Custom-fit knees

Specially fitted implants for total knee replacements can now be made for each patient.

TOTAL knee replacement (TKR) is the surgical procedure of choice for advanced osteoarthritis of the knee.

Modern TKR is a reliable procedure that consistently alleviates the pain of arthritis and improves function. It is, however, continuously evolving to make it a faster and safer procedure while improving the long-term survivorship of the implants.

Built-to-fit

A fairly recent technology, which promises to satisfy all these requirements, is the use of patient-specific instruments (PSIs). These PSIs are manufactured with the aid of magnetic resonance images (MRIs) or computed tomography (CT) of the patient’s limb. These are then used during surgery to consistently and reliably improve the mechanical alignment of the limb, which has been proven to increase long-term success.

The surgical time is also significantly reduced.

Bone models of a patient’s femur and tibia, with the respective PSIs.

The entire planning of the surgery is done before the actual operation, with the dimensions, angles, and rotation of the bone cuts determined beforehand. Even the appropriate sizes of the implants are known before the actual surgery.

The large inventory that is necessary for the conventional procedure is greatly reduced, from several large trays, to a single box of instruments specific to the patient.

A set of bone models in exact dimensions as the patient’s own bone is provided by implant manufacturers such that the cuts can be simulated and measured for accuracy days before the operation.

During the actual surgery, the PSIs are mounted onto the patient’s bone and cuts are made after simply checking the components for accuracy.

The process of inserting large metal rods into the shaft of the bone in conventional surgery, which could lead to fat embolism, is avoided.

Bone models with the patient-specific implants (PSIs) mounted.

Reduced operative time and smaller number of instruments have been individually proven to reduce the infection rates of surgery in large-scale national registry data involving hundreds of thousands of patients.

The faster operation and smaller incisions in the muscle that is necessary with the use of PSIs could allow even faster mobilisation of the patient, and this too has proven efficacious in reducing the rare but potentially fatal thromboembolic complications of this surgery.

The mechanical alignment of the limb has been previously reliably improved with the use of computer navigated total knee replacement. The surgical time with computer navigation however, is significantly higher than conventional surgery, even in those who have published results of more than 1,000 cases.

The entire planning of the surgery, the dimensions of the cuts, and size of the implants are decided during the surgery. Computer navigation also utilises a larger inventory of instruments than conventional surgery, including overhead tracking monitors, which could result in a greater infection risk.

Additional measures proven to significantly reduce the risk of infection during surgery is the use of body-exhaust suits.

Computer navigation is also expensive and cannot reliably restore rotational alignment of the components (rotational malalignment has been shown to be the leading cause of unresolved anterior knee pain after surgery, causing poor patient satisfaction).

Another problem that has plagued computer navigation is with the multiple reports of fractures within weeks of the surgery, which requires another surgery to fix the fracture and prolonged immobilisation for the fracture to heal. This is caused by the large tracker pins which are drilled into the shaft of the femur (thigh bone) and tibia (leg bone) for computer navigation.

The mechanical alignment is also lost when such fractures occur.

Waiting period

The only downside of PSIs is that the patient will need to wait a month between the CT or MRI scans and the actual surgery. This is the time taken for the scanned images to be exported to a design centre where biomedical engineers use computer-aided design and manufacturing suites to chalk up a draft plan from the images.

This plan will be sent back to the surgeon for verification and approval before the PSIs are manufactured and shipped to the surgeon. The cost is hardly prohibitive, in the range of an additional 10% of the cost of conventional surgery.

Having used both computer navigation in the past and PSIs currently, I find that PSIs are a safer and more reliable option of restoring mechanical alignment when compared to computer navigation.

It also provides several added benefits that make it advantageous both for the elderly patient who requires a quick and less invasive surgery, as well as for the young who demand faster return to function and long-term survival of the implants.

When utilising this technology with several evidence-based practices, the overall safety and reliability of the procedure is enhanced. Advanced perioperative pain management techniques allow patients to actively bend their knee while being wheeled out of the operation room and walk with support the day after surgery with minimal pain (early mobilisation has been proven in studies to significantly reduce the incidence of deep-vein thrombosis, which could lead to the potentially fatal complication of pulmonary embolism).

No injections are given to the patient in most instances after the first post-operative day, and pain has been reliably managed with oral medications alone.

Occasionally, patients have been allowed to return home as early as the third day after surgery (at request).

On the whole, this is likely one of the more significant advances in knee replacement surgery in recent times. PSIs improve mechanical alignment without the added risks of computer navigation, provide a low learning curve in the hands of trained surgeons, and have several other added benefits that make it an attractive option for the treatment of advanced arthritis of the knee.

In essence, it is computer navigation in a safe little box.

Sumber

Custom-fit knees