Partial knee replacement preserves healthy knee structures while replacing only damaged compartments. Unlike total knee replacement, which resurfaces all three knee compartments, partial replacement targets specific areas, typically the medial (inner) or lateral (outer) compartment. The ROSA Partial Knee System by Zimmer Biomet is a robotic-assisted platform designed to support surgeons with intraoperative planning and real-time feedback during bone preparation.
ROSA uses an imageless workflow, where planning is carried out during surgery based on the patient’s own knee anatomy. It is designed to help surgeons preserve healthy bone and support accurate implant positioning. Individual results may vary.
Understanding Partial Knee Replacement
The knee contains three compartments: medial (inner), lateral (outer), and patellofemoral (kneecap). For patients whose arthritis is confined to the kneecap rather than the medial or lateral compartment, patellofemoral partial knee replacement may be a more suitable option than the standard unicompartmental approach described here. Partial replacement addresses damage in one compartment while preserving the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), and undamaged cartilage.
Surgeons make a 3-4 inch incision compared to 8-12 inches for total replacement. The procedure removes damaged cartilage and minimal bone before securing metal and plastic components. Natural ligaments guide knee movement, resulting in more natural kinematics than total replacement.
Candidacy Requirements
Ideal candidates have:
- Osteoarthritis limited to one compartment confirmed by X-ray or MRI
- Intact ACL and PCL ligaments
- Minimal angular deformity (less than 10 degrees varus or valgus)
- Body mass index below 35
- Age typically between 50-75 years
- Failed conservative treatments including physical therapy and injections
Exclusions include inflammatory arthritis like rheumatoid arthritis, significant ligament damage, or patellofemoral arthritis with lateral compartment involvement.
Robotic-Assisted Surgical Technology
The ROSA Partial Knee System by Zimmer Biomet uses an imageless workflow. During surgery, the surgeon registers the patient’s knee anatomy to the system, which helps guide planning of implant size, positioning, and alignment before any bone cuts are made. The system is designed to work with the Persona Partial Knee implant. The surgeon controls the saw, while the robotic arm assists with cutting guide positioning.
The system uses tracking technology to monitor leg position and can display:
- Implant alignment relative to the surgical plan
- Cut guidance and validation feedback
- Soft tissue feedback through the range of motion
- Leg alignment measurements (hip-knee-ankle angle)
Surgical Planning Process
Planning takes place in the operating room once the knee is exposed. The surgeon registers anatomical landmarks, and the system provides measurements and soft tissue feedback that help inform:
- Implant size and positioning
- Limb alignment and the degree of correctable deformity
- Soft tissue tension through the range of motion
Surgeons can review and adjust the plan before any bone cuts are made, accounting for individual anatomical variations.
Intraoperative Execution
After exposing the knee joint, the surgeon registers anatomical landmarks so the system can reference the patient’s anatomy. The robotic arm assists in positioning the cutting guide according to the surgical plan, while the surgeon controls the saw.
Robotic functions may include:
- Assisting with the planned angles for tibial cuts
- Providing real-time alignment and cut validation feedback
- Providing soft tissue balance information before and after resection
- Allowing the surgeon to switch to the ROSA Knee System if clinically needed
Benefits of Robotic Assistance for Partial Knee Replacement
Zimmer Biomet reports that tibial resection with the ROSA Partial Knee System has been shown to be more accurate and reproducible than conventional instrumentation. This may help preserve healthy bone, which can matter for younger patients who may need revision surgery years later for their partial knee implant. Individual results may vary.
Improved Alignment
Component malalignment has been associated with increased wear and loosening in published research. Robotic assistance is designed to help surgeons achieve their planned implant alignment for partial knee components. Implant longevity depends on many factors, including activity level and bone quality.
Soft Tissue Protection
Real-time soft tissue feedback is designed to help surgeons assess ligament tension before bone resections are made during partial knee replacement. Guidance during bone preparation is designed to support accurate cuts and may help protect surrounding structures such as the ACL. Experiences vary between patients.
Reproducible Results
Manual techniques rely on visual estimation and anatomical landmarks that can vary between patients. Robotic systems are designed to execute the surgical plan with a consistent workflow, though clinical judgment remains central to plan creation and intraoperative decisions. Outcomes depend on many factors, including patient selection and surgical technique.
💡Did You Know?
The ROSA Partial Knee System allows surgeons to assess soft tissue feedback and plan implant positioning before making any bone resections. It also lets the surgeon switch to the ROSA Knee System during surgery if needed.
Recovery Timeline and Expectations
Patients typically walk with assistance within 24 hours post-surgery. Hospital discharge occurs after 1-2 days when patients demonstrate:
- Independent transfers
- Walking 50-100 feet with walker
- Knee flexion to 90 degrees
- Adequate pain control with oral medications
Week 1-2 Post-Surgery
Initial recovery focuses on:
- Ice application 20 minutes every 2-3 hours
- Ankle pump exercises hourly while awake
- Heel slides to improve flexion
- Straight leg raises for quadriceps strength
- Walking with walker or crutches
Range of motion typically reaches 90-100 degrees flexion. Swelling peaks around day 3-4 before gradually improving.
Week 3-6 Recovery Phase
Physical therapy intensifies with:
- Stationary cycling when flexion reaches 100 degrees
- Progressive weight-bearing exercises
- Balance training on stable surfaces
- Gait normalization without assistive devices
Most patients discontinue walking aids by week 4. Driving resumes when patients demonstrate adequate reaction time and pain control, typically 3-4 weeks for left knee surgery, 4-6 weeks for right knee.
Long-term Outcomes
Full recovery encompasses:
- Return to low-impact activities at 6-8 weeks
- Swimming and cycling at 8-12 weeks
- Golf and doubles tennis at 3-4 months
- Hiking on even terrain at 4-6 months
⚠️ Important Note
High-impact activities like running or basketball place excessive stress on partial replacements. Choose cycling, swimming, or elliptical training for cardiovascular fitness while protecting your implant longevity.
Comparing Robotic-Assisted Surgery and Conventional Techniques
Conventional partial knee replacement uses mechanical cutting guides aligned to anatomical landmarks. Surgeons estimate bone cuts based on pre-operative X-rays and intraoperative assessment.
Robotic-assisted approaches may offer:
- Guidance designed to reduce variation in component positioning
- Planning and soft tissue assessment before bone resections
- Real-time alignment feedback during bone preparation
Conventional technique benefits:
- Operative time that may be shorter in some cases
- Lower equipment costs
- Availability at more surgical centres
- Long-term follow-up data spanning decades
Clinical Outcomes
Some studies suggest similar pain scores and function between robotic-assisted and conventional partial knee replacement at around one year. Robotic assistance may offer more reproducible implant alignment. Longer-term data on revision rates is still being collected, and individual results may vary.
Potential Risks and Considerations
Partial knee replacement, like any surgery, carries risks, which may differ from those of total knee replacement. These include:
- Infection requiring antibiotics or, uncommonly, implant removal
- Blood clots in the leg veins or, less commonly, the lungs
- Implant loosening requiring revision surgery
- Persistent pain from arthritis in other compartments
- Knee stiffness requiring manipulation under anaesthesia
Robotic-Specific Considerations
Pin site fractures are rare when securing the tracking arrays to bone. Surgeons place pins in mechanically strong areas of bone. Robotic assistance may extend operative time in some cases, and studies to date have not shown a clear difference in infection rates.
In the uncommon event of a technical issue, the surgeon can continue with conventional instruments.
When to Seek Medical Advice
Consult a specialist who treats knee conditions if you experience:
- Knee pain isolated to one area that disrupts sleep
- Catching or locking sensations during movement
- Swelling that persists despite rest and elevation
- Difficulty with stairs due to inner or outer knee pain
- Failed improvement after 3-6 months of conservative treatment
- Visible knee deformity or feeling of instability
- Pain medication dependency for daily activities
Commonly Asked Questions
How long do partial knee replacements last?
Studies suggest that many modern partial knee implants remain functioning at 10 years and beyond, with reported survival rates of around 85 to 90% at 10 years and 75 to 85% at 15 years. Younger patients face a higher revision risk due to longer life expectancy and higher activity levels. Implant longevity depends on several factors, including alignment, activity level, and bone quality. Long-term data on robotic-assisted partial knee implants is still being collected.
Can I have an MRI after robotic-assisted partial knee replacement?
In most cases, yes. Modern knee implants use MRI-compatible materials such as titanium and cobalt-chromium. Inform the MRI technician about your implant. Some image distortion may occur near the implant, but it typically does not prevent diagnostic imaging of other body areas.
What happens if arthritis develops in other compartments?
Conversion to total knee replacement may be required if arthritis progresses to other compartments. This occurs in some partial replacement patients over time. Conversion surgery may take longer than a primary total replacement, and outcomes are generally comparable, though individual results vary.
Does robotic surgery eliminate human error?
Robotic systems are designed to support accuracy in bone cutting but rely on surgeon judgment for planning and soft tissue management. Surgeons control all decisions. The ROSA system supports the surgeon’s plan but cannot independently assess tissue quality or patient-specific variations.
How soon can I travel after surgery?
Short car trips (under 2 hours) may resume at 2 to 3 weeks. Air travel requires adequate knee flexion for seating and blood clot prevention measures. Many surgeons approve flights after 4 to 6 weeks. Long-haul flights may require compression stockings and regular walking, as advised by your surgeon.
Next Steps
Robotic-assisted partial knee replacement using the ROSA Partial Knee System is designed to support accurate implant positioning and bone preservation in suitable patients with single-compartment arthritis. Success depends on appropriate patient selection, surgical expertise, and structured rehabilitation.
If you’re experiencing persistent knee pain localised to one area despite conservative treatment, our orthopaedic specialist can evaluate your candidacy for robotic-assisted partial knee replacement and discuss personalised treatment options.
