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T R Oxland

Publications and source records attributed to T R Oxland.

At least 19 recordsLinked to original sources
PubMed2006

Femoral neck cortical geometry measured with magnetic resonance imaging is associated with proximal femur strength.

INTRODUCTION: Magnetic resonance imaging (MRI) is a promising medical imaging technique that we used to assess femoral neck cortical geometry. OBJECTIVES: Our primary objective was to assess whether cortical bone in the femoral neck assessed by MRI was associated with failure load in a simulated sideways fall, with and without adjustment for total bone size. Our secondary objective was to assess the reliability of the MRI measurements. MATERIALS AND METHODS: We imaged 34 human cadaveric proximal femora using MRI and dual-energy X-ray absorptiometry (DXA). MRI measurements of cross-sectional geometry at the femoral neck were the cortical cross-sectional area (CoCSA(MRI)), second area moment of inertia (x axis; Ix(MRI)), and section modulus (x axis; Zx(MRI)). DXA images were analyzed with the standard Hologic protocol. From DXA, we report the areal bone mineral density (aBMD(DXA)) in the femoral neck and trochanteric subregions of interest. The femora were loaded to failure at 100 mm/s in a sideways fall configuration (15 degrees internal rotation, 10 degrees adduction). RESULTS AND OBSERVATIONS: Failure load (N) was the primary outcome. We observed that the femoral neck CoCSA(MRI) and Ix(MRI) were strongly associated with failure load (r (2)=0.46 and 0.48, respectively). These associations were similar to those between femoral neck aBMD and failure load (r (2)=0.40), but lower than the associations between trochanteric aBMD and failure load (r (2)=0.70). CONCLUSION: We report that MRI holds considerable promise for measuring cortical bone geometry in the femoral neck and for predicting strength at the proximal femur.

Absorptiometry, Photon↗
PubMed2005

Ipsilateral shoulder and elbow replacements: on the risk of periprosthetic fracture.

BACKGROUND: Ipsilateral shoulder and elbow replacements may leave only a short segment of bone bridging the two implants in the humerus. The potential for high stress concentrations as a result of this geometry has been a concern with regard to periprosthetic fracture, especially with osteoporotic bone. The study aims to determine the optimum length of the bone-bridge between shoulder and elbow humeral implants, and to assess the effect of filling the canal with cement. METHODS: A three-dimensional finite element model was used to compare the stresses between a humerus with a solitary prosthesis and a humerus with both proximal and distal cemented prostheses. The length of the bone-bridge and the effect of filling the canal with cement were studied under bending and torsion. FINDINGS: Gradual load transfer from prosthesis to bone was observed for all cases, and no stress concentration was evident. The length of the bone-bridge had no deleterious effect on stresses in the humerus, and filling the canal with cement did not appreciably decrease the loads carried by the humerus. INTERPRETATION: The length of the bone-bridge between stem tips has little effect on the resultant stresses in the humerus. Filling the canal with cement adds little benefit to the structural integrity of the humerus. Ipsilateral shoulder and elbow prostheses may be considered independent of one another in terms of risk of periprosthetic fracture.

Computer Simulation↗
PubMed2004

Allograft impaction and cement penetration after revision hip replacement. A histomorphometric analysis in the cadaver femur.

We studied various aspects of graft impaction and penetration of cement in an experimental model. Cancellous bone was removed proximally and local diaphyseal lytic defects were simulated in six human cadaver femora. After impaction grafting the specimens were sectioned and prepared for histomorphometric analysis. The porosity of the graft was lowest in Gruen zone 4 (52%) and highest in Gruen zone 1 (76%). At the levels of Gruen zones 6 and 2 the entire cross-section was almost filled with cement. Cement sometimes reached the endosteal surface in other Gruen zones. The mean peak impaction forces exerted with the impactors were negatively correlated with the porosity of the graft.

Arthroplasty, Replacement, Hip↗
PubMed2003

Fixation of trochanteric slide osteotomies: a biomechanical study.

OBJECTIVE: (1) Determine the effect of a compressive force on the stability of trochanteric slide osteotomies repaired with a cable repair system or a suturing technique. (2) Develop an approach to surgical decision making for trochanteric repair. DESIGN: Muscle forces acting on the greater trochanter were experimentally modeled by the application of shear and compressive loads to osteotomized greater trochanters. A repeated measures design was used to compare suture and cable fixation. BACKGROUND: The use of cables and wires for trochanteric repair has been associated with a high incidence of acetabular loosening and trochanteric bursitis. With trochanteric slide osteotomies, the vastus lateralis remains attached to the trochanter, which results in a compressive force being generated across the osteotomy and relatively small shear forces. The use of less rigid fixation techniques for trochanteric repair, such as sutures, may reduce the complications of cables and wires. METHODS: Seven cadaveric femora with trochanteric osteotomies were tested sequentially after repair with a cable system and with a suturing technique. A cyclic shear load of constant amplitude was applied while a compressive load was decreased in a stepwise fashion. Migration and cyclic motion of the trochanter were measured, and the coefficient of friction was also determined. RESULTS: Cyclic motions of the trochanter in both superior and anterior directions were generally less than 0.5 mm and were not significantly different between the cables and sutures at high compressive loads. At low compressive loads, cyclic motion was significantly lower with the cable system. CONCLUSIONS: Compression across the trochanteric slide osteotomy has a significant effect on stability. Cyclic motion of the trochanter is similar for both suture or cable repair of a trochanteric slide with good preservation of soft tissue attachments. RELEVANCE: Based on theoretical and experimental evidence, repair of trochanteric slide osteotomies with a suture technique may be a viable alternative to the use of cables and wires in selected cases.

Arthroplasty, Replacement, Hip↗
PubMed2001

Does anterolateral cage insertion enhance immediate stabilization of the functional spinal unit? A biomechanical investigation.

STUDY DESIGN: The three-dimensional flexibility of six human lumbar functional spinal units was measured after the anterolateral insertion of an interbody cage. OBJECTIVES: To determine whether an interbody cage inserted from an anterolateral direction stabilizes the spine with respect to the intact state and to compare the finding with that from the same cage inserted from an anterior direction. SUMMARY OF BACKGROUND DATA: Several biomechanical studies have shown that interbody cages do not stabilize the spine in extension. It is suspected that this may be caused by the destruction of the anterior longitudinal ligament and anterior anulus fibrosus. METHODS: Six human cadaveric lumbar functional spinal units were tested under pure moments of flexion, extension, bilateral axial rotation, and bilateral lateral bending to a maximum of 10 Nm. The relative intervertebral motions were measured by an optoelectronic camera system with the spinal units in the intact condition, after discectomy, after anterolateral interbody cage stabilization, and with additional translaminar screw fixation. The implant used was a central, porous, contoured implant with endplate fit. The results were compared with those of a previous study, which used the same implant inserted from an anterior direction. RESULTS: The anterolateral cage insertion significantly decreased the motion in comparison with the intact situation in flexion and lateral bending, but not in extension or axial rotation. No differences were found between the anterior and anterolateral insertion approaches in flexion or extension, but differences were observed in axial rotation and lateral bending, in which the anterolateral approach resulted in more motion. Additional translaminar screw fixation reduced motion to below intact levels in all loading directions. None of the surgical procedures introduced asymmetrical behavior. CONCLUSIONS: Anterolateral cage insertion did not stabilize the spine in extension or axial rotation and was not different from the anterior approach in flexion and extension. Additional translaminar screw fixation stabilized in all directions.

Biomechanical Phenomena↗
PubMed2001

The effect of nucleotomy on lumbar spine mechanics in compression and shear loading.

STUDY DESIGN: An in vitro biomechanical investigation on human cadaveric specimens was conducted before and after nucleotomy. Endplate and vertebral body deformation patterns were measured under compression and shear loading, in addition to kinematics and disc pressure. OBJECTIVE: The working hypotheses of this study were that in compression, nucleotomy results in an altered deformation pattern of the endplate and that in shear, nucleotomy does not result in an altered endplate deformation pattern or disc pressure. SUMMARY OF BACKGROUND DATA: The pressure distributions within the intervertebral disc have been studied in compression loading but not in shear loading. Severe degeneration and surgical nucleotomy result in small nuclear pressure and altered loading distribution in compression. The effect of these changes on the vertebral endplate and the response under shear loads are not well understood. METHODS: Five L3-L4 and two L4-L5 functional spinal units were tested under compression and shear loading, intact and after nucleotomy. Vertebral body deformations, intradiscal pressure, and intervertebral kinematics were measured. A series of compression-type (maximum 1000 N) and shear-type (maximum 500 N) loads were applied. RESULTS: With nucleotomy, the disc pressure and the endplate strains decreased under compression, but the vertebral rim strains did not change. In shear, the vertebral rim and endplate strains did not change with nucleotomy. Disc pressure was lower in shear than in compression. CONCLUSION: Nucleotomy resulted in decreased disc pressure, decreased endplate deformation, and modified loading patterns onto the inferior vertebra in compression loading. However, nucleotomy did not appreciably affect the behavior of the disc in shear loading.

Adult↗
PubMed2001

Mapping the structural properties of the lumbosacral vertebral endplates.

STUDY DESIGN: A biomechanical investigation using indentation tests in a human cadaveric model to seek variation in the structural properties across the lower lumbar and sacral endplates. OBJECTIVES: To determine 1) if there are regional differences in endplate strength and 2) whether any differences identified are affected by spinal level (lumbar spine vs. sacrum) or endplate (superior vs. inferior). SUMMARY OF BACKGROUND DATA: It has been postulated that some regions of the vertebral body may be stronger than others. Conclusive data, either supporting or disproving this theory, would be valuable for both spine surgeons and implant designers because one mode of failure of interbody implants is subsidence into one or both adjacent vertebrae. METHODS: Indentation tests were performed at 27 standardized test sites in 62 bony endplates of intact human vertebrae (L3-S1) using a 3-mm-diameter, hemispherical indenter with a test rate of 0.2 mm/sec to a depth of 3 mm. The failure load and stiffness at each test site were determined using the load-displacement curves. Three-way analyses of variance were used to analyze the resulting data. RESULTS: Both the failure load and stiffness varied significantly across the endplate surfaces (P < 0.0001), with posterolateral regions being stronger and stiffer than the central regions. Characteristic distributions were identified in the lumbar superior, lumbar inferior, and sacral endplates. The failure load distributions were found to differ in 1) the superior lumbar and sacral endplates (P = 0.0077), 2) the inferior lumbar and sacral endplates (P = 0.0014), and 3) the superior and inferior lumbar endplates (P < 0.0001). The sacral and inferior lumbar endplates were both found to be stronger than the superior lumbar endplates (sacrum, P = 0.054; inferior, P = 0.008) but were not themselves significantly different (P = 0.89). CONCLUSIONS: Highly significant regional strength and stiffness variations were identified in the lumbar and sacral endplates. The center of the bone, where implants are currently placed, is the weakest part of the lumbar endplates and is not the strongest region of the sacral endplate.

Aged↗
PubMed2001

Design and evaluation of a cryogenic soft tissue fixation device -- load tolerances and thermal aspects.

Mechanical studies of soft connective tissues often encounter methodological difficulties, particularly in the secure fixation of the tissues. A simple, inexpensive technique which allowed stable cryofixation of soft tissues in uniaxial loading machines was developed. The cryogenic fixation device was evaluated in terms of its fixation strength and the temperature gradients within the tested tissues. Human patellar ligaments and quadriceps tendons were tested successfully to an average failure load of 2219N (S.D. 448N) with mid-substance failures occurring in 90% of the specimens. The temperature gradients within porcine flexor and extensor tendons were determined and found to exhibit a typical diffusion profile. The fixation quality was dependent upon the initial block temperature and the desired testing time. In summary, the cryofixation device presented here is an effective tool for soft tissue fixation but the effect of this type of fixation on internal tissue temperatures and possible testing times must be acknowledged.

Adult↗
PubMed2000

Biomechanics of stand-alone cages and cages in combination with posterior fixation: a literature review.

Interbody cages in the lumbar spine have met with mixed success in clinical studies. This has led many investigators to supplement cages with posterior instrumentation. The objective of this literature review is to address the mechanics of interbody cage fixation in the lumbar spine with respect to three-dimensional stabilization and the strength of the cage-vertebra interface. The effect of supplementary posterior fixation is reviewed. Only three-dimensional stabilization evaluations in human cadaveric models are included. These studies involve the application of different loads to the spine and the measurement of vertebral motion in flexion-extension, axial rotation, and lateral bending. There are no published studies which detected any differences between different cage designs. However, it does seem that cages inserted from an anterior direction provide better stabilization to the spine than those inserted from a posterior direction. In general, anterior cages stabilize better than posterior cages in axial rotation and lateral bending. Cages from both directions stabilized well in flexion, but not in extension. Supplementary posterior fixation with pedicle or translaminar screws substantially improves the stabilization in all directions. The strength of the cage-vertebra interface from studies using human cadaveric specimens is also reviewed. The axial compressive strength of this interface is highly dependent upon vertebral body bone density. Other factors such as preservation of the subchondral bony end-plate and cage design are clearly less important in the compressive strength. Supplementary posterior instrumentation does not enhance substantially the interface strength in axial compression.

Biomechanical Phenomena↗
PubMed2000

In vitro axial preload application during spine flexibility testing: towards reduced apparatus-related artefacts.

Presently, there is little consensus about how, or even if, axial preload should be incorporated in spine flexibility tests in order to simulate the compressive loads naturally present in vivo. Some preload application methods are suspected of producing unwanted "artefact" forces as the specimen rotates and, in doing so, influencing the resulting kinematics. The objective of this study was to quantitatively compare four distinct types of preload which have roots in contemporary experimental practice. The specific quantities compared were the reaction moments and forces resulting at the intervertebral disc and specimen kinematics. The preload types incorporated increasing amounts of caudal constraint on the preload application vector ranging from an unconstrained dead-load arrangement to an apparatus that allowed the vector to follow rotations of the specimen. Six human cadaveric spine segments were tested (1-L1/L2, 3-L2/L3, 1-L3/L4 and 1-L4/L5). Pure moments were applied to the specimens with each of the four different types of compressive preload. Kinematic response was measured using an opto-electronic motion analysis system. A six-axis load cell was used to measure reaction forces and moments. Artefact reaction moments and shear forces were significantly affected by preload application method and magnitude. Unconstrained preload methods produced high artefact moments and low artefact shear forces while more constrained methods did the opposite. A mechanical trade-off is suggested by our results, whereby unwanted moment can only be prevented at the cost of shear force production. When comparing spine flexibility studies, caution should be exercised to ensure preload was applied in a similar manner for all studies. Unwanted moments or forces induced as a result of preload application method may render the comparison of two seemingly similar studies inappropriate.

Artifacts↗
PubMed2000

A comparative biomechanical investigation of anterior lumbar interbody cages: central and bilateral approaches.

BACKGROUND: Some biomechanical studies have been performed to evaluate the stabilization provided by interbody cages, but there are virtually no comparative data for the different designs. Furthermore, most investigators have used animal models, which may have led to different results due to morphological variation in the end plates and articular facets. The objectives of the current study were to evaluate whether two different anterior cage designs (BAK and SynCage) performed differently with respect to immediate stabilization of the spine, whether the cages stabilized the spine significantly compared with its intact condition, and whether the addition of supplementary translaminar screw fixation further stabilized the spine. Stabilization was defined as a reduction in motion after insertion of an implant. METHODS: Twelve lumbar functional spinal units from human cadavera were tested under pure moments of flexion, extension, bilateral axial rotation, and bilateral lateral bending to a maximum of ten newton-meters. The relative intervertebral motions were measured, with use of an optoelectronic camera system, under three test conditions: with the spine intact, after insertion of anterior interbody cages, and after insertion of anterior interbody cages supplemented with translaminar screw fixation. Six specimens were tested for each type of cage: a bilateral, porous, threaded cylinder (BAK) and a central, porous, contoured implant with end-plate fit (SynCage). RESULTS: The cages performed in a similar manner in all directions of loading, with no significant differences between the two designs. The cages significantly stabilized the spine compared with its intact condition in flexion, axial rotation, and lateral bending (the median value for motion was 40, 48, and 29 percent of the value for the intact condition, respectively; p = 0.002 for all three directions). Compared with the cages alone, translaminar screw fixation provided no additional stabilizing effect in these directions but it significantly increased the stability of the spine in extension (the median value for motion was 34 percent of the value with the cages alone; p = 0.013). CONCLUSIONS: There were no differences in the stabilization provided by the two different cage designs. Use of the cages alone stabilized the spine in all directions except extension, and use of supplementary translaminar screw fixation provided additional stabilization only in extension. CLINICAL RELEVANCE: This study demonstrated that interbody cages do not stabilize the lumbar spine in extension, and this observation was not altered by the use of substantially different designs. If the lack of stabilization in extension is a clinical problem, possible solutions include the avoidance of extension postoperatively or the use of supplementary fixation.

Biomechanical Phenomena↗
PubMed1999

Biomechanical properties of sterilized human auditory ossicles.

Bone allograft material is treated with sterilization methods to prevent the transmission of diseases from the donor to the recipient. The effect of some of these treatments on the integrity of the bone is unknown. This study was performed to evaluate the effect of several sterilization methods on the mechanical behaviour of human middle ear bones. Due to the size and composition of the bones (approximately 1.5 mm diameter by 4 mm long), mechanical testing options were limited to the traditional platens compression test. Experiments were first performed with synthetic bone to evaluate the precision of this test applied to small specimens. Following this, fresh frozen human ossicles were thawed and sterilized with (i) 1 N NaOH (n = 12); (ii) 0.9% LpH, a phenolic solution (n = 12); or (iii) steam at 134 degrees C (n = 18). A group of 26 control specimens did not receive any sterilization treatment. Material and structural properties were determined from axial compression testing. Results from the synthetic bone showed that the test was reproducible, with standard deviations less than 20% of the means. Significant differences occurred in stiffness and ultimate force values between NaOH-treated and autoclaved bones when compared to normals (p<0.05), but not for LpH-treated bones. LpH is not approved for medical use, so NaOH is the most appropriate of the treatments studied for the sterilization of ossicle allografts.

Analysis of Variance↗
PubMed1999

Subfailure injury affects the relaxation behavior of rabbit ACL.

OBJECTIVE: To study changes in viscoelasticity of a ligament due to an incomplete or a subfailure injury. DESIGN: An in vitro study of anterior cruciate ligament preparations. BACKGROUND: The viscoelastic properties are an inherent part of the physical characteristics of a ligament. An injury to a ligament alters both its elastic and viscous properties. Although the effects of several parameters on the mechanical properties of a ligament have been studied, there is no information in the literature concerning the effect of an incomplete or subfailure injury on its viscoelastic behavior. METHODS: Ten pairs of rabbit femur-anterior cruciate ligament-tibia specimens were used. A standardized relaxation (Relax) test was adopted to quantify the viscoelastic behavior, before and after a subfailure injury. One member of the pair was subjected to three sequential tests: Relax 1; Relax 2; and stretch to failure. The other member of the pair was subjected to other three tests: Relax 3; 80% subfailure injury, i.e. stretch of 80% of failure deformation; and Relax 4. RESULTS: We found that the relaxation test by itself (Relax 1 vs Relax 2), did not affect the viscoelasticity of the ligament. On the other hand, the 80% subfailure injury (Relax 3 vs Relax 4) affected the ligament viscoelastic behavior. The force was decreased by about 50% at time zero (10.46 vs 4.79 N, p = 0.014), and at 180 s (8.14 vs 4.11 N, p = 0.018). Fitting a three-element linear viscoelastic solid model to our data, we found the serial spring stiffness to decrease by about 50% (p = 0.01), the parallel spring remained unchanged, and there was a tendency for the dashpot coefficient to decrease (by 57%, p = 0.09). CONCLUSIONS: The 80% subfailure injury decreased the initial stiffness of the ligament, and tended to decrease its viscoelastic property. RELEVANCE: Subfailure or incomplete injuries of ligaments are more common than the complete injuries. The present study describes the effects, on both the elastic and viscous properties, of a ligament subjected to a subfailure injury.

Analysis of Variance↗
PubMed1999

The external spinal fixator does not reduce anterior column motion under axial compressive loads. A mechanical in vitro study.

We performed an in vitro study to investigate the effect of external spinal fixation on anterior column motion under physiological axial compression loading. The AO external spinal fixator (ESF) was applied to 5 human cadaveric lumbar spine specimens (L3-S1) at levels L4 to S1. All specimens were tested in 4 configurations: i) intact, ii) ESF in a neutral position, iii) ESF in distraction (12 mm), and iv) ESF in compression (8-12 mm). Cyclic sinusoidal axial compressive loads from 60 to 600 N were applied for 10 cycles in each test condition. The axial displacement of the load application point was recorded as an indicator of anterior column axial translation. The axial motion with the fixator in distraction was significantly greater than all other conditions, including intact. Compression of the fixator resulted in the least axial displacement. External fixation in the neutral position did not significantly affect the overall axial translation, when compared to the intact state. In conclusion, the external spinal fixator did not significantly reduce anterior column axial translation and, in distraction, this motion exceeded that of the intact specimen. Since pain relief is frequently observed during distraction of the painful segment/s with the external fixator, the mechanical basis of the pain relief is not well understood.

Adult↗
PubMed1998

Moments and forces during pedicle screw insertion. In vitro and in vivo measurements.

STUDY DESIGN: Moments and forces during pedicle screw insertion were measured in vivo and in vitro and were correlated to several parameters of the screw-bone interface. OBJECTIVES: To compare the in vitro and in vivo screw insertion loads and to relate these measurements to bone mineral density, pedicle size, and other screw parameters (material, diameter). SUMMARY OF BACKGROUND DATA: The in vitro screw insertion torque has been correlated to the screw pullout forces and the number of cycles to ultimate interface failure. However, there are no comparable in vivo data. METHODS: One hundred three pedicle screws were included in the study, 43 in vivo and 60 in vitro. Duel-energy x-ray absorptiometry boen mineral density data were available for 20 in vivo and 32 in vitro specimens. A custom-made sterilizable six-axis load cell was integrated into a torque wrench, enabling the recording of the applied moments and forces during screw insertion. Statistical analysis was performed to detect differences and correlations. RESULTS: The mean in vivo insertion torque (1.29 Nm) was significantly greater than the in vitro value (0.67 Nm). The linear correlation between insertion torque and bone mineral density was significant for the in vitro data but not for the in vivo data. No correlation was observed between insertion torque and pedicle diameter. Two patterns of torque were observed during the insertion process. CONCLUSIONS: There is a significant difference between the insertion loads measured in vivo and those measured in vitro. Additional research is needed to verify whether this method provides an indication of screw fixation quality.

Absorptiometry, Photon↗
PubMed1998

Constrained testing conditions affect the axial rotation response of lumbar functional spinal units.

STUDY DESIGN: Human cadaveric spine specimens were tested in axial rotation using constrained and unconstrained methods. OBJECTIVES: To determine the degree to which constrained methods affect the response of the functional spinal unit in axial rotation at lumbar and lumbosacral levels. SUMMARY OF BACKGROUND DATA: A substantial controversy exists in the literature regarding the appropriateness of different testing methods. No study has been found in which the effect of constraint on axial rotation behavior was objectively examined. METHODS: Ten human cadaveric spine specimens (five L3-L4, five L5-S1) were tested in axial rotation, using both constrained and unconstrained methods. In the unconstrained test, pure moments were applied to the upper vertebra, and its complete three-dimensional motion was measured using an optoelectronic camera system. In the constrained test, the specimens were loaded in a fixed-axis servohydraulic test machine individually around five rotational axis positions within the vertebral body, and the rotational motion was measured. RESULTS: The rotational angles in the constrained tests were not different among the five rotational axis positions. However, the maximum rotation from the five axis positions was approximately 40% greater than the minimum rotation, a significant difference. The axial rotational motion of the unconstrained tests was always less than the maximum rotation measured in the constrained test. However, the total rotational angle using the helical axis of motion was not significantly different from the constrained angles. CONCLUSIONS: The large differences between maximum and minimum rotation angles demonstrate that the behavior of the functional spinal unit in axial rotation is sensitive to the axis's position but the location of the axis is not repeatable. This supports the use of unconstrained methods in spinal testing.

Adult↗