[Surface characterization of Al2O3-blasted titanium implants in total hip arthroplasty]

Unexpected early loosening of rectangular straight femoral Zweymüller stems with an alumina-reduced surface after total hip arthroplasty-a prospective, double-blind, randomized controlled trial

BACKGROUND

Alumina particles from the grit blasting of Ti-alloy stems are suspected to contribute to aseptic loosening. An alumina-reduced stem surface was hypothesized to improve osseointegration and show comparable short-term outcomes to those of a standard stem.

METHODS

In this prospective, double-blind, randomized trial, 26 standard (STD) and 27 experimental new technology (NT) stems were implanted. The latter were additionally treated by acid etching and ice blasting to remove alumina particles from the grit-blasting process. Follow-up occurred at 12 and 24 months. Bone mineral density (BMD) around the stem was measured by a dual-energy x-ray absorptiometry device (DEXA). Radiographs were reviewed for alterations. Clinical scoring comprised the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Harris Hip Score (HHS). Survival rates were calculated up to 50 months.

RESULTS

Lower mean BMD and more severe cortical hypertrophies were found in the NT group. At 12 months, radiolucent lines were observed mostly in the metaphyseal zone for both groups, with a progression tendency in the NT group at 24 months. At 12 months, pain scores and the WOMAC total and physical activity scores were significantly lower in the NT group, without any differences thereafter. The number of NT stem revisions amounted to 6 (24%) and 11 (41%) at 24 and 50 months, respectively.

CONCLUSION

In the NT group, unexpected catastrophic failure rates of 41% caused by early aseptic loosening were noted within 50 months. Compared with the STD stems, NT stems lead to poor clinical and radiographic results.

LEVEL OF EVIDENCE

II.

TRIAL REGISTRATION

NCT05053048.

High Revision Rates of a Cementless Beta-Titanium Alloy Stem with Contamination-Free Roughened Surface in Primary Total Hip Arthroplasty

Optimal osseointegration of cementless total hip arthroplasty is essential for high stability and long-term survival. The purpose of this follow-up study was to evaluate the clinical and radiological outcome, the complications, and survival rates of a beta-titanium alloy stem with a specific grit-blasted-free surface. In 192 patients (mean age of 64.4 years), 202 consecutive primary total hip arthroplasties were performed using a cementless Hipstar^® stem (Stryker, Duisburg, DE). The Harris Hip Score (HHS) was assessed pre-operatively and post-operatively. Radiolucent lines were evaluated and the implant survival rate was calculated using Kaplan-Meier analysis. The mean follow-up was 7.71 years (range of 5.0–14.0 years). Overall, 15 revisions were performed. Early aseptic stem loosening was observed in six cases (2.97%). Radiolucent-lines adjacent to the stem were detected in 73 cases (83.02%), especially (70.46%) in the Gruen zones 1, 7, 8, and 14. The mean postoperative HHS was 92.65 points (range 42–100). The cumulative survival probability of the stem was 94.4% (95% CI 90.3 to 98.5%). Considering aseptic failure as an endpoint, the cumulative survival rate of the stem was 95.3% (95% CI 0.914 to 0.992) at six years of follow-up. Overall, an inferior mid-term implant survival was observed in comparison to well-established cementless stem designs.

The removal of Al2O3 particles from grit-blasted titanium implant surfaces: effects on biocompatibility, osseointegration and interface strength in vivo

For the improvement of surface roughness and mechanical interlocking with bone, titanium prostheses are grit-blasted with Al(2)O(3) particles during manufacturing. Dislocated Al(2)O(3) particles are a leading cause of third-body abrasive wear in the articulation of endoprosthetic implants, resulting in inflammation, pain and ultimately aseptic loosening and implant failure. In the present study, a new treatment for the removal of residual Al(2)O(3) particles from grit-blasted, cementless titanium endoprosthetic devices was investigated in a rabbit model. The cleansing process reduces residual Al(2)O(3) particles on titanium surfaces by up to 96%. The biocompatibility of the implants secondary to treatment was examined histologically, the bone-implant contact area was quantified histomorphometrically, and interface strength was evaluated with a biomechanical push-out test. Conventional grit-blasted implants served as control. In histological and SEM analysis, the Al(2)O(3)-free implant surfaces demonstrated uncompromised biocompatibility. Histomorphometrically, Al(2)O(3)-free implants exhibited a significantly increased bone-implant contact area (p=0.016) over conventional implants between both evaluation points. In push-out testing, treated Al(2)O(3)-free implants yielded less shear resistance than conventional implants at both evaluation points (p=0.018). In conclusion, the new surface treatment effectively removes Al(2)O(3) from implant surfaces. The treated implants demonstrated uncompromised biocompatibility and bone apposition in vivo. Clinically, Al(2)O(3)-free titanium prostheses could lead to less mechanical wear of the articulating surfaces and ultimately result in less aseptic loosening and longer implant life.

Biomaterials in orthopaedics

At present, strong requirements in orthopaedics are still to be met, both in bone and joint substitution and in the repair and regeneration of bone defects. In this framework, tremendous advances in the biomaterials field have been made in the last 50 years where materials intended for biomedical purposes have evolved through three different generations, namely first generation (bioinert materials), second generation (bioactive and biodegradable materials) and third generation (materials designed to stimulate specific responses at the molecular level). In this review, the evolution of different metals, ceramics and polymers most commonly used in orthopaedic applications is discussed, as well as the different approaches used to fulfil the challenges faced by this medical field.