[home] [Personal Program] [Help]

---

Session: Medical Instruments - Surgery I
Session starts: Friday 25 January, 10:30
Presentation starts: 10:45
Room: Lecture room 557

---

Martijn Wessels (UT)
Edsko Hekman (UT)
Bart Verkerke (UT/UMCG)

Abstract:
Introduction - Surgical treatment of scoliosis generally consists of performing spondylo-desis, a technique which invokes vertebral fusion [Deyo, 2004]. Complications related to this technique are inhibition of spinal flexibility and growth. For that reason, non-fusion surgery is increasingly explored [Maruyama, 2008], however results are still not satisfying. The University of Twente developed a novel revolutionary non-fusion correction system which consists of two functional implants that are extremely flexible and extendable. The first implant (XS-TOR) generates a torque to correct the axial rotation of the spine. The second implant (XS-LAT) generates a lateral bending moment to correct the lateral curvature. Application of torque and bending moment is achieved by using cross-bridges that are anchored to three different vertebrae, using a three-point-bending mechanism. To deliver the appropriate moment, both implants are pre-stressed before final anchoring to the spine. Methods - For animal experiment applications, inverse versions of the implants were tested, which means that the systems were designed to induce scoliosis. The XS-TOR and XS-LAT were measured using an apparatus that simulates different spinal configurations. The implants were anchored to three metal vertebrae containing 6D force sensors, after which the vertebrae were rotated and translated e.g. axially and laterally towards the demanded position. The reaction forces and moments were recorded in all configurations. Results - The XS-TOR generates a torque which increases during growth of the system. Similarly, the XS-LAT generates a bending moment that slightly increases during growth of the system. The contribution to the spinal stiffness is limited, between 0.01 and 0.03 Nm/° in bending and between 0.04 and 0.08 Nm/° in torsion. Discussion - Although the inverse functionality of the implants results in altered behaviour, the magnitudes of moments are similar. The actual applied bending moment is dependent on the obtained correction and will reduce during correction. However, the decrease of the correction moment will be much less than observed in conventional fusion constructs which generally have a 300 to 400% higher bending stiffness. The contribution of XS-TOR and XS-LAT on spinal stiffness is very low since the stiffness of vertebral region is approximated between 2 and 3 Nm/° in (lateral) flexion and torsion [Panjabi, 1976], thus allowing flexibility of the spine, which will prevent fusion References Deyo et al, Spine J 4(S1): 138, 2004; Maruyama et al, Scoliosis 3(1): 6, 2008; Panjabi et al, JBJS Am 58(5): 642-652, 1976.