastic bodies with predefined elastic modulus and Poisson’s ratio values for:
Screws
Cortical bone
Cancellous bone
▲Schematic diagram of model constraints and loads, showing the positions of fixed supports and the locations and magnitudes of applied external forces in the calcaneal finite element model.
Preliminary stress analysis under standing conditions demonstrated that stress was primarily concentrated in the anteromedial calcaneus, especially around:
The sustentaculum tali
The anterior calcaneal process
These findings provided important anatomical and biomechanical guidance for screw trajectory design.
▲Pre-experimental stress distribution diagram, showing that the stress on the calcaneus is mainly distributed in its anteromedial region.
Across all six fracture models:
The study groups showed lower maximum calcaneal stress
Fracture fragment displacement was smaller than in the control groups
The differences were particularly significant in:
Sanders IIC
Sanders IIIAC
Sanders IIIBC fractures
No significant differences were observed between crossed and non-crossed screw configurations in the study groups, indicating that screw crossing had minimal influence on stress distribution and fragment displacement.
▲Peak stress diagram of the calcaneus (unit: MPa), used to compare the differences in maximum stress borne by the calcaneus across different fracture types and fixation groups.
▲Peak displacement diagram of fracture fragments (unit: mm), used to compare the maximum displacement values of fracture fragments across different fracture types and fixation groups.
Screw stress in the study groups was higher than in the control groups
Minimal differences in screw stress among all fixation groups
Screw stress in the study groups was lower than in the control groups
Stress levels remained well below the fixation failure threshold of 600 MPa
Importantly, the medial longitudinal screw in the study groups demonstrated higher stress-bearing capability, suggesting a more effective load-sharing mechanism and superior biomechanical performance.
▲Peak stress diagram of screws (unit: MPa), showing the maximum stress experienced by screws in each fixation group under different fracture types.
▲Screw stress distribution diagrams of different internal fixation methods in six fracture models, where a–d correspond to type IIA fractures, e–h correspond to type IIB fractures, i–l correspond to type IIC fractures, m–p correspond to type IIIAB fractures, q–t correspond to type IIIAC fractures, and u–x correspond to type IIIBC fractures, showing the screw stress distribution under the four screw fixation methods, respectively.
▲Displacement cloud diagrams between fracture fragments, where a–d, e–h, i–l, m–p, q–t, and u–x correspond to the four screw fixation methods for Sanders types IIA, IIB, IIC, and types IIIAB, IIIAC, IIIBC calcaneal fractures, respectively, showing the distribution of inter-fragmentary displacement.
▲Schematic diagram of longitudinal screw fixation of the sustentaculum tali fragment in Sanders type II calcaneal fractures, where a–d correspond to Sanders type IIA calcaneal fractures, e–h correspond to Sanders type IIB calcaneal fractures, and i–l correspond to Sanders type IIC calcaneal fractures; a, e, and i represent the study group, b, f, and j represent Control Group 1, c, g, and k represent Control Group 2, and d, h, and l represent Control Group 3. The diagram shows that the longitudinal screws in Control Group 2 and Control Group 3 lost their fixation effect on the sustentaculum tali, while in Sanders type IIC calcaneal fractures, the longitudinal screws in all four groups achieved corresponding fixation.
The study revealed that the size of the sustentaculum tali fracture fragment significantly affected fixation performance.
In fracture types such as:
Sanders IIC
Sanders IIIAC
Sanders IIIBC
Longitudinal screws needed to engage the sustentaculum tali directly to maintain fixation stability.
Fixation directed only toward the anterior process resulted in significantly increased fracture fragment displacement.
In Sanders IIA and IIB fractures:
Differences between screw trajectories were less pronounced
The optimal longitudinal screw configuration for Sanders Type II and III calcaneal fractures was identified as:
A lateral longitudinal screw extending from the calcaneal tuberosity to the anterior calcaneal process
A medial longitudinal screw extending from the calcaneal tuberosity along the medial wall to the sustentaculum tali
This configuration provided:
The best biomechanical stability
Reduced stress concentration
Lower fracture fragment displacement
Improved load distribution across the calcaneus
Another study conducted by the team at Shanghai Sixth People’s Hospital focused specifically on the biomechanical stability of percutaneous screw fixation for Sanders IIB intra-articular calcaneal fractures.
This research combined:
Three-dimensional finite element analysis
Clinical validation
to identify the optimal screw placement strategy for minimally invasive fixation.
Displaced intra-articular calcaneal fractures with more than 2 mm displacement generally require surgical treatment.
Traditional extensile lateral open reduction and internal fixation (ORIF) techniques are associated with high rates of soft tissue complications, including:
Infection
Skin necrosis
Wound healing problems
Percutaneous screw fixation has emerged as a reliable minimally invasive alternative, especially for Sanders IIB fractures.
However, there is still no consensus regarding the ideal screw configuration for:
Tongue-type fractures
Joint depression-type fractures
The study aimed to compare the biomechanical stability of different screw fixation strategies using three-dimensional finite element analysis.
CT scans of healthy adult calcanei were imported into Mimics software to establish Sanders IIB fracture models.
Two fracture subtypes were created:
Tongue-type fractures
Joint depression-type fractures
Each subtype included:
One lateral plate fixation group
Five percutaneous screw fixation groups
The fracture models were simplified into four major fragments:
Anterior fragment
Sustentaculum tali fragment
Posterior articular fragment
Posterior tuberosity fragment
▲Sanders Type IIB calcaneal fracture model, including two subtypes: tongue-type fracture (A) and depressed-type fracture (B). The fracture model is simplified into four main bone fragments: the anterior bone fragment (Fragment 1, orange area), the sustentaculum tali fragment (Fragment 2, purple area), the posterior articular facet fragment (Fragment 3, green area), and the posterior tuberosity fragment (Fragment 4, yellow area).
Physiological loading conditions were simulated by applying combined stress to:
The posterior subtalar joint
The middle subtalar joint
The Achilles tendon insertion
Abaqus software was used to evaluate:
Maximum displacement
von Mises stress
Implant stress distribution
▲Percutaneous screw internal fixation protocols A1–A5 for the Sanders Type IIB tongue-type fracture model.
▲Percutaneous screw internal fixation protocols B1–B5 for the Sanders Type IIB depressed-type fracture model.
The A4 fixation configuration, which included a medial supporting screw, demonstrated the best performance.
Overall calcaneal displacement: 0.22 mm
Internal fixation displacement: 0.14 mm
Calcaneal stress: 26.83 MPa
Implant stress: 72.97 MPa
Stress distribution was more balanced, and fixation stability was superior.
▲ Stress nephograms and bone fragment displacement nephograms of internal fixation under identical loading conditions for each tongue-type fracture model.
The B2 fixation configuration, which also included medial support screw fixation, showed the best biomechanical performance.
Maximum calcaneal stress: 22.04 MPa
Maximum implant stress: 41.14 MPa
Minimal overall displacement: 0.14 mm
▲ Stress nephograms and bone fragment displacement nephograms of internal fixation under identical loading conditions for each depressed-type fracture model.
Percutaneous screw fixation is a reliable minimally invasive treatment option for Sanders IIB calcaneal fractures.
Its biomechanical stability is comparable to traditional plate fixation while significantly reducing soft tissue complications.
The most effective fixation strategies were:
A4 configuration for tongue-type fractures
B2 configuration for joint depression-type fractures
Both configurations incorporated medial supporting screws that improved:
Varus resistance
Calcaneal height maintenance
Stress distribution
Fragment stability
The study emphasized that screw placement should follow the biomechanical principle of:
Stabilizing the sustentaculum tali
Stabilizing the posterior tuberosity
Stabilizing the anterior calcaneus
Supporting the posterior articular surface
Special attention should be paid to:
Sustentaculum tali fixation
Medial column support
5.0 mm screws for maintaining calcaneal length and height
3.5 mm screws for fixation of the posterior articular surface
