A dropped shoulder, or shoulder asymmetry, occurs when one shoulder girdle sits noticeably lower than the other. This uneven appearance signifies an imbalance in the muscular and skeletal structures supporting the upper torso. The shoulder girdle, composed of the clavicle and the scapula, must be level for optimal movement and posture. While slight asymmetry is common, a pronounced difference can lead to muscle strain, discomfort, and altered movement patterns over time. This postural deviation is often treatable once the root cause of the imbalance is properly identified.
Habitual and Occupational Posture
Daily repetitive actions, such as consistently carrying a heavy bag, purse, or backpack strap on the same shoulder, are a frequent source of shoulder height disparity. This forces the muscles on that side to contract continually, leading to the elevation of one shoulder and a corresponding shortening of the neck and shoulder muscles. The constant, uneven load alters the resting position of the scapula over time.
Occupational habits, particularly seated desk work, also contribute significantly. Poor computer ergonomics, such as resting an elbow too low or high, can encourage a sustained side-bend or slouch. Cradling a phone between the ear and shoulder causes immediate lateral flexion of the neck and a lift of the corresponding shoulder. When maintained for hours each day, these asymmetrical postures reinforce muscle memory that favors uneven alignment.
Prolonged standing or sitting with weight shifted heavily to one side can also impact upper body alignment. This lower-body compensation causes a pelvic tilt, which propagates upward through the spine to affect the shoulder line. Any activity that repeatedly causes an uneven distribution of weight trains the body into a state of asymmetry. Correcting these modifiable habits is often the first step in addressing a dropped shoulder.
Muscular Imbalance and Weakness
Maintaining a level shoulder line relies on the coordinated effort and balanced strength of muscle groups attached to the scapula and spine. A dropped shoulder often indicates a deficiency in the muscles responsible for elevating and stabilizing the shoulder girdle. The upper trapezius, levator scapulae, and rhomboids are the primary muscles that hold the scapula high and close to the spine.
If the shoulder elevators are weak or inhibited, the shoulder will naturally drop under the weight of the arm. Conversely, the dropped position can be caused by over-tightness in the opposing muscles, known as the depressors. Depressor muscles include the lower trapezius, pectoralis minor, and latissimus dorsi, which pull the shoulder blade downward and forward. An imbalance occurs when depressors become chronically shortened, pulling one shoulder down, while the elevators on the opposite side become overstretched and weak.
Chronic bad posture directly leads to specific muscular deficiencies by altering the muscle length-tension relationship. For example, a forward-head and rounded-shoulder posture lengthens and weakens the middle and lower fibers of the trapezius. The serratus anterior, a muscle that anchors the scapula to the rib cage, is important for shoulder stability and proper movement rhythm. Dysfunction in this muscle can lead to the scapula winging or tipping, which contributes to an uneven shoulder profile.
Underlying Structural Conditions
In cases where the dropped shoulder is not solely attributable to posture or muscular habit, the cause may lie in underlying structural or skeletal conditions. A significant contributor is scoliosis, which is an abnormal, sideways curvature of the spine. Since the shoulder girdle rests upon the rib cage and spine, a spinal curve in the thoracic region directly tilts the base upon which the shoulders sit, making one shoulder appear lower than the other. This type of asymmetry is a symptom of the underlying vertebral misalignment.
Another common structural factor is a leg length discrepancy (LLD), where one leg is physically shorter than the other, either anatomically or functionally. An LLD can be caused by bones of different lengths or by functional issues like a pelvic imbalance. Even a small difference forces the pelvis to tilt on the short side, initiating a kinetic chain compensation that travels up the body. The resulting pelvic tilt and subsequent compensatory spinal curve can cause a noticeable difference in shoulder height.
Past injuries to the shoulder joint or collarbone can also result in permanent asymmetry. A clavicle fracture or an acromioclavicular (AC) joint separation that healed improperly may leave the affected side structurally lower or with altered joint mechanics. Congenital bone structure variations, though less common, can cause the shoulder blade or collarbone to be naturally positioned differently on one side. These structural causes require a medical diagnosis to differentiate them from postural and muscular imbalances.