Isthmic spondylolisthesis with pars interarticularis defect is a “ fatigue” fracture. In most cases there is no instability and moderate pain, with no need for treatment. Twenty per cent of the patients have severe back pain, and some also radicular pain, while some young patients have progressive lumbosacral kyphosis and instability with high grade spondylolisthesis. The sacral deformity and kyphosis result from the fracture and could be avoided by healinfg of the defect. Histological studies have shown that the pars defect can be a source of pain.

Patients with severe back pain and some with radicular pain or increasing deformity are candidate to surgery. Since many years, the only treatment was fusion with or without instrumentation and with or without correction of the deformity, by anterior or posterior approach. Fusion was mandatory in case of associated disc degeneration, including all the pathological discs into the fusion area. Isthmic repair has been done since many years using several techniques, but only in the absence of olisthesis and disc degeneration. However, it is known that many adult or senile subjects have degenerated discs and no back pain. Thus, what is the rationale to perform fusion in all patients with spondylolisthesis? The problem is to know the source of pain and to treat patients rather than x-rays. This can be achieved by anaesthetic injection of the lytic zone, MRI and discography, which can be helpful to differentiate patients who need fusio from those who do not need it. Initially we used, for isthmic repair, the Morscher hook-screw instrumentation, but in the last ten years we are using DOS instrumentation, which is stiffer. The indications and surgical technique, as well as the results of a comparative study between fusion (91 patients with 40-month follow-up) and repair (95 patients with 30-month followup), wil be presented in terms of duration of surgery, hospital stay, complication rate, number of revisions and return to previous activities.

This study shows less postoperative complications and higher rate of return to work or sports for pars repair versus lumbar fusion in a rather similar population. Therefore, isthmic repair seems to be the first surgical option for mild isthmic spondylolisthesis even in the presence of degenerated discs.