Introduction: Realigning the foot and good ligament balancing have been recognized to be the mainstay for successful reconstruction of complex hindfoot disorders and deformities. This is particularly true for posttraumatic conditions, where deformities and scarring might be the underlying cause of foot dysfunction. For surgical reconstruction, i.e. osteotomies, arthrodeses and total ankle replacement, references are needed for restoration of the anatomy and the function. Most surprisingly to date no data is available regarding dimensions on standard X-rays of the hindfoot. The purpose of this prospective study therefore was 1) to define relevant and reproducible measures on lateral hindfoot X-rays and 2) to assess their reliability.

Methods: 100 lateral view X-rays were taken. Dimensions assessed were the talar area covered by the tibia, the angle of the distal tibial joint plane to the tibial axis (tilt), the width of the tibia on the joint level, the height of the talus, the joint radius of the ankle joint and the offset of the centre of rotation from the tibial axis.

Results: The tibial coverage of the talus was 88.1 degrees (SD = 0.36), the angle of the distal tibial joint plane to the tibial axis (tilt) was 83 degrees (SD 3.6), the width of the distal tibia 33.6 mm (SD = 2.4), the radius of the ankle joint 18.6 mm (SD = 4.0) with an anterior offset of the centre of rotation of 1.7 mm and the height of the talus was 28.2 mm (SD = 2.1).

Conclusions: In case of symptomatic deformity any reconstruction, i.e. correcting osteotomies, ligament reconstruction, arthrodeses or arthroplasty, should aim to correct the foot in a physiological way; respecting the original dimensions of the hindfoot to achieve maximal benefit. Anterior-posterior translation of the talus may be a source of pain, restriction of motion and a cause of degenerative joint disease because of eccentric joint loading. This is also true for the height of the talus, which may have a significant impact on the hindfoot physiology. To achieve good biomechanical function, the positioning of the talus in relation to the tibia needs to be planned carefully prior to surgery. Poor coverage of the talus by the tibia and too much tilt of the distal tibia lead to higher joint forces and may be the cause of instability. Surgical procedures may fail if this is not recognized preoperatively. Several easily accessible measures on X-rays were found to be reliable to describe the hind-foot, as only small variation was found on the evaluated X-rays. If reconstruction of the hindfoot is required, care should be taken to identify the physiological joint geometry.