Proximal Junctional Kyphosis in Adolescent Idiopathic Scoliosis Following Segmental Posterior Spinal Instrumentation and Fusion: Minimum 5 Years Follow Up

Information provided by

Keith Bridwell, MD

Orthopaedic Surgeon

Washington University School of Medicine

Lawrence G. Lenke, MD

The Jerome J. Gilden Professor of Orthopedic Surgery

Co-Chief Pediatric & Adult Spinal, Scoliosis & Reconstructive Surgery

Purpose: To analyze the long term proximal junctional change in adolescent idiopathic scoliosis (AIS) following segmental posterior spinal instrumentation and fusion after a minimum 5 years postoperative.

Methods: Radiographic data on 193 (166 female and 27 male) consecutive AIS patients with minimum 5 years follow-up (average 7.3 years, range 5-16.7 years) treated with segmental posterior spinal instrumentation and fusion was collected. Radiographic measurements analyzed included sagittal Cobb angle at the proximal junction on preoperative, early postoperative, 2 years postoperative, and final follow-up (> 5 years) with standing long cassette radiographs. Additional measurements used for analysis included C7-Sacrum sagittal plumb, thoracic sagittal Cobb angle between T5 and T12, and coronal Cobb angles. Postoperative SRS-24 outcome scores were also evaluated. Abnormal proximal junctional kyphosis (PJK) was defined by final proximal junctional sagittal Cobb angle between the lower end plate of the uppermost instrumented vertebra and the upper end plate of 2 supra-adjacent vertebrae which was greater than 10º and at least 10º greater than the preoperative measurement.

Results: Incidence of PJK at 6.7 years (7.3 years for the demoninator group/193 patients) postoperative was 26% (50 patients, 41 female and 9 male). The average proximal junctional angle increased 15.2º until 2 years postop and then increased 1.7º until final follow up in PJK group (n=50). The average proximal junctional angle increased 1.4º until 2 years postop and then decreased 0.2º until final follow-up in non-PJK group (n=143). The average C7 sagittal plumb demonstrated significant anterior displacement at final follow-up in the PJK group compared to non- PJK group (p<0 .001). The number of fused vertebrae was also related with PJK (23 PJK/69 patients more than 12 vertebra vs 27 PJK/121 or less fused) (P="0.079)." Hybrid group (proximal hooks and distal pedicle screws) (38%, 21/56 patients) demonstrated higher incidence compared to Hooks only (21%, 29/137 (p="0.029)." according preoperative sagittal thoracic Cobb angle 44% (7/16 if T5-T12>40º), 29% (39/137 if T5-T12 10º-40º), and 10% (4/40 if T5-T12<10 º) (Hyperkyphosis vs Hypokyphosis, p="0.494" Thoracoplasty (41%, 28/69) procedure demonstrated a higher incidence (No thoracoplasty 18%, 22/124) (p="0.538" Uppermost instrumented vertebra did not affect the PJK incidence. The SRS-24 outcome scores demonstrate any significant differences. (total score 97 and self-image subscales 21 in group 95 respectively non-PJK group) for total subscale) (See attachment).

Conclusion: Incidence of proximal junctional kyphosis at a minimum 5 years postop was 26% and did not progress significantly after 2 years postop. Hybrid (proximal hooks and distal pedicle screws) instrumentation, thoracoplasty, and preoperative larger sagittal thoracic Cobb angle (hyperkyphosis >40º) were identified as risk factors for developing PJK. The SRS-24 outcome instrument was not affected by PJK.