J Korean Neurosurg Soc.  2021 Nov;64(6):901-912. 10.3340/jkns.2020.0305.

Posterior Floating Laminotomy as a New Decompression Technique for Posterior Cervical Spinal Fusion Surgery

Affiliations
  • 1Department of Neurological Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea

Abstract


Objective
: In the cervical spine, many surgical procedures have been developed to achieve optimal results for various disorders, including degenerative diseases, traumatic injury, and tumor. In this study, we report our experience and follow-up results with a new surgical technique for cervical spine entitled posterior floating laminotomy (PFL) in comparison with conventional laminectomy and fusion (LF).
Methods
: Data for 85 patients who underwent conventional LF (n=66) or PFL (n=19) for cervical spine disorders between 2012 and 2019 were analyzed. Radiological parameters, including cervical lordosis (CL), T1 slope (T1S), segmental lordosis (SL), and C2–7 sagittal vertical axis (SVA), were measured with lateral spine X-rays. Functional outcomes, comprising the modified Japanese Orthopaedic Association (mJOA), neck disability index (NDI), and visual analog scale (VAS) scores, were also measured. For the patients who underwent PFL, postoperative magnetic resonance image (MRI) was performed in a month after the surgery, and the degree of decompression was evaluated at the T2-weighted axial image, and postoperative computed tomography (CT) was conducted immediately and 1 year after the operation to evaluate the gutter fusion.
Results
: There was no difference in CL, T1S, SL, and C2–7 SVA between the groups but there was a difference in the preoperative and postoperative SL angles. The mean difference in the preoperative SL angle compared with that at the last follow-up was -0.3° after conventional LF and 4.7° after PFL (p=0.04), respectively. mJOA, NDI, and VAS scores showed significant improvements (p<0.05) during follow-up in both groups. In the PFL group, postoperative MRI showed sufficient decompression and postoperative CT revealed gutter fusion at 1 year after the operation.
Conclusion
: PFL is a safe surgical method which can preserve postoperative CL and achieve good clinical outcomes.

Keyword

Cerivcal vertebrae; Pedicle screw; Spinal fusion; Lateral mass screw; Posterior floating laminotomy

Figure

  • Fig. 1. Posterior bony structures are restored on the spinal cord and linked to the adjacent paraspinal muscles and tendons in order to protect the cord and fill the empty space in the posterior floating laminotomy group.

  • Fig. 2. Schematic images of the posterior floating laminotomy surgery. A : Laminotomy was performed using a high-speed drill with a small round burr to make gutter. B : Only the lamina without ligamentum flavum was disconnected en bloc and shifted to posteriorly with Allis forceps while some proportion of ligamentum flavum was preserved, since the isolated lamina is unstable and difficult to reattach to the original sites. If the inner layer of the lamina compressed the spinal cord even after posterior shifting, additional internal decompression through removal of inner wall of lamina, central part of ligamentum flavum, or epidural fat was performed. C : Posteriorly shifted floating lamina was adhered to the paraspinal muscles, tendons, and upper and lower spinous processes with threads.

  • Fig. 3. Radiological parameters are shown. A : Cervical lordosis. B : T1 slope. C : Segmental lordosis. D : C2–7 sagittal vertical axis.

  • Fig. 4. From the T2-weighted axial magnetic resonance image, the area of the cord (marked as blue line) and the spinal canal (marked as red line) were measured from C3 to C7, before (A) and after (B) the posterior floating laminotomy surgery.

  • Fig. 5. Radiological parameters, including CL, T1S, SL, and C2–7 SVA, were not different between the groups. However, there was a difference in SL between the preoperative time and the last follow-up (marked with a star). The difference was -0.3° in the conventional LF group and 4.7° in the PFL group (p=0.04). CL : cervical lordosis, LF : laminectomy and fusion, PFL : posterior floating laminotomy, T1S : T1 slope, SL : segmental lordosis, SVA : sagittal vertical axis.

  • Fig. 6. Functional outcomes, including mJOA, NDI, VAS-N, and VAS-A scores, at three time points (preoperative, postoperative 6 months, and postoperative 12 months) were significantly different (p<0.05) in both groups. There were also significant differences between the preoperative score and the scores 6 and 12 months postoperatively with Bonferroni correction (marked with stars). mJOA : modified Japanese Orthopaedic Association, LF : laminectomy and fusion, PFL : posterior floating laminotomy, NDI : neck disability index, VAS-N : visual analog scale for the neck, VAS-A : visual analog scale for the arm.

  • Fig. 7. The graph showing the area of the cord and the spinal canal from C3 to C7 which was measured at the T2-weighted axial magnetic resonance image. There were statistically significant differences in the area of the spinal canal from C3 to C7, between before and after the surgery (marked with stars).

  • Fig. 8. Postoperative computed tomography (CT) images of a 67-year old man who received posterior floating laminotomy at C5–7. Follow-up CT 1 year after the operation revealed the formation of bony continuity at the gutter between the lateral mass and the lamina (B and D), whereas immediate postoperative CT showed a gap between the lateral mass and the lamina (A and C). Red arrows indicate the formation of bony continuity at the gutter and yellow arrows indicate the gap between the lateral mass and the lamina.

  • Fig. 9. Postoperative computed tomography (CT) images of an 80-year old woman who received posterior floating laminotomy (PFL) at C3–7. She had received anterior cervical discectomy and fusion and was diagnosed with an instrument malposition via postoperative X-ray. She underwent instrument removal and another PFL surgery. Follow-up CT 1 year after the operation revealed the formation of bony continuity at the gutter between the lateral mass and the lamina (B and D), whereas immediate postoperative CT showed a gap between the lateral mass and the lamina (A and C). Red arrows indicate the formation of bony continuity at the gutter and yellow arrows indicate the gap between the lateral mass and the lamina.

  • Fig. 10. Postoperative seroma is demonstrated. A : Postoperative magnetic resonance image 12 days after conventional laminectomy and fusion (A) showed T2 hyperintense fluid collection overlaying the C2–7 levels consistent with a postoperative seroma. B : The superficial wound was clear except for some pinkish margins at the middle of the wound due to the pressure of the seroma. C : The aspirated seroma in revision surgery was a clear and reddish fluid, which did not reveal any bacterial growth.


Reference

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