Polymethyl Methacrylate Replacement Prosthesis: An Alternative For Leg Amputation

The Department of Podiatric Surgery at the Amrita Institute of Medical Sciences and Research Center (AIMS), Kochi, Kerala, India, recently successfully replaced the destroyed foot and ankle bones in a 30-year-old patient with a novel prosthesis using polymethyl methacrylate (PMMA). The patient had developed a spinal cord injury, four years ago, due to a fall from height. This caused fracture of his spine which was operated in a hospital near his home town in Kerala. 

The spinal injury resulted in severe neurological deficit to his lower limbs. In some time, muscle strength of the lower limbs improved and he started walking. However the foot and ankle bones had become osteoporotic. When he started weight bearing, the bones of his right foot and ankle started developing micro fractures and then marked destruction, a condition called Charcot’s osteoarthropathy  which occurs due to autonomic neuropathy and is usually seen in patients with diabetes and other neurological problems. He was advised a “below the knee amputation” at many hospitals in South India, where he had taken consultation for his problem. 

However, this was not to be. He was saved from the ignominy of losing his right leg, leading to lifelong physical disability when three doctors of AIMS came to his rescue and salvaged his limb. The prosthesis was affixed through a surgical technique, now known as the 'Amrita Sling Technique', which was pioneered in 2009 by Dr. Ajit Kumar Varma, the lead surgeon of the operation. This was a one of its kind operation as PMMA replacement prosthesis does not seem to have been used by any major diabetic foot centre in the world for the replacement of destroyed foot and ankle bones. 

In conventional surgeries carried out worldwide, titanium compression screws are used to fix and fuse destroyed foot and ankle bones. As the bones become severely osteoporotic, the compression screws do not hold well, and once the patient is ambulant for a few months, re-collapse of the bones occurs. Severe peripheral neuropathy makes the foot and ankle bones soft, brittle and of very poor density. In such cases, if the patient starts walking or weight bearing, the bones become eroded with micro-fractures which later lead to severe bone destruction. This, in most cases, ends in a below-knee amputation.  However PMMA, also known as bone cement, has excellent tissue compatibility.

Speaking to Citizen News Service, Dr Varma explained that, “We took three dimensional colour CT images of the patient’s normal foot and ankle on the left side. By creating a mirror image of these pictures, we got a clear idea about how to mould the PMMA, to the shape of the damaged right foot and ankle bones. We made PMMA moulds of the damaged bones, sterilised them and implanted them in the patient’s foot. Seven such damaged bones of the patient’s right foot were replaced. By affixing the PMMA prosthesis, we prevented below-knee amputation and improved the quality of life for the patient.”

The Amrita Sling Technique was devised by the Amrita Podiatry Team for reconstructing and stabilizing destroyed Charcot's foot and ankle bones.  In the past three years the team has used this technique in over fifty foot and ankle reconstruction surgeries without any major complications. All the patients are ambulant in prescription diabetic footwear, and many are walking for over one and half years. The department boasts of performing six such PMMA replacement surgeries for foot bones destroyed by infection or by diabetes, in the past one-and-half years, where till now single foot bones were replaced, all with excellent results. Now with PMMA prosthesis, the Department of Podiatric Surgery at Amrita has marked a new beginning in foot and ankle reconstructive and corrective surgical techniques. 

Shobha Shukla - CNS
(The author is the Managing Editor of Citizen News Service (CNS). She is a J2J Fellow of National Press Foundation (NPF) USA. She has worked earlier with State Planning Institute, UP and taught physics at India's prestigious Loreto Convent. She also co-authored a book (translated in three languages) "Voices from the field on childhood pneumonia" and a report on Hepatitis C and HIV treatment access issues in 2011. Email: shobha@citizen-news.org, website: http://www.citizen-news.org) 

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