Biomedical subjects

D R Sumner

Publications and source records attributed to D R Sumner.

At least 73 records · Page 4Linked to original sources

PubMed1993

Stem curvature and load angle influence the initial relative bone-implant motion of cementless femoral stems.

A 6 df measurement system was used to investigate the initial relative bone-implant motion of two types of cementless total hip replacement femoral components-a straight stem and a curved stem. Five pairs of fresh frozen femurs from human cadavers were tested with loads applied to the femoral head at angles characteristic of level walking, stair-climbing, and rising from a chair. The most important findings were that (a) the resultant proximal translations were twice as high with the straight stem as with the curved stem at load angles encountered in stair-climbing and rising from a chair, (b) both stem types had more motion at load angles encountered in stair-climbing and rising from a chair than in level walking, with the increases ranging from 3 to 14-fold, (c) there was as much as 66-fold more motion distally than proximally, and (d) the amount of interface motion varied by 5-fold between the medial and lateral surfaces of the distal part of the implant because of the combined effects of translation and rotation. The amount of initial bone-implant motion of the femoral component was found to be particularly sensitive to off-axis loading; this suggests that stair-climbing and rising from a chair should be avoided in the early postoperative period when a cementless porous-coated femoral stem has been used.

Adult↗

PubMed1993

A quantitative study of bone and soft tissues in cementless porous-coated acetabular components retrieved at autopsy.

The authors examined 11 cementless acetabular components of one design retrieved at autopsy and made observations concerning tissue ingrowth and local tissue reaction, radiographic-histologic correlation, and the distribution of particulate wear debris. The cups were hemispherical in design with a commercially pure titanium fiber-metal porous coating. All of the prostheses were implanted with screws. The implants were in place for an average of 41 months (range, 5 weeks to 75 months). Ten of the cups had bone ingrowth, with the average volume fraction being 12.1 +/- 8.2%. There were no differences in the amount of bone ingrowth when the component was partitioned into nine anatomic regions. However, there was more bone adjacent to screw holes through which screws were inserted compared with empty screw holes. As the number of radiolucent zones increased on the clinical radiographs less bone ingrowth was observed histologically. The amount of metal debris in holes with screws and holes without screws was similar. In the longest term cases, polyethylene debris was noted within empty screw holes, but no granulomatous reactions or osteolytic processes were observed.

Acetabulum↗

PubMed1993

Revision of the acetabular component without cement after total hip arthroplasty. Three to six-year follow-up.

One hundred and thirty-eight consecutive revisions of an acetabular component were performed in 132 patients between 1983 and 1986. The revision prosthesis was a hemispherical component that was coated with porous titanium mesh and was secured to the pelvis with a variable number of screws. There were seventy-five women and fifty-seven men, and the mean age at the time of the revision was fifty-two years (range, twenty to seventy-nine years). Due to defects in the acetabulum, 80 per cent of the hips were treated with bone grafts, usually a mixture of local autogenous graft and freeze-dried allograft. One hundred and twenty-four patients (129 hips) were available for follow-up, at a mean of forty-four months (range, thirty-six to eighty months). Seven hips (5 per cent) were revised again: four because of infection and three because of instability. There were no revisions for loosening without infection, and none of the components migrated in the absence of infection. Radiolucent lines were common and usually corresponded to regions in which allograft had been used. All bone grafts united by twelve months. Non-contained medial grafts underwent a phenomenon of resorption, consolidation, and remodeling to a sclerotic rim by twenty-four months. There were no complications related to placement of the screws. The results in this series were superior to results of revisions of acetabular components with the use of cement, which were associated with rates of failure of almost 10 per cent after a similar duration of follow-up. The technique of maximization of host-bone coverage and of packing of all defects with cancellous autogenous graft or allograft, or both, was successful for all classes of acetabular deficiencies.

Acetabulum↗

PubMed1993

Revision, without cement, of aseptically loose, cemented total hip prostheses. Quantitative comparison of the effects of four types of medullary treatment on bone ingrowth in a canine model.

A model that replicated the radiographic and histological features of aseptic loosening of the femoral component of a total hip replacement that had been done with cement was created in thirty-seven dogs. A deep wound infection developed in one dog, and that dog was excluded from the study. Revision was performed without cement in twenty-nine dogs, which were then followed for six months. The remaining seven dogs were used for histological study only. The components that were used for revision were made from Ti-6-Al-4-V, and a titanium fiber-metal porous surface had been applied to the anterior, posterior, and medial surfaces of the proximal part of the stem. The femora were revised either with no graft material applied to the osseous defect; with hydroxyapatite/beta-tricalcium phosphate placed in the defect; with application of an autologous cancellous bone graft as part of a one-stage revision; or with application of an autologous cancellous bone graft as the first part of a two-stage revision, with implantation of the component four months later. The use of an autologous bone graft led to greater and more consistent ingrowth of bone. The greatest amount of bone ingrowth was found in the group in which the procedure had been done in two stages (18 +/- 4.1 per cent), followed by the group in which the prosthesis and the graft had been inserted in a single stage (15 +/- 5.0 per cent), the group that had been treated with hydroxyapatite/beta-tricalcium phosphate (10 +/- 9.1 per cent), and the control group, in which no graft had been used (7 +/- 7.0 per cent). Notably, all of the components in the animals in which an autologous graft had been used were well fixed by bone ingrowth, while the component in two of the animals in the group in which no graft had been used in one animal in the hydroxyapatite/beta-tricalcium phosphate group had only fibrous-tissue ingrowth. In contrast to the findings with respect to bone ingrowth, there was more medullary bone adjacent to the lateral aspect of the implant in the groups in which hydroxyapatite/beta-tricalcium phosphate or no graft had been inserted than in the groups that had had an autologous graft.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Histology of porous-coated acetabular components. 25 cementless cups retrieved after arthroplasty.

25 hemispherical acetabular components retrieved from patients who had a total hip arthroplasty (THA) were studied histologically. All of the components had titanium fiber metal porous coatings and were implanted with adjuvant screw fixation, 18 in primary THA and 7 in revision THA. None of the cups had been removed because of infection or failure of fixation. The components had been in place an average of 30 (1-140) weeks. 18 cups had bone ingrowth into the porous coating. Up to one third of the available void space within the porous coating was occupied by bone, while the maximal proportion of the area of the bone-implant interface with bone ingrowth was over 80 percent. Bone ingrowth was more often observed at the dome and in the vicinity of sites of screw fixation than elsewhere. Peripherally, bone ingrowth was less consistent, and in isolated areas fibrocartilage and mineralized fibrocartilage were occasionally observed. The longer-term cases had more bone ingrowth than the shorter-term cases. Apparent metallic debris was observed within histiocytes adjacent to screw holes, and the amount of this material increased with duration of implantation.

Acetabulum↗

PubMed1993

Mechanisms of bone loss associated with total hip replacement.

The pathogenesis of bone loss after total hip arthroplasty is discussed. Two separate processes are considered: adaptive bone remodeling ("stress-shielding") and osteolysis. Clinical and experimental studies that provide the basis for current and future strategies to minimize the occurrence and severity of these phenomena are summarized.

Adaptation, Physiological↗

PubMed1992

Efficacy of autograft and freeze-dried allograft to enhance fixation of porous coated implants in the presence of interface gaps.

Autogenous cancellous bone and freeze-dried allogeneic cancellous bone were tested in a total of 41 adult male mongrel dogs. In each humerus, an implant with a commercially pure titanium fiber metal porous coating was placed in an overreamed cavity so that a uniform 3-mm gap was present between the implant and host cancellous bone. Graft material was placed in the gap of one humerus while the gap of the other humerus was left empty and served as a paired negative control. Histologically, both autograft and allograft appeared to aid repair of the defect, but quantitatively only autograft enhanced new bone formation within the defect. Treatment with autograft significantly increased the amount of bone ingrowth within the implants by nearly three-fold at 4 weeks and eight-fold at 8 weeks. The enhancing effect was recognizable as early as 2 weeks. The strength of fixation was increased by nearly seven-fold at 4 weeks and two-fold at 8 weeks in the autograft group, but this was only statistically significant at 4 weeks. Treatment with allograft did not enhance bone ingrowth at any time period, but had a small positive effect on strength of fixation at 4 weeks.

Analysis of Variance↗

PubMed1992

Experimental studies of bone remodeling in total hip arthroplasty.

Experimental studies of bone remodeling after total hip arthroplasty are reviewed. Most of the studies have been motivated by the introduction of cementless hip replacements in which porous coatings are used to provide fixation by bone ingrowth. Stress shielding is thought to be the main factor responsible for bone loss after hip replacement. Experimentally, design features related to (1) the nature of the bone-implant interface and (2) stem stiffness have been tested to determine if the effects of stress shielding can be decreased. The dominant long-term design feature controlling bone remodeling in hip replacement appears to be stem stiffness.

Animals↗

PubMed1992

Remodeling and ingrowth of bone at two years in a canine cementless total hip-arthroplasty model.

Remodeling and ingrowth of bone in association with the use of uncemented femoral components were examined at two years in a canine total hip-arthroplasty model. Twenty-two dogs received a unilateral uncemented femoral stem that was made of Ti6A14V and was covered with one of three types of titanium porous coating: fiber-metal, beads, or plasma flame-spray. The amount and distribution of ingrowth of bone differed somewhat among the groups at two years, but the patterns of remodeling of bone in the medullary canal and cortex were similar. In general, about 15 to 18 per cent of the cortical bone was lost adjacent to the levels of the stem that were covered with the porous coating. Most of the loss of cortical bone was due to subperiosteal resorption proximally and endosteal resorption at the middle and distal levels of the stem. Increased cortical porosity accounted for only a small fraction of the loss of cortical bone. The amount of medullary bone increased proximally and distally, so that the loss of total bone mass was significantly only at the mid-part of the stem. The amount of loss of cortical bone was similar to that observed in a previous six-month study, suggesting that a steady state was achieved in the present model.

Animals↗

PubMed1992

Local response to biomaterials: bone loss in cementless femoral stems.

While cementless, porous-coated prosthetic components have shown a high percentage of satisfactory clinical results in short and intermediate term follow-up, there are biologic problems associated with implantation of cementless devices that may predispose to clinical failure at longer term follow-up. Central to the issue of long-term performance is the problem of bone loss secondary either to adaptive bone remodeling processes or to the phenomenon of focal osteolysis. The stiffness of the femoral stem and the relative biologic inertness of the materials used are two properties of critical importance. In the future, continuing developments in the areas of prosthetic design, enhancement of fixation, biocompatibility, and biomaterials research will seek to address and resolve these problems.

Animals↗

PubMed1992

Determinants of stress shielding: design versus materials versus interface.

Experimental studies of cementless porous-coated total hip arthroplasty indicate that a critical design variable for femoral remodeling is stem stiffness. In the long term (two years) in the canine model, other variables, including the presence, type, and placement of the porous coating, did not significantly affect the pattern of bone remodeling when tested with metallic stems. The basic pattern of bone remodeling was characterized by proximal cortical atrophy, and distal cortical and medullary bone hypertrophy. In the short term (six months), the use of low-stiffness stems altered this pattern, leading to reduced proximal bone loss, increased proximal medullary bone hypertrophy, and no distal cortical hypertrophy, suggesting that stem stiffness had a profound effect on stress shielding.

Animals↗

PubMed1991

Changes in tibial bone mass after primary cementless and revision cementless total hip arthroplasty in canine models.

The purpose of this study was to examine right-left differences in tibial bone mass after unilateral (left) cementless total hip arthroplasty (THA). Of 39 dogs with THAs, 9 had primary cementless porous-coated femoral stems for 6 months and 15 had similar stems for 2 years. Five dogs had aseptically failed cemented hips, and 10 had aseptically failed cemented hips that were revised with cementless porous-coated femoral stems (5 without bone graft and 5 with autogenous bone graft). These animals were sacrificed 6 months after the revision surgery. The primary cementless dogs showed no right-left difference in tibial bone mineral content (BMC) or cortical bone cross-sectional geometry after 6 months, but after 2 years there was a distal right-left difference in BMC of 6% caused by expansion of the medullary canal in the tibia of the operated limb. Tibial BMC was more than 20% lower in the operated limb of the failed cemented dogs, approximately 15% lower in the nongrafted group, and 7% lower in the grafted group. The right-left tibial difference in BMC in the 2-year primary cementless group is most probably because of subclinical disuse of the operated limb. Among the dogs with failed cemented stems, the lower right-left difference in the two revised groups compared with the non-revised group suggests that improved limb function after cementless revision THA may cause gain of previously lost bone.

Animals↗

PubMed1990

Measuring the volume fraction of bone ingrowth: a comparison of three techniques.

The need for quick, accurate, and reproducible methods to measure the amount of bone within porous metals has increased as the use of these materials has become more common within orthopedics. The purpose of this paper is to compare measurements of bone ingrowth using microradiography, stained histology, and backscattered electron imaging-scanning electron microscopy (BEI-SEM) in cementless, porous-coated acetabular components retrieved from human patients. BEI-SEM of bone ingrowth into porous metal provided excellent images for quantitative analysis. The stained sections and BEI-SEM images provided very comparable results, while microradiography consistently underestimated the porosity of the porous coating and overestimated the amount of bone ingrowth.

Acetabulum↗

PubMed1990

The geometry of the adult canine proximal femur.

The canine is often used as a model to study functional bone adaptation after total hip replacement. To improve our understanding of the model, we defined the central tendencies and statistical variations in the cross-sectional geometry, angle of anteversion, and cervicodiaphyseal angle of the proximal femur in 15 adult male mongrel dogs and compared the results with published reports of the human femur. Numerous similarities in the cross-sectional geometry of the canine and the human femur were noted, supporting the use of the canine as a model. The two species differed in that the orientation of the principal axes in the proximal cross sections was not related to the angle of anteversion in the canine femur, whereas these angles are related in humans. In addition, the canine medullary canal is larger than the human medullary canal relative to the external dimensions of the femur, and hence the canine has relatively thinner cortical bone. This difference in femoral cross-sectional geometry may explain, in part, why the canine provides an accentuated model of bone loss in hip arthroplasty experiments.

Animals↗

PubMed1990

Effects of radiation on fixation of non-cemented porous-coated implants in a canine model.

A non-weight-bearing porous-coated rod was implanted bilaterally in the proximal part of the humerus in thirty-five adult male mongrel dogs. In all of the animals, one limb was treated with radiation and the opposite limb served as the control. In twenty-one animals, the dose was 1000 centigrays (rads) and in fourteen, it was 500 centigrays. The strength of fixation and the volume fraction of ingrowth of bone were determined two, four, and eight weeks after the operation in the group that received 1000 centigrays and two and four weeks after the operation in the group that received 500 centigrays. Treatment with 500 centigrays had no significant effect on the strength of fixation or the amount of ingrowth of bone. In contrast, at two weeks, treatment with 1000 centigrays had reduced the strength of fixation to 50 per cent of the control value (p less than 0.01), although, at four and eight weeks, the strength of fixation was not significantly different than that in the control limb. The amount of ingrowth of bone in the irradiated limb was significantly reduced at two weeks (30 per cent of the control value) (p less than 0.01), four weeks (70 per cent of the control value) (p less than 0.05), and eight weeks (56 per cent of the control value) (p less than 0.05).

Animals↗

PubMed1989

Apparent age-related bone loss among adult female Gombe chimpanzees.

Apparent age-related bone loss among adult females was observed in a skeletal sample derived from the free-ranging Gombe chimpanzee population of Tanzania. Photon absorptiometric and computed tomographic bone scans indicated that, as in humans, bone was lost from the endosteal surface, but, in contrast to humans, more bone was lost from cortical sites than from cancellous sites. The etiology of this bone loss may be related to a number of factors, including hormonal changes, nutritional inadequacy, and decreased physical activity late in life coupled with the demands of pregnancy and lactation.

Aging↗

PubMed1989

Bone ingrowth into the tibial component of a canine total condylar knee replacement prosthesis.

The purpose of this study was to evaluate the occurrence of bone ingrowth in a porous coated tibial component of a canine total condylar design knee replacement model. The entire undersurface of the tibial prosthesis was covered by a titanium fiber metal porous composite pad. Projecting from this surface were three short, cylindrical, fiber metal coated pegs that along with a posterior screw provided initial stabilization of the device. Left total knee replacements were performed on six dogs using alignment and cutting jigs to prepare the bony surfaces. The dogs were killed 6 months following surgery. Extensive bone ingrowth was present in all pegs of every tibial component. Bone ingrowth was present in 12% of the pad area of one component, 22.7 to 41.6% in four components, and 81.1% in another. The void spaces in other areas were filled with fibrous tissue or in the periphery of the device with fibrocartilage. Bone ingrowth in the pad was consistent in the vicinity of the pegs and was variable in regions not adjacent to the pegs, suggesting that the pegs exerted a strong influence on the pattern of bone ingrowth into the pad.

Animals↗

PubMed1989

Computed tomographic measurement of cortical bone geometry.

In this study digital images of bone cross-sections obtained by computed tomography were analyzed with an automated outlining method. It was shown that unbiased cross-sectional geometric measurements of cortical bone could be obtained if the periosteal and endosteal surfaces were defined at separate thresholds. Use of different threshold levels for these two surfaces resulted in errors of 2.6% for periosteal diameters, 7.4% for endosteal diameters and 7.3% for cortical area. If incorrect thresholds were used, cortical thickness measurements can have errors as high as 30%. In addition, simulated variation in medullary fat content did not affect measurement of medullary dimensions.

Aged↗