ABSTRACT

Background Data:

Salvage procedures are needed to restore the stability of lumbosacral arthrodesis when pedicle screw fixation in the sacrum fails.

Purpose:

The aim of this study is to determine biomechanical differences ala, polymethylmethacrylate (PMMA) augmented and larger pedicle screws as salvage techniques for failed primary sacral pedicle screw.

Material and Methods:

Primary pedicle screws were inserted to 21 fresh frozen calf’s first sacral vertebra (S1) pedicle bicorticaly. The screws were pulled out in a random order at 5mm/min Materials Testing Machine. The pull-out strengths (POS) were measured. Afterwards, these pedicle screws were randomly assigned to be replaced by PMMA augmented screws (group 1), larger screws (group 2) and ala screws (group 3) as a revision technique. Finally, POS of the revision screws were recorded.

Results:

The mean POS of all primary screws was 1981 N/m2. Group 1: The mean POS of primary screws was 1650 N/m2. After PMMA augmentation, mean POS was 1295 N/m2 (p=0,139). The mean POS ratio (primary POS/revision POS) was 1.54±0,24. Group 2: The mean POS of primary screws was 2046 N/m2. After larger screw replacement, mean POS was 1320 N/m2 (p=0,007). The mean POS ratio was 1.84±0,22. Group 3: The mean POS of primary screws was 2247 N/m2. After ala screw insertion, mean POS was 1290 N/m2 (p=0,011). The mean POS ratio was 2.98±0,91. There was no statistical differences between POS (p=0,381) and POS ratio (p=0,185) of revision pedicle screws.

Conclusion:

PMMA augmentation achieved close POS to that of the primary screw so it can be concluded that it is a stronger revision technique compare to the larger or ala screws. On the other hand, there were no statistical differences between revision screws based on POS and POS ratio.