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PubMed1993

Biomechanical analysis of a distally interlocked press-fit femoral total hip prosthesis.

This study was undertaken to compare the stability of a distally interlocked femoral prosthesis to a standard press-fit implant (Cementless Spotorno, Protek Co., Toronto, Canada). Five human femora were studied with each acting as its own control. All were tested in the locked mode followed by unlocked testing modes. The MTS 858 Biomaterials Testing System was used to test the implanted femoral stems under both pure torsional and pure axial loading. Distal interlocking increased the torsional stability by 320% (locked 4.05 Nm/degree; unlocked 1.25 Nm/degree) (P < .01) and the axial stability by 230% (locked 1,236.26 N/mm; unlocked 527.44 N/mm) (P < .01). the use of temporary distal interlock in cases where the initial stability of a press-fit implant is suboptimal should allow for improved biological fixation by minimizing micromotion at the stem-bone interface.

Bone Cements↗
PubMed1998

[Cementless hip prosthesis in inflammatory rheumatic diseases].

We compared the outcome of cementless hip arthroplasty in patients with chronic rheumatic diseases (cases) and patients with osteoarthritis (controls). Between 1985 and 1993 we implanted 26 cementless hips in 22 patients with Rheumatoid Arthritis, Psoriatic Arthritis or Ankylosing Spondylitis. From a pool of more than 600 patients with Osteoarthritis we chose 40 matched controls (41 hips). Matching variables were year of implantation, age, follow-up, height, weight, gender and type of implant. At follow-up (cases: 58 +/- 27 months; controls: 56 +/- 26 Monate) no signs of loosening or migration of the stem were found, neither in the cases nor in the controls. Loose and/or migrated cups were found in 4 patients with rheumatic diseases (after 44, 65, 65 and 107 months) and in 3 patients with osteoarthritis (after 63, 84 and 100 months). Two cups were revised within 18 months in the control group, in the case group one revision was necessary after 5 years. Loosening and revision rates did not differ significantly (p > 0.20). Clinically, those with Osteoarthritis had a better extension (p < 0.02), were more satisfied with their (artificial) hips (p < 0.05) and did better in some activities of daily living (climbing stairs, dressing, sitting/standing up). Within a mean follow-up of 5 years the results of patients with chronic rheumatic diseases seem to be comparable to those of a matched control-group of patients with Osteoarthritis. Differences between the groups concern areas, in which rheumatic patients are handicapped due to their chronic illness. Nevertheless, we need long-term-results, before we can recommend cementless implants for these patients.

Aged↗
PubMed1984

Loosening of the femoral component of the ICLH double cup hip prosthesis. A biomechanical investigation with reference to clinical results.

The cancellous bone in the proximity of the rim of the ICLH femoral cup may not only be subjected to an axial stress that is about three times the value physiologically encountered, but the cup also tends to move transversally away from the medial bone margin in this area. Hence, fracture of the trabecular structure in this area can occur, accompanied by cleavage formation. Across the gap which thus forms between cement and bone, the mating surfaces that are now no longer joined, probably move relative to each other with every subsequent walking cycle. This relative motion leads to bone resorption and the development of a thick intermediate layer of fibrous connective tissue that spreads until eventually the whole cup becomes loosened. In the meantime the bone further proximal probably undergoes atrophy due to mechanical inactivity. This presentation includes a biomechanical analysis which might explain the discouraging observations made in a series of forty-three implantations carried out between 1976 and 1979 in our clinic.

Adult↗
PubMed1989

Mathematical shape optimization of hip prosthesis design.

The long-term success of artificial-joint replacement depends partly on the chances for acrylic cement failure and interface disruption. These chances can be diminished by an optimal load-transfer mechanism, whereby stress concentrations are avoided. The present paper introduces a method for numerical shape optimization, whereby the finite element method is used iteratively to determine optimal prosthetic designs, which minimize interface stresses. The method is first applied in a simplified one-dimensional model of a cemented femoral stem fixation, using acrylic cement. The results show that 30-70% cement and interface stress reductions can be obtained in principle with an optimized design. Although the actual optimal shape is susceptible to the characteristics of the joint load, the stem length, stem modulus, cement modulus and bone properties, its general geometrical characteristics are consistent, featuring proximal and distal tapers, and a belly-shaped middle region. These general characteristics are confirmed in a more realistic two-dimensional FEM model. It is concluded that this method of shape optimization can provide a meaningful basis for prosthetic design and analysis activities in general.

Bone Cements↗
PubMed2001

Characterization of electrolytic ZrO2 coating on Co-Cr-Mo implant alloys of hip prosthesis.

An electrolytic Zr(OH)4 gel has been coated on ASTM F-75 Co-Cr-Mo alloy specimens in 0.0625 M ZrO(NO3)2 solution with pH = 2.2 at a current density of 2 mA/cm2. After annealing at 623-973 K for 120 min in air, the ZrO2-coated specimen was evaluated by electrochemical polarization in Hank's solution, wear tests with UHMWPE (Ultra-high molecular-weight polyethylene) under a load stress of 50 MPa, scratch tests, surface morphology observations, and XRD analysis. The ZrO2-coated specimen annealed at 773 K for 120 min revealed a good adhesion of 610 MPa on Co-Cr-Mo substrate, a lower wear loss of UHMWPE and a higher protection potential than the uncoated specimen in Hank's solution. A monoclinic structure with (1 1 1) preferred orientation parallel to the sheet plane was detected at 623 K < or = T < or = 673 K and a tetragonal structure of ZrO2 was detected at T > or = 773 K. Then a monoclinic structure with random orientation and a tetragonal structure were mixed at T > or = 973 K.

Alloys↗
PubMed1983

[Diffusion of rifampicin into spongy and compact bone tissue during total hip prosthesis operation].

Sixty eight patients received either an oral single dose of 300 mg (or 300 mg/12 h), or an oral single dose of 600 mg (or 600 mg/24 h) of rifampicin. In every case samples of serum and bone were collected 3 h, 12 h, and 24 h after the last oral dose. Rifampicin levels measured at 3 h and 12 h in cortical bone samples increased significantly with the dose of the drug. The only dose which determines activity in cortical bone at the 3rd hour was the dose of 600 mg. When the dose was increased from 300 mg/12 h to 600 mg/24 h the ratio spongious bone/serum increased from 0.19 to 0.41 at 3d h and from 0.24 to 0.29 at the 12th hour; the ratio cortical bone serum was 0.20 at the 3rd hour after a dose of 600 mg. In any case tissue levels varied in a parallel direction to serum levels and were superior in spongious bone to the MIC of S. aureus sensitive strains until 12 h after the 600 mg dose. According to these results, it appears that the best dose for treating S. aureus bone infection seems to be 600 mg/12 h.

Bone and Bones↗
PubMed2000

Osteolysis in cemented titanium alloy hip prosthesis.

We evaluated 132 consecutively implanted cemented titanium alloy stems (Ti6-Al7-Nb, SLS-88) after a mean follow-up of 6.6 years (range 5-7 years). Almost 30% of the stems showed significant osteolysis, mainly in the proximal stem area. The amount of osteolysis correlated significantly to a typical pain pattern: dull, circular, and occurring at rest. Six stems had already been revised, and another 7 stems were loose clinically and radiologically, which resulted in a Kaplan-Meier survivorship of 95% for stem revisions and 88% for stem failures (revisions plus loose stems). We found that smaller stem sizes tend to increase the development of osteolysis and loosening. Two factors seem to play a role in early loosening of cemented titanium alloy stems: i) increased elasticity of titanium, which leads in small stem sizes to micromotion between the stem and cement and to cement breakage, and ii) corrosion of the cemented titanium alloy stem and subsequent osteolysis in the adjacent bone. The combination of both factors (high elasticity plus corrosion) accelerates the degradation of the bone anchorage of the stem and initiates early loosening. We advise against the further use of cemented SLS-88 titanium alloy stems.

Adult↗
PubMed2005

Stress analysis of hemispherical ceramic hip prosthesis bearings.

We present design criteria and test data for ceramic hemispherical 'resurfacing' prosthesis bearings that are attached by placement on the conical trunnion of the prosthesis stem. These large diameter bearings will be subjected to higher torques than conventional 28 mm bearings. Prototypes were fabricated and tested. The pattern of failure and subsequent analysis suggests that fracture initiated on the surface of the bore and that this was preceded by the development of large circumferential hoop stresses. Widening the bore will improve stability under torque loads but this may be at the expense of bearing strength. A finite element analysis has shown that the optimum taper bore to bearing diameter ratio is 0.43 and that designs with large taper bore to bearing diameter ratios (over 0.6) should be avoided due to the development of excessively high hoop stresses on the inner bore surface. High meridional tensile stresses can appear where the internal roof surface joins the conical bore surface as the load is removed. A smooth radius between the conical bore and the roof will help to overcome this. Further improvements include a thinner roof that is smoothly arched internally. Thus, the design of the component can be optimised, making it less susceptible to fracture without compromising the stability of the ceramic head on its trunnion.

Arthroplasty, Replacement, Hip↗
PubMed1998

[Arterial vascular injuries in hip prosthesis implantation].

Implantation of total endoprosthesis (TEP) is an established method for the operative therapy of acute and chronic hip dysfunction. Beside septic complications iatrogenic injuries of the vascular system regularly occur. Immediate and adequate therapy is necessary in order to prevent loss of an extremity or even patients death. We present three patients with major vascular injuries during hip joint operations. In two patients was the external iliac artery and in one the femoral common artery injured. The cases were managed with PTFE- or Dacron-interposition. The problem of vascular injuries associated with the implantation of total hip joint endoprosthesis will be discussed and the avoidable of most vascular lesions is underlined.

Aged↗
PubMed1991

[Study of loosening and wear of total hip prosthesis. Apropos of a series followed-up over 10 years].

After reviewing 30 cases of patients having had a total hip arthroplasty by the Charnley's technique between 1970 and 1978, the authors study the radiographic parameters of the cup and of the femoral stem, using geometric buildings described by Sutherland. On the acetabulum, the inclinaition angle, the medialisation and the wear of the cup were calculated. The varisation of the stem and its migration were looked for on the femur. The presence of a radiolucent line, prosthesis--bone or cement--bone and the importance of peri-articular calcifications, was also noted. The verticalisation of the cup and its anteversion were a pejorative factor. The medialisation was disquieting only if it was associated with a verticalisation. The wear more than 2 mm was noted only in 5 cases; the radiolucent line was pejorative only if it was type cement--bone; the type cement--cup, rare, was of less bad prognostic. On the femur, the most failing was the varus of the stem which determined a loosening most often when it was present. The disquieting radiolucent line was always type cement--bone and was always associated with a bicortical reaction showing a mobility of the stem. In a last part, the authors studied the wear of expanted cups in polyethylene which was different of the fluage. A distinction between the theoretical wear and the clinical wear was made. Photographs in scanning electron microscopy which permit to describe the different types of wear are presented.

Adult↗
PubMed1996

Biomechanical and histological analysis of an HA coated, arc deposited CPTi canine hip prosthesis.

The interfacial shear strength and bone tissue response was investigated for an arc deposited (AD) commercially pure titanium implant surface, with (AD/HA) and without (AD) plasma-sprayed hydroxyapatite (HA) coating. Ten purpose bred coonhounds received bilateral femoral stem implantation (AD and AD/HA) in the proximal femurs (hemiarthroplasty). The femoral prosthesis consisted of a modular CoCr alloy head, modular Ti-6Al-4V neck, and a 10-mm diameter cylindrical Ti-6Al-4V femoral stem. The AD surface had 30-35% greater surface roughness than the AD/HA surface. The HA coating had a purity greater than 90% and a crystallinity greater than 65%. After 6, 12, and 24 weeks, the implants were retrieved and analyzed with mechanical testing, qualitative and quantitative histology, and electron microscopy. The AD/HA implants had equivalent interfacial shear strengths to the AD implants at all time periods. The AD/HA implants had significantly greater linear bone contact than the AD implants. The 6-week implants had significantly thicker cortical bone than the 12- and 24-week implants. The HA coating was very stable in vivo, evidenced by no thickness reduction at any time period. Qualitatively, the AD/HA implants primarily had bone contacting the implant surface with little fibrous tissue present, and the AD implants had bone and fibrous tissue contacting the implant surface. The electron microscopy analysis showed that the mechanically tested implants exhibited a mixed failure mode at the bone, HA coating, and titanium interfaces.

Animals↗
PubMed2004

Precision measurements of the RSA method using a phantom model of hip prosthesis.

Radiostereometric analysis (RSA) has become one of the recommended techniques for pre-market evaluation of new joint implant designs. In this study we evaluated the effect of repositioning of X-ray tubes and phantom model on the precision of the RSA method. In precision measurements, we utilized mean error of rigid body fitting (ME) values as an internal control for examinations. ME value characterizes relative motion among the markers within each rigid body and is conventionally used to detect loosening of a bone marker. Three experiments, each consisting of 10 double examinations, were performed. In the first experiment, the X-ray tubes and the phantom model were not repositioned between one double examination. In experiments two and three, the X-ray tubes were repositioned between one double examination. In addition, the position of the phantom model was changed in experiment three. Results showed that significant differences could be found in 2 of 12 comparisons when evaluating the translation and rotation of the prosthetic components. Repositioning procedures increased ME values mimicking deformation of rigid body segments. Thus, ME value seemed to be a more sensitive parameter than migration values in this study design. These results confirmed the importance of standardized radiographic technique and accurate patient positioning for RSA measurements. Standardization and calibration procedures should be performed with phantom models in order to avoid unnecessary radiation dose of the patients. The present model gives the means to establish and to follow the intra-laboratory precision of the RSA method. The model is easily applicable in any research unit and allows the comparison of the precision values in different laboratories of multi-center trials.

Arthrography↗
PubMedDate not supplied

Cellular reactions in hip prosthesis loosening.

Based on the results obtained in histological examinations carried out on periprosthetic tissues in a large series of cases of prosthetic hip joint explants, the authors analyze the cellular events that may occur in loosening phenomena as compared to what occurs in the paraphysiological repair process that is observed in the stable prosthesis. Like other authors, they believe that the principal role in the mechanism of loosening is played by macrophages which are recalled in a large number, at times together with multinucleate giant cells, at the bone-implant interface, after micromovements of the prosthesis and the formation of wear particles have occurred. The macrophages would be capable of favoring resorption of the periprosthetic bone tissue, producing areas of osteolysis in which the transmission of the mechanical stress of loading is modified. The ensuing prosthetic instability increases wear phenomena, causes a greater amount of osteolysis, and, in a vicious cycle, loss of the relationship between bone and implant, and, thus, prosthetic loosening. Finally, the authors report a hypothesis on the pathogenesis of the phenomenon, based on which non-physiological stress, associated with wear and eventually infection, leads to loosening.

Bone Cements↗
PubMed1993

[Experience with non-cemented stems in Schenker hip prosthesis].

In 1986-1988 at the Orthopaedic clinic of the Institute for Postgraduate Medical Training 56 stems on non-cemented total endoprostheses of the hip joint type Schenker were implanted. The non-cemented stem was combined in all patients with a cemented socket Poldi. The endoprosthesis was indicated in particular in young patients in 59% in hip joints affected with secondary postdysplastic arthritis of the hip joint. The group was checked by Harris' method, the mean follow-up period in 1992 was 58 months. Of 36 followed up patients 21 operated patients reported pain in the area of the hip joint, 10 patients used analgetics. In nine patients reimplantation of the non-cemented Schenker stem was performed on account of aseptic loosening, in 11 patients the X-ray check revealed obvious signs of aspectic loosening associated with subjective complaints. The dependence of aseptic loosening on the quality of primary implantation is marked. In patients with perfect cortical contact of the stem aseptic loosening developed in 27% of the patients, in patients with inadequate cortical contact aseptic loosening was recorded in 80% of the operated patients. The general evaluation according to Harris comprised 42% excellent results, 30% good results, 14% satisfactory results and 14% poor results. This evaluation does not include patients who on account of pain and loosening of the femoral Schenker component were already re-operated. Because of the considerable number of complications implantation of this type of prosthesis was discontinued at the authors' department.

Adult↗
PubMed2004

The porous-coated anatomic total hip prosthesis: 11- to 13-year results.

Of 137 consecutive primary porous-coated anatomic (PCA) arthroplasties performed, complete data was available on 107 hips in 93 patients at an average of 12.4 years (range, 11-13 years). The average Harris Hip Score improved from 44 to 85 at final follow-up, with 78% good or excellent result. Thirteen percent (14 of 107) of acetabular components and 4 porous ingrowth stems were deemed failures. Osteolytic lesions were seen in 7.5% (8 of 107) of acetabular components. Survivorship of the PCA prosthesis as a whole was 83% at 12.4 years. This first-generation femoral stem performed well, with only 4 failures, all of which occurred in patients with avascular necrosis in which unrecognized pathologic changes in the proximal femur may have inhibited bone ingrowth. The majority of the failures can be attributed to aseptic loosening of the acetabular component.

Adult↗