Subject:Leg Length Inequality Assessment Studies

Title: The relationship between pelvic torsion and anatomical leg length inequality: a review of the literature

Reference: Robert Cooperstein, DC, Wayne Rhodes, DC, PhD, Phillip Bishop, EdD...Journal of Chiropractic Medicine 2010; 9: pp.95-97

To the Editor:
Objective: The Cooperstein and Lew l article, "The relationship between pelvic torsion and anatomical leg length inequality: a review of the literature," referenced our work. We feel that their statements should distinguish between anatomical leg length inequality (LL!) and functional LU.

In the discussion section, they indicated that there was" ... poor agreement found by Rhodes et al. between visual methods of leg checking and upright radiographs." We reported the relationship between prone LLl measurements and standing radiograph as "The correlation coefficient (r) between the two variables was ... 0.719."2 Most statisticians characterize this as a moderate positive correlation and not "poor agreement."

Anatomical LLI exists. The LLI incidence is not known perhaps because of confused definitions. Mannello stated, "It appears that the least controversial issue associated with LLl is its anatomical existence." As we previously stated,2 "Structural, anatomical or actual LLl are synonymous terms and are diagnosed when either the femur or tibia is longer in one leg than in the other, as shown on X-ray." Mannello defined it similarly.

Anatomical LLl denotes different bones lengths of right and left lower extremities. The criterion standard for anatomical LL! is the scanogram, radiograph of both femurs and tibias; so comparisons can be made. Of the scanogram, Mannello said, "This procedure is considered a valid indicator of lower extremity length."

The Cooperstein and Lew review on anatomical LLI did not include any studies involving actual bony differences in leg length. However, Mannello pointed out, "Others define anatomical short leg as that which is shorter in length from the floor to the weight bearing surface of the femoral head." This seems to be the definition adopted by Cooperstein and Lew, but no definition of anatomical LLl was included in their review.

Of the 9 studies in their review, 7 involved simulated LLl, with no anatomical bone length differences seen on radiograph. Of the other 2 included, one used tape measures of legs, which have been shown to be unreliable; as Cooperstein and Lew ] pointed out in their article, "Tape measure methods for measuring LLI have been found to be of equivocal accuracy and may be less accurate than radiological criterion standard method for assessing anatomical LLl.. .. "The other study included used radiographs of the femur heads, without full views of both lower extremities (Friberg4 method). A developer of that radiograph technique stated, "The method described here is not meant to substitute the methods for measuring accurately the length of the different parts of the lower extremity,"4 One cannot distinguish anatomical (structural) LLl from functional LLI with the Friberg method of comparison.

Methods that incorporate both anatomical and functional LLl without distinction (eg, Friberg method) necessarily overestimate the incidence of anatomical LLJ5 compared with a stricter definition.

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