Are intervertebral body fusion devices, pedicle screws, allograft, and demineralized bone matrix medically necessary for lumbar and thoracic spinal fusion?

Medical Necessity Determination for Intervertebral Body Fusion Devices, Pedicle Screws, and Bone Graft Materials

Based on the highest quality guideline evidence, intervertebral body fusion devices (synthetic cages/spacers), pedicle screws, cadaveric allograft, and demineralized bone matrix are medically necessary for lumbar and thoracic spinal fusion when patients meet established criteria for fusion surgery, including documented degenerative disc disease, spondylolisthesis, or stenosis with failed conservative management. 1, 2

Intervertebral Body Fusion Devices (Synthetic Cages/Spacers)

Interbody fusion devices are medically necessary when used with allograft or autogenous bone graft for patients meeting fusion criteria. 1

Evidence Supporting Medical Necessity

• Interbody techniques are recommended as treatment options for patients with low-back pain due to degenerative disc disease at one or two levels, with placement of an interbody graft improving fusion rates and functional outcomes. 1

• Fusion rates with interbody devices range from 89-95% compared to 67-92% with posterolateral fusion alone in patients with degenerative disc disease and spondylolisthesis. 3, 4

• The American College of Neurosurgery recommends interbody fusion devices for patients with advanced degenerative disc disease when conservative treatments have failed, demonstrating higher fusion rates and better biomechanical stability. 2

Important Caveats

• The marginal improvement in fusion rates and functional outcomes with interbody techniques is associated with increased complication rates (31% vs 6% for non-instrumented procedures), particularly when combined anterior-posterior approaches are used. 1

• Multiple approaches (360° fusion) are not recommended as routine for treating low-back pain without deformity, as the addition of posterolateral fusion to anterior interbody fusion with pedicle screws increases blood loss, length of stay, and operating time without resultant benefit. 1

Pedicle Screws

Pedicle screw fixation is medically necessary when used as an adjunct to any spinal fusion that meets established criteria, particularly in high-risk patients. 1

Grade B Recommendations

• Pedicle screw fixation is recommended when posterolateral lumbar fusion is used to manage low-back pain in patients at high-risk for pseudarthrosis, including smokers, revision surgery patients, or those with medical conditions compromising fusion potential. 1

• Routine use of pedicle screw fixation as an adjunct to posterolateral fusion for degenerative disc disease is an option, though no definitive statement regarding efficacy for improving functional outcomes can be made. 1

Evidence Base

• Pedicle screw fixation increases fusion rates when assessed with dynamic radiographs, with fusion rates up to 83-95% compared to 45-67% without instrumentation. 1, 3

• The 2014 guideline update confirms no conflicting evidence with previous recommendations, maintaining that pedicle screws provide optimal biomechanical stability. 1

• Pedicle screw fixation represents the gold standard of spinal internal fixation and can be effectively used wherever a vertebral pedicle can accommodate a screw in cervical, thoracic, or lumbar spine. 5

Critical Considerations

• Consistent evidence demonstrates that pedicle screw fixation increases costs and complication rates of posterolateral fusion. 1

• The largest contemporary randomized controlled study failed to demonstrate significant clinical benefit with pedicle screw fixation in patients undergoing posterolateral fusion for chronic low-back pain, though this absence of proof should not be interpreted as proof of absence. 1

• For stenosis with spondylolisthesis, pedicle screw fixation provides consistent benefit, particularly in patients with preoperative instability or kyphosis. 1

Cadaveric Allograft and Demineralized Bone Matrix

Cadaveric allograft and demineralized bone matrix are medically necessary for spinal fusions, with allograft materials that are 100% bone considered medically necessary regardless of implant shape. 3, 4

Evidence Supporting Use

• Allograft eliminates donor site morbidity associated with autograft harvest, which causes donor-site pain in 58-64% of patients at 6 months postoperatively. 3, 4

• OLIF using allografts and demineralized bone matrix achieves solid fusion rates of 72.9% at 2 years when performed on one or two levels at L2-5. 6

• Local autograft combined with allograft or bone graft substitutes achieves fusion rates of 89-95% in instrumented single-level procedures. 3

Comparative Evidence

• Autograft demonstrates superior fusion quality compared to allograft in prospective studies, with autograft achieving grade 1 solid fusion in 80% of cases versus complete resorption of freeze-dried allografts in all cases. 7

• Frozen allografts show intermediate results with resorption in 60% of cases, while mixtures of autograft and freeze-dried allograft achieve solid fusion in 50% of cases. 7

• Despite lower fusion rates with allograft alone, the elimination of donor site morbidity and comparable clinical outcomes when combined with instrumentation support medical necessity. 3, 4

Clinical Application

• Demineralized bone matrix combined with structural allograft in interbody cages provides adequate fusion substrate when supplemented with rigid fixation. 4, 6

• Grade C evidence supports β-tricalcium phosphate/local autograft as a substitute for autologous iliac crest bone in single-level instrumented posterolateral fusion with comparable outcomes. 3

Algorithm for Medical Necessity Determination

Step 1: Verify Fusion Indication

• Document degenerative disc disease, spondylolisthesis (Grade I or higher), or stenosis with instability 2, 3
• Confirm failed conservative management for minimum 3-6 months including physical therapy, medications, and injections 2, 3
• Ensure imaging correlates with clinical symptoms 2

Step 2: Interbody Device Necessity

• Medically necessary when fusion criteria met and used with bone graft material 1, 4
• Provides higher fusion rates (89-95%) and anterior column support 3, 4
• Particularly indicated for spondylolisthesis with instability 4

Step 3: Pedicle Screw Necessity

• Medically necessary for high-risk patients: smokers, revision surgery, medical comorbidities 1
• Optional but supported for routine fusion procedures meeting criteria 1
• Strongly recommended for stenosis with spondylolisthesis, instability, or kyphosis 1

Step 4: Bone Graft Material Selection

• Allograft/DBM medically necessary for filling interbody devices and bone voids 3, 4
• 100% bone allograft materials approved regardless of shape 3
• Eliminates autograft donor site morbidity while achieving acceptable fusion rates with instrumentation 4, 6

Common Pitfalls to Avoid

• Do not approve 360° fusion routinely - combined anterior-posterior approaches without deformity increase complications without proven benefit 1

• Do not assume pedicle screws always improve clinical outcomes - while fusion rates improve, the largest RCT showed no significant clinical benefit for routine use in chronic low-back pain 1

• Do not use freeze-dried allograft alone - shows complete resorption in prospective studies; must be combined with other graft materials or used with rigid fixation 7

• Recognize increased complication rates - instrumented fusion carries 31% complication rate versus 6% non-instrumented, requiring appropriate patient selection and informed consent 1, 3