What best defines leg-length discrepancy in arthroplasty and how is it assessed intraoperatively?

• A. It is the vertical height of the prosthetic neck.
• B. It is the difference in leg lengths; assessed with trial reductions, fluoroscopy, adjust neck length/offset; verify symmetry.
• C. It is the distance between the centers of rotation on radiographs.
• D. It is the angle of abduction of the cup.

Answer: (B)

Leg-length discrepancy is the difference in effective leg length after arthroplasty, which can arise from changes in implant geometry such as neck length and offset or cup position. Intraoperatively, this is addressed by performing trial reductions with different neck lengths and offsets and comparing the limb lengths directly. Fluoroscopy is used to visualize the vertical position of the femoral head relative to the pelvis, helping confirm that the head sits at a comparable height on both sides. By adjusting neck length and offset and repeating the trial reduction, the surgeon works toward symmetrical limb length and balanced soft-tissue tension. This approach reduces the risk of postoperative limp, back pain, or instability.

The other ideas don’t define leg-length discrepancy or its intraoperative assessment. The vertical height of the prosthetic neck is just a component feature, not the overall leg-length outcome. The distance between centers of rotation on radiographs is a radiographic parameter related to cup/femoral position, not a direct intraoperative measure of leg length. The angle of abduction of the cup refers to cup orientation and does not describe limb length.