CT-Based Analysis of Rod Trace Length Changes During Posterior Spinal Correction in Adult Spinal Deformity

Area of Science:

• Spine surgery
• Orthopedic surgery
• Deformity correction

Background:

• Accurate rod length is critical in adult spinal deformity (ASD) surgery to prevent complications like proximal junctional kyphosis (PJK).
• Predicting rod trace length (RTL) changes is challenging in ASD due to complex 3D realignment, unlike adolescent idiopathic scoliosis (AIS).
• PJK is more common in ASD, increasing the importance of appropriate rod length selection.

Purpose of the Study:

• To quantitatively assess changes in rod trace length (RTL) before and after posterior corrective surgery in adult spinal deformity patients.
• To evaluate the correlation between RTL changes and spinal alignment correction, including lumbar lordosis and Cobb angle.

Main Methods:

• Retrospective analysis of 30 ASD patients undergoing staged lateral lumbar interbody fusion (LLIF) followed by posterior fusion.
• Rod trace length (RTL) measured on CT scans before and after posterior correction.
• Assessment of lumbar lordosis (LL) and Cobb angle pre- and post-correction.

Main Results:

• Postoperative RTL consistently shortened, averaging a 16-17 mm reduction across all patients.
• RTL shortening significantly correlated with lumbar lordosis (LL) correction (R=0.51) and Cobb angle correction (R=0.70).
• Greater RTL shortening occurred on the convex side in patients with a preoperative Cobb angle ≥ 10°.

Conclusions:

• Increased coronal deformity, particularly on the convex side, is linked to greater RTL shortening in ASD surgery.
• Routine preparation of excessively long rods may be unnecessary.
• Anticipating RTL shortening can help avoid excessive rod length, potentially reducing skin complications and PJK risk, especially in elderly patients.