Acrylic bone cement: current concept review

Magnan B, Bondi M, Maluta T, Samaila E, Schirru L, Dall'Oca C. Musculoskelet Surg. 2013 Aug;97(2):93-100.

This is the editor's interpretation of a paper published in the orthopaedic literature in 2013 - our attempt to make relevant medical articles accessible to lay readers. If you wish to read the original it is easy to ask your librarian to obtain a reprint for you from any medical library.


This review considers the substance - polymethylmethacrylate (PMMA) - which is a polymer which is self-curing, that is, capable of solidifying at room temperature. It is popularly known as acrylic bone cement. It has been in use in orthopaedics since the 1940s, and its use was popularised by Professor Charnley who pioneered the modern hip replacement.

Commercially it is sold in two phases - one a powdered polymer and the other a liquid catalyst. These are mixed together just before using to fix an orthopaedic implant in place, and a reaction is triggered, resulting in the mixture becoming a solid cement within 10 to 20 minutes.

 

Heat production issues

An issue of the chemical reaction and the short time before the cement sets is that the chemical process produces heat, and the heat could damage bone or soft tissue.

 

The authors discuss its use for fixing hip and knee prostheses and also its use in the spine for stabilising osteoporotic fractures, and they discuss how altering the ratio of polymer to catalyst to make the material less viscous and easier to inject in the spinal cases tends to create a hotter reaction. Apparently newer materials are less likely to get too hot and damage the nerve structures.

They also mention the addition of radio-opaque material into the mix, so that the cement can be observed when necessary via X-ray.

Broad spectrum antibiotics, such as gentamicin, may also be added to beads of bone cement which can be inserted into the tissues or added to cement 'spacers' used to hold a tissue space open when the risk of infection is high, as there is a slow release over time of the antiobiotics just where they are needed. If an old joint replacement is infected the surgeon can either remove the implant and cement and immediately insert a new one using antibiotic-impregnated cement, or the implant can be removed and a spacer of antibiotic-laden cement left to fill the gap and maintain the correct geometry of the joint for a period of time until it is deemed safe to go back into the joint and put in a new implant. The decision is generally determined by the laboratory report of the nature of the infection. Modern spacers are pre-formed by the manufacturer and release the antibiotic at a more dependable level that simply mixing it in the operating theatre, and this is now the system of choice.

In older patients with hip fractures and osteoporotic bone, excess cement may be used to help to support the shaft of the bone by cementing in a rod which attaches to the hip implant.

 

Cardiopulmonary problems

The use of cement is not without its hazards, especially in the elderly. Cardiopulmonary complications have been reported in literature. These may include a drop in blood pressure, abnormal heart rhythms and even death. Forcing the cement down the long bone to cement in the stem of an implant may also push little bits (emboli) of bone marrow into the blood stream, and these may also cause clots to the lungs and cardiovascular complications.

 

Recently, new materials such as bioglass and porous cement have been developed which may offer potential biological value by allowing the bone to integrate within the acrylic cement structure, improving mechanical and biological stability.

 

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