Adult Spinal Deformity

Overview

Adult spinal deformity (ASD) is a broad term for structural malalignments of the thoracolumbar spine in skeletally mature patients. It encompasses degenerative (de novo) scoliosis, a spinal curve that develops in adulthood, as well as adult progression of adolescent idiopathic scoliosis and primary sagittal plane imbalance, such as flatback deformity or degenerative kyphosis. In each case, the normal architecture of the spine in both the coronal (side-to-side) and sagittal (front-to-back) planes is disrupted, often with real consequences for how a person moves and functions.

The condition becomes more common with age. Some community studies have found radiographic evidence of spinal deformity in the majority of adults over sixty when sensitive imaging criteria are applied. Women are affected more often than men, in part because postmenopausal osteoporosis contributes to vertebral wedging and progressive collapse.

What causes it

Most adult spinal deformity arises from asymmetric degeneration of the intervertebral discs and facet joints. As discs lose height and joints wear unevenly, the affected segments wedge, rotate, and shift sideways, a combination called rotatory subluxation and lateral listhesis. As this process advances, the spinal canal and nerve exit openings (foramina) can narrow, producing central canal stenosis and foraminal stenosis with nerve compression.

A central event in many patients is the loss of normal lumbar lordosis, the inward curve of the lower back. When that curve flattens, the body recruits compensatory strategies to keep the head upright and the gaze horizontal: tilting the pelvis backward, bending the knees, and reducing the thoracic kyphosis. Over time these compensations become fatiguing and painful.

Key risk factors include advancing age, low bone mineral density (osteoporosis), obesity, prior spine surgery that leaves residual sagittal imbalance, a history of adolescent idiopathic scoliosis that progresses in adulthood, genetic predisposition, and deconditioning of the core and paraspinal muscles.

Symptoms and warning signs

Patients typically describe axial back pain and a sense of leaning forward or to one side that worsens over the course of the day and with prolonged standing or walking. Nerve compression in the affected segments frequently produces lumbar radiculopathy: dermatomal pain, numbness, or tingling radiating into the buttock or leg. Neurogenic claudication is also common: buttock and leg discomfort brought on by upright walking and relieved by sitting down or bending forward.

On examination, there may be a visible trunk shift or a rib or lumbar prominence on forward bending, reduced lumbar lordosis, and, in more advanced cases, the head positioned noticeably in front of the pelvis with compensatory hip and knee flexion.

Several features demand prompt evaluation. A progressive motor deficit in the legs, saddle anesthesia (numbness in the groin or inner thighs), or loss of bowel or bladder control may indicate cauda equina syndrome, which requires urgent assessment. Constitutional symptoms (fever, night sweats, or unexplained weight loss) along with unrelenting night pain should raise concern for spinal infection or malignancy rather than degenerative deformity.

How it's diagnosed

Diagnosis begins with a thorough history and physical examination, then is confirmed and quantified with imaging. Full-length standing radiographs, posteroanterior and lateral 36-inch films taken under physiologic load, are the cornerstone of assessment. They allow measurement of coronal Cobb angles, sagittal vertical axis, pelvic incidence, pelvic tilt, sacral slope, and lumbar lordosis. The mismatch between pelvic incidence and lumbar lordosis is a particularly important predictor of functional disability.

MRI is the preferred study for evaluating central canal stenosis, foraminal stenosis, and nerve-root compression, and for excluding tumor or infection when red flags are present. CT, sometimes combined with myelography for patients who cannot have an MRI, provides finer bony detail and aids surgical planning. Bone density testing is important given how often osteoporosis contributes to the deformity. Laboratory studies are ordered when infection or malignancy is suspected.

Because radiographic deformity is common and frequently produces no symptoms, imaging findings must always be interpreted in light of the patient's actual complaints. Hip osteoarthritis and sacroiliac joint pain are important mimics that can reproduce buttock and groin pain; a careful physical examination helps distinguish these articular sources from a primary spinal generator.

Treatment options

Care typically begins with a structured conservative program. Physical therapy focused on core and gluteal strengthening, postural re-education, activity modification, and weight management forms the foundation. Optimizing bone health (with attention to calcium, vitamin D, and pharmacologic treatment of osteoporosis when indicated) is also an important component. Analgesics and anti-inflammatory medications can provide symptomatic relief. For patients whose pain is predominantly radicular, image-guided epidural steroid injections or selective nerve root blocks may offer meaningful benefit. Judicious bracing can also play a supporting role in selected patients.

When surgery is considered

Surgery is considered for carefully selected patients with persistent disabling pain, progressive deformity, significant sagittal imbalance, or neurologic deficit that has not improved with appropriate non-operative care. It becomes more urgent in the setting of a progressive motor deficit or signs of cauda equina syndrome.

Operative options range from limited decompression for focal stenosis to more extensive procedures that combine decompression with posterior instrumented fusion, interbody fusion, and osteotomies designed to restore lordosis and global spinal alignment. Surgical decision-making is guided by alignment goals, bone quality, and the patient's overall health status, carefully weighing the potential gains in pain relief and function against the meaningful perioperative risks, a particularly important consideration in older patients with osteoporosis or medical comorbidities.