Understanding hip implant components at a conceptual level helps clarify how a total hip arthroplasty device recreates the function of a natural joint. This overview breaks down the four core components — the femoral stem, acetabular cup, liner, and femoral head — and their respective design roles.
What Is the Femoral Stem?
The femoral stem is the component inserted into the prepared canal of the femur (thighbone). It is designed to anchor the implant within the bone, whether through cemented fixation, cementless press-fit fixation intended to support bone ongrowth, or a combination approach. Femoral stems are commonly manufactured from titanium alloy, such as Ti-6Al-4V, chosen for its strength, corrosion resistance, and compatibility with surrounding bone tissue. Stem geometry, length, and surface treatment vary across implant systems and are selected by the surgeon based on individual patient anatomy.
What Is the Acetabular Cup?
The acetabular cup, sometimes called the acetabular shell, is placed within the prepared socket of the pelvis (acetabulum) to replace the natural hip socket. Cups are typically manufactured from metal, often titanium alloy, and may feature a porous or textured outer surface engineered to support cementless biological fixation, or a smoother surface designed for cemented fixation. The cup provides the structural shell into which the liner is subsequently placed.
What Is the Liner?
The liner is the component fitted inside the acetabular cup, forming the inner bearing surface against which the femoral head articulates. Liners are commonly manufactured from highly cross-linked polyethylene, though ceramic liners are also used in certain bearing surface combinations. The liner's material and design are engineered to support smooth, low-friction articulation while managing wear over the functional life of the implant.
What Is the Femoral Head?
The femoral head is the rounded component that attaches to the top of the femoral stem and replaces the natural ball of the hip joint. Femoral heads may be manufactured from metal alloys or ceramic materials, depending on the selected bearing surface combination. Head size is selected by the surgeon based on factors including joint stability considerations and patient anatomy.
How Do These Hip Implant Components Work Together?
Together, these four components are designed to recreate the ball-and-socket mechanics of a healthy hip joint: the stem anchors the construct within the femur, the head provides the articulating ball, the liner provides the bearing surface, and the cup anchors the socket within the pelvis. Component selection and combination are determined by the treating surgeon based on individual patient anatomy, bone quality, and clinical judgment, following the manufacturer's official Instructions for Use (IFU).
Frequently Asked Questions
Are all four hip implant components always used together?
In total hip arthroplasty, all four components are generally used together to reconstruct the joint. In certain revision or partial procedures, such as hemiarthroplasty, only some components may be used, depending on the clinical scenario as determined by the surgeon.
What materials are femoral stems typically made from?
Femoral stems are commonly manufactured from titanium alloy, such as Ti-6Al-4V, selected for its mechanical strength, corrosion resistance, and compatibility with bone tissue.
Can these components be replaced individually during revision surgery?
In some revision scenarios, only specific components may need to be exchanged rather than the entire implant construct, depending on the reason for revision and findings at the time of surgery. This determination is made by the treating orthopedic surgeon.
Related INVAMED Resources
Medical Disclaimer: This article is provided for general informational and educational purposes only and does not constitute medical advice, diagnosis, or treatment recommendation. It is not a substitute for consultation with a qualified healthcare professional. Product indications, availability, and regulatory status vary by country. Always refer to the official Instructions for Use (IFU) and consult a licensed physician for guidance specific to your situation. INVAMED devices are intended for use by trained healthcare professionals.