Abstract
The longevity of total joint arthroplasty relies on articulating surfaces that are durable and produce little polyethylene debris and consequent osteolysis and loosening. In an effort to improve wear characteristics of the acetabular line, Hylamer (Du Pont Depuy Orthopaedics, Warsaw, Indiana) was produced as an alternative to ultra high molecular weight polyethylene. To date however reports using Hylamer with Cobalt chrome, stainless steel and alumina ceramic femoral heads have yielded results that have not reached the potential of initial in vitro trials. No study has examined the outcome following a Zirconia femoral head and a Hylamer acetabular shell. The tribological properties of Zirconia make it an ideal countersurface with low friction and long term durability. This study examines the outcome when these components were used in combination with a select cohort of patients and evaluates the benefit of their continued use.
From 1994 to 1997 fifty one patients had Hylamer cup with zirconia femoral head elite total joint arthroplasty performed. Forty-seven patients with fifty-eight arthroplasties were included in this study. All patients were less that fifty years with a male preponderance. There were eleven bilateral arthroplasties all of which had the second procedure at least two months from the index procedure. The principle diagnosis was osteoarthritis in forty-three hips with rheumatoid disease in twelve hips. The remaining two patients were operated on for end stage osteonecrosis.
The Elite total joint arthroplasty (DePuy, Warsaw in.) was used in all cases. The 22.225mm zirconia head was used exclusive in this study. The Hylamer shell used was a solid polyethylene block with a minimum depth of 6mm. Both the acetabular and femoral component were cemented with Palacos polymethylmethacrelate (Howmedica, Rutherford NJ) using third generation cementing techniques.
Patients were evaluated both clinically and radiographically three months and six months following surgery and thereafter at yearly intervals. Both the SF36 questionnaire and Mayo score were used to evaluate subjectively and objectively patient outcome. Regression analysis was used to determine if the age, sex and weight of the patient as well as the angle of inclination of the acetabular cup correlated with polyethylene wear and outcome. Kaplan Meir survival analysis was used to calculate the probability of survival of the original prosthesis.
There was no correlation between age, weight nor sex of the patient and outcome. The angle of inclination was correlated with a poorer ourcome but this did not reach statistical significance. The mean linear wear rate was 0.021mm year (range 0.011–0.055). Ten year survivalship analysis was calculated at 97%. SF 36 scores were standardised and the mean post operative score was 89 (range 62–97).
The results presented are significantly better than previously described in clinical trials using Hylamer liners. The reasons for this are multifactorial. This study used 22.225 mm heads in association with a solid cemented polyethylene acetabular block. Both have been associated with lower volumetric wear but neither have been used on previous studies of Hylamer. In addition the tribological properties of Hylamer may have been undermined in previous studies by poorly conforming countersurfaces using a different manufacturer for femoral and acetabular components. Finally the use of a second generation ceramic, zirconia with a Hylamer liner has produced medium term outcomes that confound previous reports and that exceed many published reports on traditional polyethylene liners.
The abstracts were prepared by Mr Ray Moran. Correspondence should be addressed to him at the Irish Orthopaedic Association, Secretariat, c/o Cappagh Orthopaedic Hospital, Finglas, Dublin
