J Korean Soc Spine Surg.  2002 Jun;9(2):157-163.

Metal Failure of Pedicle Screw System

• Lee KY
• Kim CH
• Song CG

Abstract

STUDY DESIGN: The metal failure of pedicle screw system followed by posterolateral or posterior fusion used in variable cases(spine fracture, degenerative disorder of spine, deformity of spine) was analyzed retrospectively. PURPOSE: The goal of this study was to analyze frequency and clinical consequence of pedicle screw fixation system failure in the treatment of different etiology(spine fracture, degenerative disorder, deformity of spine) and to evaluate affected factors in metal failure.
MATERIALS AND METHODS
We performed survivorship analysis on 442 patients treated with pedicle screw system from September 1990 to December 1999. The average follow-up period was 54 months(from 18 months to 129 months). As affected factors, some variables such as etiology, kinds of system and extent of fusion were subjected to analyzed their influence on metal failure. We also performed analysis about relationship between metal failure and clinical results. We defined the metal failure as 1) breakage of screw or rod 2) screw bending above 5 degrees 3) dissociation of rod-screw coupling system and 4) screw pull out from vertebral body or pedicle.
RESULTS
We found out 33 cases of metal failure: among 2786 screws, 41 screws had a problem. The metal failure rate was different between each etiology ; 12 cases in fracture(10%), 21 cases in degenerative disorder(6.9%). There was also difference between a kinds of implants; 13 cases in side assembling type(5.4%), 20 cases in back open type(10.5%). However, there were no difference according to extent of fusion; 6 cases in one segment(6.9%), 21 cases in two segments(8.1%), 6 cases in more than three segments(6.3%). Among the overall patients with metal failure (33 cases), only eight patients were complaint significant symptoms. And three of this eight patients were improved after reoperation The mean interval to metal failure was 14.4 months from operation.
CONCLUSION
The metal failure was more common in spine fracture(p<0.05) and back open type pedicle system(p<0.05). However, there was no relationship with extent of fusion(p>0.05). And metal failure did not significantly affect the clinical results(p>0.05).

Keyword

pedicle screw system; metal failure

MeSH Terms

Congenital Abnormalities
Follow-Up Studies
Humans
Reoperation
Retrospective Studies
Spine
Survival Rate

Figure

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  Fig. 1. 69 years old female with spinal stenosis had breakage of screw and no symptom after postoperative 6 months

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  Fig. 2. 35 years old female with spinal stenosis showed screw bending above 5 degrees after postoperative 3 months

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  Fig. 3. 60 years old female with spinal stenosis showed dissociation screw rod coupling system after postoperative 2 years

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  Fig. 4. 31 years old male with fracture-dislocation showed pullout of screw from vertebral body after postoperative 20 months

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  Fig. 5. 31 years old male with fracture-dislocation showed pullout of screw from vertebral body after postoperative 20 months

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  Fig. 6. Cumulative survival rate according to instruments(

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  Fig. 7. Cumulative survival rate according to fusion levels((p>0.05)

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