Survivorship Analysis of Pedicle Screw Fixation

Shin, Byung Joon; Kim, Kyung Je; Kim, Sung Tae; Kim, Yon Il

Abstract

STUDY DESIGN: This is a retrospective study analyzing survivorship of pedicle screw fixation in various spinal lesions.
OBJECTIVES
To determine the survivorship of pedicle screw fixation and to assess the risk factors for the death of system. SUMMARY OF LITERATURE REVIEW: The previous reports of ten years survival rate of pedicle screw instruments was about eighty percent and the factors which influenced were bone quality, strength of instruments, design of instruments and compliance of patients.
MATERIALS AND METHODS
Three hundred and thirty-eight patients(178 males and 160 females), treated by pedicle screw fixation from May 1988 to Dec. 1997, were analysed. Follow-up averaged 26.8months(3 to 116 months). The survival rates according to spinal lesions which caused spinal fixation, types of instruments, level of fusion and methods of fusion were predicted by life table method. The criteria of death were 1)breakage of screw or rod 2)gross bending of screw >5 degree 3)screw pullout and 4)dissociation of rod-screw coupling mechanism.
RESULTS
Death of instrumentation was identified in twenty-six patients(7.7%). Of the 1,827 screws used, forty-three screws(2.4%) in twenty patients had broken(28) or bent(15). Thirty-nine Cotrel-Dubousset screws(3.5%) and four Diapason screws(1.6%) had involved. Four patients showed pullout of screws and two had dissociation of rod and screw. There was no rod broken. Life table calculations predicted the survivorship of instrumentation would be 88.7% at 10 years of follow-up. Single segment fixation showed higher survival rate than more than three segments fixation(93.3% vs 83.4%). Fracture had the lowest survival rate(78.3%). Screw failure was not influenced by the method of fusion. Suspected causes of death were collapse of disc space(12 patients), increased kyphosis(6), forceful reduction of fracture(3), infection(2), nonunion(2) and trauma(1).
CONCLUSIONS
Ten year survival rate of pedicle screw fixaion was 88.7%. The survival rate was influenced by 1)number of fixed segments 2)cause of fixation .