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To determine polyethylene deformation in well-functioning meniscal bearing PCL-retaining total knee prosthesis a quantitative stereophotogrammetric analysis was carried out over 5 years' follow-up. Polyethylene plastic deformation was obtained by tracking the intermarker distance variations of five tantalum beads inserted into the polyethylene prior to surgery in a known position. Plastic deformation occurred in the posteromedial part of the meniscal bearing. Radiostereometric analysis was a useful tool to monitor the load distribution in vivo on the polyethylene of this meniscal bearing prosthesis. This analysis revealed a very similar pattern of plastic deformation in the polyethylene insert of this prosthesis design to the wear pattern revealed with different methodologies in PCL-retaining fixed-bearing prosthesis.

Luxation and excessive wear of the mobile bearing in modern three-piece total ankle replacement (TAR) is reported. We conducted a systematic review of studies to explore and discuss the rate and causes of these complications.A systematic review of studies since 2000 showed 26 studies with altogether 1,318 followed up TARs which we analyzed. Of these 1,318 TARs, 188 (14.3%) were revised and 56 (4.2%) complications with the mobile bearing were reported. A total of 39 cases (3%), i.e., 20.7% of all revisions, were revised due to failure of the mobile bearing, including 17 cases with subluxation (1.3%), 15 with asymmetric load of the bearing (1.1%), 10 with fracture of the polyethylene (PE) inlay (0.76%), 7 with massive PE wear (0.53%), and 7 with luxation of the meniscal bearing (0.53%).Complications due to the meniscal mobile bearing in TARs such as luxation, subluxation, massive wear, and fracture of the PE inlay are rare complications. The cause of these complications is regularly not found in the design of this three-piece total ankle replacement. Causes of failure of the mobile bearing are mostly found in incorrect indication, incorrect soft tissue balancing, incorrect positioning of components, implantation in ankles with hindfoot malalignment and ankle instability.

Background An original total ankle replacement design was developed with the aim of establishing compatibility between the prosthetic articulating surfaces and the retained ligaments. This was achieved with a special shape of a conforming meniscal bearing, free to move forwards/ backwards on both metal components during dorsi/ plantar flexion. Careful kinematics analyses were carried out in patients after this replacement to assess the functional performance during activity of daily living. A thorough assessment shall include standard gait analysis (GA) and the more accurate motion tracking of the components by 3D fluoroscopic analysis (FA).

A mobile-bearing element, metal-backed, interchangeable knee replacement system has been designed to combine low constraint forces with low contact stresses (LCS), allowing nearly normal joint articulation and loading as well as long-term wear resistance of the implants. The system is versatile, including a large number of component options in variable sizes, and it may be used in both primary and revision arthroplasties. The overall results in the first 123 cemented cases (97 patients) with 2- to 7-year follow-up (average 3.7 years) were good to excellent in 88.6%, fair in 3.3%, and poor in 8.1%. Fair and poor results were seen predominantly in multiply operated and implant revision cases. The best results were noted in primary cases, 97.4% of which had good to excellent results. There have been no mechanical implant failures and no meniscal bearing dislocations in this series. Pain relief and restoration of function have been very gratifying with this system.