TKR in the Asian knee: a demanding procedure


The lifestyles and religious practices of Asian cultures place special demands on the knee joints of people in this region. We examine specific considerations surgeons should employ when performing TKR on Asian knees.

Myung Chul Lee, a surgeon and professor based out of the Seoul National University Hospital, South Korea, took time to speak with AO Recon about his approach to TKR in the Asian knee, educational needs of surgeons in Asia, as well as where he would like to see future research focused. (Read interview with Myung Chul Lee)

TKR surgery can alleviate knee joint pain due to trauma and/or osteoarthritis and bring better quality of life to patients. If successful, it can improve biomechanics of the joint, realign soft tissues and mitigate structural and functional deficits [1]. 

It is currently the most common orthopedic procedure performed in the US [2], and its use doubled in this country between 1999 and 2008 [3]. According to Indian arthroscopic surgeon Bharat Mody, the rate of growth in TKRs in India is close to 30 percent per year, with predictions of more than 350,000 being performed annually by the end of 2020 [4].

Part 1 and 2 in this series of articles on TKR in the Asian knee looked at cultural and anatomical factors that contribute to the comparatively higher incidence of arthritic knees in the Asian population. Here we will examine some of the surgical implications, operative challenges, and device deficiencies that are applicable to Asian TKR patients.

 

A personal choice

From a surgeon’s perspective the decision to proceed with TKR surgery may seem like a straightforward choice for candidate patients suffering from knee pain. However, not everyone chooses to have surgery at the same functional status, or elects to have surgery at all [5].

Elderly Asian patients in some countries are more likely to seek surgical intervention in a more physically compromised state than Caucasians. When looking at preoperative TKR function of both Caucasian and Chinese patients in the same community, UK researchers discovered that mean Preoperative Knee Society Clinical Rating System scores were much lower for Asian patients than for Caucasians, 32.5 and 45.0 respectively. The authors hypothesized that cultural beliefs and social support may explain this [6].

However, this doesn’t necessarily mean that postoperative functional potential is going to be lower for those who undergo surgery when they have a lower ROM. A group of Singaporean doctors looked at 302 Asian TKR patients, assessing ROM both pre-and postoperatively. Those with a preoperative ROM of <110 degrees had poorer postoperative ROM than the group with ROM ≥ 110 degrees at the 6 and 24 month follow-ups. However, the lower functioning group showed a gain in ROM, while those with ROM ≥ 110 degrees lost range of motion after the procedure [7].

When faced with making a decision for or against TKR surgery, patients of different ethnicities and genders evaluate the decision using different criteria and elect for surgical intervention at varied stages of disability [8, 9, 10]. Asian patients generally desire to be able to participate in culturally relevant religious and lifestyle activities.

 

Postoperative ROM not meeting Asian patient expectations

A 2008 US study on postoperative ROM and functional activities after posterior cruciate-retaining total knee arthroplasty found that best functional results were achieved with 128–132 degrees of motion [11]. Asian populations naturally have more flexion than Caucasian populations; 156.9–165 degrees versus 143.8–145 degrees [12]. Using ROM success determinants from a Caucasian population to evaluate Asian patient TKR success does not seem appropriate.

High levels of TKR satisfaction and improved quality of life scores have been reported by a number of studies, including ones specifically targeting Asians [13,14]. However, pre- and postoperative evaluation systems such as WOMAC, Knee Society Score, Oxford Score and Hospital for Special Surgery Score do not include scoring criteria for cross-legged sitting, prayer postures or squatting in their definition of activities for daily living (ADL) [15].

In a 2010 commentary published in Orthopedics Today Europe, Bharat Mody, Director and Chief Arthroplasty Surgeon at the Centre for Knee and Hip Surgery at Welcare Hospital, Vadodara, India noted that:

“It is not uncommon for Indian patients to consider their TKA a failure, despite “successful” outcomes measure scores. Although they may have gained relief from pain and they are able to walk a couple of blocks, they cannot perform ADL like cross-legged sitting, which are an integral part of their daily routine. It is the equivalent of telling European patients that their TKA has been successful, despite their not being able to sit on a chair.”

All surgeons will acknowledge that managing patient expectations is vital to successful outcomes, but when the methods used to measure outcomes do not capture patient expectations a problem arises.

Some device companies have developed high-flexion implants to market to surgeons serving populations who are looking for a wider ROM than standard prostheses deliver. However, a 2015 metaanalysis has found that no clinical benefit was achieved with high-flexion implants when compared to standard ones [16] and a 2009 metaanalysis found “insufficient evidence of improved range of motion or functional performance after high-flexion knee arthroplasty” [17].

 

Implant design unsuitable for Asian population, especially women

Are device companies making headway in the design and cost-effective provision of implants to meet the anatomical needs of different ethnicities and lifestyles? It does not currently appear to be the case. Anthropometric studies have suggested that currently available devices are not only designed using data from Caucasian knees [18], but also have an inappropriate femoral aspect ratio for Asian patients [19].

Chinese knees are smaller than Caucasian knees and Chinese women have a significantly narrower distal femur [20]. In 2000, an anthropometric computed tomography scan study in Indian men and women revealed that most current prostheses would meet the femoral component needs of men, however, 60.4 percent of Indian women had femoral anteroposterior diameters smaller than 55 mm, which at this time was the smallest femoral component available [21].

Surgical techniques and tools, such as cutting jigs, support the procedure in this Caucasian population. Jigs that universally require surgeons to resect predetermined amounts of bone have been suggested as the cause of altered kinematics in Asian knees, which negatively impacts postoperative ROM and patient satisfaction [22].

According to Korean arthroplasty surgeon Myung Chui Lee, patella-related problems are an issue during surgery and postoperatively. Scientific research into Asian patella difference is lacking but Kim et al identified that “Korean patients undergoing TKA had thinner and smaller patellae than Western patients” [23]. Patients who have patellar resurfacing have been shown to have significantly fewer surgical procedures due to patellofemoral complications than those who do not have resurfacing done [24].

A thin patella carries the risk of stress fracture and anteroposterior instability. Hosseinzadeh et al point out that common assumptions about the patella need to be reevaluated in the OR when treating Asian patients [25].

“It commonly is assumed that it is desirable for a resurfaced patella to be equal to its original thickness, and a bony patellar thickness of at least 15 mm should be maintained. However, it is not uncommon to find, intraoperatively, the patella is too thin to simultaneously satisfy these criteria. To solve this problem, the only versatile option is to use exclusively designed patellar prosthesis with less thickness.”

Thickness, height/width ratio, and relative position of the median ridge all impact the selection of patellar components, patellofemoral contact stress, and patellar tracking in the trochlear groove [26].

 

Comparing femoral and tibia aspect ratio data of Chinese and Caucasian men and women

(A) Average femoral aspect ratio values showed a progressive decline with increasing fAP dimension for both races. A distinct ratio offset between Chinese and white women was noted. (B) A progressive decline in the tibial aspect ratio with increasing average tAP dimension for both races was observed.

 


Variation in angular parameters between Asian and Caucasian knees includes:

  • Distal femoral coronal angle
  • Posterior femoral condylar angle
  • Proximal tibial varus angle
  • Posterior tibial slope

[Adapted from: Hosseinzadeh HRS, Tarabichi S, Shahi AS et al (2013) Special Considerations in Asian Knee Arthroplasty. Intech Creative Commons License.]


In other words, tibial base-plates designed for more symmetrical, Caucasian knees may not always be suitable.

 

Morphologic differences impact surgical approach and outcomes

Generally, what surgeons and device manufacturers consider as "normal" should be looked at subjectively since substantial individual and ethnic variations exist. Placing components so that the transverse axis of the artificial joint is perpendicular to the mechanical axes of the tibia and femur does not take into account that Chinese men and women have non-linear femoral or tibia mechanical axes [27]. Chinese women also have more varus alignment of the knee [28]. Standard recommendations to prepare and cut the distal femur and proximal tibia may disturb soft tissue tension, ligament balancing and joint ROM in Asian patients [29].

A group of Germany-based researchers looking at implant failures in Asian patients suggested that surgeons “be aware that an anatomy driven internal rotation of more than 10 degrees may cause the risk of fracture of the dorsolateral portion of mobile bearing gliding surfaces due to loading conditions exceeding the yield strength of the polyethylene material” [30]. Clearly there is opportunity to better address the lifestyle and anatomical requirements of the Asian population when it comes to TKR. The projected growth in demand for this procedure in the coming years necessitates it.

 


Interview

Developing Asian specific surgical processes

Myung Chul Lee, a surgeon and professor based out of the Seoul National University Hospital, took time to speak with AO Recon about his approach to total knee replacement (TKR) in the Asian knee, educational needs of surgeons in Asia, as well as where he would like to see future research focused.

Myung Chul Lee MD, PhD

Seoul National University Hospital
Seoul, South Korea


 

Why do we see a higher incidence of osteoarthritis in Asian patients than in the Caucasian population, particularly in women?

There are differences in the anatomy of the knee joint. Asians have higher coronal alignment which is more varus-looking. When considering proximal tibia anatomy there are higher instances of tibia vara. Additionally, Asian people usually do high-flexion activities, for example squatting, kneeling, and sitting in cross-legged position. I believe these kinds of activities can increase the incidence of osteoarthritis in the knee joint.

 

What problems do high flexion activities present for devices?

As I mentioned most Asians need high flexion for activities such as squatting, kneeling, or sitting cross-legged in the postoperative period. The problem is that these activities can increase the risks of posterior edge loading and breakage of the polyethylene post or some wear of the polyethylene in the posteromedial parts.

 

Is it difficult to attain patient satisfaction when they have high expectations for flexion?

In my opinion, in the Asian population, the range of motion, especially the deep flexion and the ability to perform high-flexion activity, is very important to achieve high patient satisfaction. There is some controversy whether or not the postoperative range of motion can affect a patient’s level of satisfaction. There have been some studies that report a decreased postoperative range of motion was significantly associated with post-operative patient dissatisfaction, but others have said there is a very weak correlation.

 

How does Asian anatomy dictate your TKR surgical approach when considering the patella?

From an anatomy perspective there is some concern about the patella as it is smaller in Asians, therefore when I remove the patella bone according to processes developed for Caucasians, I have to remove relatively more bone from the smaller Asian patella.

 

Do you make adjustments for the differences in the femur?

I must ensure the prosthesis shape respects the configuration of the distal femur. The mediolateral length (ML) for Asian people is shorter than in Caucasians, and the ML-AP ratio is smaller, so we have to respect this fact when making a femoral component. Even if the prostheses have the same AP length, the ML length should be smaller for Asian people compared to Caucasians.

 

What actions to you take to address differences in the tibia?

On the tibia side, the middle of the central tibial mechanical axis is located a little more laterally, towards the centre of the tibia, so some companies makes tibia prosthesis in the form of medial-offset prosthesis, meaning that they shift the central stem to the medial side. This can be helpful to Caucasians too because their central mechanical axis is located more on the medial side, to the centre of the proximal tibia. But the axis of the tibial shaft does not overlap the center of the tibial plateau in Asians. In other words, for Asians, this can result in contact between the stem and the medial cortex. It can cause some breakage, in extreme cases the breakage of the medial cortex of the proximal tibia. Therefore, for Asian people the stem should be in the centre of the tibial plate, or slightly on the other side to the centre of the tibial plate. Usually the position of the central tibial spine on the tibial side is a common configuration for most companies. On the femur side, the Zimmer or DePuy systems have a smaller ML size of femoral component system.

 

In what kind of situation do you engage your surgical creativity?

For example, when I encounter a patient who is relatively young and well-educated, I always try to do a proximal tibia osteotomy before total arthroplasty. And when I have to perform total arthroplasty in young active people, I think mobile-bearing prosthesis or PCL-retaining cementless total prosthesis can be helpful. However, the evidence is very weak about model-bearing or cementless prosthesis. By cementless prosthesis I mean fixed prosthesis without cement. However when I encounter a young patient who needs total arthroplasty and I cannot perform proximal tibia osteotomy, I use these kind of prostheses.

 

Is there a topic that you feel is lacking in robust scientific research that would help Asian patients?

Most patients want to have postoperative high knee flexion but we don’t know whether activities such as squatting, kneeling or sitting cross-legged has a harmful effect on prosthesis or leads to a failure of the total knee arthroplasty. I say this because many patients ask me whether they can do the kneeling position postoperatively, but there is actually no scientific evidence of whether the survival of the device decreases when the patient is in the kneeling position. I think this is a specific problem for the Asian population.

 

With growing demand for TKA and surgeons to perform it do you feel that educational opportunities in Asian countries are currently sufficient to meet this demand?

I think that if Asian doctors could access more and better quality educational programs on total arthroplasty or operations with arthroplasty then that would be quite helpful to increase the number of able surgeons. All high quality education programs should have very good information, theoretical knowledge and hands-on practice too. There are countries in the region, such as China, India, Japan and Korea, that are putting energy into educating surgeons and are at the forefront of the push for better education.

Contributing experts

This series of articles was created with the support of the following specialists (in alphabetical order):

Myung Chul Lee MD, PhD

Seoul National University Hospital
Seoul, South Korea

This issue was created by Word+Vision Media Productions, Switzerland

 

Additional Resources

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