Introduction: The aim of the study is to evaluate different operation techniques after total knee arthroplasty (TKA). Functional outcome as well as objective results in activity (activity monitor) after minimal invasive TKA was compared with functional outcomes after a standard midvastus approach.

Purpose: The primary purpose of the present study was to determine the difference between two approaches in surgery of total knee arthroplasty. Is there a difference in outcome between a standard and a minimal invasive surgery because of less muscle damage and soft tissue stress?

Material and methods: The study includes two groups with 20 patients each (MIS group versus standard group) The patients are investigated at six different times: 1 day preoperatively as well as on 1., 3., 7. day postoperatively as well as 6 and 12 weeks after surgery. We used the AMP 331 (Dynastream Innovations, Inc., Cochrane, AB) a new ankle-mounted activity monitor. Step count, distance travelled, walking speed, step length, cadence and energy expenditure were measured. 1, 6 and 12 weeks postoperatively patients got the device for 5 days.

Results: The average age in the standard group was 66.4 years and for the MIS group, 66,8. The MIS group has been shown a sig. higher KSS Score versus standard group in all follow up visits. Standard group has shown a slight higher blood loss and higher values of muscle specific lab parameter (Creatininkinase and Myoglobin). The Activity Score was better in the MIS group in comparison to the standard group. These results also mirrored the data from the activity monitor (AMP 331, Dynastream Innovations, Inc., Cochrane, AB). The average walking speed at 1, 6 and 12 weeks was sig. (p< 0.05) better than in the standard group. Same trend we have seen in cadence, step length and steps per day.

Conclusion: This study shows that patient who underwent minimal invasive surgery in knee arthroplasty have an better early outcome after surgery in activity and function because of saving muscle structure and minimise soft tissue stress.