Purpose of the study: When the acetabular component is revised alone, if the femoral stem has not been loosened, the question becomes what should be done about the osteolysis of the femur: Change the femoral piece systematically and graft the osteolysis? Curettage and grafting of the osteolysis? Curettage alone? This study reports the outcome of superior femoral osteolysis with a calcar granuloma and no other procedure (no curettage) after replacing the cup.

Material and methods: This was a retrospective analysis of 54 acetabular revisions performed from 1988 to 1998. The cemented femoral piece was stable, with no lucent line and in position since the initial implantation. The reoperation consisted in cementing a new polyethylene cup (< 32 mm) with or without a graft. The femoral head was initially ceramic (alumina 29 and zircon 25) and was preserved in ten cases (alumina) and changed systematically for the zircon heads. New heads were implanted: 20 alumina (32mm) and 24 metal. Calcar osteolysis was measured in mm² on the x-rays before and after changing the acetabular piece and then regularly every year to last follow-up (10 to 20 years).

Results: Preoperatively, superior femoral osteolysis was 156 mm² (48–576m²) situated in Guren zone 1 and 7. At last follow-up, it was 135 mm² (38–616 mm²) with no femoral loosening, decreased in 34 cases, unchanged in 11 and increased in 9. Spontaneous decline in preoperative osteolysis was observed when the bearing was alumina-polyethylne and the preoperative osteolysis was less than 100 mm². Increased osteolysis (minor but undeniable) was observed with the couple was metal-polyethylene and when the preoperative osteolysis was > 300 mm².

Discussion: If the superior femoral osteolysis does not compromise the stability of the femoral implant when undertaking isolated revision of the acetabular component alone, it can be neglected. Changing the bearing stabilizes the progression of the osteolysis and does not appear to compromise the mid-term outcome (15 years) for the femoral piece. Spontaneous decline of the osteolysis can be observed if the initial osteolysis is less than 1 cm² and if the new bearing is alumina-polyethylene.

Purpose of the study: In vivo kinematics of the knee joint (anteroposterior translation or rollback, axial rotation, elevation of the femoral condyle, range of motion) was determined for the knees of 30 subjects with a total knee prosthesis with a fixed or mobile plateau and also for the normal knees.

Material and methods: Videofluoroscopic images were recorded during gait and maximal flexion. An automatic 3D adaptation-modelling process was then applied to the fluoroscopic images to determine knee kinematics.

Results: For the normal knee, a certain degree of femoral rollback was noted for the lateral compartment (4.2 mm on average) while minimal translation was observed medially. The femoral rollback increased laterally during maximal flexion (14.4 mm on average) while the medial translation was minimal (1.5 mm on average). Thus, the average movement, which was not observed for all normal knees tested, was a pivot movement centred medially. The variability observed during maximal flexion was wide for all knee prostheses with a fixed or mobile plateau which do not have a stabilising system substituting for the absent posterior cruciate. During flexion, the normal knees exhibited mean 10° external rotation of the over the tibia. All of the rotational knee prostheses presented external rotation (mean 5°, ragne 0–10°). Inversely, the posterostabilised prostheses exhibited medial rotation of the femur over the tibia (mean 5°, range 0–10°), i.e. paradoxical movement.

Discussion: Unlike the normal knee where femoral rollback occurs during maximal flexion, paradoxical anterior translation of the femorotibial point of contact after arthroplasty, in particular in subjects with a fixed plateau prosthesis. For prostheses substituting for the posterior cruciate, femoral rollback involving the lateral condyle occurs regularly with minimal variability in the femorotibial contact point due to the regular engagement of the cam and cam follower mechanism during maximal flexion.

Purpose of the study: The alumina-polyethylene bearing has been used for many years but no study has evaluated polyethylene wear and osteolysis with a 32 mm head with a follow-up exceeding 20 years.

Material and methods: Thirty-six arthroplasties implanted between 1983 and 1985 (26 patients, mean age 54 years, range 35–65 years) were studied. The same cemented implants were used in all cases, with no loosening. Penetration of the head into the polyethylene was measured annually on digital radiographs and with computer assistance. Osteolysis was quantified in mm² on the merckel.

Results: At 20 years follow-up (minimum) or more, penetration of the femoral head into the cup was on average 0.07mm/y. The characteristic feature of the wear curve was the perfect stability after the third year and the absence of any increase over time. Extrapolation of the straight part of the curve to the origin determined the creep. True wear was limited: 0.05mm/y. It was not modified by the polyethylene thickness (eight 52mm cups, twenty-three 50mm and five 48mm). Corresponding volumetric wear was estimated at 640 mm3 at maximum follow-up. At last follow-up, osteolysis measured in mm² on the meckel was 65 mm² on average. In general, this osteolysis appeared around the second year with an imprint on the merckel; it then increased linearly and regularly to the 20th year. Acetabular osteolysis was nevertheless greater than that observed with the Al/Al bearing of controlateral hips implanted at the same period when evaluated on the scan for both hips (20 cases).

Discussion: The alumina-polyethylene bearing enables long implant survival for at least 20 years, even for relatively thin polyethylene thicknesses. The characteristic feature of the bearing is the linear polyethylene wear which does not increase with time but remains constant, undoubtedly in relation to the absence of any change in the roughness of the head despite the very long follow-up. Osteolysis remains minimal, but superior to that observed with Al/Al bearings implanted during the same period in controlateral hips.