the anterior cruciate ligament ( acl ) plays an extremely important role in resistance to 
 anterior tibia deformation and rotational load on the knee joints1 .
the treatment goal in acl rupture is to stabilize the knee 
 joint and to recover the range of motion of the knee joint and the muscle strength to a 
 normal level , to restore smooth functioning of the knee joint2 . to improve the range of motion of patients following acl 
 reconstruction , various exercise programs together with electrical therapy ,
are conducted 
 with the aim of achieving passive joint movement and pain control3 . in
closed - chain exercise simultaneous resistance is exerted on the proximal and distal 
 areas while the distal area of the upper and lower extremities remains in a fixed 
 position4 .
closed - chain exercise 
 involves simultaneous contraction of the muscles to improve their dynamic stability .
when 
 eccentric contraction is predominant , it reduces the shearing force with a joint compression 
 force , thereby providing stability to the joints .
sensitive mechanoreceptors respond to 
 changes in the pressure of the articular capsules and promote proprioception5 .
impairment of proprioceptive sense has been reported to cause instability of the knee 
 joint6 .
proprioception plays an 
 important role in inducing and promoting voluntary and involuntary movements by transmitting 
 basic information to the motor control areas involved in regulating equilibrium and the 
 vestibular senses7 . according to one 
 study , information pertaining to motor control or location
is provided largely by muscle 
 spindles8 , whereas ligaments , the 
 subacromial bursa , and capsules perform the role of mechanoreceptors9 .
proprioceptive exercises may recover impaired motor senses . to completely recover the 
 functioning of motor senses ,
proprioceptive exercises should be initiated as early as 
 possible in the early stages of the rehabilitation process10 . in particular ,
proprioceptive senses are known to affect the 
 preciseness of the articular angles of the knee joint and proprioceptive rehabilitation 
 exercise improves the proprioceptive senses of the operated side after acl construction11 . in a study of the knee joint stability of 
 patients who had undergone acl reconstruction ,
closed - chain exercise on an unstable surface 
 increased activation of the vastus medialis muscle12 . in a comparison of closed - chain exercise and open - chain exercise , 

the closed - chain exercise stimulated the mechanoreceptors and increased the muscle 
 mobilization rate more than the open - chain exercise , effectively increasing the strength of 
 the quadriceps femoris muscle and the hamstring muscle13 .
therefore , the present study examined the effects of closed - chain 
 exercise performed on a stable surface and on an unstable surface on proprioceptive 
 functions and a functional index of the knee joints .
msd : mean  standard deviation , seg : stable exercise group , ueg : unstable exercise 
 group the subjects were patients who had undergone acl reconstruction between september 2012 and 
 march 2013 and consented to participation in this study .
the subjects were 28 male patients 
 who had undergone acl reconstruction and received exercise treatment in the manual therapy 
 room of g hospital .
the stable exercise group ( seg ) performed exercise on a stable floor , 
 and the unstable exercise group ( ueg ) performed exercise on a balance pad .
those who had cruciate ligament damage 
 accompanied by multiple fractures or collateral ligament damage , or who had undergone 
 meniscus repair surgery , were excluded from the experiment .
the biodex system iii ( biodex medical systems , shirly , ny , usa ) was used to measure the 
 proprioceptive sensory functions of the knee joints on the operated side prior to the 
 exercise and six weeks after the exercise .
the subjects ' thighs and abdomen were firmly 
 fixed with straps to ensure that they were vertical at 90 against the knee joints and the 
 dynamometer tube axis , and the isometric muscle strength was measured .
the differences in the proprioceptive sense functions of the 
 knee on the operated side at 15 and 45 were measured . with the subjects ' two eyes blinded , 
 the examiner instructed the subjects to perceive the angles that had been measured and to 
 remember them ; the angles were maintained for 10 seconds .
after the 10 seconds had elapsed , 
 the subjects were asked to adopt the same angles of the knee joints .
the measurements were 
 made three times at 15 and 45 , and the average values of the three measurements were 
 recorded .
the knee joint functional index questionnaire was administered prior to the exercise and 
 after six weeks of exercise .
the lysholm knee scale , which evaluates the function of the 
 knee joint after knee joint ligament surgery , was used for the functional score test of the 
 knee joints14 .
this scale assesses the 
 following : a normal gait ( 5 points ) , instability during activities like gait , running , and 
 jumping ( 30 points ) , pain ( 30 points ) , the degree of edema ( 10 points ) , and femoral 
 amyotrophy ( 5 points ) . the maximum score that can be obtained is 100 points .
scores of , zero 
 to 6l , 62 to 81 , 82 to 90 , and 91 to 100 represent to poor , average , good , and excellent 
 knee function , respectively .
the paired t - test was conducted to verify differences in 
 the proprioceptive functions and the functional index within each group , and the independent 
 t - test was conducted to verify differences in the proprioceptive functions and the 
 functional index between the groups .
* p<0.05 , msd : mean  standard deviation , seg : stable exercise group , ueg : unstable 
 exercise group * p<0.05 , msd : mean  standard deviation , seg : stable exercise group , ueg : unstable 
 exercise group the between- and within - group changes in the proprioceptive functions of the knee joints 
 and the functional index are presented in table 
 2 and 3 , respectively .
the stable 
 exercise group ( seg ) showed statistically significant differences in the proprioceptive 
 functions and the lysholm score at 15 ( p<0.05 ) .
the unstable exercise group ( ueg ) 
 exhibited statistically significant differences in the proprioceptive functions and the 
 lysholm score at 15 and 45 ( p<0.05 ) .
prior to the exercise , there were no statistically 
 significant differences between the two groups in any of the variables ( p>0.05 ) .
after 6 
 weeks of exercise , the two groups showed a statistically significant difference in 
 proprioceptive functions at 45 ( p < 0.05 ) .
proprioceptive senses play an important role in correcting motor performance and play an 
 important role in neurological senses related to motor skills15 .
the biodex system 3 isokinetic dynamometer ( biodex medical 
 systems , shirley , new york , usa ) is a contemporary isokinetic dynamometer with an 
 electrically controlled servomechanism which is used in both clinical and research settings . 

the biodex system 3 performs with acceptable mechanical reliability and the validity of its 
 measurements has tested16 .
a previous 
 study evaluated proprioceptive functions prior to and after acl surgery following 
 rehabilitation exercise and found that the proprioceptive function of both the operated side 
 and the non - operated side significantly improved17 .
another study measured the proprioceptive functions of the knee 
 joint at angles of 15 and 45 after a rehabilitation program comprising four weeks of 
 proprioceptive exercises and reported that the proprioceptive functions of the operated 
 sides were enhanced18 . in the present 
 study ,
the six - week exercise program following acl reconstruction significantly improved the 
 proprioceptive functions at the knee angles of 15 and 45. in the between - group comparison , 
 the proprioceptive functions were significantly different at 45 , but not at 15. in the 
 ueg , the improvement in the proprioceptive senses and the scores of the functional index 
 showed that the exercise was effective .
our results demonstrate that closed kinetic chain 
 exercise on an unstable floor promoted proprioception more than closed kinetic chain 
 exercise on a stable floor .
a prior study examined knee joint function after acl 
 reconstruction and reported that a swiss ball exercise group showed greater improvement than 
 a control group19 .
similarly , in the 
 present study , there were significant differences in the knee joint functional scores after 
 the exercise in both groups , but no significant differences between the two groups .
squat exercise on a balance pad or a balance board after acl reconstruction may enhance 
 proprioceptive functions of the knee joint and the knee joint functional index .
such 
 exercise is also effective at minimizing cruciate ligament stress . therefore , closed - chain 
 exercise on an unstable surface early after surgery is a very important part of any 
 rehabilitation program .
a limitation of this study is that it failed to control for other physical activities . 
 also
, we did not control for physiological or psychological factors that may have affected 
 the results .
in addition , the subjects were confined to those who underwent cruciate 
 ligament reconstruction at g hospital located in u city , therefore the generalizability of 
 the findings is limited . to address these issues ,
further studies are required with greater 
 numbers of participants to develop effective exercises programs for a variety of therapeutic 
 interventions .
   [ purpose ] the purpose of this study was to examine the effect of closed kinetic chain 
 exercises performed by an unstable exercise group ( ueg ) and a stable exercise group ( seg ) 
 on the knee joint , proprioception , and functional scores of patients who underwent 
 anterior cruciate ligament ( acl ) reconstruction . 
 [ subjects ] twenty - eight patients 
 participated in this study . 
 the exclusion criteria were fracture or neurological disease . 
 
 [ methods ] the subjects were randomly assigned to one of two groups , each with 14 people . 
 
 each group took part in a 60-minute exercise program , three times a week for six weeks . 
 
 [ results ] the results of the clinical evaluation at 45proprioception showed statistically 
 significant differences between the two groups . 
 the results of the clinical evaluation at 
 15proprioception showed no statistically significant differences between the two groups . 
 
 [ conclusion ] the proprioception and functional scores of the patients in the ueg who 
 underwent acl reconstruction were superior to those in the seg group . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION