Stress shielding analysis on easy step staple prosthesis for calcaneus fractures

Screw Stress Distribution in a Clavicle Fracture with Plate Fixation: A Finite Element Analysis

Clavicle midshaft fractures are mostly treated surgically by open internal reduction with a superior or anteroinferior plate and screws or by intramedullary nailing. Screw positioning plays a critical role in determining the stress distribution. There is a lack of data on the screw position and the appropriate number of cortices required for plate fixation. The aim of this study is to evaluate the mechanical behavior of an anterior plate implanted in a fractured bone subjected to 120° of lateral elevation compared to a healthy clavicle using numerical simulations. Contact forces and moments used were obtained from literature data and applied to the healthy and fractured finite element models. Stresses of about 9 MPa were found on the healthy clavicle, while values of about 15 MPa were calculated on the plate of the fractured one; these stress peaks were reached at about 30° and 70° of elevation when the stress shielding on the clavicle sums all the three components of the solicitation: compression, flexion, and torsion. The stress distribution in a clavicle fracture stabilized with plates and screws is influenced by several factors, including the plate's position and design, the type of screw, and the biomechanical forces applied during movements.

Mechanical influence of tissue scaffolding design with different geometries using finite element study

The mechanical properties of tissue scaffolds are essential in providing stability for tissue repair and growth. Thus, the ability of scaffolds to withstand specific loads is crucial for scaffold design. Most research on scaffold pores focuses on grids with pore size and gradient structure, and many research models are based on scaffolding with vertically arranged holes. However, little attention is paid to the influence of the distribution of holes on the mechanical properties of the scaffold. To address this gap, this research investigates the effect of pore distribution on the mechanical properties of tissue scaffolds. The study involves four types of scaffold designs with regular and staggered pore arrangements and porosity ranging from 30% to 80%. Finite element analysis (FEA) was used to compare the mechanical properties of different scaffold designs, with von-Mises stress distribution maps generated for each scaffold. The results show that scaffolds with regular vertical holes exhibit a more uniform stress distribution and better mechanical performance than those with irregular holes. In contrast, the scaffold with a staggered arrangement of holes had a higher probability of stress concentration. The study emphasized the importance of balancing porosity and strength in scaffold design.

Outcomes of U-shaped internal fixation in the treatment of avulsion fracture of calcaneal tubercle

BACKGROUND

The purpose of this study was to analyze the efficacy of U-shaped internal fixation for calcaneal tubercle fracture after nearly 3 years of case follow-up and data collection.

METHOD

We retrospectively analyzed the collected data from 16 patients with avulsion fracture of calcaneal tubercle between December 2018 and February 2021 at our institute. All patients were required to conform to regular follow up postoperatively. X-ray film was applied to all cases. The American Orthopaedic Foot and Ankle Association (AOFAS) score, Cedell score and the visual analog scale (VAS) were used to evaluate functional results.

RESULTS

All patients achieved bone union. The preoperative AOFAS score was 26.34 ± 3.34, which was significantly different from 91.38 ± 6.15 half a year after operation (p = 0.003). The preoperative Cedell score was 31.05 ± 4.18 and the score half a year after operation was 92.17 ± 5.39(p = 0.011). The VAS score was 8.91 ± 1.51 before operation and decreased to 0.58 ± 1.31 half a year after operation (p = 0.014).

CONCLUSIONS

In the treatments of calcaneal tubercle fracture, U-shaped internal fixation is a new attempt. Through the short-term follow-up study, we found that its therapeutic effect is excellent, which is a recommended treatment in clinic.

Numerical investigation of patellar instability during knee flexion due to an unbalanced medial retinaculum loading effect

Background and aim

Healthy patellofemoral (PF) joint mechanics are critical to optimal knee joint function. Patella plays a vital role in distributing quadriceps load during the knee extension. Patellar tracking, not physiological tracking, causes an increase of strains in PF ligaments, peaks of localized stress of soft tissues and articular cartilage and bony parts, and knee pain; these problems lead to complications such as bone abnormalities and osteoarthritis. This research aimed to develop a Finite Element (FE) model to evaluate patellar instability due to the medial retinaculum asymmetric loading effect.

Methods

A numerical model of the knee was obtained by matching nuclear magnetic resonance (MRI) for soft tissues and computerized tomography (CT) for bones, carried on a normal adult. Loading setup was chosen by using literature data. The intensity of the muscle forces was calculated by a static optimization taking into account ground reaction and knee flexion/extension during walking. The effect of patellar instability was obtained by gradually unbalancing this symmetry, one side was unloaded till 90 N, and the other loaded till 110 N.

Results

Unbalanced forces of 10 N acting on the retinaculum alone can produce a real difference in displacements of about 7 mm, and an increment of about 44% on patellar contact forces.

Conclusion

This research demonstrated how an unbalanced forces acting on the retinaculum can produce significant patellar instability. Patellar instability starts at 25-30° of the knee flexion angle but tends to appear at 15° when the unbalanced muscular loading conditions are acting.

Radiographic Evaluation of Isolated Continuous Compression Staples for Akin Osteotomy Fixation

Continuous compression implants (nitinol staples) are gaining popularity secondary to their lower profile, less demanding technique, and less surgical dissection. Biomechanical support exists; however, clinical data is limited in the foot/ankle. This study's purpose is to determine the efficacy of nitinol staples to achieve stable, bony healing in Akin osteotomies and examine their clinical outcomes, complications, re-operations, and pain scores. We performed a retrospective chart review on 90 patients (93 osteotomies) who underwent an Akin osteotomy using a nitinol staple over a 2-year period. Radiographs were randomized and independently reviewed by 3 blinded foot and ankle surgeons. Osteotomies were deemed healed if greater than 50% of the osteotomy contained bridging bone, partially healed as less than 50% bridging bone, and nonunion as no healing, broken hardware, or loss of reduction. Visual analog scale pain scores were analyzed. Radiographic union was seen in 98.9% of Akin osteotomies (92/93), with no loss of reduction or broken staples (0/95). Only 3.2% (3/93) of patients returned to the operating room unplanned: 1 infection (1.1%), 1 symptomatic hardware removal (1.1%), and 1 traumatic disruption of fixation (1.1%). Postoperative pain scores were significantly lower than preoperative. Staples are lower profile and technically less demanding compared to headed screws, plates, and tension band constructs. They offer continuous compression of the osteotomy and are rigid enough to maintain reduction. Based on the findings of this paper, the use of staples provides robust and stable fixation for Akin osteotomies and has low complication and high healing rates.

Improve biomechanical stability using intramedullary nails with femoral neck protection in femoral shaft fractures

BACKGROUND AND OBJECTIVE

Elderly patients treated for femoral shaft fractures have a higher risk of hip fracture. We hypothesized that intramedullary nails protecting the femoral neck can improve mechanical strength and reduce the risk of subsequent hip fracture. This study aims to analyze the biomechanical stability using intramedullary nails with or without femoral neck protection through finite element analysis.

METHODS

Thirty finite element models (FEMs) were established, including five different conditions of femoral shaft fracture: Fracture healing, Proximal fractures (Transverse and oblique), Distal fractures (Transverse and oblique), and five different fixation methods. Femoral neck protection groups: cephalomedullary nail (CN), reconstruction nail (RN); No femoral neck protection groups: type-1 of antegrade intramedullary nail (AIN-1), type-2 of antegrade intramedullary nail (AIN-2), and retrograde intramedullary nail (RIN). The maximum stress of bone and internal fixation in the femoral neck region for all type of fixation were calculated to evaluate the biomechanical stability.

RESULTS

Maximum equivalent stress values of bone in the femoral neck region for five different conditions of femoral shaft fracture: AIN-2 (77.23 MPa) >RIN (77.15 MPa) > AIN-1 (76.71 MPa) > CN (60.74 MPa) > RN (57.66 MPa) for the fracture healing; RIN (80.05 MPa) > AIN-1 (79.15 MPa) > AIN-2(78.77 MPa) > RN (65.16 MPa) > CN (65.03 MPa) for the proximal transverse fracture; RIN (80.10 MPa) > AIN-2 (79.36 MPa) > AIN-1 (79.18 MPa) > RN (65.09 MPa) > CN (64.96 MPa) for the proximal oblique fracture; RIN (80.24 MPa) > AIN-2 (79.68 MPa) > AIN-1 (79.33 MPa) > CN (65.02 MPa) > RN (64.76 MPa) for the distal transverse fracture; RIN (80.23 MPa) > AIN-2 (79.61 MPa) > AIN-1 (79.35 MPa) > CN (65.06 MPa) > RN (64.76 MPa) for the distal oblique fracture. Maximum equivalent stress of internal fixation in the femoral neck region is greater than the maximum stress of bone and avoids stress concentration of bone for the femoral neck protection groups (CN and RN).

CONCLUSIONS

Intramedullary nails with femoral neck protection in the treatment of femoral shaft fractures improve mechanical strength and prevent secondary hip fractures and decrease the overall risk of reoperation postoperatively.

Preparation and mechanical properties analysis of porous structure for bone tissue engineering

BACKGROUND: With the increasing aging of population, the incidence rate of diseases such as fracture and osteoporosis has been increasing. The demand for implant in Department of orthopedics has increased. The elastic modulus of the existing solid metal implant is much higher than that of human bone tissue, and it is easy to produce stress shielding effect after operation, which causes complications such as loosening of prosthesis and low fusion efficiency. OBJECTIVE: In order to solve the mismatch of elastic modulus between solid metal orthopedic implants and human bone tissue, metal structures with excellent mechanical properties were prepared. METHODS: The porous structure was designed by spatial dot matrix method, and the metal porous structure was prepared based on selective laser melting 3D printing technology. The residual stress in the preparation process was eliminated by vacuum annealing heat treatment, and the static compression experiment was carried out to study the effects of different pore shape and porosity parameters on the compressive yield strength and elastic modulus of porous structure. The performance changes of porous structure before and after heat treatment were compared, and the porous structure meeting the performance requirements of human bone tissue was selected. RESULTS: The porous structure prepared by selective laser melting technology met the requirements of human bone tissue. The elastic modulus was as low as 0.74 GPa and the compressive yield strength is 201.91 MPa; After annealing heat treatment, the compressive yield strength of porous structure decreased, the maximum change was 3.69%, the elastic modulus increased, and the maximum change was 8.69%. CONCLUSIONS: For the porous structure with the same pore shape, the lower the porosity, the better the mechanical properties of the porous structure. For the same porosity, the comprehensive mechanical properties of dodecahedral porous structure were the best and octahedral porous structure was the worst; The porous structure after annealing heat treatment was more conducive to meet the performance requirements of human bone tissue.

Traumatic and non-traumatic spinal cord injury: Demographic characteristics, neurological and functional outcomes. A 7-year single centre experience

Objective

The aim of this study is to evaluate demographic and clinical characteristics of a population affected by traumatic and non-traumatic spinal cord injury (SCI) and to analyze functional outcomes after rehabilitation.

Methods

This study involved 112 SCI patients (75 male and 37 female) admitted at the Neurorehabilitation Unit of the University Hospital of Messina. The neurological outcomes were evaluated according to the American Spinal Injury Association Impairment Scale (AIS) and by using length of stay, Functional Independence Measure (FIM) and Barthel Index (BI).

Results

NT-SCI patients were significantly older, numerous (75,89%) and affected by greater lesions when admitted, than T-SCI ones. Most of lesions were incomplete (93%) and associated with paraplegia (71%). FIM and BI outcomes are similar in both groups, even if T-SCI patients showed greater improvement when discharged. No significant differences were found in the length of stay. The most common complication in non-traumatic SCI group was urinary tract infection and this was observed in 25 patients (29,41%). Linear regression models explained 26% of the variance of LOS and 38% of the variance of functional outcome. Functional status on admission was the strongest determinant of LOS and completeness of the lesion was the strongest determinant of functional outcome. Etiology (traumatic versus non-traumatic) was a weak independent determinant of LOS but was not an independent determinant of functional outcome.

Conclusion

SCI patient's rehabilitation should be carried out by taking into account etiology of the injury. It is important to consider this information while developing the targets and planning of the rehabilitation program. In particular, older age negatively influence the degree of disability on admission and the entity of functional recovery in both populations. Non-traumatic lesions could have minor benefits after rehabilitation therapy if compared with traumatic ones.

Quality of Life and Clinical Evaluation of Calcaneoplasty with a Balloon System for Calcaneal Fracture at 5 Years of Follow-Up

Calcaneal fractures are a challenging clinical problem. Management of this type of injury remains controversial, especially in the context of intra-articular fractures. Surgical treatment with open reduction and internal synthesis (ORIF) is considered the standard treatment for CF, but it is associated with many complications. Several minimally invasive techniques such as balloon-assisted reduction, pin fixation, and tricalcium phosphate augmentation have been proposed to avoid the frequent and recurrent postoperative problems related to these fractures. We retrospectively examined 20 patients (mean age was 54.5), all undergoing minimally invasive calcaneoplasty surgery at our Department of Orthopaedics and Traumatology between 2012 and 2016. X-ray and CT scan were performed preoperatively and at 5 years of follow-up (57.9 ± 6 months). The American Orthopaedic Foot and Ankle Society (AOFAS) score was used for clinical examination, and the Short-Form (36) Health Survey (SF-36) score and Visual Analogue Scale (VAS) were used to assess the Health-Related Quality of Life (HRQoL). All 20 patients were available at the final follow-up. The mean AOFAS score was 82.25/100. The VAS results attest an overall average of 2.7/10 (0–9). The average of the parameters “Physical Health” and “Mental Health” was, respectively, 81.25 and 83.55. In terms of postoperative complications, we observed no cases of superficial or deep infections. Clinical response after balloon-assisted reduction, pin fixation, and tricalcium phosphate augmentation has shown a comparable or better outcome according to the AOFAS and VAS score. Quality-of-life scores, obtained according to the SF-36 questionnaire, are considered high. From both a clinical and quality-of-life point of view, our study highlights that there is not gender distinction. Further comparative studies with a higher number of patients are needed which assess the quality of life in the various techniques used to treat calcaneal fractures.