Dr. William Barrett’s Blog

A recent paper, presented at the American Association of Hip and Knee Surgeons, noted that patients who had a frontal plane alignment of the knee that was within 3° plus or minus of ideal, had a significantly lower rate of revision knee replacement when compared to patients who fell outside the one standard deviation alignment range. They found that advancing age and malalignment of the leg were predictors of failure. The majority of surgeons can obtain this alignment using either conventional alignment methods or computer assisted surgery. The study underscores the importance of getting alignment right to minimize the risk of failure down the road for knee replacement.

Patients undergoing hip and knee replacement often do so not only to alleviate pain, but also to participate in low impact-type sports. Golf is a sport that patients are allowed and encouraged to return to after joint replacement surgery. The majority of patients undergoing hip replacement report returning to golf with minimal pain. In several studies it was found that the patients handicap typically increased by 1.1 strokes after joint replacement surgery and the average drive length increased by three yards.

Studies looking at return to golf after knee replacement found that the majority of the patients reported minimal or no pain. The average handicap increased by 1.9 strokes and average drive decreased by 12 yards. They found that right handed golfers more commonly experienced discomfort in their left knee, which is subject to more twisting motion, during the golf swing.
 

There are published reports documenting survivorship of total hip and knee replacement of approximately 90% at 15 years in the elderly individual.  Joint replacements do however fail, both in the young and the old. There are two spikes in the failure rates. The first spike is within the first few years and this is typically related to surgical technique that lead to instability or mechanical failure of the joint. The second spike is down the road 10 to 15 years and is related to wear of the implant surfaces. Traditionally, implants have been made of cobalt chrome and polyethelene, a type of plastic. These bearing surfaces with more than one million cycles per year can wear out over time. New bearing surfaces have been introduced including, metal-on-metal, ceramic-on-ceramic and new types of polyethelene that will hopefully be more durable and lead to better results down the road.

There are two factors that influence the wear rate of total hip and knee replacements. These are body weight and activity. Most total hip and knee replacements are designed to withstand moderate physical activity. However, they are not designed to withstand high impact physical activity. Several factors influence the durability of your joint replacement. These include, surgical technique, surgeon experience, design of the implant, and the material utilized. You should discuss these with your surgeon prior to joint replacement to ensure that both you and your surgeon do their best to ensure the most durable outcome.
 

A recently published article from the University of Western Ontario in the New England Journal of Medicine, calls into question the efficacy of arthroscopy for the treatment of moderate-to-severe osteoarthritis of the knee.  Researchers studied nearly 200 patients with moderate-to-severe osteoarthritis of the knee.  They divided the patients into two groups.  One group received medication, weekly physical therapy, and an exercise regimen.  The other group of patients received the same treatment plus arthroscopic surgery of the knee.  After two years, both groups of patients reported the same pain levels, physical function, and overall quality of life.  The authors of the study felt their conclusions did not support the use of arthroscopic surgery for treatment of moderate-to-severe osteoarthritis.

There have been previously published studies that have indicated for the treatment of pain alone, arthroscopic surgery for moderate-to-severe arthritis is no better than nonoperative treatment.  However, in milder forms of arthritis, particularly those associated with mechanical symptoms, i.e. catching and locking type symptoms from a torn meniscus or cartilage, arthroscopic surgery has proved beneficial.

If you have moderate-to-severe osteoarthritis of the knee and associate pain, but without significant mechanical symptoms, the use of arthroscopic surgery to treat that may be no better than nonoperative treatment methods.  You should discuss the options with your surgeon when contemplating what to do about symptoms associated with osteoarthritis of the knee.

Biomechanics is a branch of medicine that evaluates loads and stresses on a joint. The manner in which a joint is loaded will have direct effect on the health of the cartilage that covers the end of the bone in a moving weightbearing joint. Abnormal loads can lead to cartilage degeneration and subsequent osteoarthritis. Several factors can influence the way a load or stress is applied to a joint. Increase in body weight significantly above ideal puts increased stress on the cartilage and even in the face of normal ligaments and muscles can overload the cartilage. Ligament injury leading to abnormal motion and instability can also cause increased loads to be placed on that joint and subsequent arthritis. Weakened muscles can lead to decrease shock absorbing function about a joint and therefore increase the risk of osteoarthritis. All of these factors can lead to premature failure of the cartilage in a joint and subsequent osteoarthritis. After a knee has undergone knee replacement for the treatment of osteoarthritis there are several factors that can influence the longevity of that joint replacement. These include the surgical technique used and if the surgeon properly restores the alignment and implant position better results can be anticipated. The design of the implant can also influence the amount of stress that the artificial joint sees and there are variations and various implants that will influence longevity and function. There are many things that you as a patient can do to avoid the onset of osteoarthritis, such as maintaining a more normal weight, avoiding significant ligament injury, and if this occurs having this repaired and maintaining the strength of the muscles crossing that joint to improve the shock absorbing aspects of the soft tissue about the joint. Our job, as orthopedic surgeons, is to restore alignment and implant position when performing a joint replacement surgery. The patient should do everything within their power to avoid joint degeneration so as to hopefully avoid undergoing surgical intervention in the future. If this becomes necessary there are many techniques and implants available to satisfactorily restore function to the damaged joint.

A study presented at the American Academy of Orthopaedic Surgeons annual meeting in San Francisco, California, March 2008, described a prospective study in which patients were randomized to receive a minimally invasive approach to total knee replacement verses a more standard exposure total knee. The skin incisions in both knees were of equal length so that the patient would not be biased one way or another. These were all patients undergoing bilateral knee replacement. The same knee implants were used in both knees. The only difference being the exposure deep to the skin.  Postoperative evaluation included pain rating, strength, function, range of motion. There were measured at one day, two days, three days, three weeks, six weeks, and three months. There were no differences at the intervals tested between the minimally invasive side and the more standard soft tissue approach side. All of the patients received the same pre and postoperative teaching and pain management. I think this underscores that improvement in outcomes after knee replacement rely on several factors, which include a smaller soft tissue approach than has been traditionally done over the last 20 years, significantly better pain management with a multimodal pain approach and improved patient education, and dedicated teams and centers for joint replacement, all of these combined to assist the patient in their recovery after joint replacement surgery.

An article published in the July 2008 issue in The Journal of Bone and Joint Surgery, by Bitsch et al, outlined improved wear characteristics with crossed-linked polyethelene liners for total hip arthroplasty. At a minimum of five years, patients who had received a crossed-linked polyethelene liner had a 73% reduction in wear when compared to those patients who had a standard minimally crossed-linked polyethelene liner, which was commonly used prior to 2001. This improved wear finding in the crossed-linked polyethelene liners is reason for optimism. Wear of the bearing surfaces, is one of the leading causes of long-term failure of joint replacement surgery, in particular total hip replacement. If we can decrease wear through the use of crossed-linked polyethelene liners and or alternative bearings, the longevity of hip and knee replacements hopefully will improve. Further data is required before we can state that the longevity of joint replacements is improving significantly.

In a recent article published in the Journal of Bone and Joint Surgery, July 2008, authors Richard Iorio, et al, outlined the growing concern regarding the future burden of joint replacement surgeries. They looked at data from the United States Census Bureau, which predicted an 18% growth in the United States population between 2000 and 2020. During that interval, there will be a 37% increase in the number of people age 45 and older. By the year 2020, it is estimated that 59.4 million (18.2%) of Americans will be affected by arthritis. Several factors are contributing to the increase in arthritis including, the prevalence of obesity, as indicated by a body mass index greater than or equal to 30. The number of Americans between in 1990 that fit that definition was 22.9%. This increased to 30.5% by the year 2000. Patients who are of normal weight have a  risk of arthritis of approximately 16.3%, while the obese individual has a risk of 31.6% for the development of osteoarthritis. Associated with the increasing prevalence of osteoarthritis there is a decreasing number of orthopedic surgeons who specialize in joint replacement surgery. Currently there are 120 Fellowship positions for post graduate training in joint replacement surgery in the United States and only 74 (62%) of these positions were filled.  Furthermore, 20% of those filled were by international medical graduates.

Reimbursement has also influenced the number of people specializing in joint replacement surgery. During the period from 1991 to 2007, Medicare payment to hospitals for joint replacement surgery increased by 24% while during that same period the reimbursement to physicians declined by 39%. The cost of living increased 49% during that same period.

Orthopedic surgeons who specialize in joint replacement surgery typically do nine hip replacement and nine knee replacements per month, while generalists perform roughly three hip and knee replacements per month. The percentage of all surgeons performing joint replacement who perform revision procedures is only 43%, thus making revision of complex cases harder to be handled by a shrinking number of specialists in joint replacement surgery.

The article concluded that there is a significant volume of joint replacement surgery that will need to be taken  over the next 15 years. As hospital profit margins shrink and payments to physicians for joint replacements fall, the number of facilities and surgeons continuing to do the surgery may in fact decrease. This may lead to longer wait times for surgery, approaching the one to two year wait time that can occur in Canada and England. It is important that this information is disseminated to educate patients, patient advocacy groups, health care providers, and health care policy makers to help change the work force problems that may face adult joint replacement surgery in the future.

Primary total knee arthroplasty enjoys outstanding success at 10 and 15-year follow-ups. However, knee replacements will eventually wear out and fail and need revision. The most common cause of failure of knee replacement in the first few years are infection and instability of the knee. In the long run, the primary cause of failure of knee replacements is wear of the polyethelene and loosening of the components from bone. Each one of these causes of failure presents different challenges to the surgeon at the time of revision. There are several problems associated with revision surgery. First, the exposure is more challenging then in the first time surgery. Implant removed can at times be difficult resulting in some loss of bone. Reconstruction of bony defects that occur as a result of the wear or the loosening process can also prove challenging. We have several methods for making up bone loss and these include, use of metal augments that attach to the revision implants, use of bone graft either from the patient or more commonly from bone donors, and use of special metal sleeves or cones that will fill in the defects. At the time of revision surgery the surgeon will assess the defects and make a decision as how best to replace the missing bone and then build an implant that fits the knee, often using longer stems to augment fixation in the thigh bone and shin bone. Once stable reconstruction of the joint occurs rehabilitation of the knee begins. The recovery from revision knee replacement is often a bit more challenging, due to the soft tissue and bony defects and must be individualized for each particular patient. An increasingly smaller number of surgeons are taking care of the increasingly more difficult revision cases and this may prove to be a concern in the future as there will be fewer surgeons available to take care of an increasing number of revision knee replacements. 

While the success rate of total hip replacement is very high and patient satisfaction is in excess of 90%, complications can occur. Some of the early complications following hip replacement include inflection, deep venous thrombosis, and dislocation. The rate of dislocation as, reported in Medicare data, can be as high as 3.8%. Most large series of joint replacements done by specialists in joint replacement have a dislocation rate in the 1% to 2% range. The causes of dislocation are multifactorial. They can include the type of implant used, the position of the implants, the activity of the patient, and the type of approach utilized. Traditionally, posterior approaches to the hip have had a somewhat higher dislocation rate, but with the advent of capsular repair and the use of larger heads, the dislocation rate as a result of the posterior approach, has decreased. The anterior approach has had a lower rate of dislocation, as the majority of dislocations following hip replacement are posterior and an anterior approach preserves the posterior soft tissue of the hip. If a hip dislocates in the early postoperative period, most often it can be reduced with sedation and/or a general anesthetic. However, once a dislocation occurs there is a 30% risk of recurrent dislocation. If a patient has multiple dislocations then it is possible that revision surgery will be necessary and the overall success rate for recurrent dislocation is approximately 60%. Therefore, it is in everyone’s interest to minimize the risk factors for dislocation.