The Place for Pedicle Screws in Scoliosis Surgery: A Two Year Follow-Up

Andrew G. King, M.D., ChB, FRACS,
Tara E. Mills, B.S.;
Jason E. Smith, B.S.,
Norman B. Chutkan, M.D.
New Orleans, LA, USA

PURPOSE:
A retrospective review was undertaken to compare the efficacy of pedicle screw constructs to the standard hook constructs in the treatment of idiopathic scoliosis.

SIGNIFICANCE:
Data from this study will aid in determining which construct offers better correction and better maintenance of the correction after two years, in addition the paper sought to identify any complications or related to the use of pedicle screws.

METHODS:
Fifty–four patients with idiopathic scoliosis underwent posterior spinal fusion between 1992–1997. Pedicle screws were used only as the caudal anchors in thirty–four cases (Group 1). Hook constructs were used in 20 cases (Group 2). The primary method of surgical correction for both groups was cantilever bend and transverse approximation. Both groups were similar with regard to age, preoperative Cobb and tilt angles. Radiographic analysis was performed measuring pre, immediate post–op and two–year follow–up Cobb angles, tilt angle, coronal balance and sagittal balance. All data underwent statistical analysis utilizing student t–test with p£0.05 as the standard to assess significance.

RESULTS:
Percent correction of the primary Cobb angles immediately post–op was 71.4% for the screws (N=34) and 64.8% for the hooks (N=20). The percent correction at 2 year follow–up was 62.2% for screws and 58.2% for hooks. The primary tilt angle was measured preoperatively and compared to the tilt angle measured from the LIV to the sacrum postoperatively. The preoperative tilt angle for the screw patients was 29 degrees (N=28) and 28.6 degrees (N=17) for the hook patients. At two–year follow–up the measurement of the LIV to the sacrum was 6 degrees for Group 1 and 8 degrees for Group 2. No significant difference was demonstrated in comparing tilt angles between the screw patients and the hook patients. No complications arose that were specific to the placement of the pedicle screws. Five patients were later diagnosed with pseudoarthrosis, three in Group 1 and two in Group 2. The three cases in Group 1 had a pseudoarthrosis cephalic to the caudal anchor while the 2 cases in Group 2 were sited at the most caudal level instrumented. All pseudoarthroses were surgically repaired.

CONCLUSION:
Cantilever bend and translational mechanics are effective in correcting scoliosis and can be carried out using screws of hook caudal anchors. No significant differences were demonstrated between the two groups when comparing Cobb angles of tilt angles. Neither intra–operative nor postoperative complications occurred from the use of either hooks or pedicle screws. In this series, the pedicle screws did show a greater percent correction of the primary Cobb angle and of the tilt angle, but the difference was not statistically significant.

** 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).