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J Arthroplasty. 2018 Jul;33(7S):S265-S269. doi: 10.1016/j.arth.2018.02.021. Epub 2018 Feb 21.

A Computer Model of Mid-Flexion Instability in a Balanced Total Knee Arthroplasty.

Author information

1
Department of Orthopaedic Surgery, NYU Langone Orthopedic Hospital, New York, NY.
2
Orthopaedic Product Development, Smith and Nephew, Memphis, TN.
3
Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA.

Abstract

BACKGROUND:

Some patients have mid-flexion instability despite stability at 0° and 90° of flexion. This study aims to determine the effects of total knee arthroplasty (TKA) stability while changing femur implant size and position.

METHODS:

A computational analysis was performed simulating knee flexion of posterior stabilized (PS) and cruciate retaining (CR) TKA designs. Deviations from the ideal TKA implant position were simulated by adjusting tibiofemoral proximal-distal position and femur anterior-posterior position as well as implant size. Forces in ligaments connecting the femur and tibia were collected. Total tibiofemoral ligament load for mid-knee flexion of 15°-75° was analyzed vs proximal-distal implant position, implant size, implant design, and knee flexion for PS and CR knees. Posterior cruciate ligament load was also analyzed for CR knees.

RESULTS:

Total tibiofemoral ligament load was significantly reduced by a more proximal tibiofemoral and anterior femur position (P < .001). Implant size did not have a significant effect on tibiofemoral ligament load (P > .1). Implant design and knee flexion significantly influenced total tibiofemoral ligament load (P < .001), but the interactions with implant proximal-distal position were not significant (P > .2), indicating that implant proximal-distal position had a similar effect across the 15°-75° knee flexion range for both studied PS and CR implant designs.

CONCLUSION:

PS and CR TKA can be well-balanced at 0° and 90° knee flexion and have instability in mid-flexion. Elevating the joint line and shifting the femur anteriorly can cause the knee to be too loose in mid-flexion.

KEYWORDS:

computer simulation; cruciate retaining; mid-flexion instability; posterior stabilized; total knee arthroplasty

PMID:
29567003
DOI:
10.1016/j.arth.2018.02.021
[Indexed for MEDLINE]

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