Case History: partial knee replacement

PUBLISHED : Tuesday, 30 October, 2012, 12:00am
UPDATED : Tuesday, 30 October, 2012, 9:57am

Madam Chong, 50, knows that familiar feeling. It starts with a twinge in her knee. Then, over time, the pain builds to a crippling crescendo that on some days will cause her to fall in mid-step, and on others will send her to the emergency room begging for relief.

Chong (whose name has been changed for reasons of patient confidentiality) had been down the painful road before. Five years ago, osteoarthritis in her left knee had damaged one-third of the joint and required a surgery called partial knee replacement to repair the damage and restore her mobility.

Since her surgery, osteoarthritis had slowly but surely overtaken her right knee as well, causing her to walk with a pronounced limp when she was not writhing in agony. Age, overuse and excess weight had worn down the cartilage in the joint. In fact, age and obesity are two of the key risk factors in developing this painful condition. Chong's work also required her to do manual work and some heavy lifting, further stressing her vulnerable joint.

With osteoarthritis, the water content and protein make-up of the cartilage that helps cushion the joint degenerates, causing inflammation, pain and swelling.

The inflammation then stimulates new bone (spurs) to grow. When the cartilage is worn down, bone will rub on bone.

Doctors found that Chong's right knee was badly damaged by osteoarthritis, and surgery was her best chance for long-term relief. But the waiting list for knee surgery at the public hospital she visited was long. Chong could only wait.

She turned to painkillers, regular massages and icing the knee when the pain flared. In a bid to keep her comfortable while waiting for surgery, doctors gave her injections to manage the pain and increase the lubrication within the joint. But these conservative treatments failed to give Chong real relief.

Her doctors then became aware of a new partial knee replacement method being employed by the Orthopaedics and Traumatology Department at the Hong Kong Sanatorium and Hospital, and referred her to its director, Dr Stephen Wu Wing-cheung. The hospital was conducting surgery on its first few suitable patients for free.

Wu explains that the knee comprises three parts - the patellofemoral joint where the patella (knee cap) meets the femur (thigh bone); the medial femorotibial joint, which is the inside of the joint where the femur meets the tibia (large shin bone); and the lateral femorotibial joint, which is the outer part of the same joint.

Chong's patellofemoral joint and medial femorotibial joint were worn down and damaged. But as the lateral femorotibial joint was still healthy, she was a good candidate for partial knee replacement surgery. The medical team was employing a new surgical method using Asia's first Robotic Interactive Orthopaedic (RIO) system that promised greater surgical precision and better results.

Using a combination of a computer-assisted navigation system and robotic arms, RIO can detect even a 1mm deviation of the implant position, says Wu. He says that placement of the implant position is the trickiest aspect of the surgery, and the biggest factor in determining its success in removing pain and the longevity of results. Chong agreed to the surgery.

Computed Tomography scans allowed a computer to generate a three-dimensional map of Chong's entire knee joint before the surgery. This, in turn, helped the medical team visualise, plan and simulate the surgery, including which parts, and how much of the affected bone to remove, and where to place the implants, before the actual execution.

Moreover, the rotating burr, which cuts away the assigned bone, is programmed so that it is limited to the pre-assigned cutting zone to avoid removing excess bone.

The software can also quantify the soft tissue tension, says Wu, so that the medical team can express and adjust the "stiffness" of the muscles and other tissue in precise, scientific terms. Previously, doctors could only express the tightness of a joint in subjective language.

The high-precision, minimally invasive surgery left Chong with a smaller scar and shorter recovery time. It also left as much healthy bone intact as possible so that future surgeries, if necessary, remain possible, says Wu. Chong was delighted with the results. Her previous knee surgery required her to be on medical leave for six months. This time, despite a more extensive surgery of her right knee, she was walking and swimming one month later and back at work 40 days after the operation.



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