coupling of metal on conventional polyethylene have been traditionally used as bearing surface of total hip arthroplasty ( tha ) . however , this coupling could make debris of polyethylene resulting in an aseptic loosening over time is well known1 ) .
previous other studies reported young age and increased activity levels as independent risk factors for an aseptic loosening23 ) .
for this reason , an alternate bearing surfaces such as ceramic on ceramic ( coc ) , metal on highly cross - linked polyethylene ( hxlpe ) have been used in young patients45 ) . since 2004 , our adult artificial joint reconstruction institute started to use a 36 mm metal head coupling with hxlpe for primary tha , if possible . to gain better artificial hip joint stability ,
36 mm metal head have been used popularly6 ) . also , to reduce wear problem of polyethylene , the use of hxlpe have increased7 ) .
so , our institute has used 36 mm metal head coupling with hxlpe as articulation surface regardless of patient age .
currently , many papers are focusing on coc bearing surface of tha for younger cohort8910 ) . on the other hand ,
few reports were for results of 36 mm metal head coupling with hxlpe as younger cohort 's bearing surface .
the purpose of this paper is to evaluate the results of primary tha using 1st generation hxlpe in patients aged 50 years and less with minimum five year follow - up .
a retrospective review of 52 consecutive primary thas performed by one senior author was conducted . among 52 cases ,
so , we evaluated 41 hips ( 31 patients ; 14 males and 17 females ) .
all patients underwent tha with a 36 mm metal head on hxlpe between 2004 and 2010 .
osteoarthritis included 13 cases of 2nd osteoarthritis ( dysplastic hip sequela 9 cases , post - traumatic sequela 4 cases , slipped capital femoral epiphysis sequela 1 case ) .
another 9 cases were ankylosing spondylitis and 7 cases underwent primary tha due to osteonecrosis of femoral head ( table 1 ) .
mean patient 's age was 41 years ( range , 22 - 50 years ) , and mean follow - up duration was 83 months ( 62 - 139 months ) . a cementless acetabular cup with a porous coating ( trilogy ; zimmer inc . ,
warsaw , in , usa ) and a hxlpe with an inner diameter of 36 mm ( longevity ; zimmer inc . ) were placed in all patients .
acetabular components had an average outer diameter of 54 mm ( range , 50 - 60 mm ) .
1050 polyethylene , which had been pre - heated and cross - linked with a 9.5 mrad electron - beam .
the preforms were then melted to eliminate the remaining free radicals and sterilized using a gas plasma .
components were used in 32 cases underwent cementless femoral fixation ( fig . 1 ) and versys ( zimmer inc . ) components in 9 cases underwent cemented femoral fixation .
all surgical procedures was modified hardinge 's approach with the patient in the lateral position .
all acetabular components were inserted using a press fit technique with under reaming of the acetabulum by 1 to 2 mm . to secure initial mechanical stability of the acetabular component , we used adjunctive acetabular screw when needed . if cementless femoral stem had a rotational instability when subject to rotational stress test after femoral trial stem insertion , we used cemented femoral fixation regardless of patient 's age .
all cementless stems were inserted using standard press fit techniques to insure longitudinal and rotational stability , and all cemented femoral stems were inserted using meticulous third generation cementing techniques .
prophylactic antibiotics were administrated to all 41 cases , and the same postoperative protocol was used in all .
patients were allowed to sit on the first postoperative day and stand with supports , according to ability , after blood drainage removal .
no range of motion limitation was present immediately after surgery , and no abduction pillow was used in any patient .
patients were followed at 6 weeks , and at 3 , 6 , and 12 months postoperatively .
in addition , modified harris hip scores ( hhs ) and merle d'aubigne and postel score were determined .
modified hhs were classified as excellent ( 91 - 100 ) , good ( 81 - 90 ) , fair ( 71 - 80 ) , or poor ( 61 - 70 ) , and the merle d'aubigne and postel scores were used to categorize patients to six grades according to level of pain ( 1 - 6 ) , mobility ( 1 - 6 ) , and the ability to walk ( 1 - 6 ) . in cases that underwent uncemented fixation ,
the status of fixation of femoral component was assessed using the method of engh et al.11 ) , and in cases that underwent cemented fixation , femoral components were assessed the amount of cement filling using the method of barrack et al.12 ) , using immediate postoperative radiographs .
all radiographic examinations included an anteroposterior ( ap ) view of the pelvis centered over the pubis , and axial view by a shoot through lateral of the hip .
acetabular cup abduction angles were measured using the methods of engh et al.13 ) and kennedy et al14 ) .
the evidence of linear radiolucencies , bony ingrowth , fracture , and osteolysis were determined using sequential radiographic views , which also allowed comparative assessments of component position versus immediate postoperative views to determine the presence of component migration and/or loosening .
penetrations of femoral head into polyethylene liners were calculated as two - dimensional linear penetrations on ap radiographs of the pelvis using polyware pro three - dimensional distal version 5.10 software ( draftware inc . , vevay , in , usa ) by well - trained one chief resident .
2 ) . in this program , wear rate is calculated through the 3-point marked on edges of the femoral head and acetabular cup using serial plain radiograph .
this program allowed us to know volumetric wear size using pelvis ap and axial view .
so , we decided to check linear wear rate using serial pelvis ap view only .
we checked bedding in state wear using postoperative and post one year operative pelvis ap view16 ) . to check steady state wear rate ,
this program divided the result with the number of year and let us know annual wear rate automatically .
average modified hhs at final follow - up was 875 ( range , 81 - 98 ) , and it was better than ' good ' in all cases , and merle d'aubigne and postel scores were more than 15 ( range , 15 - 18 ) in all cases .
radiographic final follow - up exams showed stable fixation in all patients with uncemented femoral components , and barrack type a or b in all patients with cemented femoral components .
mean acetabular cup inclination and anteversion were 45.81(range , 36.33-54.91 ) and 13.26(range , 6.72-27.71 ) , respectively . there was no radiographic evidence of osteolysis in the pelvis or proximal femur , and no acetabular cup or femoral stem failing due to aseptic loosening .
in all patients , average femoral head penetration during the first postoperative year ( predominantly representing polyethylene creep ) was 0.0640.002 mm / year , and the average steady - state wear rate determined using radiographs taken at oneyear postoperatively and at latest follow - up was 0.0420.001 mm / year .
first is high activity of young cohort , second is patient 's remained long life span
. this condition will result in more wear rates of articulation surfaces compared with old .
improvement in prosthetic design and bearing surfaces has eliminated in concerns of wear problem in younger patients .
however , concerns of coc bearing surface 's negative property remained 1819 ) . besides problems of squeaking and fracture of ceramic head , some paper reported possibility of increasing stress on trunnion compared with metallic head when using big size of femoral head20 ) .
our institute has used 36 mm metal head coupling with hxlpe as an articulation surface regardless of patient 's age .
it has been shown that hxlpe wear rates decreased by 58% to 74% over the ultra - high molecular weight polyethylene in vitro study21 ) . during midterm follow - up for this cohort ,
steady - state wear rate was 0.0420.001 mm / year . this result is less than 0.1 mm / year regarded as osteolysis threshold wear rate established by dumbleton et al22 ) .
but , there are also some trade - offs in using 36 mm metal head coupled with hxlpe .
unfortunately , the increase in gamma radiation dose is associated with the degradations of other mechanical properties including a decrease in tensile yield strength and fatigue strength and resultant liner breakage23 ) .
previously , our institute reported a liner rim area breakage case in tha after using 1st generation hxlpe mated against 36 mm metal head21 ) .
majority of these reports pointed out high body mass index ( bmi ) , improper acetabular cup position , thin liner thickness and impingement between femoral stem and liner , etc .
this patient belonged to normal bmi and proper acetabular cup position so called ' safe zone ' on radiographs .
so , we conducted revision with larger acetabular cup than index operation to apply thicker liner .
the average liner thickness of this 41 cohorts was 7.46 mm ( range , 6.8 - 9.9 mm ) . in this cohort , there was no liner breakage during follow - up periods . during follow - ups ,
she sustained car accident and had injury of femoral head posterior dislocation with acetabular fracture .
anteversion of the index cup was 8. the patient underwent isolated acetabular revision just after second dislocation , and has done routine indoor activity well since then .
there were some reports 36 mm metal head could result in high volumetric wear compared with 28 mm metal head25 ) .
polyware software could measure volumetric wear size using pelvis ap and axial view . however , hip axial we conducted during follow - up periods showed irregularity could result in some errors of measuring wear rate .
so , we decided to check linear wear rate using serial pelvis ap view only .
it is well known inflammatory disease cohort show a lower activity compared with other disease cohort26 ) .
third , our study has some limitations on measuring wear rate . as to method of wear measurement , radiostereometric analysis ( rsa )
however , many radiographic in vivo studies of polyethylene wear in tha are restricted to measurements on plain radiographs because the rsa set - up is expensive and not widely available .
polyware software does not supply the accuracy required , and for such situations we recommend rsa .
for assessment of medium - term or long - term wear measurements in larger groups of patients , it is known as the polyware method is optimal , simple , and in relatively close agreement with the gold standard of rsa .
based on this finding , we think 36 mm metal head coupling with hxlpe as the good alternate articulation surface when planning tha for patients aged 50 years and less .
 purposewe evaluated the clinical and radiographic midterm results of primary total hip arthroplasty ( tha ) using a 36 mm diameter femoral head on 1st generation highly cross - linked polyethylene ( hxlpe ) in patients 50 years and less with minimum five year follow-up.materials and methodswe retrospectively reviewed 31 patients ( 41 hips ) aged 50 years and less underwent primary tha with a 36 mm diameter femoral head on hxlpe between 2004 and 2010 . 
 clinical follow - ups included specific measurements like modified harris hip scores ( hhs ) and merle d'aubigne and postel score . for radiologic evaluations , together with position of acetabular cup at six weeks later of postoperation , we separately calculated the penentrations of femoral head into polyethylene liners during postoperation and one year later check - ups , and during one year later check - ups and final check-ups.resultsthere were no major complications except for one case of dislocation . 
 average modified hhs at final follow - up was 88 ( 81 - 98 ) , and merle d'aubigne and postel scores were more than 15 . 
 mean acetabular cup inclination and anteversion were 45.81(36.33-54.91 ) and 13.26(6.72-27.71 ) , respectively . 
 average femoral head penetration of steady - state wear rate determined using radiographs taken at one - year postoperatively and at latest follow - up was 0.0420.001 mm / year.conclusionbased on minimum 5 years clinical results , we think 36 mm metal head coupling with hxlpe as the good alternate articulation surface when planning tha for patients aged 50 years and less . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSION