The new mini-incision method of joint replacement does indeed use a much smaller incision. The standard length opening is about eight to 10 inches. The mini-incision is about half that length at four to five inches.
The mini-incision does make it difficult for the surgeon to see everything. Special tools called retractors are used to gently pull back the skin and soft tissues.
Even so, the surgeon may not see the landmarks needed for the operation. Sometimes the guide used to cut out the old joint places the saw at a slight tilt. The implant may get put in with too much rotation resulting in poor alignment.
The mini-incision also makes it harder to remove loose bone fragments or extra cement that isn't needed.
There are advantages to this method. Shorter operation time and fewer days in the hospital add up to money saved. Less blood loss and fewer pain drugs means the patient is up and moving sooner. With less trauma to the surrounding tissues, rehab is faster and easier.