Abstract

Lumbar spine pars-interarticularis stress fractures [spondylolysis] are common and are often asymptomatic. Patients present clinically with localised low back pain which may be associated with sciatica if there is nerve root involvement. Typically at the time of presentation the disc at the affected level is already degenerate and there may be a spondylolisthesis, but a small number of patients have intact discs, and the surgical option of repair of the pars defect must be considered. Historically, the first report of a non-instrumented repair of the pars defect was in 1968; the patient lay flat for 6 weeks and had a cast for 6 months. Subsequent techniques have concentrated on repairs with instrumentation, and the complications of such surgery have been significant - wire breakage, screws loose or malpositioned, and soft tissue damage caused by the surgical access. Those papers that have adequately assessed healing with CT have reported a non-union rate of between 15-45% We report on our early experience using a minimal access tube [X-tube] or Endoscope [Metrx] to expose the pars defects bilaterally. The scar tissue between the bone ends is removed, and a trough is created 7-8mm long perpendicular to the defect using a Midas Rex. Care is taken to make the trough approximately 2/3rds of the depth of the bone, and to avoid disturbing the adjacent facets. The bone reamings from the Midas Rex are used to create a multilayered sandwich with BMP-2 soaked onto a collagen sponge [Inductoss]. Approximately 3mg Inductoss is used per side. A thin layer of Tisseal fibrin glue is placed over the Collagen sponge, and the wounds closed. The patient has a Thermoplastic TLSO made before the surgery and is mobilised in this brace the following day. The brace is worn for three months except at night and when showering. Four patients [8 defects] have been treated so far. Two patients have healed bilaterally, and two have healed unilaterally, as assessed by CT scans at between 4-6 months. The clinical results have been encouraging, all patients noting clinical improvement so far. The one patient with a two year follow up has minor residual pain from the adjacent facet joints, and rates himself as 85% improved. The technique avoids the complications associated with instrumentation, minimises soft tissue damage and preserves movement of the motion segment. We are currently working on minimal access instrumentation to see if we can make the healing more reliable.