- 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.