Issue: May 2018
Perspective from Douglas A. Dennis, MD
May 16, 2018
3 min read
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Patients with fixed spinopelvic alignment had greater incidence of dislocation after THA

Patients who had less spinal flexion, more hip flexion to achieve the seated position were at greater risk to dislocate.

Issue: May 2018
Perspective from Douglas A. Dennis, MD
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Patients undergoing total hip arthroplasty who had fixed spinopelvic alignment had a greater incidence of dislocation, according to results presented at a meeting.

“Fixed spinopelvic alignment occurs with lumbar spine disease and some having undergone spinal fusion in this group,” Seth A. Jerabek, MD, orthopedic surgeon at Hospital for Special Surgery, said. “The inability to accommodate through the spine may lead to increased hip flexion, which may be a driving mechanism for dislocation due to increased motion through the hip and resultant implant, bone or soft tissue impingement. Patients with fixed spinopelvic alignment may benefit from altered acetabular cup position, potentially more inclination and more anteversion or alternative bearing designs, such as dual mobility.”

Seth A. Jerabek, MD
Seth A. Jerabek

Spine disease in dislocators

From 2014 to 2017, Jerabek and his colleagues performed standing and sitting radiographs from the thoracolumbar junction to the ankles on 1,000 patients who underwent primary THA. The researchers measured alignment parameters, including lumbar lordosis and sacral slope, spine and hip flexion, and postoperative cup alignment in standing and sitting positions.

Results showed 12 patients experienced a dislocation within 1 year of surgery. Researchers compared these 12 patients with 1,000 patients who did not dislocate and then categorized the patients as having normal spines or spine disease.

“What we found was that patients who had [a] dislocation did have significant lumbar spine disease,” Jerabek said. “They had less spine flexion and more hip flexion to achieve the seated position,” he said.

Flexion differences noted

Spine flexion was 14° in patients who dislocated vs. 23° in patients who did not dislocate. Patients who dislocated had 72° hip flexion vs. 65° hip flexion in the patients who did not dislocate, Jerabek noted.

“The average seated inclination of the dislocator group was 45° and it was 50° in the non-dislocator group, and the seated anteversion was 32° in the dislocator group and 38° in the non-dislocators,” he said.

Jerabek told Orthopedics Today there were several limitations of the study, including that the patients performed relaxed sitting and standing positions, and these may not be the kind of positions that may normally cause patients to dislocate their hip.

“Normally, when people dislocate they are usually doing something like putting on a shoe or a sock or bending over to reach something on the ground and that is when your muscles would be firing, and that might change what happens between the spine and the pelvis as the muscles contract,” he said.

Jerabek said research in this area should not only follow more patients for a longer time, but include patients who are attempting more provocative positions, such as hyperflexing the hip. – by Casey Tingle

Disclosure: Jerabek reports no relevant financial disclosures.