Mandatory 8-hour fasting from solids and clear liquids. Comprehensive pre-anesthetic evaluation including cardiac and respiratory clearance. Optimization of glycemic control and discontinuation of antiplatelet/anticoagulant medications as directed. Administration of prophylactic intravenous antibiotics within 60 minutes of the incision. Informed consent procurement and site marking by the surgical team.
Post-operative monitoring in the recovery unit followed by ward admission. Early mobilization and physical therapy commencement within 24 hours. Implementation of venous thromboembolism (VTE) prophylaxis. Pain management via multimodal analgesia. Regular wound inspection and neurovascular assessment of the distal limb. Discharge criteria include stable vital signs, independent ambulation with aids, and adequate pain control on oral analgesics.
1. Comprehensive Introduction & Overview
Unicompartmental Knee Arthroplasty (UKA), often referred to as a "partial knee replacement," is a surgical procedure designed to address localized osteoarthritis of the knee. Unlike Total Knee Arthroplasty (TKA), which involves the resurfacing of all three compartments of the knee (medial, lateral, and patellofemoral), UKA is a conservative surgical intervention that selectively replaces only the damaged compartment—most commonly the medial compartment.
The fundamental philosophy behind UKA is the preservation of the patient's healthy anatomy, including the anterior and posterior cruciate ligaments (ACL/PCL). By retaining these structures, patients often report a more "natural" feeling knee, improved proprioception, and a gait pattern that more closely mimics native biomechanics compared to TKA.
2. Deep-Dive: Technical Specifications & Mechanisms
UKA is a biomechanical solution to compartmental wear. The procedure involves the implantation of a metallic femoral component, a metallic tibial tray, and a high-density polyethylene (poly) insert that serves as the new articular surface.
The Biomechanical Advantage
The preservation of the cruciate ligaments is the primary differentiator of UKA.
* Kinematics: Retaining the ACL allows for the natural "screw-home" mechanism of the knee during extension.
* Proprioception: By keeping the native cruciate ligaments and the healthy compartments, the neural feedback loop (proprioception) remains largely intact, leading to higher patient satisfaction scores.
* Bone Stock: UKA requires significantly less bone resection than TKA, which is a critical consideration if a revision to TKA becomes necessary later in the patient's life.
Implant Types
| Component Type | Description |
|---|---|
| Fixed-Bearing | The polyethylene insert is locked into the tibial tray. Offers high stability and lower risk of dislocation. |
| Mobile-Bearing | The polyethylene insert can rotate/slide on the tibial tray. Designed to mimic natural meniscal movement and reduce wear. |
3. Extensive Clinical Indications & Usage
UKA is not a universal solution for all knee pain. It is a highly selective procedure that requires strict adherence to clinical criteria to ensure long-term success.
Primary Indications
- Unicompartmental Osteoarthritis: Radiographic evidence of bone-on-bone contact limited to one compartment (usually medial).
- Intact Ligaments: A functional, intact Anterior Cruciate Ligament (ACL) is mandatory for the stability of the implant.
- Correctable Deformity: The knee must have a correctable varus or valgus deformity (usually <10-15 degrees) that becomes neutral under stress.
- Failed Conservative Management: Patients who have undergone at least 6 months of non-operative treatment, including physical therapy, weight loss, bracing, and intra-articular injections (corticosteroids/hyaluronic acid).
Contraindications
- Inflammatory Arthritis: Conditions like Rheumatoid Arthritis are generally contraindicated due to the risk of disease progression in other compartments.
- Patellofemoral Disease: Significant pain or radiographic changes in the patellofemoral joint.
- Fixed Deformity: Deformities that cannot be passively corrected to a neutral position.
- Obesity: High BMI is often cited as a relative contraindication due to increased stress on the implant and higher failure rates.
4. Patient Pre-Op Preparation
Preparation for UKA is a multidisciplinary process aimed at optimizing the patient’s physiological state for surgery.
- Clinical Assessment: Full-length weight-bearing radiographs (hip-to-ankle) to assess mechanical axis and compartmental wear. MRI may be used to confirm ligamentous integrity.
- Medical Optimization: Management of comorbidities such as diabetes (HbA1c optimization), hypertension, and anemia.
- Physical Therapy (Pre-hab): Strengthening the quadriceps and hip abductors prior to surgery significantly improves post-operative recovery speeds.
- Education: Patients are briefed on expectation management, specifically that UKA is a "partial" fix and requires ongoing maintenance of the remaining healthy compartments.
5. The Procedure: Surgical Protocol
The surgical intervention is typically performed under regional anesthesia (spinal or epidural) with monitored sedation.
Step-by-Step Surgical Steps:
- Incision: A minimally invasive medial parapatellar arthrotomy is performed.
- Assessment: The surgeon performs a visual and manual inspection of the ACL and the lateral/patellofemoral compartments to confirm the preoperative plan.
- Bone Preparation: Using specialized jigs, the surgeon removes minimal bone from the femoral condyle and the tibial plateau.
- Trialing: Trial components are inserted to ensure proper alignment, ligament tension, and range of motion.
- Implantation: The final components are cemented into place.
- Closure: Layered closure of the capsule, subcutaneous tissue, and skin, often using absorbable sutures.
6. Post-Op Recovery Protocol
The recovery period is generally faster for UKA than for TKA, with many patients returning to daily activities within 4 to 6 weeks.
- Days 0-2: Early mobilization. Physical therapy begins within 24 hours. Focus on passive range of motion and quad sets.
- Weeks 2-6: Progression to full weight-bearing as tolerated. Focus on gait training and strengthening exercises.
- Weeks 6-12: Return to low-impact activities (swimming, cycling, walking).
- Long-term: Maintenance of a healthy weight is paramount to prevent the progression of osteoarthritis in the non-replaced compartments.
7. Risks and Potential Complications
While UKA is safer and less invasive than TKA, it is not without risk.
- Aseptic Loosening: The most common cause of long-term failure, often due to technical errors in component positioning.
- Progression of Arthritis: The remaining compartments may eventually develop osteoarthritis, requiring a conversion to TKA.
- Infection: Periprosthetic joint infection (PJI) is a rare but serious complication.
- Fracture: Periprosthetic tibial fracture, though rare with modern techniques.
8. Alternative Treatments
Patients who do not meet the criteria for UKA or who prefer to avoid surgery should consider:
* Osteotomy (HTO): Realignment of the leg bones to shift weight away from the damaged compartment. More common in younger, active patients.
* Total Knee Arthroplasty (TKA): The gold standard for multi-compartmental disease.
* Viscosupplementation & Biologics: PRP (Platelet-Rich Plasma) or stem cell therapies, though clinical evidence for long-term disease modification remains limited.
9. Massive FAQ Section
1. How long does a UKA last?
Modern UKA implants have a 90%+ survival rate at 10 years. Longevity depends on patient activity level, weight, and surgical precision.
2. Can I run after a partial knee replacement?
High-impact activities like long-distance running are generally discouraged to protect the implant and the remaining natural compartments. Low-impact activities are encouraged.
3. Is UKA more painful than TKA?
Most patients report less post-operative pain and a faster recovery time compared to TKA because there is less soft-tissue trauma.
4. What is the difference between fixed and mobile bearings?
Fixed bearings are generally more forgiving of surgical technique. Mobile bearings are designed to provide better kinematics but require precise ligamentous balancing.
5. Will I need a "Total" knee replacement later?
There is a risk of converting to TKA if the arthritis progresses in the untreated compartments. However, many patients live the rest of their lives with the UKA intact.
6. How much bone is removed?
UKA is a bone-conserving procedure. Only a few millimeters of bone are shaved from the femoral and tibial surfaces.
7. Does it feel like a "real" knee?
Yes. Because the ACL and healthy compartments remain, the joint retains natural stability and proprioception.
8. Is there an age limit?
There is no strict age limit; however, surgeons typically avoid UKA in extremely young patients (due to high activity) or very elderly patients with significant medical comorbidities.
9. What is the success rate?
When performed on properly screened patients, clinical success rates exceed 90%.
10. Can I kneel after surgery?
Kneeling may be uncomfortable initially but is generally possible once the incision has fully healed, though it may feel different than a native knee.
Disclaimer: This guide is for informational purposes and does not constitute medical advice. Always consult with a board-certified orthopedic surgeon to discuss your specific clinical presentation and treatment options.