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    Do Larger Heads Create a Better Hip Replacement?

    At ICJR’s annual Winter Hip & Knee Course, Thomas K. Donaldson, MD, and Gwo-Chin Lee, MD, debated the issue of head size for total hip arthroplasty .

    Below are some of the key points from their debate.

    Pro: Thomas K. Donaldson, MD

    Dr. Donaldson contends that the concept of physiologic head sizes for THA is nothing new – 33 and 42 mm heads were introduced in 1961 – and that most orthopaedic surgeons are accustomed to using larger head sizes. The fact that larger head sizes are more physiologic than smaller heads is one of the primary reasons he prefers using them for primary and revision THA.

    Other reasons he cited are that they:

    • Reduce the dislocation rate
    • Increase stability
    • Increase range of motion
    • Are bone-preserving in hip resurfacing procedure

    Functionally, he said, a larger head gives a higher drop height, providing intrinsic stability so that that hip does not slide out of the joint. The result is a greater range of motion without impinging on the implant.

    In his practice, Dr. Donaldson has done 970 primary THAs with 36 mm or greater heads. None of his patients has experienced an early dislocation, and only one patient had a dislocation at 5 years after the procedure.

    Currently, Dr. Donaldson uses 36 mm metal- or ceramic-on-vitamin E polyethylene heads. A patient who has already dislocated or is at high risk for dislocation will typically receive a 36 mm or greater head. For his younger patients (defined as those less than 60 years of age), he still does metal-on-metal hip resurfacing.

    Dr. Donaldson’s presentation can be found here.

    Con: Gwo-Chin Lee, MD

    Dr. Lee believes that instead of putting emphasis on the head size, orthopaedic surgeons should focus on what will really make a difference in primary procedures: improving technique, improving component positioning, and better defining an individual safe zone for THA.

    He has three primary reasons not to use larger heads in THA:

    • Range of motion. Regardless of what cadaver studies show, in vivo studies have shown there is no improvement in range of motion functionally in a greater than 36 mm head.
    • Component positioning. Proper component positioning is crucial: Multiple studies have shown dislocation rates lower than 1% with posterior capsule repair. None of these studies used head sizes larger than 32 mm. The literature does not indicate that a larger head size can overcome poor component positioning.
    • May contribute to other issues. Wear may be a problem with larger heads. Studies have shown that over time, a 32 mm head will wear more than a 28 mm head, even when highly cross-linked polyethylene is used. There is also the possibility the patient will develop symptoms of synovitis with wear. And, there are concerns about corrosion with larger head sizes.

    In his practice, Dr. Lee’s rule of thumb is to use:

    • 28 mm heads with patients who have a cup size under 50 mm
    • 32 mm heads with cups between 52 and 56 mm (this is his default size)
    • 36 mm heads with cups above 58 mm

    Dr. Lee’s presentation can be found here.