Clinical and force plate evaluation of the effect of a high plantar nerve block in lameness caused by induced mid-metatarsal tendinitis.

To answer the question whether it is possible to differentiate, by means of a high plantar nerve block in the hind limb, flexor tendon lameness from a suspensory ligament lameness, mid-plantar tendinitis or desmitis was induced with collagenase in five Standardbred horses in two trials. Before the induction of lameness, and on the fourth (D4) and fourteenth day (D14) after the induction of lameness the horses were evaluated subjectively (clinical lameness score), objectively (ground reaction force (GRF) measurements), and ultrasonographically. Clinical evaluation and GRF measurements were also done on D4 and D14 after a high plantar nerve block. From the GRF measurements variables were selected and analysed and related to the clinical lameness score. The horses were significantly lame on D4; this lameness had decreased on D14. The clinical findings were supported by the GRF data. In the flexor tendon group, a high plantar nerve block resulted in soundness or lameness in the other hind limb, whereas in the suspensory ligament group the effect was less conclusive. The correlation between the subjective clinical lameness score and several objectively measured GRF variables proved to be moderate to high. The collagenase model proved to be useful to study the effect of a high plantar nerve block on lameness resulting from induced tendon/ligament lesion. However, a high plantar nerve block cannot be used to differentiate between flexor tendon and suspensory ligament lesions.