patellar dislocation and patellofemoral instability may occur in a young population with varying activity levels .
the overall recurrence rate of patellar dislocation after an initial event is close to 40  % .
in fact , patients who have a primary patellar dislocation have a 17  % recurrence rate , and patients who sustain repeat patellofemoral joint dislocation have a 49  % recurrence rate .
it is obvious that athletic patients have as a goal resumption of their sports activities at the same high level as prior to the episode of dislocation . for less active patients ,
an increase in their level of activity could be an attractive goal , as strength and stability of the lower limb can prevent re - injury .
information about the functional capacity that allows for a safe return to sports after either primary dislocation or surgical stabilization is sparse .
it is known that medial patellofemoral ligament ( mpfl ) reconstruction and rehabilitation improves the ability to perform routine activities of daily living [ 8 , 13 ] , but it is less evident as regards the ability to resume sports participation safely .
testing protocols are requested after patellar dislocation to assure a safe return to sport ( rts ) , but information on this issue is currently limited in the literature . thus far
, quantitative assessment was recommended , but as it will be shown in this article , qualitative measurement with a systematic video analysis has to be considered to better evaluate the dynamic stability of the knee .
this article focuses on objective patellofemoral instability and return to sport , addressing only those situations where one or more episodes of dislocation have occurred or in cases where surgery for instability has been performed .
it was attempted to answer the following two questions : ( 1 ) how and when can patients safely return to sport after primary or recurrent patellar dislocation , or after patellofemoral stabilization ? ( 2 ) what validated evaluations can be utilized to determine readiness to return to sport ? in our experience ,
return to sport can be compromised by pain , instability , weakness , and poor motor control .
a safe return to sport implies that lesions of the knee have healed and the injured lower limb has adequately recovered to face the demands of sporting activities .
successful return to sport implies : ( 1 ) no early re - injury ; ( 2 ) no further damage to the knee ; ( 3 ) return to the preinjury or higher level ; ( 4 ) no limiting pain ; ( 5 ) still playing after 5  years ; and ( 6 ) no early osteoarthrosis . a comprehensive return to sport decision - making process should be based upon : ( 1 ) clinical examination ; ( 2 ) evaluation of laxity ; ( 3 ) strength measurement ; ( 4 ) neuromuscular evaluation ; and ( 5 ) counselling with the physical conditioner and coach for professional athletes . as regards the patellofemoral joint
, the challenge is that the patella is a sesamoid bone enclosed within the extensor mechanism of the lower limb .
its function is closely associated with dynamic muscle activity while retaining its osseous and soft tissue static elements .
.   followed 74 patients ( 37 men , 37 women ) after a first dislocation that was treated conservatively .
preinjury sports activity was similar to that of patients with primary anterior cruciate ligament ( acl ) injury .
patients were authorized to return to sports after they regained full passive range of motion , had no effusion , and when quadriceps muscle strength was at least 80  % of the noninjured limb .
sports participation was limited during the first 6  months after injury , with difficulties in squatting and kneeling . at 6  months ,
58  % of patients noted limitations in strenuous activity , but no recurrence was recorded .
reported that the return to preinjury activity level varied between 44  % and 60  % regardless of the modality of treatment after the first dislocation .
there are few high - quality studies concerning rehabilitation after patellar dislocation , especially as regards the last phase of treatment before return to sport .
there are no published randomized clinical trials , but only thoughts and recommendations as summarized in the review by fisher et al . .
however , since the objectives are similar , a parallel situation exists with the information available in the literature concerning return to sport after acl reconstruction . in order to achieve a proper and safe resumption of sports activities
the strength of the lower limb muscles , especially the quadriceps [ 6 , 36 ] , and the gluteus medius is one key point .
core strength is also crucial as it plays an important role in the stability of the lower limb . indeed , if the trunk is not stable during cutting manoeuvres , the loads applied to the knee are in valgus , thus generating a situation where the patellofemoral joint is at risk of dislocation [ 13 , 18 ] . to avoid re - injury ,
the stability of the lower limb must be mastered at the end of the rehabilitation programme .
cutting manoeuvres , change of direction , and running on uneven ground are the three activities perceived to be the greatest risk factors for patellar dislocation .
therefore , the final goal of the rehabilitation programme should be to focus on the stability of the lower limb by the use of specific exercises on different surfaces , including cutting manoeuvres , side hops , and sudden change of direction . during the final phase of the rehabilitation programme , another important factor to consider for a proper return to sport concerns sport - specific activities .
the athlete should be prepared for the specific loads and demands to be experienced in their specific sport , including : ( 1 ) cutting manoeuvres and pivoting exercises , performed for most of the team sports ; ( 2 ) plyometric and landing strategies , emphasized in any sports with jumps ; ( 3 ) one - leg stability , particularly exercised for martial arts ; and ( 4 ) proprioception , side stability , and landing capacities , which are stressed with skiers .
as previously mentioned , a parallel can be made with return to sport after acl reconstruction .
specific exercises to be implemented for patients involved in soccer , basketball , alpine skiing , and american football have been described [ 7 , 20 , 37 , 38 ] .
there are few high - quality studies concerning rehabilitation after patellar dislocation , especially as regards the last phase of treatment before return to sport .
there are no published randomized clinical trials , but only thoughts and recommendations as summarized in the review by fisher et al . .
however , since the objectives are similar , a parallel situation exists with the information available in the literature concerning return to sport after acl reconstruction . in order to achieve a proper and safe resumption of sports activities
the strength of the lower limb muscles , especially the quadriceps [ 6 , 36 ] , and the gluteus medius is one key point .
core strength is also crucial as it plays an important role in the stability of the lower limb .
indeed , if the trunk is not stable during cutting manoeuvres , the loads applied to the knee are in valgus , thus generating a situation where the patellofemoral joint is at risk of dislocation [ 13 , 18 ] . to avoid re - injury , the stability of the lower limb must be mastered at the end of the rehabilitation programme .
cutting manoeuvres , change of direction , and running on uneven ground are the three activities perceived to be the greatest risk factors for patellar dislocation .
therefore , the final goal of the rehabilitation programme should be to focus on the stability of the lower limb by the use of specific exercises on different surfaces , including cutting manoeuvres , side hops , and sudden change of direction . during the final phase of the rehabilitation programme , another important factor to consider for a proper return to sport concerns sport - specific activities .
the athlete should be prepared for the specific loads and demands to be experienced in their specific sport , including : ( 1 ) cutting manoeuvres and pivoting exercises , performed for most of the team sports ; ( 2 ) plyometric and landing strategies , emphasized in any sports with jumps ; ( 3 ) one - leg stability , particularly exercised for martial arts ; and ( 4 ) proprioception , side stability , and landing capacities , which are stressed with skiers .
as previously mentioned , a parallel can be made with return to sport after acl reconstruction .
specific exercises to be implemented for patients involved in soccer , basketball , alpine skiing , and american football have been described [ 7 , 20 , 37 , 38 ] .
the same principles as mentioned above can be applied to patients after surgery for instability , regardless of the procedure performed . with respect to return to sport after medial patellofemoral ligament ( mpfl ) reconstruction , fisher et al .  
they reported on only two studies [ 11 , 25 ] concerning the rate of return to a specific level of sports and found that 77  % of patients were able to resume sports at their preinjury level of performance . in a study by ntagiopoulos et al .
, 87  % of patients returned to their previous activities after isolated trochleoplasty , but the level of activity was not specified .
studied the outcome after combined trochleoplasty and mpfl reconstruction for recurrent dislocation in patients with severe trochlear dysplasia .
twenty - eight patients at a minimum follow - up of 2-years were included in the study .
one patient returned to sport at a higher level than preoperatively , sixteen returned at the same preoperative level , and only six patients reported a return to a lower level of activity than before surgery .
unfortunately , there is no information in the literature about validated timelines for a safe return to sport after patellofemoral surgery , especially after tibial tubercle osteotomy .
however , common sense recommends to wait until the osteotomy is healed , and to delay the return until maximum recovery of muscle strength and dynamic stability .
treatment can vary according to the size of the lesion and the intrinsic stability of the patellofemoral joint .
factors to consider include size of the lesion , intrinsic healing capacity of the cartilage , and residual pain .
cartilage lesions are certainly not a favourable factor for a safe return to high - impact and high - demanding sports activities
. clearly , a large cartilage lesion ( > 2  cm ) influences the prognosis for return to sport .
however , there is no specific data in the literature that allows for solid recommendations . based on the current literature , the return to previous level of sports activities after an objective episode of instability is limited to two - thirds of patients with or without surgery .
there is little in the current literature about return to sport after objective patellar instability , and thus , no clear criteria can be as yet endorsed . however , as already mentioned , one can draw a parallel with the literature dedicated to return to sport post - acl reconstruction [ 7 , 20 , 37 , 38 ] . based upon this literature and our experience ,
we propose six clinical criteria to support our return to sport decision - making process .
as regards timing , it is no longer a matter of weeks or months , but rather a matter of clinical and testing requirements that the patient should fulfil .
these criteria are as follows : ( 1 ) no pain ; ( 2 ) no effusion ; ( 3 ) no patellofemoral instability ; ( 4 ) a full range of motion ; ( 5 ) nearly symmetrical strength ( 8590  % ) ; and ( 6 ) excellent dynamic stability .
ideally , patients should satisfy these criteria at 6  weeks after a dislocation , and 3  months after surgery .
our protocol and criteria for return to sport are currently under evaluation . in 2013 ,
the isakos sports medicine committee also defined criteria for return to sport after surgery , and their criteria are very similar to ours ( table  1 ) .
initially , the first 4 criteria listed above are assessed by the surgeon , followed by measurement of quadriceps and hamstring muscle strength in both legs with an isokinetic dynamometer . at this point ,
normal  , and a limb symmetry index ( lsi ) is thus calculated by computing side - to - side differences in the results . and
finally , in light of the results , the surgeon and patient can make a well - documented decision with regards to return to sport .
for strength evaluation , especially in high - demanding sports ( e.g. , alpine skiing , football , basketball , and handball ) , the patient should reach a lsi of at least 90  % in order to be cleared for return to sports [ 7 , 20 , 37 , 38].table  1from the isakos sports medicine committee , isakos consensus meeting on return - to - play , london 2013 . with the permission of elisabeth arendt , md and franois kelberine , mdcriteria for a safe rts after patellofemoral instability isakosif bony surgery is involved , complete radiographic healing of boneno complaints of knee pain or knee instabilityfull or near full range of motionno knee effusioncompleted neuromuscular training / proprioceptionsatisfactory core strength and enduranceacceptable control with dynamic activities ( e.g. , star excursion balance test)limb symmetry index  >  85  % on hop tests , especially if resuming pivoting sportsadequate performance with physiotherapist during sport - specific drills simulating the intensity and movement patterns of the athlete s given sportathlete demonstrates a psychological readiness to return to sport ( e.g. , sane score  >  80/100 ) from the isakos sports medicine committee , isakos consensus meeting on return - to - play , london 2013 . with the permission of elisabeth arendt , md and franois kelberine , md testing exercises are mandatory to evaluate recovery and the competence of the injured or operated limb .
there are many functional tests for the knee that have been used [ 17 , 22 , 31 , 39 ] and appear to be reliable and valuable tools . after a thorough evaluation of the different tests that have been validated in the literature , we have selected the  single - leg squat  , the  star excursion balance test  ( sebt ) , the  drop jump test  , and the  side - hop test  .
the knee must stay above the foot without going into a valgus movement , and the pelvis has to remain stable without dropping or turning .
this exercise is part of the rehabilitation programme and should be perfectly mastered . in the sebt , the knee has to stay aligned as the pelvis is moving .
the patient stands on one foot and reaches points around him like a clock quadrant [ 18 , 28 ] .
the results obtained are qualitative on the video analysis and also quantitative since distances reached during the sebt can be noted and reported .
this test is very useful for the evaluation of lower limb stability [ 9 , 16 , 21].fig .  1 
 a single - leg squat to evaluate the dynamic stability of the lower limb , b star excursion balance test(sebt ) to evaluate the limb stability while reaching the maximum distance around with the other leg 
 a single - leg squat to evaluate the dynamic stability of the lower limb , b star excursion balance test(sebt ) to evaluate the limb stability while reaching the maximum distance around with the other leg many sports demand change in direction and landing from jumps .
if the limb can not be maintained in good alignment and as well properly decelerate , this may result in pain and risk re - injury .
it is therefore important to assess these parameters during the phase of return to sport .
drop and jump is a simple test that provides valuable information about control of landing .
the patient drops from a box 35  cm high , lands on both feet , and immediately jumps as high as possible before landing a second time .
the symmetry of the reception , the alignment of both knees , deceleration , and the capacity for absorbing the shock are evaluated using video recording [ 4 , 15 , 19 , 30 ] . in this case , the results are qualitative , but highly valuable .
the side - hop test consists in jumping on one leg between two lines at a distance of 40  cm as often as possible in 30  s ( fig .  2 ) .
during this test , many aspects of physical conditioning can be observed , including speed , agility , muscle coordination , limb alignment , trunk stability , and control in change of direction . here
, the results are qualitative ( video analysis ) as well as quantitative ( number of jumps ) .
they are then shown to the patient , and the results discussed in order to outline a new set of exercises aimed at correction of any deficits noted . in this way , the training may evolve over time towards more sport - specific exercises with the aim to prepare the patient for return to sport .
have also described a series of tests that can be used to evaluate patients with patellofemoral problems or following corrective patellofemoral surgery [ 1 , 2 , 26 ] .
they assessed core and trunk stability using prone plank , side plank , and single - limb exercises .
for patients with patellofemoral problems , lower limb physical performance was evaluated with the stand and reach balance test , sebt , single - limb squat test , and retro step - up / down test.fig . 
2side hop - test on lines 40 cm away during 30 seconds . the trunk and limb alignement is observed side hop - test on lines 40 cm away during 30 seconds . the trunk and limb alignement is observed from our point of view , patient education is a key point .
very often , the patient has no idea about the importance of whole limb stability and is overly focused on the patellar problem .
experience has shown that these self - administered exercises have been very useful to return the patient to sports.fig . 
3home exercise programme : a gluteus and hamstrings strengthening , b myofascial release of itb , c rotational core stability , d lunges with trunk rotation , e single - leg squat home exercise programme : a gluteus and hamstrings strengthening , b myofascial release of itb , c rotational core stability , d lunges with trunk rotation , e single - leg squat with all , we have presented there still remains a lack of solid evidence about the criteria to determine a safe return to sports after patellofemoral dislocation or surgery .
further work needs to be conducted in this field to better understand the true capability of our functional testing , rehabilitation programme , and surgical procedures , to safely and durably bring our patient back to sports .
there is little in the current literature about return to sport after objective patellar instability , and thus , no clear criteria can be as yet endorsed . however , as already mentioned , one can draw a parallel with the literature dedicated to return to sport post - acl reconstruction [ 7 , 20 , 37 , 38 ] . based upon this literature and our experience ,
we propose six clinical criteria to support our return to sport decision - making process .
as regards timing , it is no longer a matter of weeks or months , but rather a matter of clinical and testing requirements that the patient should fulfil .
these criteria are as follows : ( 1 ) no pain ; ( 2 ) no effusion ; ( 3 ) no patellofemoral instability ; ( 4 ) a full range of motion ; ( 5 ) nearly symmetrical strength ( 8590  % ) ; and ( 6 ) excellent dynamic stability .
ideally , patients should satisfy these criteria at 6  weeks after a dislocation , and 3  months after surgery .
our protocol and criteria for return to sport are currently under evaluation . in 2013 ,
the isakos sports medicine committee also defined criteria for return to sport after surgery , and their criteria are very similar to ours ( table  1 ) .
initially , the first 4 criteria listed above are assessed by the surgeon , followed by measurement of quadriceps and hamstring muscle strength in both legs with an isokinetic dynamometer . at this point ,
normal  , and a limb symmetry index ( lsi ) is thus calculated by computing side - to - side differences in the results . and
finally , in light of the results , the surgeon and patient can make a well - documented decision with regards to return to sport .
for strength evaluation , especially in high - demanding sports ( e.g. , alpine skiing , football , basketball , and handball ) , the patient should reach a lsi of at least 90  % in order to be cleared for return to sports [ 7 , 20 , 37 , 38].table  1from the isakos sports medicine committee , isakos consensus meeting on return - to - play , london 2013 . with the permission of elisabeth arendt , md and franois kelberine , mdcriteria for a safe rts after patellofemoral instability isakosif bony surgery is involved , complete radiographic healing of boneno complaints of knee pain or knee instabilityfull or near full range of motionno knee effusioncompleted neuromuscular training / proprioceptionsatisfactory core strength and enduranceacceptable control with dynamic activities ( e.g. , star excursion balance test)limb symmetry index  >  85  % on hop tests , especially if resuming pivoting sportsadequate performance with physiotherapist during sport - specific drills simulating the intensity and movement patterns of the athlete s given sportathlete demonstrates a psychological readiness to return to sport ( e.g. , sane score  >  80/100 ) from the isakos sports medicine committee , isakos consensus meeting on return - to - play , london 2013 . with the permission of elisabeth arendt , md and franois kelberine , md testing exercises are mandatory to evaluate recovery and the competence of the injured or operated limb .
there are many functional tests for the knee that have been used [ 17 , 22 , 31 , 39 ] and appear to be reliable and valuable tools . after a thorough evaluation of the different tests that have been validated in the literature , we have selected the  single - leg squat  , the  star excursion balance test  ( sebt ) , the  drop jump test  , and the  side - hop test  .
the knee must stay above the foot without going into a valgus movement , and the pelvis has to remain stable without dropping or turning .
this exercise is part of the rehabilitation programme and should be perfectly mastered . in the sebt , the knee has to stay aligned as the pelvis is moving .
the patient stands on one foot and reaches points around him like a clock quadrant [ 18 , 28 ] .
the results obtained are qualitative on the video analysis and also quantitative since distances reached during the sebt can be noted and reported .
this test is very useful for the evaluation of lower limb stability [ 9 , 16 , 21].fig .  1 
 a single - leg squat to evaluate the dynamic stability of the lower limb , b star excursion balance test(sebt ) to evaluate the limb stability while reaching the maximum distance around with the other leg 
 a single - leg squat to evaluate the dynamic stability of the lower limb , b star excursion balance test(sebt ) to evaluate the limb stability while reaching the maximum distance around with the other leg many sports demand change in direction and landing from jumps .
if the limb can not be maintained in good alignment and as well properly decelerate , this may result in pain and risk re - injury .
it is therefore important to assess these parameters during the phase of return to sport .
drop and jump is a simple test that provides valuable information about control of landing .
the patient drops from a box 35  cm high , lands on both feet , and immediately jumps as high as possible before landing a second time .
the symmetry of the reception , the alignment of both knees , deceleration , and the capacity for absorbing the shock are evaluated using video recording [ 4 , 15 , 19 , 30 ] . in this case , the results are qualitative , but highly valuable .
the side - hop test consists in jumping on one leg between two lines at a distance of 40  cm as often as possible in 30  s ( fig .  2 ) .
during this test , many aspects of physical conditioning can be observed , including speed , agility , muscle coordination , limb alignment , trunk stability , and control in change of direction . here
, the results are qualitative ( video analysis ) as well as quantitative ( number of jumps ) .
they are then shown to the patient , and the results discussed in order to outline a new set of exercises aimed at correction of any deficits noted . in this way , the training may evolve over time towards more sport - specific exercises with the aim to prepare the patient for return to sport .
have also described a series of tests that can be used to evaluate patients with patellofemoral problems or following corrective patellofemoral surgery [ 1 , 2 , 26 ] .
they assessed core and trunk stability using prone plank , side plank , and single - limb exercises .
for patients with patellofemoral problems , lower limb physical performance was evaluated with the stand and reach balance test , sebt , single - limb squat test , and retro step - up / down test.fig . 
2side hop - test on lines 40 cm away during 30 seconds . the trunk and limb alignement is observed side hop - test on lines 40 cm away during 30 seconds . the trunk and limb alignement is observed from our point of view , patient education is a key point .
very often , the patient has no idea about the importance of whole limb stability and is overly focused on the patellar problem .
experience has shown that these self - administered exercises have been very useful to return the patient to sports.fig . 
3home exercise programme : a gluteus and hamstrings strengthening , b myofascial release of itb , c rotational core stability , d lunges with trunk rotation , e single - leg squat home exercise programme : a gluteus and hamstrings strengthening , b myofascial release of itb , c rotational core stability , d lunges with trunk rotation , e single - leg squat with all , we have presented there still remains a lack of solid evidence about the criteria to determine a safe return to sports after patellofemoral dislocation or surgery .
further work needs to be conducted in this field to better understand the true capability of our functional testing , rehabilitation programme , and surgical procedures , to safely and durably bring our patient back to sports .
patellar instability is a pathology that concerns a young active population . even after a single dislocation , return to sports at the same level of performance as before injury appears to be compromised .
analysis of the literature reveals that only two - thirds of patients return to sports at the same level .
this can be considered a poor result with respect to the young age of the affected population .
return to sport may be encouraged and promoted using home self - administered exercises and by educating the patient about the importance of regaining muscle strength and dynamic stability . finally , testing protocols for the rts should include quantitative and qualitative criteria .
 
 patellofemoral instability may occur in a young population as a result of injury during sporting activities . 
 this review focuses on return to sport after one episode of dislocation treated no operatively and as well after surgery for chronic patellofemoral instability . with or without surgery , 
 only two - thirds of patients return to sports at the same level as prior to injury . 
 a high - quality rehabilitation programme using specific exercises is the key for a safe return to sporting activities . to achieve this goal , 
 recovery of muscle strength and dynamic stability of the lower limbs is crucial . 
 the focus should be directed to strengthen the quadriceps muscle and pelvic stabilizers , as well as lateral trunk muscle training . 
 patient education and regularly performed home exercises are other key factors that can lead to a successful return to sports . 
 the criteria for a safe return to sports include the absence of pain , no effusion , a complete range of motion , almost symmetrical strength , and excellent dynamic stability.level of evidence iv . 
Introduction
Return to sport after nonsurgical treatment
Critical points in the rehabilitation for achieving a proper return to sport
Return to sports after surgery for chronic patellofemoral instability
Discussion
Criteria for a safe return to sport
Conclusion