Evaluation of midfoot function after subtalar arthrodesis

Abstract

Objective To evaluate the influence of simple subtalar arthrodesis to the motion and degeneration of midfoot.Methods Data of 37 patients (27 males,10 females) with an average age of 42.6 years who had undergone subtalar joint fusion from January 1996 to August 2011 were retrospectively analyzed.The MOS item short form health survey (SF-36),American Orthopaedic Foot and Ankle Society (AOFAS) midfoot score were used.Midfoot sagittal and coronal motion were measured on ankle radiographs of maximum plantar flexion and dorsiflexion.On sagittal plane,the Meary angle was measured and the bilateral tarsometatarsal joints mobility was compared.On coronal plane,tibio-plantar angles (TPA) on 30 degrees varus slope and 30 degrees valgus slope were respectively measured on the anterio-posterior ankle X-ray films to observe the changes of midfoot activities.Besides,single photon emission computed tomography/computed tomography (SPECT/CT) of bilateral foot and ankle was taken to estimate the degeneration of midfoot joint.Results All the 37 patients were followed-up,with mean follow-up period of 9.2 years.The average SF-36 scores was increased from 34.26± 11.02 points preoperatively to 77.59± 12.57 points postoperatively.The average AOFAS midfoot scores were 86.14± 16.79 points preoperatively and 86.43± 16.70 points postoperatively without any statistical significant difference.On sagittal plane,medial tarsometatarsal joints mobility was limited by 20％.According to coronal plane of varus slope,the average TPA of healthy side and operated side were 61.32° and 64.91°,respectively,so the varus mobility of operated side was limited by 12.5％.While standing on the valgus slope,the average TPA of both sides were 76.54° and 82.28°,which indicated that valgus mobility of operated side was reduced by 42.6％.35.1％ patients of talonavicular joint,56.8％ patients of calcaneocuboid joint,and 27.0％ patients of metatarsal cuboid joint were found mild joint degeneration on SPECT/CT images without any clinical symptoms.Conclusion Subtalar arthrodesis can affect midfoot with less limit of sagittal mobility and more limit of coronal movement.And the lateral joints degeneration is more likely to happen for their compensatory activity. Key words: Subtalar Joint; Arthrodesis; Tarsal joints; Osteoarthritis