The effect of stem stiffness on femoral bone resorption after canine porous-coated total hip arthroplasty

Bilateral noncemented total hip arthroplasty (THA) was produced in dogs to determine the effect of stem stiffness on stress-related bone resorption. Two porous-coated femoral implants of substantially different stiffnesses were designed for direct comparison. One was manufactured from cobalt-chromium (CoCr) alloy, the other from titanium alloy. The titanium stem was hollowed out to a wall thickness of 1 mm to further reduce its stiffness. The cumulative stiffness differences were about 5.4-fold axially and 3.6-fold in bending and torsion. Staged bilateral THA was performed on eight dogs. Each dog received a stiff CoCr stem on one side and a flexible titanium stem on the other. After death, the femora were removed and processed for undecalcified thin-section histology. Bone ingrowth and remodeling were quantified by computer-aided image analysis and compared between stem designs. All femoral specimens showed bone ingrowth fixation of both stiff and flexible stems along the implant length. Tetracycline labeling indicated active bone turnover in the femoral cortex and in regions of ingrowth. However, gross differences in femoral bone remodeling were observed both roentgenographically and histologically. Femora with the flexible stems consistently showed much less bone resorption than those with the stiff stems. Quantitative analysis of paired cross-sections indicated an average of 25%-35% more cortical bone area in the femora with flexible stems. Severe resorption of the cortex in the midstem region occurred in three of the femora with the stiff stems but in none with the flexible stems. Stem stiffness strongly influences bone remodeling. The flexible stem results in more uniform load transfer and less stress shielding.     

Primary total hip arthroplasty with a proximally porous-coated femoral stem

BACKGROUND: The use of cementless, proximally porous-coated femoral stems for total hip arthroplasty has increased in popularity. The purpose of the present report was to examine the five to ten-year results associated with the use of a so-called second-generation circumferentially proximally porous-coated titanium-alloy stem. METHODS: Between 1991 and 1994, 123 Harris-Galante Multilock femoral stems were implanted in 101 patients. The average age of the patients at the time of surgery was 53.8 years. The patients were followed prospectively and were reevaluated at a minimum of five years postoperatively. No patient was lost to follow-up. Twenty-five patients (thirty hips) were interviewed by telephone, and four patients (five hips) died during the study period because of problems that were unrelated to the operation. The remaining seventy-two patients (eighty-eight hips) had a minimum of five years of clinical and radiographic follow-up. RESULTS: The average duration of follow-up was seventy-eight months. At the time of the most recent follow-up, the average Harris Hip Score was 95 points. Eighty-seven (99%) of eighty-eight stems were biologically stable, with eighty-four hips (95%) having osseous ingrowth and three hips (3%) having stable fibrous fixation. One stem was revised because of loosening. Thirty-three hips (38%) had minimal proximal osteolysis, and no hip had diaphyseal osteolysis. Seventy-two hips (82%) had some degree of stress-shielding in the proximal metaphysis, but only two hips had cortical resorption. None of these patients required additional surgery, and all reported a satisfactory outcome. CONCLUSIONS: Given the young age and high activity level of these patients, this stem fared well: the levels of patient function and satisfaction were high, the rates of loosening and revision were very low, and distal osteolysis did not occur. Osseous fixation occurred reliably. Proximal stress-shielding was seen but did not seem to be clinically important.     

Trunion fracture of a fully porous-coated femoral stem. Case report

Femoral component fracture is a documented but an uncommon complication of total hip arthroplasty. A retrospective survey conducted by the American Association of Hip and Knee Surgeons estimated the prevalence of femoral component fractures at 0.27% (172 of 64483 implants over a 5-year period ending in 1993) . There have been several case reports of fatigue fractures of the prosthetic neck distal to the Morse taper in modular implants with a cobalt alloy head and a cobalt alloy stem. Here, we present a case report of stem fracture within the Morse taper of a cobalt alloy stem coupled with a cobalt alloy head.     

Comparison of porous-coated titanium femoral stems with and without hydroxyapatite coating

BACKGROUND: The purpose of this prospective, randomized study was to evaluate the clinical and radiographic results associated with proximally porous-coated titanium stems that were identical in geometry but differed with regard to proximal surface treatment (with or without hydroxyapatite coating). METHODS: A prospective, randomized study was performed to evaluate fifty patients (100 hips) who had undergone sequential bilateral primary total hip replacement. A proximally porous-coated titanium stem with hydroxyapatite coating was implanted on one side and a proximally porous-coated titanium stem without hydroxyapatite coating was implanted on the other side during the same operative setting in all fifty patients. A cementless acetabular component made of titanium was used in all hips. There were thirty-six men and fourteen women; the mean age at the time of the operation was 45.3 years. The mean duration of follow-up was 6.6 years. Clinical and radiographic evaluations were performed preoperatively; at six weeks; at three, six, and twelve months; and yearly thereafter. RESULTS: The Harris hip scores in the hydroxyapatite-coated group (mean, 94 points) and non-hydroxyapatite-coated group (mean, 92 points) were similar at the final follow-up examination. The prevalence of transient pain in the thigh was 4% in each group. No acetabular or femoral component demonstrated aseptic loosening. Bone-remodeling patterns, including calcar atrophy, were similar in the two groups. No acetabular or femoral osteolysis was seen. CONCLUSIONS: At a mean of 6.6 years postoperatively, the clinical and radiographic results associated with proximally porous-coated femoral prostheses with identical geometries that differed only with regard to the presence or absence of hydroxyapatite coating were similar.     

Hydroxyapatite-coated femoral stem/porous-coated acetabulum survivorship at 15 years

At 10 years, we reported survivorship of the Omnifit hydroxyapatite-coated femoral stem and the Omnifit-PSL porous-coated dual-radius acetabular shell (Stryker, Mahwah, NJ) with polyethylene liners sterilized by gamma radiation in air. Our 15-year follow-up examines survivorship and functional outcomes of this system. Ninety-two patients (98 hips) were identified from our database who had been involved with the prior study. The mean follow-up was 14.7 years (range, 11.8-17.0 years). Survival of the stem and cup was 98.8% and 69%, respectively. Osteolysis was seen in 56% of the proximal femur and 5% of the distal femur. This hydroxyapatite-coated stem continues to perform well at 15 years despite poor acetabular results. The performance of this acetabular component is consistent with previous literature.     

The removal of extensively porous-coated femoral stems

Cementless total hip arthroplasty (THA) is the favored fixation for primary THA in the United States. While cylindrical extensively porous-coated femoral stems have demonstrated long-term survivability, the distal ingrowth can create challenges in cases where these stems need to be extracted. This technique article outlines the current methods for extracting extensively porous-coated stems. Traditionally, the extended trochanteric osteotomy (ETO) has been used; however, we present a technique that eliminates the need for osteotomy fixation hardware, eliminates the risk of fragment migration, and nonunion while not compromising the surgeons ability to convert to an ETO if necessary.     

The outcome of rerevision of an extensively porous-coated stem with another extensively porous-coated stem

Despite excellent results, failure of osseointegration does occur in femoral revisions performed with extensively porous-coated stems. This study examined the outcome of rerevision of a failed extensively porous-coated femoral stem with yet another extensively porous-coated stem. Between 1980 and 2000, we performed 711 femoral revisions using an extensively porous-coated device. Fifteen patients (16 hips) were known to have undergone a rerevision of this femoral component using another porous-coated stem. At latest follow-up, 2 patients (3 hips) were deceased, leaving 13 patients. At a mean follow-up of 9.8 years, none of the cementless stems had required another revision (100% survivorship), and 12 (92%) of the 13 stems were bone ingrown based on radiographic examination.     

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.     

种植体磷酸钙溶胶表涂与早期骨整合研究

目的探讨磷酸钙(CaP)溶胶涂层能否传导并增强多孔型钛合金(Ti6Al4V)种植体表层的早期骨整合(即骨性愈合)。方法将制备有极薄的CaP溶胶表面涂层的多孔型钛合金种植体作为实验组,将未经CaP涂层的种植体作为对照组,分别植入16只兔的胫骨中。种植区愈合2周后,取含种植体的骨组织标本,利用反向扫描电镜摄像技术和Bioquant图像分析系统进行形态观测研究。结果在多孔型钛合金种植体表面,CaP涂层组所测量出的绝对骨接触长度(ACL:1.18mm)、接触长度分数比(CLF:40.4%)、骨生长直线距离(SLBG:1.19mm)各数据均高于对照组种植体(分别为0.74mm,27.0%,1.04mm),两组差异有统计学意义(P<0.01)。结论多孔型种植体CaP溶胶涂层能有效传导并增强骨组织长入,形成骨与种植体界面的广泛骨整合。     

The effect of femoral stem geometry on interface motion in uncemented porous-coated total hip prostheses. Comparison of straight-stem and curved-stem designs.

We compared the magnitudes of motion between the prosthesis and bone during axial and torsional loading in seven matched pairs of fresh-frozen femora of cadavera in which an uncemented, collarless, isthmus-filling, straight-stem (Harris-Galante) prosthesis had been placed in one femur and an uncemented, collarless, proximal-filling, curved-stem (anatomic) prosthesis had been placed in the other femur. The comparison was performed in order to determine the effect of the geometry of the stem on the magnitude of motion. Single-limb-stance loads and combined axial and torsional loads were applied to the implanted femoral prostheses with the use of a jig that simulated acetabular and trochanteric loading. Extensometers were used to measure motion at the prosthesis-bone interface. The prostheses were then removed and were reinserted, with cement applied to the proximal porous coating to simulate ingrowth of bone. The single-limb-stance and combined axial and torsional loads were reapplied and the magnitude of motion was recorded again. No significant differences in the magnitudes of the motion were found between the femora in which the straight stem had been implanted and the femora in which the curved stem had been implanted, during either simulated single-limb-stance or low-intensity torsional loading. When large torsional moments (twenty-two newton-meters) were applied, significantly less motion occurred at the bone-prosthesis interface, both proximally (p = 0.019) and distally (p = 0.0013), in the femora with the curved-stem implant than in the femora with the straight-stem implant. When cement had been applied proximally, proximal and distal motion between the prosthesis and the femur was decreased during simulated single-limb-stance and during torsional loading in the femora with the straight stem and the femora with the curved stem.     

The effect of proximally and fully porous-coated canine hip stem design on bone modeling

Porous coated canine femoral hip replacement implants were evaluated for biological fixation by bone ingrowth and the effect of the extent of porous coating on bone modeling. The Co-Cr alloy implants were either fully porous coated or coated only on the proximal 40% of the stem. Two implants of each type were studied 9, 16, and 36 months after surgery. Implant fixation and bone modeling were assessed radiographically throughout the implant periods and histologically after the test animals were killed. All 12 implants appeared stably fixed within the femur and were bone-ingrown in the porous region. Radiographic features such as proximal medial and anterior cortical thinning, proximal cancellous bone hypertrophy, and new endosteal bone formation near the stem tip were noted within the first postoperative year, with no appreciable change thereafter. The extent of proximal cortical thinning varied from virtually none to as much as 40%, being more prominent with the proximally coated implants at 16 months and with the fully coated implants at 36 months. Of consistent note was cancellous hypertrophy at the junction of porous and smooth implant surfaces with proximally coated implants and new endosteal bone formation and ingrowth at the stem tip of fully coated implants. These results indicate that the proximally porous-coated implant design causes increased proximal stress transfer, but this does not necessarily preclude proximal cortical resorption.     

Intraoperative complications of revision hip arthroplasty using a porous-coated, distally slotted, fluted femoral stem

Intraoperative complications of 175 cementless revision total hip arthroplasties done at four institutions using a porous-coated, uncemented, distally slotted, fluted femoral stem were reviewed. Three types of complications were recorded: eccentric reaming, femoral perforation, and femoral fracture. Intraoperative complications occurred in 16 patients (9.1%). There was no statistically significant association between complication rate and type of surgical approach, stem length, stem diameter, or host bone quality. This complication rate is comparable to or lower than that reported with the use of similar uncemented long femoral revision stems.     

Femoral remodeling after porous-coated total hip arthroplasty with and without hydroxyapatite-tricalcium phosphate coating: a prospective randomized trial

We prospectively assessed femoral bone remodeling using dual-energy x-ray absorptiometry for 2 years after total hip arthroplasty. Thirty-nine hips were randomized to receive a titanium proximally porous-coated femoral component with or without hydroxyapatite-tricalcium phosphate coating. Although both stems resulted in alterations in the periprosthetic bone mineral density, the hydroxyapatite-tricalcium phosphate coated stems had significantly less femoral bone loss than the uncoated stems at 2-year follow-up. This reduced femoral bone loss may provide short-term and long-term advantages over noncoated stems.     

Total hip arthroplasty with a low-modulus porous-coated femoral component

Fifty-seven patients had sixty-three total hip replacements, performed using a femoral stem with a soft, low-modulus porous coating of Proplast and a conventional acrylic-cemented acetabular component. Forty-seven of the hips were followed for an average of thirty-seven months. Seventeen (36 per cent) of the forty-seven hips were judged to be clinical failures, and five of the failures were revised by inserting a new femoral component and fixing it with acrylic cement. The prostheses were thought to have failed because they had inadequate support, due to deficiencies in the design of the stem and in the fit of the implant in the femur. The five retrieved prostheses were found to have fibrous-tissue ingrowth into the coating, which had failed by shear within its substance. Therefore, we concluded that the coating had insufficient strength to withstand normal weight-bearing loads. To improve performance, a more stable prosthesis with a stronger porous coating is needed. In addition, a posterior surgical approach through a transtrochanteric osteotomy may give better exposure of the femoral canal and facilitate the use of longer-stem (140 to 153-millimeter) designs, which are less likely to be inserted in a varus position.     

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.     

Extensively porous-coated stems for femoral revision: reliable choice for stem revision in Paprosky femoral type III defects

Between January 1999 and August 2008, ninety-six femoral revisions were performed with extensively porous-coated stems in Paprosky type III femoral defects (89 type IIIA and 7 type IIIB defects). Seven type IIIB defects with a mean canal of 16.5 mm were observed; 6 defects achieved stable bone ingrowth and 1 achieved stable fibrous condition. Average postoperative Harris Hip Score was 92.3±8 (range, 77-100), and all scores improved postoperatively. At a mean follow-up of 65.7 months, 92 stems achieved bone ingrowth, and 1 stem (type IIIB) achieved a stable fibrous condition. Three patients died from causes unrelated to the surgery during follow-up. The most frequent diagnosis for revision of the femoral component was loosening of the cementless stem (53 patients; 55.2%), followed by status after a Girdlestone procedure (21 patients; 21.8%), after total hip arthroplasty with acetabular wear (10 patients; 10.4%), loosening of the cemented stem (7 patients; 7.3%), and periprosthetic fracture (5 patients; 5.2%). The authors performed 65 total hip arthroplasty revisions, 23 femoral component revisions, and 8 revisions of femoral components with cemented liners in patients with well-fixed acetabular shells. Extensively porous-coated stems in femoral revision for Paprosky type III femoral defects provided good mid-term durability.     

Influence of stem size on clinical outcome of primary total hip arthroplasty with cementless extensively porous-coated femoral components

This study retrospectively evaluated the clinical outcome of primary total hip arthroplasty as a function of stem diameter in 1545 patients implanted with extensively porous-coated stems. Less than 2% of femoral components were loose or revised; femoral survivorship was 97.9% at 15 years. Of patients with stable components, 95 to 97% had increased function, decreased pain, and overall satisfaction. Although 17% of patients indicated activity-limiting pain, only 3% were dissatisfied with the results of their hip arthroplasty. Logistic regression demonstrated no statistical relationship between stem size and either revision, loosening, pain, or satisfaction. We conclude that patients with large-diameter, extensively porous-coated femoral components are no more likely to be revised, loose, or have thigh or activity-limiting pain than patients with smaller diameter stems.