Knee Replacement Revision - Medical Experts

In the majority of cases, Gram-positive bacteria (Staphylococcus aureus and epidermidis) are the cause of prosthetic infections. However, Gram-negative bacteria (E. coli and Pseudomonas aeruginosa) can also cause prosthetic infections in rare cases.

Patients with the following conditions are at particularly high risk of developing an infection:

• diabetes mellitus
• rheumatoid arthritis
• psoriasis
• obesity or
• previous hip replacement surgery on the same side

There are various reasons for replacing an already implanted knee prosthesis © RFBSIP | AdobeStock

Prosthetic infection is monitored using specific inflammatory markers in the blood.

These include laboratory values for:

• white blood cells
• C-reactive protein, and
• erythrocyte sedimentation rate

If patients already have a systemic inflammatory disease, the doctor must evaluate the inflammatory markers in the blood.

Further diagnostic evaluation is conducted using:

• advanced imaging (X-ray, CT, MRI, or scintigraphy) and
• joint aspiration or
• biopsy

This is followed by a microbiological examination.

The treatment strategy for knee replacement revision depends on:

• Type
• duration and
• severity of the prosthesis infection, as well as
• the patient’s physical condition

Treatment options include:

• Irrigation of the joint with replacement of the head and inlay (up to 2 weeks for early-stage infections)
• unilateral prosthesis replacement (for monoinfections with a simple bacterial spectrum and good bone stock),
• or a bilateral replacement (temporary insertion of an antibiotic-impregnated space maintainer made of bone cement).

Regardless of the implantation technique (cemented/cementless), knee prosthesis replacement for aseptic loosening of the prosthesis is usually performed unilaterally.

Instability accompanied by pain that has been present since the initial surgery is usually due to inadequate soft-tissue balancing. In many cases, it is combined with malrotation of the knee prosthesis.

If pain occurs due to instability in the knee joint, conservative treatment may help initially. 

This includes:

• Physical therapy
• Phonophoresis, and
• Injections

Conservative treatment is effective for many patients with pain caused by mild instability.

For patients whose symptoms do not improve, surgical intervention is usually necessary. The goal of the surgery is to restore soft tissue balance.

This can be achieved through various release techniques or by switching to prosthetic systems. These systems can take over either partial (partially coupled) or full (coupled) function of the collateral ligaments.

Ultrasound is one of the diagnostic tools used to assess the soft tissue structures in the knee © New Africa | AdobeStock

Periprosthetic fractures can occur due to the following factors:

• external trauma
• in cases of aseptic loosening, but also
• directly during surgery

The goal here is to restore anatomical relationships and bony continuity. 

In some cases, this may be possible while preserving the prosthesis using osteosynthesis techniques (angle-stable plate, intramedullary nail).

In most cases, however, replacement of the knee prosthesis with a cantilevered system is necessary. This system must bridge the fracture and allow for force transmission distal (tibial) or proximal (femoral) to the fracture line.

Utilizing existing surgical approaches and restoring the individual tissue layers are also critical steps in knee prosthesis replacement.

After removal of the prosthesis components, extensive bone defects are usually observed on both the tibial and femoral sides.

These can be classified as:

• non-circumferential (small to medium) and
• circumferential (large) defects

Therefore, in most revision prostheses, it is possible to install additional augmentation blocks depending on the defect.

Surgeons can also fill larger defects with allogeneic bone grafts. Due to larger bone defects with a lack of anchoring options for the prosthesis, a stemmed prosthesis may be used. 

In cases of severe defects with massive bone loss in the distal femur or proximal tibia, tumor prostheses are also used. These prostheses replace the deficient bone segments.

When reconstructing knee joints using a revision prosthesis, physicians should pay attention to the following:

• Restoration of the original joint line
• A balanced ratio between the flexion and extension gaps
• Avoidance of femoral and tibial malrotations
• Soft tissue balancing/alignment