Indications of Clinical Application of L5 Laminar Hook for the Surgical Correction of Degenerative Sagittal Imbalance

Background and Objectives: The selection of the optimal distal level of fusion in long-level fusion surgery remains controversial. Fusion ending at L5 preserves motion but increases the risk of L5–S1 disc degeneration. The L5 laminar hook has been introduced to enhance distal fixation, but its indications and clinical effects remain unclear. This study aimed to investigate the indication of the L5 laminar hook and its effect on adjacent segment degeneration when performing long-level fusion terminating at L5 in patients with degenerative sagittal imbalance (DSI). Materials and Methods: 112 patients with DSI who had undergone corrective surgery and ended at L5 were analyzed retrospectively. Finally, 64 were treated with an L5 laminar hook (Group I), while 48 were not (Group II). We compared radiographic spinopelvic parameters between the two groups and followed up disc degeneration at the L5–S1 level. Additional analysis was conducted within Group I to determine the indications for L5 laminar hook. Results: Preoperative C7 sagittal vertical axis (C7SVA), lumbar lordosis (LL), and pelvic incidence (PI)-LL mismatch were significantly greater in Group I than in Group II (p < 0.05). At 2 years of follow-up, advanced L5–S1 disc degeneration had developed in 14 patients (21.9%) in Group I and 36 patients (75%) in Group II. Patients in Group B (exacerbated L5–S1) had a significantly higher body mass index (BMI), larger preoperative C7SVA, and PI-LL mismatch than patients in Group A (preserved L5–S1). The C7SVA and PI-LL mismatch cut-off values for Group A were 15.8 cm and 40.8°, respectively. Conclusions: L5 laminar hook helps to reduce disc degeneration at the L5–S1 level and can be used to maintain the deformity correction ending at L5 in patients with DSI. We propose a series of indicators for the use of L5 laminar hooks in patients with DSI: a low BMI, a PI-LL mismatch < 40.8°, and a C7SVA < 15.8 cm.