TO THE EDITOR:
The more lordosis of cage, the better?
Recently, we have read the paper written by Hong et al.1 entitled “Does Lordotic Angle of Cage Determine Lumbar Lordosis in Lumbar Interbody Fusion?” with great interest. In this article, the authors found that the lordotic angle of the cages determined restoration of lumbar lordosis after transforaminal lumbar interbody fusion, and cages with sufficient lordotic angle showed better restoration of lumbar lordosis and prevention of loss of correction (LOC). It is very interesting, and helpful for surgeons to choose the right cage. However, several issues needed to be noted.
As we all know, many factors contribute to the construction of lumbar segmental lordosis (SL) and whole lumbar lordosis (LL), for example, the position of the cage. Kwon et al.2 suggested that a normal lordosis could be obtained by inserting a small cage as anteriorly as possible and applying compression, another factor, the diagnostic subset. Liang et al.3 found that compared with other lumbar degenerative diseases, there was a greater mobility in spondylolisthetic patients, which could allow for a greater restoration of LL and SL. Unfortunately, the current study only investigated one single factor, the lordotic angle of cage, without taking into account other factors.
Although the current study put forward 15° lordotic angle achieved better restoration of LL and prevention of LOC than 4° or 8° cages, it is certainly not the more lordosis of cage, the better. The SL is restored by opening the anterior intervertebral space (IVS) and narrowing the posterior IVS, just like a seesaw. Theoretically, the excessive narrowing of posterior IVS could result in decrease of foramen volume, thus might causing nerve root compression for those patients with foraminal stenosis. As Bernhardt and Bridwell 4 pointed, the normal SL should be 15° to 20° at the lower lumbar spine.
What is more, the author only investigated the radiographic sagittal alignment of the spine, without taking into account the clinical outcome. We should not treat patients only for nice-looking curvature instead of their chief symptoms. Therefore, further studies are needed to investigate the connection between clinical outcome and radiographic sagittal alignments.
All in all, it is a good study exploring the relationship between lordotic angle of cage and LL. We still need more well designed, randomized controlled trials to answer those controversial problems.
1. Hong TH, Cho KJ, Kim YT, et al. Does lordotic angle of cage determine lumbar lordosis in lumbar interbody fusion? Spine (Phila Pa 1976)
2. Kwon BK, Berta S, Daffner SD, et al. Radiographic analysis of transforaminal lumbar interbody fusion for the treatment of adult isthmic spondylolisthesis. J Spinal Disord Tech
3. Liang Y, Shi W, Jiang C, et al. Clinical outcomes and sagittal alignment of single-level unilateral instrumented transforaminal lumbar interbody fusion with a 4 to 5-year follow-up. Eur Spine J
4. Bernhardt M, Bridwell KH. Segmental analysis of the sagittal plane alignment of the normal thoracic and lumbar spines and thoracolumbar junction. Spine (Phila Pa 1976)