Background: Although the clinical relevance still remains unclear there is an increased interest in the incidence of proximal junctional kyphosis (PJK) following posterior spinal scoliosis surgery. Several authors suppose patients with hybrid instrumentation (cranial laminar hooks, caudal pedicle screws and sublaminar wires) to be at greater risk for developing PJK. The aim of our study was to evaluate the incidence of PJK and to determine risk factors in our series of AIS patients with hybrid instrumentation after a minimum follow up of 5 years.

Methods: 60 consecutive AIS patients (56 female, 4 male, average age 16 years, range 14 to 18 years) underwent scoliosis surgery using pedicle screws caudal and laminar hooks cranial at our institution. Pre - and postoperative Cobb angle, junctional kyphosis angle, number of fused levels and upper instrumented vertebra were assessed on lateral and anteriorposterior standing long cassette radiographs after an average follow up of 8 years (range 5 to 12 years). As published by Glattes et al. proximal junction was defined as the caudal end-plate of the upper instrumented vertebra to the cranial endplate two vertebrae proximal. A Cobb angle of the proximal junction greater than 10° and at least 10° greater than preoperative was defined abnormal.

Results: Average number of fused levels was 10.2 (range 8.1 to 12.3). Average Cobb angle decreased from pre-operative 65° (range 50° to 80°) to 32° (range 22° to 40°). T 4 was the upper instrumented vertebra in 30 patients, T 5 in 18 and below T 6 in 12 patients. Average Preoperative saggital PJK Cobb was 7° (range 4° to 13°). 5 patients (12%) showed abnormal proximal junctional kyphosis angel at latest follow up (average 18°, range 14 to 28°). There was no positive correlation found between upper instrumented vertebra and abnormal PJK (r² = 0.01). A greater preoperative PJK angle however showed positive correlation (r² = 0.8).

Conclusion: Compared to literature our data show a low rate (12%) of PJK after an average follow up of 8 years. We could not find any positive correlation between upper instrumented vertebra and incidence of PJK, a preoperative increased proximal kyphosis however seems to be a risk factor for developing PJK.

Study design: Prospective clinical and radiologic study.

Objective: The purpose of this study was to investigate the risk factors for adjacent segment degeneration after posterior lumbar interbody fusion (PLIF).

Summary of Background data: Although several authors have reported the adjacent segment degeneration after lumbar or lumosacral fusion, there is no consensus regarding the risk factors for adjacent segment degeneration.

Methods: Sixty-five patients were studied after PLIF after a minimum follow up time of 6 years. Plain and flexion/ extension radiographs and MRI scans were obtained and compared to preoperative and postoperative. Progression of segment degeneration was defined as a condition in which the distinction between nucleus and annulus is lost, and the disc space is collapsed according to the grading system (Grade 1–5) described by Pfirrmann et al evaluated with T2 weighted MRI scans. Patients were divided into three groups: Group 1 with no radiological progression of disc degeneration, Group 2 with radiological progression of disc degeneration, and Group 3 with radiological progression of disc degeneration and clinical deterioration. Risk factors for progression of adjacent disc degeneration as lumbar lordosis, lordosis at the fused segment, facet sagittalization, and pre-existing disc degeneration were evaluated. The images were evaluated by two independent radiologists.

Results: Fifteen patients (23%) showed no radiological progression of disc degeneration on MRI scans and were classified into Group 1. Forty patients (62%) developed some cranial or caudal deterioration of the adjacent segment without clinical deterioration and were classified into Group 2. Ten patients (15%) required reoperation for neurological and clinical deterioration caused by cranial or caudal degeneration of the adjacent disc (Group 3). No statistically significant differences were found in lumbar lordosis, lordosis at the fused segment, facet sagittalization between each group. Patients in Group 3 showed on preoperative MRI already moderate to severe alteration of the adjacent disc (mean Grade 4) compared to Group 1 (mean Grade 2) and 2 (mean Grade 2,5) (p< 0.01).

Conclusion: After PLIF disc degeneration appear homogeneously at several levels cranial and caudal to fusion over the years in most of the patients (79%). Only pre-existing degeneration of the adjacent cranial and caudal segment is a potential risk factor for clinical deterioration caused by disc collapse.