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Biomechanical risk factors for proximal junctional kyphosis: a detailed numerical analysis of surgical instrumentation variables

Marco Cammarata, BEng1,2, Carl-Éric Aubin, PhD, PEng1,3,Xiaoyu Wang, PhD1,3, Jean-Marc Mac-Thiong, MD, PhD2,3

1. Department of Mechanical Engineering, École Polytechnique de Montréal, Canada

2. Research Center, Hôpital du Sacré-Cœur de Montréal, Canada

3. Research Center, Sainte-Justine University Hospital Center, Canada


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• A total of 576 numerical simulations and a sensitivity analysis were performed for six adult spinal deformity instrumentation cases to assess four biomechanical indices related to the development of PJK:

– Immediate postoperative proximal junctional kyphotic angle;

– Thoracic kyphosis;

– Proximal junctional intervertebral flexion forces;

– Proximal junctional intervertebral flexion moment;

• The individual effect of four instrumentation variables on each of the above indices was evaluated:

– Proximal dissection procedure;

– Implant type at the upper instrumented vertebra;

– Sagittal thoracic rod curvature;

– Proximal diameter of the proximal transition rod;



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• Each of the followings biomechanically helps reducing the risk of PJK:– Preserving more intervertebral elements at the proximal end of

the instrumentation;– Using transverse process hooks instead of pedicle screws at the

upper instrumented vertebra;– Using tapered transition rods at the proximal end of the

instrumentation.• Monoaxial and multiaxial screws at upper instrumented vertebra had

similar effects on the four biomechanical indices.

Resulting average, minimum, and maximum values of each biomechanical index (PJ: proximal junctional; TK: thoracic kyphosis; UIV: upper instrumented vertebra)



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Typical results for one case (#2): FSU: intact functional spinal unit; BCF: bilateral complete facetectomy; PLD: posterior ligaments dissection; FAS: fixed angle screw; MAS: multiaxial screw; TPH: transverse process hook; PJ: proximal junctional; UIV: upper instrumented vertebra.

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