Which factors predict the loss of cervical lordosis following cervical laminoplasty? A review of various indices and their clinical implications.

BACKGROUND: Many patients undergoing laminoplasty develop postoperative loss of cervical lordosis or kyphotic alignment of cervical spine despite sufficient preoperative lordosis. This results in poor surgical outcomes.
METHODS: Here, we reviewed the relationship between multiple radiological parameters of cervical alignment that correlated with postoperative loss of cervical lordosis in patients undergoing laminoplasty.
RESULTS: Patient with a high T1 slope (T1S) has more lordotic alignment of the cervical spine preoperatively and is at increased risk for the loss of cervical lordosis postlaminoplasty. Those with lower values of difference between T1S and Cobb's angle (T1S-CL) and CL-T1S ratio have higher risks of developing a loss of the cervical lordosis postoperatively. Alternatively, C2-C7 lordosis, neck tilt, cervical range of motion, and thoracic kyphosis had no role in predicting the postlaminoplasty kyphosis.
CONCLUSION: Among various radiological parameters, the preoperative T1S is the most important factor in predicting the postoperative loss of the cervical lordosis/alignment following laminoplasty.

INTRODUCTION

Although laminectomy has better long-term clinical and radiological outcomes, laminoplasty is still favored for the management of cervical spondylotic myelopathy as it preserves the cervical range of motion (ROM) with a lower risk of postoperative kyphosis.[3,14-17]. Despite an adequate preoperative cervical lordosis, increases in the T1 slope (T1S) may result in postlaminoplasty kyphosis.[1,2,4-6] Here, we highlight the relationship between T1S and other radiological indicators of cervical alignment and correlate these with postlaminoplasty kyphosis/loss of lordosis.

METHODS

Measures of cervical alignment

Multiple studies have described various indices that help predict the risk of loss of cervical lordosis in postlaminoplasty patients [Table 1, Figure 1].[9,11-13]

Table 1:

Description of indices affecting cervical alignment.

Figure 1:

The lateral X-ray of cervical spine showing various radiological measurements.

RESULTS

T1S

The T1S is one of the most important indices that can help predict the postlaminoplasty loss of cervical lordosis. Notably, the preoperative cervical lordosis (C2-C7 Cobb’s angle) was greater in patients with higher T1S versus those with lower T1S; these patients have a higher risk of kyphosis postlaminoplasty.[2,5-7,18] Lee et al.[10] concluded that patients with a T1S of >29° are more likely to exhibit postlaminoplasty kyphosis/loss of lordosis of more than 5° versus those with T1S of <29°.

C2-C7 sagittal vertical axis (SVA)

Several studies have shown that the preoperative C2-C7 SVA had no significant correlation with the postlaminoplasty loss of cervical lordosis.[2,5,6,18] Alternatively, Zhang et al.[18] concluded that C2-C7 SVA was positively correlated with loss of cervical lordosis following laminoplasty.[2,5,6,18] Lin et al.[13] showed the combined effect of T1S and C2-C7 SVA on predicting loss of cervical lordosis. Patient with low T1S (≤20°) and large C2-C7 SVA (>22 mm) surprisingly had an increased cervical lordosis postlaminoplasty.

Other factors are predictive of postlaminoplasty kyphosis

There are multiple other factors that predict postlaminoplasty kyphosis. Li et al.[11] concluded that patients with high Cobb’s angle-T1S ratio (CL/T1S) have a higher risk of kyphosis versus those with low CL/T1S. Kim et al.[5] and Zhang et al.[18] showed no relationship between cervical ROM and the risk for postoperative kyphosis. Similar to cervical ROM, neck tilt (NT) a measure of cervical spine tilt with respect to sternum, also does not predict the loss of cervical lordosis following laminoplasty.[6] Thoracic kyphosis (TK) is, however, directly related to cervical lordosis.[8] Cephalad vertebral level undergoing laminoplasty has also emerged as a new risk factor for loss of cervical lordosis following laminoplasty.

CONCLUSION

A high T1S and C2-C7 SVA are the most predictive factors for postlaminoplasty kyphosis. Those risk factors that do not contribute to this include; (1) the preoperative C2-C7 lordosis, NT, cervical ROM, and TK.