Introduction: The stress-response to surgery, known as a variety of well-characterized hormonal, metabolic, haematological and immunological changes, may be smaller in less invasive operations. Decreased blood loss, less soft tissue damage and inflammation leading to fast recovery are arguments used in promoting minimal invasive surgery (MIS).

Purpose: Does MIS TKR with the subvastus approach lead to less inflammation and muscle damage than conventional TKR with the medial parapatellar approach?

Material and Methods: Inflammation parameters (IL-6, IL-8 and IL-10, and CRP), muscle damage parameters (myoglobin, CK) and Hb values were determined preoperative and at 5 moments postoperative in 41 patients. Twenty patients operated through a MIS subvastus approach were compared to 21 patients with the standard medial parapatellair approach.

Results: Average age in was 69.2 yrs in conventional TKR (contr) versus 68.9 yrs in MIS. The Hb levels were 13.9 g/dl preoperative and decreased to 10.8 g/dl (contr) and 11.6 g/dl (MIS) 72 hours postoperative.

The mean IL-6 concentration increased from 6.8 (contr) vs 1.3 (MIS) pg/ml to 68.8 (contr) vs 45.1 (MIS) pg/ml 6 hours postoperative. The mean myoglobin concentration increased in TKP group from 47.7 ug/l pre-operative to 90.1 ug/l 6 hours postoperative, the values for MIS were 27.8 μg/l preoperative and 202.3 ug/l 6 hours postoperative, with significant differences at 2, 4, 6 hrs and day 1 post-operative.

Conclusion: Haemoglobin levels show no significant differences between conventional and MIS approach. Inflammation parameters were not significant different between the two groups. Myoglobin was the only muscle damage parameter with significant differences on several time points between both approaches. This may be explained by the used forces on surrounded tissues. The retractors are necessary to visualise the knee joint in MIS. These results show a trend towards more muscle damage compared to conventional TKR.