Design

The SL-PLUS has evolved from years of highly successful clinical results in Europe and is well optimized.

Dual-Taper Rectangular Geometry

Trochanter Wing
Polynomial Calcar Arch
Prosthesis Neck
Trunion
Insertion/Extraction Device
Rounded Tip

High Primary Stability

Long-term success of any hip prosthesis is dependant upon achieving primary stability. This is especially true for a cementless system. The prosthesis must be stable and free of micro-motion for osseointegration to be encouraged.

The SL-PLUS is specifically designed for both primary and long-term stability. Numerical approximation was used to generate its unique contour which approximates a taper distally and the femur's anatomy proximally, providing secure axial positioning of the stem. In addition, the rectangular form anchors the stem rotationally. This initial stability allows time for osseointegration, creating secondary stability and helping ensure long term success.

Also, the intuitive surgical technique adds to long term stability. Because the site is broached instead of reamed, bone particles stay in the periprosthetic region. These bone particles are highly osteogenic, which increases the possibility of secure fixation.

	Micromotion of the SL-PLUS stem in comparison to a oval press-fit stem with respect to bone as determined using the finite element technique.

Rotational Stability

A hip prosthesis sees a number of different loads. In additional to high compressive loads, it also must handle rotational loads. The SL-PLUS's rectangular shape address this issue. The rectangular corners provide a mechanical interlock with the cortical bone. Mathematical modeling (FEA) has shown this design to have significantly reduced micro-motion compared to an idealized canal filling stem design. Micro-motion inhibits osseointegration, reducing long-term stability.

Maintains Space in Medullary Canal

For long-term prosthesis success, the surrounding bone must remain healthy and nourished. The femur's medullary space is vital for bone nutrition. Some stem designs fill the entire medullary canal, destroying the endosteal blood supply.

The SL-PLUS, with its flat sides, does not completely fill the medullary canal. By maintaining this area, the endosteal blood supply is still maintained, increasing long-term prosthesis success by promoting healthy bone.

Trochanter Wing

Primary stability is critical for a cementless stem system. In addition to the double taper rectangular geometry, the trochanter wing acts as stabilizing element. It also increases the overall proximal surface area for cementless fixation.

Polynomial Calcar Arch

The SL-PLUS incorporates a calcar arch specifically designed to replicate the natural anatomic shape of the calcar. This shape helps better approximate the natural physiologic load transfer pattern for maintenance of healthy bone stock.

Prosthesis Neck

Dislocation can result from impingement between the prosthesis neck and the acetabular cup. The SL-PLUS prosthesis neck has been optimized to provide strength and a large range of motion. It features a narrow diameter, which decreases impingement and produces greater range of motion. Strength is added to the neck by reinforcing it superiorly where the stress is concentrated.

Trunion

The interface between the ball head and the trunion is critical especially with ceramic ball heads. The ball must fit securely and have optimal contact for a correct and even load transfer. High spots at the interface can lead to stress concentrations and failures. Our trunion combines an industry standard 12/14 taper, with a micro-ridge surface. The micro-ridge surface deforms slightly to absorb local incongruencies upon ball impaction, which produces a conforming interface between the stem and ball head. Load distribution is then optimized for optimal strength.

 

Insertion/Extraction Device

Long-term success depends on precise surgical technique. The insertion device is purposefully aligned with the long axis of the stem to ensure accurate surgical placement and prevent tilting.

 

Rounded Tip

A complaint from patients with some stems is post-operative thigh pain. This is often caused by a sub optimal transition of the stem tip to the bone coupled with a material that is too stiff. To avoid this problem, the SL-PLUS has a rounded, tapered tip and utilizes titanium alloy for its low stiffness. This significantly reduces localized stresses, avoiding thigh pain.