Abstract
Background
The Flexion ABduction External Rotation (FABER) test is typically used as a provocation special test, but has also been used as a measurement of combined hip range of motion (ROM). It is thought that limited ROM with this measurement may be indicative of hip pathology. To date, normative data, reliability, and minimal detectable change (MDC) of such measurements have not been established.
Purpose
To determine normative FABER height, assess inter- and intra-rater reliability and MDC for FABER, and compare traditional FABER measurements to methods which account for differences in thigh length.
Study Design
Descriptive laboratory reliability study
Methods
Nineteen healthy participants without low back, hip, or knee pain in the preceding three months were recruited. Measurements were performed during two sessions (three to seven days between sessions) by three clinicians. FABER height and thigh length measurements were performed. Thigh length normalized FABER range of motion (ROM) and side-to-side FABER ROM symmetry were calculated. One tester also measured FABER with a digital inclinometer. Inter- and intra-rater reliability were calculated using interclass correlation coefficients (ICC) and mean MDC values were calculated.
Results
Mean values for FABER height and normalized FABER ROM were 12.4 ± 2.8 cm and 0.30 ± 0.07, respectively. Inter-rater reliability for FABER and normalized FABER were good (ICC 0.67-0.68) and between session intra-rater reliability were good to excellent (ICC 0.76-0.86). Mean FABER and normalized FABER ROM MDC were 3.7 cm and 0.04, respectively. Mean FABER ROM symmetry was 2.0 ± 0.9 cm with poor inter-rater reliability (ICC 0.20), poor to good intra-rater reliability (ICC 0.38-0.66), and mean MDC of 4.0 cm. FABER measured with a ruler, normalized FABER ROM, and inclinometry all resulted in excellent intra-rater reliability, with the highest ICC being demonstrated for inclinometry (ICC 0.86, 0.86, and 0.91).
Conclusions
Overall, FABER measurements were reliable, whether normalized to thigh length or not. Furthermore, use of inclinometry may increase reliability. Reliability was poor to good when assessing symmetry between limbs.
Level of evidence
Level 3
Keywords: FABER, femoroacetabular impingement, hip, range of motion, reliability
INTRODUCTION
The Flexion Abduction External Rotation (FABER) test is commonly utilized as a provocation test to detect hip, lumbar spine, or sacroiliac joint pathology.1 Several authors have reported the utility and reliability of FABER as a provocation test for the hip.2-6 They have also indicated that assessment of pain with FABER may be a useful addition to a comprehensive hip examination, particularly for anterior hip or groin pain.7 The FABER test has also been suggested to have clinical utility as an assessment of multi-directional hip range of motion (ROM),7-12 though research is lacking regarding the use of FABER for this purpose.
FABER ROM (height of the lateral femoral epicondyle) has been suggested to be indicative of capsular tightness,7 psoas muscle spasm,7 or posterior abutment of the femur in the acetabulum.13 The method utilized to quantify FABER ROM is to measure the perpendicular distance from the table to the lateral femoral epicondyle.7-12 In particular, it has been suggested that between limb asymmetry in FABER height may indicate potential femoroacetabular impingement (FAI) or hip pathology on the side of reduced range of motion.7,9-11 Specifically, a cut-off of 3-4 cm of asymmetry between limbs has been suggested as a possible indication of FAI.10,11
While clinical experts report the utility of FABER height,7-11 the only study, to date, which has reported FABER height measurements utilized a population of professional golfers.12 Normative values in a general population and normative side-to-side symmetry values remain unknown. Additionally, the reliability and minimal detectable change (MDC) of these measurements have not been established. Lastly, FABER height would be expected to vary with thigh length; therefore, it may be necessary to normalize FABER height to thigh length or to utilize a measurement without this limitation, such as the use of an inclinometer. Therefore, the purposes of this study were 1) to establish normative values, inter-and intra-rater reliability, and MDC values for FABER height, normalized FABER ROM, and FABER ROM symmetry and 2) to compare intra-rater reliability and MDC values of FABER measured via a ruler, normalized FABER ROM, and FABER measured via inclinometry.
METHODS
Participants
Nineteen participants (11 female, 8 male; age 23.5 ± 1.2; height 173.2 ± 8.6 cm; mass 69.2 ± 13.4 kg) were recruited from an academic setting. Participants were excluded if they reported hip, knee, low back, or sacroiliac pain within the preceding three months or if they had any history of hip or low back surgery. All participants signed the University IRB approved informed consent form.
Procedures
Three testers performed measurements during two separate testing sessions (three to seven days between sessions). Tester 1 (JJB) was a physical therapist with 10 years of experience and Testers 2 and 3 (MG, LB) were first year physical therapy students. The novice testers underwent approximately two hours of training with the experienced tester in order to standardize procedures and practiced these procedures on five volunteers prior to the study. Participants were all tested in the same order (Tester 1, 2, and then 3) with the right limb assessed prior to the left by each tester.
Passive FABER range of motion was measured with the participant in the supine Figure 4 position (Figure 1A). The tester stabilized the contralateral ASIS and applied overpressure to the ipsilateral medial knee in the direction of the table while measuring the perpendicular distance from the lateral femoral epicondyle to the table using a ruler (Figure 1A). Tester 1 repeated the FABER measurement using a digital inclinometer placed with the distal end at the medial epicondyle (Figure 1B). This position on the femur was selected for inclinometer placement in order to be consistent with the landmark utilized for the ruler measurement. Next, all testers measured thigh length between the greater trochanter and the lateral epicondyle of the femur.
Figure 1.
(A) (Top) FABER ruler measurement testing position. The tester stabilized the contralateral ASIS and applied overpressure to the ipsilateral medial knee in the direction of the table while measuring the perpendicular distance from the lateral femoral epicondyle to the table using a ruler. (B) (Bottom): FABER inclinometer measurement testing position with the digital inclinometer placed with the distal end at the medial epicondyle.
Data analysis and statistical methods
The primary outcomes included FABER height (cm), normalized FABER ROM, FABER ROM symmetry (cm), FABER ROM with an inclinometer (degrees), and FABER ROM symmetry with an inclinometer (degrees). Normalized FABER ROM was calculated as the FABER ruler height divided by thigh length. FABER ROM symmetry was calculated as the absolute value of right minus left FABER ruler measurements. With the exception of the symmetry measurements, outcomes were reported as the average of the values for the right and left limbs. Independent t-tests were used to compare normative values by sex. Inter- and intra-rater reliability were calculated for FABER height, normalized FABER ROM, and FABER ROM symmetry. Additionally, for Tester 1, between session intra-rater reliability was calculated for FABER measured with an inclinometer and FABER ROM symmetry measured with an inclinometer.
All reliability analyses were conducted in SPSS (version 23) using interclass correlation coefficients (ICC (2,1)). The qualitative cut-offs for ICC values suggested by Cicchetti (1994)14 were utilized (poor: ICC < 0.40, fair: ICC 0.40-0.59, good: 0.60-0.74, and excellent: ICC 0.75-1.0). Mean MDC was also calculated (standard error of the measure*1.96*√2) across all testers for all variables assessed.
RESULTS
Mean FABER height and normalized FABER ROM were 12.4 ± 2.8 cm and 0.30 ± 0.07, respectively (Table 1). Inter-rater reliability for FABER height and normalized FABER height were good (ICC 0.67-0.68) and between session intra-rater reliability were good to excellent (ICC 0.76-0.86) (Table 1). FABER height and normalized FABER mean MDC across the three testers were 3.7 cm and 0.04, respectively (Table 1). Mean inter-limb FABER height difference was 2.0 ± 0.9 cm with poor inter-rater reliability (ICC 0.20), poor to good intra-rater reliability (ICC 0.38-0.66), and a mean MDC of 4.0 cm (Table 1).
Table 1.
FABER Measurement Reliability and Minimal Detectible Change Measurements
| Mean ± Standard Deviation | Inter-rater ICC | Rater 1 Intra-rater ICC | Rater 2 Intra-rater ICC | Rater 3 Intra-rater ICC | Mean Minimal Detectable Change | |
|---|---|---|---|---|---|---|
| FABER Height | 12.4 ± 2.8 cm | 0.68 | 0.86 | 0.76 | 0.84 | 3.7 cm |
| Thigh Length Normalized FABER ROM | 0.30 ± 0.07 | 0.67 | 0.86 | 0.76 | 0.85 | 0.03-0.04 |
| FABER ROM Symmetry | 2.0 ± 0.9 cm | 0.20 | 0.66 | 0.51 | 0.38 | 4.0 cm |
| FABER with Inclinometer | 15.0 ± 7.6 ° | NA | 0.91 | NA | NA | 6.1 ° |
| FABER ROM Symmetry with Inclinometer | 3.9 ± 3.6 ° | NA | 0.49 | NA | NA | 7.9 ° |
ICC: Intraclass Correlation Coefficient
FABER: Flexion ABduction External Rotation
ROM: Range of Motion
For Tester 1, FABER with an inclinometer also demonstrated excellent intra-rater reliability (ICC 0.91). However, intra-rater reliability for FABER ROM symmetry using an inclinometer was only fair (ICC 0.49). With the inclinometer, the MDC for FABER and FABER ROM symmetry were 6.1 ° and 7.9 °, respectively (Table 1). With respect to sex, the authors found no significant differences in any FABER measurement (p=0.33-0.73) (Table 2). Due to the relatively small sample size when comparing sex differences, Hedges’ g effect sizes were calculated and were small to moderate (0.17-0.47) (Table 2).
Table 2.
Sex Differences in FABER Measurements
| Mean ± Standard Deviation | p-value | Effect Size | ||
|---|---|---|---|---|
| FABER Height | Female | 12.5 ± 3.1 cm | 0.65 | 0.23 |
| Male | 12.2 ± 2.6 cm | |||
| Thigh Length Normalized FABER ROM | Female | 0.12 ± 0.03 | 0.64 | 0.26 |
| Male | 0.12 ± 0.03 | |||
| FABER ROM Symmetry | Female | 1.9 ± 0.9 cm | 0.39 | 0.41 |
| Male | 2.2 ± 0.9 cm | |||
| FABER with Inclinometer | Female | 15.4 ± 8.6 ° | 0.73 | 0.17 |
| Male | 14.5 ± 7.0 ° | |||
| FABER ROM Symmetry with Inclinometer | Female | 4.5 ± 4.5 ° | 0.33 | 0.47 |
| Male | 2.9 ± 1.5 ° |
FABER: Flexion ABduction External Rotation
DISCUSSION
Expert clinicians have promoted the incorporation of FABER height measurements in a comprehensive hip examination7,9-11 and FABER range of motion impairments may exist in persons with FAI.15 However, to date, normative values for FABER height have not been reported in the general population. A single study12 of professional golfers found mean FABER height values in the lead and non-lead hip to be 9.3 ± 1.5 cm and 6.8 ± 1.2 cm, respectively. Participants in the current study demonstrated slightly larger mean FABER heights (12.4 ± 2.8 cm). These differences may be due to the different populations assessed (male professional golfers verses collegiate age males and females) or possible differences in measurement technique, as the authors of the previous study did not specify stabilization procedures or use of overpressure. In the current study, FABER height was not significantly different between males and females (p=0.65) and this effect size was small (0.23), indicating minimal differences.
This was the first study to assess reliability of FABER height and to consider FABER ROM normalized to thigh length. The findings of the current study indicate that among both experienced and novice testers, FABER height and normalized FABER ROM values have excellent intra-rater reliability and good inter-rater reliability. Furthermore, mean MDC values for FABER height and normalized FABER ROM of 3.7 cm and 0.04 indicate the smallest changes that can be detected beyond measurement error. Reliability and MDC values were assessed in both experienced and novice practitioners, which may have deflated interrater reliability values compared to inclusion of only experienced clinicians, but likely increased the external validity of the findings.
FABER range of motion was also quantified by Tester 1 using a digital inclinometer. FABER measured with a ruler, normalized FABER ROM, and FABER measured with a digital inclinometer all resulted in excellent intra-rater reliability (ICC 0.86, 0.86, and 0.91, respectively), with the best reliability for inclinometry. MDC scores indicate that a 6.1 ° change in FABER measured with an inclinometer is necessary to detect change beyond measure error. Clinicians may consider use of an inclinometer to quickly and reliably measure FABER. Because the FABER ruler measurement is in reference to the femur, the inclinometer was placed on the femur in the current study; however, the tibia has less soft tissue and future research should evaluate placement along the medial tibia. Additionally, it should be noted that inter-rater reliability and intra-rater reliability for novice examiners using a digital inclinometer were not assessed in the current study.
Regardless of method of assessment (measured with a ruler or inclinometer), FABER ROM symmetry demonstrated poor to good reliabilities. Reliability may have been lower for symmetry due to the use of multiple measurements (both left and right limb), which may have increased the opportunity for errors. For FABER ROM symmetry, the normative difference was 2.0 ± 0.9 cm and the mean MDC was 4.0 cm, indicating that a large relative change would be necessary to detect any differences beyond measurement error. A 3-4 cm between limb asymmetry has been suggested as a possible indication of FAI.10,11 It should be noted that the ICC and MDC values may be different in a population with hip pathology where greater asymmetry between the involved and uninvolved limbs may occur. Therefore, while these findings indicate that caution should be utilized when interpreting differences in FABER ROM symmetry, future research should investigate FABER values and reliability in a population with hip pathology.
CONCLUSIONS
Overall, FABER height measurements could be obtained with good reliability, whether normalized to thigh length or not. Furthermore, results indicate that use of an inclinometer may increase reliability when performed by an experienced clinician. However, caution should be utilized when assessing inter-limb differences in FABER. More research is necessary to determine if FABER asymmetry is a valid assessment of potential hip pathology, as has been suggested clinically.
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