The TNK prosthesis was developed by Dr. Takakura in Japan in 1975. It is currently the only total ankle prosthesis with alumina ceramic components. The third generation of this device has shown promising results in reports by the designer, but these have not been results have not been duplicated by others.
In 1988, Takakura et al reported a comparative study of cemented metal and uncemented ceramic TNK ankle prostheses.1 Both types were two-component prostheses with high-density polyethylene fixed to the tibial component. Before 1980, the authors implanted 30 cemented stainless steel prostheses (first generation); after 1980 they used 9 cemented and 30 uncemented ceramic prostheses (second generation). The mean follow-up time for cemented and uncemented total ankle replacements (TARs) was 8.1 and 4.1 years, respectively.
Patients who underwent TAR with an uncemented prosthesis were 67% more satisfied than those who underwent the procedure with a cemented prosthesis (27%). Five metal TARs and one ceramic TAR had to be revised (five arthrodeses and one revision arthroplasty).1
The initial encouraging results were not maintained in another study by the same working group, published in 2004.2 Significant loosening and subsidence of the prosthesis were observed in most patients with the first-generation TAR (stainless steel prosthesis). The second-generation TAR (ceramic prosthesis) was implanted in 60 ankles between 1980 and 1991 (in 12 ankles, cement fixation was used). However, loosening and significant subsidence occurred in most patients within 5 years after the surgery.
In 1991, the ceramic prosthesis (second generation) was modified by adding bead-formed alumina coated with hydroxyapatite (third generation). Between 1991 and 2001, this prosthesis type was used in 70 ankles.2,3 The mean follow up in this patient group was 5 years. In three patients, the replaced ankle had to be fused (one case with deep infection, two cases with severe subsidence of talar component). Overall results were excellent or good in the most patients (52 ankles). The patient satisfaction rate was higher in patients with osteoarthritis (OA) compared with patients with rheumatoid OA.2,3
The TNK prosthesis has been used for treatment of rheumatoid OA with poor clinical and radiographic outcomes, as shown in two studies.4,5 Nishikawa et al reviewed 26 patients (six patients received bilateral TAR) with rheumatoid OA who were treated with a TNK prosthesis between 1984 and 2000. At a mean follow up of 72 months 27 ankles in 21 patients were reviewed. Three ankles had to undergo revision surgery. Nine patients reported their outcome as excellent or good, but patients complained about residual pain in 13 ankles. A high rate of radiolucency was observed in this patient cohort: migration of the tibial component in 13 ankles and collapse of the talus in nine.4
Nagashima et al reported results of 21 TARs performed in 19 patients between 1998 and 2002 using the TNK prosthesis.5 Hybrid-type fixation (talus component cemented, tibial component not cemented) was used in 15 of 21 cases, while both components were cemented in the remaining cases. Early postoperative complications included two patients with delayed wound healing and one patient with deep infection. In 11 of 21 ankles, significant radiolucency lines were observed. Most patients experienced pain relief and functional improvement; however, postoperative improvement of ROM directly correlated with preoperative ROM.5
Shinomiya et al performed 20 TARs using TNK prosthesis in 18 selected patients with rheumatoid OA between 1988 and 1996.6 All patients were reviewed at a mean follow up of 8 years, with a range of 5 to 12 years. All patients experienced substantial pain relief and showed functional improvement superior to those who underwent ankle arthrodesis in the same period. No conversions to ankle fusion or revision arthroplasties were necessary in this cohort. However, a radiolucent line was observed in all replaced ankles at the final follow up. The authors stated that TAR may be useful in young patients with rheumatoid OA, considering their better postoperative quality of life.6
Shi et al developed a special hydroxyapatite augmentation for bone atrophy in TAR for rheumatoid patients receiving a TNK prosthesis.7 This specially designed hydroxyapatite coating was used in 16 ankles (14 patients) and results were reviewed at a mean follow up of 23 months. More than half of all ankles showed a radiolucency zone between hydroxyapatite and the tibial component on radiographs at the final follow up. However, no significant changes of coating position were registered; also, no significant subsidence was noted. The authors suggested that this new technique using hydroxyapatite may increase the primary implant fixation to the bone, especially in patients with rheumatoid OA and showing significant bone atrophy.7
Recently, Tsukamoto et al reported a case using a custom-made alumina ceramic total talar component for treatment of collapse of the talar body in one patient who received a TNK prosthesis.8 The revision surgery was performed in a 56-year-old female patient 4 years after the initial TAR. The authors achieved substantial pain relief and functional improvement especially regarding walking ability. This case report demonstrated a feasible revision treatment in patients with failed TAR.8
In summary, since its introduction in 1975, the TNK prosthesis has undergone many modifications to address the material of the components (stainless steel, polyethylene, alumina ceramic), coating (without/with hydroxyapatite), and fixation (cement/cementless fixation). Currently, this is the only TAR design with alumina ceramic components. While the studies by the designer reported favorable results using the third-generation TNK prosthesis,2,3 independent studies addressing TAR results in patients with rheumatoid OA show less-promising results.4,5
- Takakura,Y., Tanaka,Y., Sugimoto,K., Tamai,S., and Masuhara,K.: Ankle arthroplasty. A comparative study of cemented metal and uncemented ceramic prostheses. Clin Orthop Relat Res, 252:209-216, 1990.
- Takakura,Y., Tanaka,Y., Kumai,T., Sugimoto,K., and Ohgushi,H.: Ankle arthroplasty using three generations of metal and ceramic prostheses. Clin Orthop Relat Res, 424:130-136, 2004.
- Tanaka,Y. and Takakura,Y.: [The TNK ankle: short
- and mid-term results]. Orthopade, 35:546-551, 2006.
- Nishikawa,M., Tomita,T., Fujii,M., Watanabe,T., Hashimoto,J., Sugamoto,K., Ochi,T., and Yoshikawa,H.: Total ankle replacement in rheumatoid arthritis. Int Orthop, 28:123-126, 2004.
- Nagashima,M., Takahashi,H., Kakumoto,S., Miyamoto,Y., and Yoshino,S.: Total ankle arthroplasty for deformity of the foot in patients with rheumatoid arthritis using the TNK ankle system: clinical results of 21 cases. Mod Rheumatol, 14:48-53, 2004.
- Shinomiya,F., Okada,M., Hamada,Y., Fujimura,T., and Hamada,D.: Indications of total ankle arthroplasty for rheumatoid arthritis: evaluation at 5 years or more after the operation. Mod Rheumatol, 13:153-159, 2003.
- Shi,K., Hayashida,K., Hashimoto,J., Sugamoto,K., Kawai,H., and Yoshikawa,H.: Hydroxyapatite augmentation for bone atrophy in total ankle replacement in rheumatoid arthritis. J Foot Ankle Surg, 45:316-321, 2006.
- Tsukamoto,S., Tanaka,Y., Maegawa,N., Shinohara,Y., Taniguchi,A., Kumai,T., and Takakura,Y.: Total talar replacement following collapse of the talar body as a complication of total ankle arthroplasty: a case report. J Bone Joint Surg Am, 92:2115-2120, 9-1-2010.