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Minimum Distraction Gap: How Much Ankle Joint Space Is Enough in Ankle Distraction Arthroplasty?

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The success of ankle distraction arthroplasty relies on the separation of the tibiotalar articular surfaces.


The purpose of this study was to find the minimum distraction gap needed to ensure that the tibiotalar joint surfaces would not contact each other with full weight-bearing while under distraction.


Circular external fixators were mounted to nine cadaver ankle specimens. Each specimen was then placed into a custom-designed load chamber. Loads of 0, 350, and 700N were applied to the specimen. Radiographic joint space was measured and joint contact pressure was monitored under each load. The external fixator was then sequentially distracted, and the radiographic joint space was measured under the three different loads. The experiment was stopped when there was no joint contact under 700N of load. The radiographic joint space was measured and the initial (undistracted) radiographic joint space was subtracted from it yielding the distraction gap. The minimum distraction gap (mDG) that would provide total unloading was calculated.


The average mDG was 2.4 mm (range, 1.6 to 4.0 mm) at 700N of load, 4.4 mm (range, 3.7 to 5.8 mm) at 350N of load, and 4.9 mm (range, 3.7 to 7.0 mm) at 0N of load.


These results suggest that if the radiographic joint space of on a standing X-ray of an ankle undergoing distraction arthroplasty shows a minimum of 5.8 mm of DG, then there will be no contact between joint surfaces during full weight-bearing. Therefore, 5 mm of radiographic joint space, as recommended historically, may not be adequate to prevent contact of the articular surfaces during weight-bearing.

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Conflict of Interest:

Austin Fragomen, MD, is a paid consultant for Smith & Nephew and receives royalties from Small Bone Innovations (outside the work). S. Robert Rozbruch, MD, is a paid consultant for Smith & Nephew and receives royalties from Small Bone Innovations (outside the work). Thomas McCoy and Kathleen Meyers have declared that they have no conflicts of interest.

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This article does not contain any studies with human or animal subjects performed by the any of the authors.

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Correspondence to Austin T. Fragomen MD.

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This work was performed at the Hospital for Special Surgery, New York, NY.

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Fragomen, A.T., McCoy, T.H., Meyers, K.N. et al. Minimum Distraction Gap: How Much Ankle Joint Space Is Enough in Ankle Distraction Arthroplasty?. HSS Jrnl 10, 6–12 (2014).

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