Tapered femoral stems can be described by their geometry: single taper, double taper, and triple taper. Single-taper stems have a reduction (taper) in medial-lateral dimension in the frontal plane but have a constant anteroposterior dimension. Double-taper stems have tapers in the frontal plane and sagittal plane. Triple-taper stems include a reduction in anteroposterior dimension through the cross section of the stem from lateral to medial (the third taper), in addition to tapers in the frontal and sagittal planes (Fig. 17-1). Tapered femoral stems can also be described by their surface finish or coating: grit-blasted, hydroxyapatite (HA), plasma spray, or porous ingrowth. The stems vary in the degrees of tapering as well as their length. There are also differences in neck-shaft angle and/or offset. Virtually, all cementless tapered stems are made from titanium alloy because of its biocompatibility and relatively low stiffness. While there are debates regarding the benefits and trade-offs of various design variables, the tapered stem class has been clinically successful over three decades.

Preoperative radiographs need to show all of the femur that will be occupied by the stem in both the AP and lateral planes. It is recommended that templating be performed on a low AP pelvis x-ray to facilitate assessment of limb length and offset (Fig. 17-2). Acetabular templating is done first since the acetabular component establishes the center of rotation of the arthroplasty. The primary goal is obtaining adequate bony support for the component. For most cases, a target of 45 degrees of abduction is satisfactory. The acetabular tear drop is a consistent reference for the medial wall. An adequately sized acetabular component will approach the medial wall and be supported by superolateral bone.

For femoral templating, separately consider the part of the component inside the bone (the fit of the stem), from the part outside the bone (the neck and head), that determine the biomechanics of the reconstruction. An appropriately sized tapered femoral component may or may not be canal filling but fits the metadiaphyseal region (Fig. 17-2). The vertical position of the template on the radiograph influences the location of the neck osteotomy. There are essentially two ways to make limb length adjustments: the vertical position or height of the stem inside the canal and modular femoral heads. The “neck length” of a modular femoral head influences both length (vertical component) and offset (horizontal component), while the vertical position of the stem only influences length. The vertical position of the stem determines the location of the neck osteotomy.

The limb length and offset change for the proposed reconstruction can be assessed on the templates by comparing the location of the center of rotation of the acetabulum to the location of the center of rotation of the selected modular femoral head. For the templating exercise, consider the acetabular center of rotation as a fixed reference and the femoral head center as variable. When the selected head center directly overlies the acetabular center, there is no change in the limb length or hip offset when such a plan is executed surgically. If the acetabular center of rotation is medialized, then the femoral offset will be increased by a corresponding amount. When the head center on the templating is superior to the acetabular center, limb length will be gained when the hip is reduced at surgery. When the head center is medial to the acetabular center on the template, then relative femoral lateralization (increased offset) will occur when such a plan is executed surgically.

Many tapered stems are available with more than one offset, that is, standard and high. Some systems accomplish this by changing the neck-shaft angle, with the higher offset option having a lower neck-shaft angle. Other systems maintain the same neck-shaft angle and increase offset by medializing the take off point of the femoral neck (Fig. 17-3). Together with the modular heads, these options enable the surgeon to better achieve both the desired limb length and offset for a given hip.