The Incidence of Proximal Junctional Kyphosis (PJK) Based on Upper-Instrumented Vertebrae (UIV) in Patients Undergoing Circumferential Minimally Invasive Surgical (cMIS) Correction for Adult Spinal Deformity

Presented at SMISS Annual Forum 2016
By Neel Anand MD
With Eli Baron MD, Babak Khandehroo MD, Sheila Kahwaty PA-C, Ryan Cohen , Jason Cohen ,

Disclosures: Neel Anand MD None Eli Baron MD , Babak Khandehroo MD None, Sheila Kahwaty PA-C , Ryan Cohen None, Jason Cohen None,


Proximal junctional kyphosis (PJK) is a common complication following traditional ASD surgery but has not been well studied in cMIS patients. The clinical significance of PJK has been debated extensively in the literature. However the etiology remains unclear. Our study assesses the effects of UIV, baseline deformity and degree of sagittal correction on the incidence of PJK. 


UIV does not influence the incidence of PJK in patients undergoing CMIS correction of ASD.


This is a single center study from a prospective registry
of patients who had undergone cMIS correction of ASD (Cobb angle > 20 degrees or SVA>50 mm or PI/LL mismatch >10) with minimum 2yr follow-up. We identified 121patients with 4 or more levels fused and 2-year follow-up. All were instrumented to the first proximal neutral parallel disc. UIV of the cohort was as: 25 at T2-T5, 32 at T10, 24 at T11-T12, 27 at L1 and 13 at L2. PJK was defined as an angle> 10o and at least 10o greater than the baseline when measuring the lower endplate of the UIV and the upper endplate of 2 vertebra supra-adjacent (UIV+2). The groups were compared in terms of PJK rates using Chi-squared analyses (p<.05). Pre-op, latest and delta SVA and pelvic incidence-lumbar lordosis(PI-LL) mismatch were compared between patients with PJK and without.


A total of 14 patients (11.6%) met PJK criteria. Only 5 were symptomatic (all underwent revision surgery). The Incidence of PJK in the groups (T2-T5, T10, T11-T12, L1, L2) was 8%, 15.6%, 12.5%, 7.41% and 15.4% (p>.05). Comparing PJK to non-PJK patients: pre-op SVA was 53.1mm and 52.6mm, latest SVA 33.4mm and 37.1mm, delta-SVA 41.2mm and 38.4mm, pre-op PI-LL mismatch 17.4 degrees and 15.5 degree, latest PI-LL mismatch 12.7 degrees and 13.8 degrees and delta PI-LL mismatch 8.15 degrees and 7.01 degrees.


Our study shows that with CMIS the overall incidence of PJK is considerably lower than reported for open surgery. Further when patients are instrumented to the first neutral parallel disc, UIV level does not appear to influence development of PJK. Comparing PJK to non-PJK patients, the former had a higher trend in pre-op SVA and PI-LL mismatch, lower trend in post-op SVA and PI-LL mismatch and higher trend in delta-SVA and delta-PI-LL mismatch. The role of baseline deformity or overcorrection of SVA in the CMIS correction of ASD is still unclear though trending towards a greater incidence of PJK.