Which factors commonly contribute to dislocation after hip arthroplasty, and how can surgical technique mitigate them?

• A. Dislocation due to infection.
• B. Dislocation due to patient age.
• C. Dislocation due to high BMI only.
• D. Malpositioned components (inclination/anteversion), soft tissue imbalance, abductor insufficiency; mitigate with correct cup inclination/anteversion, proper soft-tissue tensioning, and possible constrained liners in high-risk patients.

Answer: (D)

Dislocation after hip arthroplasty is most often driven by how the components sit together and how the surrounding soft tissues support the joint. The best approach to reduce this risk focuses on three interrelated factors: where the components are placed, how the soft tissues balance the joint, and the function of the abductor muscles.

Component placement matters: the acetabular cup must be oriented to minimize impingement and instability. If the cup inclination is too steep or too shallow, or the anteversion is off, the hip is prone to edge-loading or posterior instability, especially with certain hip movements. Maintaining a neck–head relationship that avoids impingement and preserves a stable range of motion is key. In practice, this means aiming for a physiologic cup inclination and anteversion and validating proper version during or after implantation.

Soft-tissue balance is the other major factor. The surrounding capsule and soft tissues, including the abductors, need to be appropriately tensioned to stabilize the joint without being overly tight. If soft-tissue tensioning is inadequate, the joint can become unstable in several positions. This is addressed by careful soft-tissue repair or reconstruction when needed and by restoring proper offset and leg length so the abductors and capsule can function effectively.

Abductor insufficiency contributes to instability because the muscles that actively stabilize the hip are not providing enough dynamic control. When this occurs, strategies include repairing or augmenting the abductor mechanism and, in higher-risk cases, considering implant options that reduce dislocation risk, such as dual mobility or constrained liners.

In summary, when dislocation risk is analyzed, malpositioned components, soft-tissue imbalance, and abductor deficiency are the primary, modifiable targets. Correct cup inclination and anteversion, restore proper soft-tissue tensioning, and address abductor function; in high-risk patients, employing constrained liners or other stabilizing reconstructions can further mitigate dislocation risk. The other choices point to factors like infection, age, or BMI in a more indirect or non-mechanical way, which are not the main contributors to dislocation in the typical scenario.