The influence of approach side on facet preservation in microscopic bilateral decompression via a unilateral approach for degenerative lumbar scoliosis

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Object

The authors compared the clinical outcomes of microscopic bilateral decompression via a unilateral approach (MBDU) for the treatment of degenerative lumbar scoliosis (DLS) and for lumbar canal stenosis (LCS) without instability. The authors also compared postoperative spinal instability in terms of different approach sides (concave or convex) following the procedure.

Methods

The authors retrospectively reviewed data obtained in 50 consecutive patients (25 in the DLS group and 25 in the LCS group) who underwent MBDU; the minimum follow-up period was 2 years. Patients with DLS were divided into 2 subgroups according to the surgical approach side: a concave group (23 segment) and a convex group (17 segments). The Japanese Orthopaedic Association Scale scores for the assessment of low-back pain were evaluated before surgery and at final follow-up. The Japanese Orthopaedic Association Scale scores and recovery rates were compared between the DLS and LCS groups, and between the convex and concave groups. Cobb angle and scoliotic wedging angle (SWA) were evaluated on standing radiographs before surgery and at final follow-up. Facet joint preservation (the percentage of preservation) was assessed on pre- and postoperative CT scans, compared between the LCS and DLS groups, and compared between the concave and convex groups. The influence of approach side on postoperative progression of segmental instability was also examined in the DLS group.

Results

The mean recovery rate was 58.7% in the DLS and 62.0% in the LCS group. The mean recovery rate was 58.6% in the convex group and 60.6% in the concave group. There were no significant differences in recovery rates between the LCS and DLS groups, or between the DLS subgroups. The mean Cobb angles in the DLS group were significantly increased from 12.7° preoperatively to 14.1° postoperatively (p < 0.05), and mean preoperative SWAs increased significantly from 6.2° at L3–4 and 4.1° at L4–5 preoperatively to 7.4° and 4.9°, respectively, at final follow-up (p < 0.05). There was no significant difference in percentage of preservation between the DLS and LCS groups. The mean percentages of preservation on the approach side in the DLS group at L3–4 and L4–5 were 89.0% and 83.1% in the convex group, and those in the concave group were 67.3% and 77.6%, respectively. The percentage of preservation at L3–4 was significantly higher in the convex than the concave group. The mean SWA had increased in the concave group (p = 0.01) but not the convex group (p = 0.15) at final follow-up.

Conclusions

The MBDU can reduce postoperative segmental spinal instability and achieve good postoperative clinical outcomes in patients with DLS. The convex approach provides surgeons with good visibility and improves preservation of facet joints.

Abbreviations used in this paper: AP = anteroposterior; DLS = degenerative lumbar scoliosis; JOA = Japanese Orthopaedic Association; LCS = lumbar spinal canal stenosis; MBDU = microscopic bilateral decompression via a unilateral approach; SWA = scoliotic wedging angle.

Article Information

Address correspondence to: Akira Matsumura, M.D., Ph.D., Department of Orthopaedic Surgery, Osaka City Juso Hospital, 2-12-27 Nonakakita, Yodogawa-Ku, Osaka, 532-0034, Japan. email: amatsumura@med.osaka-cu.ac.jp.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Radiographic parameters. Dotted lines indicate Cobb angle and solid lines indicate scoliotic wedging angle.

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    Measurement of facet joint preservation on preoperative (A) and at final follow-up (B) CT scans. The length of the facet joint was measured using Scion Image software, and the percentage of facet preservation was calculated using the following equation: (percentage of facet preservation) = b/a × 100.

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    Upper: Mean JOA Scale scores in the DLS and LCS groups; there was no significant difference between the groups. Lower: Mean JOA Scale scores in the convex and concave groups; there was no significant difference between groups. FU = final follow-up.

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    Upper: Mean percentage of facet preservation in the DLS and LCS groups; there was no significant difference between groups. Lower: Mean percentage of facet preservation on the approach side in the degenerative lumbar scoliosis group. The percentage of preserved facet was significantly higher in the convex than in the concave group at L3–4 level (p = 0.003). n = number of treated segments.

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    Imaging studies obtained in a 74-year-old woman who underwent MBDU from the convex side. Preoperative standing AP radiograph (A) and preoperative axial CT scans of the L3–4 level (B) and L4–5 level (C). The spinous processes are inclined to the contralateral side, providing a wider view from the convex than the concave side. Postoperative AP radiograph (D) after 5 years demonstrating no obvious postoperative spinal instability. Postoperative axial CT images at L3–4 (E) and L4–5 (F) revealing good preservation of the facet joints (percentage of facet preservation [%-preservation] on the approach side: L3–4, 85%; L4–5, 88%).

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    Imaging studies acquired in a 71-year-old man who underwent MBDU on the concave side. Preoperative standing AP radiograph (A), preoperative axial CT images at L3–4 (B) and L4–5 (C). The spinous processes are inclined to the approach side, giving a narrower view from the concave side. Postoperative AP radiograph (D) acquired 2 years postoperatively demonstrating obvious postoperative spinal instability. Postoperative axial CT images at L3–4 (E) and L4–5 (F) showing poor preservation of the facet joints (percentage of facet preservation on the approach side: L3–4, 52%; L4–5, 58%).

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