Acetabular shell: Definition, Uses, and Clinical Overview

Acetabular shell Introduction (What it is)

An Acetabular shell is a metal “cup” implanted into the hip socket during hip replacement surgery.
It replaces or resurfaces the socket side of the hip joint so the hip can move smoothly.
It is most commonly used in total hip arthroplasty (total hip replacement) and some revision surgeries.

Why Acetabular shell used (Purpose / benefits)

The hip is a ball-and-socket joint. The “ball” is the femoral head (top of the thigh bone), and the “socket” is the acetabulum (part of the pelvis). When the socket cartilage wears down or the socket bone is damaged, the joint can become painful and stiff, and normal walking can be limited.

An Acetabular shell is used to rebuild the socket side of the joint in a controlled, durable way. In a typical total hip replacement, the shell is placed into the prepared acetabulum and then a liner is inserted into the shell. The liner creates the smooth bearing surface that contacts the new femoral head component.

In general terms, the purpose and potential benefits include:

• Restoring joint mechanics: The shell helps recreate a stable, appropriately sized socket to support hip motion.
• Providing a base for a liner: Most shells are designed to accept a modular liner (commonly polyethylene, sometimes ceramic or other designs).
• Improving stability and alignment options: Shell positioning and liner choice can help clinicians balance range of motion and stability.
• Supporting long-term fixation: Many designs aim to encourage strong attachment to bone (cementless fixation) or provide secure bonding with bone cement (cemented fixation), depending on the case.
• Addressing pain and function loss related to joint damage: Hip replacement is generally considered when joint damage contributes to persistent symptoms and disability that do not improve with non-surgical care (details vary by clinician and case).

Indications (When orthopedic clinicians use it)

Orthopedic clinicians may consider an Acetabular shell as part of hip arthroplasty planning in scenarios such as:

• Advanced hip osteoarthritis affecting the acetabulum (socket-side joint surface)
• Inflammatory arthritis with socket cartilage loss
• Certain hip fractures in older adults when total hip replacement is selected (rather than partial replacement), depending on patient factors and fracture pattern
• Avascular necrosis (osteonecrosis) with secondary arthritis involving the socket
• Hip dysplasia or other structural conditions leading to joint degeneration
• Revision hip replacement when an existing acetabular component is loose, worn, malpositioned, or otherwise failing
• Acetabular bone defects that still allow for shell fixation (often with adjuncts, varies by clinician and case)

Contraindications / when it’s NOT ideal

An Acetabular shell is not always the best option for every patient or every hip problem. Situations where it may be avoided, delayed, or modified include:

• Active infection in or around the hip joint (implanting hardware in an infected field is typically avoided)
• Insufficient bone stock for secure shell fixation without additional reconstruction (for example, severe acetabular bone loss may require augments, cages, custom implants, or alternative strategies; varies by case)
• Poor candidate for major surgery due to medical instability or inability to tolerate anesthesia and postoperative rehabilitation (determined by the care team)
• Certain fracture patterns where immediate total hip replacement is not appropriate, or where different reconstruction methods are preferred
• Complex anatomy (such as severe dysplasia or prior surgery) where a standard shell may not fit well without specialized designs
• Allergy or sensitivity concerns to specific implant materials (management varies by clinician and case; true implant allergy remains a nuanced area)

“Not ideal” does not necessarily mean “cannot be used.” It often means the approach may need to change (different shell design, different fixation method, additional reconstruction, or a different procedure altogether).

How it works (Mechanism / physiology)

Biomechanical principle

The hip joint transmits body weight and muscle forces across a large range of motion. An Acetabular shell works by:

• Replacing the damaged socket surface with a precisely shaped metal component
• Providing structural support to distribute loads through the pelvis
• Accepting a liner that acts as the low-friction bearing surface for the femoral head component

Together, the shell + liner + femoral head aim to create a smooth articulation that reduces painful bone-on-bone contact.

Relevant anatomy and tissues involved

Key structures involved include:

• Acetabulum (pelvic socket): The bony cup that normally contains the femoral head.
• Articular cartilage: The smooth tissue that normally covers the joint surfaces; it is often worn or damaged in arthritis.
• Subchondral bone: The bone beneath cartilage; surgeons prepare this surface to accept the shell.
• Labrum: A rim of fibrocartilage around the socket; in arthroplasty, the damaged joint surfaces are typically replaced rather than repaired.
• Surrounding muscles and capsule: These soft tissues contribute to hip stability after reconstruction.

Fixation, onset, and reversibility

An Acetabular shell does not have a “physiologic onset” like a medication. Its effect is mechanical and immediate: once implanted and stable, it functions as the new socket component.

Fixation can be:

• Cementless (bone-ingrowth or bone-ongrowth designs): The shell is typically press-fit into bone; porous or coated surfaces are intended to encourage bone attachment over time. The time course and robustness of fixation vary by material and manufacturer and by patient factors (bone quality, activity level, healing).
• Cemented: Bone cement is used to secure the component in place in selected situations.

Reversibility is limited. Removal or change generally requires revision surgery.

Acetabular shell Procedure overview (How it’s applied)

An Acetabular shell is an implant, not a standalone procedure. It is most commonly used during total hip arthroplasty or revision hip arthroplasty. The exact surgical plan varies by clinician and case, but a high-level workflow often looks like this:

1. Evaluation / exam – History, physical examination, and review of symptoms and functional limitations – Imaging (commonly X-rays; other imaging may be used for complex anatomy or revision planning) – Discussion of surgical goals, risks, and implant options in general terms

2. Preparation – Preoperative planning for component sizing and positioning – Medical optimization and perioperative planning (varies by patient health status) – Selection of fixation approach (cementless vs cemented) and liner type (based on anatomy, bone quality, stability considerations, and surgeon preference)

3. Intervention – Surgical exposure of the hip joint – Removal of damaged cartilage and preparation of the acetabular bone to accept the implant – Placement of the Acetabular shell into the pelvis – Liner insertion into the shell (and use of screws or adjunct fixation when selected) – Placement of the femoral components to complete the joint reconstruction

4. Immediate checks – Verification of hip stability, leg length assessment, and range of motion checks (methods vary) – Imaging may be obtained around the time of surgery to confirm component position (practice patterns vary)

5. Follow-up – Wound and symptom monitoring – Rehabilitation planning and progression (weight-bearing and activity progression vary by clinician and case) – Ongoing monitoring for function and potential implant-related issues over time

Types / variations

Acetabular component systems vary widely. Some of the most common ways they are categorized include the following.

Fixation method

• Cementless shells: Often porous-coated or textured to support bone attachment. Many modern primary hip replacements use cementless acetabular fixation, but selection depends on patient factors and surgeon preference.
• Cemented cups/shell constructs: Used in selected patients and revision scenarios; technique and cementing strategy vary.

Shell shape and design

• Hemispherical press-fit shells: A common design intended to fit a reamed hemispherical socket.
• Multi-hole shells: Designed to accept screws for additional initial fixation when needed.
• Cluster-hole shells: A pattern of holes (often near the dome) that may allow selective screw placement.
• Revision shells: Designs intended for more complex acetabular anatomy or bone loss; may be paired with augments or other reconstruction tools (varies by system).
• Monoblock cups vs modular shells:
• Modular: Separate shell and liner pieces (common).
• Monoblock: Shell and liner are integrated in some designs; the trade-offs vary by design and manufacturer.

Materials and surface technology (shell)

• Titanium alloys: Common for cementless shells due to favorable mechanical properties and compatibility with porous structures (specifics vary by manufacturer).
• Cobalt-chromium alloys: Used in some designs and revision constructs; material selection depends on system design goals.
• Porous metals and coatings: Examples include porous titanium or other porous surfaces; the exact technology varies by manufacturer.

Liner options (what goes inside the shell)

While the shell is the focus, the liner strongly affects performance:

• Polyethylene liners: Common bearing surface; may be conventional or highly cross-linked (details vary by product).
• Ceramic liners: Used in some systems; compatibility depends on the shell design.
• Dual-mobility liners: A design intended to increase stability in selected patients by allowing an additional articulation; indications vary by clinician and case.
• Constrained liners: Designed to limit dislocation in select situations, often in complex revisions or high-risk instability cases; trade-offs vary.

Pros and cons

Pros:

• Can restore the socket side of the hip joint in a way that supports smoother motion
• Provides a stable base to accept different liner options, allowing customization to anatomy and stability needs
• Multiple fixation strategies (cementless or cemented) can be matched to bone quality and surgical goals
• Component sizing and positioning can be adjusted to help optimize biomechanics (within surgical constraints)
• Widely used in modern hip arthroplasty with established surgical workflows
• Revision-specific designs exist for more complex cases (varies by system)

Cons:

• Requires surgery and implanted hardware, with risks that vary by patient health and procedure complexity
• Malposition, loosening, or wear can occur over time, potentially leading to pain or reduced function
• Dislocation or instability can occur, influenced by component position, soft tissues, and patient factors
• Bone loss can develop in some failure modes, making revision more complex (varies by case)
• Imaging artifacts can occur on some scans due to metal components (depends on imaging type and implant material)
• Some complex anatomies or severe bone defects may require additional implants or alternative reconstruction methods

Aftercare & longevity

After hip replacement, outcomes and longevity are influenced by multiple factors rather than the Acetabular shell alone. Common considerations include:

• Underlying diagnosis and anatomy: Arthritis severity, dysplasia, prior surgery, and bone shape can affect reconstruction complexity.
• Bone quality and healing capacity: Cementless fixation relies on bone attachment over time; healing potential can be influenced by age, bone density, and overall health.
• Component positioning and stability: Shell orientation and liner choice influence range of motion and dislocation risk; planning and execution vary by clinician and case.
• Activity level and load exposure: Higher-impact activities can increase mechanical demands on the bearing surface and fixation interfaces.
• Body weight and biomechanics: Greater loads can increase stress across the joint; individual gait and muscle strength also matter.
• Rehabilitation and follow-up: Physical therapy participation, adherence to the care plan, and scheduled follow-ups can influence function and early detection of issues.
• Comorbidities and medications: Conditions that affect bone, healing, or infection risk can affect outcomes.
• Material and manufacturer differences: Surface technologies, liner materials, and locking mechanisms vary by system and can influence wear patterns and fixation behavior.

Longevity is not guaranteed and cannot be predicted precisely for an individual. Clinicians typically monitor symptoms and periodic imaging to assess fixation, component position, and wear-related changes over time.

Alternatives / comparisons

An Acetabular shell is one solution within a broader set of hip care options. Comparisons are best understood by separating non-surgical management, joint-preserving procedures, and different arthroplasty choices.

• Observation/monitoring (watchful waiting):
  For mild symptoms or early disease, clinicians may track symptoms and imaging over time. This avoids surgical risks but does not replace damaged cartilage.

• Medication and injections (symptom-focused care):
  Anti-inflammatory medications or injections may reduce pain and inflammation for some conditions. These approaches do not rebuild the socket surface and results vary by diagnosis and individual response.

• Physical therapy and activity modification:
  Therapy may improve strength, walking mechanics, and tolerance for daily activities. It can be helpful for pain management and function but does not correct advanced joint surface loss.

• Hip arthroscopy (scope surgery):
  In selected patients (often earlier-stage disease), arthroscopy may address labral tears or impingement. It is generally not a substitute for total hip replacement when there is advanced arthritis.

• Periacetabular osteotomy (PAO) and other osteotomies:
  For certain structural problems like dysplasia in appropriately selected patients, bone realignment can improve joint mechanics and potentially delay arthritis progression. It is different from replacing the joint surface with an Acetabular shell.

• Hip resurfacing (selected patients):
  Resurfacing uses different implant geometry and has specific indications and trade-offs. It is not appropriate for every anatomy or bone quality profile.

• Hemiarthroplasty vs total hip arthroplasty:
  A hemiarthroplasty replaces the femoral head but typically does not replace the socket with an Acetabular shell. It may be used for certain fractures, but socket wear and groin pain can be concerns in some patients over time (varies by individual).

• Cemented vs cementless acetabular reconstruction:
  Both are established approaches. The “better” option depends on bone quality, anatomy, surgeon experience, and implant system design.

Acetabular shell Common questions (FAQ)

Q: Is an Acetabular shell the same thing as a hip “cup”?
Yes. “Cup” is a common non-technical term for the acetabular component, and the Acetabular shell is the metal part that sits in the pelvic socket. A liner typically fits inside the shell to create the bearing surface.

Q: Will I feel the Acetabular shell inside my body?
Most people do not feel the implant directly as a distinct object. What people notice is whether hip motion feels smoother and whether pain improves. Some awareness around the joint can occur during healing, and experiences vary by person and procedure type.

Q: Does placing an Acetabular shell hurt?
The implant is placed during surgery under anesthesia, so pain is managed during the procedure. Postoperative pain and stiffness are expected parts of surgical recovery and vary by individual, surgical approach, and rehabilitation plan.

Q: How long does an Acetabular shell last?
Longevity depends on many factors, including fixation quality, wear of the liner, activity level, anatomy, and the reason the hip was replaced. Some implants function for many years, while others may require revision earlier due to loosening, wear, instability, infection, or other issues. Exact timelines vary by clinician and case.

Q: What affects the risk of dislocation related to the shell?
Dislocation risk is influenced by component positioning (including shell orientation), soft-tissue tension, head size, liner design (such as dual-mobility or constrained liners), and patient-specific factors. It is not determined by the shell alone.

Q: Can I bear weight right away after surgery?
Weight-bearing plans vary based on fixation method, bone quality, additional repairs, and surgeon preference. Some patients are allowed to bear weight early, while others have restrictions for a period of time. Your care team sets this based on the specific reconstruction.

Q: When can someone drive or return to work after receiving an Acetabular shell?
Timing varies with pain control, mobility, reaction time, which leg was operated on, job demands, and clinician guidance. Sedating medications and limited hip function can affect safety for driving and work tasks. Many patients return in stages, but there is no single universal timeline.

Q: What does the Acetabular shell cost?
Costs vary widely by country, hospital system, insurance coverage, implant type, and whether the surgery is primary or revision. The implant is only one part of overall episode cost, which can include hospital, surgeon, anesthesia, imaging, rehabilitation, and follow-up care.

Q: Will the shell set off metal detectors or affect MRI scans?
Some implants may trigger metal detectors, and metal can create artifacts on MRI that reduce image clarity near the hip. Many patients with hip implants can still undergo MRI when clinically necessary, but protocols and compatibility considerations vary by implant and imaging center.

Q: If there’s a problem later, can an Acetabular shell be revised?
Revision is often possible, but complexity depends on why revision is needed and how much bone remains for fixation. In some cases, only the liner is exchanged; in others, the shell must be removed and replaced, sometimes with additional reconstruction techniques.