total hip arthroplasty ( tha ) is one of most effective surgical procedures for patients with end - stage osteoarthritis of the hip . more than one million primary tha procedure are performed annually in the world . however , longevity of tha is a critical problem for young and active patients . a study of swedish national registry reported 10-year survival rate for tha of 94.8% and 87.7% after primary cemented and primary cementless tha , respectively . many studies have shown that high volume hospitals have lower mortality rates and better clinical outcomes . both teaching hospitals and surgical specialty hospitals teach young orthopedic trainees the theory and technical skills required for tha . since trainees are new to performing surgeries , they should be supervised by experienced and skilled surgeons . this practice helps not only to avoid possible serious risks for patients but also to impart effective education regarding surgical skills . the instructor can immediately and appropriately solve any difficult situation experienced by the trainee during a surgical procedure . these systems minimize any potential risk of complications , and provide an effective educational system for trainees . the relationship between a surgeon s case volume and the risk of complications after tha is important . one group studied 37,881 peoples who underwent their first primary tha and determined that surgeons should perform at least 35 tha procedures annually to reduce the risk of surgical complications . woolson et al . reported similar clinical results for tha in teaching hospital with resident trainee and a specialty hospital with no trainees . whether teaching hospitals have better outcomes for tha than non - teaching hospitals is remains controversial . however , technical failures during surgery are likely to increase the revision rate after tha . post - operative radiographic findings such as socket and stem alignments as well as fixation pattern can significantly influence clinical results . in the united states , lower inpatient mortality after tha has been reported in high volume hospitals . the rate of complications and the quality of tha can easily be used to evaluate the technical skills of surgeons . in orthopedic surgery , the cumulative summation statistical test ( cusum test ) has been used to evaluate the quality of surgical skill after total knee arthroplasty . the purpose of this investigation was to clarify the following four points regarding the technical skills of trainees and the education system for surgical skills for primary tha . first , operative time and blood loss during surgery were compared between trainees and instructors . second , quality monitoring according to biau et al . and the incidence of three selected complications ; large vessel laceration , nerve palsy , and deep infection , were compared between trainees and instructors . third , clinical hip scores ( the japanese orthopaedic association hip score were compared between trainees and instructors . fourth , survival according to the kaplan - meier method with the endpoint defined as revision surgery was compared between trainees and instructors . we established an educational system for surgical skill training at the department of orthopedics nagoya university hospital in 1998 to provide specialist training for hip surgery . trainees had to perform a minimum of 100 hip operations to acquire adequate knowledge and surgical technical expertise for primary tha . during the 5 years of training , skilled instructors had to provide supervision . trainees also had to learn the surgical techniques required for eccentric rotational acetabular osteotomy according to hasegawa et al . the ethics committee of our institutions approved this study , and all patients provided informed and consent for this study .   between 2006 and 2010 , 589 primary tha procedures performed in two hip surgery training institutions , nagoya university hospital and aichiken saiseikai hospital , were included in this study ( figure 1 ) . the two instructors had experience of performing more than 1000 tha procedures with sufficient expertise to teach the theory and techniques for both primary and revision tha . the trainees were orthopedic surgeons receiving education on the surgical techniques of primary tha to be a hip surgery specialist . one hundred and six hips were excluded from this study : 69 because of revision tha , 12 because of complete dislocation ( crowe type 4 ) , 10 because of socket liner revision , 8 because of component removal of any component without implantation because of deep infection , and 7 because of surface replacement . trainees operated on 259 hips ( 207 with cementless fixation ) , and instructors operated on 224 hips ( 196 with cementless fixation ) . trainees performed a significantly lower number of cementless primary tha procedures than the instructors ( p = 0.013 ) . all operations were performed via a posterior approach and tight repair of the capsule and short rotators was performed in all cases . the average duration of follow - up was 5.1years ( range , 37 years ) . statistical analysis was performed using the student - t test , chi - square test , and fisher s exact test the average age of the patients in the trainees and instructor groups at the time of primary tha were 61.9  11.7 years and 60.8  11.6 years , respectively ( table 1 ) . the operative time for trainees and instructors were 87.0  28.3 min and 73.1  19.6 min , respectively ( table 2 ) . the operative time was significantly shorter for instructors than for trainees ( p = 0.031 ) . blood loss during surgery was 293  256 g for trainees and 271  176 g for instructors . complications of primary tha incidence of total complication ( p=0.099 ) surgical complications occurred in 11 hips ( 3.5% ) during surgeries performed by trainees . the complications included two cases of femoral artery lacerations requiring repair by a vascular surgeon ; two cases of sciatic nerve palsy , three acetabular facture , three hip dislocations , and one case of skin necrosis . surgical complications occurred in three hips ( 1.3% ) during surgeries performed by instructors . the complication rate was higher in the trainee group than in the instructor group , but the difference was not significant ( p=0.099 ) . quality monitoring revealed poor quality in 14 hips in the trainee group and in six hips in the instructor group ( table3 , and 4 ) , but this difference was also not statistically significant ( p=0.171 ) . quality monitoring of primary tha * same patient ; femoral fracture and deep infection primary tha quality monitoring incidence of poor quality ( p=0.171 ) in the trainees group the clinical hip score according to the japanese orthopedic association was 58.9  11.7 before surgery and was 94.1  8.6 at final follow - up . in the instructors group the clinical hip score was 57.8  10.6 before surgery and 93.8  8.1 at the final follow - up . survival rate at 5 years after primary tha according to the kaplan - meier method with revision surgery defined as the endpoint were 97.2% ( 95% confidence interval 94.2100 ) for the trainee - performed tha and 99.3% ( 95%ci : 95.4100 ) for instructor - performed tha . surgical complications occurred in 11 and 3 hips for which tha was performed by trainees and instructors , respectively . the complication rates was higher in the trainee group but was not significantly different from the instructor group ( p = 0.099 ) . poor quality according to biau et al . was identified in 14 hips in the trainees group and in six hips in the instructor group , which was also not statistically significant ( table 3 , and 4 ) . comparison of complications and the quality of primary tha between hospitals is extremely difficult because of patient attributes . the first question is whether all patients treated with primary tha have similar baseline characteristics . . reported on surgical candidate selection between surgeons at the same institution in their study of primary tha and total knee arthroplasty . they compared the cases of four surgeons using the short form 36 and the western ontario and mcmaster osteoarthritis index ( womac ) and found no difference , concluding that similar patients were treated with both primary tha and total knee arthroplasty . we evaluated three complications : large vascular laceration reqiring repair , nerve palsy , and deep infection . reported a high rate of poor quality , in 57 of 200 hips ( 28.5% ) . in our study , poor quality was noted only in 14 hips ( 5.4% ) in the trainee group and in six hips ( 2.7% ) in the instructor group . another study compared 22 hips with cementing failure within 5 years and 60 hips with good cementing outcomes after primary tha . the failure rate was 9.5 fold higher for inadequate cementing ( barrack types c [ 5099% radiolucency at the cement - bone interface ] and d [ 100% radiolucency or failure ] than for a good cement - bone interface . the definition of poor quality has not been well established ; for instance , it is uncertain whether shortening by more than 1 cm and lengthening by more than 2 cm indicates discrepancy . similarly , it is uncertain whether varus or valgus stem alignment more than 4 degrees constitutes poor quality . more precise criteria of poor surgical quality are necessary to determine long - term clinical outcomes . easier cases such as crowe type i or osteonecrosis of the hip , were operated upon by trainees , and more complicated cases such as high hip dislocation or failed femoral / acetabular osteotomy , were operated on by instructors . however , random selection of difficult hips for the scientific investigation is not only dangerous for the patients , but will also reduce the results when the quality of the surgery is measured . short - term japanese orthopedic association hip score for primary tha in trainee group were not significantly different from the instructor group . long - term follow - up will be needed to establish a better educational system for trainees . operative time in the trainee group was significantly longer than that in the instructor group . complications rate was higher , but not significantly in the trainee group than in the instructor group . short - term clinical and radiographic results of primary tha by trainees were found to be safe and satisfactory . takefumi amano discloses no financial support or relationship that may pose conflict of interest . yukiharu hasegawa discloses financial support to the department of hip and knee surgery , nagoya university graduate school of medicine from stryker co. , yoshida hospital , and nagoya orthopedic clinic .
abstracta total of 483 hips treated by primary total hip arthroplasty ( tha ) were investigated to evaluate the surgical skill of the performing surgeon . 
 surgical trainees operated on 259 hips and instructors on 224 hips . 
 the average age of the patients at the time of tha in the trainee and instructor group was 61.9 and 60.8 years old , respectively . 
 the average follow - up duration was 5.1 years . 
 the operative time in the trainee group and instructor group was 87.0 and 73.1 min , respectively ( p=0.031 ) . 
 complications were noted in 11 hips ( 3.5% ) in the trainee group ; acetabular fracture , 3 hips ; dislocation , 3 hips ; femoral artery lacerations that needed repair surgery , 2 hips ; sciatic nerve palsy , 2 hips ; and skin necrosis , 1 hip . 
 complication were noted in three hips ( 1.3% ) in the instructor group ; femoral fracture , 1 hip ; acetabular fracture , 1 hip ; dislocation , 1 hip . 
 complication rate in the trainee group was higher than in the instructor group . 
 the monitored quality of the surgeries performed by trainees and instructors was not significantly different . 
 poor quality was identified in 14 hips in the trainee group and 6 hips in instructor group . 
 no significant difference was found in the hip score between the trainees and instructors before and after surgery . 
 revision arthroplasty was defined as the end - point for primary tha . 
 kaplan - meier survivorship at 5 years after primary tha was 97.2% in trainee group and 97.3% in the instructor group . 
 short - term clinical and radiographic results of primary tha in the trainee and instructor groups were considered safe and satisfactory .