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Optimal Position of Ankle Arthrodesis

- Recommended Position of Ankle Fusion:
    - it is essential to position forefoot perpendicular to long axis of tibia;
    - if minimal resection of the joint surfaces is carried out (to minimize shortening), then it will often be necessary to lengthen the heel cord in order to obtain the optimal position;
    - hindfoot valgus: 5 deg is optimal:
            - varus of hindfoot causes forefoot to be rotated into supination, which locks transverse tarsal joints & creates a semirigid forefoot;
                    - varus is poorly tolerated because it transforms foot into rigid lever;
            - if subtalar joint is in varus, wtbearing line of lower extremity passes lateral to calcaneus, placing stress on subtalar joint, & causing pain under cuboid & fifth metatarsal;
            - when subtalar joint is inverted or in varus position, transverse tarsal joint is locked, making rigid foot that needs to be vaulted over;
            - for this reason, 5 degrees of valgus is optimal position of hindfoot in any of these fusions;
    - external rotation of foot: 10 deg is optimal;
            - foot is fused in slight external rotation, (compared to opposite foot);
            - if foot is placed in too much external rotation, strain is placed not only along medial border of foot, but also valgus stress on hallux;
                    - patient will roll off medial border of foot, leading to hallux valgus;
    - posterior translation of talus under tibia;
            - at least 5 mm of posterior translation of the talus is required, in order to decrease the lever arm of the foot during gait;
    - neutral flexion is optimal;
            - it is better to error on the side of slight equinus rather than placing the foot in a calcaneus position;
                    - slight equinus can be treated w/ a heel lift;
                    - heel lift may compensate for moderate plantar flexion (5-10 deg), but significant problems arise with excessive plantar flexion;
            - some authors feel that up to 3 deg of dorsiflexion is optimal (Monroe MT, et al (1999));
            - in some cases, a tight heel cord will make it difficult to obtain a neutral position, and in these situations, an achilles tendon lengthening is necessary;
            - equinus position, however, should not be done to accommodate for heel height in the female patient;
                    - doing so will cause excessive loading of transtarsal and midtarsal joints;
                    - genu recurvatum, or backknee, will result from a plantar-flexed foot;
                    - in effort to avoid vaulting over the plantar-flexed foot, patient's leg turns out, & secondary medial collateral laxity can occur;

- Special Situations:
    - fixed forefoot equinus:
          - ankle may need to be placed in relative dorsiflexion to accommodate for forefoot position, however, do not overcompensate for this deformity;
          - note that in these patients, correction of a varus hindfoot, a rigid pronating deformity of the forefoot may be created, which may cause a painful over load of the first ray;
    - weak quadriceps:
          - fusion in slight plantarflexion is necessary w/ quad weakness;
    - knee flexion contracture:
          - w/ a fixed knee flexion contracture, the ankle should be dorsiflexion to a corresponding degree (hence, 10 deg knee flexion contracture would require that the ankle be flexed 5-10 deg);
    - tibial-talar-calcaneal arthrodesis

The optimum position of arthrodesis of the ankle. A gait study of the knee and ankle.

Pantalar and tibiotalocalcaneal arthrodesis for post-traumatic osteoarthrosis of the ankle and hindfoot.

Tibiotalocalcaneal arthrodesis for arthritis and deformity of the hind part of the foot.

Tibiotalocalcaneal arthrodesis: anatomic and technical considerations.

Clinical Outcome of Arthrodesis of the Ankle Using Rigid Internal Fixation with Cancellous Screws.

Ankle fusion attributable to posttraumatic arthrosis: a long-term followup of 48 patients.