Background: Increased contact stress with a femoral resurfacing prosthesis implanted in the medial femoral condyle and a non-functional meniscus is of concern for potential deleterious effects on tibiofemoral contact mechanics.

Methods: Peak contact pressures were determined in seven fresh frozen human cadaveric specimens using a pressure sensitive sensor placed in the medial compartment above the menisci. A knee simulator was used to test each knee in static stance positions (5°/15°/30°/45°) and through 10 dynamic knee-flexion cycles (5°–45°) with single body weight ground reaction force (GRF) which was adjusted to the living body weight of the cadaver donor. All specimens were tested in three different conditions: Untreated knee (A); Flush implantation of a 20mm resurfacing prosthesis (HemiCAP^®) in the weight bearing area of the medial femoral condyle (B); Complete radial tear at the posterior horn of the medial meniscus with the femoral resurfacing device in place (C).

Results: On average, flush device implantation resulted in no statistically significant differences when compared to the untreated normal knee. The meniscal tear resulted in a significant increase of the mean maximum peak contact pressures by 63%, 57%, and 57% (all P ≤ 0.05) at 15°, 30° and 45° static stance positions and 78% (P ≤ 0.05) through the dynamic knee flexion cycle. No significant different maximum peak contact pressures were observed at 5° stance position.

Conclusion: Possible effects of reduced meniscal tissue and biomechanical integrity of the meniscus must be considered in an in-vivo application of the resurfacing device.

Aims: Clinical studies have revealed issues with residual particles from roughening processes on the surface of cementless stems. A new stem was therefore developed to achieve optimal primary stability in the femur but with a rough contamination-free surface for osteo-integration. Methods: TMZF, a new high strength and low modulus beta-titanium alloy was chosen for the stem to achieve optimal osseous integration. Several methods to achieve the goal of a rough and contamination free surface have been evaluated and documented by laser proþlometry, SEM and EDAX. Prototypes of the stem with different edge radii were implanted into human cadaver femora and tested with respect to their rotational stability. Early clinical experience was collected on the þrst 280 cases with currently short-term follow up. Results: With TMZF¨ a smaller neck diameter is possible, giving increased range of motion. With an improved process the required surface roughness and pattern for osteo-integration was achieved without any residual contaminants. Stems with a decreased radius of the edges of this rectangular design were less stable in the cadaver tests than those with sharp edges and the stem is manufactured accordingly. Conclusions: A straight stem (Hipstarª) with sharp edges made from a high performance titanium beta-alloy, reduced neck diameter and non contaminated rough surface, has been developed and tested in vitro and in vivo. A multicentric prospective clinical study has been initiated to conþrm the advantages of this innovative stem.