Leg length discrepancies following total hip arthroplasty have been associated with nerve palsies, gait abnormalities, and lower back pain. Leg length discrepancies are related to poorer functional outcomes and patient dissatisfaction. Failure to restore femoral offset following total hip arthroplasty has been linked to decreased range of motion and abductor muscle strength, impingement, limping, higher dislocation rates, increased polyethylene wear, and loosening of implants. Computer navigation has shown to improve the accuracy of leg length and hip offset during total hip arthroplasty. The investigators research objective is to prove the accuracy of the Intellijoint HIP™ system for determining leg length and hip offset. The investigators hypothesis was that Intellijoint HIP™, an imageless intraoperative intelligent instrument, could improve the accuracy of leg length and hip offset during primary total hip arthroplasty. The investigators plan to study this hypothesis in humans by comparing the leg length and hip offset discrepancies produced with Intellijoint HIP™ to the standard at the investigators institution, which is a pin and outrigger system.

Inclusion Criteria:

• Any patient who is undergoing a primary total hip arthroplasty at Mount Sinai Hospital.

Exclusion Criteria:

• Pre-operative flexion contracture >30°, infection, or inability to achieve rigid fixation of instruments intra-operatively.