5-10 Years Follow-up Results Of Cementless Zweymüller Hip System

BackgroundsThe value of threaded uncemented cups and rectangular stems is still controversial because some anthors consider that this kind of prosthesis is prone to loosening compared with hemispheric cups and cylindrical or elliptic stems,though a significant improvement have been caused on design,material and surface roughness of Zweym(u|")ller hip system comprising a threaded double-cone cup and a rectangular stem.Besides,due to the differences in living habit and body conditions,whether the intermediate-term or even long-term results associated with the use of Zweym(u|")ller hip system in China is comparable with previous literatures in developed countries is still unknown.This program was conducted to review the cases who were treated with total hip replacement from 1996 to 2002 by a single surgeon using cementless Zweym(u|")ller hip systems in Nanfang Hospital and to provide references for orthopedists for prosthesis selection.ObjectivesTo analyze the intermediate-term results associated with the use of Zweym(u|")ller hip system and to provide references for orthopedists for prosthesis selection.Methods1.Follow-up methodsPatients who could be contacted through telephone or letters were suggested to visit the out-patient clinic for an evaluation.Patients who were unable to return for a follow-up evaluation due to a long distance from our hospital completed a telephone interview and sent recent radiograghs.With regard to the patients who had a clear address but could not be contacted through telephone or letters, investigator dropped in and took radiograghs at their local hospitals.2.Evaluation methodsBoth clinical evaluation and radiological evaluation were performed.Harris hip score,pain extinction time,crutch walking time,functional capabilities,patient satisfaction and complications were the clinical items involved while the radiological items included cortical hypertrophy,medullary sclerosis,heterotopic ossification,radiolucent lines,osteolysis and wear rate.Data collection and evaluation was accomplished by an independent investigator.Linear wear was measured on radiograghs and was corrected for magnification by comparing the diameter of the femoral head on each individual radiogragh with the known diameter of 28 mm.Results1.116 cases(142 hips) were involved,of which 57 cases(72 hips) were available for following up.44 cases(57 hips) were evaluated both clinically and radiographically while 7 cases(8 hips) and 6 cases(7 hips) were only evaluated clinically and radiographically respectively.Unilateral arthroplasty had been performed in 42 cases,whereas 15 cases had bilateral arthroplasty.The average follow-up period was 7.4 years(range 5 to 10 years).The average age at the initial operation was 51.1 and the average body mass index was 22.7.Initial diagnosis:aseptic necrosis of femoral head(44 cases,55 hips),ankylosing spondylitis(7 cases,10 hips),congenital dysplasia of the hip(2 cases,3 hips), idiopathic osteoarthritis(2 cases,2 hips),nonunion after femoral neck fracture(2 cases,2 hips).2.The mean preoperative Harris hip score(HHS) was 46.0 while the mean postoperative HHS was 93.2.Distal cortical hypertrophy and medullary sclerosis were observed in 26 hips(44.1%) and 26 hips(49.1%) respectively.Heterotopic ossification arose in 40 hips(62.5%).Radiolucent lines occured in 23 stems(35.9%) but in no cups.Radiolucent lines were mostly observed in Gruen zone 1.Osteolysis oecured in 7 cups(10.9%) and 18 stems(28.1%).Osteolysis was mostly observed in Delee Zone 3 and Gruen zone 7.In the distal Gruen zones 3,4 and 5,no radiolucent line or osteolysis was observed.Mean linear polyethylene wear rate was 0.09mm/y and 0.12mm/y for ceramic-polyethylene prosthesis and metal-polyethylene prosthesis respectively.No hips had been revised,two cups needed revision surgery because of aseptic loosening.The survivorship with aseptic loosening as a definition of failure was 96.9%for the acetabular component and 100%for the femoral component.Conclusions1.The mean preoperative HHS was 46.0 while the mean postoperative HHS was 93.2.The incidence rate of cortical hypertrophy,medullary sclerosis,heterotopic ossification,radiolucent lines and osteolysis was 44.1%,49.1%,62.5%,35.9%and 32.8%respectively.The survivorship was 96.9%for the acetabular component and 100%for the femoral component.2.The survival rate of Zweym(u|")ller hip systems in this group was comparable with previous literatures with approximate follow-up period,but osteolysis was more common.The overall results were satisfactory.3.Of the 116 cases,57 cases were followed up and the follow-up ratio was 49.1%.The reasons for a low follow-up ratio included contact messages not detailed enough or changed and patients'ignorance.