ObjectiveTo investigate the short-term effectiveness of INBONETM Ⅱ total ankle prosthesis arthroplasty in the treatment of moderate to severe varus-type ankle arthritis. MethodsThe clinical and radiographic data of patients with moderate to severe varus-type ankle arthritis, who were admitted between May 2017 and November 2021 and treated with total ankle arthroplasty (TAA) using INBONETM Ⅱ prosthesis, was retrospectively analyzed. A total of 58 patients (58 ankles) met the selection criteria and were included in the study. Among them, there were 24 males and 34 females, with an average age of 62.6 years (range, 41-85 years). According to the preoperative tibiotalar angle (TTA), the patients were divided into a moderate varus group (group A, TTA 5°-15°, n=34) and a severe varus group (group B, TTA>15°, n=24). There was no significant difference in gender, side, etiology, preoperative American Orthopaedic Foot and Ankle Society (AOFAS) score, ankle dorsiflexion, plantarflexion, and total range of motion, and tibial lateral surface angle (TLS) between the two groups (P>0.05). Yet the patients in group A were younger than group B, the degrees of oesteoarthritis (Takakura stage) and ankle pain [visual analogue scale (VAS) score] were milder, and the TTA, talar tilt angle (TT), hindfoot alignment angle (HAA) were smaller while the tibial articular surface angle (TAS) was larger, showing significant differences (P<0.05). The pre- and post-operative VAS score, AOFAS score, the occurrence of early and late complications, the radiographic parameters of the ankle (TTA, TAS, TT, HAA, TLS), ankle dorsiflexion, plantarflexion, and total range of motion were recorded and compared. ResultsAll patients were followed up 19-72 months, with an average of 38.9 months. Compared with the preoperative data, the VAS score of all patients significantly decreased (P<0.05); the AOFAS score, ankle dorsiflexion range of motion, and total range of motion significantly increased (P<0.05); and the TTA, TAS, TT, HAA, and TLS significantly improved at last follow-up (P<0.05); but there was no significant difference in plantarflexion range of motion (P>0.05). Early complications occurred in 13 patients, and only 1 patient underwent revision surgery due to a larger size of the talar component. At last follow-up, there was no significant difference in the difference of clinical parameters before and after operation between the two groups (P>0.05); there was a significant difference in the difference of other radiographic parameters (P<0.05) except TLS. No significant difference in the incidence of complications between the two groups was found (P>0.05). ConclusionTAA using the INBONETM Ⅱtotal ankle prosthesis is an effective treatment for moderate or severe varus-type ankle arthritis, and good clinical and radiographic results can be obtained. Correcting bony deformities and balancing soft tissue are the keys to successful surgery.
ObjectiveTo discuss the influence of artificial ankle elastic improved inserts (hereinafter referred to as “improved inserts”) in reducing prosthesis micromotion and improving joint surface contact mechanics by finite element analysis. Methods Based on the original insert of INBONE Ⅱ implant system (model A), four kinds of improved inserts were constructed by adding arc or platform type flexible layer with thickness of 1.3 or 2.6 mm, respectively. They were Flying goose type_1.3 elastic improved insert (model B), Flying goose type_2.6 elastic improved insert (model C), Platform type_1.3 elastic improved insert (model D), Platform type_2.6 elastic improved insert (model E). Then, the CT data of right ankle at neutral position of a healthy adult male volunteer was collected, and finite element models of total ankle replacement (TAR) was constructed based on model A-E prostheses by software of Mimics 19.0, Geomagic wrap 2017, Creo 6.0, Hypermesh 14.0, and Abaqus 6.14. Finally, the differences of bone-metal prosthesis interface micromotion and articular surface contact behavior between different models were investigated under ISO gait load. Results The tibia/talus-metal prosthesis interfaces micromotion of the five TAR models gradually increased during the support phase, then gradually fell back after entering the swing phase. The improved models (models B-E) showed lower bone-metal prosthesis interface micromotion when compared with the original model (model A), but there was no significant difference among models A-E (P>0.05). The maximum micromotion of tibia appeared at the dome of the tibial bone groove, and the micromotion area was the largest in model A and the smallest in model E. The maximum micromotion of talus appeared at the posterior surface of the central bone groove, and there was no difference in the micromotion area among models A-E. The contact area of the articular surface of the insert/talus prosthesis in each group increased in the support phase and decreased in the swing phase during the gait cycle. Compared with model A, the articular surface contact area of models B-E increased, but there was no significant difference among models A-E (P>0.05). The change trend of the maximum stress on the articular surface of the inserts/talus prosthesis was similar to that of the contact area. Only the maximum contact stress of the insert joint surface of models D and E was lower than that of model A, while the maximum contact stress of the talar prosthesis joint surface of models B-E was lower than that of model A, but there was no significant difference among models A-E (P>0.05). The high stress area of the lateral articular surface of the improved inserts significantly reduced, and the articular surface stress distribution of the talus prosthesis was more uniform. Conclusion Adding a flexible layer in the insert can improve the elasticity of the overall component, which is beneficial to absorb the impact force of the artificial ankle joint, thereby reducing interface micromotion and improving contact behavior. The mechanical properties of the inserts designed with the platform type and thicker flexible layer are better.