Exercise for treating patellofemoral pain syndrome

  • Protocol
  • Intervention



This is the protocol for a review and there is no abstract. The objectives are as follows:

To assess the effects (benefits and harms) of exercise therapy aimed at reducing knee pain and improving knee function for people with patellofemoral pain syndrome.


Description of the condition

Patellofemoral pain syndrome (PFPS) is a common problem among adolescents and young adults. Its incidence varies from 22 new cases per 1000 persons/year in highly active populations to five to six new cases per 1000 in general practice (Boling 2009; van der Linden 2004). PFPS is characterised by retropatellar pain (behind the kneecap) or peripatellar pain (around the kneecap), mostly occurring when load is put on the knee extensor mechanism such as when climbing stairs, squatting, running, cycling or sitting with flexed knees.

Several factors have been implicated in the etiology of PFPS. These include local factors (contribution of patellofemoral joint mechanics and surrounding tissues to patellofemoral pain), distal factors (contribution of foot and ankle mechanics) and proximal factors (contribution of hip, pelvis and trunk mechanics) (Davis 2010). However, the etiology of the condition is still unclear, as is the origin of the pain.

Description of the intervention

The majority of people with PFPS are treated conservatively (non-surgically). Physically-based conservative interventions include knee orthoses, foot orthoses (Hossain 2011), patellar taping (Callaghan 2012) and exercise therapy.

Most exercise therapy programmes for PFPS have focused on strengthening the quadriceps muscles, which was seen as the most promising conservative treatment method for patellofemoral pain syndrome (Heintjes 2003; Powers 1998; Thomee 1999). More recently, studies have focused on the hip muscles as a possible origin of patellofemoral pain (Souza 2009a; Souza 2009b; Willson 2008).

Exercise therapy comprises a broad range of possible variations and accompanying terms. Activity of the quadriceps muscles - and other muscles involved in knee function - can either be concentric, eccentric or isotonic. During concentric activities the muscles shorten, whereas during eccentric activities muscles lengthen in an actively controlled manner. During isotonic activity the muscle tension remains the same. Exercises can either be static/isometric or dynamic. Exercises are referred to as static/isometric if the position of the knee does not change. If the position of the knee does change, the exercise is called dynamic. In cases where the lower leg moves at a predetermined, constant speed which requires an isokinetic dynamometer to control the velocity, the dynamic exercise is also called isokinetic. Exercises where the foot is in contact with a fixed surface are referred to 'closed kinetic chain exercises', as opposed to 'open kinetic chain' exercises where the surface is not fixed. 

Hence, exercises can be described in three dimensions: the type of muscle activity (concentric, eccentric, isotonic), joint movement (dynamic versus no movement: isometric or static) and the presence of reaction forces caused by contact of the foot with a fixed surface (closed versus open kinetic chain) (Witvrouw 2000; Witvrouw 2004). Combinations of the above denominations apply to every type of exercise, and the terminology used for exercise programmes reflects the emphasis intended by the therapist or researcher.

Besides strengthening of the quadriceps muscle, many exercises will also result in the coordination of muscle contraction. Emphasis during exercise therapy may be put on the coordinated contraction of the medial and lateral parts of the quadriceps muscle, and also on the coordinated contraction of hip adductor, hip abductor and gluteal muscles (Mellor 2005). Electromyographic biofeedback visualises specific muscle contractions and may help the patient target the required muscle during exercise.

In addition, there are other differences such as in the delivery of exercise, for example supervised exercise versus home exercise; or in the duration or intensity of exercise.

How the intervention might work

A recent published review on factors associated with PFPS concluded that patients with PFPS have lower knee extension strength, lower hip extension strength and decreased flexibility of the lower extremity muscles compared with people without PFPS (Lankhorst 2012). Exercise programmes that comprise static and dynamic muscular exercises for both quadriceps and hip muscles are aimed to improve the strength of these muscles and consequently reduce the pain. Furthermore, many exercise programmes also focus on improving the flexibility of the lower extremity by adding stretching exercises.

Why it is important to do this review

Patellofemoral pain syndrome (PFPS) is a common problem among adolescents and young adults. Its etiology, including the structures causing the pain, and treatment methods are all debated in literature, but consensus has not been reached so far. Exercise therapy to strengthen the quadriceps is often prescribed, though its efficacy is still debated. This updates and supercedes a former Cochrane review (Heintjes 2003).


To assess the effects (benefits and harms) of exercise therapy aimed at reducing knee pain and improving knee function for people with patellofemoral pain syndrome.


Criteria for considering studies for this review

Types of studies

Randomised and quasi-randomised (method of allocating participants to a treatment which is not strictly random: e.g. by hospital number) controlled clinical trials which evaluate exercise therapy for patellofemoral pain syndrome will be included.

Types of participants

Adolescents and adults with patellofemoral pain syndrome (designated by the trial author(s) as such or as 'anterior knee pain syndrome', 'patellar dysfunction', 'chondromalacia patellae' or 'chondropathy').

Studies focusing on other named knee pathologies such as Hoffa's syndrome, Osgood Schlatter syndrome, Sinding-Larsen-Johansson syndrome, iliotibial band friction syndrome, tendinitis, neuromas, intra-articular pathology including osteoarthritis, rheumatoid arthritis, traumatic injuries (such as injured ligaments, meniscal tears, patellar fractures and patellar luxation), plica syndromes, and more rarely occurring pathologies, will be excluded (Nissen 1998; Thomee 1999).

Types of interventions

We will include studies evaluating exercise therapy for patellofemoral pain syndrome. Exercises can be applied on their own or in combination with other non-surgical interventions, provided the same other intervention is applied to the whole population in the comparison. Exercises can be performed at home or under supervision of a therapist.

  1. Exercise therapy versus control (no treatment, placebo or waiting list controls). This also includes 'exercise therapy + another intervention (e.g. taping) versus the other intervention alone (e.g. taping)'.

  2. Exercise therapy versus different conservative interventions (e.g. taping).

  3. Comparisons of different exercises

    1. Delivery of exercises or exercise programmes (e.g. supervised versus home exercise; group versus individual supervision).

    2. Medium of exercises or exercise programmes (water versus land based exercise).

    3. Types of exercise (e.g. closed versus open kinetic chain exercises; dynamic versus isometric).

    4. Target of exercise (strengthening of hip or abdominal muscles versus quadriceps muscles)

    5. Duration of exercises or exercise programmes (e.g. long duration (more than three months) versus shorter duration (less than three months)).

    6. Intensity of exercises or exercise programmes (e.g. high intensity (several times per week) versus low intensity (once weekly)).

The intervention groups for comparisons of different exercises will be defined as the most novel intervention (and first listed) of the two exercises being compared. For instance, the intervention is supervised exercise and the control is home exercise in the first comparison of 3a. Consideration will also be given to consistency in the choice of control groups.

Combined interventions or treatment packages including exercise will not be tested in this review, with the exception of exercises provided with instructions or advice, where exercise is the predominant intervention.

Types of outcome measures

Primary outcomes
  1. Knee pain measured by validated self reporting methods (Visual Analog Scale [VAS], numerical rating scale [NRS] of McGill Pain questionnaire) (Melzack 1987). Pain scores are reported for pain in daily life (usual pain), for worst pain and for pain at activities (e.g. sports) if available (Crossley 2004).

Secondary outcomes
  1. Functional ability (i.e. knee function in activities of daily living). Questionnaires focusing on knee function (such as Functional Index Questionnaire (Chesworth 1989), WOMAC Osteoarthritis Index (McConnell 2001), Kujala Patellofemoral Function Scale (Kujala 1993) and Lysholm scale (Lysholm 1982)).

  2. Functional performance tests (squatting, hopping on one leg, etc) (Loudon 2002).

  3. Subjective perception of recovery. Recovery from patellofemoral pain syndrome is a outcome measure inconsistently reported in studies and different methods are used to describe recovery. In this review, 'number of patients no longer troubled by symptoms' or 'perceived recovery' measured on a Likert scale will be included as a secondary outcome measure (van Linschoten 2006).

  4. Adverse events (e.g. knee swelling or substantially increasing pain levels as a direct effect of treatment).

Changes in knee function measured on impairment level only (e.g. range of motion, muscle strength) do not directly represent changes in the symptoms of patellofemoral pain or the resulting disability, and will therefore not be considered clinically relevant outcome measures in this review (Dursun 2001; Gobelet 1992).

Timing of outcome measurement

Outcomes measured within three months after the baseline measurement will be considered short term outcomes of exercise therapy, and measurements from three months and longer will be considered long term outcomes.

Search methods for identification of studies

Electronic searches

We will search the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register, the Cochrane Central Register of Controlled Trials (The Cochrane Library), MEDLINE (1946 to present), EMBASE (1980 to present), PEDro - The Physiotherapy Evidence Database (to present), CINAHL (1982 to present) and AMED (1985 to present). We will also search the WHO International Clinical Trials Registry Platform and Current Controlled Trials for ongoing and recently completed trials.

In MEDLINE (Ovid Online), a subject-specific strategy will be combined with the sensitivity-maximizing version of the Cochrane Highly Sensitive Search Strategy for identifying randomised trials (Lefebvre 2011). Search strategies for MEDLINE and the Cochrane Central Register of Controlled Trials are shown in Appendix 1.

No language restrictions will be applied.

Searching other resources

Reference lists of included studies and other relevant articles will be checked for additional trials, and institutions and experts in the field will be contacted in order to identify unpublished studies. Furthermore, conference abstracts will be searched from specific patellofemoral pain syndrome conferences such as the international patellofemoral research retreat (Davis 2010).

Data collection and analysis

Selection of studies

Two review authors (RAH and NEL) will select potentially eligible articles by reviewing the title and abstract of each citation. After obtaining full articles, both authors will independently perform study selection. In cases of disagreement, a consensus will be reached through discussion.

Data extraction and management

Two review authors (RAH and NEL) will independently extract the data within included trials using a piloted data collection form. Any disagreements will be resolved by consensus. Where data are missing or incompletely reported, authors of trials will be contacted. Where pooling is possible and if necessary, pain scores (VAS, NRS) will be converted to a 0 to 10 scale and function scores to 0 to 100 scale.

Assessment of risk of bias in included studies

Two review authors (RAH and NEL) will independently assess the risk of bias of the included studies using The Cochrane Collaboration's 'Risk of bias' tool (Higgins 2011). The following domains will be assessed: random sequence generation; allocation concealment; blinding of participants and personnel; blinding of outcome assessment; incomplete outcome data; selective reporting; and other bias. Other sources of bias will include bias from major imbalance in baseline characteristics and performance bias such as from lack of comparability in clinician's experience with the interventions under test or differences in care other than the interventions under test.

Each of these criteria will be explicitly judged using: low risk of bias; high risk of bias; and unclear risk of bias (where 'unclear' relates to a lack of information or uncertainty over the potential for bias). Disagreements between review authors regarding the risk of bias for domains will be resolved by consensus.

Measures of treatment effect

Risk ratios with 95% confidence intervals will be calculated for dichotomous outcomes. Mean differences with 95% confidence intervals will be calculated for continuous outcomes as appropriate. When two or more studies present their data derived from the same instrument of evaluation (with the same units of measurement), data will be pooled as a mean difference (MD). Conversely, we will use the standardised mean difference (SMD) when primary studies express the same variables through different instruments (and different units of measurement).

Unit of analysis issues

The unit of randomisation in the studies likely to be included in this review is usually the individual participant. Exceptionally, as in the case of trials including people with bilateral complaints, data for trials may be evaluated for knees, instead of individual patients. Where such unit of analysis issues arise and appropriate corrections have not been made, we will consider presenting the data for such trials only where the disparity between the units of analysis and randomisation is small. Where data are pooled, we will perform a sensitivity analysis to examine the effects of pooling these incorrectly analysed trials with the other correctly analysed trials.

For multi-comparison studies, we will attempt to combine data where two or more of the groups test interventions in the same category. Should combining not be appropriate but the data are presented for the difference comparisons are presented in the same analysis, the number of participants in the shared comparison will be divided (e.g. halved where this intervention appears twice) in order to avoid the 'double-counting' of participants for the 'shared comparison' in the meta-analyses. For cross-over trials, we will present data collected prior to the crossover of the intervention.

Dealing with missing data

We will contact trial authors where further details of methodology or data are required for trial inclusion.

Where possible we will perform intention-to-treat analyses to include all people randomised. However, where drop-outs are identified, the actual numbers of participants contributing data at the relevant outcome assessment will be used. We will be alert to the potential mislabelling or non-identification of standard errors and standard deviations (SDs). Unless missing standard deviations can be derived from confidence intervals or standard errors, we will consider whether it is appropriate to estimate values based on comparable data included in this review in order to present these in the analyses. We will make clear for which trials imputed data have been used (e.g. footnotes in the forest plots).

Where data are presented as the median (inter-quartile range), we will not attempt to transform data to achieve normality or to estimate the mean and SD.

Assessment of heterogeneity

Heterogeneity will be assessed by visual inspection of the forest plot (analysis) along with consideration of the chi² test for heterogeneity and the I² statistic (Higgins 2011). Heterogeneity will be considered statistically significant at P < 0.1. Studies will also be examined for methodological and clinical heterogeneity, particularly if significant statistical heterogeneity is identified.

Assessment of reporting biases

Where data for at least 10 studies are available for pooling, we will assess for publication bias by using funnel plots (Higgins 2011).

Data synthesis

When considered appropriate, results of comparable groups of trials will be pooled using both fixed-effect and random-effects models. The choice of the model to report will be guided by a careful consideration of the extent of heterogeneity and whether it can be explained, in addition to other factors such as the number and size of studies that are included.

Subgroup analysis and investigation of heterogeneity

Where data permit, we will perform the following subgroup analyses:

  • Gender

  • Duration of complaints (acute (less than three months) versus chronic)

  • Sport participation (athletes and/or military recruits versus the general population)

We will inspect the overlap of confidence intervals and perform the test for subgroup differences available in RevMan to test whether subgroups are statistically significantly different from one another.

Sensitivity analysis

Where appropriate, we will perform sensitivity analyses investigating the effects of risks of bias by excluding trials with high or unclear risk of bias (such as for trials with lack of allocation concealment and lack of random sequence bias) and trials reported in abstracts only. Sensitivity analyses will also be performed to explore the differences between different models (fixed-effect versus random-effects) for pooling data where there is heterogeneity. Furthermore, we will perform sensitivity analysis for the trials with imputed data.

'Summary of findings' tables

Where there are sufficient data, we will summarise the results for the main comparisons described in the Types of interventions in 'Summary of findings' tables. We shall use the GRADE approach to assess the quality of evidence related to each of the primary outcomes listed in the Types of outcome measures (Higgins 2011; see section 12.2).


We would like to acknowledge Helen Handoll and Nigel Hanchard who provided valuable comments on the protocol. In addition, we are grateful to Joanne Elliott for her assistance with the search strategies.


Appendix 1. Search strategies

Central Register of Controlled Trials (Wiley Online Library)

#1 MeSH descriptor Patellofemoral Pain Syndrome, this term only
#2 MeSH descriptor Patella, this term only
#3 MeSH descriptor Knee Joint explode all trees
#4 MeSH descriptor Knee, this term only
#5 (#2 OR #3 OR #4)
#6 MeSH descriptor Arthralgia, this term only
#7 MeSH descriptor Pain explode all trees
#8 (#6 OR #7)
#9 (#5 AND #8)
#10 (anterior knee pain):ti,ab,kw
#11 (patell* or femoropatell* or femoro-patell* or retropatell*) NEAR/2 (pain or syndrome or dysfunction):ti,ab,kw
#12 ((lateral compression or lateral facet or lateral pressure or odd facet) NEAR/2 syndrome):ti,ab,kw
#13 (chondromalac* or chondropath* or chondrosis) NEAR/2 (knee* or patell* or femoropatell* or femoro-patell* or retropatell*):ti,ab,kw
#14 MeSH descriptor Chondromalacia Patellae, this term only
#15 (#1 OR #9 OR #10 OR #11 OR #12 OR #13 OR #14)
#16 MeSH descriptor Exercise Therapy explode all trees
#17 MeSH descriptor Exercise explode all trees
#18 (exercis* or strengthen* or stretch* or train* or physiotherapy or physical therap*):ti,ab,kw
#19 (#16 OR #17 OR #18)
#20 (#9 AND #15 AND #19)

MEDLINE (Ovid Online)

1   Patellofemoral Pain Syndrome/
2   Patella/ or exp Knee Joint/ or Knee/
3   Arthralgia/ or Pain/
4   2 and 3
5   anterior knee pain.tw.
6   ((patell* or femoropatell* or femoro-patell* or retropatell*) adj2 (pain or syndrome or dysfunction)).tw.
7   ((lateral compression or lateral facet or lateral pressure or odd facet) adj2 syndrome).tw.
8   ((chondromalac* or chondropath* or chondrosis) adj2 (knee*1 or patell* or femoropatell* or femoro-patell* or retropatell*)).tw.
9   Chondromalacia Patellae/
10 or/1,4-9
11 exp Exercise Therapy/ or exp Exercise/
12 (exercis* or strengthen* or stretch* or train* or physiotherapy or physical therap*).tw.
13 or/11-12
14 Randomized controlled trial.pt.
15 Controlled clinical trial.pt.
16 randomized.ab.
17 placebo.ab.
18 Drug Therapy.fs.
19 randomly.ab.
20 trial.ab.
21 groups.ab.
22 or/14-21
23 exp Animals/ not Humans/
24 22 not 23
25 and/10,13,2

Contributions of authors

RAH: searched studies to contextualise the background section, revised the protocol and approved the final version.
NEL: searched studies to contextualise the background section, revised the protocol and approved the final version.
RL: conceived the review, drafted the protocol and approved the final version.
SB-Z: conceived the review, drafted the protocol and is the guarantor of the review.
MM: conceived the review, drafted and revised the protocol, co-ordinated the protocol and approved the final version.

Declarations of interest

None known.

Sources of support

Internal sources

  • Erasmus Medical Center, Netherlands.

External sources

  • No sources of support supplied