Medial Pedicle Wall Referencing Extra-pedicular (EP) Screw Insertion Technique in Narrow Dysplastic Pedicles During Posterior Spinal Fusion (PSF) in Adolescent Idiopathic Scoliosis (AIS) Patients

STUDY DESIGN: Retrospective study. OBJECTIVES: To describe technique of medial pedicle wall referencing extra-pedicular (EP) screw insertion method. To compare the EP chord length of this technique with the conventional technique in adolescent idiopathic scoliosis (AIS) patients and report the accuracy of this technique based on computed tomography (CT) assessment. SUMMARY OF BACKGROUND DATA: Conventional EP screw technique has a high medial convergence angle, which increases the difficulty of entry into vertebral body, increasing the risk of anterior perforations. Lateral entry point requires more extensive dissection. A lateral starting point leads to malalignment of the screw heads when placed next to intra-pedicular screws. METHODS: A total of 103 AIS patients who had undergone posterior spinal fusion (PSF) from 2018 to 2023 were recruited. A total of 2472 thoracic pedicles were analyzed on preoperative CT scans and the pedicle morphometry were classified based on the Chiu et al classification. The EP chord length of both techniques was measured for narrow dysplastic pedicles (grade C and D). Postoperative CT scans were used to assess for medial perforations (Gertzbein and Robbins classification modified by Rao et al) and anterior perforations (Hansen-Algenstaedt et al grading) . RESULTS: The longest chord length in conventional technique was in left T8 (53.7±3.5 mm) and T9 (53.7±3.7 mm) versus medial pedicle referencing technique which recorded 38.6±3.2 mm and 38.3±3.2 mm, respectively (P<0.001). A total of 434 EP screws were inserted using this technique in narrow dysplastic pedicles. The prevalence of grade 1 medial perforations were 11.3% and for grade 1 anterior perforations were 4.1%. There were only 0.7% grade 2 (critical) perforations [medial: 0.2%, anterior: 0.5%]. None of the perforations were symptomatic and no grade 3 perforations were observed. CONCLUSION: The medial pedicle wall referencing EP screw technique is a safe alternative method, especially in narrow dysplastic pedicles. This technique has a shorter chord length and a less convergent trajectory with an acceptable critical perforation rate (0.7%).