The current use of a spherical prosthetic humeral head in total shoulder arthroplasty results in an imprecise restoration of the native geometry and improper placement of the center of rotation, maintained in a constant position, in comparison to the native head and regardless of glenoid component conformity. A radially-mismatched spherical head to allow gleno-humeral translation is a trade-off that decreases the contact area on the glenoid component, which may cause glenoid component wear. This finding suggests that the use of a non-spherical head with a more conforming glenoid component may reduce the risk of glenoid component wear by allowing gleno-humeral translation while increasing the contact area. A non-spherical prosthetic head more accurately replicates the head shape, rotational range of motion and gleno-humeral joint kinematics than a spherical prosthetic head, compared with the native humeral head. The combination of inversion of the bearing materials with the non-spherical configuration of the humeral head may thus decrease polyethylene wear. Aim of the present study is to evaluate in vitro wear behaviour of an all-polyethylene elliptical humeral head component against a metallic glenoid component in an anatomic configuration. The prosthetic components tested are from the Mirai® Modular Shoulder System by Permedica S.p.A.. The prosthetic bearing components were tested in their anatomic configuration: the humeral head rubbing against the glenoid inlay, assembled over the glenoid base-plate. The glenoid insert is made of Ti6Al4V alloy coated with TiNbN. The glenoid insert, as the glenoid base-plate have the same shape which reproduce the native shape of the glenoid. Moreover, the glenoid insert has a concave articular surface described by two different radii on orthogonal planes. The vitamin E-blended UHMWPE humeral head is not spherical but elliptic-shaped with an articular surface described by two different profiles in sagittal and coronal plane. The component sizes combination tested have the greatest radial mismatches allowed between humeral head and glenoid insert. The test was performed up to 2.5 million of cycles applying a constant axial load of 756 N.Background
Material and methods
We present the mid-term results of our consecutive series of 155 hips treated with ASR XL Acetabular System (ASR-XL) for large-diameter metal-on-metal total hip arthroplasty and with DePuy ASR Hip Resurfacing System (ASR) for hip resurfacing. 114 ASR-XL and 41 ASR were implanted between 2004 and 2008 in 145 patients (69 men and 76 women) with a mean age of 57 years. Twenty-one patients (23 hips) resulted lost to follow-up. All patients were recalled and monitored periodically with clinical, hematological and radiological evaluation. Average follow-up of the 155 hips was 72 months (1 to 104). The mean follow-up, excluding revised patients and those lost to follow-up, was up to 89 months.Introduction:
Methods:
Second-generation metal-on-metal bearings have been used since the late 1980s as alternative bearings to eliminate aseptic loosening due to polyethylene wear. This study is the first with a long term follow-up for Meteasul, (Zimmer GmbH, Winterthur, Switzerland) metal on metal (MoM) hip replacement; in literature most of the studies have a mean follow-up of 7 years. Metasul showed better performances than other MoM couplings, with a low failure rate at long term follow-up and low revision rate for aspetic loosening. The aim of the present study was to evaluate the long-term results of a series of Metasul implanted between January 1993 and July 1997. 145 cementless THAs with a 28 mm Metasul articulation were performed in 114 consecutive patients. Implant survivorship was calculated and clinical and radiographic evaluations were performed on 93 hips still available for follow-up at a mean of 19 years postoperatively (43 hips are dead or lost to FU, 29, 6%). Nine hips (6.2%) were revised. The cumulative probability of survival of the overall implant at 19 years postoperatively with revision for any reason as the end point, was 0.937 (95% confidence interval, 0.888 to 0.985). The cumulative probability of survival of Metasul with revision for any reason as the end point, was 0.956 (95% confidence interval, 0.916 to 0.997). Clinical outcome has been evaluated with modified Harris Hip Score for 93 hips with an average of 88.8 points. Various degrees of radiolucencies and osteolysis were found proximally around the femoral components of 25 hips (20%). Most of the patients has normal serum levels of metal ions (Co and Cr), and no cases of systemic toxicity has been reported. Cementless Metasul THAs showed high probability of survival at 19 years postoperatively.
Previous studies have indicated poor outcomes and high complication rate in patients having revision of metal-on-metal (MoM) hip implants resulting from adverse local tissue reactions. Metal ions released by MoM bearings may potentially increase infection occurrence in patients with failed implants. We reviewed all patients at our institution who sustained revision of a failed large-head metal-on-metal hip implant to determine if infection-related complications are associated with the elevation of serum metal ions concentration.Background
Questions/purposes
We present the mid-term results of our consecutive series of 155 hips treated with ASR extra-large (XL) Acetabular System (ASR XL) and with ASR Hip Resurfacing System (ASR). We reviewed the clinical records of patients with implanted ASR or ASR XL. All patients were recalled and invited to come to our hospital for a periodic clinical, hematological and radiological evaluation.114 ASR XL and 41 ASR were implanted between 2004 and 2008 in 145 patients (69 men and 76 women) with a mean age of 57 years. 21 patients (23 hips) were lost from follow-up. Average follow-up was 76 months (50 to 91). Up now 42 ASR implants have been revised (27.0%): revision involved 9 hips on 41 treated with resurfacing (21.9%) and 33 hips on 114 treated with XL total hip arthroplasty (28.9%). Main reasons for revision were aseptic loosening with or without metallosis in 23 hips (56%), infection in 3 hips (7%), recurrent dislocation in 1 hip (2%), periprosthetic fractures in 1 hip (2%), elevation of blood metal ion in 6 (14%), pain in 2 (5%), unknown in 6 (14%). The cumulative survival for our ASR implants series was 61.6% with revision for any reason as the end-point after a mean follow-up of 76 months. The cumulative survival with revision for any reason as the end-point for ASR and ASR XL were respectively 67.0% and 59.1%. For patients who did not undergone revision, the mean Harris hip score improved to 91 (57 to 100) at five years and the mean satisfaction after the operation was graded 4.4 in a score from 1 to 5. Periprosthetic osteolysis was not found around any unrevised hip. Average cup inclination was 48° for the functioning hips and 55° for the revised hips. Metal ions plasma concentration analysis was conducted in 83 patients (87 hips). Elevated metal ion concentration (>7 μg/l) was found in 39 patients (42 hips, 48%) with average plasma concentrations of 37.3 μg/l for chromium and 81.5 μg/l for cobalt. Lower metal ions levels (<7 μg/l) were found in 44 patients (45 hips, 52%) with average plasma concentrations of 1.2 μg/l for chromium and 1.9 μg/l for cobalt. Our current concerns involve our large series of 30 asymptomatic patients (31 hips) with a radiographically stable implant without osteolysis signs but with elevated blood metal ion concentrations.
Second-generation metal-on-metal bearings have been used since the late 1980s as alternative bearings to eliminate aseptic loosening due to polyethylene wear. The aim of the present study was to evaluate the long-term results of a series of Metasul (Zimmer GmbH, Winterthur, Switzerland) metal-on-metal total hip arthroplasty (THA). Between January 1993 and September 1996, 149 cementless THAs with a 28 mm Metasul articulation were performed in 111 consecutive patients. Implant survivorship was calculated and clinical and radiographic evaluations were performed on 82 hips still available for follow-up at a mean of 18 years postoperatively. Nine hips (6.0%) were revised. The cumulative probability of survival of the overall implant at 18 years postoperatively with revision for any reason as the end point, was 0.937 (95% confidence interval, 0.888 to 0.985). The cumulative probability of survival of Metasul with revision for any reason as the end point, was 0.956 (95% confidence interval, 0.916 to 0.997). Various degrees of radiolucencies and osteolysis were found proximally around the femoral components of 25 hips (20%). Cementless Metasul THA showed high survival at 18 years postoperatively.
