Minimum distraction gap: how much ankle joint space is enough in ankle distraction arthroplasty?
BACKGROUND
The success of ankle distraction arthroplasty relies on the separation of the tibiotalar articular surfaces.


OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Orthopaedic Surgery, Weill Cornell Medical College, New York, NY 10065 USA ; Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021 USA.
Austin T
AT
Fragomen
Harvard Medical School, 25 Shattuck Street, Boston, MA 02115 USA.
Thomas H
TH
McCoy
Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021 USA.
Kathleen N
KN
Meyers
Orthopaedic Surgery, Weill Cornell Medical College, New York, NY 10065 USA ; Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021 USA.
S Robert
SR
Rozbruch
Ilizarov; RAD; ankle arthritis; ankle distraction; arthrodiastasis; external fixation; joint preservation