"Biological" internal fixation of long bone fractures: a biomechanical study of a "noncontact" plate system

Finite element model with realistic bone geometries for the optimal design of internal fixation during the fibula healing process

A finite element model with realistic bone geometries is developed to design optimal internal fixation during the fibula healing process in this study. The effect of bone plate parameters on fibula fracture healing is studied. The relationship between differences in plate length, thickness and working length, and bone healing performance is focused. The optimal combination form of the bone plate parameters was selected by the orthogonal experimental design and fracture block strain to achieve bone healing maximize the performance. The model results show that the maximum equivalent force of the bone plate was below the material yield limit; the higher mean contact stresses in the bone fragments indicate that the bone plate is prone to higher contact stresses when they are long. The working length of the bone plate has a greater effect on callus healing than the thickness and length of the bone plate. The optimal internal fixation option for distal fibula fractures is achieved when it provides the stability required for internal fixation during bone healing. It ensures lower contact stresses in the fibula as well as maximum Young's modulus during callus healing process.

Biomechanical Characteristics of Biplane Multiplanar Tension-Side Fixation for Lapidus Fusion

Although plating on the plantar, tension-side of the metatarsocuneiform joint provides an inherent biomechanical advantage for Lapidus arthrodesis, it has not been widely adopted owing to the morbidity associated with plantar application. To overcome these limitations, a modification to 90-90 locked biplanar plating was developed to provide the biomechanical advantages of multiplanar fixation and tension-side fixation, allowing application through a conventional incision. We tested the hypothesis that biplanar plating with tension-side fixation (low-profile straight dorsal plate and anatomic medial-plantar plate) would demonstrate improved mechanical stability compared with a previously tested 90-90 biplanar construct (small straight plate dorsally and medially) under cyclic loading. Both constructs were tested in static load to failure (3 pairs) and cyclic loading (10 pairs) with plantar cantilever bending using surrogate anatomic bone models. With static ultimate failure, the biplanar plate construct with tension-side fixation failed at a significantly greater failure load than did the straight biplanar plate construct (247.3 ± 18.4 N versus 210.9 ± 10.4 N; p = .04). With cyclic failure testing, the biplanar plate construct with tension-side fixation endured a significantly greater number of cycles (206,738 ± 49,103 versus 101,780 ± 43,273; p < .001) and a significantly greater dynamic failure load (207.5 ± 24.3 N versus 162.5 ± 20.6 N; p < .001) compared with the straight biplanar plate construct. These results have demonstrated that under simulated static and cyclic Lapidus arthrodesis loading, biplanar plating with tension-side fixation provides superior strength compared with the straight biplanar construct. Thus, this construct shows promise for clinical application as a practical approach to tension-side fixation and an early return to weightbearing after Lapidus fusion.

Computational modelling of long bone fractures fixed with locking plates - How can the risk of implant failure be reduced?

BACKGROUND AND PURPOSE

The Locking Compression Plate (LCP) is part of a new plate generation requiring an adapted surgical technique and new thinking about commonly used concepts of internal fixation using plates. Knowledge of the fixation stability provided by these new plates is very limited and clarification is still necessary to determine how the mechanical stability and the risk of implant failure can best be controlled.

METHODS

Upon validation, a finite element model of an LCP attached to a cylinder was developed to simulate and analyse the biomechanics of a transverse long bone fracture fixed with a locking plate. Of special interest were the factors influencing the mechanical conditions at the fracture site, the control of interfragmentary movement and implant failure.

RESULTS

Several factors were shown to influence stability in compression. Increasing translation and/or fracture angle post fixation reduced construct stability. Axial stiffness was also influenced by the working length and plate-bone distance. The fracture gap had no effect on the construct stability when no bone contact occurred during loading. Stress analysis of the LCP demonstrated that the maximum Von Mises stresses were found in the innermost screws at the screw-head junction.

INTERPRETATION

For the clinical use of the LCP as a locked internal fixator in fractures with an interfragmentary gap of 1 mm, at least two to four plate holes near the fracture gap should be omitted to allow fracture motion and bone contact to occur. This will also achieve a larger area of stress distribution on the plate and reduce the likelihood of fatigue failure due to cyclic loading.

Biological fixation of fracture shaft femur in children

The aim of this work was to assess the results of biological fixation of fracture shaft femur in children with locked plates. Twenty-eight fractures in 26 children with closed fractures of the shaft of the femur were managed with biological plating using locked plates bridging the fracture site applied submuscularly through two small incisions above and below the fracture site. The mean age of the patients was 11.2 years; all patients had radiological union within a mean time of 11.9 weeks (8-14 weeks); the average follow-up was 31 months (14-40 months). No patient had frontal or sagittal plane deformity more than 10° or limb length discrepancy more than 1.5 cm. There was no infection, delayed union, nonunion or clinically evident malrotation. A significant positive correlation between the age and the time to healing (p = 0.03) was detected, whereas there was no significant correlation between time to healing and patient sex, fracture level, fracture type, mechanism of injury. Also there was no significant correlation between limb length discrepancy and patient age, sex, fracture level, fracture type, and mechanism of injury. Biological fixation of fractures of the femoral shaft in children with locked plates is a reliable method of fixation with excellent healing potential and fixation mechanics without complications.

Effects of the bone-plate material and the presence of a gap between the fractured bone and plate on the predicted stresses at the fractured bone

In the present study, 3D finite element models for fractured bones with function-graded (FG) bone-plates and traditional bone-plates made of stainless steel (SS) or titanium (Ti) alloy are generated using the ABAOUS code. The predicted Von Mises stresses at the fracture site and underlying bone-plate are examined at different healing stages. The effects on the predicted Von Mises stresses at the fracture site of the presence of a gap between the plate and fractured bone are also studied. Based on the analytical results, it is found that the stress shielding at the fracture site at the fully healed stages decreases when using FG bone-plates compared to Ti alloy or SS bone-plates. In the initial healing stages, the Von Mises stresses at the fracture site increase (stress shielding decreases) by 17% and 11% when using FG bone-plates as compared to SS bone-plates for contacted and non-contacted bone-plate system, respectively. The significant effects of using an FG bone-plate with a gap on the resultant Von Mises stresses on the bone underneath the plate and on the bone stress shielding should be taken into consideration during fractured bone fixation.

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.

Controlled plastic deformation for the fastening mechanism of an internal fixation device. The new Mennen 3 PeriPro plate

The Mennen femur plate is a fixation device used for the treatment of femoral periprosthetic fractures. It features a novel fastening method where curved prongs are plastically deformed securing the implant to the bone. Although this "clamp-on" method has been successfully used to treat fractures of long bones, there are no literature data assessing the nature of the required plastic deformation. In the present study, the parameters influencing the performance of the prongs were identified and further explored using numerical modeling. The new Mennen 3 PeriPro plate is briefly discussed focusing on the new sculpted formation of the prongs. Their design was optimized to effectively control the magnitude and position of the required plastic deformation achieving enhanced anchorage on the fractured bone with minimum effort. The work presented contains all the necessary steps in analysing a clinical problem using finite elements and illustrates how effective use of simulation techniques can accurately predict and effectively control the required plastic deformation of a structure.

Estabilização primária da diáfise umeral: estudo experimental de diferentes métodos de osteossíntese

OBJETIVO: Estudo experimental idealizado com o objetivo de se avaliar a estabilização primária das fraturas da diáfise umeral com três diferentes métodos de osteossíntese, representados por uma placa tipo DCP aplicada com técnica em ponte, uma síntese incomum, denominada SPS®, ainda sem similar na literatura, aplicada pela técnica em ponte, e um terceiro método constituído de uma haste intramedular com um método de bloqueio também incomum proporcionado por um parafuso cortical distalmente e por um fio do tipo Ender proximalmente. MATERIAL E MÉTODO: Vinte e um pares de úmeros humanos foram divididos em três grupos, utilizando-se um tipo de material para cada grupo, os quais foram submetidos a osteotomias, aos procedimentos de fixação e a ensaios não destrutivos de flexo-compressão e de torção, com limites de carga de 200N e de 100N, respectivamente e, num mecanismo de "crossing", foram submetidos secundariamente a novos ensaios de torção e de flexo-compressão, amparados por análise estatística. RESULTADOS: O grupo da placa DCP em ponte mostrou boa resistência às cargas aplicadas, o que também ocorreu no grupo do SPS®, que apesar de mostrar maiores índices de deflexão, apresentou grande capacidade elástica. O grupo da haste intramedular mostrou bons resultados nos ensaios de flexo-compressão, devido ao seu mecanismo de tutor, mas não demonstrou resistência às cargas de torção.

Development of the Mennen 3 PeriPro fixation plate for the treatment of periprosthetic fractures of the femur

The Mennen femur plate is an internal fixation device used for the management of femoral perisprosthetic fractures, usually after total hip replacement surgery. The implant uses a number of curved prongs that embrace the fractured bone around its circumference without interfering with the stem of the prosthesis. Although the device has been used with considerable clinical success since its first introduction, a number of negative clinical results have been reported in the literature. The failure modes of the device are described and an evaluation of its performance is briefly presented. Based on this assessment as well as comments in the open literature, modifications in the design of the device have been implemented. The new Mennen 3 PeriPro plate is presented, with all the necessary data for a coherent explanation of its improved characteristics as defined using numerical simulations and experimental tests. The new device has all the beneficial features of the previous plate with improved structural performance and fatigue life and new sculpted formation of the prongs, providing a simple implantation technique with maximum gripping and minimum effort from the surgeon. The unique mode of fixation has been further improved, providing ample anchorage on the fracture bone without compromising its biomechanical integrity. By combining the device with a cable system, the spectrum of applications will be further expanded, enabling the surgeon to treat a broader range of fracture patterns.

Management of a nonunion of the distal femur in osteoporotic bone with the internal fixation system LISS (less invasive stabilization system)

We present a case illustrating the successful use of the internal fixation LISS in an osteoporotic nonunion of the distal femur, where classic osteosynthesis has failed. The LISS plate with its angular stability offered the possibility to achieve excellent purchase in the severely porotic and partially destroyed bone. In combination with the use of an autologeous bone graft laterally and a strut cortical autograft medially, a mechanical support and an osteoinductive stimulus was provided and the extremity could be saved by this procedure.

Percutaneous fixation of comminuted fractures of the humerus: initial experience at Al Razi hospital, Kuwait

OBJECTIVE

To present initial experience of 12 cases of percutaneous plating of the comminuted fractures of the humerus using minimal access surgery and standard low-contact dynamic compression plate.

PATIENTS AND METHODS

Twelve patients (11 males and 1 female) with an average age of 29.8 years (range 17-46 years) with comminuted diaphyseal fractures of the humerus were treated by minimal access surgery using standard AO/ASIF implants. Fracture was reduced indirectly either by manipulation or by a femoral distractor. Image intensifier was used to monitor the reduction and fixation. The plate was fixed on the anterior surface of the humerus using proximal and distal minimal incision on the anterior aspect of the upper arm.

RESULTS

All fractures were united, and all patients had a good range of motion in the adjacent joints. In 1 patient, there was a transient neurological deficit.

CONCLUSION

Percutaneous fixation of comminuted fractures of the humeral shaft is an alternative to standard open surgery, reducing the surgical impact and giving an excellent functional result.

Biological Osteosynthesis Versus Traditional Anatomic Reconstruction of 20 Long-Bone Fractures Using an Interlocking Nail: 1994-2001

OBJECTIVE

To observe differences in surgical and healing times as well as complication rates in dogs with a comminuted long-bone fracture stabilized with an interlocking nail (IN) using either anatomic or biologic repair.

STUDY DESIGN

Retrospective study.

ANIMALS

Twenty client-owned dogs with comminuted long-bone fractures.

METHODS

Medical records for dogs with fractures repaired during a 7-year period were reviewed; 20 dogs had repair with an IN nail and radiographic evidence of healing. These 20 dogs where divided into 2 groups, anatomic (11 dogs) and biological (9) repair, for statistical evaluation. Surgical and healing time and complication rates were compared between groups.

RESULTS

Median surgical times were: anatomic (95 minutes) and biologic (110 minutes; P=.06). Median healing times were anatomic (8 weeks) and biologic (6 weeks; P=.04). No statistical differences were observed in complication rates (the likelihood that a case required a second surgery [P=.58], the likelihood of a complication that was managed non-surgically [P=.27]). Use of a bone graft did not shorten healing times (P=.55).

CONCLUSIONS

Biological osteosynthesis provides clinical advantages over anatomic reconstruction with respect to a reduction in surgical and healing time without increasing complication rates.

CLINICAL RELEVANCE

Highly comminuted long-bone fractures can be successfully repaired using an IN without reconstructing the fracture fragments in dogs.