Abstract
BACKGROUND CONTEXT Proximal Junctional Kyphosis (PJK) can occur at any segment along the spine and yet, compensation mechanisms at levels proximal to an area of PJK have not clearly been characterized. Understanding compensation mechanisms may help in determining optimal level selection when performing revision surgery for PJK. PURPOSE Evaluate the difference in compensatory mechanisms between thoraco-lumbar and thoracic PJK. STUDY DESIGN/SETTING Retrospective review of prospective database. PATIENT SAMPLE A total of 369 patients out of 496 eligible (73.2%) for 2 years follow-up. OUTCOME MEASURES Radiographic alignment of the cervical and thoracic spine as well as pelvic orientation. METHODS PJK location was based on UIV location: LT (T8–L1) or UT (T1–7). Inclusion criteria were fusion >5 levels with the LIV being S1/Ilium. PJK was defined by Glattes criteria. Alignment parameters were compared between PJK patients separated by UIV Group. Correlation Analysis was made between PJK magnitude and global or cervical alignment within UIV group. Percentage of patient reach criteria for cervical deformity according to cSVA (>4cm) were calculated overall and within each subgroup. RESULTS There were 369 patients included in the analysis; mean age of 63, BMI 28 and 81% female, LT (n=193) versus UT (n=176). The rate of radiographic PJK was 49% and higher in the LT group (55% vs. 42%, p=.01). No significant differences were found in global alignment between PJK patients, with the exception of TK being larger for PJK patients (UT:−49.4 vs. −59.0, LT: −46.5 vs. −56.4; all p CONCLUSIONS PJK location results in different compensation mechanisms of the cervical and thoracic spine. The LT group compensates with an increase in PT and CL to maintain an acceptable cSVA. The UT group increases their CL to counter the increase in T1S but continues to have TS-CL mismatch with an elevated cSVA due to maximum compensation at the cervical level. As a result, increase in cSVA led to 40.3% of patients meeting criteria for CD with focal deformity located in the cervical spine. Future studies should investigate the surgical strategy to treat PJK depending on the location of the focal deformity.
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