Purpose of the study: Cementless hydroxyapatite-coated prostheses have proven their reliability, but how about their longevity? The intimate contact between the receiver bone and the prosthetic implant, due to the bone ongrowth, allows ‘union’ between the inert and living material. The purpose of this restrospective study was to evaluate the behavior of an anatomic femoral hydroxyapatite-coated stem at long-term follow-up. Materials and Methods: One hundred and eleven total hip arthroplasties were performed with a ABG 1 HA-Coated hip prosthesis (ABG, Stryker Newbury, England) in 101 patients, by one senior operator. A posterolateral approach was done every time. Average patient age at surgery was 61, 3 years [33–83]. Results: Average follow-up was 13 years [10–17,5]. Seventy five THA were reviewed, 21 were dead and 15 were lost. Clinical outcome have been good. The average preoperative Harris hip score and Postel Merle d’Aubigné score were 56,7 and 11,8, which rose to 87,3 and 16,3 at the longest follow-up. Most patients were satisfied with the outcome, no thigh pain was deplored. There were sixteen revisions: 1 bipolar revision for loosening of both component, 14 cup revisions for osteolysis (11) and loosening (3) and 1 stem revision for periprosthetic fracture. Radiographic changes were consistent with bone remodeling. Osteointegration was achieved in 98,7%. Proximal stress-shielding was noted in 36,4%, osteolysis was developed in 66,7% focused essentially in gruen zones 1a and 7a and never below HA coating. Cancellous densifications were found to be mainly in zones 2, 6, 9 and 13 (92,7%, 94,2%, 91,3% and 85,5%), extending distally in zones 3, 5, 10 and 12 (33,3%, 31,9%, 34,8% and 39,1%). A femoral shaft hypertrophy was noted in 27,5%. Discussion: In this serie, the global survivorship of ABG 1 THA at 13 years of follow-up was 78,7%. Acetabular cup survivorship was 80%. Failure of acetabular cup was well explained by osteolysis and high wear rate. Stem survivorship was 97,3% and the failure rate of femoral stem due to aseptic loosening was only 1,3%. Excellent results of femoral stem were due to the good osteointegration, cause of the anatomic design of the stem and the hydroxyapatite coating. Conclusion: The results of our series have proven that anatomic cementless stem with HA coating provide a long term reliability and longevity

Purpose of the study: The pertinence of locking for major femoral revision remains a controversial issue. We conducted a retrospective multicentric study to assess the benefit and potential clinical and radiographic complications after using a long locked stem entirely coated with hydroxyapatite.

Material and methods: Our series included 77 patients (42 women, 35 men), mean age 71 years (range 34–90) reviewed at minimum one year. A modular implant was used; the long curved stem allowed total integration. Screws guaranteed distal locking. There were 71 revision THA on trochanteric-shaft fractures, three shaft nonunions, 34 aseptic loosenings, 9 septic loosening, 21 fractures on prosthesis, 6 implant failures and one instability. Seventy percent of patients had stage 3 and 4 bone lesions. Mean follow-up was 60 months.

Results: At last follow-up, 90% of patients were satisfied or very satisfied. The mean Harris function score improved from 32 to 83 and the PMA from 7 to 15. Sixty-four patients were pain free and 22% had pain solely under stress. There were 15 bone complications: dislocation (n=3), early infection (n=3 including 2 recurrences), implant failure (n=2), secondary femur fracture (n=5). Stem survival was 94% at nine years. Radiographically, total stem stability was noted in 73 patients (95%); instability was noted in four cases of fracture. Undeniable metaphyseal improvement was noted in 20% of cases, more modest improvement in 32%; the situation was considered unchanged in 31%. Locking was successful in all cases; cortical bone in contact with the locking screw was unchanged in 59 cases, slightly thickened in 16, including one case with a context of septic recurrence. The locking was dismantled in two cases (one empirically and one for pain), but the stem remained stable.

Discussion: Major damage to the femur can compromise stabilisation of the proximal or diaphyseal implants. Distal locking contributes to the initial mechanical stability, indispensable for secondary osteointegration of the implant. However, with total hydroxyapatite coating, rapid fixation in healthy zones is also crucial. Reconstruction of metaphyseal bone is not easy to quantify, but the absence of bone absorption is noteworthy.

The ABG stem (Anatomique Benoist Girard, How-medica) was realized of titanium alloy (TA6V) and it was designed to provide anchoring only at the femour’s metaphyseal portion. The long-term stability is achived by osteointegration of the implant at the metaphyseal region, which is coated with hydroxyapatite (HA) crystals. The plasma-sprayed HA coating has a tickness of 60 μm for the stem.

The current study presents radiographic outcomes of more than one hundred primary uncemented HA stems with a long-term follow-up. One hundred and eleven ABG hip arthroplasties were evaluated with a mean follow-up of 9.8 years. The radiographical findings have been classified observing Engh’s stability criteria according to Gruen’s subdivision of the periprosthetic femoral zones.

Dividing the hips into two different groups (in the first one the prosthesis implanted 11, 12 or 13 years ago and in the second one the prosthesis with a maximum age of 10 years) it’s possible to see as in the first group the radiolucent lines are quite reduced. Among the older prosthesis the percentage of radiolucent lines is 3.1% in zones 3 and 5 and 18.8% in zone 4. For what concerns the younger ones the percentage are 10.1% (zone 3), 21.5% (zone 4) and 15.2% (zone 5).

We believe that there is a load transfer from the metaphyseal to the metadiaphyseal portion of the femur without a worsening of the clinical outcomes. The absence of reactive lines and lucencies around the proximal HA-coated portion of the stem supports an excellent circumferential bony ingrowth in the metaphyseal area of the proximal femur. According to these percentages we can say that there’s less presence of radiolucency in the oldest prosthesis and it could be possible to argue that radiolucent lines tend to reduce along the time. This is probably due to the increase of the strength of the stem anchorage.

Periprosthetic femoral fractures (PFFs) remain a major concern following cementless total hip arthroplasty (THA). This study aimed to evaluate the association between different types of cementless tapered stems and the risk of postoperative PFF. A retrospective review of primary THAs performed at a single center from January 2011 to December 2018 included 3,315 hips (2,326 patients). Cementless stems were classified according to their design geometry using the system proposed by Radaelli et al. The incidence of PFF was compared between flat taper porous-coated stems (type A), rectangular taper grit-blasted stems (type B1), and quadrangular taper hydroxyapatite-coated stems (type B2). Multivariate regression analyses were performed to identify independent factors related to PFF. The mean follow-up duration was 61 months (range, 12‒139 months). Overall, 45 (1.4%) postoperative PFFs occurred. The incidence of PFF was significantly higher in type B1 stems than in type A and type B2 stems (1.8 vs. 0.7 vs. 0.7%; P=0.022). Additionally, more surgical treatments (1.7 vs. 0.5 vs. 0.7%; P=0.013) and femoral revisions (1.2 vs. 0.2 vs. 0%; P=0.004) were required for PFF in type B1 stems. After controlling for confounding variables, older age (P<0.001), diagnosis of hip fracture (P<0.001), and use of type B1 stems (P=0.001) were significant factors associated with PFF. Type B1 rectangular taper stems were found to have higher risks for postoperative PFF and PFF requiring surgical management than type A and type B2 stems in THA. Femoral stem geometry should be considered when planning for cementless THA in elderly patients with compromised bone quality

Introduction and Aims: This study evaluated the proximal femoral remodelling associated with three uncemented femoral prostheses of different designs and surface treatments. We hypothesised that less bone loss will occur over time with a titanium implant designed for proximal stress transfer compared to a more rigid stem that produces diaphyseal loading. Method: During total hip arthroplasty (THA), patients were implanted with either: AML cobalt-chrome alloy porous-coated stem (11 patients), Osteonics titanium alloy hydroxyapatite-coated stem (13 patients), or Sulzer titanium alloy hydroxyapatite-coated stem (eight patients). All patients followed the same surgical and post-surgical protocol for THA. Dual energy x-ray absorptiometry (DEXA) scans of the operated proximal femur were performed on all patients pre-operatively, three to seven days post-operatively, and then six weeks, six months, and annually up to five years post-operatively. Longitudinal changes in bone mineral density (BMD) were compared within and between the two groups. Results: Using the first post-op DEXA scan as baseline, the percent change in BMD (g/cm. 2. ) at one year was −17.06% in patients implanted with the AML stem. The percent change in BMD at one year was −3.06% in the Osteonics group and in the Sulzer group, the percent change in BMD at one year was −4.11%. The greater bone loss observed with the AML stem was found to be statistically different than the bone loss observed with the other two stems. These findings continued at three and five years post-operatively. Conclusion: There was a trend toward less bone atrophy and preservation of bone stock in patients implanted with both the HA and Sulzer stems. Extensively coated, diaphyseal-fitting, CoCr stems (AML) definitely caused greater bone loss, both proximally and in the diaphysis

Introduction: The results of total hip arthroplasty in patients with avascular necrosis of the hip have been variable. This study analyzed the clinical and radiographic outcome of young patients (mean age of 39 years) treated with a proximally hydroxyapatite-coated tapered stem. Materials and Methods: Sixty-seven patients (84 hips) treated with late-stage avascular necrosis of the hip with a proximally hydroxyapatite-coated tapered stem as part of their total hip arthroplasty was studied. There were 41 men and 26 women who had a mean age of 39 years (range, 18 to 80 years). Patients were followed both clinically and radiographically for a minimum of two years (mean of 3 years). Results: Overall, there were good and excellent clinical outcomes in 78 hips (93%). Fair results were found in five patients with persistent pain. There was only one stem loosening (obese patient with SLE). Radiographic zonal analysis revealed no evidence of impending failure or progressive radiolucencies. Discussion: Excellent short-term results were found with total hip arthroplasty in this difficult patient population. The proximally hydroxyapatite-coated tapered stem utilized in this study was useful in patients with avascular necrosis of the hip

We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) after twenty years, analysing polyethylene wear and osteolysis. 82 hips implanted between 1992 and 1995 were prospectively evaluated. Mean follow-up was 20.6 years (18–23). A hemispherical porous-coated cup matched to a proximally hydroxyapatite-coated anatomic stem. A 28mm PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position, eventual loosening and osteolysis were recorded over time. Penetration of the head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Six cups were revised due to wear and four cups because of late dislocation. All stems showed osseointegration and all cups appeared radiographically well-fixed. Six unrevised hips showed osteolysis on the acetabular side and two hips on the proximal femur. Creep at one year was 0.30±0.23 mm. Mean total femoral head penetration was 1.23mm at ten years, 1.52mm at 15 years and 1.92mm at 23 years. Overall mean wear was 0.12±0.1 mm/year and 0.09±0.06 mm/year after the creep period. Mean wear was 0.08±0.06 mm/year in hips without osteolysis and 0.14±0.03 mm/year in hips revised or hips with osteolysis (p<0.001). Although continued durable fixation can be observed with porous-coated cups and proximally hydroxyapatite-coated anatomic stems, true wear continues to increase at a constant level over time. PE wear remains as the main reason for osteolysis and revision surgery in uncemented THR after twenty years

Introduction. Durable bone fixation of uncemented porous-coated acetabular cups can be observed at a long-term, however, polyethylene (PE) wear and osteolysis may affect survivorship. Accurate wear measurements correlated with clinical data may offer unique research information of clinical interest about this highly debated issue. Objetive. We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) after twenty years analysing polyethylene wear and the appearance of osteolysis. Materials and Methods. 82 hips implanted between 1992 and 1995 were prospectively evaluated with a mean follow-up of 20.6 years (range, 18 to 23). A hemispherical porous-coated acetabular cup matched to a proximally hydroxyapatite-coated anatomic stem and a 28 mm standard PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position and the possible appearance of loosening and osteolysis were recorded over time. Penetration of the prosthetic head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Results. Six cups were revised due to wear and four due to late dislocation. All cups were radiographically well-fixed and all stems showed radiographic ingrowth. Six un-revised hips showed osteolysis on the acetabular side and two on the proximal femoral side. Creep at one year was 0.30 (±0.23) mm. Mean total femoral head penetration was 1.23 mm at 10 years, 1.52 mm at 15 years and 1.92 mm at 23 years. Overall mean wear was 0.12 (± 0.1) mm/year and 0.09 (±0.06) mm/year after the creep period. Mean wear was 0.08 (± 0.06) mm/year in hips without osteolysis and 0.14 (±0.03) mm/year in revised hips or with osteolysis (p<0.001). Conclusions. Although continued durable fixation can be observed with a porous-coated cups and a proximally hydroxyapatite-coated anatomic stem, true wear continues to increase at a constant level over time. PE wear remains as the main reason for revision surgery and osteolysis in uncemented THR after twenty years

Introduction. Durable bone fixation of uncemented porous-coated acetabular cups can be observed at a long-term, however, polyethylene (PE) wear and osteolysis may affect survivorship. Accurate wear measurements correlated with clinical data may offer unique research information of clinical interest about this highly debated issue. Objetive. We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) system after twenty years analysing polyethylene wear and the appearance of osteolysis. Materials and Methods. 82 hips implanted between 1992 and 1995 were prospectively evaluated. The mean follow-up was 20.6 years (range, 18 to 23). A hemispherical porous-coated acetabular cup matched to a proximally hydroxyapatite-coated anatomic stem and a 28 mm standard PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position and the possible appearance of loosening and osteolysis were recorded over time. Penetration of the prosthetic head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Results. Six cups were revised due to wear and four due to late dislocation. All cups were radiographically well-fixed and all stems showed radiographic ingrowth. Six un-revised hips showed osteolysis on the acetabular side and two on the proximal femoral side. Creep at one year was 0.30 (±0.23) mm. Mean total femoral head penetration was 1.23 mm at 10 years, 1.52 mm at 15 years and 1.92 mm at 23 years. Overall mean wear was 0.12 (± 0.1) mm/year and 0.09 (±0.06) mm/year after the creep period. Mean wear was 0.08 (± 0.06) mm/year in hips without osteolysis and 0.14 (±0.03) mm/year in revised hips or with osteolysis (p<0.001). Conclusions. Although continued durable fixation can be observed with a porous-coated cups and a proximally hydroxyapatite-coated anatomic stem, true wear continues to increase at a constant rate over time. PE wear remains as the main reason for revision surgery and osteolysis in uncemented THR and does not stop after twenty years

Background: According to the mid-term results obtained from the previous registry-based studies, survival of cementless stems for aseptic loosening in younger patients with primary osteoarthritis has been better than the survival of cemented stems. However, it has not been clear if the endurance against aseptic loosening of cementless cups is comparable to that of cemented cups. The aim of the present study was to analyze population-based long-term survival rates of the cemented and cementless total hip replacements in patients under the age of fifty-five years with primary osteoarthritis in Finland. Patients and Methods: Between 1980 and 2006, a total of 7310 primary total hip replacements performed for primary osteoarthritis in patients under the age of fifty-five years were entered in the Finnish Arthroplasty Registry. 4,032 of them fulfilled our inclusion criteria and were subjected to analysis. The implants included were classified in one of the three following groups: implants with a cementless, straight, proximally circumferentially porous-coated stem and a porous-coated press-fit cup (cementless group #1); implants with a cementless, anatomic, proximally circumferentially porous-coated and/ or hydroxyapatite-coated stem with a porous-coated and/or hydroxyapatite-coated press-fit cup (cementless group #2); and a cemented stem combined with a cemented all-polyethylene cup (the cemented group). Results: Cementless total hip replacements, as well as cementless stems and cups analyzed separately, had a significantly reduced risk of revision for aseptic loosening compared with cemented hip replacements. The 15-year survivorship of cementless stem groups for aseptic loosening was higher than that of cemented stems (89% and 90% vs. 72%). The 15-year survivorship of cementless press-fit porous-coated cups for aseptic loosening was higher than that of cemented cups (80% vs. 71%). When revision for any reason was the end point in survival analyses, however, there were no significant differences among the groups. Conclusions: Both cementless stems and cementless cups have better resistance to aseptic loosening than cemented implants in long term follow-up in younger patients. Even if liner-exchange revisions are taken into account, the long-term survival of cementless total hip replacements is comparable to that of cemented implants

Aims: The purpose of this study is to compare the clinical outcome, radiological integration and survivorship associated with a porous coated stem and those associated with a hydroxyapatite-coated stem in a consecutive serie of uncemented total hip replacements. Methods: Between 1992 and 1995, 188 primary uncemented hip arthroplasties were performed at our institution using either a proximal porous-coat or a fully HA-coated stem. Mean age and weight and distribution of sex and primary diagnosis were similar in both groups. Ninety-eight hips from the HA group (group 1) and 69 from the porous-coated group (group 2) had a complete clinical and radiographic follow-up. The average duration of follow-up period for group 1 and 2 was 10.12 and 9.8 years respectively (range,9 to 12). Parameters such as implant migration and bone remodelling were especially evaluated and compared in both groups on postoperative X-rays. Results: In group 2 , 8 hips (11.8%) needed revision for aseptic loosening and 24 additional hips (34.7%) showed non-progressive lucent lines; distal migration of the stem was seen in 9 cases(13.04%). In contrast no hip in group 1 required revision and all but two hips in this group showed radiological integration; no stem showed distal migration. Harris hip score at follow-up was better in group 1 (p= 0.05) due to a higher incidence of thigh pain in group 2 (23% vs 0%). Significant differences between both groups (p=0.02) were also observed in predicted rate of survival at 10 years with revision for aseptic loosening as the endpoint. Conclusion: In our series the HA-coated stem has provided significantly better outcomes in terms of clinical scores, radiological integration and survivorship rates than porous-coated stem

Introduction: In the last years, the use of second generation cementless anatomical stems has generated an increasing interest in primary total hip arthroplasty. They are believed to offer long term stability through appropriate stress transfer and bone remodelling in the proximal femur. We conducted a monocentric prospective study on a homogeneous series of total hip replacements performed with a cementless anatomic, hydroxyapatite-coated stem. The purpose of the study was to evaluate the contribution of this implant in terms of clinical and radiological results at a minimum 5-year follow-up. Material and Methods: The continuous homogeneous series included 176 THA performed between September 1997 and December 1998 by a single surgeon with the same implant system (SPS femoral stem and Hilock acetabular cup, Symbios Orthopédie SA). Indications were restricted to primary or secondary degenerative hip diseases. Revisions were excluded. Patients were reviewed for clinical performance (Harris hip score), satisfaction, and radiological outcome. The radiological analysis (implant migration, Ara and Engh scores, Brooker classification) was performed by an independent surgeon unaware of the clinical performance outcome. The survival curve was determined with the Kaplan-Meier method at 95% confidence interval, using exclusively implant revision as the criteria for failure. Results: The follow-up rate in the series was 93.2%. The five-year implant survival was 98.8%. Two revisions were recorded: one for early instability due to excessive joint laxity after surgery, one due to recurrent dislocation following improper cup positioning during surgery. The clinical improvement was obvious, as the Harris hip score improved significantly (p< 0.0001) from 32.9±1.2 preoperatively to 93.1±0.8 at five years follow-up. Pain was the item exhibiting the largest improvement with only 10.2% of patients complaining of mild pain at last follow-up. The radiological analysis revealed a high stability of the femoral implant with Ara and Engh scores reaching 5.0±0.2 and 20.7±0.5 respectively. The migration remained low at 2.4 mm ±0.3 (p=0.02) and had no incidence on the clinical outcome. Heterotopic ossifications at various grades were observed in a large proportion of patients (65.1%). The polyethylene wear rate was 0.075 mm/yr in the series, below most values commonly reported for Ø28mm PE inserts. Discussion: The survival rate of the SPS stem is comparable with that of other published series at same follow-up. Both the stem and cup implants used provided good clinical and radiological results at five years. The objectives of good integration and stability of the cementless anatomical stem appeared to be met, despite a significant rate of heterotopic ossifications. The excellent clinical and radiological results recorded at five years should be confirmed at longer follow-up

Purpose: The purpose of this work was to assess the quality of the bone reconstruction in contact with the long hydroxyapatite-coated locked femoral stem used in a consecutive series of patients undergoing revision total hip arthroplasty (RTHA). Material and methods: This series of 20 patients underwent RTHA for aseptic loosening (n=15) or septic loosening (n=5) of an AURA prosthesis. Mean age was 70.5 years. Mean time between insertion of the first stem and revision was 11 years for the aseptic patients and 2.6 years for the septic patients. Bony lesions of the femur were assessed with the SOFCOT classification: grade I=5, grade II=4, grade III=4, and grade IV=1. A transfemoral approach with a floating femoral segment was used in 14 patients and an endofemoral approach in six. The septic loosenings were reconstructed in two operative times in four patients and in one operation in one patient. An AURA reconstruction stem was used in 15 cases and a revision stem in five. A complementary cancellous bone graft with the endofemoral approach was used in six patients. Results: Two patients died. All others were reviewed at a mean follow-up of 26 months (range 12–46 months) for clinical and radiographic assessment (five patients also had a supplementary scan at more than three years follow-up). We had three dislocations at 15 days with no recurrence and one case of sepsis at three months which cured after wash out and adapted antibiotics. All the femoral segments healed starting on the tenth week. The PMA score improved from 9.1 to 15.66 and the Harris score from 43.5 to 85.5. At last follow-up, all femoral lesions had moved to a lower SOFCOT score. There was a tight contact between the AURA stem and the femur on the last follow-up scan which showed an increase in the cortical index from 1 to 8 cm from the metaphyseal spine of the stem. None of the patients experienced secondary unlocking or required revision for a shorter stem. Discussion: Revision after femoral failure with bone destruction using a non-cemented hydroxyapatite-coated stem allows immediate prosthetic mechanical stability and intimate bone reconstruction in the metaphyseal diaphyseal region. This reconstruction is real even if a graft is not used and appears to be favoured by the femorotomy. Implantation of the long stem is not particularly difficult and can even make the operation easier. Femorotomy has a real advantage, particularly for the revision of septic stems or in the event of difficult explantation

Introduction & aims. The magnitude and pattern of acceptable migration in clinically successful cementless stems is not well understood. Radiostereometric analysis (RSA) is a well-recognised method of assessing implant migration. Previous studies have reported long term RSA results for cemented stems. The aim of this study was to assess the long-term migration characteristics of the Corail hydroxyapatite-coated cementless stem at 10 years using RSA. Method. A prospective cohort of 30 patients undergoing primary total hip arthroplasty for primary hip osteoarthritis were enrolled into a study to characterise the migration behaviour of a cementless stem. Tantalum markers were attached to the stem and placed in the bone intraoperatively, allowing for RSA measurements to be taken in vivo. Previous 5-year results have been presented. A total of 14 patients (total 15 hips, one bilateral) with mean age 82 years (range, 69–92 years) underwent repeat long-term RSA radiographs at minimum 10 years post op. The mean time to follow up was 13.9 years (range, 13.3–14.4 years). The RSA radiographs were analysed to assess for implant rotation and translation. Results. None of the 14 patients (15 hips) followed up have been revised. The migration (rotation and translation) at 6 months, 1 year, 2 years, and 6 years has been described previously. No stems had additional subsidence of more than 0.25 mm between 6 months and 6 years. The resultant mean subsidence between 2 years and 6 years was 0.03 mm, which is below the limit measurable by RSA. The long-term, 10-year results, on implant rotation and translation will be presented. Conclusions. The Corail stem exhibited variable subsidence within the first 6 months after which there is persistent stabilisation through to 6 years. 10-year results on long-term migration show no further migration. These results can be used as a gold standard for other uncemented stems

Introduction First metatarsophalangeal (MTP) arthroplasty is a relatively uncommon procedure compared with hip and knee joint replacement. A range of different designs of first MTP prostheses have been proposed including metal hemi-arthroplasties, single-piece double-stem silicone designs, and multi-component designs. Of the latter group, a cobalt chrome-on-cobalt chrome prosthesis, which had a diamond like carbon (DLC) coating applied to its articulating faces and hydroxyapatite-coated stems, was implanted. However, due to poor clinical results the cohort of implants were removed and one was obtained for ex vivo analysis. In addition, calculation of predicted lubrication regimes applicable to this implant design was undertaken. Materials and Methods The ex vivo MTP implant was examined using standard microscopy as well as by using an environmental scanning electron microscope and a non-contacting profilometer. The latter device also allowed values of surface roughness to be determined while the radii of the articulating faces were measured using a co-ordinate measuring machine. Modelling the ball and socket implant as an equivalent ball-on-plane model and employing elastohydrodynamic theory [. 1. ] allowed the minimum film thickness to be calculated and in turn the lambda value to indicate the lubrication regime [. 2. ]. These calculations were undertaken for a 0 to 800N range of loading values, and a 0 to 50mm/s range of entraining velocities. The viscosity of the synovial fluid lubricant was taken to be 0.01Pa s, while for the cobalt chrome a Young’s modulus of 210GPa and a Poisson’s ratio of 0.3 were assumed. Results and Discussion The implant was measured to have a nominal radius of 10mm and a radial clearance of 0.1mm. Calculations showed that, for the range of entraining velocities and loads considered, the implant would almost always operate in the boundary lubrication regime. Therefore surface to surface contact would most frequently take place, with little if any separation between the articulating surfaces. This result is in contrast to resurfacing designs of hip prosthesis which can operate in the fluid film lubrication mode [. 3. ]. This outcome is due to their larger radii, greater entraining velocity and reduced surface roughness values compared with the MTP implant considered here. It is felt that these design differences, inherent in different joints around the body, should be appreciated by those concerned with such implants. The presence of scratches on the articulating faces of the ex vivo sample further implied boundary lubrication. The DLC coating had been removed from the entire face of the phalangeal component and from most of the face of the metatarsal component. From the latter it appeared as if the coating had been scratched and then flaked away parallel to the scratches. In turn this suggested a corrosion based failure of the interface between the DLC coating and the cobalt chrome subsurface, a result noted recently elsewhere [. 4. ]