patellofemoral pain ( pfp ) is a common musculoskeletal condition of the knee which is 
 believed to occur because of lateral patellar malalignment1,2,3,4,5 .
closed - chain exercises for quadriceps strengthening combined with 
 flexibility exercises for the lower limb musculature have been widely used in pfp 
 treatment6 . despite the clinical 
 effectiveness of the leg press ( lp ) exercise , which along with lower - limb stretching has 
 been shown to ease pain and promote functional ability7 , 8
, few studies have looked at 
 the strengthening and stretching exercise s effect on patellar realignment8 .
although a recent magnetic resonance 
 imaging study identified increased patellofemoral joint contact area as a potential source 
 of pain reduction8 , their results did not 
 indicate any positive effects of strengthening and stretching exercise training on patellar 
 alignment ( i.e. , patellar tilt angle ) . furthermore , there was no mention of the patellar 
 displacement8 .
the vastus medialis obliquus ( vmo ) muscle is an important medial stabilizer of the patella , 
 and it resists the lateral pull of the vastus lateralis ( vl)9 . an in vitro biomechanical study showed that an insufficient vmo 
 strength can reduce patellar lateral stability by 30%10 .
using a regression model , another in vivo dynamic computed 
 tomography ( ct ) study indicated the cross - sectional area of the vmo is predictive of 
 patellar tilt11 .
the role of the vmo is 
 therefore considered important in the rehabilitation of patients with pfp , especially those 
 with an extremely , laterally malaligned patella11 .
resistance training of the quadriceps may possibly influence patellar alignment by altering 
 the sensorimotor control of the vastus muscles or the cross - sectional area of the vmo12 , 13 .
incorporating hip adduction into lp exercises is another potential 
 way of achieving this7 , 14 .
lp with hip adduction ( lpha ) within 45 of knee 
 extension / flexion promoted a greater vmo - to - vl ratio as well as vmo hypertrophy7 , 14 . 

it was speculated by the authors that incorporating hip adduction is more likely to realign 
 the patella7 , 14 .
however , to the best of our knowledge , no studies have examined 
 this issue .
it remains unclear whether the degree of patellar alignment is mediated by a hip 
 adduction exercise strategy ( i.e. , lpha ) , and if it is , to what extent .
the importance of axial ct for examining the patellofemoral joint is well - established11 , 15,16,17,18 , and the ct gantry is spacious enough for 
 the examination of dynamic movements11 . 

thus , a dynamic technique could be used to assess the role of the quadriceps in 
 repositioning the patella .
the purposes of this study were to investigate the effects of lp combined with 
 lower - extremity stretching exercises on the patellar alignment in patients with pfp , and to 
 examine the effect of lpha exercise on patellar alignment .
the patellar alignment was 
 assessed by using ct , with the quadriceps both relaxed and contracted to determine whether 
 the exercise intervention changed both the static and dynamic patellar alignment .
it is 
 generally assumed that decreased pain is associated with changes in patellar alignment . to 
 clarify the interrelationship between patellar alignment and clinical symptoms , pain 
 severity
it was our hypothesis 
 that both exercises would reduce pain with substantial changes in patellar alignment , but of 
 differing degrees .
the inclusion criteria 
 were : insidious onset of symptoms unrelated to traumatic accident ; the presence of pain for 
 more than 1 month ; and experience of anterior or retropatellar knee pain after performing at 
 least 2 of the following activities : prolonged sitting , stair climbing , squatting , running , 
 kneeling , hopping / jumping , and deep knee flexing .
in addition , participants had to exhibit 
 at least 2 of the following positive signs of anterior knee pain during the initial physical 
 examination : patellar crepitus ; pain following isometric quadriceps contraction against 
 suprapatellar resistance with the knee in slight flexion ( clarke s sign ) ; pain following 
 compression of the patella against the femoral condyle with the knee in full extension 
 ( patellar grind test ) ; tenderness upon palpation of the posterior surface of the patella or 
 surrounding structures ; and pain following resisted knee extension .
patients were excluded 
 if they had a diagnosis of other knee pathology , a history of patellar subluxation or knee 
 surgery , central or peripheral neurological pathology , lower extremity malalignment ( i.e. , 
 pronated foot ) , or severe knee pain ( visual analog scale : vas > 8) , or had received 
 nonsteroidal anti - inflammatory drugs , injections , or physical therapy in the preceding 3 
 months .
all subjects were enrolled after providing their written informed consent and the 
 study procedure was approved by the research ethics committee of the national taiwan 
 university hospital . using numbered opaque envelopes , 9 and 8 participants were randomly assigned to the lp and 
 lpha intervention groups , respectively . of these , 6 and 5 patients , respectively , presented 
 with bilateral symptoms .
thus , a total of 15 and 13 pfp knees were studied in the lp and 
 lpha groups .
there were no significant differences in the basic demographic data between the 
 groups ( table 1table 1.demographic data of the participantslplphagender ( male : female ) 2:73:5age ( years)40.3  10.538.3  11.3height ( cm)161.1  7.4163.9  7.8weight ( kg)59.1  10.555.5  8.7involved side ( bilateral : unilateral)6:35:3results are shown as mean  standard deviation.lp : leg press exercise ; lpha : leg press with hip adduction exercise ) .
lp : leg press exercise ; lpha : leg press with hip adduction exercise patients performed triweekly lp or lpha exercise three times a week , for a total of 8 
 weeks , according to the method of song et al7 .
exercises were performed by using an en - dynamic track machine 
 ( enraf - nonius b.v . ,
patients were unilaterally trained at 60% of 1 repetition maximum for 5 sets of 10 
 repetitions each . for training resistance advancement , the 1 repetition maximum was 
 remeasured every 2 weeks , and the exercise intensity was adjusted accordingly . in addition , 
 patients were taught to perform static stretching of their quadriceps , hamstring , calf , and 
 iliotibial band muscles .
table 2table 2.exercise regimens of lp and lpha exercisesexercise regimenlp exercise1 ) hot pack to quadriceps ( 15 minutes)2 ) lp from 45 of knee flexion to full extension 2-second concentric and eccentric contractions paced by using a 
 metronome 60% of 1 rm for 5 sets of 10 repetitions left and right limbs alternatively trained in each exercise 
 set 2-second break between each repetition and a 2-minute break 
 between each set3 ) self - stretches of quadriceps , hamstrings , iliotibial bands and 
 calf muscle groups ( 30 seconds  3 repetitions/ muscle group)4 ) cold pack to knee joints ( 10 minutes)lpha exercisesame as lp exercise with the resisted hip adduction addedlp : leg press exercise ; lpha : leg press with hip adduction exercise ; rm : repetition 
 maximum summarizes the detailed exercise regimen .
the only difference between the lp 
 and lpha intervention was the resisted hip adduction .
for lpha , patients forcefully pressed 
 their leg with concurrent isometric hip adduction to resist 50 n resistance offered by the 
 blue theraband ( the hygenic corporation , akron , oh , usa ) . in the lp group , the theraband was 
 only wrapped around each patient s thigh , without resistance , to mimic the tactile received 
 by the lpha group . during the intervention period ,
all participants were asked not to 
 perform or receive any other exercise program or intervention .
lp : leg press exercise ; lpha : leg press with hip adduction exercise ; rm : repetition 
 maximum the pre- and post - training assessment of patellar alignment and pain were performed within 
 1 week before and after finishing 8 weeks of exercise intervention by the same physical 
 therapist who was blinded to patient treatment .
all participants underwent axial ct imaging by a pace general electric machine ( ge medical 
 systems , milwaukee , wi , usa ) of the symptomatic knees , with their quadriceps muscle in 
 relaxation and maximal voluntary isometric contraction for the assessment of patellar 
 alignment . the ct images ( 5-mm slice thickness )
were obtained at full knee extension through 
 the widest diameter of the patella , which facilitated an optimal view of the patellofemoral 
 joint for measurement11 , 17 .
imaging was performed with the subjects in a supine 
 position , with their ankles restrained by using felt strips to prevent leg rotation . a rigid 
 support and soft padding
centricity radiology ra 600 image software ( version 6.1 ; ge medical systems ) was used to 
 determine the patellar alignment ( i.e. , tilt and displacement ) .
the mediolateral tilt of the 
 patella was measured along the patellar tilt angle ( pta ) , which is the angle formed by the 
 line joining the maximum width of the patella and the line joining the posterior femoral 
 condyles3 , 19 .
mediolateral patellar displacement was assessed by using the 
 bisect offset index ( bso)3 , 19 .
the bso was measured by drawing a line connecting the 
 posterior femoral condyles and then projecting a perpendicular line anteriorly through the 
 deepest point of the trochlear groove .
when the trochlear groove was flattened , the 
 perpendicular line was projected from the bisection of the posterior condyle line .
this 
 perpendicular line intersected the patellar width line , and the percentage of the patella 
 lateral to the midline was calculated as the bso3 , 
 19 .
larger values of pta and bso 
 indicated more lateral tilt or displacement of the patella .
the worst pain that subjects experienced in the week before assessment was evaluated by 
 using a 10-cm vas , where 0 indicated no pain and 10 indicated extreme / maximal perceived 
 pain20 .
chicago , il , 
 usa ) . for comparisons of age , body height , and weight , the independent t - test was performed . 

the gender and number of afflicted sides ( bilateral vs. unilateral ) were compared by using 
 the  test , with an  level of 0.05 .
three - way mixed analyses of variance 
 ( anova ) were performed on both pta and bso measures with group ( lp or lpha ) as 
 between - subject factor and assessment time point ( pre- or post - training ) and muscle state 
 ( quadriceps relaxation or contraction ) as the within - subject factors .
the vas pain score was 
 compared between groups and assessment times by performing a 2-way mixed anova .
pilot work was conducted to ascertain the reliability of patellar alignment measurement on 
 the image .
the intraclass correlation coefficient ( icc(3,1 ) ) values for 
 between - day test - retest reliability of pta and bso measurements were 0.91 and 0.98 , 
 respectively , indicating high reproducibility .
the standard error of measurement ( sem ) was 
 1.2 for pta and 2% for bso . to calculate power and sample size
, we used the concept of the 
 smallest real difference ( srd = 1.96  2  sem , with sem = 1.2 from a pilot test of 
 reliability ) for predetermining the smallest measurement change that can be interpreted as a 
 real difference . using the srd between pre- and post - training of 3.4 for pta and assuming a 
 standard deviation of 3 based on previously published data21
, at least 13 pfp knees per group would attain 80% power at the  
 level of 0.05 .
table 3table 3.comparison of pre- and post - training changes in patellar alignment and pain in 
 the lp and lpha groupslp ( n = 15)lpha ( n = 13)pre - trainingpost - trainingpre - trainingpost - trainingpta ( )without contraction17.4  4.717.6  5.419.2  2.418.9  3.6with contraction 17.8  5.517.6  6.418.7  4.518.3  4.7bso ( % ) without contraction63.9  12.264.7  8.466.4  12.966.4 13.5with contraction 67.0  14.668.9  13.968.7  15.868.9  12.6vas pain score ( cm)4.65  2.182.25  2.364.55  1.902.65
lp : leg press exercise ; lpha : leg press with hip adduction exercise ; pta : patellar 
 tilt angle ; bso : bisect offset index ; vas : visual analog scale summarizes the main outcomes of the patellar alignment measures and vas pain 
 scores . both groups were similar with respect to the pta and bso at baseline , regardless of 
 the quadriceps state ( relaxation or contraction ) .
there were no significant interaction 
 effects or main effects on the pta or bso ( table 
 4table 4.insignificant main and interaction effects from the 3-way analyses of variance 
 ( group by time by muscle ) performed on the pta and bsosourceptabsosum of squaresdfmean squaresum of squaresdfmean squaretime0.81210.8120.00110.001time by group 1.01411.0140.00110.001error ( time)193.235267.4320.193260.007muscle0.86210.8620.02510.025muscle by group 3.66213.6620.00110.001error ( muscle)426.4782616.4030.251260.010time by muscle0.44510.4450.00010.000time by muscle by group0.17910.1790.00010.000error ( time by muscle)76.932262.9590.130260.005group37.767137.7670.00610.006error1,750.4542667.3251.208260.046pta : patellar tilt angle ; bso : bisect offset index ; df : degrees of freedomgroup refers to leg press exercise / leg press with hip adduction exercise ; 
 time refers to pre-/post - training ; and muscle refers to quadriceps 
 relaxation / contraction . ) , indicating there were no significant intra- or inter - group differences in 
 patellar alignment following the exercise interventions with the quadriceps either relaxed 
 or contracted . as for pain ,
no group - by - time interaction was identified with respect to the 
 vas pain score ( f= 0.198 , p = 0.66 ) .
statistically significant reductions 
 in pain were found in both groups after the intervention ( f = 14.286 , p 
 < 0.01 ) .
the mean decrease of the vas pain score was 2.4 and 1.9 for the lp and lpha 
 groups , respectively .
the degree of pain reduction , however , was not significantly different 
 between the groups ( f = 0.072 , p = 0.79 ) ( table 
 3 ) .
lp : leg press exercise ; lpha : leg press with hip adduction exercise ; pta : patellar 
 tilt angle ; bso : bisect offset index ; vas : visual analog scale pta : patellar tilt angle ; bso : bisect offset index ; df : degrees of freedom group refers to leg press exercise / leg press with hip adduction exercise ; 
 time refers to pre-/post - training ; and muscle refers to quadriceps 
 relaxation / contraction .
quadriceps strengthening together with lower - extremity stretching exercises is one of the 
 most common therapeutic approaches for clinically treating pfp clinically6 , 22 . 

consistent with a previous systematic review6 , our study provides further evidence of the effectiveness of 
 therapeutic exercise in the reduction of pain .
both the lp and lpha exercise interventions 
 for 8 weeks were found to significantly reduce pfp , but this occurred in the absence of 
 significant changes in patellar alignment .
furthermore , hip adduction had no added effect on 
 patellar realignment or pain relief . despite the fact that patellar malalignment is thought 
 to contribute to pfp1,2,3,4,5 , our findings are in 
 agreement with a recent report that weight - training exercise did not change the patellar 
 tilt angle8 .
imaging techniques are clinically helpful in the diagnosis of patellar malalignment 
 associated with pfp3 , 19 .
the pta and bso measured in this study similar in magnitude to the 
 values reported by previous studies8 , 13 , 19 , 23 . using imaging techniques to explore the 
 effect of exercise on patellar alignment , an early radiographic study had examined the 
 effects of individualized and progressive therapeutic exercises on patellar alignment at 30 
 of knee flexion in patients with pfp24 . 

the findings revealed that patients who were pain - free after exercises demonstrated 
 significant mean decreases in patellofemoral congruence angles , but not in the 
 patellofemoral index ( an indicator of patellar tilt ) .
it is noteworthy that the patients in that study 
 exhibited a mean congruence angle of 8.03 before training , leaving high scope for 
 improvement in patellar displacement .
it is difficult to compare our findings with those of 
 the cited studies mentioned , because the manner of exercise , imaging techniques , indices 
 chosen for assessing patellar alignment , and knee flexion angle tested were different . 

however , it also appears that patients who have a certain patellar malalignment type may 
 respond differently to exercise intervention .
quadriceps contraction plays an important role in mediating the patellar alignment during 
 full knee extension , when the patella is less stable15 , 25 . in the present study , 

this 
 finding is similar to the conclusions of previous studies that found no difference in 
 lateral patellar tilt or displacement between quadriceps states in extended knee 
 positions11 , 15 , 17 .
another study also 
 indicated there was a significant and proportional relationship between the ct measurement 
 of the lateral patellofemoral angle and lateral patellar shift during quadriceps contraction 
 or relaxation at either 0 or 20 of knee flexion ( r = 0.930.96 , p < 
 0.01)16 .
conversely , some investigators 
 have reported that quadriceps contraction results in increased patellar lateralization or 
 lateral tilt11 , 18 , 23 , 26 .
hence , at the present time , there is no consensus about the effect 
 of quadriceps contraction on patellar alignment26 .
resistant 
 hip adduction ( lpha ) was additionally performed to specifically target the vmo , because vmo 
 dysfunction is manifest in patients with pfp27 .
the effects of the 2 interventions were comparable , indicating 
 that there is no additive beneficial effect of incorporating hip adduction into the lp 
 exercise , at least with regarding to patellar alignment .
adding isometric hip adduction to the lp exercise did not elicit more vmo 
 hypertrophy than did lp alone7 , although 
 it is possible that the simple lp exercise simultaneously activates the hip adductor magnus 
 and longus muscles as well as the knee extensor28 .
it should be noted that the hip adduction load was fixed ( i.e. , 50 
 n ) in the present study , and vmo activation may vary with different levels of hip adduction 
 load29 . on the other hand , squat 
 exercise with hip adduction offers an alternative method of strengthening the vmo29 , 30 . although no significant changes in patellar alignment were detected following both 
 exercises , clinically significant pain reductions ( > 1.5 points on the 10-cm vas)20 were detected in both groups .
this finding 
 is in accordance with that from a patellar bracing study conducted by powers et al.19 , who reported large decreases in pain 
 without obvious changes in patellar alignment .
we speculate that the decrease in pain 
 detected in our patient cohort was probably the result of increased quadriceps muscle 
 strength and enhanced flexibility of the soft tissue surrounding the knee7 , 31 , 32 .
it is likely that quadriceps strength and 
 patellofemoral joint contact area were altered by the exercise intervention , leading to 
 redistributing joint contact pressure , and that pain was decreased as a consequence8 .
furthermore , it is known that pfp is a 
 chronic pain condition in which central pain mechanisms may be important33 , 34 .
hence , the repeated and rhythmic lp training and lower - extremity 
 stretching ( as a form of proprioceptive input ) , the patients belief in treatment or 
 therapist , and accompanying cognitive or illness behavior changes ( through 
 psychophysiological mechanism ) may evoke neuroplastic changes in the central nervous system , 
 and consequently , alter the pain34 . 

lateral patellar tilt and displacement were assessed 
 only in the fully extended knee position , and patellar alignment may exhibit changes at 
 different knee flexion angles .
future studies should examine patellar alignment changes 
 during dynamic tasks and during weight - bearing movements , because femoral motion may 
 influence the patellofemoral kinematics4 . 

it would be of interest to ascertain whether 
 patients with different types of malalignment ( e.g. , lateral displacement alone , lateral 
 tilt alone , or a combination of both ) would show different responses in terms of patellar 
 movement in response to therapeutic exercise training .
such classifications may facilitate 
 the clinical management of pfp in a more selective manner .
furthermore , because hip external 
 rotator and abductor muscle strengthening exercises are effective in pfp management35 , future studies should examine their 
 biomechanical influences on patellar alignment . in conclusion , although lp and lpha exercises were both effective at reducing pfp , neither 
 of them were beneficial for realignment of the patella .
the results indicated that patellar 
 realignment does not appear to mediate pain alleviation , since adding hip adduction to lp 
 had no more beneficial effect on patellar realignment or pain reduction than lp exercise 
 alone .
 [ purpose ] the purpose of this study was to investigate the effect of leg press and leg 
 press with hip adduction exercise training on patellar alignment and pain in patients with 
 patellofemoral pain ( pfp ) . 
 [ subjects and methods ] seventeen patients participated in this 
 study . 
 eight weeks of leg press or leg press with hip adduction training , including 
 progressive lower - limb weight - training and stretching , was given . 
 patellar alignment ( tilt 
 and displacement ) and pain measurements were conducted before and after leg press or leg 
 press with hip adduction training . 
 patellar tilt angle and the bisect offset index were 
 measured on axial computed tomography scans of the fully extended knee position with the 
 quadriceps relaxed and contracted . 
 pain was assessed by using a 10-cm visual analog scale . 
 
 [ results ] no differences were found in patellar tilt and displacement with the quadriceps 
 either relaxed or contracted after leg press and leg press with hip adduction . 
 however , 
 significant pain reduction was evident in both leg press and leg press with hip adduction . 
 
 [ conclusion ] the results indicated that patellar realignment does not appear to mediate 
 pain alleviation . 
 furthermore , hip adduction in addition to leg press training had no 
 additive beneficial effect on patellar realignment or pain reduction . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION