The Joint Revolution

The progress in the field of joint replacement surgery is closely linked to the better development and availability of joint prostheses, finds out Sonal Shukla

With the growth of the economy, there is an increase in various health problems, which in turn leads to the invention of better healthcare facilities. One such area that is evolving in the Indian healthcare industry is of prostheses, which is the heart of joint replacements.

Joint replacements become essential whenever the natural joint is damaged affecting the normal body function, the main reasons being arthritis, joint infection, injury and malignancy. A prosthesis is an artificial joint that is used to replace a worn out or destroyed joint during joint replacement surgery, primarily used to relieve pain of an arthritic joint. Additionally, they provide stability, range of motion and restoration of joint function.

Numbers don't Lie

Statistics bear testimony to the growing significance as in India alone, around 150 million people are suffering from the crippling disease of arthritis, which is around 15 per cent of the total population. On an average, one million people in India need total joint replacement, but only 30,000 to 40,000 joints are replaced yearly. The market for joint replacements is worth around Rs 200 crore. There is a whole range of prostheses available for conditions ranging from degenerative arthritis, rheumatoid arthritis, previous failed surgery, bone and joint tumours, and unstable painful joints where supporting ligaments have been damaged. For a total hip replacement, the prostheses available are cemented, uncemented or hybrid. For a total knee replacement, they are usually cemented but have a fixed or rotating platform.

Cemented hip replacement can cost between Rs 35,000 and Rs 40,000, whereas the price of an uncemented one could range between Rs 60,000 and Rs 1.5 lakh. The difference in the cost structure is because the materials used for uncemented hip prostheses are more expensive and also they are technically more challenging to manufacture. The standard cemented knee prostheses available today in the market costs around Rs 75,000, whereas the mobile bearing one which lasts longer due to decreased wear, costs Rs 10,000 to Rs 15,000 more than the fixed bearing.

"The hi-flexion knee prosthesis allows the patient to bend their knee as much as a normal knee" - Dr SKS Marya Director Institute of Joint Replacement Max Healthcare, New Delhi

"The life of a prosthesis is enhanced because of new technology used for its design" - Dr Akhil Dadi Senior Joint Replacement Surgeon Yashoda Hospital Secunderabad

"Ceramic on ceramic show extremely low wear rates and promise greater longevity" - Dr Kaushal Malhan Joint Replacement Surgeon Wockhardt Hospital Mumbai

A Serious Need

All joint replacements involve prosthesis placement. Joint replacement prostheses are available for knee, hip, shoulder and elbow joints in the human body. "Among the joints needing replacement in the Indian population, the most frequent is the knee followed by the hip and occasionally the shoulder," states Dr Girish Dewnany, Consultant Joint Replacement Surgeon, Asian Heart Institute, Mumbai. The knee is most commonly replaced, with 2,50,000 people undergoing surgery every year in the world and 25,000 in India with numbers growing every year.

Change in the Constitution

Gradual change of implant material from stainless steel to an alloy and high-density polyethylene has resulted in increased implant life with minimal wear. "Today, the life of a prosthesis is more because of new technology used for its design and introduction of computer-assisted joint replacement surgery," opines Dr Akhil Dadi, Senior Joint Replacement Surgeon, Yashoda Hospital, Secunderabad. Most prostheses today consist of a metal capping one end of the joint and a softer plastic poly capping the other end. However, there is a resurgence of smooth, highly polished metal surface used on both sides of hip replacement after three decades.

The main body of the implant is metal which can be special surgical steel, chromium cobalt alloys or titanium in most cases. Newer highly cross-linked polyethylenes are much harder with much lower wear and are beginning to be used with bearing diameters bigger than the conventional 22 and 28 mm heads in hip replacements.

"Hard-on-hard bearings like the metal-on-metal articulation and ceramic-on-ceramic show extremely low wear rates and promise greater longevity," opines Dr Kaushal Malhan, Joint Replacement/Resurfacing and Sports Surgeon, Wockhardt Hospital, Mumbai. They also allow using thinner implants as has been shown with resurfacing of the hip joint.

Hybrid surface products like the Oxynium combine the hardness of metal without the problem of metal ion release and smoothness of ceramic without the brittleness of ceramic. The outer surface of uncemented implants is designed to favour biologic bone in-growth and fixation of the prosthesis. This can be in the form of rough beads, wire-mesh or other rough porous surface of titanium, which is an osteophilic material. Hydroxyapatite coating is often used to induce bone in-growth on to the prosthetic surface. The various prostheses available in Indian market are from Depuy, Zimmer, Stryker and Aesculap. Common cemented hip prostheses available are Charnley's, Exeter, C Sten prosthesis, while non-cemented prostheses available are AML, Pinnacle, Zymuller, Corail and Proxima.

Types of Prostheses

The different kinds of prostheses used vary with the joint that is being replaced. Nexgen series of implants Total Hip Replacement (THR) rostheses: They are generally classified as cemented or uncemented (cementless). Cemented THR is indicated in the elderly age group of patients (65 years and above), while uncemented THR is the prosthesis of choice in the younger patient. Bipolar hip replacement: A type of prosthesis where the femoral component is fixed into bone, but the acetabular component (cup) is not fixed in the acetabulum thus allowing the cup to move freely in the socket. This type of prosthesis is more commonly used in patients with fractures of the neck of femur (transcervical fractures). Total knee replacement (TKR) prostheses: They are classified as fixed bearing (conventional) and mobile bearing (like the rotating platform knee). These prostheses are usually fixed using bone cement. Prostheses may be unconstrained and mimic the biomechanics of the normal joint to increase longevity by reducing stress at the prosthesis-bone interface or be constrained so as to make up for excessive ligament laxity and looseness in the joint. "These type of joints are useful in cases of severe joint damage with significant bone and soft tissue loss and therefore very unstable. Since constrained joints have a tighter articulation, they throw greater stress on the prosthesis-bone interface and are likely to loosen faster than unconstrained joint replacements," explains Dr Kaushal Malhan, Joint Replacement/Resurfacing and Sports Surgeon, Wockhardt Hospital, Mumbai.

Selection of Prosthesis

The selection of a prosthesis depends on the patients' age, activity level, and the primary pathology involving the joint. A cemented THR is the prosthesis of choice in the older and low demand patient, as opposed to an uncemented prosthesis in the younger and active patient.

"The rationale behind using an uncemented THR in the younger patient is that these patients are likely to outlive their prosthesis (average life of a prosthesis is about 15-20 years), and an uncemented prosthesis is expected to leave behind a better bone stock (quality) at the time of revision surgery than a cemented THR," explains Dr Sujit Korday, Joint Replacement & Arthroscopy Surgeon, Guru Nanak Hospital, Mumbai.

A bipolar hip replacement is indicated for an elderly patient with a transcervical (neck) fracture of the hip. With regard to TKR, a fixed bearing (conventional) prosthesis is preferred in the elderly patient while a mobile bearing TKR may be indicated in the young active patient with knee arthritis.

"These days, we are using ceramic-on-ceramic, metal-on-metal and metal-on-highly cross-linked polyethylene for hip replacements. We use larger diameter heads (to replace the normal femoral head) so that patients can have full movement and sit on the floor," informs Dr Ameet Pispati, Consultant Orthopaedic Surgeon, Jaslok Hospital, Mumbai. For knees, today surgeons are increasingly using designs that save more bone, allow more movement and use metal-on-highly-cross-linked-polyethylene. Costs have hence doubled or trebled.

Looking Forward

Some latest advancements in joint replacement surgery are the use of computer navigation during surgery and minimally-invasive surgery where the size of incision is half the size of conventional incision, which is more cosmetic. Some new hip prostheses are surface hip replacement prosthesis where the bone cut is less, hence the original bone is saved as only the surface is replaced and head and neck of the joint are largely saved, and large head metal on metal hip replacement prostheses which offer the advantage of large ball and are more stable so dislocation rate is low. Here are some of the latest prostheses: Hi-flex knee Hi-Flex TKR The newer prostheses designs are targeted towards achieving higher flexion-bending and a new era of joint replacement surgery using hi-flex knee designs. "The hi-flexion knee prosthesis allows the patient to bend their knee as much as a normal knee allowing more mobility and flexibility in the joint," informs Dr SKS Marya, Director, Orthopaedic and Institute of Joint Replacement, Max Healthcare, New Delhi. Computer-assisted Surgery (CAS) Computer-assisted Hip Resurfacing This technique helps to reproduce the biomechanics of a normal knee precisely, which is a major factor determining the longevity of prosthesis. It involves the use of a computer for the operation. Pin markers are inserted into the bones. The computer is able to communicate with markers via infrared or other signals. It is able to calculate the position and anatomy of the knee by computing the signals from these markers and other points of reference provided by the surgeon. It then assists the surgeon in taking the appropriate bone cuts. "In the conventional technique, the position of bone cuts is decided with the help of finely calibrated instruments applied to the bone in the correct way," explains Dr Malhan. The computer is like a calculator and the analysis it does is only as good as the data provided by the surgeon. It does not do the surgery for the surgeon. The basic replacement surgery and rehabilitation regime still remains the same. Experts believe that CAS has the potential to make the restoration of biomechanics more consistent. "Computer-assisted knee replacement surgery helps in ligament balancing, patello femoral tacking, equal flexion and extension gaps as well as restoration of mechanical axis of limb. In computer assisted hip replacement surgery, the system helps in range of motion analysis before surgery, restoration of soft tissue balance and of limb length," explains Dr CJ Thakkar, Joint Knee Replacement Specialist at Breach Candy Hospital, Mumbai. Gender-specific knee implant The gender-specific knee implant Gender-specific knee implants are being devised for women as these are more suited to their anatomy. "Gender-specific knee is lighter, better shaped to fit, has got a better tracking for the knee cap (patella) and allows the full flexion," opines Dr Thakkar. Surface hip replacement A newer prosthesis with an aim to preserve bone and allow a better range of movement referred to as hip resurfacing prosthesis has been in use for the last five years with good early results in the selected patient. Very few Indian patients are suitable for this procedure as the primary pathology in India is HIP AVN leading to arthritis, rather than primary hip arthritis seen in the Western world. "The same benefits of resurfacing without the risks are possible with a metal on metal large head hip prosthesis now available," says Dr Girish Dewnany, Consultant Joint Replacement Surgeon, Asian Heart Institute, Mumbai. Proxima hip is the latest implant available that offers full function to the patient with minimal bone loss. The newer knee prostheses have no change in material except the shape which is designed to give better movement while bending the knee and allow the patient to squat and sit cross-legged. Uni-compartmental knee replacement Uni-compartmental knee replacement Unicondylar knee replacement either of one or both condyle opens up the possibilities of minimally invasive surgery. This has been designed to replace only part of the arthritic knee which is significantly damaged. "The results are encouraging but only of use in patients who come early before their entire knee is damaged," states Dr Dewnany.

Looking Westward

Indian surgeons prefer imported prostheses over the prosthesis manufactured in India. The few indigenous prostheses available in the Indian market include Austin-Moore prostheses, bipolar prostheses and cemented hip system and total knee prostheses. "Their quality and instrumentation still need a lot of improvement and development. The quality check is the biggest issue, which needs strict rules and regulations," feels Dr Nutan Jain, Trauma and Joint Replacement Surgeon, Vardhman Hospital, Muzaffarnagar.

However, Dr KH Sancheti, Chairman and Chief Orthopaedic Surgeon, Sancheti Institute for Orthopaedics, Pune has developed INDUS prosthesis which is an indigenously manufactured monoblock, posterior stabilised design. This design, with minimal resection of the bone, offers high flexion, and the patient can squat too.

Issues and Concerns

The primary areas of concern in joint replacement surgeries are infection (one-two per cent) and loosening of the implant, dislocation (one-two per cent), fractures and implant failure. "The infection risk can be minimised by the use of ultra modern operating theatres (clean air theatres), body exhaust suits (space suits), appropriate prophylactic antibiotics, and strict adherence to principles of asepsis by all the theatre personnel," says Dr Korday.

"We take utmost care to prevent infection by using bacterial filters in operation theatre, sterishield space suits for the operating team and imported drapes," explains Dr Dadi.

sonal.shukla@expressindia.com