Proximal Junctional Failure (PJF)

To understand proximal junctional failure it helps to picture what a long spinal fusion does. In the treatment of adult spinal deformity, such as scoliosis or a forward-stooping posture, a surgeon may join together many vertebrae with pedicle screws and rods, often reaching down to the sacrum or pelvis. The fused length becomes a single rigid beam. Above the highest screwed vertebra, known as the upper instrumented vertebra or UIV, the spine remains mobile and flexible as normal. The point where the stiff construct meets the supple spine above is the proximal junction, and it is here that the trouble arises.

The reason is mechanical. Whenever a rigid structure is bolted to a flexible one, the boundary between them concentrates stress. Every time the body bends forward, the load that the long lever of the fused spine generates is delivered abruptly to the first free segment above the metalwork. The vertebra at the top of the construct, and the disc, ligaments and joints just above it, must absorb a sudden change in stiffness. Over time, or sometimes quite suddenly, that concentrated load can exceed what the bone and soft tissues can bear, and the junction gives way. This vulnerability is not a sign that anything was done wrongly; it is an inherent consequence of fusing a long segment of spine.

The single most important idea in this whole subject is the difference between proximal junctional kyphosis (PJK) and proximal junctional failure (PJF). They are often spoken of together, and they sit on the same spectrum, but they are not the same thing, and confusing them leads to unnecessary alarm.

PJK is a radiographic measurement. It is defined as a forward angle at the junction of at least ten degrees, measured between the top fixed vertebra and the vertebra two levels above it, and at least ten degrees greater than it was before surgery. That is all PJK is: an angle on an X-ray that has increased beyond a threshold. PJK is frequently without symptoms, often non-progressive, and in many studies patients who have it report quality-of-life scores no different from those without. Reported rates of PJK vary widely, from roughly one in ten to nearly two in five. In a large proportion of cases it is simply observed.

PJF is a mechanical, structural event. It is not merely a bigger angle. PJF means that something at the junction has actually broken or come apart: a fracture of the UIV or the vertebra just above, a tearing of the posterior bone-and-ligament complex, a pulling-out of the screws, a slip of one vertebra on another, and in some cases pressure on the spinal cord or nerve roots. Because something has physically failed, PJF tends to cause pain and deformity, can progress, and commonly requires revision surgery to extend and rebuild the construct. Hart and colleagues, working with the International Spine Study Group, formalised this in 2013 by defining PJF as PJK together with at least one of fracture, posterior ligamentous disruption, or implant pull-out, and devised a severity scale taking account of pain, neurology, instrumentation and the level involved.

The practical message is that PJK is an angle that is usually watched, whereas PJF is a failure that usually must be acted upon.

Adjacent segment disease refers to the gradual wearing out of the mobile segment next to a fusion — the disc thinning, the joints becoming arthritic and the canal narrowing — over a period of years, as the segment shoulders extra work. It is a degenerative process, slow and cumulative, and tends to declare itself long after the original operation. PJF is, by contrast, an acute or subacute structural collapse. It is not the slow grinding of degeneration but a mechanical breakdown of bone, ligament or fixation under concentrated load, and much of it happens within months of surgery rather than years.

The timing of PJF is one of its most striking features. PJF tends to occur early. Several published series report that the failure declares itself at a median of around three months after the original surgery, with much of it occurring within the first three to six months, although later presentations also occur. The acute fracture type in particular tends to appear in those first few months, while the bone is still adapting to its new mechanical role. This early window is the reason that careful follow-up in the months after long deformity surgery is emphasised so heavily.

PJF does not happen in a single way. The first mode is acute bony failure, a fracture of the UIV or the vertebra immediately above. The vertebra collapses, usually in a flexion or compression pattern, and the spine above tips forward. This is the commonest mode when the top of the construct lies in the lower thoracic or thoracolumbar region, and is strongly associated with osteoporotic bone. A fracture of this kind can, in severe cases, drive fragments of bone backwards towards the spinal canal.

The second mode is ligamentous or soft-tissue failure, a tearing of the posterior osseoligamentous complex — the bone-and-ligament hinge at the back of the spine made up of the ligaments between and over the spinous processes, the ligamentum flavum and the joint capsules. When this hinge gives way, the junction loses its restraint and falls into kyphosis. This mode is more often seen when the top of the construct lies in the upper thoracic spine.

The third mode is implant or interface failure, in which the pedicle screws pull out of the bone, a hook cuts out, or the bone around the metalwork crumbles. This is again more likely in poor-quality bone. In practice the three modes overlap, and a single failure may combine a fracture with ligament disruption and a slip of one vertebra on another.

Among patient factors, the most consistent is bone quality. Osteoporosis and osteopenia stand out as the strongest structural risks for PJF, with one body of work reporting failure in around one in five osteoporotic patients against fewer than one in fifteen of those with stronger bone. Older age, frailty, loss of muscle bulk and higher body weight are also recognised contributors.

Among factors relating to the shape of the spine and the correction performed, two themes recur: the size of the deformity being corrected, and the magnitude of the correction itself. A large correction, and in particular an over-correction that swings the spine further than is ideal for the patient's age, concentrates stress at the top of the construct. Failure can occur even when an apparently ideal, age-adjusted alignment has been achieved, which underlines that alignment is not the whole story. Among surgical and construct factors, ending the fusion at the sacrum or pelvis, using rigid pedicle screws at the very top of the construct, performing major osteotomies, and the choice of where to end the construct all influence the risk.

One of the features that most sharply separates PJF from ordinary PJK is that PJF can, in some cases, threaten the nerves. Because PJF involves real structural movement — a fracture, a slip, or a sharp kyphotic collapse — it can narrow the canal and press on the spinal cord or nerve roots. Recognised consequences range from nerve-root pain and altered sensation, through signs of spinal cord involvement such as weakness and balance disturbance, to, in the most severe acute failures, significant cord or cauda equina compromise from displaced bone. This neurological potential is one of the reasons PJF is regarded as a genuine structural problem rather than a cosmetic one.

Assessment rests on imaging interpreted against the picture before and immediately after the original surgery. Standing X-rays of the whole spine show the alignment of the junction, the proximal junctional angle, and any change from the post-operative films. Computed tomography defines the bony injury in detail: it shows a fracture of the UIV or the vertebra above, the integrity of the screws, and any bone displaced towards the canal. Magnetic resonance imaging shows the soft tissues and, most importantly, the nerves: it reveals disruption of the posterior ligament complex, swelling within a freshly fractured vertebra, and any compression of the spinal cord or nerve roots.

The central theme of prevention is softening the transition so that load is handed from the rigid construct to the mobile spine gradually rather than abruptly. Cement augmentation, in which bone cement is placed into the top one or two vertebrae, is reported in a number of cohorts and a meta-analysis to reduce failure and revision, particularly in weakened bone. Ligament or tether augmentation, in which a flexible band of tape or suture is threaded across the top vertebrae and tensioned to the rod, aims to create a graded zone of movement; a large case series reported less PJF with this technique. Using softer fixation at the top, such as hooks or tapes rather than rigid screws, follows the same logic.

Beyond the hardware, the literature emphasises gentler, matched correction — aiming for alignment appropriate to the patient's age rather than over-correcting to the alignment of a young adult — bone-health optimisation through assessment and treatment of osteoporosis, and careful selection of the upper instrumented vertebra, choosing a level that is stable rather than one already tipping into kyphosis. None of these is presented as a single solution.

When PJF has occurred and is unstable, progressive, or pressing on the nerves, the literature describes revision surgery as the usual treatment, and the principle is straightforward: the failed junction is bypassed by extending the construct upwards to a new, higher and more stable level, re-establishing a sound load path above the point of failure. In effect, a new top is built above the one that gave way. Where the junction has collapsed into a fixed forward bend, the extension is commonly combined with focal correction of that kyphosis through osteotomies. Where bone is displaced towards the canal and the nerves are compressed, decompression is undertaken alongside the fixation.

An important and sobering theme is recurrent failure. Extending a construct creates a new junction, which is itself a potential point of failure, and series following patients after fusion-extension surgery for PJF report that a substantial proportion, in some cohorts approaching half, go on to develop a further failure requiring another revision. Osteoporosis and inadequate restoration of alignment are among the factors that predict recurrence.

The outlook after PJF depends on its mode, on whether the nerves are involved, on the quality of the bone and on how well a revision re-establishes a sound and balanced construct. A failure that is recognised early, that has not damaged the nerves and that is revised into good alignment with secure fixation can do well, and many patients regain a stable spine. The principal shadows over the outlook are weakened bone and over-correction, both of which raise the risk of a further failure at the new junction, and neurological involvement, where recovery can be incomplete.

This page is general medical education and is not a substitute for individual advice. New or worsening weakness, numbness, saddle numbness or any disturbance of bladder or bowel control requires urgent assessment.

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This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.