Arthritis predominantly isolated to the front of the knee, where the kneecap meets the thighbone, can limit everyday movements like climbing stairs or rising from a chair, even when other areas of the joint remain relatively healthy.
Patellofemoral partial knee replacement addresses this specific compartment without disturbing the healthy medial and lateral compartments, preserving the cruciate ligaments and natural knee movement patterns compared to total knee replacement. Patient selection, based on imaging-confirmed isolated disease, intact ligaments, and preserved cartilage elsewhere in the joint, plays a central role when evaluating potential treatment suitability.
Understanding Patellofemoral Arthritis
Patellofemoral arthritis differs from the more common tibiofemoral arthritis that affects the main weight-bearing surfaces of the knee. The patella sits within a groove (trochlea) on the front of the femur, gliding up and down as the knee bends and straightens. Cartilage breakdown in this area results in bone-on-bone contact during knee flexion.
Symptom Patterns
Patients with isolated patellofemoral arthritis describe anterior knee pain that intensifies with:
- Stair climbing (especially descending)
- Prolonged sitting with bent knees (theatre sign)
- Rising from low chairs or the floor
- Squatting or kneeling activities
- Downhill walking
Pain during level walking at normal pace often remains minimal until the disease progresses significantly. This activity-specific pattern distinguishes patellofemoral from tibiofemoral arthritis, where weight-bearing on a straight leg typically provokes symptoms.
A doctor can usually confirm this pattern during a physical examination, checking for grinding sensations, tenderness around the kneecap, and normal knee stability elsewhere in the joint.
Diagnostic Confirmation
Clinical suspicion requires imaging confirmation before surgery can be considered. X-rays typically confirm whether wear is concentrated at the front of the knee, where the kneecap meets the thighbone.
An MRI scan may also be used to check the condition of cartilage throughout the knee, confirming that the wear is genuinely limited to this area and that the ligaments and meniscus remain healthy elsewhere in the joint.
The combination of clinical examination and imaging helps determine whether arthritis is sufficiently localised to the patellofemoral compartment for this targeted procedure to be a suitable option.
Candidacy Criteria
Orthopaedic surgeons evaluate several factors when determining suitability for patellofemoral replacement.
Patients who tend to be suitable typically have:
- Arthritis limited to the front of the knee, with the rest of the joint relatively healthy
- Stable knee ligaments
- A kneecap that tracks normally, or can be corrected to do so
- Sufficient healthy bone to support the implant
- A reasonable range of motion
- Realistic expectations and the ability to commit to rehabilitation
Younger, active patients with isolated disease may benefit because the procedure preserves bone stock for potential future procedures while aiming to support functional mobility.
Patients who typically aren’t suitable include those with:
- Arthritis affecting other parts of the knee, even mildly
- Autoimmune or inflammatory joint conditions, such as rheumatoid arthritis
- Unstable knee ligaments
- A knee that cannot fully straighten
- Kneecap misalignment that cannot be corrected with soft tissue surgery
- Previous surgery that significantly changed the knee’s alignment
- Active infection
Some factors, such as prior arthroscopic procedures, mild wear elsewhere in the joint, or higher-demand occupational needs, don’t rule out the procedure outright but call for individual assessment weighing the benefits against the risk of needing revision surgery later.
The Surgical Procedure
Patellofemoral replacement involves resurfacing the damaged area at the front of the knee, where the kneecap meets the thighbone, while leaving the rest of the joint untouched.
The surgeon works through a smaller incision than the one used for total knee replacement. The damaged surface is reshaped and fitted with a smooth metal component, and the underside of the kneecap is fitted with a matching plastic surface. Together, these recreate a natural gliding motion for the kneecap during movement.
Because the procedure preserves the knee’s ligaments and the surfaces on either side of the joint, many patients experience a more natural feeling knee and a faster recovery compared with total knee replacement.
Recovery and Rehabilitation
Postoperative recovery from patellofemoral replacement typically progresses faster than total knee replacement due to preserved structures and smaller surgical exposure.
Early Phase (Weeks 1-6)
Weight-bearing begins immediately with walking aids. Many patients transition from a walker to a cane within the first two weeks. Initial physiotherapy focuses on:
- Quadriceps activation and straight leg raises
- Patellar mobilisation to prevent adhesions
- Range of motion exercises within comfort
- Gait training and balance work
- Swelling management with ice and elevation
Discomfort generally improves within the first few weeks. Many patients transition away from regular pain medications over 3 to 4 weeks under medical guidance, depending on individual pain tolerance and recovery.
Intermediate Phase (Weeks 6-12)
Progressive strengthening replaces initial mobility work:
- Closed-chain exercises (mini squats, step-ups)
- Stationary cycling with increasing resistance
- Pool-based exercises if available
- Proprioceptive training
Return to driving occurs around 4-6 weeks for automatic vehicles (right knee surgery may require longer). Sedentary work resumes at similar timeframes; physical occupations require 8-12 weeks.
Long-term Recovery
Full recovery takes 3-6 months. Patients typically notice continued improvement in strength and confidence for up to one year. Activities involving deep knee flexion improve progressively as swelling resolves and strength returns.
Important Note: High-impact activities, including running, jumping sports, and heavy manual labour, place significant stress on any knee replacement. Surgeons typically recommend transitioning to lower-impact alternatives to help maintain implant longevity.
Difference from Total Knee Replacement
Advantages of Patellofemoral Replacement
- Preserves cruciate ligaments and normal knee kinematics
- Smaller incision and less tissue disruption
- Faster recovery and rehabilitation
- More natural “feel” reported by many patients
- Preserves bone stock for potential future revision
- Lower blood loss during surgery
Limitations
- Only suitable for isolated patellofemoral disease
- Progression in other compartments may require later revision
- Technical demands on surgeon experience
- Smaller evidence base than total knee replacement
Patients with disease limited to the patellofemoral compartment may gain advantages from the targeted approach. However, those with borderline involvement of other compartments may benefit from addressing all surfaces simultaneously with total replacement rather than risking early revision.
Long-term Outcomes
Some studies report patellofemoral replacement survivorship broadly comparable to unicompartmental (partial) replacements of the medial compartment, though results vary by prosthesis design, surgical era, and patient selection. The primary reason for revision remains progression of arthritis to other compartments rather than implant failure.
Functional outcomes show high satisfaction rates among appropriately selected patients. Activities causing preoperative pain, such as stair climbing and rising from chairs, typically improve.
A randomised comparative trial found that range of motion after patellofemoral replacement exceeded that seen after total knee replacement at early follow-up. However, longer-term follow-up of the same trial found this early advantage did not persist, with range of motion and patient-reported outcomes becoming similar between the two procedures by 6 years, and revision rates for patellofemoral replacement rising over that period while total knee replacement revision rates declined.
Your surgeon can help weigh these longer-term trends when discussing which procedure may be more suitable for you.
When to Seek Professional Help
Consult an orthopaedic surgeon if you experience:
- Anterior knee pain persisting despite physiotherapy and activity modification
- Progressive difficulty with stairs or rising from seated positions
- Knee pain limiting work or recreational activities
- Grinding or catching sensations in the front of the knee
- Swelling concentrated around the kneecap
- Night pain or pain at rest suggesting advancing disease
Commonly Asked Questions
How long does a patellofemoral replacement last?
Pooled data from systematic reviews and joint registries indicate implant survival of roughly 90% at 5 years, 82% at 10 years, and 70-75% at 15 to 20 years, with progression of arthritis in other compartments the most common reason for later revision. Implant survival depends on patient factors including activity level, body weight, and whether disease progresses to other compartments. Younger patients may eventually require revision to total knee replacement.
Can I kneel after patellofemoral replacement?
Kneeling becomes possible for many patients, though some experience discomfort due to the patellar component beneath the skin. Using a cushioned surface helps. Comfort with kneeling typically improves over the first year as tissues settle.
What activities should I avoid after surgery?
High-impact activities, such as running, jumping sports, and heavy squatting with weights, stress the implant and remaining native cartilage. Walking, swimming, cycling, golf, and doubles tennis remain appropriate. Your surgeon provides individualised guidance based on your condition and implant.
How does recovery compare to total knee replacement?
Many patients find recovery faster with less initial pain and quicker return to function. Hospital stay is typically 1-2 days. Range of motion returns more quickly because the procedure preserves more native structures. Full recovery still requires 3-6 months.
What if my arthritis spreads to other parts of the knee?
If arthritis eventually develops in the medial or lateral compartments, conversion to a total knee replacement is designed to address all joint surfaces. This procedure is generally straightforward because the initial partial surgery preserved natural bone stock.
Next Steps
Patellofemoral replacement is appropriate only when arthritis is confirmed as isolated to the front compartment through clinical examination and diagnostic imaging. Patient selection, based on ligament integrity, cartilage health in other compartments, and anatomical factors, determines whether this targeted procedure or a total knee replacement is the appropriate approach. If disease progresses to other compartments over time, conversion to a total knee replacement remains a reliable option due to preserved bone stock.
If you are experiencing anterior knee pain with stair climbing, difficulty rising from a seated position, or grinding sensations around the kneecap, scheduling a medical consultation with a qualified orthopaedic surgeon allows for a comprehensive evaluation to determine the most suitable management plan for your joint.
