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    Management of Periprosthetic Dislocation after THA

    Hip instability is one of the most common complications associated with total hip arthroplasty (THA), and it is the driving force behind the current use of large-diameter heads, according to Arlen D. Hanssen, MD, Professor of Orthopaedics at Mayo Clinic in Rochester, Minnesota.

    At the ICJR’s Revision Hip & Knee Course, Dr. Hanssen outlined his strategy for assessing and managing instability after THA.

    When evaluating the patient for the source of instability, Dr. Hanssen stressed the importance of determining whether it is caused by:

    • Component malposition
    • Inadequate soft-tissue tension
    • Impingement
    • Combination of these issues

    It is also necessary to determine whether the impingement is dependent or independent.

    Dependent

    • Component malposition
    • Small femoral head size
    • Head to neck ratio
    • Neck shape/length/offset
    • Use of liner elevation
    • Retained osteophytes

    Independent

    • Soft tissue tension imbalance
    • In sufficient offset
    • Trochanteric avulsion
    • Abductor insufficiency
    • Late wear

    In general, Dr. Hanssen manages a patient with a first-time dislocation with:

    • Relocation (closed reduction)
    • Risk factor assessment
    • Immobilization to determine if he/she will have recurrent dislocations

    A patient who is a repeat dislocator will need surgery. Dr. Hanssen uses the Paprosky Classification for recurrent dislocation to suggest the treatment options for these patients:

    Type I: Acetabular malposition and Type II Femoral malposition

    • Revise components to more adequate position
    • Upsize femoral head
    • Optimize offset

    Type III: Impingement

    • Reposition components to avoid impingement
    • Upsize femoral head
    • Optimize (offset/head neck ration/neck length)
    • Remove bony impingement, which can be subtle and difficult to see

    Type IV: Abductor Insufficiency

    • Optimize offset
    • Perform trochanteric advancement to improve soft tissue tension
    • May require constrained liners
    • May use dual-mobility designs

    Type V: Late Wear

    • Exchange polyethylene liner (may require acetabular revision)
    • Upsize femoral head

    Type VI: Indeterminate Etiology

    • Insert constrained liner/dual-mobility heads
    • Make every effort to determine etiology and optimize (head size, offset, abductor tension)

    On the acetabular side, there are a number of options to improve the variable Dr. Hanssen described:

    • Lateralized liner
    • Face-changing liner
    • Tripolar/large heads
    • Constrained liners (minimize the amount of constraint if possible)
    • Dual-mobility heads/mobile bearing

    Dr. Hanssen noted that larger-diameter heads have several well-known advantages, such as increased range of motion (ROM) to dislocation and impingement, more resistance to dislocation, soft tissue tightening, and possible closed reduction. However, these larger heads are costly and have thinner polyethylene. Tripolar heads, the original large-head solution, often have bad polyethylene, which has caused problems. Without question, constrained liners provide immediate stability. However, the disadvantages include the following:

    • Not all designs are equal
    • Impingement
    • Increased interface stresses
    • Polyethylene wear
    • Mechanical disassembly
    • Open reduction
    • Many types of failures

    Dr. Hanssen was cynical about dual-mobility heads when they were first released. Now, however, he uses them more than constrained liners for the following reasons:

    • Reduced torsional stresses at modular junction
      • Replaces some head upsizing cases
    • Replaces some constrained liners
      • Increased ROM

    He uses them in high-risk revisions, such as abductor insufficiency, reimplantation for infection, and metal-on-metal (MoM) revisions. Dr. Hanssen also prefers dual-mobility heads to treat Paprosky types III, IV, and VI instability.

    The best treatment for instability, Dr. Hanssen said, is to prevent it in the first place. But if you do have an unstable hip, define the underlying problems and try to address them with the Paprosky treatment algorithm.