one of the major goals of total knee arthroplasty ( tka ) is to restore the normal alignment and balance of the knee to ensure long - term survival after joint replacement with pain relief and functional improvement . for this purpose , continuous efforts have been made to improve knee implants , surgical techniques , and postoperative rehabilitation protocols . however , functional problems after tka that restrict daily living activities can still be encountered in some patients . in cases where such problems occur due to the patient 's intrinsic characteristics in spite of proper surgical treatment and rehabilitation and the absence of evidence of infection , stiffness following tka has been treated with manipulation under anesthesia ( mua)2 ) , arthroscopic release3 ) , open arthrolysis4 ) or revision tka5 ) . among these , mua has been considered as the most effective simple primary treatment modality for stiffness that develops within 2 - 3 months following tka . efforts to evaluate the efficacy of arthroscopic release for fibroarthrosis following tka have been made by domestic researchers6 ) ; however , the prevalence and efficacy of mua have never been investigated in korea . therefore , we attempted to investigate the prevalence and outcomes of mua for stiffness in this study . of the total 4,449 knees ( 2,973 patients ) that underwent tka performed by the first author ( yoo ) of this study between march 2000 and august 2014 at our institution , those treated with mua for stiff knee following tka were reviewed for this study . during tka , lcs system ( depuy inc . , warsaw , in , usa ) was implanted in 181 knees , maxim prosthesis ( biomet inc . , warsaw , in , usa ) in 76 knees and nexgen lps - flex fixed knee ( zimmer inc . , warsaw , in , usa ) in 4,192 knees . in the knees with the lcs system , the surgery was performed using a gap technique , whereas in the knees with either the maxim prosthesis or the nexgen prosthesis , a measured resection technique was used . from march 2000 through mid - july 2004 thereafter , a minimally invasive surgery ( mis ) quad - sparing instrumentation was used in tka on 4,120 knees : 3,785 of these that underwent mis tka after november 2005 received the modular tibial implant ( " mini - keel " nexgen mis tibial component , zimmer inc . ) . the posterior cruciate ligament ( pcl ) was retained in 128 knees ( lcs , 66 ; maxim , 50 ; nexgen , 12 ) and replaced in 4321 knees ( lcs , 115 ; maxim , 26 ; nexgen , 4,180 ) . the patella was preserved in 119 knees ( lcs , 76 ; maxim , 5 ; nexgen , 38 ) and replaced in 4,330 knees ( lcs , 105 ; maxim , 71 ; nexgen , 4,154 ) ( table 1 ) . a hemovac drain was placed in the joint during surgery , which was removed on the 2nd postoperative day . continuous passive motion exercises were initiated from the 1st postoperative day . from the 2nd postoperative day , from the 3rd postoperative day , joint exercises and physical therapy were instructed by a physical therapist for approximately 2 weeks . at the time of discharge , patients with < 80 knee flexion or those with progressive stiffness of the knee in spite of 80 knee flexion were required to visit the outpatient clinic within 1 to 2 weeks afterwards . in these patients , if the range of flexion was limited to < 80 in the outpatient visit , mua was carried out . under sufficient muscle relaxation through general or spinal anesthesia , the hip was flexed to 90. the surgeon placed one hand under the popliteal area so as to maintain the knee joint as the center of the hinge during manipulation . then , holding the proximal tibia with the other hand , the surgeon gradually applied pressure to elicit flexion of the knee , which was repeatedly performed until signs of breakage of adhesions became palpable or audible in the sufficiently flexed knee . during the process , care was taken not to cause a periprosthetic fracture or a rupture of the extensor mechanism . subsequently , patient - controlled anesthesia was maintained for two days , and continuous passive motion exercises were started from the day of mua treatment . from the day after the treatment , aggressive physical therapy was carried out with a therapist until the patient could discharge with sufficient recovery of knee joint function . the name of diagnosis , preoperative range of motion ( rom ) of the knee , postoperative outcomes , postoperative level of stiffness and the timing of manipulation procedure were retrospectively reviewed . nineteen knees that are available for a minimum 1-year follow - up after manipulation were examined to evaluate the rom and level of functional recovery . rom was measured using a goniometer as the angle between two axes that pass through the center of the femur and the center of the lower leg . data on the implant type , surgical technique , pcl preservation , and patellar resurfacing were analyzed using the fisher 's exact test to assess relationships with joint stiffness with the level of statistical significance set at p<0.05 . mua was required in 22 knees ( 16 patients , 0.5% ) of the total 4,449 knees following tka . the procedure for stiffness was performed in 2/181 ( 1.1% ) in the knees with the lcs system and in 2/76 ( 2.6% ) in the knees with the maxim complex , and it was least necessary in the knees with the nexgen system ( 18/4,192 , 0.4% ; p=0.035 ) . tka using the conventional approach resulted in the necessity of mua in 4/329 ( 1.2% ) and tka using the mis did in 18/4,120 ( 0.4% , p=0.074 ) . mua was required in 19/4,321 ( 0.4% ) of the pcl replaced knees and in 3/128 ( 2.3% ) of the pcl preserved knees ( p=0.024 ) ; and it was performed in 21/4,330 ( 0.5% ) of the patella resurfaced knees and in 1/119 ( 0.9% ) of the patella preserved knees ( p=0.45 ) ( table 1 ) . the mean age of the patients who underwent mua was 66.98.6 years , and there were one male ( 1 knee ) and 15 females ( 21 knees ) . in them , the preoperative diagnosis was osteoarthritis in 19 knees , rheumatoid arthritis in two knees and complication of infection in one . their mean preoperative rom was 102.5 ( range , 65 to 145 ) , and < 90 of flexion was observed in 6 knees ( five knees with osteoarthritis and one knee with infection sequela ) ( table 2 ) . the mean operation time was 93.216.1 minutes , and the postoperative hemorrhage volume was 648.2333.8 ml . the mean postoperative tibial component alignment was 0.10.7 valgus , posterior tibial slope was 3.91.1 , and femorotibial angle was 6.01.3 valgus . varus tibial component alignment ( 03 ) was observed in 100% and valgus femorotibial angle ( 63 ) was noted in 95.5% ( table 3 ) . mua was carried out during initial hospitalization before discharge in 11 knees and during re - hospitalization in 11 knees , which was at 4.73.0 weeks ( range , 1.4 to 13.9 weeks ) after tka . nineteen knees were available for 1-year follow - up , and the mean follow - up period was 64.341.3 months ( range , 15 to 158 months ) . at the last follow - up , including the one knee that had 0 extension ankylosis of the knee , the mean rom was recovered to 113.431.2 ( range , 0 to 145 ) , indicating a mean of 48.9 improvement in flexion . at the last follow - up , the knee society knee score was 88.313.1 points ( range , 45 to 100 points ) , knee society functional score was 65.818.9 points ( range , 30 to 100 points ) and the hospital for special surgery score was 80.110.9 points ( range , 57 to 99 points ) ( tables 4 and 5 ) . in the 60-year - old female patient who exhibited 0 extension ankylosis at the last follow - up , the indication for tka was rheumatoid arthritis . the postoperative rom was restricted to 75 in the patient ; thus , mua was carried out at 8 weeks after tka . however , limited rom recurred after the procedure , which eventually resulted in 0 extension ankylosis at 1 year after surgery ( fig . the minimum rom of the knee for resuming normal daily living activities after tka is 90 of flexion , and 110 of flexion is desirable for advanced level of activities78 ) . joint stiffness can be defined as limited rom that restricts activities of daily living . in the past , a knee with < 45 of rom and 20 of flexion contracture was considered stiff9 ) . however , the growing expectation of the patients and surgeons has raised the bar on the definition of stiffness : < 70 of rom according to christensen et al.10 ) and < 75 of rom and 15 of flexion contracture according to kim et al.11 ) . stiffness following tka can be associated with preoperative / intraoperative / postoperative patient characteristics . regarding the preoperative factors , adhesions of the extensor mechanism and joint capsule are often observed during tka in patients with functional impairment of an unknown cause , chronic inflammation , infection and previous surgery , which may eventually result in the development of stiffness in spite of adequate release during tka due to the already decreased elasticity1213 ) . intraoperative factors associated with stiff knees include flexion - extension gap imbalance , soft tissue imbalance , improper knee alignment , inadequate resection of the femur / tibia , incorrect implant position , insufficient restoration of the joint line , implant size mismatch , inaccurate anterior tibial slope , imperfect removal of the posterior femoral osteophytes , patellofemoral joint overstuffing and excessive strain on the pcl in the pcl retained knee1014 ) . possible postoperative causes include insufficient pain management after tka , patient 's low motivation and compliance , depression , intra - articular bleeding due to antithrombotic therapy , infection , improper and insufficient physical therapy15 ) , heterotopic ossification16 ) , complex regional pain syndrome17 ) and arthrofibrosis1 ) . arthrofibrosis is a specific condition characterized by formation of excessive scar tissue in response to intraoperative injury . in worst cases , stiffness can be combined with arthrofibrosis , increased scar tissue formation , formation of fibrous bands of scar tissue between the femur and the quadriceps , loss of suprapatellar bursa , shortening of the lateral expansion of the quadriceps , shortening of the rectus femoris muscle and restricted patellofemoral joint motion . postoperative knee joint stiffness is difficult to predict , and , albeit unestablished , some studies attributed it to genetic inheritance in some patients . mua has been known as the most effective first - line treatment for knees presenting with < 90 of flexion when aggressive postoperative efforts for restoration of joint motion are ineffective and specific factors , such as infection , are not responsible for the stiffness . fibrous tissue that forms after surgery needs 6 months of period for loss of cells and blood vessels until maturity . however , the extent of stiffness is more related to the amount and location of the fibrous tissue than to the level of maturity . joint stiffness tends to worsen and become persistent in 6 weeks ; therefore , manipulation for stiffness should be performed before the maturity of fibrous tissue so as to prevent complications and restore joint mobility18 ) . it has been recommended to carry out mua once joint stiffness is observed even within 2 - 3 weeks after surgery in some studies1920 ) and within 2 weeks to 3 months after surgery in other studies2122 ) . esler et al.22 ) suggested knees with < 80 of flexion be treated with manipulation irrespective of the time after surgery , preferably within 4 months after surgery . in the current study , knees with < 80 of flexion were manipulated at a mean of 4.72.9 weeks ( range , 1.4 to 13.9 weeks ) after surgery . the incidence of mua was 4.6% in 800 knees in the study of rubinstein and dehaan23 ) and 4.3% in 3,244 knees in the study of bawa et al.24 ) . in comparison , the value was relatively low with 0.5% in the current study . fox and poss20 ) reported that mua did not make any difference in the one - year outcome of tka , and esler et al.22 ) also described that patients without mua also achieved sustained gains in flexion for one year after surgery . yercan et al.13 ) observed a mean of 47 of increase in flexion after 46 tkas within 31 months . mohammed et al.2 ) found 31.6 of improvement in 21 knees at 6 months after surgery , and esler et al.22 ) reported 47 knees obtained a mean of 33 of improvement at one year after surgery . in our study , including the one knee that had 0 extension ankylosis , there was a mean of 49.9 of gain in flexion to 113.431.2 at 64.341.3 months after mua . in the current study , the incidence of mua was 0.5% and the mean increase in flexion after tka was 44.8 , indicating relatively good outcomes . we attribute these relatively favorable results to 1 ) early diagnosis of stiffness during the 2 weeks of hospitalization , 2 ) aggressive physical therapy performed under the supervision of the surgeon , and 3 ) prompt decision on the need for manipulation , which was carried out when normal range of flexion deemed unattainable with physical therapy alone during hospitalization and when early outpatient follow - up assessments indicated elevated risk of progression to stiffness in spite of some improvement in flexion . sherry et al.25 ) reported that mis total hip replacement was effective in reducing joint stiffness and mcallister and stepanian26 ) showed that the incidence of mua was lower after mis tka than tka with the conventional method required ( 2% vs. 14% ) . in the current study , we also observed mua was required more in patients with the conventional tka ( 1.2% ) than in those with mis tka ( 0.4% ) although no statistically significant difference was noted between the groups . in our opinion , considering that intraoperative soft tissue injury may result in keloid formation and fibrosis during the healing process , our efforts to minimize injury to soft tissue contributed to the reduced incidence of postoperative stiffness .
purposethis study evaluated the incidence of manipulation under anesthesia ( mua ) for stiffness after total knee arthroplasty ( tka ) and the degree of joint motion recovery after mua.materials and methodsa total of 4,449 tkas ( 2,973 patients ) were performed between march 2000 and august 2014 . 
 cases that underwent mua for stiffness after tka were reviewed . 
 tkas were performed using the conventional procedure in 329 cases and using the minimally invasive procedure in 4,120 cases . 
 the preoperative range of joint motion , timing of manipulation , diagnosis and the range of joint motion before and after mua were retrospectively investigated.resultsmua was carried out in 22 cases ( 16 patients ) , resulting in the incidence of 0.5% . 
 the incidence after the conventional procedure was 1.2% and 0.4% after the minimally invasive procedure . in the manipulated knees , the preoperative range of motion ( rom ) was 102.526.7 , and the preoperative diagnosis was osteoarthritis in 19 cases , rheumatoid arthritis in two , and infection sequela in one . 
 mua was performed 4.73.0 weeks after tka . 
 the average rom was 64.513.5 before manipulation . at an average of 64.341.3 months after manipulation , 
 the rom was recovered to 113.431.2 , which was an additional 49.9 improvement in flexion.conclusionsthe satisfactory recovery of joint movement was achieved when mua for stiffness was performed relatively early after tka .