Biomedical subjects

Anneliese D Heiner

Publications and source records attributed to Anneliese D Heiner.

11 recordsLinked to original sources

PubMed2007

Stability of fused versus nonfused THA femoral impaction grafts.

Impaction grafting for THA involves compacting morselized cancellous bone (MCB) into a cavitary defect to build up bone stock. Ideally, the MCB subsequently remodels into a new contiguous cancellous lattice. A recent laboratory model of MCB fusion allows simulating an impaction graft construct in this ideal eventual clinical state. The purpose of the present study was to determine the relative stability of femoral impaction graft constructs in which the MCB has fused versus that for MCB in the freshly impacted nonfused condition. Cemented femoral impaction graft constructs were created in composite femurs. For fused constructs, the MCB was mixed with an amine epoxy that causes the MCB to set up into a contiguous structure biomechanically comparable to intact cancellous bone in compression. The constructs were loaded with 500,000 physiologic gait cycles. Three-dimensional motion was measured between the femur and the stem. The fused femoral impaction grafts were much more stable than the nonfused grafts at the proximal stem location, but MCB fusion had only a modest effect on distal stem stability. These results indicate that most of the opportunity to reduce femoral stem micromotion and migration lies proximal, and that steps to enhance impaction graft remodeling and fusion are most effectively focused proximally.

Arthroplasty, Replacement, Hip↗

PubMed2006

In vivo measurement of translational stiffness of rabbit knees.

This paper describes the design, evaluation, and preliminary results of a specialized testing device and surgical protocol to determine translational stiffness of a rabbit knee, replicating the clinical anterior drawer test. Coronal-plane transverse pins are inserted through the rabbit leg, two in the tibia and one in the distal femur, to hold and reproducibly position the leg in the device for tests at multiple time points. A linear stepper motor draws the tibia upward then returns to the home position, and a load cell measures the resisting force; force-displacement knee stiffness is then calculated. Initial evaluation of this testing device determined the effects of preconditioning, intra-operator repeatability, rabbit-to-rabbit variability, knee flexion angle (90 degrees vs. 135 degrees ), and anterior cruciate ligament (ACL) sectioning (0%, 25%, 50%, 75%, 100%). Knee stiffness generally decreased as ACL sectioning increased. This testing device and surgical protocol provide an objective and efficient method of determining translational rabbit knee stiffness in vivo, and are being used in an ongoing study to evaluate the effect of knee instability (via partial to complete ACL sectioning) on the development of post-traumatic osteoarthritis.

Animals↗

PubMed2005

A laboratory simulation for morselized bone graft fusion: apparent modulus under operatively based femoral impaction kinetics.

The purpose of this study was to determine the apparent modulus changes accompanying a novel procedure for simulating in situ fusion of morselized cancellous bone femoral impaction grafts. An experienced surgeon's habitual intra-operative impaction grafting protocol was first quantified in human cadaver femurs, using a customized impulse force hammer. A corresponding standardized impaction procedure was then defined, and was used to prepare impaction grafts in axisymmetric metallic fixturing designed to replicate the nominal geometry of femoral canal confinement. Impaction graft fusion was simulated by mixing morselized cancellous bone with an amine-based epoxy adhesive before the impaction, then allowing the mixture to fuse after the impaction (J. Biomech. 34 (2001) 811). Force/deflection behavior of the unfused and fused impaction grafts was measured for both the (tapered) proximal and (untapered) distal portions of the grafts. Apparent modulus was then calculated from force/deflection stiffness. The impaction graft fusion simulation increased apparent modulus by an order of magnitude over the unfused state, for mixture parameters appropriate to have the fused graft apparent modulus be comparable to the compressive modulus of intact femoral cancellous bone.

Arthroplasty, Replacement, Hip↗

PubMed2004

Chondrocyte senescence, joint loading and osteoarthritis.

cellular level is not completely understood, but both aging and loading-induced stresses have been shown to undermine cell functions related to the maintenance and restoration of the cartilage matrix. Based on precedents set by studies of other age-related degenerative diseases, we have focused our laboratory work on senescence as the cause of age-dependent decline in chondrocytes and on the impact of excessive mechanical stresses in promoting senescence. We hypothesized that senescent chondrocytes accumulate with age in articular cartilage and we propose that excessive mechanical stress plays a role in this process by promoting oxidative damage in chondrocytes that ultimately causes them to senesce. To test this hypothesis, we measured cell senescence markers (beta-galactosidase expression, mitotic activity, and telomere length) in human articular cartilage chondrocytes, and determined the effects of chronic exposure to oxidative stress on chondrocyte growth and senescence. In addition, we measured the effects of abnormally high levels of mechanical shear stress on the release of oxidants in cartilage explants. We found that senescent chondrocytes accumulated with age in articular cartilage. In vitro studies showed that chronic oxidative stress caused by repeated exposure to peroxide, or by growth under superphysiologic oxygen tension caused chondrocyte populations to senesce prematurely, before extensive telomere erosion occurred. Mechanical shear stress applied to cartilage explants considerably increased the production of oxidants. These observations support the hypothesis that senescence accounts for age-related decline in chondrocyte function and indicate that mechanically induced oxidative damage plays a role in this process. This suggests that new efforts to prevent the development and progression of osteoarthritis should include strategies that slow the progression of chondrocyte senescence or replace senescent cells.

Adolescent↗

PubMed2003

A biomechanical analysis of polyethylene liner cementation into a fixed metal acetabular shell.

BACKGROUND: A common clinical scenario encountered by an orthopaedic surgeon is a patient with a secure cementless acetabular shell and a failed polyethylene liner. One treatment option is to cement a new liner into the fixed shell. The purpose of this study was to evaluate technical variables to improve the mechanical strength of such cemented liner constructs. METHODS: The contributions of shell texturing, liner texturing, and cement mantle thickness (between the liner and the shell) were evaluated by comparing torsional strength (among nine groups of constructs) and lever-out strength (among eight groups of constructs). RESULTS: Failure almost always occurred at the cement-liner interface. The two exceptions (failure at the shell-cement interface) occurred with a polished, untextured shell with no screw-holes. This finding indicates that if a shell has existing texturing (such as holes), further intraoperative scoring of the shell is unnecessary, but some sort of texturing is necessary to avoid construct failure at the shell-cement interface. Textured liners had significantly (a = 0.05) greater torsional and lever-out strength than untextured liners. The greatest construct strength occurred when liner grooves were oriented so as to oppose the applied loading. A 4-mm-thick cement mantle resulted in slightly greater torsional strength than a 2-mm-thick cement mantle, and a 2-mm-thick cement mantle resulted in considerably greater lever-out strength than a 4-mm-thick cement mantle, but these differences were not significant. CONCLUSIONS: When cementing a liner into a well-fixed shell, a surgeon should ensure that both the shell and the liner are textured, as interdigitation of the cement with the shell and the liner is crucial to the mechanical strength of this construct.

Arthroplasty, Replacement, Hip↗

PubMed2002

Measurement of cadaver lumbar spine motion segment stiffness.

STUDY DESIGN: Prospective. OBJECTIVES: To measure lumbar spine motion segment stiffness and relate it to the degree of disc degeneration. SUMMARY OF BACKGROUND DATA: The association between the instability of the lumbar spine motion segment and disc degeneration remains unclear. The traditional method for determining motion segment instability at the time of decompressive surgery is a manual test performed by the surgeon. To quantify instability of the lumbar spine, a vertebrae distractor was developed in the authors' laboratory to measure motion segment stiffness by applying a defined load at a constant rate. METHODS: Lumbar stiffness was measured by subjecting cadaver lumbar spine motion segments to a constant rate flexion-traction load and recording the magnitude of the resistance to distraction versus the range of motion. Disc degeneration was measured by pressure-volume discography and by grading of disc morphology. RESULTS: Motion segment stiffness decreased with the initial stages of disc degeneration and then increased with severe disc degeneration. This measure of motion segment stiffness correlated well with a manual stiffness measure. CONCLUSIONS: The observed results follow an accepted hypothesis of motion segment instability associated with disc degeneration.

Adult↗

PubMed2002

Intraoperative measurement of lumbar spine motion segment stiffness.

STUDY DESIGN: Prospective trial. OBJECTIVES: To test an intraoperative diagnostic tool to determine if it provided the surgeon with a safe, reproducible, accurate, quantitative measure of lumbar spine motion segment stability. SUMMARY OF BACKGROUND DATA: Several devices have been developed to measure motion segment stiffness, however, few have been tested intraoperatively on humans, and none, to the best of the authors' knowledge have been tested as extensively as the device described in this study. Objective criteria, such as those provided by an intraoperative gauge, can be helpful in determining when and what type of fusion of a degenerated spinal motion segment unit should be performed following decompressive surgery. METHODS: The spinal stiffness gauge, placed between spinous processes of adjacent vertebrae, applies a controlled, constant loading rate along the spine's longitudinal axis, producing a load-displacement curve from which stiffness, range of motion, and hysteresis can be computed. Measurements from this tool were then used to investigate differences in stiffness of the motion segment before and after decompressive surgery, between spine levels, and between male and female subjects. RESULTS: The spinal stiffness gauge stiffness measurements correlated with the surgeon's subjective stiffness measurements on the same motion segments. The stiffness measurements had excellent repeatability. Stiffness was dependent on the spine level, gender, and degree of disc degeneration. CONCLUSIONS: This study demonstrated the efficacy of the spinal stiffness gauge for providing an objective, quantitative, intraoperative stiffness (stability) measurement of the lumbar spine motion segment.

Adolescent↗

PubMed2002

The clinical usefulness of intraoperative spinal stiffness measurements.

STUDY DESIGN: Determination of clinical results at least 2 years after lumbar spine surgery during which spinal stiffness measurements were made. OBJECTIVES: To determine whether spine stiffness is predictive of clinical results after lumbar spine surgery for spinal stenosis, disc herniation, or degenerative spondylolisthesis. SUMMARY OF BACKGROUND DATA: The implied clinical wisdom is that instability of the spine portends a poor prognosis for relief of back pain after surgery in the absence of a fusion. The possibility that an objective measure of lumbar spinal motion segment unit stiffness could aid the surgeon in predicting satisfaction with treatment was considered. METHODS: A total of 298 patients were measured intraoperatively with the spinal stiffness gauge to determine motion segment stiffness. Intraoperative spinal stiffness was analyzed to determine the influence of this measurement on clinical results. RESULTS: Statistical analysis revealed that stiffness measurements did not correlate with clinical results of surgery. Patients with loose motion segment units before decompression did not demonstrate a significantly different level of satisfaction with surgical results a minimum of 2 years after surgery, whether they were fused or not fused. Based on stiffness measurements, a diagnosis of herniated nucleus pulposus or degenerative spondylolisthesis was indicative of a more unstable spine than a diagnosis of spinal stenosis. CONCLUSIONS: Intraoperative spinal stiffness measurements did not predict clinical results after lumbar spine surgery.

Biomechanical Phenomena↗

PubMed2002

Reliability of detecting prosthesis/cement interface radiolucencies in total hip arthroplasty.

A laboratory study assessed the reliability of detecting radiolucencies at the prosthesis/cement interface in femoral components for total hip replacement. Radiolucencies (thicknesses = 0.1, 0.3, 0.5 and 0.7 mm) were created by randomly masking non-tip Gruen zones (six per stem) in a group of 72 matte-finish femoral components. Only half of all Gruen zones were masked. The femoral components were reproducibly implanted in composite fiberglass replicate femurs. Anteroposterior and lateral radiographs taken using conventional techniques were then presented to 10 experienced readers, who scored each of 432 non-tip Gruen zones for radiolucency presence or absence. The series-average radiolucency detection rate was 47.1%, with a breakdown of 9.8%, 20.7%, 69.8% and 88.0, for radiolucency thicknesses of 0.1, 0.3, 0.5 and 0.7 mm, respectively. The false positive rate was 7.5%. The findings argue strongly that in many or most instances, initial cement-prosthesis debonding is not reliably detected from conventional plain film radiographs. Radiolucencies of at least 0.7 mm width are necessary to be accurately detectable by most viewers.

Arthroplasty, Replacement, Hip↗

PubMed2002

Polyethylene liner cementation into fixed acetabular shells.

A patient presenting with a secure cementless acetabular component and with femoral head penetration through the polyethylene liner is a common clinical problem. Cementing a new liner into the fixed shell is one option. We evaluated this option in a clinical series of 17 cases and with a preliminary mechanical study. In the 1 clinical failure (5.9%), the failure occurred at the cement-liner interface. The most important variable in optimizing the mechanical strength of the cemented liner construct was adequate preparation of the cement-liner interface. This approach to treating the patient with a fixed cementless shell and a worn polyethylene liner can provide a durable construct with minimal morbidity.

Aged↗

PubMedDate not supplied

Excessive radiofrequency application: effects on capsular tissue in an animal model.

Capsular attenuation has been seen after thermal capsulorrhaphy surgery. The purpose of this study was to evaluate the mechanical, histologic, and morphologic effects on capsular tissue after cumulative applications of radiofrequency energy. Ovine patellofemoral capsular tissue was treated with 1, 2, 4, or 8 applications of bipolar radiofrequency energy and then analyzed. No acute capsular ablation or destruction was seen grossly, even in the 8-application group. No definitive visual clues that excessive radiofrequency energy had been applied were seen. There was significant shrinkage and loss of tensile stiffness for all thermal application groups. Given the small sample sizes, post-application failure load, percent relaxation, and stiffness were not observed to be significantly different among the groups. Cumulative applications produced minimal further tissue shrinkage but were accompanied by larger, though not statistically significant, mechanical property losses and increased depth of tissue penetration. These findings suggest that there is no benefit to repeated applications of radiofrequency energy to capsular tissue.

Animals↗