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

HSS Journal: Volume 10, Issue 1


Austin T. Fragomen, MD

Associate Attending of Orthopaedic Surgery, Hospital for Special Surgery
Fellowship Director, Limb Lengthening and Complex Reconstruction Service, Hospital for Special Surgery
Director, Limb Lengthening Clinic, Hospital for Special Surgery
Associate Professor of Clinical Orthopaedic Surgery, Weill Cornell Medical College

Thomas H. McCoy, MD

Harvard Medical School, Boston

Kathleen N. Meyers, MS

Hospital for Special Surgery

S. Robert Rozbruch, MD

Chief, Limb Lengthening and Complex Reconstruction Service, Hospital for Special Surgery
Attending Orthopaedic Surgeon, Hospital for Special Surgery
Professor of Clinical Orthopaedic Surgery, Weill Cornell Medical College
President, Limb Lengthening & Reconstruction Society (LLRS.org)

Abstract

Background

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

Question/Purpose

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.

Conclusion

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.

This article appears in HSS Journal: Volume 10, Issue 1.
View the full article at springerlink.com.

About the HSS Journal

HSS Journal, an academic peer-reviewed journal published three times a year, February, July and October. The Journal accepts and publishes peer reviewed articles from around the world that contribute to the advancement of the knowledge of musculoskeletal diseases and disorders.


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