FOOT MOTION AFTER ANKLE ARTHRODESIS: KINEMATIC FINDINGS OF ADJACENT JOINTS USING A MULTI-SEGMENT FOOT MODEL

Abstract

Introduction: Arthrodesis is considered the primary treatment in case of non-response to conservative therapy of ankle arthritis[1]. Reports on long-term gait results after arthrodesis have been made indicating a decrease in motion concerning the hindfoot and an increase in the forefoot [2]. The aim of this study is to evaluate the gait of patients who had undergone ankle arthrodesis using a new foot model.

Material/methods: 17 subjects (10 males, 7 females) who had undergone unilateral arthrodesis returned for clinical examination and gait analysis. The median age at time of operation was 56 years, the follow-up time was 49 months (median). Operative procedures were performed as internal (n=15) and external fixations (n=2). Patients were instrumented with a set of 17 reflective markers. For data acquisition we used a Vicon system with 9 cameras. The person was asked to walk a 7m walk way. For the evaluation of foot kinematics a multi-segment foot model was used [3]. Kinematic data were also collected from the healthy side. Differences between means for the ankle arthrodesis and healthy side were tested using paired T-tests (p< 0.01).

Results: The ankle angle is the generally accepted parameter to describe motion between the shank and the foot regarded as a rigid segment (a). In our model it was defined exclusively by the angular position of the hindfoot relative to the tibia (b). The loss of motion in the ankle joint is shown by the significant decrease of ROM in the arthodesis side. Also significant is the decrease in hind- and forefoot ROM in frontal plane movement (d, e). Furthermore the results show a decrease of ROM of the medial arch (c).

1. Sag. Ankle Angle ROM (standard): 14,31 4,72 *(OP); 28,39 4,96(healthy)

2. Sag. Ankle Angle ROM (footmodel): 9,36 2,62 *(OP); 18,68 4,33

3. Sag. Med Arch ROM: 12,85 4,85 * (OP); 20,11 4,71

4. Front. Subtalar Inversion ROM: 4,59 1,44 *(OP); 7,56 1,96

5. Front. Forefoot Ankle Supination ROM: 10,23 3,71 *(OP); 13,91 3,82

(Mean standard deviation; * statistical significance from healthy side p< 0.01)

Discussion/conclusion: The operative fusion of the ankle joint limits the sagittal plane motion of the tibial to hindfoot segment due to the lack of tibiotalar motion. Since the talus can not be marked for 3D-measurements, other hind-, mid- and forefoot markers were used to determine ankle motion. The remaining motion which is found in these clinical cases must be addressed to subtalar movement. In contrast to the common clinical opinion of a higher mobility of the fore- and midfoot joints, we find a significant reduced ROM of the corresponding parameters (a, b, c, d, e) with our model.