Final answer:
To code the services for a wheelchair prescribed for a patient with a knee amputation, the medical office assistant should use the HCPCS, which provides specific codes for durable medical equipment like wheelchairs.
Step-by-step explanation:
The medical office assistant should use the HCPCS (Healthcare Common Procedure Coding System) to code the services for a wheelchair for a patient with a knee amputation. The HCPCS codes are specifically designed to cover items, supplies, and services that are not included in the CPT codes, such as durable medical equipment (DME), prosthetics, orthotics, and supplies. In this case, a wheelchair as a piece of medical equipment would be coded using HCPCS.