Background: Scoliosis is a complex three-dimensional deformity with
limited treatment options. Current treatments present potential problems that
may be addressed with use of fusionless techniques for the correction of
scoliosis. However, there are few data comparing the efficacy of different
fusionless implant strategies in controlling scoliosis or on the integrity of
rigid compared with flexible devices in an in vivo setting over time. The
objective of this study was to compare the efficacy and integrity of rigid and
flexible anterior thoracic tethers used to treat experimental scoliosis.
Methods: Experimental scoliosis was created in twenty-four Spanish
Cross-X female goats and was subsequently treated with either anterior shape
memory alloy staples or anterior ligament tethers attached to bone anchors.
Serial radiographs were analyzed to determine the efficacy of the implants in
controlling scoliosis progression as well as the integrity of the implants at
study completion. After the goats were killed, the implants were analyzed with
use of three quantitative indices of implant integrity and implant pullout
Results: Over the treatment period, scoliosis progressed from
77.3° to 94.3° in the goats treated with staples and was corrected
from 73.4° to 69.9° in the goats treated with bone anchors, with
loosening of eighteen of forty-two staples (two of the eighteen dislodged) and
evidence of drift in two of forty-nine anchors. Histologic sections revealed a
consistent halo of fibrous tissue around the staple tines but well-fixed bone
anchors at all sites. Pullout testing demonstrated that bone anchors had
greater strength than staples initially and at the study completion, with an
increase in bone anchor fixation over the course of the study.
Conclusions: In this scoliosis model, the flexible ligament tethers
attached to bone anchors demonstrated greater efficacy and integrity than the
more rigid shape memory alloy staples.
Clinical Relevance: Fusionless scoliosis surgery offers many
theoretical advantages over instrumented arthrodesis. Improvements in
fusionless implant design, with a specific focus on optimizing the fixation to
bone and maximizing the tethering effect, may lead to better control of
idiopathic scoliosis with lower rates of device loosening and failure.