Metacarpal Synostosis: A Simple Classification and a New Treatment Technique

Author(s): Foucher G, Navarro R, Medina J, Khouri RK

Source: Plastic and Reconstructive Surgery 108:  1225-1231, 2001

Summary:

The authors propose a new classification system for metacarpal synostosis, a rare congenital anomaly first described by Kelikian in 1974.  They review the current system of Buck-Gramcko and Wood, and contrast their classification, which is based on their clinical experience.  The paper retrospectively reviews 28 patients with 36 synostoses observed over a 24-year period.  In their experience, the synostoses occurred predominantly between the ring and small metacarpals (20 patients), followed by the  middle-ring interval ( 8 patients).  The authors develop a classification scheme, which is based on the shape and length of the metacarpals, the direction of the epiphysis, the deformity of the distal fingers, and the presence of webbing.  The system stratifies deformities into one of four main categories:  I-shaped, U-shaped, Y-shaped, and K-shaped.  Within each main category are sub-categories based on the length of the individual metacarpals involved in the synostosis and the degree of fusion.  The authors further describe surgical and non-surgical treatment options in each case.  They describe a new method of treating type Y synostosis, in which divergence of the main epiphyseal axes is cited as the primary deforming force.  In their three cases of Y deformity, they utilized a reversed trapezoidal bone graft taken from the metacarpal divergence itself to correct the deformity.  For type K synostosis, they recommend gradual distraction lengthening of the shortened element (5th finger), coupled with extension pinning of the MCP joint.  The average time of distraction in their five cases was 49 days in patients age 6 to 14.  The results are briefly discussed, and all patients and their families were reported to be pleased with the results.

This new classification system is straightforward and clinically useful in describing and planning treatment for this rather rare condition. Its primary advantage is the graphic categorization of the deformity, e.g., I, U, Y, or K shaped.  The treatment of each deformity is based on the basic anatomic elements involved, which should allow careful and accurate surgical planning.  The authors describe a new technique for correcting the rare and challenging Y-shaped synostosis,  with a reversed bone graft from the region of metacarpal divergence.  Their pictures are convincing but the sample size is very small (n=2).  Further experience will be required to determine the true utility of this procedure.  The most controversial element of this paper is the authors’ proposed method of correcting type Y and K synostoses.  They propose a gradual distraction-lengthening technique with callotasis over a 7-10 week period.  This is in stark contrast with the one-stage lengthening procedures described by Hooper & Lamb and Buck-Gramcko & Wood.  Individual factors such as patient age, social/familial issues related to compliance, infection risk, etc. need to be carefully considered before recommending a lengthy distraction procedure in young children.  Perhaps the one most relevant criterion is the degree of longitudinal deficit of the shorter metacarpal.  For the severely deficient ray, gradual distraction may indeed offer better results than one-stage lengthening.  This system of classification should help to better organize these deformities into rational groupings based on anatomic variation, and thus aid in careful and successful treatment planning.

 


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