It is proposed that the use of biochemical markers for muscle damage and inflammation provides an objective measure on invasiveness in total hip arthroplasty. We analyzed levels of creatine kinase and C-reactive protein (CRP) after total hip arthroplasty in patients randomized to minimally invasive direct anterior approach or direct lateral approach, also recording consumption of pain medication and levels of pain postoperatively. Eighty-three patients were operated by the use of anterior approach and eighty using lateral. Creatine kinase and CRP levels were measured preoperatively, creatine kinase directly after surgery, and both creatine kinase and CRP on postoperative day 1 through 4. The use of pain medication and levels of pain were recorded. Creatine kinase were higher in the anterior group compared to the lateral group, reaching statistical significance directly postoperative and on day 4. Levels of CRP did not differ, reaching a maximum of mean 52 mg/L on day 3. The use of pain medication was higher in the lateral group on the day of surgery (p ¼ 0.011), and pain levels were higher on all days in the lateral group (p < 0.007). In conclusion, the use of minimally invasive anterior approach caused less pain, but higher postoperative levels of CK, than the use of direct lateral approach. ß

Level I, therapeutic study.