Introduction: The goal of this study was to determine the difference between weight-bearing and non weight-bearing range of motion (ROM) for Japanese subjects having either a fixed or mobile bearing TKA with either a resurfaced (RP) or unresurfaced (UP) patella.

Methods: Forty subjects were evaluated using video fluoroscopy. Twenty subjects had a fixed bearing posterior cruciate retaining (PCR) TKA (10 RP, 10 UP) and twenty subjects had a mobile bearing (MB) TKA (10 RP, 10 UP). Under weight-bearing conditions, each subject performed successive deep knee bends to maximum flexion. Then, under passive, non weight-bearing conditions the subjects stood on one leg and passively flexed their knee to maximum flexion. Each trial was recorded and analyzed digitally. The angle between the femoral and tibial longitudinal axes was subtracted from 180o to obtain the amount of flexion.A single surgeon control was used. The average age of the subjects was 66.4, 78.1, 70.3, and 71.1 for subjects having PCR RP, PCR UP, MB RP, and MB UP, respectively. All total knee subjects were judged excellent clinically with HSS scores > 90 points. None complained of pain during testing.

Results: The preoperative ROM for the implanted knee groups was 115, 122, 110, and 120 degrees for subjects having a PCR RP, PCR UP, MB RP, and MB UP, respectively. The average passive ROM was 106 (90–131) and 108 (72–128) degrees for subjects having a PCR RP and PCR UP, respectively. Subjects having a MB TKA experienced greater passive ROM, 120 degrees for both the MB RP (105–136o) and MB UP (105–167o). Under weight-bearing conditions, ROM decreased for all groups, with the average ROM of 101 (90–125), 108 (86–128), 109 (92–134), and 114 (94–142) degrees for subjects having a PCR RP, PCR UP, MB RP, and MB UP, respectively. The greatest amount of ROM occurred for a subject having a MB UP, 167o during passive ROM and 142o during a weight-bearing ROM.

Discussion: Subjects in this study having a MB TKA experienced greater ROM for all of the compared four parameters. Subjects having a MB RP experienced greater passive (120 vs. 106) and weight-bearing (109 vs. 101) ROM compared to the PCR RP group. Similarly, subjects having a MB UP experienced greater passive (120 vs. 108) and weight-bearing (114 vs. 108) ROM compared to the PCR UP group. Interestingly, subjects having an UP TKA experienced greater ROM compared to subjects having a RP TKA. The results from this study may suggest that a mobile bearing TKA may lead to greater ROM for the Japanese populations, where achieving deep flexion is essential for normal daily activities.