The limited contact dynamic compression plate (LC-DCP)

The optimal design of 3D-printed lattice bone plate by considering fracture healing mechanism

The biomechanical stimulus is the most important factor for fracture healing and mainly determined by the structural stiffness of bone plate. Currently, the materials commonly used in bone plates are stainless steel and titanium, which often lead to stress shielding effects because of their higher elastic modulus compared with the bone. This article suggests an optimal design method of lattice bone plate based on fracture healing theory. First, the mechanical regulation model with deviatoric strain is established to simulate the tissue differentiation process during fracture healing process. The ratio of the average elastic modulus of callus at the 120th day to the elastic modulus of mature bone is used to characterize the fracture healing rate. Second, the optimal elastic modulus of the design domain is obtained by the optimization mathematical model with the maximum fracture healing rate. Then, the design domain is filled with microstructures, the porosity of which is adjusted to make it possible that the equivalent elastic modulus is equal to the optimized value. And the finite element analysis of the bone plate with microstructure is executed. Finally, the designed lattice bone plates are manufactured through 3D printing, and the mechanical test is carried out. The simulation results indicate that the fracture healing rate is maximum when the elastic modulus of material in design domain is 38 GPa under the constraints of fixation stability. And both the finite element analysis and experiment results show that the designed lattice bone plate meet the strength requirements of fracture internal fixation implants.

Effective Treatment of Femur Diaphyseal Fracture with Compression Plate - A Finite Element and In Vivo Study Comparing the Healing Outcomes of Nailing and Plating

BACKGROUND

The rigidity in osteosynthesis causes primary healing, and it takes longer to heal. The flexibility provided to the fixation allows micromotion between fragments which accelerates secondary healing.

METHODS

In this study, the healing outcomes of nailing and plating in different fixation stabilities were investigated and compared by using a finite element tool. The clinical observational study was also performed to verify the results of the finite element analysis. The nonlinear contact analysis was performed on 5 different fixation configurations capturing nail and plate in immediate post-surgery.

RESULTS

The finite element analysis results showed that flexibility instead of rigidity in interlock nail implantation increases the axial and shear micromotion near the fracture site by 47.4% (P < 0.05) and 12.4% (P < 0.05), respectively. For LCDCP implantation, the flexible fixation increases the axial and shear micromotion near fracture site by 75.7% (P < 0.05) and 25.3% (P < 0.05), respectively.

CONCLUSION

Our findings suggest that flexible fixations of interlock nail and LCDCP provide a preferred mechanical environment for healing, and hence, the LCDCP in flexible mode can be an effective alternative to interlock nail for the femur diaphyseal fracture.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s43465-022-00795-1.

Preliminary study on a novel dedicated plate for iliac fractures in dogs

Introduction

The aim of this study was to describe and evaluate a novel plate designed specifically for the canine ilium using finite element methods. The cranial portion of the plate had an elliptical shape and contained nine screw holes. The caudal portion of the plate was triangular with three screw holes. Four and three screws were used at the cranial (screw 1 to 4) and caudal (screw 5 to 7) segment of the plate. Finite element models of the plate and canine pelvis were created. A load of 300 N was applied on the femur-hip joint contact area. Values of Von Mises Stress on the plate, screws and the maximum and minimum main stresses in the bone were used to capture the mechanical factors in this study.

Results

The novel implant had a plate stress of 51.9 megapascals (MPa) with higher stress in the dorsal part of the plate. Screws 2 and 4 showed similar stress values of 17.3 MPa. Screws 1 and 3 were the most loaded (51.9 MPa and 75 MPa, respectively). Screws 5, 6, and 7 showed similar dissipation and stress values (21.55 MPa). There was traction force in the dorsal region of the pubis and compression in the ventral part, with dissipation and values of 15.4 MPa and 23.9 MPa, respectively, acquiring balance between them.

Conclusion

The novel plate is potentially applicable and specifically suitable for iliac fractures in dogs. The screws distribution modeled proved itself strategical since the simulated stresses were evenly distributed throughout the implant construct.

Undercorrection: the undesired effect of compression on the osteotomy gap of the medial opening wedge high tibial osteotomy and its clinical significance

INTRODUCTION

Undercorrection is a common problem in opening wedge high tibial osteotomy (OWHTO). We investigated the compression effect of cortex screw on the osteotomy gap and its clinical significance.

MATERIALS AND METHODS

A standard OWHTO using the TomoFix plate was conducted on 20 bone models in two groups to get a 10-mm medial osteotomy gap. A cortex screw was used temporarily in a neutral (at the center) and an eccentric position (near the inclined plane) of the dynamic hole in group 1 and group 2, respectively. The mean of undercorrection observed in the two groups was compared using an independent t test. Also, the effect of compression on the gap between the plate and medial tibial cortex, and the osteotomy gap was evaluated using a Sine rule. Besides, the mean undercorrection observed was assessed for clinical significance based on the effect on the weight-bearing axis (WBA) using a Cosine Rule.

RESULTS

The mean undercorrection was 1.3 ± 0.6 mm and 2.6 ± 0.6 mm in group 1 and group 2, respectively. A significantly greater undercorrection was observed in group 2 (p < 0.001). The correction loss in group 2 has resulted from combinations of the sliding effect of the dynamic hole and oblique compression effect over the gap between the plate and medial tibial cortex whereas in group 1 it has only resulted from the oblique compression effect. The observed undercorrection in group 2 has resulted in clinically significant WBA shift (10%) over the width of the tibial plateau.

CONCLUSIONS

In OWHTO, compression is important for the stability and healing of osteotomy, but it can also cause loss of correction. In patients requiring large correction, the surgeon should control the amount of compression required and consider making extra osteotomy gap to avoid undercorrection. Furthermore, the placement of cortex screws in neutral is essential to lower the risk of undercorrection.

Bending properties of additively manufactured commercially pure titanium (CPTi) limited contact dynamic compression plate (LC-DCP) constructs: Effect of surface treatment

Additive manufacturing of metallic materials, a layer-wise manufacturing method, is currently gaining attention in the biomedical industry because of its capability to fabricate complex geometries including customized parts fitting to patient requirements. However, one of the major challenges hindering the full implementation of additively manufactured parts in safety-critical applications is their poor mechanical performance under cyclic loading. This study investigated both quasi-static bending properties (bending stiffness, bending structural stiffness, and bending strength) and bending fatigue properties of additively manufactured (AM) commercially pure titanium (CPTi) limited contact dynamic compression plate (LC-DCP) constructs based on ASTM International standard for metallic bone plates (ASTM F382). In addition, the effect of post surface treatment methods including single shot-peened (SP), dual shot-peened (DP), and chemically assisted surface enhancement (CASE) on bending fatigue performance was also evaluated. Results indicated that bending stiffness and bending structural stiffness of AM CPTi LC-DCPs are comparable to conventionally manufactured (CM) counterparts; however, the bending strength of AM CPTi LC-DCPs is lower than CM counterparts. While the fatigue strength of as-built AM CPTi LC-DCPs is lower compared to the CM counterparts, AM CPTi LC-DCPs after post surface treatments (SP, DP, and CASE) exhibit statistically comparable fatigue strength to the CM CPTi LC-DCPs.

Treatment of two Asiatic black bears (Ursus thibetanus) with severe injuries and their subsequent release into the wild: a case report

Background

The rehabilitation of injured wildlife and their subsequent release into the wild is a humane act as well as important in wildlife conservation. However, little is known about the animals’ fate after release. Therefore, to address these uncertainties, it is essential to adequately describe how the injured animals were treated and managed before releasing into the wild; moreover, post-release monitoring should also be performed. Herein, we document for the first time the process of rescue, surgery, and rehabilitation of severely injured Asiatic black bears (Ursus thibetanus; endangered species in South Korea) and their fate after returning to the wild.

Case presentation

A six-year-old female (bear-01) and a three-year-old male (bear-02) bears were injured by an illegal snare and collision with a bus, respectively. Bear-01 had broad muscle necrosis and ruptures from the snared ankle on the right thoracic limb, with myiasis, and elbow disarticulation was performed. In bear-02, a non-reducible comminuted fracture of the left humerus was confirmed radiologically, and the operation was performed by using dual plate fixation with hydroxyapatite and recombinant human bone morphogenetic protein-2. The bear-01 and -02 were completely healed approximately 30 and 60 days after surgery, respectively. After that, they underwent rehabilitation for 8 and 25 days, respectively, in an outdoor enclosure similar to their natural habitat. Bear-01 and -02 were released into the wild after 45 and 99 days after surgery, respectively, and their mean daily movement distance during the first 30 days after releasing was 2.9 ± 2.1 and 1.3 ± 1.6 km, respectively. The annual mean 95% Kernel home-range size of bear-01 and bear-02 was 265.8 and 486.9 km², respectively. They hibernated every winter, gained weight, gave birth to cubs (bear-01), were not found to have any abnormalities in the veterinary tests, and were not involved in any conflicts with humans after returning to the wild.

Conclusions

Bears without one leg or those with dual plates could adapt well in their natural habitat, which shows that our surgical and post-operative treatments were effective. Additionally, minimizing human contact and observing/evaluating behavior during the rehabilitation is essential in reducing human-bear conflicts after release.

From creative thinking to scientific principles in clinical practice

Stephan Perren's contributions to the understanding and application of the principles of bone pathobiology, healing, and fracture fixation to clinical care remain as a lasting legacy of a great creative mind. Less well appreciated perhaps were his important contributions to the dissemination and practical application of those principles through the use of technology as applied to the learning environment. This paper describes and pays tribute to a series of initiatives in which Perren was a leading mentor and collaborator in the development of methods and instruments through which the principles of bone mechano-pathobiology could be translated through active learning environments into the practical world of clinical musculoskeletal traumatology.

Biphasic plating improves the mechanical performance of locked plating for distal femur fractures

Internal fixation by plate osteosynthesis is the gold standard treatment for distal femur fractures. Despite improvements that preserve the biological conditions for bone healing, there are concerns standard locked plating constructs may be overly stiff. Biphasic plating is a novel concept designed to provide suitable fracture motion and increased implant strength to support early full weight-bearing. This study aims to demonstrate that the Biphasic Plate can be incorporated into a pre-contoured distal femur plate while providing adequate flexibility and increased implant strength. The mechanical performance of the Biphasic Plate (BP) was investigated in comparison to a standard locking plate for the distal femur (LCP-DF). Constructs were formed by mounting the implants on a bone substitute. The construct stiffness and strength under axial loading and the magnitude of interfragmentary movement were determined using finite element analysis. The Biphasic Plate exhibited a bi-linear stiffness response; at low loads, the BP construct was 55% more compliant and at high loads 476% stiffer than the LCP-DF. The Biphasic Plate provided more consistent interfragmentary movement over a wider loading range. At partial weight-bearing loads, the Biphasic Plate produced larger interfragmentary movements (0.18 vs. 0.04 mm). However, at loads equivalent to full weight-bearing, the maximum movements were substantially smaller than the LCP-DF construct (1.5 vs. 3.5 mm). The increased flexibility at low loads was provided without sacrificing implant strength with peak stress in the Biphasic Plate 63% lower than the LCP-DF construct. The biphasic plating concept can be successfully incorporated into anatomically contoured distal femur plates while providing adequate flexibility and increasing implant strength.

Effect of Screw Insertion Torque on Mechanical Properties of a Hybrid Polyaxial Locking System

OBJECTIVE

 The aim of this study was to determine the effect of insertion torque and angulation on the push-out strength of screws in Atraumatic Rigid Fixation (ARIX) system.

MATERIALS AND METHODS

 In vitro mechanical tests of the ARIX system were conducted. Screw plate constructs (n = 120) were tested using five different insertion torques at four different angles relative to the perpendicular axis of the plate. Before the push-out test, screws were locked into the plates, and the push-out force of the screw was measured by applying a load parallel to the screw axis.

RESULTS

 Implant failure was observed at 0.8 Nm at an insertion angle of 15 degrees, and at 1 Nm at 0 degree, 5 degrees and 10 degrees. Two types of failures were observed: cold welding and plate deformation. An insertion torque of 0.8 Nm produced a significantly higher push-out force compared with 0.2 Nm. Non-angled specimens with 0.8 Nm insertion torque exhibited significantly higher screw push-out forces compared with other tested specimens and insertion angles. Insertion angle did not affect screw push-out force at insertion torques of 0, 0.2, 0.4 and 0.6 Nm.

CONCLUSION

 The ARIX locking system is much more sensitive to insertion torque than angle. An effect of insertion angle was observed only at an insertion torque of 0.8 Nm, under which all angles significantly decreased push-out force relative to zero degrees of angulation. In addition, low insertion torques can result in screws loosening over time, while greater insertion torques than 1 Nm can result in screw head stripping and plate hole deformation.

Feasibility of the Inner-Side-Out Use of the LC-DCP for Periprosthetic Femoral Fracture in Total Hip Arthroplasty

BACKGROUND

The optimal technique for plate fixation to treat type B and C periprosthetic femoral fractures (PFFs) is unclear. The purpose of this study is to evaluate the radiographic results of inner-side-out limited contact dynamic compression plate (LC-DCP) to treat PFFs during or after total hip arthroplasty (THA).

METHODS

This retrospective study comprised of four men and six women with an average age of 64.7 years who underwent open reduction and internal fixation with an inner-side-out LC-DCP technique to treat PFFs; the reduction was maintained preliminary with the use of contoured plate and cables, and the grooves on the undersurface of LC-DCP for limited contact was used to hold and prevent the cables from slippage during tightening the cables. There were five intraoperative and five postoperative PFFs after THA. According to the Vancouver classification, the intraoperative PFFs included type B2 in two, B3 in one and C3 in two patients while postoperative PFFs were categorized into type B1 in one, type B2 in two and type C in two patients. The mean follow-up duration was 5.9 years (range 1-10.4). We evaluated radiographic union and complications after index operation.

RESULTS

All patients demonstrated radiographic bone union at an average follow-up duration of 4.4 months (range 3-8). Two patients showed stem subsidence after revision THA and one patient demonstrated a subsequent peri-implant fracture around the distal end of plate after union of the initial PPF; one patient underwent re-revision THA for stem loosening while another patient went through refixation for the peri-implant fracture. There was no nonunion, infection, nerve injury, or dislocation.

CONCLUSION

The inner-side-out LC-DCP technique showed satisfactory radiographic outcome. In certain situations where locking plates are not available, this technique might be a useful alternative for treating type B and C PFFs.

Pre-operative planning for fracture fixation using locking plates: device configuration and other considerations

Most locked plating failures are due to inappropriate device configuration for the fracture pattern. Several studies cite screw positioning variables such as the number and spacing of screws as responsible for occurrences of locking plate breakage, screw loosening, and peri-prosthetic re-fracture. It is also widely accepted that inappropriate device stiffness can inhibit or delay healing. Careful preoperative planning is therefore critical if these failures are to be prevented. This study examines several variables which need to be considered when optimising a locking plate fixation device for fracture treatment including: material selection; screw placement; the effect of the fracture pattern; and the bone-plate offset. We demonstrate that device selection is not straight-forward as many of the variables influence one-another and an identically configured device can perform very differently depending upon the fracture pattern. Finally, we summarise the influence of some of the key parameters and the influence this can have on the fracture healing environment and the stresses within the plate in a flowchart.

Evolution of plate design and material composition

The evolution of plate fixation of fracture was accompanied by advances in metallurgy and improvement in understanding of the requirements for successful fracture healing. Locked internal fixation minimizes biologic damage and when used in conjunction with minimally invasive approaches may optimize fracture healing. Some current metal locked plate constructs may actually be too stiff, and various methods including screw modification, plate hole modification, and changes in plate material composition may provide a solution to optimize fracture healing. This paper reviews the evolution of plate design and describes the early clinical experience with the use of carbon fibre reinforced reinforced polyetheretherketone composite plates.

Comparison of double locking plate constructs with single non-locking plate constructs in single cycle to failure in bending and torsion

Objective: To evaluate the biomechanical properties of single 3.5 mm broad dynamic compression plate (DCP) and double 3.5 mm String-of-Pearls (SOP) plate constructs in single-cycle bending and torsion. We hypothesized that the double SOP construct would outperform the broad DCP in both bending and torsional testing.

Methods: Broad DCP plates and double 3.5 mm SOP plates were secured to a previously validated bone model in an effort to simulate bridging osteosynthesis. Constructs were tested in both four-point bending and torsional testing.

Results: The double SOP constructs had significantly greater bending stiffness, bending strength, bending structural stiffness, and torsional stiffness when compared to the broad DCP constructs. The single broad DCP constructs had significantly higher yield torque and yield angles during torsional testing.

Clinical relevance: Although the in vitro mechanical performance of the double SOP construct was significantly greater than the single broad DCP constructs under bending loads, the actual differences were small. Various patient, fracture, and implant factors must be considered when choosing an appropriate implant for fracture fixation.

In vitro mechanical evaluation of a limited contact dynamic compression plate and hybrid carpal arthrodesis plate for canine pancarpal arthrodesis

Objective: To compare the mechanical properties of pancarpal arthrodesis (PCA) constructs stabilized at 20° of extension using either a 3.5 mm limited contact dynamic compression plate (LC-DCP) or a 3.5/2.7 mm hybrid plate (HP).

Methods: Seven forelimb pairs were used from dogs of similar size. All soft tissues were removed except for supporting structures of the carpus and proximal metacarpal region. All plates were accurately bent to 20°, and then instrumented with two, 350Ω strain gauges applied at the level of the bend. Constructs were embedded in epoxy moulds then mounted onto a servo-hydraulic testing machine. Specimens were loaded for 10 cycles at 100N, 200N and 300N. Tenth cycle construct compliance (CC), maximum angular deformation (MAD), and peak plate strain (PPS) were compared using two-factor analysis of variance (ANOVA) and Student-Newman- Keuls post-hoc tests (p <0.05).

Results: Regardless of load, CC was 29% to 33% smaller in the HP than the LC-DCP group (p <0.03). In each group, the CC significantly increased with increasing loads (p <0.02). Mean MAD was 19% to 22% less in HP than LC-DCP constructs, with significant differences seen at 200N and 300N loads. In both groups, MAD was significantly greater with increasing loads (p <0.02). In addition, PPS was 37% to 43% smaller for HP than LC-DCP.

Clinical significance: The mechanical advantages of the HP over the LC-DCP make it a viable alternative for PCA. Smaller CC, MAD and PSS of the HP may reduce the risk of implant failure and postoperative morbidity following PCA.

Surgical repair of a tibial fracture in a two-week-old grey seal (Halichoerus grypus)

Objective: To report the successful management of a suspected infected tibial fracture in a common grey seal.

Study design: Case report.

Animal: Female common grey seal (Halichoerus grypus), 2 weeks old, 20 kg.

Methods: A closed, complete, transverse fracture of the left tibial distal diaphysis was debrided, reduced and stabilized using a string-of-pearls (SOP) locking plate covered with polymethylmethacrylate impregnated with gentamicin. Fracture of the ipsilateral fibula was left untreated. Postoperative radiographs were obtained immediately, and at 10 days, three weeks, and six weeks post-surgery, and a computed tomographic examination was performed 2.5 months post-surgery. A species-specific progressive rehabilitation programme was conducted.

Results: Bone healing of both fractures and absence of injury of the distal tibial growth plate were evident on the 2.5 month follow-up examination, and also full range-of-motion of the flipper was preserved and no lameness or difficulty with swimming and hunting were detected. On computed tomography, signs of chronic left coxofemoral and ilial wing trauma were incidentally detected. The seal was released three months postoperatively.

Conclusion: A transverse infected distal fracture of the tibia and fibula in a young common grey seal was successfully managed with the combination of single SOP plating of the tibia, local antibiotic release and a specific rehabilitation programme.

Clinical relevance: Surgical treatment of a long-bone fracture in a wild immature grey seal was successful with a combination of techniques adapted to the species.

Single cycle to failure in bending of three standard and five locking plates and plate constructs

Objective: To evaluate the biomechanical properties of standard and locking plates in bending. We hypothesised that titanium (Ti) constructs would have the greatest deformation and that String of Pearl (SOP) constructs would have the greatest strength and stiffness, and would behave differently compared to plates alone.

Methods: Dynamic compression plates (DCP), stainless steel (SS) limited contact (LC)-DCP®, Ti LC-DCP, locking compression plates (LCP), 10 mm and 11 mm advanced locking plate system (ALPS 10 / 11), SOP and Fixin plates were evaluated individually and as constructs applied to a validated bone model simulating a bridging osteosynthesis. Bending stiffness and strength were compared using one-way ANOVA with post hoc Tukey, and un-paired t-test (p <0.05).

Results: The SOP plates had significantly greater stiffness than all other plates Ti LCDCP, ALPS 10 and Fixin plates had significantly lower stiffness than all other plates. The SOP constructs had the highest mean bending stiffness, and strength that was significantly different from only the Ti LC-DCP, ALPS 10 and Fixin constructs. The ALPS 10 constructs had the lowest mean bending stiffness, and strength that was significantly different from only ALPS 11 and SOP constructs. Comparison of bending structural stiffness of plates versus constructs showed a significant difference in all plate pairs except for the DCP and ALPS 10.

Clinical relevance: Due to differing plate construct properties inherent to these diverse implant systems, identical approaches to fracture management and plate application cannot be applied.

Presented at the 38th Annual Conference of the Veterinary Orthopedic Society, Snowmass, CO, USA March 6, 2011 (Mark S. Bloomberg Memorial Research Award recipient).

Reduced Incision Surgical Fixation of Diaphyseal Forearm Fractures in Adults through a Minimally Invasive Volar Approach

Purpose

The study aimed to describe and evaluate the minimally invasive volar approach to the forearm for open reduction and internal fixation of diaphyseal radius fractures.

Methods

This is a matched case-control study involving patients with diaphyseal forearm fractures operated by one orthopaedic surgeon over 2 years. Cases underwent a minimally invasive volar approach, whereas controls underwent a standard Henry's approach. In total, 17 cases and 17 controls were studied based on patient demographics, injury patterns, and surgical outcomes.

Results

The duration of surgery was significantly shorter for cases than for controls in combined radius and ulna fracture fixation (58.8 minutes vs. 84 minutes; p = 0.03). There was no significant difference in operative time for isolated radius fractures, hospitalisation duration, and time to return to work. No malalignment or complications were observed.

Conclusion

The minimally invasive volar approach to the forearm is as safe and efficacious as traditional approaches in the fixation of diaphyseal radius fractures.

A Newly Designed Intramedullary Nail for the Treatment of Diaphyseal Forearm Fractures in Adults

BACKGROUND

The treatment of diaphyseal forearm fractures using open reduction and plate fixation is generally accepted as the best choice in many studies. However, periosteal stripping, haematoma evacuation may result in delayed union, nonunion and infection. Refracture after plate removal is another concern. To overcome these problems intramedullary nails (IM) with different designs have been used with various outcomes. However previous IM nails have some shortcomings such is rotational instability and interlocking difficulties. We evaluated the results of newly designed IM nail in the treatment of diaphyseal forearm fractures in adults.

MATERIALS AND METHODS

32 patients who had been treated with the interlocking IM nail for forearm fractures between 2011 and 2014 were included in this study. There were 23 males and 9 females with mean age of 36 years (range 18-68 years). 22 patients (68.8%) had both bone fractures. Nine patients (28.1%) had open fractures. The remaining ten patients (31.2%) had radius or ulna fractures. Grace and Eversmann rating system was used to assess functional evaluation. Patient reported outcomes were assessed using the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire scores.

RESULTS

Union was achieved in all patients. The mean followup was 17 months (range 13 - 28 months). According to the Grace-Eversmann criteria, 27 patients (87.5%) had excellent or good results. The mean DASH score was 14 (range 5-36). Overall complication rate was 12.5%. Superficial infection was encountered in two patients. One patient had delayed union, however fracture healed without any additional surgical procedure. One patient who had open grade 3A, comminuted proximal third radius fracture developed radioulnar synostosis.

CONCLUSIONS

The new design IM interlocking forearm nail provides satisfactory functional and radiological outcomes in the treatment of adult diaphyseal forearm fractures.

Comparison of the effect on bone healing process of different implants used in minimally invasive plate osteosynthesis: limited contact dynamic compression plate versus locking compression plate

Minimally invasive plate osteosynthesis (MIPO) has been widely accepted because of its satisfactory clinical outcomes. However, the implant construct that works best for MIPO remains controversial. Different plate designs result in different influence mechanisms to blood flow. In this study, we created ulnar fractures in 42 beagle dogs and fixed the fractures using MIPO. The dogs were randomly divided into two groups and were fixed with a limited contact dynamic compression plate (LC-DCP) or a locking compression plate (LCP). Our study showed that with MIPO, there was no significant difference between the LCP and the LC-DCP in terms of fracture fixation, bone formation, or mineralization. Combined with the previous literature, we inferred that the healing process is affected by the quality of fracture reduction more than plate selection.

Comminuted supracondylar femoral fractures: a biomechanical analysis comparing the stability of medial versus lateral plating in axial loading

The aim of this study was to compare the biomechanical properties of medial and lateral plating of a medially comminuted supracondylar femoral fracture. A supracondylar femoral fracture model comparing two fixation methods was tested cyclically in axial loading. One-centimetre supracondylar gap osteotomies were created in six synthetic femurs approximately 6 cm proximal to the knee joint. There were two constructs investigated: group 1 and group 2 were stabilized with an 8-hole LC-DCP, medially and laterally, respectively. Both construct groups were axially loaded. Global displacement (total length), wedge displacement, bending moment and strain were measured. Medial plating showed a significantly decreased displacement, bending moment and strain at the fracture site in axial loading. Medial plating of a comminuted supracondylar femur fracture is more stable than lateral plating.

Biomechanical comparison of straight and helical compression plates for fixation of transverse and oblique bone fractures: Modeling and experiments

Total deformation and stability of straight and helical compression plates were studied by means of the finite element method (FEM) and in vitro biomechanical experiments. Fixations of transverse (TF) and oblique (45°) bone (OF) fractures have been analyzed on sheep tibias by designing the straight compression (SP) and Helical Compression Plate (HP) models. The effects of axial compression, bending and torsion loads on both plating systems were analyzed in terms of total displacements. Numerical models and experimental models suggested that under compression loadings, bone fracture gap closures for both fracture types were found to be in the favor of helical plate designs. The helical plate (HP) fixations provided maximum torsional resistance compared to the (SP) fixations. The fracture gap closure and stability of helical plate fixation for transverse fractures was determined to be higher than that found for the oblique fractures. The comparison of average compression stress, bending and torsion moments showed that the FEM and experimental results are in good agreement and such designs are likely to have a positive impact in future bone fracture fixation designs.

[Mono- versus polyaxial locking plates]

Conventional plate osteosynthesis is undergoing a period of transition. The concept of locking plate osteosynthesis is of special importance. Monoaxial locking plate osteosynthesis has shown promising results (rapid bone healing via callus, minimal soft tissue irritation, advantageous in osteoporosis). Some implants allow for polyaxial locking. The first results of comparative studies concerning biomechanics and clinical outcome of mono- versus polyaxial locking plates are presented.

Effectiveness of locking versus dynamic compression plates for diaphyseal forearm fractures

This study compares the results of the locking compression plate (LCP) and the dynamic compression plate (DCP) in the treatment of diaphyseal forearm fractures in adults and defines the indications for the use of the LCP. Forty-two patients with diaphyseal forearm fractures were retrospectively analyzed. Of those, 22 had been treated with the LCP (LCP group) and 20 had been treated with the DCP (DCP group). The AO/ASIF classification was used to classify the fractures. Patients were assessed using the Grace-Eversmann criteria and the Disabilities of the Arm and Shoulder and Hand questionnaire during the final follow-up. Mean follow-up was 21 months (range, 20-24 months) in the LCP group and 23 months (range, 19-26 months) in the DCP group. Union was achieved in all patients. Mean time to union was 15 weeks (range, 12-25 weeks) in the LCP group and 17 weeks (range, 13-24 weeks) in the DCP group. In each group, 1 patient experienced delayed union, which required no additional surgical intervention. No significant difference was found regarding the time to union between the groups (P>.05). No significant difference existed between the 2 groups in terms of Grace-Eversmann criteria and Disabilities of the Arm and Shoulder and Hand scores (both P>.05). The results of these different fixation methods for forearm fractures in adults are similar. As such, the correct selection and application of surgical technique is more important than the type of plate used.

Comparing the In Vitro Stiffness of Straight-DCP, Wave-DCP, and LCP Bone Plates for Femoral Osteosynthesis

The objective of this study was to compare the Locking Compression Plate (LCP) with the more cost-effective straight-dynamic compression plate (DCP) and wave-DCPs by testing in vitro the effects of plate stiffness on different types of diaphyseal femur fractures (A, B, and C, according to AO classification). The bending structural stiffness of each plate was obtained from four-point bending tests according to ASTM F382-99(2008). The plate systems were tested by applying compression/bending in different osteosynthesis simulation models using wooden rods to simulate the fractured bone fragments. Kruskal-Wallis test showed no significant difference in the bending structural stiffness between the three plate models. Rank-transformed two-way ANOVA showed significant influence of plate type, fracture type, and interaction plate versus fracture on the stiffness of the montages. The straight-DCP produced the most stable model for types B and C fractures, which makes its use advantageous for complex nonosteoporotic fractures that require minimizing focal mobility, whereas no difference was found for type A fracture. Our results indicated that DCPs, in straight or wave form, can provide adequate biomechanical properties for fixing diaphyseal femoral fractures in cases where more modern osteosynthesis systems are cost restrictive.

Morphological evaluation of eccentric sets guide-plates of dcp-l 4.5 mm

Objective

To carry out isolated and comparative evaluations of the measurements of the set eccentric guide plates used in 4.5mm surgical implants, and to determine the effect of these measurements on compression strength.

Methods

Four eccentric guides, four large dynamic compression plates (L-DCP) from four local manufacturers, and a Vonder^® 200 mm caliper brand were used. Five standard parameter measurements were created for the set eccentric guide-plate, which were identified as A to E. Four sets were made, using materials of the same factory, and identified as groups I to IV. The analyses were performed by measuring all the parameters from a ventral view of the plate, with the eccentric guide placed in the plate hole.

Results

Groups I and II showed the same values for all the parameters. All the groups showed the same measurements for E = 8.15 e B = 3.60. Group III: A = 8.10mm, C = 3.25mm, D = 1.25mm. Group IV: A = 7.00mm, C = 3.10mm, D = 0.30mm. Maximum compression force was (F Max.): Group I 80.58 N, Group. II: F Max. 81.63 N, Group. III: F Max. 36.32N, Group. IV: F Max. 37.52N

Conclusion

The measurements evaluated show a lack of standardization in the manufacture of orthopedic instruments and its effects on the values for compression strength. Level of Evidence: Level III, analytical study.

Influence of screw insertion order on compression generated by bone plates in a fracture model

Present recommendations regarding order of screw insertion for compression plate osteosynthesis in veterinary training are variable. We hypothesized that placement of a neutrally positioned screw would reduce the magnitude of compression that could be generated by a subsequently placed compression screw. Canine tibial diaphyseal segments were fixed to a plate attached to a bone surrogate and load cell, and the compression generated by screw tightening was measured. Three different screw insertion order patterns were evaluated using both dynamic compression plate (DCP) and limited contact dynamic compression plate (LC-DCP) implants. In group CN, the first screw was placed in compression mode and the second in neutral mode; in group NC, the first screw was placed in neutral mode and the second in compression mode; in group LNC, the first screw was placed partially tightened in neutral mode and the second in compression mode followed by complete tightening of the neutral screw. Screw insertion order significantly influenced the amount of compression generated with both groups CN and LNC demonstrating significantly greater compression generation when compared with group NC (p <0.0001). Compression generated by group CN constructs was also significantly greater than group LNC (p = 0.0013). Evaluation of group CN data to assess the influence of plate and drill guide combinations on compressive force generated did not demonstrate a statistically significant difference. To maximize compression using a load screw in a bone plate, following securement of the opposite bone fragment to the plate, it should be placed before a neutral screw is placed.

Mechanical evaluation of fourth-generation composite femur hybrid locking plate constructs

Locking compression plates are routinely used for open reduction and internal fixation of fractures. Such plates allow for locking or non-locking screw placement in each hole. A combined use of both types of screw application for stabilization of a fracture is commonly applied and referred to as hybrid internal fixation. Locking screws improve the stability of the fixation construct but at the expense of significant additional cost. This study experimentally analyzes various combinations of locking and non-locking screws under simultaneous axial and torsional loading to determine the optimal hybrid locking plate-screw construct in a fourth generation composite femur. Clinically it is necessary to ensure adequate fixation stability in a worse case fracture-bone quality scenario. A locking screw near the fracture gap increased the axial and torsional strength of the locked plate system. Greater removal torque remained in non-locked screws adjacent to locked screws compared to an all non-locking screws control group.

Plate fixation of femoral nonunions over an intramedullary nail with autogenous bone grafting

OBJECTIVE

To describe a novel approach for the treatment of nonunions of diaphyseal femur fractures.

DESIGN

Retrospective review.

SETTING

University hospital.

PATIENTS

Seven patients (six men, one woman, average age 42.5 years) with diaphyseal femoral fracture nonunions treated between November 2006 and November 2007 were reviewed. The injuries included two open and five closed fractures. All were treated initially with intramedullary nail fixation (two antegrade, five retrograde) and went on to develop a symptomatic nonunion by radiographic and clinical criteria.

INTERVENTION

Nonunions were treated with operative débridement of the nonunion with plate fixation and autogenous bone grafting without removal or exchange of the intramedullary nail.

MAIN OUTCOME MEASURES

Clinical criteria of decreased pain and return to function as well as radiographic evidence of fracture consolidation.

RESULTS

All patients demonstrated radiographic evidence of fracture consolidation with an average follow-up time of 17.9 months (range 12-26 months). All were allowed immediate weightbearing and reported decreased pain with improved function. Six patients reported absolutely no pain with ambulation as related to the fracture site, whereas one noted discomfort about the distal femoral compression plate. Independent ambulation was observed in six subjects. None of the patients required additional operations for implant removal or bone grafting procedures.

CONCLUSION

Treatment of diaphyseal femoral fracture nonunion after intramedullary nail fixation with large fragmentary compression plating and bone grafting is a reasonable option, especially for complex fractures about the metadiaphyseal region. The procedure appears to be successful in reducing pain, improving function, and predictably leads to radiographic consolidation of the nonunion.

Flexible fixation and fracture healing: do locked plating 'internal fixators' resemble external fixators?

External and internal fixators use bone screws that are locked to a plate or bar to prevent periosteal compression and associated impairment of blood supply. Both osteosynthesis techniques rely on secondary bone healing with callus formation with the exception of compression plating of simple, noncomminuted fractures. External fixation uses external bars for stabilization, whereas internal fixation is realized by subcutaneous placement of locking plates. Both of these "biologic" osteosynthesis methods allow a minimally invasive approach and do not compromise fracture hematoma and periosteal blood supply. Despite these similarities, differences between the two fixation methods prevail. Locked plating "internal fixators" allow a combination of biomechanical principles such as buttressing and dynamic compression. Periarticular locking plates are anatomically contoured to facilitate fixation of articular fractures. They allow for subchondral stabilization using small-diameter angular stable screws as well as buttressing of the joint and the metaphyseal component of a fracture. Biomechanically, they can be far stiffer than external fixators, because subcutaneous plates are located much closer to the bone surface than external fixator bars. External fixators have the advantage of being less expensive, highly flexible, and technically less demanding. They remain an integral part of orthopaedic surgery for emergent stabilization, for pediatric fractures, for definitive osteosynthesis in certain indications such as distal radius fractures, and for callus distraction.

Minimally invasive locked plating of distal tibia fractures is safe and effective

Distal tibial fractures are difficult to manage. Limited soft tissue and poor vascularity impose limitations for traditional plating techniques that require large exposures. The nature of the limitations for traditional plating techniques is intrinsic to the large exposure required to approach distal tibia, a bone characterized by limited soft tissue coverage and poor vascularity. The locking plate (LP) is a new device for treatment of fractures. We assessed the bone union rate, deformity, leg-length discrepancy, ankle range of motion, return to preinjury activities, infection, and complication rate in 21 selected patients who underwent minimally invasive osteosynthesis of closed distal tibia fractures with an LP. According to the AO classification, there were 12 Type A, 5 Type B, and 4 Type C fractures. The minimum followup was 2 years (average, 2.8 years; range, 2-4 years). Two patients were lost to followup. Union was achieved in all but one patient by the 24th postoperative week. Four patients had angular deformity less than 7 degrees . No patient had a leg-length discrepancy more than 1.1 cm. Five patients had ankle range of motion less than 20 degrees compared with the contralateral side. Sixteen patients had not returned to their preinjury sporting or leisure activities. Three patients developed a delayed infection. We judge the LP a reasonable device for treating distal tibia fractures. The level of physical activities appears permanently reduced in most patients.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

[Conventional plate osteosynthesis]

Consolidation of bone is an essential clinical problem when treating fractures, fixing osteotomies and fusing joints. In most cases, the means of fixation are plates and screws. The goal is functional postoperative therapy by moving the adjacent joints and thus avoiding the deleterious disadvantages of long-lasting articular immobilization. Pre-operative planning, surgical approach, a good understanding of the precise mechanics of the structure and the biological answer for the various tissues are prerequisites of successful osteosynthesis. The choice of implants and the application of their versatility, as well as their adaptation to individual cases are the key to good results.

Innovations in osteosynthesis and fracture care

Over the years giant steps have been made in the evolution of fracture fixation and the overall clinical care of patients. Better understanding of the physiological response to injury, bone biology, biomechanics and implants has led to early mobilisation of patients. A significant reduction in complications during the pre-operative and post-operative phases has also been observed, producing better functional results. A number of innovations have contributed to these improved outcomes and this article reports on the advances made in osteosynthesis and fracture care.

Clinical implementation of a multidirectional, angular stable osteosynthesis system in maxillofacial traumatology

AIM

To investigate whether a multidirectional, angular stable osteosynthesis system is suitable for the treatment of mandibular fractures and to compare it with well established available systems.

MATERIAL AND METHODS

Following preliminary testing in an animal model, the multidirectional angular stable system TiFix 2.3 obtained from Litos (Hamburg, Germany) was utilised for internal fixation of 39 mandibular fractures. These involved four symphyseal fractures, 17 parasymphyseal, 16 of the angle of the mandible and two comminuted fractures. The surgical and postoperative course was closely scrutinised. Radiographs were taken after 6 months and all plates removed under local anaesthesia. Photographs were taken intraoperatively and the plates and surrounding soft tissues were salvaged for histological analysis. Additionally, these operations were compared with treatment of equivalent fractures which were treated with conventional, non-angular stable systems. The relative costs have also been evaluated.

RESULTS

In 33 of the 39 fractures one TiFix plate sufficed for osteosynthesis. The plate most often used was a 2-hole plate which was applied in 25 (55.5%) fractures, followed by the 4-hole plates used in 16 (35.5%) fractures. In two comminuted fractures, four 6-hole plates were used (9%). In 17 patients the operation lasted less than 30 min, in 20 patients less than 60 min, in two less than 120 min. In all cases, the operations were shorter, and due to the plates' dimensions fewer screws had to be used, thus reducing the costs.

DISCUSSION

This angular stable system enabled reduction of the amount of the implant material. Also reduced were the operation time and the cost of the procedure. Furthermore, in the future it will allow smaller access incisions and better preservation of the soft tissue integrity.

A review of locking compression plate biomechanics and their advantages as internal fixators in fracture healing

Metallic implants are often involved in the open reduction and internal fixation of fractures. Open reduction and internal fixation is commonly used in cases of trauma when the bone cannot be healed using external methods such as casting. The locking compression plate combines the conventional screw hole, which uses non-locking screws, with a locking screw hole, which uses locking head screws. This allows for more versatility in the application of the plate. There are many factors which affect the functionality of the plate (e.g., screw placement, screw choice, length of plate, distance from bone, etc.). This paper presents a review of the literature related to the biomechanics of locking compression plates and their use as internal fixators in fracture healing. Furthermore, this paper also addresses the materials used for locking compression plates and their mechanical behavior, parameters that control the overall success, as well as inherent bone quality results.

Fatigue Analysis of Plates Used for Fracture Stabilization in Small Dogs and Cats

OBJECTIVE

To evaluate the fatigue life of stacked and single, veterinary cuttable plates (VCP) and small, limited contact, dynamic compression plates (LC-DCP).

STUDY DESIGN

In vitro biomechanical study.

METHODS

Fracture models (constructs; n = 8) were assembled for each of 6 groups all with 8-hole plates: 2.0 mm LC-DCP; 2.4 mm LC-DCP; single 1.5/2.0 mm VCP; stacked 1.5/2.0 mm VCP; single 2.0/2.7 mm VCP; and stacked 2.0/2.7 mm VCP. Plate(s) were secured to 2 polyvinylchloride pipe lengths, mounted in a testing system with a custom jig, and subjected to axial loading (10-100 N) for 1,000,000 cycles at 10 Hz or until failure. Differences in number of cycles to failure among groups were compared. Failure mode was determined.

RESULTS

All LC-DCP and single VCP constructs failed before 1,000,000 cycles. Stacked 2.0/2.7 mm VCP constructs withstood 1,000,000 cycles without failure. ANOVA and Fisher's least significant difference tests demonstrated significantly more cycles to failure for the stacked 1.5/2.0 mm VCP and stacked 2.0/2.7 mm VCP compared with the single 1.5/2.0 mm VCP, single 2.0/2.7 mm VCP, 2.0 mm LC-DCP, or 2.4 mm LC-DCP. Constructs that failed did so through a screw hole adjacent to the gap.

CONCLUSION

Stacked VCP constructs have greater fatigue lives than comparably sized LC-DCP or single VCP constructs. Plates with 2.4 mm screws were not significantly different from the comparable construct with 2.0 mm screws.

CLINICAL RELEVANCE

Although these data reveal that stacked VCP create a superior construct with respect to cyclic fatigue, surgeons must decide whether this is a clinical advantage on a case-by-case basis.

Biomechanics and biology of plate fixation of distal radius fractures

The fracture management principles of anatomic or near anatomic reduction, fracture stabilization, minimal operative trauma, and early joint motion are paramount in man-aging unstable distal radial fractures. The operative approach and plate selection should correlate with the fracture configuration. Plates have the advantages of providing secure fixation throughout the entire healing process without protruding wires or pins and allowing early and intensive forearm, wrist, and digital exercises. Disadvantages include additional operative trauma, including fragment devascularization; some additional risk of wrist stiffness; occasional tendon rupture; and at times, the need for plate removal. New developments in plate and screw design and operative strategies, fragment specific fixation, and plate strength have improved results with plate fixation. Fixed angle blades and locking screws and pegs enhance overall plate stability, support the articular surface of the distal radius, and are effective in fractures occurring in osteopenic bone.

Assessment of Stiffness and Strength of 4 Different Implants Available for Equine Fracture Treatment: A Study on a 20o Oblique Long-Bone Fracture Model Using a Bone Substitute

OBJECTIVE

To compare the mechanical properties of 4 stabilization methods for equine long-bone fractures: dynamic compression plate (DCP), limited contact-DCPlate (LC-DCP), locking compression plate (LCP), and the clamp-rod internal fixator (CRIF--formerly VetFix).

STUDY DESIGN

In vitro mechanical study.

SAMPLE POPULATION

Bone substitute material (24 tubes) was cut at 20 degrees to the long axis of the tube to simulate an oblique mid-shaft fracture.

METHODS

Tubes were divided into 4 groups (n=6) and double plated in an orthogonal configuration, with 1 screw of 1 implant being inserted in lag fashion through the "fracture". Thus, the groups were: (1) 2 DCP implants (4.5, broad, 10 holes); (2) 2 LC-DCP implants (5.5, broad, 10 holes); (3) 2 LCP implants (4.5/5.0, broad, 10 holes) and 4 head locking screws/plate; and (4) 2 CRIF (4.5/5.0) and 10 clamps in alternating position left and right of the rod. All constructs were tested in 4-point bending with a quasi-static load until failure. The implant with the interfragmentary screw was always positioned on the tension side of the construct. Force, displacement, and angular displacement at the "fracture" line were determined. Construct stiffness under low and high loads, yield strength, ultimate strength, and maximum angular displacement were determined.

RESULTS

None of the implants failed; the strength of the bone substitute was the limiting factor. At low loads, no differences in stiffness were found among groups, but LCP constructs were stiffer than other constructs under high loads (P=.004). Ultimate strength was lowest in the LCP group (P=.01), whereas yield strength was highest for LCP constructs (409 N m, P=.004). CRIF had the lowest yield strength (117 N m, P=.004); no differences in yield strength (250 N m) were found between DCP and LC-DCP constructs. Differences were found for maximum angular displacement at the "fracture" line, between groups: LPC<DCP<LC-DCP<CRIF (P< or =.037).

CONCLUSIONS

DCP, LC-DCP, and LCP constructs provided sufficient biomechanical stability to withstand single-cycle loads that might be experienced postoperatively. LCP constructs showed the best performance because of the highest yield strength, above which irreversible deformation occurred. Inadequate biomechanical properties, excessive motion, and shape of the device create concern about the use of CRIF in these large sizes.

CLINICAL RELEVANCE

CRIF does not meet the demands for equine long-bone fracture treatment. With respect to biomechanical properties, DCP, LC-DCP, and LCP constructs did not show critical differences so other factors may direct clinical selection of these implants. We prefer the LCP implants because of the high yield strength, high stiffness under high-load application, and the least movement at the fracture line.

In vitro mechanical evaluation on the use of an intramedullary pin-plate combination for pantarsal arthrodesis in dogs

OBJECTIVE

To compare the biomechanical properties of pantarsal arthrodesis achieved with a dorsal bone plate-alone (BPA) or pin-plate combination (PPC).

SAMPLE POPULATION

8 pairs of cadaver canine tarsi.

PROCEDURE

Within a pair, 1 tarsus was arthrodesed by use of a 13-hole 3.5-mm broad dynamic compression bone plate applied to the dorsal aspect of the tarsus; the paired tarsus received an identical plate similarly applied, with the addition of an intramedullary pin filling approximately 40% of the tibial medullary canal, spanning the tibiotarsal joint. Plates were instrumented with strain gauges proximal and distal to the solid portion of the plate. Specimens were mounted on a servo-hydraulic testing machine and loaded at 20%, 40%, and 80% of body weight for 10 cycles at 1 Hz. Construct compliance, angular deformation, and plate strain were determined during the 10th cycle.

RESULTS

PPC specimens were less compliant than BPA specimens at all loads and had significantly less angular deformation than BPA specimens at loads of 40% and 80% of body weight. Tibiotarsal gauge microstrain was significantly less in PPC specimens, compared with BPA specimens, regardless of loads. Maximal strains were 33.5% to 40.5% less in PPC than BPA specimens.

CONCLUSIONS AND CLINICAL RELEVANCE

For pantarsal arthrodesis in dogs, our results indicate that the PPC construct is biomechanically superior to the BPA construct. By improving construct stability, addition of an intramedullary pin to the traditional BPA technique may lessen implant-related complications and improve plate fatigue life. A subsequent decrease in postoperative morbidity may occur with little addition of time or complexity to the surgical procedure.

Treatment of midclavicular nonunion: comparison of dynamic compression plating and low-contact dynamic compression plating techniques

In this study a comparison of patients with midclavicular nonunion, treated by a combination of internal fixation with dynamic compression plate (DCP) or low-contact DCP (LC-DCP) and application of autogenous corticocancellous chips or sculptured graft on nonunion areas, was performed. Time to union in the patients treated with LC-DCP fixation was shorter than in those treated with DCP fixation (P <.001). Union was obtained in all patients treated with LC-DCP fixation and in 87.5% of those treated with DCP fixation. All of those treated with LC-DCP fixation returned to their original jobs, whereas two patients treated with DCP fixation had to change jobs. According to the Disabilities of the Arm, Shoulder, and Hand functional score, at the last follow-up visit, functional outcomes of the patients treated with LC-DCP fixation were more satisfactory (P <.001). The addition of internal fixation of the clavicle with DCP or LC-DCP to application of autogenous corticocancellous chips, or sculptured graft on nonunion areas in patients with midclavicular nonunion, shortens the time to union, increases union rates, and provides satisfactory functional outcomes.

An evaluation of interface contact profiles in two low contact bone plates

Bone plate design has evolved dramatically in recent years. The Dynamic Compression Plate (DCP) has been superseded by bi- and uni-cortical plates that claim a reduced interface contact between the plate and the underlying bone. It is believed that contact reduction ameliorates the localised ischaemia that develops subsequent to plate application. In this study, the interface characteristics of the Limited Contact-Dynamic Compression Plate (LC-DCP) and the Contour Plus (CP) plating systems have been quantitated using Fuji prescale pressure sensitive film interposed between the plate and the bone. Ten-hole plates were applied to the same aspect of either the humeral, radial or ulnar diaphysis of human cadaveric bone in a reproducible manner. The average pressure, force and interface contact area were calculated using Interactive Data Language (IDL) image analysis software. The CP system was consistently lower, in terms of interface contact, than the LC-DCP in each of the specimen locations tested (P<0.0001). The CP system displayed a 'point-contact' configuration along the interface with high pressures recorded at these points, the significance of which is unknown.

The Effect of Divergent Screw Placement on the Initial Strength of Plate-to-Bone Fixation

BACKGROUND

Numerous implants exist that allow screws to be placed at varying angles for lag fixation or to fix additional fragments. This study determined how placing screws at different angles affects fixation strength.

METHODS

Using a bone model, we first investigated the pullout strength of screws inserted at varying angles; then, we studied the strength of plate-bone constructs with end screws placed at divergent angles.

RESULTS

Varying the screw angle from 0 to 10 to 20 degrees progressively weakened the screw pullout resistance. No additional decrease was found in varying the angle further. In contrast, the strength of fixation of plate to bone was higher for constructs with screws placed at 20 or 30 degrees off of perpendicular when tested in gap-open bending and axial compression (all p < 0.05). No such differences were found in torsion.

CONCLUSION

The pullout strength with angled screws is reduced, but this does not translate into reduced strength of the bone-to-plate interface.