Age-related appearance of muscle trauma in primary total hip arthroplasty and the benefit of a minimally invasive approach for patients older than 70 years

Old age is frequently associated with a poorer functional outcome after THA. This might be based upon muscular damage resulting from surgical trauma. Minimally invasive approaches have been widely promoted on the basis of the muscle sparing effect. The aim of the study was to evaluate of the functional outcome and the grade of fatty muscle atrophy of the gluteus medius muscle by magnetic-resonance-imaging (MRI) in patients undergoing minimally invasive or traditional THA. Forty patients (21 female, 19 male) underwent THA either via a modified direct lateral (mDL) or a minimally invasive anterolateral (ALMI) approach. Patients were evaluated clinically and by MRI in terms of age (< or ≥70 y) preoperatively and at three and 12 months postoperatively. The Harris hip score and Trendelenburg’s sign were recorded and a survey of a pain (using a numeric rating scale of 0–10) and satisfaction score (using a numeric rating scale of 1–6) was performed. Fatty atrophy (FA) of gluteus medius muscle was rated by means of a five-point rating scale (0 indicates no fat and 4 implies more fat than muscle). Younger patients reached a significantly higher Harris hip score, lower pain score and lower rate of positive Trendelenburg’s sign accompanied by a significantly lower rate of postoperative FA (P = 0.03; young: FA (MW) = (preop. / 3 / 12 months), 0.15 / 0.7 / 0.7; old: FA (MW) = 0.18 / 1.3 / 1.36). Older patients with an mDL-approach had the significantly lowest clinical scores, the highest rate of positive Trendelenburg’s sign and also the highest rate of fatty atrophy (P = 0.03; FA (old) mDL: 1.8; ALMI: 0.7). Interestingly, no influence of the approach could be detected within the younger group. Patients older than 70 years had a poorer functional outcome and a higher postoperative extent of FA when compared to younger patients, which must be based upon a higher vulnerability and a reduced regenerative capacity of their skeletal muscle. Through a minimally invasive approach the muscle trauma in older patients can be effectively reduced and thus the functional outcome significantly improved. Incision and detachment of tendons and muscles should be strictly avoided.