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.

Introduction: In total hip arthroplasty (THA) polyethylene (PE) wear debris is major cause of osteolysis and aseptic implant loosening. Wear particle volumes must be reduced to increase implant survival. Various ways of crosslinking the molecular chains of PE have been proposed to increase the wear resistance of the bearing material but prospective long-term follow-up studies are scarce.

Materials & Methods A crosslinked PE acetabular insert was developed by gamma irradiating in a nitrogen atmosphere at a dose of 3MRad and subsequent annealing at 50° C for 144 hours to promote further crosslinking (“Duration” process). The Duration PE was compared to a conventionally prepared PE insert (irradiated at 3 MRad in air, no annealing) in a series of small punch tests, a hip wear simulator study and in-vivo as part of a randomized double-blind clinical study at three medical centers the PE-insert being the only variable. A total of 127 patients with 133 inserts (67 conventional, 66 Duration) were followed up between three and five years post-operatively. Wear was measured yearly by using a computer-based image analysis system. Radiographic appearance of potentially wear related phenomena such as osteolysis or loosening was assessed by an independent reviewer.

Results: Higher load at break during the small punch test confirmed the elevated crosslinking levels of Duration PE against the conventional PE. In the joint simulator Duration PE showed significantly lower volumetric wear rates (Mean SD: 21.7 2.3 mm3/10E6 cycles) than conventional PE (39.7 1.5 mm3/10E6 cycles, p< 0.05). A corresponding and significant level of wear reduction for the Duration PE was identified in-vivo (Duration: 43.7 33.6 mm3/year, conventional: 60.4 42.7 mm3/year, p=0.04). Radiographic analysis at the last follow-up gave evidence of femoral osteolytic lesions in five hips with conventional PE inserts and only one hip with a Duration insert.

Conclusions: Acetabular inserts made of crosslinked PE using the Duration process can significantly reduce in-vivo wear rates and the occurrence of potentially wear related osteolytic effects in the long-term follow-up of THA patients. The reduced clinical wear rates corresponded well with the results from the wear simulator measurements. This suggests that a PE with further increased crosslinking which shows even lower wear rates in simulator studies will lead to even lower wear and associated osteolysis in long-term clinical application.