What is the standard rating for an injury involving amputation of the major thumb at the metacarpal joint?

• A. 5%
• B. 10%
• C. 20%
• D. 40%

Answer: (C)

Understanding how impairment ratings for the hand are determined is key. In the California SIP framework, the rating is based on where the amputation occurs and how much thumb function is lost, since the thumb is crucial for grip and opposition. Amputation of the major thumb at the base of the thumb (the metacarpal joint) removes the primary lever for pinch and opposition, reducing hand function significantly but not eliminating all hand use. The standard schedule assigns about 20% impairment to the hand for this level of loss, reflecting a meaningful but not maximal reduction in function. This sits between minor injuries that would yield smaller percentages and more extensive losses that would push the rating higher. So the 20% figure best represents the functional impact of losing the major thumb at the metacarpal joint under the SIP impairment guidelines. The smaller percentages correspond to less severe injuries, while the higher percentage would be used for more proximal or complete losses that cause greater impairment.