patellofemoral pain syndrome ( pfps ) is one of the most common musculoskeletal conditions , 
 which accounts for 2040% of all knee problems in adolescents and active young adults1 , 2 . 

pfps is described as retropatellar or anterior knee aching pain without any other specific 
 pathology and characterized by crepitation in the patellofemoral joint during and after 
 weight bearing activities , such as squatting , walking up or down stairs and running .
the 
 other characteristic features of pfps include pain while sitting with the knees flexed , 
 instability , occasional weakness and locking sensations2 .
the incidence of pfps is 22/1,000 persons per year and is the most 
 common cause of knee pain , with women affected more than men at a ratio of 2:13 .
although , pfps has many possible causative 
 factors that are usually connected to maladies in biomechanics , the insufficient dynamic 
 balance of the torso and lower extremity can also contribute to the development of pfps .
the 
 dynamic balance is important , especially while performing movements that incorporate loading 
 like climbing the stairs , performing squats and jumps4 , 5 .
the individuals having pfps 
 are found to have significant low- pressure pain threshold ( local hyperalgesia ) than healthy 
 subjects5 .
the first line of treatment for pfps is conservative management , which includes 
 non - operative interventions consisting of rest , ice , and drugs to manage inflammations , 
 adjustment of activities , and physical therapy .
the physical therapy management includes 
 specific exercises targeting the knee , such as strengthening exercises for the quadriceps
many studies stated that subjects who have enrolled in a program that targeted the abductors 
 and external rotators of hip reported a moderate reduction in pain7 , 8 .
the other 
 treatment techniques like stretching exercises for the iliotibial band ( it ) , tensor fascia 
 latae , hamstrings and the quadriceps , also showed greater benefits among the pfps 
 patients9 .
the common goal of rehabilitation 
 management in pfps patients is to address the pain and thereby improve the physical 
 function13 .
the physical therapists or 
 clinicians use self- reported assessment of pain and function to check the effectiveness of 
 various physical therapy interventions .
the most common tool used to measure the intensity 
 of pain in these patients is the visual analogue scale ( vas ) , which is a reliable and valid 
 measure to assess the intensity of pain2 , 14 .
dynamic balance refers to the capability of having suitable reactions regarding the motor 
 system , in order to be able to cope up with the requirements needed for the quick 
 alterations of position in the torso , while performing activities that add stress on the 
 knee joint .
operationally , the dynamic stability may be defined as the ability of the body 
 to maintain position or intended trajectory after external or internal disturbances15 , 16 . a stable erect body posture , or any specific joint ,
is controlled by 
 the neuromuscular system in relation to the shift in the involved parts at the time of 
 action including the core4 .
deficiency in the control of the neuromuscular system of the 
 body s trunk or  core
 may affect the dynamic stability of the lower extremity , which can 
 lead to injury in the tibiofemoral or patellofemoral joints16 .
the spine , abdominal region , pelvis , hips , and proximal lower extremities , are defined as 
 the core of the body .
this is sometimes defined as a muscular box , with the diaphragm as the 
 roof , the pelvic floor and hip girdle musculature as the base , abdominals in the front , and 
 the paraspinal and gluteal muscles in the back18 .
these muscles strength allows the system to stabilize the spine 
 mechanically and then distribute and deliver translational , compressive , and shear forces to 
 and from the rest of the body19 .
the core 
 or the compound of muscles consists of the static and dynamic anatomy at the zone that 
 serves as the foundation in order to move the extremity20 .
the effects of core muscle strengthening have been proven as an 
 effective method of management in various cases18 , 
 21 , 22 .
previous studies states that the knee is the frequently injured 
 joint in core instability with the decreased hip strength23 , 24 . even though there are 
 many studies on the management issues of pfps , so far , there are no studies about the 
 effectiveness of the core muscle stability program for the improvement of pain and balance 
 in pfps patients .
the objective of this study is to define the effectiveness of core muscle 
 strengthening program in improving pain and dynamic balance in females with pfps .
this was a quasi experimental study that included 20 females diagnosed with pfps , with the 
 age between 16 and 40  years , who were referred from the orthopedic department .
subjects were 
 randomly assigned to either core muscle strengthening exercise group ( exp ; n=10 ) or control 
 ( con ; n=10 ) group .
this age interval has been chosen because the majority of the women are 
 beyond puberty by 16  years of age , and after 40  years of age , there is an increased 
 prevalence of hormonal changes and arthritis development25 .
the randomization was made by an investigator who was not involved 
 in the assessment or management of patients .
the baseline 
 characteristics of the participants are presented in table 1table 1.baseline characteristics of the participantsgroupconventionalexperimentalage ( years)22.2  1.321.4  1.8height ( cm)158.7 
5.1160.3  4.6body weight ( kg)64.8  8.468.3  7.7 and it does not show any significant difference between the characteristics of 
 both groups .
the inclusion criteria were as follows : female patients aged between 1640 years , with 
 anterior knee pain for at least 4 weeks that was aggravated by at least 2 of the following 
 activities : jumping , running , prolonged sitting , stair climbing , kneeling , and squatting ; 
 positive patellar grinding test ; must be active for at least 30  min a day almost all days of 
 the week .
in addition , they should have an average pain intensity level of 30  mm on a 100  mm 
 visual analogue scale and must have an insidious onset of symptoms , unrelated to a traumatic 
 damage .
the exclusion criteria were : cruciate , meniscal , collateral ligament injuries or 
 tenderness , any intra - articular injury , tenderness over the illiotibial band , patellar 
 tendon , or pes anserine tendons , patellar apprehension sign if positive , 
 sinding - larsen - johanssen syndromes or osgood - schlatter disease , evidence of joint effusion , 
 referred pain from the hip or lumbar region , known case of articular cartilage damage ( from 
 previously obtained imaging ) , any previous surgery around the knee , any spinal or lower 
 extremity deformities , nonsteroidal anti - inflammatory drug or corticosteroid long use , 
 pregnancy , athlete type training ( a person who participates in a specific sport at least 2  h 
 /day and 3 times a week regularly)20 , 25,26,27 .
the experimental group was given core muscle strengthening exercises thrice weekly for 4 
 weeks , in addition to the conventional physical therapy program .
the control group was given 
 only the conventional intervention program during the same time period .
all the subjects 
 were recruited from king abdul aziz university hospital , in jeddah , saudi arabia . 

information was given to all subjects about the study procedures and a written , signed 
 consent form has been obtained from each subject .
the outcome measures used in the current study were : visual analog scale ( vas ) and star 
 excursion balance test ( sebt ) .
both these measures were assessed at the start of the study 
 and at the end of the 4 weeks of intervention .
the vas is a reliable tool used to assess the 
 level of pain intensity from 0 to 10 , where 0 indicates no pain and 10 indicates maximum 
 unbearable pain24 , 28 .
the sebt for the lower quarter is a functional screening tool , commonly used to examine the 
 balance of the lower extremity . for this test
, subjects were asked to adopt a single - leg 
 stance and it was requested of them to perform a maximal reach with the opposite leg , along 
 the marked lines , while keeping the weight bearing leg placed at the center , with good 
 stability , followed by return to the initial upright posture , without losing the balance . 

this test was performed in three reach directions : anterior ( ant ) , posterolateral ( pl ) and 
 posteromedial ( pm ) .
subjects were permitted 3 trials of practice in each direction before the 
 actual test performance30 .
all 
 participants performed the test on the unaffected leg first and then on the affected leg . 

participants had 15-seconds rest intervals between each test with the same leg and on the 
 same direction .
one minute of rest was given between reaches in the different directions and 
 when changing feet .
a trial was repeated if : ( a ) the subject was not able to maintain single 
 leg stance , ( b ) the heel of the stance foot did not remain in contact with the floor , ( c ) 
 weight was shifted onto reach foot , or ( d ) the subject did not maintain start and return 
 positions for one full second .
three trials of reach distances for each direction were 
 averaged and normalized to limb length ( % ll , cm ) .
the limb length was measured from the 
 anterior superior iliac spine to the medial malleolus bilaterally .
overall , 6 different sebt 
 scores were calculated : 3 directional scores on the affected ( a ) leg ( sebtant - a , sebtpl - a , 
 and sebtpm - a ) and 3 directional scores on the unaffected ( u ) leg ( sebtant - u , sebtpl - u , and 
 sebtpm - u ) .
finally , the 6 sebt was averaged in a single composite sebt score per participant 
 ( sebtcom)30 .
the core muscle strength training program lasted for 4 weeks and comprised of 3 training 
 sessions per week , with a total of 12 sessions for the study group .
each session lasted for 
 30 to 45 minutes , starting with a brief warm - up exercise program consisting of low - intensity 
 core strength exercises to prepare the neuromuscular system for the training loads and 
 ending with a cool - down program ( i.e. , dynamic stretching)31 . during the main part of the training ,
cross curl - ups : subjects were made to lie in supine position , hands folded 
 behind the neck , elbows pointed to the sides , knees in a flexed position , feet rested on a 
 mat ; subjects curled - up until the scapulae left the mat , and rotated to the left and right 
 at a moderate velocity .
side bridge ( both sides ) : subjects were told to assume a side lying 
 position with knees flexed , the supporting shoulder superior to the respective elbow , the 
 uninvolved arm held in akimbo , and the supporting forearm flat on the mat ; subjects raised 
 their hips until a straight line is reached from the knees up to the shoulders and they 
 continuously raised and lowered their hips at a moderate velocity .
quadrupedal stance ( birddog exercise ) : subjects were made to stay in a 
 quadrupedal stance , with both hands and knees flat on the surface ; they lifted a leg and the 
 contralateral arm in horizontal position at moderate velocity .
training intensity was progressively increased over the 4-weeks training program by 
 modulating lever lengths and repetitions . during training weeks 12 , participants performed 
 the  big 3  with 20 repetitions and in the weeks 34
the conventional physical therapy program was designed based on the preliminary studies , 
 which suggest that eccentric exercises are more effective than concentric exercises , because 
 the primary function of the knee joint is eccentric33 . according to that ,
isometric exercises for the quadriceps and hip abductors , like 
 illiotibial band and hamstring stretching exercises were also given as home programs34 .
the common targeted impairments during 
 the physical therapy management are : weakness of muscles , tightness of muscle and soft 
 tissues , and poor movement quality . among all these
, the quadriceps muscle weakness is the 
 most commonly addressed issue during physical therapy , because studies show that there is 
 decreased pain and increased function in patients who received a strengthening program for 
 quadriceps muscle .
however , the weakness of the hip abductors and external rotators muscle 
 was also addressed by physical therapy , because there are studies to prove that subjects 
 with pfps have weakness of these muscles and strengthening of these hip muscles may be 
 helpful to decrease pain in this population26 .
the data were statistically analyzed by using the statistical package spss for windows 
 ( version 19.0 ; spss inc . , chicago , il , usa ) .
descriptive statistics including mean , standard 
 deviation , and 95% confidence interval values were performed .
paired t test 
 was used to compare the dependent variables for balance variables between pre rehabilitation 
 and post rehabilitation testing .
the subjective outcome variable vas was compared by using 
 the non - parametric mann- whitney u test . since the results of the intergroup comparison for vas show that there is a significant 
 difference between the groups in terms of the intensity of pain ( p=0.032 
 [ p > 0.05 ] ) , which indicated that the study group had better 
 improvement ( table 2table 2.comparison of vas between the control and study groupsmean vasgroupnprepostsddifferencecontrol106.52.33.264.2experimental106.31.2 * 4.175.1*p<0.05).the results for the sebt show that there is a significant difference between 
 the groups in terms of the dynamic balance ( p= 0 .
01 [ p>0.05 ] ) and that 
 the study group had a better improvement in the dynamic balance ( table 3table 3.comparison of sebt between the control and study groupsmean sebtgroupnprepostsddifferencecontrol1056.368.74.6412.4experimental1058.178.1 * 7.3520.0*p<0.05 ) .
this study was conducted to assess the effectiveness of core muscle strengthening on 
 reducing pain and improving dynamic balance in female patients with pfps . even though the 
 effectiveness of core muscle strengthening has been proved by many previous studies in 
 various other preconditions , there is no published study to analyze the effectiveness of 
 core muscle strengthening for improving the pain and balance among the pfps patients18 , 21 , 22 , 35 .
the results of this study indicate that female patients with pfps in 
 the study group showed a significant difference in terms of reduction in the intensity of 
 pain .
this improvement could be achieved as an immediate effect , because strengthening of 
 the core muscles must have rectified the improper recruitment of the muscles , in order to 
 provide proximal stability , since patients with pfps present a different recruitment 
 pattern .
rojhani shirazi z et al.20 
 reported that improvement in core muscles could be an effective strategy in the 
 rehabilitation of patients with pfps . having a sufficient proximal stability would reduce 
 the stress load over the patellofemoral joint , which could be the other reason for the 
 significant pain reduction in the study group . combining core strengthening with the 
 traditional physical therapy program
earl je & hoch az25 
 showed in their study a significant improvement in terms of pain and function in women with 
 pfps who received a proximal strengthening program , which is similar to our findings 
 regarding the improvement in pain .
another factor that must have contributed to the 
 reduction of pain might be the change in fear and avoidance beliefs about physical activity , 
 as this is the strongest predictor of function and pain outcomes26 .
the other main focus of this study was to test the change in dynamic balance among the pfps 
 patients following a core muscle strengthening program and to the best of our knowledge ; 
 this was the first study that has been conducted to analyze the effect of core muscle 
 strengthening on improving the balance among the pfps patients .
the study findings showed 
 that there was a significant improvement in the dynamic balance in the study group .
the 
 significant increase in dynamic balance is a confirmation of the proposed hypothesis , which 
 suggested that strengthening in the core muscles provides a better stability for the lower 
 limb movements allowing the occurrence of a smooth and stable movement . strengthening
the 
 core could have resulted in a smaller displacement in the mediolateral center of pressure 
 and also , in the center of mass .
this means that , the motion at the level of the trunk and 
 hip is properly controlled , resulting in the significant dynamic balance improvement that 
 has been recorded in the study group .
this outcome signifies that amelioration in the 
 control of body balance may be related to an improved neuromuscular control , which occurs 
 due to increased postural stability .
therefore , trunk strength and stability programs of the 
 hip - lumbo - pelvic complex should be considered as a major treatment strategy in the 
 improvement of the whole body balance36 .
core muscle strengthening must have altered the sensory or motor pathways ( or both ) , which 
 in turn influenced the ability of the patient to maintain the postural control . moreover , 
 the reduced pain must have enhanced the magnitude of vastus medialis oblique ( vmo ) 
 activation for the stabilization of the knee while performing the sebt , which may allow the 
 subjects to maintain their balance in a better way , while attempting to reach far 
 distances37 . according to earl 
 & hertel38 , in normal healthy 
 subjects ,
the activity of vmo was at peak level while doing the anterior reach of the sebt . 

another explanation for increase in sebt performance could be the biomechanical corrections 
 of the other joints in the lower extremity following the core strengthening .
even though core muscle strengthening has been included as an intervention method , the 
 strength of the core muscles was not documented in the present study , as this was not an 
 objective of this study , but could be considered in the future studies .
some of the 
 limitations of our study include the relatively small sample size , although appropriate 
 statistical power was obtained . studies with larger number of subjects should be performed . 

the study has been conducted only in the female population , as it was clear from the 
 literature that pfps is more common among the female subjects , as compared to their male 
 counterparts39 . however , the results of 
 this study could be considered as a mode of treatment , even in the male population . in 
 conclusion , the study findings revealed that adding a core muscle strengthening program 
 along with the conventional physical therapy program can be beneficial for reducing the pain 
 intensity and improving the dynamic balance in females with pfps .
 [ purpose ] patellofemoral pain syndrome is a frequent musculoskeletal disorder , which can 
 result from core muscles instability that can lead to pain and altered dynamic balance . 
 
 the objective of this study is to assess the effect of core muscle strengthening on pain 
 and dynamic balance in female patients with patellofemoral pain syndrome . 
 [ subjects and 
 methods ] twenty female patients with age ranging from 16 to 40  years with patellofemoral 
 pain syndrome were divided into study ( n=10 ) and control ( n=10 ) groups . 
 both groups were 
 given 4 weeks of conventional physical therapy program and an additional core muscle 
 strengthening for the study group . 
 the tools used to assess the outcome were visual 
 analogue scale and star excursion balance test . 
 [ results ] the results of the study show 
 that participants in the study group revealed a significantly greater improvement in the 
 intensity of pain and dynamic balance as compared to the control group . 
 [ conclusion ] 
 adding a core muscle - strengthening program to the conventional physical therapy management 
 improves pain and dynamic balance in female patients with patellofemoral pain 
 syndrome . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION