Eric S. Varley

Effects of Intraoperative Tensioning of an Anterolateral Spinal Tether on Spinal Growth Modulation in a Porcine Model

STUDY DESIGN in vivo analysis in an immature porcine model. OBJECTIVE to evaluate the effect of intraoperative tensioning of an anterolateral flexible spinal tether on growth modulation manifested as deformity creation, disc response, spinal motion, and screw fixation using radiographs, computed tomography, magnetic resonance imaging, biomechanical testing, and histology. SUMMARY OF BACKGROUND DATA spinal growth modulation using an anterolateral flexible tether has been proposed as a nonfusion surgical deformity correction strategy for idiopathic scoliosis and has been successfully demonstrated in a porcine model to create spinal deformity while maintaining disc viability. METHODS twelve 7-month-old mini-pigs were instrumented with a screw-staple and polyethylene tether construct over 4 consecutive thoracic vertebrae (T8-T11). Intraoperative tensioning of the tether (250 N) was performed in alternate pigs (Pretensioned and Untensioned groups, n = 6 per group). Screws were coated with hydroxyapatite in half of the animals in each surgical group. Preoperative, postoperative, and monthly radiographs were evaluated, comparing deformity creation, vertebral body wedging, and disc wedging between the groups. Vertebral body shape was evaluated by computed tomography. Magnetic resonance and histology evaluated disc health. Biomechanical testing was performed to determine the effect of tensioning the tether on spinal motion and screw fixation. RESULTS intraoperative tensioning produced immediate coronal deformity (8° ± 4° vs. 2° ± 1° in untensioned spines; P = 0.01) and apical disc (T9-T10) wedging, vertex on tethered side, (5° ± 2° vs. 2° ± 1°; P = 0.01). After 12 months, the groups were similar in coronal deformity (28° ± 18° pretensioned, 27° ± 11° untensioned, P = 0.88), sagittal deformity (25° ± 3° vs. 22° ± 3°; P = 0.14), vertebral body wedging (10° ± 5° vs. 8° ± 3°; P = 0.45), and disc wedging (-4° ± 1° vs. -4° ± 3°; P = 0.88). There was no radiographic evidence of screw loosening. One of the discs from each group had diminished T2 signal after 12 months of tethering. Tether pretensioning did not affect spinal stiffness or motion. Interestingly, screw fixation increased with pretensioning; however, there was no significant advantage with hydroxyapatite coating. Histology demonstrated normal-appearing discs. CONCLUSION pretensioning of the tether created immediate deformity without effecting ultimate vertebral or disc deformity creation. Spinal motion and stiffness were not altered by pretensioning; however, pretensioning increased the torque required for screw extraction.

Isocentric reattachment of ligamentum teres: a porcine study.

Background: Recent reports reveal interest in the mechanical importance of ligamentum teres (LT) in hip dislocation. In the previously established procedure of anteroinferior acetabular LT reattachment in developmental dysplasia of the hip, the LT functions as a check-rein, showing promising results. However, this position of reattachment could potentially limit motion. The purpose of this study was to evaluate the feasibility of an isocentric point for reattachment of the LT and to study its impact on hip function using a young porcine model. Methods: Pelvic specimens with intact anatomy were obtained from 6 skeletally immature pigs (12 hips). Through a careful anteromedial capsulotomy, the LT was detached from its acetabular insertion then reattached to 1 of 2 positions: (1) anteroinferior lip of the acetabulum; (2) proposed isocentric position. Intra-articular stress distribution was measured through a complete range of motion with a prescale Fuji pressure film. Tension was then applied to the LT and the stresses were recorded again. In addition, radioopaque solution was injected into the substance of the LT, then floroscopy tracked the LT location initially and after the 2 reattachment positions through a full hip range of motion. Results: Reattachment of the LT at an isocentric point is feasible in a pig model. With careful physiologic tensioning of this reattachment, hip can maintain full motion with no excessive pressure areas created within the joint. On the contrary, the initial technique of anteroinferior extra-articular attachment limits external rotation and extremes of abduction. We found this LT tracking technique (with radioopaque dye injection) to be reliable and reproducible. Conclusions: The isocentric reattachment of the LT is feasible in this pig model and serves as a natural check-rein to dislocation without limiting joint motion or causing abnormal cartilage pressures. Clinical Relevance: Isocentric LT reattachment may provide a method for improving stability of open reductions when treating children with such conditions.

Calcitonin treatment in lumbar spinal stenosis: a meta-analysis.

INTRODUCTION: The management of lumbar spinal stenosis (LSS) represents a significant cost to the healthcare system resulting from the functional limitations and diminished quality of life in patients. Calcitonin is presently indicated for the treatment of postmenopausal osteoporosis, Pagets disease, spine pain related to vertebral compression fractures, and spinal metastases. In spinal stenosis patients, it has been suggested to have both analgesic and anti-inflammatory properties. The aim of this metaanalysis was to review the published randomized control trials to determine the effect of calcitonin on walking distance and Visual Analog Pain Scale (VAS) for pain in patients with lumbar spinal stenosis compared to placebo.

Intracapsular hip pressures in a porcine model: does position and volume matter?

This study outlines a relationship between joint volume, positioning, and intracapsular pressure in a healthy hip. After measuring the native intracapsular pressure in 12 porcine specimens, each joint was injected with radio-opaque-colored saline as pressures were measured. At 20 mmHg, the hip was placed in its position of ease and then in differing positions while pressures were recorded. Position significantly altered pressures, with the lowest values in neutral and the highest in hyperextension (P<0.001). Extreme hip positions may be detrimental because of high pressures created within the joint, possibly explaining complications associated with some hip diagnostic and treatment methods.

Spinal supports and physical therapy in patients with low back pain: a case series.

The association of low back pain with physical workload in seated workstation related jobs has been debated and remains controversial. Clinical studies eliciting the natural history of the disease in this emerging population are insufficient to make definitive conclusions. We report four consecutive cases of patients suffering from low back pain presenting to a tertiary spine clinic with severe non-specific low back pain. Two patients as age-matched controls with persistent low back pain were followed for 6 months after receiving conventional treatment. In comparison, two test patients received parallel conventional treatment along with orthopaedic full spinal supports as an additional treatment modality. Outcomes analysed demonstrate the efficacy of orthopaedic full spinal supports for treating low back pain. Trial registration number: NCT00553540