Scapular Mechanics
Original Editor - Ewa Jaraczewska based on the course by Ari Kaplan
Top Contributors - Ewa Jaraczewska and Jess Bell
Introduction
The scapula is influenced by the structures surrounding it, and in particular, is tightly paired with the thoracic spine. The position and mobility of the thoracic spine directly affect how the scapula rests and moves,[1] meaning that optimal scapular kinematics (i.e., upward rotation, posterior tilt, and external rotation during arm elevation) depend on appropriate thoracic posture and range of motion.[2] This page focuses on the scapula: its resting position, movements, the key muscles that drive these movements, and how clinicians can reason through a structured scapular assessment.
Scapula Resting Position
The following reference values can be used when assessing scapular resting position. However, there is considerable normal variation across healthy individuals, and these values should act as guides rather than rigid criteria.[3]
Vertical position: The superior angle aligns with T2, and the inferior angle aligns with T7.[4]
Horizontal position: The medial border sits approximately 8–10 cm from the spinous processes. Larger individuals tend toward 10 cm; smaller individuals toward 8 cm. In children or very small individuals, this distance may be around 6 cm or less.[4]
Rotation in the transverse plane: The scapula rests in approximately 30 degrees of internal rotation. This is known as the scapular plane, and it is the plane in which the glenohumeral joint functions most efficiently.[4]
Upward rotation: At rest, the scapula sits in around 5 degrees of upward rotation, so the inferior angle lies slightly lateral to the superior angle.[4]
Sagittal plane tilt: the scapula rests in approximately 10 degrees of anterior tilt, meaning the superior aspect tips slightly forward. Anterior tilt beyond this range may be clinically significant.[4]
A systematic review with meta-regression by Fernández-Matías et al. highlights individual variation in scapular resting position. They found that across healthy individuals, upward rotation at rest ranged from 1° to almost 12°, anterior tilt from under 5° to over 11°, and internal rotation from approximately 27° to 39°, depending on the measurement method used.[3]
Scapular Movements
The scapula moves across three planes (frontal, transverse and sagittal) and produces five distinct motions: upward and downward rotation, elevation and depression, abduction and adduction, internal and external rotation, and anterior and posterior tilt.
Frontal Plane
Upward and downward rotation: The scapula rotates around an axis perpendicular to its surface. During arm elevation, the inferior angle moves laterally, and the glenoid fossa faces upward, creating upward rotation. Upward rotation during arm elevation varies in response to the demands placed on the shoulder.[5] Downward rotation returns the scapula to its resting position as the arm lowers.
Elevation and depression: The scapula moves superiorly (elevation) or inferiorly (depression) along the thorax. Scapula elevation occurs with shoulder shrugging; depression is the reverse motion.
Abduction (protraction) and adduction (retraction): the scapula moves laterally around the rib cage (abduction) or back toward the midline (adduction).
Transverse Plane
Internal and external rotation: the scapula rotates around a vertical axis. In internal rotation, the medial border moves away from the spine. In external rotation, the medial border sits closer to the spine.
Clinical note: the resting position already involves 30 degrees of internal rotation, so further internal rotation takes the scapula beyond that baseline.
Sagittal Plane
Anterior and posterior tilt: the scapula tips forward (anterior tilt) or backward (posterior tilt) in the sagittal plane. Posterior tilt is required during arm elevation.
Key Muscles of the Scapula
The following sections outline the key muscles that contribute to scapular movement.
Note that this is not an exhaustive list; the focus here is on the muscles that clinicians most commonly assess and treat.[4]
Upward rotation is produced by a force couple—two or more forces acting together to produce rotation.[4] Upper trapezius pulls the acromion superiorly and laterally; lower trapezius pulls the scapula inferiorly and medially; and serratus anterior wraps around the lateral thorax and pulls the inferior angle anteriorly and laterally, driving upward rotation.[4] Each muscle must contribute proportionally for efficient movement. If one muscle dominates or underperforms, the scapulohumeral rhythm can be altered.
Downward rotation is driven primarily by the rhomboids, which pull the medial border of the scapula toward the spine, and levator scapulae, which pulls the superior angle upward.[4]
Elevation is produced by the upper trapezius and levator scapulae.[4] Depression is driven by the lower trapezius and latissimus dorsi.[4]
Abduction involves pectoralis minor, which originates at ribs three to five and inserts into the coracoid process and pectoralis major, which exerts its influence via the humerus.[4]
Adduction is driven by the rhomboids and middle trapezius, which both pull the medial border of the scapula toward the spine.[4]
Internal and external rotation can be understood when we consider how muscles that typically rotate the humerus in an open chain can instead move the scapula when the arm is fixed (closed chain).[4] Subscapularis is an internal rotator of the humerus. When the arm is fixed, subscapularis pulls the scapula into external rotation. Infraspinatus is an external rotator of the humerus. With a fixed arm, infraspinatus pulls the scapula into internal rotation. Pectoralis minor also contributes to internal rotation. Even at rest, the weight of the arm is sufficient to create a fixed-arm effect, allowing these muscles to influence scapular position.
Pectoralis minor is the primary driver of anterior tilt. When it shortens or becomes hypertonic, it tips the top of the scapula forward and lifts the inferior angle away from the thorax. This is one of the most common passive restrictions at the shoulder.[4] Excessive posterior tilt is less common and is typically the result of postural overcorrection rather than a specific muscle imbalance.[4]
This optional video discusses scapular movements and the muscles associated with them.
Scapulohumeral Rhythm
Scapulohumeral rhythm describes the coordinated movement between the humerus and the scapula during arm elevation. It is often simplified to a 2:1 ratio of glenohumeral elevation to scapular upward rotation. While this ratio has been used as a benchmark for normal versus pathological movement, it is not a fixed constant. The rhythm is complex and nonlinear, and factors such as the speed of arm elevation and the weight of the object being lifted can influence it.[7] Clinicians should treat the scapulohumeral relationship as a variable that exists within a wide normal range.[3]
Scapulothoracic Dyskinesis
Scapular dyskinesis refers to an abnormal resting position or movement pattern of the scapula during motion. It can manifest as excessive movement, asymmetry, or "winging" of the scapula.[8][9] Scapular dyskinesis is rarely a primary, isolated condition; it typically occurs as a secondary consequence of underlying shoulder and upper quadrant pathologies, such as acromioclavicular joint injury, rotator cuff pathology, impingement syndrome, or labral injury (e.g., SLAP lesions).[8]
The Scapular Dyskinesis Test (SDT) is a commonly used observational tool that classifies scapular movement during shoulder elevation using either a "Yes/No" classification or a three-level rating (none, subtle, obvious). However, both methods have demonstrated only moderate reliability, sensitivity and interrater agreement, so the SDT should not be the sole determinant in clinical decisions.[10]
Scapula Assessment Clinical Reasoning
Scapular assessment is about understanding what restricts normal motion, what drives compensatory patterns, and whether the issue lies in mobility, motor control, strength, or the thorax beneath the scapula.[4]
The clinical assessment follows a sequence where each step informs the next: (1) resting position, (2) passive mobility, (3) active motion and observation for dyskinesia, and (4) strength testing. This sequence matters because findings at each stage provide context for what follows—for example, a muscle may appear weak during strength testing, but this may reflect a passive mobility limitation rather than a true strength deficit. When planning treatment, passive restrictions should be addressed before motor control and strengthening work can be fully effective.[4]
Resources
- Reliability of Clinical Assessment Methods to Measure Scapular Upward Rotation: A Critically Appraised Topic
- Innovative diagnostic framework for shoulder instability: a narrative review on machine learning-enhanced scapular dyskinesis assessment in sports injuries
- Scapula
References
- ↑ Kebaetse M, McClure P, Pratt NA. Thoracic position effect on shoulder range of motion, strength, and three-dimensional scapular kinematics. Arch Phys Med Rehabil. 1999 Aug;80(8):945-50.
- ↑ Yabata K, Fukui T. Characteristics of the scapula movement during shoulder elevation depend on posture. J Phys Ther Sci. 2022 Jul;34(7):478-484.
- ↑ 3.0 3.1 3.2 Fernández-Matías R, Ballesteros-Frutos J, Gallardo-Zamora P, Requejo-Salinas N, Caballero-Pozo I, Ludewig P, Lluch-Girbés E. Scapular kinematics variability in individuals with and without rotator cuff-related shoulder pain: A systematic review with multilevel meta-regression. Braz J Phys Ther. 2025 Nov-Dec;29(6):101261.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 Kaplan A. Scapula Evaluation in Shoulder Clinical Reasoning Course. Physiopedia Plus, 2026.
- ↑ Lee EC, Young NM, Lawrence RL, Rainbow MJ. Scapular kinematics and task specificity: The effect of load direction. Journal of Biomechanics. 2025 Aug 27:112932.
- ↑ Dr Matt & Dr Mike. Scapula Movement | Functional Anatomy. Available from: https://www.youtube.com/watch?PPKlGlwxr5s [last accessed 4/3/2026]
- ↑ Cho H, Hur S, Kim J, Kim K, Park J. Shoulder range of motion rehabilitation robot incorporating scapulohumeral rhythm for frozen shoulder. Journal of Bionic Engineering. 2025 Sep;22(5):2456-73.
- ↑ 8.0 8.1 Jildeh TR, Ference DA, Abbas MJ, Jiang EX, Okoroha KR. Scapulothoracic Dyskinesis: A Concept Review. Curr Rev Musculoskelet Med. 2021 Jun;14(3):246-254.
- ↑ Wen M, Hu X, Bao G. Scapular dyskinesis-based exercise therapy versus multimodal physical therapy for subacromial impingement syndrome in young overhead athletes with scapular dyskinesis: a randomized controlled trial. BMC Sports Science, Medicine and Rehabilitation. 2025 Jul 16;17(1):204.
- ↑ Vila-Dieguez O, Cazorla-Rey A, Michener LA. Clinicians who think scapular dyskinesis is important are more likely to identify it in healthy individuals. Shoulder & Elbow. 2026 Feb 23:17585732261424438.