Joint complaints secondary to any pathology is an extremely prevalent health concern in middle age to the elderly population, which requires frequent medical attention. In the majority of cases, the hip and knee joints are the most commonly affected sites that produce visible gait deformity and discomfort during regular activities. Difficulty in walking, getting in and out of the chair, bending, etc. are few frequent complaints observed in patients with stiff or painful joints. The above-mentioned conditions can be debilitating for the affected individuals and may cause hindrance in their everyday routine and activities.

Conservative management of the primary cause is the first-line management in such cases.  However, In patients that do not observe satisfactory outcomes with medication, lifestyle changes, and walking support, etc. surgical replacement of joint is recommended. Total joint arthroplasty or replacement is a cost-effective, reliable solution for pain management and functional restoration in patients with arthritic joints. According to the Agency for Healthcare Research and Quality, more than 300,000 total hip replacements are performed annually in the United States. According to another statistic, 95% of patients receiving joint replacement surgeries report improvement of symptoms.

Anatomy of the hip and knee joint

Like any other surgical procedure, joint replacement has its own set of benefits and limitations, that we plan to explore today. But first, let us understand the anatomy of large joints and how it is manipulated in replacement surgery. 

HIP JOINT: 

The hip joint is one of the largest joints in the body and is of ball and socket variety. Here the head of the femur aka the ball fits into the socket formed by the pelvis bone. The surfaces of both bones are lined by articular cartilage, that together with its fluid cushions the friction created by their movement together. Strong strands of tissue called ligaments provide additional security and hold the joint together.

KNEE JOINT:

The knee joint is a hinge type synovial joint that is formed between three ones called the femur, tibia, and patella. It allows movement such as extension, flexion, and a small degree of rotation. 

Conditions that may require joint replacement surgery:

The following conditions produce chronic joint pain and difficulty in movement and may require a joint replacement in extreme cases.  

• Osteoarthritis is the most common chronic joint disorder that causes wear and tear to the affected joints.  This is age-related arthritis usually manifests in individuals over the age of 50 years and frequently with positive family history. On an estimate, osteoarthritis affects more than 30 million men and women in the United States and is reported to be the leading cause of disability. Osteoarthritis occurs when the joint spaces between the two bones decrease causing increased friction and injury to the cartilage. This results in extreme pain and stiffness in joint rendering patient disabled due to discomfort. In some individual’s irregularities in joint formation since birth can accelerate osteoarthritis development. Symptomatic osteoarthritis remains the most common indication for surgery in more than 90% of patients, with its incidence increasing rapidly due to the aging population and the obesity epidemic.
• Rheumatoid arthritis. It is an autoimmune disorder that affects the synovial membrane lining the inner surfaces of the joint. Here the chronic inflammation causes thickening of the membrane within and imposes serious damage to the cartilage producing pain and stiffness.  
• Post-traumatic arthritis: occurs following a serious joint injury, where the damage to the cartilage during the trauma predispose arthritis.
• Avascular necrosis occurs when blood supplying the joint or bone is disturbed either due to a dislocation or trauma. The lack of blood supply causes injury and eventual death of the joint causing arthritis formation. 

What happens during a replacement surgery?

The Orthopaedic Evaluation

Consist of the collection of medical history and duration of complaints, followed by a physical examination that assesses the joint stability and range of motion. The most important aspects are the imaging studies that determine the extent of the damage and joint deformity. These include X-rays and MRI scans that define the joint bone and soft tissue status pre and post-surgery.

Selection of an implant

A wide variety of designs and materials are currently being used for joint replacement procedures. These include prosthesis made from metals, ceramics, and plastic materials. The most commonly used metals are titanium alloys, stainless steel, special high-strength alloys, alumina, zirconia, and zirconia toughened alumina (ZTA). These artificial components are usually pressed fit into the bone to allow bone growth into the component. 

Procedure:

During a total joint replacement, the damaged bone and cartilage is resected and replaced by their equivalent prosthetic component. 

In a hip replacement, the damaged femoral head is removed and replaced with a metal head that is fixed over the remaining femur. The damaged cartilage over the socket is also detached and substituted with a metallic socket. A spacer made from plastic ceramic or metal is then inserted between the new ball and socket to ensure a smooth gliding surface.

Similarly, in knee replacement procedure the diseased bones are removed and replaced by their alternative prosthesis. The prosthesis placed mimics the shape and movement of a natural joint.

Recovery

Shortly after the procedure, the patient is shifted to the recovery room to monitor their progress from the recovery of anesthesia. Depending upon the success of surgery the patient is discharged in a few days with detailed home care instructions. 

Restoring Activity

Exercising appropriately is the key to healthy and quick recovery and should be initiated as soon as possible. Usually, doctors recommend resuming light activities within 3-6 weeks post-op to gradually restoration of activity. It is also to prevent the development of any blood clot that may occur due to prolonged immobility.

Complications associated with total joint replacement:

Deep venous thrombosis and pulmonary emboli

Patients with joint replacement procedures are at high risk of developing blood clots in the initial days after surgery due to extended immobility. Therefore, they are frequently prescribed with blood-thinning agents, support hose, inflatable leg coverings, ankle pump exercises, and encouraged early mobilization.  Patients are also closely monitored for any warning signs such as tenderness, pain, or redness in legs unrelated to incision site pain. This clot is also highly susceptible to travel to other sites and produces acute emergencies such as pulmonary embolism.

Infection

In comparison to other surgical procedures, prosthetic replacement of joints is at higher susceptibility to develop post-operative infection (1%) due to foreign body placement. The origin of this infection can be an infectious organism that enters the bloodstream during dental procedures, urinary tract infections, or skin infections. In almost all cases patients are prophylactically administered with antibiotics before or after the procedure. 

Dislocation of replaced joint 

occurs in 1% of the operated patient and may require additional surgeries in recurrent cases.

How long does a prosthetic joint last?

A total joint replacement usually lasts approximately 15-20 years with an annual failure rate between 0.5-1.0%. these statistics differ patient to patient depending upon the material used, patients’ co-morbid, functional activity, and effective physiotherapy.