Koonin Leg Length Caliper – Small 

Utilizes a 5/32″ (4mm) pin in the wound just proximal to the acetabulum and a 1/8″ (3.2mm) pin in the greater trochanter. (The soft tissue is cleared away and a single drill hole is drilled in the trochanter to accommodate the distal pin, and the hole is marked with methyline blue so it can be easily found.) Alternatively, a 7.3mm cannulated screw that accepts a 3.2mm pin may be used in the greater trochanter. Using the sliding caliper, the difference in leg length before hip dislocation and after the THR procedure helps show the change in leg length.