Aims: In recent years, radiation crosslinking has become an important processing step in the manufacture of ultra-high molecular weight polyethylene (PE) components of joint replacement prostheses due to its associated high wear resistance. Gamma or electron beam radiation treatment is usually followed by a heating step, either complete melting or annealing of PE close to but below the melting temperature for a specific time duration. The heat treatment is performed to decrease free radical concentration within the crystalline lamellae in order to make PE more oxidation resistant.

In this study, we hypothesized that high pressure processing of PE would be advantageous if it is performed only after irradiation and quenching of free radicals and that it would be detrimental if it preceded irradiation. We used accelerated oxidation, mechanical tests and wear tests to show

Methods: Ram-extruded rod stock of GUR 1050 PE (Ticona, Bayport, TX) was purchased from MediTECH Medical Polymers (Fort Wayne, IN) and machined into cylinders to snugly fit into a custom-built high-pressure cell. A Carver hydraulic press was used to apply a pressure of 500MPa to PE specimens preheated to various temperatures, slow cooled to room temperature followed by pressure release. The PE cylinders and untreated control PE were subjected to 50kGy gamma radiation, which is a dose sufficient for a high degree of crosslinking in PE. A Parr bomb reactor filled with oxygen gas and operating at 5atm pressure and 70_C temperature was used to oxidize PE for a period of 14 days, according to ASTM standard F2003–02, and later characterized using Fourier Transform Infrared Spectroscopy (FTIR). A second batch of PE was first irradiated, melted and then subjected to high pressure processing. ASTM standard tensile tests were conducted to determine whether there was any increase in mechanical properties. Scanning electron microscopy (SEM) and differential scanning calorimeter (DSC) were used to characterize the lamellar morphology.

Results: The morphological characterization techniques, SEM and DSC, showed that high pressure processing increased the crystallinity as well as lamellar thickness regardless of whether the process was conducted prior to or after irradiation. FTIR showed that there was a monotonic increase in oxidation with lamellar thickness if the irradiation was carried out after high pressure processing. Several mechanical properties such as modulus and yield stress of PE increased with increase in crystallinity, which is desirable for applications where PE is subjected to high stresses.

Conclusions: High-pressure processing benefits the mechanical properties of crosslinked PE when it is conducted after irradiation and melting. However, if it conducted prior to irradiation and is not followed by thermal treatment, it can lead to more trapped free radical and excessive oxidation. Therefore, it is important to employ this processing method after irradiation so that it improves the mechanical properties of crosslinked PE.

Introduction: In the two-stage revision procedure for infected total hip arthroplasty (THA), healing of the infection can be enhanced by using an antibiotic-loaded acrylic cement (ALAC) spacer. The spacer also acts as a temporary implant, preserving the gap between bone segments and a certain degree of joint motion.

Materials and methods: Between 1995 and 2003, 19 infected THAs were surgically treated by two-stage revision procedures, using gentamicin-loaded spacers. The infections were sustained by Staph. aureus in 7 cases, Staph. aureus + Enterococcus faecalis in 1 case, Staph. epidermidis in 4 cases, Strept, agalactiae in 1 case and Strept, β-haemoliticus in 1 case. In 5 hips presenting with secreting fistulae, no causative microrganisms were isolated.

Average interval between the two surgical stages was 5.5 months (range, 2 weeks to 13 months). Systemic antibiotics were administered to all patients for a minimum period of 6 weeks after removal of the infected implant. The revision stem was cemented in 5 patients and not cemented in 13 patients. All the acetabular components were uncemented. In one patient, the second stage procedure consisted exclusively in removal of the spacer and debridement, owing to persisting infection sustained by Staph. aureus + Staph. epidermidis.

Results: Seventeen patients were evaluated at an average follow up of 42.3 months (range, 6 to 92 months).

Recurrence of infection (Staph. aureus) occurred in 1 patient and was treated by resection-arthroplasty. Aseptic loosening of the stem was observed in 1 patient, who was subsequently treated by stem revision. Average Harris Hip Score was 78 points (range, 65 to 90 points).

Conclusions: The low incidence and the pathophysiologic heterogeneity of THA infections do not allow to identify standardised protocols for their treatment. Two-stage revision is one available option and several authors demonstrated higher rates of success when compared to one-stage revision. The use of ALAC spacers increases the efficacy of the procedure and in our experience positively influenced the clinical-functional outcome.

The biomechanical objective in total knee prostheses with mobile bearings was, and still is, to reduce UHMWPE wear and fracture. This does not mean that such prostheses do not produce polyethylene debris.

In our clinical experience we have used several types of prosthesis, in which over time, plastic materials have become diversified and various methods of sterilisation have been used, the prostheses becoming more and more sophisticated.

In our work we present the results of using a posterior cruciate ligament-retaining prosthesis with two mobile bearings (follow up 7–14 years), a posterior cruciate ligament-sacrificing prosthesis with a rotating platform (follow up 10 years to today) and a posterior cruciate ligament-retaining prosthesis with a rear-front translation platform (follow up 7 years to today).

Data on fractures and dislocation are only presented for the posterior cruciate ligament-retaining prosthesis with two mobile bearings. In no other cases were fractures or dislocation observed, except for one patient who had a dislocation after suffering a rotational tendon tear.

Our results show that larger surfaces tolerate the prosthesis stress better, although the type of polyethylene (with or without stearate, more or less crosslinked, sterilisation with or without air, sterilisation by high energy radiation or using gamma radiation, etc.) can influences debris production.

The purpose of our study was to determine the effect of 4 weeks and 12 weeks of implantation on the strength of a tendon graft in a bone tunnel using a low-profile fixation device, Evolgate, in an extra-articular ovine model. Moreover, we evaluated the histological changes.

The common digital extensor tendon was detached from the lateral femoral condyle and fixed with the Evolgate device in a 30-mm-long tunnel placed obliquely across the dense metaphyseal bone of the proximal tibia. We performed either biomechanical or histological study. Three sheep were sacrified at time 0 and their posterior limbs were used for biomechanical tests. Six sheep were used for biomechanical tests at time 1 (4 weeks) and at time 2 (12 weeks). The other three sheep were used for histological evaluation after 4 and 12 weeks of implantation. The biomechanical tests included a 50 N preload applied for 10 s and a cyclic load test in 50-N increments until failure to evaluate the ultimate failure load. We used a paired t-test to evaluate the difference between group at T1 and group at T2 with the control group at time 0, respectively. Tests were performed using an electromechanic machine (Zwick-Roell Z010, Zwick-Roell, Ulm, Germany). Data were recorded with dedicated software (Textexpert 8.1, Zwick-Roell).

The biomechanical results show an improvement of about 50% in strength after 4 and 12 weeks post-implantation, respectively. The histological evaluation shows a layer of cellular, fibrous tissue between the tendon and the bone, along the length of the bone tunnel; this layer progressively matured and reorganised during the healing process. The collagen fibres that attached the tendon to the bone resembled Sharpey fibres.

The strength of the interface was noted to have significantly and progressively increased between the second and the 12th week after the transplantation. The progressive increase in strength was correlated with the degree of bone ingrowth, mineralisation, and maturation of the healing tissue, noted histologically.