**REPAIR OF THE PARS INTERARTICULARIS DEFECT WITH A CABLE–SCREW CONSTRUCT

Matthew N. Songer, MD
*(d – Pioneer Surgical Technology)
Marquette, MI, USA

PURPOSE:
The purpose of this study is to report on the results of repairing and reconstructing the pars interarticularis with a cable–screw construct. Previous techniques to repair a pars defect have not been very successful. This technique utilizes the advancements in spinal instrumentation technology to effectively stabilize the pars interarticularis.

METHODS:
Patients with pars interarticularis defects were carefully selected based on resistant low back pain with no or little radicular symptoms. The patient must have had grade 1 or less spondylolisthesis, had little or no desiccation on MRI, and had pain reproduced with injection of the pars defect. The surgical technique involved placing a 6.25 or 4.5 mm screw into the pedicle of L5. A double cable was passed sublaminar. Each cable was passed through a hole in the specially made pedicle screw. The soft tissue was previously removed from the pars defect until good healthy, bleeding bone was encountered on each side, and the defect was grafted with autologous tricortical bone graft. The cables were simultaneously tensioned between the screw and the spinous process (each cable was wrapped under the lamina and around the spinous process in a figure of 8), thereby creating compression between the bone graft and the lamina on one side and the pedicle on the other.

RESULTS:
A total of 10 cases have been performed with a mean follow up period of 43 months (range 24–70). The pars defect was at L5 in 8 cases, L4–5 in one and L3–4 in one. Six were males and four were female and ranged in age ranged from 11 to 44. The average duration of symptoms was almost 3 years prior to the operation. All patients had severe pain pre–op preventing participation in sports and normal activities. Post–op the pain was gone in 9 cases with resumption of normal activities. Two patients had cable breakage 1 and 2 years post op after significant trauma, however the pars were noted to have healed when the cables were removed. The oldest patient was pain free for one year, then fell and required a spinal fusion after conservative treatments failed. The improvement in pain level and functional state has been excellent. The Prolo scoring method rated eight as excellent and 2 good.

DISCUSSION AND CONCLUSION:
The concept of repairing the pars defect is not new. The precious techniques have been inadequate structurally to effectively stabilize the pars interarticularis or were technically difficult to achieve. The cable–screw construct utilizes the strongest anchors (the pedicle and the lamina) and compression obtained by use of the cables to stabilize the pars interarticularis. The results indicate that this is a safe and effective technique for this difficult problem.

·* If noted, the author indicates something of value received. The codes are identified as: a research or institutional support miscellaneous funding, c–royalties, d–stock options, e–consultant. For full information, refer to page 3.

** The FDA has not cleared a drug and/or medical device for the use described in this presentation. (i.e., the drug or medical device is being discussed in an “off–label: use).