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Tuesday, March 16, 2000

Cubitus varus may be more than cosmetic concern

Cubitus varus, traditionally thought to be of cosmetic concern only, may be of greater clinical significance than is recognized, said Shawn W. O'Driscoll, PhD, MD, Mayo Clinic, Rochester, Minn, co-author of scientific paper 85 presented on Wednesday.

Twenty-three patients (24 limbs) with long-standing cubitus varus deformities developed tardy posterolateral rotatory instability approximately two to three decades after their distal humeral fracture (or in three cases, congenital anomaly). At a minimum one-year follow-up, good or excellent results were achieved in 19 of the 22 limbs that underwent operation.

The causal relationship between the anatomic deformity and the instability was confirmed by dynamically stimulating the triceps muscle to contract eccentrically while resisting extension of the elbow in three patients. This produced posterolateral rotatory subluxation of the elbow, which was reversed by corrective osteotomy and lateral transposition of a portion of the medial triceps that had been attached to the elongated, deformed medial olecranon. The treatment corrected the instability in all but three patients.

Operative procedures most commonly consisted of lateral collateral ligament reconstruction with or without osteotomy. The researchers believe these clinical findings can be explained on a biomechanical basis. Cubitus varus displaces the mechanical axis of the upper limb medial to the ulnotrochlear joint. Varus deformity at the supracondylar level also displaces and rotates the olecranon medially. This creates a supinatory moment (torque) by the triceps.

The medial overpull on the olecranon, in turn, places additional stress on the lateral collateral ligament complex which can attenuate or rupture. The deforming forces represent the initial forces that cause posterolateral rotatory instability of the elbow, and the lateral collateral ligament complex laxity would put these patients at risk for such posterolateral rotatory instability.

"Understanding the biomechanical forces of this combination of deformities will guide treatment rationale in the future," said Dr. O'Driscoll. "In the meantime, it behooves us to consider the possibility that cubitus varus deformity secondary to distal humeral malunion or congenital deformity is not necessarily a benign condition, and may have significant long-term implications relating to elbow instability, medial elbow pain from subluxation of the medial triceps over the epicondyle, and ulnar neuritis or neuropathy from dislocation of the ulnar nerve. Preventative corrective osteotomy is an intervention that may merit consideration."

Co-authors of the study are Robert J. Spinner, MD, and Bernard F. Morrey, MD, both of Mayo Clinic, Rochester, Minn.; Michael D. McKee, MD, University of Toronto, Toronto, Ont.; and W. Ben Kibler, MD, Lexington Clinical Sports Medicine Center, Lexington, Ken.

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