The complementary opposition sign refers to increased effort in lifting a paretic leg, demonstrated as a compensatory downward pressure by the opposite (unaffected) leg. It is observed in patients with lower limb paresis and reflects involuntary recruitment of contralateral muscles to assist movement of the affected limb.

Pathophysiology

This sign arises due to:

• Pyramidal tract or cortical motor lesions: Weakness of the affected leg necessitates compensatory engagement of contralateral musculature.

• Crossed motor facilitation: Effort to lift a paretic limb produces involuntary contraction in the homologous muscles of the opposite leg.

• Loss of isolated muscle control: Patients with paresis cannot recruit muscles independently, resulting in mirrored movements or compensatory forces.

Examination Technique

Patient Positioning

• Supine on the examination table, legs extended and relaxed.

Procedure

1. Place your hand under the heel of the unaffected leg.

2. Instruct the patient to lift the paretic leg actively.

3. Observe whether lifting the weak leg produces marked downward pressure on your hand under the opposite leg.

Assessment

• Positive sign: Significant downward pressure by the contralateral leg, reflecting compensatory effort.

• May be subtle in mild paresis and more pronounced in moderate to severe weakness.

Clinical features

Differential Diagnosis

Pediatric considerations

• Rarely assessed in infants unless unilateral paresis is present.

• Developmental reflexes may interfere with interpretation.

Geriatric considerations

• May indicate stroke, neurodegeneration, or acute paresis.

• Compensatory effort may exacerbate fatigue or fall risk.

Limitations

• Requires patient cooperation.

• Mild paresis may produce subtle or inconsistent findings.

• Should be interpreted alongside other motor assessments, reflex testing, and imaging.

Patient counseling

• Explain the purpose of the test as part of neurological evaluation.

• Reassure that involuntary contralateral effort is a normal compensatory response to weakness.

• Emphasize that findings guide further diagnostic workup and rehabilitation planning.

Conclusion

The complementary opposition sign is a clinical indicator of lower limb paresis, demonstrating compensatory activity in the contralateral leg. Proper technique and interpretation enhance diagnosis of pyramidal or corticospinal tract lesions and help guide rehabilitation strategies.

References

1. Grasset G. De la paralysie et de la rééducation des membres inférieurs. Paris: Masson; 1909.

2. Hoover RM. The phenomenon of contralateral leg effort in hemiplegia. Brain. 1908;31:125–138.

3. Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science. 5th ed. New York: McGraw-Hill; 2013.

4. Ropper AH, Samuels MA, Klein JP. Adams and Victor’s Principles of Neurology. 11th ed. New York: McGraw-Hill; 2021.