the advance medial pivot knee ( wright medical technology inc . , memphis , tn , usa ) was designed to reproduce the kinematics of the medial pivot motion in the normal knee1,2,3,4,5 ) .
the medial compartment of the prosthesis has ball - in - socket geometry to improve joint congruity for stability and the lateral compartment allows for rolling and gliding during knee flexion as in the intact knee6,7,8,9 ) .
other major benefits of the prosthesis include reduced incidences of condylar lift - off and polyethylene wear due to the improved conformity of the polyethylene insert6,10 ) .
however , the influence of such biomechanical characteristics of the advance medial pivot knee on patient satisfaction and implant survivorship has not been sufficiently investigated in studies .
long - term studies have never been published and short - term or mid - term follow - up studies are rare11,12,13 ) . in this study
, we investigated the clinical and radiological results and complications of total knee arthroplasty ( tka ) using the advance medial pivot knee for a minimum follow - up of 5 years under the hypothesis that the posterior cruciate ligament sacrificing , non - substituting ( ps ) implant designed to replicate the medial pivot motion in the non - arthritic knee would yield satisfying functional improvement without significant complications .
of the patients who had undergone tka using the ps advance medial pivot knee between october 2004 and december 2006 , 80 patients ( 120 knees ) who were available for more than 5-year follow - up were retrospectively reviewed .
there were 9 males ( 15 knees ) and 71 females ( 105 knees ) .
their mean age at the time of surgery was 66.4 years ( range , 42 to 83 years ) .
the mean follow - up period was 64.7 months ( range , 60 to 86 months ) .
the preoperative diagnosis was osteoarthritis in 108 knees ( 90.0% ) , rheumatoid arthritis in 4 knees ( 3.3% ) , and osteonecrosis in 8 knees ( 6.7% ) .
the indications for surgery were defined as severe pain or difficulty in performing daily living activities without any improvement with conservative therapy , kellgren - lawrence grade 3 or 4 in cases of patients 65 years of age , and kellgren - lawrence grade 4 in cases of patients with < 65 years of age .
the number of patients aged 60 years was 24 , 20 of which had osteoarthritis and the remaining 4 had rheumatoid arthritis .
all the operations were performed by the same surgeon . after a midline skin incision , limited medial parapatellar arthrotomy was performed and traditional sequential medial release was carried out .
the distal femoral cut was performed using an intramedullary alignment guide and the proximal tibial cut was done using an extramedullary alignment guide .
the femoral component was placed in a 3 externally rotated position with reference to the posterior condylar axis . in order to maintain the medial pivot motion during flexion and extension ,
care was taken not to cause excessive release of the medial collateral ligament ( mcl ) . however , if an unavoidable excessive ligament release in the case of varus knee results in a 3 mm medial gap , the ligament was sutured to the pes anserinus attachment site after implant insertion to maintain proper tension for < 2 - 3 mm medial gap during flexion . the mcl suturing was required in 11 knees in whom the postoperative rehabilitation regimen was identical to that in the other patients .
the medial / lateral ligament balance and flexion / extension gap balance were adjusted to confirm the absence of abnormal findings on the valgus / varus stress test , the ability to get full knee extension , and absence of medial / lateral laxity or lift off of a trial component during flexion .
patellar resurfacing was selectively performed : the patella was resurfaced in all knees with rheumatoid arthritis and in all of the remaining knees except for 16 knees with relatively good articular surface . immediately after surgery
, patients were allowed to undertake quadriceps strengthening exercises and active straight leg - raising as instructed prior to surgery . on the first postoperative day
, continuous passive motion exercises were initiated . at 3 - 4 days after surgery , when straight leg - raising could be performed without difficulty , progressive weight bearing was started with an assistance of a walker or a cane .
clinical evaluation was based on the pre- and postoperative range of motion ( rom ) , knee society ( ks ) knee score and function score , western ontario and mcmaster universities osteoarthritis index ( womac ) score , and postoperative complications .
the maximum further flexion without pain was measured in supine position using a goniometer . on the radiological evaluation , the standing anteroposterior view and the 30 flexion lateral view taken at the last follow - up
were assessed according to the american knee society roentgenographic evaluation system . in particular , fluoroscopy was used to determine the appearance of radiolucency around the femoral and tbial components .
the femorotibial angle (  ) change was measured . to assess the implant position , the valgus angle of the femoral component (  ) and the varus angle of the tibial component (  ) were measured on the anteroposterior view and the flexion angle of the femoral component (  ) and the posterior slope of the tibial component (  ) were measured on the lateral view .
the kaplan - meier method was used for survival analysis with revision or the need for revision defined as failure .
the paired t - test was used to determine the significance of clinical results and changes in the femorotibial angle .
of the patients who had undergone tka using the ps advance medial pivot knee between october 2004 and december 2006 , 80 patients ( 120 knees ) who were available for more than 5-year follow - up were retrospectively reviewed .
there were 9 males ( 15 knees ) and 71 females ( 105 knees ) .
their mean age at the time of surgery was 66.4 years ( range , 42 to 83 years ) .
the mean follow - up period was 64.7 months ( range , 60 to 86 months ) .
the preoperative diagnosis was osteoarthritis in 108 knees ( 90.0% ) , rheumatoid arthritis in 4 knees ( 3.3% ) , and osteonecrosis in 8 knees ( 6.7% ) .
the indications for surgery were defined as severe pain or difficulty in performing daily living activities without any improvement with conservative therapy , kellgren - lawrence grade 3 or 4 in cases of patients 65 years of age , and kellgren - lawrence grade 4 in cases of patients with < 65 years of age .
the number of patients aged 60 years was 24 , 20 of which had osteoarthritis and the remaining 4 had rheumatoid arthritis .
, limited medial parapatellar arthrotomy was performed and traditional sequential medial release was carried out .
the distal femoral cut was performed using an intramedullary alignment guide and the proximal tibial cut was done using an extramedullary alignment guide .
the femoral component was placed in a 3 externally rotated position with reference to the posterior condylar axis . in order to maintain the medial pivot motion during flexion and extension ,
care was taken not to cause excessive release of the medial collateral ligament ( mcl ) . however ,
if an unavoidable excessive ligament release in the case of varus knee results in a 3 mm medial gap , the ligament was sutured to the pes anserinus attachment site after implant insertion to maintain proper tension for < 2 - 3 mm medial gap during flexion .
the mcl suturing was required in 11 knees in whom the postoperative rehabilitation regimen was identical to that in the other patients .
the medial / lateral ligament balance and flexion / extension gap balance were adjusted to confirm the absence of abnormal findings on the valgus / varus stress test , the ability to get full knee extension , and absence of medial / lateral laxity or lift off of a trial component during flexion .
patellar resurfacing was selectively performed : the patella was resurfaced in all knees with rheumatoid arthritis and in all of the remaining knees except for 16 knees with relatively good articular surface . immediately after surgery
, patients were allowed to undertake quadriceps strengthening exercises and active straight leg - raising as instructed prior to surgery . on the first postoperative day , continuous passive motion exercises were initiated . at 3 - 4 days after surgery , when straight leg - raising could be performed without difficulty , progressive weight bearing was started with an assistance of a walker or a cane .
clinical evaluation was based on the pre- and postoperative range of motion ( rom ) , knee society ( ks ) knee score and function score , western ontario and mcmaster universities osteoarthritis index ( womac ) score , and postoperative complications .
the maximum further flexion without pain was measured in supine position using a goniometer . on the radiological evaluation , the standing anteroposterior view and the 30 flexion lateral view taken at the last follow - up
were assessed according to the american knee society roentgenographic evaluation system . in particular , fluoroscopy was used to determine the appearance of radiolucency around the femoral and tbial components . the femorotibial angle (  )
change was measured . to assess the implant position , the valgus angle of the femoral component (  ) and the varus angle of the tibial component (  ) were measured on the anteroposterior view and the flexion angle of the femoral component (  ) and the posterior slope of the tibial component (  )
the kaplan - meier method was used for survival analysis with revision or the need for revision defined as failure .
the paired t - test was used to determine the significance of clinical results and changes in the femorotibial angle .
there was significant improvement in the rom between the preoperative and last follow - up assessments : the mean flexion contracture decreased from 7.6 to 1.5 and the mean range of further flexion increased from 115.1 ( rom , 107.5 ) to 120.5 ( rom , 119 ) ( p<0.05 ) .
the ks knee score and function score , and the womac score for pain and stiffness and function were significantly improved ( p<0.05 ) ( table 1 ) .
the femorotibial angle was improved from a mean of 4.64.5 varus preoperatively to a mean of 5.82.4 valgus postoperatively .
the mean  ,  ,  and  angle were 96.22.1 , 89.11.7 , 2.51.5 and 84.42.7 , respectively . except for 2 cases of aseptic loosening
, 2 mm radiolucency was not observed in any case when assessed according to the american knee society roentgenographic evaluation system ( table 2 ) .
complications occurred in 4 knees ( 3.3% ) : periprosthetic patellar fracture in 2 ( 1.7% ) and aseptic loosening in 2 ( 1.7% ) . there was no case of infection .
periprosthetic patellar fractures were caused by aggressive flexion exercises in one and by trauma in the other .
conservative treatment for the former with no displacement and open reduction and internal fixation using tension band wiring for the latter resulted in satisfactory outcomes .
aseptic tibial component loosening was observed at 1 year and 9 months after surgery in one knee , which was revised using structural allograft and stemmed tibial component ( fig .
aseptic loosening in the other case was observed at 5 years and 7 months after surgery , and the plain radiography revealed osteolysis in the femur and aseptic loosening in the tibia .
the 7-year survival rate according to the kaplan - meier method was 98.1% ( 95% confidence interval , 0.96 to 1.00 ) ( fig .
the clinical and radiological results of tka using the ps advance medial pivot knee were satisfactory without significant complications after the minimum 5-year mid - term follow - up . the significance of this study can be found in the fact that the mid - term results of advance medial pivot knee in tka have never been addressed in domestic studies and our results were comparable to those described in international mid - term follow - up studies11,12,13 ) .
fan et al.11 ) reported minimum 5-year follow - up results of 58 medial pivot tkas : the mean rom was improved from 103.5 preoperatively to 115.4 at the last follow - up ; non - progressive radiolucent lines were observed in only 2 cases ; and there was no case of revision for loosening . in a mean 6.7-year follow - up study by karachalios et al.12 ) , the mean rom was improved from 101 preoperatively to 117 at the last follow - up and the 5-year survival rate and 9-year survival rate were 99.1% and 97.5% , respectively .
vecchini et al.13 ) followed 160 patients ( 172 knees ) for a mean of 7 years after medial pivot tka : the mean rom was improved from 97.7 preoperatively to 112.5 at the last follow - up and the survival rate was 98.6% . in our mean
6.1-year follow - up study , the mean rom was improved from 107.5 preoperatively to 119 at the last follow - up , showing more favorable results than the above - mentioned studies . the 7-year survival rate ( 98.1% )
, significant clinical improvement was noted in all patients after tka using the ps advance medial pivot knee . although we used the ps type implant in all knees during tka , there are some studies providing comparisons with other types of implants .
bae et al.14 ) reported there was no notable difference in the clinical and radiological results of tka between the cruciate retaining ( cr ) type advance medial pivot knee group ( 67 cases ) and the ps type group ( 70 cases ) .
pritchett15 ) investigated patient preferences in knee prostheses for a mean of 7 years after bilateral tka : 77% of the 344 patients preferred the medial pivot knee prosthesis to other ps type prostheses .
youm et al.16 ) showed that the minimum 2-year follow - up results of tka using the ps type advance medial pivot knee were comparable to those of tka using the nexgen lps system . on the other hand , kim et al.17 ) reported that the satisfaction rate in the cr type advance medial pivot knee group was significantly low compared to that in the pfc sigma mobile - bearing prosthesis group and the complication rate was remarkably higher in the former group during the mean 2.6-year follow - up .
however , we believe their results should be interpreted with caution because it is difficult to associate the complications occurred in their patients ( infection , persistent flexion contracture , and constant swelling ) with the design features of the implant .
most ps type implants necessitate an extensive box cutting to enable the cam - post mechanism .
however , the ps type advance medial pivot knee does not require box cutting because the ultracongruent polyethylene insert that has no post provides anteroposterior stability .
accordingly , considering that more bone stock preservation would be of benefit for possible revisions , we preferred to use the advance medial pivot knee in young patients with a relatively high likelihood of revision , if they met the indications .
this is why relatively young patients 60 years of age ( 19 patients , 24 knees ) were included in the study .
however , we believe long - term follow - up studies should be conducted to assess the influence of bone stock preservation in the box of the femur on future revision surgery . of the 2 cases of aseptic loosening , the early loosening of the tibial component in one knee can be attributed to surgical errors : 2 of varus cutting of the proximal tibia .
in addition , the use of a 10-mm metal augment without a stem for proximal tibial bone loss may have resulted in increased stress in the medial aspect of the proximal tibia , eventually resulting in subsidence of the medial tibia and tibial component loosening .
regarding the other case in which osteolysis of the femur and aseptic loosening of the tibia were found at 5 years and 7 months after surgery , it is difficult to identify whether the complications were associated with the ultracongruent design of the advance medical pivot knee .
rather , minoda et al.10 ) reported that the medial pivot knee prosthesis caused significantly less wear particles than other ps type prostheses . in the other aforementioned mid - term follow - up studies , the incidences of osteolysis and loosening were not significantly high in the knees with medial pivot knee prostheses .
thus , we believe this should be elucidated in further long - term follow - up biomechanical studies .
one of the limitations of this study is that due to the retrospective study design , the level of evidence was relatively low compared to prospective studies . in addition , the number of cases was small and the follow - up was not maintained for the long term .
finally , the study did not examine whether replication of medial pivoting , the biomechanical advantage of the medial pivot knee , was successfully realized after tka .
the clinical and radiological results of tka using the ps advance medial pivot knee designed to reproduce normal knee kinematics were satisfactory after the minimum 5-year mid - term follow - up .
and the incidence of tibial component loosening after using this ultracongruent implant was not remarkable .
 purposeto evaluate minimum 5-year follow - up clinical and radiological results of total knee arthroplasty ( tka ) using a posterior cruciate ligament sacrificing ( ps ) , non - substituting advance medial pivot knee.materials and methodsone hundred and twenty knees in 80 patients who could be followed up for more than 5 years after tka using the ps advance medial pivot knee were evaluated retrospectively . 
 the evaluations included the preoperative and postoperative range of motion ( rom ) , tibiofemoral angle , knee society ( ks ) knee and function scores , and western ontario and mcmaster universities arthritis index ( womac ) score . 
 the kaplan - meier method was used for survival analysis.resultsthe rom increased from a preoperative mean flexion contracture of 7.6 and further flexion of 115.1 to a postoperative mean flexion contracture of 1.5 and further flexion of 120.5. the tibiofemoral angle was changed from 4.6 varus preoperatively to 5.8 valgus postoperatively . 
 the ks knee and function scores as well as womac score significantly improved after surgery ( p<0.05 ) . 
 complications developed in 4 cases ( 3.3% ) : 2 cases of periprosthetic patellar fracture ( 1.7% ) and 2 cases of aseptic loosening ( 1.7% ) . 
 the seven - year survival rate was 98.1% in the kaplan - meier survival analysis.conclusionsthe minimum 5-year follow - up results of tka using the ps medial pivot knee were satisfactory . 