Sagittal laxity in vivo after total knee arthroplasty.
BACKGROUND
A stress arthrometry study of 77 knees undergoing total knee arthroplasty was performed to determine the difference in anteroposterior (AP) laxity between posterior cruciate ligament (PCL)-retaining (PCLR) and PCL-substituting (PCLS) prostheses using the Genesis I TKA.


METHODS
Fifty-three knees had PCLR and 24 had PCLS prostheses. The selected patients had successful arthroplasties after a minimum follow-up of 5 years. AP laxity was measured with a KT-2000 arthrometer (Medmetric, San Diego, CA, USA) using standard protocols.


RESULTS
At 30 degrees of flexion, there was no statistical difference in anterior (PCLR: 4.7 mm, PCLS: 4.5 mm), posterior (PCLR: 1.1 mm, PCLS: 0.7 mm), or total (PCLR: 5.8 mm, PCLS: 5.3 mm) displacement. At 75 degrees , significant differences were seen in both anterior (PCLR: 3.3 mm, PCLS: 2.3 mm) and total (PCLR: 4.8 mm, PCLS: 3.4 mm) displacement (p=0.001 and p=0.009, respectively), although there was no statistical difference in posterior displacement (PCLR: 1.5 mm, PCLS: 1.1 mm).


CONCLUSIONS
The above values are considered the suitable degree of AP laxity in total knee arthroplasty for a satisfactory clinical outcome 5-9 years after surgery. The PCL in a PCLR prosthesis and the central tibial spine and femoral cam in a PCLS prosthesis might play comparable roles in determining the laxity in the posterior direction in these prostheses.
Ishii Orthopaedic and Rehabilitation Clinic, 361-0037 Gyoda, Saitama, Japan. ishii@sakitama.or.jp
Yoshinori
Y
Ishii
Yoshikazu
Y
Matsuda
Ryo
R
Ishii
Shigeo
S
Sakata
Go
G
Omori
D000293:Adolescent; D000328:Adult; D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D016119:Posterior Cruciate Ligament / Q000503:physiopathology / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology; D016896:Treatment Outcome