Acute severe unilateral lameness associated with proliferative bone on
the dorsal aspect of the middle phalanx: an evaluation of 19 cases
Abstract
Background: Injury resulting in proliferative new bone
formation on the dorsal aspect of the middle phalanx (P2) has been
recognised by equine veterinarians and is generally referred to as
capsulitis. Objectives: Describe the clinical features,
treatment, and outcomes of this condition. Study Design: Case
series (n=19) Methods: Clinical cases in which the horse
presented for lameness and were diagnosed with acute formation of
proliferative bone on the dorsal aspect of P2 were included in the study
(cases collected from 2005-2022). Signalment, history, presenting
clinical signs, diagnostics, treatments administered, and outcome were
evaluated. Results: Horses presented with unilateral lameness
that were all classified as either a moderate lameness at a trot (n=6),
or a moderate to severe lameness at a walk (n=13). The presentation of
lameness was recorded as acute in 15/19 horses and not reported in the
remainder. Bone proliferation on the dorsal aspect of P2 was diagnosed
on radiographic evaluation in all horses (as part of the inclusion
criteria). In horses with sequential radiographs made from the time of
acute presentation, the bone production developed rapidly over a period
of a few weeks to 2 months. A variety of therapeutic options were
implemented, and 13/19 (68%) of the cases were subject to humane
euthanasia with only one horse returning to its previous athletic
function. Milder cases were more likely to have better outcomes.
Main Limitations: Small sample size.
Conclusions: Acute new bone proliferation on the dorsal aspect
of P2 may be associated with moderate to severe lameness and carries a
poor prognosis for return to athletic performance and survival.