Abstract
Introduction
PJK is a well-described post-operative complication associated with long instrumented fusion constructs. The surgical creation of a stiff upper segment along with patient osteoporosis has been suggested as etiologies.
Materials and Methods
Fifteen fresh-frozen ligamentous T6 - pelvis specimens were divided equally into three Groups: Group 1 - Bilateral pedicle screw and rod instrumentation from T10 to S1, no cement; Group 2 - Instrumentation + 4cc of cement injected into T10 (UIV) and 4cc into T9 (UIV + 1), 2cc of cement injected through each pedicle; & Group 3 - Instrumentation + 4cc of cement in T10 (UIV), 3cc total in T9 (UIV + 1), and 2cc total in T8 (UIV + 2). The pelvis and T6 vertebra were potted. Eccentric axial compression was applied 10mm anterior to the center of T6 using an MTS actuator. Maximum load to failure was measured in newtons (N). The spines were evaluated using fluoroscopy and CT.
Results
There was a significant reduction in the number of fractures in Group 3 versus Groups 2 and 1 (p = 0.0019). There was only one fracture in Group 3, which occurred at T8 (UIV + 2); all five specimens suffered a fracture in Group 2; and five in Group 1. Posterior ligamentous rupture occurred in four specimens in Group 3; three in Group 2; and only one in Group 1. The mean peak load-to-failure values showed an increasing trend from Groups 1 to 3 (p = 0.38). There was no difference in specimen DEXA values (p = 0.71). There was no hardware failure in any Group. FEA mirrored the cadaveric data and the maximum load to failure increased from Group 1 to 3. Endplate stresses were reduced in Group 3 versus Groups 1 and 2.
Conclusions
In both cadaveric and FEA models, this novel technique of tapering the dose of prophylactic vertebroplasty cement in the UIV, UIV + 1, UIV + 2 decreased the endplate stresses, increased the load required for failure, and significantly reduced the incidence of VCFs above long-segment instrumented constructs. Clinically, this technique may reduce the risk of PJK, PJF, and revision surgery.