Purpose of the study: The Al/PE sandwich is a relatively new massive alumina insert for alumina-on-alumina prostheses using a meta-back press-fit cup. Theoretically, the advantages are a less rigid system and easier positioning and removal. The reliability is however still debated. The purpose of this study was to evaluate the 7-year outcomes of a homogenous series of 53 Al/Al sandwich total hip arthroplasties (THA) implanted without cement.

Material and methods: The series included 48 consecutive patients (53 hips) implanted by the same surgeon from 1998 to 2004 using the posterolateral approach. There were 26 men and 22 women, mean age 58 years (42–69). The prosthesis used a metal back cup totally coated with HA, an Al/PE sandwich insert, a modular anatomic femoral head with partial HA coating, and an alumina head (28 mm). All patients were reviewed and assessed clinically using the Harris score (/100) and the PMA score (/18) and radiographically using the Engh and Gruen and Amstutz scores.

Results: None of the patients were lost to follow-up and none died. One patient underwent revision surgery at 84 months for fracture of the alumina insert: the sandwich insert and the head were changed, and the outcome was very good at three years. At mean 84 months follow-up (47–109), the PMA and Harris scores were, on average, 17.7 and 98 (versus 12.3 and 54 preoperatively, p< 0.05). None of the patients complained of squeaking. There was no acetabular migration or lucency and no osteolysis. A partial and isolated lucent line was observe in the Gruen and Amstutz zone 1 and 8 of the femur in 26% of the hips. Calcar atrophy was noted in 17%. Wear was note radiographically measurable.

Discussion: The clinical and radiographic results appear to be very encouraging at mid term, illustrating the excellent resistance to wear of the alumina-on-alumina bearing, particularly in young and active subjects. With the type of implant used, the improvements provided by the anchorage of the alumina insert in the PE and the increased thickness (minimal 4.5 mm), the high rate of insert fracture reported by certain series in the literature was not observed here.

Conclusion: The absence of wear and osteolysis, improved implant design, and potential advantages in terms of positioning should make this system an attractive alternative for alumina-on-alumina implants.

Purpose: We tested the reliability of a digitalised x-ray reading system, Imagika(r), used to measure linear wear of total hip arthroplasy on the AP view of the pelvis.

Material and methods: Wear measurements were taken for total hip arthroplasties without cement (n=20) and with cement (n=19) using the distance between the centre of the acetabular cup and the femoral ball. The system delivered measures in hundredths of millimetres that were rounded off to the nearest tenth millimetre. For non-cemented implants, the centre of the acetabular cup was found automatically on the digitalised radiograms using the contour of the metal socket. For cemented cups, the centre of the cup was determined from five points situated on the metallic ellipse included in the polyethylene circumference. The software placed the point clicked by the reader on the adjacent intermediary zone showing the greatest contrast. Five observers read the radiograms twice at 15 day intervals. The observers were a young resident, a senior traumatology surgeon,and a senior surgeon specialised in hip surgery. Results were compared to determine inter- and intra- observer variability.

Results: Intra-observer variability was low since the standard deviation (at alpha error set at 5%) ranged from one tenth of a millimetre to six-tenths of a millimetre for four observers. It was higher (2 millimetres) for the fourth observer. The younger observers achieved the best reproducibility, to the order of a tenth of millimetre. Conversely, interobserver variability was high with standard deviation of several millimetres for an alpha risk of 5%. Comparing the two observers who achieved the best performances, the standard deviation of the measures was in the 3 to 4 millimetre range.

Discussion: Measurement precision was greater for cemented cups. Conversely, for press-fit cups, the contour of the head was sometimes difficult to distinguish even with optimal contrast and measurement deviations were to the order of one millimetre.

Conclusion: The reproducibility of the Imagika(r) system is insufficient to measure wear of total hip arthroplasty where the precision must be to the order of a tenth of a millimetre.