RESUMEN

Orthopedic surgeons apply torque to metal screws manually by "subjective feel" to obtain adequate fracture fixation, i.e. stopping torque, and attempt to avoid accidental over-tightening that leads to screw-bone interface failure, i.e. stripping torque. Few studies have quantified stripping torque in human bone, and only one older study from 1980 reported stopping/ stripping torque ratio. The present aim was to measure stopping and stripping torque of cortical and cancellous screws in artificial and human bone over a wide range of densities. Sawbone blocks were obtained having densities from 0.08 to 0.80g/cm(3). Sixteen fresh-frozen human femurs of known standardized bone mineral density (sBMD) were also used. Using a torque screwdriver, 3.5-mm diameter cortical screws and 6.5-mm diameter cancellous screws were inserted for adequate tightening as determined subjectively by an orthopedic surgeon, i.e. stopping torque, and then further tightened until failure of the screw-bone interface, i.e. stripping torque. There were weak (R=0.25) to strong (R=0.99) linear correlations of absolute and normalized torque vs. density or sBMD. Maximum stopping torques normalized by screw thread area engaged by the host material were 15.2N/mm (cortical screws) and 13.4N/mm (cancellous screws) in sawbone blocks and 20.9N/mm (cortical screws) and 6.1N/mm (cancellous screws) in human femurs. Maximum stripping torques normalized by screw thread area engaged by the host material were 23.4N/mm (cortical screws) and 16.8N/mm (cancellous screws) in sawbone blocks and 29.3N/mm (cortical screws) and 8.3N/mm (cancellous screws) in human femurs. Combined average stopping/ stripping torque ratios were 80.8% (cortical screws) and 76.8% (cancellous screws) in sawbone blocks, as well as 66.6% (cortical screws) and 84.5% (cancellous screws) in human femurs. Surgeons should be aware of stripping torque limits for human femurs and monitor stopping torque during surgery. This is the first study of the effect of sawbone density or human bone sBMD on stopping and stripping torque.

Asunto(s)

Densidad Ósea , Tornillos Óseos , Fémur/fisiología , Fémur/cirugía , Fijación Interna de Fracturas/métodos , Torque , Fenómenos Biomecánicos , Biomimética , Fijación Interna de Fracturas/instrumentación , Humanos , Falla de Prótesis

RESUMEN

This work is part of an ongoing program to develop a new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite material for use as an orthopaedic long bone fracture plate, instead of a metal plate. The purpose of this study was to evaluate the mechanical properties of this new novel composite material. The composite material had a "sandwich structure", in which two thin sheets of CF/epoxy were attached to each outer surface of the flax/epoxy core, which resulted in a unique structure compared to other composite plates for bone plate applications. Mechanical properties were determined using tension, three-point bending, and Rockwell hardness tests. Also, scanning electron microscopy (SEM) was used to characterize the failure mechanism of specimens in tension and three-point bending tests. The results of mechanical tests revealed a considerably high ultimate strength in both tension (399.8MPa) and flexural loading (510.6MPa), with a higher elastic modulus in bending tests (57.4GPa) compared to tension tests (41.7GPa). The composite material experienced brittle catastrophic failure in both tension and bending tests. The SEM images, consistent with brittle failure, showed mostly fiber breakage and fiber pull-out at the fractured surfaces with perfect bonding at carbon fibers and flax plies. Compared to clinically-used orthopaedic metal plates, current CF/flax/epoxy results were closer to human cortical bone, making the material a potential candidate for use in long bone fracture fixation.

Asunto(s)

Materiales Biocompatibles/química , Placas Óseas , Carbono/química , Resinas Epoxi/química , Lino/química , Fuerza Compresiva , Módulo de Elasticidad , Diseño de Equipo , Análisis de Falla de Equipo , Dureza , Ensayo de Materiales , Resistencia a la Tracción

RESUMEN

For hip resurfacing, this is the first biomechanical study to assess anterior and posterior femoral neck notching and femur flexion and extension. Forty-seven artificial femurs were implanted with the Birmingham hip resurfacing (BHR) using a range of notch sizes (0, 2, and 5 mm), notch locations (superior, anterior, and posterior), and femur orientations (neutral stance, flexion, and extension). Implant preparation was done using imageless computer navigation, and mechanical tests measured stiffness and strength. For notch size and location, in neutral stance the unnotched group had 1.9 times greater strength than the 5-mm superior notch group (4539 N versus 2423 N, p=0.047), and the 5-mm anterior notch group had 1.6 times greater strength than the 5-mm superior notch group, yielding a borderline statistical difference (3988 N versus 2423 N, p = 0.056). For femur orientation, in the presence of a 5-mm anterior notch, femurs in neutral stance had 2.2 times greater stiffness than femurs in 25° flexion (1542 N/mm versus 696 N/mm, p = 0.000). Similarly, in the presence of a 5-mm posterior notch, femurs in neutral stance had 2.8 times greater stiffness than femurs in 25° extension (1637 N/mm versus 575 N/mm, p = 0.000). No other statistical differences were noted. All femurs failed through the neck. The results have implications for BHR surgical techniques and recommended patient activities.

Asunto(s)

Artroplastia de Reemplazo de Cadera/instrumentación , Artroplastia de Reemplazo de Cadera/métodos , Fémur/fisiopatología , Fémur/cirugía , Prótesis de Cadera , Prótesis Articulares de Metal sobre Metal , Fuerza Compresiva , Módulo de Elasticidad , Análisis de Falla de Equipo , Humanos , Diseño de Prótesis , Estrés Mecánico , Resistencia a la Tracción

RESUMEN

The femur is the most common long bone involved in metastatic disease. There is consensus about treating diaphyseal and epiphyseal metastatic lesions. However, the choice of device for optimal fixation for distal femur metaphyseal metastatic lesion remains unclear. This study compared the mechanical stiffness and strength of three different fixation methods. In 15 synthetic femurs, a spherical tumor-like defect was created in the lateral metaphyseal region, occupying 50% of the circumference of the bone. The defect was filled with bone cement and fixed with one of three methods: Group 1 (retrograde nail), Group 2 (lateral locking plate), and Group 3 (lateral nonlocking periarticular plate). Constructs were tested for mechanical stiffness and strength. There were no differences between groups for axial stiffness (Group 1, 1280 +/- 112 N/mm; Group 2, 1422 +/- 117 N/mm; and Group 3, 1403 +/- 122N/mm; p = 0.157) and offset torsional strength (Group 1, 1696 +/- 628N; Group 2, 1771 +/- 290N; and Group 3, 1599 +/- 253 N; p = 0.816). In the coronal plane, Group 2 (296 +/- 17 N/mm) had a higher stiffness than Group 1 (263 +/- 17N/mm; p = 0.018). In the sagittal plane, Group 1 (315 +/- 9 N/mm) had a higher stiffness than Group 3 (285 +/- 19 N/mm; p = 0.028). For offset torsional stiffness, Group 1 (256 +/- 23 N/mm) had a higher value than Group 3 (218 +/- 16 N/mm; p = 0.038). Group 1 had equivalent performance to both plating groups in two test modes, and it was superior to Group 3 in two other test modes. Since a retrograde nail (i.e. Group 1) would require less soft-tissue stripping in a clinical context, it may be the optimal choice for tumor-like defects in the distal femur.

Asunto(s)

Clavos Ortopédicos , Placas Óseas , Fracturas del Fémur/fisiopatología , Fracturas del Fémur/cirugía , Neoplasias Femorales/fisiopatología , Neoplasias Femorales/cirugía , Fijación Interna de Fracturas/instrumentación , Módulo de Elasticidad , Análisis de Falla de Equipo , Fracturas del Fémur/etiología , Neoplasias Femorales/complicaciones , Fijación Interna de Fracturas/métodos , Humanos , Diseño de Prótesis , Estrés Mecánico , Resistencia a la Tracción , Resultado del Tratamiento

RESUMEN

This study examined changes in femoral cortical porosity resulting from femoral canal preparation during cemented total hip arthroplasty (THA). Twenty-four canines were randomly assigned to 3 groups: (1) reaming only, (2) cementing without pressurization, and (3) cementing with pressurization. Femoral cortical porosity was measured from histologic samples of the femurs at 7 positions. Reaming during canal preparation significantly increased cortical porosity. Cementing further increased cortical porosity, whereas pressurization of cement helped to counteract the increase in cortical porosity caused by cementing alone. Cortical porosity was considered to be a marker for bone mineral density (BMD) during the early phase of peri-implant healing around cemented stems. To maximize bone mineral density after cemented total hip arthroplasty, we suggest using implants that do not require reaming and pressurizing cement appropriately.

Asunto(s)

Fémur/fisiología , Fémur/cirugía , Fijación Intramedular de Fracturas , Animales , Cementos para Huesos , Modelos Animales de Enfermedad , Perros , Porosidad , Cicatrización de Heridas

RESUMEN

We aimed to establish if radiological parameters, dual energy x-ray absorptiometry (DEXA) and quantitative CT (qCT) could predict the risk of sustaining a femoral neck fracture following hip resurfacing. Twenty-one unilateral fresh frozen femurs were used. Each femur had a plain digital anteroposterior radiograph, DEXA scan and qCT scan. Femurs were then prepared for a Birmingham Hip Resurfacing femoral component and loaded to failure. Results demonstrated that gender and qCT measurements showed strong correlation with failure load. QCT could be used as an individual measure to predict risk of post-operative femoral neck fracture. However, when qCT is unavailable; gender, pre-operative DEXA scan and Neck Width measurements can be used together to assess risk of post-operative femoral neck fracture in patients due to undergo hip resurfacing.

Asunto(s)

Fracturas del Cuello Femoral/etiología , Hemiartroplastia/efectos adversos , Fracturas Periprotésicas/etiología , Anciano , Anciano de 80 o más Años , Femenino , Fracturas del Cuello Femoral/fisiopatología , Fémur/diagnóstico por imagen , Humanos , Técnicas In Vitro , Masculino , Persona de Mediana Edad , Fracturas Periprotésicas/fisiopatología , Radiografía , Estrés Mecánico

RESUMEN

OBJECTIVES: The femur is the most common long bone affected by cancerous metastasis. Femoral tumor defects are known to induce pain and functional impairment in patients. Although prior studies exist evaluating the clinical and biomechanical effect of tumor defect size, no biomechanical studies have experimentally examined the risk of pathological fracture with respect to the anterior, posterior, medial, and lateral surfaces on which a proximal tumor defect is located on the femur. METHODS: Circular tumor-like defects of 40-mm diameter were created proximally in the subtrochanteric region on the Anterior (n = 5), Posterior (n = 5), Medial (n = 5), and Lateral (n = 5) sides of 20 synthetic femurs. Intact femurs served as a control group (n = 4). Femurs were tested for lateral, "offset" torsional, and axial stiffness, as well as axial strength. RESULTS: Lateral stiffnesses (range, 121-162 N/mm) yielded no differences between groups (P = 0.069). "Offset" torsional stiffnesses (range, 135-188 N/mm) demonstrated that the Medial group was less stiff than the Intact, Anterior, and Lateral groups (P ≤ 0.012). Axial stiffnesses (range, 1057-1993 N/mm) showed that the Medial group was less stiff than the Intact group (P = 0.006). Axial strengths (range, 3250-6590 N) for the Medial group were lower than Anterior (P = 0.001) and Posterior (P = 0.001) specimens, whereas the Lateral group had a lower strength than Anterior specimens (P = 0.019). No other statistical differences were noted. Axial failure of Medial and Lateral specimens involved the tumor-like defect in 100% of cases, whereas 100% of Intact femurs and 80% of Anterior and Posterior femur groups failed only through the neck. CONCLUSIONS: In 2 of 3 test modes, the Medial tumor-like defect group resulted in statistically lower stiffness values compared with Intact femurs and had lower strength than Anterior and Posterior groups in axial failure.

Asunto(s)

Fracturas del Fémur/etiología , Fracturas del Fémur/fisiopatología , Neoplasias Femorales/etiología , Neoplasias Femorales/fisiopatología , Fémur/fisiopatología , Fracturas Espontáneas/etiología , Fracturas Espontáneas/fisiopatología , Materiales Biomiméticos , Sustitutos de Huesos , Fuerza Compresiva , Simulación por Computador , Módulo de Elasticidad , Humanos , Modelos Biológicos , Resistencia a la Tracción , Torque

RESUMEN

There is no "gold standard" treatment for femoral mid-shaft fractures near the tip of a hip implant. Moreover, no study has quantified the changes in a femur's mechanical properties from injury through to healing. The present aim was to predict overall stiffness and peak bone stress in the same femur after injury, repair, and healing with respect to its intact condition. Stage 1 was an intact femur. Stage 2 mimicked a femur with a hip stem. Stage 3 had a 5-mm fracture gap repaired with a plate and screws. Stage 4 represented complete fracture union. Experiments were done on a synthetic femur with strain gages and subjected to 1500 N of axial force. Finite element (FE) models were validated against experiments and then re-analyzed using a clinical-level force of 3000 N. At 1500 N, FE vs. experimental strains had excellent linear agreement (R=0.94; slope=0.97). At 3000 N, FE stiffnesses were 2167 N/mm (Stage 1), 2359 N/mm (Stage 2), 973 N/mm (Stage 3), and 3348 N/mm (Stage 4), showing that Stage 3 was the least stable compared to Stage 1. At 3000 N, FE bone stresses yielded peaks of 75.7 MPa at the load application point (Stage 1), 29.0 MPa near the hip implant tip (Stage 2), 126.3 MPa at the distal portion of the plate (Stage 3), and 69.3 MPa at the proximal portion of the plate (Stage 4), showing that Stage 3 was most vulnerable to re-injury compared to Stage 1. Stress shielding and high stresses were present not only after hip implantation and plating, but also after healing.

Asunto(s)

Fémur/lesiones , Fémur/fisiología , Análisis de Elementos Finitos , Ensayo de Materiales , Fenómenos Mecánicos , Cicatrización de Heridas , Fenómenos Biomecánicos , Humanos , Reproducibilidad de los Resultados , Estrés Mecánico

RESUMEN

Femur fracture plates are applied using cortical bone screws. Surgeons do this manually by subjective 'feel' without monitoring torque. Few studies have quantified stripping torque in human bone. No studies have measured stripping torque in the artificial bones from Sawbones (Vashon, WA, USA) that are frequently used in biomechanical studies. The present aim was to measure stripping torque of cortical screws in human versus artificial femurs. Sixteen fresh-frozen human femurs and eight artificial femurs were used. Using a digital torque screwdriver, each femur had a 3.5-mm diameter uni-cortical screw manually inserted into the anterior midshaft until failure of the screw-bone interface. Results were normalized by cortical thickness and the screw-bone interfacial area. There were no statistical differences in human versus artificial data, respectively, for stripping torque (1741 +/- 442 N.mm, 2012 +/- 176 N.mm, p = 0.11), stripping torque/thickness (313 +/- 59 N, 305 +/- 30 N, p = 0.74), and stripping torque area (28.5 +/- 5.3 N/mm, 27.8 +/- 2.8 N/mm, p = 0.74). Artificial unicortical thickness (6.6 + 0.3 mm) was greater than human thickness (5.6 +/- 1.1 mm) (p = 0.02). For human specimens, there was a moderate linear correlation of absolute and normalized stripping torque versus standardized bone mineral density (R > or = 0.32) and clinical T-score (R = 0.29), but not with age (R < or = 0.29). Surgeons should be aware of the stripping torque limits for human femurs and potentially take steps to monitor these values during surgery. The artificial femurs being increasingly used in research accurately replicate human cortical properties during screw insertion. To date, this is the first series of human femurs evaluated for cortical screw stripping.

Asunto(s)

Tornillos Óseos , Fémur/fisiología , Fémur/cirugía , Análisis de Falla de Equipo , Humanos , Diseño de Prótesis , Resistencia a la Tracción/fisiología , Torque

RESUMEN

BACKGROUND: Prediction of negative postoperative outcomes after long-bone fracture treatment may help to optimize patient care. We recently completed the Study to Prospectively Evaluate Reamed Intramedullary Nails in Patients with Tibial Fractures (SPRINT), a large, multicenter trial of reamed and unreamed intramedullary nailing of tibial shaft fractures in 1226 patients. Using the SPRINT data, we conducted an investigation of baseline and surgical factors to determine any associations with an increased risk of adverse events within one year of intramedullary nailing. METHODS: Using multivariable logistic regression analysis, we investigated fifteen baseline and surgical factors for any associations with an increased risk of negative outcomes. RESULTS: There was an increased risk of negative events in patients with a high-energy mechanism of injury (odds ratio [OR] = 1.57; 95% confidence interval [CI], 1.05 to 2.35), a stainless steel compared with a titanium nail (OR = 1.52; 95% CI, 1.10 to 2.13), a fracture gap (OR = 2.40; 95% CI, 1.47 to 3.94), and full weight-bearing status after surgery (OR = 1.63; 95% CI, 1.00 to 2.64). There was no increased risk with the use of nonsteroidal anti-inflammatory agents, late or early time to surgery, or smoking status. Open fractures had a higher risk of events among patients treated with reamed nailing (OR = 3.26; 95% CI, 2.01 to 5.28) but not in patients treated with unreamed nailing (OR = 1.50; 95% CI, 0.92 to 2.47). Patients with open fractures who had wound management either without any additional procedures or with delayed primary closure had a decreased risk of events compared with patients who required subsequent, more complex reconstruction (OR = 0.18 [95% CI, 0.09 to 0.35] and 0.29 [95% CI, 0.14 to 0.62], respectively). CONCLUSIONS: We identified several baseline fracture and surgical characteristics that may increase the risk of adverse events in patients with tibial shaft fractures. Surgeons should consider the predictors identified in our analysis to inform patients treated for tibial shaft fractures. LEVEL OF EVIDENCE: Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Asunto(s)

Clavos Ortopédicos , Fijación Intramedular de Fracturas/métodos , Curación de Fractura/fisiología , Fracturas de la Tibia/cirugía , Adulto , Intervalos de Confianza , Femenino , Fijación Intramedular de Fracturas/efectos adversos , Humanos , Puntaje de Gravedad del Traumatismo , Modelos Logísticos , Masculino , Persona de Mediana Edad , Análisis Multivariante , Oportunidad Relativa , Ontario , Dimensión del Dolor , Selección de Paciente , Cuidados Posoperatorios/métodos , Complicaciones Posoperatorias/diagnóstico por imagen , Complicaciones Posoperatorias/fisiopatología , Valor Predictivo de las Pruebas , Pronóstico , Estudios Prospectivos , Radiografía , Medición de Riesgo , Fracturas de la Tibia/diagnóstico por imagen , Resultado del Tratamiento , Soporte de Peso , Adulto Joven

RESUMEN

Biomechanical preconditioning of biological specimens by cyclic loading is routinely done presumably to stabilize properties prior to the main phase of a study. However, no prior studies have actually measured these effects for whole bone of any kind. The aim of this study, therefore, was to quantify these effects for whole bones. Fourteen matched pairs of fresh-frozen intact cadaveric canine femurs were sinusoidally loaded in 4-point bending from 50 N to 300 N at 1 Hz for 25 cycles. All femurs were tested in both anteroposterior (AP) and mediolateral (ML) bending planes. Bending stiffness (i.e., slope of the force-vs-displacement curve) and linearity R(2) (i.e., coefficient of determination) of each loading cycle were measured and compared statistically to determine the effect of limb side, cycle number, and bending plane. Stiffnesses rose from 809.7 to 867.7 N/mm (AP, left), 847.3 to 915.6 N/mm (AP, right), 829.2 to 892.5 N/mm (AP, combined), 538.7 to 580.4 N/mm (ML, left), 568.9 to 613.8 N/mm (ML, right), and 553.8 to 597.1 N/mm (ML, combined). Linearity R(2) rose from 0.96 to 0.99 (AP, left), 0.97 to 0.99 (AP, right), 0.96 to 0.99 (AP, combined), 0.95 to 0.98 (ML, left), 0.94 to 0.98 (ML, right), and 0.95 to 0.98 (ML, combined). Stiffness and linearity R(2) versus cycle number were well-described by exponential curves whose values leveled off, respectively, starting at 12 and 5 cycles. For stiffness, there were no statistical differences for left versus right femurs (p = 0.166), but there were effects due to cycle number (p < 0.0001) and AP versus ML bending plane (p < 0.0001). Similarly, for linearity, no statistical differences were noted due to limb side (p = 0.533), but there were effects due to cycle number (p < 0.0001) and AP versus ML bending plane (p = 0.006). A minimum of 12 preconditioning cycles was needed to fully stabilize both the stiffness and linearity of the canine femurs. This is the first study to measure the effects of mechanical preconditioning on whole bones, having some practical implications on research practices.

Asunto(s)

Fémur , Ensayo de Materiales/métodos , Fenómenos Mecánicos , Animales , Fenómenos Biomecánicos , Cadáver , Perros , Modelos Lineales , Ensayo de Materiales/instrumentación

RESUMEN

Few studies have evaluated the 'bulk' mechanical properties of human longbones and even fewer have compared human tissue to the synthetic longbones increasingly being used by researchers. Distal femur fractures, for example, comprise about 6% of all femur fractures, but the mechanical properties of the distal condyles of intact human and synthetic femurs have not been well quantified in the literature. To this end, the distal portions of a series of 16 human fresh-frozen femurs and six synthetic femurs were prepared identically for mechanical testing. Using a flat metal plate, an axial 'crush' force was applied in-line with the long axis of the femurs. The two femur groups were statistically compared and values correlated to age, size, and bone quality. Results yielded the following: crush stiffness (human, 1545 +/- 728 N/mm; synthetic, 3063 +/- 1243 N/mm; p = 0.002); crush strength (human, 10.3 +/- 3.1 kN; synthetic, 12.9 < or = 1.7 kN; p = 0.074); crush displacement (human, 6.1 +/- 1.8 mm; synthetic, 2.8 +/- 0.3 mm; p = 0.000); and crush energy (human, 34.8 +/- 15.9J; synthetic, 18.1 +/- 5.7J; p = 0.023). For the human femurs, there were poor correlations between mechanical properties versus age, size, and bone quality (R2 < or = 0.18), with the exception of crush strength versus bone mineral density (R2 = 0.33) and T-score (R2 = 0.25). Human femurs failed mostly by condyle 'roll back' buckling (15 of 16 cases) and/or unicondylar or bicondylar fracture (7 of 16 cases), while synthetic femurs all failed by wedging apart of the condyles resulting in either fully or partially displaced condylar fractures (6 of 6 cases). These findings have practical implications on the use of a flat plate load applicator to reproduce real-life clinical failure modes of human femurs and the appropriate use of synthetic femurs. To the authors' knowledge, this is the first study to have done such an assessment on human and synthetic femurs.

Asunto(s)

Densidad Ósea , Fracturas del Fémur/fisiopatología , Fracturas por Compresión/fisiopatología , Traumatismos de la Rodilla/fisiopatología , Anciano , Anciano de 80 o más Años , Fuerza Compresiva , Módulo de Elasticidad , Femenino , Humanos , Técnicas In Vitro , Masculino , Persona de Mediana Edad

RESUMEN

OBJECTIVES: Intravasation of bone marrow contents into venous circulation and pulmonary embolization after intramedullary nailing may be coupled with the activation of coagulation and fibrinolytic cascades. The objective of this study was to assess hemostatic response to pulmonary extravasated marrow contents. We hypothesize that activation of platelet activity and the coagulation cascade may occur after embolization of marrow contents in an experimental animal model of intramedullary nailing. METHODS: Fifteen New Zealand white male rabbits were randomly assigned to control or fat embolism (FE) groups. In the FE group (n = 8), femurs were surgically instrumented with retrograde intramedullary nails and pressurized with bone cement. In the control group (n = 7), a sham knee incision was made that was immediately closed without drilling, reaming, or pressurization. Fibrinogen, D-dimer latex screen assay, 1 stage prothrombin time, and activated partial thromboplastin time were analyzed. RESULTS: As the main platelet activation indicators, the marker Annexin-V percent binding increased in the FE group at 2 hours (P = 0.04) and 4 hours (P = 0.04), and the marker CD62P percent expression increased in the FE group at 2 hours (P = 0.04). CONCLUSIONS: This preliminary study showed that pressurization of marrow and intravasation of fat and marrow products cause activation of platelets and the coagulation cascade, with or without tissue trauma. This may be relevant to the treatment of multiply injured patients with prior respiratory and coagulation abnormalities. A future larger study may be needed.

Asunto(s)

Plaquetas/inmunología , Médula Ósea/inmunología , Embolia Grasa/etiología , Embolia Grasa/inmunología , Embolización Terapéutica/efectos adversos , Fijación Intramedular de Fracturas/efectos adversos , Activación Plaquetaria/inmunología , Animales , Masculino , Proyectos Piloto , Conejos

RESUMEN

In the presence of a tumor defect, completed humeral shaft fractures continue to be a major surgical challenge since there is no "gold standard" treatment. This is due, in part, to the fact that only one prior biomechanical study exists on the matter, but which only compared 2 repair methods. The current authors measured the humeral torsional performance of 5 fixation constructs for completed pathological fractures. In 40 artificial humeri, a 2-cm hemi-cylindrical cortical defect with a transverse fracture was created in the lateral cortex. Specimens were divided into 5 different constructs and tested in torsion. Construct A was a broad 10-hole 4.5-mm dynamic compression plate (DCP). Construct B was the same as A except that the screw holes and the tumor defect were filled with bone cement and the screws were inserted into soft cement. Construct C was the same as A except that the canal and tumor defect were filled with bone cement and the screws were inserted into dry cement. Construct D was a locked intramedullary nail inserted in the antegrade direction. Construct E was the same as D except that bone cement filled the defect. For torsional stiffness, construct C (4.45 ± 0.20 Nm/deg) was not different than B or E (p > 0.16), but was higher than A and D (p < 0.001). For failure torque, construct C achieved a higher failure torque (69.65 ± 5.35 Nm) than other groups (p < 0.001). For the failure angle, there were no differences between plating constructs A to C (p ≥ 0.11), except for B versus C (p < 0.05), or between nailing groups D versus E (p = 0.97), however, all plating groups had smaller failure angles than both nailing groups (p < 0.05). For failure energy, construct C (17.97 ± 3.59 J) had a higher value than other groups (p < 0.005), except for A (p = 0.057). Torsional failure always occurred in the bone in the classic "spiral" pattern. Construct C provided the highest torsional stability for a completed pathological humeral shaft fracture.

Asunto(s)

Fracturas del Húmero/complicaciones , Fracturas del Húmero/terapia , Húmero , Ensayo de Materiales/métodos , Fenómenos Mecánicos , Adulto , Fenómenos Biomecánicos , Neoplasias Óseas/secundario , Humanos , Ensayo de Materiales/instrumentación , Estrés Mecánico , Torque

RESUMEN

Femurs are the heaviest, longest, and strongest long bones in the human body and are routinely subjected to cyclic forces. Strain gages are commonly employed to experimentally validate finite element models of the femur in order to generate 3D stresses, yet there is little information on a relatively new infrared (IR) thermography technique now available for biomechanics applications. In this study, IR thermography validated with strain gages was used to measure the principal stresses in the artificial femur model from Sawbones (Vashon, WA, USA) increasingly being used for biomechanical research. The femur was instrumented with rosette strain gages and mechanically tested using average axial cyclic forces of 1500 N, 1800 N, and 2100 N, representing 3 times body weight for a 50 kg, 60 kg, and 70 kg person. The femur was oriented at 7° of adduction to simulate the single-legged stance phase of walking. Stress maps were also obtained using an IR thermography camera. Results showed good agreement of IR thermography vs. strain gage data with a correlation of R(2)=0.99 and a slope=1.08 for the straight line of best fit. IR thermography detected the highest principal stresses on the superior-posterior side of the neck, which yielded compressive values of -91.2 MPa (at 1500 N), -96.0 MPa (at 1800 N), and -103.5 MPa (at 2100 N). There was excellent correlation between IR thermography principal stress vs. axial cyclic force at 6 locations on the femur on the lateral (R(2)=0.89-0.99), anterior (R(2)=0.87-0.99), and posterior (R(2)=0.81-0.99) sides. This study shows IR thermography's potential for future biomechanical applications.

Asunto(s)

Fémur , Rayos Infrarrojos , Ensayo de Materiales/instrumentación , Prótesis e Implantes , Estrés Mecánico , Termografía/métodos , Fenómenos Biomecánicos , Peso Corporal , Fémur/fisiología , Humanos , Soporte de Peso

RESUMEN

BACKGROUND: The gamma nail has an option to statically lock its lag screw (static mode) or to allow its lag screw to move within the nail to compress the intertrochanteric fracture (dynamic mode). The purpose of this study was to compare the biomechanical stiffness of static and dynamic lag screw modes for a cephalomedullary nail used to fix an unstable peritrochanteric fracture. METHODS: Unstable four-part peritrochanteric fractures were created in 30 synthetic femurs and fixed with Long Gamma 3 Nails. Mechanical tests were conducted for axial, lateral, and torsional stiffness with intact femurs, femur-nail constructs with static lag screw mode,and femur-nail constructs with dynamic lag screw mode. A paired Student's t test was used for all statistical comparisons between test groups. RESULTS: Axial and torsional stiffness of intact femurs was significantly greater than femur-nail constructs (p < 0.01 all comparisons),whereas lateral stiffness was significantly less (p < 0.01 all comparisons). Axial stiffness of the femur-nail construct was significantly greater (p < 0.01) in static mode (484.3 N/mm 80.2 N/mm) than in dynamic mode (424.1 N/mm 78.0 N/mm).Lateral stiffness was significantly greater (p < 0.01) in static mode (113.9 N/mm 8.4 N/mm) than in dynamic mode (109.5N/mm 8.8 N/mm). Torsional stiffness was significantly greater (p = 0.02) in dynamic mode (114.5 N/mm 28.2 N/mm) than in static mode (111.7 N/mm 27.0 N/mm). DISCUSSION: There is a 60 N/mm (12.4%) reduction in axial stiffness when the lag screw is in dynamic mode. Given the statistically significant reduction in axial and lateral stiffness with use of the dynamic mode, static lag screw mode should be further explored clinically for treatment of unstable peritrochanteric fractures.

Asunto(s)

Clavos Ortopédicos , Tornillos Óseos , Fijación Intramedular de Fracturas/métodos , Fracturas de Cadera/cirugía , Fenómenos Biomecánicos , Fijación Intramedular de Fracturas/instrumentación , Fracturas de Cadera/fisiopatología , Humanos , Técnicas In Vitro , Estrés Mecánico , Torque

RESUMEN

OBJECTIVES: Intramedullary reaming of long bones before nail insertion has been known to cause an increase in fat emboli introduction into the bloodstream, which is a potentially fatal phenomenon. The goal of this study was to assess whether the reamer irrigator aspirator (RIA) reamer can reduce fat embolic load compared with the standard AO reamer. METHODS: Fifteen pigs were prepared using an intravenous catheter inserted into the marginal ear vein for fluid balance and drug administration. One third of the pig's blood volume was withdrawn to simulate hemorrhagic shock. Each animal underwent bilateral retrograde femoral reaming, cementing, and nailing using either an RIA or AO reamer. Assignment of a reamer type to the left or right side was done randomly and allowed for direct comparison of matching femur results. Outcome measures were obtained, namely, pulmonary arterial pressure, mean arterial pressure, partial pressure of arterial oxygen, and cardiac output. Staining techniques were used to ascertain fat emboli counts from lung tissue samples. RESULTS: For mean arterial pressure, partial pressure of arterial oxygen, and cardiac output after cement injection, the RIA reamer group showed statistically higher values than the AO reamer group. In corollary, the RIA showed statistically lower pulmonary arterial pressure levels. No differences were noted at baseline, during hypovolemia, and post resuscitation. With the Student t test, no statistical differences were found between reamers regarding fat emboli counts for both staining methods. With the Mann-Whitney test, the RIA reamer showed statistically fewer emboli (7.0 versus 74.5) (P = 0.02, Z = 2.33) using Oil Red "O" staining. CONCLUSIONS: The RIA reamer demonstrated superior results with respect to physiologic measures and fat emboli counts and may provide optimal results compared with the AO reamer.

Asunto(s)

Embolia Grasa/prevención & control , Fémur/cirugía , Fijación Intramedular de Fracturas/instrumentación , Animales , Cementos para Huesos , Clavos Ortopédicos , Modelos Animales de Enfermedad , Embolia Grasa/etiología , Embolia Grasa/fisiopatología , Femenino , Fémur/fisiopatología , Succión/instrumentación , Porcinos , Irrigación Terapéutica/instrumentación

RESUMEN

OBJECTIVES: The purpose of this study was to determine if lag screw position affects the biomechanical properties of a cephalomedullary nail used to fix an unstable peritrochanteric fracture. METHODS: Unstable peritrochanteric fractures were created in 30 synthetic femurs and repaired with Long Gamma 3 Nails using one of 5 lag screw positions: superior, inferior, anterior, posterior, or central. Radiographic measurements including tip-apex distance and a calcar referenced tip-apex distance were calculated from anteroposterior and lateral radiographs. Specimens were tested for axial, lateral bending, and torsional stiffness and then loaded to failure in the axial position. Analysis of variance and linear regression were used for statistical analysis. RESULTS: The inferior lag screw position had significantly greater mean axial stiffness than superior (P < 0.01), anterior (P = 0.02), and posterior (P = 0.04) positions. Analysis revealed significantly less mean torsional stiffness for the superior lag screw position compared with other lag screw positions (P < 0.01 all 4 pairings). No statistical differences were noted for lateral bending stiffness. Superior and central lag screw positions had significantly greater mean load-to-failure than anterior (P < 0.01 and P = 0.02) and posterior (P < 0.01 and P = 0.05) positions. There were significant negative linear correlations between stiffness with distance from the calcar on anteroposterior radiographs and load-to-failure with distance from the center of femoral neck on the lateral radiographs. CONCLUSIONS: The inferior lag screw position produced the highest axial and torsional stiffness. Anterior and posterior lag screw positions produced the lowest stiffnesses and load-to-failure. Inferior placement of the lag screw on the anteroposterior radiograph and central placement on the lateral radiographs is recommended.

Asunto(s)

Clavos Ortopédicos , Cabeza Femoral/cirugía , Fijación Intramedular de Fracturas/instrumentación , Fijación Intramedular de Fracturas/métodos , Fracturas de Cadera/cirugía , Fenómenos Biomecánicos , Tornillos Óseos , Elasticidad , Análisis de Falla de Equipo , Humanos , Falla de Prótesis , Estrés Mecánico

RESUMEN

Few experimental studies have examined surgical drilling in human bone, and no studies have inquired into this aspect for a popular commercially-available artificial bone used in biomechanical studies. Sixteen fresh-frozen human femurs and five artificial femurs were obtained. Cortical specimens were mounted into a clamping system equipped with a thrust force and torque transducer. Using a CNC machine, unicortical holes were drilled in each specimen at 1000 rpm, 1250 rpm, and 1500 rpm with a 3.2 mm diameter surgical drill bit. Feed rate was 120 mm/min. Statistical significance was set at p < 0.05. Force at increasing spindle speed (1000 rpm, 1250 rpm, and 1500 rpm), respectively, showed a range for human femurs (198.4 ± 14.2 N, 180.6 ± 14.0 N, and 176.3 ± 11.2 N) and artificial femurs (87.2 ± 19.3 N, 82.2 ± 11.2 N, and 75.7 ± 8.8 N). For human femurs, force at 1000 rpm was greater than at other speeds (p ≤ 0.018). For artificial femurs, there was no speed effect on force (p ≥ 0.991). Torque at increasing spindle speed (1000 rpm, 1250 rpm, and 1500 rpm), respectively, showed a range for human femurs (186.3 ± 16.9 N·mm, 157.8 ± 16.1 N·mm, and 140.2 ± 16.4 N·mm) and artificial femurs (67.2 ± 8.4 N·mm, 61.0 ± 2.9 N·mm, and 53.3 ± 2.9 N·mm). For human femurs, torque at 1000 rpm was greater than at other speeds (p < 0.001). For artificial femurs, there was no difference in torque for 1000 rpm versus higher speeds (p ≥ 0.228), and there was only a borderline difference between the higher speeds (p = 0.046). Concerning human versus artificial femurs, their behavior was different at every speed (force, p ≤ 0.001; torque, p < 0.001). For human specimens at 1500 rpm, force and torque were linearly correlated with standardized bone mineral density (sBMD) and the T-score used to clinically categorize bone quality (R ≥ 0.56), but there was poor correlation with age at all speeds (R ≤ 0.37). These artificial bones fail to replicate force and torque in human cortical bone during surgical drilling. To date, this is the largest series of human long bones biomechanically tested for surgical drilling.

Asunto(s)

Órganos Artificiales , Fémur/cirugía , Torque , Adulto , Factores de Edad , Anciano , Anciano de 80 o más Años , Animales , Miembros Artificiales , Fenómenos Biomecánicos , Bovinos , Femenino , Humanos , Masculino , Persona de Mediana Edad , Porcinos

RESUMEN

OBJECTIVES: We investigated the accuracy of reduction of intramedullary nailed femoral shaft fractures in human cadavers, comparing conventional and computer navigation techniques. METHODS: Twenty femoral shaft fractures were created in human cadavers, with segmental defects ranging from 9 to 53 mm in length (Winquist 3-4, AO 32C2). All fractures were fixed with antegrade 9 mm diameter femoral nails on a radiolucent operating table. Five fractures ("Fluoro" group) were fixed with conventional techniques and fifteen fractures ("Nav 1" and "Nav 2" groups) with computer navigation, using fluoroscopic images of the normal femur to correct for length and rotation. Postoperative CT scans compared femoral length and rotation with the normal leg. RESULTS: Mean leg length discrepancy in the computer navigation groups was smaller, namely, 3.6 mm for Nav 1 (95% CI: 1.072 to 6.128) and 4.2 mm for Nav 2 (95% CI: 0.63 to 7.75) vs. 9.8 mm for Fluoro (95% CI: 6.225 to 13.37) (p<0.023). Mean rotational discrepancies were 8.7° for Nav 1 (95% CI: 4.282 to 13.12) and 5.6° for Nav 2 (95% CI: -0.65 to 11.85) vs. 9.0° for Fluoro (95% CI: 2.752 to 15.25) (p=0.650). CONCLUSIONS: Computer navigation significantly improves the accuracy of femoral shaft fracture fixation with regard to leg length, but not rotational deformity.

Asunto(s)

Fracturas del Fémur/cirugía , Fijación Intramedular de Fracturas/métodos , Diferencia de Longitud de las Piernas/prevención & control , Cirugía Asistida por Computador/métodos , Cadáver , Femenino , Fracturas del Fémur/diagnóstico por imagen , Humanos , Diferencia de Longitud de las Piernas/diagnóstico por imagen , Masculino , Mesas de Operaciones , Reproducibilidad de los Resultados , Tomografía Computarizada por Rayos X