Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1992-04-27
1993-07-13
Green, Randall L.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 238
Patent
active
052269167
DESCRIPTION:
BRIEF SUMMARY
This invention concerns prosthetic femoral components of tricompartmental form for replacement of the patellar facet and both tibal facets of the distal femur.
Components of this kind have been in routine use for some years, typically, although not exclusively, for total knee joint replacement in association with other components to replace the femoral facets of the proximal tibia and also the femoral facet of the patella. However, there is a current concern with the rates of failure found to arise with such other components due to various causes.
An object of the present invention is to reduce these failure rates and pursuit of this objective finds its basis in an on-going programme of development and analysis which began in the early 1970s. The first practical result of this programme was a proposal for an improved knee joint device, described in GB Patent No. 1,534,263, involving femoral, tibial and meniscal components co-operable to allow movement closely simulating that of the natural joint of flexion-extension and, at the same time, congruence at the articulation interfaces of the device. A feature of this proposal was that the femoral components could have spherically shaped tibial facets.
It has, since then, been found that the tibial facets in the natural femur in fact closely approximate spherical shaping. More recently, it has been found that the sulcus of the trochlea, the base of the patellar facet of the distal femur, closely approximates circular arcuate shaping in the sagittal plane. Most recently, it has been found that there is a sufficiently predetermined relationship between the dimensions and spacing of these shapings to allow adoption of the same in a tricompartmental femoral component.
One benefit of such a component is that it further extends the possibilities for knee joint replacement while attaining benefits similar to those of the above mentioned patent, that is to say, a capability for closer simulation of natural femoral shaping as well as close simulation of natural movement with a high degree of congruence at articulation interfaces. Another benefit is that production of such a component is facilitated by simplification of its geometry relative to prior art tricompartmental femoral components in current use whereby, when made in metal as will normally be the case, the former is more readily amenable to finish machining while the latter is usually polished directly from a cast form.
In any event, a tricompartmental femoral component according to the present invention comprises an integrated body defining two articulation surfaces of spherical shape in spaced side-by-side disposition to assume the roles of respective tibial facets, and a further articulation surface in the form of a groove extending longitudinally in off-set manner sagittally between said two surfaces to assume the role of patellar facet, said groove having circular arcuate longitudinal shape.
In terms of dimensions, the spherical shapes are preferably of the same radius of curvature as each other and the circular arcuate shape is of the same order of radius. As presently contemplated the arcuate shape will normally be of greater radius than the spherical shape by a minor proportion of the latter, suitable at about 1.2:1.
In terms of spatial relationship, the centres of the spherical shapes are coincident as seen in a lateral aspect, with the centre of the arcuate shape being relatively off-set by about 0.4 R superiorly and 0.6 R anteriorly, where R represents the radius of the spherical shapes, and the arcuate shape is essentially centrally located between the spherical shapes when viewed along a sagittal direction with the centres of the latter spaced at about 2.3 R.
The transverse cross-section of the groove may be of circular, rounded triangular or other shape to accommodate the natural patella or a patellar component.
These features of the present invention are exemplified by way of an initial embodiment of the latter illustrated in the accompanying drawings, in which:
FIGS. 1, 2 and 3 diagrammatically il
REFERENCES:
patent: 3728742 (1973-04-01), Averill et al.
patent: 3806961 (1974-04-01), Muller
patent: 4085466 (1978-04-01), Goodfellow et al.
patent: 4094017 (1978-06-01), Matthews et al.
patent: 4215439 (1980-08-01), Gold et al.
patent: 4309778 (1982-01-01), Buechel et al.
patent: 4340978 (1982-07-01), Buechel et al.
Goodfellow John W.
O'Connor John J.
British Technology Group Limited
Green Randall L.
Jones Mary Beth O.
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