Introduction and aims

Recently many implants for ankle arthroplasty have been developed around the world, and especially some mobile bearing, three-component implants have good results. Nevertheless, at our institution fixed two-component, semi-constrained alumina ceramic total ankle arthroplasty (TAA) with TNK Ankle had been performed since 1991 and led to improved outcomes. We report clinical results and in vivo kinematic analyses for TNK Ankle.

We have performed two-component total ankle arthroplasty (TNK ankle) since 1991 and reported good clinical results. However, in vivo kinematics of this implant are not well understood. The purpose of this study was to measure three-dimensional kinematics of total ankle arthroplasty during non-weightbearing and weightbearing activities.

Forty-seven patients with a mean age of 71 years were enrolled. Preoperative diagnosis was osteoarthritis in 36 patients and rheumatoid arthritis in 11 patients, and the mean followup was 50 months. Radiographs were taken during nonweightbearing maximal dorsiflexion and plantarflexion, and weightbearing maximal dorsiflexion and plantarflexion. Three-dimensional kinematics were determined using 3D-2D model registration techniques. Anatomic coordinate systems were embedded in the tibial and talar implant models, and they were projected onto the radiographic image. Three-dimensional positions and orientations of the implants were determined by matching the silhouette of the models with the silhouette of the image.

From non-weightbearing dorsiflexion to plantarflexion, the talar implant showed 18.1, 0.3, and 1.2 degrees of plantarflexion, inversion, and internal rotation respectively. It also translated 0.8mm posteriorly. There was not significant difference between non-weightbearing and weightbearing kinematics except for the plantarflexion angle (p = 0.007). Posterior hinging, in which tibiotalar contact was seen at only the posterior edge of the talar implant, was observed in 16 patients at either non-weightbearing or weightbearing plantarflexion. There was significantly larger plantarflexion in patients with posterior hinging than patients without hinging (p < 0.001). Nine patients showed anterior hinging at maximum dorsiflexion, and 11 patients showed talar lift-off at maximum plantarflexion.

More than half of the patients showed anterior or posterior edge contact, which might cause excessive contact stress and lead to implant failure in the longer term. This phenomenon is due to the difference in rotation axis between the natural ankle and the implant ankle arthroplasty.

The results of total ankle arthroplasty using metal (first generation) and ceramic (second) prostheses were not good for loosening sinking. Then, we have replaced on 159 ankles in 146 cases using beads-formed alumina ceramic prostheses (third) from 1991 to 2006. The follow-up periods were ranged from 2 to 17 years (average 6.5 years). Revision was performed for 13 cases (arthrodesis, 3; re-replacement by artificial talus. 10). Overall satisfactory result of new prostheses for OA was 88%, RA was 74%. Results of OA were better than RA. Furthermore, we have re-replaced using ceramic talar whole body for 10 revision cases. These results until present have been good. It is convinced that total arthroplasty with talar whole body can be indicated for cases with severe deformity and revision.

The material properties of gamma irradiated Ultra High Molecular Weight (UHMW) polyethylene are known to degrade during exposure to air. Though gamma inert-sterilization has been developed to decrease free radicals, the rate of degeneration of UHMW polyethylene in vivo has not well known. This study aimed to compare the properties of gamma inert-irradiated highly-cross-linked UHMW polyethylene samples after exposure to air and the properties of gamma inert-irradiated highly-crosslinked UHMW polyethylene samples after exposure to liquid.

UHMW polyethylene samples were machined from heat-compressed sheet made of medical grade GUR 1050 (Ticona, Kelsterbach, Germany). Samples were rectangular, where the dimensions were 50mm in length, 5 mm in width and 2 mm in thickness. Samples were divided into four groups of 0, 60, 100 and 200 kGy irradiation in N2 gas. These samples were then exposed to air or Ringer’s solution for half a year. Dynamic vis-coelastic measurements and, Fourier Transform Infrared Spectrometry (FTIR) and Electron Spin Resonance (ESR) analyses were performed on samples immediately after inert-irradiation, after half-year-exposure to 25°C air (Air-exposure) and after half-year-exposure to 37°C Ringer’s solution (Liquid-exposure). Dynamic viscoelastic measurements were conducted over a temperature range of −150 to 350°C using a Dynamic Mechanical Spectrometer (Seiko Instruments, Osaka, Japan). FTIR analysis was conducted using a Perkin-Elmer Spectra BX (Norwalk, CT) with 100-μm thick slices. ESR analysis was also conducted using a JES-TE200 (Nippon-Denshi, Akishima, Japan).

Although the dynamic viscoelastic performance of 0 kGy irradiated storage sample was not different from that of original sample, the loss tangent value (tanδ, E”/E’) of 60, 100 and 200 kGy irradiated storage samples was different from that of original samples (Fig. 1). The difference of Liquid-exposure was larger than that of Air-exposure. Although a FTIR peak at 1718 cm-1 wave numbers was not observed in 0 kGy irradiated storage sample, obvious peak was observed in 100 and 200 kGy irradiated storage samples (Fig. 2). The peak of Liquid-exposure was larger than that of Air-exposure. The ESR analysis showed free radicals in storage samples.

The dynamic viscoelastic performance of 60, 100, 200 kGy irradiated storage sample was different from that of original sample, whereas the performance of 0 kGy irradiated storage sample was not different from that of original sample. The difference of Liquid-exposure was larger than that of Air-exposure. The storage modulus value of 60, 100, 200 kGy irradiated Liquid-exposure decreased and the reason for this was thought to be chain scission by oxidation for half-year exposure to Ringer’s solution. Obvious FTIR peak at 1718 cm-1 wave numbers was observed in 100 and 200 kGy irradiated storage samples. The peak of Liquid-exposure was larger than that of Air-exposure. This indicated that the oxidation of Liquid-exposure quickly progressed during half-year storage and the reason for this was thought to be chain scission by high liquid temperature. The results of the present study suggested that the properties of gamma irradiated UHMW polyethylene quickly degraded in vivo.

To investigate the limitation of proximal spherical metatarsal osteotomies for feet with severe hallux valgus, a follow-up study was performed on the patients whose preoperative hallux valgus angles were 40 degrees or more.

Forty-eight feet in 37 patients (11 male, 37 female, 60 years range 20 to 84 years) were investigated. Mean follow-up was 4 years and 1 month ranging from two to eight years. The spherical osteotomy, performed using a curved chisel, was devised for correcting not only varus deviation of the first metatarsal but also pronation and dorsiflexion. A distal soft tissue procedure was done at the same time. Twenty feet received combined operations for their combined deformities.

Eighty-one percent of the patients were satisfied with the results. However, six of twelve patients whose preoperative hallux valgus angles were 50 degrees or more were unsatisfactory. Mild metatarsalgia remained in eight feet at the follow-up, but no new metatarsalgia developed in any patients. The mean value of the hallux valgus angle improved from 46.6 degrees to 11.1 degrees. The patients whose preoperative hallux valgus angle were 50 degrees or more showed 16.4 degrees of average hallux valgus angle at follow-up. Their results varied widely and most of them had inadequate correction. The mean correction toward plantar flexion was 0.7 degrees. Average shortening of the first metatarsal was 3.4mm. The shortening of the first metatarsal had not caused worsening of metatarsalgia if adequate correction of hallux valgus was achieved and malunion toward dorsi-flexion was prevented.

The proximal spherical osteotomy could consistently achieve satisfactory results for the patients whose hallux valgus angles are under 50 degrees. However, the results were worse in feet with more severe deformities. Other procedures for hallux valgus or proper combined operations were necessary for such patients.