Trauma

International Perspectives

A Focus on Spine Research
Orthopaedic Research Society, Las Vegas
Report from Amy Hoang-Kim
ISFR coordinator
March, 2009

At the 55th Annual Meeting of the Orthopaedic Research Society, several research topics focused on vertebral fractures. Currently there are various operative techniques for preparing the endplate of vertebral bodies for implant attachment and spinal fusion. In some studies, the endplate is completely removed to achieve the bleeding bone effect but penetration depth has not been quantified. Bell S et al (Utah, US) showed that while the deeper region of penetration may provide a faster and more active remodeling site, the structural stability of the vertebral body may be compromised at such an extensive penetration depth. Therefore, when designing intervertebral implants, it may be necessary to increase stability of the implant to accommodate the slower remodeling rate beyond the layer of calcified fibrocartilage, which is a non-remodeling tissue on the endplates of vertebral bodies in sheep and human cadaveric vertebrae.

A study was presented by Bessho M et al (Tokyo, Japan), on “Predicting strengths of the femur and vertebra in patients with postmenopausal osteoporosis by a CT based finite element method—The predicted fracture load of the proximal femur is correlated with that of the lumbar vertebra”. The right femur and the second lumbar vertebra (L2) in 40 female patients with postmenopausal osteoporosis (age: 52-89, average 70.1) were evaluated. Axial CT scans of the proximal femura and L2 were obtained (slice thickness: 3mm femur, 2mm L2, Aquilon Super 4, Toshiba Medical Systems Co, Tokyo, Japan), as well as scans of a calibration phantom. The element size was set to allow for bone heterogeneity and the mechanical properties of each element were computed from the Hounsfield unit value. Its equivalent ash density was derived with a linear regression model. Data was collected to evaluate the correlation between femoral and vertebral predicted fracture loads (PFLs). The average PFL of the proximal femur in stance configuration was 3910 N range: 2830 – 5800 N, SD:719N). The investigators found that femoral PFL in stance configuration could be utilized to estimate vertebral PFL and femoral PFL in fall configuration.

The degradation in quality of life following the onset of a vertebral compression fracture is well known. Mortality risk has been shown to increase by 23% following the onset of VCFs. Edidin, AA et al (Sunnyvale, CA) established the mortality risk associated with vertebral fractures for elderly patients of all ages, ethnicities, and gender in the healthcare system. The risk of mortality at short-term follow-up was significantly higher for patients that did not undergo operative treatment following VCF diagnosis. The risk of mortality for kyphoplasty patients was also significantly lower than that for vertebroplasty patients. It is to be determined by a long-term follow-up whether these trends will continue.

According to Raley TJ et al., the typical treatment for a vertebral compression fracture (VCF) involves the injection of bone cement into the vertebral body to fixate the fracture. This involves either injection of a low viscosity cement directly into the vertebral body (vertebroplasty) or the use of a balloon to create a void in the cancellous bone and injection of the bone cement into this created void (balloon kyphoplasty). The study investigated the potential height restoration ability of the two VCF treatment methods as well as an innovative vertebral augmentation system. Four female cadaver spines with a mean age at time of death of 72.8 ± 7.9 years (66-84 years old) maintained at -20ºC until approximately 24 hours prior to testing were used. A student t-test found no significant difference between the specimen groups for age or BMD. There was a significant difference in height between the prefracture and post-fracture specimens for all three groups. The mean anterior height restoration for the balloon kyphoplasty, vertebral augmentation, and vertebroplasty systems were 74.8 ± 9.4%, 83.7 ± 17.5% and 32.8 ± 8.1% respectively. There was no significant difference between the balloon kyphoplasty and vertebral augmentation system groups (p=0.40). The balloon kyphoplasty and vertebral augmentation system procedures both restored significantly more height compared to the vertebroplasty procedure (p P 0.001 and p P 0.002). Extravasation was noted for 1 balloon kyphoplasty, 0 for the vertebral augmentation, and 2 vertebroplasty specimens post treatment. In conclusion, the authors state that mechanical VCF height elevation equivalent to that observed in balloon-assisted kyphoplasty was achieved using an innovative ultrahigh viscosity cement vertebral augmentation system. In contrast, the conventional vertebroplasty procedure, in which cement simply fills existing VCF voids prior to extravasation via the path of least resistance, was unable to restore comparable height.

References:

• Bell S et al. The ideal penetration depth of the vertebral endplate to reach actively remodeling bone.
  Poster 1782, ORS, Las Vegas, Nevada. February 22-25, 2009.
  
  
• Bessho M et al. Predicting strengths of the femur and vertebra in patients with postmenopausal osteoporosis by a CT based finite element method
  Poster 637, ORS, Las Vegas, Nevada. February 22-25, 2009.
  
  
• Edidin AA et al. Mortality risk for operated and non-operated vertebral fracture patients in the medicare population.
  Poster 1800, ORS, Las Vegas, Nevada. February 22-25, 2009.
  
  
• Raley TJ et al. Comparative height restoration of three vertebral augmentation systems for treatment of vertebral compression fractures.
  Poster 639, ORS, Las Vegas, Nevada. February 22-25, 2009.