Downloaded from http://bjsm.bmj.com/ on July 14, 2017 - Published by group.bmj.com
Review
Is hip strength a risk factor for patellofemoral pain? A systematic review and meta-analysis M S Rathleff,1,2 C R Rathleff,1 K M Crossley,3 C J Barton4,5,6,7 1
Orthopaedic Surgery Research Unit, Research and Innovation Center, Aalborg University Hospital, Aalborg, Denmark 2 Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark 3 Division of Physiotherapy, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane, Queensland, Australia 4 Complete Sports Care, Melbourne, Victoria, Australia 5 Pure Sports Medicine, London, UK 6 Centre for Sport and Exercise Medicine, Queen Mary University of London 7 Musculoskeletal Research Centre, La Trobe University, Melbourne, Australia Correspondence to Dr Michael Skovdal Rathleff, Orthopaedic Surgery Research Unit, Research and Innovation Center, Aalborg University Hospital, Soendre Skovvej 15, Aalborg 9000, Denmark; [email protected] Accepted 5 March 2014 Published Online First 31 March 2014
ABSTRACT Objective To evaluate and synthesise the literature on hip strength among patients with patellofemoral pain (PFP) to address the following: (1) differentiate between hip strength as a risk factor and associated deficit in PFP; (2) describe hip strength in men and women with PFP across different age ranges; (3) investigate the effects of hip strengthening on biomechanical knee variables associated with PFP development. Methods MEDLINE, CINAHL, Web of Science, SportDiscus and Google Scholar were searched in November 2013 for studies investigating hip strength among patients with PFP. Two reviewers independently assessed papers for inclusion and quality. Means and SDs were extracted from each included study to allow effect size calculations and comparisons of results. Results Moderate-to-strong evidence from prospective studies indicates no association between isometric hip strength and risk of developing PFP. Moderate evidence from cross-sectional studies indicates that men and women with PFP have lower isometric hip musculature strength compared to pain-free individuals. Limited evidence indicates that adolescents with PFP do not have the same strength deficits as adults with PFP. Conclusions This review highlights a possible discrepancy between prospective and cross-sectional research. Cross-sectional studies indicate that adult men and women with PFP appear to have lower hip strength compared to pain-free individuals. Contrary to this, a limited number of prospective studies indicate that there may be no association between isometric hip strength and risk of developing PFP. Therefore, reduced hip strength may be a result of PFP rather than the cause.
INTRODUCTION
To cite: Rathleff MS, Rathleff CR, Crossley KM, et al. Br J Sports Med 2014;48:1088–1088.
The incidence and prevalence of patellofemoral pain (PFP) are high in both adolescent and adult populations.1–7 Importantly, despite the implementation of conservative rehabilitation, the long-term prognosis for PFP is poor, with only one-third being pain-free, 1 year after the initial diagnosis.8–11 Identifying modifiable risk factors will facilitate targeted rehabilitation and prevention strategies for PFP, thus reducing the burden of PFP.12 The aetiology of PFP is thought to be multifactorial.13 Local factors, such as lower knee extension strength,14 delayed onset of vastus medialis relative to vastus lateralis,4 greater knee abduction impulse during running15 and knee abduction moment during drop jump landing16 have been associated with increased risk of PFP development. While all factors can contribute to PFP and are likely to be interrelated, recently much attention has been paid to the relationship between hip function and PFP.12 It is proposed that greater hip adduction and
Rathleff MS, et al. Br J Sports Med 2014;48:1088–1088. doi:10.1136/bjsports-2013-093305
internal rotation, especially during weight-bearing activities, may lead to altered knee and patellofemoral joint (PFJ) kinematics with subsequent increase in lateral PFJ stress.17 Recent prospective studies support this hypothesis, reporting increased peak hip internal rotation angle during landing in military recruits,6 and greater peak hip adduction angle in recreational female runners18 to be risk factors for PFP development. These altered movement patterns may result from impaired hip muscle function.6 18 Lower hip muscle strength has been explored in people with PFP. The most recent systematic review of hip strength included a search completed in January 2008, and focused only on women.19 This review concluded that women demonstrated lower hip abduction, external rotation and extension strength in the affected side compared to asymptomatic individuals.19 However, no prospective research was identified to allow evaluation of a causal relationship between hip muscle function and PFP.20 Since the publication of this systematic review, many studies, including those with prospective designs, have evaluated the link between hip strength and PFP, and it is timely to conduct an updated high-quality (HQ) systematic review in this field. In line with the belief that impaired hip muscle function is associated with PFP, the clinical effects of hip muscle strengthening programmes have recently been evaluated.21–24 However, in order to gain a deeper understanding of the role of hip muscle strength in PFP, an evaluation of the relationship between hip strengthening interventions and changes in knee biomechanics are required. The gaps in the literature call for the investigation of the following: (1) differentiate between hip strength as a risk factor and associated deficit in PFP; (2) association of hip strength with PFP in men and women across different age ranges and (3) the effects of hip strengthening on biomechanical knee variables associated with PFP development.
METHODS Search strategy MEDLINE, EMBASE, CINAHL, Web of Science, Google Scholar, SportDiscus databases were searched from inception until November 2013. No data limits were used during searching. Without any modification, the search strategy from a Cochrane systematic review on exercise therapy for PFP was used for diagnostic search terms (see online supplementary appendix 1).25 The diagnostic search terms were then combined with the terms: strength, torque, force, moment, isokinetic, isometric, eccentric, concentric, power, isotonic, 1 of 12
Downloaded from http://bjsm.bmj.com/ on July 14, 2017 - Published by group.bmj.com
Review endurance, kinematics, moments and kinetics. Reference lists and citing articles of included papers were also screened. Additionally a cited reference search for each included paper was completed in Google Scholar for additional publications of interest. Unpublished work was not sought in this review. This could potentially lead to publication bias because significant results are more likely to be published.26 In addition, it would have been unfeasible to contact all institutions and authors around the world for unpublished work. No review protocol exists.
Inclusion and exclusion criteria Data from prospective studies investigating risk factors for PFP were included to answer objective 1. Cross-sectional and prospective studies evaluating hip strength were considered for inclusion to answer objective 2 if they contained data on hip strength from a comparison between (1) participants with PFP and pain-free individuals or (2) women and men with PFP. Data from prospective and randomised trials investigating the effect of hip strengthening on knee kinematics were included to help answer objective 3. Hip strength in all six movement directions was included (flexion, extension, abduction, adduction, internal rotation and external rotation). The inclusion criteria required patients to be diagnosed with PFP, anterior knee pain or chondromalacia patellae. Studies including participants with other knee conditions such as patellar tendinopathy or osteoarthritis, where individuals with PFP could not be separately analysed, were excluded. Studies using manual assessment of hip strength without a dynamometer or similar (ie, manual muscle tests) were excluded.
Review process Titles and abstracts identified in the search were downloaded into Endnote V.X4 (Thomson Reuters, Carlsbad, California, USA), cross-referenced, and duplicates deleted. All potential publications were independently assessed for inclusion by two reviewers (MSR and CRR), and full texts were obtained if necessary. Any discrepancies were resolved during a consensus meeting, and a third reviewer was available (CJB) if needed.
Quality assessment and risk of bias Included papers were assessed for methodological quality by two independent raters (MSR and CRR), with any disagreements resolved by consultation with a third party. Title, journal and author details were removed to de-identify articles prior to rating. Quality ratings were performed using the Epidemiological Appraisal Instrument (EAI)27 using similar methodology as Nix et al.28 The EAI was designed as ‘a critical appraisal system rooted in epidemiological principles’ for use in systematic reviews and meta-analysis, and developed by a team of epidemiologists, physicians and biostatisticians. The robust development consisted of an eight-step process including content and criterion validation, consultation with individuals outside the research team, two associated revised versions and establishment of the scales reliability.27 Utilising the method described by Nix et al,28 the EAI was adjusted to the intended purpose of this review and 26 of the original 43 items were used. Items relating to interventions, randomisation, follow-up period or loss to follow-up that were not applicable to three individual objectives were excluded by MSR and CJB. Identical to Nix et al,29 we used a median approach to divide included studies into higher and lower quality groups, that is, describing 50% as higher quality and 50% as lower quality based on the scores from the EAI. 2 of 12
In addition a PFP diagnosis checklist was used.30 The diagnosis checklist is a seven-item scale summarising the reporting of key inclusion and exclusion criteria for the diagnosis of PFP, with higher scores indicating a greater number of desired criteria is reported. Each scale was applied by two reviewers (MSR and CRR) with discrepancies resolved during a consensus meeting, and a third reviewer was available (CJB) if needed.
Study analysis Sample sizes, participant demographics, population sources and pain duration were extracted by MSR and checked by CRR. Sample sizes, means and SDs of all outcomes were extracted or sought from original authors to allow calculation of the standardised mean difference (SMD) as a measure of effect size. MSR extracted all outcomes from the papers into a spreadsheet. After the content of the spreadsheet was checked by CRR and CJB for data accuracy, the SMDs were calculated using a random effects model in Review Manager V.5.2 (Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration). Following the methodology used by Hume et al,30a the individual or pooled SMDs were categorised as small (≤0.59), medium (0.60–1.19) or large (≥1.20). These criteria were chosen to be more stringent than traditional criteria.31 Furthermore these criteria have been used in previous systematic reviews on PFP, which facilitates comparison.32 33 Forest plots were used to allow easy visualised comparisons between studies and outcomes. The level of statistical heterogeneity for pooled data was established using the χ2 and I2 statistics. The χ2 and I2 statistics describe heterogeneity or homogeneity of the comparisons with p0.05)—may be associated with a statistically significant or non-significant pooled result. Moderate evidence: statistically significant pooled results derived from multiple studies, including at least one HQ study, which are statistically heterogeneous ( p0.05). Limited evidence: results from multiple LQ studies which are statistically heterogeneous ( p
Review
Is hip strength a risk factor for patellofemoral pain? A systematic review and meta-analysis M S Rathleff,1,2 C R Rathleff,1 K M Crossley,3 C J Barton4,5,6,7 1
Orthopaedic Surgery Research Unit, Research and Innovation Center, Aalborg University Hospital, Aalborg, Denmark 2 Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark 3 Division of Physiotherapy, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane, Queensland, Australia 4 Complete Sports Care, Melbourne, Victoria, Australia 5 Pure Sports Medicine, London, UK 6 Centre for Sport and Exercise Medicine, Queen Mary University of London 7 Musculoskeletal Research Centre, La Trobe University, Melbourne, Australia Correspondence to Dr Michael Skovdal Rathleff, Orthopaedic Surgery Research Unit, Research and Innovation Center, Aalborg University Hospital, Soendre Skovvej 15, Aalborg 9000, Denmark; [email protected] Accepted 5 March 2014 Published Online First 31 March 2014
ABSTRACT Objective To evaluate and synthesise the literature on hip strength among patients with patellofemoral pain (PFP) to address the following: (1) differentiate between hip strength as a risk factor and associated deficit in PFP; (2) describe hip strength in men and women with PFP across different age ranges; (3) investigate the effects of hip strengthening on biomechanical knee variables associated with PFP development. Methods MEDLINE, CINAHL, Web of Science, SportDiscus and Google Scholar were searched in November 2013 for studies investigating hip strength among patients with PFP. Two reviewers independently assessed papers for inclusion and quality. Means and SDs were extracted from each included study to allow effect size calculations and comparisons of results. Results Moderate-to-strong evidence from prospective studies indicates no association between isometric hip strength and risk of developing PFP. Moderate evidence from cross-sectional studies indicates that men and women with PFP have lower isometric hip musculature strength compared to pain-free individuals. Limited evidence indicates that adolescents with PFP do not have the same strength deficits as adults with PFP. Conclusions This review highlights a possible discrepancy between prospective and cross-sectional research. Cross-sectional studies indicate that adult men and women with PFP appear to have lower hip strength compared to pain-free individuals. Contrary to this, a limited number of prospective studies indicate that there may be no association between isometric hip strength and risk of developing PFP. Therefore, reduced hip strength may be a result of PFP rather than the cause.
INTRODUCTION
To cite: Rathleff MS, Rathleff CR, Crossley KM, et al. Br J Sports Med 2014;48:1088–1088.
The incidence and prevalence of patellofemoral pain (PFP) are high in both adolescent and adult populations.1–7 Importantly, despite the implementation of conservative rehabilitation, the long-term prognosis for PFP is poor, with only one-third being pain-free, 1 year after the initial diagnosis.8–11 Identifying modifiable risk factors will facilitate targeted rehabilitation and prevention strategies for PFP, thus reducing the burden of PFP.12 The aetiology of PFP is thought to be multifactorial.13 Local factors, such as lower knee extension strength,14 delayed onset of vastus medialis relative to vastus lateralis,4 greater knee abduction impulse during running15 and knee abduction moment during drop jump landing16 have been associated with increased risk of PFP development. While all factors can contribute to PFP and are likely to be interrelated, recently much attention has been paid to the relationship between hip function and PFP.12 It is proposed that greater hip adduction and
Rathleff MS, et al. Br J Sports Med 2014;48:1088–1088. doi:10.1136/bjsports-2013-093305
internal rotation, especially during weight-bearing activities, may lead to altered knee and patellofemoral joint (PFJ) kinematics with subsequent increase in lateral PFJ stress.17 Recent prospective studies support this hypothesis, reporting increased peak hip internal rotation angle during landing in military recruits,6 and greater peak hip adduction angle in recreational female runners18 to be risk factors for PFP development. These altered movement patterns may result from impaired hip muscle function.6 18 Lower hip muscle strength has been explored in people with PFP. The most recent systematic review of hip strength included a search completed in January 2008, and focused only on women.19 This review concluded that women demonstrated lower hip abduction, external rotation and extension strength in the affected side compared to asymptomatic individuals.19 However, no prospective research was identified to allow evaluation of a causal relationship between hip muscle function and PFP.20 Since the publication of this systematic review, many studies, including those with prospective designs, have evaluated the link between hip strength and PFP, and it is timely to conduct an updated high-quality (HQ) systematic review in this field. In line with the belief that impaired hip muscle function is associated with PFP, the clinical effects of hip muscle strengthening programmes have recently been evaluated.21–24 However, in order to gain a deeper understanding of the role of hip muscle strength in PFP, an evaluation of the relationship between hip strengthening interventions and changes in knee biomechanics are required. The gaps in the literature call for the investigation of the following: (1) differentiate between hip strength as a risk factor and associated deficit in PFP; (2) association of hip strength with PFP in men and women across different age ranges and (3) the effects of hip strengthening on biomechanical knee variables associated with PFP development.
METHODS Search strategy MEDLINE, EMBASE, CINAHL, Web of Science, Google Scholar, SportDiscus databases were searched from inception until November 2013. No data limits were used during searching. Without any modification, the search strategy from a Cochrane systematic review on exercise therapy for PFP was used for diagnostic search terms (see online supplementary appendix 1).25 The diagnostic search terms were then combined with the terms: strength, torque, force, moment, isokinetic, isometric, eccentric, concentric, power, isotonic, 1 of 12
Downloaded from http://bjsm.bmj.com/ on July 14, 2017 - Published by group.bmj.com
Review endurance, kinematics, moments and kinetics. Reference lists and citing articles of included papers were also screened. Additionally a cited reference search for each included paper was completed in Google Scholar for additional publications of interest. Unpublished work was not sought in this review. This could potentially lead to publication bias because significant results are more likely to be published.26 In addition, it would have been unfeasible to contact all institutions and authors around the world for unpublished work. No review protocol exists.
Inclusion and exclusion criteria Data from prospective studies investigating risk factors for PFP were included to answer objective 1. Cross-sectional and prospective studies evaluating hip strength were considered for inclusion to answer objective 2 if they contained data on hip strength from a comparison between (1) participants with PFP and pain-free individuals or (2) women and men with PFP. Data from prospective and randomised trials investigating the effect of hip strengthening on knee kinematics were included to help answer objective 3. Hip strength in all six movement directions was included (flexion, extension, abduction, adduction, internal rotation and external rotation). The inclusion criteria required patients to be diagnosed with PFP, anterior knee pain or chondromalacia patellae. Studies including participants with other knee conditions such as patellar tendinopathy or osteoarthritis, where individuals with PFP could not be separately analysed, were excluded. Studies using manual assessment of hip strength without a dynamometer or similar (ie, manual muscle tests) were excluded.
Review process Titles and abstracts identified in the search were downloaded into Endnote V.X4 (Thomson Reuters, Carlsbad, California, USA), cross-referenced, and duplicates deleted. All potential publications were independently assessed for inclusion by two reviewers (MSR and CRR), and full texts were obtained if necessary. Any discrepancies were resolved during a consensus meeting, and a third reviewer was available (CJB) if needed.
Quality assessment and risk of bias Included papers were assessed for methodological quality by two independent raters (MSR and CRR), with any disagreements resolved by consultation with a third party. Title, journal and author details were removed to de-identify articles prior to rating. Quality ratings were performed using the Epidemiological Appraisal Instrument (EAI)27 using similar methodology as Nix et al.28 The EAI was designed as ‘a critical appraisal system rooted in epidemiological principles’ for use in systematic reviews and meta-analysis, and developed by a team of epidemiologists, physicians and biostatisticians. The robust development consisted of an eight-step process including content and criterion validation, consultation with individuals outside the research team, two associated revised versions and establishment of the scales reliability.27 Utilising the method described by Nix et al,28 the EAI was adjusted to the intended purpose of this review and 26 of the original 43 items were used. Items relating to interventions, randomisation, follow-up period or loss to follow-up that were not applicable to three individual objectives were excluded by MSR and CJB. Identical to Nix et al,29 we used a median approach to divide included studies into higher and lower quality groups, that is, describing 50% as higher quality and 50% as lower quality based on the scores from the EAI. 2 of 12
In addition a PFP diagnosis checklist was used.30 The diagnosis checklist is a seven-item scale summarising the reporting of key inclusion and exclusion criteria for the diagnosis of PFP, with higher scores indicating a greater number of desired criteria is reported. Each scale was applied by two reviewers (MSR and CRR) with discrepancies resolved during a consensus meeting, and a third reviewer was available (CJB) if needed.
Study analysis Sample sizes, participant demographics, population sources and pain duration were extracted by MSR and checked by CRR. Sample sizes, means and SDs of all outcomes were extracted or sought from original authors to allow calculation of the standardised mean difference (SMD) as a measure of effect size. MSR extracted all outcomes from the papers into a spreadsheet. After the content of the spreadsheet was checked by CRR and CJB for data accuracy, the SMDs were calculated using a random effects model in Review Manager V.5.2 (Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration). Following the methodology used by Hume et al,30a the individual or pooled SMDs were categorised as small (≤0.59), medium (0.60–1.19) or large (≥1.20). These criteria were chosen to be more stringent than traditional criteria.31 Furthermore these criteria have been used in previous systematic reviews on PFP, which facilitates comparison.32 33 Forest plots were used to allow easy visualised comparisons between studies and outcomes. The level of statistical heterogeneity for pooled data was established using the χ2 and I2 statistics. The χ2 and I2 statistics describe heterogeneity or homogeneity of the comparisons with p0.05)—may be associated with a statistically significant or non-significant pooled result. Moderate evidence: statistically significant pooled results derived from multiple studies, including at least one HQ study, which are statistically heterogeneous ( p0.05). Limited evidence: results from multiple LQ studies which are statistically heterogeneous ( p
