The two major schools of laminoplasty derive from the Hirabayashi “open-door” procedure and Kurokawa’s “French-door” technique. Other subsequently described techniques are variations on these themes. These techniques are illustrated in Figure 2. Most differ in how the surgeon secures the laminae in their new position or in how the exposure is made. Initially, hinges were either tethered open with suture or wire or propped open with bone grafts or other spacers, such as ceramic or polyethylene blocks. Recent innovations have adapted plates and screws to securely fix the laminae in place.

The preoperative diagnostic imaging workup should consist of plain radiographs of the cervical spine, including AP and neutral lateral radiographs (Figure 3). Flexion-extension views have been shown in some studies to be useful in determining the presence of instability, such as spondylolisthesis. Sakai et al³ showed that the presence of a posterior spondylolisthesis resulted in significantly lower Japanese Orthopaedic Association recovery rates compared with anterior spondylolisthesis or no spondylolisthesis (which had equivalent outcomes).

The K-line (kyphosis line) concept was introduced by Fujiyoshi et al⁴ as a tool to determine if laminoplasty could be used successfully in patients with OPLL. This tool can also be extended to address large ventral lesions or fixed kyphoses, which are often contraindications to laminoplasty. The K-line was defined as the line connecting the
midpoints of the spinal canal at C2 and C7 on a lateral cervical radiograph.⁴ A positive (+) K-line did not have an OPLL lesion crossing it, whereas a negative (−) K-line was present when the pathology extended dorsally beyond the line (Figure 4). In the (+) K-line group, the average neurologic recovery rate following laminoplasty was 66%, compared with 19% in the (−) K-line group. An MRI study is useful in preoperative planning to determine which levels need to be included in the laminoplasty. Moreover, MRI allows the surgeon to determine if a C2 dome laminectomy should be included with the laminoplasty technique. Factors such as hypertrophied flavum, congenital stenosis, and cervical spine lateral architecture can result in impingement of the cord at the C2 level after laminoplasty due to cord drift-back and cause postoperative myelopathy.

The use of a CT study or a CT myelogram study is surgeon and patient specific. A CT scan gives the surgeon a more precise appreciation of the bone anatomy, including the presence of OPLL (Figure 5), ossified ligamentum flavum, or foraminal stenosis with osteophyte formation. Foraminal stenosis detected on CT and correlated with physical examination can be addressed during the surgical procedure, with a foraminotomy on the affected side. Myelography enhances structural detail, including details of patterns of compression and thickness and shape of lamina. At times, it is indicated when the MRI leaves some doubt as to the nature and extent of the pathology. A CT scan also helps determine the “occupation ratio” for a large ventral lesion (AP diameter of the lesion/AP diameter of the canal × 100). An occupation ratio of more than 50% to 60% is often considered a relative contraindication to laminoplasty. These additional anatomic details can provide important tactical information to be used intraoperatively.