Convergent validity of the position-reposition and thoracolumbar dissociation tests in patients with recurrent low back pain in remission

Highlights

• •Position–reposition and thoracolumbar dissociation (TLD) are frequently used tests.
• •Persons with recurrent low back pain in remission performed both clinical tests.
• •All criteria of the position-reposition test showed sufficient convergent validity.
• •For TLD, range of motion and smoothness were valid, while muscle activation was not.
• •Both tests can be recommended for use in clinical practice.

Abstract

Background

Lumbopelvic sensorimotor control (SMC) impairments during remission from low back pain (LBP) may contribute to its recurrence. Clinical assessment of lumbopelvic SMC can support management of recurrent LBP. Such assessments should demonstrate sufficient convergent validity, as outcomes inform clinical decision-making for SMC-therapy implementation.

Objective

To evaluate the convergent validity of two SMC tests (position-reposition test and thoracolumbar dissociation test) in individuals with recurrent LBP in remission according to COSMIN guidelines.

Methods

Fifty-three participants with recurrent LBP in remission (19 female) performed the position-reposition and thoracolumbar dissociation tests. A blinded examiner scored both tests, while objective measures were collected using spinal inclinometers and surface electromyography of trunk muscles. COSMIN-based hypotheses were used to evaluate convergent validity. Relationships between clinical scores and objective measures were examined with Spearman’s rho.

Results

The position-reposition test showed sufficient convergent validity for all criteria and the total score. For the thoracolumbar dissociation test, L5 range of motion (ROM), T5/L5-ratio, L5 movement smoothness, and their combined z-score demonstrated sufficient convergent validity. In contrast, muscle activation and L1/L5-ratio showed insufficient convergent validity. Including muscle activation in the combined z-score of ROM and smoothness did not improve the convergent validity.

Conclusion

The position-reposition test can be clinically evaluated with sufficient convergent validity. The clinical assessment of thoracolumbar dissociation should prioritize pelvic and thoracic ROM and the smoothness of pelvic movement, while muscle activation should be interpreted with caution. Both tests can be used in clinical practice and may help guide clinical decision-making in managing recurrent LBP.

Introduction

Low back pain (LBP) is a global health problem with a lifetime prevalence of 60–80%.¹ Although acute LBP often resolves within weeks,² up to 69% of people experience LBP recurrence within one year following initial recovery.³ Impairments in lumbopelvic sensorimotor control (SMC) that remain present during remission are hypothesized to contribute to LBP recurrence.4, 5, 6, 7 Based on this premise, evaluation of lumbopelvic SMC in people with recurrent LBP has been recommended.

In research, lumbopelvic SMC is typically evaluated using sophisticated equipment (e.g., kinematic measurement devices),⁸ which is often unavailable in clinical settings. As an alternative, clinical tests based on inspection or palpation remain the most accessible methods to evaluate lumbopelvic SMC in clinical practice.⁹ A prerequisite of these tests is that the clinically assessed SMC parameters correspond to objectively measured SMC parameters, ensuring sufficient convergent validity.¹⁰ Our recent systematic review showed that only two clinically assessed lumbopelvic SMC tests have been examined for convergent validity in individuals with LBP and the quality of evidence was (very) low due to small sample sizes and the lack of assessor blinding.¹¹ Studies addressing these limitations are urgently needed to inform clinical practice.

The position-reposition and thoracolumbar dissociation tests are frequently used to clinically assess lumbopelvic SMC.^12,13 Despite their clinical relevance, the convergent validity of the position-reposition test has not been investigated, and the convergent validity of the thoracolumbar dissociation test has only been examined in a preliminary study involving a mixed sample of pain-free controls and individuals with chronic LBP.¹⁴ The convergent validity of trunk muscle activation was not evaluated, despite its inclusion in the thoracolumbar dissociation test. Since the preliminary study, the COnsensus-based Standards for the selection of health status Measurement INstruments (COSMIN) guidelines have been updated to provide more rigorous methodological standards for evaluating convergent validity.¹⁵ Further validation is needed using studies that meet these updated guidelines.

This study investigated the convergent validity of the position-reposition and thoracolumbar dissociation tests in individuals with recurrent LBP who were in remission. Evaluation was conducted in accordance with the COSMIN guidelines.

Methods

Design

This cross-sectional study was conducted and reported in accordance with the COSMIN guidelines^15,16 and the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement.¹⁷ Baseline data from a randomized controlled trial were used (ClinicalTrials.gov: NCT05706103).

Participants and recruitment

Participants were recruited between January 2023 and September 2024 via online advertisements, flyers, and posters in public places. Inclusion criteria were: (1) age between 18 and 55 years; (2) recurrent LBP with ≥2 episodes/year.¹⁸ An episode was defined as LBP ≥2/10 on the Numeric Rating Scale (NRS), lasting ≥24 hours, interfering with daily activities, and preceded and followed by ≥1 month with no or minimal LBP (NRS of 0-1/10)¹⁸; (3) the first LBP episode occurred ≥6 months ago; and (4) participants had ≥1 prior consultation with a healthcare provider for their LBP. All participants were evaluated during remission from their LBP. Exclusion criteria were: (1) any presentation of LBP other than recurrent LBP (i.e., acute, subacute, chronic); (2) serious underlying conditions (e.g., multiple sclerosis); and (3) previous spinal surgery. This study was approved by the Ethics Committee of the Ghent University Hospital (B670201420984). All participants provided written informed consent.

Sample size

The COSMIN guidelines recommend a sample size of ≥50 participants for studies on convergent validity.¹⁵ To compensate for possible data loss from technical issues, we aimed to include 53 participants.

Examiners

The position-reposition and thoracolumbar dissociation tests were clinically evaluated by the same examiner (M.B.), who was blinded to kinematic and electromyography (EMG) data. The examiner holds a Master of Science degree in Rehabilitation Sciences and Physiotherapy and has over five years of experience in the clinical assessment of lumbopelvic SMC. Moreover, clinical assessment of both tests was practiced during two one-hour sessions, supervised by two physiotherapists (L.D. and T.M.) with over 20 years of expertise in lumbopelvic SMC assessment.

Instruments

Spinal kinematics were measured using three gravity-referenced inclinometers (Noraxon Desktop DTS, USA) placed on the spinous processes of T5, L1 and L5 with the participant in habitual standing. Furthermore, reflective markers were placed on T1 and S1 spinous processes to measure trunk inclination during the position-reposition test. An OptiTrack Flex 3 highspeed camera (100 Hz; NaturalPoint, Inc., USA) was positioned perpendicular to the spine at a height of 75 cm to visualize the reflective markers and capture video data in the sagittal plane.

Trunk muscle activation was recorded using a wireless 16-channel surface EMG system (Noraxon Desktop DTS, USA). After skin preparation (shaving, scrubbing with Nuprep® gel [Weaver and Company, USA], and cleaning with diethyl ether [Chem-Lab NV, Belgium]), surface electrodes (Ag/AgCl, Ambu® Blue Sensor N, 30 × 22 mm, Ballerup, Denmark; 1 cm² contact; 20 mm interelectrode distance) were applied bilaterally on the external oblique (EO),19, 20, 21, 22 internal oblique/transverse abdominis (IO/TrA),21, 22, 23, 24, 25 iliocostalis lumborum pars thoracis (ILT) at L1,26, 27, 28, 29, 30 iliocostalis lumborum pars lumborum (ILL) at L4,26, 27, 28, 29, 30 and superficial fibers of lumbar multifidus (LM).^21,22,24, 25, 26, 27, 28, 29^,31,32 Data were sampled at 1500 Hz.

Procedure

The following sequence was used: (1) collection of sociodemographic information and LBP recurrence characteristics; (2) assessment of the position-reposition test; (3) assessment of the thoracolumbar dissociation test; and (4) evaluation of maximum voluntary isometric contractions.

Sociodemographic information and LBP recurrence characteristics

Sex and age were self-reported, and height and weight were measured in the laboratory by two examiners (M.B. and H.M.). The reported characteristics of LBP recurrence were time since first and last LBP episode, average duration and intensity (0–10 NRS; 0=no pain; 10=worst imaginable pain) of LBP during episodes, average duration and intensity (0–10 NRS) of pain-free periods, and number of LBP episodes in the past year.

Position-reposition test

Participants sat on a stool of standardized height (i.e., 110% of the vertical distance between the mid fibular head and the floor), with feet shoulder-width apart, arms relaxed on the thighs, and eyes looking forward. Prior to the test, instructions were given on the test's aim. The examiner positioned participants in a neutral sitting position (i.e., slight lumbar lordosis and relaxed thorax)³³ for 5 s, which they were asked to memorize (i.e., starting position).34, 35, 36 Participants then moved to maximum spinal extension with anterior pelvic tilt and a slouched position with maximum spinal flexion and posterior pelvic tilt at their preferred speed (Supplementary material 1) for three repetitions. Participants were asked to return from the slouched position to match the starting position as accurately as possible (i.e., resumed position). Kinematic data at the starting and resumed positions were stored. The test was performed once without prior familiarization.

Four criteria were assessed through visual inspection with reference to how closely they matched the target start position: (1) position of the pelvis, (2) lumbar spine curvature, (3) thoracic spine curvature, and (4) trunk inclination (Table 1). Total scores ranged from 0 (= worst score) to 10 (= best score).¹²

Table 1.

Clinical scores, objective parameters, and hypotheses concerning sufficient convergent validity for the position-reposition test.

Variable	Clinical score	Objective parameters	Hypotheses
1. Position of the pelvis
Perfect repositioning	3	AE pelvic tilt. Pelvic tilt = L5 sagittal inclination (i.e., angle (in degrees) of a vertebra relative to the vertical, recorded with a gravity-referenced inclinometer).	ρ ≤ −0.50
Small deviation	2
Large deviation	1
Impossible to reposition	0
2. Lumbar spine curvature
Perfect repositioning	3	AE lumbar angle. Lumbar angle = L1 sagittal inclination – L5 sagittal inclination.	ρ ≤ −0.50
Small deviation	2
Large deviation	1
Impossible to reposition	0
3. Thoracic spine curvature
Perfect repositioning	2	AE thoracic angle. Thoracic angle = T5 sagittal inclination – L1 sagittal inclination.	ρ ≤ −0.50
Small deviation	1
Large deviation	0
4. Inclination of the thorax
Perfect repositioning	2	AE trunk inclination. Trunk inclination = the angle between T1 and S1 reflective markers relative to the horizontal.	ρ ≤ −0.50
Small deviation	1
Large deviation	0
Total score	/10	Weighted mean:1 • AE pelvic tilt (weight: 30%) • AE lumbar angle (weight: 30%) • AE thoracic angle (weight: 20%) • AE trunk inclination (weight: 20%)	ρ ≤ −0.50

AE = absolute error (i.e., absolute values of the difference between the neutral starting position and the resumed position).

¹The weighted mean from all individual criteria was calculated for the total score. Criteria 1 and 2 were scored on a 3-point scale, each contributing 30% to the total score, and criteria 3 and 4 were scored on a 2-point scale, each contributing 20% to the total score. This weighting reflects the different maximum scores of the criteria, resulting in a total score of 10 points.

Thoracolumbar dissociation test

Participants started in the same position as the position-reposition test. A screen at eye level displayed a video showing a person performing 10 repetitions of perfect thoracolumbar dissociation (i.e., smooth anterior and posterior pelvic tilts without thoracic movement or excessive muscle activation).^13,14 Participants first observed the video without moving. Next, participants viewed the same video a second time but were instructed to imitate the person’s movements as accurately as possible.^13,14

Five criteria were assessed through visual inspection with reference to the desired performance of the task: (1) quality of pelvic motion, (2) control of adjacent regions, (3) directional preference, (4) breathing, and (5) repetition (Table 2). Total scores ranged from 0 (= worst score) to 10 (= best score).^13,14

Table 2.

Clinical scores, objective parameters, and hypotheses concerning sufficient convergent validity for the thoracolumbar dissociation test.

Variable	Clinical score	Objective parameters	Hypotheses
1. Quality of pelvic motion – direction with best quality
Moves the pelvis into anterior/posterior tilt in manner that is smooth, controlled and to the end of available ROM with gentle activation of lumbar back muscles (not forced with strong muscle activation)	3	L5 ROM Smoothness: spectral arc length Muscle activation • Anterior tilt: ILT/LM-ratio, ILL & LM • Posterior tilt: EO & IO/TrA Z-score of ROM, smoothness & muscle activation: • Anterior tilt: ILT/LM-ratio • Posterior tilt: EO & IO/TrA	ROM: ρ = 0.30 to 0.50 Smoothness: ρ = 0.30 to 0.50 Muscle activation: ρ = −0.30 to −0.50 Z-score: ρ ≥0.50
Moves the pelvis but not ideal in terms of smoothness, range or with too much muscle activation	2
Jerky, uncoordinated, limited motion of the pelvis ± excessive muscle activation	1
Inability to move the pelvis into anterior or posterior tilt	0
2. Control of adjacent regions – direction with best quality
Moves pelvis with gentle lordosis/kyphosis of the lumbar spine but limited movement at the thoracolumbar junction during pelvic rotation, minimal or no activation of the long erector spinae or superficial abdominal muscles and no pushing through the legs.	3	ROM: • T5/L5-ratio • L1/L5-ratio Muscle activation: • Anterior tilt: ILT/LM-ratio & ILT • Posterior tilt: EO & IO/TrA Z-score of ROM & muscle activation: • Anterior tilt: ILT/LM-ratio • Posterior tilt: EO & IO/TrA	ROM: ρ = −0.30 to −0.50 Muscle activation: ρ = −0.30 to −0.50 Z-score: ρ ≥0.50
Moves pelvis mild thoracolumbar extension or activation of thoracolumbar erector spinae activation	2
Moves pelvis but with excessive thoracolumbar extension and activation of thoracolumbar erector spinae, or excessive pushing through the feet	1
Moves into thoracolumbar extension/flexion with no motion of pelvis	0
3. Directional preference
Moves with high quality1 into anterior and posterior tilt	2	Z-score of L5 ROM, smoothness, T5/L5-ratio, ILT/LM-ratio (anterior tilt), EO (posterior tilt), & IO/TrA (posterior tilt)	Z-score: ρ ≥0.50
Moves with high quality1 in one direction	1
Does not move with high quality1 in either direction	0
4. Breathing
Able to maintain quiet breathing during the task	1	Not determined	Not determined
Unable to maintain quiet breathing during the task	0
5. Repetition
Able to perform 10 repetitions with high quality1	1	Z-score of L5 ROM, smoothness, T5/L5-ratio & muscle activation: • Anterior tilt: ILT/LM-ratio • Posterior tilt: EO & IO/TrA	Z-score: ρ ≥0.50
Able to perform some (between 1 and 10) repetitions with high quality1	0.5
Unable to perform any repetitions with high quality1	0
Total score	/10	Z-score of L5 ROM, smoothness, T5/L5-ratio & muscle activation: • Anterior tilt: ILT/LM-ratio • Posterior tilt: EO & IO/TrA	Z-score: ρ ≥0.50

¹High quality pelvic control - Moves into anterior/posterior tilt in a manner that is initiated with the pelvis in a smooth, controlled manner to the end of available range of motion with gentle activation of lumbar back muscles (not forced with strong muscle activation) and limited movement at the thoracolumbar junction.

EO = external oblique, ILT/LM = iliocostalis lumborum pars thoracis/lumbar multifidus, IO/TrA = internal oblique/transversus abdominis, ROM = range of motion.

Maximum voluntary isometric contraction

Maximum voluntary isometric contractions (MVIC) were performed for EMG normalization by two examiners (M.B. and H.M.) with over five years of experience in EMG data collection. For back muscles, participants lay prone with the calves strapped to the table and performed maximal trunk extension against manual resistance by M.B. at the thoracic spine and scapulae.³⁷ For abdominal muscles, participants lay supine with the trunk supported, hips at 45°, and the upper legs strapped to the table, and performed maximal trunk flexion with left and right rotation against manual resistance by M.B. at the contralateral shoulder.³⁷ For both back and abdominal muscle MVICs, three 5-second trials were performed with 30-second rest intervals. Verbal encouragement was given throughout the trials. The EMG amplitudes were normalized to the peak of three trials.³⁸

Data analysis

Position-reposition test

The absolute error was calculated as the difference in each angle (pelvic tilt, lumbar angle, thoracic angle, and trunk inclination) between the starting and resumed position (Table 1).^34,36,39

Thoracolumbar dissociation test

Only complete movements from the participant’s maximal anterior to maximal posterior pelvic tilt (or vice versa) were included, resulting in 9 anterior and 9 posterior tilts per participant.

For criterion 1 (i.e., quality of pelvic motion), criterion 2 (i.e., control of adjacent regions), and criterion 5 (i.e., repetition), clinical scores are based on the direction with the best movement quality (i.e., anterior or posterior tilt). Accordingly, the test was segmented into anterior and posterior tilts using OptiTrack video data, and objective data were analyzed in the clinically scored direction(s). If the clinical score was based on a single direction, the mean range of motion (ROM) and smoothness from 9 repetitions in that direction were used, along with either back muscle activation during anterior tilt or abdominal muscle activation during posterior tilt. In cases where participants performed equally well in anterior and posterior tilt and both directions were clinically scored, objective data from all 18 repetitions were analyzed, including back muscle activation during anterior tilt and abdominal muscle activation during posterior tilt. For criterion 3 (i.e., directional preference), the objective parameters in both directions were analyzed for all participants, regardless of the direction assigned in the clinical score. Criterion 4 (i.e., breathing) was not objectively measured. Table 2 provides an overview of the analyzed parameters.

Range of motion

For criterion 1 (i.e., quality of pelvic motion), pelvic ROM was calculated as the difference in L5 position between maximal anterior and posterior tilt. For criterion 2 (i.e., control of adjacent regions), thoracic (T5) and thoracolumbar (L1) ROM were expressed relative to pelvic (L5) ROM by dividing T5 and L1 ROM by L5 ROM, respectively.

Smoothness

For criterion 1 (i.e., quality of pelvic motion), L5 movement smoothness was quantified using spectral arc length (SPARC).^40,41 Following recommendations, SPARC was calculated as the negative arc length of the Fourier magnitude spectrum within 0–20 Hz of the speed profile, using an amplitude threshold of 0.05.^40,41 SPARC-values are negative, with values closer to 0 representing greater smoothness.⁴¹

Muscle activation

Raw EMG signals were processed using MyoResearch 3.18.126 (Noraxon U.S.A. Inc., Arizona) in the following order: electrocardiogram reduction, 25 Hz high-pass filtering, and smoothing (root mean square, 100 ms). The mean EMG amplitude for all repetitions in each direction was analyzed. The mean of the left and right %MVIC was used, as no differences between sides were detected (Supplementary material 2).

The target performance of thoracolumbar dissociation during anterior tilt was expected to involve “gentle” lumbar muscle activation with limited or no thoracic muscle activation. During active lumbar extension (lordosis) movements, greater thoracic erector spinae activation and less (deep) multifidus activation is often displayed in individuals with (recurrent) LBP.^42,43 Therefore, in addition to evaluating individual ILT, ILL, and LM activation during anterior tilt, we calculated a ILT/LM-ratio (i.e., ILT activation divided by LM activation), with lower ILT/LM-ratios expected to represent better performance. The target performance for thoracolumbar dissociation during posterior tilt was expected to involve limited or no activation of the abdominal muscles. EO and IO/TrA activation during posterior tilt was analyzed, with lower amplitudes indicating better performance.

Criteria for good measurement properties

According to COSMIN guidelines, hypotheses regarding the expected direction and magnitude of correlations between clinical scores and objective parameters were defined a priori.^44,45 The COSMIN guidelines state that convergent validity is sufficient if correlations (absolute values) are ≥0.50 for similar constructs or between 0.30 and 0.50 for related but dissimilar constructs.^44,45

For each criterion of the position-reposition test, a single parameter (i.e., repositioning accuracy) was both clinically evaluated and objectively measured. We considered these constructs as similar and hypothesized correlations ≥0.50 between clinical scores and kinematic data (Table 1).

For the thoracolumbar dissociation test, each criterion involves multiple parameters (e.g., ROM, smoothness, and muscle activation). The clinical score and each individual objective parameter (e.g., L5 ROM) were considered related but distinct constructs, and we expected correlations of 0.30–0.50 (Table 2). To obtain a single objective parameter corresponding to a clinical criterion, we calculated the mean z-score of the objective parameters relevant for that criterion. Higher z-scores correspond with better performance (i.e., greater L5 ROM, smoother movement, lower L1/L5 & T5/L5 ratios, and lower muscle activation). Because muscle activation parameters showed insufficient convergent validity for criteria 1 and 2 (see Results), additional z-scores excluding these parameters were computed. Because the clinical score and the mean z-score are based on the same parameters, correlations ≥0.50 were hypothesized (Table 2).

Statistical analysis

All statistical analyses were performed using SPSS (31.0). Given the nature of the variables, Spearman’s rho (ρ) was used to examine relationships between clinical scores (ordinal variables) and objective measures (continuous variables).^46,47 Sensitivity analyses were conducted by excluding the identified outliers. Outliers were identified as objective measures with z-scores outside the range −3 to +3 for normally distributed data, or as values >1.5 times the interquartile range below the Q1 or above Q3 for non-normally distributed data.⁴⁸ Normality was determined via inspection of Q–Q plots and histograms.

Results

Participant characteristics

Fifty-three participants were included in the study (Table 3).

Table 3.

Sociodemographic information and recurrence characteristics of the participants (n = 53).

Female sex, n (%)	19 (36)
Age (years)	40 ± 11
Weight (kg)	76.5 ± 13.1
Height (cm)	178 ± 10
BMI (kg/m²)	24.2 ± 3.3
Time since first LBP episode (years)	10 ± 10
Time since last LBP episode (days)	49 ± 38
Mean duration of a LBP episode (days)	8 ± 9
Mean pain intensity during a LBP episode (NRS, 0–10)	5.8 ± 1.2
Mean duration of pain-free periods (days)	89 ± 43
Mean pain intensity during pain-free periods (NRS, 0–10)	0.4 ± 0.5
Number of episodes in past year (frequency)	4.8 ± 2.6

Data are presented as mean ± standard deviation.

BMI, body mass index; NRS, numeric rating scale.

Convergent validity

Position-reposition test

All the individual criteria and the total score of the position-reposition test had sufficient convergent validity (ρ = −0.52 to −0.70) (Table 4, Supplementary material 3).

Table 4.

Clinical scores, objective parameters, and correlation coefficients for the position-reposition test.

Variable	Clinical score	Objective parameters	Spearman’s rho
Criterion 1: position of the pelvis	2.1 ± 0.8	AE pelvic tilt (°): 5.0 ± 3.7	ρ =−0.68
Criterion 2: lumbar spine curvature	2.0 ± 0.8	AE lumbar angle (°): 5.1 ± 3.9	ρ =−0.65
Criterion 3: thoracic spine curvature	1.2 ± 0.7	AE thoracic angle (°): 6.1 ± 4.2	ρ =−0.52
Criterion 4: trunk inclination	1.5 ± 0.5	AE trunk inclination (°): 2.5 ± 1.9	ρ =−0.62 (one outlier excluded: ρ =−0.60)
Total score	6.8 ± 2.0	Weighted AE (°): 4.6 ± 2.5	ρ =−0.70

The clinical scores and objective parameters are presented as mean ± standard deviation.

Correlation coefficients are underlined if they met the hypothesis.

AE = absolute error.

Thoracolumbar dissociation test

Thirty-seven participants were scored for anterior tilt, 13 for posterior tilt, and 3 for both directions. Consequently, correlations involving back muscle activation included 40 participants, while those involving abdominal muscle activation included 16 participants. Table 5 summarizes clinical scores, objective parameters, and correlation coefficients.

Table 5.

Clinical scores, objective parameters, and correlation coefficients for the thoracolumbar dissociation test.

Variable	Clinical score	Objective parameters	Spearman’s rho
Criterion 1: quality of pelvic motion	2.1 ± 0.8	L5 ROM (°): 15.3 ± 7.3	ρ =0.63 (one outlier excluded: ρ =0.62)
		Smoothness: −2.0 ± 0.4	ρ =0.45 (two outliers excluded: ρ =0.40)
		Muscle activation: • ILT/LM-ratio: 0.74 ± 0.6 • ILL: 6.0 ± 3.6 %MVIC • LM: 8.8 ± 5.5 %MVIC • EO: 4.0 ± 2.7 %MVIC • IO/TrA: 7.6 ± 4.1 %MVIC	ρ = 0.11 (one outlier excluded: ρ = 0.19) ρ = −0.04 (one outlier excluded: ρ =−0.09) ρ = 0.01 ρ = −0.09 ρ = 0.07
		Z-score of ROM & smoothness Z-score of ROM, smoothness & • ILT/LM-ratio • EO • IO/TrA	ρ =0.57 ρ = 0.46 ρ = 0.43 ρ = 0.36
Criterion 2: control of adjacent regions	2.2 ± 0.8	T5 ROM (°): 7.1 ± 3.6 • T5/L5-ratio: 0.56 ± 0.5 L1 ROM (°): 5.7 ± 2.6 • L1/L5-ratio: 0.49 ± 0.4	ρ =−0.62 (one outlier excluded: ρ =−0.61) ρ = −0.18 (one outlier excluded: ρ = 0.14)
		Muscle activation: • ILT/LM-ratio • ILT: 5.2 ± 3.6 %MVIC • EO • IO/TrA	ρ = −0.18 (one outlier excluded: ρ = −0.13) ρ = −0.06 (one outlier excluded: ρ = −0.05) ρ = −0.11 ρ = −0.16
		Z-score of T5/L5-ratio & • ILT/LM-ratio • EO • IO/TrA Z-score of L1/L5-ratio & • ILT/LM-ratio • EO • IO/TrA	ρ =0.50 ρ =0.73 (one outlier excluded: ρ =0.68) ρ =0.64 (one outlier excluded: ρ =0.56) ρ = 0.14 ρ = 0.37 ρ = 0.42
Criterion 3: directional preference	0.3 ± 0.6	Z-score of L5 ROM, smoothness & T5/L5-ratio Z-score of L5 ROM, smoothness, T5/L5-ratio, ILT/LM-ratio, EO, & IO/TrA	ρ = 0.44 (one outlier excluded: ρ = 0.44) ρ = 0.45
Criterion 4: breathing	0.8 ± 0.4	Not determined	Not determined
Criterion 5: repetition	0.1 ± 0.2	Z-score of L5 ROM, smoothness & T5/L5-ratio • Z-score of L5 ROM, smoothness, T5/L5-ratio & • ILT/LM-ratio • EO • IO/TrA	ρ =0.52 (one outlier excluded: ρ =0.51) ρ = 0.41 ρ =0.72 ρ =0.56 (one outlier excluded: ρ =0.56)
Total score	5.6 ± 2.1	Z-score of L5 ROM, smoothness & T5/L5-ratio Z-score of L5 ROM, smoothness, T5/L5-ratio & • ILT/LM-ratio • EO • IO/TrA	ρ =0.60 (one outlier excluded: ρ =0.58) ρ = 0.47 ρ =0.74 ρ =0.64 (one outlier excluded: ρ =0.56)

The clinical scores and objective parameters are presented as mean ± standard deviation.

Correlation coefficients are underlined if they met the hypothesis.

EO = external oblique, ILT/LM = iliocostalis lumborum pars thoracis/multifidus, IO/TrA = internal oblique/transversus abdominis, MVIC= maximum voluntary isometric contraction, ROM = range of motion.

For criterion 1 (i.e., quality of pelvic motion), L5 ROM (ρ = 0.62 to 0.63) and smoothness (ρ = 0.40 to 0.45) showed sufficient convergent validity, whereas muscle activation did not (ρ = −0.09 to 0.19). The combined z-score of L5 ROM and smoothness provided sufficient convergent validity (ρ = 0.57), whereas adding muscle activation to this z-score produced insufficient convergent validity (ρ = 0.36 to 0.46) (Supplementary material 4).

For criterion 2 (i.e., control of adjacent regions), T5/L5-ratio showed sufficient convergent validity (ρ = −0.62 to −0.61), whereas L1/L5-ratio (ρ = −0.18 to 0.14) and muscle activation (ρ = −0.18 to −0.05) did not. The combined z-score of T5/L5-ratio and muscle activation yielded sufficient convergent validity (ρ = 0.50 to 0.73), whereas the combined z-score of L1/L5-ratio and muscle activation demonstrated insufficient convergent validity (ρ = 0.14 to 0.42) (Supplementary materials 5 and 6).

For criterion 3 (i.e., directional preference), the mean z-score combining L5 ROM, smoothness, and T5/L5-ratio showed insufficient convergent validity (ρ = 0.44). Adding muscle activation to this combination resulted in similar results (ρ = 0.45) (Supplementary material 7).

For criterion 5 (i.e., repetition), the mean z-score combining L5 ROM, smoothness, and T5/L5-ratio demonstrated sufficient convergent validity (ρ = 0.51 to 0.52). Adding muscle activation to this z-score showed sufficient convergent validity for EO and IO/TrA activation (ρ = 0.56 to 0.72), but insufficient convergent validity for ILT/LM-ratio activation (ρ = 0.41) (Supplementary material 8).

For the total score, the mean z-score combining L5 ROM, smoothness, and T5/L5-ratio showed sufficient convergent validity (ρ = 0.58 to 0.60). Adding muscle activation to this z-score yielded mixed results (ρ = 0.47 to0.74) (Supplementary material 9).

Discussion

This study investigated the convergent validity of the position-reposition and thoracolumbar dissociation tests in people in remission from recurrent LBP. The position-reposition test demonstrated sufficient convergent validity for all individual criteria and the total score. For the thoracolumbar dissociation test, L5 ROM, the T5/L5-ratio, and L5 movement smoothness demonstrated overall sufficient convergent validity, whereas measures of muscle activation did not. The combined z-scores of ROM parameters and smoothness showed convergent validity ranging from nearly sufficient to sufficient (ρ = 0.44 to 0.60). Adding muscle activation to the combined z-scores did not improve the convergent validity.

Research on repositioning accuracy in individuals with recurrent LBP in remission is scarce.⁴⁹ In one study,⁵⁰ participants repositioned to a self-perceived “good” sitting posture. Although the position might be similar in range to our neutral sitting position, we provided instruction and guidance to adopt a standardized position. In the earlier study, which used an electro-goniometer spanning L1–S1, the recurrent LBP group showed a mean absolute error of 3.95 ± 2.84 degrees over 10 trials.⁵⁰ The repetition of the task might have enabled learning to improve accuracy. The present study found a mean absolute error of 5.1 ± 3.9 degrees per trial, thereby avoiding any learning-related impact.

Results of the thoracolumbar dissociation test can only be compared with those of a single preliminary study by Elgueta-Cancino et al. (2015), which included pain-free individuals and people with chronic LBP.¹⁴ While Elgueta-Cancino et al. (2015) reported a weak correlation coefficient (ρ = 0.15) for smoothness in criterion 1,¹⁴ we found sufficient convergent validity with much larger correlation coefficients (ρ = 0.40 to 0.45). Besides differences in participant populations, methodological differences in quantifying smoothness might explain this discrepancy. Elgueta-Cancino et al. (2015) used jerk-analysis (degrees/s³),¹⁴ which is influenced by movement amplitude and duration.⁴¹ Although movement duration was standardized by copying the pace of a video recording and is likely to be relatively consistent across participants, movement amplitude varied considerably between participants (Table 5), which has some impact on jerk-based calculations. The current study used SPARC analysis, a more recent method shown to be largely insensitive to movement amplitude and duration.⁴¹ This approach demonstrated that pelvic movement smoothness can be clinically evaluated with sufficient convergent validity.

Concerning criterion 2 (i.e., control of adjacent regions), sufficient convergent validity was found for T5/L5-ratio (ρ = −0.62 to −0.61), but not for L1/L5-ratio (ρ = −0.18 to 0.14). This is in line with Elgueta-Cancino et al. (2015), which showed a ρ = −0.45 for T5/S1-ratio and a ρ = −0.14 for T12/S1-ratio.¹⁴ The higher convergence for T5/S1 than T12/S1 suggests clinicians place greater emphasis on thoracic than thoracolumbar movement when judging criterion 2, as previously hypothesized.¹⁴

Data from the current study show that muscle activation had insufficient convergent validity (ρ = −0.18 to 0.19) for criteria 1 (i.e., quality of pelvic motion) and 2 (i.e., control of adjacent regions). There are several possible interpretations. First, when the score was developed, the interpretation of muscle activation was intended to be one feature that might indicate the quality of performance, and it was not intended to imply that all individuals with poor performance would exhibit excessive muscle activation. Inspection of the raw data shows that the highest activation was observed among individuals with the poorest scores, but only in a few individuals, explaining why a linear correlation was not observed. Second, the mean EMG amplitudes were generally low (≤8.6 ± 6.2 %MVIC) for all muscles (Supplementary material 2), which might make it challenging for clinicians to discriminate between performance qualities. Taken together, these findings suggest that visual inspection may have limited validity in assessing muscle overactivation during the thoracolumbar dissociation test and may only clearly discriminate excessive activation. In other cases, clinicians should therefore interpret visually assessed muscle activation with caution when scoring the thoracolumbar dissociation test.

L5 ROM for criterion 1 (ρ = 0.62 to 0.63) and T5/L5-ratio for criterion 2 (ρ = −0.62 to −0.61) exceeded our predefined hypotheses of correlations (absolute values) between 0.30–0.50 (Table 2). These results indicate that the clinical scores and objective ROM are more strongly related than initially expected. Accordingly, future studies investigating lumbopelvic SMC tests may consider revising their hypotheses to anticipate correlations ≥0.50 between clinical scores and objective ROM measures.

Strengths and limitations

A strength of the current study is its adherence to the COSMIN guidelines, reinforcing its methodological rigor.¹⁵ Small sample sizes and a lack of assessor blinding were key limitations identified in our recent systematic review on the convergent validity of clinically assessed lumbopelvic SMC tests.¹¹ Both limitations were explicitly addressed in the current study, thereby strengthening our conclusions.

Several limitations require consideration. First, pelvic ROM and smoothness were measured using an inclinometer on L5, because placement on the sacrum was hampered by the LM EMG-electrodes and S1 reflective marker. Nonetheless, sufficient convergent validity was observed for the combined z-scores of L5 ROM and smoothness. Second, participants were assessed during a period of remission from recurrent pain and may not generalize to other LBP presentations. Although other populations should be tested, larger absolute errors and variability in people with chronic LBP, as demonstrated in a systematic review,⁵¹ might be easier to detect clinically, thereby improving the convergent validity of position–reposition in chronic LBP.

Conclusions

Both tests demonstrate sufficient convergent validity among patients with recurrent low back pain in remission, a prerequisite for clinical usefulness and a preliminary support for their clinical application. However, additional measurement properties, such as responsiveness, remain to be established. For the clinical assessment of the thoracolumbar dissociation test, pelvic and thoracic ROM and pelvic movement smoothness should be prioritized over muscle activation. Although muscle activation patterns might assist, they cannot alone be used to score the thoracolumbar dissociation test.

Funding

This work was supported by the Research Foundation – Flanders (FWO) under Grant (G0B3718N) received by Lieven Danneels, Jessica Van Oosterwijck and Paul Hodges. The funding source was not involved in the design of this study and will not have any role during its execution, data collection, data analysis, interpretation of data, writing reports and decisions to submit results for publication.

Declaration of generative AI and AI-assisted technologies in the writing process

None.

Declarations of competing interest

Jessica Van Oosterwijck was funded by 2 post-doctoral research fellowships from the FWO (grant numbers: 12L5619N and 12L5616N) during the course of this study. Paul Hodges is funded by a Fellowship from the National Health and Medical Research Council of Australia (grant number: 1194937). The authors declare no conflict of interest.