Physical Factors Associated with Non-Specific Neck Pain: Correlations Among Pain, Disability, Posture, Endurance, and Compensatory Movement

Introduction

Non-specific neck pain refers to neck pain for which no specific cause is found in medical examinations such as radiographs [1]. More than 90% of neck pain without radiating pain was found to be non-specific pain with no direct patho-anatomical cause identified [2].

Non-specific neck pain is very common. It is estimated that 22–70% of the population will experience it at least once in their lifetime [3]. Between 10% and 20% of the population report having neck problems at any time [4], and up to 54% of people have experienced neck pain within the last 6 months [5]. In a systematic review conducted by Haldeman et al, the 1-year prevalence of non-specific neck pain ranged from 30% to 50%, and the incidence of disorders associated with neck pain ranged from 2% to 11% [6].

Non-specific neck pain is characterized by easy recurrence and chronicity [7]. Neck pain can be chronic, and 14% of those who have experienced neck pain have symptoms that persist for more than 6 months [8]. A high recurrence rate of 31% was observed in a large prospective study conducted in patients with non-specific neck pain who received nonsurgical treatment, and 90% of patients experienced mild pain again during 6-year follow-up [1].

In a systematic review by McLean et al, gender, age, work intensity, smoking history, level of social/occupational support, and back pain were found to be risk factors for non-specific neck pain [9]. Paksaichol et al reviewed 7 cohort studies and found that past experience of neck pain was a risk factor for neck pain in office workers [10]. However, although these risk factors can help establish a treatment plan by identifying the patient’s current physical and psychological state, information is insufficient to establish the specific type of exercise or the intensity and frequency of exercise.

Among various risk factors for non-specific neck pain, physical risk factors include cervical flexion mobility limitation, motor coordination impairment, and cervical headache. In cases accompanied by cervical headache, it was found that there was a limitation in range of rotation of the cervical vertebra 1 and cervical vertebra 2 [2]. In addition, a systematic review of 36 studies by Hesby et al found that people with non-specific neck pain had reduced active cervical ROM, reduced movement speed, and decreased joint position sense [11].

Several prior studies have investigated physical risk factors for non-specific neck pain. These studies compared differences in joint ROM, joint position sense, and muscle strength between subjects with non-specific neck pain and those without pain. However, there have been no studies analyzing the correlation with various physical variables such as active ROM of the cervical spine, muscular endurance, compensatory movements, and poor posture that can affect the pain intensity and degree of disability in patients with non-specific neck pain. Previous studies have focused on several physical risk factors, but it remains unclear which physical risk factors are more important. Therefore, to establish a treatment plan and exercise program for patients with non-specific neck pain, it is necessary to find out which factors are more correlated through investigations including various physical risk factors. In this study, we investigated the correlation between pain, disability index, cervical joint ROM, endurance, and compensatory movements in 50 patients with non-specific neck pain visiting a hospital in Korea.

Material and Methods

PARTICIPANTS:

This study was approved by the Research Ethics Committee of Kyungnam University (NO. 104060-A-2022-001). This study was conducted on patients who visited the physical therapy center of J Hospital in Changwon-si, Gyeongsangnam-do due to neck pain, and recruited through recruitment notices on the bulletin board in the hospital for 6 months from May to November 2022.

The inclusion criteria were: 1) diagnosed with non-specific neck pain by a doctor, and 2) had neck pain more than half of the time in the past 12 weeks. The exclusion criteria were: 1) a fracture, spine surgery, or other orthopedic disease, 2) central nervous system diseases such as brain damage, 3) neurological symptoms such as numbness and burning sensation in the upper limbs, and 4) systemic inflammatory disease. We recruited 53 patients with non-specific neck pain. All participants listened to an explanation of the procedure and purpose of the study and signed the consent form.

PROCEDURE:

This was a cross-sectional study. The correlation between active cervical ROM, upper cervical rotation ROM, endurance of deep cervical flexor, compensatory movement of cervical flexion, forward head posture, shoulder height difference, and rounded shoulder posture according to pain intensity and disability index in patients with non-specific neck pain was investigated.

Participants filled out questionnaires about pain intensity and disability index. The pressure pain threshold of the upper trapezius was measured, and the active ROM of the cervical vertebrae, the range of rotation of the upper cervical vertebrae, endurance of deep cervical flexor, compensatory movements of cervical flexion, forward head posture, shoulder height difference, and rounded shoulder posture were measured. Forward head posture and shoulder height asymmetry were measured by taking pictures of the cervical vertebrae and shoulders. Compensatory movements for neck flexion were measured through video recording. All variables were measured 3 times and the average value was used. Measurements of all variables were performed by a physical therapist with more than 3 years of clinical experience working in the physical therapy department of J Hospital, who was blinded to the purpose of this study. To reduce measurement errors, training on all measurement methods was conducted 3 times.

PAIN INTENSITY:

Pain intensity was measured based on the pain felt on the day of measurement, and the Numeric Pain Rating Scale (NPRS) was used. Patients were asked to choose their level of pain as a number, with 0 points representing no pain and 10 points representing unbearable pain. The test-retest reliability of the NPRS was ICC=0.61–0.77, and the validity was ICC=0.85 [12].

PRESSURE PAIN THRESHOLD:

The pressure pain threshold was measured by using a digital pressure gauge (FPX25, Wanger, CT, USA) to measure the pressure pain of the upper trapezius muscle. With the participant in a sitting position, the digital pressure gauge was placed perpendicular to the upper trapezius fibers 5–8 cm above the superior angle of the scapula. The pressure intensity was set to about 4–5 N/s, and the patient verbally indicated the moment when the feeling of pressure became painful. The contralateral upper trapezius was measured repeatedly in the same way. Each part was measured 3 times and the average value was recorded, with at least 30 s between tests. The test-retest reliability of pressure threshold was ICC=0.75–0.87 [13].

NECK DISABILITY INDEX:

The degree of disability of patients with non-specific neck pain was measured using the neck disability index (NDI), which is widely used to identify the degree of disability in patients with neck pain. It consists of 2 questions related to pain and 8 questions related to personal care and daily life. Each item has a score of 0 to 5, and the total score is expressed as a percentage, and the higher the score, the more severe the disability: 0–8% no disability, 10–28% mild disability, 30–48% moderate disability, 50–68% severe disability, and 70% or more complete disability (Vernon, 2008). The test-retest reliability of the neck disability index was ICC=0.88 and the validity was ICC=0.86 [14].

ACTIVE CERVICAL ROM:

To measure the active ROM of the cervical vertebrae, a digital dual inclinometer (Dualar IQ, JtechM, UT, USA) was used, and the average value was recorded after 3 repeated measurements. To measure the cervical flexion ROM, the first inclinometer was placed at the first thoracic vertebrae and the second inclinometer was placed at the apex of the head in the sitting position. After instructing the participant to bend the neck, the angle was measured at the end range of cervical vertebrae flexion.

To measure the cervical spine extension ROM, an inclinometer was placed at the 1^st thoracic vertebrae and the apex of the head, with participants in a sitting position. After instructing the participants to tilt their neck back, the angle was measured at the end range of cervical extension.

To measure the cervical spine rotation ROM, an inclinometer was placed at the center of the forehead in the supine position. After instructing participants to turn their heads, the angle was measured in the final range of cervical rotation. The inter-rater reliability of the measurement of the active ROM of the cervical spine using a digital inclinometer was ICC=0.98 and the validity was r=0.98 [15,16].

UPPER CERVICAL ROTATION ROM:

To measure the upper cervical rotation ROM, the cervical flexion-rotation test was performed, and the average value was recorded after 3 repeated measurements. With the participant lying supine, the examiner bends the participant’s cervical vertebrae to their end range and then rotates the head to the right and left. The angle was measured by placing a digital inclinometer at the center of the forehead [2]. The test-retest reliability of the cervical vertebrae flexion-rotation test was highly reliable, with ICC=0.92 [17].

DEEP CERVICAL FLEXOR ENDURANCE:

To measure deep cervical flexor muscle endurance, the cranio-cervical flexion test was conducted using a pressure biofeedback device (Stabilizer, Chattanooga, TN, USA), and the average value was recorded after 3 measurements. The participant places a pressure biofeedback device on the back of the cervical vertebrae in a supine position. The subject was asked to increase the pressure by pulling the chin. The pressure was divided into 5 stages – 20, 22, 24, 28, and 30 mmHg – and the number of times that could be maintained for 10 s was measured and converted into a score. Scores were set based on 22 mmHg=2 points, 24 mmHg=4 points, 26 mmHg=6 points, 28 mmHg=8 points, and 30 mmHg=10 points, and were measured by multiplying the number of repetitions possible: 30 mmHg held for 10 s 10 times was converted into 100 points, and 22 mmHg held for 10 s only once was converted into 2 points [18]. The intra-rater reliability of the cranio-cervical flexion test is ICC=0.98 [19].

FORWARD HEAD POSTURE:

Forward head posture was measured using the cranio-vertebral angle [20]. Photographs were taken of the lateral aspect of the cervical vertebrae of the subjects, and the angle at which the line connecting the tragus to the 7th cervical vertebra and the horizontal line intersected was measured and recorded. As this angle increases, the head is judged to be located more forward. To take pictures, the camera was installed horizontally with the floor using a tripod, and the height from the ground was 1.5 m and the distance from the subject was 1 m. The intra-rater reliability of the cranial-vertebral angle is ICC=0.86~0.94, and the inter-rater reliability is ICC=0.85~0.91, making it a reliable test [20].

ROUNDED SHOULDER POSTURE:

To measure the height of rounded shoulders, the subjects measured the distance between the floor of the table and the acromion using a ruler in a supine position [21].

SHOULDER HEIGHT:

To measure the difference in shoulder height, the subjects were asked to stand upright with their feet spread apart at pelvic width and arms at their sides. Photographs were taken after attaching markers to both acromions of the subjects. To measure the difference in shoulder height, the angle between the line connecting both acromions and the horizontal line was measured [22].

COMPENSATIONAL MOVEMENTS FOR CERVICAL FLEXION:

To measure the compensatory motion for cervical flexion, subjects performed cervical flexion motions while lying on a table. A video was taken from the side while the subject performed cervical flexion. In the video data, the sagittal head angle was measured at the point of completion of the subject’s cervical vertebrae bending. The sagittal head angle is a measurement of the angle between the horizontal line and the line connecting the canthus and tragus, and the larger the angle, the greater the compensatory movement [23]. The intra-rater reliability of the sagittal head angle is ICC=0.88, and the inter-rater reliability is ICC=0.83, making it a reliable test [20].

STATISTICAL ANALYSIS:

Statistical analysis in this study was performed using SPSS 21.0. All data were tested for normality through the Kolmogrov-Smirnov test. Descriptive statistics were used to analyze the general characteristics of the subjects. Pearson’s correlation was used to analyze the correlation among pain intensity, tenderness threshold, active ROM, upper cervical joint ROM, muscular endurance, forward head posture, height of rounded shoulders, and shoulder height difference. The significance level (α) was set at.05 or less.

Results

CHARACTERISTICS OF STUDY PARTICIPANTS:

A total of 53 subjects were recruited for this study, and 3 subjects were excluded because they met the exclusion criteria – 2 patients with upper-extremity neurological symptoms and 1 patient with a history of surgery for cervical disc herniation. Finally, 50 people were included – 31 males (62%) and 19 females (38%), with an average age of 38.02 years, average height of 170.1 cm, and average weight of 68.64 kg. The pain intensity and disability index of the subjects were 4.94 points and 20.2%, respectively (Table 1).

CORRELATION BETWEEN NON-SPECIFIC NECK PAIN, PRESSURE PAIN THRESHOLD, AND POSTURE:

There was a strong positive correlation between pain intensity and disability index (P<.05). There was a strong negative correlation between pain intensity and pressure pain threshold, and a weak positive correlation with left rounded shoulder posture (P<.05). However, there was no correlation with right rounded shoulder posture (P<.05). Additionally, pain intensity had a moderate positive correlation with forward head posture and shoulder height (P<.05).

The degree of neck disability had a negative, moderate correlation with pressure pain threshold, and a strong positive correlation with rounded shoulder posture (P<.05). However, there was no correlation between forward head posture and shoulder height (Table 2).

CORRELATION BETWEEN NON-SPECIFIC NECK PAIN AND CERVICAL RANGE OF MOTION:

There was a moderate negative correlation between pain intensity and left neck rotation, and a weak negative correlation with right neck rotation (P<.05). There was a negative moderate correlation with left upper cervical vertebra rotation (P<.05), but no correlation with right upper cervical vertebra rotation. There was no correlation between pain intensity and neck flexion and extension. There was a weak negative correlation between the degree of disability and the ROM of the neck with left rotation, and a negative moderate correlation with right rotation (P<.05). There was a moderate negative correlation with upper cervical rotation on both the left and right sides (P<.05). However, there was no correlation between bending and extension (Table 3).

CORRELATION BETWEEN NON-SPECIFIC NECK PAIN, CERVICAL ENDURANCE, AND COMPENSATORY MOTION:

There was a negative moderate correlation between pain intensity and endurance of the deep cervical flexors (P<.05), but there was no correlation with compensatory movement of cervical flexion. There was no correlation between the degree of neck disability and deep cervical flexor endurance, but there was a positive moderate correlation with compensatory movement of cervical flexion (P<.05) (Table 4).

Discussion

This study was conducted to investigate the correlation between various physical risk factors in patients with non-specific neck pain. Pain intensity, pressure pain threshold, disability index, active cervical ROM, upper cervical rotation ROM, deep cervical flexor endurance, forward head posture, rounded shoulder posture, shoulder height difference, and compensatory movements were measured in patients with non-specific neck pain and the correlation between each variable was analyzed.

Cervical rotation ROM was found to have a significant correlation with neck pain intensity and disability index. In addition, the cervical spine extension ROM was found to have a significant correlation with the pressure pain threshold. In a systematic review conducted by Stenneberg et al, patients with non-specific neck pain tended to experience limitations in the cervical rotation ROM [24]. Lee et al investigated the ROM of the cervical spine in subjects with and without non-specific neck pain and found that the ROM in the group with non-specific neck pain was limited [25]. The results were similar to those of this study. An increase in muscle tone due to continuous posture or repetitive movements causes an imbalance in the muscles around the cervical vertebrae, limiting the ROM of the cervical vertebrae [22]. Therefore, in this study, as the degree of non-specific neck pain increased, the active ROM decreased, and a statistically significant correlation was found.

Upper cervical rotation ROM was found to have a significant correlation with pain intensity, pressure pain threshold, and disability index. Ernst et al reported that people with non-specific neck pain and headache generally had limited upper cervical ROM [26]. In this study, there was also a negative correlation between non-specific neck pain and upper cervical rotation ROM. We found a significant correlation between pain intensity and cervical rotation ROM in patients with non-specific neck pain. In previous studies, patients with non-specific neck pain had limitations in the ROM of the cervical vertebrae, especially in the upper cervical extension and lower cervical flexion ROM [27]. The function of the upper cervical vertebra is mainly involved in rotational movements because it has flexion and extension of 15° to 20° and rotation of 75° to 80° [28]. Therefore, in this study, it is considered that the upper cervical vertebra rotation range was also limited as the range of rotation of the cervical vertebrae was limited due to the causes such as continuous postural alignment, increase in muscle tension, and muscle imbalance described above.

A significant correlation was established between rounded shoulder posture, forward head posture, and pain intensity in patients with non-specific neck pain. Kim et al found a significant correlation between rounded shoulders and neck disability index [29]. A systematic review by Mahmoud et al analyzed the relationship between forward head posture and pain intensity, and found that forward head posture can affect the occurrence of non-specific neck pain [30]. Subjects who participated in that study were used computers for 21 h per week and smartphones for 20 h per week. The study found that prolonged use of computers and smartphones can cause forward head posture and rounded shoulders [14]. When round shoulders occur, the muscles around the shoulders are constantly in a tense state. Among the muscles around the shoulder, the upper trapezius and levator scapula are connected to the cervical vertebrae and generate stress on the cervical vertebrae, ligaments, and discs [31]. When forward head posture occurs, the muscles at the back of the neck become hypertonic, and as the head tilts forward, lordosis of the cervical vertebrae decreases, causing unnecessary stress on muscles, bones, ligaments, and discs [32], showing the correlation among pain intensity, rounded shoulders, and forward head posture.

There was a significant correlation among disability index, neck flexion compensatory movement, active joint ROM, upper cervical rotation ROM, and forward head posture. In a study conducted by Jull and Falla, patients with non-specific neck pain had decreased activities of deep cervical flexors and increased activities of superficial cervical flexors, resulting in increased compensatory movements for cervical flexion [33]. They also found a correlation between pain intensity and cervical spine flexion compensatory movements. Subjects who participated in that study may have had a forward head posture due to long-term computer and smartphone use. In addition, due to the forward head posture, the activity of the deep cervical flexor muscles is low, and the sternocleidomastoid and scalene muscles become overactive. Due to this condition of the neck muscles, when performing a cervical flexion motion, the lower cervical vertebrae are bent and the upper cervical vertebrae are extended to make compensatory movements, which increase abnormal stress on the cervical vertebrae [2]. It is thought that non-specific neck pain occurred in that study due to these causes.

The present study has several limitations. First, it is difficult to generalize the correlation between each variable because the number of subjects who participated in this study was small and personal characteristics such as occupation, current exercise, and physical ability of the subjects were not considered. Second, only correlation analysis was performed and no regression analysis was performed, so cause and effect cannot be determined. Third, since this study was conducted to find physical risk factors, psychosocial factors that can affect pain were not considered. As a result, it is difficult to apply the results of this study to non-specific neck pain patients with psychological and social problems. Fourth, it was impossible to eliminate all factors that could affect non-specific neck pain, such as treatment at other institutions and current medications; therefore, it is difficult to apply the results of this study to all patients with non-specific neck pain. Studies with larger samples are, and research should be conducted that considers individual characteristics and psychological and social problems.

Conclusions

As a result of analyzing various physical risk factors in patients with non-specific neck pain, cervical rotation ROM, upper cervical rotation ROM, rounded shoulder posture, shoulder height difference, forward head posture, and neck flexion compensatory movements are important physical risk factors. The results of this study of physical risk factors for non-specific neck pain may be used in various fields such as effective patient treatment and development of exercise programs.