Ultrasonic Osteotome and Spinal Osteotomy Types Explained

An osteotomy is a planned cut through the spine's bone that lets a surgeon reshape a rigid or deformed spine. The three spinal osteotomy types, all performed from behind, are Ponte osteotomy, pedicle subtraction and vertebral column resection, and they differ in how much bone is removed and how much correction each gives.

Dr. Puneet Girdhar, Chairman - Max Institute of Robotics and Minimal Invasive Spine Surgery - Ortho Spine, MIS & Robotic Spine Surgery, BLK-Max Super Speciality Hospital, New Delhi, India, performs all three. He cuts bone with an ultrasonic osteotome, an instrument that does not heat the bone and that he says stops cutting when it touches the dura. This article sets out how the three cuts differ, why a sharp kyphosis threatens the spinal cord, and how failed earlier operations are revised.

The three spinal osteotomy types, from smallest to largest

The three osteotomies differ in how much bone is removed and how much correction they give.

1. Ponte osteotomy. All-posterior surgery in which the facet joints are removed and the spine is decompressed from behind, and the correction is then obtained with screw fixation. Ponte osteotomies shorten the back of the spine in many small steps and suit curves that still have some flexibility.
2. Pedicle subtraction osteotomy. The surgeon removes both pedicles and a wedge of the vertebral body, and closes the gap from behind, which angles the spine back. It is used for a fixed kyphosis that a Ponte osteotomy cannot correct.
3. Vertebral column resection (VCR). The entire vertebral body is removed from behind, with ultrasonic osteotomes and a high-speed drill. This is the largest correction and is reserved for the most severe deformities, including those caused by a hemivertebra (a vertebra formed as a half) or by spinal tuberculosis.

For a hemivertebra, Dr. Girdhar describes the sequence as removing the hemivertebra, performing the vertebral column resection, placing a cage in the front and fixing the spine.

The ultrasonic osteotome: what it adds

A chisel and mallet transmit shock through bone. An ultrasonic osteotome vibrates a tip at high frequency to cut mineralised tissue. Dr. Girdhar names four advantages:

• It does not heat the bone, so there is no thermal damage, in his words.
• It does not send cracks through the surrounding bone, which a chisel and mallet can do.
• It allows irrigation alongside the cut.
• It produces precise cuts, and the bone removed can be used as bone graft.

He also says the tip stops cutting automatically when it touches the dura (the membrane around the spinal cord), so the neural structures are not injured. Ultrasonic cutting does generate a little heat, which is why irrigation is used alongside, but far less than a high-speed drill. Ultrasonic cutters act selectively on mineralised tissue, so soft tissue such as the dura is relatively spared, but a dural tear remains possible and care around the cord is still essential.

Why kyphosis is the dangerous deformity

Scoliosis is a sideways curve and kyphosis is a forward angulation. Dr. Girdhar says scoliosis alone is the easier problem, but that most of the deformity patients he sees have kyphosis as well. Kyphosis creates a hump and can cause cord compression, which is why these combined cases are very challenging. Scoliosis alone rarely compresses the cord.

A post-tuberculous kyphosis shows the point. A girl arrived in a wheelchair with an angular kyphosis of about 85 to 90 degrees left by spinal tuberculosis, a spastic paraparesis (stiff weakness of both legs) and loss of bladder control. Dr. Girdhar performed a vertebral column resection: the vertebra was excised, the cord was decompressed and the deformity was corrected to about 40 degrees, which is close to the normal thoracic kyphosis. Within six months to a year, she was back on her feet and her bladder had recovered. Left alone, he says, she would never have recovered from a bad angular kyphosis. He adds that kyphosis is also about the weakness produced by compression of the cord against the internal gibbus (the bony prominence inside the curve).

Hemivertebra: operate early

A hemivertebra is a congenital malformation in which half of a vertebra fails to form. Dr. Girdhar says that the moment a hemivertebra is seen on an X-ray or mentioned in a report it is a matter of concern, especially in the thoracolumbar and cervicothoracic junctional areas, because the deformity can increase rapidly. Ideally the operation is performed at the age of 4 to 5 years. At that age it is a small surgery.

The common advice, that a child is too young for an operation, has a cost. A small segmental problem left alone becomes a global deformity that needs a long correction. He showed an 11-year-old with a D7 hemivertebra that was excised and corrected, and neglected cases in which a small surgery had turned into a big one with a long correction. In the Q&A, asked about an older patient he had shown, he gave the ideal window for these deformities as 4, 5, 6 or 7 years. He said that correction can still be done in a patient of around 20 or 25 years, and that it has to be done because there is no other option, but that surgical outcomes become more challenging.

His scoliosis and revision deformity operations are performed under neuromonitoring, and he is explicit about the goal: a functioning child with intact neurology who walks within one or two days, not a good X-ray alone. For syndromic children as young as about seven, he uses a growth-modulation technique, which lets the spine keep growing as the child grows.

When a previous operation has failed

Dr. Girdhar's unit performs 20 to 30 revision operations a month, and the cases he presented included these failure patterns.

A cord compression missed before a fusion. A patient had a multilevel lumbar fusion but then developed paraparesis, because a cord compression with signal change at the dorsolumbar junction had gone unnoticed. He stresses the value of a screening MRI in every patient before surgery: a lumbar MRI alone may not be enough when there is gait imbalance or hyperreflexia, even without obvious spasticity. He decompressed the junction with an ultrasonic osteotome and extended the fusion three levels above the old one. The patient started walking.

A scoliosis fusion that stopped at the apex. A young woman had been operated elsewhere, and the fusion had stopped at the apex of the curve rather than extending to the upper end vertebra, so the curve worsened and her shoulders were unbalanced. Dr. Girdhar made the correction around the apex, where the curve peaks, and took the fixation up to D1, with a good result for her balance. The case was demanding because of her very low body weight, her syndrome, the scar from earlier surgery and the small blood volume she could afford to lose, and it depended on advanced anaesthesia and a coordinated team. In a revision scoliosis he described separately, an earlier lumbar fixation had been left at the apex and the Cobb angle (the standard measure of curve size) had reached about 100 degrees; revision brought it down to about 25 degrees with balanced shoulders.

Osteoporotic collapse and junctional failure. Some patients have been cemented but never treated for osteoporosis, and then collapse or develop proximal junctional kyphosis (a kyphosis that forms just above the end of the fixation). For these, Dr. Girdhar restores balance and extends the fusion, using fenestrated screws (hollow screws with side holes through which cement is injected) to anchor osteoporotic bone. Some patients are fixed from D1 or D2 down to the pelvis. When a patient's other illnesses make a long construct unwise, he uses extended connectors to attach to the upper levels instead of going lower.

A failed two-level cervical fusion. In one patient the middle vertebra collapsed, and bone density was severely reduced. Dr. Girdhar approached from the front and the back: he removed the vertebral body anteriorly to decompress the cord and placed an expandable cage with a plate, then reinforced it with posterior fixation one level above and one below.

A disc prosthesis that failed elsewhere. An implanted disc had been pushed in, with a bony component pressing into the foramen, and the patient still had severe radiculopathy. Dr. Girdhar removed the prosthesis after distraction, decompressed the nerve root posteriorly with micro-drills and fused the segment. He says such operations are difficult because of scar, an impacted implant and ossified bone, but that his unit handles them routinely with its range of techniques and a team that works in tandem.

Connected reading

The decision to operate and the referral steps are covered in Indications for Spine Surgery: A Complete Guide. For the minimally invasive side of the unit, see Endoscopic and Robotic Spine Surgery: A Complete Guide. Robotic screw placement in revision cases is in Robotic Spine Surgery for Revision and Complex Cases.

Dr. Girdhar's earlier Jivo Masterclasses also discussed childhood scoliosis and kyphosis timing and revision scoliosis and neglected deformity. The questions put to him on this occasion are in the Live Discussion, and his profile is on the doctor page. For budgeting, see the guide to scoliosis and spinal deformity correction.