Biomedical subjects

William H Harris

Publications and source records attributed to William H Harris.

At least 19 recordsLinked to original sources

PubMed2007

Contact stress assessment of conventional and highly crosslinked ultra high molecular weight polyethylene acetabular liners with finite element analysis and pressure sensitive film.

Stress magnitude and distribution of both conventional polyethylene versus a crosslinked polyethylene in the liner of a total hip replacement (THR) were examined using finite element analysis and pressure sensitive film. Both types of polyethylene were assessed against head sizes of 22 and 28 mm with 5-mm thick polyethylene liners and head sizes of 28, 38, and 46 mm with 3-mm thick polyethylene liners. Liners with 5-mm conventional polyethylene represented successful combinations with long track records. Our hypothesis was that although the combination of the large head and the lower modulus of the highly crosslinked polyethylene would lead to lower stresses, the stresses would be excessive if the liner was extremely thin at 3 mm. Von Mises stresses at the articulating surface of the highly crosslinked liners were lower, when compared to conventional polyethylene, in every THR size examined. Specifically, however, the 38- and 46-mm inner diameter (ID) highly crosslinked polyethylene even at the extreme of only 3-mm thick had lower stresses than the 22-mm ID conventional liner of 5-mm thickness. These data indicate that the use of a large head against highly crosslinked material even at 3-mm thickness results in lower stresses than in an existing conventional 22-mm head and 5-mm thick combination. Obviously, other considerations will influence the minimum thickness to be recommended.

Acetabulum↗

PubMed2006

In vivo oxidation of retrieved cross-linked ultra-high-molecular-weight polyethylene acetabular components with residual free radicals.

Wear of ultra-high-molecular-weight polyethylene (UHMWPE) contributes to debris that can lead to periprosthetic osteolysis in total hip arthroplasty. Irradiation not only decreases wear of UHMWPE but also generates residual free radicals that can oxidize the UHMWPE in the long term. Melting or annealing is used to quench the free radicals. Melting is more effective than annealing. We hypothesized that the postirradiation annealed UHMWPE components would oxidize in vivo and that postirradiation melted ones would not. We analyzed surgical explants of UHMWPE acetabular liners. The irradiated and annealed explants showed embrittlement, oxidation, and an increase in crystallinity. The irradiated and melted UHMWPE explants showed no oxidation, no increase in crystallinity, and no embrittlement. To prevent long-term chemical changes in highly cross-linked UHMWPE components, the residual free radicals must be stabilized after irradiation, preferably by melting and not annealing.

Acetabulum↗

PubMed2006

Polished vs rough femoral components in grade A and grade C-2 cement mantles.

The ideal surface for cemented femoral components remains controversial. Six polished stems were compared with 6 rough stems both with good cement mantle and also with poor cement mantles in a stair-climbing model. With good cement mantles, both the polished and the rough stems were loose by 6 million cycles. However, none were loose by radiographic criteria. With the poor cement mantle, both stems became loose earlier and developed more micromotion, the polished stems having significantly higher and earlier motion than the rough. Radiographic evidence of debonding was not visible until the stems had motion of more than 2,000 microm. In the presence of a good cement mantle in this laboratory model there was no significant difference in the development of micromotion under fatigue stair-climbing conditions between a polished or grit-blasted femoral component. However, in the presence of a poor cement mantle, the polished components had earlier and higher micromotion. This study reinforces the importance of centralization and cement technique, particularly if using a polished surface finish.

Arthroplasty, Replacement, Hip↗

PubMed2006

The effect of surface finish and of vertical ribs on the stability of a cemented femoral stem: an in vitro stair climbing test.

The search for improved femoral fixation in cemented total hip arthroplasty is ongoing. Two design variables, surface finish and stem contour, were evaluated. Sixteen titanium femoral stems of one design were cemented into fiberglass femora. One half of the components had a polished surface and the rest had a roughened finish. Within each group, 4 stems had vertically oriented ribs on the proximal portion and 4 did not. Micromotion was measured in a stair climbing simulator with loading to a joint reaction force of 200 kg for 6 million cycles. Micromotion increased throughout the course of the experiment. Stems with a polished surface had significantly higher micromotion. Although stems with ribs had less micromotion compared with those without ribs, this difference was not statistically significant.

Analysis of Variance↗

PubMed2006

Steady-state penetration rates of electron beam-irradiated, highly cross-linked polyethylene at an average 45-month follow-up.

Steady-state penetration rates were determined on 53 total hip arthroplasties with a minimum 3-year follow-up using electron beam highly cross-linked melted polyethylene by determining the femoral head penetration occurring after the first year in vivo. These data were compared with that of a matched control group. The average steady-state penetration rate of the control group was 144 +/- 191 mum/y, significantly higher than that of the highly cross-linked polyethylene group, 25 +/- 99 microm/y (P = .0001). Linear regression analysis indicated that the magnitude of femoral head penetration did not increase with time in the cross-linked groups. Also, no significant difference existed between the steady-state wear rates of the highly cross-linked groups with two head sizes (28 vs 32 mm, P = .39).

Arthroplasty, Replacement, Hip↗

PubMed2006

In vitro comparison of frictional torque and torsional resistance of aged conventional gamma-in-nitrogen sterilized polyethylene versus aged highly crosslinked polyethylene articulating against head sizes larger than 32 mm.

BACKGROUND: The advent of highly crosslinked polyethylene has allowed the re-evaluation of the use of femoral heads larger than 32 mm for metal-on-polyethylene total hip arthroplasties. However, the effect of larger heads on the frictional torque of highly crosslinked polyethylene is unknown. METHODS: We performed an in vitro examination of the effect of larger chrome cobalt femoral heads (40 mm diameter) on the frictional torque and torsional resistance of hip articulations on aged liners of polyethylene that were sterilized by gamma rays while in nitrogen, and aged highly crosslinked polyethylene. The frictional torque at the femoral head articulation was usually higher for the highly crosslinked polyethylene than for the conventional polyethylene. The aged conventional liners oxidized considerably, which led to gross failure of the polyethylene at the anti-rotation portion of the rim. The aged crosslinked polyethylene showed no such failures despite the higher frictional torque. INTERPRETATION: Our findings suggest that in terms of torsional resistance to fatigue when studied as a device, rather than as an isolated material, under these conditions, aged highly crosslinked polyethylene is preferable to aged conventional polyethylene.

Arthroplasty, Replacement, Hip↗

PubMed2006

Large diameter femoral heads on highly cross-linked polyethylene: minimum 3-year results.

Contemporary highly cross-linked polyethylenes have become the most widely used alternative bearing surfaces in total hip replacement and may be paired with large diameter femoral heads (> 32 mm) in patients considered to be at high risk for dislocation. We report on a prospective series of 42 patients (45 hips) who had total hip replacement using large diameter cobalt-chrome femoral heads articulating with a highly cross linked polyethylene after a minimum of 3 years followup (mean 3.3 years). At final followup, the final patient cohort showed excellent clinical results with no radiographic failures or episodes of loosening. There was no evidence of pelvic or femoral osteolysis. One patient sustained a dislocation due to a grossly malpositioned acetabular component necessitating early isolated acetabular revision. The average yearly steady state wear rate was -0.06 +/- 0.41 mm/year. The results of our short-term prospective series indicated total hip replacement with large femoral heads articulating with a highly cross linked polyethylene showed excellent wear characteristics and clinical results and could be considered in patients at increased risk for dislocation.

Aged↗

PubMed2006

Standing versus supine radiographs in RSA evaluation of femoral head penetration.

Evaluation of polyethylene acetabular component wear in total hip arthroplasties commonly is performed using serial radiographs of the hip by measuring the change in the location of the center of the femoral head in relation to the acetabular component. Of the different methods currently used for this purpose, radiostereometric analysis (RSA) is considered the most accurate and precise. In all such radiographic studies, it is assumed the femoral head is seated into the deepest portion of the acetabular component during all radiographic examinations. Although most radiographs used for wear measurements are taken with the patient supine, we questioned whether standing radiographs, with substantial joint load, are better suited for these measurements. We evaluated two groups of patients having total hip arthroplasty who had radiostereometric radiographs taken in supine and standing positions. The average femoral head penetration that occurred between the 6-month and 2-year time interval was measured with radiographs taken in the standing or supine position. We found no difference between the average total femoral head penetration when using supine or standing radiographs.

Arthrography↗

PubMed2006

Comparison of femoral head penetration using RSA and the Martell method.

UNLABELLED: Radiostereometry has high precision and accuracy measuring polyethylene wear in total hip arthroplasty but requires a specialized setup. The Martell method is simpler and can be used on larger populations. The hypothesis that the radiostereometry analysis and the Martell analysis would yield comparable wear data from the same group of patients having total hip arthroplasty was tested. A group of twenty-five total hip arthroplasty patients who had both radiostereometry and standard anterior-posterior pelvic and cross-table lateral radiographs of sufficient quality for analysis were identified. The films were taken at postoperative periods of 6 weeks, 1 year, 2 years, and 5 years. Femoral head penetration was measured by both methods at each time point. The median penetration rates measured by each method decreased over time. Penetration results were affected by method of analysis, time, and dimension, with greater penetration for Martell compared with radiostereometry at each time point, greater penetration with increasing time for each method, and larger three-dimensional magnitude compared with two-dimensional analysis. LEVEL OF EVIDENCE: Case series Level IV. See Guidelines for Authors for a complete description of levels of evidence.

Arthrography↗

PubMed2006

An integrated solution to acetabular revision surgery.

The three salient reasons for failure of acetabular revision surgery have been failure of fixation, wear and lysis, and dislocation. This review focuses on the major progress made in addressing these three items, leading to an overall approach integrating three contemporary techniques with a strong likelihood of improving acetabular revision surgery. These three techniques are the use of hemispheric cementless acetabular components, alternate bearings, and big heads.

Acetabulum↗

PubMed2006

High placement of noncemented acetabular components in revision total hip arthroplasty. A concise follow-up, at a minimum of fifteen years, of a previous report.

We previously reported the average ten-year results associated with the use of porous-coated noncemented acetabular shells that were placed at a high hip center at the time of revision total hip arthroplasty in thirty-four patients (thirty-six hips) with severe acetabular bone loss. We now report the average 16.8-year results for twenty-one patients (twenty-three hips). Of the original cohort of forty-four patients (forty-six hips), thirty-nine patients (forty-one hips; 89%) retained the shell. Two shells (4.3%) were revised because of aseptic loosening, and three (6.5%) were revised because of infection. Six femoral components were revised because of femoral osteolysis, and seven were revised because of aseptic loosening without osteolysis. On the basis of our results after an average duration of follow-up of 16.8 years, we believe that the placement of an uncemented acetabular component at a high hip center continues to be an excellent technique for revision total hip arthroplasty in selected patients with severe acetabular bone loss.

Acetabulum↗

PubMed2006

Revision of failed acetabular components with use of so-called jumbo noncemented components. A concise follow-up of a previous report.

Acetabular revision in the presence of major bone-stock deficiency is a difficult clinical and surgical problem. Of an original pool of twenty-four consecutive patients treated with an acetabular revision with a so-called jumbo (>65-mm) cementless hemispherical acetabular component, fifteen were followed for an average of seven years in our previous study. The current report presents the results for the twelve patients in this group who were alive at a minimum of twelve years (mean, 13.9 years) postoperatively and agreed to return for follow-up. The average final Harris hip score was 79 points. No acetabular shell had been revised because of aseptic loosening, and none was loose as seen radiographically. The complication rate was high but was largely related to infection. In the patients without infection, the fixation of these large sockets remained excellent at the time of long-term follow-up.

Acetabulum↗

PubMed2006

Primary cementless acetabular components in hips with severe developmental dysplasia or total dislocation. A concise follow-up, at an average of sixteen years, of a previous report.

UNLABELLED: We previously reported the seven-year results of the use of a hemispherical, porous-coated acetabular component in twenty consecutive primary total hip arthroplasties in a highly selected group, namely, patients with severe developmental dysplasia or total dislocation of the hip. The present report describes the outcomes of those hips nine years later, at an average follow-up of sixteen years (range, 11.5 to nineteen years). Since the time of our prior report, two shells were revised; one revision was done because of aseptic loosening and the other, because of polyethylene liner dissociation without tine fracture. The remaining shells were well fixed. No pelvic osteolysis was evident on plain radiographs. The average polyethylene liner wear rate was 0.09 mm/yr. With failure defined as aseptic loosening of the shell, the average sixteen-year survival for the shell was 92%. We believe that this cup had excellent fixation at a long duration of follow-up of sixteen years in this highly selected set of patients with difficult hip problems. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

Arthroplasty, Replacement, Hip↗

PubMed2005

The effect of real-time aging on the oxidation and wear of highly cross-linked UHMWPE acetabular liners.

Irradiation decreases the wear of ultra-high molecular weight polyethylene (UHMWPE) but generates residual free radicals, precursors to long-term oxidation. Melting or annealing is used in quenching free radicals. We hypothesized that irradiated and once-annealed UHMWPE would oxidize while irradiated and melted UHMWPE would not, and that the oxidation in the former would increase wear. Acetabular liners were real-time aged by immersion in an aqueous environment that closely mimicked the temperature and oxygen concentration of synovial fluid. After 95 weeks of real-time aging, once-annealed components were oxidized; the melted components were not. The wear rate of the real-time aged irradiated and once-annealed components was higher than the literature reported values of other contemporary highly cross-linked UHMWPEs. Single annealing after irradiation used with terminal gamma sterilization may adversely affect the long-term oxidative stability of UHMWPE components.

Acetabulum↗

PubMed2005

A new approach for the Martell 3-D method of measuring polyethylene wear without requiring the cross-table lateral films.

Due to the uneven and often inadequate quality of cross-table lateral hip radiographs, many radiographic studies of femoral head penetration into polyethylene in total hip arthroplasty are limited to the two-dimensional measurement of femoral head penetration using the A/P film only. We postulated that the use of two oblique frontal projections at 90 degrees to each other would improve the three-dimensional evaluation. Using an established hip phantom, the idealized accuracy and precision of the three-dimensional Martell method was evaluated, contrasting the standard A/P and cross-table lateral projections versus a pair of oblique projections by four independent readers. Accuracy and precision resulting from the use of two oblique projections (average accuracy +/-63 microm, precision +/-26 microm) were similar to that obtained using the conventional A/P and cross-table lateral views (accuracy +/-54 microm, precision +/-22 microm), though the results of the two oblique views were slightly more variable. These observations suggest that by using two oblique A/P projections, the major disadvantage of using the cross-table lateral films, namely the variable quality of the images, is avoided. Perhaps, therefore, the utility and availability of three-dimensional data in comparable clinical studies may be improved.

Arthrography↗

PubMed2005

Effect of oral alendronate on net bone ingrowth into canine cementless total hips.

Alendronate has been shown to prevent osteolysis in a canine total hip arthroplasty (THA) model. However, the effect of alendronate on bone ingrowth and remodeling around canine cementless hip replacement components remains unclear. We hypothesized that oral alendronate would increase net bone ingrowth into the porous surface of THA components when intimate bone/implant contact exists. To test this hypothesis, six mature dogs received unilateral cementless THA and were treated with five milligrams of oral alendronate daily from day seven to day eighty-four postoperatively. Six comparable dogs served as controls. Quantitative analysis of net bone ingrowth into the porous surface did not show a significant difference between the two groups, (control 7.9 +/- 1.5, alendronate 7.5 +/- 1.4, P < 0.6). These results did not support the hypothesis that oral alendronate would increase net new bone formation into the porous surface of THA components. Key words: alendronate, bone ingrowth, total hip arthroplasty.

Administration, Oral↗

PubMed2005

Range of motion and stability in total hip arthroplasty with 28-, 32-, 38-, and 44-mm femoral head sizes.

The purpose of this study was to evaluate, via experimental models, the effect of larger head sizes for total hip arthroplasty on the type of impingement, range of motion (ROM), and joint stability. Testing was conducted using an anatomic full-size hip model (anatomic goniometer) and a novel anatomic dislocation simulator with 28-, 32-, 38-, and 44-mm diameter femoral heads within a 61-mm acetabular shell. Femoral heads >32-mm provided greater ROM and virtually complete elimination of component-to-component impingement. A significant increase in both flexion before dislocation and displacement between the femoral head and acetabulum to produce dislocation occurred with femoral heads >32-mm in diameter. These data indicate that larger femoral heads offer potential in providing greater hip ROM and joint stability.

Hip Prosthesis↗

PubMed2005

The measurement of creep in ultrahigh molecular weight polyethylene: a comparison of conventional versus highly cross-linked polyethylene.

Quantification of creep of highly cross-linked polyethylene would enable separation of creep from wear when evaluating femoral head penetration into polyethylene. We compared creep magnitude of a highly cross-linked versus conventional polyethylene in the laboratory. Twelve acetabular liners of each material were tested, 6 of which had a 32-mm inner diameter (ID) and 6 had 28-mm ID. Creep was measured using coordinate measuring machines during loading at 2 Hz without motion to 4 million cycles. Penetration into 32-mm ID conventional liners reached 97 microm versus 107 microm for highly cross-linked material, not significant. Penetration into 28-mm conventional liners was 132 microm versus 155 microm for highly cross-linked material (P = .017). Ninety percent of the creep had occurred by 2.5 million cycles.

Arthroplasty, Replacement, Hip↗