Can experimental data in humans verify the finite element-based bone remodeling algorithm?

STUDY DESIGN: A finite element analysis-based bone remodeling study in human was conducted in the lumbar spine operated on with pedicle screws. Bone remodeling results were compared to prospective experimental bone mineral content data of patients operated on with pedicle screws. OBJECTIVE: The validity of 2 bone remodeling algorithms was evaluated by comparing against prospective bone mineral content measurements. Also, the potential stress shielding effect was examined using the 2 bone remodeling algorithms and the experimental bone mineral data. SUMMARY OF BACKGROUND DATA: In previous studies, in the human spine, the bone remodeling algorithms have neither been evaluated experimentally nor been examined by comparing to unsystematic experimental data. METHODS: The site-specific and nonsite-specific iterative bone remodeling algorithms were applied to a finite element model of the lumbar spine operated on with pedicle screws between L4 and L5. The stress shielding effect was also examined. The bone remodeling results were compared with prospective bone mineral content measurements of 4 patients. They were measured after surgery, 3-, 6- and 12-months postoperatively. RESULTS: After 1 year, there was an average experimental bone loss of 9.78% below the positions of pedicle screws, and the results for the 2 bone remodeling algorithms showed an average bone gain of 8.41% and 1.61%. There were no similarities between the bone remodeling and experimental data. CONCLUSION: The bone remodeling data showed no resemblances when compared to the prospective data of BMC measurements. There was no basis for confirming the validity of the bone remodeling algorithms in this study.

Effect of hydroxyapatite-coated tibial components on changes in bone mineral density of the proximal tibia after uncemented total knee arthroplasty: a prospective randomized study using dual-energy x-ray absorptiometry.

Sixteen patients scheduled for an uncemented total knee arthroplasty (TKA) were randomized to receive a tibial component either with (n = 8) or without (n = 8) hydroxyapatite (HA) coating. In 4 regions of interest, prospective measurements of bone mineral density (BMD) using dual-energy x-ray absorptiometry were performed in the proximal tibia. Two years after the operation, the only significant change in BMD was in the lateral tibial condyle, where BMD had increased by 6.1% (95% confidence interval: 2.3%-9.9%) in patients with tibial components without HA. The intragroup changes (0-24 months) in the uncoated group and HA-coated group were significantly different (P = .003) in these regions of interest. There was no significant effect of HA coating on bone remodeling pattern of the proximal tibia.

Nonlinear finite-element analysis and biomechanical evaluation of the lumbar spine.

A finite-element analysis (FEA) model of an intact lumbar disc-body unit was generated. The vertebral body of the FEA model consisted of a solid tetrahedral core of trabecular bone surrounded by a cortical shell. The disc consisted of an incompressible nucleus surrounded by nonlinear annulus fibers embedded in a solid ground substance. The purpose was to create a FEA model suitable for clinical purposes as fracture assessment, instrumentation with pedicle screws, and bone remodeling. Testing of the FEA model was performed nonlinear for a number of loading conditions, and the results were compared with experimental data from the literature. The results showed good agreement. The formulation of the FEA model can be justified for the tested loading conditions.

No difference in clinical outcome after posterolateral lumbar fusion between patients with isthmic spondylolisthesis and those with degenerative disc disease using pedicle screw instrumentation: a comparative study of 112 patients with 4 years of follow-up.

We compared the clinical outcome after spinal fusion between patients with isthmic spondylolisthesis and those with degenerative disc disease of the lumbar spine, using multiple logistic regression analysis. A questionnaire describing medication, pain, vocational status and patient satisfaction was mailed to all the patients at a median interval of 4 years after their operation. Fusion was evaluated on plain radiographs at a minimum of 12 months after surgery, and patients were classified as fused or not fused. The overall satisfaction rate was 70%. The results of the present study showed no difference in the outcome after spinal fusion between the two groups of patients. The factors that significantly increased the likelihood of an optimal result - defined as patient satisfaction, return to work, and reduced medication - were male gender, being in work prior to surgery, and being a non-smoker. Since spinal fusion is an expensive treatment with potentially serious risks, and leaves one-third of the patients with an unsatisfactory result, we believe that more studies focusing on the indications for surgery should be performed.