The knee sled prosthesis, also known as a unicondylar knee prosthesis or partial knee replacement, is a proven and minimally invasive treatment method for osteoarthritis-related knee pain. Despite the advantages and faster recovery compared to total knee replacement, postoperative pain after sled prosthesis can also occur. This comprehensive guide highlights the common causes of pain after a sled prosthesis and presents effective treatment measures. We also discuss late complications such as retropatellar osteoarthritis or residual knee joint osteoarthritis that can occur.

What is a sled prosthesis?

The sledge prosthesis is used for unilateral advanced osteoarthritis, often in the medial or less frequently in the lateral knee joint compartment. Unlike total knee replacement, the sledge prosthesis replaces only the affected part of the joint and leaves healthy structures intact.

• Advantages of unicompartmental knee arthroplasty:
• Minimally invasive procedure.
• More natural feeling of movement.
• Faster healing process.
• Limitations:
• Not suitable for all patients, e.g. in case of inflammatory joint diseases.

Possible causes of pain after a sled prosthesis

1. Postoperative overload

• Description: Immediately after the operation the knee is sensitive. Pain can arise from too early or intensive loading.
• Therapy: Rest, physiotherapy, intake of mild painkillers.

2. Scar pain or skin irritation

• Description: Scar formation or nerve irritation in the surgical area can cause discomfort.
• Therapy: Local massages, silicone patches, laser therapy.

3. Instability of the knee joint

• Description: Instability can occur if the knee ligaments are overstrained after the operation or are not optimally balanced.
• Therapy: Adjustment of rehabilitation, targeted muscle training, possibly surgical correction.

4. Suboptimal prosthesis placement

• Description: Misalignments can cause friction and pain.
• Therapy: Imaging procedures for diagnostics, possibly revision of the prosthesis.

5. Residual knee joint osteoarthritis

• Description: A sled prosthesis treats only a part of the joint. Over time können wear signs may appear in other joint areas.
• Special feature: Retropatellar arthrosis, where the cartilage layer behind the kneecap degenerates, is häufig.
• Therapy:  in severe Fällen expansion to a total endoprosthesis.

Diagnosis of postoperative pain after unicompartmental knee arthroplasty

1. Clinical examination

• Palpation of the knee to localize pain.
• Range of motion tests to check function.

2. Imaging procedures

• Röntgen: Control of prosthesis placement.
• MRT: Detection of Weichteilveränderungen or remaining Knorpelschäden.
• CT: Detailed analysis in case of suspected prosthesis misalignment.

3. Laboratory tests

• Exclusion of infections through blood tests and joint puncture.

Postoperative therapy approaches

1. Medications

• Pain medication: NSAIDs or paracetamol for pain relief.
• Entzündungshemmer: Cortisone injections for swelling.

2. Physiotherapy and rehabilitation

• Goal: Improvement of Gelenkstabilität, Mobilität and musculature.
• Measures:
• Manual therapy.
• Electrotherapy.
• Aquatherapy for joint-friendly strengthening.

3. Surgical Options

• Prosthesis revision: In case of loosening or misalignment.
• Extension to total endoprosthesis: In progressive arthritis in other joint areas.

Long-term problems with a knee replacement

1. Progressive Joint Wear

• Even after successful surgery, wear and tear can occur in the non-prothetically treated knee area.

2. Retropatellar Arthrosis

• Affected individuals complain of pain behind the kneecap.
• Solution: Depending on the severity, adjust the therapy or surgical intervention.

3. Prosthesis Loosening

• Can be triggered by material fatigue or inadequate bone substance.
• Treatment options include revision surgery.

Preventive measures to avoid pain

1. Optimal Rehabilitation

• Regular physiotherapy.
• Training patients on the correct loading of the knee.

2. Weight Control

• Avoiding overweight, as it reduces the strain on the knee joint.

3. Adapted Sports

• Joint-friendly activities such as swimming or cycling.

Conclusion

Postoperative pain after a knee replacement is possible in rare cases and can be triggered by various factors. Accurate diagnosis and individually tailored therapy are crucial to effectively treat complaints and improve quality of life. The knee replacement remains an excellent option for patients with localized knee osteoarthritis if the indication is carefully made.