Partial Versus Total Knee Replacement

Knee arthritis remains an incredibly common source of pain and disability for many men and

women, especially as patient’s get older. If non-operative means of controlling pain and

disability are no longer effective, operative management may be discussed as another option.

Operative treatment options in which artificial components are placed in the knee can include

both partial and total knee replacements. These surgical options differ in their scope, operative

procedure, recovery, and potential complications, which will all be discussed in further detail

here.

What’s the difference?

The knee joint is a complex structure involving cartilage, bone, and many soft tissue

components. For much of this conversation, however, the joint can be simplified by thinking of

the knee as a joint composed of three compartments. These include the medial (inner), lateral

(outer), and patellofemoral (involving the knee cap) compartments. All three compartments

are lined with cartilage that becomes damaged over time and worn away in patients with

arthritis. In some patients, all three compartments may be worn out simultaneously, while

other patients may only have one or two compartments with cartilage wear. A partial knee

replacement is usually designed to replace only one of these compartments. A total knee

replacement involves the reconstruction of the entire knee joint.

When might a partial knee replacement be a better option?

If a patient has cartilage wear isolated to one particular knee compartment, they may be a

candidate for partial knee replacement. Several factors are involved in this decision with your

surgeon, however, and some of these factors continue to be debated in the orthopedic

literature. Most surgeons agree that the best candidates for a partial knee replacement have

arthritis isolated to one compartment, good range of motion throughout the knee joint, and a

joint without much deformity. For patients that are significantly bow-legged, knock-kneed, or

cannot completely straighten the knee, a partial knee replacement is more likely to fail and

require additional surgery. Other factors such as obesity, patient age, and activity level are less

clear regarding their influence on the success of partial knee replacement and continue to be

researched.

When might a total knee replacement be a better option?

In general, patients who do not meet the criteria above for a partial knee replacement are likely

to achieve more benefit from a total knee replacement. Especially in situations where

significant joint deformity is present, range of motion is significantly reduced, or there is

significant cartilage wear in more than one compartment, total knee arthroplasty is typically a

better option.

Surgical Decision Making

Another important aspect regarding partial knee replacement is the potential need to change

plans during the surgery. If you and your surgeon discuss a surgical plan for partial knee

replacement, there may be several situations where the surgeon transitions to a total knee

replacement while in the operating room. For example, consider the situation of a patient’s

arthritis that was expected to be isolated to a single compartment based on imaging studies or

the physical exam before surgery, but the surgeon sees significant arthritis in two or three

compartments during the procedure. In this situation, the patient would be more likely to have

continued pain throughout the knee if only one of the compartments is addressed at that time.

These patients would also be more likely to need additional surgery in the future, such as

changing the implants to a total knee replacement.

Another scenario may occur where the actual surgical procedure does not progress optimally

and the surgeon feels that a change of plan to a total knee replacement would be a better

option at that point. Due to these possible situations and several others, most surgeons will

discuss both treatment options and ask their patient for surgical consent for either procedure.

As a result, the surgeon may proceed with the best surgery for that particular patient at the

time of the procedure.

Clinical Results

Partial knee replacement

A partial knee replacement typically involves a smaller surgical procedure for the patient. This

includes less bone removal, usually a smaller incision, and potentially a shorter surgery. As a

result, many patients are able to recover more quickly following their procedure. In fact, a

study in over 101,330 patients who underwent partial or total knee replacement showed that

the patients undergoing partial knee replacement had less pain, a shorter hospital stay, a lower

rate of hospital readmission, and lower overall mortality. 1 Another study showed that 94% of

patients still had their partial knee replacement 12 years after surgery and over 80% of those

patients were able to return to some sports as well. 2

Despite these advantages, partial knee replacements have limitations as well. Partial knee

replacements have been shown to have a higher loosening rate requiring further surgery as

compared to total knee replacements. 3 A large study performed in Sweden also showed no

advantage of partial knee replacements over total knee replacement regarding patient

satisfaction or function after surgery. 4

Total knee replacement

Total knee replacements have been thoroughly researched in the orthopedic literature and

consistently demonstrate high rates of long-term survival and improvement in patient function.

A large review performed in 2013 that combined the results of several other studies showed

that 93.8% of total knee replacements survived more than 10 years in those patients. 5 Several

major advancements in implant design and manufacturing will likely result in those rates

increasing in the future as well. Patient outcomes following total knee replacement

consistently show significant improvements in pain, function, and quality of life. Despite this,

however, it is important to note that multiple studies have shown that 15-20% of total knee

replacement patients are not completely satisfied with their result after surgery.

Recovery After Surgery

Recovery following partial and total knee replacement is slightly different for each patient.

Factors playing a role in the recovery include age, obesity, medical problems, functional level

prior to surgery, surgical technique, and any complications after surgery. Despite these

variables, however, some generalizations can be made. Most patients use wheeled walkers

initially after surgery for balance while moving around out of bed. Physical therapists are

typically utilized to assist with the use of the walker and help guide the transition from the

walker to a cane and eventually to no assistive devices. This transition is variable in timing and

may require a few days to a few weeks. Range of motion gradually improves over the course of

about 6 weeks to 3 months. Pain following the surgery is most significant in the first 7-10 days,

but often takes several months to decrease completely. It is also important to note that

patients with knee replacements may still have some discomfort in their knee following the

procedure, but clearly one of the main goals of surgery is a significant decrease in pain as

compared to that experienced before the procedure. Overall recovery following these

procedures may take up to a year or more before a patient reaches their final level of

improvement.

Conclusions

As with all aspects of medicine, orthopedic surgery continues to develop knee replacement

components and techniques in an effort to provide the best care for patients. In the area of

partial knee replacement, this has led to new techniques such as implants that replace more

than one compartment simultaneously and the incorporation of robotic techniques into the

surgeries in an effort to more precisely place the components. Surgical innovation will continue

to develop, so additional treatment options may become available in the future. As a result,

the information above should be used as a background for discussing partial and total knee

replacement with your orthopedic surgeon. Many factors will be considered in determining the

best surgical option for a given patient, but a basic understanding of the information above will

allow you to engage with your surgeon more thoroughly and develop the best operative plan

that is tailored to you.

1 Liddle AD, et al. Adverse Outcomes After Total and Unicompartmental Knee Replacement in 101,330 Matched

Patients: A Study of Data from the National Joint Registry for England and Wales. Lancet 2014;384(9952):1437-

1445.

2 Felts E, et al. Function and Quality of Life Following Medial Unicompartmental Knee Arthroplasty in Patients 60

Years of Age of Younger. Orthop Traumatol Surg Res 2010;96(8):861-867.

3 Bini SA, et al. Midterm-adjusted Survival Comparing the Best Performing Unicompartmental and Total Knee

Arthroplasties in a Registry. J Arthoplasty 2017:32(11):3352-3355.

4 Robertsson O, et al. Patient Satisfaction After Knee Arthroplasty: A Report on 27,372 Knees Operated on Between

1981 and 1995 in Sweden. Acta Orthop Scand 2000;71(3):262-267.

5 Pabinger C, et al. Revision Rates after Knee Replacement. Cumulative Results from Worldwide Clinical Studies

Versus Joint Registers. Osteoarthr Cartil 2013;21(2):263-268.