Femoral fixation in the face of considerable bone loss: the use of modular stems

Considerable femoral bone loss can be encountered in the multiply revised total hip arthroplasty patient. Deficient proximal bone requires either a bulk allograft or a femoral component that allows stable distal fixation. Extensively coated stems have shown excellent results for many revisions but have shown higher rates of failure among patients with femoral remodeling in retroversion, an enlarged endosteal diameter, or an ectatic canal. A modular tapered stem is an alternative in this subset of patients. A modular tapered implant provides axial and rotational stability through the use of distal splines, and the proximal body segments can allow independent adjustment of leg length, offset, and anteversion.     

Failure of cementless fixation of the femoral component in total hip arthroplasty.

The basic concepts involved in cementless fixation of the total hip arthroplasty femoral component have been controversial. Some clinicians advocate fixation only of the proximal portion of the stem so that weight-bearing loads will be transferred proximally, and proximal stress shielding will be avoided. Others advocate distal fixation to ensure rigidity of fixation but concede that it will lead to proximal stress shielding and bone loss. However, clinical evidence suggests that the design of the implant is one important factor in determining stress shielding. When the stem is smooth and cylindrical distally, proximal stress relief does not occur, even when the stem is fixed tightly distally. Because femoral component loosening is the most common clinical problem with cementless total hip arthroplasty, every effort should be made to achieve fixation of the implant. Proximal and distal fixation can be achieved with most of the available implants. For tight proximal fixation, a good proximal implant design and a precise line-to-line preparation technique are critical, but aggressive broaching and interference-fit techniques result in a high rate of proximal femoral fracture during preparation and implantation. When the conditions are good for excellent proximal fixation, a flexible stem should be selected to apply a large amount of stress proximally. The stress transferred through distal fixation will be small in this situation, and the reaming technique of the femoral diaphysis does not need to be very aggressive. Approximately 10 to 20 mm of tight distal fit combined with the 0.5-mm underreaming technique provides sufficient distal fixation, and the chance of distal femoral fracture during insertion of the stem is minimum with this technique. When conditions are unfavorable for excellent proximal fixation, such as in revision hip arthroplasty, or when a proximal deformity or osteoporosis is present, a relatively rigid stem should be selected to avoid overloading proximal fixation and, thus, generating large proximal micromotion. The stress transferred through distal fixation will be large in this situation, and a relatively aggressive but well-controlled reaming technique of the diaphysis is required. Approximately 20 to 40 mm of tight distal fit combined with a 0.5-mm underreaming technique is adequate to obtain sufficient distal fixation and still avoid distal femoral fracture. Implant design features that improve proximal fixation and instrumentation features that improve bone preparation and decrease the risk of failure will broaden the indications for cementless fixation. As fixation and instrumentation improve, more flexible implants can be developed to improve bone preservation and avoid proximal stress relief.(ABSTRACT TRUNCATED AT 400 WORDS)     

Fixation of the Quatroloc femoral component: a biomechanical and clinical study.

The current study was designed to test the hypothesis that press-fit femoral components with proximal press-fit and distal mechanical interlock can achieve fixation sufficient to allow bone ingrowth in osteoporotic and in normal bone. The addition of steps along the tapered distal stem improved fixation in osteoporotic bone enough to reduce micromotion to less than 20 microm in response to physiologic axial and torsional load. The clinical portion of the study included 226 consecutive hips (223 patients) with 2- to 4-year clinical results after total hip arthroplasty with a rectangular femoral component using proximal porous coating and distal mechanical interlock. Patient age ranged from 36 to 92 years. At 2 years postoperative, 4% of the patients with Type A (normal) femoral bone, 3% with Type B (intermediate) bone, and no patients with Type C (osteoporotic) bone had thigh pain. No clinical cases of loosening have occurred in normal or osteoporotic femurs.     

The effect of diaphyseal biologic fixation on clinical results and fixation of the APR-II stem

This study evaluated the effect of a grit-blasted diaphyseal surface on noncemented fixation of the Anatomic Porous Replacement II stem (APR-II, Sulzer Medica Orthopaedics, Austin, TX) for improvement of clinical results and fixation. A total of 107 consecutive total hip arthroplasties with the APR-II stem, which has proximal porous coating and a diaphyseal grit-blasted surface, were performed without cement, and 99 were studied at average 4 years. Of these hips, 37 had hydroxyapatite sprayed onto the proximal porous coating, but because there were no statistical differences for performance in any category, all stems were considered as 1 group. Clinical results were measured by the Harris hip score. Radiographic measurements of fixation, osteolysis, and bone remodeling were studied by reference to Gruen zones. Of hips, 99% had a good or excellent result by Harris hip score, with an average pain score of 42.3. Of hips, 98% had >40 points, with no patient reporting thigh pain after 3 years. There were no radiolucent lines in 94% of stems, and 100% had proximal bone ingrowth fixation. Distal cortical hypertrophy associated with tip fixation occurred in 49%, whereas proximal stress shielding was present in 43% of hips. Comparison of these clinical and radiographic results with our previous experience of bone ingrowth implants (smooth stem) suggests that bone ingrowth proximally with ongrowth in the diaphysis of the femoral stem provides better clinical and radiographic results.     

Biomechanics of the Birmingham hip resurfacing arthroplasty

The effects of the method of fixation and interface conditions on the biomechanics of the femoral component of the Birmingham hip resurfacing arthroplasty were examined using a highly detailed three-dimensional computer model of the hip. Stresses and strains in the proximal femur were compared for the natural femur and for the femur resurfaced with the Birmingham hip resurfacing. A comparison of cemented versus uncemented fixation showed no advantage of either with regard to bone loading. When the Birmingham hip resurfacing femoral component was fixed to bone, proximal femoral stresses and strains were non-physiological. Bone resorption was predicted in the inferomedial and superolateral bone within the Birmingham hip resurfacing shell. Resorption was limited to the superolateral region when the stem was not fixed. The increased bone strain observed adjacent to the distal stem should stimulate an increase in bone density at that location. The remodelling of bone seen during revision of failed Birmingham hip resurfacing implants appears to be consistent with the predictions of our finite element analysis.     

Revision total hip arthroplasty with a custom cementless stem with distal cross-locking screws. Early results in femora with large proximal segmental deficiencies

BACKGROUND: Revision total hip arthroplasty in the setting of a large proximal segmental femoral deficiency and/or discontinuity between the proximal and distal parts of the femur remains a challenging problem. We describe the use of a cementless stem with distal cross-locking screws to provide stability of the femoral implant in this situation. METHODS: Seventeen custom fully porous and hydroxyapatite-coated titanium femoral stems with distal cross-locking titanium screws were implanted in sixteen patients during revision total hip arthroplasty. Preoperatively, all of the patients had Paprosky grade-IIIB or IV femoral deficiencies. At the time of follow-up, the Harris hip scores were calculated and radiographs were made. A successful result was defined as a postoperative increase in the Harris hip score of >20 points, a radiographically stable implant, and no additional femoral reconstruction. RESULTS: At the time of final follow-up, at a mean of 5.3 years postoperatively, the result was successful in sixteen of the seventeen hips, the mean Harris hip score had improved from 35 to 76 points, and all implants were clinically and radiographically stable. There were no postoperative infections or hip dislocations. CONCLUSIONS: The use of a custom femoral stem with distal cross-locking screws can provide at least intermediate-term clinical and radiographic stability in patients with Paprosky grade-IIIB or IV femoral deficiencies. Longer follow-up will be required to determine the longevity of these implants.     

Treatment of Vancouver B3 periprosthetic femur fractures with a fluted tapered stem

Periprosthetic femur fractures around a hip arthroplasty associated with a loose stem and severely deficient or comminuted bone typically have been treated with substitution for the proximal femur using an allograft prosthetic composite or a tumor prosthesis. Eight patients (mean age, 68 years; range, 34-80 years) with Vancouver Type B3 femur fractures were treated with revision using a long modular fluted tapered uncemented stem with retention of the proximal femur. Access to the failed prosthesis and joint was gained through the fracture or osteotomy and soft tissue attachments to the fracture fragments were maintained. One patient died within 1 week. The remaining patients were followed up 1 to 2 years (mean, 1.5 years). At final followup, all patients had stable implants and all acute fractures were healed. Marked reconstitution of proximal femoral bone stock was observed consistently. All surviving patients were ambulatory and none had more than mild pain. The preliminary results of this method show a high rate of stable implant fixation and fracture healing with preservation and reconstitution of the host femur.     

Unstable versus stable uncemented femoral stems: a radiological study of periprosthetic bone changes in two types of uncemented stems with different concepts of fixation

Introduction Uncemented stems in total hip arthroplasty (THA) are used increasingly often because they are believed to offer a reliable long-term fixation. However, periprosthetic bone remodelling has been a worrying issue. A proximal demineralization has been noted in femurs with well-fixed stems, and it has been explained as by-passing of mechanical forces along the fixed implant (stress-shielding). Aseptic loosening has been a major problem in several uncemented series with earlier designs. The objective for this study was to investigate how the host bone adapts to a loose stem compared with a well-fixed stem after a long time.Materials and methods An investigation with dual-energy X-ray absorptiometry (DEXA), scintimetry and radiological assessment was carried out in 20 patients 8 years after a THA for arthrosis with two different uncemented stems. Ten patients received a stem coated with polytetrafluoroethylene (Anaform); all prostheses showed migration and were considered unstable. Ten patients received a hydroxyapatite-coated stem (Bi-Metric); no prosthesis migrated.Results Different remodelling patterns were seen. In the unstable group, the periprosthetic bone mineral density (BMD) was significantly reduced along the entire stem, while in the stable group only proximal bone loss was seen. The scintigraphic uptake was increased under the stem tip in both groups, and among unstable stems uptake was also increased in the calcar region.Conclusion The assessment of periprosthetic bone remodelling after uncemented THA with long-term observation shows a different host-bone response in stable versus unstable femoral implants. Prior to a femoral revision, measurement of the BMD could be beneficial; it may guide the surgeon when deciding which surgical technique to use.     

Porous-coated hip replacement. The factors governing bone ingrowth, stress shielding, and clinical results

Total hip replacement using porous-coated cobalt-chrome femoral implants designed for biological fixation has been evaluated in 307 patients after two years and in 89 patients after five years. Histological study of 11 retrieved specimens showed bone ingrowth in nine and fibrous tissue fixation in two. Fixation by bone ingrowth occurred in 93% of the cases in which a press fit of the stem at the isthmus was achieved, but in only 69% of those without a press fit. The clinical results at two years were excellent. The incidence of pain and limp was much lower when there was either a press fit of the stem or radiographic evidence of bone ingrowth. Factors such as age, sex, and the disease process did not influence the clinical results. Most cases showed only slight resorptive remodelling of the upper femur, but in a few cases with a larger, more rigid stem, more extensive bone loss occurred. The results after five years showed no deterioration with time. Fixation by the ingrowth of bone or of fibrous tissue both appeared to be stable, but bone ingrowth gave better clinical results.     

Hydroxylapatite-coated hip implants. Multicenter three-year clinical and roentgenographic results.

The application of a thin coating of hydroxylapatite to total hip implants has provided the opportunity to realize stable fixation of a press-fit prosthesis without a porous coating or an intervening fibrous tissue layer. This series consists of 436 total hip arthroplasties, of which 320 cases have a minimum two-year follow-up period and 142 cases have a minimum three-year follow-up period. The femoral prosthesis used was a roughened titanium alloy with a 50-microns surface treatment of hydroxylapatite applied to the proximal one third. The acetabular components implanted included porous-coated implants (132), hydroxylapatite-coated acetabular shells of varying geometries (285), and bipolar implants (16). Analysis of the clinical results demonstrates a mean Harris Hip Score of 93 at six-months postarthroplasty, 95 at one and two years, and 96 at three years. At the three-year follow-up evaluation, 4.2% of patients complained of mild to moderate pain in the operative limb, whereas only 2.2% at two years and 1.4% at three years complained of activity-related thigh pain. The femoral mechanical loosening rate representing stems revised for aseptic loosening (two) plus roentgenographically unstable stems (zero) is 0.46%. Three hydroxylapatite-coated acetabular cups (1%) have shown measurable migration at two years, but none have been revised for aseptic loosening. The roentgenographic evaluation provides evidence for excellent proximal femoral fixation with distal stress transfer. Radiolucencies typically occur around the uncoated distal tip of the femoral stem (74%), but rarely in the proximal hydroxylapatite-coated anterior (3%) and lateral (2%) zones. Femoral cancellous condensation characteristically is seen at the transition zone of hydroxylapatite coated-to-uncoated stems (86%), whereas up to 32% of cases show cortical hypertrophy at the medial distal stem. These roentgenographic changes are progressive from one through three years postoperatively.     

Total hip arthroplasty for acute femoral neck fractures using a cementless tapered femoral stem

The purpose of this study was to evaluate the osseointegration potential and implant-related complications of cementless total hip arthroplasty with a titanium alloy collarless, tapered, wedge-shaped femoral stem with a proximal circumferential plasma-spray coating in patients with acute hip fractures. The cohort consists of 85 patients with a mean age of 78.1 years. The mean duration of follow-up was 3.8 years. Total hip arthroplasty conferred significant improvement in function for all patients. All femoral components were stable with evidence of bone ingrowth (84 hips) or fibrous fixation (1 hip). Mild thigh pain was present in 3 patients. The complications included dislocation (3 cases), intraoperative femoral fracture (2 cases), and periprosthetic femoral fracture in the postoperative period (1 case). There was one reoperation for revision of the femoral component in the patient with a periprosthetic fracture. There were 25 (29%) deaths. Cementless total hip arthroplasty using a tapered proximally coated femoral stem is a viable option for the treatment of a displaced hip fracture and preexistent arthritis.     

Hydroxyapatite-coated total hip prostheses. Two-year clinical and roentgenographic results of 100 cases

Studies of implant fixation have shown that hydroxyapatite (HA) coatings provide early and strong fixation to bone. This is a report of 100 consecutive cases of total hip arthroplasties, using HA coating, which were mainly for osteoarthrosis, avascular necrosis, or revision for failed implants. The average prospective follow-up period was two years. Titanium femoral components had a proximal HA coating, usually with an HA-coated screw cup. For both HA-coated components, the average Harris hip score was 96 points after one year and 98 after two years. Analysis of data shows that the incidence of pain was low immediately after surgery and at 4% one year postoperatively. There was no difference between the results of primary cases and revisions after the one-year interval. On roentgenographic examination, there was a rapid bony integration of implants with bone apposition on the coating within six months, accompanied by specific patterns of remodeling. No radiolucent line formation was detected around HA-coated implant parts. There were no revisions for loose implants. After two years, 97% of the patients had positive roentgenographic evidence of femoral ingrowth compared to 55% for HA-coated acetabular cups, with a statistical significance between bone ingrowth and clinical results. Implant fixation using HA coatings is a reliable procedure for good bony fixation and clinical results.     

Ten-year results with hydroxyapatite-coated total hip femoral components in patients less than fifty years old. A concise follow-up of a previous report

We report the results of total hip arthroplasty with use of a proximally hydroxyapatite-coated femoral component after a minimum follow-up of ten years in a group of patients who were less than fifty years old at the time of the primary procedure. In the five years since the original publication of our study, two additional stems have undergone revision. Thus, a total of six stems have been revised. A small amount of erosive scalloping of the proximal part of the femur was seen in nearly one-half of the hips; however, all unrevised stems were radiographically stable and no hip had intramedullary osteolysis. The revision rate because of aseptic loosening of the stem was 0.9%, which compares favorably with that for other stems and other fixation methods in young patients at this point in time. This stem is currently being paired with a highly cross-linked polyethylene liner because of cup failures and the need for reoperation secondary to excessive polyethylene wear and proximal femoral osteolysis.     

A prospective short-term outcome study of a short metaphyseal fitting total hip arthroplasty

The purpose of this study was to determine whether the short, metaphyseal fitting femoral stem would achieve stable fixation without diaphyseal fixation. A total of 126 patients (144 hips) were included in the study, and their mean age was 53.9 years (26-65 years). The mean duration of follow-up was 4.5 years (4-5 years). The predominant diagnosis was osteonecrosis of femoral head (88 of 144 hips, or 61%). The mean preoperative Harris hip score was 45 points, which improved to 96 points by the final follow-up. Western Ontario and McMaster Universities Osteoarthritis score and patient's activity score were improved substantially at the final follow-up. This short, metaphyseal fitting cementless femoral component achieved stable fixation without diaphyseal fixation, and there was minimal stress-shielding bone resorption in the calcar region.     

Design rationale for intraoperatively machined uncemented femoral components in total hip replacement

First-generation uncemented femoral components failed to improve the results of total hip replacement. Insteadof maintaining the health and strength of the femur, the proximal femur was often injured either by stress-shielding, resulting from extensive coatings on the stems, or by osteolysis, resulting from unimpeded migration of particulate (primarily polyethylene) debris. Further, the incidence of thigh pain, intraoperative fractures, and early loosening increased. although the designs and surgical technique for cemented femoral components have improved, these stems still result in dramatic reductions and alterations in proximal femoral stresses. Disuse of the proximal femur will eventually have adverse consequences for the bone even if the primary implants remain well fixed. Therefore, the goals of providing long-term, stable fixation while maintaining nearly normal, healthy proximal femur have not been met with either first-generation uncemented stems or modern cemented components. although first-generation uncemented components have failed to achieve their desired goals, proximally coated, collarless press-fit stems do achieve the most normal proximal bone strains. Uncemented femoral components, therefore, still hold great promise if stable fixation, impedence of debris migration, and elimination of thigh pain can be achieved. To achieve the goals of long-term bone health and stable fixation, the flaws in design and surgical technique of first-generation uncemented stems must be identified and addressed.Based on early experiences, second-generation uncemented femoral component systems must include several essential features. The femur should primarily be prepared with accurate machine tools instead of broaches to improve initial implant-bone apposition and reduce the risk of intraoperative fracture. The component should not be extensively coated as this has clearly resulted in stress shielding.at this point, femoral components should be made of titanium, as cobalt-chromium stems have clearly been associated with higher incidences of both stress-shielding and thigh pain.The addition of flutes distally is essential because they dramatically reduce initial micromotion to the level of a cemented stem before osseointegration and have not been associated with stress shielding.Some method of stem stiffness reduction is also important. The addition of a coronal slot in the stem tip, for example, has been shown to reduce the incidence of thigh pain dramatically. Finally, stems that are not circurnferentially coated proximally have been associated with a high incidence of endosteolysis and must be avoided so that particulate debris migration can be inhibited.Preliminary evidence suggests that macrotextured-Ha components inhibit polyethylene debris migration to a level that is comparable with or better than cemented stems while maintaining and increasing bone and density proximally. In summary, second-generation uncemented components should be intraoperatively machined, avoid extensive coating, encourage proximal stress transfer, be made of titanium alloy, inhibit particulate migration, and include mechanisms for proximal and distal rotational control. Preliminary experience with such a second-generation stem suggests that these essential design features do result in excellent immediate implant stability, early osseointegration, and the eliminations of intraoperative fractures and activity-related thigh pain.     

Novel approach for designing a low weight hip implant used in total hip arthroplasty adopting skeletal design techniques

Aseptic loosening is the major cause of failure of hip implants after total hip arthroplasty. Stress shielding of the femur is known to be the principal factor involved in the aseptic loosening of hip implants. Solid stems are found to have a greater rigidity; therefore, they transfer less load proximally, which results in greater stress shielding of the proximal femur. A stem of low stiffness alone would not suffice in achieving a reduced or optimal stress shielding. The femoral stem of the light weight hip implant has a skeletal design with a hexagonal base and neck cross-section. This novel design would ameliorate the implant fixation, aid in optimal rigidity, enhance the medullary revascularization, and offer better mobility to the patient.     

Maintenance of proximal bone mass with an uncemented femoral stem analysis with dual-energy x-ray absorptiometry

Bone ingrowth into uncemented femoral implants with proximal porous coatings has been designed to avoid proximal stress shielding and preserve femoral strength. Dual-energy x-ray absorptiometry allows repeated quantitative analysis of anteroposterior scans of the proximal femur. By use of dual-energy x-ray absorptiometry and qualitative radiographic changes, 31 total hip arthroplasties with an individually designed, proximally porous-coated prosthesis were evaluated after surgery and at intervals up to 2 years. All implants appeared to achieve successful bone ingrowth and subsequent remodeling. At the most proximal level around the neck osteotomy, the postoperative loss of bone density at 6 months was −14.5%, which persisted at 24 months with −11.6%. At the level of the distal portion of the porous coating in the lower metaphysis, the density change was −8.7%, but bone had remodeled at 24 months with a change in density of only −1.0% compared with the immediate postoperative scan. With a design that results in reliable proximal ingrowth, this study predicts that after an initial decline in bone density, a positive bone remodeling response occurs that could lead to long-term stable fixation of the femoral implant.     

羟基磷灰石涂层股骨柄假体全髋关节置换术的中期疗效

目的 评价羟基磷灰石涂层股骨柄假体伞髋关节置换术的中期疗效.方法 2000年2月至2001年2月,采用U2钛合金羟基磷灰石涂层股骨柄假体行非骨水泥全髋关节置换术65例(70髋),男20例,女45例;年龄40～82岁,平均63岁.术前诊断:股骨颈骨折30例,髋关节骨关节炎15例,股骨头缺血性坏死9例,人工股骨头术后松动8例,类风湿髋关节炎2例,髋关节融合术后1例.分别于术后1周、3个月、6个月随访,以后每年随访1次,对髋关节功能(Harris评分)和X线片进行复查.结果 4例死于癌症,余61例(66髋)获7～8年随访,平均7.5年.末次随访时髋关节Harris评分85～100分,平均96分.3髋(4.5%)出现轻度大腿痛,无一髋需行翻修术治疗.术后1年内假体下沉小于1.5 mm者7髋,此后未再出现假体下沉.术后3～6个月在Gruen 2区和6区近段羟基磷灰石涂层部位出现典型的骨锚固征及松质骨和皮质骨密度增高影像.此后所有患者包括年龄大于70岁和Dorr C型髓腔者均无柄端周围的骨质增生或"底座征",也尤股骨近段或远段髓内骨溶解及假体松动.按Engh标准评定全部患者均获骨性固定.结论 羟基磷灰石涂层能增强股骨柄假体的初始固定,促进早期骨长入和生物学固定,阻止聚乙烯磨屑的髓内迁移和远段髓内骨溶解,用于非骨水泥全髋置换术中期疗效满意.