Total Knee Replacement

What is knee replacement?

Total knee replacement (TKR) is surgery to replace the worn or damaged surfaces of the knee joint with an implant. The ends of the thigh bone (femur) and shin bone (tibia) are reshaped to accept precisely-fitting metal components, and a medical-grade plastic (polyethylene) spacer sits between them to act as the new cartilage surface. The result is a smooth, gliding joint that replaces a painful, arthritic one.

Like hip replacement, modern knee replacement is a highly successful operation. For the right patient, it reliably relieves pain, restores function, and gets people back to walking, working, cycling, bushwalking, and doing the everyday things that arthritis had been quietly taking away.

Dr de Hoog performs approximately 150-200 hip and knee replacements each year across his Townsville practice. His knee replacement practice is built around three specific clinical decisions - the Zimmer Persona Knee System, cementless (uncemented) fixation, and robotic assistance with the ROSA Knee system with OptimiZe. Each of these is discussed below.

When is knee replacement considered?

Knee replacement is generally considered when:

• Knee pain is persistent despite non-surgical treatment
• Pain is limiting daily activities - walking, sleeping, climbing stairs, standing from a chair, or your usual work
• Imaging confirms significant joint damage (most commonly osteoarthritis, but also rheumatoid or other inflammatory arthritis, or post-traumatic arthritis after a previous injury)
• You’ve genuinely trialled non-operative treatment

Before recommending surgery, Dr de Hoog will typically want to see that you’ve tried one or more of: activity modification, weight management where relevant, simple analgesia, a course of physiotherapy and strengthening, a walking aid if appropriate, and in selected cases an intra-articular injection.

Knee replacement is an elective operation. The right time to proceed is when knee pain is interfering with your life more than the surgery and recovery would. That decision is always made together.

The implant - Zimmer Persona Knee System

The Persona Knee is Zimmer Biomet’s contemporary total knee implant system, developed to provide more anatomical sizing and improved fit across the range of knee shapes seen in patients. Compared to earlier generations of knee implants, the Persona offers more precisely matched component sizes - which translates to better coverage of the tibia (shin bone), better soft tissue balance, and a more natural-feeling knee.

The Persona has been in widespread clinical use for more than a decade and is now one of the most commonly used knee implant systems in Australia and internationally. Peer-reviewed outcome studies have consistently shown excellent early and mid-term patient-reported outcomes and low revision rates.

Cementless (uncemented) fixation - both components

Total knee replacements can be fixed to the bone in one of two ways:

• Cemented - the femoral and tibial components are bonded to the prepared bone surfaces using acrylic bone cement (PMMA). This has been the standard approach for decades and has an excellent long-term track record.
• Cementless (uncemented) - the implants have a porous surface that allows the patient’s own bone to grow directly into the implant over the first 3 months after surgery. No cement is used.

Dr de Hoog typically uses cementless fixation for both the femoral and tibial components. The rationale for this choice:

• Biological fixation. With cementless fixation, the bond between bone and implant is your own bone growing into the implant’s surface - a living, biological interface rather than a layer of cement. Once fully ingrown, this interface is designed to last for the life of the implant.
• Preservation of bone stock. Cement fills a small but real amount of space at the bone-implant interface. Cementless fixation preserves more of your native bone, which is relevant if revision surgery is ever needed later in life.
• Modern surface technologies. Current-generation cementless knee implants use highly porous surface treatments (including 3D-printed and trabecular-metal surfaces) that enable much more reliable bone ingrowth than older cementless designs.
• Alignment with robotic precision. Cementless fixation relies on a precise fit between bone and implant. Robotic-assisted bone preparation delivers the millimetre-level accuracy that makes reliable cementless fixation achievable.

Cementless TKR is not right for every patient - those with significantly weaker bone (advanced osteoporosis) or certain anatomical considerations may do better with a cemented implant or a hybrid (cementless femur, cemented tibia). If that’s true in your case, Dr de Hoog will discuss it openly with you.

Robotic-assisted knee replacement - ROSA Knee with OptimiZe

Dr de Hoog uses the ROSA Knee system with OptimiZe (Zimmer Biomet) for his knee replacements. This is the most recent generation of the ROSA robotic platform, designed to work seamlessly with the Persona Knee.

How it works:

• Before surgery, imaging of your knee (standard X-rays in the ROSA system - a CT scan is not required) is used to build a three-dimensional model of your individual knee anatomy.
• A personalised surgical plan is developed on that model - the size, position, and rotation of the femoral and tibial components are planned to match your anatomy, your alignment, and your soft tissue balance.
• During the operation, the robotic system provides real-time guidance and feedback. As Dr de Hoog moves the knee through its range of motion, the robot measures ligament tension and joint balance in real time, and the surgical plan can be fine-tuned before any bone is cut.
• The bone cuts themselves are then executed within tight tolerances defined by the pre-operative plan.

What robotic assistance adds. Robotic TKR has been shown in peer-reviewed studies to improve the accuracy of component positioning, reduce the number of alignment outliers, and improve soft tissue balance compared with conventional instrumentation. Early clinical studies also show potentially lower pain scores in the first few months and faster early functional recovery, although long-term functional differences between robotic and conventional TKR are still being investigated.

The technology doesn’t replace surgical judgement - Dr de Hoog remains in control of every decision and every cut. Robotic assistance provides more accurate information and a more precise execution of the plan, particularly useful when pairing a modern cementless implant system like the Persona with a surgical approach that relies on fit-to-fit bone contact for fixation.

Surgical approach

Dr de Hoog uses a standard medial parapatellar approach to the knee - the well-established and most commonly used approach worldwide, with decades of published data supporting it. The approach is familiar, reliable, and gives the direct visualisation needed to perform the operation well. The bone cuts and implant positioning are then executed with robotic guidance, as described above.

A note on the patella

Your kneecap (patella) has a cartilage surface that can also be affected by arthritis. Historically, surgeons have taken two different approaches to this:

• Patellar resurfacing - replacing the back of the kneecap with a small plastic button.
• Non-resurfacing - leaving the native kneecap in place, on the basis that a well-designed femoral component provides a smooth surface for the patella to track on.

Dr de Hoog does not routinely resurface the patella. This is consistent with longstanding Australian practice. A 2025 analysis from the Australian Orthopaedic Association National Joint Replacement Registry, published in The Journal of Arthroplasty, reviewed 42,105 Australian primary knee replacements performed with an unresurfaced patella. The study found no increased risk of patella-related revision when comparing the two modern polyethylene liner designs most commonly paired with an unresurfaced patella - providing reassuring contemporary evidence for this approach in Australian practice.

Reference: Onggo JR, Holder C, McAuliffe MJ, Babazadeh S. No Increased Risk of Patella-Related Revisions When Comparing Ultra-Congruent versus Cruciate-Retaining Polyethylene Liners in Primary Total Knee Arthroplasties With an Unresurfaced Patella: An Australian Registry Study of 42,105 Knee Arthroplasties. J Arthroplasty. 2025;40(5):1225-31.

The advantages of leaving the patella unresurfaced:

• Preserves your native kneecap - avoids the small risks associated with patellar resurfacing itself (implant loosening, fracture of the kneecap, or mechanical wear of the button).
• Simplifies future revision - if the knee needs any further surgery later in life, starting with an unresurfaced patella gives you more options.
• Matches contemporary Australian outcomes data - Australian registry data shows no survival disadvantage to unresurfaced patellae when paired with modern implant designs.

Approximately 95-98% of patients with an unresurfaced patella are satisfied with their kneecap function after total knee replacement. A small number of patients develop persistent anterior (front-of-knee) pain that can, in rare cases, be addressed with a later patellar resurfacing procedure if needed. Dr de Hoog will discuss this with you, and if there are specific features of your knee that favour resurfacing, that option remains available.

What the operation involves

Before the day. You’ll have pre-admission appointments, blood tests, imaging for the robotic planning, and a review with your anaesthetist. You’ll also meet the physiotherapy team and start any pre-habilitation exercises.

On the day. Most patients have a spinal anaesthetic combined with light sedation, rather than a full general anaesthetic. This tends to mean less nausea, better pain control in the first 24 hours, and a faster return to feeling yourself. A regional nerve block is also used to provide targeted pain relief around the knee.

The procedure. The operation itself typically takes 60 to 90 minutes. A vertical incision is made down the front of the knee (usually 12-18 cm), and the knee is replaced through this incision. The robotic system guides bone preparation and implant positioning, with real-time feedback on alignment and soft tissue balance. Blood loss is modest and transfusion is uncommon.

After surgery. You’ll be encouraged to stand and take a few steps within a few hours of surgery.

Recovery timeline

Knee replacement recovery follows a typical expected course. Realistic expectations for most patients:

• Day of surgery - standing and walking a few steps with a frame
• Day 1 - walking the ward, stairs practice, discharge home
• Week 1-2 - walking at home with a frame or crutches, short distances; focus on range of motion and reducing swelling
• Weeks 2-6 - off most walking aids, driving in most cases (usually around the 6-week mark), returning to light desk work; ongoing physiotherapy is important
• Weeks 6-12 - walking without aids, returning to more demanding work, exercise bike, pool walking, light gym work
• 3-6 months - golf, bushwalking, cycling, most recreational activities; most patients can do essentially what they want by this point
• 6-12 months - subtle improvements in strength, confidence, and the knee feeling “natural” continue

Full recovery from TKR genuinely takes about a year. The first 6 weeks are the most intensive in terms of rehabilitation; after that, improvements continue but are gradual. Patient commitment to physiotherapy in the first 3 months is the single biggest modifiable factor in how good a knee replacement feels at 12 months.

Risks

Knee replacement is a very safe operation, but like any major surgery it carries risks. The most important to understand:

• Infection - approximately 1 in 100 cases. Management ranges from antibiotics to further surgery in severe cases.
• Stiffness - some patients struggle to regain full bending or straightening. Active physiotherapy in the first 6-12 weeks is the best protection. Occasionally a manipulation under anaesthetic is needed.
• Blood clots (DVT / PE) - reduced by early mobilisation, compression stockings, and blood-thinning medication.
• Persistent pain - a small proportion of patients (somewhere between 10-20% depending on the study) have more ongoing discomfort than they expected. Robotic assistance and careful soft-tissue balancing are designed to reduce this, but cannot eliminate it.
• Anterior (front-of-knee) pain - can occur with or without patellar resurfacing. Usually settles in the first year.
• Instability or mechanical problems - rare; most often related to soft tissue balance, which robotic assistance aims to optimise.
• Periprosthetic fracture - rare (~1%), more common in patients with weaker bone.
• Implant wear or loosening - addressed with revision surgery if and when needed.
• Medical and anaesthetic complications - individualised to your overall health.

Dr de Hoog will discuss your specific risk profile with you. Patients with diabetes, a higher BMI, a smoking history, or significant medical conditions carry higher risks, and these are best addressed before surgery where possible.

How long do modern knee replacements last?

This is the question almost every patient asks. The honest answer draws on Australian data, with an important caveat.

The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) tracks every knee replacement performed in Australia - with over 1.1 million primary knee replacements recorded since 1999, it is one of the most comprehensive joint replacement registries in the world. The 2025 AOANJRR Annual Report provides the most up-to-date picture.

For modern primary total knee replacements performed for osteoarthritis, the registry reports approximate survivorship (the implant still in place and working) of:

• Approximately 95% at 10 years
• Approximately 93% at 15 years
• Approximately 91% at 20 years

The caveat about cementless TKR. Long-term (20-year) registry data for total knee replacement is dominated by cemented fixation, because cement has been the standard for decades. The widespread use of modern cementless TKR is more recent, so the very longest follow-up data specifically for cementless is still maturing. That said, contemporary registry analyses from Australia, Canada, and the United States have shown that modern cementless TKR using current porous surface technologies achieves revision rates that are equivalent to - and in some studies slightly better than - cemented fixation at 5- to 10-year follow-up.

The biological rationale and the contemporary data both support cementless fixation in appropriately selected patients. Dr de Hoog will discuss your individual expected outcome in the context of your age, bone quality, health, and goals - and will recommend a cemented or hybrid approach if cementless is not the right choice for you.

Who is - and isn’t - a good candidate?

Knee replacement is most appropriate when:

• Non-surgical treatment is no longer adequate
• Pain is affecting your daily function and quality of life
• Imaging supports the clinical picture
• You’re medically fit for anaesthesia and surgery
• You’re committed to the rehabilitation process

It’s reasonable to delay or reconsider if your pain is intermittent and well-controlled, if you haven’t yet trialled non-surgical options, if there is active infection elsewhere in the body, or if medical issues (diabetes control, cardiac assessment, weight, smoking) should be optimised first.