Subcrestal Iliac-Screw: A Technical Note Describing a Free Hand, In-line, Low Profile Iliac Screw Insertion Technique to Avoid Side-connector Use and Reduce Implant Complications

Study Design. Case-series. Objective. To report our modified iliac-screw insertion technique and its clinical outcomes. Summary of Background Data. Iliac-screws are one of the preferred methods for modern spinopelvic-fixation. However, the technique is not without complications, predominantly because of iliac-screw head prominence, leading to pain and revisions. Conventional iliac-screw entry point is sited superficially at the posterior-superior-iliac-spine (PSIS) contributing to screw-head prominence. We propose a more low-profile, subcrestal entry point that is more medial and inferior to the PSIS at the medial wall of the iliac crest, lying underneath the crest but above the sacroiliac joint. This position keeps the screw-head low profile and in-line with proximal instrumentation to ease rod engagement. Methods. Ten consecutive patients who underwent spinal deformity correction surgery using the modified iliac-screw entry point fixations were enrolled. Clinical, radiological, and surgical parameters were reviewed. Results. Five males and five females with average age of 66 years and average follow up of 29 months were reviewed. Mean preoperative Cobb angle and C7-SVA were 32.1° and 10.3 cm, respectively. Surgical indication was progressive deformity and neurogenic claudication in eight cases and fracture in two cases. Twenty noncannulated, polyaxial iliac-screws with median dimension of 7.5 x 75 mm were inserted free hand. Bilateral S1 screws were used in all except two cases. Only five out of 16 iliac-screws with concomitant S1 screws needed side-connectors. At the last follow up only one iliac-screw head was felt to be prominent but without pain in a Parkinson's patient. None of the 10 patients had cases of revision, breakages, or sacroiliac pain. Conclusion. Subcrestal iliac-screw insertion is feasible, safe, and has the potential to reduce screw-head complications and avoid the use of side-connectors, lowering construct complexity and cost. The technique has the advantage of both the low-profile S2 alar iliac screw and the ease of free-hand insertion of the traditional iliac-screw. Level of Evidence: 4

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