The value of Weight-Bearing CT scan in the evaluation of subtalar distraction bone block arthrodesis: Case report

- Subtalar distraction arthrodesis is performed in certain situations where there is loss of subtalar height, reduced talar declination and evidence of anterior tibiotalar impingement.
- Standard evaluation includes the assessment of the lateral talocalcaneal angle, calcaneal pitch, talocalcaneal height and talar declination angle on a weight bearing lateral radiograph.
- pedCAT (Curvebeam, Warrington, USA) is a novel technology that allows 3D CT imaging with full weight bearing. Its use in the pre and post-operative evaluation of subtalar distraction arthrodesis has not been described.
- It allows accurate:
- Measurement of functional clinical valgus.
- Measurement of relevant angles and distances, to evaluate deformity and aid pre-operative planning.
- Visualisation of posterior osteophytes to aid surgical planning of entry to posterior subtalar joint.
- Visualisation of Anterior impingement, osteophytes and evidence of tibiotalar osteoarthritis.
- Visualisation of subfibular impingement, to help plan required lateral resection.
- Post operative outpatient radiographic and functional assessment with minimal radiation exposure.

Subtalar distraction arthrodesis is performed in certain situations where there is loss of subtalar height, reduced talar declination and evidence of anterior tibiotalar impingement. Standard evaluation includes the assessment of the lateral talocalcaneal angle, calcaneal pitch, talocalcaneal height and talar declination angle on a weight bearing lateral radiograph. We present a case of erosive valgus subtalar osteoarthritis with subtalar collapse managed with a subtalar distraction arthrodesis. A weight bearing CT (WB-CT) scan was used in the assessment. The value of WB-CT for this indication is discussed, along with a discussion on surgical technique, complications and future directions.