Proximal Junctional Kyphosis in Adult Spinal Deformity Following Long Instrumented Posterior Spinal Fusion: Incidence, Outcomes and Risk Factors Analysis

Purpose: To analyze patient outcomes and risk factors associated with proximal junctional kyphosis (PJK) in adults undergoing long instrumented posterior spinal fusion. The proximal junction is defined as the caudal endplate of the upper instrumented vertebrate (UIV) to the cranial endplate two vertebrate proximal. Abnormal PJK was defined by 2 criteria: 1. Proximal junction sagittal Cobb angle > +10 degrees and 2. Proximal junction sagittal Cobb angle at least 10 degrees greater than the preoperative measurement. Presence of both criteria necessary to be considered abnormal.

Hypotheses: 1. Patients with PJK will have significantly lower SRS-24 outcomes scores.2. PJK is associated with significant increases in the sagittal C7 plumb.3. Patient characteristics are associated with PJK: age at surgery, length of time between surgery and final follow-up, smoking status at surgery. 4. Instrumentation variables and certain radiographic variables are associated with developing PJK.

Methods: Radiographic data on 81 consecutive adult deformity patients (average age 45 years (range 23-66) with complete radiographic follow-up (minimum 2 year f/u, range 2-16 years, mean 5.3 years) treated with instrumented segmental posterior spinal fusion at a minimum 6 motion segments reviewed retrospectively. Preoperative diagnosis was adult idiopathic scoliosis in 68/81 patients (84%) and sagittal imbalance in 13/81 (16%). Thoracic major curves in 14/68; average coronal Cobb 54 degrees (range 43-70). Lumbar major curve in 20/68; average coronal Cobb 49 degrees (range 40-74). Double major curve in 34/68; average thoracic curve 59 degrees (range 43-115), average lumbar curve 59 degrees (range 41-82) Radiographic measurements analyzed included sagittal Cobb angle at the proximal junction on pre-operative, immediate post-operative and final follow-up standing long cassette radiographs. Additional measurements used for analysis included C7-Sacrum coronal and sagittal plumb, C7-UIV sagittal plumb, T5-T12 sagittal Cobb angle. Hook or screw patterns at the UIV and the number of proximal fixation points were recorded. Final postoperative SRS-24 scores available for 73/81 patients (separate analysis performed).

Results: Incidence of PJK as defined is 26% (21/81). Patients with PJK did not have lower total or "last 9" SRS-24 outcomes scores (table 1). PJK did not produce significant increases in the sagittal C7 plumb at final f/u (table 2). Finally, no patient, instrumentation, nor radiographic factors analyzed were associated with developing PJK (table 3).

Conclusions: Incidence of proximal junctional kyphosis is high but SRS-24 scores were not significantly affected in patients with PJK.The sagittal C7 plumb was not significantly higher in patients with PJK. No patient characteristics, instrumentation types or radiographic factors were identified as risk factors for developing PJK.

KEY WORDS: kyphosis, junctional, scoliosis, fusion, outcomes

Table 1 SRS-24 Scores at last followup

Table 2

Table 3