The purpose of the present investigation was to evaluate muscle damage one year after anterior minimally invasive THA by MRI and to compare these findings with MRI investigations performed in asymptomatic patients one year after THA using a conventional direct lateral approach.

Institutional review board approved this study and patients gave signed informed consent. The minimally invasive group consisted of a consecutive series of 25 patients 1 year after anterior minimally invasive THA. The historic control group consisted of a consecutive series of 25 asymptomatic patients (no pain, no limb, full abduction strength) 1 year after conventional THA. Excluded were patients having prior hip surgery or suffering lumbar spine pathology. Tendon defects and degenerations within the insertion of the Gluteus medius and minimus muscles as well as fatty atrophy within these muscles were recorded according to the protocol of Pfirrmann et al. A Mann-Whitney U Test, two sided t-test and Chi-square test were used for appropriate comparison of quantitative and qualitative variables, respectively.

In terms of gender, age, BMI and side no significant differences were shown between the two groups. When compared to the conventional group, tendon defects, diameter changes and signal alterations of the Gluteus medius and minimus insertion were significantly less frequent in the minimally invasive group (p= 0.001–0.03). Fatty atrophy within the gluteus minimus and gluteus medius musculature was significantly less in the minimally-invasive group (p=0.001–0.04).

In terms of structural damage to muscles and tendons of the hip abductors, the anterior minimally invasive approach proves to be less invasive than the direct lateral approach.