What is Kyphosis?
Kyphosis is an abnormal, dorsally convex (posterior) curvature of the spine in the sagittal plane, most commonly affecting the thoracic region 1, 2.
Definition and Normal vs. Pathological Curvature
While the spine naturally has some posterior curvature in the thoracic region, pathological thoracic kyphosis is defined as a Cobb angle greater than 50 degrees 2. This represents an excessive rounding of the back beyond the normal physiological curve.
The term describes a three-dimensional structural deformity where:
- The spine curves excessively backward (posteriorly)
- Vertebral bodies may become wedge-shaped at one or multiple levels
- The deformity shifts the center of gravity forward, increasing flexion-bending moments on the spine 2
Common Types and Etiologies
Kyphosis develops through multiple mechanisms 1:
Scheuermann's Kyphosis is the most well-defined structural form, characterized by:
- Three or more contiguous vertebrae with at least 5 degrees of anterior wedging 3, 4
- Rigid structural deformity developing before puberty and worsening during adolescence 5
- Prevalence between 0.4% to 10% 3
Other causes include:
- Congenital developmental anomalies
- Post-traumatic deformity
- Degenerative disc disease
- Infectious diseases (e.g., tuberculosis) 6
- Iatrogenic (post-laminectomy kyphosis)
- Neuromuscular conditions
- Tumor-related 1
Clinical Significance
The main concerns with kyphosis are:
- Cosmetic deformity (primary concern in adolescents) 4
- Back pain (main complaint in adults) 4
- Sagittal imbalance affecting posture and gait
- In severe cases: neurological compromise, cardiopulmonary restriction 3
Positive sagittal balance from kyphosis is particularly difficult to compensate, unlike negative sagittal balance which can be offset through hip flexion 1.