**5. Surgical techniques**

Ames et al. [39] proposed a cervical osteotomy classification scheme that ranges from least invasive to most invasive and includes: (I) partial facet joint resection, (II) complete facet joint/(Ponte) osteotomy, (III) partial or complete corpectomy, (IV) complete uncovertebral joint resection to the transverse foramen, (V) opening wedge osteotomy, (VI) closing wedge osteotomy, and (VII) complete vertebral column resection.

Osteotomies are the mainstay of treatment in deformity correction. In the thoracolumbar region, posterior osteotomies are well established, including opening wedge osteotomy and pedicle subtraction osteotomy (PSO). However, these techniques are limited in the cervical region due to the presence of the vertebral artery, the sensitivity of the cervical nerve roots to traction, and the small size of the cervical vertebrae. Pioneered by Simmons [40], a posterior column osteotomy with controlled osteoclasis of the anterior column of the cervical spine can result in significant improvement in cervical spine alignment and in the patients' ability to maintain forward gaze and adequately perform activities of daily living.

Osteotomies utilizing an anterior approach for cervical deformity corrections have been described by Riew [41] and Kim [41]. Common anterior techniques include anterior cervical discectomy and fusion (ACDF), cervical corpectomy, anterior osteotomy (ATO), and the Riew osteotomy [42, 43]. Anterior techniques can often be combined with posterior techniques to achieve circumferential spinal

#### **Figure 3.**

*New cervical deformity morphologies described by Diebo et al. [38]: Group 1 (46.1%): Flatneck with lack of compensation, largeT1S-CL, flexible CL; Group2 (30.8%): Focal deformity, large focal kyphosis between 2 segments, No large regional cervical kyphosis under the setting of a low T1S; group 3 (23.1%): Cervico-thoracic deformity, very large T1S, hyperlordosis of the cervical spine, no extension reserve left.*

*Planning Cervical Deformity Surgery Including DJK Prevention Strategies DOI: http://dx.doi.org/10.5772/intechopen.94390*

reconstruction. It remains inconclusive whether adding a posterior approach augments angular correction and improves stability [43]. As a general rule, the amount of lordosis obtained is about 3–5 degrees for single-level ACDF, 10 degrees for the Smith-Petersen osteotomy (SPO), 17 degrees for ATO, and up to 35 degrees for C7 PSO [44–46].

In severe cases, upper thoracic and cervical PSO's may not get the same correction as a Vertebral Column Resection (VCR). Hoh et al. [47] reported the use of two-stage (posterior–anterior) VCR for the treatment of ankylosing spondylitis. Garg et al. [48] reported the use of three-stage (anterior–posterior–anterior) VCR for a patient with kyphotic cervical deformity following tuberculosis infection. Funayama [49] reported a case of severe kyphotic deformity which showed an improvement from 75 degrees to 21 degrees with a three-stage VCR.

Several retrospective studies [23, 50, 51] presented a large potential of coronal and sagittal correction with posterior VCR. However this procedure can be associated with significant morbidity, particularly in the correction of kyphotic deformity.

Due to the complexity of the neurovascular anatomy in the cervicothoracic region, posteriorly based osteotomy techniques are challenging. Riew et al. [52] makes a case for combining ATO with SPO and posterior cervical fusion, which generated a mean angular correction of 28 degrees per level, providing equal or better corrections than isolated PSOs [9, 53–55] (**Figure 3**).

### **6. Planning the tailored strategy**

In the pre-surgical planning, radiographic measurements of spinopelvic parameters are determined using validated software such as Surgimap (Nemaris Inc., New York, NY). The senior surgeon (TSP) maps out the correction with planning software.

Measuring Hounsfield units (HU) on clinical CT scans of the thorax, abdomen or pre-operative spine CTs demonstrated a reliable correlation between T values of the DEXA measurement and HU of the same vertebral body [56, 57].

Preoperative CT-scan determination of bone density can predict the risk of screw loosening and impact on the technical preferences [57] and has proven to be superior to a pre-operative DEXA scan in the assessment of screw loosening in degenerative spine disease [58].

The LIV is planned for an area with no kyphosis, that is, in an area of neutral alignment. Bone quality is evaluated with CT Hounsfield units, particularly at the LIV and LIV-1 level where failure tends to occur.

Subjacent reciprocal compensation is anticipated at the distal end of the instrumentation construct. The increase of thoracic kyphosis/(the DJK angle change) below the fusion is predicted with a mathematical formula, which includes the change in cervical lordosis (change in CL), and most importantly the actual change in construct alignment (change in C2-LIV SA) [59]:

( ) ( ) ( ) ( ) = + \*- + \* + \*D post post post pre DJKA DJKA .DJKA 9.365 0.315 C2 LIV 0.504 DJKA 0.123 CL (1)

The formula also includes the preoperative DJK angle, underscoring the importance of planning the LIV in a region where there is no preoperative kyphotic alignment.
