Asymmetric tibial components for a knee prosthesis
An orthopedic tibial prosthesis includes a tibial baseplate with features designed for use with small-stature knee-replacement patients. The tibial prosthesis may include a shortened tibial keel, tibial keel fins which define a large angle with respect to a longitudinal axis of the keel, and/or tibial keel fins which extend along less than the entire longitudinal extent of the keel.
1. A small-stature tibial baseplate comprising one of a smallest two nominal sizes of baseplate in a family of baseplates of similar design, the baseplate comprising:
a tibial plateau comprising:
a distal surface sized and shaped to substantially cover a proximal resected surface of a tibia;
a proximal surface opposite the distal surface, the proximal surface having a lateral compartment and a medial compartment opposite the lateral compartment, wherein the lateral compartment is asymmetric with respect to the medial compartment about a component anteroposterior axis to define a component asymmetry; and
a peripheral wall extending between the distal surface and the proximal surface, wherein a total surface area bounded by the peripheral wall of the tibial plateau is between about 1390 mm 2 and about 1580 mm 2 ;
a tibial keel extending distally from a junction with the distal surface to an opposing distal tip, the tibial keel having a longitudinal extent defined between the junction and the distal tip; and
a medial fin and a lateral fin extending from the tibial keel and together having a medial/lateral fin extent at the junction of about 40 mm;
wherein the tibial plateau of the small-stature tibial baseplate has a periphery less than a periphery of any other nominal size of baseplate in the family, and a ratio of the medial/lateral fin extent to the longitudinal extent is greater than the same ratio for any other nominal size of baseplate in the family.
2. The small-stature tibial baseplate of claim 1 , wherein the longitudinal extent of the tibial keel is about 27 mm.
3. The small-stature tibial baseplate of claim 1 , wherein a first diameter of the tibial keel at the junction is greater than a second diameter of the tibial keel at the distal tip, and the tibial keel has a tapered outer profile extending between the first diameter and the second diameter.
4. The small-stature tibial baseplate of claim 3 , wherein the tapered outer profile of the tibial keel defines a taper angle of about 9 degrees.
5. The small-stature tibial baseplate of claim 1 , wherein at least one of the medial fin and the lateral fin extends along less than an entire longitudinal extent of the tibial keel.
6. The small-stature tibial baseplate of claim 5 , wherein at least one of the medial fin and the lateral fin extends along about 74% of the entire longitudinal extent of the tibial keel.
7. The small-stature tibial baseplate of claim 1 , wherein the tibial keel has a minimum diameter along the longitudinal extent of at least 13 mm.
8. The small-stature tibial baseplate of claim 1 , wherein the tibial keel defines a tapered bore extending proximally into the tibial keel from the distal tip of the tibial keel, the tapered bore sized to receive a correspondingly tapered proximal end of a tibial stem extension, such that the tapered proximal end of the tibial stem extension forms a locking taper connection with the tapered bore.
9. The small-stature tibial baseplate of claim 8 , wherein:
the tibial keel comprises a set screw aperture extending from an outer surface of the tibial keel to an inner surface defined by the tapered bore; and
the tapered proximal end of the tibial stem extension comprises an annular groove positioned to align with the set screw aperture when the locking taper connection is formed between the tibial stem extension and the tapered bore.
10. The small-stature tibial baseplate of claim 9 , in combination with a set screw receivable within the set screw aperture, the set screw extending into the annular groove to form a secondary locking mechanism preventing relative axial movement between the tibial stem extension and the tibial keel when the locking taper connection is formed between the tibial stem extension and the tapered bore.
11. The small-stature tibial baseplate of claim 1 , wherein the tibial plateau defines an overall medial/lateral extent of between about 57 mm and about 61 mm.
12. The small-stature tibial baseplate of claim 1 , wherein the medial fin and the lateral fin each span only a portion of the junction between the tibial keel and the tibial plateau, and wherein each of the medial fin and the lateral fin have a fin edge comprising a planar portion defining an angle of about 45 degrees with respect to a longitudinal tibial keel axis.
13. The small-stature tibial baseplate of claim 12 , wherein the medial/lateral fin extent comprises about 40 mm.
14. A small-stature tibial baseplate comprising one of a smallest two nominal sizes of baseplate in a family of baseplates of similar design, the baseplate comprising:
a tibial plateau comprising:
a distal surface sized and shaped to substantially cover a proximal resected surface of a tibia;
a proximal surface opposite the distal surface, the proximal surface having a lateral compartment and a medial compartment opposite the lateral compartment, the lateral compartment is asymmetric with respect to the medial compartment about a component anteroposterior axis to define a component asymmetry; and
a peripheral wall extending between the distal surface and the proximal surface, wherein a total surface area bounded by the peripheral wall of the tibial plateau is between about 1390 mm 2 and about 1580 mm 2 ;
a tibial keel extending distally from a junction with the distal surface to an opposing distal tip, the tibial keel having a longitudinal extent defined between the junction and the distal tip, the tibial keel comprising a first diameter at said junction between said distal surface and said tibial keel and a second diameter at said distal tip of said tibial keel, each of the first diameter and the second diameter equal to or greater than 13 mm, the first diameter greater than the second diameter; and
a medial fin and a lateral fin extending from the tibial keel and adjoining the distal surface of the tibial plateau, together the medial fin and the lateral fin have a medial/lateral fin extent at the distal surface, wherein the tibial plateau of the small-stature tibial baseplate has a periphery less than a periphery of any other nominal size of baseplate in the family, and a ratio of the medial/lateral fin extent to the longitudinal extent is greater than the same ratio for any other nominal size of baseplate in the family.
15. The small-stature tibial baseplate of claim 14 , wherein each of the medial fin and the lateral fin has a fin edge comprising a planar portion defining an angle of about 45 degrees with respect to a longitudinal tibial keel axis.
16. The small-stature tibial baseplate of claim 14 , wherein a first diameter of the tibial keel at the junction between the distal surface and the keel is greater than a second diameter of the keel at the distal tip, and the tibial keel has a tapered outer profile extending between the first diameter and the second diameter, and wherein the medial and lateral fins extend along less than an entire longitudinal extent of the tibial keel.
17. The small-stature tibial baseplate of claim 14 , wherein the medial fin mates with the distal surface at the medial compartment, the lateral fin mates with the distal surface at the lateral compartment, and wherein the medial/lateral fin extent is about 40 mm.
18. The small-stature tibial baseplate of claim 14 , wherein the tibial plateau has an overall medial/lateral extent of between about 57 mm and about 61 mm.