Abstract: An enhancer element for use in intraoperative assessment of coupling of an orthopaedic implant to a bone is disclosed. The implant and the bone form an implant-bone system having a first set of vibrational modes with a first mode density in a frequency range, wherein the enhancer element is mechanically couplable to the orthopaedic implant to form an enhancer-implant-bone system having a second set of vibrational modes with a second mode density in the frequency range, wherein the second mode density is greater than the first mode density. The enhancer element is mechanically couplable to a first end of the orthopaedic implant so that it is adapted to receive impaction blows for introducing the implant to the bone. During a vibrational measurement, the vibrational response of the enhancer-implant-bone system provides information about the stiffness of the enhancer-implant-bone system.

Abstract: A protective helmet is described comprising: an outer layer (1); an inner layer (5) for contact with a head of a wearer; and an intermediate layer (3, 4) comprising an anisotropic cellular material comprising cells having cell walls, the anisotropic cellular material having a relatively low resistance against deformation resulting from tangential forces on the helmet. The anisotropic material can be a foam or honeycomb material. The foam is preferably a closed cell foam. The helmet allows tangential impacts to the helmet which cause less rotational acceleration or deceleration of the head of the wearer compared to helmets using isotropic foams while still absorbing a significant amount of rotational energy.