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Biomedical subjects

C A Engh

Publications and source records attributed to C A Engh.

At least 91 records · Page 5Linked to original sources
PubMed1994

Cortical bone density of the proximal femur following cementless total hip arthroplasty.

A quantitative analysis of cortical bone remodeling was performed using calibrated videodensitometry. Six femoral specimens were obtained at autopsy from 3 patients treated with unilateral porous coated femoral components in situ > 6 years. Transverse thick sections of the remodeled and normal femora were obtained. Slab radiographs of the sections were analyzed using computer assisted videodensitometry. Detailed density plots of each section were constructed and the average density in defined quadrants was recorded. The density plots were also used to measure the cortical bone area present on each section. Two cases showed a gradient of resorptive remodeling change with the greatest density loss noted medially at the proximal levels (33% and 36%). The 3rd case had porotic cortical bone in the normal femur and demonstrated a different remodeling pattern, with the greatest average resorptive change (57%) measured in the midstem region. Changes in cortical area were variable: 1 showed cortical thickening in the midstem region; another had decreased cortical area in the entire region adjacent to the porous coating; and the 3rd had decreased cortical area proximally, with minimal changes noted in the distal levels. The volumetric densities measured by videodensitometry were compared with area densities measured with dual energy xray absorptiometry. There was a strong linear correlation between the 2 methods (r2 = 0.80).

Absorptiometry, Photon↗
PubMed1994

Porous-coated total hip replacement.

Fifteen years of clinical experience with porous-coated prostheses demonstrated the durability of this type of fixation. This experience was documented by clinical follow-up study of the 393 cases treated by the senior author before 1985. Only six of these femoral components have been revised: three for loosening, two for stem breakage, and one for infection. Thus, the revision rate for the porous-coated stems was 1.5%. Porous-coated acetabular components were used in 227 of the arthroplasties. Five of these porous-coated cups have been revised: four for malposition leading to dislocation and one for late loosening secondary to osteolysis. Thus, the revision rate for these porous-coated acetabular components was 2.2%. Twenty bipolar and 146 cemented acetabular components were used in the remaining 166 cases treated before 1985. Eleven (7.5%) of the cemented acetabular components were revised. Revisions of the porous-coated components were rare in the first ten postoperative years. The clinical data were supplemented with analysis of postmortem specimens from 15 patients. Mechanical testing of the femoral specimens showed the relative micromotion at the porous surface to be exceptionally small (less than 40 microns). Seven of these postmortem retrievals involved cases with unilateral arthroplasties. In these cases, the contralateral normal femur also was removed, and a prosthesis identical to that in the in vivo implanted side was inserted to simulate the immediate postoperative condition. Dual-energy X-ray absorptiometry (DEXA) of the seven paired femora demonstrated that bone remodeling can be expected to produce a 5%-52% loss of periprosthetic bone mineral content, with the greatest loss occurring in the more osteoporotic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1994

Failure of structural acetabular allografts in cementless revision hip arthroplasty.

We investigated the radiographic and clinical course of 31 patients in whom a bulk acetabular allograft had been used during the cementless revision of a total hip replacement. Two patients died and two were lost to follow-up within 24 months, but of the remaining 27 acetabular components, 12 (44%) showed radiographic evidence of instability at a mean of 46 months. Five of these have been revised. In the 12 failures, signs of instability had been noted at an average of 29 months (1 to 60). Failures during the first 24 months were usually due to technical errors, later failures to gradual migration of the cup into the graft. The cups with the greatest amount of their surface supported by grafts were most likely to migrate, but this migration was usually asymptomatic. Screw fixation of the cup, used in 24 cases, appeared to control the mechanism of failure. Femoral head allografts and distal femoral allografts had been used, with failure in 6 of 16, and 6 of 11 respectively; distal femoral allografts were used only for large defects. The insidious course of late cup migration and graft failure necessitates close radiographic follow-up of patients treated with bulk allografts.

Acetabulum↗
PubMed1993

Mechanical evaluation of cadaver retrieval specimens of cementless bone-ingrown total hip arthroplasty femoral components.

Early retrieval prior to gross failure of implants can provide valuable information for critical issues in total joint arthroplasty. To evaluate fixation of the femoral component in total hip arthroplasty, two femoral specimens--one Mallory-Head (Biomet, Warsaw, IN) specimen and one AML (DePuy, Warsaw, IN) specimen--were retrieved after 2-8 years of successful use in active patients. Radiographs were made and evaluated for trabecular apposition to the porous-coated areas of the stem, then torsional and axial load tests were performed for each specimen to determine micromotion and displacement at the bone-implant interface. Both implants had radiographic signs of bone ingrowth. No permanent rotational displacement was found in either specimen during torsional load testing, but rotational and axial micromotion were found in both. These findings indicate excellent fixation of implant to bone, and no slippage at the bone-implant interface. The Mallory-Head implant had much greater elastic displacement than the AML, and histological examination showed cancellous bone ingrowth into the porous-coated portion of the Mallory-Head stem. The AML implant, which withstood much higher torsional loads, was found upon histological evaluation to have dense cortical-cancellous bone ingrowth. Strength of attachment of the metal implant to bone was good in both specimens, and neither had slippage at this interface. Differences in mechanical behavior can be attributed to the type of bone supporting the implant. The Mallory-Head implant had a severely worn titanium femoral head, so the joint was full of particulate metal debris.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Histological and radiographic assessment of well functioning porous-coated acetabular components. A human postmortem retrieval study.

Nine porous-coated acetabular components were retrieved post mortem. All components had been inserted at our institution and had been in situ for a mean of fifty months (range, seventeen to eighty-seven months). Clinical records revealed that all had been functioning well at the time of death, and clinical radiographs showed signs that all had been stable. Standard backscattered scanning electron microscopy was used to quantitate the amount of bone ingrowth into the porous coating. For each component, the histological appearance of the bone-metal interface was compared with the appearance on clinical radiographs. Light microscopy was used to study the non-ossified areas. Every component had growth of bone into the porous coating, with the ingrowth occupying a mean of 32 per cent (range, 3 to 84 per cent) of the fields that were examined. In areas where bone ingrowth had occurred, the mean area density was 48 per cent (range, 26 to 65 per cent). Use of radiographs consistently led to an underestimation of the presence of gap areas and an overestimation of the occurrence of bone apposition. When fibrous tissue was present in non-ossified areas, it was extremely dense and well organized. Within the limits of light microscopic examination, there was no evidence of granulomatous formation in the non-ossified regions. This is particularly encouraging since the fibrous tissue-bone interfaces seem to prohibit the deposit of particulate debris.

Acetabulum↗
PubMed1993

Severe osteolysis of the pelvic in association with acetabular replacement without cement.

We reviewed the cases of fourteen patients (fifteen lesions) who had osteolysis following the replacement of the acetabulum without cement. Nine women and five men, seventeen to sixty-seven years old, were involved in the study. One woman had bilateral pelvic osteolysis. Eight of the fifteen index acetabular reconstructions were done with a titanium-alloy implant and seven, with a chromium-cobalt-alloy implant. Eleven of the fifteen acetabular components had holes in the metal shell that may have acted as a conduit through which wear debris could gain access to the implant-bone interface, but only two of the acetabular components had been fixed with screws. In these two acetabular components, all available screw holes were not filled. The polyethylene liner was eight millimeters thick or less in twelve of the fifteen acetabular components; all of the liners were ten millimeters thick or less. The diameter of the head of eleven of the fifteen femoral components was thirty-two millimeters. Fourteen of the fifteen femoral components were placed without cement, and all but one was radiographically stable. The duration from the index operation to the appearance of pelvic osteolysis ranged from fifty-three to eighty-four months (mean, sixty-five months). At the time of the diagnosis, the patients were functioning well clinically, and all but three had a Harris hip score of 90 points or better, despite extensive destruction of bone in some instances. Since these patients were functioning well, the pelvic osteolysis was diagnosed radiographically at a regular follow-up examination. Only one patient had evidence of migration of the acetabular component on serial radiographs.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗
PubMed1993

Evaluation of initial surface apposition in porous-coated acetabular components.

The initial surface apposition of the acetabular bone-implant interface was investigated for acetabular components of three different designs: hemispherical with spikes, hemispherical, and threaded hemispherical. Four acetabular components of each design were implanted into fresh anatomic specimen acetabula that were underreamed by 1 mm to the size of the component. Each acetabular specimen then was embedded in methylmethacrylate, sectioned, and examined under magnification. Although acetabular implantation was carefully performed by an experienced surgical team in an idealized laboratory environment, less than complete interface contact was achieved in most cases. Surface contact was limited by five factors: (1) bony anatomy, (2) asymmetric acetabular reaming, (3) retention of the subchondral plate, (4) acetabular component design, and (5) incorrect version of the acetabular component. The bony acetabulum is an incomplete hemisphere because of the acetabular notch and a deep acetabular fossa, and therefore cannot be machined to a perfect hemisphere. Asymmetric reaming occurs because of the anisotropic quality of bone. Retention of the subchondral plate causes incomplete seating of components with spikes or threads. The acetabular design determines the amount of porous coating available for bony apposition and varies depending on the surface area used for screw holes, apical holes, and thread segments. Increased, stable initial surface contact of acetabular components will increase the chances of stable biologic fixation. Improved surface contact will require changes in component design, instrumentation, and technique.

Acetabulum↗
PubMed1993

Revision total hip arthroplasty. Long-term results without cement.

The authors present their results for cementless femoral revision arthroplasty using extensively porous coated implants. Patients have been prospectively followed for 5 to 11 years (mean 7.4 years). The revision rate was 5.7%, and the radiographic loosening rate was 1.1%, to give a mechanical failure rate of only 6.9%. As a result of the revision procedure, the pain level was improved for 89.1% of the patients, walking status was improved for 82.8% of the patients, and functional level was improved for 88.5% of the patients. These results compare very favorably with any reports on revision arthroplasty using cement with a similar length follow-up.

Adult↗
PubMed1993

Roentgenographic densitometry of bone adjacent to a femoral prosthesis.

A digital imaging method was developed to quantitate the stress-related changes in roentgenographic bone density after total hip arthroplasty. A technique termed "histogram-directed equalization" was used to compensate for differences in postimaging data caused by the effects of variable quality obtained from ten patients. Quantitative change due to variation in delivered energy was decreased by 7% for roentgenograms obtained with a 2 kVp variation and 31% for roentgenograms obtained with a 4 kVp variation. The method allowed the authors to accurately describe the changes observed on annual postoperative roentgenograms obtained over the past decade. The utility of the method was demonstrated in 15 of the senior author's long-term cases treated with fully porous-coated implants. These cases were divided into two groups based on the diameter of the prosthetic stem implanted in each case. Five patients were grouped with small-diameter stems and ten with large-diameter stems. Both groups showed substantial decrease in roentgenographic bone density (from 11% to 28%) in the medial and lateral proximal regions. The large-diameter group had an overall larger decrease in roentgenographic bone density at two and five years. Roentgenographic bone remodeling changes were most pronounced in the first two years. Changes between two and five years progressed at a slower rate. The results also confirmed the predicted effect of stem diameter on bone remodeling patterns.

Absorptiometry, Photon↗
PubMed1992

Quantification of implant micromotion, strain shielding, and bone resorption with porous-coated anatomic medullary locking femoral prostheses.

Fourteen femora containing porous-coated anatomic medullary locking (AML) femoral prostheses were retrieved from 12 patients at autopsy. Clinical roentgenograms in 13 femora showed bone remodeling changes, indicating that the implants were fixed by osseointegration. Under simulated physiologic loading, micromotion between the implant and the bone was measured using electrical displacement transducers connected to the implant and to the adjacent cortex. The micromotion between the implants at the areas of porous coating and the adjacent cortex in the one case of failed bone ingrowth measured 150 microns. Maximum relative motion between the cortex and the implant in the areas of porous coating for the 13 cases showing signs of bone ingrowth was 40 microns, and this was completely elastic relative displacement. With all implants, the micromotion between the cortex and the stem was always greatest over the uncoated portion of the stem. Four of the implants were proximally porous coated. With these, the micromotion was greater over the uncoated areas than with more extensively coated stems and was always greatest at the uncoated tip of the prosthesis. The amount of micromotion was directly related to the extent of porous coating on the implant. Maximum tip motion for the proximally coated implants was 210 micra, whereas for the fully porous-coated implants, it was 40 microns. In nine of the autopsies, the contralateral normal femur was obtained in addition to the femur containing the AML (the in vivo remodeled femur). These were used for comparative studies of strain shielding and femoral remodeling. Cortical strains were measured in the in vivo remodeled femora and were compared with measurements made in the contralateral normal femora before and following implantation of a stem identical to that present on the clinically treated side. The data showed major strain reductions in all the postmortem implanted normal femora. Comparison of the strain data from the postmortem implanted normal femora with those from the in vivo remodeled femora clearly indicated that extensive bone remodeling did not result in restoration of cortical strain levels anywhere near normal. Strain shielding continued to exist in all of the remodeled specimens, even up to 7.5 years after surgery. This strain shielding was associated with bone remodeling changes that resulted in regional reductions in bone mineral content that ranged from 7% to 78%. These observations are unique, important, and valuable in defining the in vivo function and clinical behavior of this type of porous-coated femoral component.

Aged↗
PubMed1992

The removal of porous-coated femoral hip stems.

During a ten-year period, 70 porous-coated femoral hip components of several designs were removed for various reasons. Based on this experience, techniques for the removal of porous-coated stems have evolved and are described, including a newer method for the safe removal of extensively coated bone-ingrown stems. Preoperative roentgenograms were highly predictive of fixation mode as corroborated by intraoperative mechanical testing, gross inspection, and histologic examination. Stable implants (17 bone-ingrown and 11 fibrous tissue-encapsulated) required interface access and division before their removal. Minimal bone damage was incurred, and in no case was reconstruction precluded by stem removal. There were no unplanned cortical perforations. Two minor femoral fractures occurred. The authors present an overall approach and specific surgical techniques that facilitate the safe removal of porous-coated femoral stems on a consistent basis.

Adolescent↗
PubMed1992

A quantitative evaluation of periprosthetic bone-remodeling after cementless total hip arthroplasty.

Dual-energy x-ray absorptiometry analysis was used to determine the periprosthetic bone-mineral content of ten femora that had been obtained at the autopsies of five elderly patients who had had an AML (anatomic medullary locking) prosthesis in situ for seventeen to eighty-four months. Clinical radiographs showed resorptive remodeling changes characteristic of femora containing this implant. Before the absorptiometry was performed, an identical prosthesis had been inserted into the contralateral, normal femur of each cadaver. The mean difference in the periprosthetic bone-mineral content between the remodeled femora and the femora in which the prosthesis had been implanted post mortem ranged from 7 to 52 per cent, with the bone-mineral content always less in the remodeled femora. The greatest mean decrease in bone-mineral content (45 per cent) occurred adjacent to the proximal one-third of the remodeled femora. The percentage decrease in periprosthetic bone-mineral content in the remodeled femora had an inverse linear relationship with the corresponding bone-mineral content of the contralateral control femora. Preoperative analysis of bone density may therefore be useful for prediction of the extent of resorptive bone-remodeling after total hip replacement.

Absorptiometry, Photon↗
PubMed1992

Producing and avoiding stress shielding. Laboratory and clinical observations of noncemented total hip arthroplasty.

Experimental canine model studies of stiff versus flexible, fully porous-coated, metallic femoral stems (differing by three- to fivefold in stiffness characteristics) revealed markedly different resorptive bone remodeling patterns. The flexible stem resulted in about 30% more cortical bone retention adjacent to the implant at one-year postimplantation and larger differences in dogs killed two and three years after surgery. Strain-gauge studies confirmed that there are differences in cortical bone strains with the two stem designs, the flexible stem producing a more uniform and more nearly normal strain distribution medially. Differences in cortical bone remodeling were quantified using dual energy X-ray absorptiometry (DEXA). The bone mineral content in femora with the flexible stem decreased less than 20%, compared to normal. At three years postimplantation, the bone mineral content of the femora with the stiff stem was about 50% that of the femora with the flexible stem. Clinically, DEXA revealed that 5%-15% changes in bone mineral density at various periimplant sites were common within the first two years after surgery; these changes were not usually evident roentgenographically. Serial roentgenographically distinct bone resorption was usually associated with bone mineral density changes of 20%-50%. Five- to 13-year roentgenographic follow-up observations of 213 cases with the Anatomic Medullary Locking prosthesis showed that pronounced bone resorption occurred in 33% of patients. Larger stems (greater than 13 mm in diameter) and stems with extensive porous coating had a significantly higher incidence of pronounced bone resorption than smaller stems and those with proximal coating. The stiffness characteristics of the human femur were established as a function of canal size and compared with those of noncemented hip prostheses. Increased mechanical compatibility was found for stems made of titanium alloy and with design features that reduce cross-sectional area and moment of inertia. Clinical data suggest that to reduce the likelihood of pronounced bone resorption, it would be beneficial for the implant to possess a bending stiffness of about one half to one third that of the human femur.

Absorptiometry, Photon↗
PubMed1992

Torsional fixation of the femoral component in total hip arthroplasty. The effect of surgical press-fit technique.

Rotational loading of the femoral component has recently emerged as a prime factor for causing loosening and failure of total hip replacements. In this study the effect of surgical press-fit technique on torsional fixation of the femoral component was evaluated. The commonly used line-to-line reaming technique was compared to an underreaming technique using both four-fifths and one-third porous-coated anatomic medullary locking (AML) implants. Rotational micromotion, permanent rotational displacement, and slop displacement between bone and implant were measured with linearly variable differential transducers under torsional loading. The line-to-line reamed group showed significantly greater motion than both underreamed groups for all micromotion parameters. This was especially true for the slop displacement test, which revealed large amounts of displacement after a single moderate torsional load, whereas in the underreamed groups significantly less loosening was found. The line-to-line reaming technique did not achieve good rotational fixation of the femoral component. Superior rotational stability was accomplished only when the diaphysis was underreamed and tight diaphyseal fixation was achieved. The extent of the porous coating on the stem did not have a significant effect.

Hip Prosthesis↗
PubMed1991

Comparison of porous-threaded and smooth-threaded acetabular components of identical design. Two- to four-year results.

Between April 1985 and April 1987, 82 smooth-threaded and 62 porous-threaded acetabular components of identical design were implanted without structural bone grafting as primary acetabular replacements. At a minimum two year follow-up examination, statistically significant differences were found in the roentgenographic and clinical results between the two matched groups. Twenty-nine percent of the smooth-threaded cups and none of the porous-threaded acetabular components were classified as roentgenographically unstable. Clinically, groin or buttock pain was present in 25% of patients with smooth-threaded cups and in only 7.5% of the patients with the porous-threaded components. Six smooth-threaded components and none of the porous-threaded components have been revised to date. Because of the unacceptable high incidence of instability at short-term follow-up, the smooth-threaded acetabular component is no longer being used at this institution. The addition of the porous coating was associated with the superior results noted in this group.

Acetabulum↗
PubMed1990

Cementless total hip arthroplasty with femoral head bone grafting for hip dysplasia.

Femoral head bone grafting was required to augment acetabular bone stock in 19 cases of hip dysplasia treated with cementless total hip arthroplasty. All acetabular grafts provided mechanical support for the cementless acetabular component. Radiographic evaluation of the fixation of the femoral components at an average of 3 years after surgery revealed an optimum appearance in all cases. All porous-coated acetabular components remained stable, but only one of six (17%) nonporous threaded acetabular components maintained stability. One threaded acetabular component has been revised for symptomatic loosening. Acetabular graft healing was suspected in 18 of 19 cases (95%). Significant graft resorption was observed only in the cases with unstable threaded acetabular components. The clinical scores were high. Cementless total hip arthroplasty with structural acetabular grafting and porous acetabular components appears to produce satisfactory short-term results.

Acetabulum↗
PubMed1990

Cementless acetabular components.

Four hundred and fifteen patients with cementless acetabular components of either a smooth threaded (130) or porous surfaced (285) variety were compared for clinical symptoms and radiographic signs of component loosening. At a mean 4.8 year follow-up none of the patients with porous acetabular components had signs of component instability. At a mean 3.9 year follow-up 27 (21%) of the patients with a smooth threaded acetabular component showed radiographic signs of instability and 33 (25%) had clinical symptoms. The disappointing short-term results with these threaded cups in our hands have prompted us to abandon their use in favour of the porous surfaced hemispherical cups.

Adolescent↗