Adult Degenerative Scoliosis and Sagittal Balance: Modern Surgical Correction for Complex Spinal Deformity

Unlike adolescent idiopathic scoliosis, which develops primarily during the pubertal growth spurt in an otherwise healthy skeleton, Adult Degenerative Scoliosis (ADS)—also termed de novo scoliosis—arises later in life as a consequence of asymmetric disc degeneration, facet joint arthrosis, and progressive osteoporosis. As intervertebral discs collapse unevenly, the structural foundation of the lumbar spine destabilizes, producing rotatory subluxation, lateral listhesis (slipping), and coronal curvature.

However, modern spinal deformity research has confirmed a critical clinical truth: the lateral (coronal) curve is rarely the primary driver of disability. Instead, patient-reported pain, chronic fatigue, and functional limitations correlate directly with the loss of sagittal balance—the forward pitch of the trunk that occurs when natural lumbar lordosis collapses. Patients find themselves expending immense muscular energy simply to maintain an upright horizontal gaze, leading to chronic paraspinal muscle exhaustion, severe neurogenic claudication, and progressive loss of independent ambulation.

Historically, correcting complex adult spinal deformities required extensive, open, multi-level osteotomies through broad posterior incisions, which carried high blood loss, substantial infection rates, and high pseudarthrosis risk. Today, advanced spinopelvic parameter alignment, computer-guided robotic navigation, and hybrid minimally invasive surgical (cMIS) techniques have redefined deformity correction.

In South Florida, Dr. Evan Trapana is a fellowship-trained orthopedic spine surgeon and Assistant Professor of Orthopaedic Spine Surgery at the University of Miami Miller School of Medicine and UHealth Tower. Having completed his orthopedic surgery residency at the University of Miami/Jackson Memorial Hospital and advanced spine surgery fellowship training at the University of California San Diego (UCSD) Medical Center, Dr. Trapana specializes in complex spinal deformity, robotic reconstruction, and motion-sparing realignments. Through precise spinopelvic planning and tailored corrective osteotomies, Dr. Trapana reconstructs global spinal balance to relieve mechanical pain, decompress nerve roots, and restore upright posture.

The Biomechanics of Sagittal Balance: The Spinopelvic Parameters

Evaluating adult spinal deformity begins not with localized lumbar X-rays, but with full-length, 36-inch standing radiographs capturing the entire skeletal axis from the skull to the femoral heads. Spinal balance is governed by a tightly coupled geometric relationship between the spine and the pelvis:

┌──► 1. Pelvic Incidence (PI)

│ ──► Fixed anatomical angle of pelvic morphology (does not change)

│

[SPINOPELVIC BALANCE PARAMETERS] ─┼──► 2. Pelvic Tilt (PT)

│ ──► Compensatory retroversion/rotation of the pelvis (Target < 20°)

│

└──► 3. Lumbar Lordosis (LL)

──► Inward inward curve matching the pelvis: Target LL = PI ± 10°

[DEGENERATIVE DISC & FACET COLLAPSE]

│

▼

[LOSS OF LUMBAR LORDOSIS (Flatback Deformity)]

│

▼

[SAGITTAL VERTICAL AXIS (SVA) SHIFTS FORWARD (> 5 cm)]

(The C7 plumb line falls far in front of the posterior superior sacral margin)

│

▼

[COMPENSATORY FATIGUE MECHANISMS]

(Pelvic retroversion [High PT], knee flexion, thoracic hypokyphosis ──► Severe Muscular Exhaustion)

1. Pelvic Incidence (PI): A fixed morphological measurement unique to each individual that dictates how much lumbar curvature is required to remain balanced.
2. The Schwab-SRS Alignment Targets: To achieve a durable, pain-free reconstruction, surgical planning must satisfy three foundational alignment rules:
   • $LL = PI \pm 10^\circ$: Lumbar lordosis must be proportional to the patient’s individual pelvic incidence.
   • Sagittal Vertical Axis (SVA) $< 5\text{ cm}$: The C7 plumb line (a vertical line dropped from the center of the C7 vertebral body) must land within 5 centimeters of the postero-superior corner of the S1 sacral endplate.
   • Pelvic Tilt (PT) $< 20^\circ$: Correcting lumbar alignment allows the pelvis to roll forward out of retroversion, relaxing strained hamstring and hip extensor muscles.

Pathoanatomy: The Dual Challenge of Deformity and Stenosis

Adult degenerative scoliosis is rarely a purely cosmetic or structural issue—it is almost always complicated by debilitating neurological compression:

[ASYMMETRIC DISC COLLAPSE & ROTATORY SUBLUXATION]

│

┌────────────────┴────────────────┐

▼ ▼

[CONCAVE APEX COMPRESSION] [CONVEX TRACTION RADICULOPATHY]

(Bone spurs & asymmetric disc (Exiting nerve roots stretched over

telescope into foramen ──► the structural apex of the curve)

Severe foraminal stenosis)

• Concavity Stenosis: On the inside (concave) curve of the scoliosis, the collapsed disc and hypertrophied facet joints collapse directly into the neuroforamen, causing severe, localized nerve root pinching and radiculopathy.
• Convexity Traction: On the outer (convex) curve, the exiting spinal nerves are stretched over the apex of the deformity.
• Central Canal Squeeze: Rotational listhesis (where one vertebra twists and slips laterally off the one below) produces multi-level spinal stenosis and neurogenic claudication.

Modern Surgical Correction Strategies: The Hybrid Minimally Invasive (cMIS) Approach

Rather than relying solely on high-morbidity open posterior approaches, Dr. Trapana frequently utilizes circumferential minimally invasive surgery (cMIS) or hybrid reconstructive protocols to minimize surgical trauma while achieving global alignment:

[STAGE 1: LATERAL ANTERIOR RECONSTRUCTION (LLIF / ALIF)]

(Multi-level lateral disc access spares posterior muscle, releases rigid curves, & restores lordosis)

│

▼

[STAGE 2: PERCUTANEOUS ROBOTIC POSTERIOR FIXATION]

(Sub-millimeter pedicle screw navigation across deformity curves through keyhole portals)

│

▼

[STAGE 3: TARGETED POSTERIOR OSTEOTOMIES (As Needed for Rigid Curves)]

(Schwab Grade 1/2 facetectomies to close posterior columns and lock in sagittal balance)

1. Anterior/Lateral Realignment (LLIF / XLIF / ALIF)

Through small retroperitoneal flank incisions, large lordotic interbody spacers are placed across the collapsed apex levels.

• Coronal and Sagittal Correction: These cages reconstruct disc height, restore lordosis, and uncoil the lateral rotatory subluxation through ligamentotaxis.
• Indirect Decompression: Restoring intervertebral disc height expands narrowed neuroforamina, relieving radicular nerve compression without requiring extensive bone drilling around the thecal sac.

2. Posterior Column Osteotomies (PCO / Ponte Osteotomies)

In stiff, fixed adult deformities, releasing anterior discs alone may not provide adequate lordosis. Through targeted posterior releases, the facet joints, ligamentum flavum, and spinous processes are excised across multiple levels (Schwab Grade 1 and 2 osteotomies). When the spine is subsequently extended and secured to contoured rods, the posterior gaps close, producing 5 to 10 degrees of additional segmental lordosis per level.

3. Robotic-Assisted Stereotactic Instrumentation

Scoliotic anatomy features dysplastic, rotated, and hypoplastic pedicles that challenge conventional freehand instrumentation. Dr. Trapana employs real-time 3D navigation and robotic stereotaxy to guide pedicle screws through small portals with sub-millimeter precision, protecting neurological structures and ensuring stable anchor purchase across poor-quality osteoporotic bone.

Comparative Overview: Traditional Open Correction vs. Modern Hybrid cMIS Deformity Surgery

Pelvic Fixation and Preventing Complications

When adult deformity corrections extend down into the lower lumbar spine, ending a fusion construct at L5 carries an unacceptably high rate of mechanical failure, pseudarthrosis, and subsequent L5–S1 disc collapse.

• Spinopelvic Anchoring (S2-Alar-Iliac [S2AI] Screws): In long reconstructive constructs spanning from the lower thoracic spine (e.g., T10) down to the sacrum, Dr. Trapana anchors the hardware into the ilium using low-profile S2AI screws. These screws cross the dense cortical bone of the sacroiliac joint, providing a rigid anchor that shields the L5–S1 junction from massive cantilever forces.
• Preventing Proximal Junctional Kyphosis (PJK): A primary long-term challenge in adult deformity surgery is PJK—where the vertebrae immediately above the fusion construct collapse or fracture. Dr. Trapana mitigates this risk through precise preoperative spinopelvic planning (avoiding over-correction), utilizing transition rods, and placing soft-tissue tethering bands at the upper-instrumented vertebra (UIV).

Conclusion

Adult Degenerative Scoliosis and loss of sagittal balance are complex structural disorders that do not have to result in permanent spinal hunching, debilitating claudication, or chronic pain. Through modern spinopelvic parameter alignment, minimally invasive lateral releases, and robotic-assisted navigation, Dr. Evan Trapana provides patients with comprehensive reconstructive solutions designed to restore global balance, decompress nerves, and return patients to an active, upright life.

• Surgeon: Dr. Evan Trapana, MD
• Academic Role: Assistant Professor of Orthopaedic Spine Surgery, University of Miami Miller School of Medicine
• Clinical Focus: Complex Adult Spinal Deformity, Robotic Spine Reconstruction, Minimally Invasive Spine Surgery (cMIS), Motion Preservation & Scoliosis Correction
• Primary Practice Locations:
  • UHealth Tower (University of Miami Hospital): 1400 NW 12th Ave, Suite 2, Miami, FL 33136
  • UHealth at Coral Gables: 5555 Ponce de Leon Blvd, Coral Gables, FL 33146
• Appointments & Consultations: (305) 243-3000 / (305) 689-4979