Proximal Junctional Degeneration and Failure Modes: A Novel Classification and Clinical Implications

Case-control study.

To introduce a classification system that will include the major types of degenerative changes and failures related to the proximal junction, and to determine the clinical course and characteristics for the different types of proximal junctional degeneration.

Proximal junctional kyphosis and failures are well recognized after adult spinal fusion; however, a standardized classification is lacking.

The proposed system identified 4 different patterns of proximal junctional degeneration: (1) Type 1 (multilevel symmetrical collapse), (2) Type 2 (single adjacent level collapse), (3) Type 3 (fracture), and (4) Type 4 (spondylolisthesis). A single-center database was reviewed from 2018 to 2021. Patients 18 years or older of age, who underwent posterior spinal fusion of ≥3 levels with an upper instrumented vertebral level between T8 and L2, and a follow-up of ≥2 years were included. Radiographic measurements, revision surgery, and time to revision were the primary outcomes.

One hundred fifty patients were included with a mean age of 65.1 (±9.8) years and a mean follow-up of 3.2 (±1) years. Sixty-nine patients (46%) developed significant degenerative changes in the proximal junction and were classified accordingly. Twenty (13%) were type 1, 17 (11%) were type 2, 22 (15%) were type 3, and 10 (7%) were type 4. Type 3 had a significantly shorter time to revision with a mean of 0.9 (±0.9) years. Types 3 and 4 had greater preoperative sagittal vertical axis, and types 1 and 3 had greater final follow-up lumbar lordosis. Bone density measured by Hounsfield units showed lower measurements for type 3. Types 1 and 4 had lower rates of developing proximal junctional kyphosis. Type 1 had the lowest revision rate with 40% (types 2, 3, and 4 were 77%, 73%, and 80%, respectively, P = 0.045).

This novel classification system defines different modes of degeneration and failures at the proximal junction, and future studies with larger sample sizes are needed for validation.

Level III.