Hip and knee replacement are two of the most performed operations in orthopedic surgery in the U.S., according to the American Academy of Orthopedic Surgeons. And both procedures are getting more common every day, as they have proven widely successful at eliminating pain, correcting deformity and improving mobility so patients can regain quality of life and get back to some of the activities they enjoy.
In a study published by The Journal of Rheumatology, researchers estimate that about 700,000 knee replacements and more than 400,000 hip replacements are performed annually in the U.S. — and those numbers are rising rapidly each year due to the aging population and other factors.
Throughout the human body, where two or more bones join to allow motion the surfaces of the bones are surrounded with cartilage to form a normal, smooth-gliding joint. Over time, however, the cartilage can deteriorate leading to bone-on-bone friction which can cause inflammation and pain.
Total joint replacement is a surgical procedure where a damaged joint is removed and replaced with a metal, plastic or ceramic device called a prosthesis or implant. The implant is designed to reproduce the shape and motion of the original joint.
The most common conditions that lead to joint replacement surgery are osteoarthritis and rheumatoid arthritis. Other causes of joint pain include bursitis (inflammation or irritation of a bursa sac), dislocation due to injury, fractures due to a fall, hereditary disorders, developmental problems and trauma.
Hip Replacement Surgery
In hip replacement procedures, the damaged ball of the hip ball and socket joint is removed and replaced with a metal or ceramic ball that attaches to a stem that fits into the femur. The prosthesis is usually coated with a special material into which the bone will grow over time. In some instances, however, the prosthesis is cemented into the bone.
The socket portion of the ball and socket joint is also replaced with a metal cup that is placed into the pelvis. A plastic liner is then snapped into the metal cup and rotates with the new ball on the end of the femoral stem. The prostheses and implants come in a variety of shapes and sizes that can be tailored to the individual.
Both the process and recovery time are much quicker and less intrusive than most prospective patients realize. “Ninety five percent of my procedures are done under a spinal anesthetic and patients can go home the same day or the early next morning,” says Dr. David Morawski of Fox Valley Orthopedics in Geneva. “Additionally, greater than 50% of my procedures are done in an orthopedic specialized ambulatory surgery center.”
Surgical Approaches to Hip Replacements
There are a variety of surgical approaches to performing a total hip replacement, but the two common ones are the posterior approach (incisions on the back of the hip) or the anterior approach (incisions on the front of the hip). “There are several differences between all the various techniques and there are pros and cons to each of them,” says Dr. Kevin Bigart, an orthopedic surgeon at AMITA Health Saint Joseph Medical Center in Joliet, adding that there are also patient factors like age, bone quality and others that can influence the type of surgery that is performed.
“There is not a current consensus that one approach is better than all the others — patients can have excellent results with any of the approaches,” says Bigart. “The best advice I can give is to pick your surgeon and not the approach.”
Recovery time after hip replacement can also vary patient to patient, but on average patients are generally feeling good within the first few weeks to a month after surgery. They can usually go for longer walks and do some of their normal (pre-surgery) activities. They often feel like they are back to their normal selves within a few months after surgery.
Advancements in Hip Replacement
Some of the biggest advancements in hip replacement over the past few decades involve the materials used in the implants and the methods used to process them. The metals used and the various textures and coatings employed on their surfaces have advanced to improve the initial fixation of the implants within the bone, and to promote bone growth into the implants for long term stability.
“One of the most significant changes is the development of cross-linked polyethylene — the plastic liner that sits in the joint between the ball and the cup,” says Dr. Ryan Sullivan, an orthopedic surgeon and Hip & Knee Replacement/Revision Specialist at Edward-Elmhurst Health. The new technology allows the polymers to form highly cross-linked chains between them which makes the plastic liner more durable so it will wear down much more slowly. As a result, current hip replacement components are now expected to last 25 years or more, which means for most patients, their hip replacements will last a lifetime, says Sullivan.
Knee Replacement Surgery
During knee replacement surgery, a thin amount of bone along the surface of the joint is removed from the end of the femur or thigh bone, the top of the tibia or leg bone, as well as the underside of the kneecap. The surfaces of the bone are then shaped with tools and sized to allow an appropriate implant to fit for each individual knee. The major ligaments and tendons of the knee are typically kept in place to provide stability and normal motion of the knee joint. Like hip replacements, knee replacements can either be cemented into place or are covered in a special material into which the bone will grow.
One of the most common reasons people opt for knee surgery is due to arthritic pain in the joints that is restricting movement and affecting the daily quality of life. There are alternatives to knee replacement surgery that are non-surgical. Treatment options to help relieve knee pain can range from weight loss, activity modifications, physical therapy and non-steroidal anti-inflammatory medications to steroid (cortisone) and viscosupplementation (gel) shots, the latter of which acts as a lubricant to enable bones to move more smoothly.
“All these treatments are aimed at alleviating the pain. But there is no treatment that restores the joint naturally or regrows the cartilage,” says Sullivan. So when symptoms become significantly bothersome and interfere with activities of daily life despite the nonsurgical treatments, then it is reasonable to consider proceeding with surgery.
Partial Knee Replacement Versus Full Knee Replacement
The adult knee has three anatomical compartments — the medial compartment which is to the inside of the knee, the lateral compartment which is toward the outside of the knee, and the patella femoral compartment which is underneath the kneecap. If a patient has joint degeneration that is largely isolated to one of the compartments, then a partial knee replacement may be performed where only that one single compartment is replaced. For patients that have degeneration of two or more compartments, a total knee replacement where the entire knee joint is replaced is a better option.
“Partial knee replacements are associated with a quicker recovery time because they are smaller. But they also tend to have less longevity than a full knee replacement,” explains Morawski. “With the advent of minimally invasive total knee arthroplasty, patients are gravitating to getting their full knee replaced so no future surgery is necessary.”
Knee replacement surgery is considered a less straightforward procedure than hip replacement. That’s because the hip is a basic ball-and-socket joint, so it is potentially easier to create and implant parts to replace that joint effectively.
In contrast, the knee is a complex joint that allows for a wider range of motion and more flexibility. While the knee joint can be replaced successfully, the technique to do so tends to be more complicated and generally requires a longer and more involved recovery after surgery than the hip. “Part of this has to do with a knee incision requiring more stress immediately after surgery as patients work on range of motion. This is different from the stress a hip incision is exposed to and likely contributes,” says Bigart.
Recovering from Surgery
For the first few weeks after knee replacement, the goals are to minimize pain and swelling through multimodal treatments like medications, icing, elevation, and compression wrapping. As post-surgical swelling and pain stabilize and improve, patients progress through physical therapy which most commonly occurs in an outpatient setting.
This involves working on motion of the knee with a focus on achieving full extension and straightening, bending to a sufficient degree, improving strength of the muscles around the knee and lower extremity, transitioning off the assistive device (walker or cane) and getting back to normal overall function. The first few weeks can sometimes be challenging after knee replacement, but by two or three months patients are usually feeling pretty good.
“Studies show that more than 90% of hip and knee replacements done 20-plus years ago are still in place so joint replacement surgery can be an excellent long-term solution for hip and knee pain,” says Morawski.
In people who receive a total hip replacement, about 90 to 95 percent receive almost total relief of pain following the surgery. Because of the intricacy of the joint, that number drops slightly for knee replacement to about 80 to 85 percent.
There are a few preventative restrictions following hip and knee replacements other than the general guidelines of avoiding repetitive pounding of lower extremities with intense workouts that can accelerate the wearing out or loosening of components over time.
“The more load you put on them, the quicker they could theoretically wear out,” says Bigart, who acknowledges this can become a bit of a double-edged sword. “On one hand, the joint replacement is being done to give pain relief and allow a return to doing what you love. But like so many things, this is a risk and benefit situation for each patient. The common themes are typically to avoid high impact activities, maintain a healthy weight and continue with good overall health and hygiene habits to improve the longevity of the implants.”