Over the last few years, various device manufacturers have developed and marketed “High Flex knees”. The hope with these newer designs was that patients would gain greater range of motion with regard to postoperative flexion or bending of the knee. There have been several studies comparing conventional with High Flex knee designs over the last few years, and the majority of these studies have failed to demonstrate any improved range of motion with the newer designs. The new designs take into account continued articulation or “mating” of the thigh bone to the shin bone component past 140 degrees of flexion.
What has been learned from this is that range of motion following a total knee replacement is dependent on several factors. These include patient factors, specifically the amount of motion the patient had in the knee prior to the operation; the patient’s size, as a larger lower extremity can block motion by the soft tissue girth of the leg; and motivation of the patient to perform their postop physical therapy. Surgical technique can also influence range of motion. This can include the alignment and placement of the implants, removal of bone and soft tissue that can interfere with flexion at the time of surgery, and balancing of the soft tissue with the new knee implants. Lastly, the implant can have an influence, but it seems to be the least important of the factors noted above.
In summary, range of motion following knee replacement is influenced by the amount of motion the patient has before surgery, the participation of the patient in a rehab program after surgery, the surgical technique used by the surgeon which involves proper placement and alignment of the implants and balancing of the soft tissue, and to a lesser degree, the implant. The length of incision has nothing to do with range of motion after knee replacement.
William P. Barrett, MD
