Background Femoroacetabular impingement (FAI) and associated pathologies are associated with pain and reduced quality of life. Physical impairments can be associated with worse symptoms and may be an important target of rehabilitation programmes in this patient group. Knowledge regarding physical impairments in people with symptomatic FAI is limited.
Hypothesis In adults aged 18–50 years with symptomatic FAI: (1) to identify physical impairments in range of motion (ROM), hip muscle function and functional tasks; (2) to compare physical impairments with healthy controls; and (3) to evaluate the effects of interventions targeting physical impairments.
Study design Systematic review.
Methods A systematic review of the literature was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The modified Downs and Black checklist was used for quality appraisal. Studies of adults aged 18–50 years with symptomatic FAI that examined ROM, hip muscle function and functional tasks were included. Standardised mean differences were calculated where possible or best evidence synthesis and study conclusions were presented.
Results Twenty-two studies fulfilled all inclusion criteria. Methodological quality was varied. Results for hip joint ROM differences between people with symptomatic FAI compared and control subjects were varied. People with symptomatic FAI demonstrated some deficits in hip muscle strength and reduced balance on one leg when compared with control subjects. For hip joint ROM and hip muscle strength results for within-group differences between preintervention and postintervention time points were limited and inconclusive. No randomised controlled trials evaluated the effect of different types of interventions for symptomatic patients with symptomatic FAI.
Conclusions People with symptomatic FAI demonstrate impairments in some hip muscle strength and single leg balance. This information may assist therapists in providing targeted rehabilitation programmes for people with FAI and associated pathology. Further research is needed to determine whether symptomatic FAI affects other aspects of functional performance; and to evaluate whether targeted interventions are effective in symptomatic FAI.
Clinical relevance This information may assist therapists in providing targeted rehabilitation programmes for people with symptomatic FAI.
- femoro-acetabular impingement
- muscle strength
- physical impairment
- range of motion
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What is already known
Femoroacetabular impingement (FAI) is associated with pain and reduced quality of life. Physical impairments can be associated with worse symptoms and may be an important target of rehabilitation programmes in this patient group. Knowledge regarding physical impairments in people with symptomatic FAI is limited.
What are the new findings
People with symptomatic FAI demonstrate impairments in some hip muscle strength and single leg balance. This information may assist therapists in providing targeted rehabilitation programmes for people with symptomatic FAI.
Femoroacetabular impingement (FAI) is a recognised cause of hip pain in young and middle-aged adults, and is associated with an increased risk of end-stage radiographic hip osteoarthritis (OA) and total hip arthroplasty.1 FAI is a clinical condition, where affected patients may present with a morphological variant in hip shape on radiographs, with or without associated labral and/or chondral pathology,2 resulting in increased hip/groin pain3 and reduced activity and quality of life.1 4 FAI and associated pathologies are characterised by abutment of the femoral neck against the acetabular rim. Impingement occurs via the jamming of a non-spherical extension of the femoral head into the acetabular cavity5 causing damage to the anterosuperior acetabular cartilage and potentially leading to OA changes in the hip.1 6 FAI and associated pathologies may be considered to represent early-stage hip degenerative joint disease in the disease continuum.4 7 These pathologies will be referred to collectively as ‘symptomatic FAI’ in this systematic review.
Symptomatic FAI can have a significant impact on pain, function and quality of life outcomes in young and middle-aged people4 8 that may ultimately reduce their capacity to lead active and productive lives. Identifying potentially modifiable impairments in patients with symptomatic FAI is important. If they can be identified when hip degenerative disease is in its early stages, it may be possible to design rehabilitation interventions to slow the symptomatic progression of symptomatic FAI. Arthroscopic surgery of the hip to reshape impingement lesions and salvage acetabular labarum and chondral surfaces is the most common treatment at present.9 Postsurgical rehabilitation programmes have been described in detail.10 11 High-quality evidence to support the effect of either surgical, non-surgical or postsurgical interventions for patients with symptomatic FAI is currently lacking. At present the impairments and disabilities of patients with symptomatic FAI are poorly understood.12 A greater understanding may lead to the development of effective interventions (both non-operative and postoperative) that can reduce pain, improve activity and enhance quality of life in affected individuals.
The physical impairments and activity limitations of people with all forms of FAI (cam, pincer and mixed) have been previously systematically reviewed,12 however that study combined clinical and laboratory-based biomechanical data and did not provide standardised effect size measures to facilitate comparisons between studies. Moreover, a large number of studies have been published since the search date of the previous review (June 2013). The goal of this review was to examine physical impairments that can be measured in the clinical setting and encompass much of the rapidly expanding knowledge and available literature in the area of physical impairments in people with symptomatic FAI.
The aim of this review was to systematically appraise the literature: (1) to identify physical impairments in adults aged 18–50 years with symptomatic FAI; (2) to compare physical impairments in people with symptomatic FAI with healthy controls; and (3) to evaluate the effects of interventions targeting physical impairments in patients with symptomatic FAI.
The systematic review protocol was developed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement.13 Literature search criteria and methods were proposed and agreed on by two authors and were established a priori to minimise selection bias.
A comprehensive, reproducible search strategy was performed on the following databases for dates of publication between 1 January 1990 and 22 August 2015: Scopus, Medline, CINAHL, PubMed, Ausport, SportDiscus, PEDro, PsycINFO and Google Scholar. January 1990 was selected as the earliest retrieval record due to the paucity of literature on FAI prior to this date.9 Reference lists of appropriate studies were manually searched for relevant papers. The search strategy used the PICO format, and included:
P=human adults with symptomatic FAI, diagnosed by MRI or at arthroscopy (‘femoracetabular impingement’, ‘labr*’, ‘chondr*’, ‘pathology’, ‘osteoarthritis’, ‘arthritis’, ‘pain’, ‘hip joint’)
I=surgical and non-surgical interventions (‘arthroscop*’, ‘physiotherapy’, ‘physical therapy’, ‘exercise’, ‘therapy’)
C=people without FAI, labral or chondral pathology (‘control’, ‘healthy’, ‘asymptomatic’)
O=physical impairments of the hip. This may include hip joint ROM, hip muscle strength, measures of functional performance, EMG, gait analysis (‘hip’, ‘muscle strength’, ‘range of motion’, ‘range of movement’, ‘range’, ‘movement’, ‘EMG’, ‘impairment’, ‘musculoskeletal’, ‘proprioception’, ‘balance’, ‘motor control’, ‘gait’, ‘kinematic’. ‘stiffness’, ‘weakness’, ‘function*’, ‘performance’).
The strategy was modified for each database. Titles and abstracts were screened for relevant studies by two independent reviewers (JLK, IS). Any disagreements regarding inclusion were resolved by an independent arbitrator (KMC). All potential references were imported into Endnote X6 (Thomson Reuters, Carlsbad, California, USA) and duplicates were removed. Full-text versions of identified papers were then retrieved for final eligibility screening by a single reviewer (JLK).
Studies were eligible for inclusion if they were reported in English; report level IV evidence or above; contained human subjects with symptomatic FAI assessed using preoperative diagnostic imaging techniques or hip arthroscopy; had at least five participants; and examined physical impairments of the hip or functional performance. Symptomatic FAI was defined as the presence of an impingement variant at the head-neck junction, and/or associated impingement-type pathologies (such as chondral or labral pathology). Physical impairments included hip joint range of motion (ROM), hip muscle function (including strength test and measures of muscular activity collected as electromyography (EMG), motor control; balance or proprioception) and functional task performance (including squatting, walking and other activities of daily living). Studies specifically examining kinematics or joint torques were excluded. All quantitative study designs were considered, including randomised controlled trials (RCT), prospective or retrospective approaches.14 Studies were excluded if they were case series with less than five participants, published abstracts, non-peer reviewed or in a language other than English.
The Downs and Black checklist was used to appraise the methodological quality of included studies.15 This has adequate reliability and validity for assessing non-randomised studies. The original 27 items were modified to 17 items following the exclusion of criteria 4, 13, 14, 15, 17, 19, 22, 23, 24 and 27. There were no RCTs found, therefore only criteria that were applicable for non-randomised studies were evaluated. Included studies were rated by two independent reviewers (IS, MF). A third reviewer audited the ratings of a random selection of included studies (JLK). Any disagreements between reviewers were discussed and consensus determined by an independent arbitrator (JLK). Studies were considered high quality with a score of more than 60% (10 points or more out of 17).16
Statistical analyses and data management
All statistical analyses were performed by a single author (JLK) using SPSS V.21.0 software (SPSS). The 'meta' package (version 4.9-5), from the R statistical software package (version 3.5.1) was used to calculate effect sizes (wth 95% CI) and present forest plots (https://www.r-project.org/). Eligible papers were grouped where possible based on (1) type of physical impairment or functional performance task reported; and (2) whether a between-group comparison (symptomatic FAI vs healthy controls) or within-group comparison (preintervention to postintervention) was undertaken. Inter-rater agreement on the included Downs and Black criteria was evaluated using the kappa (κ) statistic, where 0.01–0.20 represents slight agreement; 0.21–0.40 represents fair agreement; 0.41–0.60 represents moderate agreement; 0.61–0.80 represents substantial agreement; and 0.81–1.0 represents almost perfect agreement.14 17
Data from included studies were extracted by two reviewers (JLK, IS). Authors of included studies were contacted for additional data where reported data were inadequate for standardised mean difference (SMD) calculation. Findings were summarised in tables. Population characteristics (age, gender, type and description of hip OA, duration of symptoms), and details of level of evidence, outcome measures, length of follow-up and any intervention undertaken were collated. SMDs were calculated to determine the magnitude of differences in impairments between groups; and was calculated as the mean difference between groups (between-group), divided by the patient group SD. Standardised paired differences (SPD) were calculated to determine the magnitude of the effect between time points in the patient group (within-group); divided by the preintervention SD. SMD or SPD magnitude was interpreted as: ≥0.8 large effect; 0.5–0.79 moderate effect; and 0.2–0.49 weak effect. Where SMDs or SPDs could not be calculated, study conclusions were presented. Meta-analysis was undertaken where study homogeneity and available data allowed. A best-evidence synthesis18 was conducted where pooling of data was not possible for each of hip joint ROM, hip muscle function and functional task performance. In the best-evidence syntheses, where a study may have examined an impairment in the same patients using two different methods, we only counted that study once, to ensure double counting did not occur. If one study used two different measurement techniques, and the results from the study were conflicting, we removed this study from the best-evidence synthesis. Evidence was categorised as ‘strong’ if there were multiple high-quality cohort studies; ‘moderate’ if there was either one high-quality cohort study and more than two high-quality case–control studies, or more than three high-quality case–control studies; ‘limited’ if there were either one or two case–control studies, or multiple cross-sectional studies; and ‘insufficient’ if there was not more than one cross-sectional study. Evidence was summarised as ‘conflicting’ if findings were consistent in <75% of the studies, taking into account the participants, interventions, controls, outcomes and methodological quality of the original studies. These classifications were based on the recommendations of van Tulder et al. 18
Results of the search strategy are contained in figure 1. One hundred and eighteen full texts were screened, however 96 papers did not meet inclusion criteria, leaving 22 papers in the final analyses.
Initial agreement between the two raters was substantial (κ=0.626). Agreement was reached on 328 items out of 381 items in total (81%) (online supplementary appendix 1). Consensus was obtained on the quality rating for the remaining 77 items. The methodological quality scores ranged from 14 points out of 17 (82%)19 20 to 8 points out of 17 (47%).3 21–23 The overall mean (SD) rating was 10.69 (1.89) points out of 17 (63%).
The 22 included studies contained 819 patients with FAI in total, with sample sizes ranging from 7 21 to 112 patients.20 Sixteen studies included age-matched healthy control groups (12 non-surgery, 1 presurgery, 3 postsurgery) and five within-group studies investigated the change in outcome before and after intervention. One study contained men only.21 The remaining 21 studies contained both men and women. The mean (SD) ages for patients in the included studies ranged from 245 21 to 3712 24 years. All studies included participants based on a diagnosis of FAI and associated labral and/or chondral pathology. The method of diagnoses ranged from arthroscopic findings19 20 24 25 to positive clinical signs on physical examination,21 23 26–30 to radiographic, CT or MRI diagnosis.3 21–23 26–29 31–35
Physical impairment outcomes reported included hip joint ROM,3 19 20 22 24 30 31 33 34 36–39 hip muscle function,19 23 26–28 30 simulated hip joint ROM using three-dimensional CT or three-dimensional kinematics,21 25 29 31 35 40 hip muscle volume,28 hip muscle EMG,26 27 and functional performance tasks such as single leg balance,24 squat depth and pelvic ROM,41 and number of strides per day.32 The reliability of physical impairment outcomes measured was reported in 7 out of the 23 studies. Reported intracorrelation coefficients ranged from 0.7224 to 1.0.28
Due to study heterogeneity, it was not possible to conduct meta-analyses, and therefore a best-evidence synthesis was conducted. The results for hip joint ROM, hip muscle function and functional task performance are outlined below. Data were obtained on request for two papers.19 38 There were no RCTs or non-randomised trials found examining the effect of different types of interventions for patients with FAI on physical impairments. All papers included were case–control or case series studies only, and SMDs and SPDs have been reported for these studies where able.
Hip joint ROM
Between-group comparison of hip ROM in symptomatic FAI to pain-free controls
Twelve studies examined hip joint ROM in people with FAI using goniometers,3 19 20 22 24 30 31 33 34 36–38 while simulated hip joint ROM was reported in five studies (table 1).21 25 29 31 35 Between-group SMD data for case–control studies examining hip muscle ROM are contained in figure 2. SMDs were able to be calculated for eight case–control studies.3 19 22 25 29–31 33 34 Compared with healthy controls there is limited evidence that those with FAI syndrome have reduced hip abduction and flexion ROM, no differences in hip adduction or extension ROM and conflicting results for external rotation (ER) and internal rotation (IR) ROM. In studies where SMDs were not able to be calculated, results were also conflicting. Ross et al reported no difference in ROM, except flexion (p=0.03) between hockey goalies with greater alpha angles and femoral retroversion, compared with positional players.37 In contrast, Philippon et al compared the painful with the non-painful leg in people with symptomatic FAI prior to hip arthroscopy, and reported reduced ROM in all planes of movement (p=0.001 to p<0.001).20
Within-group comparison of effect of intervention on hip ROM
Within-group SPD data for studies examining hip joint ROM are contained in figure 3 and table 2. Evidence for within-group change from preintervention to post-treatment time points remains limited and inconclusive. Three studies examined within-group change over time, and results were mixed in each, and therefore remain inconclusive. One high-quality case series,31 one moderate-quality case series29 and one low-quality case series22 all demonstrated conflicting SPDs comparing prephysiotherapy to postphysiotherapy treatment for FAI.
Hip muscle function
Hip muscle function (including strength, electrical activity and muscle volume) was examined in six studies.19 23 26–28 30 Results are contained in tables 2 and 3. Between-group SMD for hip muscle function contained in table 2 and figure 4 and within-group SPDs contained in table 3 and figure 5. Hip muscle strength was measured and reported in all six studies,19 23 26–28 30 in addition hip muscle cross-sectional area was examined in one study28 and two studies reported on hip muscle EMG activity.26 27 SMDs for hip muscle strength were able to be calculated for all six studies.19 23 26–28 30 Results were mixed, with moderate conflicting evidence for greater strength in hip adduction and ER; limited evidence for greater hip flexion strength; and limited conflicting evidence for greater hip extension and abduction strength favouring controls, compared with FAI syndrome participants (table 3). In addition, strength deficits are apparent in women with FAI in all hip muscle compared controls, whereas deficits in men appear only in flexion and adduction strength. For muscle size, results were mixed, where tensor fascia lata (TFL), sartorius and psoas were significantly smaller in the injured leg of the person with FAI compared with healthy controls.28 Hip muscle EMG amplitude was reported in two studies, and SMDs were able to be calculated for both studies.26 27 There were significant between-group effects for rectus femoris and TFL EMG activity when comparing people with FAI to controls during a resisted hip flexion exercise task in standing.27 For within-group effects, one study compared hip muscle strength before hip arthroscopy with 2.5 years after hip arthroscopy.23 Calculation of SPDs revealed no significant within-group change from the preoperative to the postoperative time point for hip muscle strength measures except hip IR.
Best-evidence synthesis for hip muscle strength indicated evidence of limited quality, with one high-quality case–control study19 and no RCTs. The remaining studies were moderate or low in quality.
Functional tasks (squat depth, pelvic ROM, single leg balance, number of strides)
A number of different clinical measures of functional tasks were reported. SMD data for case–control studies examining hip functional tasks are contained in table 3 and figure 6. These included squat depth, pelvic ROM, single leg balance and number of strides.24 26–28 32 41 There were no significant differences for squat depth41 pelvic ROM,41 or total number of daily strides32 between people with FAI and controls. In addition, when people after hip arthroscopy undertook a dynamic single leg squat task, significant moderate between-group effects were noted compared with controls, where patients with FAI demonstrated increased medial-lateral sway (effect size (ES) −0.57, 95% CI −0.76 to −0.38) and worse anterior-posterior control (−0.45, 95% CI −0.57 to −0.34),24 both indicators of reduced dynamic balance.24
Best-evidence synthesis for functional tasks provided varying evidence depending on the challenges of the activity. One high-quality case–control study24 reported significant between-group SMDs for a dynamic balance task, while the remaining study was of moderate quality and reported no differences in number of strides.32
This systematic review included 22 studies (16 case–control studies—level III evidence, 1 cross-sectional comparison—level IV evidence, 5 case series—level IV evidence) to establish whether people with symptomatic FAI demonstrated physical impairments and/or functional limitations compared with people without symptomatic FAI. No RCTs were found. Four of the studies evaluated the ‘within group’ effects of surgical and conservative intervention on ROM (three studies) and muscle strength (one study). This review found limited evidence that people with symptomatic FAI have significant differences in hip muscle function in both ‘between group’ (favouring the control group) and ‘within group’ (favouring postintervention) studies. There was limited, conflicting evidence to suggest ROM and functional deficits exist when compared with individuals without symptomatic FAI or for postintervention using ‘within group’ comparisons.
Reduced hip ROM into flexion, IR and adduction3 20 29 31 33 42–46 is commonly reported in FAI research. In the current review, these restrictions were only significant for abduction and flexion. The five between-group studies with sufficient data for SMD calculations3 19 25 29–31 33 34 were limited in quality, and demonstrated mixed findings for measures of hip ROM. This suggests that while cam abnormalities may be associated with increased bony impingement/abutment and soft tissue damage,47 it is unclear whether symptomatic FAI is associated with lower hip ROM. It is possible that computer simulations or X-ray studies that rely on direct bone contact to predict impingement may be unrealistic.48 It might also reflect that some studies evaluated participants after surgery, which may have influenced the results. Surgical interventions had no significant effect on hip ROM. Evaluation of ‘within group’ studies describing surgical intervention to remove the cam abnormality29 31 indicated no significant changes to ROM. Surgery to restore hip ROM should be questioned in light of these findings. Thus, while further high-quality studies are clearly needed, the best available evidence for impairments in ROM in people with symptomatic FAI is limited in quality, and may not be the most appropriate primary target for treatment regimes.
Hip muscle function was somewhat impaired in those with FAI, although the evidence was limited by the small number and overall low quality of included studies. The six studies where SMD could be calculated19 26–28 30 49 indicated mixed results, with limited evidence for hip flexion strength, and moderate and conflicting evidence for adduction and ER strength favouring the control group. While the overall results were mixed, in a single high-quality case–control study, women were impaired in all hip muscle strength measures, whereas men were only impaired in flexion and adduction strength.19 This suggests that future research should consider examining hip muscle function for men and women separately. One study showed significant difference in hip flexor EMG activity in people with FAI compared with controls.27 However, the EMG amplitude in this study was not normalised to a submaximal or maximal contraction reference value and the validity of comparing raw EMG signals between groups is not considered valid because it can be affected by factors such as adiposity, position of electrodes and skin impedance.50 The impingement pain induced by symptomatic FAI3 43 may play a role in inhibiting muscle contraction around the hip. Studies have shown experimentally induced knee joint pain reduces flexion and extension muscle strength by 5%–15% compared with the control conditions51 and patients suffering with knee OA reported 20%–40% less quadriceps strength than healthy controls.52 For sufferers of knee OA, resistance training may increase strength by 5%–71%52 and has been shown to be beneficial for sufferers of hip OA.53 The strength deficits noted in this study suggest that programmes to improve strength may provide a positive rehabilitation intervention for both presurgical and postsurgical symptomatic FAI sufferers. There are no studies comparing temporal EMG measures such as muscle contraction onset, offset and duration. Further studies are required to investigate strength and muscle activity in people with symptomatic FAI across all movement directions and should include asymptomatic control groups that have been imaged to ensure absence of cam abnormalities. These studies may include measuring preoperative muscle strength and progress to follow muscle strength changes through postoperative rehabilitation programmes.
Functional task performance was not impaired in people with symptomatic FAI. While there was no difference in static balance on one leg with eyes closed between people after hip arthroscopy compared with controls, the same patients demonstrated reduced balance via increased medial-lateral sway and worse anterior-posterior control during a dynamic single leg squat task.24 The control groups used were only age, sex and physical activity matched for one study.24 One study had low numbers of controls significantly older than the symptomatic group and defined only by age,32 the remaining study matched only by age and body mass.41 A lack of consistency in the control groups makes it difficult to have confidence in the validity of between-group differences reported. These findings are similar to those in a recent study by Charlton et al that reported patients’ posthip arthroscopy having increased frontal plane hip adduction and knee valgus compared with controls.54 The authors suggested that this may perpetuate impingement load in the hip during single leg functional tasks and called for targeted rehabilitation programmes to improve lower limb control during these tasks.54 Biomechanically, some studies suggest that symptomatic FAI affects walking by reducing speed55 and limiting ROM in the sagittal and frontal planes55–57 as well as reducing peak hip extension, abduction,56 57 adduction and IR during the stance phase of gait.55 These findings contradict the conclusions of this review where evidence for ROM differences between individuals with symptomatic FAI and normal controls was limited and mixed. It should also be noted that normal gait does not require hip joint motion to end of range so non-significant ROM reductions should not affect gait by restricting movement. More studies are required in functional limitations in individuals with symptomatic FAI.
This review enhances the body of literature examining the physical impairments and functional limitations within sufferers of symptomatic FAI. When reviewing the physical impairments and activity limitations in people with FAI impingement, Diamond et al 12 reported decreased ROM into directions of hip joint impingement, altered sagittal and frontal plane hip ROM during gait, altered sagittal plane hip ROM during stair climbing and decreased hip adductor and flexor muscle strength. The conclusions of this paper differed. While 9 out of the 14 papers cited by the Diamond study were included in this review, five were excluded as not having clinically useable measures of strength and ROM. The current review included evidence gained from an additional 13 papers; these data resulted in a different conclusion regarding the effect of symptomatic FAI on ROM and function. The utilisation of effect size measures has allowed an unbiased appraisal of existing literature to clarify physical examination findings that can be expected during the objective assessment of individuals presenting with symptomatic FAI. However, we acknowledge the limitations of utilisation of effect sizes only based on case–control studies, not based on RCTs (as there are no RCTs within this topic). These important findings can be used to develop rehabilitation programmes for both conservative management and postsurgical rehabilitation. Emara et al 22 suggest modifications to those activities of daily living that may be exacerbated by FAI and maintaining function within ‘safe range of movement’ as a means of improving function and reducing symptoms. Other modifiable impairments such as greater hip flexion range and adduction strength have been associated with higher quality-of-life patient-reported outcome scores in patients with chondrolabral pathology 12–24 months after hip arthroscopy.8 Programmes targeted at improving these specific impairments as well as other strength and functional movement patterns around the hip may help improve functional outcomes for those with symptomatic FAI.
This review was able to use 22 articles in an area of rapidly expanding research, some with conflicting observations. Studies were eligible for inclusion if they contained human participants with symptomatic FAI assessed using preoperative diagnostic imaging techniques or hip arthroscopy; had at least five participants; and examined physical impairments of the hip. In an effort to make this paper clinically relevant, only papers including measures of ROM and strength were reviewed. Despite meeting these criteria, some of the inclusions may have suffered from relatively small sample sizes and poorly described methodology. As 15%–29% of the population58–61 have asymptomatic cam-type abnormalities, their potential inclusion within the control group may have affected results. When examining the evidence for the effect of symptomatic FAI, all papers containing ‘impingement related pathology’ were included. Restricting searches to the English language may have potentially omitted studies that could have been included in this review and the findings should be interpreted in light of these limitations. It is recommended that future populations studied need more specific diagnostic labelling to be able to examine the differences between specific patient groups. There is an urgent need for RCT designs to address questions related to differences between groups for different types of interventions. Future research should also examine the relationship between symptoms and impairments in symptomatic FAI.
The strengths of this review include using a thorough search strategy, comprehensive evaluation of multiple databases and usage of the Downs and Black checklist to appraise the methodological quality of included studies.15 This has adequate reliability and validity for assessing non-randomised studies. This review also included the calculation of SMDs, ensuring an unbiased evaluation of effect sizes, taking into account sample sizes and variability of data within individual studies. Areas for future research should aim at providing a better understanding of the ROM, strength and functional limitations encountered by sufferers of symptomatic FAI. These studies should include age, weight, sex and activity matching of controls and participants as well as radiographic screening to prevent the inclusion of asymptomatic cam abnormalities among the controls which may potentially compromise the normal data.
In conclusion, people with symptomatic FAI demonstrate some deficits in hip muscle strength when compared with a control population, as well as reduced dynamic balance on one leg. However, no RCTs have evaluated the effect of different types of interventions for symptomatic patients with symptomatic FAI. Furthermore, the evidence for hip joint ROM deficits in people with symptomatic FAI to control subjects was mixed. In the papers assessed, there was no other compromise of function in squatting, total daily strides or static balance. Further research is needed to determine whether symptomatic FAI affects other aspects of functional performance; and to evaluate whether targeted strength training or skill acquisition interventions can improve hip muscle strength and physical function in symptomatic FAI.
Correction notice This article has been corrected since it published Online First and in print.
Due to a formula error, the authors have re-run the correct confidence intervals with the following changes noted: all figures redrawn; all tables amended; reflection of corrections shown in the text.
Contributors All nominated authors fulfilled the BJSM criteria as follows: made substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; and assisted in drafting the work or revising it critically for important intellectual content; gave final approval of the version to be published; and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. Kate Croft (Queensland and School of Health and Rehabilitation Sciences, University of Queensland, Australia) assisted in reviewing the quality of papers included in this manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.