M. Visentin

Early diagnosis of ceramic liner fracture. guidelines based on a twelve-year clinical experience

Osteolytic lesions due to wear debris are the major long-term problem associated with total hip replacement1. To avoid wear debris, hard-bearing-surface total hip prostheses with improved tribological properties have been introduced into surgical practice. Ceramic surfaces have had some promising long-term results2, and modern metal-backed alumina cups have been associated with very good clinical results3-5. Alumina has excellent tribological properties and a very high Youngs modulus that leads to very good compression strength, but it has poor bending strength: it has no way to deform6. This means that ceramic can break without warning. Under normal physiologic conditions, modern ceramics never reach their fatigue limit, so ceramic head fractures are rare (a rate of 0.004%7 in one study). In contrast, ceramic liner fractures are not well recognized, and their frequency could be underestimated (Fig. 1). In addition, it is difficult to identify patients who are at risk because liner fractures can be due to multiple causes: dislocation, impingement, malpositioning, and microseparation8,9. Fig. 1 A ceramic liner fracture. The diagnosis is often difficult to make on the basis of standard radiographs. A fragment of ceramic is visible near the calcar (arrow). The liner was found to be fractured (arrow) at revision surgery. While many efforts have been made to improve the ceramic manufacturing process and the surgical technique for inserting ceramic components10, little has been reported regarding the early diagnosis of ceramic fracture. When a ceramic fracture involves the liner and is the consequence of repeated microtrauma, the diagnosis is rarely made early, except when ceramic fragments are visible on radiographs. Moreover, decision-making regarding revision surgery after a ceramic-on-ceramic prosthesis has failed is difficult: the ceramic fragments that have spread into the periarticular space are abrasive and …

Improvement of the bone-pin interface with hydroxyapatite coating: an in vivo long-term experimental study.

The present study was designed to comparatively evaluate the bone-pin interface in a long-term unloaded experimental study in two groups of pins, uncoated and coated with hydroxyapatite. Forty pins made of stainless steel were used. Half of the pins were plasma-sprayed with hydroxyapatite, and the other half remained uncoated. Four adult sheep were selected. Each sheep tibia was implanted with five pins. Two sheep were euthanized 4 months after surgery and the remaining two 12 months after surgery. Extraction torque was higher in the hydroxyapatite-coated pins compared with the uncoated ones at both 4 (p < or = 0.0005) and 12 months (p < or = 0.0005) after implantation. The histological patterns observed in the sheep euthanized 4 and 12 months after implantation were very similar. An extensive bony coverage of the hydroxyapatite-coated pins without any coating resorption and delamination from the metallic substrate was observed. Fibrous tissue encapsulation was found in the uncoated pins. These results demonstrate that the hydroxyapatite coating significantly improved the bone-pin interface. A similar improvement of bone-pin interface rigidity in many clinical situations is likewise possible.

Biomechanical, scanning electron microscopy, and microhardness analyses of the bone-pin interface in hydroxyapatite coated versus uncoated pins.

OBJECTIVE To evaluate the bone-pin interface in hydroxyapatite coated versus uncoated pins. DESIGN Eighty-four bicylindrical stainless steel external fixation pins were implanted in a test group of 14 sheep. One-half of the pins were coated with hydroxyapatite and the rest remained uncoated. INTERVENTION Six coated pins were implanted in the left tibia of seven sheep, and six uncoated pins were implanted in the left tibia of the other seven sheep. In all sheep, the right tibia was left intact. During pin implantation, the final insertion torque was measured, and a linear external fixator was mounted on the pins. Then the medial tibial mid-diaphysis was exposed and a 5-mm resection osteotomy was performed. The sheep were killed six weeks after surgery. MAIN OUTCOME MEASURES The extraction torque was measured on four pins removed from each sheep. Radiographic pin tract rarefaction was measured on all the pins. Two pins from each sheep were used for histologic, scanning electron microscopy (SEM), and microhardness analysis. Histomorphometric analysis was carried out on the SEM specimens at x 36 magnification. RESULTS Radiographic pin tract rarefaction was significantly lower in the hydroxyapatite coated pins than in the uncoated pins (P < 0.001). Group average insertion torque was 960 +/- 959 N/mm in the hydroxyapatite coated pins, and 709 +/- 585 N/mm in the uncoated pins (p = not significant). Group average extraction torque was 1485 +/- 1308 N/mm and 298 +/- 373 N/mm, respectively (p = 0.0001). Histomorphometric analysis showed that the group average bone-pin contact was 50.7 +/- 16.9% in the hydroxyapatite coated pins and 27.6 +/- 7.1% in the uncoated pins (p < 0.01). Microhardness analysis showed that bone tissue close to the pins was softer than bone tissue far from them. CONCLUSION Hydroxyapatite coating is an effective method of refining the bone-pin interface and may improve the clinical results of the external fixation technique.

High-performance liquid chromatography assay of N,N-dimethyl-p-toluidine released from bone cements: evidence for toxicity

Five commercially available bone cements were analysed by high-performance liquid chromatography for detecting the residual content of an accelerator, the amine N,N-dimethyl-p-toluidine (DMPT), after curing. It was found that the concentration of DMPT in aqueous extracts decreases with time, being almost absent 7 days after curing. Differences were noticed among the cements; residual DMPT is higher in cements prepared with higher content of the amine. It is verified that DMPTs toxic effect on cell cultures is dose-related; a delay in the cell replication cycle is induced in vitro. Damage is reversible, thus justifying the low bone cement toxicity that is clinically ascertained.

Sister chromatid exchanges and ion release in patients wearing fracture fixation devices

The quantification of sister chromatid exchange (SCE) during mitosis is a useful index for evaluating genotoxic effects in subjects occupationally or incidentally exposed to potentially toxic substances. The authors investigated the hypothesis that ions released by corrosion from prosthetic components of fracture fixation devices are associated with change in SCE incidence. In the present study, ten patients with implants were examined, and fifteen subjects with no implants were used as controls. SCE and high frequency cell (HFC) numbers were evaluated in circulating lymphocytes. In addition, nickel (Ni) and chromium (Cr) ion values in the serum were measured because, after iron, these metals are major components of stainless steel. A significant increase in SCE numbers was observed in patients compared to the control population (4.9 +/- 1.3 vs. 3.5 +/- 1.4). Ni concentration was 1.71 +/- 1.49 ng/mL in patients and 0.72 +/- 0.52 ng/mL in control subjects; Cr concentration was, respectively, 1.01 +/- 0.77 ng/mL and 0.19 +/- 0. 27 ng/mL. The increase of serum Cr and Ni was statistically significant. No correlation was found between the increased Cr concentrations and SCE number while Cr ion levels were found to be significantly correlated to HFC. An inverse correlation between Ni level and SCE numbers was observed. Our findings suggest that Cr release by stainless steel implants could have a genotoxic effect; thus it would be useful to carefully monitor implanted subjects with regard to serum ion dosage, SCE analysis, and HFC evaluation. In any case, it would be appropriate to remove the implant when fracture fixation is reached.

Nitric oxide synthase in tissues around failed hip prostheses

Nineteen patients who had undergone hip revision surgery for aseptic loosening of joint prostheses were studied. Tissue samples were harvested at the interface between bone and implant, either at the stem or at the cotyle level. Immunohistochemistry was performed on tissue sections to detect nitric oxide synthase (NOS), the enzyme which enables the synthesis of nitric oxide (NO), a molecule which can activate bone resorption. Quantitative analysis of the positive cells and correlation with the presence of particulate wear debris and radiological data were performed. The authors observed a trend towards a moderate increase in positive cells due to inducible NOS in tissues containing particulate wear debris, especially of a plastic material. This increase, however, did not achieve statistical significance. On the contrary, there was a statistical correlation between iNOS (inducible NOS) and the severity of osteolysis around the prosthetic implant. Pharmacological control of the biosynthesis of NO may be considered in the prevention or treatment of loosening.

Assessment of five interleukins in human synovial fluid as possible markers for aseptic loosening of hip arthroplasty

One of the most important factors that seems to be involved in total hip replacement is periprosthetic osteolysis. As it is well documented that several interleukins (ILs) are triggered in periprosthetic osteolysis, this article investigates the role of five ILs in primary and replacement total hip arthroplasty, understanding if one of them can also predict hip implant loosening, secondary surgery, and prosthesis breakage. The levels of IL-1alpha, 1beta, 6, 8, and 10 in synovial fluid were examined, using a high sensitivity enzyme-linked immunosorbent assay (ELISA) test kit (Pierce Biotechnology, Inc., Rockford, IL, USA) to determine whether these cytokines could be used as markers of enhanced periprosthetic osteolysis, leading to aseptic loosening of total/partial hip arthroplasty or revision surgery. Synovial fluid was harvested from 23 patients undergoing primary total hip arthroplasty and 35 patients undergoing total/partial hip revision due to aseptic loosening. In the revision group, four cases had suffered a prosthesis fracture and five were second revisions. ILs 6 and 8 were significantly higher in the revisions (305 and 817 pg/mL) compared with the primary arthroplasties (151 and 151 pg/mL), including cases with prosthesis fracture and those requiring a second revision. IL-10 levels were lower (not significantly) in second revision samples compared with those of revision samples. IL-1beta levels were significantly higher in prosthesis fracture samples compared with those of all the other revision samples. No statistically significant differences in IL levels were found between osteoarthritis samples and those of other diseases. These results are a step forward to elucidating the complex network of events that are involved in loosening of hip implants.

Determination of crystallinity and crystal structure of Hylamer polyethylene after in vivo wear.

Hylamer™ polyethylene is a crystalline form of polyethylene of 70% crystallinity whereas conventional polyethylene (PE) has 50% crystallinity. Crystallinity is the percentage by weight of the crystalline phase present in the whole polymer, which comprises both amorphous and crystalline phases. Clinical experience has shown that Hylamer™ components used in joint prostheses, if sterilized by gamma rays in the presence of oxygen, are easily affected by wear, which leads to osteolysis. The authors have analyzed the crystallinity of polyethylene liners removed from seven patients who had received Hylamer™ polyethylene implants sterilized by gamma rays in air and had suffered prosthetic loosening, using Raman spectroscopy coupled with partial least squares (PLS) analysis. The results have been compared to those of two controls who had received Hylamer™ polyethylene implants sterilized by gamma irradiation in a nitrogen atmosphere. The crystal structure of wear particles released into the tissues from the Hylamer™ liners sterilized by gamma rays in air is also studied. The materials undergoing two different types of sterilization methods show different crystallinity values (71.50 vs. 69.43), but the crystallinity do not change according to wear (worn and unworn liner region). Both monoclinic and orthorhombic phases are present in the liner, while in wear debris prevalently monoclinic crystals are found in both types of sterilized liners. Different crystallinity rates can explain different wear rates observed in vivo.

The interface of bone microstructure and an innovative coating: An X‐ray diffraction study

The in vivo compatibility and degradation aspects of an innovative coating to be sprayed onto titanium implants were investigated. The surface of fluorinated apatite (fHA), consisting of fluorhydroxyapatite plasma sprayed in a vacuum atmosphere, was treated with carbonate to improve its biological compatibility. fHA coating was compared with titanium implants coated (a) with hydroxyapatite (HA) by the traditional plasma spraying, and (b) with titanium oxide (TiOx). Screw-shaped implants were inserted in the cortical bone of sheep tibiae. X-ray diffraction (XRD) analysis of bone tissue and coatings was carried out at 2, 4, 12 and 36 weeks after surgery. The crystallographic habit of the implant-facing bone, as well as the structural stability of the coating, were evaluated. For each time period and type of ceramic bone apatite lattice at the interface, no significantly different reference apatite lattice and no foreign peak were recorded. Two weeks after implantation, the bone at the interface was strongly unmineralized in all samples; after 4 weeks, poorly mineralized bone microareas decreased. At 12 weeks, the newly formed bone tissue at the interface with both the new coating and HA coating was shown to be fully mineralized; this crystallographic habit was retained at 36 weeks, when particle release from the tested material was lower compared to the controls. The XRD pattern of bone apatite surrounding the coating particles was unmodified. The innovative coating did not alter the mineralization process at the interface. It improved implant osteointegration, mainly due to a limited release of particles. Consequently, clinical performance of external fixation treatment could be improved by modifying the chemical composition of the implant surface.

Isolation and characterization of wear debris generated in patients wearing polyethylene hylamer inserts, gamma irradiated in air

Hylamer polyethylene was used in the early 1990s to make hip-joint components. Clinical experience has shown that these components, if sterilized by gamma rays in the presence of oxygen, are easily affected by wear, which then leads to osteolysis. The authors analyzed polyethylene wear particles in seven patients who had received Hylamer polyethylene implants sterilized by gamma rays in air and had suffered prosthetic loosening. The results were compared to those of six controls, who had received traditional polyethylene implants, sterilized by the same method. The frequency distribution of globular and fibrillar particles was similar in both groups (38.5% in Hylamer, 45.2% in controls). The globular particles in the Hylamer samples had a mean area of 0.12 mm2, which was significantly lesser than that of the controls (0.30 mm2). The width of fibrillar particles in the Hylamer samples was significantly lesser than that of the controls. Therefore, the two materials, despite undergoing the same type of sterilization, produced different types of wear, due to their different properties. In conclusion, the difference in the morphology of Hylamer polyethylene wear particles in comparison with PCA might have caused a more intensive biological response, early and massive osteolysis, and therefore, early loosening.