DYNAMIC LEG LENGTH MEASUREMENT IS A VALID METHOD FOR DETECTING ANATOMIC LEG LENGTH DISCREPANCY

¹Dana Children’s Hospital, Tel Aviv Sourasky Medical Center, Department of Pediatric Orthopedics, Gait and Motion Analysis Laboratory, Tel Aviv, Israel, ²IMACS Israeli Motion Analysis Center for Sports, Tel Aviv, Israel

Background: Even though the importance of leg length discrepancy (LLD), with its potential of causing several pathological conditions or gait deviations, is well known, measuring LLD is still challenging with limited reliability and validity. Based on the kinematical compensation for LLD, dynamic leg length (DLL) measurement, a recently proposed method for measuring the dynamic changes in leg length throughout the gait cycle, has been suggested as a means of detecting asymmetry due to LLD. DLL is the dynamic length of the lower extremity and a resultant factor of true bone leg length and lower limb movement during the gait cycle.

Purpose: ​​​​To assess the capability of the dynamic leg length measurement in detecting the presence of anatomic LLD.

Methods: A lower limb x-ray was performed on 15 participants with suspected LLD in addition to a gait analysis study using a motion analysis system to measure DLL (the absolute distance from the hip joint centre to the heel, to the ankle joint centre and to the forefoot). Average DLLs were compared between sides for symmetry by the paired t-test at 51 sample points during the gait cycle in conjunction with the differences between the sides based on the maximal stance phase and minimal swing phase DLLs. P-values were corrected with the Benjamin-Hochberg (BH) procedure which guaranteed a false discovery rate (FDR) control of 0.05. The difference between the anatomically shorter and longer limb in the functional change in leg length was evaluated and compared. Differences were correlated with the anatomic LLD by the Pearson correlation.

Results: Nine participants presented with a significant longer anatomical right lower limb (p<0.05) of 17.4mm (6.69-28.10) (average (95% CI)). Six participants presented with a significant longer anatomical left lower limb (p<0.05) of 12.66mm (2.28-23.04) (average (95% CI)).
The functional change in leg length, defined as the ratio between the maximal DLLs during the stance phase to the minimal ipsilateral DLLs during the swing phase, presented significant asymmetry (p<0.05). The ratio was higher on the longer limb and lower on the shorter limb. Correlation between the differences in ratios between the sides and LLD were significant (p<0.05). The Pearson correlation between anatomic LLD and the functional discrepancy were (r=0.54, P<0.05, r=0.54, p < 0.05, r=0.57, P <0.05).

Conclusions: DLL measurement can identify anatomic LLD, which causes compensatory gait deviations, thus, altering functional leg length during the gait cycle. Anatomical LLD can be identified by asymmetric changes in the DLLs based on the difference between sides in the ratio between the maximal stance phase and the ipsilateral minimal swing phase DLLs, and based on the difference between the maximal stance phase and the contra lateral minimal swing phase DLLs.

Implications: DLL measurement is a method which can potentially be integrated into gait analysis studies. It is capable of detecting anatomic leg length differences based on functional changes in leg length and functional discrepancy, altered due to kinematic compensatory strategies. DLL measurement enables the clinician to further improve the detection of mild LLD, provide a more precise measurement,thus, a more reliable recommendation for intervention.

Funding acknowledgements:​None

Keywords:
Gait analysis
Leg length discrepancy
Symmetry

Topics:
Musculoskeletal: lower limb
Orthopaedics

Did this work require ethics approval? Yes

Institution: Tel Aviv Sourasky Medical Center

Committee: Israel’s Ethics Committee

Ethics number: (0055-20-TLV)