Sunway Medical Centre, Kuala Lumpur

COMPUTER AIDED TOTAL JOINT REPLACEMENT

Ever since the first Charnley hip was implanted at the Wrightington Hospital for Joint Diseases in Wigan in 1961, millions of patients worldwide have benefited from total joint replacement. Although the basic principle has remained, there have been great strides in development in this field since Charnley’s time.

The main challenge today is to improve implant longevity and function and to this end there is a push for better material, improved design and improved surgical technique. One of the most recent innovations is computer aided total joint replacement.

Traditionally, preparation of the joint surfaces to accept the prosthesis is done by mechanical jigs and visual aids. Although this is acceptable in the majority cases, problems are encountered in obese patients, severe deformities and soft tissue abnormalities. One of the common causes for early prosthesis failure is misalignment of the new joint which is basically a technical error. It is envisaged that with computer assistance, this can be overcome.

Most suppliers in the joint replacement market will provide a computer assisted module for implantation of their products for the lower limb. Although the specifications may vary, the principle is the same i.e. to position the implant so as to re-establish the mechanical axis (hip-knee-ankle) of the lower limb.

They use GPS type technology for the surgeon-computer interface. Wireless trackers inserted in the patient relays information through infrared optics to the computer. The computer with its’ unique tracker software will in turn inform the surgeon continuously as to the position of the patient’s limb in space at any given time.

The procedure starts with registration of the patient’s anatomy. Unlike image guided surgery which requires pre-operative imaging (either MRI, CT or Fluoroscopy), computer aided surgery uses the information gathered by the surgeon during the operation to allow for the creation of a “morph” of the patient’s anatomy. The cutting jigs use trackers to communicate with the computer to ascertain that the saw cuts to be done will align the implant in the appropriate alignment to the accuracy of 0.5º.

Since the computer allows for real time display of the patient’s joint in space, one can ascertain the alignment and kinematics of the joint with the trials in place, allowing the surgeon to modify the implant position or balance the ligaments at the trial stage if necessary. This instantaneous feedback remains one of the major advantages of computed aided surgery over the traditional jig-based procedure where in the latter the surgeon can only ascertain the implant position from the post-operative X-ray.

There are other advantages. As the medullary canals are not breached (as in the traditional jigs), blood loss is less and therefore negating or minimising blood transfusion. This also leads to a lower incidence of fat embolism. As the alignment of the implant is optimal and with ability of the kinematics to be modified intra-operatively, post operative function is improved. Being an extra tool to “help us see”, there is also a great potential in doing joint replacement procedures through minimal incisions, again improving post-operative rehabilitation.

In prospective randomised studies 1,2 comparing computer assisted knee arthroplasty to conventional technique, the former has been shown to give significantly better results in terms of post-operative alignment and blood loss. We have performed computed aided total knee and hip replacement at the Sunway Medical Centre since October 2005. Comparing to a matched group of traditional jig-based total knee replacement done in the same centre, the computer aided group showed consistent result in terms of femoral, tibial and tibio-femoral alignment. Out-liers seen in the jig-based group were not detected in the computer aided group. Measurement using CT scannogram showed that the femoral, tibial and tibio-femoral mechanical axis together with the joint line coronal alignment all fall in the acceptable range of ± 3º. Out of these, 85%, 94%, 82% and 94% respectively fall in the ± 1º range.

We are encouraged by our initial results. It is envisaged that the computer will replace traditional methods in all total joint replacement in our centre and elsewhere in the future.

• 1st private hospital to perform the total joint replacement surgery using computer navigation. To date, approximately 400 cases have been performed
• Hip replacement, knee replacement and total joint replacements are performed on patients who suffer from pain and deformity
• An implant can last between 15 – 20 years
• Surgery done via computer navigation has proven to show accurate alignment in the patient. The patients’ legs look straighter, the implant lasts longer and the patient can also bend their knees a lot better
• In younger people, using the minimally invasive uni-compartmental knee replacement technique, the patient has an incursion of only between 6-8cm. For these patients, their range of movement remains. They can even start driving within six weeks from the operationbetter
• Patients are advised not to take any herbal medications as they tend to cause high bleeding
• Joint replacement surgery does not prolong a patient’s life but it enables patient to carry out activities of normal living and enjoy a better quality of life
• 95% of the patient population that undergo joint replacement surgery tend to be from the elderly group. The elderly population who live longer and have had an active lifestyle are more prone to undergo a joint replacement surgery. Those who have been involved in a lot of sports and have sustained many sports injuries are also likely to undergo a joint replacement surgery
• 10 – 15% of patients with Rheumatoid arthritis also opt for joint replacement surgery
• One can avoid having a joint replacement surgery if they seek professional help early when they suffer from any injuries, maintain an ideal body weight and avoid high impact exercises