Scoliosis is an abnormal, sideways curvature of the spine that causes the vertebral column to look more like an “S” or a “C” shape when viewed from the back. This condition is broadly categorized into two major types: structural scoliosis, where the spine itself has a fixed deformity, and functional scoliosis, which is a temporary, non-fixed curve. Understanding the distinction between these two forms is important because it dictates the appropriate clinical approach and outlook.
Defining Functional Scoliosis
Functional scoliosis, also known as non-structural scoliosis, is a temporary lateral curve of the spine that occurs without any underlying bony deformity in the vertebrae. The spine itself is structurally typical, meaning the bones are properly formed and aligned. This type of curve is compensatory, developing as the body attempts to maintain an upright posture and keep the head centered over the pelvis. The defining characteristic is that the spinal curvature is flexible and can be corrected or reduced by a change in body position. For instance, the curve will often disappear completely when a person lies down or hangs freely.
Key Differences from Structural Scoliosis
The most significant factor distinguishing a functional curve from a structural curve is the presence of vertebral rotation. True structural scoliosis is a three-dimensional deformity involving a side-to-side curve, a forward or backward curve, and a rotational twist of the vertebrae. This rotation is what causes the rib cage or back muscles to visibly protrude on one side, often creating a “rib hump.”
In contrast, functional scoliosis is a simple two-dimensional bend without this rotational component. The lack of fixed vertebral rotation means the curve is not progressive and does not cause the permanent, fixed spinal changes associated with the structural type. Clinicians often use the Adam’s forward bend test to differentiate the two conditions. During this examination, a person bends forward at the waist. A fixed structural curve will remain visible, often showing the rib hump, but a functional curve will typically flatten out or disappear entirely. Furthermore, structural scoliosis is diagnosed when the curve measures 10 degrees or more using the Cobb angle measurement on an X-ray. Functional curves are generally milder and may not meet this minimum diagnostic threshold.
Common Underlying Causes
The appearance of a functional curve is a symptom, not the root problem, as it is caused by an imbalance or irregularity originating outside of the spine itself. The body creates the curve as a mechanism to balance the torso over an uneven foundation.
Leg Length Discrepancy
A frequent cause is a leg length discrepancy, where one leg is measurably shorter than the other. This difference causes the pelvis to tilt, and the spine must then curve upward to level the shoulders and keep the head aligned.
Muscle Spasm or Pain
Another common reason is the presence of muscle spasm or pain, sometimes referred to as sciatic scoliosis. When a person experiences significant pain from a herniated disc or nerve root irritation, the surrounding muscles in the back will often tighten severely on one side. This protective spasm pulls the spine into a sideways tilt to minimize nerve compression and reduce discomfort.
Poor Postural Habits
Poor postural habits can also contribute to a functional curve, such as habitually standing with weight shifted heavily onto one leg or consistently carrying a heavy bag on the same shoulder. These prolonged asymmetrical postures lead to muscle imbalances that temporarily pull the spine out of alignment.
Diagnosis and Resolution
Diagnosing functional scoliosis begins with a thorough physical examination and observation of the patient’s posture and movement. The physician will look for signs of asymmetry, such as uneven shoulders or hips, and confirm the flexibility of the curve using positional changes like the Adam’s test. Imaging studies, particularly X-rays, are instrumental in confirming the diagnosis and ruling out a structural issue.
A physician may take X-rays while the patient is standing, which shows the curve at its maximum, and then while the patient is lying down (supine). If the curve significantly decreases or vanishes when the patient is supine, it confirms the non-structural, flexible nature of the condition. Treatment for functional scoliosis is entirely focused on identifying and eliminating the underlying cause, not on treating the spinal curve directly. This typically involves non-invasive methods, such as custom shoe inserts or orthotics to correct a leg length discrepancy. Physical therapy is often utilized to address muscle spasms, strengthen weakened postural muscles, and correct poor movement patterns. Since the spine is structurally sound, conservative treatments that resolve the primary imbalance are usually sufficient to allow the spine to return to a typical alignment.