Review Question - QID 218216

An increase in the prosthetic neck shaft angle relative to the native anatomy would cause a decrease in offset and an increase in leg length.

Total hip arthroplasty (THA) is a common procedure performed to improve pain and function in patients with hip osteoarthritis. Component design and position are important considerations with regard to making sure the THA recreates native anatomy and maximizes patient function. Offset is made up of the femoral and acetabular offset and changes with the medial/lateral movement of the components. Modifications of the global offset cause changes to soft tissue tension and can affect the biomechanics and stability of the hip prosthesis. Leg length is affected by changes in the femoral neck length and the neck-shaft angle that is chosen by the surgeon. The combination of changes that occur due to these modifications should be carefully considered by the surgeon as abnormalities of leg length and offset can be detrimental to long-term patient outcomes.

Rubash and Parvataneni published an article about leg length inequality after THA, noting that careful preoperative planning is critical. That being said, intraoperative assessment of component positioning remains the most important step. Newer digital templating techniques and image-guided/ robotic surgeries may help to further prevent leg length inequalities in the future.

Sculco et al. wrote a review article on avoiding hip instability and limb length discrepancy after THA. They talk about key elements of preoperative templating, anatomic landmarks for component placement, and how to accurately assess soft tissue tension intraoperatively. They also talk about how limb length discrepancy and component positioning are intertwined with hip instability and the need for revision surgery.

Flecher et al. looked at lower limb length and offset in THA, noting that restoration of normal biomechanics is an important component of THA planning. They further state that errors can adversely affect patient function, quality of life, and prosthetic survival. They recommend the use of preoperative templating software and the use of different implants to accurately restore the patients' native anatomy as appropriately as possible.

Incorrect Answers:
Answer 1: Medialization of the acetabular component due to aggressive acetabular reaming would decrease the global THA offset.
Answer 3: The use of a standard offset component would decrease the offset relative to a high offset component but would not affect the leg length.
Answer 4: An increase in prosthetic femoral neck length would increase the offset and the leg length.
Answer 5: The use of a constrained acetabular liner would not affect the offset or leg length, rather provides an extended lip to prevent instability.