Proximal Junctional Kyphosis in Adult Spinal Deformity:Comparison of Hook versus Pedicle Screw Constructs
Methods: 123 consecutive patients (Group-1-79 pedicle screw constructs vs. Group-2-44 hook constructs) with a diagnosis of adult scoliosis having 2-year follow-up(mean=5.63+2.45SD yrs) were evaluated. Sagittal plane radiographic measurements were analyzed. Proximal junctional kyphosis was defined as the Cobb angle between the inferior endplate of the upper instrumented vertebrae(UIV) and the superior endplate of two levels cephalad to the UIV measuring >10 and having an absolute value of >10 . Significance was defined as p<0 .05.
Results: The prevalence of PJK was 36.6%(45/123pts) overall, with 38% in Group-1(Screws) and 34% in Group-2(Hooks)(p=0.11). Using prior surgery, age and osteotomy as a covariate, Group-1(Screws) demonstrated a significant increase in PJK preoperatively to postoperatively, and progressed until FFU(p<0 .0001). Group-2(Hooks) showed a significant increase preop to postop, with maintenance until FFU(p<0.0001 and p="0.08,respectively)." did not show any change in the C7 sagittal alignment, while Group-1(Screws) negative balance plumb postoperatively, progression towards positive at FFU(p<0.0001). In terms of thoracic alignment(T5-12), Group-2(hooks) immediately but develop progressive kyphosis FFU(p="0.01)," demonstrated initially, maintained their correction(p="0.0001)." Confounding variables such as smoking, complications nor SPO's influenced either group.
Conclusions: At an average of 2.5-years of follow-up, the overall incidence of proximal junctional kyphosis was 36.6%, averaging 38% in Group-1(Screws) and 34% in Group-2(Hooks) after prior surgery, age and osteotomy were subtracted out as a covariate. Although PJK was nearly equal in both groups, PJK continued to progress postoperatively in the hook patients, but not in the screw group.