Introduction: In the last few years minimally invasive surgery in hip replacement is becoming more popular among orthopaedic surgeons because of less morbidity and faster rehabilitation. However several complications have been reported expecially in the so called “learning curve” (first twenty cases). The purpose of this study is to evaluate the learning curve of three different minimally invasive approaches.

Methods and Materials: In this study three different surgical approaches of THA were evaluated: lateral mini incision (GroupA), minimally invasive anterior approach (GroupB) and minimally invasive antero lateral approach (GroupC). The first twenty cases of each surgical approach were selected and compared with a control group (GroupD) of 149 total hip replacement operated using a lateral standard approach (> 12 cm) in the same period by the same experienced surgeon.

In all cases a specialized dedicated surgical instrumentation was used. Inclusion criteria to enter the study group (A-B-C Groups) were:BMI< 30, diagnosis of primary osteoarthritis, age< 75 years.

Following parameters were evaluated: intra and post operative complications, total blood loss, time of surgery, component placement, length of hospital stay and functional outcomes (HHS, WOMAC) at six weeks.

Results: No dislocations, infections and early aseptic loosening were detected in groups A, B and C. No significant differences were detected regarding the length of hospital stay in all groups. In group B the time of surgery was significantly higher than in group D. The total blood loss of group A, B and C was statistically lower than group D. Clinical outcomes at six weeks in groups B and C were significantly better that in group A and D. The following complications were detected:

Group A: two sciatic nerve palsy (one transient and one permanent), one greater trochanter fracture, one femoral stem malposition.

Group B: one greater trochanter fracture, one proximal femoral fracture, one rupture of tensor fasciae latae, two haematomas.

Group C: no complications were detected.

In control group D (149 patients) the following complications were observed: one proximal femoral fracture, one case of cup malposition and one infection.

Conclusions: The main advantages of all MIS approaches seem to be the reduced total blood loss, even in the learning curve. However during learning curve the minimally invasive approaches seem to have a higher rate of complications than the standard procedures even in selected patients. In muscle sparing approaches (anterior and antero lateral) the early functional outcomes are better than other approaches (standard and mini incision). Among the evaluated minimally invasive procedures, the antero lateral approach seems to be safer and less demanding than others.

Polyethylene wear is the most important risk factor affecting the durability of total knee arthroplasty. We developed a new method of measuring wear of the tibial polyethylene insert in total knee arthroplasty (TKA) on standard standing radiographs.

Methods: We developed a new method of measuring the shortest distance between the femoral component and the tibial metal tray taking its 3-D position into consideration. The accuracy of the method was examined in 3 conditions. An in vitro examintion measured the thickness of the polyethylene on radiographs of a new PFC prosthesis set on a table. The radiographs were taken from various directions. An in vivo examination measured the polyethylene thickness on patient discharge radiographs of 78 knees. These measurements were compared with known thicknesses of the used inserts. In the third study, wear of the tibial polyethylene insert was measured retrospectively in a series of 84 PFC TKAs with follow-up of 2 to 10 years (6.6 years on average).

Results: The average measurement error was 0.05 mm (SD 0.09 mm) in the in vitro study and 0.14 mm (SD 0.17 mm) in the in vivo study using discharge radiographs. In the series of 84 PFC TKAs, impending failure occurred in 7 knees, 4 of which were revised. Radiographically measured wear of the tibial insert was significantly greater in these failed TKAs than in the other TKAs. The radiographic measurements were well correlated with 3-D measurements of 4 retrieved inserts.

Discussion: Although the radiographic measurement of the tibial insert in TKA was less accurate than that of the socket in THA, it is useful enough to identify TKAs at risk of failure. When the radiographic wear exceeded 1mm, there was a significantly increased probability of impending failure or need for revision.