Polyaxial Pedicle Screws for the Treatment of Idiopathic Scoliosis**

PURPOSE: To evaluate the efficacy of polyaxial pedicle screws inserted in a segmental fashion for the operative treatment of idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA: Suk has introduced Segmental pedicle screw instrumentation for scoliosis correction in 1994. Superior correction was achieved compared to nonsegmental techniques. Polyaxial screws have been shown to facilitate rod insertion due to the variable position of the screw head. There are no reports in the literature about scoliosis correction using polyaxial screws, however, there has been criticism for using polyaxial screws for correction based on the inability to rotate the rod. The polyaxial heads will move with the rod, however, the vertebral body will remain stationary until the screw head is in a fixed position. This report presents polyaxial pedicle screws for the correction of idiopathic scoliosis.

METHODS: 24 patients with idiopathic primary thoracic scoliosis were treated with posterior instrumentation between 1996 and 2001. The average age was 16 years (11 - 49). Curve classification according to Lenke et al showed an even distribution between Type 1, 2, 3 and 4 curves. In all curves a segmental screw placement was performed on the concavity of both the thoracic and the lumbar curve and almost all pedicles were instrumented on the convexity. To gain a maximum mobility, facet joints were mobilized; costotransverse release was performed as well as anterior release in rigid curves. The rods were prebent in order to restore a physiological profile. The correction maneuver included derotation, translation and cantilever.

RESULTS: The average thoracic curve measured 64°(43 - 113) preoperatively and 20°(2 ? 30) postoperatively (79 % avg. correction), for the lumbar curves 40°(10 - 69) and 10°(0 - 27) pre-op and post-operatively respectively (78 % avg. correction). Average thoracic kyphosis was 37°(5 - 76) preoperatively and 32°(12 - 45) postoperatively. Average lumbar lordosis measured 56°(26 - 85) preoperatively and 57°(30 - 70) postoperatively. There were no neurological complications and no implant failure seen at the last follow-up.

DISCUSSION: Polyaxial screws provided very good correction in the coronal and sagittal plane as well as effective derotation compared with the results of studies using monoaxial screws. Clinically derotation has been highly effective, however, radiographic measurements underestimate the results. This technique facilitates rod insertion even in severe curves. Translational correction was effective due to the polyaxial screw head. Correction forces are distributed over more segments avoiding shear stresses at the screw-bone interface resulting in a stable screw placement with no screw pullouts.

CONCLUSION: The technique has proven to be safe in the hands of experienced surgeons who are familiar with pedicle screw placement in scoliotic spines. Whether the instrumentation is shorter compared to other posterior techniques must be evaluated in the future.

** 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).