of an IM Pin
Submitted by Toby Eshelman, DVM | Veterinary Specialty Center
Radiograph of a dog with plate and rod fixation of a chronic left femur fracture
Images courtesy of Toby Eshelman, DVM | Veterinary Specialty Center
Countersinking of intramedullary pins is occasionally required in femoral, tibial, and humeral fractures to minimize morbidity due to joint interference or soft tissue impingement, most notably sciatic nerve irritation dorsal to the trochanteric notch. This procedure is traditionally done with a mallet and a pointed countersink, similar to a carpenter’s tool, which is placed against the end of the intramedullary pin. Difficulty visualizing the pin end in soft tissues and oblique or irregular (cut) ends of the intramedullary pin can make this a frustrating exercise. Small diameter pins may be inadvertently bent if struck slightly off-axis, and confirmation of satisfactory depth can be difficult, particularly in the trochanteric fossa of the femur.
An IMEX drill sleeve and Interface no-point pin of appropriate size can be used to simplify the process, at least for IM pins of the appropriate diameter:
|IM Pin Size||Drill Sleeve Size||Interface No-Point ESF Pin Size|
|5/64"||2.0 mm||2.0 mm or 5/64"|
|3/32"||2.3 mm||2.4/3.2 mm (3/32" | 1/8")|
|1/8"||3.1 mm||3.2/4.0 mm (1/8" | 5/32")|
|5/32"||3.9 mm||4.0/4.8 mm (5/32" | 3/16")|
FIGURE 1 | Two-week recheck radiographs of a dog who underwent plate and rod fixation of a chronic (> three weeks) left femur fracture. Severe lameness and sciatic pain was noted at this recheck exam. Pin removal was not considered prudent due to slight IM pin bending noted and limited screw purchase in the proximal fragment (2/3 were monocortical). The IM pin was countersunk in the manner described.