Value of Additional Instrumented Fusion in the Treatment of Thoracic Ossification of the Ligamentum Flavum

Abstract

Objective: The ossification of the ligamentum flavum (OLF) is one of the major causes of thoracic myelopathy. Surgical decompression with or without instrumented fusion is the mainstay of treatment. However, few studies have reported on the added effect of instrumented fusion. The objective of this study was to compare clinical and radiological outcomes between surgical decompression without instrumented fusion (D-group) and that with instrumented fusion (F-group).

Methods: A retrospective review was performed on 28 patients (D-group, n=17; F-group, n=11) with thoracic myelopathy due to OLF. The clinical parameters compared included scores of the Japanese Orthopedic Association (JOA), the Visual analogue scale of the back and leg (VAS-B and VAS-L), and the Korean version of the Oswestry disability index (K-ODI). Radiological parameters included the sagittal vertical axis (SVA), the pelvic tilt (PT), the sacral slope (SS), the thoracic kyphosis angle (TKA), the segmental kyphosis angle (SKA) at the operated level, and the lumbar lordosis angle (LLA; a negative value implying lordosis). These parameters were measured preoperatively, 1 year postoperatively, and 2 years postoperatively, and were compared with a linear mixed model.

Results: After surgery, all clinical parameters were significantly improved in both groups, while VAS-L was more improved in the Fgroup than in the D-group (-3.4±2.5 vs. -1.3±2.2, p=0.008). Radiological outcomes were significantly different in terms of changes in TKA, SKA, and LLA. Changes in TKA, SKA, and LLA were 2.3°±4.7°, -0.1°±1.4°, and -1.3°±5.6° in the F-group, which were significantly lower than 6.8°±6.1°, 3.0°±2.8°, and 2.2°±5.3° in the D-group, respectively (p=0.013, p<0.0001, and p=0.037). Symptomatic recurrence of OLF occurred in one patient of the D-group at postoperative 24 months.

Conclusion: Clinical improvement was achieved after decompression surgery for OLF regardless of whether instrumented fusion was added. However, adding instrumented fusion resulted in better outcomes in terms of lessening the progression of local and regional kyphosis and improving leg pain. Decompression with instrumented fusion may be a better surgical option for thoracic OLF.

Keywords: Instrumentation; Ligamentum flavum; Ossification; Recurrence; Thoracic.

Fig. 1.

Computed tomography images showing the degree of facets removed to remove lateral parts of ossification of the ligamentum flavum (OLF) from the F-group and D-group. In the F-group (A and B), more than half of the facets were sufficiently removed to remove the lateral parts of OLF, but in the D-group (C), residual OLF was observed at the lateral part (arrows).

Fig. 2.

Measurements of radiographic parameters. Thoracic kyphosis angle (TKA) indicating the angle between the upper endplate of T4 and the lower endplate of T12 (A). Segmental kyphosis angle (SKA) indicating the angle between the upper and lower endplates at the disc level where surgery was performed (B). Lumbar lordosis angle (LLA) indicating the angle between the upper endplate of L1 and the upper endplate of S1 (C). Pelvic incidence (PI) indicating the angle between the line perpendicular to the sacral plate and the line connecting the midpoint of the sacral plate to the bicoxofemoral axis, sacral slope (SS) indicating the angle between the sacral plate and the horizontal plane, and pelvic tile (PT) indicating the angle between the lines connecting the midpoint of the sacral plate to the bicoxofemoral axis and the vertical plane (D).

Fig. 3.

Linear mixed-effects model graphs for VAS-L (A), TKA (B), SKA (C), and LLA (D) measurements over the periods with baseline correction for the D-group and F-group. The variable analyzed is the amount of change from the baseline. ^*p<0.05 for group analysis.

Fig. 4.

Recurrence case of ossification of the ligamentum flavum (OLF). A 43-year-old man underwent decompression surgery because of weakness in both legs (manual motor grade IV/V), decreased sensation, and voiding difficulty. Magnetic resonance (MR) imaging and computed tomography scan showed thoracic myelopathy due to OLF (A-C). The OLF was removed and laminoplasty was performed without instrumented fusion (D and E). Residual OLF was observed in the lateral part (D, arrows). Symptomatic thoracic myelopathy recurred at postoperative 2 years, and MR imaging revealed regrowth of the residual OLF (F).