The indications for fusion in elderly patients are often not definitive. Of particular note are, in general, greater comorbidities, greater risk of complications, and less focus on work and strenuous activities. Alternatives to fusion have thus emerged including interspinous devices and dynamic stabilisation, writes Scott L Blumenthal.
There are many designs of interspinous devices. The goals of such devices are to reduce pain and improve function, assist spinal stability, facilitate neural decompression, and reduce surgical risks associated with fusion. Several non-fusion options have been introduced including interspinous spacers, flexible rods, and total facet replacements. The best clinical application has been with the interspinous devices. These are designed for minimally invasive surgical techniques which provide the potential advantage of day surgery and the option for use of local anaesthesia. It is of note that none are designed for use at L5–S1. The concept of interspinous spaces was introduced in the 1950s with the use of a steel cylinder.
Unfortunately, there were problems with loosening and migration of that device. In the 1980s, Seneges reported on the use of what became the Wallis device (Abbott Spine) which was held in place by straps that looped around the spinous processes. Some of the modern interspinous implants that have been reported for clinical use include the Wallis, X-Stop (Medtronic), DIAM (Medtronic), Superion (VertiFlex), and Coflex (Paradigm Spine).1–5
Currently, the most commonly used device appears to be the Coflex. In the FDA investigational device investigation (IDE) trial for this device, decompression was compared with decompression and fusion in a prospective, randomised, multicentre study with 24-month follow-up.6 Both groups improved significantly, with the interspinous group having better outcomes on some measures. A recent review of interspinous devices found that although patients may have some benefit from the devices, their use is associated with a greater re-operation rate and higher treatment costs.7 With any interspinous devices careful patient evaluation and adherence to indications is paramount for achieving good outcomes. A variety of problems have been reported for some of the interspinous devices including migration, spinous process fracture, and simply failing to provide pain relief.8,9 Poor outcomes are often due to the use of poor indications, though poor device placement and, less frequently, device failure are also factors.9,10
In a recent study the costs, complications, and re-operations were compared for interspinous devices and laminectomy in matched patient cohorts with lumbar stenosis.11 The laminectomy group had a significantly longer hospital stay and greater 90-day complication rate. The interspinous group had a significantly greater index surgery hospital cost as well as significantly greater re-operation rate at 12 month follow-up.
In addition to interspinous devices, the use of dynamic stabilisation has also been suggested as a non-fusion alternative in older patients. Recently, Lee et al reported on the use of dynamic stabilisation in a small series of older patients with degenerative scoliosis.12 Patients had significant improvement on clinical outcome measures, but 14.2% had lucencies around screws, without progression of the curve. The authors suggested dynamic stabilisation as a viable treatment for adult scoliosis if the curves are less than 30 degrees. Other authors have reported that dynamic stabilisation with pedicle screws in addition to decompressive laminectomy was safe in elderly patients with degenerative scoliosis, maintained enough stability to prevent condition progression and instability and provided significant clinical improvement.13 The same authors noted the potential benefits of decompression and dynamic stabilisation rather than fusion in elderly patients with lumbar scoliosis including lower operative time and blood loss.14 At five year follow-up, both groups maintained good clinical outcomes. Radiographic results were better in the fusion group, but re-operations were lower in the dynamic stabilisation group. Dynamic stabilisation has also been reported to be beneficial in older patients undergoing decompression for degenerative spondylolisthesis.15,16
With the exception of the IDE trials which incorporated rigorously-defined selection criteria, the indications for interspinous devices and dynamic stabilisation devices as an alternative to fusion are not clear. More research is needed to determine the extent to which scoliosis, spondylolisthesis and stenosis can be treated effectively with these devices. Certainly, given the comorbidities and increased risks of complications in elderly patients, fusion alternatives are attractive for this population.
Scott L Blumenthal is a spine surgeon at the Texas Back Institute, Plano, USA
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