Scoliosis is a general term describing a sideways curvature of the spine, where the vertebral column deviates from its normal, straight alignment. While many people associate the condition with a fixed, bony deformity, not all spinal curves are permanent or structural in nature. A significant distinction exists between a true, or structural, scoliosis and a functional scoliosis, which is a temporary and reversible misalignment. Understanding this difference is important because it changes the entire approach to diagnosis and treatment. Functional scoliosis is not a disease of the spine itself but rather a physical manifestation of an underlying issue elsewhere in the body.
Defining Functional Scoliosis
Functional scoliosis presents as an abnormal sideways curve in the spine without any fixed deformity in the vertebrae. This type of curvature is a compensation mechanism, where the body shifts the spine to maintain balance or avoid pain. For a curve to be considered functional, it must typically measure less than 10 degrees on an X-ray, which is the minimum threshold for a structural scoliosis diagnosis.
A defining characteristic is that the curve disappears or significantly reduces when the patient changes position, such as when they lie down or hang freely. Because the condition is not rooted in a bony abnormality, it does not involve the vertebral rotation typical of structural curves. This lack of rotational component means the spine only bends laterally, without the twisting that causes rib cage or back asymmetry.
Structural vs. Functional Key Differences
The primary distinction between functional and structural scoliosis lies in the flexibility and underlying cause of the curve. Structural scoliosis involves a fixed, three-dimensional deformity where the vertebrae are rotated and permanently wedged, making the curve uncorrectable by simple repositioning. This fixed rotation is why structural curves cause a noticeable rib hump or prominence on one side of the back, which is clearly visible during the Adam’s forward bend test.
In contrast, a functional curve is non-fixed and will resolve when the underlying issue is temporarily removed or the person bends forward, as the spine’s flexibility remains intact. Functional curves generally lack this rotational element, meaning the Adam’s test will not reveal a prominent rib hump. Doctors often use physical maneuvering, such as having the patient lie down or putting a block under one foot, to determine if the curve is flexible and therefore functional. If the curve straightens out when the spine is relaxed or the body is leveled, it points toward a functional diagnosis.
Structural scoliosis, particularly the most common type, adolescent idiopathic scoliosis, is often progressive, meaning the curve can worsen over time, especially during growth spurts. Functional scoliosis is non-progressive; the curve will not increase in severity as long as the underlying cause remains stable.
Common Underlying Causes
Functional scoliosis develops in response to an asymmetry or pain outside the spine. One of the most frequent causes is a leg length discrepancy (LLD), where one leg is measurably shorter than the other. This difference forces the pelvis to tilt, which the spine compensates for by curving laterally to keep the head centered over the pelvis. LLD commonly results in a lumbar curve that bulges outward toward the shorter limb.
Another common trigger is severe, unilateral back pain or muscle spasms caused by injury or inflammation. When a person experiences intense pain on one side, the surrounding muscles often tighten dramatically in a protective response known as muscle guarding. This sustained, uneven muscle contraction pulls the spine out of alignment, creating a temporary curve that reduces stress on the injured area. Poor postural habits, such as habitually leaning on one leg while standing, can also contribute to a functional curve by creating chronic muscular imbalance.
Addressing the Root Cause
The management of functional scoliosis focuses on identifying and correcting the non-spinal issue that is causing the compensatory curve. For curves caused by a measurable leg length discrepancy, treatment involves the use of a shoe insert or heel lift. Placing an orthotic under the shorter leg effectively levels the pelvis, which then allows the spine to naturally realign and straighten.
If the curve is a result of muscle spasms or acute pain, treatment will involve physical therapy, targeted stretching, and pain management techniques. A physical therapist can create a custom program of exercises to address muscle imbalances, strengthen core support, and encourage the spine to return to its normal position. Functional scoliosis has a positive outlook, as the curve typically resolves completely once the root cause is successfully treated.