Letter to The Editor

We have greatly benefited from reading the article published in the Journal of Arthroplasty, titled “A Randomized Controlled Trial Comparing High-Flex vs Standard Posterior Cruciate Substituting Polyethylene Tibial Inserts in Total Knee Arthroplasty,” by McCalden and MacDonald, Vol. 24, No. 6, Suppl. 1.

It is a remarkable job to put together a prospective randomized study such as this one with this great number of patients. We would like to thank the authors for their diligence and hard work. They have addressed an issue that we believe raises a lot of questions in the minds of orthopedic surgeons worldwide. Many manufacturers in an attempt to improve knee replacement designs have turned to modifications of prosthesis design, the efficacy of which remain unknown. In this study, the authors compared 2 groups of randomized patients, all of whom had knee ranges of motion no more than 125° and who were implanted with either a Genesis II PS insert or a Genesis II High Flex insert. They concluded that ranges of flexion postoperatively were similar in both groups.

We wonder whether the basic characteristics of these groups affected the outcome of this study, a thought that arises from our own experience with knee arthroplasty performed on a population that requires high flexion for daily life. Daily life in the Western world requires less flexion than that in the Eastern world, where patients kneel routinely many times a day for dining, prayer, and hygiene. It has been previously stated that 110° of flexion would be enough for many patients in the Western world to perform their daily routine, whereas it can be far from sufficient for a different population. Also, a patient who does not have more than 135° of flexion preoperatively and does not require it during daily life could not reasonably be expected to achieve this range of motion postoperatively. Previous literature has demonstrated that conventional total knee arthroplasty limits the flexion ability of all patients to around 125° at most. New high-flexion designs are intended to respond to flexion requirements of patients who premorbidly used to have a flexion range of 140° to 150°. It is our question whether necessity and premorbid knee flexion (that may be determined by referencing the contralateral knee in unilateral cases) would make a difference in the results of this study.