Second generation intramedullary nailing of subtrochanteric femur fractures: a biomechanical study of fracture site motion. 2002.
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Biomechanical Phenomena↗
Biomedical subjects
Craig S Roberts
Publications and source records attributed to Craig S Roberts.
Review article: diagnostic ultrasonography: applications in orthopaedic surgery.
Diagnostic ultrasonography of musculoskeletal diseases in the United States has been used most often for detection of rotator cuff tears or developmental dysplasia of the hip. Diagnostic ultrasonography also is useful in imaging the periarticular soft tissues about the knee, hip, ankle, occult pediatric fractures, muscle injury, bone healing, and foreign bodies. Recent technologic improvements have made this imaging modality increasingly more accurate while providing significant benefits over traditional modalities such as magnetic resonance imaging, particularly regarding cost, patient satisfaction, and ease of usage. Increasing use in the future of diagnostic ultrasonography for musculoskeletal conditions is likely as acceptance grows. This review focuses on recent, practical applications of diagnostic ultrasonography of the musculoskeletal system.
Humans↗
Second generation intramedullary nailing of subtrochanteric femur fractures: a biomechanical study of fracture site motion.
OBJECTIVES: To compare fracture site motion between different second-generation intramedullary nails used to fix subtrochanteric fractures of the proximal femur with and without femoral neck fractures. DESIGN: Nondestructive mechanical testing of four types of femoral intramedullary nails was undertaken to evaluate fracture site motion using a model that simulated single-leg and double-leg stance. METHODS: Three types of reconstruction nails (the Russell-Taylor Delta [Smith & Nephew, Memphis, TN], the Uniflex [Biomet, Warsaw, IN], Alta CFX [Howmedica-Osteonics, Rutherford, NJ]) and the Long Gamma nail (Howmedica-Osteonics, Rutherford, NJ), each measuring 11 x 380 mm, were inserted in fiberglass composite femurs. Four fracture patterns were studied (transverse subtrochanteric, subtrochanteric with posteromedial wedge comminution, subtrochanteric with one-centimeter gap, and a one-centimeter gap with a subcapital neck fracture). Single-and double-leg stance loading was simulated using a servohydraulic load frame (MTS, Eden Prairie, MN). Two-way analysis of variance and post hoc t tests were used to determine any statistically significant differences between groups. RESULTS: In single-leg stance there were significant differences in coronal plane rotation, shear, and axial translation across the subtrochanteric fracture site between the different nail types and the different fracture patterns (p < 0.001). In double-leg stance there were significant differences in coronal plane rotation and femoral head vertical motion between the different nail types and the different fracture patterns (p < 0.001), and there were significant differences in shear and axial translation between the different fracture patterns (p < 0.001) but not the different nail types (p > 0.05). CONCLUSIONS: For simple, well-reduced fractures the choice of implant is not critical. As fracture severity increased (comminution, gap, and combined neck fracture), the choice of implant, particularly with reference to proximal nail dimensions and implant materials, was a significant factor in reducing fracture site motion. Therefore, our laboratory data suggest that when subtrochanteric fractures are unstable (e.g., comminution, segmental bone loss) and early weight bearing is desirable, the choice of implant is critical and should be restricted to implants that allow minimal fracture site motion (Long Gamma and Russell-Taylor).
Biomechanical Phenomena↗
Magnetic resonance imaging analysis of the subacromial space in the impingement sign positions.
External shoulder impingement is commonly diagnosed by passively moving the shoulder into various positions of elevation and internal rotation in order to perform impingement sign maneuvers. There is a lack of agreement among clinicians regarding the positions of the anatomic structures in the subacromial space when these maneuvers are performed. The purpose of this study was to use magnetic resonance imaging to identify and measure the changes in anatomic structures in the subacromial space as the arm was moved from complete rest to 160 degrees of forward flexion during the Neer and Hawkins impingement sign maneuvers. Ten subjects with normal shoulders (mean age, 32 years) were studied. The acromiohumeral interval was smallest with the arm at the side (mean, 6.4 mm) and progressively increased as the arm was elevated from 90 degrees to 160 degrees (mean, 7.7-14.2 mm). In no instance was the rotator cuff found to be in contact with the anterior acromion. The rotator cuff insertion appeared to be in closest proximity to the anteroinferior acromion, not at full elevation (Neer sign position), but at 90 degrees of flexion (Hawkins sign position). Our data suggest that a clinically positive Hawkins sign is consistent with external shoulder impingement. Clinical suspicion that mechanisms other than impingement may be involved, particularly if the Neer impingement sign is also positive, is nonetheless advised.
Acromioclavicular Joint↗
Biomechanics of external fixation of distal tibial extra-articular fractures: is spanning the ankle with a foot plate desirable?
OBJECTIVES: To compare the mechanical stability of external fixation with and without spanning of the ankle joint with a foot plate in an in vitro model of extra-articular distal tibia fractures. DESIGN: A laboratory investigation was performed to evaluate the mechanical behavior of external fixation of extra-articular distal tibia fractures using a fixator with and without a foot plate. Ten fresh-frozen lower extremities (5 pairs) with a simulated OTA 43-A3.3 fracture were stabilized with an Ilizarov hybrid fixator with and without a foot plate. SETTING: All mechanical testing was performed with a servohydraulic test frame (MTS Bionix 858, Minneapolis, MN). MAIN OUTCOME MEASUREMENT: Deformation characteristics as a function of load were compared for an Ilizarov fixator with and without a foot plate under identical conditions of forefoot loading from 0 to 100 N. Relative interfragmentary motions (vertical and horizontal translations and rotation) were measured. RESULTS: There was significantly more vertical translation (2.57 +/- 0.97 mm vs. -0.83 +/- 0.64 mm) and angular displacement (4.49 +/- 0.45 degrees vs. -1.15 +/- 0.61 degrees ) of the distal fragment in the arrangement without a foot plate compared with the construct with a foot plate. The anterior translation of the distal fragment was similar with (1.12 +/- 0.98 mm) and without a foot plate (1.19 +/- 1.23 mm). CONCLUSIONS: This study supports the mechanical importance of spanning of the ankle with a foot plate in most cases of external fixation for unstable extra-articular and periarticular distal tibia fractures. Further studies are needed to validate these results before widespread changes in clinical treatment can be recommended.
Aged↗
Mechanical study of the safe distance between distal femoral fracture site and distal locking screws in antegrade intramedullary nailing.
OBJECTIVE: To determine the safe distance for distal femoral fractures relative to the distal locking screws in antegrade intramedullary femoral nailing using a currently available titanium alloy nail design. DESIGN: Cyclic (fatigue) mechanical testing study. SETTING: Biomechanics laboratory. INTERVENTION: Intramedullary nailing of left synthetic fiberglass composite femora with type 32/33-C fractures at 1, 2, 3, and 4 cm from the more proximal of the distal locking screws. MAIN OUTCOME MEASUREMENT: The number of loading cycles to failure of the nail. RESULTS: A load level of 700 N through the femoral mechanical axis was validated as adequate to cause fatigue failure within 200,000 cycles in slotted stainless- steel nails. In the nonslotted titanium alloy nails, this load level caused failure in only 1 of 3 nails with a fracture at 2 cm from the more proximal of the 2 distal locking screws and in 2 of 3 nails with a fracture at 1 cm from the more proximal of the 2 distal locking screws. All of the other nails did not fail >1 million cycles. CONCLUSIONS: Under laboratory conditions, it is safe to assume that an antegrade titanium alloy nail will survive 1 million compression/bending cycles when the fracture is > or = 3 cm from the more proximal of the 2 distal locking screws.
Biomechanical Phenomena↗
Biomechanics of olive wire positioning and tensioning characteristics.
The effect of the olive wire on the stiffness of external fixation has been studied previously, but there are limited data on the effect of the olive wire positioning and tensioning characteristics on the stiffness of external fixation. This study evaluated the influence of olive wire positioning (medially, laterally, posteriorly, and anteriorly) and tensioning characteristics (tensioning one end or both ends) on the stiffness of ring external fixation. A fiberglass composite tibia fixed into an idealized ring external frame was tested. All mechanical testing was performed with a servohydraulic test frame (MTS Bionix 858, Minneapolis, MN). Load-deformation behavior was compared among different wire design and olive wire positioning and tensioning characteristics under central axial compression, medial compression-bending, posterior compression-bending, posteromedial compression-bending, and torsion. The differences between tension values on opposite ends of the wire during different modalities of olive wire tensioning were also investigated. Olive wires tensioned on both ends provided significantly greater bending stiffness compared with smooth wires and olive wires tensioned only on the end opposite to the olive (P < 0.05). There was a significant difference between the tension values on opposite ends of the olive wire during tensioning (P < 0.05). Tensioning both ends of the olive wires and positioning the olives on the side of bending significantly increase the bending stiffness of ring external fixation. This work provides a rationale for clinical decision-making about the use of tensioned olive wires opposed to smooth wires in ring external fixation.
Biomechanical Phenomena↗
Transfixion wire positioning within the bone: an option to control proximal tibia external fixation stiffness.
PURPOSE: The greatest angle that can be formed by the crossing wires at the proximal tibia level without altering safe corridors approaches only 60 degrees. Consequently, the wires are positioned more in the coronal than the sagittal plane. Looking for an increase in sagittal bending stiffness, we evaluated different wire positioning within the proximal tibia and their effect on the stiffness of external fixation of proximal tibia. STUDY DESIGN: A fiberglass composite tibia fixed into an idealized ring external frame was tested with a servohydraulic test frame. Load-deformation behavior was compared among the different wire positioning within the proximal tibia under identical conditions of central axial compression, medial compression-bending, posterior compression-bending, posteromedial compression-bending, and torsion. Stiffness values were calculated from the load-deformation and the torque-angle curves. RESULTS: The sample with 3 wires positioned within the bone-2 wires crossed 1 cm posteriorly from the center of the tibia and the third wire placed in coronal plane 1 cm anteriorly from the center of the tibia-was significantly (P < 0.05) stiffer in posterior, posteromedial, and torsional loading configurations compared with all other wire positions within the bone. CONCLUSIONS: This new wire positioning within the proximal tibia-2 wires crossed 1 cm posteriorly from the center of the tibia and the third wire placed in coronal plane 1 cm anteriorly from the center of the tibia-increased overall stiffness of external fixation, predominantly in sagittal plane. CLINICAL RELEVANCE: This work provides a rationale to control proximal tibia external fixation stiffness in sagittal plane.
Bone Wires↗