Strength recovery in fractured sheep tibia treated with a plate or an internal fixator: an experimental study with a two-year follow-up

A Retrospective Short-Term Evaluation Using a Polyaxial Plating System in 60 Small Animal Fractures

OBJECTIVE

 The aim of this study was to retrospectively evaluate the use, complications and outcomes of the Liberty Lock System (LLS) used to repair fractures in dogs and cats.

STUDY DESIGN

 Medical records (October 2016-June 2019) of dog and cat fractures repaired with the LLS were reviewed. Data reviewed included signalment, fracture classification, complications and radiographic outcome.

RESULTS

 The LLS was used to repair 60 fractures (57 appendicular and 3 axial) in 54 dogs and 6 cats. Mean time to radiographic union was 6 weeks (range: 4-16). Radiographic union was achieved in all 60 fractures with 55/60 healing without recorded complications. Major complications 4/60 and minor complication 1/60 rates were low and no catastrophic complications occurred. The most common major complication was surgical site infection.

CONCLUSION

 The LLS allowed for successful repair in all 60 cases with a wide variety of fractures. The LLS had a similar complication rate and time to radiographic union to that reported in other veterinary locking plate systems. The LLS is a reliable locking plate system which offers some advantages such as a low-profile plate with the ability to place non-polyaxial to angled polyaxial screws, to treat fractures in dogs and cats.

An additively manufactured locking fixation system for potential application in patient-specific implants

This study introduces a novel technique to implement a locking hole system into AM patient-specific implants without the need of additional post-processing steps such as mechanical machining. This has the potential to decrease the time and cost of manufacturing these implants, providing surgeons with an additional option, that is better suited in cases where the underlying bone is already weakened or bone porosis is an inherent risk. A commercially available locking system was chosen and replicated using high-resolution X-ray CT. A biocompatible material, 316L stainless steel was used to print specimen on a L-PBF machine in different orientations. The specimen were heat treated to tune the mechanical properties to enable the locking system to work. The accuracy of the printed holes was confirmed using a nominal/actual comparison between the original and printed holes. The strength of the system was evaluated by measuring the force needed to push the screw out of the locking plate. The 316L stainless steel samples, when annealed to tailor hardness, performed similarly to the commercial system. This included different build orientations that suggest the locking system can be included in AM implants without the need for additional post-processing steps.

Biomechanical Comparison of Tibial Plateau Leveling Osteotomy Performed With a Novel Titanium Alloy Locking Plate Construct vs. an Established Stainless-Steel Locking Plate Construct

A novel canine tibial plateau leveling osteotomy (TPLO) fixation device was recently developed with design features such as titanium alloy (TA) material, distal monocortical screw fixation, and a point contact undersurface specifically targeted to reduce surgical site infection rates by ensuring tissue perfusion under the plate. The strength of the novel TPLO construct was compared with that of a predicate stainless steel (SS) locking plate construct with bicortical screws in 16 paired cadaveric canine limbs. The mean loads to failure were 716.71 ± 109.50 N (range 455.69–839.69 N) and 629.50 ± 176.83 N (range 272.58–856.18 N) in the TA and SS groups, respectively. The average ratio of the loads to failure of the paired specimens was 1.18 (p = 0.031). No failure of the TA constructs involved the distal fixation with monocortical screws. Substantial mechanical equivalence of this novel TA monocortical/bicortical fixation construct to an established SS bicortical screw fixation construct is demonstrated. Clinical investigation of potential merits of this novel TA, monocortical/bicortical locking screw/plate system is now warranted.

Biomechanical Assessment of the Validity of Sheep as a Preclinical Model for Testing Mandibular Fracture Fixation Devices

Mandibular fracture fixation and reconstruction are usually performed using titanium plates and screws, however, there is a need to improve current fixation techniques. Animal models represent an important step for the testing of new designs and materials. However, the validity of those preclinical models in terms of implant biomechanics remains largely unknown. In this study, we investigate the biomechanics of the sheep mandible as a preclinical model for testing the mechanical strength of fixation devices and the biomechanical environment induced on mandibular fractures. We aimed to assess the comparability of the biomechanical conditions in the sheep mandible as a preclinical model for human applications of fracture fixation devices and empower analyses of the effect of such defined mechanical conditions on bone healing outcome. We developed 3D finite element models of the human and sheep mandibles simulating physiological muscular loads and three different clenching tasks (intercuspal, incisal, and unilateral). Furthermore, we simulated fractures in the human mandibular body, sheep mandibular body, and sheep mandibular diastema fixated with clinically used titanium miniplates and screws. We compared, at the power stroke of mastication, the biomechanical environment (1) in the healthy mandibular body and (2) at the fracture sites, and (3) the mechanical solicitation of the implants as well as the mechanical conditions for bone healing in such cases. In the healthy mandibles, the sheep mandibular body showed lower mechanical strains compared to the human mandibular body. In the fractured mandibles, strains within a fracture gap in sheep were generally not comparable to humans, while similar or lower mechanical solicitation of the fixation devices was found between the human mandibular body fracture and the sheep mandibular diastema fracture scenarios. We, therefore, conclude that the mechanical environments of mandibular fractures in humans and sheep differ and our analyses suggest that the sheep mandibular bone should be carefully re-considered as a model system to study the effect of fixation devices on the healing outcome. In our analyses, the sheep mandibular diastema showed similar mechanical conditions for fracture fixation devices to those in humans.

Locking Screws With a Threaded Degradable Polymer Collar Reduce Construct Stiffness Over Time

OBJECTIVES

The stiffness of locking plates provide increased stability for early fracture healing but may limit late interfragmentary motion (IFM) necessary for secondary bone healing. An ideal plating construct would provide early rigidity and late flexibility to optimize bone healing. A novel screw plate construct utilizing locking screws with a degradable polymer locking mechanism is a dynamic option.

METHODS

Conventional locked plating constructs (group A) were compared with locking screws with a threaded degradable polymer collar before (group B) and after polymer dissolution (group C). Monotonic axial compression, monotonic torsion, cyclic axial load to failure, and IFM at the near and far cortices were tested on synthetic bone models.

RESULTS

One-way analysis of variance and post hoc Tukey-Kramer testing demonstrated similar axial stiffness in group A (873 ± 146 N/mm) and B (694 ± 314 N/mm) but significantly less stiffness in group C (379 ± 59 N/mm; F(2,15) = 9.12, P = 0.003). Groups A and B also had similar IFM, but group C had significantly increased IFM at both the near (F(2, 15) = 48.66, P = 2.76E-07) and far (F(2, 15) = 11.78, P = 0.0008) cortices. In cyclic axial load to failure, group A (1593 ± 233 N) and B (1277 ± 141 N) were again similar, but group C was significantly less (912 ± 256 N; F(2, 15) = 15.00, P = 0.0003). All failures were above the 500-N threshold seen in typical weight-bearing restrictions for fracture care. Torsional stiffness demonstrated significant differences between all groups (F(2, 15) = 106.64, P = 1.4E-09).

CONCLUSIONS

Use of locking plates with a degradable polymer collar show potential for in vitro construct dynamization. Future in vivo studies are warranted to assess performance under combined loading and the effects of decreasing construct stiffness during the course of bony healing.

Retrospective evaluation of perioperative and short term clinical outcomes in appendicular long bone skeleton fractures repaired via the string of pearls (SOP) locking plate system

BACKGROUND

Internal plate fixation and, more recently, locking plate fixation are commonly used in the repair of fractures in small animal surgery. This retrospective study reviewed the use of the String of Pearls locking plate system in the fixation/repair of appendicular long bone skeleton fractures in 31 small animal veterinary patients (33 fractures).

RESULTS

Major complications necessitating revision surgery occurred in 7/33 (21%), with implant failure as the inciting cause in all cases. Variables corresponding to an unsuccessful outcome were evaluated, and a correlation was found with plates placed in a bridging manner (placed without rigid anatomic reconstruction, p = 0.02) and length of follow-up (p = 0.01).

CONCLUSIONS

The SOP plating system can be used in the repair of appendicular longbone skeletal fractures, however, the authors propose that adjunct fixation, such as intramedullary pin, double plating, or external coaptation would likely improve results and should be considered imperative in cases in which anatomic reconstruction is either not desirable or achievable.

Clinical application of a minimally invasive cement-augmentable Schanz screw rod system to treat pelvic ring fractures

PURPOSE

The purpose of this study is to analyze the results using the USS fracture MIS system (DePuy Synthes) to treat instable pelvic ring fractures. As its outstanding feature, it is the only Schanz screw and rod system at present that combines angular stability, perforation/fenestration of the screws for cement-augmentation, a variable screw length, and a large screw diameter.

MATERIALS AND METHODS

Retrospective investigation of 134 pelvic ring fractures treated in 2012-2013. Twenty-five patients obtained the abovementioned implant. Besides baseline characteristics of the included patients and the surgical procedure, a clinical/radiological follow-up of six months was analyzed.

RESULTS

Dividing the collective into two groups, I high-energy trauma and II fragility fracture of the pelvis, the following results were recorded: group I: ten patients, six male, age 48.4 ± 19.7 years. Mean ISS 41 ± 22.5, fracture classification: AO/OTA type 61 B₁/C₁/C₃ = 1/5/4. Operative treatment: three transiliac internal fixator, seven iliolumbar fixation, one implant was cement-augmented. Group II: 15 patients, 14 female, age 77.5 ± 10.1 years. Fracture classification according to Rommens: FFP_II/_III/_IV = 6/1/8. Operative treatment: eight transiliac internal fixator, seven iliolumbar fixation, 14 implants were cement-augmented. Overall surgical side complications: 16%. Radiological examination: correct positioning of all ilium screws. Follow-up after six month (16 patients): all showed fracture consolidation. One ilium screw was broken close to the connecting clamp.

CONCLUSION

The investigated Schanz screw rod system is a suitable implant to broaden the established procedures to stabilize dorsal pelvic ring fractures.

TRIAL REGISTRATION

The study is registered at the Clinical Trial Registry University of Regensburg (Number Z-2017-0878-3).

Surgical repair of a severely comminuted maxillary fracture in a dog with a titanium locking plate system

A four-year old male Labrador Retriever was admitted with head trauma after being hit by a car. The dog had sustained multiple nasal, maxillary, and frontal bone fractures that resulted in separation of the maxilla from the base of the skull. A severely comminuted left zygomatic arch fracture was also present. These fractures were all repaired using a point contact, locking titanium plate system, in a single procedure that resulted in excellent postoperative occlusion and immediate function. Healing was uneventful. Full function and excellent cosmetic appearance were evident 13 months after surgery. This case illustrates the ease of repair and the success of treatment of severely comminuted maxillofacial fractures by conforming to basic biomechanical principles taken directly from the human experience and successfully applied to the dog; these included multiple plate application along the buttresses and trusses of the facial skeleton. The plate fixation was applied to bridge the multiple fractures along the most appropriate lines of stress. The small size of the plates, and the ability to easily contour them to adapt to the bone surface in threedimensions, allowed their placement in the most appropriate positions to achieve sufficient rigidity and lead to uncomplicated healing without any postoperative complications.

Complex angular and torsional deformities (distal femoral malunions)

Objective: To describe the surgical technique of complex distal femoral deformity correction with the aid of stereolithography apparatus (SLA) biomodels, stabilized with locking plate fixation.

Methods: Full-size replica epoxy bone bio-models of the affected femurs (4 dogs/5 limbs) were used as templates for surgical planning. A rehearsal procedure was performed on the biomodels aided by a guide wire technique and stabilized with locking plate fixation. Surgery performed in all dogs was guided by the rehearsal procedure. All pre-contoured implants were subsequently used in the definitive surgical procedure with minimal modification.

Results: All dogs had markedly improved, with near normal functional outcomes; all but one had a mild persistent lameness at the final in-hospital follow-up examination (mean: 54.4 weeks; range: 24–113 weeks after surgery). All femurs healed without complications (mean: 34 weeks, median: 12 weeks; range: 8–12 weeks for closing osteotomies, and 26–113 weeks for opening wedge osteotomies). Long-term follow-up examination (mean: 28.6 months; range: 5–42 months) revealed all but one owner to be highly satisfied with the outcome. Complications were observed in two dogs: prolonged tibiotarsal joint decreased flexion that resolved with physical therapy. In one of these dogs, iatrogenic transection of the long digital extensor tendon was repaired, and the other had a peroneal nerve neurapraxia.

Clinical significance: Stereolithography apparatus biomodels and rehearsal surgery simplified the definitive surgical corrections of complex femoral malunions and resulted in good functional outcomes.

Online supplementary material is available for this paper at: http://dx.doi.org/10.3415/VCOT-15-08-0145

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

Objectives: The biomechanical properties of standard plates and recently designed locking plates were compared in torsion. We hypothesized that titanium (Ti) constructs would have the greatest deformation, and String of Pearls (SOP) constructs the greatest strength and stiffness.

Methods: Dynamic compression plates (DCP), stainless steel (SS) limited contact (LC)-DCP, Ti LC-DCP, locking compression plate (LCP), 10 mm and 11 mm Advanced Locking Plate System (ALPS) 10 and 11, SOP and Fixin plates were applied to a validated bone model simulating a bridging osteosynthesis. Yield torque (strength), yield angle (deformation) and stiffness were compared using one-way ANOVA with post hoc Tukey (p <0.05).

Results: The ALPS 11 constructs had significantly greater elastic deformation than all constructs except for the ALPS 10. There were not any differences in strength observed except for the ALPS 10 constructs, which was less than that for the SOP, LCP, DCP and ALPS 11 constructs. No differences in construct torsional stiffness were observed with the SS LCDCP, DCP, LCP and SOP constructs however all had greater stiffness than all remaining constructs. The ALPS 10 construct had lower stiffness than all constructs.

Clinical significance: Modulus of elasticity of Ti explains the higher deformation and lower stiffness of these systems, with similar results for the Fixin due to its lower section modulus compared to all other plates. The SOP and standard constructs had surprisingly similar biomechanical properties in torsion. The rationale for selecting these implants for fracture repair likely needs to be based upon their differing biomechanical properties inherent to the diverse implant systems.

Presented at the 38th Annual Conference of the Veterinary Orthopedic Society, Snowmass, Colorado, USA March 6, 2011.

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.

New cementless fixation in hip arthroplasty: a radiostereometric analysis

INTRODUCTION

Scyon Orthopaedics AG developed a new mode of cementless fixation of the femoral component that provides immediate and permanent anchorage by monocortical locking screws. The aim of this study was to evaluate the stability of the Scyon total hip replacement (THR) stem in-vivo.

METHODS

A total of 15 patients, with an average age of 50 years had surgery between 2008 and 2011. Each patient received a Scyon THR. Standard questionnaires were completed at each follow-up visit for evaluation of functional outcomes. RSA, patient reported outcomes, and plain radiographic follow-up were obtained at 6 months, 1 year, 2 years, and 5 years postoperatively.

RESULTS

The median ± standard error (SE) stem subsidence (negative y-translation) was 0.07 ± 0.07 mm at 1 year, 0.05 ± 0.04 mm at 2 years and 0.04 ± 0.13 mm at 5 years. The median ± SE stem rotation (y-rotation) was 0.1 ± 0.21 degrees at 1 year, 0.51 ± 0.31 degrees at 2 years and 0.60 ± 0.37 degrees at 5 years. Plain radiographs showed bone on-growth onto medial aspect of the stem. Median HHS improved from 55 preoperatively to 93 at 1 year and 97 at 5 years. The median UCLA Activity Score improved from 4 preoperatively to 6 at 1 year and 5 years.

CONCLUSIONS

RSA results indicate that the Scyon stem with its 5 monocortical locking screws is stable at 5 years. Immediate surgical fixation of the stem and bony on-growth onto the femoral component may ultimately decrease the rate of aseptic stem loosening in these THR patients.

Residual Hole Orientation After Plate Removal: Effect on the Clavicle

Clavicle fractures account for 2.6% to 4% of all fractures. Surgical stabilization of this type of injury is becoming more common. Anterior inferior plating and superior plating are 2 popular approaches to open reduction and internal fixation. Reports of plate removal have raised concerns about reinjury. The goal of the current study was to determine whether the orientation of screw holes in clavicles after removal of an anterior inferior plate vs a superior plate have different biomechanical effects on stiffness and load to failure. The medial and lateral ends of 28 matched pairs of fresh clavicles were potted. Pilot holes, 2.5 mm in diameter, were drilled and oriented anterior inferiorly or superiorly, simulating those left after removal of a plate for a middle-third fracture. The clavicles underwent dynamic axial compression and 3-point load to failure, replicating forces associated with reinjury. Clavicles with anterior inferior holes had a statistically significant higher median maximal load difference of 139 N compared with those with superior holes (P=.013). Anterior inferior holes showed a statistically significant median increase in stiffness of 16.3 N/mm compared with superior holes (P=.036). Clavicles with anterior inferior holes had a statistically significant increase in median maximal load to failure and an increase in median stiffness compared with those with superior holes. This finding is relevant for patients who undergo hardware removal and return to activities that put them at risk for repeat high-impact injuries to the clavicle.

Preclinical testing of drug delivery systems to bone

Bone defects do not heal in 5-10% of the fractures. In order to enhance bone regeneration, drug delivery systems are needed. They comprise a scaffold with or without inducing factors and/or cells. To test these drug delivery systems before application in patients, they finally need to be tested in animal models. The choice of animal model depends on the main research question; is a functional or mechanistic evaluation needed? Furthermore, which type of bone defects are investigated: load-bearing (i.e. orthopedic) or non-load-bearing (i.e. craniomaxillofacial)? This determines the type of model and in which type of animal. The experiments need to be set-up using the 3R principle and must be reported following the ARRIVE guidelines.

A novel locking screw hip stem to achieve immediate stability in total hip arthroplasty: A biomechanical study

INTRODUCTION

As total hip arthroplasty is now applicable for younger, healthier, and more active patients, bone preservation becomes even more essential, and proximal fixation, resulting in less stress shielding, draws special attention with focus on new strategies and implant designs. Recently, a new type of non-cemented fixation of the femoral component, featured with the locking screw hip (LSH) stem, was developed by Scyon Orthopaedics AG (Au-Waedenswil, Switzerland). The idea to rigidly fix the femoral component of a prosthesis for total hip replacement in this fashion evolved from the very good results achieved with the internal point-contact fixator PC-Fix. The purpose of this study was to investigate the unique characteristics of the LSH-stem and to assess its biomechanical performance in comparison to a conventional cemented prosthesis (Mueller straight stem).

MATERIAL AND METHODS

Six paired human cadaveric femora were preserved with the method of Thiel, split in two study groups, implanted with either cemented Mueller straight stem or LSH-stem prostheses and biomechanically tested under progressively increasing axial loading until catastrophic failure. Bone mineral density (BMD) of all femora was evaluated in the femoral head prior to implantation. Axial construct stiffness, failure load and cycles to failure were calculated from the machine data and statistically evaluated at a level of significance p = 0.05.

RESULTS

No statistically significant difference between the LSH-stem and the Mueller straight stem was found in terms of axial construct stiffness (2031.5 N/mm ± 483.1 N/mm and 2403.6 N/mm ± 705.2 N/mm, p = 0.115), failure load (4958.8 N ± 1094.1 N and 5907.2 N ± 1562.8 N, p = 0.138) and cycles to failure (7917.7 ± 2188.1 and 9814.3 ± 3125.6, p = 0.138). BMD showed no significant difference between the two study groups, p = 0.616.

CONCLUSION

The LSH-stem seems to be stable enough to carry loads experienced during the rehabilitation period of a patient after THR. Its stability, which is similar to that of the Mueller straight stem, may justify the clinical application of the LSH-stem under thorough investigation.

Concept of variable angle locking--evolution and mechanical evaluation of a recent technology

Applications for fracture-adapted screw positioning offered by variable angle locking screws are increasing. The locking strength of the variable angle locking mechanism at different insertion angles was compared to conventional fixed angle locking screws. Stainless steel (S) and titanium (Ti) variable and fixed angle 2.4 mm locking screws, inserted at different inclinations (0°-15°), and locked at 0.8 Nm were subjected to a load-to-failure test. Ultimate failure moment at the screw-head interface and failure mode of the screws were determined. Significant differences were detected by one-way ANOVA (p < 0.05). Stainless steel and titanium variable angle locking screws inserted at 2°-10° inclination exhibited a failure moment comparable to the 0° position (S 1.67± 0.04 Nm; Ti 1.67 ± 0.14 Nm) and failed predominantly at the screw neck, with the head remaining fixed to the plate. Inserted at 15° inclination, screws revealed a lower failure moment (S 1.33 ± 0.06 Nm, Ti 1.58 ± 0.05Nm), and failed predominantly by breakout of the head thread. Fixed angle locking screws inserted at an inclination >2° did not lock properly in the plate hole, providing insufficient locking strength. Variable angle locking screws offer a stable head-locking mechanism at different inclinations, comparable to the locking strength of orthogonal inserted fixed angle locking screws. Marginal inclinations >15° should be used with care.

Biplanar fixation of a locking plate in the diaphysis improves construct strength

BACKGROUND

Elevation of a locking plate over the bone surface not only supports biological fixation, but also decreases the torsional strength of the fixation construct. Biplanar fixation by means of a staggered screw hole arrangement may combat this decreased torsional strength caused by plate elevation. This biomechanical study evaluated the effect of biplanar fixation on the torsional strength of locking plate fixation in the femoral diaphysis.

METHODS

Custom titanium plates were manufactured with either a linear or staggered hole pattern to evaluate planar and biplanar fixation, respectively. Fixation strength under torsional loading was evaluated in surrogates of the femoral diaphysis representative of osteoporotic and non-osteoporotic bone. Furthermore, fixation strength was determined for plate fixation with unicortical or bicortical locking screws. Five specimens per configuration were loaded to failure in torsion to determine their strength, stiffness, and failure mode.

FINDINGS

In osteoporotic bone, biplanar fixation was 32% stronger (P=0.01) than planar fixation when unicortical screws were used and 9% stronger (P=0.02) when bicortical screws were used. In non-osteoporotic bone, biplanar fixation was 55% stronger (P<0.001) than planar fixation when unicortical screws were used and 42% (P<0.001) stronger when bicortical screws were used.

INTERPRETATION

A biplanar screw configuration improves the torsional strength of diaphyseal plate fixation relative to a planar configuration in both osteoporotic and normal bone. With biplanar fixation, unicortical screws provide the same fixation strength as bicortical screws in non-osteoporotic bone.

Net change in periosteal strain during stance shift loading after surgery correlates to rapid de novo bone generation in critically sized defects

In an ovine femur model, proliferative woven bone fills critically sized defects enveloped by periosteum within 2 weeks of treatment with the one-stage bone-transport surgery. We hypothesize that mechanical loading modulates this process. Using high-definition optical strain measurements we determined prevailing periosteal strains for normal and surgically treated ovine femora subjected ex vivo to compressive loads simulating in vivo stance shifting (n = 3 per group, normal vs. treated). We determined spatial distribution of calcein green, a label for bone apposition in first the 2 weeks after surgery, in 15°, 30°, and 45° sectors of histological cross sections through the middle of the defect zone (n = 6 bones, three to four sections per bone). Finally, we correlated early bone formation to either the maximal periosteal strain or the net change in maximal periosteal strain. We found that treatment with the one-stage bone-transport surgery profoundly changes the mechanical environment of cells within the periosteum during stance shift loading. The pattern of early bone formation is repeatable within and between animals and relates significantly to the actual strain magnitude prevailing in the periosteum during stance shift loading. Interestingly, early bone apposition after the surgery correlates well to the maximal net change in strain (above circa 2000-3000 με, in tension or compression) rather than strain magnitude per se, providing further evidence that changes in cell shape may drive mechanoadaptation by progenitor cells. These important insights regarding mechanobiological factors that enhance rapid bone generation in critically sized defects can be translated to the tissue and organ scale, providing a basis for the development of best practices for clinical implementation and the definition of movement protocols to enhance the regenerative effect.

Estudo da força de tração utilizando parafuso excêntrico em Placa de Compressão Dinâmica Larga (DCP-L)

OBJETIVO: Avaliar comparativamente a força de tração (F) determinada com a utilização de parafuso excêntrico em placas do tipo compressão dinâmica larga (DCP-L). MÉTODOS: Foram utilizadas três placas de tipo DCP-L de quatro fabricantes nacionais, todas em aço inoxidável austenítico ASTM F 138, e instrumentais disponíveis nas caixas de 4.5mm. As placas foram fixadas a dois corpos de prova sintéticos de polietileno e a força de tração foi obtida pela utilização de parafuso de 4.5mm, introduzido em furo excêntrico, realizado com instrumentais específicos de cada fabricante. Os resultados foram obtidos por uma máquina servo-hidráulica BME 2000 160/AT, Brasválvula. Os implantes foram divididos em grupos. (Fab. I, II, III, IV). Os testes foram interrompidos após atingir uma força de aperto do parafuso excêntrico de 5 N. RESULTADOS: O grupo I apresentou média de Força máxima (F Max.) 80.58 N; grupo II: F Max. 81.63 N; Grupo III: F Max. 36.32N; Grupo IV: F Max. 37.52N. Utilizando a Análise de Variância de Krukal-Wallis (ANOVA não paramétrica), sendo p= 0,05 existe diferença significativa na força máxima entre os grupos (p = 0,039). CONCLUSÃO: As placas DCP-L do grupo II apresentaram maior força (N) com fixação da placa utilizando parafuso excêntrico. Nível de Evidência: Nível III, estudo analítico.

Long-term effects of saw osteotomy versus random fracturing on bone healing and remodeling in a sheep tibia model

This article is about the evaluation of possible differences in biomechanical or histomorphological properties of bone healing between saw osteotomy and random fracturing after 6 months. A standardized, 30 degrees oblique monocortical saw osteotomy of sheep tibia was carried out, followed by manual fracture completion of the opposed cortical bone. Fixation was performed by bridge plating (4.5 mm, LCDCP, broad). X-rays were taken immediately after surgery and at the end of the study. Polychrome fluorescent staining was performed according to a standardized protocol in the 2nd, 4th 6th, 10th, 14th, 18th, 22th and 26th week. Ten sheep were comprehensively evaluated. Data for stiffness and histomorphology are reported. The average bending stiffness of the operated bone was higher (1.7 (SD 0.3) with plate (MP) vs. 1.5 without plate) than for the intact bone (1.4 (SD 0.2), though no significant differences in bending stiffness were observed (P>0.05). Fluorescence staining revealed small numbers of blood vessels and less fragment resorption and remodeling in the osteotomy gap. Bone healing after saw osteotomy shows a very close resemblance to 'normal' fracture healing. However, vascular density, fragment resorption, fragment remodeling, and callus remodeling are reduced at the osteotomy.

Stiffness modulation of locking plate constructs using near cortical slotted holes: a preliminary study

OBJECTIVES

Axial stiffness is a critical mechanical parameter in fracture plating. Standard locked plates allow minimal opportunities for stiffness alteration, and current methods are arbitrary and may lead to stiffness mismatch between the implant and bone. Milling the near cortex into a slot allows for an increase in translation of the screw shaft at the near cortex. The purpose of this proof of concept study was to determine the effects of slots on stiffness and their ability to maintain fixation of locking plates under cyclic loading.

METHODS

Using segments of fourth-generation synthetic diaphyseal bone, a simulated fracture with a gap was created and locked plates were applied with 4 bicortical locked screws in each fragment. On one fragment, the 4 near cortex holes were sequentially milled to 5 x 6-mm slots. Axial and torsional stiffnesses were determined for constructs with 0 through 4 slots. Specimens with 4 slots then underwent axial cyclic loading to determine the change in stiffness and loss of fixation. Extraction torque was measured for all screws to assess for screw loosening with cycling.

RESULTS

In constructs with 4 slots, axial stiffness decreased by 73% (P < 0.05) relative to the 0-slot constructs. Torsional stiffness of the 3- and 4-slot specimens decreased by 20% (SD, 13%; P < 0.05) and 17% (SD, 13%; P < 0.05), respectively, compared with the 0-slot specimens. With cyclic loading, no failures occurred in any specimen. No change in stiffness had occurred by the end of cycling (106% of initial stiffness; SD, 4%; P = 0.96). No screw loosening occurred during cyclic loading.

CONCLUSIONS

Purposeful stiffness modulation in fracture fixation is critical to facilitate uneventful fracture healing. Converting near cortical holes to slots allowed selective axial stiffness adjustment without sacrificing fixation stability under cyclic loading. With further refinement, this simple modification of standard implant application may allow the surgeon to decrease the modulus mismatch between plating constructs and bone to decrease the risk of fixation failure.

The challenge of establishing preclinical models for segmental bone defect research

A considerable number of international research groups as well as commercial entities work on the development of new bone grafting materials, carriers, growth factors and specifically tissue-engineered constructs for bone regeneration. They are strongly interested in evaluating their concepts in highly reproducible large segmental defects in preclinical and large animal models. To allow comparison between different studies and their outcomes, it is essential that animal models, fixation devices, surgical procedures and methods of taking measurements are well standardized to produce reliable data pools and act as a base for further directions to orthopaedic and tissue engineering developments, specifically translation into the clinic. In this leading opinion paper, we aim to review and critically discuss the different large animal bone defect models reported in the literature. We conclude that most publications provide only rudimentary information on how to establish relevant preclinical segmental bone defects in large animals. Hence, we express our opinion on methodologies to establish preclinical critically sized, segmental bone defect models used in past research with reference to surgical techniques, fixation methods and postoperative management focusing on tibial fracture and segmental defect models.

Analysis of anatomic periarticular tibial plate fit on normal adults

Implant manufacturers are producing anatomically contoured periarticular plates to improve the treatment of proximal tibia fractures. We assessed the accuracy of the designation anatomic. We applied eight-hole medial and lateral anatomically contoured periarticular plates to 101 cadaveric tibiae. The tibiae and the plate fits were mapped, quantified, and analyzed using a MicroScribe G2LX digitizer, Rhinoceros software, and MATLAB software. By corresponding the clinical appearance of good fit with our digital findings, we created numerical criteria for plate fit in three planes: coronal (volume of free space between the plate and bone), sagittal (alignment with the tibial plateau and shaft), and axial (match in curvature between the proximal horizontal part of the plate and the tibial plateau). An anatomic fit should mirror the shape of the tibia in all three planes, and only four medial and four lateral plate fits qualified. Recognizing and understanding the substantial variations in fit that exist between anatomically contoured plates and the tibia may help lead to a more stable fixation and prevent malreduction of the fracture and/or soft tissue impingement.

Locked internal fixator: sensitivity of screw/plate stability to the correct insertion angle of the screw

OBJECTIVE

Internal fixators with angular stability have been developed to provide high stability without compression of the plate on to the bone. Angular and axial stability of a plate-screw construct can be achieved using a conically threaded screw head undersurface and a corresponding conically threaded plate hole. Furthermore, the insertion angle of the screw must correspond precisely to the axis of the screw hole. This is not always achieved in clinical practice and may result in screw loosening. The objective of this study was to examine the relationship between the stability of the locked screw-plate on the insertion angle of the screw.

METHODS

Locking screws were inserted in an isolated (Point Contact Fixator, PC-Fix) or combined (Locking Compression Plate, LCP 4.5) locking hole with the use of an aiming device. The optimal insertion angle for these plates is perpendicular to the plate surface. The screws were inserted with an axis deviation of 0 degrees (optimal condition), 5 degrees , and 10 degrees respective to the optimal angle (variance +/- 1 degrees ). The samples were tested under shear or axial (push out) loading conditions until failure occurred. An Instron materials testing machine was used.

RESULTS

Locking screws inserted in the isolated locking hole (PC-Fix) showed a significant decrease of failure load if inserted at 5 degrees and 10 degrees angle. Using an optimal insertion angle (0 degrees ), failure load was 1480 +/- 390 N, with 5 degrees axis deviation 780 +/- 160 N, P = 0.0001, and with 10 degrees axis deviation 550 +/- 110 N, P = 0.0001. Screws inserted in the combined locking hole (LCP) also showed a significant decrease of push-out force of 77% (4960 +/- 1000 N versus 1120 +/- 400 N) with 10 degrees axis deviation. Compared to optimal insertion angle (0 degrees ), bending load to failure did decrease up to 69% (1240 +/- 210 N vs. 390 +/- 100 N) with 10 degrees axis deviation.

CONCLUSION

A locking head screw exhibits high stability with a moderate axis deviation in the angle of insertion of up to 5 degrees . However, there is a significant decrease in stability with increasing axis deviation (>5 degrees ). An aiming device is recommended to provide optimal fixation with angular stability.

Plate stabilization with bone rivets: an alternative method for internal fixation of fractures

OBJECTIVES

Bone rivets were developed as an alternative method to fasten plates during internal fixation of fractures when screw anchorage may be inadequate. This study examined whether such rivets allow proper fracture healing without eliciting adverse bone remodelling and whether they can be removed safely.

METHODS

A proximal diaphyseal fracture of the tibia was stabilized with a conventional plate (low-contact dynamic compression plate, Synthes) in 10 sheep. The distal fragment was anchored using bicortical screws, and the proximal fragment (1-2.5 mm thick cortex) with 3 rivets following screw stripping. Postoperative care included immediate weight bearing and biweekly radiographs. After 12 weeks, implants were removed from 6 sheep and the tibial strength measured. Tibiae with empty and filled rivet holes (at 12 and 24 weeks) were examined histologically.

RESULTS

In all sheep, secondary bone healing was observed without length and angulation deformities. All fracture gaps were bridged and filled with new bone. The average torsional strength after 12 weeks was 75 +/- 11% of the intact tibia (mean +/- SD), and failure never occurred through an empty rivet hole. After 12 weeks, there was intensive cortical remodelling at the rivets correlating with slight to moderate nonprogressive periosteal radiolucency around 55% of the rivets. However, there was also endosteal appositional bone growth at 85% of the rivets. There was no observable macroscopic or microscopic osseous damage after implant removal. After 24 weeks, remodelling activity had decreased and was noted only sporadically.

CONCLUSIONS

In this study, the efficacy of bone rivets for the internal fixation of a fracture with plates, where anchorage of screws may be difficult and/or insufficient, was demonstrated.

Biomechanical evaluation of healing in a non-critical defect in a large animal model of osteoporosis

Current methods for fracture treatment in osteoporosis are not always sufficient. To develop new fixation strategies (both mechanical and biological) requires pre-clinical testing utilizing appropriate models. The aim of this study was to apply a recently developed sheep model of osteoporosis to the study of healing in a non-critical long bone defect. A standardized transverse mid-shaft tibial osteotomy (with a fracture gap of 3 mm) was performed in seven osteoporotic and seven normal sheep and stabilized with a special external fixator for 8 weeks. The fixator was used for weekly in vivo bending stiffness measurements. Ex vivo bending stiffness and torsional stiffness of the callus zone were also determined. Callus area, callus density, and osteoporosis status were determined at 0, 4, and 8 weeks using peripheral quantitative computed tomography. The increase of in vivo bending stiffness of the callus was delayed approximately 2 weeks in osteoporotic animals. A significant difference (33%) in torsional stiffness was found between the osteotomized and contralateral intact tibia in osteoporotic animals, but no significant difference occurred in normal sheep (2%). In osteoporotic animals, ex vivo bending stiffness was reduced 21% (p=0.05). Bending stiffness was correlated with callus density (r=0.76, r=0.53); torsional stiffness was correlated with callus area (r=0.60) and to a lesser extent with callus density (r=0.53). This study demonstrated a delay of fracture healing in osteoporotic sheep tibiae with respect to callus formation, mineralization, and mechanical properties.

The evolution of modern plate osteosynthesis

Plate osteosynthesis is still recognized as the treatment of choice for most articular fractures, many metaphyseal fractures, and certain diaphyseal fractures such as in the forearm. Since the 1960s, both the techniques and implants used for internal fixation with plates have evolved to provide for improved healing. Most recently, plating methods have focused on the principles of 'biological fixation'. These methods attempt to preserve the blood supply to improve the rate of fracture healing, decrease the need for bone grafting, and decrease the incidence of infection and re-fracture. The purpose of this article is to provide a brief overview of the history of plate osteosynthesis as it relates to the development of the latest minimally invasive surgical techniques.

A new era in orthopedic trauma care

The previous 20 years have truly opened a new era of orthopedic trauma care. Rapid advances in the development of systems for internal and external fixation have been made. Improvements in technology and surgical technique have allowed fracture reduction and fixation to be achieved with less-invasive surgical approaches. This has reduced postoperative morbidity, decreased hospitalization, and expedited the recovery of function. A new understanding of processes at the cellular and molecular levels offers the possibility, for the first time, of directly influencing the biology of fracture union and soft-tissue healing. Transitional research has introduced new therapies that are moving rapidly from the laboratory to biotech industry and the clinical arena. Given the present state of scientific acceleration, orthopedic trauma care in the new millennium will be shaped by important developments that physicians can now only imagine.

Influence of the design for fixation implants on local infection: experimental study of dynamic compression plates versus point contact fixators in rabbits

OBJECTIVES

Comparison of infection resistance after local bacterial challenge associated with two different designs for fixation implants: the conventional dynamic compression plate (DCP) and the point contact fixator (PC-Fix).

DESIGN

Randomized, prospective study in experimental animals. Grouped sequential experimental procedure. Observation time was twenty-eight days, with twenty animals per group.

SETTING

Following surgery, animals were kept without restrictions in individual hutches.

ANIMALS

Forty White New Zealand rabbits. Thirty-eight animals, nineteen per group, were included in the final evaluation.

INTERVENTION

Under sterile conditions, specially manufactured titanium DCP or PC-Fix of identical dimensions were fixed to rabbit tibiae. After wound closure, different concentrations of Staphylococcus aureus, between 2 x 10(4) and 2 x 10(8) colony-forming units (CFU), were inoculated percutaneously at the implant site.

MAIN OUTCOME MEASUREMENTS

Implants, underlying bone, and surrounding soft tissues were removed under sterile conditions and quantitatively evaluated for bacterial growth. Infection was defined as positive bacterial growth at the bone-implant interface.

RESULTS

The overall infection rate was 45 percent. The infection dose of 50 percent (ID50) was 7.08 x 10(5) CFU for the DCP group and 8.51 x 10(6) CFU for the PC-Fix group. The infection rate was 63 percent (twelve of nineteen animals) for the DCP group and 26 percent (five of nineteen animals) for the PC-Fix group. This difference was statistically significant (p = 0.022).

CONCLUSIONS

After local bacterial challenge, we found a statistically significant difference in the infection rates depending on the implant design. The higher infection resistance associated with the PC-Fix design seems to be related to the reduced contact area at the bone-implant interface.

The torsional strength of bones with residual screw holes from plates with unicortical and bicortical purchase

OBJECTIVE: To evaluate the effect of unicortical and bicortical screw holes on residual bone strength by comparing the in vitro torsional strength of cadaveric sheep tibiae with screw holes from plates with unicortical and bicortical purchase relative to each other and to intact bone. DESIGN: The paired tibiae were grouped randomly and torsion tested to failure as follows: Group I -- unicortical screw holes versus intact bone; Group II -- bicortical screw holes versus intact bone; and Group III -- bicortical versus unicortical screw holes. BACKGROUND: Recently the point contact fixator, or PC-Fix (using screws with unicortical purchase), was designed to minimize bone devascularization beneath the plate compared to the conventional dynamic compression plate, or DCP (bicortical purchase), and possibly reduce refracture rates after plate removal. However, the effects of unicortical versus bicortical residual screw holes on potential refracture are unknown. METHODS: Screw holes were drilled and tapped through either a 7-hole bicortical DCP or a unicortical PC-Fix in 18 paired cadaveric sheep tibiae. The bones were then tested in torsion. RESULTS: The average decreases in the torsional strength of unicortical screw holes versus intact bone, bicortical screw holes versus intact bone, and bicortical versus unicortical screw holes were 21.6, 31.4, and 26.7% respectively. Mean torque values to failure were statistically significant within each of the three groups: P<0.01, 0.001, and 0.001 respectively. CONCLUSIONS: Bones with unicortical screw holes are significantly weaker in torsion than intact bones, but significantly stronger than bones with bicortical holes. RELEVANCE: Refracture after hardware removal is a recognized clinical complication of the traditional bicortical screw fixation. In combination with the demonstrated biological advantages, implants with unicortical purchase may be associated with less risk for early refracture upon removal.