John M. Mathis

The biomechanics of vertebroplasty : The effect of cement volume on mechanical behavior

Study Design. Ex vivo biomechanical study using osteoporotic cadaveric vertebral bodies. Objective. To determine the association between the volume of cement injected during percutaneous vertebroplasty and the restoration of strength and stiffness in osteoporotic vertebral bodies, two investigational cements were studied: Orthocomp (Orthovita, Malvern, PA) and Simplex 20 (Simplex P with 20% by weight barium sulfate content; Stryker-Howmedica-Osteonics, Rutherford, NJ). Summary of Background Data. Previous biomechanical studies have shown that injections of 8–10 mL of cement during vertebroplasty restore or increase vertebral body strength and stiffness; however, the dose–response association between cement volume and restoration of strength and stiffness is unknown. Methods. Compression fractures were experimentally created in 144 vertebral bodies (T6–L5) obtained from 12 osteoporotic spines harvested from female cadavers. After initial strength and stiffness were determined, the vertebral bodies were stabilized using bipedicular injections of cement totaling 2, 4, 6, or 8 mL and recompressed, after which post-treatment strength and stiffness were measured. Strength and stiffness were considered restored when post-treatment values were not significantly different from initial values. Results. Strength was restored for all regions when 2 mL of either cement was injected. To restore stiffness with Orthocomp, the thoracic and thoracolumbar regions required 4 mL, but the lumbar region required 6 mL. To restore stiffness with Simplex 20, the thoracic and lumbar regions required 4 mL, but the thoracolumbar region required 8 mL. Conclusion. These data provide guidance on the cement volumes needed to restore biomechanical integrity to compressed osteoporotic vertebral bodies.

Biomechanical efficacy of unipedicular versus bipedicular vertebroplasty for the management of osteoporotic compression fractures

STUDY DESIGN Cadaveric study on the biomechanics of osteoporotic vertebral bodies augmented and not augmented with polymethylmethacrylate cement. OBJECTIVES To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and 1) not augmented, 2) augmented with unipedicular injection of cement, or 3) augmented with bipedicular injection of cement. SUMMARY OF BACKGROUND DATA Percutaneous vertebroplasty is a relatively new method of managing osteoporotic compression fractures, but it lacks biomechanical confirmation. METHODS Fresh vertebral bodies (L2-L5) were harvested from 10 osteoporotic spines (T scores range, -3.7 to -8.8) and compressed in a materials testing machine to determine intact strength and stiffness. They were then repaired using a transpedicular injection of cement (unipedicular or bipedicular), or they were unaugmented and recrushed. RESULTS Results suggest that unipedicular and bipedicular cement injection restored vertebral body stiffness to intact values, whereas unaugmented vertebral bodies were significantly more compliant than either injected or intact vertebral bodies. Vertebral bodies injected with cement (both bipedicular and unipedicular) were significantly stronger than the intact vertebral bodies, whereas unaugmented vertebral bodies were significantly weaker. There was no significant difference in loss in vertebral body height between any of the augmentation groups. CONCLUSIONS This study suggests that unipedicular and bipedicular injection of cement, as used during percutaneous vertebroplasty, increases acute strength and restores stiffness of vertebral bodies with compression fractures.

An ex vivo biomechanical evaluation of an inflatable bone tamp used in the treatment of compression fracture

Study Design. Ex vivo biomechanical study using osteoporotic cadaveric vertebral bodies. Objectives. To determine if the inflatable bone tamp (tamp) restores height to compressed vertebral bodies and to compare the biomechanical properties of isolated, fractured osteoporotic vertebral bodies treated by kyphoplasty (tamp) or vertebroplasty. Summary of Background Data. Previous biomechanical studies have shown that vertebroplasty increases vertebral body strength and restores vertebral body stiffness, but does not restore vertebral body height lost as a result of compression fracture. Methods. Compression fractures were experimentally created in 16 osteoporotic VBs assigned to either the tamp or percutaneous vertebroplasty group. The tamp treatment consisted of inserting balloon-like devices into the vertebral body, inflating the bone tamp, and filling the void with Simplex P (Howmedica, Rutherford, NJ) bone cement. The percutaneous vertebroplasty treatment consisted of directly injecting Cranioplastic bone cement (CMW, Blackpool, UK) into the vertebral body. Pre- and posttreatment heights were measured, and the repaired vertebral bodies were recompressed to determine posttreatment strength and stiffness values. Results. The tamp treatment resulted in significant restoration (97%) of vertebral body height lost after compression, whereas percutaneous vertebroplasty treatment resulted in a significantly lower restoration of lost height (30%) (P < 0.05). Both treatments resulted in significantly stronger vertebral bodies relative to their initial state (P < 0.05). The tamp treatment restored vertebral body stiffness to initial values, but the percutaneous vertebroplasty treatment did not (P < 0.05). Conclusions. Tamp treatment resulted in significantly greater height restoration than did percutaneous vertebroplasty, without loss of vertebral body strength or stiffness.

Biomechanical Evaluation of a New Bone Cement for Use in Vertebroplasty

STUDY DESIGN Comparative ex vivobiomechanical study. OBJECTIVES To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and subsequently stabilized via bipedicular injection of one of two bone cements: one is a commercially available polymethylmethacrylate (Simplex P) and one is a proprietary glass-ceramic-reinforced BisGMA/BisEMA/TEGDMA matrix composite that is being developed for use in vertebroplasty (Orthocomp). SUMMARY OF BACKGROUND DATA Osteoporotic compression fractures present diagnostic and therapeutic challenges for the clinician. Vertebroplasty, a new technique for treating such fractures, stabilizes vertebral bodies by injection of cement. Little is known, however, about the biomechanics of this treatment. METHODS Five vertebral bodies (L1-L5) from each of four fresh spines were harvested from female cadavers (age, 80 +/- 5 years), screened for bone density using DEXA (t = -3.4 to -6.4), disarticulated, and compressed in a materials testing machine to determine initial strength and stiffness. The fractures then were repaired using a transpedicular injection of either Orthocomp or Simplex P and recrushed. RESULTS For both cement treatments, vertebral body strength after injection of cement was significantly greater than initial strength values. Vertebral bodies augmented with Orthocomp recovered their initial stiffness; however, vertebral bodies augmented with Simplex P were significantly less stiff than they were in their initial condition. CONCLUSIONS Augmentation with Orthocomp results in similar or greater mechanical properties compared with Simplex P, but these biomechanical results have yet to be substantiated in clinical studies.

Percutaneous vertebroplasty treatment of steroid-induced osteoporotic compression fractures

This report describes the case of a woman in whom multiple compression fractures of the lower thoracic and lumbar spine occurred in association with long-term corticosteroid therapy for systemic lupus erythematosus. Pain markedly limited the patients mobility and daily activities, and conservative therapy with bracing and narcotic analgesics gave little improvement. Affected vertebrae were treated with polymethylmethacrylate, introduced percutaneously under fluoroscopic guidance. The resulting reinforcement of the fractured vertebral bodies eliminated the pain and the need for narcotic analgesics. The utilization of percutaneous verterbroplasty as a therapeutic alternative for the treatment of pain resulting from osteoporotic compression fractures is described.

An ex vivo biomechanical evaluation of a hydroxyapatite cement for use with vertebroplasty

Study Design. Comparative ex vivo biomechanical study. Objective. To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and stabilized via bipedicular injections of the following: 1) Simplex P (Stryker-Howmedica-Osteonics, Rutherford, NJ), 2) Simplex P formulated consistent with the practice of vertebroplasty (F2), or 3) BoneSource (Stryker-Howmedica-Osteonics). Summary of Background Data. Little is known about the mechanical stabilization afforded by new materials proposed for use with vertebroplasty. Methods. Vertebral bodies (T8–T10 and L2–L4) from each of 10 fresh spines were harvested from female cadavers (81 ± 12 years), screened for bone density (t score, −3.8 ± 1.1; bone mineral density, 0.75 ± 15 g/cm2), disarticulated, and compressed to determine initial strength and stiffness. The fractured vertebral bodies were stabilized via bipedicular injections of 4 mL (thoracic) or 6 mL (lumbar) and then recrushed. Results. Vertebral bodies repaired with Simplex P resulted in significantly greater strength (P < 0.05) relative to their prefracture states, those repaired with BoneSource resulted in the restoration of initial strength for both the thoracic and lumbar level, and those repaired with F2 resulted in significantly greater strength (P < 0.05) in the thoracic region and restoration of strength in the lumbar region. All cement treatments resulted in significantly less stiffness compared with initial values. Conclusions. All three materials tested restored or increased vertebral body strength, but none restored stiffness. Both new materials show promise for use in percutaneous vertebroplasty, but they need clinical evaluation.

1999 Young Investigator Research Award Runner-up: Effect of Augmentation on the Mechanics of Vertebral Wedge Fractures

Study Design. The effect of cement augmentation of wedge-fractured vertebral bodies on spine segment compliance was studied in 16 cadaver specimens. Objectives. 1) To assess the mechanical effects of cement augmentation of vertebral wedge fractures. 2) To determine whether a new reduction/injection procedure has the same mechanical effects as the established direct injection procedure. Summary of Background Data. Although wedge fractures cause pain and disability in hundreds of thousands of people, few effective treatments are available. Clinical studies have shown that cement augmentation, a new procedure, effectively relieves pain and restores mobility in patients suffering from weak or fractured vertebrae. However, only a few studies have examined the mechanics of vertebral augmentation. Methods. A wedge fracture was created in the middle vertebra of 16 three-vertebra cadaver spine segments. Neutral and full-load compliance of each fractured spine segment in flexion/extension and lateral bending were assessed by measuring the relative rotation of the vertebral bodies in response to applied moments. Eight of the fractured vertebral bodies were then augmented using direct injection, while the remaining eight fractured vertebral bodies were augmented using a combined reduction/injection procedure. Compliance of the augmented segments was then assessed. Results. Augmentation significantly reduced the neutral compliance (reduction of 25% ± 23%) (mean ± standard deviation) and the full-load compliance (reduction of 23% ± 20%) in flexion/extension (P < 0.005). Augmentation also significantly reduced the neutral compliance (reduction of 34% ± 20%) and the full-load compliance (reduction of 26% ± 17%) in lateral bending (P < 0.0001). No significant difference was found between the two procedures for compliance reduction. Conclusions. Augmentation of wedge fractures using both direct injection and reduction/injection reduces spine segment compliance significantly.

Vertebroplasty versus Kyphoplasty: A Comparison and Contrast

The phrase “vertebroplasty versus kyphoplasty” evokes images of competitive procedures and groups of entrenched physicians locked in battle. Our involvement in the development and introduction of percutaneous vertebroplasty (PV) and kyphoplasty (KP) in the United States has given us a unique

Technical considerations on intra-arterial papaverine hydrochloride for cerebral vasospasm

Abstract Intra-arterial infusion of papaverine hydrochloride for subarachnoid hemorrhage-induced cerebral vasospasm has become an adjunctive endovascular therapy along with cerebral angioplasty. Our knowledge concerning the mechanism of action, method of administration and potential side effects of this therapeutic alternative are reviewed.

Intra-arterial papaverine-induced seizures: case report and review of the literature.

BACKGROUND Microcatheter-guided intra-arterial (IA) papaverine infusion in conjunction with balloon angioplasty is an available therapy for patients with symptomatic vasospasm after subarachnoid hemorrhage (SAH) that is refractory to hypertensive, hypervolemic therapy. However, side effects and complications have been reported in association with its use. CASE DESCRIPTION We report on a patient who developed symptomatic vasospasm after subarachnoid hemorrhage due to rupture of a left terminal internal carotid artery (ICA) saccular aneurysm. Seven days after the hemorrhage and 4 days after surgical clipping, the patient developed aphasia and right hemiparesis due to vasospasm, which was refractory to maximal medical treatment with volume and blood pressure elevation. Cerebral angiography identified severe narrowing of distal ICA and proximal middle cerebral artery segments bilaterally. These findings partially resolved after balloon angioplasty. However, after 300 mg of IA papaverine, the patient developed generalized convulsions. This occurred despite therapeutic serum levels of phenytoin. Twenty-four hours later, after brief neurologic improvement, recurrent neurologic deficits prompted repeat papaverine administration. Seizures again occurred after the administration of 240 mg of IA papaverine and prevented administration of the full dose. The patient did not develop further seizures and her neurologic deficits continue to resolve. CONCLUSIONS IA papaverine-induced seizures are infrequently reported. This potential complication should be considered when papaverine administration is entertained in the treatment of anterior circulation refractory symptomatic vasospasm after SAH.