PROXIMAL JUNCTIONAL KYPHOSIS FOLLOWING HYBRID INSTRUMENTATION IN AIS PATIENTS: A MINIMUM FIVE YEARS FOLLOW UP

Abstract

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.