Peter F Jarzem

Publications (2)3.28 Total impact

• Article: The Effect of Angular Mismatch Between Vertebral Endplate and Vertebral Body Replacement Endplate on Implant Subsidence.

  Mohammad H Mohammad-Shahi, Vassilios S Nikolaou, Demetrios Giannitsios, Jean Ouellet, Peter F Jarzem
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  ABSTRACT: STUDY DESIGN:: Comparative biomechanical study. OBJECTIVE:: To determine whether an angular mismatch between the vertebral body replacement (VBR) endplate and the simulated foam vertebral endplate leads to accelerated subsidence in a cyclic compression model of the VBR-vertebra interface. SUMMARY OF BACKGROUND DATA:: One of the main complications of the VBR surgery is postoperative subsidence and collapse of the VBR implant into the adjacent vertebral bodies. Although numerous factors affecting intervertebral cage subsidence have been cited, few studies have proposed factors responsible for VBR cage subsidence. METHODS:: Hardwood blocks at 0-30-degree angles and polyurethane foam blocs have been used as base for this experimental setting. One end of the Synex (Synthes) expandable cage was attached to a material testing machine. The endplate of the implant was placed at a similar spot on the block in such a manner that there was an exact match between the Synex endplate and the foam block at 0 degrees, subsequent angled blocks would tilt the foam endplates by the 10-, 20-, and 30-degree increments as needed. Cyclic axial loads were applied in 9 load-unload cycles. RESULTS:: Five samples were tested at each mismatch angle (0, 10, 20, and 30 degrees), for a total of 20 trials. Implant subsidence significantly increased for each 10-degree increase in mismatch angle. This effect, however, did not follow a uniform trend at all angles. The curve appeared exponential at 0 degree of angular mismatch, became linear at 10-20 degrees of mismatch, and then demonstrated some ability to resist load at 30 degrees, leading to a plateau at the higher loads. CONCLUSIONS:: Increasing mismatch angles are an important factor in leading to increased cage subsidence into polyurethane blocks. Consequently, the incidence of subsidence in the clinical setting could be reduced by paying careful attention to ensuring that both the prosthetic and bony endplates are well apposed at the end of surgery.
  Journal of spinal disorders & techniques 01/2012; · 1.21 Impact Factor
• Article: An in vitro study on the effects of freezing, spine segment, repeat measurement, and individual cord properties on cord interstitial pressure.

  Mahdi Bassi, Peter F Jarzem, Matthew Steibel, Peter Barriga, Jean Ouellet, Rudy Reindl
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  ABSTRACT: In vitro study of the spinal cord tension and pressure relationships before and after thawing in 6 different spinal cord segment from 2 individual pigs. To determine if frozen and thawed spinal cord segments had different tension/cord interstitial pressure(CIP) relationships to fresh spinal cord segments. In addition, we will determine if the cord level, individual cord properties, and repeated CIP measurements affect the tension/CIP relationships. Spinal cord distraction is a known cause of spinal cord injury. Several articles published on the pathophysiology of the cord distraction injury suggest that the underlying mechanism of injury is a microvascular ischemic event. We have previously described an increase in CIP with spinal cord distraction, pressures average 23 mmHg at 1 kg loads. Six cord segments harvested from 2 pigs contained cervical, thoracic, and lumbar segments, and underwent distraction using a series of 7 calibrated weights from 0 to 1000 g weight. The cords were measured at each level of distraction. The cords were then frozen at -20 degrees C for a period of 2 weeks, and then thawed and retested. Multiple linear regression was then performed. There was no difference between the fresh and the frozen-thawed cords; there was statistical difference between the 2 pigs (18 mmHg) (P < 0.001). There are differences between the cervical and the thoracic cord segments (P < 0.001), and between cervical and lumbar cord segments (P = 0.056). There is a significant relation between the tension applied and CIP. Repeated trials showed no drift with repeated measures. Freezing and thawing spinal cords has no effect on the CIP/tension curves. Cord interstitial pressure developed is dependant on cord tension, cord level, individual cord properties, but not on the number of repetitions carried out while testing the spinal cord.
  Spine 02/2009; 34(4):351-5. · 2.08 Impact Factor