Effect of hydroxyapatite coating on risk of revision after primary total hip arthroplasty in younger patients: findings from the Danish Hip Arthroplasty Registry

Background The effect of hydroxyapatite (HA) on implant survival in the medium and long term is uncertain. We studied the effect of HA coating of uncemented implants on the risk of cup and stem revision in primary total hip arthroplasty (THA).

Patients and methods Using the Danish Hip Arthroplasty Registry (DHR), we identified patients less than 70 years old who had undergone uncemented primary THA during 1997-2005. 4,125 HA-coated and 7,737 non-HA-coated cups and 3,158 HA-coated and 4,749 non-HA-coated stems were available for analysis. The mean follow-up time was 3.4 years for cups and 3.2 years for stems. We estimated the relative risk (RR) of revision due to aseptic loosening or any cause, and adjusted for possible confounders (age, sex, fixation of opposite implant part, and diagnosis for primary THA) using multivariate Cox regression analysis.

Results The adjusted RRs for revision of HA-coated cups and stems due to aseptic loosening were 0.89 (95%CI: 0.37-2.2) and 0.71 (95%CI: 0.27-1.9) with up to 9 years of follow-up, compared to non-HA-coated implants. When taking all causes of revision into consideration, the risk estimates were 0.85 (95%CI: 0.68-1.1) and 0.81 (95%CI: 0.61-1.1) for HA-coated cups and stems, respectively.

Interpretation In this medium-term follow-up study, the use of HA-coated implants was not associated with any clearly reduced overall risk of revision compared to non-HA-coated implants.     

Total hip arthroplasty for primary osteoarthrosis in younger patients in the Finnish arthroplasty register. 4,661 primary replacements followed for 0-22 years

BACKGROUND: Many studies have found a higher risk of revision after hip arthroplasty in younger patients. We evaluated the population-based survival of total hip arthroplasty (THA) in patients under 55 years of age and the factors affecting survival. METHODS: The Finnish Arthroplasty Register was established in 1980, and 74,492 primary THAs were entered into the register between 1980 and 2001. 4,661 of these were evaluated, all of which had been performed for primary osteoarthrosis on patients under 55 years of age. RESULTS: Proximally circumferentially porous-coated uncemented stems implanted between 1991 and 2001 had a 10-year survival rate of 99 (95% CI 98.5-99.6)% with aseptic loosening as endpoint. The risk of stem revision due to aseptic loosening was higher in cemented stems than in proximally porous-coated (RR 5.5, p < 0.001) or HA-coated (RR 6.6, p = 0.01) uncemented stems implanted during the same period. According to Cox regression analysis of cups implanted 1991-2001, the risk of revision for all-polyethylene cemented cups was 3.0 times as high as that for press-fit porous-coated uncemented cups with aseptic loosening as endpoint (p = 0.01). However, when the endpoint was defined as any revision (including exchange of liner), there was no longer any difference between these two concepts, the 10-year survival rates being 94 (92.1-95.5)% for press-fit porous-coated uncemented cups and 93 (88.5-97.6)% for all-polyethylene cemented cups (p = 0.9). INTERPRETATION: Modern uncemented stems seem to have better resistance to aseptic loosening than cemented stems in younger patients. Thus, for younger patients, uncemented proximally circumferentially porous- and HA-coated stems are the implants of choice. Press-fit porous- and HA-coated uncemented cups may have better endurance against aseptic loosening than cemented cups in younger patients. However, when all revisions (including exchange of liner) are taken into account, the survival of modern uncemented cups is no better than that of all-poly cemented cups.     

Effects of hydroxyapatite coating on survival of an uncemented femoral stem. A Swedish Hip Arthroplasty Register study on 4,772 hips

Background and purpose

Hydroxyapatite (HA) is widely used as a coating for uncemented total hip arthroplasty components. This has been suggested to improve implant ingrowth and long-term stability. However, the evidence behind the use of HA coating on femoral stems is ambiguous. We investigated survival of an uncemented, tapered titanium femoral stem that was available either with or without HA coating (Bi-Metric).

Patients and methods

The stem had been used in 4,772 total hip arthroplasties (THAs) in 4,169 patients registered in the Swedish Hip Arthroplasty Register between 1992 and 2009. 59% of the stems investigated were coated with HA and 41% were uncoated. Kaplan-Meier survival analysis and a Cox regression model with adjustment for age, sex, primary diagnosis, and the type of cup fixation were used to calculate survival rates and adjusted risk ratios (RRs) of the risk of revision for various reasons.

Results

The 10-year survival rates of the HA-coated version and the uncoated version were about equal when we used revision for any reason as the endpoint: 98% (95% CI: 98–99) and 98% (CI: 97–99), respectively. A Cox regression model adjusting for the covariates mentioned above showed that the presence of HA coating did not have any influence on the risk of stem revision for any reason (RR = 1.0, 95% CI: 0.6–1.6) or due to aseptic loosening (RR = 0.5, CI: 0.2–1.5). There was no effect of HA coating on the risk of stem revision due to infection, dislocation, or fracture.

Interpretation

The uncemented Bi-Metric stem showed excellent 10-year survival. Our findings do not support the use of HA coating on this stem to enhance implant survival.It is generally believed that coating of total hip arthroplasty (THA) components with hydroxyapatite (HA) improves implant ingrowth and long-term stability. Thus, a large number of prostheses designed for uncemented hip arthroplasty are coated with HA. In Europe, some manufacturers mainly or exclusively market uncemented hip prostheses with such a coating.The evidence behind the use of HA is ambiguous, however. Several reports on smaller series have described varying outcomes after the use of HA-coated cups or stems. Good or even excellent results were found after the use of some HA-coated implants, with survival rates close to 100% when using revision or impending revision for aseptic loosening as the endpoint (Oosterbos et al. 2001, Capello et al. 2003, Shah et al. 2009). On the other hand, mediocre to obviously inferior results of HA-coated hip arthroplasty components have also been reported (Havelin et al. 2000, Reikerås and Gunderson 2002, Cheung et al. 2005, Kim et al. 2006). A large Danish registry analysis on uncemented hip implants found that HA coating did not reduce the risk of revision in patients younger than 70 years of age (Paulsen et al. 2007). In a recent analysis based on data from the Swedish Hip Arthroplasty Register, we found that HA coating of acetabular cups could even increase the risk of revision due to aseptic loosening (Lazarinis et al. 2010).In this study, we analyzed survival of uncemented femoral stems in the Swedish Hip Arthroplasty Register that were used either with or without HA coating. Our main hypothesis was that HA coating influences the risk of stem revision for any reason, which was our primary endpoint. Secondary endpoints were stem revision due to aseptic loosening, infection, fracture, or dislocation.     

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

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

Total hip arthroplasty for rheumatoid arthritis in younger patients: 2,557 replacements in the Finnish Arthroplasty Register followed for 0–24 years

Background?The results of total hip arthroplasty (THA) in young patients with rheumatoid arthritis (RA) have been reported in only a few studies. On a nationwide level, the outcome of THA in these patients is unknown. We evaluated the population-based survival of THA in patients under 55 years of age with RA and factors affecting the survival.

Patients?Between 1980 and 2003, 2,557 primary THAs performed for RA in patients less than 55 years of age were reported to the Finnish Arthroplasty Register.

Results?Proximally circumferentially porous-coated uncemented stems had a 15-year survival rate of 89% (95% CI 83–94) with aseptic loosening as endpoint. The risk of stem revision due to aseptic loosening was higher with cemented stems than with proximally porouscoated uncemented stems implanted during the same period (RR 2.4; p < 0.001). In contrast, Cox regression analysis showed that the risk of cup revision was significantly higher for all uncemented cup concepts than for all-polyethylene cemented cups with any cup revision as endpoint. There were no significant differences in survival between the THR concepts.

Interpretations?Uncemented proximally circumferentially porous-coated stems and cemented all-poly-ethylene cups are currently the implants of choice for young patients with RA.     

Total hip arthroplasty for rheumatoid arthritis in younger patients: 2,557 replacements in the Finnish Arthroplasty Register followed for 0-24 years

BACKGROUND: The results of total hip arthroplasty (THA) in young patients with rheumatoid arthritis (RA) have been reported in only a few studies. On a nationwide level, the outcome of THA in these patients is unknown. We evaluated the population-based survival of THA in patients under 55 years of age with RA and factors affecting the survival. PATIENTS: Between 1980 and 2003, 2,557 primary THAs performed for RA in patients less than 55 years of age were reported to the Finnish Arthroplasty Register. RESULTS: Proximally circumferentially porous-coated uncemented stems had a 15-year survival rate of 89% (95% CI 83-94) with aseptic loosening as endpoint. The risk of stem revision due to aseptic loosening was higher with cemented stems than with proximally porouscoated uncemented stems implanted during the same period (RR 2.4; p < 0.001). In contrast, Cox regression analysis showed that the risk of cup revision was significantly higher for all uncemented cup concepts than for all-polyethylene cemented cups with any cup revision as endpoint. There were no significant differences in survival between the THR concepts. INTERPRETATIONS: Uncemented proximally circumferentially porous-coated stems and cemented all-poly-ethylene cups are currently the implants of choice for young patients with RA.     

Loss of hydroxyapatite coating on retrieved,total hip components

The goal of this study was to examine the early retrievals of hydroxyapatite-(HA) coated hip prostheses to assess evidence of osteoconductivity, resorption of HA, and the integrity of the HA/implant bond. Six retrieved HA-coated hip prostheses (3 femoral hip stems, 3 acetabular cups) were analyzed for the amount of bone ongrowth or ingrowth of the HA-coated surface and the extent to which the coating was still present after in vivo service. The examination of these six HA-coated prostheses indicates that HA appeared to be osteoconductive. There was evidence of debonding of HA from the smooth-surfaced femoral prosthesis, although that may have been a result of the extraction process. The five plasma-spray surfaced, HA-coated prostheses showed evidence of considerable loss of the HA coating at the time of receipt in the authors' laboratory, although it is was not possible to determine the cause of the loss of coating.     

Rheumatoid arthritis and hydroxyapatite-coated hip prostheses: Five-year results

Medium- and long-term results from cemented total hip arthroplasty (THA) in patients with rheumatoid arthritis (RA) show a higher incidence of infection and aseptic loosening when compared to other diagnoses. Early results using uncemented prostheses are variable. Hydroxyapatite (HA) coatings are thought to improve early osseointegration in uncemented THA. In a prospective, international, multicenter clinical study, 32 RA patients who received 33 uncemented HA-coated prostheses were followed up for a minimum of 5 years. Medium-term clinical results are excellent. No infection or aseptic loosening has been recorded. Excellent osseointegration was observed radiographically. Bone remodeling was consistent with mainly proximal to midstem stress transfer. We conclude that uncemented, proximally HA-coated prostheses are a promising alternative to cemented prostheses for RA patients.     

Effects of hydroxyapatite coating of cups used in hip revision arthroplasty: A Swedish Hip Arthroplasty Register study of 1,780 revisions

Background and purpose

Coating of acetabular revision implants with hydroxyapatite (HA) has been proposed to improve ingrowth and stability. We investigated whether HA coating of revision cups can reduce the risk of any subsequent re-revision.

Methods

We studied uncemented cups either with or without HA coating that were used at a primary acetabular revision and registered in the Swedish Hip Arthroplasty Register (SHAR). 2 such cup designs were identified: Harris-Galante and Trilogy, both available either with or without HA coating. These cups had been used as revision components in 1,780 revisions of total hip arthroplasties (THA) between 1986 and 2009. A Cox proportional hazards model including the type of coating, age at index revision, sex, cause of cup revision, cup design, the use of bone graft at the revision procedure, and the type of cup fixation at primary THA were used to calculate adjusted risk ratios (RRs with 95% CI) for re-revision for any reason or due to aseptic loosening.

Results

71% of the cups were coated with HA and 29% were uncoated. At a mean follow-up time of 6.9 (0–24) years, 159 (9%) of all 1,780 cups had been re-revised, mostly due to aseptic loosening (5%), dislocation (2%), or deep infection (1%). HA coating had no significant influence on the risk of re-revision of the cup for any reason (RR = 1.4, CI: 0.9–2.0) or due to aseptic loosening (RR = 1.1, 0.6–1.9). In contrast, HA coating was found to be a risk factor for isolated liner re-revision for any reason (RR = 1.8, CI: 1.01–3.3). Age below 60 years at the index cup revision, dislocation as the cause of the index cup revision, uncemented cup fixation at primary THA, and use of the Harris-Galante cup also increased the risk of re-revision of the cup. In separate analyses in which isolated liner revisions were excluded, bone grafting was found to be a risk factor for re-revision of the metal shell due to aseptic loosening (RR = 2.1, CI: 1.05–4.2).

Interpretation

We found no evidence to support the notion that HA coating improves the performance of the 2 studied cup designs in revision arthroplasty. In contrast, patient-related factors such as younger age and dislocation as the reason for cup revision, and technical factors such as the choice of revision cup were found to influence the risk of subsequent re-revision of the cup. The reason for inferior results after revision of uncemented cups is not known, but it is possible that these hips more often had pronounced bone loss at the index cup revision.The most common cause of re-revision of the hip after revision surgery is failure of the acetabular component (Swedish Hip Arthrolasty Register (SHAR) 2010). Acetabular revision with cemented implants has shown up to 20% failure at 10 years of follow-up, whereas contemporary designs of uncemented acetabular cups have substantially reduced this failure rate (Callaghan et al. 1985, Kavanagh et al. 1985, Katz et al. 1997, Lie et al. 2004). Loosening of the primary acetabular component often leaves substantial bone loss and a sclerotic acetabular bed. Fixation of revision cups is therefore demanding, and several techniques have been used to restore bone loss and achieve long-term fixation of the revision cup—such as screw fixation, bone grafting, and different cup designs (Palm et al. 2007, Pulido et al. 2011). The use of hydroxyapatite (HA) coating on cups used as revision implants has been proposed to be an improvement over uncoated cups (Dorairajan et al. 2005, Geerdink et al. 2007).HA is the main inorganic component of human bone. It has therefore been hypothesized that coating of metallic implants with HA enhances ingrowth of bone and thus leads to improved stability (Soballe et al. 1999). Indeed, some HA-coated cups perform well and are still in use, while other HA-coated cups have shown high failure rates in the long term. For instance, inferior results were achieved with the Romanus cup where the combination of an inferior locking mechanism of the liner with an inferior type of polyethylene resulted in excessive osteolysis in the acetabular region (Puolakka et al. 1999, Lyback et al. 2004, Lazarinis et al. 2010, SHAR 2010). Due to the relatively small numbers of revision procedures, very few authors have reported results after hip revision arthroplasty using HA-coated implants. To our knowledge, there have been no registry studies specifically investigating the performance of HA-coated hip revision implants. Thus, the question of whether the use of HA coating on revision cups is beneficial remains to be answered.In this study, we analyzed the outcome of acetabular revision surgery using uncemented cups with or without HA coating recorded in the Swedish Hip Arthroplasty Register (SHAR). Our hypothesis was that coating of revision acetabular cups with HA reduces the risk of re-revision of the acetabular component inserted. The primary endpoint was re-revision of the acetabular component for any reason and the secondary endpoint was re-revision of the cup due to aseptic loosening.     

Hydroxyapatite coating improves 8- to 10-year performance of the link RS cementless femoral stem

In a prospective randomized clinical study, 12 hydroxyapatite (HA)-coated and 8 identical but non-coated stems were implanted in 20 patients. At 8- to 10-year follow-up, the HA-coated stems displayed excellent clinical and radiographic results in 11 out of 12 patients, whereas 7 out of 8 non-coated stems were failures and had been subject to revision. Despite the small number of patients in this series, HA coating seems to improve the long-term stable fixation of uncemented femoral implants.     

Hydroxyapatite coating does not improve uncemented stem survival after total hip arthroplasty!: An analysis of 116,069 THAs in the Nordic Arthroplasty Register Association (NARA) database

ResultsUnadjusted 10-year survival with the endpoint revision of any component for any reason was 92.1% (CI: 91.8–92.4). Unadjusted 10-year survival with the endpoint stem revision due to aseptic loosening varied between the stem brands investigated and ranged from 96.7% (CI: 94.4–99.0) to 99.9% (CI: 99.6–100). Of the stem brands with the best survival, stems with and without HA coating were found. The presence of HA coating was not associated with statistically significant effects on the adjusted risk of stem revision due to aseptic loosening, with an HR of 0.8 (CI: 0.5–1.3; p = 0.4). The adjusted risk of revision due to infection was similar in the groups of THAs using HA-coated and non-HA-coated stems, with an HR of 0.9 (CI: 0.8–1.1; p = 0.6) for the presence of HA coating. The commonly used Bimetric stem (n = 25,329) was available both with and without HA coating, and the adjusted risk of stem revision due to aseptic loosening was similar for the 2 variants, with an HR of 0.9 (CI: 0.5–1.4; p = 0.5) for the HA-coated Bimetric stem.InterpretationUncemented HA-coated stems had similar results to those of uncemented stems with porous coating or rough sand-blasted stems. The use of HA coating on stems available both with and without this surface treatment had no clinically relevant effect on their outcome, and we thus question whether HA coating adds any value to well-functioning stem designs.Hydroxyapatite (HA) is thought to improve early implant ingrowth and long-term stability in bone (Overgaard et al. 1997), and many stems intended for uncemented total hip arthroplasty (THA) are thus manufactured with HA coating. Several uncemented stems are only available with HA coating. Some HA-coated stems have excellent long-term outcomes in terms of the risk of revision, both for any reason and due to aseptic loosening (Capello et al. 2003, Shah et al. 2009). Registry data from Norway and Finland also indicate that certain HA-coated stems have excellent survivorship up to 10 years (Eskelinen et al. 2006, Hallan et al. 2007, Makela et al. 2008).On the other hand, a number of studies on stem survival in the setting of randomized trials or smaller observational studies have failed to show beneficial effects of HA coating on clinical outcome and implant survival when compared to alternatives such as porous coating and sand-blasted rough surfaces (McPherson et al. 1995, Tanzer et al. 2001, Kim et al. 2003, Parvizi et al. 2004, Sanchez-Sotelo et al. 2004). Meta-analyses that have pooled data from randomized or cohort studies have come to the conclusion that there is “[…] no clinically beneficial effect to the addition of HA to porous coating alone in primary uncemented hip arthroplasty” (Gandhi et al. 2009, Li et al. 2013). In addition, a Danish registry analysis found that the use of HA coating does not reduce the risk of stem revision (Paulsen et al. 2007). Furthermore, a comparison of 4,772 uncemented Bimetric stems with or without HA coating implanted between 1992 and 2009 did not reveal any difference in survival between the 2 variants (Lazarinis et al. 2011).HA was initially introduced as an implant coating to speed up and facilitate ongrowth and ingrowth of bone and thereby improve fixation, based on comprehensive preclinical and promising clinical documentation (Geesink et al. 1987, Bauer et al. 1991, Overgaard et al. 1997, Karrholm et al. 1998). Later on, concerns were raised due to findings of delamination and generation of HA particles originating from the coating with the potential to trigger osteolysis, acceleration of polyethylene wear, and subsequent implant loosening (Bloebaum and Dupont 1993, Morscher et al. 1998, Lazarinis et al. 2010). Today, there is renewed interest in HA coatings due to possible properties as a carrier for agents aimed at preventing infection (Ghani et al. 2012). Theoretical arguments for and against the use of HA coating can therefore be found. Given the renewed interest in uncemented stems—instigated by favorable outcomes after uncemented stem fixation in younger patients—the question of whether HA coating is beneficial or not is highly relevant (Eskelinen et al. 2006, Hooper et al. 2009, Swedish Hip Arthroplasty Register 2011). We therefore investigated uncemented stems with and without HA coating that are in frequent use in the Nordic countries, regarding early and long-term survival.     

Failure of hydroxyapatite-coated acetabular cups. Ten-year follow-up of 85 Landos Atoll arthroplasties

Between March 1990 and May 1991 we performed 85 primary total hip replacements in 74 patients using the Landos Atoll hydroxyapatite (HA)-coated cup and the Corail HA-coated stem. The patients were followed up for a mean of ten years. Of the 85 cups, 26 (31%) have already been revised and a further six are radiologically unstable and awaiting revision. Two femoral stems have been revised for infection without loosening. The retrieved acetabular cups were studied by SEM and image-processing techniques to quantify the amount of residual HA on the cup. This was correlated with the clinical variables and modes of failure. The residual HA (as a percentage of the surface) on the loose cups correlated negatively with the duration of implantation (r = -0.732, p < 0.001). Six cups were stable at revision and had more residual HA coating than those which were loose (p < 0.01). The rate of failure of the Landos Atoll HA-coated, smooth hemispherical cup with screw fixation is unacceptably high. Resorption of the HA coating is markedly increased in loose cups compared with stable cups. HA coating cannot substitute for stable mechanical fixation.     

Measurement of extent of bone ongrowth and hydroxyapatite absorption in retrieved acetabular cups

BACKGROUND: To understand why hydroxyapatite (HA)-coated acetabular cups did not produce satisfactory results, we measured the extent of bone ongrowth and HA absorption of the retrieved cups. METHODS: Between March 1992 and June 1998, a total of 289 patients underwent total hip arthroplasty with an HA-coated ABG (Anatomical Benoist Giraud) prosthesis in our hospital. We revised 71 cups in our hospital, 43 of which were included in this study. The cups were in situ for an average of 80.4 months. We revised 21 cups for polyethylene wear and osteolysis, 20 for loosening, and 2 for recurrent dislocation. The outer surfaces of the cups were subdivided by two circular grooves into three areas: central, middle, peripheral. Bone ongrowth and HA absorption was measured in terms of area and thickness. The areas were graphically calculated using a computer imaging analysis system. The thickness of the HA coating remaining on the retrieved cup was measured by an x-ray coating thickness measurement instrument. RESULTS: Of the 43 cups, 37 had bone ongrowth. Bone ongrowth was observed on the central surface in 23 cups, on the middle surface in 27 cups, and on the peripheral surface in 15 cups; 6 of the 37 cups had bone ongrowth only in the groove. Altogether, 37 cups showed bone ongrowth on 6.43% of the outer acetabular surface. HA absorption appeared in all 43 cups, and an average 63.21% of the HA coating area was absorbed. there was a proportional relation between the rate of HA absorption and implantation duration, but there was no consistent trend between the thickness of the HA coating and implantation duration. CONCLUSIONS: We suggest that progressive HA absorption and minimal bone ongrowth are related to the failure of HA-coated acetabular cups at long-term follow-up after total hip arthroplasty.     

Superior sealing effect of hydroxyapatite in porous-coated implants

Background Migration of wear debris to the periprosthetic bone is a major cause of osteolysis and implant failure. Both closed-pore porous coatings and hydroxyapatite (HA) coatings have been claimed to prevent the migration of wear debris. We investigated whether HA could augment the sealing effect of a porous coating under both stable and unstable conditions.

Methods We inserted porous-surfaced knee implants, with and without HA coating, in 16 dogs, according to a paired, randomized study design. 8 dogs had 2 implants inserted into each knee using a stable implant device and 8 dogs received 1 implant in each knee using a micro-motion (500 μm) implant device. Implants had a periimplant gap of 0.75 mm. We then injected polyethylene (PE) particles or a control solution into the knee joints on a weekly basis.

Results After 16 weeks, the rating of particles around stable implants was reduced by the HA coating from a median value of 2 (1–4) to 1 (0–1) (p = 0.01) and during micromotion from 3 (2–4) to 1 (0–3) (p = 0.002). HA-coated implants had superior bone ongrowth during stable and unstable conditions. We found no difference in bone ongrowth between PE-exposed and vehicle-exposed implants.

Interpretation Compared to a pure plasma-sprayed porous coating, a layer of HA coating provides better bone ongrowth and protects the bone-implant interface against the migration of wear debris under both stable and unstable conditions.     

Early clinical results with the hydroxyapatite-coated porous long-term stable fixation total hip system

The design and early clinical results with uncemented porous-coated long-term stable fixation anatomic and midstem total hip systems (Implant Technology, Inc, Secaucus, NJ) are described. In an ongoing Food and Drug Administration-approved Investigational Device Exemption-Premarket Approval Program, a random selection method is used to determine patients receiving implants with a hydroxyapatite (HA) coating applied to the porous surface and those receiving uncoated implants. The early clinical results with the HA-coated systems show them to appear superior to the uncoated systems. A greater percentage of patients with HA-coated systems have clinical scores in the excellent to good range, which is primarily a reflection of less prostheses-related pain. Radiographically, all components appear well fixed, with evidence of bone ingrowth. The HA-coated systems have a decreased incidence of radiolucencies, particularly in proximal zones.     

No superior performance of hydroxyapatite-coated acetabular cups over porous-coated cups

Background and purpose Hydroxyapatite (HA) coating is believed to improve bone-implant ingrowth and long-term survival of prostheses. Recent studies, however, have challenged this view. Furthermore, HA particles may produce third-body wear and initiate aseptic loosening of implants. We report the performance of HA- and porous-coated acetabular cups in a prospective randomized trial.

Methods This was an 8-year follow-up study of our previously published prospective randomized study to compare clinical outcomes, survival, periprosthetic bone mineral density, migration, and wear rates of HA- and porous-coated acetabular cups. Dual X-ray absorptiometry (DXA) and Ein Bild Roentgen Analyse (EBRA) measurements were used. 100 patients who underwent unilateral cementless total hip arthroplasty were randomized to either porous-coated cups or HA-coated cups. Patients were examined preoperatively and at 3, 6, and 9 months, and also 1, 3, and 8 years after surgery. 81 patients were available for 8-year follow-up, 40 with porous-coated cups and 41 with HA-coated cups.

Results Age, sex, bone mineral density, and clinical results (Harris hip score) were similar in the 2 groups. The survival, wear, and migration patterns of the cups were also similar in both groups. The results of periprosthetic bone mineral density scans in region of interest 2 was in favor of the porous-coated cups, but there were no differences between the 2 groups in all the remaining regions of interest.

Interpretation HA coating had no statistically significant effect on clinical results, survival, wear, or migration at the 8-year follow-up.     

Total Hip Arthroplasty in Patients With Postpolio Residual Paralysis: A Systematic Review

BackgroundPatients with postpolio residual paralysis can develop disabling hip arthritis in paralytic as well as a nonparalytic limb, warranting total hip arthroplasty (THA). Limited literature is available on the results of THA among these patients in the form of small series or case reports. We have undertaken a systematic review to evaluate the clinical outcome of THA in patients with poliomyelitis with hip pathologies.MethodsA systematic search of electronic databases of PubMed, Scopus, and Web of Science pertaining to English literature was undertaken from 1945 to August 2020 to assess the results of THA in patients with poliomyelitis. Information was gathered about demographics, indication, clinical course, complications, functional outcome, survival, and need for any revision surgery in these patients.ResultsThe literature search revealed 81 articles. Finally, after deduplication and manual selection, 16 relevant articles (128 hips) were included for evaluation. There is a paucity of literature evaluating THA in patients with poliomyelitis over the last 2 decades. The principal reason for arthroplasty was osteoarthritis of the hip in the ipsilateral (paralyzed) limb. A combination of cemented, uncemented, and hybrid implant fixation system was found to be used by surgeons. Addressing instability and perioperative management of limb length discrepancy were found to be challenging propositions.ConclusionTHA remains an effective intervention to relieve pain and improve quality of life in patients of poliomyelitis afflicted with either primary or secondary arthritis of the hip. The use of uncemented nonconstrained hip implant designs appears to demonstrate better results than constrained implants.     

Calcium phosphate coatings for fixation of bone implants: Evaluated mechanically and histologically by stereological methods

The osteoconductive properties of HA coatings are well-documented. HA coating is able to enhance bone ingrowth and to reduce early migration of both hip and knee prostheses. Despite the clinical use of HA-coated prostheses several aspects relevant to HA coatings have not been elucidated. The optimum coating quality and surface texture is still a matter of debate. Moreover, the significance of coating resorption is controversial. It has been suggested that resorption disintegrates the coating and reduces the bonding strength between implant and bone and the strength of the coating-implant interface, which might lead to implant loosening, coating delamination and acceleration of third body wear processes. This thesis aimed to investigate the effects of Ca-P coating type, quality and surface texture on mechanical fixation, bone ingrowth and loss of coating in experimental models in dogs and man. Furthermore, the significance of systematic sampling in bone histomorphometry using the unbiased stereological vertical section method was analyzed. Results . The first group of studies showed that HA-coated implants with porous-coated surface demonstrated increased energy absorption compared with grit-blasted implants during both non weight-bearing and weight-bearing conditions with controlled micromotion of 500 &#119 m. In addition, the HA coating delaminated on gritblasted implants during mechanical testing in contrast to porous-coated implants. Histomorphometry showed increased bone ingrowth to grit-blasted implants demonstrating that surface topology influenced surface activity. The next series of studies focused on the effects of Ca-P coating type, HA versus FA, during stable weight-bearing and non weight-bearing conditions. In dogs, no difference in mechanical fixation and bone ingrowth was demonstrated. However, in humans, HA-coated implants had significantly greater bone ongrowth than FA-coated implants after one year. The third group of studies evaluated the effects of HA coating crystallinity during controlled micromotion of 250 &#119 m. After 16 weeks, low crystalline (50%) HA coating accelerated mechanical fixation and bone ingrowth compared with high crystalline HA (75%). High crystalline HA achieved significantly better anchorage from 16 to 32 weeks whereas mechanical fixation of low crystalline HA was unchanged. In all studies, loss of Ca-P coating was evaluated. It was demonstrated that the coatings were resorbed, partially, in vivo irrespective type and quality of the coating. HA coverage on porouscoated implants was significantly more reduced than on grit-blasted implants in dogs. No difference in overall resorption between HA and FA coatings was demonstrated. However, in humans, significantly less HA and FA coating was resorbed when bone was present on the coating surface compared with bone marrow or fibrous tissue. In addition, resorption of HA was greater than FA in the presence of bone marrow indicating that FA was more stable than HA. Low (50%) crystalline HA coating was significantly more reduced compared with high (75%) crystalline HA at both 16 and 32 weeks. However, no further coating loss was observed from 16 to 32 weeks suggesting two phases of coating resorption: Phase I (0-16 weeks) with rapid coating loss, and phase II (16-32 weeks) with slow loss. Another important finding was that continuous loading and micromovements of 150 &#119 m accelerated resorption in contrast to immobilization of the implant. In addition, unstable fibrous anchored implants had significantly more loss of HA coating as compared with bony anchored implants. In all studies, resorbed coating was partly replaced by bone in direct contact with the implant surface suggesting durable implant fixation. Sampling efficiency in the unbiased stereological vertical section method was analyzed in order to find an optimal sampling design for histomorphometric analyzes at different sampling levels (humans, sections, fields of view and number of counting items) with different sampling intensities. The analysis showed that only minor changes in variances were observed when the initial scheme of 14 sections from each implant was reduced to include only one of the two possible implant sides, every third field of view and half the probe density, reducing the total workload at the microscope to less than 10% on all sections. In addition, the number of sections for analysis could be reduced to every fourth section per implant (3-4 sections for evaluation) without significantly increase in variance. The study demon strated that biological variation contributed to the majority of the total observed variance. Conclusion . The present series of investigations demonstrated that Ca-P coating type and quality and the underlying surface texture had significant influence on either mechanical fixation, bone in/ongrowth and loss of coating in dogs and man. In addition, the sampling design for histomorphometry could be optimized without reducing the quality of the data.     

Excellent Long-Term Survival Rate of Polished,Tapered, Cemented Stems in Patients Aged 35 Years or Younger With Avascular Necrosis or Inflammatory Arthritis of the Hip

BackgroundTotal hip arthroplasty (THA) for avascular necrosis (AVN) or inflammatory arthritis (IA) comes with a relatively high risk of aseptic stem loosening, especially in young patients. There are limited long-term data on the survivorship of polished, tapered, cemented stems in this population. We therefore performed a single-center retrospective study investigating the survival of this particular stem type in young patients with AVN or IA.MethodsAll patients aged ≤35 years who had received a THA for AVN or IA operated on by the senior author between 1990 and 2010 at the University Hospitals Leuven were identified. In total, 85 THAs in 62 patients were included. Primary endpoint was revision of the femoral component for aseptic loosening. Secondary endpoints were revision of the acetabular component for aseptic loosening, revision for other reasons, and the presence of radiolucencies around the components.ResultsThe mean follow-up for the entire cohort was 18.0 ± 5.3 years (range 8.0-28.9). Taking revision for aseptic loosening as endpoint, the survival of cemented stems was 100% after 15 years and 95.1% after 20 years. Survival of uncemented cups (91.3%) was significantly better than survival of cemented cups (50.3%) after 20 years of follow-up for aseptic loosening. Taking revision for any reason as endpoint, the survival of THAs with uncemented and cemented cups was 90% and 43.1% at 20 years respectively. Radiolucencies developed in the cement mantles around 11 of the 81 nonrevised stems, mainly in zones 1 and 7.ConclusionIn this cohort of young patients with high-risk profiles for aseptic stem loosening, polished, tapered, cemented stems showed excellent long-term survival rates and they therefore remain a viable alternative to uncemented stem designs.