What do we know about taper corrosion in total hip arthroplasty?

Mechanically assisted crevice corrosion (MACC) at metal/metal modular junctions in which at least one of the components is fabricated from cobalt-chromium alloy, has reemerged as a potential clinically significant complication in total hip arthroplasty. The clinical manifestation of MACC may include the development of an adverse local tissue reaction (ALTR), similar to what has been described in association with metal-on-metal bearing total hip and resurfacing arthroplasty. The clinical presentation of MACC-associated ALTRs may include pain and possibly late recurrent dislocations. Abnormal metal artifact reduction sequence magnetic resonance images and elevated serum metal levels (cobalt elevations out of proportion to chromium elevations) can be helpful in the diagnosis of these MACC-associated ALTRs.

Additive enhancement of implant fixation following combined treatment with rhTGF-beta2 and rhBMP-2 in a canine model.

BACKGROUND: Gaps at the interface between implant and bone increase the risk of diminished implant fixation and eventual loosening. The purpose of the present study was to determine if combined use of recombinant human transforming growth factor-beta 2 (rhTGF-beta2) and bone morphogenetic protein 2 (rhBMP-2) led to greater implant fixation strength in the presence of interface gaps than the use of either growth factor alone. METHODS: Twenty-eight skeletally mature adult male dogs received one porous-coated titanium implant in the proximal part of each humerus, for a total of fifty-six implantation sites. Spacers were used to establish an initial 3-mm gap between the implant and the host bone at all fifty-six sites. Forty-two implants were coated with hydroxyapatite-tricalcium phosphate and were used in three growth-factor-treatment groups in which the implants placed in the left humerus were loaded with 12 microg of rhTGF-beta2 (Group 1, seven animals), 25 microg of rhBMP-2 (Group 2, seven animals), or 12 microg of rhTGF-beta2 combined with 25 microg of rhBMP-2 (Group 3, seven animals). In these animals, the twenty-one implants that were placed in the right humerus were loaded with buffer only to serve as contralateral controls. In Group 4 (seven animals), the implants were not coated with hydroxyapatite-tricalcium phosphate, the gap in the left humerus was lightly packed with autogenous bone graft, and the gap in the right humerus was left empty to serve as a contralateral control. All animals were killed at twenty-eight days. The primary end points included three mechanical variables: fixation strength, interface stiffness, and energy to failure. Secondary end points included bone ingrowth and bone volume and trabecular architecture in the gap and in a region located 2 mm medial to the implantation site. RESULTS: The hydroxyapatite-tricalcium phosphate coating had no effect on implant fixation, bone ingrowth, or bone formation in the 3-mm gap. Individual growth factor treatments led to 2.3 to 3.2-fold increases in fixation strength and stiffness as compared with the values for the contralateral controls (p < 0.05). The combined growth factor treatment led to 5.7-fold increases in fixation strength and stiffness compared with the values for the contralateral controls (p < 0.01). Autogenous bone graft treatment was associated with 4.5 to 6.4-fold increases in implant fixation strength and stiffness as compared with the values for the contralateral controls (p < 0.01). Compared with the relevant contralateral controls, energy to failure was increased 3.5-fold in association with TGF-beta2 alone (p < 0.05), 4.5-fold in association with TGF-beta2 combined with BMP-2 (p < 0.01), and 2.5-fold in association with autogenous bone-grafting. As much as 63% of the variance in the mechanical end points was associated with variance in bone volume and architecture in the 3-mm gap and in the region of interest located 2 mm medial to the implantation site (p < 0.01). CONCLUSIONS: In this animal model, the combined use of TGF-beta2 and BMP-2 led to more secure mechanical fixation of the implant than did the use of either growth factor alone and demonstrated results that were similar to those associated with the use of autogenous bone graft.

Aging does not lessen the effectiveness of TGFbeta2-enhanced bone regeneration.

Controversy exists over the potency of bone healing in the aged skeleton, and there is concern that enhancement of bone regeneration after use of bone-stimulating growth factors may not be effective in the aged. In this study, 30 skeletally mature beagles (1-2 or 10-12 years old) had titanium implants placed bilaterally in the proximal humerus for a period of 4 weeks in a model of intramembranous bone regeneration. A bony defect made at the time of surgery created a 3-mm gap between the implant surface and the host bone. Some of the implants were treated with recombinant human TGFbeta2 (rhTGFbeta2) at various does (0.32-35 microg per implant), and some served as paired controls. The dose response was similar in young and old animals. The most effective dose, 35 microg, led to a 3-fold increase in the volume fraction of new bone within the gap in both the young (p = 0.001) and old (p = 0.002) animals. At this dose, there was a 5-fold increase in osteoblast surface. While age did not significantly affect the quantity of new bone formed as assessed by backscatter scanning electron microscopy, the older animals had thinner regenerated trabeculae that tended to be spaced more closely than the younger animals. Coupled with the finding that the increase in osteoid was greater in the old animals compared with the young animals, these qualitative differences suggest that there may have been a slight delay in the rate or a defect of mineralization in the old animals.

Malignant neoplasms associated with orthopedic implant materials in rats.

The carcinogenic potential of 22 orthopedic prosthetic materials was studied by implantation in bone in Sprague-Dawley rats and evaluated by complete autopsy examination performed at the time of death or at the end of the 30 month experimental period. When the number of malignancies in these rats was compared with control and sham-operated animals, a small increase in sarcomata was observed in animals bearing metal alloy implants containing high contents of cobalt, chromium, or nickel. An increased incidence of lymphomata with bone involvement was also observed in rats bearing metal implants when compared with control and sham-operated animals.

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.

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.

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.

Locally delivered rhBMP-2 enhances bone ingrowth and gap healing in a canine model.

The purpose of the present study was to determine if recombinant human bone morphogenetic protein-2 (rhBMP-2) enhances bone ingrowth into porous-coated implants and gap healing around the implants. In the presence of a 3-mm gap between the implant and host bone, porous-coated implants were placed bilaterally for four weeks in the proximal humeri of skeletally mature, adult male dogs. In three treatment groups, the test implant was treated with HA/TCP and rhBMP-2 in buffer at a dose of 100 microg/implant (n=5), 400 microg/implant (n=6), or 800 microg/implant (n=5) and placed in the left humerus. In these same animals, an internal control implant was treated only with HA/TCP and buffer and placed in the right humerus. These groups were compared with a previously reported external control group of seven animals in which no growth factor was delivered [J. Orthop. Res. 19 (2001) 85]. The BMP treated implants in the two lower dose groups had significantly more bone ingrowth than the external controls with the greatest effect in the 100 g/implant group (a 3.5-fold increase over the external control, p=0.008). All three dose groups had significantly more bone formation in the 3-mm gap surrounding the BMP treated implants than the external controls with the greatest effect in the 800 microg group (2.9-fold increase, p<0.001). Thus, application of rhBMP-2 to a porous-coated implant stimulated local bone ingrowth and gap healing. The enhancement of bone formation within the implant (bone ingrowth) was inversely related to dose.

Metal ion release from titanium-based prosthetic segmental replacements of long bones in baboons: a long-term study.

Forty-five baboons that had received titanium-based fiber metal composite segmental bone replacements were studied along with 13 controls without implants. Thirty-eight baboons with implants were sacrificed, and titanium, aluminum, and vanadium levels were assayed in homogenized lung, kidney, spleen, liver, adjacent muscle, and regional lymph nodes. In seven living baboons with implants, blood and urine samples were obtained for trace metal analysis as well as for biochemical and hematological profiles. In the 38 sacrificed baboons with implants, increased titanium levels were noted in the lungs, spleen, adjacent muscle (quadriceps, soleus, and triceps), and regional lymph nodes (inguinal, axillary, and popliteal) in comparison to those of six sacrificed controls without implants. In addition, vanadium was significantly elevated in the lungs of some animals, while aluminum increases were noted in adjacent muscle (quadriceps, soleus, and triceps), lung, and regional lymph nodes (inguinal, axillary, and popliteal). In the seven living baboons with implants, a sixfold increase (p less than 0.0005) in the urine titanium level was noted in comparison to that of seven living controls without implants. Additionally, elevated aluminum levels were found in the serum (p less than 0.0005) of the group with implants. Biochemical and hematological studies did not indicate statistically significant differences in serum electrolytes, in liver and renal function tests, or in complete blood counts between the seven living baboons with implants and their controls.

Locally delivered rhTGF-beta2 enhances bone ingrowth and bone regeneration at local and remote sites of skeletal injury.

The purposes of the present study were to determine if recombinant human transforming growth factor-beta-2 (rhTGF-beta2) enhances bone ingrowth into porous-coated implants and bone regeneration in gaps between the implant and surrounding host bone. The implants were placed bilaterally for four weeks in the proximal humeri of skeletally mature, adult male dogs in the presence of a 3-mm gap. In three treatment groups of animals, the test implant was treated with hydroxyapatite/tricalcium phosphate (HA/TCP) and rhTGF-beta2 in buffer at a dose per implant of 1.2 microg (n = 6), 12 microg (n = 7), or 120 microg (n = 7) and placed in the left humerus. In these same animals, an internal control implant treated only with HA/TCP and buffer was placed in the right humerus. In a non-TGF-beta treated external control group of animals (n = 7), one implant was treated with HA/TCP while the contralateral implant was not treated with the ceramic. In vitro analyses showed that approximately 15%, of the applied dose was released within 120 h with most of the release occurring in the first 24 h. The TGF-beta treated implants had significantly more bone ingrowth than the controls with the greatest effect in the 12 microg/implant group (a 2.2-fold increase over the paired internal control (P = 0.004) and a 4-fold increase over the external control (P < 0.001)). The TGF-beta treated implants had significantly more bone formation in the gap than the controls with the greatest effect in the 12 and 120 microg groups (1.8-fold increases over the paired internal controls (P = 0.003 and P = 0.012, respectively) and 2.8-fold increases over the external controls (P < 0.001 and P = 0.001, respectively)). Compared to the external controls, the internal control implants tended to have more bone ingrowth (1.9-fold increase, P = 0.066) and had significantly more bone formation in the gap (1.7-fold increase. P = 0.008). Thus, application of rhTGF-beta2 to a porous-coated implant-stimulated local bone ingrowth and gap healing in a weakly dose-dependent manner and stimulated bone regeneration in the 3-mm gap surrounding the contralateral control implant, a site remote from the local treatment with the growth factor.

Human monocyte/macrophage response to cobalt-chromium corrosion products and titanium particles in patients with total joint replacements.

The responses of human peripheral blood monocytes of 10 normal volunteers and 14 patients with total hip replacements to particles of commercially pure titanium and chromium orthophosphate (a corrosion product from cobalt-chromium alloy implants) were studied. In addition, these phagocytosable particles were added to cultured mononuclear cells isolated from the interfacial membrane of 14 patients with failed implants. Peripheral blood monocytes from patients who had had a total hip replacement produced significantly higher levels of interleukin-1 (both interleukin-1 alpha and interleukin-1 beta) and prostaglandin E2 following particulate stimulation than those from normal volunteers. Supernatants from both titanium and chromium orthophosphate-stimulated peripheral blood monocytes from the volunteers and patients with total hip replacement induced bone resorption (assayed in organ cultures of newborn mouse calvariae) and the proliferation of human fibroblasts. The levels of bone resorption were significantly higher (p < 0.05) in patients with implants than in normal volunteers. There were no significant differences in the responses of cells between patients with focal osteolysis and those without osteolysis. Interfacial membrane mononuclear cells also produced high levels of interleukin-1 alpha, interleukin-1 beta, and prostaglandin E2 and expressed bone resorptive activities following stimulation with either titanium or chromium orthophosphate. More importantly, interfacial membrane mononuclear cells "spontaneously" produced high levels of prostaglandin E2 that were comparable with the response of peripheral blood monocytes stimulated with particulate wear debris. The clinical relevance of this study is 2-fold. First, mononuclear cells from patients with total hip replacement were some-how "sensitized" to metal particles in comparison with mononuclear cells from individuals without an implant. Second, the chromium orthophosphate corrosion product was a potent macrophage/monocyte activator and may contribute to macrophage-mediated osteolysis and aseptic loosening.

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)

Migration of corrosion products from modular hip prostheses. Particle microanalysis and histopathological findings.

Migration of solid corrosion products from the modular head-neck junction of fifteen total hip replacements to the periprosthetic tissues was studied. The devices and tissues were recovered at the time of a revision procedure or at autopsy after a mean of sixty-four months (range, eight to ninety-seven months). The prostheses had a cobalt-chromium-alloy head coupled with a cobalt-chromium-alloy or a titanium-alloy stem. The solid corrosion product was identified by electron microprobe analysis and Fourier transform infrared microprobe spectroscopy as a chromium orthophosphate hydrate-rich material. The product was present at the junction of the modular head and neck and as particles within the periprosthetic tissues as early as eight months postoperatively. In several hips, it was also present on the polyethylene bearing surface. The particles in the tissues ranged in size from less than one to 500 micrometers. They were present within histiocytes or were surrounded by foreign-body giant cells in the pseudocapsule of the hip joint; in the membranes of the femoral bone-implant interface; and at sites of femoral endosteal erosions, with and without loosening of the femoral component.

A comparative study of porous coatings in a weight-bearing total hip-arthroplasty model.

The purposes of this study were to compare ingrowth of bone into three types of porous coating and to determine the effect of the type of porous coating and the degree of coverage of the stem on the remodeling of bone on the femoral side in cementless hip arthroplasty. A left total hip arthroplasty was performed in forty dogs. Thirty of the dogs had a titanium-alloy femoral prosthesis that had had one of three types of commercially pure titanium porous material applied along the length of the anterior and posterior surfaces of the stem: ten with sintered fiber-metal, ten with sintered beads, and ten with plasma flame-spray coating. The remaining ten dogs had a femoral component that was circumferentially coated with commercially pure titanium that was plasma flame-sprayed along the length of the stem. In each group, five animals were killed at one month and five were killed at six months. Ingrowth of bone into all three types of porous coating was observed, indicating secure fixation of all components. By six months, there was more ingrowth of bone and new medullary bone adjacent to the proximal and distal aspects of the stems compared with the middle level of the stems in all groups. No significant difference in ingrowth of bone was observed in the beaded surface (25.2 per cent) and the fiber-metal surface (16.6 per cent) at one month, but at six months there was significantly less ingrowth into the beaded surface (23.3 per cent) than into the fiber-metal surface (37.3 per cent). In all groups, a proximal-to-distal gradient of loss of cortical bone was observed by six months. The group of dogs that had the stem with the circumferential coating experienced more severe loss of bone than did the three groups that had a stem with a partial coating. The magnitude of loss of bone was dependent on the extent rather than the type of porous coating.

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.

Release and excretion of metal in patients who have a total hip-replacement component made of titanium-base alloy.

Serum concentration and urinary excretion of titanium, aluminum, and vanadium were measured for patients who had a well functioning cementless primary total hip replacement of one of two different designs, for patients who had a loose total hip replacement that was to be revised, and for control subjects who had no implant. Serum concentrations of titanium were elevated approximately twofold in the patients who had a loose implant, compared with the values for the control subjects. No major differences in terms of urine concentration of titanium, serum concentration of aluminum, or urine concentration of aluminum were observed among any of the groups that were studied. Concentrations of vanadium were uniformly low in all groups.

Maintenance of proximal cortical bone with use of a less stiff femoral component in hemiarthroplasty of the hip without cement. An investigation in a canine model at six months and two years.

A canine model of hemiarthroplasty of the hip was used to determine if the use of a less stiff femoral stem can reduce the amount of bone loss induced by stress-shielding. Two types of stem were used: the stiffer stems were made of a titanium alloy, and the less stiff stems were composed of a cobalt-chromium-alloy core with an outer polymer layer. The stems were identical in shape, and both types were circumferentially coated along their entire length (except for the distal five millimeters) with commercially pure titanium fiber metal. Ten dogs with each type of stem were followed for six months, and twelve dogs with each type of stem were followed for two years. Loss of cortical bone from the proximal part of the femur was associated with both types of stem, but typically 50 per cent less bone was lost with the less stiff implants. Most of the cortical loss occurred at the subperiosteal surface. The amount of medullary bone adjacent to the proximal and distal aspects of both types of stem increased; the less stiff stems were associated with a greater increase in the proximal region, and the stiffer stems were associated with a greater increase in the distal region. Similarly, there were peaks in the amount of bone growth into the proximal and distal portions of both types of stem, with a greater peak in proximal bone growth into the less stiff stems and a greater peak in distal bone growth into the stiffer stems.

Dissemination of wear particles to the liver, spleen, and abdominal lymph nodes of patients with hip or knee replacement.

BACKGROUND: The importance of particles generated by wear and corrosion of joint replacement prostheses has been understood primarily in the context of the local effects of particle-induced periprosthetic osteolysis and aseptic loosening. We studied dissemination of wear particles in patients with total hip and knee replacement to determine the prevalence of and the histopathological response to prosthetic wear debris in the liver, spleen, and abdominal para-aortic lymph nodes. METHODS: Postmortem specimens from twenty-nine patients and biopsy specimens from two living patients with a failed replacement were analyzed. Specimens of tissue obtained from the cadavera of fifteen patients who had not had a joint replacement served as controls. The concentration of particles and the associated tissue response were characterized with the use of light microscopy of stained histological sections. Metallic particles were identified by electron microprobe analysis. Polyethylene particles were studied with the use of oil-red-O stain and polarized light microscopy. The composition of polyethylene particles was confirmed in selected cases by Fourier transform infrared spectroscopy and hot-stage thermal analysis. Twenty-one of the patients studied post mortem had had a primary total joint replacement. Eleven of them had had a hip prosthesis for a mean of sixty-nine months (range, forty-three to 171 months), and ten had had a knee replacement for a mean of eighty-four months (range, thirty-one to 179 months). The other eight patients studied post mortem had had a hip replacement in which one or more components had loosened and had been revised. The mean time between the initial arthroplasty and the time of death was 174 months (range, forty-seven to 292 months), and the mean time between the last revision procedure and the time of death was seventy-one months (range, one to 130 months). RESULTS: Metallic wear particles in the liver or spleen were more prevalent in patients who had had a failed hip arthroplasty (seven of eight) than in patients who had had a primary hip (two of eleven) or knee replacement (two of ten). The principal source of wear particles in the majority of these patients involved secondary nonbearing surfaces rather than wear between the two primary bearing surfaces as intended. In one living patient, dissemination of titanium alloy particles from a hip prosthesis with mechanical failure was associated with a visceral granulomatous reaction and hepatosplenomegaly, which required operative and medical treatment. Metallic wear particles were detected in the paraaortic lymph nodes in 68 percent (nineteen) of the twenty-eight patients with an implant from whom lymph nodes were available for study. In 38 percent (eleven) of all twenty-nine patients with an implant who were studied post mortem, metallic particles had been further disseminated to the liver or spleen, where they were usually found within small aggregates of macrophages occurring as infiltrates without apparent pathological importance. Polyethylene particles elicited a similar response. They were identified in the paraaortic lymph nodes of 68 percent (nineteen) of the twenty-eight patients and the liver or spleen of 14 percent (four) of the twenty-nine patients. The majority of the disseminated wear particles were less than one micrometer in size. Currently available methods lack the sensitivity and specificity necessary to detect very low concentrations of submicrometer polyethylene particles and probably underestimated the prevalence of polyethylene wear debris in the liver and spleen. CONCLUSIONS: In this study, systemic distribution of metallic and polyethylene wear particles was a common finding, both in patients with a previously failed implant and in those with a primary total joint prosthesis. The prevalence of particles in the liver or spleen was greater after reconstructions with mechanical failure. (ABSTRACT TRUNCATED)

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).

Focal osteolysis at the junctions of a modular stainless-steel femoral intramedullary nail.

BACKGROUND: During routine follow-up of patients treated with a three-piece stainless-steel modular femoral nail, osteolysis and periosteal reaction around the modular junctions of some of the nails were noted on radiographs. The purpose of this study was to evaluate the prevalence, etiology, and clinical relevance of these radiographic findings. METHODS: Forty-four femoral fractures or nonunions in forty-two patients were treated with a modular stainless-steel femoral intramedullary nail. Seventeen nails were excluded, leaving twenty-seven intramedullary nails in twenty-seven patients for this study. All patients had had a femoral diaphyseal fracture; nineteen had had an acute fracture and eight, a nonunion. These twenty-seven patients returned for radiographs, a physical examination, assessment of functional outcomes, assessment of thigh pain with a visual analog scale, determination of serum chromium levels, and nail removal if desired. A control group of sixteen patients treated with a one-piece stainless-steel femoral intramedullary nail was evaluated with use of the same outcome measures and was compared with the group treated with the modular femoral nail with regard to prevalence of thigh pain and serum chromium levels. Twelve modular femoral nails were removed according to the study protocol. The modular nail junctions were analyzed for corrosion products, and histopathologic analysis of tissue specimens from the femoral canal was performed. RESULTS: The twenty-seven patients were seen at a mean of twenty-one months after fracture fixation; twenty-six of the twenty-seven fractures healed. Twenty-three femora had at least one of three types of abnormalities-osteolysis, periosteal reaction, or cortical thickening--localized to one or both modular junctions. Eighteen patients had severe reactions, defined as osteolysis of > or =2 mm, cortical thickening of > or =5 mm, and/or a periosteal reaction (group 1). Nine patients had mild or no reactions (group 2). Serum chromium levels in group 1 (mean, 1.27 ng/ mL; range, 0.34 to 3.12 ng/mL) were twice as high as those in group 2 (mean, 0.53 ng/mL; range, 0.12 to 1.26 ng/mL). However, this difference did not reach significance with the numbers available. The differences in serum chromium levels between group 1 and the control group with a one-piece nail (mean, 0.26 ng/mL; range, 0.015 to 1.25 ng/mL) (p<0.01) and a control group without an implant (mean, 0.05 ng/mL; range, 0.015 to 0.25 ng/ mL) (p<0.01) were significant. The level of thigh pain recorded on the visual analog scale was also significantly different between group 1 and the control group with a one-piece implant (p = 0.03). Retrieved modular nails had signs of fretting corrosion as well as stainless-steel corrosion products adherent to the junction where the osteolysis occurred. Histologic and spectrographic analysis revealed two types of corrosion products that were consistent with stainless-steel within the peri-implant tissue and were associated with a foreign-body granulomatous response. CONCLUSIONS: The presence of corrosion products at the taper junctions suggests that particulate debris was a major factor in the etiology of the radiographic findings of osteolysis, periosteal reaction, and cortical thickening. Serum chromium levels were substantially elevated in the patients with a modular femoral nail, and such levels may serve as a marker of fretting corrosion of these devices.