Isokinetic dynamometry and gait analysis reveal different hip joint status in patients with hip dysplasia

Background: Objective assessment of hip dysplasia patients’ functional hip joint status routinely involves gait analysis
or isokinetic dynamometry. However, these methods have shown equivocal results and have not been employed in the
same groups of patients and controls.

Purpose: To assess hip flexor and abductor moments by isokinetic dynamometry in the dysplasia patient and controls,
for which we previously reported smaller flexor and slightly larger abductor moments during gait in patients compared
to controls.

Methods: The study was designed as a prospective cohort study (Level of Evidence II) and conducted in a biomechanics
laboratory at Aarhus University, Denmark, during 2011. Participants comprised 32 dysplasia patients and 32 age and
gender matched controls. Outcome measures were static peak hip flexion moment at 15, 45 and 75° hip flexion;
dynamic eccentric and concentric peak hip flexion moment at 60° and 120°/second; dynamic eccentric and concentric
hip abductor moment at 30° and 60°/second.

Results: Hip dysplasia patients had smaller eccentric peak flexion moments and smaller eccentric and concentric peak
abduction moments at all tested velocities.

Conclusion: Although dysplasia patients have weaker hip flexion and abductor muscles than controls, their abductor
muscles are sufficiently strong to ensure normal function during gait. Hence, gait analysis alone might not reveal the
true, subnormal hip joint status in dysplasia patients. We suggest that comprehensive assessment of hip joint function in
dysplasia patients should include more strenuous activities than gait, particularly in young(er) patients who are likely to
prefer a more active lifestyle.