The Role of Minimally Invasive Vertebral Body Stent on Reduction of the Deflation Effect After Kyphoplasty: A Biomechanical Study.

STUDY DESIGN: Biomechanical investigation using cadaver spines. OBJECTIVE: The aim of the present study was to assess the magnitude of the deflation effect after balloon kyphoplasty (BKP) or use of minimally invasive vertebral body stent (MIVBS) in in vitro biomechanical condition. SUMMARY OF BACKGROUND DATA: BKP is a well-established minimally invasive treatment option for osteoporotic vertebral compression fractures. However, this technique can lead to a secondary height loss-known as the "deflation effect"-causing intrasegmental kyphosis and an overall alignment failure. METHODS: The study was conducted on 24 human cadaveric vertebral bodies (T12-L5). After creating a compression fracture model, the fractured vertebral bodies were reduced by BKP (n = 12) or by MIVBS (n = 12) and then augmented with polymethyl methacrylate bone cement. Each step of the procedure was performed under fluoroscopic guidance and the results were analyzed quantitatively. Finally, the strength and stiffness of augmented vertebral bodies were measured by biomechanical tests. RESULTS: Complete initial reduction of the fractured vertebral body height was achieved by both systems. Secondary loss of reduction after balloon deflation was significantly greater in the BKP group (2.36 ±â€Š0.63 mm vs. 0.34 ±â€Š0.43 mm in the MIVBS group; P < 0.05). Height gain was significantly higher in the MIVBS group (77.68% ±â€Š11.46% vs. 34.87% ±â€Š13.16% in the BKP group; P < 0.05). Increase in the kyphotic angle gain (relative to the preoperative kyphotic angle) was significantly more in the MIVBS group (95.60% ±â€Š6.12% vs. 77.0% ±â€Š4.94% in the BKP group; P < 0.05). Failure load was significantly higher in the MIVBS group (189% ±â€Š16% vs. 146% ±â€Š14%; P < 0.05). However, stiffness was not significantly different between the two groups. CONCLUSION: The deflation effect after BKP can be significantly decreased with the use of the MIVBS technique. LEVEL OF EVIDENCE: N/A.

Effects of a new shape-memory alloy interspinous process device on pressure distribution of the intervertebral disc and zygapophyseal joints in vitro.

OBJECTIVE: To quantify the pressure distribution of lumbar intervertebral discs and zygapophyseal joints with different degrees of distraction of the interspinous processes by using a new shape-memory interspinous process stabilization device, and to research the relationship between changing disc and zygapophyseal joint loads and the degree of distraction of interspinous processes, and thus optimize usage of the implant. METHODS: Six cadaver lumbar specimens (L(2)-L(5)) were loaded. The loads in disc and zygapophyseal joints were recorded at each L(3-4) disc level. Implants with different spacer heights were then placed by turn and the pressure measurements repeated. RESULTS: An implant with 10 mm spacer height does not significantly share the load. A 12 mm implant reduces the posterior annulus load, and meanwhile decreases the zygapophyseal joints pressure, but only in extension. A 14 mm implant shares the loads of posterior annulus, nucleus, and zygapophyseal joints in extension and the neutral position, but slightly increases the anterior annulus' load. Though 16-20 mm implants do decrease the loads in the posterior annulus and zygapophyseal joints, the anterior annulus' load was apparently increased. CONCLUSION: Different degrees of distraction of the interspinous processes lead to different load distribution on the intervertebral disc. The implant tested is not appropriate in cases of serious spinal stenosis because of the contradiction that, while over-distraction of the interspinous processes decreases the posterior annulus and the zygapophyseal joints load and distracts the intervertebral foramina, it leads to a marked increase in the load of the anterior annulus, which is recognized to accelerate disc degeneration.

[Prevention and treatment of bone cement leakage in percutaneous kyphoplasty for osteoporotic vertebral body compression fracture].

OBJECTIVE: To investigate the causes and preventive methods of the bone cement leakage in percutaneous kyphoplasty (PKP) for osteoporotic vertebral body compression fracture (OVCF). METHODS: From April 2003 to November 2007, 116 patients with OVCF were treated with PKP, including 57 males and 59 females aged 65-92 years old (average 67.7 years old). All the patients suffered from trauma and the course of disease was 1-14 days (average 5.7 days). There were 159 compressed and fractured vertebral bodies, including one vertebral body in 83 cases, two vertebral bodies in 24 cases, three vertebral bodies in 8 cases, and four vertebral bodies in 1 case. The diagnosis of OVCF was confirmed by imaging examination before operation. All the patients had intact posterior vertebral walls, without symptoms of spinal and nerve root injury. During operation, 3.5-7.1 mL bone cement (average 4.8 mL) was injected into single vertebral body. RESULTS: The operation time was 30-90 minutes (average 48 minutes). Obvious pain relief was achieved in all the patients after operation. X-rays examination 2 days after operation revealed that the injured vertebral bodies were well replaced without further compression and deformation, and the bone cement was evenly distributed. Fourteen vertebral bodies had bone cement leakage (4 of anterior leakage, 4 of lateral leakage, 3 of posterior leakage, 2 of intervertebral leakage, 1 of spinal canal leakage). The reason for the bone cement leakage included the individuality of patient, the standardization of manipulation and the time of injecting bone cement. During the follow-up period of 12-30 months (average 24 months), all the patients got their normal life back, without pain, operation-induced spinal canal stenosis, obvious height loss of injured vertebral bodies and other complications. CONCLUSION: For OVCF, PKP is a mini-invasive, effective and safe procedure that provides pain relief and stabilization of spinal stability. The occurrence of bone cement leakages can be reduced by choosing the suitable case, improving the viscosity of bone cement, injecting the proper amount of bone cement and precise location during operation.