Abstract
Introduction
Diagnosis of degenerative sacroiliitis and surgical interventions are increasing. Open and minimally invasive sacroiliac joint (MIS SIJ) techniques exist. Optimal rod placement requires adequate training to minimize risk of breaching vital structures such as sacral anterior cortex (AC) and neural foramina (NF). CTbased image guidance navigation increases accuracy of rod placement. This study describes a retrospective singlesurgeon postoperative assessment of implant position in navigated MIS SIJ fusion procedures over a 5-year period.
Materials and Methods
Early (1st 3 years) versus late (past 2 years) cases were evaluated to assess learning curve of implant placement accuracy. Grading scheme was created to assess SIJ fusion rod placement and potential risk of guide pin breaching either AC and/or NF. Grade 1 denotes least risk of breach; Grade 2 denotes partial risk of breech by the implant but not the guide pin; Grade 3 denotes risk of breach of both pin and implant; Grade 4 denotes actual breach. Rod fixation grading was based on bony purchase ratio between iliac and sacral side of the joint where: Grade 1: > 50% of rod occupies sacral side; Grade 2: 50% of rod is fixed on sacral side; Grade 3: < 50% of rod is fixed on sacral side and Grade 4: rod does not cross SIJ.
Results
From 2010 to 2014, 110 implants in 39 SI joint fusions in 33 patients were assessed. Of these 55% were placed atS1 level, 40% were S2 and 5% were in S3. Majority of rods were placed in optimal position (Grade 1 40%68%). The position of 48 rods in 1st 3 years were compared 62 rods in past 2 years. Greater percentage of rods were classified as Grade 1 in the last two years (68%, 65%) compared with the first 3 years (56%, 33%, 25%) indicating a learning curve and improved safety profile of rod placement over time.
Conclusions
This study demonstrates that a learning curve exists with the use of 3D CT guidance for SI joint implant placements. This proposed grading system can be used to aid in optimal placement of SI joint implants.