Case Study

RAD – Pin migration and loosening plate 7 years post acetabular and trochanteric osteotomy in a Saint Bernard

This Saint Bernard has a history of traumatic pelvic fractures with surgical repair 7 years ago. Presented for evaluation of migrating pin

DX

• Pin migration and loosening plate 7 years after leftsided acetabular fracture and trochanteric osteotomy without evidence of complication • Lefsided muscle and bone atrophy owing to chronic disuse • Bilateral moderate coxarthrosis

Image Interpretation

Rads fo the pelvic bones and spine –

The patient had traumatic pelvic fractures involving the left acetabulum with surgical repair 7 years ago. A non-locking acetabulum plate was used fixed with 5 screws as well as 4 pins for a trochanteric osteotomy.

Three pins are in situ within the left femoral trochanter. One of the pins has migrated into the hypaxial muscles of the caudal spine. The pin is situated in an oblique craniodorsal-to-caudoventral position with the tip pointing craciad. There is no obvious soft tissue swelling or other reaction surrounding the pin. The rectal wall does not present any abnormalities radiographically.

Both hip joints present signs of moderate osteoarthritis. On the right side this is a consequence of mild hip dyplasia exclusively and the change are mainly restricted to the femoral head and neck. On the left side this is a composite effect of the mild hip dysplasia and the traumatic injury of the acetabulum. The osteoarthritic changes involve the acetabular groove here as well. Bone healing of the left acetabulum is complete. The implant is inert but loosening of all screw heads and mild bone atrophy under the plate is noted. The left femoral head and neck reveal demineralization consistent with disuse osteopenia. The volume of the right thigh musculature is moderately reduced indicating chronic disuse as well.

Outcome

Generally removing migrating pins is discouraged as long as there are no clinical or other signs of complication. The soft tissue injury in the tedious attempts to remove the pins surgically way overweigh the damage of the pins in most cases.
The close proximity to the rectum is a concern here. However, the position of the pin does not necessarily favor migration towards and preforation of the rectal wall.