Definition
Term | Description |
BMD | Absolute, patient-specific score determined from certain anatomic areas |
Osteopenia | L2-4 lumbar density of 1 to 2.5 standard of deviations (T score -1 to -2.5) below the peak bone mass of a 25-year-old individual |
Osteoporosis | a bone disease in which the amount of normally mineralized bone therapy unit volume decreases, which results in an increased risk of fractures. L2-4 lumbar density > 2.5 standard of deviations (T score <-2.5) below the peak bone mass of a 25-year-old individual |
Osteomalacia | characterized by delayed or impaired mineralization of bone matrix. |
Comparison between osteoporosis vs osteomalacia
Category | Osteoporosis | Osteomalacia |
Definition | Reduced bone mass, normal mineralization | Bone mass variable, reduced mineralization |
Age | Postmenopausal (Type I) or elderly (Type II) | Any age |
Etiology | Endocrine abnormality, age, idiopathic, inactivity, alcohol, calcium deficiency | Vitamin D deficiency or abnormal pathway, hypophosphatemia, hypophosphatasia, renal tubular acidosis |
Symptoms & Signs | Pain and tenderness at fracture site | Generalized bone pain and tenderness |
X-ray Findings | Axial fracture predominance | Appendicular fractures, symmetric, includes pseudofractures (Looser zones) |
Serum Calcium | Normal | Low or normal |
Serum Phosphate | Normal | Low or normal |
Alkaline Phosphatase (ALP) | Normal | Elevated (except in hypophosphatasia) |
Urinary Calcium | High or normal | Normal or low (high in hypophosphatasia) |
Bone Biopsy | Tetracycline labeling normal | Tetracycline labeling abnormal |
Numbers
- male: female ratio is 1:4
- men have a higher prevalence of secondary osteoporosis (60%) including
- hypogonadism
- glucocorticoid excess
- alcoholism
- Incidence of osteoporosis in adult patients undergoing spinal reconstructive surgery: 10% to 50%.
- Incidence of osteopenia is between 41.4% and 58.6%.
- 78.7% of patients undergoing spinal surgery had either osteopenia or osteoporosis.
- High incidence of unrecognized osteoporosis in patient undergoing spinal surgery: 64%.
Location
- Vertebral body > peritrochanter femur > distal radius
Types
Category | Type I (Postmenopausal) | Type II (Senile) |
Age group | Postmenopausal (highest incidence in 50-70 years old) | >70 years old |
Bone affected | Almost exclusively trabecular | Trabecular > cortical |
Bones fractured | Distal radius and vertebral | Hip and pelvis |
Effect on calcium | Net negative change in calcium levels because of decreased intestinal absorption and increased urinary excretion of calcium. | Poor calcium absorption |
Effect on Vit D | Reduced circulating levels of total (but not free) 1,25 dihydroxyvitamin D. | Same |
Investigation
- Labs
- 25 hydroxyvitamin D level
- low 25 hydroxy cholecalciferol levels (25 hydroxy vit D) in patients sustaining low energy fractures
- Other labs may be drawn to rule out other causes of osteoporosis (endocrine, hematologic, malignancy, etc)
- labs are generally normal in osteoporosis
- Biopsy
- After tetracycline labelling
- Indications
- May be helpful to rule out osteomalacia
- Histology
- thinned trabeculae
- decreased osteon size
- enlarged Haversian and marrow spaces
- osteoclast ruffled border
- Increases osteoclast ruffled border seen with
- PTH
- 1,25 dihydroxy Vit D3
- Prostaglandin E
- flattened ruffled border seen with
- Bisphosphonates
- Calcitonin
- Imaging for osteoporosis
- Definitions
- usually performed in
- Lumbar spine:
- measures BMD from L2 to L4 and compiles scores
- Hip:
- measure BMD from femoral neck, trochanter, and intertrochanter region and compiles scores
- Sensitivity and specificity
- Most accurate with the least radiation exposure
- DEXA scans of the spine can be inaccurate due to
- Scoliosis
- Osteophytes spuriously elevating BMD,
- Presence of spinal fusion or instrumentation.
- Sardar 2022: Hip and Spine DEXA scans for diagnosing osteoporosis in patients aged 50 and above (using T-score) and between 20-50 (using Z-score).
- Most optimal method for measuring BMD in the spine due to its volumetric analysis of trabecular bone mineral density.
- A QCT BMD less than 90 mg/mL indicates an increased risk of pedicle screw loosening.
- Pros
- Precision
- Cons
- Limited availability
- Higher cost
- Increased radiation
- Aiding in bone health assessment decisions.
- Measurements (typically at L1-4) correlate with DEXA-based BMD.
- An L1 CTHU of <100 is considered abnormal,
- Lower CTHU values are associated with vertebral fracture, adjacent segment fractures, and cage subsidence.
- while >150 is normal,
- Pros
- Commonly used: routinely performed before spinal instrumentation.
- Measures vertebral body strength using finite element analysis (FEA) and trabecular BMD.
- BCT has been reported to predict the risk of vertebral body fracture independently of BMD.
- Patients testing positive for osteoporosis using BCT had a
- 5 times higher risk of vertebral fractures
- 4 times the risk of reoperation after spinal fusion.
DEXA Scan (Dual Energy Xray Absorptiometry)
Score type | Description |
T-Score | BMD relative to normal young matched controls (30-year-old women) |
Z-Score | BMD relative to similar-aged patients |
Quantitative Computed Tomography (QCT):
Opportunistic CT Scan-Based Hounsfield Units (CTHU):
Biomechanical Computed Tomography analysis (BCT):
Natural history
- Vertebral fractures
- associated with 15% increase in 5-year mortality
- associated with increased morbidity
- back pain
- loss of height
- poor balance
- respiratory compromise
- restrictive lung disease
- pneumonia
- history of 1 vertebral fracture results in 5 fold increased risk of 2nd vertebral fracture and 5 fold increased risk of hip fracture
- history of 2 vertebral fractures is the strongest indicated for further compression fractures in postmenopausal women
Fracture Risk Assessment Tool (FRAX)
Adverse Events Related to Osteoporosis in Spinal Surgery
- Vertebral fractures.
- Instrumentation failure and screw loosening.
- Pseudarthrosis (non-union), with patients having osteoporosis or osteopenia being at a 2 times higher risk.
- Proximal or distal junctional kyphosis (PJK/DJK), with osteoporotic patients estimated to have up to 2 times the risk of PJK. Low BMD is a recognised risk factor for PJK.
- Unplanned reoperation, with osteoporotic or osteopenic patients facing a 3 or more times higher risk.
Management
Intraoperative Fixation Strategies
Optimizing Screw Fixation
- Aim to maximize pullout resistance and stability.
- Larger-Diameter Screws:
- The use of larger-diameter screws (typically 4.0–5.5 mm) is recommended over standard 3.5 mm screws when anatomic constraints allow.
- Screw length and trajectory correlate with pullout resistance; for instance, each additional millimeter of screw length may increase pullout resistance by approximately 16 N.
(A) Lateral cervical spine radiograph shows haloing across the C1/C2 screws, indicating instrumentation loosening.
(B) Axial CT at C1 confirms haloing of the C1 screws bilaterally.
(C) Lateral cervical spine radiograph shows placement of larger screws with additional fixation at C3.
(D) Axial CT shows large-diameter C1 screws with bone graft across the C1 ring.
- Bicortical Fixation:
- Bicortical placement substantially improves biomechanical strength compared to unicortical fixation.
- Bicortical fixation of the C1 lateral mass and the occiput
- Bicortical screw placement at the occipital keel achieved 50% greater pullout resistance than unicortical fixation.
- Bicortical subaxial lateral mass screw fixation
- Offered slightly higher pullout resistance than unicortical fixation (565 N vs. 519 N)
- Risky due to potential
- Nerve root injury (17%)
- Vertebral artery injury (6%).
- Subaxial Cervical Pedicle Screw Fixation:
- Provides 3.5 to 4 times the pullout resistance of lateral mass screws.
- Challenging placement due to
- Small pedicle diameter
- Proximity to the vertebral artery.
- Maximising Fixation Points:
- Increasing the number of fixation points helps distribute mechanical stress at the bone/screw interfaces.
- Supplemental fixation using laminar hooks or sublaminar wires may be considered, especially when distal fixation into the thoracic spine is compromised by poor bone quality.
- Three-Point Fixation at C2:
- When patients with osteoporosis undergo subaxial cervical fusion, instrumentation should be strongly considered for extension to C2.
- C2 offers several fixation options (pedicle, pars, and laminar screws)
- C2 pedicle screws providing roughly twice the pullout resistance of pars screws.
- Occipital Tethering Technique:
- This technique is utilized when stronger proximal fixation is necessary, such as in cases of severely compromised bone quality or complex revision surgeries.
- It involves placing bicortical occipital screws with an occipital plate, without extending arthrodesis above C1.
- The occipital instrumentation is removed after 6–12 months once fusion is achieved, restoring upper cervical motion.
Ancillary Load Sharing Column Strategies
- Circumferential Fixation with Anterior Column Reconstruction:
- The principle of load sharing makes circumferential (combined anterior and posterior) cervical spine surgery central to management, particularly in patients with compromised bone quality.
- Pros
- Greater rigidity vs anterior instrumentation alone.
- Greater biomechanical support vs anterior instrumentation alone.
- Better fusion rates vs standalone anterior or posterior approaches
- Cons
- Longer surgical time
- Greater blood loss
- Multirod Construct:
- Increases rigidity therefore reduce failure
- Posterior Third Column Construct:
- This technique involves additional anchoring, often using a combination of a C2 translaminar screw and an upper thoracic translaminar screw, to provide support through a third rod.
- This strategy enhances construct rigidity and reduces mechanical stress, particularly beneficial for patients with severe osteoporosis undergoing 3-column osteotomy.
Cement Augmentation
- Polymethylmethacrylate cement augmentation associated with
- Reduced pedicle screw pullout
- Biomechanical studies have shown a 2-fold increase in both pullout strength and energy to failure in polymethylmethacrylate-augmented screws compared with nonaugmented screws in osteoporotic vertebrae.
- Improved fusion rates in patients with osteoporosis
- The use of fenestrated screws enables more targeted delivery of cement.
- In cervical and cervicothoracic constructs, augmentation is routinely performed at the most distal thoracic screw to enhance biomechanical stability at the lower end of the construct, helping reduce immediate distal junctional complications in long-segment fusions.
- Some even place cement in the LIV + 1 to reduce the strain and therefore vertebral body collapse of the LIV.
- Vertebral cement augmentation at the LIV+1 and UIV+1 has been studied to decrease proximal junctional kyphosis.
Perioperative Management
Pharmacologic Treatment of Osteoporosis
Aim
- Improve fusion rates
- Reduce instrumentation failure
- Prevent adjacent segment fractures.
Anabolic Agents
- Teriparatide (TP):
- A parathyroid hormone analog
- it is an anabolic (bone-forming) medication.
- Perioperative TP treatment significantly
- decreases complication rates (e.g., screw loosening, rod fracture, adjacent vertebral fracture, pseudarthrosis) and
- improves bone union rates and time to fusion compared to bisphosphonates or no treatment.
- Evidence
- Studies show outcomes for osteoporotic patients treated with TP can be equivalent to those with normal BMD.
- Seki 2017: A prospective study showed that patients treated with teriparatide had a significantly higher fusion rate (89%) compared to those receiving bisphosphonates (77%) in the context of spinal fusion.
Teriparatide has demonstrated superior outcomes in spinal fusion when compared directly to bisphosphonates.
- Abaloparatide:
- Another anabolic medication, effective in improving BMD and decreasing vertebral fractures, considered an alternative to teriparatide, though its use in spine surgery specifically is not yet in the literature.
- Sardar et al. (2022) guidelines recommend Teriparatide or Abaloparatide as the first-line agents for osteoporosis in patients undergoing spinal reconstruction.
Antiresorptive Agents
- Bisphosphonates (BPs):
- The most common medications for osteoporosis.
- General
- 1st line therapy for osteoporosis
- Indication
- Paget’s disease
- Osteoporosis
- Hip or vertebral fracture
- T-score <2.5 at the femoral neck or spine (after exclusion of secondary causes)
- Low bone mass (T-score between -1.0 and -2.5) and
- 10-year probability of a hip fracture ≥ 3% or greater or
- 10-year probability of a major osteoporosis-related fracture ≥ 20% based on WHO algorithm/FRAX
- Mech:
- Accumulate at sites of bone remodelling and are incorporated into bone matrix
- Are released into acid environment once bone is resorbed, and are then taken up by osteoclasts
- Pyrophosphate analogues that bind to hydroxyapatite crystals and inhibit reabsorption.
- Decrease osteoclastic bone resorption, flattening of osteoclast ruffled border and increased osteoclast apoptosis
- Exact mechanism depends on presence of nitrogen on alkyl chain
- Pharmacokinetics
- They are retained in bone until it is resorbed.
- Oral absorption of all is poor (especially in the presence of food).
- Bone formed during treatment is lamellar rather than woven.
- Renal excretion without undergoing metabolism
- Types
- Etidronate (Didronel) (AKA EHDP):
- reduces normal bone mineralization (especially at doses ≥ 20 mg/kg/d),
- producing mineralization defects (osteomalacia) which may increase the risk of fracture but which tend to heal between courses.
- Contraindicated in patients with
- renal failure,
- osteomalacia, or
- severe lytic lesions of an LE.
- ℞ 5–10 mg/kg PO daily (average dose: 400 mg/d, or 200–300 mg/d in frail elderly patients) for 6 months, may be repeated after a 3–6 month hiatus if biochemical markers indicate relapse.
- Tiludronate (Skelid):
- unlike etidronate, does not appear to interfere with bone mineralization at recommended doses.
- Side effects: abdominal pain, diarrhea, N/V. ℞ 400mg PO qd with 6–8 ounces of plain water > 2 hrs before or after eating × 3 months. Available: 200mg tablets.
- Pamidronate (Aredia):
- much more potent than etidronate.
- May cause a transient acute flu-like syndrome.
- Oral dosing is hindered by GI intolerance, and IV forms may be required.
- Mineralization defects do not occur in doses < 180 mg/course. ℞ 90 mg/d IV × 3 days, or as weekly or monthly infusions.
- Alendronate (Fosamax):
- does not produce mineralization defects (p. 1051).
- Some studies showed alendronate improving fusion rates and decreasing complications, while others found no effect.
- Zoledronate also showed varied effects on fusion rate and complications across studies. While no negative effect has been shown,
- Clodronate (Ostac, Bonefos):
- ℞ 400–1600 mg/d PO × 3–6 months. 300 mg/d IV × 5 days (may be available outside the U.S.).
- Risedronate (Actonel):
- does not interfere with bone mineralization in recommended doses.15 ℞: 30mg PO q d with 6–8 oz. of water at least 30 minutes before the first meal of the day.
- Outcomes
- Osteoporosis
- Alendronate reduces the rate of hip, spine, and wrist fractures by 50%
- Risedronate reduces vertebral and non-vertebral fractures by 40% (each) over 3 years
- IV zoledronic acid reduces the rate of spine fractures by 70% and hip fractures by 40% over 3 years
- When administered during the perioperative period, bisphosphonates have been associated with better clinical outcomes, higher fusion rates, and a lower incidence of vertebral compression fractures
- Denosumab:
- Similar to bisphosphonates, it is an antiresorptive medication. One study showed improved fusion rates when combined with teriparatide. It is well-demonstrated in preventing osteoporotic fractures.
- Romosozumab:
- A newer monoclonal anti-sclerostin antibody with both anabolic and anti-resorptive effects. It has significantly improved lumbar spine CTHU and decreased new vertebral fractures, though not specifically studied in spine surgery.
- Antiresorptive agents such as Denosumab or Zoledronate are recommended if anabolic agents are contraindicated or not tolerated.
Vitamin D and Calcium
- Optimising Vitamin D and calcium levels is an important component of medical treatment. Vitamin D deficiency is common and often undiagnosed. Higher vitamin D levels have been linked to improved clinical outcomes, including better ODI scores and reduced pain after spine surgery, and potentially improved fusion rates.
Bracing
- No consensus on the routine use of bracing after cervical fusion.
- Postoperative external cervical spine immobilization (bracing) is routinely used for patients with severe osteoporosis.
- In the context of severe osteoporosis, especially following circumferential fusion, the use of a cervical collar provides an added layer of biomechanical support
Made with Bullet