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Acetabular component safe zones should be patient-specific for hip replacement

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Andrew M. Shimmin

WAIKOLOA, Hawaii — Sagittal-pelvis mobility varies in patients who undergo total hip replacement; therefore, universal acetabular component position safe zones do not exist, according to a presenter at Orthopedics Today Hawaii.

“[Sagittal-pelvis] mobility varies from patient to patient,” Andrew M. Shimmin, MBBS, FRACS, said during his presentation. “Single, acetabular component safe zones do not exist. This makes light why dislocations frequently [happen] when components are oriented within that historical [Lewinnek] safe zone.”

He said the concept of the Lewinnek safe zone is dead and that surgeons need to now focus on the relationship between the spine, pelvis and hip when they determine the position of the acetabular component.

“The sagittal motion of the pelvis affects the functional orientation of the acetabular component in total hip replacements,” he said. This can affect wear and stability, which indeed are the common causes of failure of total hip replacements.”

He said patients who undergo total hip replacements should have their pelvis-sagittal mobility assessed preoperatively. Shimmin said it is important to identify patients with extreme mobility.

“So, you [have] to identify these people because they are rotating more than 13°. Therefore, their functional cup position is changing 10°,” Shimmin said. “On the other side, for the people who are at risk in flexion, they have more than 13° of anterior rotation when they sit. Therefore, their functional landing version will change 10°.”

He added, “Therefore, it is kind of obvious. We are going to have a safe zone for one patient, the next patient it will be a different safe zone and a different patient, again, it’s going to be a third safe zone. Safe zones should be patient-specific.”– by Monica Jaramillo

Reference:

Shimmin AM. Relevance of sagittal pelvic mobility in THR. Presented at: Orthopedics Today Hawaii; Jan. 13-17, 2019; Waikoloa, Hawaii.

Disclosure: Shimmin reports he is a consultant for and receives royalties from Corin and MatOrtho and is a consultant for Smith and Nephew.