In trialing for a total hip replacement, what is the critical step to ensure proper offset and leg length?

• A. Only check leg length after final components are implanted.
• B. In trialing, verify appropriate head/neck length, offset, and cup position; check leg length equality and soft-tissue tension with patient in 1-2 positions.
• C. Focus exclusively on head size.
• D. Adjust cup position without considering leg length.

Answer: (B)

Restoring the hip’s natural biomechanics hinges on matching the femoral offset and leg length while ensuring the cup (center of rotation) is properly placed. During trialing, you bring in provisional head/neck length and offset and the cup position, then actively check that the legs end up at equal length and that soft-tissue tension feels balanced with the patient in a couple of positions. This combination lets you see how changes in neck length and offset affect leg length, tension, and stability before committing to final components. If a discrepancy or imbalance is found, you can adjust neck length or offset, and verify the cup’s position to maintain proper biomechanics.

Choosing to wait until after final implants to assess leg length misses the opportunity to fine-tune mechanics and can lead to persistent limp or instability. Focusing only on head size ignores the crucial role of offset and leg length. Adjusting the cup without considering leg length risks an improper center of rotation and mismatch in limb length.