The Association of Tibia Femur Ratio and Degenerative Disease of the Spine, Hips, and Knees

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Abstract

Background:

When individuals with asymmetric lower extremities present for evaluation of limb-length inequality, correction can occur at the tibia, femur, or in both bones; however, there are limited data available to justify either technique. The aim of this study is to examine the normal ratio of tibia length/femur length (T/F), and to explore the relationship between T/F ratio and osteoarthritis of the spine, hips, and knees.

Methods:

Bone lengths of 1152 cadaveric femora and tibiae from the Hamann-Todd osteological collection were measured. Degenerative joint disease was graded in the hip, knee, and spine. Correlations between the ratio of T/F and osteoarthritis were evaluated with multiple regression analysis.

Results:

The average ratio of T/F was 0.80±0.03. There was a strong correlation between age and arthritis at all sites, with standardized β ranging from 0.44 to 0.57 (P<0.0005 for all). There was a significant correlation between increasing T/F and hip arthritis (standardized β=0.08, P=0.006), and knee arthritis (standardized β=0.08, P=0.008).

Discussion:

Increasing tibia length relative to femur length was found to be a significant predictor of ipsilateral hip and knee arthritis. Therefore, we recommend that when performing limb lengthening, surgical planning should lean toward recreating the normal ratio of 0.80. In circumstances where one bone is to be overlengthened relative to the other, bias should be toward overlengthening the femur. This same principle can be applied to limb-reduction surgery, where in certain circumstances, one may choose to preferentially shorten the tibia.

Clinical Relevance:

This is the first study to report long-term consequences of lower extremity segment disproportion.

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