Ceramic Femoral Heads Research Articles

Proof testing of ceramic femoral heads for hip joint implants

A proof test procedure for the rejection of defective ceramic hip ball heads in the production line is presented. The procedure consists of applying a load to each ceramic ball head. This load, being somewhat higher than the maximum physiological load, should not cause any damage in cases where the highly stressed areas are free of flaws. In this procedure, a polymer ring is positioned inside the ball head bore between a socket and the head of a tie bolt. Once the tie bolt is pulled downwards, the ring creates a radial pressure on the inner bore surface of the ball head. With an iterative approach based on finite element analysis, the proof test design was optimized in order to obtain a stress distribution in the ball head similar to that resulting in in vivo conditions. The calculated results were validated by strain gauge measurements performed on an assembled proof test apparatus. Several polymers were considered for the ring. Ultrahigh-molecular-weight polyethylene (UHMWPE grade RCH 1000) showed the best durability properties and lowest wear rates. The requirement to perform 1000 reruns without significant reduction of stress in the ball head was fulfilled. Although other proof test procedures for ceramic femoral heads already exist, the procedure presented in this article shows advantages concerning maintenance and operating costs.

Ceramic Femoral Heads

Ceramic Femoral Heads

Scratch and wear performance of prosthetic femoral head components against crosslinked UHMWPE sockets

Total hip arthroplasty is a highly successful procedure where the hip joint is replaced by an artificial ball and socket joint. Bearing wear continues to be a contributing factor to implant failure. Prosthetic femoral heads roughen in vivo which leads to increased wear. Along with the introduction of improved polyethylene which reduces wear by up to 99%, improved femoral head materials have been introduced to improve resistance to abrasion. The abrasion resistance of two of these improved femoral heads was assessed in this study and compared to a cobalt chromium (CoCr) femoral head. The resulting wear performance against a polyethylene acetabular component was assessed. The bulk ceramic (zirconia toughened alumina) femoral head exhibited superior abrasion resistance compared to CoCr (97% reduction in damage) as well as reduced wear after abrasion (97% reduction in wear). The oxide coated zirconium niobium femoral head showed inferior abrasion resistance compared to CoCr (99% increase in damage) as well as increased wear after abrasion (161% increase in wear). Both femoral head surfaces utilize hard ceramic materials, however, the thin ceramic coating on top of a softer metallic substrate of the oxide coated bearing was unable to withstand aggressive abrasion.

Clinical Comparison of Polyethylene Wear with Zirconia or Cobalt-Chromium Femoral Heads

Ceramic femoral heads were developed to reduce the wear of conventional ultrahigh-molecular-weight polyethylene (UHMWPE) bearing surfaces in THA. We compared the wear rates of PE acetabular components bearing against femoral heads of zirconia (Zr) or cobalt-chromium (CoCr) in young patients. One surgeon inserted CoCr femoral heads in all 33 patients (33 hips) having THA for primary osteoarthritis from 1996 to 1997 and then Zr femoral heads in all 34 patients (36 hips) from 1998 to 1999. The mean age of the entire cohort was 52.5 years (range, 29-64 years). The shells were solid and hydroxyapatite (HA) -coated, liners were argon-sterilized UHMWPE, and head size was 28 mm. The minimum clinical followup was 56 months (mean, 65 months; range, 56-77 months); minimum 5-year radiographs were available for 62 of the 68 patients. Wear analysis of digitized anteroposterior (AP) radiographs was performed with a computerized method. Demographic data were comparable in the two groups. Mean femoral head penetration rate was similar in the two types of heads (CoCr: 0.25 mm/year; range, 0.21-0.33 mm/year; Zr: 0.23 mm/year; range, 0.20-0.29 mm/year), as was mean linear wear (CoCr: 1.22 mm; range, 0.28-3.78 mm; Zr: 1.11 mm; range, 0.15-2.05 mm). There were no revisions. These data support skepticism regarding the clinical wear advantage of Zr compared with CoCr femoral heads. The explanation for the clinical similarity of wear, despite the theoretical advantages of ceramic heads, needs further investigation. Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Wear resistance of artificial hip joints with poly(2-methacryloyloxyethyl phosphorylcholine) grafted polyethylene: Comparisons with the effect of polyethylene cross-linking and ceramic femoral heads

Aseptic loosening of artificial hip joints induced by wear particles from the polyethylene (PE) liner remains the ruinous problem limiting their longevity. We reported here that grafting with a polymer, poly(2-methacryloyloxyethyl phosphorylcholine (MPC)) (PMPC), on the PE liner surface dramatically decreased the wear production under a hip joint simulator condition. We examined that the effect of properties of both PE by cross-linking and femoral head by changing the materials on wearing properties of PE. The PMPC grafting on the liners increased hydrophilicity and decreased friction torque, regardless of the cross-linking of the PE liner or the difference in the femoral head materials. During the hip joint simulator experiments (5 × 10 6 cycles of loading), cross-linking caused a decrease of wear amount and a reduction of the particle size, while the femoral head materials did not affect it. The PMPC grafting abrogated the wear production, confirmed by almost no wear of the liner surface, independently of the liner cross-linking or the femoral head material. We concluded that the PMPC grafting on the PE liner surpasses the liner cross-linking or the change of femoral head materials for extending longevity of artificial hip joints.

Protrusio of a Ceramic Femoral Head Through the Acetabular Metallic Shell, Extensive Metallosis and ‘Bubble Sign’

A 24-year-old patient with a history of juvenile rheumatoid arthritis underwent a primary cementless left total hip arthroplasty (THA). The original THA consisted of an Optifix 54 cup with a 3-mm thick polyethylene liner, an Optifix size 4 stem (Smith & Nephew Richards, Memphis, Tennessee) and a Biolox aluminum 32-mm femoral head. Fourteen years later, radiographs demonstrated extensive wear of the polyethylene liner resulting in direct articulation and abrasion wear of the ceramic femoral head on the cup and a bubble sign. This article presents a case of a catastrophic failure of a ceramic/polyethylene bearing with destruction of the polyethylene liner and the metallic shell and protrusio of the nonfractured ceramic head through the metallic shell. To our knowledge this is the first description of extensive metallosis and subsequent radiograph bubble sign not presenting as a result of wear of a metal-on-metal articulation. At the time of revision surgery-Hydrocel TNT Monoblock 58 cup (Zimmer, Warsaw, Indiana), Wagner 265/14 stem (Zimmer), and a Co/Cr 28-mm head-copious metallic debris was seen both macroscopically and histologically, with the ceramic head protruding behind the metallic shell. Multiple factors may have been responsible for this failure including a thin polyethylene shell, a suboptimal locking mechanism, gamma in air sterilization for polyethylene, multiple screw-holes that reduce the contact surface between shell and polyethylene, the rough surface on the inside of the shell and non-articular wear at the metal polyethylene interface within the acetabular component and the high demands of this active young patient.

Medium-term Analysis of Modern Ceramic-On-Ceramic Bearing in THA

A variety of different bearing surfaces have been used to avoid osteolysis following hip replacement. We report a retrospective review of medium-term results of a modern ceramic-ceramic bearing (Biolox, CeramTec, Plochingen, Germany) and uncemented components (Alpha Cera Fit Alphanorm, Lassnitzhohe, Austria) in 107 hip arthroplasties. The clinical outcome based on serial radiographs and scoring was assessed with a minimum follow-up of 7 years (mean, 7, 6 years; range, 7, 1-8, 3 years). The average age of the patients at surgery was 64, 6 + 11, 7 years (range: 21-88 years). The mean Harris hip score was 90, 4 (range, 84, 7-99, 2). Three patients with an extra long femoral neck experienced fracture of the ceramic femoral head, resulting in cessation of use of this combination. Radiological evaluation did not reveal any signs of lysis or loosening. Massive heterotopic ossification was seen in three patients. Medium-term follow-up showed excellent clinical and radiological results. Continued follow-up will be required to determine if this ceramic-on-ceramic bearing is associated with extended survivorship.

Optimization of the stress distribution in ceramic femoral heads by means of finite element methods

Ceramic ball heads for total hip replacement are highly loaded in vivo and must meet the sternest requirements concerning strength and safety. High stresses inside the ball head originate from the press fit between the conical stem (made of titanium alloy or steel) and the borehole of the ball. The aim of this study was the development of an optimized contour at the fillet inside the ball head by means of numerical methods, in order to reduce local stress concentrations. The computer-aided optimization method was applied on the customary engineering fillet radius to reduce local stress peaks. The local notch stress of the examined ball head design was reduced by up to 27 per cent for the relevant load cases. Verification by rupture testing of prototypes turned out to be difficult for axisymmetric load cases, since the static fracture load is governed by the hoop stresses in the contact area of the taper (global maximum), thus making it difficult to prove a local improvement. The sensitivity of the design to asymmetric loading was clearly shown (varying the load angle and bearing type). Stress relocation in the ball-stem interface at higher burst loads indicated the necessity of optimizing each ceramic femoral head design individually (i.e. for different borehole depths).

Severe Cobalt Intoxication Due to Prosthesis Wear in Repeated Total Hip Arthroplasty

Our study describes a 55-year-old man with a total hip prosthesis (ceramic femoral head and polyethylene [PE] inlay). After a fall, the ceramic head broke into several pieces, and a subsequent revision surgery with metal femoral head and PE inlay was performed. Three months later, the so far healthy patient complained of multiorganic symptoms. The subsequent clinical examinations revealed hypothyroidism, peripheral neuropathy, and cardiomyopathy for the first time. In a second revision surgery, a massive deterioration of the metal femoral head by overlooked particles of the broken ceramic head was found. The cobalt concentration in blood exceeded a never before observed level. After replacement of the scraped femoral head, the cobalt concentration decreased considerably, and most of the symptoms disappeared.

Similar Wear in Total Hip Arthroplasties with Metallic or Zirconia Femoral Heads

Ceramic femoral heads have been used in an attempt at reducing polyethylene wear of total hip arthroplasties. Clinical results with zirconia femoral heads have been mixed. This study was undertaken to compare the polyethylene wear and incidence of periprosthetic osteolysis in total hip replacements performed using a 28-mm zirconia versus a 28-mm cobalt chromium femoral head. Thirty-five hips with a 28-mm cobalt chromium head and 68 hips with a 28-mm zirconia head were evaluated after a minimum follow-up of 2 years (average, 4.0 years; range, 2.0 to 9.1 years). A monoblock acetabular component was used in all patients. Polyethylene wear was measured in serial radiographs from 58 of the hips utilizing a computer-assisted vector wear technique. Periacetabular osteolysis developed in three patients (two with a zirconia head and one with a cobalt chromium head). The total wear and the annual wear rate were 0.48 mm and 0.11 mm/year for the cobalt chromium heads and 0.53 mm and 0.14 mm/year for the zirconia heads, respectively. We found no benefit with respect to the rate of polyethylene wear or incidence of osteolysis with the use of zirconia femoral heads.

Failure analysis of in vivo fractured ceramic femoral heads

Ceramics are more and more used for hip joint implants due to their excellent biocompatibility, longevity, corrosion and wear resistance. Despite these excellent material properties, their fracture toughness is low compared to metals. Various studies reported the probability of in vivo fracture occurring on an implanted ceramic femoral head is in the range of 0.004–0.05%. Besides material flaws and overloading, improper handling during implantation may induce fractures of the ceramic ball head on the long term. Even though the exact cause of failure could not be clarified in most of the cases, there is strong suspicion that the presence of biological contaminants may constitute the primary cause of failure. Asymmetric wear traces observed on fragments of in vivo fractured alumina femoral head endorse the assumption that a non-uniform load was introduced in the ball head. This study focuses on the influence of blood and bone chips located in the stem–ball interface and of scratches on the metal tapers on the strength of alumina ball heads. Mechanical tests on 26 samples according to ISO 7206-10 were performed to identify the effect of contaminants and altered taper on the static fracture load. The experimental study showed that relatively small contaminants induce considerable decreases of the static fracture load. A blood drop of 30 mg reduced the fracture load by more than 60% while a bone chip as small as 4 mg reduced it to less than half the reference fracture load. In a third experimental series, the change of fracture load with a 5–10 mm scratch on the stem was found to be in the range of the standard deviation and thus no clear influence could be observed. Since any alteration of the interface between metal taper and ceramic ball head through contaminants yields a non-uniform load introduction leading to a reduction of the static fracture load, an absolute clean interface is of primary importance.

Fracture-Dissociation of Ceramic Liner

The use of BIOLOX delta ceramic (CeramTec AG, Plochingen, Germany) has been increasing. This ceramic prevents cracking by restraining the phase transformation due to the insertion of nano-sized, yttria-stabilized tetragonal zirconia into the alumina matrix. This restrains the progress of cracking through the formation of platelet-like crystal or whiskers due to the addition of an oxide additive. We observed a case of BIOLOX delta ceramic liner (CeramTec AG) rim fracture 4 months postoperatively. Radiographs showed that the ceramic liner was subluxated from the acetabular cup. Scratches on the acetabular cup and femoral neck were seen, and the fracture was visible on the rim of the liner. Under electron microscope, metal particle coatings from the ceramic liner were identified. The ceramic liner, fracture fragments, and adjacent tissues were removed and replaced with a ceramic liner and femoral head of the same size and design. We believe the mechanism of the fracture-dissociation of the ceramic liner in this case is similar to a case of separation of the ceramic liner from the polyethylene shell in a sandwich-type ceramic-ceramic joint. To prevent ceramic liner fracture-dissociation, the diameter of the femoral neck needs to be decreased in a new design, while the diameter of the femoral head needs to be increased to ensure an increase in range of motion.

Catastrophic Failure of Ceramic-Polyethylene Bearing Total Hip Arthroplasty

Complications of ceramic-polyethylene bearing total hip arthroplasty (THA) include osteolysis, loosening, dislocation, and component failure. Catastrophic acetabular component failure involves severe damage to both the polyethylene liner and metal shell. This case study presents the first reported complete wear-through of the acetabular portion of a ceramic-polyethylene arthroplasty presenting as a dislocation and a review of the literature. In this study, a patient's alumina ceramic femoral head penetrated the polyethylene liner and titanium shell and presented as a dislocated THA. The contributing factors for this catastrophic failure include young patient age, high activity level, thin polyethylene liner, backside wear, component positioning, polyethylene sterilization with γ irradiation in air, and lack of appropriate follow-up. Revision THA was performed without complications.

Tribological and material analyses of retrieved alumina and zirconia ceramic heads correlated with polyethylene wear after total hip replacement

It has been suggested that the wear of ultra-high molecular weight polyethylene (UHMWPE) in total hip replacement is substantially reduced when the femoral head is ceramic rather than metal. However, studies of alumina and zirconia ceramic femoral heads on the penetration of an UHMWPE liner in vivo have given conflicting results. The purpose of this study was to examine the surface characteristics of 30 alumina and 24 zirconia ceramic femoral heads and to identify any phase transformation in the zirconia heads. We also studied the penetration rate of alumina and zirconia heads into contemporary UHMWPE liners. The alumina heads had been implanted for a mean of 11.3 years (8.1 to 16.2) and zirconia heads for a mean of 9.8 years (7.5 to 15). The mean surface roughness values of the explanted alumina heads (Ra 40.12 nm and Rpm 578.34 nm) were similar to those for the explanted zirconia heads (Ra 36.21 nm and Rpm 607.34 nm). The mean value of the monoclinic phase of two control zirconia heads was 1% (0.8% to 1.5%) and 1.2% (0.9% to 1.3%), respectively. The mean value of the monoclinic phase of 24 explanted zirconia heads was 7.3% (1% to 26%). In the alumina group, the mean linear penetration rate of the UMWPE liner was 0.10 mm/yr (0.09 to 0.12) in hips with low Ra and Rpm values (13.22 nm and 85.91 nm, respectively). The mean linear penetration rate of the UHMWPE liner was 0.13 mm/yr (0.07 to 0.23) in hips with high Ra and Rpm values (198.72 nm and 1329 nm, respectively). This difference was significant (p = 0.041). In the zirconia head group, the mean linear penetration rate of the UHMWPE liner was 0.09 mm/yr (0.07 to 0.14) in hips with low Ra and Rpm values (12.78 nm and 92.99 nm, respectively). The mean linear penetration rate of the UHMWPE liner was 0.12 mm/yr (0.08 to 0.22) in hips with high Ra and Rpm values (199.21 nm and 1381 nm, respectively). This difference was significant (p = 0.039). The explanted zirconia heads which had a minimal phase transformation had similar surface roughness and a similar penetration rate of UHMWPE liner as the explanted alumina head.

Die anatomisch angepaßte Endoprothese des proximalen Femurendes

The marrow-cavities of several human femora were cleaned and filled with plastics; the femoral component design was developed based on these moulds. Different sizes of the stem were obtained by scaling down the biggest mould in steps of 10%. The stem has an oval cross-section and is twisted similar to the form of the marrow-cavity; therefore different designs for the left and right femur are necessary. As the marrow-cavity of the femur tapers down to the middle of the shaft the length of the prosthetic stem cannot be selected arbitrarily. The stem must end above the narrowest site of the cavity. Data are presented. To avoid disadvantageous frictional stresses between the collar of the prosthesis and the plane of resection of the femoral neck both must be aligned perpendicular to the most common direction of the load of the hip joint. Therefore a step-like osteotomy of the femoral neck becomes necessary without disturbing the calcar femorale instead of an inclined osteotomy. A firm contact between the femoral wall and the collar, which forms an angle of 64 degrees with the axis of the femoral shaft, guarantees that only small frictional stresses occur between collar and femoral cortex if the load of the hip joint varies within the physiological range. A set of ceramic femoral heads with three different conical borings yield different lengths of the neck of the prosthesis. Independent of which femoral head and which size of prosthesis are chosen the direction of the maximum hip load in any case thrusts the contact area between collar and femoral wall. Thus dangerous tilting moments round the medial calcar femorale do not occur, the incidence of a fracture of the prosthesis shaft is therefore reduced. After implantation of the anatomically designed femoral component both remodeling and resorption of the calcar femorale are observed. This reaction is independent of the kind of fixation, i.e. if a smooth stem was fixed with cement or a stem with a porous, cancellous bone-like metallic surface was implanted without cement fixation.(ABSTRACT TRUNCATED AT 250 WORDS)

Fracture of an Alumina Femoral Head Used in Ceramic-on-Ceramic Total Hip Arthroplasty

A case report regarding the fracture of an alumina ceramic femoral head used in ceramic-on-ceramic total hip arthroplasty is presented. The patient, who was seen in the emergency room with pain, grinding, and instability in the hip immediately after a slip-without-fall event, also reported having fallen from a height of 8 ft 6 months earlier. Characterization of the alumina fracture surfaces by light and scanning electron microscopy suggests that the previous fall may have favored the nucleation and growth of subcritical cracks in the ceramic, which lead to fracture during the slip-without-fall event. The case report addresses the significance of impact trauma on the structural integrity of ceramic materials, which should not be ignored by patient or physician regardless of perceived severity.

Clinical Results for 19 to 21 Years on Total Hip Prosthesis with Ceramic Head Combined with UHMWPE Socket

In total hip prosthesis (THP), we have been using alumina ceramic femoral heads to reduce polyethylene debris and the modified cementing technique, which was named “interface bioactive bone cement (IBBC)” method to improve implant fixation. In this study, we investigated the long-term clinical performance of THPs with an alumina ceramic head and IBBC method. From 1986 to 1988, 285 joints (215 patients) were operated on by a senior surgeon, and 265 joints (192 patients) could be followed up. The presence of radiolucent lines, loosening, osteolysis and ultrahigh-molecular-weight polyethylene (UHMWPE) socket wear were observed. In IBBC, a radiolucent line appeared as a ’space’, and loosening appeared as a ’separation’ between the HA layer and the cement. A ‘space’ appeared in 3 joints (1.4%) on the acetabulum and in 4 joints (1.8%) on the femur, while a ‘separation’ appeared in 3 joints (1.4%) on the acetabulum. Osteolysis was noted in 1 joint (0.5%) on the acetabulum and in 2 joints (0.9%) on the femur. No revision surgery was required. In our previous study, we reported that the thickness of the socket affected its clinical wear rate and that the wear rate of sockets with an alumina ceramic head was 20% lower than that of sockets with a metal head. By reducing wear debris through the use of ceramic heads, osteolysis could be reduced. Long-term fixation of THPs to the bone has been achieved by using IBBC. Thus, the long-term clinical results of THPs with an alumina head that were fixed using IBBC were excellent.

Modular Ceramic Bearings on a CFRP Total Hip Replacement Femoral Stem

A modular ceramic femoral head was selected for use as the bearing on a novel carbon fibre reinforced plastic (CFRP) total hip replacement femoral stem. Mechanical testing was required to validate this novel combination of materials for load bearing implant application. The Ceramic Head-CFRP Stem Taper interface was tested under axial fatigue loads according to BS/ISO 7206-5, followed by static loading to failure. The assembly survived the fatigue loads and exceeded the required FDA post-fatigue strength by 50%. In parallel, the test was simulated in a Finite Element Analysis study, resulting in recommendations for the adhesive bonding technique used to attach the modular head to the CFRP stem to further improve its strength.

Alumina Femoral Head Fracture in Uncemented Total Hip Arthroplasty With a Ceramic Sandwich Cup

In total hip arthroplasty, insertion of a UHMWPE-coated ceramic sandwich liner dramatically reduces any risk related to the stiffness of the ceramic-ceramic coupling. We present a case of an alumina ceramic head fracture with a ceramic sandwich cup. The fracture occurred 16 months after the initial operation, without trauma. Impingement between the neck and posteroinferior portion of the liner rim had occurred. This was related to the traditional cross-legged sitting position of Koreans, which caused impingement between the neck and liner rim. Consequently, the taper became loose, and the resulting force bent the taper and fractured the head. We examined a peculiar case of ceramic femoral head fracture after implantation of an uncemented total hip arthroplasty with a ceramic sandwich cup and investigated the underlying cause.

Zirconia versus Co-Cr Femoral Heads in Total Hip Arthroplasty

Polyethylene wear and associated osteolysis are major limitations to the long-term success of total hip arthroplasty. In vitro laboratory studies suggest polyethylene wear in THA may be substantially reduced with ceramic femoral heads. We evaluated the potential value of zirconia ceramic on conventional polyethylene as an "alternative bearing" for total hip arthroplasty in a prospective, randomized clinical trial in comparison with femoral heads made of Co-Cr-Mo. Patients were evaluated with standardized clinical outcome instruments, and measurement of head penetration was performed with computerized wear measurement software. Study enrollment was halted because of a recall of the zirconia heads. At that time, 30 total hip arthroplasties with Co-Cr-Mo heads and 30 total hip arthroplasties with zirconia heads had been performed. Mean followup was similar for both groups (Co-Cr- Mo = 51.7 months; zirconia = 51.2 months). The mean annual head penetration rate was low and similar for both groups (Co-Cr-Mo = 0.060 mm/year; and zirconia = 0.055 mm/year). In view of the recently reported potential for zirconia ceramics to undergo monoclinic phase transformation in vivo, with resultant increased fracture risk and degradation of wear properties, we do not recommend use of zirconia femoral heads as an "alternative bearing" for total hip arthroplasty.