“Why would you resurface only part of the knee, when you could replace the entire thing?” When I discuss knee replacement options, I am often confronted with this question.
In my previous blog, I discussed the emerging epidemic of knee arthritis in the USA. Indeed, approximately 20% of us will get knee arthritis, and 1 in 10 people in the US will undergo a knee resurfacing procedure in our lifetime. The overall economic burden of this epidemic will be a significant portion of the GDP (up to 1% in 2030).
The Rise of the Total Knee Replacement (TKR)
Since this is such an enormous health and socioeconomic issue, it makes sense to understand the history of the treatment of knee arthritis in this country. Total knee replacement emerged as a treatment for knee arthritis in the 1970s primarily because it relieved pain and improved function in a durable manner. In those days, it was difficult to get an implant to last more than 5-10 years. The issue of durability became a primary focus for a generation of orthopedic surgeons and researchers. The modern day total knee replacement was developed at Hospital for Special Surgery in the 1970s; incredibly, through advances in materials and fixation, this design has proved to be incredibly durable with implants now often lasting over 30 years.
Limits of TKR
Total knee replacement has accomplished the goals set out by its pioneers nearly a half century ago: durable pain relief with improved ability to walk. However, total knee replacement in 2012 often does not meet the expectations of those who currently undergo the procedure. Designed to allow patients to walk but not to run or play sports, the modern day total knee replacement removes the major ligaments in the knee (the ACL and PCL for example). Recent studies have demonstrated no functional limitations during swimming and biking after TKR; however, significant limitations were noted during more strenuous activities such as kneeling, squatting, moving laterally, turning and cutting, carrying loads, stretching, leg strengthening, tennis, dancing, gardening, and even sexual activity(1). Increasingly, this operation is performed on younger patients with over 40% of total knee replacements performed in patients under the age of 65 years old (there has been a 3 fold increase in TKR for this group over the last decade)(2)! The demands of this group often include a rapid return to work, participation in sports, and normal or near normal knee function.
Unfortunately expectations are not always met with TKR. Indeed 15-25% of patients who undergo TKR would not do the operation again(3)!! This is particularly sobering considering that we will spend up to 1% of the GDP on this operation in 2030. An emerging alternative to TKR is partial knee replacement. With this strategy, only the damaged portion of the knee is resurfaced; this is akin to filling a cavity rather than capping the entire tooth (as is the case with TKR).
History of Partial Knee Resurfacing (UKR)
Partial knee replacement, also referred to as unicondylar knee replacement (or UKR), was nearly abandoned over 40 years ago due to concerns about durability. In these early days, the materials and fixation were not developed enough for a partial solution to provide long lasting pain relief. However, over the past quarter century, the material and fixation improvements pioneered for total knee replacement have resulted in durable solutions for partial replacements as well.
Partial knee replacement is not possible for all patients with arthritis; indeed, it is indicated when the arthritic condition is fairly localized. However, when it is appropriate, it is important to educate patients of the pros and cons of partial vs total knee replacement.
UKR vs TKR – How to choose
Here is a list of the issues that are important to my patients and a review of the pros and cons of the two operations. The choice is personal as different patients have different goals and realities. Often, either operation would appropriately service the needs of an individual.
Both TKR and UKR are expected to provide excellent and durable pain relief. In general 85-90% of patients are satisfied with pain relief from either operation.
Most studies suggest that TKR is more durable than partial knee resurfacing (UKR). 95% of TKR are expected to last 10 years and 80% are expected to last 20 years. Conversely, 90% of partial knee replacements are expected to last 10 years and 40-80% are expected to last 20 years. These numbers are evolving as it takes 20 years to accumulate data; for example, I have been using robotic technology to insert partial knee resurfacing implants for the past 5 years and I expect these implants to last longer than the prior generation of implants.
If a total knee replacement fails, a revision total knee replacement is necessary. This requires specialized implants to make up for the loss of bone. Conversely, if a partial knee replacement fails, it can usually be converted to a normal total knee replacement.
Return to sport
Return to sport and leisure activities is an important goal of many patients after knee resurfacing and the ability to return to sport is highly variable. In general, return to sport is easier and more predictable after partial knee replacement than total knee replacement. In a recent comparison study, 96% of patients returned to preoperative level of sports after partial knee replacement whereas only 64% of patients returned to their preop level after TKR(4). Another recent study demonstrated that the level of leisure activity participation after TKR failed to meet patient expectations; in this study, at 1 year post op, no TKR patients were playing tennis, skiing, jumping rope, skating, playing basketball or jogging. Less than 4% were golfing, hunting or fishing(5). In another study, 28% of patients walked the golf course preoperatively whereas only 14% of patients walked the golf course after a TKR(6). In active golfers, the length of their drives decreased by an average of 12 yards and their handicap rose by an average of 4.6 strokes after TKR(7). Alternatively, 90% of patients maintained or improved their sporting activities after partial knee replacement(8).
Return to work
Return to work after knee repair is highly variable; indeed, many patients are retired at the time of their surgery. However, I recommend 2-3 months off prior to return to work after total knee replacement. Alternatively, I consider partial knee replacement a back to work operation. I encourage patients to go back to work after 2-3 weeks after a partial knee replacement.
The recovery time for any operation varies. Here is a comparison of typical recovery times for partial vs total knee replacement.
|Total Knee Replacement||Partial Knee Replacement|
|Hospital Stay||3-4 days||1-2 days|
|In Patient Rehab Stay||1-2 weeks||None|
|Outpatient Rehab||12 weeks||6 weeks|
|Time using walker or crutches||6 weeks||2 weeks|
|Need for pain meds||6 weeks||2 weeks|
|Loss of work||6-12 weeks||2-3 weeks|
|Complete Recovery||6-12 months||6-12 weeks|
Cost to patient
Insurance covers both partial and total knee replacement. However, there are hidden costs to the procedures. A study from Canada demonstrated that patient costs are 30% of the mean total costs of total knee replacement; most of these costs occur after the acute inpatient stay. The mean cost of a total knee replacement to the patient in this study was approximately $7500; the majority of this is due to loss of work(9). Obviously, since partial knee replacement results in much quicker return to work, less need for rehabilitation, and less pain medication requirement, the cost to the patient is significantly lower.
Risks of the Procedure
A recent study demonstrated that the risks associated with total knee replacement are over 3 times higher than partial knee replacement(10). These risks are both systemic risks such as heart attack or death as well as local risks such as infection, persistent pain, loss of motion requiring a manipulation, nerve injury and instability. Infection is particularly concerning after knee replacement; it is estimated that total knee replacement has twice the risk of infection as partial knee replacement.
There is only one randomized prospective clinical study comparing long term outcomes of total knee replacement versus partial knee replacement. In this study, partial knee replacement had better early and long term outcomes in terms of pain relief and function. Surprisingly, partial knee replacement demonstrated superior survivorship at 15 years than total knee replacement(11).
Both partial and total knee replacement can provide durable pain relief and improve function in patients with knee arthritis. Partial knee replacement is not appropriate for all patients with knee arthritis and may only be possible in 10-30% of patients.
Total knee replacement is a very durable operation that can last for 30 years. It predictably allows patients to walk, hike, ride a bike, and swim. It is less predictable in return to sporting activity. The recovery is long and arduous.
Partial knee replacement has a quicker recovery, permits rapid return to work, and often allows patients to expand their sports participation. In addition, the surgery has fewer risks than total knee replacement and is less costly to the patient. Though many studies have demonstrated excellent and long lasting durability, I still caution patients that partial knee replacement has a higher revision rate than total knee replacement.
In my next blog, I will discuss the use of robotics for partial knee replacement and how surgeon experience and robotics make this operation more reliable.
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10. Sikorski JM, Sikorska JZ. Relative risk of different operations for medial compartment osteoarthritis of the knee. Orthopedics 2011 Dec 6;34(12):e847-54.
11. Newman J, Pydisetty RV, Ackroyd C. Unicompartmental or total knee replacement: the 15-year results of a prospective randomised controlled trial. J Bone Joint Surg Br 2009 Jan;91(1):52-7.