Unicompartmental Knee Arthroplasty (UKA): Partial Knee Fast-Track Protocols and ACL Preservation
In short
Replacing only the damaged medial or lateral compartment preserves native knee ligaments. Learn partial knee replacement fast-track protocols, natural kinematics, and recovery.
In this guide (5 sections)
The Concept of Unicompartmental Knee Arthroplasty (UKA)
In approximately 30 to 40 percent of individuals presenting with knee osteoarthritis, cartilage degeneration is strictly localized to a single compartment, predominantly the medial compartment (anteromedial osteoarthritis).
Total Knee Arthroplasty (TKA) replaces all three compartments (medial, lateral, and patellofemoral) and routinely sacrifices the Anterior Cruciate Ligament (ACL).
Unicompartmental Knee Arthroplasty (UKA), or Partial Knee Replacement, resurfaces only the damaged compartment with a metal femoral component, metal tibial tray, and mobile or fixed polyethylene bearing, while preserving both cruciate ligaments (ACL and PCL) and the healthy lateral and patellofemoral compartments.
UKA vs TKA: Biomechanical and Recovery Advantages
Preserving the native ACL maintains normal knee proprioception, joint kinematics, and screw-home rotational mechanisms, allowing the knee to 'feel like a normal knee' (forgotten joint phenomenon).
| Clinical Feature | Partial Knee Replacement (UKA) | Total Knee Replacement (TKA) | Physiological Mechanism | |
|---|---|---|---|---|
| 1. Ligament Preservation | Both ACL and PCL completely preserved | ACL sacrificed; PCL often substituted | Preserves native joint proprioception and stability. | |
| 2. Hospital Length of Stay | Outpatient / Day 1 discharge (24 hours) | Inpatient stay (2 to 4 days) | Smaller incision; minimal blood loss; less quadriceps trauma. | |
| 3. Range of Motion Achieved | Rapid recovery; average flexion 125 to 135 deg | Gradual recovery; average flexion 110 to 120 deg | Soft tissue envelopes and healthy compartments intact. | |
| 4. Patient Satisfaction | Significantly higher 'natural knee' sensation | Up to 20% report residual unnatural joint stiffness | Normal rollback and femoral roll kinematics preserved. |
Fast-Track Outpatient Rehabilitation Protocol
Because the quadriceps tendon is minimally disrupted during UKA (medial parapatellar or subvastus approach), quadriceps shutdown is minimal, permitting rapid accelerated recovery.
- Day 1 Full Weight Bearing: Walk independently with a single elbow crutch or cane within 2 to 4 hours post-operatively; ascend and descend stairs before hospital discharge.
- Rapid Range of Motion Targets: Achieve 90 degrees flexion and full 0-degree extension by Day 3; reach 115 degrees flexion by end of Week 2.
- Crutch Weaning within 7 to 10 Days: Wean completely from walking aids to unassisted walking within 7 to 14 days as gait balance normalizes.
- Early Stationary Cycling and Closed Chain Power: Begin stationary cycling and mini-squats on Day 7, returning to brisk walking and light sports by Weeks 4 to 6.
Patient Selection Criteria and Cautions in India
UKA has strict surgical indications (Kozinn and Scott criteria): intact ACL, flexion contracture < 10 degrees, correctable varus deformity, and an asymptomatic lateral compartment.
In India, patients who delay surgery until bone-on-bone tricompartmental destruction occurs are no longer candidates for UKA and require total knee replacement.
Frequently Asked Questions
How long does a partial knee replacement last?
Modern registry data confirms that when performed by high-volume surgeons, partial knee replacements achieve over 90 percent survivorship at 15 to 20 years, comparable to total knee replacements.
Can a partial knee be converted to a total knee if arthritis spreads?
Yes. If osteoarthritis develops in the remaining compartments 10 to 15 years later, the partial knee can be easily revised to a standard primary total knee replacement with excellent outcomes.
Can I sit cross-legged after a partial knee replacement?
Because the ACL and native joint kinematics are preserved, many UKA patients comfortably achieve 130+ degrees of flexion, allowing seated floor prayer or yoga cross-legged sitting after 3 to 4 months of healing.
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