Twenty-Year Evaluation of Cementless Mobile-Bearing Total Ankle Replacements

Abstract

Two consecutive series of patients who had cementless, porous-coated, congruent-contact, mobile-bearing total ankle replacements were evaluated during a 20-year interval using the New Jersey Orthopaedic Hospital ankle scoring scale to determine clinical outcome and overall implant survivorship with revision as an end point. The initial series of 38 patients (40 ankle replacements) using a shallow-sulcus design had diagnoses of: osteoarthritis, seven (17.5%); rheumatoid arthritis, nine (22.5%); posttraumatic arthritis, 21 (52.5%); and failed fusion, three (7.5%). Clinical results after 2-20 years, (mean, 12 years) were 28 (70%) good to excellent, two (5%) fair, and 10 (25%) poor. Postoperative ankle motion ranged from 10°-47°total arc (mean, 25°total arc). The 20-year overall survivorship for the shallow-sulcus design was 74.2%. A second series of 74 patients (75 ankle replacements) using a deep-sulcus design had diagnoses of: osteoarthritis, eight (11%); rheumatoid arthritis, nine (12%); osteonecrosis, three (4%); and posttraumatic arthritis, 55 (73%). Clinical results after 2-12 years, (mean 5 years) were 66 (88%) good to excellent, four (5%) fair, and five (7%) poor. Postoperative ankle motion ranged from 10°-50°t otal arc (mean, 29°total arc). The 12-year overall survivorship for the deep-sulcus design was 92%.Improved total ankle replacement results using mobile bearings have been reported. 3,4,7,16,24 It is postulated that these results have been produced by allowing normal kinematic function of the bones and ligaments as seen in gait analysis 20 and load-bearing cineradiographic studies. 17 Allowing distal fibular rotation to optimize lateral ligamentous function during dorsiflexion and planter flexion motion is an ideal goal. Such rotation can average 2.2°(range, 1.4°-4.8°). 13 Fixed-bearing devices that attempt to eliminate or minimize this fibular motion or restrict axial rotation can be subjected to torsional loads that can loosen tibial component fixation 1,10,11,15,21,25,26 or result in nonunion of the syndesmosis. 12,23 The current study involves the use of rotationally unconstrained mobile bearings that articulate with a flat tibial plate superiorly and a biconcave trochlear talar component surface inferiorly (Fig 1). The surface geometry remains fully congruent, even during inversion and eversion motions to reduce contact stresses below the medical load limit for UHMWPE of 5 MPa. 8 Inversion and eversion congruity is essential to prevent edge-loading wear and deformation, which has been reported with flat-on-flat knee replacement designs. 19 Deepening the trochlear sulcus angle tends to center the meniscal bearing and prevent bearing subluxation under normal load-bearing conditions. 7 The improved stability of the deep-sulcus geometry over the shallow-sulcus geometry has been reported in the short term. 7 Our study reflects longer-term use of both designs with more detailed analysis. MATERIALS AND METHODSTwo consecutive series of patients with cementless, porouscoated, congruent-contact, mobile-bea...

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