Internal architecture of the calcaneus: implications for calcaneus fractures

Trabecular bone variation in the gorilla calcaneus

OBJECTIVES

Calcaneal external shape differs among nonhuman primates relative to locomotion. Such relationships between whole-bone calcaneal trabecular structure and locomotion, however, have yet to be studied. Here we analyze calcaneal trabecular architecture in Gorilla gorilla gorilla, Gorilla beringei beringei, and G. b. graueri to investigate general trends and fine-grained differences among gorilla taxa relative to locomotion.

MATERIALS AND METHODS

Calcanei were micro-CT scanned. A three-dimensional geometric morphometric sliding semilandmark analysis was carried out and the final landmark configurations used to position 156 volumes of interest. Trabecular thickness (Tb.Th), trabecular spacing (Tb.Sp), and bone volume fraction (BV/TV) were calculated using the BoneJ plugin for ImageJ and MATLAB. Non-parametric MANOVAs were run to test for significant differences among taxa in parameter raw values and z-scores. Parameter distributions were visualized using color maps and summarized using principal components analysis.

RESULTS

There are no significant differences in raw BV/TV or Tb.Th among gorillas, however G. b. beringei significantly differs in z-scores for both parameters (p = <0.0271). All three taxa exhibit relatively lower BV/TV and Tb.Th in the posterior half of the calcaneus. This gradation is exacerbated in G. b. beringei. G. b. graueri significantly differs from other taxa in Tb.Sp z-scores (p < 0.001) indicating a different spacing distribution.

DISCUSSION

Relatively higher Tb.Th and BV/TV in the anterior calcaneus among gorillas likely reflects higher forces associated with body mass (transmitted through the subtalar joint) relative to forces transferred through the posterior calcaneus. The different Tb.Sp pattern in G. b. graueri may reflect proposed differences in foot positioning during locomotion.

3D mapping of intra-articular calcaneal fractures

To determine the pattern of intra-articular calcaneal fractures (ICFs) by a three-dimensional (3D) mapping and determine whether there were consistent fracture patterns and comminution zones. In this study, 67 patients with ICFS by CT scan were included. The calcaneal fractures fragments in CT were multiplanar reconstructed and virtual reduced. 3D heat mapping was subsequently created by graphically superimposing all fracture lines onto a standard calcaneal template. The cohort included 26 (38.8%) left calcaneal fractures, 27 (40.30%) right calcaneal fractures, and 14 (20.9%) cases with bilateral fractures. Comminuted fractures accounted for 92.5%. Sagittal 3D mapping shows that the fracture line is mainly concentrated at the critical angle of Gissane and extending rear to the posterior of the tuberosity of the lateral wall and the anterior of the medial process of the calcaneus tuberosity but with more significant variation in the medial wall. The average angle of fracture lines concerning the long calcaneal axis (LCA) was 29.1° and 19.2° in the lateral and medial walls. Axial 3D mapping shows that fracture lines were primarily concentrated in the anterior area to the posterior joint facet and extending along the rear joint facet and calcaneus sulcus to the posteriorly of the tuberosity. The mean angle of fracture lines concerning the LAC was 11° in the axial wall. Our data provided elucidated that ICFs have consistent characteristic fracture patterns and comminution zones. This study provides visual guidelines for understanding fracture morphology, which may assist with fracture classification, preoperative planning, development of fixation concepts.

Percutaneous fixation of intraarticular joint-depression calcaneal fractures with different screw configurations - a biomechanical human cadaveric analysis

PURPOSE

The aim of this study was to assess the biomechanical performance of different screw configurations for fixation of Sanders type II B joint-depression calcaneal fractures.

METHODS

Fifteen human cadaveric lower limbs were amputated and Sanders II B fractures were simulated. The specimens were randomized to three groups for fixation with different screw configurations. The calcanei in Group 1 were treated with two parallel longitudinal screws, entering superiorly the Achilles tendon insertion, and two screws fixing the intraarticular posterior facet fracture line. In Group 2 two screws entered the tuberosity inferiorly to the Achilles tendon insertion and two transverse screws fixed the posterior facet. In Group 3 two screws were inserted along the bone axis, one transverse screw fixed the posterior facet and one oblique screw was inserted from the posteroplantar part of the tuberosity supporting the posterolateral part of the posterior facet. All specimens were biomechanically tested to failure under progressively increasing cyclic loading.

RESULTS

Initial stiffness did not differ significantly between the groups, P = 0.152. Cycles to 2 mm plantar movement were significantly higher in both Group 1 (15,847 ± 5250) and Group 3 (13,323 ± 4363) compared with Group 2 (4875 ± 3480), P ≤ 0.048. No intraarticular displacement was observed in any group during testing.

CONCLUSIONS

From a biomechanical perspective, posterior facet support by means of buttress or superiorly inserted longitudinal screws results in less plantar movement between the calcaneal tuberosity and the anterior fragments. Inferiorly inserted longitudinal screws are associated with bigger interfragmentary movements.

Calcaneal fracture maps and their determinants

Background

Calcaneal fractures are associated with numerous complications and a poor prognosis with significant long-term quality-of-life issues, regardless of treatment. Therefore, in-depth research into the underlying mechanism of calcaneal fracture is still of great interest, with the goal of improving treatment for patients suffering from this condition. This study aimed to investigate the relationship between the distribution of calcaneal fracture lines and their determinants, especially those related to the internal structure of the calcaneus. This goal was achieved by fracture maps created by copying and stacking fracture lines as viewed from six surfaces of the calcaneus.

Methods

A total of 210 consecutive patients with 226 calcaneal fractures were retrospectively analyzed. Fracture lines were copied from a reduced 3D calcaneal fracture model and stacked on calcaneal templates to generate fracture maps. The stacked images of six calcaneus surfaces were also converted into spectrograms with MATLAB to highlight the fracture frequency at specific locations.

Results

There were four concentrated bands of fracture lines and two fracture hot spots on the superior surface. Three dense bands of fractures were observed on the medial surface, and four fracture bands were observed lateral to the calcaneus. Vertical fracture lines dominated the anterior calcaneal fracture map. On the posterior surface, the fracture lines appeared to be centered superiorly. All fracture locations coincided with the interfaces between the trabecular groups.

Conclusions

The fracture maps showed fracture patterns and recurrent fracture zones on all calcaneal surfaces. The shape of the talus and calcaneus and the architecture within the calcaneus, especially the arrangement of the trabeculae, are essential factors for calcaneal fractures.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-02930-y.

How Does Mechanism of Injury Relate to Similar Fracture Patterns in Bilateral Displaced Intra-articular Calcaneal Fractures?

Several biomechanical/cadaver studies have established a correlation between mechanism of injury and fracture classification in calcaneal fractures. However, this has never been backed up by clinical studies. In this study, the hypothesis is tested whether the alleged similar mechanism of injury for both feet in bilateral calcaneal fractures leads to similar fracture types. In this retrospective cross-sectional cohort study, patients with unilateral and bilateral calcaneal fractures treated between 2000 and 2017 were classified according to Essex-Lopresti and Sanders. Positive predictive values were computed, signifying the chance that the fracture type in the left foot corresponded to that in the right foot. These were compared to the a priori chance of a fracture type (percentage of fracture type in unilateral fractures) by constructing 95% confidence intervals of the positive predictive value of each fracture type. Of the 451 patients, 413 (91.6%) had unilateral and 38 (8.4%) bilateral calcaneal fractures. Mechanisms of injury were similar for uni- and bilateral fractures. Using the Essex-Lopresti fracture classification, 34 cases (90%) had the same classification in both feet, compared with 24 (63%) in the Sanders classification. The chance of a fracture type in the left, with the right foot as reference, was significantly larger than expected from a priori chance in the unilateral population. This leads to a new hypothesis, that, more than mechanism of injury, the magnitude of the impact and the position of the foot are important in predicting fracture classification in the calcaneus.

An Experimentally Validated Finite Element Model of the Lower Limb to Investigate the Efficacy of Blast Mitigation Systems

Improvised explosive devices (IEDs) used in the battlefield cause damage to vehicles and their occupants. The injury burden to the casualties is significant. The biofidelity and practicality of current methods for assessing current protection to reduce the injury severity is limited. In this study, a finite-element (FE) model of the leg was developed and validated in relevant blast-loading conditions, and then used to quantify the level of protection offered by a combat boot. An FE model of the leg of a 35 years old male cadaver was developed. The cadaveric leg was tested physically in a seated posture using a traumatic injury simulator and the results used to calibrate the FE model. The calibrated model predicted hindfoot forces that were in good correlation (using the CORrelation and Analysis or CORA tool) with data from force sensors; the average correlation and analysis rating (according to ISO18571) was 0.842. The boundary conditions of the FE model were then changed to replicate pendulum tests conducted in previous studies which impacted the leg at velocities between 4 and 6.7 m/s. The FE model results of foot compression and peak force at the proximal tibia were within the experimental corridors reported in the studies. A combat boot was then incorporated into the validated computational model. Simulations were run across a range of blast-related loading conditions. The predicted proximal tibia forces and associated risk of injury indicated that the combat boot reduced the injury severity for low severity loading cases with higher times to peak velocity. The reduction in injury risk varied between 6 and 37% for calcaneal minor injuries, and 1 and 54% for calcaneal major injuries. No injury-risk reduction was found for high severity loading cases. The validated FE model of the leg developed here was able to quantify the protection offered by a combat boot to vehicle occupants across a range of blast-related loading conditions. It can now be used as a design and as an assessment tool to quantify the level of blast protection offered by other mitigation technologies.

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.

Development of customized finite element models of medial column fixation using an intramedullary beam: A computational sensitivity analysis

Intramedullary beaming is commonly used for medial column arthrodesis to prevent or correct rocker-bottom deformities; however, the biomechanics of these reconstructions have not been rigorously studied. Customized FE models of intramedullary beaming of the medial column were developed and compared to a previous cadaveric study, which resulted in a strong correlation in medial column stiffness (ρ = 0.83, p = .079) and implant failure locations. A design of experiments was performed to quantify the models' sensitivities to varying cortical shell and cartilage thicknesses, cancellous bone and cartilage elastic moduli, and surgical medial column compression distance. Cartilage thickness and cartilage elastic modulus had the largest impact on medial column stiffness and compression distance had the greatest effect on cartilage contact area. Cortical shell thickness and cancellous bone properties did not have a significant effect on the measured parameters for the values tested. Overall, the FE models exhibited behavior that is consistent with known mechanical principles related to bending and composite structures as well as the experimental results. This study elucidates the effects of varying commonly assumed model parameters that can aid future studies aimed at screening implant designs.

Using point clouds to investigate the relationship between trabecular bone phenotype and behavior: An example utilizing the human calcaneus

OBJECTIVES

The objective of this study is to demonstrate a new method for analyzing trabecular bone volume fraction and degree of anisotropy in three dimensions.

METHODS

We use a combination of automatic mesh registration, point-cloud correspondence registration, and P-value corrected univariate statistical tests to compare bone volume fraction and degree of anisotropy on a point by point basis across the entire calcaneus of two human groups with different subsistence strategies.

RESULTS

We found that the patterns of high and low bone volume fraction and degree of anisotropy distribution between the Black Earth (hunter-gatherers) and Norris Farms (mixed-strategy agriculturalists) are very similar, but differ in magnitude. The hunter-gatherers exhibit higher levels of bone volume fraction and less anisotropic trabecular bone organization. Additionally, patterns of bone volume fraction and degree of anisotropy in the calcaneus correspond well with biomechanical expectations of relative forces experienced during walking and running.

CONCLUSIONS

We conclude that comparing site-specific, localized differences in trabecular bone variables such as bone volume fraction and degree of anisotropy in three-dimensions is a powerful analytical tool. This method makes it possible to determine where similarities and differences between groups are located within the whole skeletal element of interest. The visualization of multiple variables also provides a way for researchers to see how the trabecular bone variables interact within the morphology, and allows for a more nuanced understanding of how they relate to one another and the broader mechanical environment.

Trabecular health of vertebrae based on anisotropy in trabecular architecture and collagen/apatite micro-arrangement after implantation of intervertebral fusion cages in the sheep spine

Healthy trabecular bone shows highly anisotropic trabecular architecture and the preferential orientation of collagen and apatite inside a trabecula, both of which are predominantly directed along the cephalocaudal axis. This makes trabecular bone stiff in the principally loaded direction (cephalocaudal axis). However, changes in these anisotropic trabecular characteristics after the insertion of implant devices remain unclear. We defined the trabecular architectural anisotropy and the preferential orientation of collagen and apatite as parameters of trabecular bone health. In the present study, we analyzed these parameters after the implantation of two types of intervertebral fusion cages, open and closed box-type cages, into sheep spines for 2 and 4months. Alteration and evolution of trabecular health around and inside the cages depended on the cage type and implantation duration. At the boundary region, the values of trabecular architectural anisotropy and apatite orientation for the closed-type cages were similar to those for isotropic conditions. In contrast, significantly larger anisotropy was found for open-type cages, indicating that the open-type cage tended to maintain trabecular anisotropy. Inside the open-type cage, trabecular architectural anisotropy and apatite orientation significantly increased with time after implantation. Assessing trabecular anisotropy might be useful for the evaluation of trabecular health and the validation and refinement of implant designs.

Avulsion fracture of the posterosuperior tuberosity of the calcaneus managed with lag screw fixation

BACKGROUND

To review the efficacy of lag screw fixation in management of avulsion fracture of the posterosuperior tuberosity of the calcaneus.

METHODS

Since 2002, thirteen patients with displaced fracture of the posterior tuberosity of the calcaneus were treated with emergency reduction of the fracture and lag screw fixation. The medical records and radiographs of the patients were reviewed and the patients were assessed according to the Kerr calcaneal fracture scoring system during the latest follow up.

RESULTS

There was no skin necrosis, but one wound dehisced in a patient with unstable diabetes and hypothyroidism. All fractures healed, but two had separation of the fracture fragments after the plaster was removed, both of them were elderly osteoporotic patients. The overall average calcaneal score was 93 (range, 77-100). The average calcaneal score of the patients with closed reduction was 91 (range, 77-100). The average calcaneal score of the patients with open reduction was 94 (range, 79-100). Complications occurred in seven patients (54%).

CONCLUSIONS

Percutaneous or open reduction of the avulsion fracture of the posterosuperior tuberosity of the calcaneus together with lag screw fixation and equinus short leg cast immobilization can provide good results without skin necrosis. The surgeon should pay attention of the details of the operation and the rehabilitation program in order to minimize the complications.

Calcaneal Fractures in Non-Racing Dogs and Cats: Complications, Outcome, and Associated Risk Factors

OBJECTIVE

To estimate the prevalence of complications and describe the outcome associated with calcaneal fractures in non-racing dogs and in cats.

STUDY DESIGN

Retrospective multicenter clinical cohort study.

ANIMALS

Medical records of client-owned dogs and cats (2004-2013).

METHODS

Medical records were searched and 50 animals with calcaneal fractures were included for analysis. Complications were recorded and an outcome score applied to each fracture. Associations between putative risk factors and both major complications, and final outcome scores were explored.

RESULTS

Complications occurred in 27/50 fractures (61%) including 23 major and 4 minor complications. At final follow-up, 4 animals (10%) were sound, 27 (64%) had either intermittent or consistent mild weight-bearing lameness, 7 (17%) had moderate weight-bearing lameness, and 1 (2%) had severe weight-bearing lameness. Fractures managed using plates and screws had a lower risk of complications than fractures managed using pin and tension band wire, lag or positional screws or a combination of these techniques (Relative risk 0.16, 95% CI 0.02-1.02, P=.052). Non-sighthounds had reduced odds of a poorer outcome score than sighthounds (Odds ratio 0.11, 95% CI 0.02-0.50, P=.005) and fractures with major complications had 13 times the odds of a poorer outcome score (Odds ratio 13.4, 95% CI 3.6-59.5, P<.001).

CONCLUSION

This study reports a high occurrence of complications associated with calcaneal fracture stabilization in non-racing dogs and in cats, and a poorer outcome score was more likely in animals with complications. A more guarded prognosis should be given to owners of non-racing dogs or cats with calcaneal fractures than previously applied to racing Greyhounds with calcaneal fractures.

Measurement of the Human Calcaneus In Vivo Using Ultrasonic Backscatter Spectral Centroid Shift

OBJECTIVES

The aim of this study was to determine the relationship between the backscattered spectral centroid shift and the bone mineral density (BMD) in vivo and investigate the feasibility of using the backscattered spectral centroid shift to characterize the cancellous bone status.

METHODS

Ultrasonic backscatter measurements were performed in vivo on 1216 participants at the right calcaneus using an ultrasonic backscattered bone diagnostic system, and the backscattered spectral centroid shift was calculated at central frequencies of 3.5 and 5.0 MHz. The BMD values were measured at the sites of the lumbar spine and left hip by dual energy x-ray absorptiometry.

RESULTS

The study population included 592 male and 624 female participants aged 20 to 89 years. The correlations between the backscattered spectral centroid shift in the calcaneus and the spine and hip BMD were found to be statistically significant in both the male and female groups (P < .0001). Linear regression showed that the spectral centroid shift at 3.5 MHz had negative correlations with the spine BMD (R = -0.65 for male participants; R = -0.67 for female participants) and hip BMD (R = -0.64 for male participants; R = -0.64 for female participants). The spectral centroid shift at 5.0 MHz was also found to be closely related to the spine BMD (R = -0.68 for male participants; R = -0.68 for female participants) and hip BMD (R = -0.66 for male participants; R = -0.64 for female participants).

CONCLUSIONS

The moderate correlations observed between the spectral centroid shift and the spine and hip BMD demonstrate that the ultrasonic backscattered spectral centroid shift may be a useful measurement for assessment of the cancellous bone status.

Finite Element Analysis of Foot and Ankle Impact Injury: Risk Evaluation of Calcaneus and Talus Fracture

Introduction

Foot and ankle impact injury is common in geriatric trauma and often leads to fracture of rearfoot, including calcaneus and talus. The objective of this study was to assess the influence of foot impact on the risk of calcaneus and talus fracture via finite element analysis.

Methods

A three-dimensional finite element model of foot and ankle was constructed based on magnetic resonance images of a female aged 28. The foot sustained a 7-kg passive impact through a foot plate. The simulated impact velocities were from 2.0 to 7.0 m/s with 1.0 m/s interval.

Results

At 5.0 m/s impact velocity, the maximum von Mises stress of the trabecular calcaneus and talus were 3.21MPa and 2.41MPa respectively, while that of the Tresca stress were 3.46MPa and 2.55MPa. About 94% and 84% of the trabecular calcaneus and talus exceeded the shear yielding stress, while 21.7% and 18.3% yielded the compressive stress. The peak stresses were distributed around the talocalcaneal articulation and the calcaneal tuberosity inferiorly, which corresponded to the common fracture sites.

Conclusions

The prediction in this study showed that axial compressive impact at 5.0 m/s could produce considerable yielding of trabecular bone in both calcaneus and talus, dominantly by shear and compounded with compression that predispose the rearfoot in the risk of fracture. This study suggested the injury pattern and fracture mode of high energy trauma that provides insights in injury prevention and fracture management.

Biomechanical Performance of Lateral Versus Dual Locking Plates for Calcaneal Fractures

Given the high rates of wound complications with a standard lateral extensile incision, small dual incision techniques might result in less soft tissue destruction. The goal of the present study was to compare the biomechanical performance between a single locking plate and a dual locking plating system for an intra-articular calcaneal fracture model. A Sanders IIB type joint depression calcaneal fracture was created in 10 paired, fresh-frozen, cadaveric calcanei (age 47 ± 12, range 35 to 78 years). The calcanei of each pair were randomly assigned for fixation using either a lateral locking reconstruction plate or lateral and medial locking reconstruction plates. The specimens were axially loaded in cyclic fashion for 1000 cycles, followed by load to failure. The relative fragment movement was monitored optically in both the sagittal and the coronal planes. The amount of overall construct displacement increased with cycling, although no difference was found between the plating techniques. For fragment movement during cycling, the lateral joint fragment migrated anteroinferiorly along the fracture line relative to the tuberosity fragment for dual plated specimens by a small, but statistically significant, amount. This same translation was smaller for lateral plated specimens but was not found to be significant. During load to failure testing, no statistically significant differences were found for construct stiffness. A tendency was seen toward more interfragmentary motion in the sagittal plane (lateral joint fragment movement relative to the fracture line), with less movement overall in the coronal plane (anterior fragment translation and twist) for dual plating, although the difference from the lateral plate was not statistically significant. The present study demonstrated that for this calcaneal fracture model, the dual plating technique experienced a small amount of fragment translation during cycling that was significantly different statistically from that with lateral plating but was not clinically relevant. During the load to failure, the dual plating technique was comparable to the lateral plate. Thus, dual plating could be a viable biomechanical option for fracture reduction if avoidance of a large extensile lateral approach associated with lateral plating is warranted.

Mini-open sinus tarsi approach with percutaneous screw fixation of displaced calcaneal fractures: a prospective computed tomography-based study

BACKGROUND

Open reduction and internal fixation (ORIF) of calcaneal fractures using an extended lateral approach results in soft tissue disruption and theoretically subtalar joint stiffness. A minimally invasive sinus tarsi approach for posterior facet exposure and percutaneous screw fixation of the calcaneal body has been implemented. This report details the reduction and stability of the internal fixation resulting from this approach.

METHODS

Twenty-one consecutive patients (18 male, 3 female, 45 ± 16 years) with 22 calcaneal fractures underwent ORIF with minimal exposure through the sinus tarsi for reduction, lateral plate fixation, and percutaneous screw fixation. There were nine Sanders type II fractures and 13 type III fractures. Sixteen fractures had calcaneocuboid joint involvement. Nineteen patients (19 fractures) were available for follow-up (mean, 32 ± 14 months). Two computed tomography scans were obtained on each patient, one immediately postoperatively and one after a minimum of 1 year, to evaluate reduction and fixation stability, respectively. The posterior facet and calcaneocuboid joint were graded excellent, good, fair, or poor, according to articular step, defect, and angulation. Any change was considered loss of stability. Similarly, on a conventional two-dimensional radiograph, more than 5° of Bohler's angle difference was defined as loss of calcaneal height.

RESULTS

Postoperative posterior facet and calcaneocuboid joint reduction was good (step < 1 mm, defect < 5 mm, angulation < 5°) or excellent (no step, defect, angulation) in 14/22 (64%) and 11/16 fractures, respectively. At follow-up, no loss of reduction at the posterior facet and calcaneocuboid joint was noted. More than 5° of Bohler's angle decrease was found in three patients.

CONCLUSION

Even complex calcaneal fractures can be sufficiently exposed by a minimally invasive sinus tarsi approach for anatomic reduction and stable fixation. Most patients had good or excellent functional results, which may have resulted from minimal soft tissue disruption.

Mechanical stress redistribution in the calcaneus after autologous bone harvesting

The calcaneus is a desirable site for harvesting autologous bone for use in foot surgery. However, fracture of the calcaneus is a serious complication associated with bone harvesting from this site. Currently it is unknown how much bone may be safely harvested from the calcaneus without inducing a fracture. The purpose of this study was to investigate the effect of progressive bone removal from the calcaneus onto the mechanical stress redistribution of the foot, and therefore on the increase in fracture risk. Different loads were applied on the talus to evaluate the calcaneus stress distribution at different situations. Because of the potential increase in mechanical stress in the calcaneus, secondary to contraction of the Achilles tendon, we also evaluated the mechanical behavior properties of the foot with increasing traction force in the Achilles tendon. A three-dimensional (3D) finite element (FE) model developed from CT images obtained from a healthy individual was used to compute displacement, tension and compression stresses in six situations, including intact foot, and five depth of the bone block removed, with a maximum depth of 7.5 mm. The results from these simulations indicated that when the maximum load was applied at the Achilles tendon, the tension stress increased from 42.16 MPa in the intact foot to 86.28 MPa with maximum bone harvesting. Furthermore, as the volume of bone extracted from the calcaneus increases, there is a redistribution of stresses that differs significantly from the intact foot. In fact, although the maximum stress was not significantly affected by increasing the volume of bone harvested-except when increasing the Achilles tendon force-, stresses did increase in areas of the calcaneus is vulnerable to injury, leading to an increase in fracture risk.

Biomechanical stability of intramedullary technique for fixation of joint depressed calcaneus fracture

BACKGROUND

Internal fixation of the os calcis is often complicated by prolonged soft tissue management and posterior facet disruption. An ideal calcaneal construct would include minimal hardware prominence, sturdy posterior facet fixation and nominal soft tissue disruption. The purpose of this study was to develop such a construct and provide a biomechanical analysis comparing our technique to a standard internal fixation technique.

METHODS AND MATERIALS

Twenty fresh-frozen cadaver calcanei were used to create a reproducible Sanders type-IIB calcaneal fracture pattern. One calcaneus of each pair was randomly selected to be fixed using our compressive headless screw technique. The contralateral matched calcaneus was fixed with a nonlocking calcaneal plate in a traditional fashion. Each calcaneus was cyclically loaded at a frequency of 1 Hz for 4000 cycles using an increasing force from 250 N to 1000 N. An Optotrak motion capturing system was used to detect relative motion of the three fracture fragments at eight different points along the fracture lines. Horizontal separation and vertical displacement at the fracture lines was recorded, as well as relative rotation at the primary fracture line.

RESULTS

When the data were averaged, there was more horizontal displacement at the primary fracture line of the plate and screw construct compared to the headless screw construct. The headless screw construct also had less vertical displacement at the primary fracture line at every load. On average those fractures fixed with the headless screw technique had less rotation than those fixed with the side plate technique.

CONCLUSION

A new headless screw technique for calcaneus fracture fixation was shown to provide stability as good as, or better than, a standard side plating technique under the axial loading conditions of our model. Although further testing is needed, the stability of the proposed technique is similar to that typically provided by intramedullary fixation.

CLINICAL RELEVANCE

This fixation technique provides a biomechanically stable construct with the potential for a minimally invasive approach and improved post-operative soft tissue healing.

In-vitro comparison of biomechanical efficiency of three cannulated screws for arthrodesis of the hindfoot

BACKGROUND

Sufficient inter-fragmentary compression is helpful to achieve successful bony fusion in hindfoot arthrodesis using internal fixation by screws. Beside bone quality, the design of a screw influences inter-fragmentary compression. Compressive force is achievable for any kind of screw system; however, the primary deformation of the bone is different for the different screw systems. The work necessary to achieve compressive force for primary stability was measured for different screw systems and compared to an AO screw with washer.

MATERIALS AND METHODS

The compressive force was determined as a function of screw advancement for 3 different cannulated screw types (7.3-mm AO screw with and without washer, the 6.5-mm Herbert screw and the 6.5-mm Ideal Compression Screw (I.CO.S) using different synthetic bone density (0.16, 0.24, 0.48 g/ccm). Compressive force was measured indirectly, via screw tension measurement with strain gauges.

RESULTS

We calculated the work to reach a limit of 60 N and the corresponding ratios to the value of the golden standard: I.CO.S (35.2%), Herbert (89.0%), AO screw without washer (116%).

CONCLUSION

All screw systems yielded acceptable results but the ICOS did produce greater compression. The essential differences were the primary deformation of the bone before reaching the sufficient compressive force for primary stability.

Clinical significance of musculoskeletal finite element model of the second and the fifth foot ray with metatarsal cavities and calcaneal sinus

AIM

The aim of this study was to establish musculoskeletal finite element (FE) model of the second and the fifth foot ray accounting for metatarsal cavities and calcaneal sinus. The model was then used to predict the effects of metatarsal cavities and calcaneal sinus on internal stresses/strains of plantar longitudinal arches.

MATERIALS AND METHODS

The geometry of foot bones and soft tissues were constructed by CT and MRI images of Virtual Chinese Human "female No. 1". Two types of nonlinear FE models of sagittal foot rays were developed with or without metatarsal cavities and calcaneal sinus using ANSYS software package. The sagittal trabecular architecture of metatarsals and calcaneus were obtained by cutting, defatting and bleaching fresh foot specimen of a cadaver.

RESULTS

The model proposed was able to describe the isostatic stress flows in sagittal planes of plantar longitudinal arches. The size of metatarsal cavity or calcaneal sinus could affect stress/strain distributions on metatarsals and calcaneus, but had almost no effects on stress/strain of other foot bones and plantar soft tissues. During balance standing, the maximum von Mises stresses were predicted at the shaft and the basis of metatarsals, while the maximum strains of bony regions were found around metatarsal cavities. Among plantar soft tissues, relative high tensions were burdened by plantar fascia, followed by long plantar ligament. The minimum tensions occurred in plantar intrinsic muscles.

CONCLUSIONS

The study shows that the tension/compression stress flows are geometrically similar with the tension/compression trabecular architectures in sagittal sections of metatarsal and calcaneus. The FE predictions of stress/strain concentration on metatarsals and fascia are useful in enhancing biomechanical knowledge on metatarsal stress fractures and plantar fasciitis.

Calcaneus malunion and nonunion

Though the debate continues between operative interventions versus conservative therapy, there is significant evidence that the deformity that results from calcaneus malunions causes significant disability for the patient. Knowledge of the fracture patterns in the original calcaneal fracture aids in both understanding the deformity of the malunion and the necessary steps for correction of the deformity. Increased heel width, subfibular impingement, tibiotalar impingement, varus/valgus deformity of the hindfoot, peroneal tendon dysfunction, and subtalar arthrosis are well established consequences of calcaneal malunion. Different surgical options have been postulated either trying to address all the deformities or concentrating on certain aspects that are most clinically pressing. The simplest form of treatment is isolated lateral wall decompression, and if applied to a patient who has minimal subtalar arthrosis and no hindfoot deformity, good results are produced. The more complex surgical interventions aim to correct the lateral ankle symptoms, subtalar arthrosis, and hindfoot varus. These surgeries result in a more functional foot but should be considered a salvage procedure because there is still considerable disability as indicated by lower functional scores on the Short Form 36 and American Orthopaedic Foot and Ankle Society hindfoot surveys. Nonunion in calcaneal fractures has limited incidence within the literature for both operative and nonoperative management. Thus, any conclusion as to why there would be such a low incidence can only be made on speculation that the vascularity of the calcaneus and ability to immobilize both the subtalar and calcaneocuboid joints allow the fracture to heal.

Nonlinear finite element analysis for musculoskeletal biomechanics of medial and lateral plantar longitudinal arch of Virtual Chinese Human after plantar ligamentous structure failures

BACKGROUND

Musculoskeletal diseases of the foot such as stress fractures, tendonitis and subsequent pain are commonly associated with elevated stresses/strains of abnormal plantar arch after plantar ligamentous structure failures. The goal of this study was to develop anatomically detailed, finite element models of the medial and lateral plantar longitudinal arch, and to investigate bone and muscle stresses resulting from plantar fasciotomy and major plantar ligament injuries.

METHODS

Nonlinear finite element models of the second ray and the fifth ray of plantar longitudinal arches were constructed on the basis of CT and MR images of Virtual Chinese Human "female No. 1". The models assumed a balanced standing load configuration. Three different degrees of passive intrinsic muscle tensions (weak, moderate, or severe) were used in conjunction with simulations of plantar fasciotomy and major plantar ligament injury.

FINDINGS

Plantar fasciotomy caused von Mises stress increases in the bones and plantar ligaments while major plantar ligament injuries caused stress increases in the bones, flexor tendons, and plantar fascia. Increasing intrinsic muscle passive tensions decreased stress/strain levels in the medial and lateral arch, and adjusted abnormal tension/compression stress flows of both arches to close to the normal biomechanical states.

INTERPRETATION

This study shows that plantar longitudinal arches are concordant combination of bony structures, intrinsic muscles, plantar fascia and ligaments. After plantar ligamentous structure failures, intrinsic muscles have to contribute to stabilize the plantar arches. This mechanism may reduce the risk of developing stress fractures, tendonitis and pain syndrome.

Mathematical analysis of trabecular 'trajectories' in apparent trajectorial structures: the unfortunate historical emphasis on the human proximal femur

Wolff's "law" of the functional adaptation of bone is rooted in the trajectory hypothesis of cancellous bone architecture. Wolff often used the human proximal femur as an example of a trajectorial structure (i.e. arched trabecular patterns appear to be aligned along tension/compression stress trajectories). We examined two tenets of the trajectory hypothesis; namely, that the trabecular tracts from the tension- and compression-loaded sides of a bending environment will: (1) follow 'lines' (trajectories) of tension/compression stress that resemble an arch with its apex on a neutral axis, and (2) form orthogonal (90 degrees ) intersections. These predictions were analysed in proximal femora of chimpanzees and modern humans, and in calcanei of sheep and deer. Compared to complex loading of the human femoral neck, the chimpanzee femoral neck reputedly receives relatively simpler loading (i.e. temporally/spatially more consistent bending), and the artiodactyl calcaneus is even more simply loaded in bending. In order to directly consider Wolff's observations, measurements were also made on two-dimensional, cantilevered beams and curved beams, each with intersecting compression/tension stress trajectories. Results in the calcanei showed: (1) the same nonlinear equation best described the dorsal ("compression") and plantar ("tension") trabecular tracts, (2) these tracts could be exactly superimposed on the corresponding compression/tension stress trajectories of the cantilevered beams, and (3) trabecular tracts typically formed orthogonal intersections. In contrast, trabecular tracts in human and chimpanzee femoral necks were non-orthogonal (mean approximately 70 degrees ), with shapes differing from trabecular tracts in calcanei and stress trajectories in the beams. Although often being described by the same equations, the trajectories in the curved beams had lower r(2) values than calcaneal tracts. These results suggest that the trabecular patterns in the calcanei and stress trajectories in short beams are consistent with basic tenets of the trajectory hypothesis while those in human and chimpanzee femoral necks are not. Compared to calcanei, the more complexly loaded human and chimpanzee femoral necks probably receive more prevalent/predominant shear, which is best accommodated by non-orthogonal, asymmetric trabecular tracts. The asymmetrical trabecular patterns in the proximal femora may also reflect the different developmental 'fields' (trochanteric vs. neck/head) that formed these regions, of which there is no parallel in the calcanei.

Calcaneus fractures: a review article

Calcaneus fractures are a significant burden to society. Assessment and treatment of these injuries has improved significantly. The use of CT scanning has allowed a greater understanding of the pathologic anatomy of these fractures, and has provided for prognostic classification systems with respect to outcome. The treatment options are diverse and are reviewed.

Comparison of the trabecular architecture and the isostatic stress flow in the human calcaneus

It is a common theory that the architecture of trabecular bone follows the principal stress trajectories, as suggested by Wolff's pioneering studies of the proximal femur. Since first published in the late 19th-century, this observation (popularized as "Wolff's law") has been supported by numerous studies, but nearly all of them have been focused on the femoral head and neck. In this study, the manifestation of Wolff's law in the human calcaneus has been analyzed. For this purpose, finite element (FE) analysis of the entire complex of the foot during standing was undertaken. Orientation of the principal stress flow through the calcaneus was compared with the trabecular alignment in a single cadaveric calcaneal specimen, by fitting second-order polynomials to real trabecular paths and FE-predicted isostatics and calculating their angle of inclination with the calcaneal cortex at their insertion points. Four dominant trabecular patterns were identified in the cadaveric sagittal section of the specimen of the calcaneus: one directed primarily in the dorsal-plantar direction, one aligned anteriorly-posteriorly, and two that are strongly oblique. Subsequent numerical simulations showed that the dorsal-plantar oriented and posterior oblique trabecular paths are aimed to support compressive stresses, while the antero-posteriorly directed and anterior oblique groups act to bear tension. Insertion angles of real trabecular paths into the calcaneal cortex were similar to those of the isostatics that were computed under musculoskeletal loading conditions of standing (maximum absolute local difference 13 degrees, maximum local error 60%). This suggests that the trabecular patterns of the calcaneus are mainly shaped by isostatics (static principal stress flow) that are characteristic of the standing posture. The present modeling approach can be utilized to explore effects of abnormal alterations in the isostatic flow on the microarchitecture of the calcaneal trabeculae, as well as for better understanding of the mechanisms of calcaneal fractures.