Biomedical subjects

C A Engh

Publications and source records attributed to C A Engh.

At least 19 recordsLinked to original sources

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↗

PubMed1990

Roentgenographic assessment of the biologic fixation of porous-surfaced femoral components.

Certain roentgenographic signs have value in predicting the fixation of a cementless femoral component to bone by osseointegration. Other signs have value in predicting the gross stability of a cementless femoral component. The authors have determined the specificity and sensitivity of the signs for osseointegration in cases in which the histologic fixation has been confirmed after implant removal. The authors have also determined the specificity and sensitivity of the signs for gross implant stability in cases in which the stability has been confirmed at reoperation. Statistical methods were used to determine a numeric value for each of these roentgenographic signs, and these values were combined into a score. The score was divided into fixation by osseointegration and mechanical implant stability. The two scores were then combined into an overall score. When signs of osseointegration were present, the implant was always stable, and the overall scores were the highest. When signs of osseointegration were absent, the mechanical stability varied, and the scores were lower. A neutral or slightly negative score correlated with failed osseointegration but secondary successful implant stabilization. A very low negative score correlated with gross implant instability. To confirm the validity of the scoring system, the two-year postoperative score was determined for 1005 cases in which the clinical outcome was known. A strong correlation between the presence of symptoms and a low score confirmed the value of the scoring system for diagnosing implant loosening as the cause of symptoms. As a second test, the two-year and five-year postoperative results were compared in the same patients. A high two-year score correlated with durable implant stability through five years. A low two-year score correlated with a higher incidence of late symptomatic loosening.

Adult↗

PubMed1990

The case for porous-coated hip implants. The femoral side.

A series of 1163 total hip arthroplasties (THAs) using porous-coated femoral components were roentgenographically assessed for implant fixation. For 959 primary THAs followed from two to 12 years, the femoral revision rate was 1% and the ten-year survivorship rate was 96.4%; 150 young patients had a fixation failure incidence of only 1.3% at a mean follow-up period of 6.4 years; in 204 revision THAs, the femoral re-revision rate was 4% at a mean follow-up period of 53.4 months. Failures were largely related to inadequate femoral canal filling. Because of refinements in implant design and surgical techniques, a press fit of the implant is currently achieved in 94% of cases compared to 36% during the first five years. Porous-coated femoral components have yielded results equivalent to those with cement in primary THAs. Excellent results were observed in relatively young patients and patients with revisions.

Adolescent↗

PubMed1989

Evaluation of cementless acetabular component migration. An experimental study.

Roentgenograms of two human cadaveric pelves with three implanted acetabular components were taken in anatomic, tilted, and rotated positions to determine their effect on the measurement of cup migration. The best landmark for measuring migration along a vertical axis was the distance between the center of the cup and the teardrop line. The best measurement for cup migration along an horizontal axis was the distance between the center of the cup and the vertical line through the teardrop. When the teardrop is not visible, one should use the distance between the bottom of the cup and the obturator line, and the distance between the center of the cup and Kohler's line. Guidelines for roentgenographic comparability are as follows: at 10% magnification, the variation in distance between the obturator line and the teardrop line should be less than 5 mm, and the distance between the middle of the sacroiliac line and the vertical line through the pubis should be less than 0.5 cm.

Acetabulum↗

PubMed1989

Cementless total hip arthroplasty using the anatomic medullary locking stem. Results using a survivorship analysis.

Three hundred forty-three primary hip arthroplasties performed prior to June 1984 were followed for two years, and an additional 204 were followed for five years. Anteroposterior and lateral roentgenograms taken at annual intervals were used for comparison. At two years, 78% of the hips showed roentgenographic signs of stem osseointegration. Seventeen percent were clinically stable but demonstrated reactive lines surrounding the porous surface, indicating lack of bone-ingrowth fixation. Four percent showed late implant migration. Using late migration as an end point, a survivorship analysis of the stem stability was performed. The cumulative survival rate for stable fixation was 94% at five years and 88% at eight years. Among the 143 undersized stems, 17 showed late migration and two failed by stem fracture at six and eight years, giving a cumulative survival rate of 77% at eight years. By contrast, there were no roentgenographic failures among 200 canal-filling stems. Three stems were revised: two for stem fracture and one for loosening with infection. Proximal stress shielding occurred only in bone-ingrowth stems and was slightly progressive. Unstable implants produced progressive intramedullary canal widening. The clinical results were superior when the roentgenograms showed signs of bone-ingrowth fixation. Functional recovery in such cases was equivalent to that for cemented arthroplasty.

Adolescent↗

PubMed1989

Cementless total hip replacement using the AML stem. 0-10 years results using a survivorship analysis.

343 primary arthroplasties using the AML stem were performed between 1978 and June, 1984 with a mean follow-up of 4.8 years. All had a two-year reading of stem fixation as: 1) bone ingrown or optimum (81%), 2) fibrous encapsulated or suboptimum stable (16%), or 3) unstable (3%). Using a roentgenographic end-point, we performed a 0-8 year survivor analysis of stem fixation. The cumulative survivorship rate (CSR) was 85% at eight years. Among 142 undersized stems, thirteen failed by migration after one year and two by stem fracture, giving a CSR of 71% at eight years. By contrast, no failure was recorded in 201 canal filling stems. Proximal stress shielding occurred only in bone ingrown stems and was slightly progressive. Widening of the intramedullary canal occurred with unstable stems. The clinical results were superior in patients with bone ingrown stems and functional recovery in those cases was equivalent to that of cemented arthroplasty.

Adolescent↗

PubMed1989

Femoral fracture during non-cemented total hip arthroplasty.

A study of the data on 1,318 consecutive non-cemented total hip-replacement arthroplasties revealed thirty-nine intraoperative fractures of the femur (3 per cent), only half of which were diagnosed intraoperatively. The fractures occurred in the proximal region of the femur or at the tip of the stem of the prosthesis. Most were incomplete and minimally displaced, and they did not jeopardize the stability of the femoral component. All complete proximal fractures were stabilized with a four-fifths-coated or fully coated prosthesis to provide distal fixation, and, when diagnosed intraoperatively, were fixed with cerclage wiring. When an incomplete fracture near the tip of the stem was discovered postoperatively and the posterior part of the femoral cortex was intact, a spica cast was applied, and the patient was instructed in protected weight-bearing. For a complete fracture at the tip of the stem, we recommend open reduction and internal fixation. No statistical difference was found with respect to residual pain, the score for walking, or the stability of the implant when we compared the results for the patients who had a fracture with those for the patients who did not. Modifications in surgical technique resulted in a decrease in the incidence of fractures (p less than 0.05).

Cementation↗

PubMed1988

Radiography and histology of a threaded acetabular implant. One case studied at two years.

Threaded acetabular components are widely used in cementless total hip replacement, despite a poor understanding of the nature of the bone-implant interface. We have examined one case in which the threaded titanium ring appeared to be well incorporated with no discernible radiolucency. Microradiography and histology surprisingly showed that the threads were entirely encapsulated in fibrous tissue. This raises doubt about the relevance of plain radiography to the analysis of the acetabular interface.

Acetabulum↗

PubMed1988

The influence of stem size and extent of porous coating on femoral bone resorption after primary cementless hip arthroplasty.

The influence of stem size and extent of porous coating on femoral bone resorption was examined in 411 cases of primary cementless hip arthroplasty. Moore design, cobalt alloy femoral implants with powder-made sintered porous coating on either one-third, two-thirds, or the full implant length were compared radiographically two years after surgery. A semiquantitative method was adopted for assessing resorption that involved dividing the anteroposterior (AP) and lateral roentgenograms into a total of 16 discrete sites. The 16 sites were qualitatively examined for evidence of resorption by either thinning or darkening of bone relative to the time immediately following surgery. Based on the number of sites that demonstrated resorption, the bone loss was classified as either minor and not likely to cause problems (0 to 4 sites) or pronounced and of potentially harmful clinical consequence (5 or more sites). Pronounced resorption occurred in 18% of the 411 cases. The use of larger stems resulted in increased occurrence of marked bone resorption: stems greater than or equal to 13.5 mm in diameter showed five times the incidence of pronounced resorption compared with stems less than or equal to 12.0 mm in diameter. Stems with two-thirds and full porous coating resulted in a twofold to fourfold increase in the incidence of pronounced bone resorption. The theoretic degree of stress shielding of the femoral shaft in bending was calculated for cases with complete canal filling and a radiographic appearance of bone ingrowth. There was a strong correlation between this theoretic factor and the observed bone resorption.

Aged↗

PubMed1988

Results of cementless revision for failed cemented total hip arthroplasty.

The goals of revision total hip arthroplasty (THA) are to reestablish and maintain stable implant fixation. Based upon promising early results in primary THA, porous-surfaced implants designed for bone ingrowth fixation are being increasingly used in hopes of more successfully achieving these goals than has been the case using cement. One hundred and sixty such revisions were followed for a mean of 4.4 years, with specific reference to implant fixation. Roentgenographic evaluation of implant fixation suggested four categories of femoral and acetabular components: (1) bone ingrown, (2) stable fibrous encapsulation, (3) questionable, with signs of impending instability, or (4) definitely unstable implant migration, indicative of the need for rerevision. Not surprisingly, success in achieving and maintaining stable implant fixation following revision THA is dependent upon component design, surgical technique, and preexistent bone stock damage. This classification according to bone stock damage should be borne in mind when critically evaluating the results from various revision series.

Acetabulum↗

PubMed1987

A technique of extensile exposure for total hip arthroplasty.

A technique of trochanteric osteotomy that allows extensile exposure of the hip and wide exposure of the proximal femoral diaphysis for total joint replacement is described. Pathologic conditions of the shaft encountered during arthroplasty can therefore be addressed. The approach is based on the preservation of an intact musculoosseous-muscular sleeve comprised of the gluteus medius, greater trochanter, and vastus lateralis and allows physiologic reconstruction of the hip's soft tissue envelope. This versatile approach is particularly useful in revision surgery and in difficult primary interventions where leg length is adjusted. The surgical technique, indications, and advantages are described. Early clinical results of 90 cases are presented.

Femur↗