Effect of overcorrection on proximal junctional kyphosis in adult spinal deformity: analysis by age-adjusted ideal sagittal alignment

Abstract

BACKGROUND CONTEXTThe effect of the degree of lumbar lordosis (LL) correction on proximal junctional kyphosis (PJK) has not been analyzed in context of the age-adjusted sagittal alignment goal. PURPOSETo determine the effect of sagittal correction on the incidence of PJK after an age-adjusted analysis in patients with adult spinal deformity (ASD). STUDY DESIGN/SETTINGRetrospective comparative study. PATIENT SAMPLESeventy-eight ASD patients who underwent deformity correction. OUTCOME MEASURESVisual analog scale (VAS), Oswestry Disability Index (ODI), and imaging. METHODSThis study included 78 ASD patients who underwent deformity correction and were followed-up more than 2 years. Patients were grouped according to the degree of LL correction relative to pelvic incidence (PI) by adjusting for age using the following formula: (age-adjusted ideal PI - LL) - (postoperative PI - LL). These were group U (undercorrection; <−10˚, N=15), group I (ideal correction; −10˚–10˚, N=34), and group O (over correction, >10˚, N=29). Various clinical and radiological parameters were compared among groups. The risk factors for PJK were also evaluated. RESULTSThe overall incidence of PJK was 32.1% (25/78), with significantly higher PJK rate in group O (48.3%) compared with groups U (13.3%) and I (26.5%) (p=.041). The degree of postoperative LL correction relative to the PI by adjusting for age was a risk factor for the development of PJK (11.4° for PJK vs. 0.2° for non-PJK, p=.033). In addition, 2-year postoperative VAS (7.0 vs. 3.4, p<.001) and ODI (28.9 vs. 24.8, p=.040) scores were significantly higher in the PJK group than in the non-PJK group. A small PI (PI < 45°) was associated with a tendency of overcorrection (73.3%, P < 0.001) and thereby with the high incidence of PJK (53.3%, p=.005). CONCLUSIONSOvercorrection of LL relative to PI considering age-adjusted ideal sagittal alignment tends to increase the incidence of PJK. The incidence of PJK is expected to be high in patients with low PI (<45°) because of the tendency of overcorrection. To reduce the risk of PJK, surgeons should take age-adjusted parameters into account and exercise caution not to overcorrect patients with low PI, since this can result in suboptimal clinical outcomes.