The Effect of Three Foot Types on the Achilles Tendon Lever Arm

Category: Hindfoot Introduction/Purpose: During locomotion, propulsion of the body is created by the force of the triceps surae complex as it is transmitted to the metatarsal heads. The amount and pattern of the resulting propulsion force highly depends on the moment arm of the Achilles tendon. To our knowledge, no data exists on how and to which extent position and morphology of the foot affects the moment arm of the Achilles tendon. The aim of this study was 1) to develop a method to determine the Achilles tendon moment arm, and 2) to calculate the Achilles tendon moment arm with the foot in different degrees of dorsi- and plantarflexion for 3 foot types (normal arched foot, pes planus, and pes cavus). Methods: 99 study participants with a healthy ankle joint (males, 40; females, 59; mean age 49 [range, 14 – 78] years) were included. Participants’ foot type was classified as a normal arched foot (n = 33), as pes planus (n = 33), or as pes cavus (n = 33) based on the calcaneal inclination angle (CI) (Figure 1). Besides the foot type, the foot length (FL), the calcaneal insertion of the Achilles tendon (ATI), the angle (a) between the line (L) connecting ATI with the center of rotation of the ankle (COR) and the horizontal line (L’) were measured on the lateral radiographs. The interrater reliabilities of measuring a on radiographs and on MRIs were compared. The lever arm of the Achilles tendon (L’calculated) was calculated as following (foot and tibia were regarded as two rigid segments; the influences of other muscles were neglected): L’calculated = cos(a - plantarflexion)*L Results: The interrater reliability of a was higher on radiographs (ICC = 0.84, [0.73 – 0.91]) than on MRIs (ICC = 0.61, [0.27 – 0.81]). The ICC comparing a measured on MRIs and radiographs was 0.63 [0.50-0.74]. There was no difference in FL between the three foot types (p = 0.199). However, the average a was significantly different (normal arched foot 31°, pes planus 24°, pes cavus 36°, p = 0.021), resulting in a statistically significant shorter Achilles tendon lever arm for pes cavus than for pes planus (p < 0.0001) and normal arched feet (p = 0.006) in neutral position. The maximum lever arm for the three different foot types was reached at different degrees of plantarflexion (Figure 2). Conclusion: The assessment of the Achilles tendon lever arm using radiographs is reliable. The foot configuration determines the lever arm of the Achilles tendon for a given flexion position of the foot. It also determines the plantarflexion position where the Achilles tendon reaches the maximum of its lever arm. This has to be taken into consideration when planning surgeries that change a or L, as they may also result in changes of plantarflexion power

Subtalar Joint Alignment in Ankle Osteoarthritis

Category: Ankle Arthritis, Hindfoot Introduction/Purpose: The influence of the subtalar joint on the evolution of ankle joint osteoarthritis is still a matter of debate. Although subtalar joint compensation of deformities above the ankle joint was proposed until mid-stage of ankle osteoarthritis, the evidence of this assumption is weak. In this study, we investigated the subtalar joint alignment in different stages of ankle joint osteoarthritis using weightbearing CT scans. The influence of the tibio-talar tilt and presence of subtalar joint osteoarthritis was additionally assessed. We hypothesized, that the subtalar joint compensates for deformities above the ankle joint in early- to mid-stage of ankle osteoarthritis. We also hypothesized, that subtalar joint compensation increases with a pronounced tibio-talar tilt and decreases with the presence of subtalar joint osteoarthritis. Methods: We included patients with ankle joint osteoarthritis treated in our institution from January 2013 to April 2016. A control group of 28 patients was additionally assessed. Varus and valgus ankles were subdivided according to the modified Takakura classification, the tilt of the talus in the ankle mortise and stage of subtalar joint osteoarthritis. The type of ankle osteoarthritis was diagnosed on a plain weightbearing anterior to posterior radiograph of the ankle. The medial distal tibial angle (TAS) and the angle between the tibial shaft and the surface of the talar dome (TTS) were measured. The subtalar joint alignment was assessed using weightbearing CT scans. Two angles were assessed: The subtalar inclination angle (SIA) was measured to investigate the subtalar compensation. For assessment of the morphology of the talus, the inftal-subtal angle (ISA) was determined. Results: This analysis showed significant differences of the subtalar inclination between varus feet and the controls (SIA, P=.001). Regarding the talar morphology, significant differences were found between varus/ valgus feet and the controls (ISA, P=.001 and .036, respectively). No significant differences of the subtalar joint inclination and talar morphology could be identified comparing different stages of ankle joint osteoarthritis inside the varus or valgus group. No relationship between the tilt of the talus in the ankle joint mortise and the subtalar joint inclination or talar morphology was identified. Neither presence nor absence of subtalar joint osteoarthritis influenced the subtalar joint inclination and talar morphology. Conclusion: Varus ankles compensate in the subtalar joint for deformities above the ankle joint. Compensation had no influence on the stage of ankle osteoarthritis, extent of the tibio-talar tilt and stage of subtalar joint osteoarthritis. Consequently, the progression of ankle joint osteoarthritis is more depended on the supramalleolar alignment and integrity of the periarticular structures (i.e. ligaments and tendons) than on the osseous alignment of the subtalar joint

Supramalleolar Osteotomy for Tibial Component Malposition in Total Ankle Replacement

Category: Ankle Introduction/Purpose: A key for success in total ankle replacement is a balanced ankle joint. If the tibial component is misaligned, the ligamentous structures, the malleoli and the tendons may be overused, which, may lead to pain and impairment during gait. A misaligned tibial component can be revised using a corrective bone resection and re-insertion of a new component or using a corrective osteotomy of the distal tibia above the stable implant. The aim of this study was to review a series of patients, in whom a corrective supramalleolar osteotomy was performed to realign a misaligned tibial component in total ankle replacement. Methods: Twenty-two patients (nine male; 13 female; mean age, 62.6 years; range, 44.7 – 80.0) were treated with a supramalleolar osteotomy to correct a painful dysbalanced ankle, following a varus implanted tibial component. Following radiological and clinical outcomes were recorded preoperatively and at the follow-up examination within the first 24 months: the tibial anterior surface angle (TAS), the tibial lateral surface angle (TLS), patient’s pain measured with the Visual Analogue Scale (VAS), the American Orthopedic Foot and Ankle Society (AOFAS) hindfoot score, range of motion (ROM) of the ankle and patient’s satisfaction. Furthermore, postoperative complications were reviewed. Results: The TAS changed on average from 85.2 ± 2.5 degrees preoperatively to 91.4 ± 2.9 degrees postoperatively (p < 0.0001), the AOFAS score increased from 46 ± 14 to 66 ± 16 points (p < .0001) and the VAS pain score decreased from 5.8 ± 1.9 to 3.3 ± 2.4 (p < .001). No statistical difference was found in the TLS and the range of motion. The osteotomy healed in 19 patients (86%), re-osteosynthesis was successful in the remaining three patients. In one of these three patients, a chronic infection of the ankle joint led to a below-knee amputation. Fifteen patients (68%) were (very) satisfied, four (18%) moderately satisfied and three (14 %) patients were not satisfied with the obtained postoperative result. Conclusion: The supramalleolar osteotomy was found to be an efficient alternative to correct the misaligned tibial component in total ankle replacement. Pain could be successfully addressed in the majority of the patients. The treatment of a malpositioned, well anchored tibial component with a supramalleolar osteotomy, instead of exchanging the tibial component, allows preservation of the bone stock. However, non-union should be mentioned as a possible complication of this surgery. Nonetheless, this method might be a feasible treatment option, especially for younger patients