Partial knee replacement preserves healthy bone and ligaments while replacing only the damaged compartment of the knee, and it typically supports faster recovery and more natural movement than total knee replacement.
Like any surgery, it carries its own set of risks worth understanding beforehand, ranging from infection and blood clots to implant-specific concerns such as bearing dislocation or arthritis progressing in the untreated parts of the knee. Knowing what to watch for helps you and your surgical team catch issues early.
Surgical and Anaesthetic Risks
Before scheduling surgery, your orthopaedic surgeon carries out a thorough evaluation to understand your anatomy and overall fitness for the procedure.
- Physical and medical review: A physical examination, X-rays, and detailed medical history review are combined with blood tests checking anaemia, kidney function, and clotting ability.
- Cardiac screening: An electrocardiogram assesses heart rhythm, and patients over 50 or with a cardiac history may need cardiology clearance.
- CT-based planning: A CT scan, taken one to two weeks before surgery and involving no contrast dye, captures detailed images of your femur, tibia, and patella, which software converts into a three-dimensional model used to plan implant size, positioning, and alignment.
Infection
Surgical site infection is one of the more serious complications following partial knee replacement, though current data suggest it’s less common than after total knee replacement.
- Superficial infection: Typically appears within the first few weeks with wound redness, warmth, drainage, and localised pain, and usually responds well to oral antibiotics and wound care.
- Deep infection: More challenging to treat around the implant, since bacteria can form biofilms on metal and polyethylene surfaces, and may require surgical debridement or, in established cases, implant removal with staged reimplantation.
Registry and cohort data suggest infection rates after partial knee replacement generally fall in the range of roughly 0.1 to 0.8 per cent, lower than the 1 to 2 per cent typically reported for total knee replacement.
Risk factors for infection include diabetes, obesity, rheumatoid arthritis, immunosuppressive medications, and previous knee surgery. Pre-operative steps such as blood glucose control and treating dental infections beforehand may help reduce this risk.
Blood Clots
Venous thromboembolism, which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), is a recognised risk after lower limb surgery due to reduced mobility and surgical trauma.
DVT typically develops in the calf or thigh veins, causing swelling, pain, warmth, or discolouration, though some clots remain asymptomatic. PE occurs when a clot fragment travels to the lungs, and symptoms can range from mild breathlessness to a medical emergency, so it requires immediate attention.
Prevention typically combines blood-thinning medication, mechanical compression devices, early mobilisation, and adequate hydration, with most patients on anticoagulation for several weeks depending on individual risk factors.
Did You Know?
Early mobilisation after partial knee replacement, often beginning the day of surgery, does more than support rehabilitation. Walking activates the calf muscle pump that assists venous return, which may help reduce blood clot formation in the deep leg veins.
Implant-Specific Complications
Partial knee replacement components face mechanical challenges distinct from those seen in total knee replacements.
Mobile-bearing designs allow the polyethylene insert to move between components for more natural knee kinematics, but this mobility introduces a small risk of the bearing dislocating, which typically requires surgical repositioning.
Fixed-bearing designs remove that dislocation risk but may wear differently, and your surgeon selects the design based on your anatomy and activity level.
Component loosening, where the bond between implant and bone fails, can result from inadequate initial fixation, infection, or gradual wear over time, and is typically picked up through routine X-rays before symptoms appear.
Arthritis Progression in the Untreated Compartments
Because partial knee replacement leaves the rest of the knee untouched, those areas can go on to develop arthritis over time.
National joint registry data identify disease progression in other compartments and aseptic loosening as the two leading reasons for partial knee replacement revision.
Careful patient selection, including truly isolated single-compartment arthritis and intact ligaments, tends to lead to more favourable long-term outcomes. If progression does occur, conversion to total knee replacement is generally a straightforward option, and many patients benefit from years of good function from their partial replacement before that point, if it’s ever needed at all.
For some patients, robotic-assisted techniques are one option that may support more precise implant alignment, which some studies associate with a lower risk of loosening and malalignment-related revision, though outcomes still depend heavily on individual factors and surgical experience.
Stiffness and Range of Motion Issues
While partial replacement typically preserves more natural motion than total replacement, some patients still develop stiffness.
- Excessive scar tissue within the joint capsule, known as arthrofibrosis, can restrict movement even with well-positioned components, and risk factors include delayed rehabilitation, infection, and individual healing patterns.
- Component malpositioning may mechanically limit motion or cause impingement, occasionally requiring revision to correct alignment.
- Intensive physiotherapy is the first line of treatment, with manipulation under anaesthesia considered if conservative measures don’t resolve the stiffness.
Important Note:
Persistent stiffness beyond three months after surgery is worth discussing with your surgeon. Addressing it early tends to bring better results than waiting, since mature scar tissue becomes more difficult to treat over time.
Nerve and Vessel Injury
Structures surrounding the knee carry some injury risk during surgery, though careful technique keeps this uncommon.
The infrapatellar branch of the saphenous nerve crosses the surgical field and is the nerve most often affected, typically causing numbness around the incision and the inner knee rather than functional problems. Peroneal nerve injury, which can cause foot drop, is rare with partial replacement but requires prompt splinting and possibly surgical exploration if recovery doesn’t occur naturally.
Major vessel injury is uncommon but can occasionally cause significant bleeding or, rarely, complications such as pseudo-aneurysm formation after surgery.
Persistent Pain
A small number of patients experience ongoing discomfort despite a technically well-positioned implant and no identifiable complication. The procedure is designed to reduce arthritic pain and improve function. However, your new knee typically won’t feel identical to a natural, healthy joint, and some patients notice awareness of the implant or occasional clicking.
- Complex regional pain syndrome involves abnormal pain processing, causing burning pain, swelling, and hypersensitivity out of proportion to the surgery. Early recognition with multidisciplinary treatment may improve outcomes.
- Unexplained pain without a clear cause on investigation sometimes relates to referred pain from the hip or spine, soft tissue irritation, or subtle instability.
Thorough evaluation helps identify treatable causes where they exist, while also managing expectations when no specific abnormality is found.
Reducing Your Risk of Complications
Several steps before and after surgery can meaningfully lower your risk profile.
- Optimise your health beforehand. Manage blood glucose if you have diabetes, consider smoking cessation, address weight where relevant, and treat any active dental or other infections before surgery.
- Follow medication guidance closely. Stop blood thinners as directed, adjust regular medications per your surgeon’s instructions, and take prescribed antibiotics on schedule.
- Engage fully with rehabilitation. Starting exercises early, attending physiotherapy, and staying consistent with home exercises helps reduce stiffness and clot risk.
- Watch for warning signs. Check your wound daily and report calf pain, swelling, or breathing difficulty to your medical team promptly.
- Keep up with follow-up appointments. Regular clinical and X-ray review helps catch early complications when they’re easiest to treat.
When to Seek Professional Help
Contact your surgical team promptly if you notice:
- Fever above 38 degrees Celsius in the weeks after surgery
- Increasing wound redness, warmth, or discharge
- New or worsening calf pain and swelling
- Sudden chest pain or difficulty breathing
- Severe pain not controlled by prescribed medication
- Sudden giving way or mechanical catching in the knee
- Progressive stiffness despite rehabilitation efforts
Commonly Asked Questions
How common are serious complications after partial knee replacement?
Serious complications requiring intervention occur in a small minority of patients, and most recover without significant issues when appropriate preventive measures are followed.
Does partial knee replacement carry fewer risks than total knee replacement?
Partial replacement generally involves lower blood loss, blood clot risk, and stiffness than total replacement, owing to its less invasive nature. It does, however, carry its own risks, including bearing dislocation and the possibility of arthritis progressing in the untreated compartments, which may eventually call for conversion surgery.
What factors increase my risk of complications?
Diabetes, obesity, smoking, inflammatory arthritis, and immunosuppressive medication are associated with higher complication risk, as is previous knee surgery, particularly if infection was involved. Addressing these factors beforehand and confirming you’re a suitable candidate can help reduce risk.
How long after surgery can complications occur?
Infection and blood clots are most likely to develop within the first few weeks, though late infection from bacteria elsewhere in the body can occur years later. Implant loosening and wear typically appear after several years, while arthritis progression in untreated compartments may take many years to become significant.
What happens if my partial knee replacement fails?
Most failed partial knee replacements can be converted to total knee replacement, a procedure that removes the partial components and implants a total knee system. While revision surgery is more complex than the original procedure, many patients achieve good outcomes following conversion.
Next Steps
Optimising modifiable risk factors before surgery, including blood glucose control, smoking cessation, and treating active infections, has a direct bearing on complication rates. After surgery, keeping up with follow-up appointments allows early detection of implant loosening or wear through X-rays before symptoms appear. Signs of deep infection, bearing dislocation, or persistent unexplained pain warrant prompt evaluation rather than waiting.
If you’re experiencing persistent knee pain, progressive stiffness, or mechanical symptoms such as giving way or catching, an accredited orthopaedic surgeon in Singapore can assess your suitability for partial knee replacement and walk you through the risks specific to your condition.
