Patients dealing with debilitating knee problems like arthritis are often faced with a decision to proceed with a partial or total knee replacement.  Both surgeries can produce excellent results but there are significant differences between the two procedures that can affect overall satisfaction. Here are some things to take into consideration when deciding between partial vs total knee replacement.

1. Age
2. Overall Health
3. Fitness level
4. Recreational Activities
5. Previous Injuries or Procedures

Run-Down of Partial and Total Knee Replacements

The human knee is made up of three compartments:

1. Medial (inside)
2. Lateral (outside)
3. Patellofemoral (under the kneecap).

A total knee replacement involves resurfacing all three compartments with metallic biomaterials designed to function similarly to cartilage.  A partial knee replacement selectively resurfaces one of the three compartments with similar but smaller implants. The most commonly used biomaterials are cobalt chrome, titanium, and polyethylene plastic.

While many problems can lead to knee replacement, the most common diagnosis is osteoarthritis.  This “wear and tear” disease results in the destruction of the protective, white, cartilage layer on the ends of the bones in a joint.  When all of the cartilage has been destroyed, exposing the underlying bone, it is commonly referred to as “end-stage” or “bone on bone” arthritis.  This and other signs of arthritis can easily be seen on a plain x-ray. Advanced imaging techniques such as CT scan or MRI are typically not needed to diagnose osteoarthritis.  Patients can often maintain good function for years with non-operative treatment. When symptoms worsen and stop responding to conservative treatment, knee replacement procedures can be considered.

How do Partial Knee Replacements Work?

A good candidate for a partial knee replacement would have radiographic signs of “bone on bone“ arthritis in only one compartment of the knee with localized pain to that same compartment.  Patients with widespread pain in the knee who are unable to localize their symptoms are typically better candidates for total knee replacement.

A partial knee replacement can be performed manually or with robotic assistance.  A manual partial knee replacement requires the surgeon to prepare the ends of the bones for implants using specialized jigs that help to align the components. A robotic-assisted partial knee replacement uses a robotic arm to help prepare the ends of the bones in a more accurate and precise way. Validation studies have shown better alignment of implants can be achieved with robotic technology. It is hoped that better alignment will lead to longer-lasting implants.  Although robotic technology has only been available for partial knee replacements for about 10 years early survivorship studies are encouraging.

Robotic-Assisted Procedures

Robotic-assisted procedures help provide a more thorough and efficient method of surgery. A robotic partial knee replacement starts with a CT scan of a patient’s knee. The CT scan is used to construct a three-dimensional image which is stored in the robotic system memory.  This allows the robot to understand the unique bony anatomy of a patient’s knee. At the time of surgery special reflectors are fixed to the patient’s femur and tibia.

The surgeon then identifies unique landmarks on the patient’s knee using special probes that the robot can “see“.  The robot can then confirm that the three-dimensional CT scan image in its memory is accurate and since it knows where the patient’s “knee” is in relation to the two reflectors it can “track“ the patient’s knee as the surgeon moves it in space.

In this way when the surgeon identifies the system, the best location for the implants the robot knows exactly where that position is.  The robot’s arm, holding either a saw or a burr, is then used by the surgeon to remove bone in the precise location where the implants are to be placed.  Although the surgeon has to manipulate the robotic arm to remove bone the system “guides” the surgeon’s hands by allowing only the precise amount of bone to be removed to accommodate the implants.  After preparing the bone with the robotic arm the implants are typically cemented in place and the knee incision is repaired with suture.

The majority of partial knee replacements are performed on an outpatient basis with most patients leaving the surgery center or hospital within one hour of waking from Anesthesia. Physical therapy is generally not required and most patients return to work within two weeks of surgery.  Patients usually experience 2 to 3 days of discomfort following the procedure and sometimes require pain medicine. Bandages are removed three days following the procedure and patients are allowed to shower provided there is no bleeding or drainage from the incision. Along with lasting longer than a traditional replacement, there are numerous advantages to partial knee replacement but also some disadvantages.

Pros:

1. Minimally invasive
2. Quick recovery
3. No PT (Physical Therapy) required
4. Minimal discomfort
5. All ligaments are retained
6. More natural knee motion
7. No long term activity restrictions
8. Lower complication rates than total knee replacement

Cons:

1. Potential for additional surgery if arthritis develops in other knee compartments
2. Risk of implants wearing out

How do Total Knee Replacements Work?

Total knee replacement can also be performed either manually or with robotic assistance.  Robotic assistance, similar to partial knee replacement, has consistently been shown to be a more accurate and precise technique for aligning and placing implants in a human knee.  Unlike partial knee replacement where a single compartment is replaced, total knee replacement resurfaces all three compartments with biomaterials. The incision is slightly longer than a partial knee incision to accommodate the larger implants.  The overall procedure is similar in that a CT scan is obtained prior to surgery and used to “visualize“ the patient’s knee. Similar trackers are placed in the femur and tibia during the surgery so that the robotic system can “locate” the patient’s knee in space.  After the surgeon determines the best position for implants the robotic arm precisely controls the saw used to shape the ends of the bones so that the implants fit in that exact location. Fine control of the saw-blade also protects the surrounding soft tissue such as ligaments, tendons, and skin.  After the implants are fixed to the ends of the bones the knee incision is repaired and the patient is awoken from anesthesia.

Pros:

1. Less pain than with traditional knee replacement
2. No chance of arthritis recurring
3. High patient satisfaction
4. Excellent function with few activity restrictions

Cons:

1. Larger incision
2. Longer recovery
3. Greater blood loss
4. Higher complication rates

Recovery after knee replacement surgery is a very individual process with many factors influencing the speed of recovery. Recovery can be defined in many different ways. For the purposes of this blog, recovery will be defined as either a return to work or activities of daily living.  Patients should never compare their recovery time to others but some generalities do exist. In general, patients recover from partial knee replacement faster than from total knee replacement. Most patients are able to return to work within 2 weeks of having a partial knee replacement but closer to 6 weeks for total knee replacement depending on work conditions.

Physical therapy is another concern after knee replacement. Most partial knee patients do not require physical therapy but most total knee patients participate in 4 weeks of therapy.  In terms of pain, most patients report varying degrees of discomfort for 2 – 3 days after partial knee replacement but more like 2 – 3 weeks after total knee replacement. While full healing requires 6 to 12 months most patients report 80% improvement in symptoms two weeks after partial knee replacement and six weeks after total knee replacement.

From a functional standpoint, both partial and total knee replacements can provide excellent results. Most patients after either procedure can resume all activities.  The only exception is a general recommendation against impact type exercise such as running. The concern is that the repetitive loads placed on knee implants with running can lead to increased wear and premature failure. Kneeling can initially be difficult for patients undergoing either procedure but with proper instruction, most patients can perform this activity.  Competitive athletes who place huge demands on their knees may notice improved function with a partial knee replacement. This is likely due to the retention of the anterior cruciate ligament (ACL) which allows for more natural knee motion and increased proprioception. Total knee replacements compensate for the removal of the ACL with implants that fit more tightly together.

Both partial and total knee replacement are excellent options for patients with advanced degenerative diseases of the knee who have failed conservative treatment. Both procedures can result in a highly functional knee that allows patients to resume almost all activities.  There are some differences however between partial and total knee replacement that should be taken into consideration when planning surgery. These differences should be discussed with your surgeon so that you can choose the procedure that fits you and your lifestyle the best.