Locomotor biomechanics after total sacrectomy: a case report.

STUDY DESIGN: Biomechanical analysis of locomotion after total sacrectomy in a single patient case. OBJECTIVE: To describe the biomechanics of locomotion after successful total sacrectomy and spinopelvic reconstruction. SUMMARY OF BACKGROUND DATA: Total sacrectomy is a complex surgery that has significant consequences for mobility after surgery due to loss of lower lumbar and sacral innervation to the lower extremities, and the anatomic dissociation of the spine from the pelvis. There is no existing literature quantifying locomotor biomechanics after total sacrectomy. METHODS: A 22-year-old female with a sacral osteosarcoma underwent an en bloc sacrectomy with L3 to pelvis instrumented fusion. Neuromuscular function was tested 1 year after surgery using monopolar needle electromyography. Three-dimensional motion capture and surface electromyography were used to quantify spatiotemporal characteristics of locomotion and lower extremity kinematics, kinetics, and muscle function during locomotion at 6 months and 1 year after surgery. RESULTS: Electrodiagnostic testing suggested partial preservation and reinnervation of S1 nerve root function on the right, resulting in greater than expected activity in the hamstrings, gluteus maximus, and triceps surae postsurgically. Unexpectedly on the left, there was residual activity in the hamstrings, despite the loss of sacral innervation and the sciatic nerve. At 1 year after surgery, the patient was able to walk independently. Kinematic and kinetic impairments and compensations were most evident in the sagittal and coronal planes. CONCLUSION: Excellent locomotor outcomes are possible after total sacrectomy.

The analysis of axisymmetric viscoelasticity, time-dependent recovery, and hydration in rat tail intervertebral discs by radial compression test.

The goal of this study was to develop a nondestructive radial compression technique and to investigate the viscoelastic behavior of the rat tail disc under repeated radial compression. Rat tail intervertebral disc underwent radial compression relaxation testing and creep testing using a custom-made gravitational creep machine. The axisymmetric viscoelasticity and time-dependent recovery were determined. Different levels of hydration (with or without normal saline spray) were supplied to evaluate the effect of changes in viscoelastic properties. Viscoelasticity was found to be axisymmetric in rat-tail intervertebral discs at four equidistant locations. Complete relaxation recovery was found to take 20 min, whereas creep recovery required 25 min. Hydration was required for obtaining viscoelastic axisymmetry and complete viscoelastic recovery.