Changes in the three-dimensional load-bearing axis after mobile-bearing total knee arthroplasty.
BACKGROUND
The purpose of this study was to assess changes in the three-dimensional (3D) load-bearing mechanical axis (LBMA) preoperatively and at 3 weeks and more than 1-year follow-up after total knee arthroplasty (TKA), and effects of the degree of constraint in the anteroposterior (AP) direction because of the retention of the posterior cruciate ligament (PCL) and the implant design on the changes in LBMA.


METHODS
We evaluated 157 knees from 131 patients, including 79 knees that received meniscal-bearing-type (PCL-retaining) and 78 knees that received rotating-platform-type (PCL-substituting) prostheses. Quantitative 3D computed tomography was used to assess changes in the location of the pre- and postoperative LBMA at the tibial plateau level.


RESULTS
Changes in the 3D axis were mainly found from medial to lateral and posterior to anterior in both implant designs with no significant differences. Change in the mediolateral (ML) direction was improved soon after TKA, but change in the AP direction improved more gradually over time. The different constraints in the AP direction because of the retention of the PCL and different implant designs did not affect the changes in the LBMA.


CONCLUSIONS
The LBMA in the AP direction more than 1 year postoperatively, as well as the LBMA in the ML direction at 3 weeks, appears to shift toward the location found in normal knees after TKA, regardless of the type of prosthetic constraint. These changes may be an important factor that influences the periarticular knee bone mineral density which load bearing may be related to.


METHODS
Level II, Prognostic study.
Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan. ishii@sakitama.or.jp.
Yoshinori
Y
Ishii
Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan.
Hideo
H
Noguchi
Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan.
Junko
J
Sato
Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan.
Nobukazu
N
Ezawa
Division of Information Science and Biostatistics, Graduate School of Medical and Dental Sciences, Niigata University, 1 Asahimachi Dori Niigata, Niigata, 951-8520, Japan.
Shin-Ichi
S
Toyabe
D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods; D001696:Biomechanical Phenomena; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007564:Japan; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000601:surgery*; D010043:Outcome and Process Assessment, Health Care; D016119:Posterior Cruciate Ligament / Q000503:physiopathology; D011183:Postoperative Complications / Q000175:diagnosis / Q000209:etiology / Q000517:prevention & control; D011474:Prosthesis Design; D011859:Radiography / Q000379:methods; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D016474:Weight-Bearing
Bone mineral density; Meniscal-bearing TKA; Mobile-bearing total knee arthroplasty; Rotating-platform TKA; Three-dimensional load-bearing mechanical axis