The human spine features a gentle, natural S-shape when viewed from the side, consisting of distinct curves that help the body absorb shock and maintain balance. The cervical spine (neck) and the lumbar spine (lower back) curve inward, while the thoracic spine (mid-back) curves outward. Scoliosis represents a deviation from this structure, defined as an abnormal side-to-side curvature and rotation of the vertebrae, often forming a C- or S-shape. Its most defining feature is the lateral, or sideways, bend.
Kyphosis Defining the Outward Curve
The condition most often considered the directional opposite of scoliosis’s lateral curve is kyphosis, which involves an excessive forward or outward curvature. While a degree of outward curve is normal in the thoracic spine, an exaggeration beyond the typical 20 to 45 degrees is classified as hyperkyphosis, or simply kyphosis. This excessive curve causes the upper back to appear abnormally rounded, leading to the common term “hunchback” or “roundback.” The deformity is situated in the sagittal plane, meaning it is viewed from the side of the body. A medical diagnosis for kyphosis is typically given when the curvature measures 50 degrees or greater on an X-ray. Postural kyphosis, which is often flexible and reversible, is the most common form, developing from persistent slouching during adolescence.
Lordosis Defining the Inward Curve
Lordosis represents another form of exaggerated spinal curvature, defined as an excessive concave, or inward, curve. When this inward curve becomes overemphasized, the condition is termed hyperlordosis, commonly known as “swayback.” This excessive anterior curvature is also assessed in the sagittal plane, like kyphosis. Hyperlordosis most commonly affects the lumbar spine in the lower back, though it can also occur in the neck as cervical lordosis. The primary visual manifestation of excessive lumbar lordosis is an exaggerated arch in the lower back, causing the pelvis to tilt forward. Individuals with severe lumbar lordosis may find it difficult or impossible to flatten their lower back against the floor when lying down.
How the Curvatures Differ
The key distinction between these three spinal conditions lies in the direction of the abnormal bend relative to the body’s three planes of movement. Scoliosis is uniquely defined by its lateral deviation, meaning the spine curves sideways in the coronal plane. The presence of vertebral rotation is also a defining feature of true scoliosis, making it a complex, three-dimensional deformity. Kyphosis and Lordosis, by contrast, are conditions defined by excessive curvature in the sagittal plane. Kyphosis is an excessive curve that projects outward (posteriorly or convexly), giving the rounded-back appearance, while Lordosis projects inward (anteriorly or concavely), creating the hollow-back or swayback posture.
Causes and Treatment Options
The causes for kyphosis and lordosis are varied, often falling into categories like postural, congenital, or disease-related. Postural issues, such as chronic slouching or weak abdominal muscles, are a common source of both conditions, especially in adolescents. Structural causes include underlying diseases like osteoporosis, which can lead to vertebral compression fractures, or Scheuermann’s disease, which causes wedging of the vertebrae in the mid-back. Neuromuscular conditions, such as cerebral palsy or muscular dystrophy, can also contribute to either excessive curve.
Treatment for mild to moderate cases begins with non-surgical interventions focused on strengthening and flexibility. Physical therapy is often prescribed to build core and back muscles to better support the spine and improve posture. Growing children with moderate structural curves may be treated with a spinal brace to prevent the curve from progressing further. Surgical intervention is generally reserved for severe cases where the curvature is significantly impacting daily function, causing neurological symptoms, or progressing rapidly past a certain degree threshold, often exceeding 70 to 75 degrees.