Reliability and Concurrent Validity of Dynamic Rotator Stability Test–A Cross Sectional study

Abstract

Purpose of the study

To find intra rater and inter rater reliability of Dynamic Rotator Stability Test (DRST) and to find concurrent validity of Dynamic Rotator Stability Test (DRST) with University of Pennsylvania Shoulder Score (PENN) Scale.

Material and method

40 subjects of either gender between the age group of 18–70 with painful shoulder conditions of musculoskeletal origin was selected through convenient sampling. Tester 1 and tester 2 administered DRST and PENN scale randomly. In a subgroup of 20 subjects DRST was administered by both the testers to find the inter rater reliability. 180° Standard Universal Goniometer was used to take measurements.

Results

For intra-rater reliability, all the test variables were showing highly significant correlation (p=.94 – 1). For inter -rater, with tester 2, test variables like position, ROM, force, direction of abnormal translation, pain during the test, compensatory movement during test were found to be significant (p=.71–1).only some variables of DRST showed significant correlation with PENN scale (P=.320–.450)

Conclusion

Dynamic Rotator Stability Test has good intra rater and moderate inter rater reliability. Concurrent validity of Dynamic Rotator Stability Test was found to be poor when compared to PENN Shoulder Score.

Introduction

Shoulder pain is estimated to be the third most common cause of musculoskeletal consultation in primary care.¹ The incidence of shoulder pain is quite high.²

Shoulder pain often impairs the ability to sleep, and restricted and/or painful range of motion of the shoulder influences performance of activities of daily living.³ Four basic mechanical abnormalities causing pain at the shoulder are stiffness, instability, weakness, and roughness. Instability is a functional complaint. Asymmetry, reproduction of symptoms, and apprehension are possible signs of instability.⁴

The shoulder joint instability occurs due to an imbalance in the interaction of both static and dynamic-stabilizing structures. Static stabilizers include the bony anatomy, negative intra-articular pressure, the glenoid labrum, and the Gleno-humeral ligaments along with the joint capsule provide mainly end range stability.⁵

The dynamic stabilizing structures include the rotator cuff muscles and other shoulder muscles. Mid-range stability is provided by rotator cuff muscles by ‘concavity compression’.⁶

Failure of function of rotator cuff muscles in their stabilizing role leads to creation of an abnormal axis of rotation and abnormal translation of the head of humerus.⁷ Excessive translation of the humeral head along the glenoid results in pain and functional impairment.⁸

Commonly used tests for shoulder joint stability were mostly done at end range or mid range which were passive and assess only integrity of the capsular and ligamentous structures.⁹

Recent research findings have shown the need to consider dynamic joint stability and the local muscle system in the treatment of segmental spinal pain.¹⁰ Strong evidence is available that pain alters the timing of contraction in stabilizing muscles – transversus abdominis and multifidus in relation to the lumbar spine,vastus medialis obliquus in relation to the knee.⁶ Tests to detect lumbar and cervical dynamic stability are routinely used in clinical practice.¹¹

Such tests developed to assess and treat dynamic stability of the shoulder is Dynamic Rotator Stability Test and Dynamic Relocation Test developed by Mary Magarey and Mark Jones.^{6, 11} DRST is more important for assessment of humeral head translation due to abnormal rotator cuff activity and the test involves multiple positions which might mimic function.

In order for any type of measurement tool to be used with confidence when making decisions regarding patient care, the psychometric or measurement properties of reliability, validity, and responsiveness must be established.¹² To date, research on reliability and validity and on establishing normative values for DRST is incomplete.^6,11 But no study has been published which confirms reliability and validity of this test.¹³ The purpose of this study is to find reliability and concurrent validity of Dynamic Rotator Stability Test in subjects with painful shoulder.

Methodology

Source of data

Department of physiotherapy KMC Hospitals, Mangalore.

Study design

Cross sectional design for which ethical clearance granted by the institutional ethical committee

Subjects

40 subjects of either gender between the age group of 18–70 with painful shoulder conditions of musculoskeletal origin referred to KMC Hospitals, Attavar and Ambedkar Circle were recruited for the study.

Inclusion criteria

1. Subjects with painful shoulder of musculoskeletal origin

2. Availability of active shoulder ROM up to 120°

3. Subjects with pain, apprehension or click with active shoulder movement.

4. Willingness to participate in the study

5. Capable of understanding instructions given by the tester.

Exclusion criteria

1. History of recent fracture of the shoulder complex

2. History of recurrent shoulder dislocation

3. Subjects with diagnosed neurological problems pertaining to trunk and upper extremity

4. Worsening of symptoms or high irritability with movement of shoulder complex.

Procedure

Dynamic Rotator Stability Test (DRST)

The subject seated on a stool. The therapist holds around the head of the humerus as shown in the figure.(Fig:2)

Fig: 2.

Hand positioning of therapist for Humeral Head Palpation during DRST

The test is done as described by Mary Magarey and Mark Jones.¹¹The movement is done first in Scaption between 0–120 degrees.(Fig:1) All the movements are started in internal rotation direction(Fig:3); later movement to external rotation is done. The force initially used is isometric (30% of max. voluntary contraction force).As progression free active (Fig: 4), resisted concentric and eccentric force is used. If no abnormal humeral head translation is detected in Scaption, the test progress to flexion (sagittal) and abduction (coronal) plane. The test stops at the position where abnormal translation is detected and measurement is taken using Goniometer. (Fig: 5)

Fig: 1.

Fig: 3.

Therapist hand placement-manual resistance with subject’s arm in Scaption for Isometric internal rotation

Fig: 4.

Free active internal rotation

Fig: 5.

Goniometric measurement of the arm position in DRST positive position

University Of Pennsylvania Shoulder Score (Penn) Scale. ¹²

Penn Scale,100-point self-report scale consisting of 3 sections: pain, satisfaction, and function. There are 3 questions regarding pain (30 points), 1 regarding satisfaction of shoulder function (10 points), and 20 regarding function (60 points). Measurement properties have been established for the Penn scale in patients with various shoulder pathologies.¹²

Prior to starting of study, testers underwent a habituation programme to habituate with the test variables or parameters of assessment in dynamic rotator stability test. Dynamic Rotator Stability Test was done in shoulders of 4 asymptomatic subjects of age between 20–25y.

Penn shoulder score was also administered in a sample population of 40 asymptomatic subjects of either gender between the ages of 20–30 for cross cultural validation.^{14, 15}

Subjects were selected through convenient sampling. Written informed consent was obtained after explaining them about the objectives and methodology of the study. Subjects were then screened using screening check-list for inclusion and exclusion criteria.

Part- I Reliability of DRST

Order of the tester for the performance of DRST was randomized and the testers were blinded to each other’s findings.

Part-II Validity-Concurrent Validity

One tester evaluated the patient by administering score. Other tester did Dynamic Rotator Stability Test. Randomization of the tester was done for selected test for each subject. Each tester was blinded to other tester’s finding. Only one trial of assessment was done.

Statistical analysis

All statistical testing was carried out using Statistical Package for Social Science version 13.0 software. Differences were considered statistically significant at p<0.05.

For reliability, Spearman’s correlation coefficient was used for pair wise comparison regarding agreement with the test variables between testers.

For validity, Spearman’s correlation coefficient was used for pair wise comparison of test variables of DRST and test variables of Penn Shoulder Score.

Results

40 subjects between the ages 0f 18 to 70 was included in the study. 22 subjects were males and 18 were females. All the subjects were right hand dominant. In the subgroup of 20 for finding inter rater reliability 11 were males and 9 were females.

The subjects’ demographic characteristics were as shown:

	Intra Rater Reliability- DRST (Tester 1)	Inter- Rater Reliability- DRST (Tester 1&2 )
Sample Size	40	20
Age Mean SD	47.35±14.94	47.38±14.94
Gender- Total (M/F)	22/18	11/9
Hand Dominance(R/L)	40/0	20/0
Side of Shoulder Pain (R/L)	23/17	14/6
Duration of pain- Median (Range)	71.50 (2–3650)	87.00 (2–3640)

M=male, F=female,R=right, L=left

Reliability- Results for DRST (Spearman’s Correlation Co-efficient Rho)

	Intra Rater (Trial 1 & 2)	Inter Rater (1&2)
Position (S/F/Ab)	1.00*	1.00*
ROM	.94*	0.70*
Force	1.00*	.72*
Rotation	1.00*	.12
Direction of Abnormal Translation	1.00*	.71*
Pain during DRST	1.00*	.75*
Click during DRST	.95*	.546
Compensatory movements during DRST	1.00*	.76*

^*denotes significant findings S=Scaption, F=flexion, Ab=abduction

S=Scaption, F=flexion, Ab=abduction

For intra-rater reliability, all the test variables were showing highly significant correlation. For inter -rater, with tester 2, test variables like position, ROM, force, direction of abnormal translation, pain during test, compensatory movement during test were found to be significant.

Concurrent Validity- Results (Spearman’s Correlation Co-efficient Rho)

	Pain at rest	Pain with normal activities	Pain with Strenuous activities	Pain Subscale	Satisfaction Subscale	Functional Subscale
Position
ROM	.107	.065	−.094	−.018	−.145	−.138
Force	.062	−.060	−.019	−.045	.318*	−.100
Rotation	−.228	.010	.129	.000	.329*	−.196
Direction of Abnormal Translation	.041	−.121	−.327*	−.207	−.284	.088
Pain during DRST	.074	.210	.048	.109	.201	.358*
Click during DRST	.143	−.129	.077	−.011	.237	−.091
Compensatory movements during DRST	.137	.320*	.170	.280	.061	.450*

For concurrent validity of Dynamic Rotator Stability Test with Penn Shoulder Score, variables which showed significance are Force and satisfaction subscale, Direction of rotation and satisfaction subscale, Direction of abnormal translation and pain with strenuous activities, Pain during DRST and functional subscale, Compensatory movements during DRST and pain with normal activities, Compensatory movements during DRST and functional subscale

Discussion

The result of intra-rater reliability shows highly significant correlation among all test variables. This can be attributed to the habituation underwent by tester 1. To avoid recall bias DRST was administered randomly on either shoulder of the subjects. Preliminary screening was only done prior to the administration of the test. Clinical implication of the intra-rater results shows that DRST is a useful test for detecting dynamic instability in clinical practice, especially when the tester uses the test on a one to one basis.

In inter-rater reliability, apart from clicks and rotation during DRST, all other variables showed significant agreement between the testers.

There was mutual agreement between the testers regarding the position where DRST were positive. For all the subjects the abnormal translation of humeral head occurred in scaption. Scaption is defined as 30 degree anterior to the coronal plane.⁷ In the scaption plane, the capsular fibers of the glenohumeral joint are relaxed.¹⁶ Hence the joint relies more on rotator cuff muscles for stability. So any alteration in rotator cuff muscle activation results in instability.

Range of motion showed moderate correlation between the testers. Minor variations in the position of arm, force applied by the subjects and placement of Goniometer while taking reading might have caused this variation.

Force used during testing and direction of abnormal translation in DRST showed correlation. In an unstable shoulder, or one in which dynamic control is lacking, humeral head translate when the rotator cuff is loaded, usually anteriorly during resisted lateral rotation and posteriorly with resisted medial rotation. Studies had shown consistent activation of rotator cuff prior to more superficial delto-pectoral muscles in normal subjects.⁶ Strong evidence is available that pain alters timing of contraction in stabilizing muscles.¹¹

Pain during DRST showed good agreement between testers. The result can be attributed to the habituation programme and efficiency of examiners in collecting subjective feed back during test.

Compensatory movements showed good correlation. It is demonstrated that increase of upper trapezius activity occur during external rotation in shoulder pain patient group and decreased activity in the middle trapezius.⁸

Inter rater reliability of DRST was moderate in our study. This is in agreement with Inter-rater reliability of physical tests for shoulder in other studies showing moderate reliability.^{17, 18, 19, 20} Differences in clinical experience between testers would still have caused this effect. A great variability in reliability exists even in other physical tests of shoulder girdle.²⁰

For concurrent validity, some variables of DRST showed significant correlation with Penn Shoulder Score.

Force and satisfaction correlation can be attributed to the fact that satisfaction is purely subjective. The patient’s satisfaction with the ability to use the shoulder is an important construct to measure for both the patient and clinician.¹² Rotation and satisfaction showed significant correlation. It may be due to the fact that subjects with more external rotation range may be more satisfied. Maximum elevation on all planes of shoulder required external rotation of humerus. Loss of external rotation results in significant functional disability.¹⁶

Pain with DRST and function showed significance. Greater functional loss may be associated with pain with DRST. Functional disability due to pain in the shoulder at rest or during movement or functional disability due to restricted range of motion is frequently observed in painful shoulder subjects.²¹

Overall all of our subjects had a better Penn Shoulder Score, near normal. DRST can be positive even in the absence of any symptoms. Studies in low back pain subjects showed motor control deficits persisting even after the reduction of symptoms.²²

We do not have as on data, an established gold standard measure for dynamic stability of the shoulder. So we chose Penn Shoulder as a first line attempt. Condition-specific questionnaires of the shoulder have demonstrated greater responsiveness than generic measures in patients with shoulder disorders.¹²Although DRST seems to have face validity, concurrent validity could not be found.

The study however is the first of its kind on DRST, after the initial description given by the developers which opens a new era of research and future studies.

One of the limitations of the study was small sample size which had reduced the statistical power. The important observations of the study are that DRST was well tolerated, had produced no adverse effects and no latent symptoms occurred. So the test is very safe to use in clinical practice though it depends solely on the thorough patient understanding. This could be solved by testing and explaining on the unaffected side first.