The impact of segmental spinal alignment on the development of proximal junctional kyphosis after instrumented posterior spinal fusions for idiopathic scoliosis.

Abstract

To assess if the preservation of preoperative kyphosis within the cephalad two motion segments of instrumented posterior spinal fusions (PSF), for idiopathic scoliosis (IS), would be associated with lower frequency of proximal junctional kyphosis (PJK) at 2years postoperatively. Previous studies on PJK in IS have reported conflicting findings; none has evaluated the relationship between segmental kyphosis within the cephalad instrumented construct and PJK. One hundred consecutive patients undergoing PSF for IS by a single surgeon with minimum 2-year follow-up were evaluated. Radiographic evaluation focused on sagittal alignment of the upper instrumented vertebrae (UIV), the 1 and 2 vertebrae cephalad (UIV + 1, UIV + 2) and caudal (UIV - 1, UIV - 2). This was measured between the inferior endplate of the UIV and the superior endplate of the UIV + 1 and UIV + 2 or between the superior endplate of the UIV and the inferior endplate of the UIV - 1 and UIV - 2. PJK was defined as present if the final UIV + 2 ≥ 10° and final UIV + 2-preop UIV + 2 ≥ 10°. There were 78 females and 22 males whose mean age was 14.6 (± 2.1) years at surgery; mean follow-up was 3.9 (2-9.3) years. The overall frequency of PJK was 25% (25/100) at final follow-up. Preoperative mean coronal curve measured 63° (40°-107°) with a mean 66% correction at final follow-up. UIV was T2 (n = 15), T3 (n = 47) or T4 (n = 38). More caudal UIVs were associated with PJK development (p = 0.04): T2 (13%), T3 (21%) and T4 (34%). Greater preoperative T5-T12 thoracic kyphosis and UIV - 2, and lower major curve apex (below T12) were more likely to develop PJK (p = 0.019, p = 0.004 and p = 0.007, respectively). Post-operatively, larger values for UIV - 1 (p ≤ 0.001) and UIV - 2 (p = 0.002) were associated with PJK at final follow-up. Longer fusion lengths (10-13 vs. 6-9 segments, p = 0.02) and the presence of thoracolumbar/lumbar structural curves (Lenke 3-6 vs. 1-2, p = 0.032) had higher rates of PJK (32% vs 10% and 37% vs 18%, respectively). Changes in UIV - 1 and UIV - 2 (preoperatively to immediately post-op) did not influence the development of PJK. At final follow-up, no patient required revision surgery for symptomatic proximal junctional kyphosis. In this study, changes in UIV - 1 and UIV - 2 at surgery were not related to PJK. Greater preoperative T5-T12 thoracic kyphosis and UIV - 2, lower major curve apex (T12 and below), and greater post-operative UIV - 1 and UIV - 2 were associated with higher frequencies of PJK. Higher UIV (T2 vs. T4) and LIV levels had a protective effect against PJK. Based on this study, the preservation of segmental kyphosis within the instrumented cephalad two levels of the PSF did not minimize the occurrence of radiographic PJK. Level IV.