By Steven D Glassman
Surgical treatment for adult spinal deformity is a substantial intervention and complications associated with the surgery have always been a major concern. Historically, the discussion has focused on medical complications (in older patients) and neurologic complications, which are uncommon but can be devastating. However, in recent years, proximal junctional kyphosis appears to have become epidemic and has substantially altered the discussion surrounding complications.
Proximal junctional kyphosis was first described in patients with idiopathic scoliosis (by Betts and Clements in 1999) and has since been reported in both children and adults. However, it was generally thought to be clinically insignificant. In 2009 and 2010, a more catastrophic version of proximal junctional kyphosis—described as proximal junctional failure—was first reported.
As reports of both proximal junctional kyphosis and proximal junctional failure mounted, conventional thinking was that these complications were associated with more aggressive deformity correction in older patients with significant comorbidities (particularly osteoporosis). The increased rate of catastrophic failure, as opposed to asymptomatic deformity, was thought to be associated with the use of more rigid instrumentation and all pedicle screw constructs.
Based on these assumptions, surgeons have tried to remedy the increase in proximal junctional kyphosis and proximal junctional failure with an array of mechanical solutions. For example, efforts to decrease the force applied in deformity reduction have included more aggressive releases and more widespread use of osteotomies. Surgeons have also tried to diminish the force gradient at the proximal aspect of the instrumentation with the use of hooks, cement injection, and other non-fusion technologies. However, none of these strategies really appear to have been effective.
Therefore, while we certainly need to pay attention to the mechanical implications of our surgical strategies, we also need to think more about natural history if we are to decrease proximal junctional kyphosis and proximal junctional failure. In particular, we need a better understanding of the innate balancing mechanisms of the spine. Progressive kyphosis is unquestionably a part of normal ageing and it may be that, at least to some degree, we need to work with that reality rather than to try to reverse it.
It is well established that deformity correction is difficult and often unsustainable in the face of significant neuromuscular diseases such as Parkinson’s disease. But while obviously less overt, lesser degrees of neurogenic abnormality—such as diabetic neuropathy—may also affect the patient’s ability to rebalance after deformity correction. There is also conflicting evidence as to whether or not aggressive correction of sagittal imbalance increases or decreases subsequent proximal junctional kyphosis. This may require some refinement in our assessment and understanding of the relationship between pelvic parameters and spinal balance with ageing.
Adult spinal deformity correction is a major undertaking, and both the clinical and economic rationale underlying this surgery is based upon a durable result. It is therefore critical that we develop a better understanding of the aetiology of proximal junctional kyphosis and proximal junctional failure as well as more effective strategies for limiting its occurrence.
Steven D Glassman is at Norton Leatherman Spine Center, Louisville, USA
