Joint Replacement Materials: What's in an Implant?

More than a million people in the U.S. each year experience relief from pain and improved function as a result of total joint replacement surgery.  This life-altering procedure is regarded as one of the most valued developments in the history of surgery.  Currently Hip Replacement is the single most reliable operative procedure developed by modern medicine followed closely by second place winner, Knee Replacement surgery.  Although the procedure has been made routine in major centers, ongoing clinical research, design improvements, and improved wear resistance of the man-made materials used in the implants remain an evolving science.

WHY ARE MATERIALS IMPORTANT?

A “bearing surface” is a mechanical engineering term that describes the area of contact between two objects. Nature’s joint bearing surface is articular cartilage. When healthy articular cartilage rubs against itself in a healthy joint, very little friction is produced and virtually no wear particles are made.  Articular cartilage has no nerve endings so the natural rubbing of a joint is painless.  Articular cartilage gets all its nutrients from the fluid in a joint and has no blood supply.  This makes articular cartilage vulnerable to damage over one’s lifetime.  Some of this damage cannot be repaired and in arthritis, loss of the articular cartilage covering in a joint ensues. When arthritis develops in a joint, the articular cartilage is initially worn and eventually lost.  The result is bone rubbing on bone. Bone is a particularly poor bearing surface.  Not only is bone on bone a high friction bearing surface, it is also a very painful one.

Joint replacement components bearing surfaces are made of a variety of materials. These materials include highly cross-linked polyethylene (plastic), cobalt-chromium alloy (metal), and ceramic. Rubbing between these material couplings naturally produces some wear particles.  Man made materials still produce more friction than natural joint surfaces, and therefore experience a greater wear rate. This can impact the longevity of the implants. In addition, the wear particles produced can cause tissue inflammation surrounding the joint. We as joint designers and surgeons want to minimize both the production of wear particles and any inflammation they may stimulate around the replaced joint.  Optimal joint replacement implants are made from materials which produce very low friction and produce very little wear particles. This combination will help to maximize the longevity of an implant. The average age of joint replacement patients is getting younger.  The reasons are many.  A more active patient population is one, longer life-spans is another, and unfortunately, increasing obesity is a third.

IMPLANT MATERIAL OPTIONS AND COMBINATIONS

All materials used in joint replacement implants are very safe and only rarely cause localized or systemic reactions in the body.  Friction in an artificial joint results in the release of miniscule particles, hundreds of times smaller than a grain of sand, into the area surrounding the joint cavity.  This may occasionally result in an inflammatory response that can trick the body into reacting in an inflammatory manner and resorbing bone around the implant.  This is called osteolysis and, when extensive, can cause discomfort, loosening of the implant, and the need for revision surgery.  The best way to combat the development of this problem and increase the joint replacement implant life is by improving the wear resistance of the bearing materials in the man-made implants.

As new materials are developed and introduced, projecting long term effectiveness is a challenge.  Prior to use in joint replacement surgery, implant “wear” is tested in laboratory simulators that to the best of their ability, mimic the activity of the joint being tested. Testing in a lab outside of the body is an inexact science.  Although we can measure the size and volume of the wear particles produced, the biological reaction to them is absent.  Once safety is established with a simulator, the best way to determine the effectiveness of the implant surfaces is to implant them in patients and follow the performance carefully over years.  Prospective, randomized clinical studies tell us the performance in people!  Nothing is as reliable to tell us what works better and what does not as data from these studies.  The downside is it takes years to get the information.  National databanks called “Joint Replacement Registries” can both increase the reliability of this data and give us answers sooner because of the large volumes involved.

WHAT IMPLANT MATERIAL IS BEST?

Your surgeon will carefully evaluate your individual situation and goals to determine the material or combination of materials that is best for your joint replacement surgery.  Age, level of activity, gender, weight, deformity, and many other variables, are all factors when choosing the implant that is best for you.

MATERIALS

·         Metal-on-Metal Bearings

These materials were the first to be used in total hip replacements in the 1960’s, but less than optimal design and the development of newer materials over time resulted in these falling out of favor until recent times.  Improved manufacturing processes, recognition of the importance of a smooth surface finish, the recognized strength of cobalt-chromium alloys, and an improved understanding of the physical and chemical behaviors of metals have led to resurgence in the use of metal-on-metal materials for hip replacement.

Concerns remain about the wear particles that are generated by metal-on-metal implants and the hypersensitivity to the wear particles that may result.  Metal-on-metal implants are not used in patients with poorly functioning kidneys (the means for excretion of the particles) or in women of child-bearing age.  These implants are mostly reserved for young, active, and healthy male patients.

·         Metal-on-Polyethylene Bearings

These are the most commonly used combinations with the longest term clinical data available.  Polyethylene is a type of high durability plastic.  Although these are subject to the principles of wear as well, the results are locally less profound than metal-on-metal bearings and there is a long and successful track record for hip and knee replacements using these materials.  Ongoing research and development with these materials continue to result in implant wear improvements.  Various methods of sterilization of the polyethylene have resulted in altering the molecules in a way that strengthens them and decreases wear (a process called cross linking).  This combination of materials is commonly used in both hip and knee implants.  Dramatic improvement of polyethylene wear resistance in the last ten years is generally accepted as the biggest advance in joint replacement technology of the last 30 years.

·         Ceramic Bearings

Ceramic surfaces have been shown to be more wear resistant due to their ability to be polished to a very smooth finish and remain resistant to scratching.  Because of their brittleness, however, they are more susceptible to fracture than other materials.  Patients with highly active lifestyles who are subject to high impact activities are not the best candidates for ceramic implants.

Ceramic materials can be combined with polyethylene or ceramic itself and are most commonly found in hip implants.  A small number of patients with ceramic-on-ceramic hip implants experience an annoying “squeaking” sound during normal movement and activity.

The future evolution of joint replacement materials promises to bring newer materials with hopes of longer implant life and less wear characteristics.  One example of new technology advancement is a hybrid metal-ceramic material.  Through special manufacturing conditions, the surface of the metal material can be converted to ceramic which results in an implant with the favorable characteristics of both metal and ceramic.  More discoveries of this nature are undoubtedly on the horizon.  Long term clinical studies are essential to prove that any improvements in materials actually lead to longer lasting implant life with improved outcomes.

CONCLUSION

Joint replacement surgery is currently a highly successful procedure resulting in exceptional outcomes.  There is no combination of materials that works best in all joints for all patients.  Your surgeon will determine the implant materials that are are optimal for your individual situation. 

For more information about this topic, watch YNN, Ch. 10 news on Saturday, July 16^th to hear Dr. Brett Greenky discuss implant materials used in hip and knee replacement surgery.

Knee Pain in the Elderly: Common symptoms, varied causes

Knee pain in the elderly is a very common occurrence. The knee is the largest and most complex joint in the body. Injuries and diseases of the knee are frequent sources of disability, pain, and lost days from work.  Discomfort may be associated with many different diseases. The pain can affect the ability to ambulate, participate in daily activities and sleep comfortably.    The causes of pain usually originate in the knee joint.  Occasionally, a problem elsewhere can trigger pain that is referred to the vicinity of the knee.  Problems that originate in the knee joint itself are generally easy to diagnose and can be treated by your primary care physician, rheumatologist, or orthopedic surgeon.  Referred pain to the knee usually comes from either the hip or the spine and can be more difficult to diagnose.

Statistically, Americans are nearly 100% likely to have an episode of knee pain at least once in their lifetime. The incidence of knee pain is higher with increasing age and therefore is very common in the elderly. Initial attacks of knee pain, may respond to home remedies such as the use of rest, ice or heat, anti-inflammatory medications, weight loss, and a low impact exercise program.  Knee pain that lasts more than 10 days and is associated with swelling in the joint or inability to weight bear generally requires a visit to your physician.  Physical exam x-rays and occasionally blood testing are included in the diagnostic evaluation. 

Common causes of knee pain

            Inside the knee joint

a.       Osteoarthritis

b.      A torn meniscus

c.       Rheumatoid or Inflammatory Arthritis

d.      Gout

e.       Knee joint infection

f.        Tendonitis or Bursitis

Outside of the knee joint

a.       Hip arthritis

b.      Sciatica

                       

Osteoarthritis (OA) is the most common cause of knee pain in the elderly.  OA is the wear and tear type of arthritis that we are all subject to.  The incidence is slightly higher in women than men.  Increasing rates of obesity and decreased rates of exercise have resulted in an epidemic of OA in our society.  Most patients experience a slow gradual increase in pain and swelling.  Physically, there is often a bow legged appearance especially with weight bearing.  Inside the knee, a patch like loss of covering cartilage on the end of the bones allows the bones to rub together. Commonly the arthritis is also associated with a longstanding meniscus tear.   Initial treatment consists of rest, ice, anti-inflammatory medicines, weight loss and a low impact exercise program.  Injectable lubricates are available for arthritic knees and can temporarily diminish symptoms in moderate cases.  Dietary supplements are commonly advocated (glucosamine and chondroitin) but have never been shown effective in scientific studies. For severe arthritis, knee replacement surgery has extremely high success and patient satisfaction rates.

The meniscus is a structure in the knee shaped much like a washer. It is rubbery in nature and acts to help increase the contact area between the thigh and shinbone as they meet in the joint. Twisting and squatting activities are known to facilitate tears of the meniscus and can be the inciting event to bring on pain. A torn meniscus or cartilage can occur at any age.  Although this condition is common in young athletes, it can occur in the elderly as well.  In the elderly, the tear usually occurs incrementally and gradually over a period of months or years.  As a result, the appearance of a problem can be sudden or insidious.  Most torn menisci are on the medial or inside joint line of the knee and are associated with swelling, intermittent locking, difficulty with squatting or rising from a chair. When the tear catches, the patient will have a snapping or a grinding sensation. This problem can turn on and off like a light switch. With large tears the ability to ambulate is limited. A physical exam can establish the diagnosis.  Initial treatment includes rest, ice, and anti-inflammatory medications.  A steroid injection into the joint may help dramatically. Occasionally arthroscopic surgery is necessary to resolve the symptoms.

Rheumatoid arthritis is less common overall than osteoarthritis and presents more in women by a ratio of 8 to 1. Rheumatoid arthritis is an autoimmune disease in which the immune system of the patient begins attacking the synovial lining and covering cartilage within the joint.  Hallmarks of the disease include: at least an hour of morning stiffness, rashes, symmetrical involvement, and joint deformity especially in the hands. The disease process eventually destroys the joint surface. Laboratory data frequently can confirm the presence of rheumatoid arthritis. Over the last decade the use of disease-modifying medications have become prevalent and for the first time in modern history, the disease can actually be slowed dramatically by the appropriate use of these medications. Generally after the diagnosis of rheumatoid arthritis is made the patient should come under the care of a family doctor or rheumatologist who can administer and monitor the use of these medications appropriately. If and when rheumatoid arthritis causes significant destruction of the cartilage covering the end of the bone, knee replacement surgery is an appropriate next step.

Gout is more common in elderly men.  It occurs in genetically sensitive patients when uric acid levels in their blood exceed the saturation point and they crystallize in synovial joints.  The crystals cause sudden intense pain, swelling and redness. The big toe knuckle is most commonly involved, followed by the ankle and the knee joint.  Attacks can be triggered by diet (foods high in urates), alcohol and aggravation.  Some diuretics are known to trigger an attack.  The diagnosis requires a reasonable suspicion and can be confirmed by the finding the presence of gout crystals in fluid from the knee joint.  An attack will subside rapidly after the administration of the right medications.  Prevention of further attacks is accomplished by diet, and prophylactic medicine.  Although infection of the knee joint is unusual, it closely mimics gout with the main difference being the presence of fever and malaise. Infection can occur after a penetrating injury, or in immuno-compromised patients. 

Tendonitis and bursitis of the knee are common in patients of all ages. They can occur as a result of injury, repetitive activities, arthritic conditions or even gout. Generally the location of the pain is specific to the presence of a tendon or a bursal sack and treatment is supportive with anti-inflammatory medications and rest. The conditions usually resolve promptly.

Osteoarthritis(OA) of the hip joint can cause pain radiating to the knee. Patients sometimes arrive convinced that the knee is the source of the problem, only to find out that x-rays of the knee are normal and x-rays of the hip on the same side show severe arthritis. Generally the type of limp caused by a bad hip has a characteristic John Wayne waddle while the knee limp is more stiff-legged.

Sciatic pain emanating from the low back commonly results in pain radiating across the knee. Nerves exit the spine and coalesce into the sciatic nerve. Pressure on these nerves from arthritis or disk problems can produce pain down the back of the leg and the posterior aspect of the knee.  Cramping, spasms, and numbness often accompany pain from sciatica. 

Summary

There are many causes of knee pain in the elderly; most conditions are not serious and can be treated using anti-inflammatory medications, rest, ice, and activity modification. If the symptoms don’t resolve over 10 days to 2 weeks a visit to your doctor is advised.  A diagnosis will likely be made quickly and appropriate treatment begun.  Longstanding and increasing knee pain in the elderly is most likely arthritis related.  Arthritis is the loss of the cartilage covering on the end of the bones that meet in the knee joint.  If this becomes severe, and medication, physical therapy, exercise and weight loss do not resolve the problem, knee replacement surgery results in extremely high success and satisfaction rates in appropriately selected patients.

Musings on Nepal



Namaste.  (nah-mah-stay).  This simple Hindu greeting is expressed by pressing the palms of the hands together in front of the heart.  The head is bowed slightly as the word is spoken.  It literally means “the spirit or light within me recognizes and honors the spirit or light within you.”

We very recently returned from a journey to Kathmandu, Nepal, a valley burrowed deep in the recess of the Himalayas, the highest mountains on earth.  Our primary purpose—to assess the medical facilities and prepare for Operation Walk Syracuse’s November trip to Nepal to perform desperately needed hip and knee replacement surgery.

The stark contrasts of reality that we witnessed are staggering and pervasive in both city and village life.  The region and the people are primordial, yet caught in the throes of modernization.  It is a place of breath-taking beauty and unspeakable poverty.  Sanitation is more than a pervasive issue.

Kathmandu lies deeply isolated in a valley surrounded by mountains.  City roads are dangerously crowded, unguided due to the lack of traffic signs and signals.  Travel by car, bus, or motorbike is a treacherous, grueling affair.  Most mountain villages are reachable only by dirt roads and footpaths.

The pollution is pervasive.  Noxious fumes hang low over the city and we observed many people struggling to protect their airways through the use of masks or scarves placed over their mouths and noses.

The hospital environment will be challenging.  The medical facility falls far short of those we comfortably use in the U.S.  The challenges in providing effective medical and surgical care are very apparent.  Paucity of resources, a hospital physical plant that is lacking hot water, adequate toileting facilities, and up-to-date equipment and supplies add to the already challenging care environment.

By contrast, the physicians and orthopedic clinical staff areknowledgeable, enthusiastic, motivated, and committed to meet the needs of their patients.  We were warmly greeted and welcomed to the Medical College.  Our hosts were extraordinarily gracious.  We collaboratively planned for our November surgical joint replacement marathon which will include our team of nearly 40 health care providers who will travel with us to Nepal.  In addition to the cordial welcome from the medical staff, hospital administration, and the Minister of Health, we were warmly greeted by twenty of the prospective patients.  We left the hospital bearing the x-rays for fifty (50) patients who are hoping to receive ninety-three (93) joint replacement procedures during our abbreviated visit in November.  A daunting and overwhelming task is at hand.

We saw so very little during our short visit but more than enough to make us appreciate what we have here, and how much we take that for granted each and every day.

It was all about the people.  We were struck by the extremes of everything they experience, yet are sincerely welcoming and positive.  Ox-drawn carts and cows share the roads with taxis and other motorized vehicles.  T-shirt clad teenagers sell roadside wares next to sari-clad women washing clothes at a public well.  As we wandered through the narrow brick streets of Bhaktapur, an ancient city with Hindu and Buddhist temples that seem unchanged for centuries, or gazed across the terraced-fields that lie at the gateway to Everest after hiking to the highest point of Nagarkot, we remained most in awe of the remarkable inhabitants of this country. 

As we departed Kathmandu dreading the long, jet-lag filled return to Syracuse, we were energized by what we had seen and what promises to lie ahead.  We eagerly look forward to the next time that we will be met with the greeting we received from everyone in Nepal, rich or poor:  Namaste.  This humbling gesture is meant to recognize that we essentially are all on equal standings.  We are one with these people as we prepare to travel more than 7,500 miles to the other side of the world on this life-altering trip.  Until then, we will hold on to the people of Nepal and so many of the lessons learned.

 

Himalayas



In the Streets of Bhaktapur



Granting the Wish to Walk

Greetings from Nepal.  I have embarked on our "pre-trip" to Nepal a few days early to spend some "adventure-time" with two of my sons.  We will enjoy exploring and trekking for a week and will then meet up with Kim Murray and Mike O'Hara in Kathmandu to begin the exciting process of planning for our surgery visit in November.

Should you be wondering what a trekk in Nepal might involve, our approximate itinerary is as follows:

31 May’2011: Fly Pokhara to Jomsom [15-20 minutes] and trek to Kagbeni [approx 04 hours walk]:
It will be a sunny and windy day and the temperature will be approx 20 – 28 degree Celsius.  On the way to Kagbeni they have to cross Kali Gandaki River via wooden bridge and Lubra River. Enroute you will pass through small village.

01 June’2011: Trek Kagbeni to Muktinath (3800m) – 03 hours:
Usually the weather and climate will be the same as Kagbeni. On the way we will pass through small villages called Khing and Jarkot and reach to Muktinath for overnight stay.

02 June’2011: Trek back visit Lubra village and Jomsom – 4 hoursAfter breakfast we descent to Lubra river. We are high above the river again and must cross two bigger side-valleys on the way downstream. Eventually we come to some fenced-in fields and a garden with apple trees, near Lubra’s village school.

After Lubra, the trail leads to the Kali Gandaki and we have to leap across the river Panga a couple of times! At the confluence of the two rivers we join the caravan of tourists going to Jomsom The climate will be similar to Muktinath and in the afternoon it will be a windy day.

03 June’2011: Trek to Tukche village (2590m): 3 hoursThe climate will be similar to Muktinath. On the way we will pass small village called Syang and then to Marpha which is very famous for Apple wine and there is big agriculture farm and this area is very famous for apple and then to Tukche village.

04 June’2011: Trek to Gasa (1080m) 5-6 hours:Day will be warmer but possibility of rainfall.  This day we have to cross Kali Gandaki river couple of times and we will reach Kalapani, from here we have to walk through pine forest and descent to Lete village and after crossing the river, level walk to through forest to Gasa village for overnight stay.

05 June’2011: Drive from Gasa by local jeep to Beni and to Pokhara:
Today after breakfast we will drive from Gasa by local jeep to Beni via tatopani and from Beni we will have a private transfer from to Pokhara. Total driving hours will be approx 06 hours. From Gasa to Beni off road and from Beni to Pokhara is black topped.

 

Once back in Kathmandu we will tour all relevant portions of the hospital, spend time with a representative from the Ministry of Health, meet several of our prospective patients, and most importantly, assess the environment in which we will be performing surgery this fall.

Look forward to reading many exciting observations and stories upcoming blogs after we return.  Stay tuned for photos as well.

Seth

Joint Replacement Surgery: Solo Sport or Team Event?

Deciding to have total hip or knee replacement surgery and the timing of the surgery  is a personal and individualized process which can only made by the person experiencing the pain,  mobility and function deterioration.  Once the decided should “go it alone” or develop a carefully crafted plan to surround yourself with family and friends to assist you to reach your goals?  A recently released study supports previous findings that having a dedicated family member, significant other, or friend providing support every step of the way before, during, and after surgery positively impacts surgical outcomes.

This study included nearly 2000 patients who experienced joint replacement surgery.  The findings suggest that patients with strong social support, especially in the form of a “coach” experienced optimal outcomes including:

·         Shorter hospital stays

·         A greater likelihood to be discharged to their own home

·         Were more likely to achieve transfer out of bed and ambulation target goals

·         Reported feeling more ready and confident at the time of discharge

·         Were more likely to rate the overall quality of their care as excellent.

The findings replicate those of other studies which also found that preoperative education, as well as the use of coaches, positively impacts the quality and timeline for postoperative recovery from joint replacement surgery.

This particular study not only specifically explored the impact of a coach on outcomes, but also drilled down further to identify those time intervals that were most positively influenced by an active coach participating in the surgical experience:

·         Family or friend presence during the preoperative classes

·         Family or friend presence in the preoperative holding area while awaiting surgery

·         Family or friend presence during the last physical therapy session.

One additional finding was that the patient’s decision to use a coach for social support closely correlated with the view of his or her surgeon in this regard.  If the surgeon emphasized the importance of this role to the patient, this emerged as an important priority to the patient during the planning process.

One message is pervasive.  Once you have made the important decision to move forward with joint replacement surgery it is also important to identify those family members and friends who can function in the role of coach.  Discuss this with your physician early in the process.  When it comes to joint replacement surgery and rehabilitation these are no individual events, only team athletics.

Reference:

Theiss, M.M., Ellison, M. W.l, & Tea, C.G.  The Connection Between Strong Social Support and Joint Replacement Outcomes.  Orthopedics.  2011; 34(5):357.

LifeWings: A Commitment To Safety

The Orthopedic Team is eagerly anticipating the launch of the LifeWings Patient Safety Program at St. Joseph’s Hospital in early June.  Through our organized service line efforts we have made tremendous progress in improving operational efficiencies and patient outcomes over the years but also recognize that continued and sustained improvement requires ongoing effort and intervention.

Physicians, nurses, and other support team members will participate in intensive training sessions specifically designed for St. Joseph’s Hospital by LifeWings Partners.  LifeWings is a team of physicians, nurses, pilots, and former astronauts that have adapted for healthcare the teamwork training framework used by commercial aviation.  Through interactive exercises, experiential examples, evidence-based strategies, and tools and checklists we will learn how to avoid the mistakes that are occasionally made by teams and improve the safety for our patients.

We recognize that the system and environment of care at St. Joseph’s can be purposely and methodically redesigned to achieve results even better than those produced now.  We applaud the investment that St. Joseph’s Hospital has made to bring this program to us.  It truly demonstrates the commitment to creating and sustaining a culture of safety for our patients.

Unicompartmental Knee Replacement: A Bone Sparing Alternative for Some Knee Arthritis Sufferers

Alternative Names:  Partial Knee Replacement, Unicondylar Knee Replacement, Unicompartmental Knee Replacement, Unicompartmental Knee Arthroplasty, Minimally Invasive Partial Knee Replacement

More than 500,000 people in the United States undergo total knee replacement each year.  Some of these patients and an additional gorup of other indivudals with knee arthritis might be candidates for partial knee replacement. 

Knee Anatomy

Three bones join together to form the knee joint

·         Thighbone (femur)

·         Shinbone (tibia)

·         Kneecap (patella)

The knee components are held together by muscles, ligaments, and soft tissue.  The shock-absorbing material inside the joint that cushions during weight-bearing activities is called the cartilage.

The knee is comprised of three separate section:

·         The medial compartment (inside part of the knee)

·         The lateral compartment (outside part of the knee)

·         The patellofemoral compartment (front part of knee between the kneecap and thigh bone)

Knee Arthritis

Osteoarthritis, or wear-and-tear arthritis, often results in symptoms such as stiffness, pain, and/or a sensation that the knee has “locked” during walking or other activity.  The cartilage in the knee degenerates over time until the surfaces are rubbing directly with each other without any cushioning (bone on bone).

Rheumatoid arthritis is an inflammatory process resulting in damage to the surface of the knee joint.  Partial knee replacement (PKR) is not indicated in rheumatoid arthritis.

Unicompartmental arthritis is wear and tear disease that affects only one of the three compartments of the joint instead of the entire knee.

Partial Versus Total Knee Replacement

Knee replacement surgery is intended to relieve knee pain and to imporve the function and motion of the knee. 

A total knee replacement (TKR) involves the complete repalcement of all three components in the knee.  Unicompartmental, or partial knee replacement, allows the surgeon to resurface (or replace) only the damaged compartment of the knee while preserving the health y bone in the other two compartments.

Patients suffering from osteoarthritis that is isolated to only one part/compartment of the knee might be candidates for partial knee replacement.  The healthy parts remain untouched during the surgery.  Patients also have the opportunity to undergo a standard total knee replacement in the future if the arthritis progresses and additional surgery is needed. 

Historical Perspective

Partial knee replecement actually predated Total Knee Replacement.  In the 1960’s when the idea of resurfacing an arthritic knee joint was first successfully accomplished, it was with a partial design.  It was only after the intial success of these designs that surgeon developers linked together two partials to make the first “Total Knee”-- the Duopatellar.  Over the years “total” knee designs have become more and more anatomic following the lead of nature.  At the same time partial knee replacement was overshadowed by the success of the “total” design despite the fact that it works so well in certain circumstances.  The continued improvement in material science has increased the longevity of both partial and total knee components.  Partial knee replacement, when applied to the correct patient, can have superior fuctional results when compared to”total” knee replacement.  The operative procedure remains more technically demanding for the surgeon, and is therefore usually provided only by orthopedic surgeons who are Joint Replacement Specialists.

The Procedure

Although the surgeon is able to predict with a high degree of accuracyby review of the x-ray if a patient is a candidate for PKR, the first step in the actual surgical procedure is to examine the three compartments of the knee directly to verify that cartilage damage is present in only one compartment of the knee.  If the damage is more significant than was visible on the preoperative x-ray, the surgeon will perform a total knee replacement instead.  He or she will discuss this possibility during the preoperative visit.

The term minimally invasive is often thought to relate to incision size.  In the hands of a skilled surgeon, the incision size is approximately half the size of the incision made during total knee replacement.  In terms of a partial knee replacement, the descripion of minimally invasive also correlates most closely to:

·         Preservation of two of the three compartments in the knee joint

·         Preservation of the stabilizing ligaments of the knee

o   Anterior cruciate ligament (ACL)

o   Posterior cruciate ligament (PCL)

During total knee replacement surgery these ligaments are usually cut or loosened.  Keeping these intact helps retain a more normal sensation of movement and range of motion.

If the intraoperative examination supports partially resurfacing the knee:

·         The damaged bone is removed and replaced with implants (prostheses) made of plastic and metal

·         The ends of the thigh and shin bones are cut and reshaped

·         The metal implants are secured in place with a fixative substance called bone cement

·         A plastic insert is placed between the two metal components to enable the surfaces to freely glide

Advantages of PKR

·         Quicker recovery and return to normal activities of daily living

·         Smaller incision

·         No disruption of the knee cap

·         Less pain

·         Improved range of motion

·         Little to no blood loss

·         Reports of a more natural feel in the knee

Disadvantages of PKR

·         Potential for additional surgery in the future (if other compartments become damaged by osteoarthritis)

As possible with any surgical procedure, complications can rarely develop:

·         Blood clots

·         Infection

·         Nerve injury

·         Persistent pain

·         Implant failure

Activity

Most patients can resume normal activities after partial knee replacement when they have regained adequate strength and flexibility.  Most exercise and activity are acceptable after surgery including walking, swimming, biking, gardening.  Activities that result in repetitive joint trauma such as running, jumping, or twisting should be avoided.

Conclusion

Partial knee replacement can achieve excellent results when performed on the appropriate population of patients.  This procedure may be an option for patients who are experiencing significant lifestyle limitations as the result of osteoarthritis isolated to one part of the knee.

If you believe that you may be a candidate for PKR talk to your doctor to determine what treatment is best for you.  Since this procedure is technically more challenging and surgeon experience is a key driver of positive surgical outcomes, don’t be hesitant to discuss with your surgeon his or her experience with this procedure.

References

AAOS:  http://orthoinfo.aaos.org/topic.cfm2topic=A00585

Berger RA, Meneghini RM, Jacobs JJ, et al.  Results of unicompartmental knee arthroplasty at a minimum of ten years of follow-up.  Journal Bone Joint Surgery Am.  2005; 87(5): 999-1006.

Smith & Nephew:  www.RediscoverYourGo.com