المتخصصون في المجالات الطبية

Jan. 28, 2023

Osteoporosis and osteopenia are common among spinal surgery patients ages 50 and older. Bone density issues contribute to proximal junctional kyphosis and failure, which can have a devastating impact on patients. Mayo Clinic works to avoid these complications by optimizing bone health before individuals have spinal fusion or deformity surgery.

"We are seeing evidence that improving bone density seems to lower the rate of surgical complications," says Benjamin D. Elder, M.D., Ph.D., a neurosurgeon at Mayo Clinic in Rochester, Minnesota, who has fellowship training in complex spinal surgery and adult spinal deformities. "The biggest challenge in adult spinal surgery — in addition to achieving proper alignment — is ensuring correct healing. Our goal is to get everything optimized before patients go into surgery."

Mayo Clinic is among the few centers that uses quantitative CT scans to screen individuals at risk of bone issues. Working closely with endocrinologists in the Osteoporosis-Calcium Disorders Specialty Group, Mayo Clinic neurosurgeons might recommend anabolic medications to improve bone mineral density.

Clinician-researchers also are developing new regenerative medicine and tissue engineering approaches for the repair of spinal bone and cartilage. "These efforts are aimed at restoring the native spinal tissue that degenerates over time, so patients can avoid these complex spinal surgeries," Dr. Elder says.

Technology and collaboration

Numerous risk factors for proximal junctional kyphosis and failure have been proposed. A Mayo Clinic study published in the November 2022 issue of the Journal of Neurosurgery: Spine found that preoperative bone density was the only independent predictor of those complications among patients who had upper thoracic-to-pelvis spinal reconstruction.

Mayo Clinic assesses bone health in all spinal surgery candidates ages 50 or older. Individuals under age 50 who are at risk of bone issues due to other factors — such as chronic steroid use or early menopause — also are assessed.

Standard dual-energy X-ray absorptiometry (DXA or DEXA) can yield falsely elevated lumbar bone mineral density measurements, in the setting of degenerative changes or prior instrumentation. CT scans overcome these challenges by providing quantifiable measurements of bone density expressed in Hounsfield units (HUs).

"Normal HUs are in the 200-plus range. That's usually good, strong bone," Dr. Elder says. "Some of our patients have HUs in the 20-to-39 range, which isn't much different from the measurements of muscle or fat."

Patients with compromised bone health are referred to Mayo Clinic endocrinologists specializing in bone metabolism. "They are a fantastic resource," Dr. Elder says. "Our endocrinologists can determine what is causing poor bone health — whether it's due to aging, smoking, steroid use, vitamin D deficiency, hyperparathyroidism or some other cause. That diagnosis can then dictate the optimal anabolic medication."

Mayo Clinic endocrinologists are also able to guide patients through additional strategies for improving bone health, such as smoking cessation, weight loss and diabetes control.

The duration of pre-surgical treatment varies, according to individual patients' bone quality and the complexity of their procedures. At least two months of preoperative treatment is usually needed to see any change, but some individuals need up to two years of optimization.

"We explain to patients that if the surgery is done on weak bone and fails, additional repair might be impossible," Dr. Elder says. "These are 12-hour surgeries that require a week in the hospital and a year for complete recovery. They have an exceedingly high complications rate. That's why we try to do everything possible to maximize results."

Dr. Elder stresses that maintenance therapy for bone health is essential after spinal surgery. "Within a couple of months of stopping anabolic medications, you can lose all the bone density you've gained," he says.

Regenerative medicine approach

As principal investigator of the Mayo Clinic stem cell therapeutics and tissue engineering laboratory, Dr. Elder studies the use of stem cells and biomaterials to repair spinal bone and cartilage, with the ultimate goal of avoiding major fusion surgeries. One upcoming study involves implanting biomedically engineered facet joint cartilage in laboratory animals.

"Engineering strategies for cartilage have been explored in other orthopedic joints but not the facet joint," Dr. Elder says. "The challenge is getting the cartilage to integrate with the adjacent bone so the graft stays within the joint. We're translating cartilage therapy that has been used in the knee to the facet joint."

Another project targets bone regrowth. With a National Institutes of Health grant, Dr. Elder and Lichun Lu, Ph.D., who directs Mayo Clinic's Biomaterials and Regenerative Medicine Laboratory, are developing an injectable polymer that promotes bone growth. The polymer could be used to perform minimally invasive spinal fusions, or as a bone cement for kyphoplasty that could actually regrow the bone.

"The disk would be removed through a tube and the bone scaffold would then be injected into the disk space," Dr. Elder says. "Over about 20 to 30 minutes, the scaffold hardens and fills up the disk space to form structural support as well as to allow for bone growth." Stem cells and growth factors also are injected into the disk space to promote bone formation.

Optimizing the likelihood of successful spinal surgery — and working to find cutting-edge alternatives to surgery — are part of Mayo Clinic's commitment to patient care.

"We have a highly collaborative environment," Dr. Elder says. "As a result, we're able to coordinate patient care and research teams quickly and efficiently. The focus is doing what's best for the patient."

For more information

Osteoporosis-Calcium Disorders Specialty Group. Mayo Clinic.

Mikula AL, et al. Association between lower Hounsfield units and proximal junction kyphosis and failure at the upper thoracic spine. Journal of Neurosurgery: Spine. 2022;37:694.

Biomaterials and Regenerative Medicine Laboratory. Lichun Lu. Mayo Clinic.

Refer a patient to Mayo Clinic.