Measurement of leg length discrepancy is an important part in planning a successful total hip arthroplasty (THA). Many clinical and radiological methods with variable degrees of accuracy have been advocated to carry out this measurement. We studied the accuracy of a commonly used clinical method by comparing it to a well-known and reliable radiological method. A total of 139 patients aged 44-89 (mean: 67.5 years) scheduled to undergo THA were examined for clinical and radiological leg length discrepancy measurements before and after the operation by the same observers. There was a poor correlation between the clinical and radiological methods preoperatively [r =0.21, intra-class correlation coefficient (ICC)=0.33]. The correlation was better postoperatively (r =0.45, ICC=0.62). The clinical method used is not recommended for leg length discrepancy measurement preoperatively. Caution should even be taken when using this method postoperatively. The authors recommend using the radiological method when measuring leg length discrepancy as a part of planning for THA.Résumé Objectif: La mesure de l'inégalité de longueur est une part importante de la planification des prothèses totales de hanche. De nombreuses méthodes cliniques et radiologiques ont été utilisées pour permettre de telles mesures. Nous avons voulu étudier une méthode clinique habituelle comparée à une méthode radiologique fiable. Patients et méthode: 139 patients âgés de 44 à 89 ans (en moyenne 67,5 ans) devant bénéficier d'une prothèse totale de hanche ont été examinés sur le plan clinique et radiologique avec mesure de l'inégalité de longueur avant et après l'intervention chirurgicale par les mêmes observateurs. Résultats: il y a peu de corrélations entre les méthodes cliniques et radiologiques pré-opératoires (r =0.21, ICC=0.33). La corrélation est bien meilleure en post-opératoire (r =0.45, ICC=0.62). En conclusion, la méthode clinique n'est pas recommandée en pré-opératoire, elle doit être utilisée avec méfiance. En post-opératoire il est recommandé d'utiliser une méthode radiologique afin de mesurer l'inégalité de longueur des membres inférieurs. Celle-ci doit faire partie du planning d'une prothèse totale de hanche.

Objective:Leg length discrepancy is common both in healthy subjects and after total hip arthroplasty (THA). Studies that evaluated leg length following THA have demonstrated a notable inconsistency in restoring leg length. The effects concerning joint load during gait is however not well known. The purpose of this study was to use three-dimensional (3D) gait analysis to evaluate joint load during gait with a simulated leg length discrepancy of 2 and 4 cm. Nine healthy subjects without any history of hip injury participated.Method:A 3D gait analysis (Vicon, Motion System, Oxford, England) was performed with 6 cameras and 2 force palates using a standard biomechanical gait model. Hip joint moments of force were calculated for all three degrees of motion freedom. ANOVA for repeated measurements was used for statistical calculations.Results:Abduction peak moment was significantly increased at the short side (P < 0.05) but unaffected on the long side. The adduction moment decreased on the long side between 0 and 4 cm (P < 0.01) but was unaffected on the short side. The internal hip rotation moments were unchanged for both the long and the short side. The external rotation moment was unchanged on the short side and decreased between bare foot and 4 cm on the long side (P < 0.05).Conclusion:A leg length discrepancy of 2 cm or more creates biomechanical changes concerning hip joint load both on the long and the short side and that the effects are larger on the short side. The increased stress may cause problems in the long run.

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