Cervical and Non-Cervical Muscle Thickness Changes in Forward Head Posture

Head-forward posture (FHP) is one of the most common postural disorders and is increasing worldwide. Most studies examining FHP have focused on the relationship between craniovertebral angle (CVA) and cervical muscle thickness. However, FHP is a postural disorder that affects the entire musculoskeletal system, not just the cervical region. It creates a chain of adaptations in the body, generating both local and global effects. The aim of this study is to evaluate the relationship between postural changes triggered by CVA and the thickness of the trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, multifidus, sternocleidomastoid (SCM), transversus abdominis (TrA), internal oblique (IO), external oblique (EO), gluteus maximus, tibialis anterior, rectus femoris, and gastrocnemius (GK) medial muscles, as measured by ultrasonography (USG), since postural changes triggered by CVA can affect the spine, hips, and lower extremities. If this relationship can be confirmed, this information could be used as a basis for evaluating abnormal posture.

The sample size calculation was based on a similar study previously conducted by Kyung Woo Kang et al., which recorded the ultrasound appearance of the TrA, IO, and EO muscles obtained with head-forward posture and reduced CVA. Adequacy in the strength analysis, based on abdominal muscle measurements using G*Power 3.0.10a, was calculated with a minimum of 21 volunteers in each group, with a 5% type 1 error and 99% power. Considering losses, it was planned to recruit 23 patients in each group.

Participants included in the study will be divided into two groups. The first group will consist of 23 female volunteers diagnosed with forward head posture (FHP), while the second group will include 23 female volunteers with normal posture who do not meet any of the exclusion criteria.

For both groups, postural assessment and ultrasonographic evaluation of muscle thickness will be performed on the same day they receive their clinical diagnosis, in a manner that does not interfere with their treatment. No interventional procedure will be applied.

To determine the presence of forward head posture (FHP), the craniovertebral angle (CVA) measurement method will be used in this study for postural assessment. For CVA measurement, participants will be instructed to stand in a comfortable position with their arms relaxed at their sides. The spinous process of C7 will be identified by palpation and marked. Subsequently, participants will be asked to perform head flexion and extension movements 3-4 times to obtain a self-balanced head position. A digital camera will be positioned 1.5 meters from the participant at shoulder level, and lateral digital images of the head, neck, and shoulders will be captured for further analysis. The angle formed between the line connecting the spinous process of C7 to the tragus of the ear and a horizontal line passing through C7 will be defined as the CVA. A CVA of less than 48° will be considered indicative of forward head posture.Based on a previous study, only female participants with right-hand dominance will be included, as no difference is expected between the right and left sides of the spine in healthy individuals. Therefore, only right-sided muscle thickness will be measured, and the obtained data will be analyzed.

Demographic data of the participants, cervical range of motion measurements, Visual Analog Scale (VAS) scores, and Neck Disability Index (NDI) scores will be recorded. Muscle thickness measurements obtained by ultrasonography (USG) will be recorded in millimeters (mm).

To minimize inter-operator variability, clinical assessments, ultrasonographic (USG) measurements, and statistical analyses will be performed by different researchers. For all muscles, the average of three thickness measurements will be used for statistical analysis.

Ultrasonographic imaging of the posterior neck muscles will be performed at the C4 level using a 7-12 MHz high-frequency linear array probe. Participants will be seated comfortably with their hands resting on their thighs during the procedure. The spinous process of the fourth cervical vertebra (C4) will be identified by palpation. The transducer will then be placed horizontally at the level of the C4 spinous process and moved slowly to the right, and slightly upward and downward, until the echogenic vertebral lamina is clearly visualized. Muscle thickness of the posterior cervical muscles-including the trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus-will be measured at the C4 level as the greatest distance between the anterior and posterior fascia. Measurements will be taken three times, and the mean value will be recorded.

The sternocleidomastoid (SCM) muscle consists of sternal and clavicular heads and five compartments with different attachments. Due to its superficial location, it is easy to palpate and visualize. To identify the SCM muscle, imaging will be performed using a 7-12 MHz high-frequency linear array probe positioned in the axial plane at the C5 and C6 levels. The mean of three measurements will be recorded.

For imaging the transversus abdominis (TrA), internal oblique (IO), and external oblique (EO) muscles, a 7-12 MHz high-frequency linear array probe will be used. Participants will lie in a comfortable position with their knees flexed and hips at approximately 45°. The transducer will be placed between the anterior superior iliac spine (ASIS) and the lowest rib, approximately 3 cm superomedial to the iliac crest. Using B-mode ultrasonography, the deepest muscle layer visible on the screen will be identified as the TrA. From superficial to deep, EO, IO, and TrA will be visualized sequentially. The average of three thickness measurements will be used for statistical analysis.

Participants will be asked to lie in the prone position with both lower extremities in a neutral position. Ultrasonographic imaging will be performed using a 2-5 MHz convex probe in B-mode. Measurements will be taken within the proximal 30% of the distance between the posterior superior iliac spine (PSIS) and the greater trochanter of the femur, specifically within the first third of this region. Depth and zoom settings will be adjusted until the image of the left third of the sacrum is no longer visible. Once the optimal image is obtained, it will be frozen, and the thickness of the gluteus maximus muscle fibers will be measured. The mean of three measurements will be used for statistical analysis.

A 7-12 MHz linear probe will be used to obtain images of the rectus femoris (RF), tibialis anterior (TA), and medial head of the gastrocnemius (MG) muscles.

For rectus femoris imaging, the participant will be in the supine position. Measurements will be taken at the midpoint between the anterior superior iliac spine (ASIS) and the superior border of the patella. In the axial plane, muscle thickness will be determined as the perpendicular distance between the superficial and deep fascia at the thickest portion of the muscle. The mean of three measurements will be recorded.

For imaging of the medial gastrocnemius, the participant will lie in the prone position with the ankle in a neutral position. Muscle thickness will be measured at the midpoint between the fibular head and the medial malleolus. In the axial plane, thickness will be determined as the perpendicular distance between the superficial and deep fascia at the thickest region. The mean of three measurements will be recorded.

For tibialis anterior imaging, the participant will be in the supine position. Muscle thickness will be measured at one-third of the distance along the line extending from the medial aspect of the patella to the lateral malleolus, using a standardized transducer placement. In the axial plane, thickness will be determined as the perpendicular distance between the superficial and deep fascia at the thickest portion of the muscle. The mean of three measurements will be recorded.

Inclusion criteria

• Age >18 years
• Female sex
• Right-hand dominance

Exclusion criteria

• Presence of a systemic disease that may cause forward head posture (FHP)
• Presence of osteoarthritis in the ankle, knee, hip, or spine
• History of surgery involving the cervical region, lumbar region, or lower extremities
• Presence of neurological disorders affecting muscles or nerves
• Presence of pain originating from the cervical region
• Presence of radiculopathy
• Presence of mental retardation or neuropsychiatric disorders preventing participation
• Unwillingness to participate
• Pregnancy