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Section 8, Chapter 6: Osteoporosis: Diagnosis, Treatment, and Preoperative Bone Optimization

Corinna C. Zygourakis, Darryl Lau, and Christopher P. Ames

INTRODUCTION

The prevalence of osteoporosis is increasing as our population ages and lifespan increases. A recent study estimated that 53.6 million older U.S. adults had osteoporosis or low bone mass in 2010.1 In conjunction with this increase is a rise in spinal fractures and spinal deformity associated with osteoporosis. One group found that over half of women and nearly 15% of men over the age of 50 undergoing spine surgery had osteoporosis.2 Another retrospective review revealed that 10% of women undergoing scoliosis surgery had osteoporosis.3

Osteoporosis is associated with higher rates of complications, particularly in spinal surgery involving hardware.4,5 This is because many spinal fixation techniques rely on bone quality and adequate bone healing, which are impaired in osteoporosis. In an analysis of over one million patients undergoing cervical spine surgery in the National (Nationwide) Inpatient Sample (NIS), patients with osteoporosis stayed in the hospital for one day longer on average, had 30% costlier hospitalizations, and had a 1.5-times greater chance of requiring revision surgeries, as compared to patients without osteoporosis.6 It is therefore important for us to proactively identify, diagnose, and treat patients with osteoporosis before performing spine surgery.

DIAGNOSIS

Osteoporosis is defined as “a skeletal disorder characterized by compromised bone strength leading to an increased risk of fracture.”7 Clinically, it is diagnosed by the non-invasive assessment of bone mineral density (BMD) using the dual-energy X-ray absorptiometry, i.e., DEXA scan. More specifically, the DEXA scan uses X-rays to measure bone density at specific locations in the body, such as the lumbar spine, hip, and distal forearm.

World Health Organization (WHO) criteria defines BMD relative to the value for a normal healthy young adult: this is called the T-score. A T-score at the hip of -1 standard deviations (SD) or higher is normal; -1 to -2.5 SD characterizes osteopenia or low bone mass; a score of less than -2.5 SD defines osteoporosis.8 BMD can also be expressed relative to an age-matched healthy control (the Z-score), although the T-score is preferred for diagnostic use.8

Primary care guidelines recommend DEXA scans for all women at age 65 and men at age 70 in the absence of other risk factors.9 Screenings should be performed earlier in patients with risk factors that include low body weight, early menopause (before age 45), family history of osteoporosis, personal history of rheumatoid arthritis, inflammatory bowel disease or chronic obstructive pulmonary disease, and patients who take drugs such as glucocorticoids, proton pump inhibitors, or selective serotonin reuptake inhibitors.9

Despite these recommendations, many patients come to their spine surgeons without appropriate osteoporosis screening, and many spine surgeons do not routinely request DEXA scans. A recent survey revealed that only 60% of spine surgeons obtained DEXA scans before surgery for spinal fractures; 44% of surgeons checked DEXAs before instrumented fusion; and only 19% performed DEXA scans before non-instrumented fusions.10

TREATMENT

Adequate calcium, vitamin D, and weight-bearing exercise are important for bone health in all patients.9 For those with osteoporosis, several medications are currently approved by the US Food and Drug Administration to increase bone strength by reducing bone resorption. These include two oral bisphosphonates, alendronate and risedronate, that specifically inhibit osteoclasts and thereby prevent bone breakdown. Non-oral options are denosumab (a RANKL inhibitor that prevents the development of osteoclasts), zoledronic acid (another bisphosphonate), and teriparatide (also known as Forteo®, a recombinant form of PTH that stimulates osteoblasts to build bone mass).9

Bisphosphonates

Animal studies show that bisphosphonates induce the formation of large fracture calluses containing less mature bone.11-13 However, their overall effect on the mechanical strength of healed bone is unclear, as there is conflicting evidence from animal work.14-17 A meta-analysis of the eight randomized controlled trials looking at the effect of bisphosphonates on fracture healing for a variety of orthopedic procedures in humans found that bisphosphonate infusion after lumbar fusion may promote bone healing and shorten post-op fusion time.18 (See Table 6-1.)

TABLE 6-1. Evidence for the effect of bisphosphonates on bone fusion
Study Model/Population Results
Animal
Lenehan et al., 198513 Dog Low doses of ethane-1-hydroxy-1,1 disphophonate improve ultimate load at failure and flexural rigidity of fractured limbs
Nyman et al., 199312 Rat Clodronate increases the calcium content of fracture calluses
Tarvainen et al., 199416 Rat Clodronate delays fracture remodeling and does not improve bone strength
Nyman et al., 199611 Rat Clodronate increases formation of new bone matrix, but it is not well organized compared to controls
Peter et al., 199615 Dog Alendronate has no effect on union, strength, or mineralization of bone
Li et al., 200117 Rat Long-term incadronate treatment delays fracture healing
Amanat et al., 200514 Rat Single dose of pamidronate increases bone mineral content, volume, and strength of healing fractures
Human
Xue et al., 201418 Meta-analysis of 8 clinical trials: 2,509 patients total Bisphosphonates do not have a statistically significant effect on indirect bone healing; however, in spinal fusion surgery, bisphosphonates can promote bone healing and shorten time to fusion

Teriparatide

In addition to several animal studies showing that teriparatide accelerates and enhances spinal fusion in rats and rabbits,19-25 multiple clinical trials suggest that teriparatide is effective at promoting spinal fusion in humans and is superior to bisphosphonates.26 (See Table 6-2.) In one study of 57 postmenopausal women who underwent instrumented posterolateral lumbar fusion with local autograft, the rate of bone fusion was 82% in the group that received teriparatide versus 68% in the bisphosphonate group. Patients received both medications for 2 months before and 8 months after surgery. The average time to fusion was 8 months for the patients receiving teriparatide, compared to 10 months for those getting bisphosphonates.27 The same researchers also reported lower rates of pedicle screw loosening in 62 women with osteoporosis who underwent instrumented posterolateral lumbar fusion: 7-13% in the teriparatide group, versus 13-26% in the bisphosphonate group and 15-25% in the control not receiving either medication.28 They found higher rates of fusion and shorter time to bony fusion in patients getting teriparatide for longer periods of time: 92% fusion rate in patients receiving teriparatide for an average of 13 months versus 80% fusion in those getting teriparatide for an average of 5.5 months.29

Another group confirmed higher insertional torque on pedicle screws placed in patients receiving teriparatide for a minimum of one month before spinal fusion surgery.30 A study of 58 osteoporotic Japanese females undergoing adult spinal deformity surgery found lower rates of adjacent vertebral disease and implant or fusion failure, as well as better pain and ODI scores, in patients getting teriparatide versus bisphosphonates.31 Yet another group showed earlier fusion in patients on teriparatide as compared to bisphosphonates, although fusion rates were similar.32 (See Table 6-2.)

TABLE 6-2. Evidence for the effect of teriparatide on bone fusion
Study Model/Population Results
Animal
Lawrence at al., 200625 Rat There is a trend towards greater fusion rate with daily injections of parathyroid hormone
Abe et al., 200724 Rat Intermittent parathyroid hormone enhances bone turnover
O’Loughlin et al., 200923 Rabbit Intermittent parathyroid hormone increases posterolateral fusion success
Lehman et al., 201022 Rabbit Teriparatide is associated with higher histologic fusion rates and less motion in flexion/extension, lateral bending and axial rotation
Ming et al., 201221 Rat High-dose teriparatide has anabolic skeletal effects and significantly enhances spinal fusion rate
Qiu et al., 201320 Rat High-dose parathyroid hormone enhances quantity of fusion callus, reduces healing time of posterolateral spinal fusion
Suguira et al., 201519 Rat Intermittent teriparatide stimulates bone formation at the fusion mass and increases the fusion rate
Human
Ohtori et al., 201227 57 women with osteoporosis who underwent 1-2 level spinal fusion 82% rate of bone union in teriparatide group vs. 68% in bisphosphonate group; average duration of bone union is 8 months in teriparatide versus 10 in bisphosphonate group
Ohtori et al., 201328 62 women with osteoporosis who underwent 1-2 level spinal fusion 7-13% incidence of pedicle screw loosening at 1 year in teriparatide group vs. 13-26% in risedronate group vs. 15-25% in control
Inoue et al., 201430 29 women with osteoporosis undergoing thoracolumbar fusions Teriparatide injections beginning at least 1 month prior to surgery significantly increase the insertional torque of pedicle screws
Ohtori et al., 201529 45 women with osteoporosis who underwent posterolateral fusion Longer duration of teriparatide treatment (>6 months) has higher bone union rate (92%) and shorter duration for bone union (7.5 months) compared to short-duration teriparatide treatment (fusion rate=80%, 8.5 months to union)
Cho et al., 201532 47 osteoporotic patients who underwent posterolateral interbody fusion Teriparatide group has faster union (6.0 vs. 10.4 months) and higher bone mineral density scores than those getting bisphosphonates; no significant difference in overall fusion rate or clinical outcome
Seki et al., 201731 58 women with osteoporosis who underwent fusion for adult spinal deformity Patients receiving teriparatide have lower rates of adjacent vertebral fractures and implant or fusion failure, and lower pain sores than those getting bisphosphonates

PREOPERATIVE BONE OPTIMIZATION

Our preoperative bone optimization protocol incorporates the elements of the American Orthopedic Association’s “Own the Bone” program. These include (1) nutritional counseling: improving calcium and vitamin D intake, (2) physical activity counseling: promoting weight-bearing and muscle-strengthening exercises and fall prevention education, (3) lifestyle counseling: promoting smoking cessation and limiting excessive alcohol intake, (4) pharmacotherapy, (5) DEXA testing, and (6) communication with the referral physician and the patient to discuss their risk factors and recommendations for bone health treatment.33

In our adult spinal deformity practice, we routinely obtain DEXA scans on all patients undergoing fusion surgery. Any patients with hip and distal radius T-scores less than -2.5 are started on teriparatide 20 micrograms daily via subcutaneous injection. We delay elective surgery in order to provide patients with at least 2-3 months of teriparatide before surgery, and then continue the medication for at least 6 months after surgery.

In addition, we check pre-operative metabolic laboratories including calcium, vitamin D, and parathyroid hormone (PTH). We order calcium and vitamin D supplementation if patients have low serum levels. Physical activity, smoking cessation, and clear communication with patients are also essential parts of preparing our deformity patients for spinal fusion surgery.

We encourage others to consider similar steps for preoperative bone optimization as part of an enhanced recovery after surgery (ERAS) protocol at their own institutions. ERAS protocols are multimodal perioperative care pathways designed to achieve early recovery after surgery by maintaining preoperative organ function and reducing the profound stress of the post-operative state.34 They have been implemented successfully in many areas of surgery.34-37

CONCLUSIONS

Osteoporosis is increasingly common and associated with worse outcomes in spinal surgery. Patients with osteoporosis are more likely to experience fractures and surgical complications, particularly hardware-related complications including junctional kyphosis and screw pull-out. It is of utmost importance that spine surgeons are able to identify high-risk osteoporotic patients so they can optimize their bone health pre-operatively with multimodal protocols that incorporate pharmacological as well as non-pharmacological therapies.

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