Low back pain — sometimes accompanied by sciatica, pain radiating from the lower back down the leg — is among the most common reasons patients consult a spine surgeon. Imaging of the lumbar spine (MRI, CT, or flexion-extension radiographs) may then reveal spinal instability: vertebral displacement, slippage, or fractures that compromise normal vertebral movement.
It is particularly common for surgeons to propose spinal fusion on the basis of instability identified on imaging. Spinal fusion refers to the use of implants — screws, rods, plates, and grafts — with the aim of stabilizing the spinal structures and, ultimately, reducing the patient’s symptoms.
Unfortunately, this procedure has very low efficacy when performed indiscriminately or in the wrong patient population, with satisfaction rates that may fall below 50%. Those rates improve substantially when proper patient selection is applied.
Two key problems arise in everyday clinical practice and hinder appropriate patient selection.
The first, and foremost, is establishing the diagnosis of instability. Many physicians, on observing even a minor vertebral displacement or a simple fracture, will recommend fusion. This haste often serves the surgeon’s needs rather than the patient’s. Instability must first exist and, second, be severe enough to justify a fusion. A very minor vertebral shift or a small fracture rarely causes true instability and rarely warrants fusion. Conversely, a significant displacement, or a fracture causing major deformity, may be sufficient to establish true or impending instability. To claim instability in lesser injuries, however, flexion-extension radiographs must be obtained — that is, films taken in different positions of the spine — to determine whether actual vertebral movement exists, and to what degree. Only if significant instability is confirmed can fusion begin to be considered. In many cases these studies are never performed, and instability is cited without truly being present.
The second, and equally important, is defining the efficacy of the proposed operation. Many surgeons quote success rates of 90%, 95%, even 97–100%. Such figures belong more to marketing than to the published evidence. Radiological success rates may indeed approach these numbers — meaning that, on imaging, the vertebrae appear well stabilized with no visible motion. This is the efficacy surgeons most commonly refer to. But the efficacy that matters to patients — and should matter equally to surgeons — is clinical efficacy: the proportion of patients who remain satisfied with the outcome in terms of pain relief and limb function. Those rates are considerably lower, and never reach 90–100%.
The reality is that with indiscriminate fusion, or very poor patient selection, clinical efficacy falls below 50%. Even with careful selection, clinical success does not exceed 70–80%. Nevertheless, 70% in a patient with genuine spinal instability and severe symptoms is meaningful. Patients with these conditions often present with intense symptoms for which most interventions have limited efficacy: for a patient in whom injections achieve 50% and pharmacotherapy 30%, a 70% success rate is markedly superior to every other option — especially given the severity of pain and the degree to which daily life is affected. Even a 10% gain in function can be life-changing. The accurate terminology, then, is that targeted patient selection for fusion offers better — not good — outcomes; and that is more than sufficient for the population in which fusion belongs among our therapeutic options.
The appropriate candidate for fusion must be very carefully evaluated, both clinically and radiologically. Patients with neurological deficits and concomitant instability that demonstrably causes their symptoms are clearly suitable. It should be emphasized that the primary symptom addressed by fusion is axial low back pain, not pain radiating down the legs. Patients with significant, predominant low back pain that has not responded to conservative management for more than a year are therefore reasonable candidates, with considerably better success rates than with other options. Also suitable are patients with significant bony displacement constituting impending instability, and those with instability confirmed on flexion-extension radiographs — provided the instability is clearly linked to their symptoms and they are otherwise good surgical candidates.
Patients with minor lesions and no confirmed instability are generally not appropriate candidates. In particular, patients with radicular pain — sciatica — not attributable to vertebral displacement are by no means suitable for fusion. Many of them are excellent candidates for far simpler procedures: direct decompression by laminectomy or discectomy. It is not uncommon for fusion to be performed without adequate decompression in a patient with sciatica, leaving the symptoms unchanged. Had the same patient undergone a straightforward one-hour procedure without implants, there would have been an excellent probability of complete symptom resolution — without even an overnight hospital stay. (See: Awake Same-Day Minimally Invasive Lumbar Decompression.)
Poor patient selection exposes patients to the risk of complications without delivering adequate benefit. The complication rate of spinal fusion approaches 10% and includes permanent neurological injury, such as lasting weakness in a lower limb. Furthermore, up to roughly 30% of patients may develop symptomatic adjacent segment disease within ten years of fusion — radiographic degeneration of the adjacent level is more frequent still, but it is the symptomatic form that matters clinically. This is instability developing at the level immediately above the instrumented segment, a consequence of the forces of body weight being transferred directly above a construct that is completely immobilized. In practice, it means a recurrence of symptoms after an average of ten years, with the possible need to extend the fusion one level higher — carrying a new set of complications with it.
In conclusion, patient selection must be approached with great care. The instability that serves as the indication for fusion must be properly established, and the causal relationship between that instability and the patient’s symptoms clearly defined. The patient must be informed of the true — not the inflated — efficacy rates, and should proceed with surgery in full awareness of the potential complications and risks. That decision should be made only when we are confident that fusion offers better outcomes than the alternatives available to us, and when it is genuinely necessary in the patient’s interest — and theirs alone. With this philosophy, the contribution of surgeons to society is enhanced, and patients derive greater quality of life from our care.
