Reliability of the assessment of scapular posterior tilt angle using the smartphone and scapular movement during arm elevation in healthy individuals and patients with frozen shoulder: a cross-sectional study

Abstract

Background

Frozen shoulders are associated with abnormal scapular movements. However, scapular posterior tilt movement in frozen shoulders has not been investigated using simple clinical methods. This study aimed to clarify the reliability of scapular posterior tilting movement using a smartphone and scapular posterior tilting movement in healthy individuals and patients with frozen shoulder.

Methods

The participants were 22 healthy young (age 25.9 ± 4.1 years), 22 healthy middle-aged (age 52.6 ± 4.4 years), and 37 individuals with frozen shoulder (age 56.0 ± 7.0 years). Scapular posterior tilting movement was measured at shoulder flexion 0° (0° posterior tilt), shoulder flexion 90° (90° posterior tilt), and scapular tilt excursion using a smartphone. The intrarater reliability was calculated using the intraclass correlation coefficient (1, 3).

Results

Intrarater reliability at 0° posterior tilt and 90° posterior tilt was 0.76 and 0.84, respectively. The 0° posterior tilt was not significantly different among the three groups (P = .90). The 90° posterior tilt was not significantly different among the three groups (P = .06). The scapular tilt excursions were significantly greater in the frozen shoulder group than in the middle-aged group (P = .03).

Conclusion

Measurement of scapular posterior tilting movement using a smartphone was highly reliable. The frozen shoulder might compensate for the limited arm elevation of the glenohumeral joint by scapular posterior tilting movement.

Frozen shoulder is a condition that causes pain and contracture of the shoulder without any injuries or trauma.⁶ The coordinated motion of the three anatomic joints and two functional joints maintains great mobility of the shoulder joint.¹ The scapular movement of the frozen shoulder has been reported to increase the upward rotation of the scapula during arm elevation.^4,15

To assess the scapula, static scapular alignment is evaluated by measuring scapular spine distance^5,13 and acromial distance from the table surface.¹¹ The advantages of using scapular spine distance and acromial distance are their simplicity and convenience in clinical practice. However, scapular movement during arm elevation cannot be assessed. Meanwhile, an electromagnetic tracking device^8,10 and 3D-to-2D registration technique with computed tomography has been used to assess dynamic scapular alignment.⁹ Through the electromagnetic tracking device and 3D-to-2D registration technique, quantifying the scapular movement in three dimensions is possible. However, such device is expensive and requires a large equipment and space, making it less versatile. Therefore, it cannot easily quantify scapular movement in a clinical setting.

In this study, we focused on the assessment of clinically simple and quantifiable scapular movement using a smartphone. In the recent years, assessment of the lumbar spine angle¹² and ankle dorsiflexion angle² using smartphones has been reported, and such technique has been reported to be highly reliable. However, the reliability of the assessment of scapular movement using a smartphone has not been investigated, and the scapular posterior tilting movement in patients with frozen shoulder remains unclear. Therefore, we hypothesized that assessment using smartphones is clinically simple and quantifiable. This study aimed to clarify the reliability of the assessment of scapular posterior tilting movement using a smartphone and different scapular posterior tilting movements during arm elevation between healthy individuals and patients with frozen shoulder.

Materials and methods

Participants

This study design was a cross-sectional study. The participants were 22 healthy young individuals with 22 shoulders (15 men, 7 women, age 25.9 ± 4.1 years, height 171.9 ± 7.3 cm, weight 63.8 ± 11.6 kg, and body mass index 21.4 ± 2.7), 22 healthy middle-aged individuals with 22 shoulders (7 men, 15 women, age 52.6 ± 4.4 years, height 164.6 ± 7.6 cm, weight 60.6 ± 4.5 kg, and body mass index 22.1 ± 3.7), and 34 patients with 37 frozen shoulders (12 men, 22 women, age 56.0 ± 7.0 years, height 163.0 ± 9.1 cm, weight 61.3 ± 11.8 kg, and body mass index 22.7 ± 2.7). The sample size was estimated from the preliminary study, showing the effect size of 0.62 for the differences in scapular posterior tilting movement among the three groups. With a power (1 − β) of 0.80 and an α of 0.05, it was shown that at least 22 participants per group were necessary. The inclusion criterion for the young and middle-aged groups was no present or past symptoms of frozen shoulder. The frozen shoulder group included patients clinically diagnosed with frozen shoulder. The diagnostic criteria for frozen shoulder were based on the International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine classification.⁶ The exclusion criteria were previous shoulder surgery. This study protocol was approved by the University Ethics Review Committee (2020-111). This study also complied with the Declaration of Helsinki and was conducted only after written informed consent was obtained from the study participants, who had been fully informed of the nature of the experiment in the oral and written form.

Methods

An iPhone 11 (iOS 14.4., Apple Inc., Cupertino, CA, USA) was used to measure scapular posterior tilting and upper thoracic spine tilt angles. The application used to measure the scapular posterior tilt angle was the simple angle meter (ver.1.1., NEKO SYSTEM., Osaka, Japan). Thoracic spine tilt angle was measured using the Measure (iOS 14.4., Apple Inc., Cupertino, CA, USA). A physical therapist performed all measurements. The scapular posterior tilt angle was assessed by placing it over the line connecting the midpoint from the posteroinferior angle of the acromion and the root of the spine of the scapula with the inferior angle of the scapula (Fig. 1A). The motion axis of the simple angle meter was set by placing the iPhone parallel to the floor and resetting the application to 0°. The tilt angle of the upper thoracic spine was assessed by placing it over the spinous processes of the first and second thoracic spine (Fig. 1B). The scapular anterior–posterior tilt axis was defined as presented in Fig. 2.

Figure 1.

Measurement methods of scapular posterior tilt (A) and upper thoracic spine tilt angles (B). a: posteroinferior angle of the acromion; b: root of the spine of the scapula; c: midpoint from the posteroinferior angle of the acromion and the root of the spine of the scapula; d: inferior angle of the scapula; e: spinous processes of the first thoracic spine; f: spinous processes of the second thoracic spine.

Figure 2.

Scapular anterior–posterior tilt axis.

The measurement positions were shoulder flexion at 0° and 90° of the sagittal plane in the sitting posture. Shoulder flexion angle was set using a standard goniometer. Shoulder flexion angle was defined as the angle between the vertical line to the floor through the acromion and the long axis of the humerus. The sitting posture was hip flexion at 90° and intermediate internal and external rotation of the hip without excessive thoracolumbar kyphosis. The upper limb on the non-measured side was placed in shoulder flexion at 0°, elbow full extension, and intermediate pronation and supination of the forearm. Participants who deviated from the measurement rules underwent remeasurement.

The scapular posterior tilt angle was measured at active shoulder flexion 0° (0° posterior tilt) and active shoulder flexion 90° (90° posterior tilt). The posterior tilt angle of the scapula was calculated using the following formula to avoid reflecting the motion of the upper thoracic vertebrae: scapular posterior tilt angle (°) = anterior posterior tilt angle on a simple angle meter (upper thoracic spine tilt angle, 90°). The scapular posterior tilt angle was given a positive value for the posterior tilt and a negative value for the anterior tilt. Scapular tilt excursion was defined as the amount of change from 0° posterior tilt to 90° posterior tilt. The reliability was investigated at 0° posterior tilt and 90° posterior tilt for 11 healthy young individuals with 11 shoulders. The measurement interval was at least 15 minutes. Mean values were calculated from three measurements. The retests were performed three times. All retests were performed on the same day.

Statistical analysis

Intrarater reliability was assessed using the intraclass correlation coefficient (ICC) (1,3). The criteria for ICC were as follows⁷: <0.00 = poor; 0.00-0.20 = slight; 0.21-0.40 = fair; 0.41-0.60 = moderate; 0.61-0.80 = substantial; and 0.81-1.00 = almost perfect. Minimal detectable change at the 95% confidence interval (MDC95%) was calculated as follows³: MDC95% = 1.96 × √2 × SEM. SEM is the standard error of measurement, calculated as SEM = SD√(1 − ICC). The Kruskal–Wallis test was used to compare 0° posterior tilt, 90° posterior tilt, and scapular tilt excursion between the three groups. The Bonferroni test was used for post hoc tests. SPSS statistics ver. 25.0 (IBM Corp., Tokyo, Japan) was used for all the statistical analyses. The level of statistical significance was set at P < .05.

Results

Intrarater reliability

Intrarater reliability and MDC95% at 0° posterior tilt and 90° posterior tilt are presented in Table I. In this study, measurements of the 0° posterior tilt and 90° posterior tilt were substantial and almost perfect, respectively, according to the criteria of Landis and Koch.⁷

Table I.

Intrarater reliability of the 0° posterior tilt and 90° posterior tilt.

	ICC (1, 3)	95% CI	SEM	MDC95%
0° posterior tilt	0.76	0.36-0.93	2.07	5.72
90° posterior tilt	0.84	0.57-0.95	3.87	10.74

ICC, intraclass correlation coefficient; CI, confidence interval; SEM, standard error of the mean; MDC95%, minimal detectable change at the 95% confidence interval.

Scapular movement in healthy individuals and patients with frozen shoulder

Figure 3 presents the results for 0° posterior tilt, 90° posterior tilt, and scapular tilt excursion. The 0° posterior tilt of the young group was −5.5 ± 4.8°, that of the middle-aged group was −6.0 ± 6.2°, and that of the frozen shoulder group was −5.8 ± 7.0°, with no significant differences among the three groups (P = .90). The 90° posterior tilt of the young group was 14.5 ± 16.8°, that of the middle-aged group was 4.6 ± 10.9°, and that of the frozen shoulder group was 14.5 ± 14.0°, with no significant differences among the three groups (P = .06). The scapular tilt excursion of the young group was 20.0 ± 14.9°, that of the middle-aged group was 10.7 ± 9.9°, and that of the frozen shoulder group was 20.4 ± 13.6°. The frozen shoulder group had significantly higher values than the middle-aged group (P = .03). No significant difference was observed between the young and middle-aged groups (P = .06). No significant difference was observed between the young and frozen shoulder groups (P = .99).

Figure 3.

Comparison of scapular posterior tilt movements between the three groups. (A): 0° posterior tilt. (B): 90° posterior tilt. (C): Scapular tilt extension. Significant difference: ∗P < .05.

Discussion

In this study, the intrarater reliability at 0° posterior tilt and 90° posterior tilt was 0.76 and 0.84, respectively. The frozen shoulder group demonstrated a significantly greater scapular tilt excursion than the middle-aged group. Thus, the measurement of scapular posterior tilting movement using a smartphone was substantial reliable, and it was clarified that frozen shoulder was associated with an increase in scapular tilt excursion.

In a previous study, Vermeulen et al¹⁵ assessed scapular movement during arm elevation using an electromagnetic tracking device in patients with frozen shoulder. They have reported that a frozen shoulder increased scapular upward rotation during arm elevation compared with an unaffected shoulder. Fayad et al⁴ assessed the scapular angle at maximum arm elevation using an electromagnetic tracking device in patients with frozen shoulders. They have reported that a frozen shoulder demonstrated increased scapular upward rotation and decreased protraction at maximal arm elevation compared with an unaffected shoulder. In summary, previous studies using electromagnetic tracking devices have reported that frozen shoulder increased scapular upward rotation and decreased protraction during arm elevation; however, no study has investigated the scapular posterior tilting movement in frozen shoulder. Here, we identified an increase in scapular posterior tilting movement during arm elevation in patients with frozen shoulder.

Frozen shoulder has been reported to cause limited range of motion of the glenohumeral joint due to inflammation of the synovium.¹⁴ Therefore, the frozen shoulder may compensate for the limited arm elevation of the glenohumeral joint by scapular posterior tilting movement.

Yang et al¹⁶ have reported that patients with a frozen shoulder with a large scapular posterior tilt at treatment initiation had a higher rate of improvement in range of motion with physical therapy. Based on these studies, the scapular posterior tilting movement can be quantitatively assessed in a clinical setting, which may influence the clinical decision-making of physical therapy for frozen shoulder.

This study has several limitations. First, scapular movement was assessed based only on scapular posterior tilting. In the future, scapular upward and external rotation should be measured. Second, the scapular posterior tilting movement above shoulder flexion at 90° could not be assessed. The reason was that the patients with frozen shoulder had small a shoulder flexion angle and evaluating the scapular posterior tilting movement with shoulder flexion of ≥90° was difficult. Third, this study could not reduce bias because it was evaluated by only one examiner. Fourth, this is a cross-sectional study. Therefore, whether the results of this study were the cause or result of frozen shoulder is unclear. The relationship between frozen shoulder and scapular movement should be prospectively investigated in future studies.

Conclusion

This study investigated scapular posterior tilting movement in healthy individuals and patients with frozen shoulder using a smartphone. We hypothesized that assessment using smartphones is clinically simple and quantifiable. We observed that scapular posterior tilting movement was increased in patients with frozen shoulder compared with that in healthy individuals. Our results showed that measurement of scapular posterior tilting movement using a smartphone was highly reliable.

Acknowledgments

We would like to thank Editage (www.editage.com) for English language editing.

Disclaimers

Funding: No funding was disclosed by the authors.

Conflicts of interest: The authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.