Total Knee Replacement

Mackenzie Montero, MS2, Brian Gilmer, MD

Overview

Total knee arthroplasty (TKA) also known as a total knee replacement is a common orthopedic procedure used to replace worn out surfaces of the knee joint and is replaced with synthetic components. The knee is composed of three bones: the femur (thigh bone), tibia (shin bone), and the patella (kneecap).¹ The medial and lateral menisci, rubbery cartilage between the femur and tibia act as shock absorbers helping the knee to move smoothly.

Diseases of the joint, most commonly arthritis, can damage this protective layer of cartilage resulting in severe pain and difficulty completing everyday tasks.² TKA is a treatment option to repair this surface and restore function of the knee if non operative treatments do not relieve these symptoms. Nonoperative treatment modalities consist of weight loss, physical activity or low impact exercise, physical therapy, use of canes and walkers, NSAIDs, and corticosteroid injections, and sometimes hyaluronic acid or injections called viscosupplementation.³

Indications

Over 95% of TKAs in the United States are performed for osteoarthritis.⁴ Although the cause of Osteoarthritis is not known it is often referred to as “wear and tear” arthritis. Osteoarthritis is commonly associated with increased age and weight, repetitive overuse, injury to the joint, inflammatory conditions, and hormone disorders. Other indications for TKA includes fractures, dysplasia (abnormal alignment that leads to early wear), and even malignancy (cancer).

In a normal knee, the cartilage and synovial fluid (which is normally thick like motor oil) help to relieve friction and aid in smooth movement across the joint.⁵ However, in an arthritic knee, the cartilage becomes thinner allowing your bones to rub together. The normal thick and viscous synovial fluid becomes watery making it a less effective lubricant. In addition, cartilage damage can lead to bone spurs (growths) around the joint further leading to restricted movement and pain.

Symptoms⁶

Common symptoms which may indicate the need for a TKA include:

• Persistent or recurrent pain that occurs during rest or that is worsened with weight-bearing activities.
• Pain that limits your daily activities, including walking or climbing stairs.
• Knee inflammation and warmth that is not alleviated with rest or medications.
• Symptoms that are not alleviated by medications, injections, or physical therapy.

In general, patients will awaken feeling stiff, improve through the day but then with increasing activity will develop pain and swelling. This will tend to improve overnight and the process beings again. With time the pain free intervals become less frequent and the arthritis interferes more with daily activity

Diagnosis

A diagnosis is typically made following a medical history (meaning typical symptoms as above), a physical exam (a surgeon feeling which parts of the knee are tender, evaluating for swelling and crepitance or roughness of motion, and evaluation of X-rays of the knee. X-rays typically show narrowing of the joint space in the affected knee.

Xrays should be taken weight bearing to evlauate for arthritis, with the patient standing up. Cartilage cannot be seen well on xray, but we can infer that it is there because of the space between the bones when the joint is loaded, as happens when you are standing up. As arthritis progresses, the space between the bone appears to grow smaller as the cartilage wears away. Ultimately this results in a pattern often referred to as bone on bone.

The knee can become arthritic on the medial (inside), lateral (outside), or patellofemoral (under the knee cap) location. These have different patterns and symptoms. Patients with more wear in the medial or lateral knee will have trouble walking over level surfaces, but patients with patellofemoral symptoms will often be fine walking on level ground but have difficulties with ascending stairs or walking up and down hills, squatting or kneeling. It is most common to have arthritis in more than one compartment. When arthritis is present in 2 or more compartments and the arthritis fails the conservativbe treatments listed above, total knee replacement is considered.

Procedure⁷

Knee replacement is common, but still a major procedure. In order to minimize risk in Dr. Gilmer’s practice we generally maintain a few restrictions, namely on smoking, poorly controlled diabetes, or being overweight. Usually these risks can and should be optimized prior to any major surggery. There are other specialists who perform knee replacements in higher risk individuals.

Healthy patients will still have a complete workup with their primary care doctor to assess and optimize risk factors. Once cleared for surgery the surgery is usually scheduled approximately 1-2 months after the initial consultation. During this time we have a complete total joint handbook and there are several important preparations for surgery and recovery which are all set up in advance.

The procedure itself typically takes approximately one hour. We begin by making an incision across the affected knee to expose the joint. There has been some debate about approach in the past, but “minimally invasive” approaches have not been demonstrated to improve outcomes in terms of pain or function and may limit exposure and effective completion of the correction of alignment, and for this reason Dr. Gilmer prefers a standard medial parapatellar arthrotomy.

After confirming appropriate alignment with a combination of manual guides and/or computer navigation cuts are made in proper alignment that remove the diseased areas of bone. Dr. Gilmer uses both computer navigated and fully robotic knee replacement techniques. The choice between the two is based on a variety of factors and is discussed at the preoperative visit. While some patients strongly prefer a fully robotic approach, good results can be achieved with computer assisted planning and precision manual surgery and it may yield shorter surgery times for patients without significant deformity which means less dissection and potentially a faster recovery.

The take home message here is that the approach should be tailored to the particular patient and they should have a full understanding of the pros and cons of any approach. A thorough evaluation allows for joint decision making between patient and surgeon.

Regardless of the approach and alignment, the goal of excellent alignment is planned for. This also involves some controversy and decision making. Some surgeons prefer an anatomic alignment where the tibia is cut so that it is perfectly even and perpendicular to the ground when walking over level surfaces. This is a so-called mechanical axis approach. It means that even if the patient’s knee was somewhat malaligned for their whole life, this will be corrected after surgery. This has been a tried and true approach for many years and is an excellent way to approach many arthritic knees which have minimal deformity. The advantage is that it may reduce wear of the plastic liner by spreading the forces evenly across the knee. The disadvantage is that it may alter the alignment which a patient has had for their whole life and thus it may feel less ‘normal’, or different from the other knee.

More recently an approach called “KA” or kinematic alignment has gradually evolved. Here the trade off is that the patient retains their native alignment, a little bow-legged or knock-kneed for example, and thus the knee may feel more ‘normal’ relative to what they are used to. On the down side, this means that the wear of the plastic liner may not be as equal and thus the joint replacement may wear out faster. The long term data on kinematic alignment seem favorable but it does not have as long as track record as a mechanical alignment approach.

As Dr. Gilmer often says in the office, “there is no free lunch, only trade offs.”

Surgeons can debate for hours about the merits and risks of each alignment approach, and each surgical approach, AND each rehab approach, etc. etc. In general, Dr. Gilmer prefers a nuanced approach that considers all of the below:

• Patient preference
• Anatomic factors
• Patient goals
• Patient specific factors

Dr. Gilmer tends to prefer a kinematic approach when the deformity is mild and prefers a fully robotic procedure when there are compelling reasons to do so.

Regardless of the above debates, once optimized, we then prepare the bones for placement of the components by removing the damaged cartilage and a thin wafer of bone. A metal component will be fitted to the surface of the joint and may be cemented onto the bone or press fit. Press-fit is when newer components are used that do not require cement and may heal directly into bone. Generally speaking a patient must have good bone density and is typically, but not always, of a younger age to have a non-cemented, press-fit implant. The decision to press-fit or cement is determined ultimately at the time of surgery unless the patient has a specific request discussed before hand. Dr. Gilmer is happy to discuss the pros and cons and honors patient requests and preferences whenever possible.

In a similar process the patella is resurfaced, and the underside is replaced with a plastic component. A plastic spacer called a polyethylene liner or ‘poly’ for short, is then inserted between the metal components of the tibia and femur to create a smooth gliding surface. With all the new knee components in place the joint is actively tested to ensure its range of motion and stability. The incision is then closed in layers.

In almost all cases, with careful planning the surgery can be planned as an outpatient surgery, meaning you go home the same day.

Post-Operative Care⁹

In the immediate days/ weeks following surgery it is important to monitor for infection and review your post-operative instructions thoroughly. You will be given crutches to aid in mobility.

We take planning for total knee replacement very seriously and have a hand book which guides patients through all the steps, from ‘pre’habilitation making sure you are in the best shape for surgery, to pre-operative optimization (ensuring you are in optimum health to reduce risk of complications), to postoperative care and therapy. We know that total joint replacement is a process and take every step to achieve the best possible outcome.

Rehabilitation is started almost immediately following a TKA. Our target is to initiate therapy within 3 days on an outpatient basis. Patients typically require opioids regularly for a week or two and then occasionally for up to 6 weeks. We do not routinely refill medications beyond 6 weeks postoperatively. A physical therapist will take you through exercises that will help you regain mobility and strengthen your muscles following surgery. You can expect to be able to walk without an assistive device (ex. Crutches or a cane) within 4-6 weeks from your surgery. Typical recovery to full return to activities can take as long as 4-6 months to higher level activities such as skiing or hiking.

Risks and complications

Even though TKA’s are one of the most common orthopedic procedures in the United States, all surgical procedures have the potential for risks and complications.⁷ Furthermore, with improved manufacturing technology, implant design, and surgical expertise many risks that were of previous concern are now obsolete.¹⁰ Potential risks and complications include:^11,12

• Blood clot
• Knee stiffness
• Joint instability
• Aseptic loosening: failure of the joint prostheses without an infectious or mechanical cause
• Wound infection
• Nerve and blood vessel damage
• Metal hypersensitivity
• Persistent pain and patient dissatisfaction

Talk to your surgeon about potential risks, realistic surgical expectations, and post-operative care to minimize the risk of complications.

Dr. Gilmer’s Take

Total knee arthroplasty is a great procedure for patient’s who have end-stage arthritis. While there is no specific criteria that tell you that you need joint replacement, once walking is limited to a few blocks before pain starts and once a trial of other treatments is no longer effective, a thorough discussion can be had and surgery considered.

In my practice it is important to optimize all factors and expectations in advance to ensure the best outcomes. It is critical to say that even in the best circumstances up to 20% of patients will have some pain even after a technically successful joint replacement. Rarely, serious complications can even threaten the limb or result in long term need for multiple additional surgeries and loss of function. For these reasons, knee replacement should not be undertaken lightly.

I prefer to use computer navigation to ensure the proper position of the critical bone cuts. I do also use robotic total knee techniques. The difference between robotic surgery and computer navigated surgery is that in robotic surgery a machine makes the bone cuts, while in a navigated knee a surgeon makes the cuts that a machine has verified to be correct. Both methods can achieve excellent outcomes as disucussed above.

Another consideration is kinematic alignment. Typically a patient’s knee is slightly bow legged or knock kneed and in traditional total knee replacement the bone is cut to make the knee perfectly straight. In some cases, it may be more desirable to restore the native alignment in order to provide a more natural feeling knee. The downside is there may be some concern about the joint wearing out faster than if it was aligned perpendicular to the leg bone. This is a conversation that is individualized for each patient.

Brian Gilmer, MD. May 2023

Mackenzie Montero, MS2
Mackenzie Montero is a second-year medical student at the University of Nevada. Reno School of Medicine.

References

1. Cox CF, Sinkler MA, Hubbard JB. Anatomy, Bony Pelvis and Lower Limb, Knee Patella. 2022 Aug 8. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 30137819.
2. Ghosh A, Chatterji U. An evidence-based review of enhanced recovery after surgery in total knee replacement surgery. J Perioper Pract. 2019 Sep;29(9):281-290. doi: 10.1177/1750458918791121. Epub 2018 Sep 13. PMID: 30212288.
3. Krych AJ, Reardon PJ, Johnson NR, Mohan R, Peter L, Levy BA, Stuart MJ. Non-operative management of medial meniscus posterior horn root tears is associated with worsening arthritis and poor clinical outcome at 5-year follow-up. Knee Surg Sports Traumatol Arthrosc. 2017 Feb;25(2):383-389
4. Vasso M, Antoniadis A, Helmy N. Update on unicompartmental knee arthroplasty: Current indications and failure modes. EFORT Open Rev. 2018 Aug;3(8):442-448.
5. Gupton M, Munjal A, Terreberry RR. Anatomy, Hinge Joints. 2022 Jul 25. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 30085509.
6. Heisinger S, Hitzl W, Hobusch GM, Windhager R, Cotofana S. Predicting Total Knee Replacement from Symptomology and Radiographic Structural Change Using Artificial Neural Networks-Data from the Osteoarthritis Initiative (OAI). J Clin Med. 2020 May 1;9(5):1298. doi: 10.3390/jcm9051298. PMID: 32369985; PMCID: PMC7288322.
7. Varacallo M, Luo TD, Johanson NA. Total Knee Arthroplasty Techniques. [Updated 2022 Nov 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022.
8. Patient education in orthopedic surgery. OrthoIllustrated. (n.d.). Retrieved January 2, 2023, from https://www.orthoillustrated.com/animation/44-knee-replacement-with-the-ibalance-tka-system
9. Ditton E, Johnson S, Hodyl N, Flynn T, Pollack M, Ribbons K, Walker FR, Nilsson M. Improving Patient Outcomes Following Total Knee Arthroplasty: Identifying Rehabilitation Pathways Based on Modifiable Psychological Risk and Resilience Factors. Front Psychol. 2020 May 29;11:1061. doi: 10.3389/fpsyg.2020.01061. PMID: 32670136; PMCID: PMC7326061.
10. 1Tarazi JM, Chen Z, Scuderi GR, Mont MA. The Epidemiology of Revision Total Knee Arthroplasty. J Knee Surg. 2021 Nov;34(13):1396-1401. doi: 10.1055/s-0041-1735282. Epub 2021 Sep 10. PMID: 34507367.
11. 1Scott AM. Total Knee Replacement and Imaging. Radiol Technol. 2015 Sep-Oct;87(1):65-86. PMID: 26377268.
12. 1Postler A, Lützner C, Beyer F, Tille E, Lützner J. Analysis of Total Knee Arthroplasty revision causes. BMC Musculoskelet Disord. 2018 Feb 14;19(1):55. doi: 10.1186/s12891-018-1977-y. PMID: 29444666; PMCID: PMC5813428.

If you would like to have additional information on knee treatments or would like to learn more about total knee replacement, please contact Dr. Gilmer, serving the communities of Reno, NV.