Elisa C. Bass

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-1β, IL-6, and TNF-α, 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-1β in tail discs 4 days following injury. No significant changes in IL-1β, IL-6, or TNF-α 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-1β. 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.

Effect of frozen storage on the creep behavior of human intervertebral discs.

Study Design. A biomechanical study of the compressive creep behavior of the human intervertebral disc before and after frozen storage. Objectives. To determine whether frozen storage alters the time-dependent response of the intact human intervertebral disc. Summary of Background Data. The biomechanical properties of the intervertebral disc are generally determined using specimens that have been previously frozen. Although it is well established that freezing does not alter the elastic response of the disc, recent data demonstrate that freezing permanently alters the time-dependent mechanical behavior of porcine discs. Methods. Twenty lumbar motion segments from 10 human spines were harvested between 12 and 36 hours postmortem. The specimens were randomly assigned to one of two groups: Group 1 was tested promptly, stored frozen for 3 weeks, then thawed, and tested a second time; Group 2 was stored frozen for 3 weeks, thawed, and then tested. Each specimen was subjected to 5 cycles of compressive creep under 1 MPa for 20 minutes, followed by a 40-minute recovery under no load. After testing each specimen was graded on a degeneration scale. A fluid transport model was used to parameterize the creep data. Results. There was no statistically significant effect of freezing on the elastic or creep response of the discs. The degree of pre-existing degeneration had a significant effect on the creep response, with the more degenerated discs appearing more permeable. Conclusions. Frozen storage for a reasonable time with a typical method does not significantly alter the creep response of human lumbar discs. Freezing may produce subtle effects, but these potential artifacts do not appear to alter the discs’ time-dependent behavior in any consequential way. These results may not apply to tissue kept frozen for long durations and with poor packaging.

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.

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.

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.

Intradiscal thermal therapy using interstitial ultrasound : An in vivo investigation in ovine cervical spine

Study Design. In vivo investigation of intradiscal ultrasound thermal therapy in ovine cervical spine model. Objective. To evaluate the potential of interstitial ultrasound for selective heating of intradiscal tissue in vivo. Summary of Background Data. Application of heat in the spine using resistive wire and radiofrequency current heating devices is currently being used clinically for minimally invasive treatment of discogenic low back pain. Treatment temperatures are representative of those required for thermal necrosis of ingrowing nociceptor nerve fibers and disc cellularity alone, or with coagulation and restructuring of anular collagen in the high temperature case. Methods. Two interstitial ultrasound applicator design configurations with directional heating patterns were evaluated in vivo in ovine cervical intervertebral discs (n = 62), with up to 45-day survival periods. Two heating protocols were employed in which the temperature measured 5 mm away from the applicator was controlled to either <54 C (capable of nerve and cellular necrosis) or >70 C (for coagulation of collagen) for a 10-minute treatment period. Transient and steady state temperature maps, calculated thermal doses (t43), and histology were used to assess the thermal treatments. Results. These studies demonstrated the capability to control spatial temperature distributions within selected regions of the in vivo intervertebral disc and anular wall using interstitial ultrasound. Conclusions. Ultrasound energy is capable of penetrating within the highly attenuating disc tissue to produce more extensive radial thermal penetration, lower maximum intradiscal temperature, and shorter treatment times than can be achieved with current clinical intradiscal heating technology. Thus, interstitial ultrasound offers potential as a more precise and faster heating modality for the clinical management of low back pain and studies of thermal effects on disc tissue in animal models.

Effects of thermal therapy on intervertebral discs: investigations using a miniaturized RF heating probe in a small animal model (Invited Paper)

Several studies have suggested that thermal therapy has a beneficial effect on degenerated intervertebral discs. Possible therapeutic mechanisms include collagen denaturation, cell ablation, and nerve tissue coagulation, however the precise mechanism or combination of mechanisms is unknown. To investigate the in vivo effects of thermal therapy on intervertebral discs using a murine model, a monopolar RF heating probe was developed and characterized. In addition, the effect size of several different thermal exposures was investigated by quantifying regions of cell death and collagen denaturation in rat discs. The heating probes were fabricated to have a 0.3mm outer diameter, 0.9mm exposed heating tip, and contain a thermocouple to monitor probe temperature. Using less than 2 Watts of RF energy produced high temperatures close to the probe and a steep radial temperature falloff. Five discs were treated at each of seven thermal exposures: 80°C for 10min, 80°C for 1min, 75°C for 5min, 62°C for 10min, 55°C for 15min, 48°C for 15min, and 48°C for 5min. A cell death region was observed in all treated discs and was significantly greater at the 80°C for 10min exposure than any of the lower exposures. Denaturation area was significantly greater at the 80°C for 10min exposure than at the four lowest temperature exposures. Denaturation was not observed in the 48°C exposures and was inconsistent in the 55°C and 62°C exposures. These results demonstrate that it is possible to limit and target the effects of thermal therapy to a portion of the murine disc using this RF probe.