Heat-induced changes in porcine annulus fibrosus biomechanics.

The intervertebral disc is implicated as the source of low-back pain in a substantial number of patients. Because thermal therapy has been thought to have a therapeutic effect on collagenous tissues, this technique has recently been incorporated into several minimally invasive back pain treatments. However, patient selection criteria and precise definition of optimum dose are hindered by uncertainty of treatment mechanisms. The purpose of this study was to quantify acute changes in annulus fibrosus biomechanics after a range of thermal exposures, and to correlate these results with tissue denaturation. Intact annulus fibrosus (attached to adjacent vertebrae) from porcine lumbar spines was tested ex vivo. Biomechanical behavior, microstructure, peak of denaturation endotherm, and enthalpy of denaturation (mDSC) were determined before and after hydrothermal heat treatment at 37 degrees C, 50 degrees C, 60 degrees C, 65 degrees C, 70 degrees C, 75 degrees C, 80 degrees C, and 85 degrees C. Shrinkage of excised annular tissue (removed from adjacent vertebrae) was also measured after treatment at 85 degrees C. Significant differences in intact annulus biomechanics were observed after treatment, but the effects were much smaller in magnitude than those observed in excised annulus and those reported previously for other tissues. Consistent with this, intact tissue was only minimally denatured by treatment at 85 degrees C for 15 min, whereas excised tissue was completely denatured by this protocol. Our data suggest that in situ constraint imposed by the joint structure significantly retards annular thermal denaturation. These findings should aid the interpretation of clinical outcomes and provide a basis for the future design of optimum dosing regimens.

Ventral approach to the lumbar spine of the Sprague-Dawley rat.

Lumbar intervertebral disc repair is an important tissue-engineering research area. In creating an in vivo rat model to evaluate repair techniques, the authors developed a surgical transperitoneal approach that permits the easy exposure of four lumbar vertebral bodies with no surgery-related peri- or postoperative complications.

Stab incision for inducing intervertebral disc degeneration in the rat.

STUDY DESIGN: The degenerative response of rat tail and lumbar intervertebral discs to a stab incision was evaluated. OBJECTIVE: To examine and compare the postinjury degenerative response of lumbar and tail discs. SUMMARY OF BACKGROUND DATA: Although successful in larger animals, a stab incision for inducing disc degeneration in rats has not been evaluated. Rodents are desirable models for disc repair studies due to their low cost, ease of care, and fast healing times. METHODS: Lumbar and tail discs were exposed surgically and stabbed with a number 11 blade. Disc architecture, levels of IL-1beta, IL-6, and TNF-alpha, and biomechanical properties were analyzed. A functional disability secondary to multilevel lumbar disc injury was quantified and compared with that of rats undergoing sham surgery. RESULTS: Histologic evaluation of stabbed tail discs demonstrated a nucleus pulposus size decrease, anular collagen layer disorganization, and cellular metaplasia of anular fibroblasts to chondrocyte-appearing cells. Besides the continued presence of the stab injury tract, few changes were observed in the lumbar disc histology. Cytokine measurements indicated a transient peak in IL-1beta in tail discs 4 days following injury. No significant changes in IL-1beta, IL-6, or TNF-alpha were measured. No significant differences in biomechanical properties were observed between stab injury and sham surgery discs. Yet, despite insignificant differences in histologic, cytochemical, or biomechanical properties in the lumbar discs, the rats with lumbar stab injury had a significant decrease in walking ability 28 days after surgery. CONCLUSIONS: Tail disc stab injury was successful in creating morphologic signs of degeneration and transient high concentrations of IL-1beta. However, the degenerative response in the lumbar discs was much slower, suggesting that site-specific factors, such as increased stability due to posterior elements and torso musculature, helped facilitate healing. Yet, functional assessment indicated that the rats were partially disabled by multiple lumbar injuries.

Intradiscal thermal therapy does not stimulate biologic remodeling in an in vivo sheep model.

STUDY DESIGN: Thermal energy was delivered in vivo to ovine cervical discs and the postheating response was monitored over time. OBJECTIVES: To determine the effects of two distinctly different thermal exposures on biologic remodeling: a "high-dose" regimen intended to produce both cellular necrosis and collagen denaturation and a "low-dose" regimen intended only to kill cells. SUMMARY OF BACKGROUND DATA: Thermal therapy is a minimally invasive technique that may ameliorate discogenic back pain. Potential therapeutic mechanisms include shrinkage of collagenous tissues, stimulation of biologic remodeling, and ablation of cytokine-producing cells and nociceptive fibers. METHODS: Intradiscal heating was performed using directional interstitial ultrasound applicators. Temperature and thermal dose distributions were characterized. The effects of high (>70 C, 10 minutes) and low (52 C-54 C, 10 minutes) temperature treatments on chronic biomechanical and architectural changes were compared with sham-treated and control discs at 7, 45, and 180 days. RESULTS: The high-dose treatment caused both an acute and chronic loss of proteoglycan staining and a degradation of biomechanical properties compared with low-dose and sham groups. Similar amounts of degradation were observed in the low-dose and sham-treated discs relative to the control discs at 180 days after treatment. CONCLUSIONS: While a high temperature thermal protocol had a detrimental effect on the disc, the effects of low temperature treatment were relatively minor. Thermal therapy did not stimulate significant biologic remodeling. Future studies should focus on the effects of low-dose therapy on tissue innervation and pro-inflammatory factor production.

Predictors of outcomes after posterior decompression and fusion in degenerative spondylolisthesis.

No consensus has been reached regarding surgical management of degenerative spondylolisthesis. The optimal type of surgical procedure and surgical indications have not been precisely defined. In order to screen for predictors of outcome, we retrospectively studied patient outcomes after posterior decompression and fusion for isolated lumbar degenerative spondylolisthesis. Twenty-four consecutive patients (age range 50-78 years) underwent primary surgery for isolated lumbar degenerative spondylolisthesis. The surgical procedure consisted of posterior decompression and pedicle screw instrumented fusion using autogeneous bone graft, with or without interbody fusion. Clinical and radiologic status were assessed using the Beaujon functional score and plain AP and lateral radiographs. A multivariate analysis was used to correlate the functional score increase with surgical procedure modifications and preoperative clinical and radiologic features in order to determine which of them led to better results. Eighteen patients completed the evaluation. Six others were lost to follow-up after a minimum of 0.87 years. Combining all the results, the mean follow-up was 2.87 years. The Beaujon score was improved in the 24 patients (P<0.001), and fusion was successful in all cases. Additional interbody fusion and preoperative leg pain were significantly correlated with larger score increase (P=0.016 and P=0.003). Posterior decompression and fusion is successful in treating lumbar degenerative spondylolisthesis. From this study, circumferential fusion improves the outcomes and leg pain is a fair indication for surgery.