The restoration of sagittal alignment is correlated with the improvement of health-related quality of life in patients with adolescent idiopathic scoliosis (AIS).1 Ponte osteotomy, a surgical technique to restore normal thoracic kyphosis in AIS, has been increasingly used in recent years. This osteotomy was first described by Alberto Ponte in 1987 for use in correcting thoracic kyphosis by surgically shortening the posterior column obtained by closing the gaps of osteotomies to obtain greater corrective power.2 The original technique combined resection of spinous processes from the base, complete facetectomies, wide inferior and superior laminectomies, and removal of the ligamentum flavum.

In the last 2 decades, the indications for Ponte osteotomy have been expanded to corrective surgery of AIS through posterior spinal fusion.3 Several investigators have found that Ponte osteotomy can improve thoracic kyphosis restoration in patients with AIS, as well as provide better coronal correction; however, some argue that Ponte osteotomy increases the risk of intraoperative neuromonitoring changes.3,4 In the original Ponte technique, the spinous process, ligamentum flavum, and laminae are removed with a Kerrison and Leksell rongeur, starting middle of the ligamentum flavum and going in a medial to lateral direction. The open spinal canal becomes a potential risk for damage and/or neuromonitoring changes. In this paper, we describe the “closed canal Ponte” technique. In this technique, there are no instruments introduced into the spinal canal, and the ligamentum flavum stays intact to the end or through most of the procedure This decreases the risk of instrument or floating fragment-related injury due to no instruments entering the spinal canal.

TECHNIQUE Indication

Indications for this procedure are in line with indications for the Ponte osteotomy, including kyphosis and kyphoscoliosis, as well as all types of AIS with moderate/larger and asymmetric curves.

Description of Procedure

A routine posterior midline incision is made to expose and clear soft tissues from the desired surgical site. Wide subperiosteal exposure with meticulous bleeding control is needed to visualize the lateral border of facet joints. All soft tissues, including pericapsular attachments, are removed to prevent future bleeding during the facetectomies. Intraspinous and supraspinous ligaments are removed as demonstrated in Supplemental Video 15 (Supplemental Digital Content 1, https://links.lww.com/TIO/A72). In this technique, Ponte osteotomies are done before the screw placement, which allows for easier and safer work.

Step 1: Removal of the Inferior Part of the Spinous Process and Base of the Lamina

The inferior part of the spinous process is resected with a large Leksell rongeur while preserving the superior part. Preserving the superior part prevents implant prominence. Then the base of the lamina is removed to allow for further release and better visualization and working space. Using a large rongeur instead of a small one can decrease the risk of inadvertent violation of the spinal canal. All removed bones should be kept to use later as an autograft.

Step 2: Excision of the Inferior Facet

The inferior articular process and facet are removed with a large rongeur. This exposes the superior facet. An ultrasonic bone scalpel can be used for excision, however, using rongeur is a cost-saving method and clears away the resected bone at the same time.

Step 3: Removal of the Superior Facet

The superior facet is removed with the largest rongeur that the anatomy allows or Kerrison (4 or 5 depending on patient size). The resection is performed lateral to medial, in an outside—in direction and the ligamentum flavum stays intact. The Kerrison is introduced by pushing its foot laterally and deep at the lateral edge of the lamina, pushing away the rib which forms the floor of this “potential space.” Rotation of the foot of the instrument allows it to “pop” into the edge of the foramen. The Kerrison needs to be angled caudally to fit into the upper edge of the foramen. It is entirely buried so that it can resect a maximal amount of the superior articular process. The segmental nerve is in the more caudal portion of the foramen, traveling to its groove in the underside of the rib. Several passes of the instrument may be needed to create a wide, clear resection channel.

Removing of superior facet may cause bleeding, which can be stopped by using mono or bipolar cauterization. After bony removal, a hemostatic agent and gel foam are applied before proceeding to the next level. Pedicle screws are placed after all the osteotomies are completed.

Optional Step 4: Removal of the Ligamentum Flavum

After pedicle screw placement, the ligamentum flavum is removed with a small Leksell rongeur or #2 Kerrison rongeur. This is best done when the spine is being distracted in the early process of correcting the instrumented deformity. The laminae can be seen to “spring apart” noticeably at each level as this is done. In AIS cases, it is usually unnecessary to remove the entire ligamentum flavum, as it can be left intact on the convex side. Ligamentum flavum excision is needed mainly in Scheuermann kyphosis cases as the goal is to shorten the posterior canal and close down those osteotomies. Complete resection of the ligamentum is recommended when the surgeon is trying to lengthen the posterior column to correct thoracic kyphosis.

EXPECTED OUTCOMES

If performed correctly and carefully, this procedure should allow for optimal deformity correction in both sagittal and coronal planes and the ability to place desired instrumentation without problems. It can also help with derotation maneuvers and decrease the need for anterior releases.

COMPLICATIONS

While the benefits of this technique limit exposure to the spinal canal, one must be careful of neurological injury with instrumentation within proximity of the spinal canal. Utilization of the largest rongeur allowed by the anatomy prevents inadvertent violation of the spinal canal. The surgeon can further minimize the risk of slipping medially by keeping the elbows at the sides and hands stabilized. We have not experienced any neurological problems from this. The risk of pseudarthrosis can be minimized by using all removed bone, such as bone from the inferior portion of the spinous process and base of lamina during the first step of the technique, and later as an autograft. Frequently, there is bleeding after bony removal. Intraoperative bleeding can be controlled through the application of hemostatic agents and gel foam before proceeding to the next vertebral level.

REFERENCES 1. Lonner B, Yoo A, Terran JS, et al. Effect of spinal deformity on adolescent quality of life: comparison of operative Scheuermann kyphosis, adolescent idiopathic scoliosis, and normal controls. Spine. 2013;38:1049–1055. 2. Ponte A. Surgical treatment of Scheuermann’s hyperkyphosis. Orthop Trans. 1985;9:127. 3. Shah SA, Dhawale AA, Oda JE, et al. Ponte osteotomies with pedicle screw instrumentation in the treatment of adolescent idiopathic scoliosis. Spine Deform. 2013;1:196–204. 4. Floccari LV, Poppino K, Greenhill DA, et al. Ponte osteotomies in a matched series of large AIS curves increase surgical risk without improving outcomes. Spine Deform. 2021;9:1411–1418. 5. Human Anatomy Atlas (Version 2019.1.26). Retrieved June 1, 2023. Accessed: August 1, 2023: http://www.visiblebody.com.