AMA Guides Impairment Ratings Explained

The AMA Guides to the Evaluation of Permanent Impairment, 5th Edition, is the standardized reference manual used to assess permanent impairment in most workers' compensation jurisdictions and many personal injury contexts. It provides objective, evidence-based methodology for rating whole person impairment (WPI) resulting from injuries or diseases.

Key Concepts:

• Impairment: A medical condition—an alteration in health status assessed by medical means
• Disability: An activity limitation—assessed in the context of one's occupation and life activities
• Whole Person Impairment (WPI): The rating expressed as a percentage of the whole person

The AMA Guides provides two methods for rating spine impairment:

Diagnosis-Related Estimate (DRE) Method

Used for most spine conditions with single-level pathology. Categories I through V based on severity:

• Category I: Complaint of pain, no objective findings (0-3% WPI)
• Category II: Minor findings, recovered from injury (5-8% WPI)
• Category III: Radiculopathy or surgery with recovery (10-13% WPI)
• Category IV: Radiculopathy with loss of motion or multi-level surgery (20-23% WPI)
• Category V: Multi-level radiculopathy with significant findings (25-28% WPI)

Range of Motion (ROM) Method

Used when DRE doesn't apply (multi-level degeneration, recurrent surgery, bilateral radiculopathy). Involves precise measurement of spine motion in all planes using inclinometry. Generally results in lower ratings than DRE for similar conditions.

1. Base Spine Impairment

DRE category or ROM calculation provides base rating for the spine condition itself.

2. Neurological Impairment

Additional impairment for specific neurological deficits:

• Motor deficits: 5-37% per nerve root depending on severity (0-5 strength scale)
• Sensory deficits: 1-5% per nerve root depending on severity
• Reflex loss: May indicate nerve deficit warranting rating

3. Combining Impairments

Spine impairment and neurological impairments are combined using the Combined Values Chart, not simply added. Example: 10% spine + 10% neurological = 19% WPI (not 20%).

Typical Ranges:

• Simple microdiscectomy (good outcome): 5-8% WPI
• Microdiscectomy with residual radiculopathy: 10-15% WPI
• Single-level lumbar fusion: 10-13% WPI (can be higher with complications)
• Two-level lumbar fusion: 20-25% WPI
• Failed back surgery with radiculopathy: 20-30% WPI
• Cervical fusion (one level): 10-15% WPI
• Multi-level cervical fusion with myelopathy: 25-40% WPI

Note: These are approximate ranges. Actual ratings depend on specific clinical findings, neurological deficits, and methodology used.

1. DRE vs. ROM Selection

DRE typically yields higher ratings. Dispute over whether case qualifies for DRE or requires ROM method. Some examiners inappropriately use ROM to minimize ratings when DRE is indicated.

2. DRE Category Placement

Even within DRE method, there's a range (e.g., Category III is 10-13%). Placement at low or high end of range can be disputed. Factors include surgery success, residual symptoms, and objective findings.

3. Neurological Deficit Assessment

Controversy over whether weakness or sensory loss is present and its severity. Subjective aspects (patient effort) can affect strength testing. Multiple examinations may show different findings.

4. Apportionment

When pre-existing conditions present, some jurisdictions require apportionment—separating work-related impairment from pre-existing degeneration. Methodology and percentages often contested.

5. Premature Rating

Ratings performed before MMI are invalid. Disputes arise when defense experts rate too early to minimize impairment, before full recovery achieved.

Required Elements:

• Patient must be at Maximum Medical Improvement (MMI)
• Thorough physical examination with objective measurements
• Review of all imaging and medical records
• Range of motion measurements (if using ROM method)
• Neurological examination (strength, sensation, reflexes)
• Documentation of methodology and calculations
• Explanation of rating rationale