R. Philippot

Understanding wear in dual mobility total hip replacement: first generation explant wear patterns

PurposeDual mobility was introduced by Pr. G. Bousquet to improve the dislocation risk of total hip arthroplasty (THR). The wear mechanisms of this implant remain to be understood. Could enhanced explant wear analysis explain liner wear behaviour?MethodsSixty-six explanted liners were selected. Non-destructive 3D scanning and heat colour treatment allowed reporting wear patterns on both convex and concave sides of the liners.ResultsFor many liners, liner convexity wear was found to be homogeneous, and linked to a longer implantation time. A few liners had signs of blocking of the convexity, leading to excessive internal damage. Intra prosthetic dislocations were found to only have internal circular wear without liner penetration.ConclusionHeat colour treatment showed its effectiveness for highlighting wear patterns. Optimal convexity mobility seemed to be leading to a longer implantation time, with decreased contact stresses on concavity. The retentive rim should have a distinct wear analysis.

The linear penetration rate is not relevant for evaluating wear of dual mobility cups: an explant study

PurposeThe linear penetration rate (LPR) has been used to estimate volumetric wear ever since metal-on-polyethylene bearings were first introduced. Annual volumetric wear and osteolysis are interrelated. The use of dual mobility cups has increased; however, the presence of two bearings needs paraclinical monitoring of wear to anticipate potential wear-related complications. Is LPR correlated to volumetric wear?MethodsNinety-eight dual mobility liner retrievals were mapped in three-dimensions (3D) with a fully automatic stripe light scanner. Martell’s method was applied to 3D maps of the explants to determine how much the centres of the inner and outer bearings had shifted in the three planes, and in particular, penetration of the femoral head in the “z” axis. The total, inner and outer wear volumes were then compared to the shift in the centres of rotation (COR) and the pre-operative X-rays.ResultsThere was no relationship between wear and head penetration into the liner. There was a statistically significant relationship between the 3D centre of rotation shift and inner wear or total wear. Wear was multidirectional.ConclusionsLPR is ineffective for estimating wear of dual mobility inserts, since its wear not two-dimensional. In the future, a 3D imaging method with very thin slices could be used to monitor the wear of dual mobility inserts by measuring the shift in the centres of rotation, once artifacts are overcome.

The effect of femoral tunnel widening on one-year clinical outcome after anterior cruciate ligament reconstruction using ZipLoop® technology for fixation in the cortical bone of the femur

BACKGROUND The effect of femoral tunnel widening on clinical outcomes of anterior cruciate ligament (ACL) reconstruction has been rarely investigated. In this study, ACL reconstructions were performed using semitendinosus and gracilis (STG) tendon grafts and single cortical fixation on the femoral side. The aim was to analyze femoral tunnel widening at one year and to evaluate its effect on clinical and laximetric outcomes. METHODS A total of 46 patients were enrolled in this prospective continuous single-operator monocenter study. Clinical protocol included pre-operative and one-year evaluation with subjective and objective International Knee Documentation Committee (IKDC) clinical scores. Computed tomography (CT) scan was used for radiographic examination during the follow-up period. The femoral tunnel widening was measured as a three-dimensional (3D) image using OsiriX software. The cross-sectional area of each tunnel was measured at four different locations. RESULTS The subjective preoperative IKDC score was 50 and one-year postoperative score was 81.8. The side-to-side difference in knee laxity decreased from 2.94 to 0.74 mm. The objective IKDC score during the final follow-up was rated A in 27 patients and B in 17. CT scan data revealed an average of 49.32% cone-shaped widening of the femoral tunnel. Femoral tunnel widening at the level of the joint (F4) was negatively correlated with the IKDC subjective score at one year. CONCLUSIONS This study revealed a significant widening of the femoral tunnel by demonstrating its conical shape at one year post-surgery. A significant correlation could be established between femoral tunnel widening close to the joint and IKDC scores.