You may be talking about the minimally invasive (MIS) quadriceps-sparing total knee replacement (TKR). In the standard TKR operation the quadriceps muscle in front of the knee and thigh is either split open or cut and moved out of the way while replacing the joint.
Problems can occur when the muscle is disrupted this way. Blood vessels and nerves can be cut causing swelling and weakness after the operation. Quadriceps sparing doesn't avoid the muscle completely, but it reduces the amount of trauma by quite a bit.
Patients with rheumatoid arthritis who do not have osteoporosis can have this operation. Younger patients with normal weight and no knee deformity have the best chances of a good result from surgery.