Ligamentous Augmentation to Prevent Proximal Junctional Kyphosis and Failure: A Biomechanical Cadaveric Study.

Study design: Biomechanical cadaveric study (level V).

Objective: To evaluate the effectiveness of polyethylene bands looped around the supra-adjacent spinous process (SP) or spinal lamina (SL) in providing strength to the cephalad unfused segment and reducing junctional stress.

Background: Proximal junctional kyphosis (PJK) is a pathologic kyphotic deformity adjacent to posterior spinal instrumentation after fusion constructs. Recent studies demonstrate a mismatch in stiffness between the instrumented construct and nonfused adjacent levels to be a causative factor in the development of PJK and proximal junction failure. To our knowledge, no biomechanical studies have addressed the effect of different methods of polyethylene band placement at the proximal junction.

Materials and methods: Twelve fresh frozen cadavers were divided into 3 groups of 4: pedicle screw-based instrumentation from T10 to L5 ("control"), T10-L5 instrumentation with a polyethylene band to the T9 "SP," T10-L5 instrumentation with 2 polyethylene bands to the T9 "SL." Specimens were tested with an eccentric (10 mm anterior) load at 5 mm/min for 15 mm or until failure occurred. Failure was defined by the inflection point on the load versus deformation curves. Linear regression was utilized to evaluate the effect of augmentation on the load-to-failure. Significance was set at 0.05.

Results: Fractures occurred in all specimens tested. The mean peak load to failure was 2148 N (974-3322) for the SP group, and 1248 N (742-1754) for the control group ( P > 0.05) and 1390 N (1080-2004) for the SL group. No difference existed between the control group and the SP group in terms of fracture level ( P > 0.05). Net kyphotic angulation shows no differences among these 3 groups ( P > 0.05).

Conclusion: Although statistical significance was not achieved, ligament augmentation to the SP increased mean peak load-to-failure in a cadaveric PJK model.