the use of a modular neck in total hip arthroplasty ( tha ) was first introduced by toni et al.1 ) in 2001 . compared to conventional single neck - head taper or monolithic design , the modular neck system is a beneficial choice in cases with anatomical variations as it allows for increased intraoperative flexibility through more independent control over leg length , femoral offset and femoral version2 ) . moreover , a modular neck allows changes of the neck without the removal of well - fixed stems in revision surgery2 ) . on the other hand , disadvantages have been identified when using modular necks including corrosion , metallosis3 ) , modular neck fracture4 ) and others at the second taper junction . this study aimed to investigate the need for and radiological and clinical outcomes of modular necks in primary tha . this study retrospectively reviewed 30 patients ( 34 cases ) who could be followed up for a minimum of three years after undergoing primary tha using a modular neck from april 2011 to january 2013 . the mean postoperative follow - up was 48.2 months ( range , 39 - 59 months ) . the subjects were 19 men ( 23 cases ) and 11 women ( 11 cases ) . no patients had anatomical deformities such as acetabular dysplasia , deformity of the proximal femur and others . the implants used were the m / l taper prosthesis with kinectiv technology ( zimmer , warsaw , in , usa ) ( fig . 1 ) as femoral stems and the continuum acetabular system ( zimmer ) as acetabular cup components in all cases . ceramic - on - ceramic bearings were used in 15 cases , and ceramic - on - polyethylene bearings were used in 9 cases . the head sizes were 32 mm in 14 cases , and 36 mm in 16 cases . all surgical procedures were performed by a single surgeon using an anterolateral ( modified watson - jones ) approach . the size of the femoral component was predicted by overlaying a template on anteroposterior ( ap ) radiographs to determine whether the body of femoral component can fill the femoral metaphysis . the medial portion of the body of the component was made to fit the medial cortex of the proximal metaphysis as full as possible . after deciding the height of the femoral component , the length and offset of the neck component were determined according to the center of rotation . after preoperative templating and intraoperative trial reduction , modular neck selection was finally determined by checking hip joint range of motion ( rom ) , leg length and soft tissue tension . during the trial , necks with impingement or dislocation were replaced . the version angle of the modular neck used was straight in all cases ; anteverted or retroverted necks were not used . a standard offset neck was used in 31 hips ( 91.2% ) , a varus or valgus neck was required in 3 hips ( 8.8% ) , including a varus neck in 2 and a valgus neck in 1 ( fig . partial weight bearing walking was begun on the second postoperative day , and walker or crutch walking was carried out for 4 weeks after surgery . all patients underwent clinical and radiological follow - up at 6 weeks , 3 , 6 , and 12 months , and every year postoperatively . clinical results were measured using the harris hip scores ( hhs)5 ) at each follow - up . pain , febrile sense , swelling , fullness and soft tissue mass at the surgical site were identified . in radiographic analysis , ap view and translateral view of the operated hip were checked . periprosthetic proximal femoral osteolysis caused by corrosion was examined in gruen zones 1 and 76 ) . on the final follow - up radiographs , the position , stability and leg length discrepancy of cup and stem components were checked . the stability of femoral stems were classified according to the criteria described by engh et al.7 ) , and acetabular cup inclination and anteversion were evaluated using measurements established by woo and morrey8 ) . leg length discrepancy was defined as the difference between the distances from horizontal interischial line to the greater trochanter . at the first month postoperatively , laboratory tests of inflammatory profiles , including erythrocyte sedimentation rate ( esr ) , c - reactive protein ( crp ) and white blood cell count ( wbc ) were evaluated . all statistical analyses were performed with dbstat software version 5.0 ( barun lab , yongin , korea ) . this study retrospectively reviewed 30 patients ( 34 cases ) who could be followed up for a minimum of three years after undergoing primary tha using a modular neck from april 2011 to january 2013 . the mean postoperative follow - up was 48.2 months ( range , 39 - 59 months ) . the subjects were 19 men ( 23 cases ) and 11 women ( 11 cases ) . no patients had anatomical deformities such as acetabular dysplasia , deformity of the proximal femur and others . the implants used were the m / l taper prosthesis with kinectiv technology ( zimmer , warsaw , in , usa ) ( fig . 1 ) as femoral stems and the continuum acetabular system ( zimmer ) as acetabular cup components in all cases . ceramic - on - ceramic bearings were used in 15 cases , and ceramic - on - polyethylene bearings were used in 9 cases . the head sizes were 32 mm in 14 cases , and 36 mm in 16 cases . all surgical procedures were performed by a single surgeon using an anterolateral ( modified watson - jones ) approach . the size of the femoral component was predicted by overlaying a template on anteroposterior ( ap ) radiographs to determine whether the body of femoral component can fill the femoral metaphysis . the medial portion of the body of the component was made to fit the medial cortex of the proximal metaphysis as full as possible . after deciding the height of the femoral component , the length and offset of the neck component were determined according to the center of rotation . after preoperative templating and intraoperative trial reduction , modular neck selection was finally determined by checking hip joint range of motion ( rom ) , leg length and soft tissue tension . during the trial , necks with impingement or dislocation were replaced . the version angle of the modular neck used was straight in all cases ; anteverted or retroverted necks were not used . a standard offset neck was used in 31 hips ( 91.2% ) , a varus or valgus neck was required in 3 hips ( 8.8% ) , including a varus neck in 2 and a valgus neck in 1 ( fig . partial weight bearing walking was begun on the second postoperative day , and walker or crutch walking was carried out for 4 weeks after surgery . all patients underwent clinical and radiological follow - up at 6 weeks , 3 , 6 , and 12 months , and every year postoperatively . clinical results were measured using the harris hip scores ( hhs)5 ) at each follow - up . pain , febrile sense , swelling , fullness and soft tissue mass at the surgical site were identified . in radiographic analysis , ap view and translateral view of the operated hip were checked . periprosthetic proximal femoral osteolysis caused by corrosion was examined in gruen zones 1 and 76 ) . on the final follow - up radiographs , the position , stability and leg length discrepancy of cup and stem components were checked . the stability of femoral stems were classified according to the criteria described by engh et al.7 ) , and acetabular cup inclination and anteversion were evaluated using measurements established by woo and morrey8 ) . leg length discrepancy was defined as the difference between the distances from horizontal interischial line to the greater trochanter . at the first month postoperatively , laboratory tests of inflammatory profiles , including erythrocyte sedimentation rate ( esr ) , c - reactive protein ( crp ) and white blood cell count ( wbc ) were evaluated . all statistical analyses were performed with dbstat software version 5.0 ( barun lab , yongin , korea ) . hhs improved from an average 64.09.5 points to 88.76.3 points in 24 patients , excluding 6 patients with a femur neck fracture ( p=0.000 ) . pain , febrile sense , swelling , fullness and soft tissue mass and other complications at the surgical site were not observed during follow - up . during follow - up periods , radiolucency of more than 2 mm manifesting proximal periprosthetic femoral osteolysis was not seen on radiographs . at the final follow - up , the mean lateral inclination of the acetabular cup was 45.3(36-61 ) and the mean anteversion was 21.7(11-29 ) on radiographs . femoral stems were inserted in a neutral position ( 29 hips ) and a varus position ( 5 cases ) . the stability of femoral components was graded as bony stable ( 31 hips ) and fibrous stable ( 3 hips ) . leg length discrepancy with the contralateral side was less than 5 mm in 31 hips ( 91.2% ) and greater than 5 mm in 3 hips ( 8.8% ) ( table 2 ) . at the first month postoperatively , esr , crp and wbc values were within the normal range ( table 3 ) . additional wiring was done in one patient case due to femur crack , an intraoperative complication , during stem insertion , and bone union was achieved during follow up . although dislocation , a complication developed on the second postoperative week , occurred in a patient , this complication did not recur after reduction . revision - free survival was 100% at a maximum follow - up of 59 months . the use of a modular neck in tha has been found to reduce postoperative dislocation , a serious complication , by allowing intraoperative adjustment of length , version and offset910 ) . however , numerous studies have reported modular neck fracture and mechanical failure as a second taper junction serves as an additional site for failure1112131415161718 ) . furthermore , the occurrence of local , systemic metallic debris and increase in metallic ions are problematic clinically , and these seem to cause fretting and crevice corrosion at the modular neck - stem junction and head - neck junction1920 ) . more severe fretting and crevice corrosion at the neck - stem junction appear to be attributable to the eccentric load that leads to increased stress on the neck - stem connection , while the forces at the head - neck connection are transmitted through the spherical bearing resulting in relatively lower stresses221 ) . favorable outcomes have been addressed in several long - term follow - up studies on tha performed using s - rom ( depuy , warsaw , in , usa ) , a device consisting of titanium - titanium junction2223 ) . moreover , good clinical results have been achieved in studies on tha conducted with devices composed of titanium - titanium neck - stem junction24 ) . on the contrary , de martino et al.25 ) have reported corrosion at the neck - stem taper in all 60 cases retrieved after undergoing tha with cobalt - chromium alloy neck segment and titanium - alloy femoral stem components . in the retrieval analysis of 7 different types of modular total hip designs , kop et al.21 ) observed severe corrosion and fretting in cobalt - chromium alloy devices and mild corrosion in titanium alloy devices in 57 cases . in the present study , the reason for no complications associated with corrosion seems to be the use of devices consisting of titanium - titanium neck - stem junction with corrosion resistance properties . in retrieval studies of kop et al.21 ) , de martino et al.25 ) , and lanting et al.26 ) , the average time to revision surgery due to corrosion or periprosthetic fracture was 12 , 21.4 , and 20.4 months , respectively . in this investigation , the mean duration of postoperative follow - up was 48.2 months , sufficient enough to observe complications in the modular junction . in cases requiring revision due to adverse local tissue reaction or periprosthetic fractures , symptoms were found to be associated in 80% according to de martino et al.25 ) and 100% according to lanting et al26 ) . in the current study , there were no laboratory findings or symptoms suspected of adverse local tissue reaction caused by corrosion . even though archibeck et al.27 ) and sariali et al.28 ) have proposed that the use of modular stems in tha is beneficial in restoration of hip geometry , gerhardt et al.29 ) have suggested no clear benefit . although the authors decided femoral stems through preoperative templating in hips with without anatomical deformity , we experienced intraoperative dislocation , leg lengths discrepancy and impingement in some cases . the main reason that we used modular necks was to resolve these clinical problems by increasing intraoperative flexibility even in hips with normal anatomy . modular necks were finally chosen by comprehensively considering hip rom , leg length , and soft tissue tension after intraoperative trial reduction . our study used two varus necks and a valgus neck , and these neck components were selected intraoperatively to optimize leg length without affecting offset . taking into consideration the fact that varus or valgus necks were used in 8.8% of cases , the effectiveness of the modular neck is partially expected in normal anatomical hip . first , no comparative analysis was done with the group that underwent surgery using monoblock stems instead of modular necks . this retrospective study was limited by the relatively small sample size and short follow - up period . additional studies with a larger sample size are warranted to further identify factors that influence postoperative outcomes through long - term follow - up and explore the occurrence of complications . in addition , we did not measure serial metal ion levels necessary to quantitatively analyze corrosion . we did not perform any revision surgery and our study identified that the use of the modular neck had satisfactory clinical and radiographic results . this suggests that the use of the modular neck in primary tha without anatomical deformity is safe at a follow - up of 39 months .
purposethis study aimed to investigate the outcomes of modular neck - utilization in primary total hip arthroplasty ( tha).materials and methodsthirty patients ( 34 hips ) who had modular stem tha between april 2011 and january 2013 were evaluated . 
 there were 19 men and 11 women with a mean age of 61.2 years at the time of surgery . 
 there were 20 cases of osteonecrosis of femoral head , 7 cases of osteoarthritis , 6 cases of femur neck fracture , and 1 case of rheumatoid arthritis . 
 no patients presented with anatomical deformity of hip . 
 patients were operated on using a modified watson - jones anterolateral approach . 
 all patients underwent clinical and radiological follow - up at 6 weeks , 3 , 6 , and 12 months , and every year postoperatively . 
 the mean duration of follow - up was 48.2 months ( range , 39 to 59 months).resultsthe average harris hip score improved from 63.7 to 88.1 at the final follow - up . 
 radiographically , mean acetabular cup inclination was 45.3(range , 36-61 ) and anteversion was 21.7(range , 11-29 ) . 
 all were neutral - positioned stems except 5 which were varus - positioned stems . in only 3 cases ( 8.8% ) , varus or valgus necks were required . a case of linear femoral fracture occurred intraoperatively and 1 case of dislocation occurred at postoperative 2 weeks . 
 no complications at modular junction were occurred.conclusionour study shows that the use of modular necks had favorable clinical and radiographic results . 
 this suggests that the use of modular neck in primary tha without anatomical deformity is safe at a follow - up of 39 months .