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These are some publications where we have used the SNAPPS questionnaire, researchers around the world have used it, or that were relevant to the SNAPPS's questionnaire creation.

Our studies using SNAPPS
Our studies
The prevalence of patellofemoral pain in the Rugby League World Cup (RLWC) 2021 spectators: A protocol of a cross-sectional study

Authors: María B. Sánchez, James Selfe, & Michael Callaghan


Patellofemoral pain (PFP) can cause significant pain leading to limitations in societal participation and physical activity. PFP is usually associated with athletes undergoing intensive physical training, or military recruits; but recent evidence shows that PFP is common in the general population. The relationship of PFP with physical activity is not entirely clear. Our aim is to provide a better estimate of the general population prevalence of PFP and to relate this to the level of physical activity, and demographic characteristics.

The Survey instrument for Natural history, Aetiology and Prevalence of Patellofemoral pain Studies (SNAPPS) was developed as a PFP screening tool to be used in the community. The electronic version of the SNAPPS (eSNAPPS) has recently been validated and was used to survey attendees at mass-participation running events.

We will use an electronic survey to collect data from a sample of 1100 Rugby League World Cup spectators. The survey will have four sections: i) general and demographic; ii) knee pain (eSNAPPS); iii) level of physical activity; and iv) quality of life in relation to knee pain. The primary analytic approach will be descriptive of PFP prevalence. Secondary analyses will explore the relationships of the presence of PFP and the other variables.

We will disseminate this work by publication of peer-reviewed papers in scientific journals, presentations at scientific conferences, and on the dedicated SNAPPS website

Keywords: SNAPPS; eSNAPPS; Patellofemoral Pain; Knee Pain; Prevalence; survey; General

Validation and utilisation of a digital version of the Survey instrument for Natural history, Aetiology and Prevalence of Patellofemoral pain Studies (eSNAPPS)

Authors: Mohamed Yusuf, Paola Dey, Michael Callaghan, Nicola Relph, Phillip Gichuru, Susan Pinner, Jane Ashbrook, Joanne Ashman, Peter Goodwin, Ruth Macdonald, & James Selfe


Objective: This study validated the newly adapted electronic SNAPPS (eSNAPPS) against the original paper SNAPPS. Subsequently, the study estimated the prevalence of PFP in running participants and spectators attending three massparticipant running events in the United Kingdom by using the eSNAPPS tool.

Methods: This study had two parts. Firstly, a validation of the original paper version of the SNAPPS tool. Secondly, if validation was achieved, eSNAPPS was used in a prevalence study. A convenience sample of running participants and spectators aged 18-40 years attending the mass participation running events was used. 12-month prevalence of PFP was used as the main outcome.

Results: eSNAPPS was valid in identifying those with PFP (ICC 0.99 for Overall agreement, p<0.0001). In the prevalence study, a total of 1,080 running participants and spectators completed the eSNAPPS. The overall prevalence of PFP was 17.4% (95%CI: 15.2%, 19.8%); 20.5% of males (16.5, 24.9) and 15.7% of females (13.1, 18.7) had PFP. Prevalence was 17.4% (15.2, 19.8) in spectators and 16.7% in running participants (14.5, 19.0).

Conclusion: The overall PFP prevalence in this study was slightly smaller than those previously reported in the literature. Findings also show that there were similar prevalence estimates in spectators and running participants.

Keywords: Patellofemoral Pain, Knee pain, Epidemiology, Prevalence

Knee problems are common in young adults and associated with physical activity and not obesity: the findings of a cross-sectional survey in a university cohort

Authors: Chukwuemeka Ibeachu, James Selfe, Chris J. Sutton & Paola Dey


Background: Obesity and sedentary behaviour, risk factors for knee osteoarthritis in middle-age, are increasing in younger adults. The objectives of this study were to estimate the prevalence of knee problems in young adults, to characterise these problems and explore the relationship with physical activity, physical inactivity and obesity.

Methods: Presence of knee problems was collected through self-report questionnaire from staff and students of one university aged 18–39; direct measurement of weight and height was taken and activity measured using the International Physical Activity Questionnaire. Twelve-month prevalence of knee problems was estimated. Logistic regression was used to investigate the relationship between knee problems and physical activity levels, sitting time and body mass index.


Results: The prevalence of knee problems was high (31.8% [95% CI 26.9 to 37.2%]) among the 314 participants; knee pain was the most common dominant symptom (65%). Only high physical activity levels (OR 2.6 [95% CI 1.4–4.9]) and mental distress (OR 2.3 [95% CI 1.2–4.6]) were independent risk factors for knee problems.


Conclusions: Knee problems were common among young adults, who were staff and students of a university. With increasing obesity prevalence, populations are being encouraged to become more active. More attention may need to be paid towards prevention of knee problems in such programmes, and further research is warranted.

The Prevalence of Patellofemoral Pain in the Community

Authors: Jennifer Thorpe, Paola Dey & Jennier Earl-Boehm


Background: Previous research on PFP prevalence has been based on research in closed populations (i.e. athletic, military, hospital/clinic). Not all PFP patients may elect to seek medical attention for their pain. The Survey instrument for natural history, Aetiology, and Prevalence of Patellofemoral pain Studies (SNAPPS) was created to identify those in the community with PFP. This study aimed to determine the prevalence of PFP in South East Wisconsin using SNAPPS and identify demographic factors that may be associated with having sought medical attention.

Methods: The study used a cross-sectional survey design; shared via social media, email, and in-person. Males & females aged between 18 and 40 were recruited. Results were presented as prevalence rate and stratified by sex. In addition to this, heat-map plots were created to illustrate the frequency of location. Prevalence between sexes, having sought medical attention between sexes and duration of symptoms for > 1 month and < 1 month were all compared using separate chi-square tests of independence (p < 0.05).

Results: Overall there were 513 respondents, of which 393 (76%) had reported knee and 136 (27%) scored as likely to have PFP. PFP prevalence in males was 19%, and in females, it was 31.9%. There was no significant relationship between having seen a doctor for pain and sex (χ21=0.046, p=0.830). While those with symptoms for more than 1 month were significantly more likely to seek medical attention (χ2=7.52, p=0.006).

Conclusion: Prevalence of PFP in individuals from South East Wisconsin is consistent with other research, in particular, the prevalence rate in males and females. Also, this study found that symptom duration appears to influence whether those with PFP seek medical attention. Future research is needed to further explore this relationship due to the influence on treatment outcomes.

How do health professionals translate and cross-culturally validate self-reported health measure? an example: the German SNAPPS tool

Authors: James Selfe, Michael Callaghan, Nicola Relph, Phillip Gichuru & Paola Dey.


Background: Many studies have established the importance of having a rigorous and robust framework for the translation and cross-cultural adaptation of self-report outcome measures. This abstract reports on the use of the guidelines developed by Beaton and colleagues (2001) on a translation process as part of a pan-European epidemiological project on knee pain (SNAPPS).

Methods: Two independent, native German speakers translated the SNAPPS tool into German and afterwards reconciled their differences to produce one final translation. Subsequently, two English-German speakers translated the tool back into English, after which an expert panel reviewed the translation to see if it was close enough to the original version of the tool.

Results: During the forward translation, several questions needed to be changed slightly with regards to the chosen terms, as cultural and linguistic differences rendered verbatim translation impossible. Although minor adjustments were made, no profound content had to be changed, demonstrating the close resemblance between English and German cultures.

Conclusion: A forward-backwards translation of SNAPPS into German has been completed. The SNAPPS expert committee reached a consensus on the final translation; assuring equivalence between the translated and the original document. The last stage of the translation and cultural validation of the SNAPPS tool is to carry out a pilot study using the questionnaire in a German-speaking population.

A questionnaire to identify patellofemoral pain in the community: An exploration of measurement properties

Authors: Paola Dey, Michael J Callaghan, Neil Cook, Ruth Sephton, Chris Sutton, Elaine Hough, Jonathan James, Rukhtam Saqib & James Selfe


Background: Community-based studies of patellofemoral pain (PFP) need a questionnaire tool that discriminates between those with and those without the condition. To overcome these issues, we have designed a self-report questionnaire which aims to identify people with PFP in the community.

Methods Study designs: comparative study and cross-sectional study.

Study population: comparative study: PFP patients, soft-tissue injury patients and adults without knee problems. Cross-sectional study: adults attending a science festival.

Intervention: comparative study participants completed the questionnaire at baseline and two weeks later. Cross-sectional study participants completed the questionnaire once.The optimal scoring system and threshold was explored using receiver operating characteristic curves, test-retest reliability using Cohen’s kappa and measurement error using Bland-Altman plots and standard error of measurement. Known-group validity was explored by comparing PFP prevalence between genders and age groups.

Results: Eighty-four participants were recruited to the comparative study. The receiver operating characteristic curves suggested limiting the questionnaire to the clinical features and knee pain map sections (AUC 0.97 95 % CI 0.94 to 1.00). This combination had high sensitivity and specificity (over 90 %). Measurement error was less than the mean difference between the groups. Test–retest reliability estimates suggest good agreement (N = 51, k = 0.74, 95 % CI 0.52–0.91). The cross-sectional study (N = 110) showed expected differences between genders and age groups but these were not statistically significant.

Conclusion: A shortened version of the questionnaire, based on clinical features and a knee pain map, has good measurement properties. Further work is needed to validate the questionnaire in community samples.

Around the world studies using SNAPPS
Around the world studies
Prevalence of patellofemoral pain and knee pain in the general population of Chinese young adults: a community-based questionnaire survey

Authors: Xingquan Xu, Chen Yao, Rui Wu, Wenjin Yan, Yao Yao, Kai Song, Qing Jiang and Dongquan Shi


Background: Previous studies that have described the prevalence of patellofemoral pain (PFP) have been limited to samples of military personnel or sporting populations, and convincing data in the general Chinese population are lacking. The present study defined the prevalence of PFP and knee pain in the general population of Chinese young adults and evaluated whether gender, age, or body mass index (BMI) were associated with PFP.

Methods Study designs: An anonymous online questionnaire survey was open to the general public in China. A self-report questionnaire was used to specifically identify PFP. The population aged 18–40 years were enrolled in the study and completed the questionnaire. The prevalence of PFP and knee pain in the overall sample and in subgroups stratified by sex, age, and BMI was estimated. Logistic regression analysis was conducted to determine if there was a significant association between PFP and sex, age, or BMI.

Results: A total of 1153 participants were enrolled in the study. The prevalence of PFP in the overall sample and among the male and female participants was 20.7, 20.3, and 21.2%, respectively. The prevalence of the knee pain in the overall sample and among the male and female participants was 35.6, 38.2, and 33.7%, respectively. The prevalence of PFP in the subgroups stratified by age and BMI did not differ significantly between the groups. Gender, age, and BMI did not have significant associations with the prevalence of PFP.

Conclusion: PFP is common in the general Chinese population. Clinicians should direct more attention toward the early diagnosis of and interventions for PFP.s.

Patellofemoral pain syndrome: prevalence and coping strategies of amateur runners in Lagos state

Authors: Ashiyat Akodu & Nkechi Nwakalor


Background: Patellofemoral pain syndrome (PFPS) is an overuse injury of the patellofemoral joint which is characterized by pain in the anterior aspect of the knee, aggravated by activities. However little is known about the prevalence and coping strategies of PFPS in amateur runners in Nigeria. This study therefore investigated the prevalence and coping strategies of patellofemoral pain syndrome among amateur runners in Lagos, south west, Nigeria.

Material and Method: A cross sectional survey was carried out among 203 amateur runners within the ages of 18-40 years recruited from various sports centers in Lagos state, south west, Nigeria. The instruments used for this research were a 32 item questionnaire of Survey instrument for Natural history, Etiology and Prevalence of Patellofemoral pain Studies (SNAPPS) and pain coping inventory (PCI).

Results: The 12month prevalence of PFPS was observed to be 45.3%. There was a high prevalence of PFPS among females 45(53.6%). It was also observed that the coping strategies adopted mostly by the respondents were passive coping strategy 65(70.70%). Sex was significantly associated with 12 months prevalence of PFPS.

Conclusion: There was a high prevalence of PFPS among amateur runners in Lagos state with females having a 1.35times higher prevalence than males. Passive coping strategies of worrying and resting were mostly adopted by the respondents. Key words: patellofemoral pain syndrome, prevalence, coping strategies, runners.

SNAPPS supporting references
SNAPPS support
A loaded self-managed exercise programme for patellofemoral pain: a mixed methods feasibility study

Authors: Benjamin Smith, Paul Hendrick, Marcus Bateman, Fiona Moffatt, Michael Skovdal Rathleff, James Selfe, Toby Smith & Pip Logan


Background: A novel loaded self-managed exercise programme that includes pain education and self-management strategies may result in better outcomes for people with patellofemoral pain (PFP). However, establishing program feasibility is an essential first step before testing efficacy. The purpose of this study was to evaluate the feasibility and acceptability of conducting a definitive RCT which will evaluate the clinical and cost-effectiveness of a loaded self-managed exercise programme for people with PFP compared with usual physiotherapy.


Methods: In a mixed methods, pragmatic, randomised controlled feasibility study, 60 participants with PFP (57% female; mean age 29 years) were recruited from a physiotherapy clinic within a large UK teaching hospital. They were randomly allocated to receive either a loaded self-managed exercise programme (n = 30) or usual physiotherapy (n = 30). Feasibility indicators of process, resources, and management were collected through follow-up of standardised questionnaires six months after recruitment and semi-structured interviews with 20 participants and physiotherapists.


Results: Recruitment rate was 5 participants per month; consent rate was 99%; adherence to intervention appointments was 87%; completeness of questionnaire data was 100%; and adherence to intervention delivery was 95%.

Three exercise diaries were returned at six months (5%). At six months, 25 questionnaire booklets were returned (9 in the loaded self-managed group, 16 in the usual physiotherapy group), with a total retention rate of 42%.

At six months, 56% (5/9) of respondents in the loaded self-managed group and 56% (9/16) in the usual physiotherapy group were classified as ‘recovered’.

Both groups demonstrated improvements in average pain (VAS), kinesiophobia, pain catastrophizing, general self-efficacy and EQ-5D-5 L from baseline to six months.


Conclusion: The results of this feasibility study confirm that it is feasible and acceptable to deliver a loaded self-managed exercise programme to adults with PFP in an NHS physiotherapy outpatient setting. However, between group differences in lost to follow up and poor exercise diary completion mean we are uncertain on some feasibility aspects. These methodological issues need addressing prior to conducting a definitive RCT.

Exploration of the current evidence base for the incidence and prevalence of patellofemoral pain syndrome.

Authors: Jennifer L. Oakes, Paula Jill Mccandless & James Selfe


Objectives: No consensus has been reached regarding the incidence and prevalence of patellofemoral pain syndrome (PFPS). This literature review aims to explore and present research conducted on the incidence and prevalence data for PFPS to date.

Methods: The literature search employed databases Ovid SP, AMED, Ovid Medline (R) and EMBASE, accessed via the University of Central Lancashire Library Online service, and search terms ‘adolescen*’ ‘anterior knee pain’, ‘incidence’, ‘outcome measure’, ‘patellofemoral pain’, ‘patellofemoral pain syndrome’, ‘prevalence’, ‘questionnaire’ and ‘response rate’. All articles were filtered by hand to determine relevance, as were reference lists of applicable studies/reviews to identify key articles. Pertinent journals were included as recommended by a specialist in the field.

Results: Ten studies were selected for review, spanning 22 years of study that apparently focused on incidence over prevalence. Despite a lack of United Kingdom based research, this topic is of international interest. The participant groups demonstrate a large age span, comprising mainly military recruits, along with students, healthcare patients and athletes. The selection and definition of terminology differed greatly, as did methodologies, specifically the data collection tools. Despite questionnaires being well suited to incidence and prevalence data collection, none were identified as being valid and reliable.

Discussion: Two major research gaps were identified: investigation into PFPS prevalence (and incidence) within athletic adolescents, and the development of a questionnaire to collect incidence and or prevalence data. Such research could facilitate clinical practice and the development of health strategies.

Activity-associated pain in patellofemoral pain syndrome:
How does it inform research and practice?

Authors: Michael Callaghan, James Selfe & Paola Dey


Has the prevalence of patellofemoral pain in the general population in the United Kingdom been properly evaluated?

Authors: Michael J Callaghan & James Selfe


Background and purpose: The aims of this paper were to investigate the cited incidence, and to establish the source data for quoted figures, ratios, prevalence or incidence of patellofemoral pain syndrome (PFPS) for the British general adult population.

Method: A literature search of all English language peer reviewed publications from January 2000 to December 2005 with the search terms ‘patellofemoral pain’, ‘patellofemoral pain syndrome’ and ‘anterior knee pain’.

Results: Of the papers retrieved, 40 cited some sort of percentage figure or a ratio for the incidence or prevalence of PFPS. An incidence rate for PFPS of 25% (or 1:4) was cited in 13/40 papers, but other incidence rates cited ranged from 3% to 40%. There seemed to be 4 key references that other authors used to substantiate their cited values for PFPS prevalence or incidence or rate. There were no epidemiological papers studying the incidence or prevalence of PFPS in the United Kingdom.

Conclusion: The evidence for the cited incidence of PFPS or anterior knee pain in the adult general population is taken almost entirely from source data in the sports medicine or the military settings. Of these, only one was set in the United Kingdom. We conclude that the prevalence of PFPS in the United Kingdom has not been properly evaluated and consequently there is clearly a need for a study on the incidence rates of PFPS in this country’s general population.

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