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Biomechanical limitations of partial pediculectomy in endoscopic spine surgery
Anna-Katharina Calek1, Christos Tsagkaris2, Marie-Rosa Fasser3
1Department of Orthopedics, Balgrist University Hospital, University of Zurich, Forchstrasse 340, CH-8008, Zurich, Switzerland; University Spine Center Zurich, Balgrist University Hospital, University of Zurich, Forchstrasse 340, CH-8008, Zurich, Switzerland.
Background Context:
Transforaminal endoscopic decompression is an emerging minimally invasive surgical technique in spine surgery. The biomechanical effects and limitations of resections associated with this technique are scarce.
Purpose:
The objective of this study was to analyze the effects of three different extents of reduction at the craniomedial pedicle (10%, 25%, and 50%) and to compare them with the intact native side. In addition, the influence of bone quality on the resistance of the pedicle after reduction was investigated.
Study Design:
Biomechanical cadaveric study.
Methods:
Thirty lumbar vertebrae originating from six fresh frozen cadavers were tested under uniaxial compression load in a ramp-to-failure test: (1) the reduced pedicle on one side, and (2) the native pedicle on the other side. Of the 30 lumbar vertebrae, ten were assigned to each reduction group (10%, 25%, and 50%).
Results:
On the intact side, the median axial compression force to failure was 593 N (442.4-785.8). A reduction of the pedicle by 10% of the cross-sectional area resulted in a decrease of the axial load resistance by 4% to 66% compared to the intact opposite side (p=.046). The median compression force to failure was 381.89 N (range: 336-662.1). A reduction by 25% resulted in a decrease of 7% to 71% (p=.001). The median compression force to failure was 333 N (265.1-397.3). A reduction by 50% resulted in a decrease of 39% to 90% (p<.001). The median compression force to failure was 200.9 N (192.3-283.9). At 10% pedicle reduction, the Hounsfield units (HU) value and the absolute force required to generate a pedicle fracture showed significant correlations (ρ=.872; p=.001). At 25%, a positive correlation between the two variables could still be identified (ρ=.603; p=.065). At 50%, no correlation was found (ρ=-.122; p=.738).
Conclusion:
Resection of the inner, upper part of the pedicle significantly reduces the axial resistance force of the pedicle until a fracture occurs.
Clinical Significance:
The extent of pedicle reduction itself plays only a limited role: once the cortical bone in the pedicle region is compromised, significant loss of resistance to loading must be anticipated.
