Orthopaedic implants are artificial parts that replace or repair bones and joints. They include artificial hips, artificial knees, and the screws, rods and plates used in the spine and in broken bones. Orthopaedic means to do with bones and joints. An operation that replaces a worn-out joint is called a joint replacement, or arthroplasty.
An artificial knee has three main pieces. A metal cap fits over the end of the thigh bone. A metal tray fits on top of the shin bone. A plastic insert between them lets the joint bend and slide. The metal is usually a cobalt-chromium alloy or titanium, and the plastic is a hard-wearing polyethylene. An artificial hip has a ball on a metal stem, which goes into the thigh bone, and a cup fixed into the pelvis.
Bones differ in size from person to person. So each implant is made in a range of sizes, often eight or more for each piece. The surgeon must choose the size, and the angle at which to place it. Traditionally, the surgeon chose from X-rays, and by trying trial pieces during the operation. Now the choice is more and more often made in advance, on software, from a 3D model of the patient's own bones.
Consider a 64-year-old homemaker in Vadodara whose knee is worn out by arthritis. A CT scan of her leg is taken on medical imaging equipment. Planning software builds a 3D model of her knee from the scan. It fits the implant pieces onto the model, and suggests a size 5 cap and a size 4 tray, angled to match her leg. The surgeon checks the plan and approves it. The hospital books the theatre through operating room scheduling. It orders her sizes, plus one size above and one below, in case the bone looks different during the operation. In the theatre, an orthopaedic surgical robot can guide the cuts to match the plan.
Each implant carries a label with its lot number, which identifies the batch in which it was made. A copy of the label goes into her hospital record. If that batch is ever recalled, the hospital can find her. The trays of instruments used to fit the implant are tracked by surgical instrument tracking. For some patients, the cutting guides, or even the implant itself, are 3D-printed to fit, as explained in mass customisation with 3D printing.
Hospitals buy most implants through distributors, who keep stock of every size ready for each operation. In India, the government also caps the price of knee implants. Artificial joints are high-risk devices under the Medical Devices Rules, so each design must be approved by CDSCO before it is sold.