Joint Replacement Surgery

Joint replacement surgery is a surgery done to replace the damaged parts of a joint with prosthetic/manmade parts. The artificial joint is designed to replicate the function of a natural healthy joint. During the surgery, various biomechanical forces acting upon the joint are balanced to aid in smooth function.

Replacement surgery is one of the most common surgical procedures performed by orthopaedic surgeons. Hip and knee joints remain the most commonly replaced joints. Although numerous joints including shoulder, elbow, ankle and finger joints can be replaced. Hip replacement is considered the most successful surgery in the entire history of medicine.

According to research, the number of patients receiving total hip (THR) and knee replacements (TKR) is projected to grow. By 2030, THR  and TKR are expected to grow by 171 percent and 189 percent respectively1. Arthritis remains the most common cause of joint dysfunction requiring replacement surgery. Any patient with joint pain that is not relieved with less invasive treatments is a candidate for joint replacement.

Total Knee Replacement

Anatomy

A joint is formed when ends of two bones meet. Depending upon the anatomy they could be ball and socket joint (hip, shoulder, etc), hinge joint (knee, elbow, etc). Other types of joints are pivot joint, saddle, plane, and condylar joint. Besides the bones, various structures form a vital part of a joint. 

Articular cartilage is a glistening white smooth tissue covering the ends of the bones. The tissue is flexible and cushions the smooth gliding of the bones during the joint motion. Apart from reducing friction, it acts as a shock absorber for the joint. Damaged cartilage may lead to arthritis of the joint.

Ligaments are tough fibrous tissues holding the bones together. They maintain stability and prevent the bones forming the joint to pop out of the joint. Ligament damage could lead to instability and laxity in a joint.

Synovium is a thin tissue that lines the inner surface of the joint. Synovial fluid is severed by the lining, which is watery thin, sticky and a clear fluid. The synovial fluid provides nourishment to the articulating cartilage and helps reduce friction during joint movements. 

Bursae are small fluid-filled sacs present around the joint. They help in the smooth gliding of various structures crossing the joint. The knee joint in addition has special pads of tissues known as a meniscus. Meniscus dampens the impact of the bones of the joint.

Causes

Osteoarthritis also known as wear and tear arthritis is the most common of joint dysfunction. With growing age, there is degeneration of the structures forming the joint. The wear and tear of the articulating cartilage cause loss of smooth gliding of the joint. Although the exact cause is unclear, Osteoarthritis sometimes runs in the family.

Some individuals have abnormal development of the joint leading to arthritis. Inflammatory conditions such as rheumatoid arthritis can cause damaged joints if not managed properly. In the case of rheumatoid arthritis, multiple joints are involved such as hips, fingers, knees, toes, etc. 

Sports injuries to the joints can lead to instability of the joint and early onset of arthritis. Major injuries involving joint surfaces can lead to arthritis secondary to incongruous joint surfaces. Obesity may contribute to joint problems which may lead to early onset of arthritis.

Procedure & Materials

Joint replacement surgery involves replacing/resurfacing the damaged parts of the joint. The forces of the tissues acting on the joints are balanced. The prosthetic/manmade parts are then attached to the resurfaced bone with or without cement. 

The prosthetic parts forming the joint may be made of alloys of titanium, cobalt-chromium, polyethylene, ceramic or stainless steel. The prosthetic joint is attached either with special bone cement or is press-fit in the bone. The press-fitted implants allow the bone to grow onto them.

Candidates

The patients with arthritis are usually given a trial of conservative management. Conservative management includes physical therapy, heat pads, medications, visco-supplement injections, or cortisone injections. Unfortunately, arthritis is a progressively worsening condition. At some point the patients may have exhausted all less invasive treatment options, they are a candidate for joint replacement.

Before the Surgery

The patients requiring joint replacement are evaluated and assessed for any medical conditions. Baseline tests which are performed before the surgery include blood tests and EKG. The patients are also assessed for the kind of anesthesia they would be receiving. Surgery is usually performed under general anesthesia or regional anesthesia, such as spinal anesthesia.

After the Surgery

In the case of more commonly performed replacement surgeries, the patients are allowed to walk the same day of the procedure. They are usually discharged the next day of the surgery if stable. The patients undergo extensive physical therapy and rehabilitation. 

Gait training and muscle strengthening exercises are usually advised to the patients. Most patients are able to walk without support (cane or walker) by the end of 8-12 weeks. They are advised to avoid high impact activities such as running or jumping. Most casual activities such as walking, navigating stairs, riding a bicycle, and golf are allowed.

Complications

As with any surgical procedure, joint replacement surgery may have potential complications. There may be medical complications including stroke, heart attack, pneumonia or urinary tract infections. During the surgery, there may be complications such as fractures, nerve damage, blood vessel damage, shortening, instability or dislocation. 

After the surgery, during the first few weeks, there is an increased risk of infections which may be superficial or deep. There may be complications of joint dislocation or blood clots in the blood vessels. Blood thinners are usually prescribed after the surgery to prevent blood clots. 

In the long term, there may be persistent pain, weakness, dislocation or loosening of the implant. Implants like any man-made parts have a lifespan. Towards the end of the lifespan, they may wear out or become loose.

Success

Successful joint replacement surgery lasts for many years. On average, a total hip replacement or total knee replacement would last for the next 15-20 years or more. The patients report an increased range of motion about the joint which relieves pain caused by arthritis. They are able to get back to their baseline daily activities with a high quality of life.

Patients report satisfaction on account of increased mobility and leading a pain-free lifestyle. A greater number of patients today are undergoing joint replacement surgeries owing to the successful outcomes. 

References:

• https://aaos-annualmeeting-presskit.org/2018/research-news/sloan_tjr/