In a prospective study of 14 patients undergoing total hip replacement we have used dual-energy X-ray absorptiometry (DEXA) to investigate remodelling of the bone around two different designs of cementless femoral prosthesis. The bone mineral density (BMD) was measured at 12-weekly intervals for a year. Eight patients (group A) had a stiff, collarless implant and six (group B) a flexible isoelastic implant. Patients in group A showed a decrease in BMD from 14 weeks after operation. By 12 months, the mean loss in BMD was 27%, both medially and laterally to the proximal part of the implant. Those in group B showed an overall increase in BMD which reached a mean of 12.6% on the lateral side of the distal portion of the implant. Our results support the current concepts of the effects of stem stiffness and flexibility on periprosthetic remodelling

We revised seven alumina-blasted cementless hip prostheses (Ti-alloy stems, cp Ti threaded sockets) with low- or high-carbon Co-alloy bearings at a mean of 20.1 months after implantation because of pain and loosening. Histological examination of the retrieved periprosthetic tissues from two cases in which the implant was stable and three in which the socket was loose showed macrophages with basophilic granules containing metal and alumina wear particles and lymph-cell infiltrates. In one of the two cases of stem loosening the thickened neocapsule also contained definite lymphatic follicles and gross lymphocyte/plasma-cell infiltrates. Spectrometric determination of the concentration of elements in periprosthetic tissues from six cases was compared with that of joint capsules from five control patients undergoing primary hip surgery. In the revisions the mean concentration of implant-relevant elements was 693.85 μg/g dry tissue. In addition to Cr (15.2%), Co (4.3%), and Ti (10.3%), Al was predominant (68.1%) and all concentrations were significantly higher (p < 0.001) than those in the control tissues. The annual rates of linear wear were calculated for six implants. The mean value was 11.1 μm (heads 6.25 μm, inserts 4.82 μm). SEM/EDXA showed numerous fine scratches and deep furrows containing alumina particles in loosened sockets, and stems showed contamination with adhering or impacted alumina particles of between 2 and 50 μm in size

The tissues surrounding 65 cemented and 36 cementless total joint replacements undergoing revision were characterised for cell types by immunohistochemistry and for cytokine expression by in situ hybridisation. We identified three distinct groups of revised implants: loose implants with ballooning radiological osteolysis, loose implants without osteolysis, and well-fixed implants. In the cemented series, osteolysis was associated with increased numbers of macrophages (p = 0.0006), T-lymphocyte subgroups (p = 0.03) and IL-1 (p = 0.02) and IL-6 (p = 0.0001) expression, and in the cementless series with increased numbers of T-lymphocyte subgroups (p = 0.005) and increased TNFα expression (p = 0.04). For cemented implants, the histological, histochemical and cytokine profiles of the interface correlated with the clinical and radiological grade of loosening and osteolysis. Our findings suggest that there are different biological mechanisms of loosening and osteolysis for cemented and cementless implants. T-lymphocyte modulation of macrophage function may be an important interaction at prosthetic interfaces

The reduced stability of hydroxyapatite (HA)-coated implants in osteopenic conditions is considered to be a major problem. We therefore developed a model of a boosted cementless implantation in osteopenic rats. Twelve-week-old rats were either ovariectomised (OVX) or sham-operated (SO), and after 24 weeks plain or HA-coated implants were inserted. They were treated with either a prostaglandin EP4 receptor agonist (ONO-4819) or saline for one month. The EP4 agonist considerably improved the osteoporosis in the OVX group. Ultrastructural analysis and mechanical testing showed an improvement in the implant-bone attachment in the HA-coated implants, which was further enhanced by the EP4 agonist. Although the stability of the HA-coated implants in the saline-treated OVX rats was less than in the SO normal rats, the administration of the EP4 agonist significantly compensated for this shortage. Our results showed that the osteogenic effect of the EP4 agonist augmented the osteoconductivity of HA and significantly improved the stability of the implant-bone attachment in the osteoporotic rat model

In an attempt to increase the life of cementless prostheses, an hydroxyapatite-coated implant which releases a bisphosphonate has been suggested as a drug-delivery system. Our in vitro study was designed to determine the maximum dose to which osteoblasts could be safely exposed. Our findings demonstrated that zoledronate did not impair the proliferation of human osteoblasts when used at concentrations below 1 μ. m. Murine cells can be exposed to concentrations as high as 10 μ. m. . A concentration of 0.01% of titanium particles did not impair the proliferation of either cell line. Zoledronate affected the alkaline phosphatase activity of murine osteoblasts through a chelation phenomenon. The presence of titanium particles strongly decreased the alkaline phosphatase activity of murine osteoblasts. We did not detect any synergic effect of zoledronate and titanium particles on the behaviour of both human and murine osteoblasts

We investigated the circulating levels of the main cytokines involved in bone resorption (IL-1β, IL-6, TNF-α), prostaglandins (PGE. 2. ) and metalloproteases (MMP-1), as possible early markers of osteolysis, in the serum of eight patients with periprosthetic osteolysis and ten patients without osteolysis. All had received a cementless hip prosthesis (ABG-1). We also assessed the serum levels of IL-11 and TGF-β anti-inflammatory cytokines exerting protective effect on bone resorption. The mean serum levels of IL-1β, IL-6, TNF-α, TGF-β, MMP-1, and PGE. 2. in patients with periprosthetic osteolysis did not differ significantly from those of patients without osteolysis or from those of normal controls. IL-11 serum levels were not detectable at all in any of the patients, while they were detected within normal reference values in the control subjects (significant inverse correlation). We believe that circulating cytokines cannot be regarded as markers of osteolysis, a condition characterised by a local inflammation without systemic signs of inflammation. On the contrary, the undetectable levels of IL-11 in implanted patients could provide evidence for a lack of balance between pro- and anti-inflammatory cytokines in these patients

We collected 16 samples of the membrane which surrounds loose hip prostheses from patients undergoing revision operations for aseptic loosening. To serve as the control group, samples of the synovial tissue and the fibrous capsular tissue were collected from 11 patients undergoing primary hip arthroplasties. Analyses of the expression levels of inducible nitric oxide synthase (iNOS), tumour necrosis factor-α (TNF-α), and cytosolic phospholipase A. 2. (cPLA. 2. ) mRNAs were performed by a reverse transcription polymerase chain reaction, and the content of nitrite was measured by the Griess reaction using sodium nitrite as the standard. The expression levels of iNOS, TNF-α, and cPLA. 2. mRNAs in the membranes were significantly higher than those in the control samples (p < 0.05). The expression levels of iNOS mRNA and the nitrite content in the membranes significantly correlated with those of TNF-α and cPLA. 2. mRNAs, respectively. In addition, the expression levels of iNOS, TNF-α, and cPLA. 2. mRNAs were significantly higher in membranes from cementless than in those from cemented implants (p < 0.05). Our results suggest that the expression levels of iNOS, TNF-α, and cPLA. 2. mRNAs in the membranes are regulated by closely-related mechanisms and that these have a significant role in aseptic loosening

We have studied the effect of hydroxyapatite (HA) coating in 15 ovariectomised and 15 normal rats which had had a sham procedure. Twenty-four weeks after operation, HA-coated implants were inserted into the intramedullary canal of the right femur and uncoated implants into the left femur. The prostheses were removed four weeks after implantation. Twelve specimens in each group had mechanical push-out tests. Sagittal sections of the other three were evaluated by SEM. The bone mineral density (BMD) of the dissected left tibia was measured by dual-energy x-ray absorptiometry. The difference in BMD between the control and ovariectomised tibiae was 35.01 mg/cm. 2. (95% CI, 26.60 to 43.42). The push-out strength of the HA-coated implants was higher than that of the uncoated implants in both groups (p < 0.0001), but the HA-coated implants of the ovariectomised group had a reduction in push-out strength of 40.3% compared with the control group (p < 0.0001). Our findings suggest that HA-coated implants may improve the fixation of a cementless total hip prosthesis but that the presence of osteoporosis may limit the magnitude of this benefit

Two acetabula which contained large bone allografts introduced at revision arthroplasty were obtained at post-mortem. The allografts had been placed in superior defects to support cementless acetabular components, and both hips were functioning well at the time of death. Clinical radiographs demonstrated apparent healing of graft to host bone, no graft collapse and stability of the acetabular components. Microscopic examination of sections through these specimens showed that the bulk allografts were encapsulated in fibrous tissue. Vascularity was increased at the host-graft interface, but there was limited evidence of bone union between the graft and the host. In the few areas where union had occurred, revascularisation extended no more than 2 mm beyond the graft-host interface. Within the body of the graft, the acellular matrix of trabecular bone maintained structural integrity up to 48 months after surgery. In areas where the allograft was adjacent to an implant, there was fibrous tissue orientated parallel to the implant surface. The acetabulum which contained a porous-coated component showed evidence of bone growth into the porous surface where it was in contact with viable host bone. No ingrowth occurred in areas where the porous coating was in contact with the graft. Although the grafts were functioning well, allograft revascularisation and remodelling were minimal, and the radiological appearance of healing did not correlate with histological findings

Bone growth into cementless prosthetic components is compromised by osteoporosis, by any gap between the implant and the bone, by micromotion, and after the revision of failed prostheses. Recombinant human transforming growth factor-β1 (rhTGF-β1) has recently been shown to be a potent stimulator of bone healing and bone formation in various models in vivo. We have investigated the potential of rhTGF-β1, adsorbed on to weight-loaded tricalcium phosphate (TCP) coated implants, to enhance bone ongrowth and mechanical fixation. We inserted cylindrical grit-blasted titanium alloy implants bilaterally into the weight-bearing part of the medial femoral condyles of ten skeletally mature dogs. The implants were mounted on special devices which ensured stable weight-loading during each gait cycle. All implants were initially surrounded by a 0.75 mm gap and were coated with TCP ceramic. Each animal received two implants, one with 0.3 μg rhTGF-β1 adsorbed on the ceramic surface and the other without growth factor. Histological analysis showed that bone ongrowth was significantly increased from 22 ± 5.6% bone-implant contact in the control group to 36 ± 2.9% in the rhTGF-β stimulated group, an increase of 59%. The volume of bone in the gap was increased by 16% in rhTGF-β1-stimulated TCP-coated implants, but this difference was not significant. Mechanical push-out tests showed no difference in fixation of the implant between the two groups. Our study suggests that rhTGF-β1 adsorbed on TCP-ceramic-coated implants can enhance bone ongrowth

Our aim was to determine if the serum levels of bone-resorbing cytokines (IL-1β, TNF-α, IL-6, GM-CSF) are altered in patients with aseptic loosening of a total hip prosthesis, and if such levels are influenced by the type of implant. We determined cytokine levels in sera from 35 patients before revision for failed total hip arthroplasty and compared them with those in 25 healthy donors. We also assessed the soluble receptor of interleukin-2 (sIL-2r) in serum as an indication of a specific immune reaction against the implant. Our findings showed that the sIL-2r and TNF-α serum level did not change. The IL-6 level was not significantly altered, but was higher in patients with TiAlV prostheses than in those with a CrCoMo implant and in patients with cemented prostheses. The IL-1β level was found to be higher in those with a TiAlV cemented prosthesis than in the control group (p = 0.0001) and other groups of patients (p = 0.003 v uncemented TiAlV, p = 0.01 v cemented CrCoMo, p = 0.001 v uncemented CrCoMo). The GM-CSF level significantly increased in patients compared with healthy subjects (p = 0.008), and it was higher in those with cemented than with uncemented implants (p = 0.01). Only patients with cementless CrCoMo prostheses had levels of GM-CSF similar to those of the control group. The highest GM-CSF concentrations were observed in patients treated with non-steroidal anti-inflammatory drugs (NSAIDs) in the last months before revision (p = 0.04). In addition, when massive osteolysis was observed, the level of GM-CSF tended to decrease to that of the control group

We have reviewed 70 patients with bilateral simultaneous total hip arthroplasties to determine the rate of failure and to compare polyethylene wear and osteolysis between an implant with a cobalt-chrome head and Hylamer liner with that of a zirconia head and Hylamer liner. The mean thickness of the polyethylene liner was 11.0 mm (8.8 to 12.2) in the hip with a zirconia head and 10.7 mm (8.8 to 12.2) in that with a cobalt-chrome head. At follow-up at 6.4 years no acetabular or femoral component had been revised for aseptic loosening and no acetabular or femoral component was loose according to radiological criteria in both the cemented and cementless groups. The mean rate of linear wear and annual wear rate were highest in the 22 mm zirconia femoral head (1.25 mm (SD 1.05) and 0.21 mm (SD 0.18), respectively) and lowest in the 22 mm cobalt-chrome femoral head (0.70 mm (SD 0.39) and 0.12 mm (SD 0.07), respectively). The mean volumetric wear was highest in the 28 mm zirconia femoral head (730.79 mm. 3. ) and lowest in the 22 mm cobalt-chrome femoral head (264.67 mm. 3. ), but if the results were compared by size of the femoral head and type of material there was no statistical difference (p > 0.05). Sequential measurements of annual wear showed that the zirconia femoral head had a relatively higher rate of penetration than the cobalt-chrome head over the first three years; thereafter the rate of wear was reduced and compared favourably with that of cobalt-chrome heads. There was a statistically significant relationship between the wear of the polyethylene liner and the age of the patient, male gender and the degree of abduction angle of the cup, but not diagnosis, weight, hip score, range of movement, or amount of anteversion. Osteolysis was identified on both sides of the acetabulum in six patients (9%). Of 12 hips with acetabular osteolysis, six had a 28 mm cobalt-chrome femoral head and the remaining six a 28 mm zirconia head. Osteolysis was observed in zones 1A and 7A of the femur in two hips (3%) with a 28 mm zirconia head (cemented hip) and in four (6%) with a 28 mm cobalt-chrome femoral head (cementless hip). Our findings suggest that although the performance of a zirconia femoral head with a Hylamer liner was not statistically different from that of a cobalt-chrome femoral head and Hylamer liner, there was a trend for the zirconia head to be worse than the cobalt-chrome femoral head

Finite element analysis was used to examine the initial stability after hip resurfacing and the effect of the procedure on the contact mechanics at the articulating surfaces. Models were created with the components positioned anatomically and loaded physiologically through major muscle forces. Total micromovement of less than 10 μm was predicted for the press-fit acetabular components models, much below the 50 μm limit required to encourage osseointegration. Relatively high compressive acetabular and contact stresses were observed in these models. The press-fit procedure showed a moderate influence on the contact mechanics at the bearing surfaces, but produced marked deformation of the acetabular components. No edge contact was predicted for the acetabular components studied.

It is concluded that the frictional compressive stresses generated by the 1 mm to 2 mm interference-fit acetabular components, together with the minimal micromovement, would provide adequate stability for the implant, at least in the immediate post-operative situation.

Bone surface strains were measured in cadaver femora during loading prior to and after resurfacing of the hip and total hip replacement using an uncemented, tapered femoral component. In vitro loading simulated the single-leg stance phase during walking. Strains were measured on the medial and the lateral sides of the proximal aspect and the mid-diaphysis of the femur. Bone surface strains following femoral resurfacing were similar to those in the native femur, except for proximal shear strains, which were significantly less than those in the native femur. Proximomedial strains following total hip replacement were significantly less than those in the native and the resurfaced femur.

These results are consistent with previous clinical evidence of bone loss after total hip replacement, and provide support for claims of bone preservation after resurfacing arthroplasty of the hip.

An experimental sheep model was used for impaction allografting of 12 hemiarthroplasty femoral components placed into two equal-sized groups. In group 1, a 50:50 mixture of ApaPore hydroxyapatite bone-graft substitute and allograft was used. In group 2, ApaPore and allograft were mixed in a 90:10 ratio. Both groups were killed at six months. Ground reaction force results demonstrated no significant differences (p > 0.05) between the two groups at 8, 16 and 24 weeks post-operatively, and all animals remained active. The mean bone turnover rates were significantly greater in group 1, at 0.00206 mm/day, compared to group 2 at 0.0013 mm/day (p < 0.05). The results for the area of new bone formation demonstrated no significant differences (p > 0.05) between the two groups. No significant differences were found between the two groups in thickness of the cement mantle (p > 0.05) and percentage ApaPore-bone contact (p > 0.05).

The results of this animal study demonstrated that a mixture of ApaPore allograft in a 90:10 ratio was comparable to using a 50:50 mixture.

Studies on the migration of an implant may be the only way of monitoring the early performance of metal-on-metal prostheses. The Ein Bild Roentgen Analyse - femoral component analysis (EBRA-FCA) method was adapted to measure migration of the femoral component in a metal-on-metal surface arthroplasty of the hip using standard antero-posterior radiographs. In order to determine the accuracy and precision of this method a prosthesis was implanted into cadaver bones. Eleven series of radiographs were used to perform a zero-migration study. After adjustment of the femoral component to simulate migration of 3 mm the radiographs were repeated. All were measured independently by three different observers.

The accuracy of the method was found to be ± 1.6 mm for the x-direction and ± 2 mm for the y-direction (95% percentile). The method was validated using 28 hips with a minimum follow-up of 3.5 years after arthroplasty. Seventeen were sound, but 11 had failed because of loosening of the femoral component. The normal (control) group had a different pattern of migration compared with that of the loose group. At 29.2 months, the control group showed a mean migration of 1.62 mm and 1.05 mm compared with 4.39 mm and 4.05 mm in the failed group, for the centre of the head and the tip of the stem, respectively (p = 0.001). In the failed group, the mean time to migration greater than 2 mm was earlier than the onset of clinical symptoms or radiological evidence of failure, 19.1 versus 32.2 months (p = 0.001) and 24.8 months (p = 0.012), respectively.

EBRA-FCA is a reliable and valid tool for measuring migration of the femoral component after surface arthroplasty and can be used to predict early failure of the implant. It may be of value in determining the long-term performance of surface arthroplasty.

This study explored the relationship between the initial stability of the femoral component and penetration of cement into the graft bed following impaction allografting.

Impaction allografting was carried out in human cadaveric femurs. In one group the cement was pressurised conventionally but in the other it was not pressurised. Migration and micromotion of the implant were measured under simulated walking loads. The specimens were then cross-sectioned and penetration of the cement measured.

Around the distal half of the implant we found approximately 70% and 40% of contact of the cement with the endosteum in the pressure and no-pressure groups, respectively. The distal migration/micromotion, and valgus/varus migration were significantly higher in the no-pressure group than in that subjected to pressure. These motion components correlated negatively with the mean area of cement and its contact with the endosteum.

The presence of cement at the endosteum appears to play an important role in the initial stability of the implant following impaction allografting.