human
***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background and purpose Short femoral stems have been introduced in total hip arthroplasty in order to save proximal bone stock . We hypothesized that a short stem preserves periprosthetic bone mineral density ( BMD ) and provides good primary stability . Methods We carried out a prospect i ve cohort study of 30 patients receiving the collum femoris-preserving ( CFP ) stem .  Preoperative total hip BMD and postoperative periprosthetic BMD in Gruen zones 1–7 were investigated by dual-energy x-ray absorptiometry ( DXA ) , stem migration was analyzed by radiostereometric analysis ( RSA ) , and the Harris hip score ( HHS ) was determined . Results 2 patients were excluded intraoperatively and 1 patient was revised due to a deep infection , leaving 27 patients for analysis . The mean HHS increased from 49 ( 24–79 ) preoperatively to 99 ( 92–100 ) after 2 years . DXA after 1 year showed substantial loss of BMD in Gruen zone 7 ( –31 % ) , zone 6 ( –19 % ) , and zone 2 ( –13 % , p < 0.001 ) compared to baseline BMD determined immediately postoperatively . The bone loss in these regions did not recover after 2 years , whereas the more moderate bone loss in Gruen zones 1 , 3 , and 5 partially recovered . There was a correlation between low preoperative total hip BMD and a higher amount of bone loss in Gruen zones 2 , 6 and 7 . RSA showed minor micromotion of the stem : mean subsidence was 0.13 ( 95 % CI : –0.28 to 0.01 ) mm and mean rotation around the longitudinal axis was 0.01º ( 95 % CI : –0.1 to 0.39 ) after 2 years . Interpretation We conclude that substantial loss in proximal periprosthetic BMD can not be prevented by the use of a novel type of short , curved stem , and forces appear to be transmitted distally . However , the stems showed very small migration — a characteristic of stable uncemented implants Bone stock-preserving short stem prostheses have gained importance in  total hip arthroplasty ( THA ) with the use of minimally invasive surgical procedures . Because of their metaphyseal fixation and their dependency on the calcar radius , it is unknown whether the femoral offset can be reproduced with the same accuracy following short stem vs st and ard stem THA . This study clarifies whether it is possible to restore the femoral offset using a short stem prosthesis ( Fitmore ; Zimmer , Warsaw , Indiana ) compared with a conventional straight stem prosthesis ( CLS ; Zimmer ) following minimally invasive implantation using an anterolateral approach . In a prospect i ve , r and omized , double-blinded study , 80 patients underwent THA using a short stem ( SS group ; n=40 ) or CLS implant ( control group ; n=40 ) . Follow-up examinations were conducted 6 weeks postoperatively . Radiological and functional outcomes were measured . Subjective assessment of quality of life was evaluated using the Harris Hip Score ( HHS ) , the Short Form 36-item health survey ( SF-36 ) , and the Western Ontario and McMaster Universities Osteoarthritis Index ( WOMAC ) . Pre- and postoperative comparison of the groups ' change in offset showed no significant differences ( SS group difference from pre- to postoperative , 6.1±6.5 mm ; control group difference from pre- to postoperative , 6.5±7.1 mm ; P=.93 ) . Group comparison after 6 weeks revealed no significant differences in HHS , SF-36 , or WOMAC . Based on these data , an equivalent reproducibility of the femoral offset was demonstrated following short stem and straight stem THA using a minimally invasive anterolateral approach . If the long-term results of short stems show a comparable survival , they represent a sensible alternative to st and ard stems Purpose On the basis of positive clinical results with mid- and long-term follow-up using the Mayo short stem , the Metha neck-preserving stem ( BBraun , Aesculap , Tuttlingen , Germany ) was introduced . The purpose of this study was to vali date the implant design by direct acquisition of bone remodelling data from total hip arthroplasty ( THA ) recipients using dual-energy X-ray absorptiometry ( DEXA ) . Methods After power analysis , 25 patients were included in this prospect i ve study . Patients were examined clinical ly and underwent DEXA examinations preoperatively and postoperatively at one week , six months and one and two years after THA . Gruen zones were adapted to the short stem design ( R1–R7 ) . Results The Harris Hip Score ( HHS ) increased significantly by 31 points . No stem had to be revised . Bone mineral density ( BMD ) in the greater trochanter decreased significantly from 0.78 g/cm2 postoperatively to 0.72 g/cm2 two years after surgery . Marginal changes were seen in the lateral distal regions ( R4–R5 ) . In the minor trochanter region , BMD increased significantly after two years by 12.9 % . In the calcar region , BMD exceeded the baseline value by 6.1 % two years after implantation . Conclusions Stress shielding seems to occur at the greater trochanter due to the vast cross-section of the implant . However , the aim of proximal load transfer of the Metha stem seems to be partially achieved . DEXA analysis revealed a concentrated load distribution on the medial portion of the femur , which is an important region to guarantee long-term implant survival Background Stress shielding of the proximal femur has been observed in a number of conventional cementless implants used in total hip arthroplasty .  Short femoral-neck implants are cl aim ing less interference with the biomechanics of the proximal femur . The goal of this study was to investigate the changes of bone-mineral density in the proximal femur and the clinical outcome after implantation of a short femoral-neck prosthesis . Methods We prospect ively assessed the clinical outcome and the changes of bone mineral density of the proximal femur up to one year after implantation of a short femoral neck prosthesis in 20 patients with a mean age of 47 years ( range 17 to 65 ) . Clinical outcome was assessed using the Harris Hip Score . The WOMAC was used as a patient-relevant outcome -measure . The bone mineral density was determined using dual energy x-ray absorptiometry , performed 10 days , three months and 12 months after surgery . Results The Harris Hip Score improved from an average preoperative score of 46 to a postoperative score at 12 months of 89 points , the global WOMAC index from 5,3 preoperatively to 0,8 at 12 months postoperatively . In contrast to conventional implants , the DEXA-scans overall revealed a slight increase of bone mineral density in the proximal femur in the 12 months following the implantation . Conclusion The short femoral neck stem lead to a distinct bone reaction . This was significantly different when compared to the changes in bone mineral density reported after implantation of conventional implants Flaws in the design , conduct , analysis , and reporting of r and omised trials can cause the effect of an intervention to be underestimated or overestimated . The Cochrane Collaboration ’s tool for assessing risk of bias aims to make the process clearer and more Ceramic-on-ceramic hip replacements might stress the bone interface more than a metal-polyethylene because of material stiffness , microseparation , and sensitivity to impingement . To ascertain whether this potentially increased stress caused an increased cup migration we compared a ceramic-on-ceramic with a metal-on-polyethylene implant for cup migration . Sixty one patients ( 61 hips ) undergoing THA for osteoarthritis were  r and omized to ceramic on ceramic ( Ce/Ce ) or cobalt-chromium on cross-linked polyethylene bearings ( PE ) in the same uncemented cup shell . Migration was followed with RSA . At 2 years we observed similar mean cup translations in the 3 directions ( 0.07 - 0.40 mm vs. 0.05 - 0.31 mm , Ce/Ce vs. PE ) , as well as similar rotations around the 3 axes ( 0.31 - 0.92 ° vs. 0.57 - 1.40 ° ) . WOMAC and SF-36 scores were also similar and no radiolucent lines or osteolysis found . The large migration seen in some cups in both implant groups will require close monitoring to ascertain the reasons . Mean proximal wear of the polyethylene liners measured 0.016 mm between 2 and 24 months . Our data suggest there is no increased cup migration in the ceramic-on-ceramic implant compared with the metal-on-polyethylene , and they seem an equally safe choice . However , the low wear measured with the more versatile and less expensive cross-linked polyethylene makes it a strong contender . Levels of Evidence : Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence Introduction Short stem prostheses have been developed to preserve proximal femoral bone stock . This prospect i ve , r and omized study compared periprosthetic bone remodelling following short and straight stem implantation 1 year after surgery . Material s and methods One hundred and forty-four consecutive patients undergoing total hip arthroplasty were r and omized to either a Fitmore short or a cementless straight stem ( both Zimmer , Winterthur , Switzerl and ) . Periprosthetic bone mineral density ( BMD ) was measured using dual-energy X-ray absorptiometry performed the day before surgery and at 7 days , 3 months and 1 year postoperatively . Furthermore , the HHS and the WOMAC were obtained . Results One hundred and thirty-eight patients completed 1-year follow-up . Periprosthetic BMD changes at 1 year were most pronounced in the proximal medial region of interest ( ROI ) 7 with −17.2 % after short stem and −16.7 % after straight implantation ( p = 0.67 ) . However , there was significantly less BMD reduction in ROI 6 following short ( −4.7 % ) versus straight stem ( −10.8 % ) implantation ( p = 0.01 ) . There were no significant differences between the two groups in terms of the HHS and the WOMAC either before or after surgery . Conclusion One year after surgery , both stems showed an implant-specific periprosthetic bone remodelling . Nevertheless , proximal load transfer was more pronounced after short stem implantation than with a straight stem Background and purpose — We hypothesized that an ultra-short stem would load the proximal femur in a more physiological way and could therefore reduce the adaptive periprosthetic bone loss known as stress shielding . Patients and methods — 51 patients with primary hip osteoarthritis were r and omized to total hip arthroplasty ( THA ) with either an ultra-short stem or a conventional tapered stem . The primary endpoint was change in periprosthetic bone mineral density ( BMD ) , measured with dual-energy x-ray absorptiometry ( DXA ) , in Gruen zones 1 and 7 , two years after surgery . Secondary endpoints were change in periprosthetic BMD in the entire periprosthetic region , i.e. Gruen zones 1 through 7 , stem migration measured with radiostereometric analysis ( RSA ) , and function measured with self-administered functional scores . Results — The periprosthetic decrease in BMD was statistically significantly lower with the ultra-short stem . In Gruen zone 1 , the mean difference was 18 % ( 95 % CI : −27 % to −10 % ) . In zone 7 , the difference was 5 % ( CI : −12 % to −3 % ) and for Gruen zones 1–7 the difference was also 5 % ( CI : −9 % to −2 % ) . During the first 6 weeks postoperatively , the ultra-short stems  migrated 0.77 mm more on average than the conventional stems . 3 months after surgery , no further migration was seen . The functional scores improved during the study and were similar in the 2 groups . Interpretation — Up to 2 years after total hip arthroplasty , compared to the conventional tapered stem the ultra-short uncemented anatomical stem induced lower periprosthetic bone loss and had equally excellent stem fixation and clinical outcome Our aim in this prospect i ve study was to compare the bone mineral density ( BMD ) around cementless acetabular and femoral components which were identical in geometry and had the same alumina modular femoral head , but differed in regard to the material of the acetabular liners ( alumina ceramic or polyethylene ) in 50 patients ( 100 hips ) who had undergone bilateral simultaneous primary total hip replacement .  Dual energy X-ray absorptiometry scans of the pelvis and proximal femur were obtained at one week , at one year , and annually thereafter during the five-year period of the study . At the final follow-up , the mean BMD had increased significantly in each group in acetabular zone I of DeLee and Charnley ( 20 % ( 15 % to 26 % ) , p=0.003 ) , but had decreased in acetabular zone II ( 24 % ( 18 % to 36 % ) in the alumina group and 25 % ( 17 % to 31 % ) in the polyethylene group , p=0.001 ) . There was an increase in the mean BMD in zone III of 2 % ( 0.8 % to 3.2 % ) in the alumina group and 1 % ( 0.6 % to 2.2 % ) in the polyethylene group ( p=0.315 ) . There was a decrease in the mean BMD in the calcar region ( femoral zone 7 ) of 1 
    Output:
    
agent
Our results suggest that compared with CS , SS may provide superior bone remodelling and similar survival rates and clinical outcomes .
However , the short-term follow-up of the included studies was inadequate to determine the long-term performance of SS
***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background and purpose Short femoral stems have been introduced in total hip arthroplasty in order to save proximal bone stock . We hypothesized that a short stem preserves periprosthetic bone mineral density ( BMD ) and provides good primary stability . Methods We carried out a prospect i ve cohort study of 30 patients receiving the collum femoris-preserving ( CFP ) stem .  Preoperative total hip BMD and postoperative periprosthetic BMD in Gruen zones 1–7 were investigated by dual-energy x-ray absorptiometry ( DXA ) , stem migration was analyzed by radiostereometric analysis ( RSA ) , and the Harris hip score ( HHS ) was determined . Results 2 patients were excluded intraoperatively and 1 patient was revised due to a deep infection , leaving 27 patients for analysis . The mean HHS increased from 49 ( 24–79 ) preoperatively to 99 ( 92–100 ) after 2 years . DXA after 1 year showed substantial loss of BMD in Gruen zone 7 ( –31 % ) , zone 6 ( –19 % ) , and zone 2 ( –13 % , p < 0.001 ) compared to baseline BMD determined immediately postoperatively . The bone loss in these regions did not recover after 2 years , whereas the more moderate bone loss in Gruen zones 1 , 3 , and 5 partially recovered . There was a correlation between low preoperative total hip BMD and a higher amount of bone loss in Gruen zones 2 , 6 and 7 . RSA showed minor micromotion of the stem : mean subsidence was 0.13 ( 95 % CI : –0.28 to 0.01 ) mm and mean rotation around the longitudinal axis was 0.01º ( 95 % CI : –0.1 to 0.39 ) after 2 years . Interpretation We conclude that substantial loss in proximal periprosthetic BMD can not be prevented by the use of a novel type of short , curved stem , and forces appear to be transmitted distally . However , the stems showed very small migration — a characteristic of stable uncemented implants Bone stock-preserving short stem prostheses have gained importance in  total hip arthroplasty ( THA ) with the use of minimally invasive surgical procedures . Because of their metaphyseal fixation and their dependency on the calcar radius , it is unknown whether the femoral offset can be reproduced with the same accuracy following short stem vs st and ard stem THA . This study clarifies whether it is possible to restore the femoral offset using a short stem prosthesis ( Fitmore ; Zimmer , Warsaw , Indiana ) compared with a conventional straight stem prosthesis ( CLS ; Zimmer ) following minimally invasive implantation using an anterolateral approach . In a prospect i ve , r and omized , double-blinded study , 80 patients underwent THA using a short stem ( SS group ; n=40 ) or CLS implant ( control group ; n=40 ) . Follow-up examinations were conducted 6 weeks postoperatively . Radiological and functional outcomes were measured . Subjective assessment of quality of life was evaluated using the Harris Hip Score ( HHS ) , the Short Form 36-item health survey ( SF-36 ) , and the Western Ontario and McMaster Universities Osteoarthritis Index ( WOMAC ) . Pre- and postoperative comparison of the groups ' change in offset showed no significant differences ( SS group difference from pre- to postoperative , 6.1±6.5 mm ; control group difference from pre- to postoperative , 6.5±7.1 mm ; P=.93 ) . Group comparison after 6 weeks revealed no significant differences in HHS , SF-36 , or WOMAC . Based on these data , an equivalent reproducibility of the femoral offset was demonstrated following short stem and straight stem THA using a minimally invasive anterolateral approach . If the long-term results of short stems show a comparable survival , they represent a sensible alternative to st and ard stems Purpose On the basis of positive clinical results with mid- and long-term follow-up using the Mayo short stem , the Metha neck-preserving stem ( BBraun , Aesculap , Tuttlingen , Germany ) was introduced . The purpose of this study was to vali date the implant design by direct acquisition of bone remodelling data from total hip arthroplasty ( THA ) recipients using dual-energy X-ray absorptiometry ( DEXA ) . Methods After power analysis , 25 patients were included in this prospect i ve study . Patients were examined clinical ly and underwent DEXA examinations preoperatively and postoperatively at one week , six months and one and two years after THA . Gruen zones were adapted to the short stem design ( R1–R7 ) . Results The Harris Hip Score ( HHS ) increased significantly by 31 points . No stem had to be revised . Bone mineral density ( BMD ) in the greater trochanter decreased significantly from 0.78 g/cm2 postoperatively to 0.72 g/cm2 two years after surgery . Marginal changes were seen in the lateral distal regions ( R4–R5 ) . In the minor trochanter region , BMD increased significantly after two years by 12.9 % . In the calcar region , BMD exceeded the baseline value by 6.1 % two years after implantation . Conclusions Stress shielding seems to occur at the greater trochanter due to the vast cross-section of the implant . However , the aim of proximal load transfer of the Metha stem seems to be partially achieved . DEXA analysis revealed a concentrated load distribution on the medial portion of the femur , which is an important region to guarantee long-term implant survival Background Stress shielding of the proximal femur has been observed in a number of conventional cementless implants used in total hip arthroplasty .  Short femoral-neck implants are cl aim ing less interference with the biomechanics of the proximal femur . The goal of this study was to investigate the changes of bone-mineral density in the proximal femur and the clinical outcome after implantation of a short femoral-neck prosthesis . Methods We prospect ively assessed the clinical outcome and the changes of bone mineral density of the proximal femur up to one year after implantation of a short femoral neck prosthesis in 20 patients with a mean age of 47 years ( range 17 to 65 ) . Clinical outcome was assessed using the Harris Hip Score . The WOMAC was used as a patient-relevant outcome -measure . The bone mineral density was determined using dual energy x-ray absorptiometry , performed 10 days , three months and 12 months after surgery . Results The Harris Hip Score improved from an average preoperative score of 46 to a postoperative score at 12 months of 89 points , the global WOMAC index from 5,3 preoperatively to 0,8 at 12 months postoperatively . In contrast to conventional implants , the DEXA-scans overall revealed a slight increase of bone mineral density in the proximal femur in the 12 months following the implantation . Conclusion The short femoral neck stem lead to a distinct bone reaction . This was significantly different when compared to the changes in bone mineral density reported after implantation of conventional implants Flaws in the design , conduct , analysis , and reporting of r and omised trials can cause the effect of an intervention to be underestimated or overestimated . The Cochrane Collaboration ’s tool for assessing risk of bias aims to make the process clearer and more Ceramic-on-ceramic hip replacements might stress the bone interface more than a metal-polyethylene because of material stiffness , microseparation , and sensitivity to impingement . To ascertain whether this potentially increased stress caused an increased cup migration we compared a ceramic-on-ceramic with a metal-on-polyethylene implant for cup migration . Sixty one patients ( 61 hips ) undergoing THA for osteoarthritis were  r and omized to ceramic on ceramic ( Ce/Ce ) or cobalt-chromium on cross-linked polyethylene bearings ( PE ) in the same uncemented cup shell . Migration was followed with RSA . At 2 years we observed similar mean cup translations in the 3 directions ( 0.07 - 0.40 mm vs. 0.05 - 0.31 mm , Ce/Ce vs. PE ) , as well as similar rotations around the 3 axes ( 0.31 - 0.92 ° vs. 0.57 - 1.40 ° ) . WOMAC and SF-36 scores were also similar and no radiolucent lines or osteolysis found . The large migration seen in some cups in both implant groups will require close monitoring to ascertain the reasons . Mean proximal wear of the polyethylene liners measured 0.016 mm between 2 and 24 months . Our data suggest there is no increased cup migration in the ceramic-on-ceramic implant compared with the metal-on-polyethylene , and they seem an equally safe choice . However , the low wear measured with the more versatile and less expensive cross-linked polyethylene makes it a strong contender . Levels of Evidence : Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence Introduction Short stem prostheses have been developed to preserve proximal femoral bone stock . This prospect i ve , r and omized study compared periprosthetic bone remodelling following short and straight stem implantation 1 year after surgery . Material s and methods One hundred and forty-four consecutive patients undergoing total hip arthroplasty were r and omized to either a Fitmore short or a cementless straight stem ( both Zimmer , Winterthur , Switzerl and ) . Periprosthetic bone mineral density ( BMD ) was measured using dual-energy X-ray absorptiometry performed the day before surgery and at 7 days , 3 months and 1 year postoperatively . Furthermore , the HHS and the WOMAC were obtained . Results One hundred and thirty-eight patients completed 1-year follow-up . Periprosthetic BMD changes at 1 year were most pronounced in the proximal medial region of interest ( ROI ) 7 with −17.2 % after short stem and −16.7 % after straight implantation ( p = 0.67 ) . However , there was significantly less BMD reduction in ROI 6 following short ( −4.7 % ) versus straight stem ( −10.8 % ) implantation ( p = 0.01 ) . There were no significant differences between the two groups in terms of the HHS and the WOMAC either before or after surgery . Conclusion One year after surgery , both stems showed an implant-specific periprosthetic bone remodelling . Nevertheless , proximal load transfer was more pronounced after short stem implantation than with a straight stem Background and purpose — We hypothesized that an ultra-short stem would load the proximal femur in a more physiological way and could therefore reduce the adaptive periprosthetic bone loss known as stress shielding . Patients and methods — 51 patients with primary hip osteoarthritis were r and omized to total hip arthroplasty ( THA ) with either an ultra-short stem or a conventional tapered stem . The primary endpoint was change in periprosthetic bone mineral density ( BMD ) , measured with dual-energy x-ray absorptiometry ( DXA ) , in Gruen zones 1 and 7 , two years after surgery . Secondary endpoints were change in periprosthetic BMD in the entire periprosthetic region , i.e. Gruen zones 1 through 7 , stem migration measured with radiostereometric analysis ( RSA ) , and function measured with self-administered functional scores . Results — The periprosthetic decrease in BMD was statistically significantly lower with the ultra-short stem . In Gruen zone 1 , the mean difference was 18 % ( 95 % CI : −27 % to −10 % ) . In zone 7 , the difference was 5 % ( CI : −12 % to −3 % ) and for Gruen zones 1–7 the difference was also 5 % ( CI : −9 % to −2 % ) . During the first 6 weeks postoperatively , the ultra-short stems  migrated 0.77 mm more on average than the conventional stems . 3 months after surgery , no further migration was seen . The functional scores improved during the study and were similar in the 2 groups . Interpretation — Up to 2 years after total hip arthroplasty , compared to the conventional tapered stem the ultra-short uncemented anatomical stem induced lower periprosthetic bone loss and had equally excellent stem fixation and clinical outcome Our aim in this prospect i ve study was to compare the bone mineral density ( BMD ) around cementless acetabular and femoral components which were identical in geometry and had the same alumina modular femoral head , but differed in regard to the material of the acetabular liners ( alumina ceramic or polyethylene ) in 50 patients ( 100 hips ) who had undergone bilateral simultaneous primary total hip replacement .  Dual energy X-ray absorptiometry scans of the pelvis and proximal femur were obtained at one week , at one year , and annually thereafter during the five-year period of the study . At the final follow-up , the mean BMD had increased significantly in each group in acetabular zone I of DeLee and Charnley ( 20 % ( 15 % to 26 % ) , p=0.003 ) , but had decreased in acetabular zone II ( 24 % ( 18 % to 36 % ) in the alumina group and 25 % ( 17 % to 31 % ) in the polyethylene group , p=0.001 ) . There was an increase in the mean BMD in zone III of 2 % ( 0.8 % to 3.2 % ) in the alumina group and 1 % ( 0.6 % to 2.2 % ) in the polyethylene group ( p=0.315 ) . There was a decrease in the mean BMD in the calcar region ( femoral zone 7 ) of 1 
    Output:
    