What ICD‑10 code should be used for a patient unable to lift a leg, distinguishing between paralysis (monoplegia) and muscle weakness?

ICD-10 Coding for Inability to Lift Leg

For a patient unable to lift a leg, use G83.1- (monoplegia of lower limb) if there is complete paralysis, or M62.81 (muscle weakness/generalized) if the patient has weakness but retains some movement capability.

Distinguishing Between Paralysis and Weakness

The critical first step is determining whether the patient has complete absence of movement (paralysis) versus reduced strength with preserved movement (weakness) 1:

Motor Assessment Framework

• Grade 0 (No movement): No active motion visible, even with palpation of muscle—this represents true paralysis and warrants G83.1- codes 1
• Grade 1-4 (Any movement present): Any flicker of movement, partial motion, or ability to move against gravity indicates weakness rather than paralysis—use M62.81 1

Test specifically for straight-leg raise: If the patient cannot perform straight-leg raise but demonstrates any knee flexion or foot movement, this is weakness, not paralysis 2, 1

ICD-10 Code Selection Algorithm

For Complete Paralysis (Motor Grade 0):

• G83.10: Monoplegia of lower limb affecting unspecified side
• G83.11: Monoplegia of lower limb affecting right dominant side
• G83.12: Monoplegia of lower limb affecting left dominant side
• G83.13: Monoplegia of lower limb affecting right nondominant side
• G83.14: Monoplegia of lower limb affecting left nondominant side

Select the specific fifth digit based on laterality and dominance 1.

For Muscle Weakness (Motor Grade 1-4):

• M62.81: Muscle weakness (generalized)—use when patient demonstrates any active movement but cannot perform normal function 1

For Acute Vascular Causes:

If inability to lift leg occurs in the context of acute limb ischemia with paralysis (rigor), this represents Rutherford Class III (irreversible) and requires both:

• Primary code for acute arterial occlusion (I74.3 for lower extremity)
• Secondary code G83.1- for the resulting paralysis 2

Common Clinical Scenarios

Post-Neuraxial Anesthesia:

• If unable to straight-leg raise at 4 hours post-epidural/spinal, use Bromage Scale for documentation 2
• Bromage Score 1 (complete block, unable to move feet or knees) = temporary paralysis, code as complication of anesthesia (T88.59) rather than monoplegia 2
• Persistent inability beyond expected recovery (>24-48 hours) warrants G83.1- coding 2

Acute Stroke Presentation:

• New-onset inability to lift leg with other neurological deficits requires immediate imaging 3
• Code the stroke (I63.-) as primary diagnosis, with G83.1- as secondary to describe the deficit 3

Critical Pitfalls to Avoid

• Do not code paralysis (G83.1-) if any movement is present—even a flicker upgrades to weakness (M62.81) 1
• Do not attribute new inability to lift leg solely to expected post-anesthesia effects without first excluding epidural hematoma or other complications requiring urgent intervention 2
• Do not confuse absence of voluntary movement with flaccidity—Grade 0 specifically refers to no active motion regardless of tone 1
• Ensure the patient understands the command and is attempting movement before coding as paralysis, to distinguish from sensory deficits or comprehension issues 1

Documentation Requirements

Document the specific motor grade (0-4) for medical record completeness, even though ICD-10 does not capture this granularity 1. This supports accurate code selection and facilitates clinical communication about severity and progression 2, 1.