The implantation of an artificial joint represents a significant improvement in quality of life for many people. Hip and knee prostheses enable patients to be mobile and active again after years of pain. However, despite advances in endoprosthetics, a feared complication remains: prosthetic loosening. It is particularly critical in total hip replacement and total knee replacement, as untreated loosening not only causes pain but also increases the risk of serious secondary diseases. In this article, you will learn everything about the causes, symptoms, diagnostic procedures, and treatment options for prosthetic loosening.

What is prosthesis loosening?

A prosthesis loosening occurs when the artificial joint component loses its firm anchorage in the bone. This loosening can be mechanical or infectious in nature. Unlike normal age-related changes to an implant, true loosening always results in a limitation of function and usually also causes pain.

There are two main forms:

• Aseptic prosthesis loosening: Without bacterial involvement, usually mechanically caused.
• Septic prosthesis loosening: Caused by bacterial infections.

Both forms require different diagnostic and therapeutic approaches.

Causes of prosthesis loosening

Aseptic causes of loosening

Aseptic loosening is the most common form. The following factors play a role:

• Abrasion particles: Wear of polyethylene or metal releases tiny particles that can trigger an inflammatory reaction in the bone. This leads to osteolysis (bone degradation).
• Incorrect loading
• Material fatigue: Long-term mechanical stress can weaken the implants.
• Poor bone quality: Osteoporosis or bone necrosis impair implant anchorage.

Septic causes of loosening

A septic loosening is a serious complication:

• Periprosthetic infections: Bacteria (e.g., Staphylococcus aureus, Staphylococcus epidermidis) colonize on the prosthesis surface and form a biofilm that is difficult to treat.
• Hematogenous spread: Infections such as dental root inflammation or urinary tract infections can transport germs to the joint via the bloodstream.

Symptoms of prosthesis loosening

Prosthetic loosening is not always immediately apparent. Typical symptoms include:

• Load-bearing pain, often also rest pain
• Instability feeling in the affected joint
• Swelling and overheating
• Limited mobility
• Clicking or scraping noises during movement
• Fever (in case of septic loosening)
• Loss of strength in the leg

The symptoms can start insidiously and become more severe over time.

Diagnostics: How is prosthesis loosening diagnosed?

Diagnosis of a prosthesis loosening requires a combination of clinical examination and imaging as well as laboratory chemical procedures:

1. Clinical examination

• Assessment of gait, leg length, mobility, pain, effusions

2. Imaging procedures

• X-ray: Standard method for assessing loosening signs such as gap formation or migration
• CT: Detailed representation of bone structures and implant position
• Bone scintigraphy or PET-CT: Early detection of loosening through increased activity in bone metabolism

3. Laboratory tests

• Inflammatory markers: CRP, erythrocyte sedimentation rate (ESR)
• Blood cultures in case of septic suspicion

4. Joint puncture

• Analysis of joint fluid to determine the pathogen

Why bone scintigraphy can reliably detect loosening only after 1.5 years

The bone scintigraphy is considered sensitive but not very specific in the diagnosis of prosthetic loosening. In the first 12 to 18 months after surgery, scintigraphy often shows a normal postoperative increased metabolic activity in the area of the prosthesis. However, this does not constitute evidence of loosening. Only when this activity persists beyond the expected time or newly develops can a pathological change be assumed. Therefore, scintigraphy is only meaningfully interpretable at least 1.5 years postoperatively, as previous results are too often false-positive.

More information:  bone scintigraphy in the diagnosis of prosthesis loosening

Treatment options for prosthesis loosening

Depending on the cause, the procedure differs significantly:

• Aseptic loosening: Revision surgery of the loosened components or the entire prosthesis.
• Septic loosening:
• Two-stage procedure: removal of the prosthesis, antibiotic therapy, and later reimplantation.
• Rarely one-stage: Only in highly specialized centers and under certain conditions.

The choice of the new prosthesis depends on the bone situation. Often, so-called revision implants are used.

Hip joint – loosening of a hip prosthesis (hip TEP)

Causes of loosening of a hip TEP

In the case of loosening of a hip TEP the following factors play a role:

• Abrasion of polyethylene inlays
• Malalignment after primary implantation
• Aging processes of the implant
• Primary infections or late infections

Symptoms of a loose hip prosthesis

Patients often complain about:

• Groin pain
• Stabbing pain in the thigh
• Pain when climbing stairs or standing up
• Gait uncertainty
• Shortened leg or changed leg axis

Diagnosis of loosening of hip prosthesis

• X-rays (overview of the pelvis, axial beam path)
• Bone scintigraphy
• Laboratory controls
• CT in complex cases
• Puncture in case of suspected infection

Therapy for loosening of hip TEP

• Replacement of the loosened components (only cup or only shaft)
• Switch to modular shaft systems or revision cups
• Bone reconstruction using spongiosa plasty for defects
• Antibiotic therapy for septic cause

Special challenges

• Restoration of leg length
• Reconstruction of the rotation centers
• Prevention of further loosening

Knee joint - loosening of a knee prosthesis (knee TEP)

Causes of loosening of a knee TEP

The loosening of a knee TEP can result from:

• Polyethylene wear and abrasion
• Loosening of the tibial shaft
• Malalignment (e.g., valgus or varus gonarthrosis)
• Ligament instabilities
• Infections

Symptoms of a loose knee prosthesis

Typical symptoms are:

• Load-dependent pain
• Instability sensations when walking
• Swelling, especially after stress
• Effusions in the knee joint
• Movement restrictions
• Cracking or knocking noises

Diagnosis of loosening of knee prosthesis

• X-rays under load
• Long-leg-view to assess the leg axis
• Bone scintigraphy or PET-CT
• Laboratory tests to search for infection
• Puncture if septic loosening is suspected

Therapy for loosening of knee prosthesis

• Replacement of the tibial component, femoral component or both components
• Use of modular revision prostheses with axial guidance
• Bone reconstruction using metal or bone augmentations
• Targeted antibiotic therapy for infection

Prevention: Preventing prosthetic loosening

• Weight reduction
• Regular dental check-ups
• Avoidance of risk infections
• Gentle sports (swimming, cycling)
• Regular follow-up examinations

Prognosis after revision surgery for loosening

The results after revision surgeries are very good in specialized centers:

• 80-90% of revision prostheses last at least 10 years.
• Mobility can largely be restored.

FAQ: Frequently Asked Questions about Prosthesis Loosening

How does a loosened hip TEP feel?

• Frequent groin pain, feeling of instability and limited resilience.

How long does a knee TEP last?

• Modern knee prostheses last on average 15-20 years, sometimes longer.

Is every loosening an emergency operation?

• No, but a significant loosening should be treated promptly to avoid consequential damage.

Outlook: Rehabilitation, follow-up care, and prevention

A structured rehabilitation after revision surgery is crucial for returning to mobility. Preoperative education and planning should already be started. During inpatient rehabilitation, mobilization, physiotherapy, and pain management are the focus. Subsequent outpatient programs are recommended, which specifically address gait, muscle strength, and joint function.

Prevention of prosthesis loosening starts long before the first operation:

• Careful selection of the implant
• Correct positioning
• Treatment of risk factors (e.g. osteoporosis)
• Regular follow-up examinations
• Patient education on everyday behavior (e.g., fall prevention, joint-friendly loading)

Scientific studies and evidence

Numerous studies demonstrate the relevance and frequency of prosthesis loosening:

• A large registry analysis of the German Endoprosthesis Registry (EPRD) shows that about 5–10 % of all endoprostheses need to be revised within 10 years due to loosening.
• Studies on aseptic loosening describe wear as the main cause – especially in older generation polyethylene inlays.
• In septic loosening, a meta-analysis showed that the two-stage revision procedure has a higher success rate compared to the one-stage revision (success rate >90%).
• Modern imaging techniques such as PET/CT with labeled leukocytes are being further developed and offer improved sensitivity in unclear cases.

Influencing factors according to study data:

• Smoking, diabetes mellitus, and obesity significantly increase the risk of loosening.
• Men are slightly more frequently affected than women.
• Patients under 60 years with a higher activity level have an increased revision risk.

Conclusion: Early diagnosis of prosthesis loosening protects mobility

An early diagnosed prosthesis loosening can usually be treated successfully. Those who take typical symptoms such as pain or instability seriously and seek timely medical help protect their quality of life in the long term.

Do you have pain in your hip or knee prosthesis?
Make an appointment now at ENDOPROTHETICUM, your specialized practice for endoprosthetics.
➡️ Together we will find the optimal solution for your mobility!