Polymethyl methacrylate (PMMA) Foot & Ankle replacement Prosthesis

Today, in India, there are more than 63 million people living with diabetes, second only to China, as per the latest 5th Diabetes Atlas statistics. Being a disease of the blood vessels diabetes affects all organs. By the time the blood supply to the foot has been compromised due to peripheral obstructive vascular disease, the heart is also involved.

The use of prosthesis in a patient living with diabetes increases the cardiac strain to over 15%, leading to cardiac failure over a period of time. World statistics show that when walking even with the best of prosthesis, mortality at 5 years after unilateral below knee amputation is 50%, and there is 50% mortality after above knee amputation in 3 years, due to cardiac failure.

The prevalence of osteomyelitis in the diabetic foot has been found to vary from 18% to 68%. The diabetic foot is also very prone to Charcot’s osteo-arthropathy (‘Charcot’s Foot’ is a severe complication of diabetes, which leads to soft and brittle foot and ankle bones).

Both these conditions result in the destruction or excision of foot bones which leads to deformed feet with altered biomechanics and the appearance of new pressure points in regions of the foot unaccustomed to bearing such forces. This results in formation of recurrent calluses and ulcers, which can get infected.

The infection and progression of these ulcers very often lead to loss of the limb in the immune compromised patients of diabetes. Arthrodesis of the foot and ankle may be the only alternative when the joints are destroyed. Amputation above the infected part may have to be considered when limb salvage is not possible. Amputations of the toes and/or part of the foot and limb not only place limitations on the physical activity of the patient, but are also not cosmetically appealing. An estimated 50,000 amputations occur every year in India due to diabetes related foot problems.

The concept of re-shaping of a deformed foot or toes by surgical correction has evolved recently and is presently being done routinely only in a few countries worldwide, (like the U.S, U.K, Russia, Germany, Spain and Australia) through internal fixations, supported by external fixators for a few months. However external fixators can frequently cause pin tract infections leading to disastrous consequences. In osteopenic bones of many deformed Charcot foot and ankle patients, internal fixation with compression screws, plates and staples can lead to high rates of re-collapse and further complications, within one and a half to two years of patient starting ambulation.

The Department of Endocrinology and Podiatric Surgery at the Amrita Institute of Medical Sciences (AIMS), Kochi, Kerala, is the only centre in India where a new type of reconstructive and corrective foot and ankle surgery is being performed in large numbers in high-risk diabetic foot patients under the able guidance of diabetic lower limb and foot and ankle reconstructive surgeon Professor Dr Ajit Kumar Varma.

He has pioneered a novel foot and ankle reconstruction surgery, using PMMA (Poly Methyl Methacrylate), also called Bone Cement, as foot bone replacement prosthesis for severely destroyed foot and ankle bones.

By employing these novel surgical techniques, a large number of amputations in patients living with diabetic foot ulcers and deformed diabetic feet are being prevented. As a result, AIMS has been able to maintain a lower-limb salvage rate of 91.5%, in diabetic foot and ankle diseases, which is comparable to the best centres in the world, said Dr. Varma to Citizen News Service – CNS. PMMA is a powder that hardens with an exothermic reaction when a monomer reagent is added to it, forming a hard substance with a consistency similar to bone.

Before setting and hardening completely it may be moulded to the desired shape. This material is almost inert and has excellent tissue compatibility. Poly Methyl Methacrylate Antibiotic Laden Cement (PMMA-ALC) is formed when bone culture specific heat stable antibiotics are added to the bone cement in cases with osteomyelitis. This modality has been shown to be very effective in chronic and acute osteomyelitis where sustained higher bone and tissue concentrations can be achieved compared to systemic administration.

Prophylactic antibiotics may be added when the prosthesis is made for replacing the non-infected, destroyed bones of a Charcot foot. PMMA is approved by the FDA for human use, and is being extensively used in many surgeries including, total hip replacement, knee replacement surgeries, spinal and maxillofacial surgeries. However, except for AIMS, PMMA Replacement Prosthesis has probably never been used by any other major diabetic foot centre in the world for the replacement of destroyed foot and ankle bones.

AMRITA SLING TECHNIQUE

In the last three years, the destroyed foot and ankle bones in over fifteen patients have been successfully replaced at AIMS with the help of this technique. The prosthesis is fixed to the lower end of the Tibia to form an ankle joint, through a surgical technique named the ‘Amrita Sling Technique’, devised by the Amrita Podiatric Surgery Team for stabilizing after reconstruction. Patients have not reported any complications after these foot and ankle reconstruction surgeries using PMMA prosthesis, and all the operated patients are now able to walk normally, using prescribed diabetic footwear. This new surgical technique has been published in the international ‘Journal of Diabetic Foot Complications’, in December 2012.

Dr. Varma has another innovation to his credit. A few months back, he did a reconstruction with PMMA for severely destroyed ankle bones, creating a mobile ankle joint. This PMMA replacement prosthesis for destroyed Charcot's foot and ankle bones is the first of its kind in the world. The surgical video can be viewed online at: http://www.youtube.com/watch?v=U4tIu6TONbo

The technique of prosthetic replacement and arthroplasty is an effort to salvage the diabetic foot by replacing the damaged bones rather than simply removing them. With good patient compliance the results have been very encouraging. Being cosmetically more acceptable and having the potential to provide the patients with a biomechanically stable and functional foot is a major advantage of the procedure.