Influence of plate material and screw design on stiffness and ultimate load of locked plating in osteoporotic proximal humeral fractures

Inflammatory tissue response in human soft tissue is caused by a higher particle load near carbon fiber-reinforced PEEK compared to titanium plates

Titanium as the leading implant material in locked plating is challenged by polymers such as carbon fiber-reinforced polyetheretherketone (CFR-PEEK), which became the focus of interest of researchers and manufacturers in recent years. However, data on human tissue response to these new implant materials are rare. Osteosynthesis plates and peri‑implant soft tissue samples of 16 healed proximal humerus fractures were examined (n = 8 CFR-PEEK, n = 8 titanium). Soft tissue was analyzed by immunohistochemistry and µCT. The entrapped foreign bodies were further examined for their material composition by FTIR. To gain insight into their origin and formation mechanism, explanted and new plates were evaluated by SEM, EDX, profilometry and HR-CT. In the peri‑implant soft tissue of the CFR-PEEK plates, an inflammatory tissue reaction was detected. Tissues contained foreign bodies, which could be identified as tantalum wires, carbon fiber fragments and PEEK particles. Titanium particles were also found in the peri‑implant soft tissue of the titanium plates but showed a less intense surrounding tissue inflammation in immunohistochemistry. The surface of explanted CFR-PEEK plates was rougher and showed exposed and broken carbon fibers as well as protruding and deformed tantalum wires, especially in used screw holes, whereas scratches were identified on the titanium plate surfaces. Particles were present in the peri‑implant soft tissue neighboring both implant materials and could be clearly assigned to the plate material. Particles from both plate materials caused detectable tissue inflammation, with more inflammatory cells found in soft tissue over CFR-PEEK plates than over titanium plates. STATEMENT OF SIGNIFICANCE: Osteosynthesis plates are ubiquitously used in various medical specialties for the reconstruction of bone fractures and defects and are therefore indispensable for trauma surgeons, ENT specialists and many others. The leading implant material are metals such as titanium, but recently implants made of polymers such as carbon fiber-reinforced polyetheretherketone (CFR-PEEK) have become increasingly popular. However, little is known about human tissue reaction and particle generation related to these new implant types. To clarify this question, 16 osteosynthesis plates (n = 8 titanium and n = 8 CFR-PEEK) and the overlying soft tissue were analyzed regarding particle occurrence and tissue inflammation. Tissue inflammation is clinically relevant for the development of scar tissue, which is discussed to cause movement restrictions and thus contributes significantly to patient outcome.

Biomechanical design optimization of proximal humerus locked plates: A review

BACKGROUND

Proximal humerus locked plates (PHLPs) are widely used for fracture surgery. Yet, non-union, malunion, infection, avascular necrosis, screw cut-out (i.e., perforation), fixation failure, and re-operation occur. Most biomechanical investigators compare a specific PHLP configuration to other implants like non-locked plates, nails, wires, and arthroplasties. However, it is unknown whether the PHLP configuration is biomechanically optimal according to some well-known biomechanical criteria. Therefore, this is the first review of the systematic optimization of plate and/or screw design variables for improved PHLP biomechanical performance.

METHODS

The PubMed website was searched for papers using the terms "proximal humerus" or "shoulder" plus "biomechanics/biomechanical" plus "locked/locking plates". PHLP papers were included if they were (a) optimization studies that systematically varied plate and screw variables to determine their influence on PHLP's biomechanical performance; (b) focused on plate and screw variables rather than augmentation techniques (i.e., extra implants, bone struts, or cement); (c) published after the year 2000 signaling the commercial availability of locked plate technology; and (d) written in English.

RESULTS

The 41 eligible papers involved experimental testing and/or finite element modeling. Plate variables investigated by these papers were geometry, material, and/or position, while screw variables studied were number, distribution, angle, size, and/or threads. Numerical outcomes given by these papers included stiffness, strength, fracture motion, bone and implant stress, and/or the number of loading cycles to failure. But, no paper fully optimized any plate or screw variable for a PHLP by simultaneously applying four well-established biomechanical criteria: (a) allow controlled fracture motion for early callus generation; (b) reduce bone and implant stress below the material's ultimate stress to prevent failure; (c) maintain sufficient bone-plate interface stress to reduce bone resorption (i.e., stress shielding); and (d) increase the number of loading cycles before failure for a clinically beneficial lifespan (i.e., fatigue life). Finally, this review made suggestions for future work, identified clinical implications, and assessed the quality of the papers reviewed.

CONCLUSIONS

Applying biomechanical optimization criteria can assist biomedical engineers in designing or evaluating PHLPs, so orthopaedic surgeons can have superior PHLP constructs for clinical use.

Management of severe defects of humerus in combat patients injured in Russo-Ukrainian war

INTRODUCTION

Russo-Ukrainian war is associated with application of high-energy weapon, causing severe multifragmental injuries to the bones an associating with severe bone defects. The aim of the study was to evaluate various methods to treat combat patients with severe defects of humerus and to demonstrate the experience of orthopedic war surgeons in managing gunshot injuries to the humerus defects in the ongoing war.

PATIENTS AND METHODS

A 24 patients were active-duty military personnel of Armed Forces of Ukraine. These patients were diagnosed with severe humerus defects due to gunshot injury in battlefield zone in various areas of Ukraine. Data was collected within period between February, 24th 2022 till January, 01st 2023. The following approaches were applied to replace bone defect: preoperative 3D printing with polyetheretherketone (PEEK) as orthobiological material; closed reduction, percutaneous lag screw and Ilizarov external fixation; vascularized fibula grafting.

RESULTS

Data analyses of the segmental defects of humerus showed 5 cm defect in 3 (13 %) patients, from 5 to 10 cm in 4 (17 %) patients, over 10 cm in 17 (71 %) patients. Analyses were performed in these 17 (71 %) patients, showing 5 patients treated with 3D-printed PEEK implants, 6 patients with vascular-pedicle graft of fibula, 6 patients with closed reduction, percutaneous lag screw, Ilizarov external fixation. Osteomyelitis was diagnosed in one case (20 %) after the use of PEEK implants, requiring to remove both PEEK implant and metal implants followed by application of the antibiotic joint spacers and Ex-Fix fragments of the humerus. In our opinion, the osteomyelitis happened due to inadequate debridement of the wound and non-compliance with the conversion criteria (replacement of the fixation method). The mean length of hospital stay was 5.5 months for patients treated with 3D-printed PEEK implants.

CONCLUSIONS

Closed reduction, percutaneous lag screw and Ilizarov external fixation as well as vascularized fibula grafting are associated with good outcomes in management of the patients with severe humerus defect due to gunshot injury. 3D printing and PEEK implants could also be considered for the reconstructions of the humerus multifragmental fractures with a bone defect over 10 cm associated with gunshot injury due to high-energy weapon in the war settings.

Biomechanical testing of osteosynthetic locking plates for proximal humeral shaft fractures - a systematic literature review

Proximal humeral shaft fractures can be treated with helically deformed bone plates to reduce the risk of iatrogenic nerve lesion. Controversially to this common surgical technique that was first established in 1999, no biomechanical investigation on humeral helical plating is recorded by other reviews, which focus on proximal fractures exclusively. Does an additional scope for shaft fractures reveal findings of helical testing? The present systematic literature review was performed based on guidelines by Kitchenham et al. to systematically search and synthesize literature regarding biomechanical testing of osteosynthetic systems for proximal humeral shaft fractures. Therefore, a systematic approach to search and screen literature was defined beforehand and applied on the findings of the database PubMed®. Synthesized information of the included literature was categorized, summarized and analyzed via descriptive statistics. Out of 192 findings, 22 publications were included for qualitative synthesis. A wide range of different test methods was identified, leading to a suboptimal comparability of specific results between studies. Overall, 54 biomechanical test scenarios were identified and compared. Physiological based boundary conditions (PB-BC) were referenced in 7 publications only. One study of testing straight and helical dynamic compression plates without PB-BCs was identified, showing significant differences under compressional loading. The absence of test standards of specific fields like humeral fractures lead to a high variance in biomechanical testing of osteosynthetic locking plates for proximal humeral shaft fractures. Physiological approaches offer realistic test scenarios but need to be uniformed for enhanced comparability between studies. The impact of helically deformed locking plates under PB-BC was not identified in literature.

Clinical Outcome of Carbon Fiber Reinforced Polyetheretherketone Plates in Patients with Proximal Humeral Fracture: One-Year Follow-Up

BACKGROUND

Proximal humerus fractures are seen frequently, particularly in older patients. The development of new osteosynthesis materials is being driven by the high complication rates following surgical treatment of proximal humerus fractures. Plate osteosyntheses made of steel, titanium and, for several years now, carbon fiber-reinforced polyetheretherketone (CFR-PEEK) are used most frequently.

METHODS

A prospective, randomized study was conducted in order to evaluate whether there are differences in the functional postoperative outcome when comparing CFR-PEEK and titanium implants for surgical treatment of proximal humerus fractures. The primary outcome of shoulder functionality 1 year after surgery was measured with the DASH score, the Oxford Shoulder Score, and the Simple Shoulder Test.

RESULTS

Bony consolidation of the respective fracture was confirmed in all the patients included in the study within the scope of postoperative follow-up care. No significant differences in the DASH score, Oxford Shoulder Score, or Simple Shoulder Test were observed 1 year post-operatively when comparing the implant materials CFR-PEEK and titanium.

CONCLUSIONS

There are no differences in terms of the functional outcome between CFR-PEEK plates and titanium implants 1 year after surgery. Studies on the long-term outcomes using CFR-PEEK plates in osteoporotic bone should be the subject of further research.

Correct positioning of the calcar screw leads to superior results in proximal humerus fractures treated with carbon-fibre-reinforced polyetheretherketone plate osteosynthesis with polyaxial locking screws

BACKGROUND

Plate osteosynthesis with implants made of carbon-fibre-reinforced polyetheretherketone (CFR-PEEK) has recently been introduced for the treatment of fractures of the proximal humerus (PHFs). The advantages of the CFR-PEEK plate are considered to be its radiolucency, its favourable modulus of elasticity, and the polyaxial placement of the screws with high variability of the angle. The primary aim of this study is to investigate the influence of calcar screw positioning on the complication and revision rates after CFR-PEEK plating of PHFs. The secondary aim is to assess its influence on functional outcome.

MATERIAL AND METHODS

Patients were identified retrospectively. Minimum follow-up was 12 months. The cohort was divided into two groups depending on the distance of the calcar screw to the calcar (group I: < 12 mm, group II: ≥ 12 mm). The range of motion (ROM), Subjective Shoulder Value Score (SSV) and Constant-Murley Score (CS) were analysed at follow-up examination. Subjective complaints, complications (e.g. humeral head necrosis, varus dislocation) and the revision rate were evaluated.

RESULTS

51 patients (33 female, 18 male) with an average age of 68.6 years were included after a period of 26.6 months (group I: 32 patients, group II: 19 patients). Apart from the gender distribution, no significant differences were seen in the patient characteristics. The outcome scores showed significantly better clinical results in group I: SSV 83.4 vs 71.2, p = 0.007; CS 79.1 vs 67.8, p = 0.013. Complications were seen less frequently in group I (18.8 % vs 47.4 %, p = 0.030).

CONCLUSION

This study shows that the positioning of the calcar screw is relevant for CFR-PEEK plate osteosynthesis in PHFs with a good reduction of the fracture. Optimal positioning of the calcar screw close to the calcar (< 12 mm) is associated with a lower rate of complications, resulting in significantly superior functional outcomes.

LEVEL OF EVIDENCE

III, retrospective cohort study.

A biomechanical comparison of three fixation methods for unstable femoral neck fractures with medial calcar defect

BACKGROUND

Unstable femoral neck fractures with medial calcar defects are difficult to manage. The optimal fixation methods for these fractures have been a subject of ongoing debate among orthopedic surgeons. In this study, three different fixation techniques for vertical, medial defected femoral neck fractures were compared.

METHODS

In this study, a biomechanical analysis was conducted to compare three fixation methods: cannulated screws (Group 1), cannulated screws combined with a medial buttress plate (Group 2), and intramedullary nails (Group 3). Synthetic composite bone models representing vertical collum femoris fractures with medial calcar defects were used. Each group consisted of seven specimens, and, to maintain consistency, a single surgeon performed the surgical procedure. Biomechanical testing involved subjecting the specimens to axial loading until failure, and the load to failure, stiffness, and displacement values were recorded. Normality was tested using the Shapiro-Wilk test. One-way ANOVA and Tukey's HSD post hoc test were used for comparisons.

RESULTS

The difference in the load to failure values was statistically significant among the groups, with Group 2 exhibiting the highest load to failure value, followed by Group 3 and Group 1. Stiffness values were significantly higher in Group 2 than in the other groups. Displacement values were not significantly different between the groups. Fracture and displacement patterns at the point of failure varied across the groups.

CONCLUSION

The results of this study indicate that fixation with a medial buttress plate in combination with cannulated screws provides additional biomechanical stability for vertical femoral neck fractures with medial calcar defects. Intramedullary nail fixation also demonstrated durable stability in these fractures. These findings can be used to better understand current management strategies for these challenging fractures to promote the identification of better evidence-based recommendations.

Functional results and unfavorable events after treatment of proximal humerus fractures using a new locking plate system

BACKGROUND

Proximal humerus fractures are often treated with a fixed-angle titanium plate osteosynthesis. Recently, plates made of alternative materials such as carbon fibre-reinforced polyetheretherketone (CFR-PEEK) have been introduced. This study presents the postoperative results of patients treated with a CFR-PEEK plate.

METHODS

Patients with proximal humerus fractures treated with a CFR-PEEK plate (PEEKPower™ Humeral Fracture Plate (HFP)) were included. In follow-up examination, age and gender adjusted Constant-Murley Score (ACS), Subjective Shoulder Value (SSV), Quick Disabilities of the Arm, Shoulder and Hand Score (QDASH) and pain score (Visual Analog Scale (VAS)) were analyzed. General condition at follow-up was measured by European Quality of Life 5 Dimensions 3 Level Version (EQ-5D-3L). Range of motion was recorded. In addition, radiographs at follow-up, unfavorable events and revision rate were analyzed.

RESULTS

In total, 98 patients (66.0 ± 13.2 years, 74 females, 24 males) were reexamined. Mean follow-up was 27.6 ± 13.2 months. There were 15 2-part, 28 3-part and 55 4-part fractures. The functional scores showed good results: SSV 83.3 ± 15.6%, QDASH 13.1 ± 17.0 and ACS 80.4 ± 16.0. A 4-part-fracture, head split component, nonanatomic head shaft reposition and preoperative radiological signs of osteoarthritis were significant negative predictors for poorer clinical scores. Unfavourable events were observed in 27 patients (27.6%). Revision surgery was performed in 8 (8.2%) patients. Risk factors for an unfavourable event were female gender, age of 50 years and older, diabetes, affected dominant hand, 4-part fracture, head split and preoperative radiological signs of osteoarthritis.

CONCLUSION

There are several advantages of the CFR-PEEK plate (PEEKPower™ Humeral Fracture Plate (HFP)) such as the polyaxial screw placement and higher stability of locking screws. In summary, the CFR-PEEK plate osteosynthesis is a good alternative with comparable clinical results and some biomechanical advantages. Proximal humerus fractures show good clinical results after treatment with a CFR-PEEK plate. The revision rate and the risk of unfavorable events are not increased compared to conventional titanium plate osteosynthesis.

LEVEL OF EVIDENCE

IV.

Catastrophic failure of a titanium locking plate in a proximal humeral fracture: case report and literature review

Background

Angular stable locking plates have shown good clinical results in treating proximal humeral fractures, but complications are not uncommon. This study reported a rare case of catastrophic failure of a titanium locking plate. A retrieval analysis of the implants was performed using an optic microscope and a scanning electron microscope.

Case presentation

A 69-year-old male reported a right proximal humeral fracture at the surgical neck and was treated by open reduction and internal fixation with a locking plate system. Ninety-six days after surgery, the patient came to clinic for acute local pain over the shoulder without any trauma. The radiographs showed a complete breakage of the implant accompanying displaced fracture. Revision surgery was performed to restabilize the fracture with a longer locking plate. The follow-up radiographs at 9 months showed complete union of the bone fracture.

Conclusions

From the retrieval analysis, repetitive torsion loads on the vulnerable area of the implant are assumed to cause this catastrophic event. It is recommended that adequate activity restriction, such as reaching, be undertaken to avoid this rare complication. Current study also provides contributive information for the modification of plate design and pre-operative planning for device configuration to improve the success rate of locking plate fixation.

Carbon Fiber Implants in Orthopaedic Oncology

Carbon fiber offers numerous material benefits including reduced wear, high strength-to-weight ratio, a similar elastic modulus to that of bone, and high biocompatibility. Carbon fiber implants are increasingly used in multiple arenas within orthopaedic surgery, including spine, trauma, arthroplasty, and oncology. In the orthopaedic oncologic population, the radiolucency of carbon fiber facilitates post-operative imaging for tumor surveillance or recurrence, the monitoring of bony healing and union, and radiation mapping and delivery.

Locking Plates With Computationally Enhanced Screw Trajectories Provide Superior Biomechanical Fixation Stability of Complex Proximal Humerus Fractures

Joint-preserving surgical treatment of complex unstable proximal humerus fractures remains challenging, with high failure rates even following state-of-the-art locked plating. Enhancement of implants could help improve outcomes. By overcoming limitations of conventional biomechanical testing, finite element (FE) analysis enables design optimization but requires stringent validation. This study aimed to computationally enhance the design of an existing locking plate to provide superior fixation stability and evaluate the benefit experimentally in a matched-pair fashion. Further aims were the evaluation of instrumentation accuracy and its potential influence on the specimen-specific predictive ability of FE. Screw trajectories of an existing commercial plate were adjusted to reduce the predicted cyclic cut-out failure risk and define the enhanced (EH) implant design based on results of a previous parametric FE study using 19 left proximal humerus models (Set A). Superiority of EH versus the original (OG) design was tested using nine pairs of human proximal humeri (N = 18, Set B). Specimen-specific CT-based virtual preoperative planning defined osteotomies replicating a complex 3-part fracture and fixation with a locking plate using six screws. Bone specimens were prepared, osteotomized and instrumented according to the preoperative plan via a standardized procedure utilizing 3D-printed guides. Cut-out failure of OG and EH implant designs was compared in paired groups with both FE analysis and cyclic biomechanical testing. The computationally enhanced implant configuration achieved significantly more cycles to cut-out failure compared to the standard OG design (p &lt; 0.01), confirming the significantly lower peri-implant bone strain predicted by FE for the EH versus OG groups (p &lt; 0.001). The magnitude of instrumentation inaccuracies was small but had a significant effect on the predicted failure risk (p &lt; 0.01). The sample-specific FE predictions strongly correlated with the experimental results (R2 = 0.70) when incorporating instrumentation inaccuracies. These findings demonstrate the power and validity of FE simulations in improving implant designs towards superior fixation stability of proximal humerus fractures. Computational optimization could be performed involving further implant features and help decrease failure rates. The results underline the importance of accurate surgical execution of implant fixations and the need for high consistency in validation studies.

Osteosynthesis Metal Plate System for Bone Fixation Using Bicortical Screws: Numerical–Experimental Characterization

Simple Summary

This study addresses an important issue concerning the evaluation of stresses in bone shafts stabilized by osteosynthesis metal plates, following routine surgical procedures to repair severe fractures in bone. It is recognized that bone regeneration following fracture is highly dictated by the stress state in the damaged regions. Since metallic inserts, like plates and screws, are usually employed to assure the stabilization of fractures in bone, it is important to evaluate the effect of those parts on the developed stresses in bone tissue. In the present work fracture was induced in a femoral bone of an animal model, which was suitably stabilized with a dynamic compression plate (DCP) using bicortical screws. This system was submitted to bending to trigger damage in bone tissue in the vicinity of metal inserts. Finite element modelling was then performed to mimic damage initiation and propagation in bone, thus simulating the results observed experimentally. Stress distributions in the vicinity of the screwed regions due to fastening of DCP allowed to identify very significant differences, which can affect bone hilling processes. It can be concluded that the developed procedure may be used to help surgeons to support decisions regarding bone repair using standard DCP.

Abstract

This study reports the numerical and experimental characterization of a standard immobilization system currently being used to treat simple oblique bone fractures of femoral diaphyses. The procedure focuses on the assessment of the mechanical behavior of a bone stabilized with a dynamic compression plate (DCP) in a neutralization function, associated to a lag screw, fastened with surgical screws. The non-linear behavior of cortical bone tissue was revealed through four-point bending tests, from which damage initiation and propagation occurred. Since screw loosening was visible during the loading process, damage parameters were measured experimentally in independent pull-out tests. A realistic numerical model of the DCP-femur setup was constructed, combining the evaluated damage parameters and contact pairs. A mixed-mode (I+II) trapezoidal damage law was employed to mimic the mechanical behavior of both the screw–bone interface and bone fractures. The numerical model replicated the global behavior observed experimentally, which was visible by the initial stiffness and the ability to preview the first loading peak, and bone crack satisfactorily.

Minimum 2-year results of the second-generation CFR-PEEK locking plate on the proximal humeral fracture

PURPOSE

The aim of this study was to analyse and compare the 24-month range of motion results of patients treated with CFR-PEEK2 versus conventional titanium plate osteosyntheses (TAL-P). We hypothesized similar clinical outcomes but a better range of motion in the CFR-PEEK2 group than the TAL-P group in the 2-year follow-up.

METHODS

This retrospective study analysing prospectively collected data included all patients that presented with a PHF and were treated with CFR-PEEK2 between November 2016 and April 2018. Follow-up was performed after a minimum of 24 months, evaluating the functional degree of movement functional scores, including the Subjective Shoulder Value (SSV) as well as an age- and sex-adapted Constant-Murley score (CMS). The 2-year results were compared to the results of a matched pair group comprising patients that were treated with TAL-P during the same period.

RESULTS

Of the 35 patients included (mean age: 61.2 [18-78] years), 30 (86%) patients completed the 24-month follow-up in the CFR-PEEK2-group. After 24 months, the mean CMS was 89.9 points (pt) (44.5-100 pt) and the mean SSV was 86.7% (35-100%). Compared to the matched-pair TAL-P cohort, the 24-month follow-up showed similar results (CMS: 88.6 pt. (40.5-100 pt.) [p = 0.9]; SSV: 76% (30-100%) [p = 0.05]). However, significantly better degrees of forward flexion and internal rotation as well as a better range of motion in abduction was recorded in patients treated with CFR-PEEK2 plates than TAL-P.

CONCLUSION

At the 24-month follow-up, patients who received treatment with CFR-PEEK2 compared to those that received TAL-P showed enhanced range of motion whilst having similar clinical scores.

Age-Independent Clinical Outcome in Proximal Humeral Fractures: 2-Year Results Using the Example of a Precontoured Locking Plate

INTRODUCTION

The optimal treatment strategy for the proximal humeral fracture (PHF) remains controversial. The debate is centered around the correct treatment strategy in the elderly patient population. The present study investigated whether age predicts the functional outcome of locking plate osteosynthesis for this fracture entity.

METHODS

A consecutive series of patients with surgically treated displaced PHF between 01/2017 and 01/2018 was retrospectively analyzed. Patients were treated by locking plate osteosynthesis. The cohort was divided into two groups: Group 1 (≥65 years) and Group 2 (<65 years). At the follow-up examination, the SSV, CMS, ASES, and Oxford Shoulder Score (OS), as well as a radiological follow-up, was obtained. The quality of fracture reduction is evaluated according to Schnetzke et al. Results: Of the 95 patients, 79 were followed up (83.1%). Group 1 consists of 42 patients (age range: 65-89 years, FU: 25 months) and Group 2 of 37 patients (28-64 years, FU: 24 months). The clinical results showed no significant differences between both groups: SSV 73.4 ± 23.4% (Group 1) vs. 80.5 ± 189% (Group 2). CMS: 79.4 ± 21 vs. 81.9 ± 16, ASES: 77.2 ± 20.4 vs. 77.5 ± 23.1, OS: 39.5 ± 9.1 vs. 40.8 ± 8.2; OS: 39.5 ± 9.1 vs. 40.8 ± 8.2. In the radiological follow-up, fractures healed in all cases. Furthermore, the quality of fracture reduction in both groups is comparable without significant differences. The revision rate was 9.5% in Group 1 vs. 16.2% in Group 2.

DISCUSSION

Both age groups show comparable functional outcomes and complication rates. Thus, the locking plate osteosynthesis can be used irrespective of patient age; the treatment decision should instead be based on fracture morphology and individual patient factors.

Primary stability of cement augmentation in locking plate fixation for proximal humeral fractures: A comparison of absorbable versus non-absorbable cement

BACKGROUND

Cement augmentation has been suggested to increase the stability of screw anchoring in osteoporotic humeral fractures. Initial results are promising but may be jeopardized by cement leakage into the joint and difficult implant removal. Absorbable cement might have advantages in this regard, but it is unclear if the primary stability of both techniques is equivalent to each other. Therefore, this study aimed to compare its primary stability with that of non-absorbable cement augmentation.

METHODS

Nineteen cadaveric humeri with two-part fracture models were treated with locking plate osteosynthesis and cement augmentation using either absorbable calcium phosphate cement (group 1) or polymethylmethacrylate (group 2). Fracture movement, stiffness, failure mode, and ultimate load under cyclic compressive loading were examined and compared between the groups.

FINDINGS

The absolute and relative stiffness values in group 1 were significantly smaller than those in group 2 after 50 cycles (group 1: 114 ± 38 N/mm and 94 ± 8% vs. group 2: 188 ± 71 N/mm and 106 ± 9%; p₅₀ = 0.022), 2000 cycles (group 1: 97 ± 34 N/mm and 81 ± 15% vs. group 2: 153 ± 47 N/mm and 88 ± 15%; p₂₀₀₀ = 0.028), and 5000 cycles (group 1: 98 ± 40 N/mm and 81 ± 22% vs. group 2: 158 ± 40 N/mm and 92 ± 16%; p₅₀₀₀ = 0.028). The failure load was not statistically significantly different between the groups.

INTERPRETATION

Although the PMAA group showed higher values for absolute and relative stiffness, no statistically significant difference was found in the primary stability between absorbable and non-absorbable cement augmentation supporting plate osteosynthesis in proximal humeral fractures. In view of the potential advantages of bio-absorbable cement during the healing process, its use should be considered for the augmentation and stabilization of osteoporotic fractures.

A Failed 4-Corner Arthrodesis Using a Polyether-Ether-Ketone Implant: A Case Report

CASE

A 59-year-old man underwent scaphoidectomy and 4-corner arthrodesis with a polyether-ether-ketone (PEEK) circular plate for scapholunate advanced collapse of the wrist. Five years later, he presented with a symptomatic nonunion and radiocarpal arthritis. Total wrist arthrodesis with a dorsal plate was performed. During revision surgery, considerable synovitis was encountered. Histological evaluation revealed a foreign body response likely secondary to PEEK particles.

CONCLUSION

Use of PEEK implants can result in an adverse local tissue reaction if particles are generated. This is a rare biomaterial-related complication, and surgeons should be aware of this adverse tissue response when using this or other PEEK implants.

The forgotten fragment: additional lesser tuberosity fixation of 4-part proximal humeral fractures-a biomechanical investigation

BACKGROUND

Fractures of the proximal humerus are common. The most frequent surgical treatment option is open reduction and locking plate fixation. Multifragmentary fractures, including 3- and 4-part fractures, are especially challenging to treat because they correlate with an increased risk of fixation failure. In the past, several mechanisms of additional fixation were investigated, but none directly addressed the lesser tuberosity (LT). The goal of this study was to investigate the biomechanical impact of additional anterior fracture fixation in lateral locked plating (LLP) of 4-part proximal humeral fractures (PHFs).

METHODS

Twenty-seven fresh frozen human shoulder specimens (mean age, 80 years) with intact rotator cuffs (RCs) were randomized into 4 groups: 3-part PHF with LLP and RC cerclage (n = 6); 4-part PHF with LLP and RC cerclage as standard of care (n = 7); 4-part PHF with LLP, RC cerclage, and 2 anterior 3.5-mm cortical screws (n = 7); and 4-part PHF with LLP, RC cerclage, and additional anterior one-third tubular plate (additional anterior plating [AAP], n = 7). Static load of the RC was simulated with weights. A force-controlled cyclic loading test was performed with a servo-hydraulic testing machine, followed by load-to-failure testing. An optical motion capture system recorded humeral head range of motion.

RESULTS

LLP of a 4-part PHF showed more humeral head motion than LLP of a 3-part PHF without fracture of the LT (P < .001). Fixing the LT to the humeral head with two 3.5-mm screws significantly reduced humeral head motion compared with LLP with RC cerclage alone (P < .006). Using AAP significantly increased the construct stiffness compared with the standard of care (P = .03).

CONCLUSION

LLP of a 4-part PHF is biomechanically less stable than LLP of a 3-part PHF without fracture of the LT. Additional screw fixation of the LT in 4-part PHFs improves stability compared with LLP alone. In case of metaphyseal comminution, AAP is favorable from a biomechanical perspective.

The effect of surgeon-controlled variables on construct stiffness in lateral locked plating of distal femoral fractures

Background

Nonunion following treatment of supracondylar femur fractures with lateral locked plates (LLP) has been reported to be as high as 21 %. Implant related and surgeon-controlled variables have been postulated to contribute to nonunion by modulating fracture-fixation construct stiffness. The purpose of this study is to evaluate the effect of surgeon-controlled factors on stiffness when treating supracondylar femur fractures with LLPs:

Does plate length affect construct stiffness given the same plate material, fracture working length and type of screws?

Does screw type (bicortical locking versus bicortical nonlocking or unicortical locking) and number of screws affect construct stiffness given the same material, fracture working length, and plate length?

Does fracture working length affect construct stiffness given the same plate material, length and type of screws?

Does plate material (titanium versus stainless steel) affect construct stiffness given the same fracture working length, plate length, type and number of screws?

Methods

Mechanical study of simulated supracondylar femur fractures treated with LLPs of varying lengths, screw types, fractureworking lenghts, and plate/screw material. Overall construct stiffness was evaluated using an Instron hydraulic testing apparatus.

Results

Stiffness was 15 % higher comparing 13-hole to the 5-hole plates (995 N/mm849N vs. /mm, p = 0.003). The use of bicortical nonlocking screws decreased overall construct stiffness by 18 % compared to bicortical locking screws (808 N/mm vs. 995 N/mm, p = 0.0001). The type of screw (unicortical locking vs. bicortical locking) and the number of screws in the diaphysis (3 vs. 10) did not appear to significantly influence construct stiffness (p = 0.76, p = 0.24). Similarly, fracture working length (5.4 cm vs. 9.4 cm, p = 0.24), and implant type (titanium vs. stainless steel, p = 0.12) did also not appear to effect stiffness.

Discussion

Using shorter plates and using bicortical nonlocking screws (vs. bicortical locking screws) reduced overall construct stiffness. Using more screws, using unicortical locking screws, increasing fracture working length and varying plate material (titanium vs. stainless steel) does not appear to significantly alter construct stiffness. Surgeons can adjust plate length and screw types to affect overall fracture-fixation construct stiffness; however, the optimal stiffness to promote healing remains unknown.

Homogenized finite element models can accurately predict screw pull-out in continuum materials, but not in porous materials

BACKGROUND AND OBJECTIVE

Bone screw fixation can be estimated with several test methods such as insertion torque, pull-out, push-in and bending tests. A basic understanding of the relationship between screw fixation and bone microstructure is still lacking. Computational models can help clarify this relationship. The objective of the paper is to evaluate homogenized finite element (hFE) models of bone screw pull-out.

METHODS

Experimental pull-out tests were performed on three materials: two polyurethane (PU) foams having a porous microstructure, and a high density polyethylene (HDPE) which is a continuum material. Forty-five titanium pedicle screws were inserted to 10, 20, and 30 mm in equally sized blocks of all three materials (N = 5/group). Pull-out characteristics i.e. stiffness (S), yield force (F_y), peak pull-out force (F_ult) and displacement at F_ult (d_ult) were measured. hFE models were created replicating the experiments. The screw was modeled as a rigid body and 5 mm axial displacement was applied to the head of the screw. Simulations were performed evaluating two different conditions at the bone-screw interface; once in which the screw fitted the pilot hole exactly ("free-stressed") and once in which interface stresses resulting from the insertion process were taken into account ("pre-stressed").

RESULTS

The simulations representing the pre-stressed condition in HDPE matched the experimental data well; S, F_y, and F_ult differed less than 11%, 2% and 0.5% from the experimental data, respectively, whereas d_ult differed less than 16%. The free-stressed simulations were less accurate, especially stiffness (158% higher than the pre-stressed condition) and d_ult (30% lower than pre-stressed condition) were affected. The simulations representing PU did not match the experiments well. For the 20 mm insertion depth, S, F_y and F_ult differed by more than 104%, 89% and 66%, respectively from the experimental values. Agreement did not improve for 10 and 30 mm insertion depths.

CONCLUSIONS

We found that hFE models can accurately quantify screw pull-out in continuum materials such as HDPE, but not in materials with a porous structure, such as PU. Pre-stresses in the bone induced by the insertion process cannot be neglected and need to be included in the hFE simulations.

Latest Trends in the Current Treatment of Proximal Humeral Fractures - an Analysis of 1162 Cases at a Level-1 Trauma Centre with a Special Focus on Shoulder Surgery

BACKGROUND

The management of proximal humeral fracture (PHF) is not only complex but ever changing. Published epidemiological data are often dated and do not factor in demographic changes or the latest developments in implant material and surgical techniques.

AIMS

The primary aim of this study was to evaluate changes in the epidemiology and actual treatment of PHF at a level-1 trauma centre, with a special focus on shoulder surgery.

HYPOTHESES

1. Between 2009 to 2012 and 2014 to 2017, an increase in complex PHF entities can be observed. 2. In correlation with fracture complexity, an increasing number of comorbidities, especially osteoporosis, can be observed.

METHODS

Between 2014 and 2017, a total of 589 patients (73% female; mean age: 68.96 ± 14.9 years) with 593 PHFs were treated. Patient records and imaging (XRs and CTs) of all patients were analysed. Fractures with ad latus displacement of a maximum of 0,5 cm and/or humeral head angulation of less than 20° were classified as non-displaced. Patients with displaced fractures were included in the analysis of the therapeutic algorithm. These results were compared to those of a cohort 2009 to 2012 (566 patients, 569 PHFs), which used the same inclusion criteria.

RESULTS

The two cohorts showed comparable patient numbers, as well as gender and age distributions. Between 2009 to 2012 and 2014 to 2017, a decrease in 2-part fractures (13.9 to 8.6%) and a simultaneous increase in 4-part fractures (20.4 to 30%), and thus fracture complexity was observed. Further decreases were observed in conservative therapy (27.8 to 20.6%), nail osteosynthesis (10.7 to 2.7%) and anatomic shoulder arthroplasty (5,4 to 1%). Furthermore, there was an increase in the use of locking plate osteosynthesis (43.2 to 56.7%) and reverse shoulder arthroplasty (9 to 18.4%). The general trend shows an increase in surgical therapy between the years (72.2 to 79.4%), as well as an increase in osteoporosis incidence (13 to 20.6%). The greatest numbers of comorbidities were found in 3- and 4-part fractures.

CONCLUSION

There is an increase in both the complexity of fractures and the number of surgically treated fractures between 2009 and 2012. Furthermore, an increase in osteoporosis numbers can be observed. New implants (PEEK, fenestrated screws for cement augmentation) and new surgical techniques (double plating osteosynthesis) were used as a result of increasing fracture complexity. Moreover, reverse total shoulder arthroplasty was used more commonly.

Overdrilling increases the risk of screw perforation in locked plating of complex proximal humeral fractures - A biomechanical cadaveric study

Locked plating of proximal humerus fractures (PHF) is associated with high failure rates (15-37%). Secondary screw perforation is a prominent mode of failure for PHF and typically requires reoperation. The anatomical fracture reduction is an essential factor to prevent fixation failure. However, recent studies indicate that the risk of secondary screw perforation may increase if the articular surface is perforated during predrilling of the screw boreholes (overdrilling). This study aimed to determine whether overdrilling increases the risk of secondary screw perforation in unstable PHF. Nine pairs of human cadaveric proximal humeri were osteotomized to simulate a malreduced and highly unstable 3-part fracture (AO/OTA 11 B1.1), followed by their assignment to two study groups for overdrilling or accurate predrilling in paired design, and fixation with a locking plate. Overdrilling was defined by drilling the calcar screw's boreholes through the articular surface. All humeri were cyclically loaded to screw perforation failure. Number of cycles to initial screw loosening and final perforation failure were analysed. The accurately predrilled group revealed a significantly higher number of cycles to both initial screw loosening (p < 0.01) and final screw perforation failure (p = 0.02), compared to the overdrilled one. This is the first study reporting that drilling to the correct depth significantly increases endurance until screw perforation failure during cyclic loading after locked plating in a highly unstable PHF model. Prevention of overdrilling the boreholes could help reduce failure rates of locked plating. Future work should investigate the prevalence and consequences of overdrilling in clinics.

Experimental and numerical investigation of secondary screw perforation in the human proximal humerus

Surgical treatment of proximal humerus fractures remains challenging, with a reported failure rate ranging from 15% to 35%. The dominant failure mode is secondary, i.e. post-operative screw perforation through the glenohumeral joint. A better understanding and the ability to predict this complication could lead to improved fracture fixation and decreased failure rate. The aims of this study were (1) to develop an experimental model for single screw perforation in the human humeral head and (2) to evaluate the ability of densitometric measures and micro finite element (microFE) analyses to predict the experimental failure event. Screw perforation was investigated experimentally in twenty cuboidal specimens cut from four pairs of fresh-frozen human cadaveric proximal humeral heads. A centrally inserted 3.5 mm screw was pushed quasi-statically at a constant displacement rate until perforation of the articular cartilage in each specimen. Force and displacement were recorded and evaluated at both initial screw loosening and perforation events. Bone volume was calculated around and in front of the screw and tip-to-joint distance was measured on the combined pre- and post-instrumentation micro computed tomography (microCT) scans. Implicit linear and explicit non-linear microFE models were created based on the microCT scans. The strength of these densitometric, geometrical and microFE methods to predict the experimental results was evaluated via correlation analysis. The bone volume measures were optimized in a parametric analysis to maximize correlation coefficients. The strongest and quantitatively correct predictions of perforation force (R² = 0.93) and displacement (R² = 0.77) were achieved using the explicit, non-linear microFE models. Linear microFE simulations provided the strongest predictions of loosening force (R² = 0.90). Correlation strengths reached by optimized bone volume measures for predicting experimental force and by tip-to-joint distance for predicting displacement were only slightly inferior compared to the results of microFE models. The strong correlations achieved with densitometric and geometric measures indicate that monotonic perforation of single screws through the articular surface of the humeral head can be well predicted with these easily accessible measures. However, non-linear microFE models delivered even stronger correlations and quantitatively correct predictions of perforation force and displacement. This indicates that if computational resources are available, non-linear simulations may have a high potential to investigate more complex fixations and loading scenarios.

A biomechanical matched-pair comparison of two different locking plates for tibial diaphyseal comminuted fracture: carbon fiber-reinforced poly-ether-ether-ketone (CF-PEEK) versus titanium plates

Background

Several methods have been proposed to reduce plate construct stiffness and promote secondary bone healing. In this study, we explored the stiffness and strength of the new carbon fiber-reinforced poly-ether-ether-ketone (CF 50) plate compared with the titanium alloy plate (Ti6Al4V).

Methods

Titanium and CF-PEEK locking plates were tested in a tibial non-osteoporotic diaphyseal comminuted fracture model to determine construct stiffness in axial compression, torsion, and bending. Subsequently, constructs were loaded until construct failure to determine construct strength.

Results

Relative to the titanium locking plate, the stiffness of the CF-PEEK locking plate was 6.8% and 30.8% lower in 200 N and 700 N axial compression, respectively (P < 0.05), 64.9% lower in torsion (P < 0.05), and 48.9% lower in bending (P < 0.05). The strength of the CF-PEEK locking plate was only 2.6% lower under axial compression, 7.8% lower in torsion, and 4.8% lower in bending than the titanium locking plate (P > 0.05).

Conclusions

The CF-PEEK locking plate significantly reduced axial, torsion, and bending stiffness compared with the titanium locking plate. Nonetheless, axial, torsional, and bending strength showed only a modest reduction. Considering its other advantages, which include radiolucency and artifact-free imaging, the CF-PEEK locking plate therefore deserves further clinical investigation.

Cross-elements to enhance fixation in osteoporotic bone with application to proximal humeral locking plates: a biomechanical study

BACKGROUND

Proximal humeral fractures occur predominantly in elderly, osteoporotic individuals, especially women, with surgery performed in one-fifth. Proximal humeral locking plates are the gold standard operative treatment; however, complications are frequent, partially because of poor screw purchase in osteoporotic bone. A new method uses threaded posts through which threaded cross-elements orthogonally pass to create a 3-dimensional scaffold for bone engagement. We examined the pullout characteristics of the posts with (1 or 2) or without the cross-elements and tested 2 types of 3.5-mm cortical locking screws for comparison.

METHODS

Low-density closed-cell polyurethane foam served as a model osteoporotic bone substrate. Following implantation in the substrate, the devices were axially loaded by a mechanical test system. Quantities of interest included failure mode, peak load, displacement to peak load, initial stiffness, and work expended.

RESULTS

The post groups outperformed the 3.5-mm screw groups, as expected. Relative to posts with no cross-elements, 1 and 2 cross-elements increased the peak load by 29% and 87% and increased the work to peak load by 126% and 343%, respectively. After reaching peak load, 1 and 2 cross-elements increased the work-resistance to further displacement by 158% and 330%, respectively.

CONCLUSION

Cross-elements significantly increased the ability of the threaded posts to resist axial displacement from a model osteoporotic bone substrate. This suggests that posts, used in conjunction with cross-elements, have the potential to enhance the stability of proximal humeral locking plates in osteoporotic bone.

Secondary Perforation Risk in Plate Osteosynthesis of Unstable Proximal Humerus Fractures: A Biomechanical Investigation of the Effect of Screw Length

Secondary perforation of screws into the joint surface is a commonly reported mechanical fixation failure mode in locked plating of proximal humerus fractures (PHF). This study investigated the influence that screws tip to joint distance (TJD) has on the biomechanical risk of secondary screw perforation and the stability of PHF. Ten pairs of cadaveric proximal humeri with a wide range of bone mineral density were used. Each specimen was osteotomized and instrumented with the PHILOS plate, simulating a highly unstable 3-part fracture. Bones were randomized into a long screw group (LSG) with 4 mm TJD, or a short screw group (SSG) with 8 mm TJD. A custom biomechanical setup was used to test the samples to failure cyclically with a constant valley load and an increasing ramp. The number of cycles to the initial screw loosening event was significantly higher for the LSG (mean ± standard deviation: 17,532 ± 6,458) compared with the SSG (11,102 ± 5,440) (p < 0.01). The mode of failure during testing was lateral-inferior displacement combined with varus collapse, with calcar screws perforating first. The number of cycles to failure event for LSG (27,849 ± 5,648) was not significantly different compared with SSG (28,782 ± 7,307) (p = 0.50). Screws that purchase closer to the joint had better initial stability and resistance against loosening. Placing longer screws, within limits dictated by the surgical guide, is expected to decrease the risk of secondary perforation failures in unstable PHF. These findings require clinical corroboration. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2625-2633, 2019.

The Treatment of Proximal Humerus Fracture Using Internal Fixation with Fixed-angle Plates

BACKGROUND

Implants made of various types of material can be used for the internal fixation of fractures. Carbon fiber reinforced polyetheretherketone (CFR-PEEK) is a radiolucent material that may have advantageous handling properties compared with titanium implants.

METHODS

Seventy-six patients with proximal humerus fractures requiring surgery were randomized to receive a fixed-angle plate made out of either titanium or CFR- PEEK. To measure the functional outcome, the DASH score (Disabilities of Arm, Shoulder, and Hand; primary endpoint), the Simple Shoulder Test (SST), and the Oxford Shoulder Score (OSS) were determined in 63 patients at 6 weeks, 12 weeks, and 6 months after surgery, accompanied at each time point by radiological evaluation.

RESULTS

Both groups displayed improvement in DASH scores 6 months after surgery (CFR-PEEK: 27.5 ± 20.5; titanium: 28.5 ± 17.9; p = 0.82). Sensitivity analysis with multiple imputations confirmed this result (27.4 ± 19.2 versus 28.5 ± 16.6). The OSS and SST scores were likewise improved in both groups. All patients displayed full bony consolidation 12 weeks after surgery. In no case was material failure, secondary dislocation, or screw perforation seen. No difference was seen in the maintenance of postoperative reposition between the CFR-PEEK group and the titanium group.

CONCLUSION

The internal fixation of proximal humerus fractures with either CFR-PEEK or titanium led to clinical improvement 6 months after surgery. No clinical or radiological difference in outcomes was seen between the two groups. Because of the study design, however, the equivalence of the two interventions was not con- clusively demonstrated; a non-inferiority study would have been needed for this purpose.

Biomechanical Testing of Additive Manufactured Proximal Humerus Fracture Fixation Plates

Achieving satisfactory fracture fixation in osteoporotic patients with unstable proximal humerus fractures remains a major clinical challenge. Varus collapse is one of the more prominent complications that may lead to screw cutout. This aim of this study was to compare the fixation provided by conventional locking plates with novel design concepts that are only feasible through additive manufacturing (AM) techniques. In addition to reversed engineered implants, two novel implant designs with integrated struts were included in the study to provide medial support to humeral head. The medial strut was either solid or included a porous lattice structure intended to promote bone ingrowth. Biomechanical tests were performed using low density synthetic bones with simulated 3-part comminuted fractures. Nondestructive torsion and compression were performed, followed by increasing cyclic loading. The relative displacements between the bone fragments were determined using a 3D motion capture system. The AM manufactured implants with medial strut showed significant reduction of varus displacement during the increasing cyclic loading when compared to conventional designs. AM reversed-engineered locking plates showed similar mechanical behavior to conventional plates with identical geometry. This study demonstrates the feasibility and potential of employing alternative design via AM for fixation of unstable comminuted proximal humerus fractures to reduce fragment displacement.

Finite Element- and Design of Experiment-Derived Optimization of Screw Configurations and a Locking Plate for Internal Fixation System

Objectives

The optimization for the screw configurations and bone plate parameters was studied to improve the biomechanical performances such as reliable internal fixation and beneficial callus growth for the clinical treatment of femoral shaft fracture.

Methods

The finite element analysis (FEA) of internal fixation system under different screw configurations based on the orthogonal design was performed and so was for the different structural parameters of the locking plate based on the combination of uniform and orthogonal design. Moreover, orthogonal experiment weight matrixes for four evaluation indexes with FEA were analyzed.

Results

The analytical results showed the optimal scheme of screw configuration was that screws are omitted in the thread holes near the fracture site, and single cortical screws are used in the following holes to the distal end, while the double cortical screws are fixed in thread holes that are distal to the fracture; in the other words, the length of the screws showed an increasing trend from the fracture site to the distal end in the optimized configuration. The plate structure was optimized when thread holes gap reached 13 mm, with a width of 11 mm and 4.6 mm and 5 mm for thickness and diameter of the screw, respectively. The biomechanical performance of the internal fixation construct was further improved by about 10% based on the optimal strain range and lower stress in the internal fixation system.

Conclusions

The proposed orthogonal design and uniform design can be used in a more efficient way for the optimization of internal fixation system, which can reduce the simulation runs to about 10% compared with comprehensive test, and the methodology can be also used for other types of fractures to achieve better internal fixation stability and optimal healing efficiency, which may provide a method for an orthopedist in choosing the screw configurations and parameters for internal fixation system in a more efficient way.

Carbon-Fiber-Reinforced Polymer Intramedullary Nails Perform Poorly in Long-Bone Surgery

BACKGROUND

Carbon-fiber-reinforced (CFR) polymer has produced great excitement in the orthopedic community as a material that will reduce bone healing times and provide improved image quality. Osteotomy stabilized with an intramedullary (IM) nail has become a common technique to address post-traumatic malalignment of the lower extremity.

PURPOSES/QUESTIONS

The following questions were asked: (1) Did CFR polymer nails provide a rapid healing time after long bone osteotomy, shortening, or fracture? (2) Did the CFR polymer nails produce unexpected complications?

METHODS

A retrospective review was conducted in patients who received CFR polymer IM nails for various indications, from April 2016 to January 2017 in a deformity and trauma practice, using patient charts and radiographs. The primary outcomes were time to union and incidence of complications including nonunion, hardware failure, neurovascular injury, venous thromboembolism, and infection.

RESULTS

Twelve patients who received CFR polymer IM nails in 16 limbs for various indications were included in our analysis. Patients were followed for an average of 16.9 months. Eleven limbs underwent realignment and were corrected an average of 23° through a diaphyseal osteotomy. Three limbs underwent limb-shortening surgery, an average of 25 mm, through an open, excisional osteotomy of the femoral diaphysis. Two diaphyseal, closed tibia fractures underwent routine IM nailing. The average time to union was 107.6 days, which included all limbs that united (11/16, 69%). Nonunion occurred in 5/16 (31%) of limbs. Complications recorded included nonunion and hardware failure, most of which resulted in unplanned surgery.

CONCLUSIONS

The use of the CFR polymer IM nail was associated with loss of fixation and nonunion after surgeries that have traditionally healed uneventfully. The increased elasticity of the CFR polymer allows for more motion at the osteotomy/fracture interface than the stiffer titanium counterparts, exposing long-bone osteotomies to delayed union and nonunion, a finding seen with CFR polymer plates. The overwhelmingly poor early results of this device applied to a long-bone deformity practice have led these authors to abandon the use of this implant.

Intraosseous metal implants in orthopedics: A review

Metal implants are biomaterials widely used in orthopedics. They are both used in osteosynthesis and arthroplasty. Their mechanical properties, biocompatibility and resistance to corrosion make them a widely used option in orthopedics. Alloys are the most commonly used metals in orthopedics. As far as physical traumas are concerned, implants such as screws, plates and/or nails are used for osteosynthesis as they ensure the stability of the fractured area and contribute to bone healing. Prostheses are used in arthroplasty to restore joint function for as long as possible. Contact between bone and the prosthesis induces bone remodeling at the interface between metal and bone even if the metal is recognized as biocompatible. Upon time, the interface between the metal implant and the bony tissue is continuously modified and adapted. Hip prosthesis is a typical example of intraosseous metal implant whose bone/implant interface has been extensively studied. Metal can be altered in vivo by different mechanisms including corrosion and fretting. An altered torque friction leads to wear debris that accumulate in the peri-prosthetic tissues causing metallosis.

Biomechanical evaluation of hybrid double plate osteosynthesis using a locking plate and an inverted third tubular plate for the treatment of proximal humeral fractures

Background

Treating proximal humerus fractures can be challenging because of large metaphyseal defects that conceal anatomical landmarks. In such cases, medial cortical support with, for example, calcar screws, is mandatory. Nevertheless, varus dislocations and implant failures in patients with impaired bone quality persist. Thus, the need for effective treatment of these patients exists. Hybrid double plate osteosynthesis was introduced as an alternative, yielding similar results as calcar screws. However, a biomechanical comparison of the stability of these two techniques is pending.

Methods

Cadaveric humeral specimens were treated with plate osteosynthesis and calcar screws (group 1, n = 9) or hybrid double plate osteosynthesis (group 2, n = 9) using a proximal humerus fracture model with a two-part fracture. Displacement, stiffness, failure mode, and ultimate load were examined biomechanically in a cyclic compressive-loading scenario.

Results

Although the hybrid double plate osteosynthesis (group 2) tended to confer higher stiffnesses than the medial support screws at higher cycles (group 1), this trend was below the level of significance. The displacement revealed non-significantly lower values for group 1 as compared with group 2 for cycles 50 and 2000, but at 5000 cycles, group 2 offered non-significantly lower displacement values than group 1. The ultimate load tended to be non-significantly higher in the hybrid double plate osteosynthesis group (group 2: 1342±369 N, group 1: 855±408 N). Both groups yielded similar failure rates, with the majority of failures in group 2 being gap closures (n = 8), whereas those in group 1 being plate dislocations (n = 4).

Conclusions

The use of an additive plate osteosynthesis in the region of the bicipital groove may be a potential alternative to the previously-established method of using calcar screws. The biomechanical data obtained in this study suggests that hybrid double plate osteosynthesis is as rigid and robust as calcar screws.

Comparison of CFR-PEEK and conventional titanium locking plates for proximal humeral fractures: a retrospective controlled study of patient outcomes

BACKGROUND

Metal plates are the fixation devices used most frequently to proximal humeral fractures (PHFs). However, in recent years carbon fiber-reinforced polyetheretherketone (CFR-PEEK) plates have become increasingly common. This study compares the clinical and radiographic outcomes of 42 Neer three- and four-part PHFs treated with CFR-PEEK or metal (titanium) plates.

MATERIALS AND METHODS

Forty-two PHF patients were managed with CFR-PEEK plates (n = 21, males/females 9/12; mean age 57.4 years; mean follow-up 30.7 months; CFR-PEEK group) or metal plates (n = 21; males/females 7/14; mean age 55.8 years; mean follow-up 52.7 months; Metal group). Active shoulder mobility (anterior elevation, lateral elevation, external rotation, and internal rotation), the Constant-Murley Score, the Simple Shoulder Test Score, and the pain score were recorded. Preoperative computed tomography scans and X-rays were obtained. Postoperative fracture healing and displacement, tuberosity resorption and/or malposition, hardware position, and cortical thinning (CT) under the plate were assessed radiographically.

RESULTS

Shoulder mobility, clinical, and pain scores were similar in both patient groups. CT was significantly greater in CFR-PEEK patients (mean difference, 1.14 mm; p = 0.0003). In both groups, incomplete or poor calcar reduction was associated to a significantly higher complication rate, especially stiffness and muscle weakness (p = 0.016). The rate of tuberosity resorption was significantly higher in the Metal group (p = 0.040). Two patients required revision to a hemiarthroplasty (CFR-PEEK) and reverse arthroplasty (Metal group).

CONCLUSIONS

CFR-PEEK plates provide a viable alternative to conventional titanium plates in PHFs, ensuring similar clinical outcomes and a lower rate of tuberosity resorption, but they involve higher stress shielding under the plate.

A Preliminary Comparison Suggests Poor Performance of Carbon Fiber Reinforced Versus Titanium Plates in Distal Femoral Osteotomy

BACKGROUND

Carbon fiber-reinforced (CFR) polymer implants have theoretical advantages over titanium plates.

QUESTIONS/PURPOSES

The aim of the present study was to assess our early outcomes with CFR plates in lateral opening-wedge distal femoral osteotomy to correct valgus lower limb malalignment. We asked the following: (1) Did the CFR polymer implant change time to union when compared with the titanium implant? (2) Did the incidence of displacement of medial cortical fractures differ between the implants? (3) Did the incidence of complications differ between the two techniques, and did other factors, such as bone graft material used, affect healing?

METHODS

A retrospective review of 16 limbs treated with an opening-wedge distal femoral osteotomy for genu valgum using either titanium (n = 10) or CFR plates (n = 6) was performed. Patient and clinical covariates as well as the primary outcome of time to union and secondary outcome of fracture displacement were collected and analyzed.

RESULTS

Those treated with CFR plates had longer times to union than did those in the titanium-treated group (median, 121.5 vs 81.5 days, respectively). The incidence of fracture displacement was higher in the CFR plate-treated group (CFR, n = 5/6; titanium, n = 1/10). Although the CFR plate-treated group had a 33% nonunion incidence while the titanium group had no nonunions, the study lacked the power to show significance. Bone graft material used did not affect outcome. Complication rates were higher in the CFR plate-treated patients.

CONCLUSION

The CFR plate was associated with a longer time to unite and higher fracture displacement rate than the titanium plate. As this is a retrospective case series, further research is required to confirm these results and clarify best practices in plating of distal femoral osteotomy for deformity correction.

Biomechanical comparison between stainless steel, titanium and carbon-fiber reinforced polyetheretherketone volar locking plates for distal radius fractures

INTRODUCTION

As the popularity of volar locked plate fixation for distal radius fractures has increased, so have the number and variety of implants, including variations in plate design, the size and angle of the screws, the locking screw mechanism, and the material of the plates.

HYPOTHESIS

Carbon-fiber reinforced polyetheretherketone (CFR-PEEK) plate features similar biomechanical properties to metallic plates, representing, therefore, an optimal alternative for the treatment of distal radius fractures.

MATERIALS AND METHODS

Three different materials-composed plates were evaluated: stainless steel volar lateral column (Zimmer); titanium DVR (Hand Innovations); CFR-PEEK DiPHOS-RM (Lima Corporate). Six plates for each type were implanted in sawbones and an extra-articular rectangular osteotomy was created. Three plates for each material were tested for load to failure and bending stiffness in axial compression. Moreover, 3 constructs for each plate were evaluated after dynamically loading for 6000 cycles of fatigue.

RESULTS

The mean bending stiffness pre-fatigue was significantly higher for the stainless steel plate. The titanium plate yielded the higher load to failure both pre and post fatigue. After cyclic loading, the bending stiffness increased by a mean of 24% for the stainless steel plate; 33% for the titanium; and 17% for the CFR-PEEK plate. The mean load to failure post-fatigue increased by a mean of 10% for the stainless steel and 14% for CFR-PEEK plates, whereas it decreased (-16%) for the titanium plate. Statistical analysis between groups reported significant values (p<001) for all comparisons except for Hand Innovations vs. Zimmer bending stiffness post fatigue (p=.197).

DISCUSSION

The significant higher load to failure of the titanium plate, makes it indicated for patients with higher functional requirements or at higher risk of trauma in the post-operative period. The CFR-PEEK plate showed material-specific disadvantages, represented by little tolerance to plastic deformation, and lower load to failure.

LEVEL OF EVIDENCE

N/A.

Validated computational framework for efficient systematic evaluation of osteoporotic fracture fixation in the proximal humerus

The high rate of fixation failure in osteoporotic proximal humerus fractures indicate the need for improved solutions. Computer simulations may help to overcome the limitations of the gold standard biomechanical testing in evaluating the performance of new implants and enhance the effectivity and outcome of the design process. This study presents a framework for automated computational analysis that facilitates efficient and systematic evaluation of proximal humerus fracture plating under a variety of conditions including bone quality, fracture pattern, implant configuration and loading regime. The underlying finite element methodology was previously validated. The capabilities of the software tool are demonstrated by virtually reproducing a previously published biomechanical study on the effect of screw augmentation and showing that the models capture the essence of the experimental results. Due to the modular design of the framework, the currently available set of angle-stable plate implants can be readily expanded to include other fixations such as intramedullary nails. Besides the capability to compare already existing solutions, the tool can provide rapid feedback on novel ideas. Therefore, it is expected to efficiently complement and partially replace expensive experimental tests and aid development and optimization of implant designs for improved fixation of osteoporotic proximal humerus fractures.

Biomechanical analysis of plate systems for proximal humerus fractures: a systematic literature review

BACKGROUND

Proximal humerus fractures are the third most common in the human body but their management remains controversial. Open reduction and internal fixation with plates is one of the leading modes of operative treatment for these fractures. The development of technologies and techniques for these plates, during the recent decades, promise a bright future for their clinical use. A comprehensive review of in vitro biomechanical studies is needed for the comparison of plates' mechanical performance and the testing methodologies. This will not only guide clinicians with plate selection but also with the design of future in vitro biomechanical studies. This review was aimed to systematically categorise and review the in vitro biomechanical studies of these plates based on their protocols and discuss their results. The technologies and techniques investigated in these studies were categorised and compared to reach a census where possible.

METHODS AND RESULTS

Web of Science and Scopus database search yielded 62 studies. Out of these, 51 performed axial loading, torsion, bending and/or combined bending and axial loading while 11 simulated complex glenohumeral movements by using tendons. Loading conditions and set-up, failure criteria and performance parameters, as well as results for each study, were reviewed. Only two studies tested four-part fracture model while the rest investigated two- and three-part fractures. In ten studies, synthetic humeri were tested instead of cadaveric ones. In addition to load-displacement data, three-dimensional motion analysis systems, digital image correlation and acoustic emission testing have been used for measurement.

CONCLUSIONS

Overall, PHILOS was the most tested plate and locking plates demonstrated better mechanical performance than non-locking ones. Conflicting results have been published for their comparison with non-locking blade plates and polyaxial locking screws. Augmentation with cement [calcium phosphate or poly(methyl methacrylate)] or allografts (fibular and femoral head) was found to improve bone-plate constructs' mechanical performance. Controversy still lies over the use of rigid and semi-rigid implants and the insertion of inferomedial screws for calcar region support. This review will guide the design of in vitro and in silico biomechanical tests and also supplement the study of clinical literature.

PEEK versus titanium locking plates for proximal humerus fracture fixation: a comparative biomechanical study in two- and three-part fractures

INTRODUCTION

The high rigidity of metal implants may be a cause of failure after fixation of proximal humerus fractures. Carbon fiber-reinforced polyetheretherketone (PEEK) plates with a modulus similar to human cortical bone may help to overcome this problem. The present study assesses the biomechanical behavior of a PEEK plate compared with a titanium locking plate.

MATERIALS AND METHODS

Unstable two- and three-part fractures were simulated in 12 pairs of cadaveric humeri and were fixed with either a PEEK or a titanium locking plate using a pairwise comparison. With an optical motion capture system, the stiffness, failure load, plate bending, and the relative motion at the bone-implant interface and at the fracture site were evaluated.

RESULTS

The mean load to failure for two- and three-part fracture fixations was, respectively, 191 N (range 102-356 N) and 142 N (range 102-169 N) in the PEEK plate group compared with 286 N (range 191-395 N) and 258 N (range 155-366 N) in the titanium locking plate group. The PEEK plate showed significantly more bending in both the two- and three-part fractures (p < 0.05), an increased relative motion at the bone-implant interface and lower stiffness values (p < 0.05).

CONCLUSION

In this biomechanical study on unstable proximal humerus fractures, fixation with a PEEK plate showed lower fixation strength and increased motion at the bone-implant interface compared with a titanium locking plate.

Outcomes of proximal humeral fracture fixation with locked CFR-PEEK plating

PURPOSE

To investigate the outcomes of proximal humeral fracture (PHF) fixation with a novel carbon-fiber-reinforced (CFR)-PEEK plate and to compare results with outcomes after conventional locked titanium plating.

METHODS

Twenty-one patients (7 male, 14 female) with operative treatment of unilateral displaced PHFs (mean age, 66.8 ± 9.9 years) with a novel CRF-PEEK plate were prospectively enrolled. Patients were followed up clinically (Constant Score, Simple Shoulder Test and Simple Shoulder Value) and radiologically 3 months postoperative and again clinically 12 months postoperative. Implant-related complications were evaluated after 3 and 12 months. Results at 1-year follow-up were compared with results of 21 patients (7 male, 14 female; mean age, 67.4 ± 9.7 years) with conventional titanium locked plating by matched case-control analysis.

RESULTS

All functional outcomes improved after CFR-PEEK plating (p < 0.05). Twelve months postoperatively, the mean age- and gender-related Constant Score was 99.8 ± 21.2%. All fractures healed by the 3-month follow-up without evidence of secondary screw perforation, fragment displacement or loss of fixation. There were no significant differences between the functional outcomes of patients with the CF-PEEK plate and patients with locked titanium plating (p > 0.05). Patients with locked titanium plating were significantly more likely to require revision surgery related to articular screw perforations (p = 0.048).

CONCLUSIONS

Fracture fixation of displaced PHFs with a novel CFR-PEEK plate resulted in good to excellent 1-year functional outcomes which were similar to outcomes of conventional locked titanium plating. The stiffer locked titanium plating was associated with a higher risk of articular screw perforations than the more elastic CFR-PEEK plate.