Patellofemoral arthroplasty: Definition, Uses, and Clinical Overview

Patellofemoral arthroplasty Introduction (What it is)

Patellofemoral arthroplasty is a partial knee replacement focused on the kneecap joint.
It resurfaces the underside of the patella and the groove of the femur where the patella glides.
It is most commonly used for arthritis limited to the patellofemoral compartment.
It is different from a total knee replacement because the rest of the knee joint is preserved.

Why Patellofemoral arthroplasty used (Purpose / benefits)

The primary purpose of Patellofemoral arthroplasty is to reduce pain and improve function when the damaged area is mainly the patellofemoral joint (the joint between the patella and the femur). In many people with patellofemoral arthritis, symptoms are triggered by activities that load the front of the knee—such as stairs, hills, squatting, getting up from a chair, or sitting with the knee bent for long periods.

At a high level, the procedure aims to:

• Replace worn cartilage surfaces in the patellofemoral compartment with smooth implant surfaces, reducing painful bone-on-bone contact.
• Improve patellar tracking (how the kneecap moves in the femoral groove) when maltracking is related to joint surface wear or shape, and when alignment issues are correctable.
• Preserve the tibiofemoral compartments (medial and lateral) when they remain relatively healthy, keeping more native bone and tissue than a total knee arthroplasty.
• Maintain more “normal” knee kinematics in appropriate candidates because ligaments and non-resurfaced compartments are typically left intact.
• Provide a surgical option between nonoperative care and total knee replacement, especially for isolated patellofemoral disease.

Benefits are case-dependent and can vary by clinician, implant design, and patient anatomy. The key concept is compartment-specific treatment: addressing the part of the knee that is diseased while leaving other areas untouched when feasible.

Indications (When orthopedic clinicians use it)

Orthopedic clinicians may consider Patellofemoral arthroplasty in scenarios such as:

• Isolated patellofemoral osteoarthritis (cartilage loss mainly behind the patella and/or in the trochlear groove) confirmed clinically and on imaging
• Persistent anterior knee pain and functional limitation after an adequate trial of nonsurgical management (varies by clinician and case)
• Post-traumatic patellofemoral arthritis, such as after a patellar fracture or injury affecting the joint surface
• Degenerative change related to long-standing patellar maltracking or instability, when other compartments are relatively preserved and alignment issues are addressed as needed
• Failed prior patellofemoral cartilage procedures (for example, certain cartilage restoration or resurfacing attempts), depending on remaining bone and soft-tissue status
• Patients with preserved cruciate and collateral ligament function and relatively stable knee mechanics (as assessed by the treating team)

Contraindications / when it’s NOT ideal

Patellofemoral arthroplasty is typically less suitable when symptoms are not primarily coming from the patellofemoral compartment or when other factors predict poor mechanics or progression of arthritis. Common reasons it may not be ideal include:

• Significant tibiofemoral arthritis (medial or lateral compartment disease) seen on imaging or suggested by symptoms (for example, joint-line pain rather than anterior pain)
• Inflammatory arthritis (such as rheumatoid arthritis) where multi-compartment involvement is common and progression can be less predictable
• Uncorrected malalignment of the limb (varus/valgus) that shifts load into the tibiofemoral compartments
• Knee instability from ligament deficiency or poor neuromuscular control that cannot be adequately addressed
• Active or recent joint infection, or systemic infection concerns (general surgical contraindication)
• Severe stiffness or poor range of motion that limits function regardless of resurfacing
• Extensor mechanism problems (significant quadriceps weakness, patellar tendon disruption, or major tracking disorders) that are not correctable with adjunctive procedures
• Substantial bone loss in the patella or trochlea that complicates secure implant fixation (varies by implant system and surgeon preference)

In some borderline situations, another approach may be preferred—such as realignment surgery, cartilage-focused procedures, or total knee arthroplasty—depending on the overall pattern of arthritis and mechanics.

How it works (Mechanism / physiology)

Core biomechanical principle

The patellofemoral joint is a high-load contact area. The patella acts like a pulley for the quadriceps, improving the leverage of the extensor mechanism as the knee straightens. When cartilage is worn, pressure across damaged surfaces can cause pain, swelling, grinding (crepitus), and reduced function.

Patellofemoral arthroplasty works by:

• Resurfacing the trochlea (femoral groove) with a metal component shaped to provide a smooth track.
• Resurfacing the back of the patella with a plastic (polyethylene) button in many designs, creating a low-friction articulation.

This changes joint contact from damaged cartilage and exposed bone to engineered bearing surfaces intended to glide more smoothly.

Relevant anatomy (what structures are involved)

• Patella (kneecap): A sesamoid bone embedded in the quadriceps tendon; its undersurface articulates with the femur.
• Trochlea (femoral groove): The anterior groove of the distal femur where the patella tracks during flexion/extension.
• Articular cartilage: Smooth tissue covering bone ends; loss here is central to arthritis pain and mechanics.
• Quadriceps tendon and patellar tendon (extensor mechanism): Drive knee extension and influence tracking; not replaced in this procedure but critically affect outcomes.
• Menisci and tibial cartilage: Typically not resurfaced in Patellofemoral arthroplasty; their condition matters because disease there may shift the treatment toward other options.
• Ligaments (ACL, PCL, MCL, LCL): Usually preserved; overall stability affects function and wear patterns.

Onset, duration, and reversibility

This is a surgical reconstruction, not a medication, so “onset” is better described as postoperative recovery and rehabilitation rather than an immediate pharmacologic effect. Longevity is influenced by implant design, fixation method, alignment, activity demands, and progression of arthritis in other compartments. Reversibility is limited, but conversion to total knee arthroplasty is sometimes performed if arthritis progresses or symptoms persist (appropriateness varies by clinician and case).

Patellofemoral arthroplasty Procedure overview (How it’s applied)

Below is a high-level workflow that commonly appears in clinical practice. Specific steps and timing vary by surgeon, facility, and patient factors.

1. Evaluation / exam – History focused on anterior knee pain patterns (stairs, squats, prolonged sitting) and mechanical symptoms. – Physical exam assessing patellar tracking, stability, alignment, range of motion, and tenderness location. – Review of prior surgeries, instability episodes, or trauma.

2. Imaging / diagnostics – Standard knee radiographs often include patellofemoral-focused views to assess joint space narrowing, osteophytes, and alignment. – MRI or CT may be used in selected cases to evaluate cartilage distribution, trochlear shape, prior injury changes, or maltracking contributors (use varies by clinician and case).

3. Preparation (preoperative planning) – Determination that disease is primarily patellofemoral rather than tibiofemoral. – Implant selection and sizing plan (implant design varies by material and manufacturer). – Consideration of whether adjunctive realignment or soft-tissue balancing is needed.

4. Intervention (the operation) – Surgical exposure of the patellofemoral joint. – Preparation of the femoral trochlear surface and placement of the trochlear component. – Preparation of the patella and placement of a patellar component in many systems. – Assessment of tracking through knee motion; balancing steps may be performed if needed.

5. Immediate checks – Verification of component position and patellar tracking. – Wound closure and postoperative imaging per facility routine.

6. Follow-up / rehabilitation – Early postoperative follow-ups to monitor wound healing, swelling, motion, and function. – A rehabilitation plan typically emphasizes restoring range of motion, quadriceps strength, gait mechanics, and functional tolerance. – Ongoing monitoring for symptoms that could indicate progression of arthritis in other compartments.

Types / variations

Patellofemoral arthroplasty is not a single uniform technique. Common variations include:

• Inlay vs onlay trochlear designs
• Inlay systems are designed to sit within the prepared trochlear cartilage region.

• Onlay systems cap the anterior femur more broadly; selection depends on anatomy and surgeon preference.

• Patellar resurfacing choices

• Many systems include a patellar button (polyethylene) resurfacing the underside of the patella.

• Some surgeons may modify resurfacing decisions based on patellar bone stock and tracking (varies by clinician and case).

• Fixation method

• Cemented fixation is common in many joint replacements.

• Cementless or porous-coated options exist in some designs; suitability varies by implant and bone quality.

• Technique assistance

• Conventional instrumentation vs computer navigation or robotic-assisted workflows may be used to support alignment and sizing (availability varies).

• Combined procedures (selected cases)

• Patellofemoral arthroplasty may be paired with realignment procedures (for example, tibial tubercle osteotomy) or soft-tissue balancing to address maltracking contributors, depending on the underlying anatomy.

Pros and cons

Pros:

• Preserves uninvolved knee compartments when disease is isolated to the patellofemoral joint
• Replaces painful, worn cartilage surfaces with smooth bearing materials
• Can improve function for activities that load the front of the knee (stairs, rising from sitting)
• Typically maintains native cruciate ligaments and much of the knee’s original structure
• May be easier to revise to total knee arthroplasty than revising some other joint reconstructions (varies by clinician and case)
• Offers a compartment-specific option when total knee arthroplasty may be more than is needed for isolated disease

Cons:

• Not appropriate if arthritis is present in the medial or lateral tibiofemoral compartments
• Symptoms can persist if pain is coming from non-patellofemoral sources (tendons, hip/spine, meniscus, etc.)
• Risk of progression of arthritis in other compartments over time, potentially leading to additional surgery
• Patellar tracking issues can continue if malalignment or soft-tissue factors are not fully addressed
• As with any arthroplasty, there are general surgical risks (infection, stiffness, blood clots, implant-related problems), with rates varying by population and setting
• Outcomes may be more sensitive to patient selection and implant positioning than some broader procedures

Aftercare & longevity

Aftercare for Patellofemoral arthroplasty is typically centered on restoring motion, strength, and efficient patellar mechanics while the surgical tissues heal. Exact protocols differ by surgeon and rehabilitation team, so the most useful way to think about aftercare is in terms of factors that influence recovery and durability, rather than a one-size-fits-all schedule.

Common factors that affect outcomes and longevity include:

• Extent and location of arthritis
• Best durability is generally expected when arthritis truly is isolated to the patellofemoral compartment.

• If tibiofemoral degeneration is already present, symptoms may evolve over time.

• Implant design and materials

• Bearing materials, component geometry, and fixation approach vary by material and manufacturer.

• Design choices can influence tracking and contact mechanics.

• Alignment and tracking

• Limb alignment, trochlear anatomy, and soft-tissue balance affect how the patella loads the implant.

• Persistent maltracking can increase wear or discomfort.

• Rehabilitation participation and follow-up

• Regaining quadriceps strength and knee motion supports function and may reduce overload patterns.

• Follow-ups help identify stiffness, swelling, or evolving compartment symptoms.

• Activity demands and load

• High-load activities and occupational demands can increase stress across the patellofemoral articulation.

• Load tolerance varies by individual conditioning, technique, and anatomy.

• Body weight and overall health

• Higher body weight can increase joint forces; the impact on longevity varies by case.
• Conditions that affect healing or infection risk (for example, diabetes or smoking status) can influence surgical recovery in general.

Longevity is not a fixed number and is best described as variable, influenced by selection, technique, and whether arthritis develops elsewhere in the knee.

Alternatives / comparisons

Patellofemoral arthroplasty sits within a spectrum of care options for anterior knee pain and patellofemoral arthritis. Alternatives are chosen based on diagnosis, severity, compartment involvement, and patient goals.

• Observation / monitoring
• Appropriate when symptoms are mild, intermittent, or not clearly linked to structural arthritis.

• Often paired with activity modification strategies and periodic reassessment (details vary by clinician and case).

• Physical therapy and exercise-based care

• Common first-line approach for many anterior knee pain syndromes and early patellofemoral degeneration.

• Focus may include hip and quadriceps strength, movement retraining, flexibility, and patellar tracking mechanics.

• Medications

• Non-opioid analgesics or anti-inflammatory medications may be used for symptom control, depending on medical history and clinician recommendations.

• Medications do not restore cartilage but can reduce pain and swelling for some people.

• Bracing and taping

• Patellar braces or taping can sometimes reduce symptoms by altering tracking or pressure distribution.

• Responses are variable and may be used as a diagnostic clue (not definitive).

• Injections

• Options may include corticosteroid or viscosupplement-type injections, depending on region and practice patterns.

• Injections may help symptoms temporarily for some patients but do not replace severely worn joint surfaces.

• Arthroscopy

• Generally limited in treating established arthritis, but may be considered when there is a specific mechanical problem (for example, a loose body) coexisting with patellofemoral disease.

• The role of arthroscopy varies by clinician and case.

• Realignment procedures

• Procedures such as tibial tubercle osteotomy may be considered when maltracking or instability is a key driver and cartilage damage is not end-stage.

• These aim to redistribute forces rather than replace surfaces.

• Total knee arthroplasty (total knee replacement)

• More comprehensive resurfacing for multi-compartment arthritis.
• Often preferred when medial/lateral tibiofemoral compartments are clearly involved or when inflammatory arthritis affects the whole joint.

In brief: Patellofemoral arthroplasty is most comparable to a compartment-specific solution, while total knee arthroplasty is a whole-joint solution, and nonoperative approaches focus on symptom control and mechanics without resurfacing.

Patellofemoral arthroplasty Common questions (FAQ)

Q: Is Patellofemoral arthroplasty the same as a total knee replacement?
No. It is a partial knee replacement limited to the patellofemoral compartment (kneecap and femoral groove). A total knee replacement resurfaces the medial and lateral tibiofemoral compartments as well, and typically addresses the entire joint surface system.

Q: What kind of pain does it usually target?
It is designed for pain arising mainly from the front of the knee (anterior knee pain) related to patellofemoral arthritis. People often describe pain on stairs, squatting, or after sitting with the knee bent. Pain patterns can overlap with other knee conditions, so diagnosis is important.

Q: What type of anesthesia is used?
Many knee arthroplasty procedures are performed under general anesthesia, regional anesthesia (such as spinal), or a combination with nerve blocks. The exact plan depends on patient factors, anesthesiologist preference, and institutional practice.

Q: How long do the results last?
Longevity varies by clinician and case. Major influences include implant positioning, alignment, activity demands, and whether arthritis develops in other parts of the knee over time. Some patients later need conversion to total knee arthroplasty if other compartments become symptomatic.

Q: How painful is recovery?
Pain experiences vary widely. Early postoperative soreness and swelling are common after any joint surgery, and pain control strategies typically combine multiple approaches. Rehabilitation and gradual return of motion and strength are central parts of recovery.

Q: When can someone walk or put weight on the leg?
Weight-bearing status is determined by the surgeon based on the procedure details, implant fixation method, and whether additional realignment work was done. Many patients begin walking with assistance early, but the specifics vary by clinician and case.

Q: When can someone drive or return to work?
Timing depends on which leg was operated on, pain control, reaction time, mobility, and job demands. Sedating medications and limited strength can affect driving safety. Clinicians commonly individualize guidance based on function and recovery progress.

Q: Is Patellofemoral arthroplasty considered “safe”?
It is a widely performed orthopedic procedure for selected patients, but it still carries the general risks of surgery and implants (infection, stiffness, blood clots, and implant-related complications). Safety depends on patient health, surgical technique, and postoperative course, so risk is individualized.

Q: What does it cost?
Costs vary widely by country, hospital system, insurance coverage, implant selection, and whether additional procedures are performed. Charges may include surgeon fees, facility costs, anesthesia, imaging, and rehabilitation services. For accurate estimates, patients typically request a bundled or itemized quote from their care system.

Q: Can it be revised or converted later if arthritis progresses?
In some cases, yes. If tibiofemoral arthritis develops or symptoms persist, conversion to a total knee arthroplasty may be considered. Whether revision is appropriate and how complex it is depends on implant type, bone quality, and the overall knee condition.