Excellent Initial Stability - 3D SEE Trabecular Titanium Cup

Excellent initial stability is a prerequisite for achieving robust bone integration in non-cemented acetabular cups. This high initial stability effectively restrains micromotion, which is essential for both osseous attachment and long-term biomechanical fixation.

Key technical factors influencing the initial stability of non-cemented total hip arthroplasty (THA) acetabular cups include Acetabular Cup Surface Characteristics, Cup Geometry, Press-Fit Technique, and Acetabular Screw Fixation.

Acetabular Cup Surface Characteristics

The surface characteristics of acetabular cups, including porosity and friction properties, are crucial technical factors for enhancing stability. Clinical studies indicate that highly porous surfaces of trabecular metal acetabular cups exhibit a friction coefficient that is 40% to 75% higher compared to regular coated cups. This surface attribute facilitates adequate initial stability even in cases of suboptimal press-fit but also aids in countering micromotion induced by joint motion displacement forces.

• Stability

The JUST 3D-printed trabecular metal acetabular cup, produced using electron beam melting (EBM) technology, boasts a high surface roughness and a design with a 75% to 80% porosity rate. This design achieves a friction coefficient of 1.08, ensuring exceptional initial stability.

Acetabular Cup Geometry

The acetabular cup cavity's dimensions and depth significantly impact the cup's initial stability.

Clinical studies have revealed that stability is a function of the contact area between the cup rim and the host bone. If the cup cavity is too small or shallow, and the host bone is challenging, the cup might not sit securely on the acetabular rim, compromising stability. Furthermore, if there are bone defects at the acetabular boundary, the interface contact area diminishes, which in turn affects stability.

Acetabular cups designed with an actual hemispherical shape offer a larger interface contact area at the rim than "low-profile" cups, resulting in more excellent stability. From a surgical perspective, the design of hemispherical cups allows for accurate insertion into the acetabular component without excessive force. This approach avoids incomplete articulation due to suboptimal positioning of the acetabular component, inadequate residual compressive forces, and consequent excessive micromotion of the prosthesis.

• Stability

The JUST 3D SEE Trabecular Titanium Cup incorporates the well-proven exterior design and cup liner locking mechanism of the clinically validated HARMONY 180° cup, ensuring exceptional initial stability.

Press-fit technique for acetabular cups

The initial stability of a press-fit cup follows the anchoring principle of a rigid body being slightly larger than an elastic body: axial load increases press-fit, thereby enhancing initial stability. Clinical recommendations advocate using a 1-2mm press-fit technique to ensure ample contact between the acetabular implant and the surrounding bone while minimizing any gap at the cup's apex.

• Stability

The bone trabecular porous layer thickness of JUST 3D SEE Trabecular Titanium Cup is 1.5mm, taking into full consideration the clinical requirements for the press-fit technique.

Acetabular Screws

In cases where the host bone of the acetabulum is extremely hard, or the dome formed by reaming is smaller than expected, the acetabular cup may have difficulty contacting the bottom of the bony bed. This is due to the fact that the extreme point of the acetabular cup cannot reach the intended depth. In such situations, a gap may form between the bone and the implant, and attempting forceful impaction to eliminate the gap might lead to periprosthetic bone fractures.

Conversely, in cases where reaming is more considerable, particularly in elderly patients with osteoporotic bone, initial press-fit fixation might not suffice to achieve excellent initial stability.

In both scenarios, surgeons can consider using screws for supplementary fixation to achieve optimal initial stability.

JUST 3D SEE Trabecular Titanium Cup offers three different models: Dysplasia (DDH), Standard Primary, and Revision. Each model comes with distinct screw-hole designs. Notably, the Trabecular Titanium Cup and HARMONY Acetabular Cup share compatible screw options.

References

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