Did you know that your kneecap experiences forces up to seven times your body weight during deep squatting activities? Patellofemoral arthroplasty, commonly known as knee cap replacement surgery, is designed to address arthritis damage limited to the kneecap (patella) and the groove where it sits on the thighbone (trochlea). Unlike total knee replacement, this procedure preserves healthy cartilage in other knee compartments while addressing isolated patellofemoral joint degeneration.
The surgery involves resurfacing only the damaged cartilage surfaces where the kneecap meets the thighbone, leaving the rest of the knee joint intact. Much like a partial knee replacement in Singapore, this targeted approach may potentially result in faster recovery times, improved knee movement, and a more natural-feeling joint in suitable candidates. Surgeons may recommend this option when arthritis affects only the front compartment of the knee, particularly in younger patients who want to maintain an active lifestyle.
The patellofemoral joint consists of the undersurface of the kneecap and the groove (trochlea) at the front of the thighbone. This joint experiences significant stress during activities like climbing stairs, squatting, or rising from a chair. The kneecap acts as a pulley, increasing the leverage of the quadriceps muscle during knee bending.
Isolated patellofemoral arthritis develops when cartilage breakdown occurs specifically in this joint while other knee compartments remain healthy. Common causes include:
The condition often affects people who have been active in sports involving jumping, squatting, or repeated knee bending.
? Did You Know?
The kneecap experiences significant forces during deep squatting activities, making it particularly vulnerable to wear in athletes and active individuals.
Candidates for knee cap replacement surgery have arthritis confined to the patellofemoral compartment with healthy cartilage in the medial and lateral compartments. X-rays and MRI scans confirm this isolated damage pattern. Patients typically experience anterior knee pain that worsens with stairs, prolonged sitting, or squatting movements.
Age considerations play a role, with surgeons often considering this procedure for patients over 40 years old due to implant longevity concerns, though younger patients may also be suitable candidates. However, younger patients with severe isolated patellofemoral arthritis may still qualify, particularly if non-surgical treatments have failed. Body weight impacts outcomes, as excess weight increases stress on the implant. Surgeons evaluate knee alignment, muscle strength, and overall joint stability during assessment, as poor knee mechanics can often cause compensatory pain that might eventually require evaluation by a hip specialist in Singapore.
Contraindications include inflammatory arthritis affecting multiple joints, significant malalignment requiring corrective osteotomy, or arthritis extending beyond the patellofemoral compartment. Previous surgeries, particularly those altering knee anatomy, may affect candidacy. Your orthopaedic surgeon conducts thorough imaging and physical examination to determine suitability.
Pre-operative preparation includes medical clearance, blood tests, and discontinuing certain medications. Patients undergo either general anaesthesia or regional nerve blocks combined with sedation. The procedure typically takes 60-90 minutes.
The surgeon makes a 10-15cm vertical incision at the front of the knee, accessing the patellofemoral joint through a minimally invasive approach when possible. After exposing the joint, instruments measure the dimensions of the patella and trochlear groove. The surgeon removes damaged cartilage and a thin layer of underlying bone from both surfaces.
Computer-assisted navigation or robotic guidance may be used to assist with bone cuts and implant positioning in some cases. The prosthetic components consist of a metal backing cemented to the patella and a metal groove component fixed to the femur. Current implants feature anatomic designs that match natural joint geometry. The surgeon tests knee tracking throughout the range of motion before closing the incision in layers.
⚠️ Important Note
Proper implant positioning affects long-term outcomes. Malalignment can cause accelerated wear or persistent pain after surgery.
Hospital discharge commonly occurs within 1-2 days post-surgery, though this varies based on individual recovery. Patients walk with crutches or a walker immediately, bearing weight as tolerated. The surgical dressing remains for 48-72 hours before switching to waterproof coverings. Sutures or staples are typically removed around the 10-14 day mark.
Weeks 1-2: Focus on reducing swelling through elevation and ice application. Perform ankle pumps and quadriceps sets hourly while awake. Begin knee bending exercises aiming for 90 degrees flexion. Walk short distances every 2-3 hours.
Weeks 3-4: Increase walking distance gradually. Add stationary cycling once achieving 90 degrees flexion. Start straight leg raises and mini squats against a wall. Physical therapy sessions 2-3 times weekly guide progression.
Weeks 5-8: Progress to resistance exercises using bands or light weights. Practice step-ups on low platforms. Swimming and water walking provide low-impact conditioning. Some patients may discontinue walking aids during this phase, depending on individual progress.
Months 3-6: Gradual return to normal daily activities including driving (often around week 6 for suitable candidates), office work, and light recreational activities. Low-impact sports like cycling, swimming, and golf typically resume. High-impact activities require surgeon approval.
Full recovery with maximum strength and function occurs around 6-12 months. Some patients report their knee feels more natural compared to a total knee replacement in Singapore, with potential improvements in ability to kneel and proprioception, though individual experiences vary.
While complications remain uncommon, patients should recognize warning signs requiring immediate medical attention. Infection can occur but requires prompt treatment. Signs include:
Blood clots may occasionally develop after knee surgery or limited mobility, a risk that is also closely monitored after other major lower-body procedures like hip replacement surgery in Singapore. To lower this risk, your healthcare team may recommend blood-thinning medication, compression stockings, and early movement as soon as it is safe to do so.
Certain implant-related issues can also arise over time, such as loosening, wear, or progression of arthritis in other parts of the knee. Regular follow-up visits, often with X-ray assessments, help your orthopaedic surgeon monitor the position of the implant and the condition of surrounding joint surfaces.
Some patients may continue to experience discomfort at the front of the knee even after a technically successful procedure, which is sometimes linked to soft-tissue sensitivity. Joint stiffness that limits bending may require additional physiotherapy, and in selected cases, manipulation under anaesthesia if flexibility does not improve adequately. Kneecap instability or maltracking can occasionally occur, particularly in individuals who already have alignment concerns.
✅ Quick Tip
Document your recovery progress with weekly photos and range of motion measurements. This helps identify any deviation from expected healing patterns early.
Modern patellofemoral implants demonstrate good survivorship, with many functioning well beyond 15-20 years. Implant longevity depends on patient factors including activity level, body weight, and bone quality. Younger, more active patients may experience faster wear rates.
Regular monitoring includes annual X-rays for the first few years, then every 2-3 years thereafter. Surgeons assess implant position, wear patterns, and adjacent compartment health. Early detection of problems allows for simpler revision procedures if needed.
Activity modifications help preserve implant function. Activities that may be suitable include:
Activities that may need to be avoided include:
Maintaining healthy body weight reduces implant stress and wear rates. A healthcare professional can provide specific guidance on appropriate activities and weight management.
Conversion to total knee replacement remains an option if arthritis develops in other compartments. This revision surgery may be less complex than revising a failed total knee replacement, as most native bone stock remains intact.
How long before I can drive after knee cap replacement surgery?
Most patients resume driving 4-6 weeks post-surgery once they can bend their knee adequately and have stopped narcotic pain medications. Right knee surgery typically requires longer recovery before driving. Your surgeon confirms readiness based on your strength and reaction time.
Will I be able to kneel after patellofemoral replacement?
Many patients regain kneeling ability within 6-12 months, though comfort varies individually. Using a cushion or knee pad helps. This is one difference compared to total knee replacement, where kneeling often remains uncomfortable long-term.
What happens if I need a total knee replacement later?
Converting patellofemoral replacement to total knee replacement involves removing the existing implants and inserting full knee prostheses. The procedure is less complex than revising a failed total knee replacement since most bone stock remains preserved.
Can both knees undergo patellofemoral replacement simultaneously?
Bilateral simultaneous surgery is possible for appropriate candidates but requires careful consideration. Most surgeons prefer staging procedures 3-6 months apart to optimize rehabilitation and reduce perioperative risks.
How do I know if arthritis has progressed to other compartments?
Progressive pain in the inner or outer knee, worsening with weight-bearing activities, suggests arthritis spread. Regular follow-up X-rays detect joint space narrowing in adjacent compartments before symptoms develop.
Successful outcomes from knee cap replacement depend on proper patient selection and commitment to rehabilitation. Schedule comprehensive evaluation including weight-bearing X-rays and MRI to confirm isolated patellofemoral arthritis. Optimize your physical condition pre-operatively through quadriceps strengthening exercises.
If you are experiencing persistent anterior knee pain, difficulty with stairs, or catching sensations in your knee, consult with an orthopaedic surgeon in Singapore to evaluate whether patellofemoral replacement is appropriate for your specific condition.
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Dr Kau (许医生) is a Fellowship trained Orthopaedic Surgeon with a subspecialty interest in Hip and Knee surgery and has been in practice for more than 15 years.
He is experienced in trauma and fracture management, sports injuries, and joint replacement surgery.
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