Biomechanical and neuromuscular adaptations before and after realignment surgery for ankle osteoarthritis

Osteoarthritis (OA) of the ankle joint develops mainly after trauma. It is less frequent than OA of the knee or hip joint but often affects younger and physically active people. More than half of the patients present with a malalignment of the hindfoot, more frequently into varus. Such patients with asymmetric ankle OA often have partially intact articular cartilage and may thus benefit from joint preserving realignment surgery. With supramalleolar and hindfoot osteotomies, the ankle is surgically realigned to unload the degenerated cartilage and improve the joint congruency. While clinical outcome studies already showed a reduction of pain, as well as improvements in the joint function and the patients’ general well-being, the effects of supramalleolar osteotomies on the patients’ gait patterns are largely unknown. The aim of this thesis was therefore to first identify and quantify the gait patterns of patients with asymmetric (varus or valgus) ankle OA and secondly to assess the biomechanical and neuromuscular rehabilitation potential after joint preserving realignment surgery.
The results of the gait analyses in patients with early- to mid-stage asymmetric ankle OA showed that these patients had a lower hindfoot dorsiflexion and rotation range of motion, as well as reduced peak ground reaction forces, external ankle dorsiflexion moment, and ankle joint power. Additionally, the application of a principal component analysis on the temporal waveforms of the hindfoot dorsiflexion angle and the vertical ground reaction force resolved features that influenced the amplitudes and timing of the waveforms. Using selected principal component scores of patients and healthy subjects in a linear support vector machine classifier resulted in a successful classification (recognition rate: > 95%). Regarding the neuromuscular changes, patients with asymmetric ankle OA produced lower isometric torques in plantarflexion and dorsiflexion compared to healthy subjects. This weakness of the lower leg muscles was also associated with changes in the muscle activation patterns. For the tibialis anterior the wavelet power spectrum (maximal isometric contraction) and the wavelet pattern (walking) contained more low frequency components than those of healthy subjects. During walking, the calf muscles were active with a lower intensity and over a broader time-frequency region. Additionally, it seemed that a valgus hindfoot alignment led to an altered intermuscular coordination between the calf muscles. While the gastrocnemius medialis was maximally active before the gastrocnemius lateralis and soleus in healthy subjects and patients with varus ankle OA, it lagged behind in patients with valgus ankle OA. This altered coordination could be due to a reduced or missing varisation of the hindfoot during push off from the floor. Further changes were seen in the wavelet patterns of peroneus longus that contained more low frequency components in patients with a valgus hindfoot alignment than in those with a varus alignment. This could be related to a lower muscle activation level that has previously been described for healthy subjects with flat-arched feet.
Based on the described gait adaptations in patients with asymmetric ankle OA, we further investigated the effects of the joint preserving realignment surgery and the following rehabilitation on the biomechanical and neuromuscular gait patterns. In patients measured at least seven years after surgery, the spatiotemporal, kinematic, and kinetic gait parameters showed fewer differences to controls than to patients with asymmetric ankle OA. The postoperative patients walked faster, with a higher cadence, and a slightly higher ankle dorsiflexion moment. However, the range of motion in hindfoot and hallux dorsiflexion remained reduced compared to healthy subjects. Additionally, prospective gait data for patients before and after realignment surgery were collected and presented together with data on long-term follow-up patients. Patients with ankle OA, short-term (prospective) and long-term follow-up patients had similar changes in the foot kinematics. Principal component scores that affected the range of motion of the sagittal hindfoot and hallux movement were reduced compared to healthy subjects in all patient groups. For the forefoot dorsiflexion angle (range of motion) and the temporal muscle activation of gastrocnemius medialis and soleus (peak activity), the principal component scores were only altered in the patients with ankle OA and the short-term follow-up patients. However, both studies showed that despite remaining changes in the gait patterns, patients had less pain, higher functional ankle scores, and a better general health after supramalleolar osteotomies. Thus, our results indicated that joint preserving realignment surgeries are a promising alternative treatment for asymmetric ankle OA.