Study on implant stability in cementless total knee arthroplasty

Radiographic Study in Patients Submitted to Cementless Total Knee Arthroplasties: Minimum Follow-Up of 2 Years

Objective  Radiographic evaluate if there are signs of early loosening of the cementless total knee arthroplasties Amplitude-Score® (Amplitude Surgical SAS, Valence, France), checking with a follow-up time ranging from 2 to 5.75 years (mean of 3.75 years).

Methods  Descriptive longitudinal investigation of observational nature, non-comparative, through a static radiographic study of annual control, of a case series, in a single center, all operated on by the same surgeon (S.M.). All cementless arthroplasties that met the inclusion and exclusion criteria performed from March 2012 to October 2014 were included.

Results  Among the 46 cementless knee arthroplasties evaluated in 40 patients, no radiographic signs of early loosening were verified.

Conclusion  Cementless arthroplasty promotes optimal osteointegration, with no early release, and it is essential that the surgical technique is perfectly respected.

Evaluation of Polyethylene Wear in a Brazilian Ultracongruent Knee Prosthesis with a Rotating Platform

Objective  To evaluate the wear of polyethylene in a Brazilian ultracongruent knee prosthesis with a rotating platform (Rotaflex, Víncula, Rio Claro, SP, Brasil). Methods  We used the test method with the loading and preparation parameters mentioned in the standards regulation ISO 14243-1:2009 , and the measurement methods mentioned in the standards regulation ISO 14243-2:2009 , for the evaluation of the wear behavior of a Brazilian prosthesis with a rotating platform. The equipment used for the wear test was the ISO 14243-1 gait simulator (EndoLab, Riedering, Germany). Results  After 10 million cycles, the evaluation of the polyethylene wear showed a regular appearance of surface wear at a mean rate of 2.56 mg per million cycles. Conclusion  The wear of the polyethylene of the evaluated prosthesis was minimal after the tests performed and with safety limits higher than those recommended by biomechanical engineering.

Comparative Fixation and Subsidence Profiles of Cementless Unicompartmental Knee Arthroplasty Implants

BACKGROUND

Aseptic loosening is the primary cause of failure for both cemented and cementless unicondylar knee replacements (UKRs). Micromotion and subsidence of tibial baseplate are two causes of failure, due to poor fixation and misalignment, respectively.

METHODS

Stair ascent activity profiles from Bergmann et al and Li et al were used. Biphasic Sawbones models were prepared according to the surgical techniques of traditional and novel cementless UKRs. Implants were tested for 10,000 cycles representing post-operative bone interdigitation period, and micromotion was observed using speckle pattern measurements, which demonstrated sufficient resolution. Additionally, the test method proposed by Liddle et al was used to measure subsidence with pressure sensors under increasingly lateralized loading.

RESULTS

Mean displacement due to micromotion for mediolateral and anteroposterior plane was consistently greater for traditional cementless UKR. Mean displacement for axial micromotion was significantly higher for traditional UKR at the anterior aspect of the implant; however, values were lower for the medial periphery of the implant. Subsidence was significantly lower for the novel design with increasingly lateralized loading, and indentation was not observed on the test substrate, when compared to the traditional design.

CONCLUSION

Our findings demonstrate that the novel cementless design is capable of fixation and elimination of subsidence in laboratory test settings. Both designs limit micromotion to below the established loosening micromotion value of 150 μm. The L-shaped keel design resists both micromotion and subsidence and may prevent failure modes that can lead to aseptic loosening for UKRs. These findings are highly relevant for clinical application.