Pseudarthrosis is the most common reason patients require revision surgery after scoliosis fusion, yet it is also one of the most frequently unrecognized complications of spinal surgery. Patients with pseudarthrosis are often told for months or years that their X-rays look fine — because on plain X-rays, they often do. The fusion mass can appear present and intact on standard imaging while harboring a fibrous non-union that is the true source of persistent pain and, ultimately, hardware failure.
What Is Pseudarthrosis?
Spinal fusion surgery achieves its goal when the bone graft placed between vertebrae consolidates into continuous, solid bone — the same process that heals a fracture. When this consolidation fails to occur, the result is a pseudarthrosis: a false joint at the non-union site, where fibrous tissue rather than solid bone bridges the gap. The vertebrae in this zone are not truly fused; they retain a small degree of micromotion at the non-union site, and this persistent micromotion is the source of the pain and mechanical stress that eventually causes hardware to fail.
Why Does Pseudarthrosis Happen?
Bone fusion requires adequate bone graft material, mechanical stability, good blood supply, and a biological environment that supports new bone formation. Pseudarthrosis occurs when one or more of these conditions is not met:
- Insufficient bone graft or poor graft incorporation — the biological material needed for new bone formation was inadequate or failed to integrate at a specific level within the fusion mass
- Excessive motion at the non-union site — even with hardware in place, micromotion at specific segments can prevent consolidation if the construct is not sufficiently rigid
- Osteoporosis or poor bone quality — reduced bone density impairs both screw purchase and the bone’s capacity to form new fusion mass
- Smoking — one of the most well-established risk factors for pseudarthrosis; nicotine impairs the vascular supply required for bone healing
- Nutritional deficiencies — inadequate protein, vitamin D, or calcium impair the biological environment for bone formation
- Long fusion constructs — the longer the fusion, the more levels that must all consolidate simultaneously; longer constructs are at higher risk of isolated pseudarthrosis at one or more levels within the fusion mass
How Pseudarthrosis Presents
The classic presentation is persistent back pain at or near the fusion site that never fully resolved after surgery — or that improved initially and then returned or worsened. This pain is often positional: worse with loading (standing, walking), better with rest and unloading. Some patients notice a subtle mechanical quality to the pain — a sense of movement or instability at a specific spinal level. Leg pain may accompany back pain if the micromotion at the pseudarthrosis site irritates adjacent nerve roots.
The eventual hardware failure that reveals the pseudarthrosis is often dramatic by comparison: a broken rod detected on routine follow-up imaging, or a sudden change in pain character when the rod fractures. A clean transverse rod fracture at a single level — rather than at a connector or screw junction — is the classic imaging pattern that points to an underlying pseudarthrosis at that segment. The rod failed because it was absorbing all the mechanical load that solid bone should have been absorbing.
Why X-Rays Miss It
Plain X-rays assess the overall alignment of the fusion construct and the gross appearance of the bone. They are not designed to detect the difference between solid cortical fusion and fibrous non-union within the fusion mass. A pseudarthrosis that has not yet caused rod fracture or obvious lucency around hardware can look completely normal on AP and lateral X-rays. This is why many patients with pseudarthrosis are told repeatedly that their images look acceptable.
CT scanning with fine-cut sequences through the fusion mass is the gold standard for diagnosing pseudarthrosis. The key finding is the absence of continuous trabecular bridging bone across the fusion levels — a gap in the fusion mass that represents the non-union site. CT can also detect subtle hardware loosening, early rod stress fractures before complete fracture, and screw halo signs (lucency around the screw-bone interface indicating micromotion).
What Revision Surgery Involves
Revision surgery for pseudarthrosis addresses both the mechanical failure and its biological cause. The procedure typically involves:
- Removal of any failed hardware (broken rod, loosened screws) at and around the pseudarthrosis site
- Thorough debridement and preparation of the pseudarthrosis site — removing fibrous tissue and creating fresh, vascularized bone surfaces capable of supporting new graft consolidation
- Placement of abundant, high-quality bone graft at the non-union site; bone morphogenetic protein (BMP) may be used to enhance fusion biology in difficult revision cases
- Re-instrumentation with new hardware providing adequate stability across the non-union; in some cases the construct is extended proximally or distally to improve mechanical stability
- Correction of any associated deformity or imbalance that may have contributed to or resulted from the pseudarthrosis
Published series report bony union rates of approximately 98 percent with revision surgery for pseudarthrosis after scoliosis fusion — making this one of the most reliably fixable revision scenarios when properly identified and addressed. The key is making the diagnosis before the mechanical consequences become more complex to address.
For a comprehensive overview of all scoliosis revision scenarios, see the main When Scoliosis Surgery Doesn’t Go As Planned page. For more on the revision surgery process generally, see Complex Revision Spine Surgery.
About Dr. Zeeshan Sardar
Dr. Sardar, MD, MSc, F.R.C.S.C, is Co-Chief of Spinal Deformity Surgery at NewYork-Presbyterian / Columbia University, specializing in revision scoliosis surgery including pseudarthrosis repair and re-instrumentation. To schedule a consultation, call 212-932-5187 or visit the contact page.
This post is for educational purposes only and does not constitute individualized medical advice.