# Diagnosis and Treatment of an Ununited Anconeal Process in a California Sea Lion (Zalophus californianus)

## TL;DR

This paper describes the first case of a bone development disorder in a California sea lion, similar to one found in dogs, and highlights the challenges of diagnosing and treating such conditions in marine mammals.

## Contribution

The first documented case of an ununited anconeal process in a California sea lion, expanding the known species range for this condition.

## Key findings

- Surgical removal of the abnormal bone fragment led to short-term improvement in the sea lion's lameness.
- Histological and morphometric analyses confirmed the condition was developmental, not inflammatory or neoplastic.
- The case introduces UAP as a possible differential diagnosis for forelimb lameness in pinnipeds.

## Abstract

Lameness in marine mammals is not well understood, making diagnosis and treatment challenging. This study reports the case of a California sea lion with an ununited anconeal process, a developmental bone condition affecting the elbow joint, similar to a disorder found in domestic dogs. The sea lion had increasing difficulty using its front flipper, and medical treatment did not improve its condition. Surgery was performed to remove the abnormal bone fragment, leading to short-term improvement. Unfortunately, the animal later passed away due to an unrelated medical condition. By studying the removed bone and using advanced imaging techniques, scientists confirmed that the sea lion’s condition was a failure of normal bone development rather than an injury. This finding suggests that similar conditions may exist in other marine mammals but could go unrecognized.

This case report describes the first documented occurrence of an ununited anconeal process (UAP) in a California sea lion (Zalophus californianus), expanding the species range of this orthopedic pathology beyond domestic canids. A 13-year-old female presented with chronic progressive right forelimb lameness. Diagnostic imaging revealed a large mineralized intra-articular bone fragment at the level of the elbow joint, accompanied by secondary osteoarthritic changes. The fragment was surgically excised via a lateral humero-ulnar arthrotomy. Histologic evaluation of the excised tissue confirmed an ununited ossification center with preserved trabecular architecture and no evidence of inflammation or neoplasia, supporting the diagnosis of UAP. Three-dimensional morphometric analysis demonstrated substantial remodeling of the ulna, humerus, and radius, with morphological deviation in pathological elements exceeding inter-individual variation observed in healthy conspecifics. Despite initial postoperative improvement, the animal succumbed to complications from an unrelated chronic diaphragmatic hernia, four weeks post-surgery. This report introduces UAP as a novel differential diagnosis for forelimb lameness in pinnipeds, and underscores the feasibility of surgical management. The findings provide crucial insights into the comparative pathology related to UAP and orthopedic surgical approaches in marine mammals.