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Mobile bearings do not improve fixation in cemented total knee arthroplasty
Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences.
2006 (English)In: Clinical Orthopaedics and Related Research, ISSN 0009-921X, Vol. 448, 114-121 p.Article in journal (Refereed) Published
Abstract [en]

Mobile bearings were introduced to improve wear and knee kinematics. By uncoupling the forces generated at the articulation from the implant-bone interface this would, theoretically, also improve the fixation of the implant to bone. We did this study to evaluate whether mobile bearings improve the fixation of the tibial component to bone. Fifty-two consecutive knees in 47 patients (average age, 72 years; range, 62-84 years) with primary osteoarthrosis were randomized into two groups to receive a cemented total knee arthroplasty with either a fixed-bearing or mobile-bearing tibial component. The quality of fixation was analyzed with radiostereometric analysis for up to 2 years. Mobile bearings did not improve fixation. Both magnitudes and directions of component rotations were similar, and the number of implants with continuous migration was almost identical. Both implant types had a combination of subsidence and lift-off, but where the mobile bearing implants displayed more of subsidence, the fixed bearing knees showed more lift-off. It might be that the somewhat stiffer cobalt-chromium baseplate or the different joint conformity used in the mobile-bearing knees counteracts any potential effects of the mobile bearing.

Place, publisher, year, edition, pages
2006. Vol. 448, 114-121 p.
Keyword [en]
Aged, Aged; 80 and over, Arthroplasty; Replacement; Knee/*methods, Bone Cements, Female, Follow-Up Studies, Humans, Knee Prosthesis, Male, Middle Aged, Osteoarthritis; Knee/physiopathology/*surgery, Prosthesis Design, Range of Motion; Articular, Treatment Outcome
URN: urn:nbn:se:umu:diva-3192DOI: 10.1097/01.blo.0000224004.40883.abOAI: diva2:141689
Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2009-05-04Bibliographically approved
In thesis
1. Total knee arthroplasty: aspects on improved fixation in the younger patient
Open this publication in new window or tab >>Total knee arthroplasty: aspects on improved fixation in the younger patient
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The results of total knee arthroplasty are inferior in younger patients. The challenge today is therefore to develop designs and concepts that will last at least 25 years.

This thesis has evaluated the fixation to bone of modern designs of knee prostheses uring RSA analysis. Coating implant surfaces with hydroxy-apatite have proven to enhance fixation to bone. Addition of screws for fixation of the tibial component enhances the fixation, but has negative side effects such as osteolysis around the screws, in turn leading to a higher risk of component loosening. The magnitude and pattern of migration was studied in a randomized study of uncemented tibial implants coated with hydroxy-apatite with and without additional screw fixation in patients younger than 65 years. The uncemented implants migrated initially more than the cemented implants that constituted the control group. Both uncemented groups stabilized at 3 monthes with no further migration, while the cemented implants showed a continuous migration up to the 2 year follow-up, indicating continuous bone resorption at the implant-bone interface, a fact that might lead to an increased risk of late implant loosening. This may not be a problem in older patients, but may have consequences for long-term fixation in younger patients. There was no difference between the two uncemented groups indicating that screws do not improve fixation. Hydroxy-apatite coated knee implants might be well suited for younger patients.

Mobile bearing total knee arthroplasty theoretically uncouples the forces at the implant-bone interface, thus improving fixation of the implant to bone. The magnitude and pattern of migration of a cemented mobile bearing knee arthroplasty and a fixed bearing total knee arthroplasty was compared in a randomized study. The results showed that mobile bearings did not improve fixation.

Trabecular metal, a new material recently introduced for total knee arthroplasty, has several theoretical advantages. Trabecular metal tibial implants were evaluated in a randomized study in patients younger than 60 years. The implants displayed the typical migration pattern for uncemented implants with greater migration initially followed by early stabilization. The majority of the trabecular metal implants subsided into the bone with no lift-off. Lift-off has the potential of exposing the interface to joint fluid with the potential risk of bone resorption and late loosening, and is commonly seen in metal-backed implants. The finding of absence of lift-off is regarded beneficial for uncemented fixation. Trabecular metal tibial implants might be suited for younger patients.

The optimal mode of fixation of the femoral component is yet to be established. Comparing cemented femoral components with uncemented femoral components in a randomized study in patients younger than 60 years revealed no differences of the magnitude or the pattern of migration. Uncemented femoral component seems equally as good as cemented components in younger patients.

Place, publisher, year, edition, pages
Umeå: Ortopedi, 2008. 73 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1172
Surgery, Total knee arthroplasty, total knee replacement, mobile bearing, trabecular metal, hydroxy-apatite coating, Kirurgi
Research subject
urn:nbn:se:umu:diva-1648 (URN)978-91-7264-549-3 (ISBN)
Public defence
2008-05-30, Föreläsningssalen, Falu lasarett, Falun, 09:00 (English)
Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2010-01-21Bibliographically approved

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