Anterior Hip Replacement

Hip replacement surgery is considered one of the most successful operations in modern medicine. The surgery relieves the pain and stiffness caused by various affections of the hip joint promising patients a lifestyle they enjoyed before the disease. 

Traditionally the surgery has been usually performed from the back (posterior approach) and side (lateral) of the hip. Recently, surgeons have been performing surgeries from the front known as the anterior approach. The anterior approach offers a faster recovery rate and less postoperative pain. 

Hip replacement & anatomy of hip joint

Hip replacement is a surgery to replace the diseased parts of the hip joint with prosthetic parts duplicating the function as well as balancing the muscular forces acting around the joint. The hip joint is a large weight-bearing ball and socket joint. 

The ball is formed by the upper part of the thigh bone (femur), which fits into the cavity formed by the lower part of the pelvis (acetabulum). The ball and socket are covered by a smooth glistening white tissue known as articular cartilage. The articular cartilage helps in the smooth gliding of the joint in various movements of the joint such as walking, running, squatting, and sitting cross-legged. 

The anterior approach for hip replacement

Traditionally, the surgery has been performed from behind known as the posterior approach or from the side known as the lateral approach. The more recent approach from the front, known as the anterior approach, promises a faster recovery with a decreased hospital stay. 

The surgery is performed with the patient lying on his back under regional (spinal) or general anesthesia. A skin incision is made starting from the bony prominence in front of the pelvis towards the outer side of the kneecap. 

In comparison to the posterior approach here, the tissues (muscles and tendons) are separated instead of being cut to reach the joint capsule. 

Fewer tissues are separated from the thigh bone and pelvis compared to other approaches. Regardless of the approach, the necessary steps of replacing the diseased parts remain the same.

Arthritic bone is removed from the sides of the joint, and the ball of the femur is cut. The ball is removed to expose the socket. 

• The damaged part of the acetabular socket is removed, and a cup made of metal alloy or ceramic is fixed with screws or press-fitted in the socket.
• A unique form of highly durable plastic called polyethylene is placed in the socket to allow smooth gliding
• A stem made of metallic alloy is inserted in the femur, which may be press-fit or fixed using a particular form of bone cement, allowing the bone to hold the implant.
• A prosthetic head made of metal alloy or ceramic is placed on the stem replacing the natural head of the femur.
• The prosthetic head is relocated back in the socket
• Skin and soft tissues are closed in layers, and a sterile dressing is placed on the wound 

The acetabular shell may be made of cobalt chromium alloy and has a porous outer shell. The outer porous shell has a structure similar to bone trabeculae and aids in bone ingrowth. The ingrowth of bone allows a rigid fixation. The acetabular shell may also be fixed with acetabular screws that are carefully directed in the pelvic bone to prevent damage to neurovascular structures. The shell is lined by a liner which is made of highly cross linked polyethylene. The cross linking is achieved using radiation and the polyethylene is then treated with anti-oxidants to prevent wear and tear damage.

 Benefits of anterior approach

The anterior approach is also known as the “muscle-sparing hip arthroplasty,” has several benefits over the traditionally performed posterior approach. 

• In the inter-muscular approach, fewer muscles are damaged during the procedure. The Hip abductors and IT band muscles are spared, which are traditionally cut in other approaches. 
• There is less postoperative pain owing to fewer muscles being damaged therefore decreasing the need for postoperative analgesics
• Faster recovery is possible as fewer tissues are damaged. The patients can walk bearing weight with crutches after the anesthesia wears off in a few hours. In some cases, the patients can go home the day of surgery.
• The joint is more superficial in the front giving the surgeon the ability to reach the joint more easily without cutting through layers of tissue in the back.
• The approach provides excellent exposure of the socket, helping in proper placement of the components.
• There is an added advantage to using X-ray during the surgery, aiding the surgeon in proper placement of the implant. Correct placement of implants prevent complications such as leg length discrepancies and assures maximum longevity of the implant.
• In cases where both the hips are needed to be replaced in a single surgery, the anterior approach offers a straightforward approach to the other Hip without changing positions.
• Less postoperative complications such as hip dislocation in case of an anterior approach
• Fewer postoperative restrictions in case of anterior Hip replacement

 Candidates for anterior hip replacement

Not everyone is a candidate for the anterior approach of Hip replacement. Large/obese/muscular patients are generally approached with more traditional approaches. 

Hip pain due to arthritis remains the most common indication for hip replacement. Chronic hip pain not relieved by conservative/nonsurgical management such as weight loss, diet, exercise, medications (Tylenol and Anti-Inflammatory), intra-articular injections, physical therapy, and assistive devices. Hip pain can be due to several causes 

• Osteoarthritis is also known as wear, and tear arthritis is common in the elderly population but can also affect the younger age group due to trauma or sports injuries. The risk factors for osteoarthritis are age, obesity, genetics, diet, and sedentary lifestyle.
• Childhood hip joint infections and a growing hip joint mismatch can lead to chronic hip pain.
• Inflammatory and metabolic systemic disorders such as rheumatoid arthritis and gout generally affect both the hip joints. Rheumatoid arthritis is a medical condition where the body’s cells destroy the structures forming the joint.
• Osteonecrosis or avascular necrosis leads to the destruction of the Hip joint as a result of damaged or reduced blood supply.

Challenges in anterior hip replacement

The anterior approach to the hip joint has a steep learning curve being technically difficult. The surgical approach also has a problematic exposure to place femoral stem. It is also challenging to address intraoperative complications with increased blood loss. 

Some patients report numbness over the outer surface of the thigh as a nerve supplying the part can be pressed or cut during the approach. The approach also becomes challenging to perform in the case of large and obese patients or patients with deformities. 

 Success & Expectations

The patient’s undergoing hip replacement experience a dramatic decrease in hip pain and can perform daily activities. Activities such as running, jogging, jumping, or other high impact sports are not advised. 

Although events such as swimming, walking, biking, hiking, or playing golf can be performed with ease. Successful hip replacement implants last for a long time. On average, the patient may not require revision surgery for several years. Most of the patients achieve complete recovery by three months post-surgery and can resume daily activities. 

The pain usually subsides in the first two weeks after surgery. Patients can walk bearing weight with crutches on the day of operation after the anesthesia wears off. Physical therapy to regain mobility and strength is started at home. Most patients can return to activities they enjoy in a few weeks and get back to work in a month.

Complications

The possibility of complications in hip replacement surgery is low. Having a long term medical illness increases the chances of complications. The recovery is usually prolonged in such patients. Some of the difficulties are:

• A blood clot may form in the leg veins, which may travel to the lungs with life-threatening implications. The physician prescribes blood thinner medications and a range of exercises to prevent blood clots.
• Infection may occur superficially on the incision wound or may occur deep in the tissues. Rarely it may occur after years of surgery and may require another surgery.
• The ball may come out of the socket, dislocating the joint, especially during the initial recovery period. The physician advises certain precautions to prevent it. 
• There may be complications of shortening or lengthening of the leg, or the implant may become loose if the patient engages in high impact activities after the surgery.