Finite element analysis of an intramedulary anatomical strut for proximal humeral fractures with disrupted medial column instability: A cohort study

Finite element analysis and biomechanical study of "sandwich" fixation in the treatment of elderly proximal humerus fractures

Proximal humerus fractures (PHFs) are common in the elderly and usually involve defects in the medial column.The current standard for medial column reconstruction is a lateral locking plate (LLP) in combination with either an intramedullary fibula support or an autogenous fibula graft. However, autogenous fibula graft can lead to additional trauma for patients and allogeneic fibular graft can increase patients' economic burden and pose risks of infection and disease transmission. The primary objective of this study was to introduce and assess a novel "Sandwich" fixation technique and compare its biomechanical properties to the traditional fixation methods for PHFs. In this study, we established finite element models of two different internal fixation methods: LLP-intramedullary reconstruction plate with bone cement (LLP-IRPBC) and LLP-intramedullary fibula segment (LLP-IFS). The biomechanical properties of the two fixation methods were evaluated by applying axial, adduction, abduction, torsional loads and screw extraction tests to the models. These FEA results were subsequently validated through a series of biomechanical experiments. Under various loading conditions such as axial, adduction, abduction, and rotation, the LLP-IRPBC group consistently demonstrated higher structural stiffness and less displacement compared to the LLP-IFS group, regardless of whether the bone was in a normal (Nor) or osteoporotic (Ost) state. Under axial, abduction and torsional loads, the maximum stress on LLPs of LLP-IRPBC group was lower than that of LLP-IFS group, while under adduction load, the maximum stress on LLPs of LLP-IRPBC group was higher than that of LLP-IFS group under Ost condition, and almost the same under Nor condition. The screw-pulling force in the LLP-IRPBC group was 1.85 times greater than that of the LLP-IFS group in Nor conditions and 1.36 times greater in Ost conditions. Importantly, the results of the biomechanical experiments closely mirrored those obtained through FEA, confirming the accuracy and reliability of FEA. The novel "Sandwich" fixation technique appears to offer stable medial support and rotational stability while significantly enhancing the strength of the fixation screws. This innovative approach represents a promising strategy for clinical treatment of PHFs.

Digital smart internal fixation surgery for coronal process basal fracture with normal joint spaces or radius-shortening: Occult factor of radius-ulna load sharing

BACKGROUND

Reasonable postoperative humeroradial and humeroulnar joint spaces maybe an important indicator in biomechanical stability of smart internal fixation surgery for coronoid process basal fractures (CPBF). The aim of this study is to compare elbow articular stresses and elbow-forearm stability under smart internal fixations for the CPBF between normal elbow joint spaces and radius-shortening, and to determine the occult factor of radius-ulna load sharing.

METHODS

CT images of 70 volunteers with intact elbow joints were retrospectively collected for accurate three-dimensional reconstruction to measure the longitudinal and transverse joint spaces. Two groups of ten finite element (FE) models were established prospectively between normal joint space and radius-shortening with 2.0 mm, including intact elbow joint and forearm, elbow-forearm with CPBF trauma, anterior or posterior double screws-cancellous bone fixation, mini-plate-cancellous bone fixation. Three sets of physiological loads (compression, valgus, varus) were used for FE intelligent calculation, FE model verification, and biomechanical and motion analysis.

RESULTS

The stress distribution between coronoid process and radial head, compression displacements and valgus angles of elbow-forearm in the three smart fixation models of the normal joint spaces were close to those of corresponding intact elbow model, but were significantly different from those of preoperative CPBF models and fixed radius-shortening models. The maximum stresses of three smart fixation instrument models of normal joint spaces were significantly smaller than those of the corresponding fixed radius-shortening models.

CONCLUSIONS

On the basis of the existing trauma of the elbow-forearm system in clinical practice, which is a dominant factor affecting radius-ulna load sharing, the elbow joint longitudinal space has been found to be the occult factor affecting radius-ulna load sharing. The stability and load sharing of radius and ulna after three kinds of smart fixations of the CPBF is not only related to the anatomical and biomechanical stability principles of smart internal fixations, but also closely related to postoperative elbow joint longitudinal space.

Pectoralis major pedicle bone grafting vs. tricortical iliac grafting for Neer 4-part proximal humerus fractures: a randomized controlled trial

BACKGROUND

The risk of avascular necrosis, nonunion, or malunion is high in osteoporosis-related 4-part fractures. We evaluated the results of patients who underwent plate osteosynthesis with a vascularized pectoralis major graft compared with tricortical iliac grafting to treat 4-part proximal humerus fractures.

MATERIAL AND METHODS

Thirty-four patients aged 50-75 years with Neer 4-part proximal humerus fractures were studied. Group A (n = 17) underwent osteotomy of a 2.5 ± 1 cm pectoralis major pedicle bone graft and plate application, whereas group B (n = 17) underwent plate osteosynthesis using iliac autogenous grafts. Final follow-up assessments included evaluation using Constant and American Shoulder and Elbow Surgeons scoring systems, humeral neck-shaft angle (HNSA), humeral head height, and humeral head avascular necrosis.

RESULTS

Reduction loss was observed in 3 patients (17.6%) in group A, whereas it was observed in 10 patients (58.8%) in group B (P = .013). Humeral head avascular necrosis was found in 1 patient (5.8%) in group A, whereas it was found in 5 patients (29.4%) in the other group (P = .071). The HNSA was normal in 12 (70.5%) of group A patients, whereas it was normal in 6 (35.2%) of group B patients. The HNSA was weak or bad (<1200) in 29.4% of group A patients, whereas this rate was 64.7% in group B patients. Humeral head height was 2.64 ± 1.45 mm in group A and 3.66 ± 1.65 mm in group B. There were no statistically significant differences between the 2 groups in terms of Constant and American Shoulder and Elbow Surgeons scoring systems.

CONCLUSION

Pectoralis major bone pedicle graft in Neer 4-part proximal humerus fractures reduces the risk of avascular necrosis and nonunion rates. Our technique yielded excellent clinical and radiological results. We achieved recovery without creating additional donor site morbidity.

Biomechanical evaluation of novel intra- and extramedullary assembly fixation for proximal humerus fractures in the elderly

Purpose: A novel intra- and extramedullary assembly fixation method was introduced, which achieved good clinical results in complex proximal humeral fractures; however, evidence of its comparability with traditional fixation is lacking. This biomechanical study aimed to compare it with traditional fixation devices in osteoporotic proximal humeral fractures. Methods: Three-part proximal humeral fractures with osteopenia were created on 12 pairs of fresh frozen humerus specimens and allocated to three groups: 1) lateral locking plate, 2) intramedullary nail, and 3) intra- and extramedullary assembly fixation. The specimens were loaded to simulate the force at 25° abduction. Thereafter, an axial stiffness test and a compound cyclic load to failure test were applied. Structural stiffness, number of cycles loaded to failure, and relative displacement values at predetermined measurement points were recorded using a testing machine and a synchronized 3D video tracking system. Results: In terms of initial stiffness and the number of cycles loaded to failure, the intra- and extramedullary assembly fixation group showed notable improvements compared to the other groups (p <0.017). The mean relative displacement value of measurement points in the intra- and extramedullary assembly fixation group was smaller than that in the other two groups. However, there was no significant difference until 10,000 cycles. The mean relative displacement of the intramedullary nail group (3.136 mm) exceeded 3 mm at 7,500 cycles of loading. Conclusion: In this test model, axial fixation can provide better mechanical stability than non-axial fixation. The intra- and extramedullary assembly fixation is better able to prevent the varus collapse for elderly proximal humeral fractures with posteromedial comminution.

Finite element study of the biomechanical effects on the rotator cuff under load

Rotator cuff injuries account for 50% of shoulder disorders that can cause shoulder pain and reduced mobility. The occurrence of rotator cuff injury is related to the variation in shoulder load, but the mechanical changes in the rotator cuff caused by load remain unclear. Therefore, the mechanical results of the rotator cuff tissue during glenohumeral abduction and adduction were analyzed based on a finite element shoulder model under non-load (0 kg) and load (7.5 kg) conditions. The results showed that the maximum von Mises stress on the supraspinatus muscle was larger than that on the subscapularis, infraspinatus, and teres minor muscles during glenohumeral abduction. Compared with the non-load condition, the maximum von Mises stress on the supraspinatus muscle increased by 75% under the load condition at 30° abduction. Under the load condition, the supraspinatus joint side exhibited an average stress that was 32% greater than that observed on the bursal side. The von Mises stress on the infraspinatus muscle was higher than that in other rotator cuff tissues during adduction. The stress on the infraspinatus muscle increased by 36% in the load condition compared to the non-load condition at 30° adduction. In summary, the increased load changed the mechanical distribution of rotator cuff tissue and increased the stress differential between the joint aspect and the bursal aspect of the supraspinatus tendon.

Positive medial cortical support versus anatomical reduction for trochanteric hip fractures: Finite element analysis and biomechanical testing

BACKGROUND AND OBJECTIVES

The anatomical reduction (AR) is usually considered the best option for fractures. Nevertheless, in unstable trochanteric hip fractures (UTHF), previous clinical reports found that the positive medial cortical support (PMCS, an over-reduction technique) attained higher mechanical stability, but this challenging clinical finding still needs experimental validation.

METHODS

This study constructed in-silico and biomechanical PMCS and AR models, with the use of the most clinically-representative geometry design of fracture models, the multi-directional design in FE analysis, and the subject-specific (osteoporotic) bone material properties, to make the models better mimic the actual condition in clinical settings. Then multiple performance variables (von-Mises stress, strain, integral axial stiffness, displacement, structural changes, etc.) were assessed to uncover details of integral and regional stability.

RESULTS

Among in-silico comparison, PMCS models showed significantly lower maximum displacement than AR models, and the maximum von Mises stress of implants (MVMS-I) was significantly lower in PMCS models than in AR models (highest MVMS-I in -30°-A3-AR of 1055.80 ± 93.37 MPa). Besides, PMCS models had significantly lower maximum von Mises stress along fracture surfaces (MVMS-F) (highest MVMS-F in 30°-A2-AR of 416.40 ± 38.01 MPa). Among biomechanical testing comparison, PMCS models showed significantly lower axial displacement. Significantly lower change of neck-shaft angle (CNSA) was observed in A2-PMCS models. A fair amount of AR models converted into the obvious negative medial cortical support (NMCS) condition, whereas all PMCS models kept the PMCS condition. The results were also validated through comparison to previous clinical data.

CONCLUSIONS

The PMCS is superior to the AR in the UTHF surgery. The current study opens up the second thought of the role of over-reduction technique in bone surgery.

Finite element analysis of a novel anatomical locking plate for scapular neck fracture

OBJECTIVES

Reconstruction plates (RPs) are commonly used in scapular neck fractures (SNFs): however, RPs have many defects. In this study, we evaluated a newly designed scapular neck anatomical locking compression plate (SNALCP).

METHODS

An SNF finite element model (Miller-type IIB) was constructed. Plates were subsequently implanted into the scapula and fixed with screws that were grouped according to the plate used: SNALCP (A) and RP (B). Finally, loads were applied to record and analyze performance.

RESULTS

Under lateral, anteroposterior, and vertical compression loads, the maximum von Mises stresses on the scapula and implants of group A were smaller than those of group B. There were some differences in stress distribution between the two groups.

CONCLUSIONS

SNALCP can effectively reduce the stress of the scapula and implant, making stress distribution more uniform and continuous, and has mechanical conduction advantages. Compared to RP, it provides improved stability and more reliable fixation.

How to improve the biomechanical stability of endosteal augmentation for proximal humerus fracture with osteopenia? A cadaveric study

BACKGROUND

Endosteal augmentation enhances the stability of osteoporotic proximal humeral fracture fixation, but the optimal configuration is unknown. The purpose of this study was to compare the biomechanical properties of different lengths of fibula with or without calcar screw in osteoporotic proximal humeral fracture.

METHODS

Three-part proximal humeral fractures with osteopenia were created on 20 pairs of fresh-frozen humeri specimens and allocated to four groups: (1) locking plate with a 6-cm fibular strut allograft, (2) locking plate with a 6-cm fibular strut allograft and additional calcar screws, (3) locking plate with a 12-cm fibular strut allograft，and (4) locking plate with a 12-cm fibular strut allograft and additional calcar screws. Specimens were loaded to simulate the force at 25° abduction. Thereafter, an axial stiffness test and a compound cyclic load to failure test were applied. Structural stiffness, number of cycles loaded to failure and relative displacement values for 5000 cycles at predetermined measurement points were recorded using a testing machine and a synchronized 3D video tracking system.

FINDINGS

In terms of initial stiffness, number of cycles loaded to failure, and relative displacement values, the groups with 12-cm fibular strut showed obvious improvement compared to the groups with 6-cm fibular strut irrespective of the influence of calcar screw implementation. Further, the groups implemented with calcar screws also showed promising biomechanical stability irrespective of fibular length.

INTERPRETATION

Lateral locking plate with longer endosteal fibular augmentation and calcar screw can significantly improve biomechanical stability for elderly proximal humeral fractures with posteromedial comminution.

Treatment of elderly comminuted proximal humeral fracture using endosteal anatomical support system: A case report

INTRODUCTION

Intramedullary anatomical medial strut with allograft bone (IAMSAB), which accommodates the shape of the proximal humeral cavity and provides rotational stability and direct support to the medial column, was successfully introduced to augment Lateral locking plate (LLP) in the treatment of elderly comminuted proximal humeral fractures. Based on the LLP-IAMSAB construct, a newly titanium endosteal anatomical support system (EASS) was developed.

CASE PRESENTATION

Reported here is a single case of a highly comminuted proximal humeral fracture. The fractures were treated with EASS. The patient's fracture healed properly. The 24-month follow-up demonstrated no pain and a good functional outcome, with no signs of reduction loss, absorption of greater tuberosity, varus displacement and avascular necrosis of humeral head.

CLINICAL DISCUSSION

The newly developed EASS had several special considerations contributing to satisfactory surgical outcome. The flat plane construct of the proximal end of the EASS directly support humeral head to prevent varus displacement of the humeral head, instead of the purchase between the screw thread and the cancellous bone inside the humeral head in the nail or plate fixation. Medial anatomical shape of proximal end helps to reduce medial cortex reduction. Greater tuberosity support block with rotator cuff suture fixation might promote greater tuberosity healing and prevent its absorption. However, there is no similar construct in the nail or plate fixation.

CONCLUSION

The newly developed endosteal anatomical support system might be a promising option in the treatment of elderly comminuted proximal humeral fractures. Although the effectiveness of this system requires additional evaluation upon more patients being treated with this surgical method, the newly developed EASS may serve as a humeral head-preserving method for elderly patients with comminuted proximal humeral fractures.

Technique and clinical results of a new intramedullary support nail and plate system for fixation of 3- or 4- part proximal humeral fractures in older adults

BACKGROUND

Internal fixation of complex proximal humeral fractures (PHF) with osteoporosis is associated with a high incidence of complications. This study introduces the technique and clinical results of a novel intramedullary support nail and plate system (ISNPs) for the internal fixation of 3- or 4- part PHF in older adults. The ISNPs combines the concept of intramedullary support and dynamic fixation into a locking plate fixation system that can be applied using a minimally invasive surgical approach.

METHODS

A total of 46 consecutive patients diagnosed with 3- or 4-part PHF that met the criteria were included in this study, including 18 in the ISNPs group and 28 in the conventional locking plate (LP) group. Clinical results, including operative time, intraoperative bleeding, reduction quality, subjective outcome ratings, and complications, were compared between the two groups. Functional outcomes were evaluated using the Constant score and disability of the arm, shoulder, and hand (DASH) questionnaire at 1-year follow-up.

RESULTS

There were no significant differences in age, sex, local bone quality, Neer-fracture type, and follow-up time between the ISNPs and LP groups. For clinical analysis, there were no significant differences in intraoperative bleeding and operation time between the ISNPs and LP groups. Significant differences were observed in the percentage of the malreduced cases, Constant and DASH score analysis, and the patients' subjective evaluation ('excellent' and 'good' %) between the two groups.

CONCLUSION

The ISNPs technique proposed in this study provides a novel hybrid internal fixation model for complex PHF with osteoporosis. The clinical results at 1-year follow-up confirmed the advantage of applying it to 3- or 4- part PHF in older patients. Further studies are required to optimize its design and explore its optimal indications.

Finite Element Analysis of Fracture Fixation

PURPOSE OF REVIEW

Fracture fixation aims to provide stability and promote healing, but remains challenging in unstable and osteoporotic fractures with increased risk of construct failure and nonunion. The first part of this article reviews the clinical motivation behind finite element analysis of fracture fixation, its strengths and weaknesses, how models are developed and validated, and how outputs are typically interpreted. The second part reviews recent modeling studies of the femur and proximal humerus, areas with particular relevance to fragility fractures.

RECENT FINDINGS

There is some consensus in the literature around how certain modeling aspects are pragmatically formulated, including bone and implant geometries, meshing, material properties, interactions, and loads and boundary conditions. Studies most often focus on predicted implant stress, bone strain surrounding screws, or interfragmentary displacements. However, most models are not rigorously validated. With refined modeling methods, improved validation efforts, and large-scale systematic analyses, finite element analysis is poised to advance the understanding of fracture fixation failure, enable optimization of implant designs, and improve surgical guidance.

[Research progress on medial support augmentation of plate osteosynthesis for proximal humeral fractures]

Objective

To review the literature about the clinical application and research progress on medial support augmentation of plate osteosynthesis for proximal humeral fractures, and to provide reference for clinical treatment.

Methods

The literature concerning medial support augmentation of plate osteosynthesis for proximal humeral fractures in recent years was extensively reviewed, as well as the biomechanical benefit and clinical advantage were analyzed thoroughly.

Results

Medial support augmentation of plate osteosynthesis for proximal humeral fractures is very important, especially in osteoporotic and/or comminuted fractures. Many medial support augmentation methods have been proposed which can be divided into extramedullary support and intramedullary support. It can also be divided into autogenous bone support and allogenic bone support according to the material and source, divided into medial column support, calcar support, and humeral head support according to the support site, and divided into fibular shaft support, femoral head support, anatomic fibula support according to the shape of the augmented fixation. At present, clinical and biomechanical researches show that medial support augmentation is an effective treatment for proximal humeral fractures.

Conclusion

As an important treatment strategy for the treatment of proximal humeral fractures, the medial support augmentation of plate osteosynthesis gets the focus from the biomechanical studies and clinical treatment. However, there are still widespread controversies among orthopedic surgeons regarding the support mode, site, implant shape, and material of medial column support for augmentation of proximal humeral fractures. More high-quality clinical trials and biomechanical researches as well as multi-disciplinary integration, are needed to provide better strategy treatment for the treatment of proximal humeral fractures.