J Korean Neurosurg Soc.  2015 Apr;57(4):229-234. 10.3340/jkns.2015.57.4.229.

Pullout Strength after Expandable Polymethylmethacrylate Transpedicular Screw Augmentation for Pedicle Screw Loosening

• Kang SH
• Cho YJ
• Kim YB
• Park SW

• KMID: 1956419
• DOI: http://doi.org/10.3340/jkns.2015.57.4.229

Abstract

OBJECTIVE
Pedicle screw fixation for spine arthrodesis is a useful procedure for the treatment of spinal disorders. However, instrument failure often occurs, and pedicle screw loosening is the initial step of a range of complications. The authors recently used a modified transpedicular polymethylmethacrylate (PMMA) screw augmentation technique to overcome pedicle screw loosening. Here, they report on the laboratory testing of pedicle screws inserted using this modified technique.
METHODS
To evaluate pullout strengths three cadaveric spinal columns were used. Three pedicle screw insertion methods were utilized to compare pullout strength; the three methods used were; control (C), traditional transpedicular PMMA augmentation technique (T), and the modified transpedicular augmentation technique (M). After control screws had been pulled out, loosening with instrument was made. Screw augmentations were executed and screw pullout strength was rechecked.
RESULTS
Pedicle screws augmented using the modified technique for pedicle screw loosening had higher pullout strengths than the control (1106.2+/-458.0 N vs. 741.2+/-269.5 N; p=0.001). Traditional transpedicular augmentation achieved a mean pullout strength similar to that of the control group (657.5+/-172.3 N vs. 724.5+/-234.4 N; p=0.537). The modified technique had higher strength than the traditional PMMA augmentation technique (1070.8+/-358.6 N vs. 652.2+/-185.5 N; p=0.023).
CONCLUSION
The modified PMMA transpedicular screw augmentation technique is a straightforward, effective surgical procedure for treating pedicle screw loosening, and exhibits greater pullout strength than traditional PMMA transpedicular augmentation. However, long-term clinical evaluation is required.

Keyword

Biomechanics; Osteoporosis; Postoperative complication; Prosthesis loosening; Polymethylmethacrylate; Surgical technique

MeSH Terms

Arthrodesis
Cadaver
Osteoporosis
Polymethyl Methacrylate*
Postoperative Complications
Prosthesis Failure
Spine
Polymethyl Methacrylate

Figure

• 

  Fig. 1 Schematic illustrations of modified transpedicular polymethylmethacrylate (PMMA) screw augmentation. A : The vacant pedicle hole after loose pedicle screw removal is filled with PMMA of a toothpaste-like viscosity, the dead space was filled with 1 cc of PMMA for the biomechanical study. B : The inserted PMMA hardened after inserting a small pilot screw. C : An inner thread was left by the small screw after its removal. D : PMMA expansion (red arrows) caused by inserting the thicker permanent screw improved screw holding power (referred to as the anchor bolt effect). Adapted from Kang et al. J Korean Neurosurg Soc 49 : 75-78, 20119).

• 

  Fig. 2 Schematic diagram presenting pullout strengths (N) for the control (C), traditional (T), and modified (M) techniques. A 6 mm screw was used to measure pullout strengths. The paired t test was used for the statistical analysis. Lt. : left, Rt. : right.

• 

  Fig. 3 Schematic illustrations of loosening holes, showing a loosened screw hole on the left side and modified transpedicular polymethylmethacrylate (PMMA) augmentation on the right. Loosened pedicle screw hole exhibits a conical shape with no flange (red arrows). Modified transpedicular screw augmentation increases screw holding power (short red arrows) even without a flange and with only slight PMMA interdigitation.

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