JBJS Classics: The Moseley Straight-Line Graph for Leg-Length Discrepancies

jbjsclassics-2016OrthoBuzz regularly brings you a current commentary on a “classic” article from The Journal of Bone & Joint Surgery. These articles have been selected by the Editor-in-Chief and Deputy Editors of The Journal because of their long-standing significance to the orthopaedic community and the many citations they receive in the literature. Our OrthoBuzz commentators highlight the impact that these JBJS articles have had on the practice of orthopaedics. Please feel free to join the conversation about these classics by clicking on the “Leave a Comment” button in the box to the left.

One of the hallmarks of a great journal article is whether it changes practice. In 1977, Colin Moseley presented a new method of predicting future leg growth that automatically takes into consideration the child’s growth percentile and the amount of growth inhibition in the short leg. Dr. Moseley’s method has been widely accepted because it is user-friendly and only requires three data points at each visit to the clinic – skeletal age and length of the long and the short legs. The accuracy of the prediction relies on serial measurements at different time points during the child’s growth. The more data points,  the more accurate the prediction. Unlike other methods, no mathematical calculations are necessary.

Then as now, the beauty of the method is that the growth of both the long and short legs can be represented by straight lines on a graph. Dr. Moseley accomplished this by mathematically converting Green and Anderson’s growth-remaining data into a logarithmic form. The straight-line graph improved upon the Green and Anderson data, as it was able to address the influence of the child’s growth in height by providing a nomogram to plot longitudinal skeletal age data to determine the end of growth. Moseley’s graph also provided reference slopes to aid in decision-making about when epiphysiodesis should be performed.

Dr. Moseley compared the accuracy of his method to that of the Green and Anderson growth-remaining method by doing a retrospective study based on data from 30 children treated with epiphysiodesis who had adequate scanograms and skeletal-age radiographs. The patients came from the Shriner’s Hospitals for Crippled Children in Montreal, Canada and the Alfred duPont Institute in Wilmington, Delaware.

Dr. Moseley found that the straight-line graph proved to be as accurate as the growth-remaining method—and more accurate in cases of high growth inhibition. It is interesting to note that Dr. Moseley was the only person doing this study and there was no test for interobserver error, which would certainly be one of the concerns raised by today’s reviewers for JBJS. The study could also have been strengthened if Dr. Moseley had validated his method with a series of prospective cases.

Dr. Moseley made certain assumptions in developing this method for predicting leg-length discrepancy at maturity. He used skeletal age and not chronological age as the norm. He assumed that growth of both the long and short legs was linear and that each individual child would remain in the same growth percentile with respect to skeletal age.

In 1982, Frederic Shapiro from Boston Children’s Hospital reported five developmental patterns in leg-length discrepancies in JBJS. Interestingly, type 1, which comprised a large proportion of the 803 cases reviewed, had a linear growth pattern where the discrepancy increased at the same proportionate rate. This finding supported the assumptions that Dr. Moseley made for the majority of his cases, but it also confirmed that not all discrepancies progress at the same rate, the notable exceptions being in children with Perthes disease and leg-length discrepancies arising from femoral fractures.

Eng Hin Lee, MD, FRCS(C)
JBJS Deputy Editor

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