Computer-assisted navigation of surgical tools can improve the accuracy and alignment of total knee replacement surgeries.
Knee pain is one of the most common complaints among the elderly, and it could be a sign of degenerative osteoarthritis (OA). OA is a common wear-and-tear disease associated with ageing. It is characterised by the breakdown of cartilage – the firm, rubbery material that cushions the ends of the bones and allows easy movement.
In OA patients, the cartilage begins to deteriorate, and subsequently, the bones begin to rub against each other. Over time, this may lead to joint stiffness and pain, and damage of the ligaments, menisci and muscles.
Most patients experience a slow gradual increase in pain and swelling. They may also have a bow-legged appearance, especially when carrying weight. Patients suffering from severe OA of the knee will have difficulties performing simple activities, e.g. walking and climbing stairs.
In the initial stages, the knee pain may respond well to home remedies such as the use of ice or heat, rest, anti-inflammatory medications, weight loss and a low-impact exercise programme. If these non-surgical treatments are no longer helpful, some patients may want to consider a total knee replacement surgery.
Total Knee Replacement
A total knee replacement (TKR) is a surgical procedure whereby the diseased knee joint is replaced with metal and plastic implants to allow continued motion of the knee. The knee is a hinge joint, which provides motion at the point where the thigh meets the lower leg. The thigh bone (or femur) abuts the large bone of the lower leg (tibia) at the knee joint.
During a TKR, the lower end of the femur is removed and replaced with a metal shell. The upper end of the tibia is also removed and replaced with a metal stem with an attached plastic piece. Depending on the condition of the knee cap portion of the knee joint, a plastic “button” may also be added under the knee cap surface.
TKR surgeries are usually highly successful, and patients can have “new” pain-free knee joints for another 15-20 years. Successful outcomes depend on several factors, e.g. the accuracy of implant position, restoration of limb alignment and balancing of the soft tissues.
Malpositioning of the femoral or tibial component can lead to early loosening, increased polyethylene wear and poor patellar tracking. Gap balancing affects the final knee kinematics, and inadequate correction of soft tissue imbalances is considered an important factor for early TKR failure.
Challenges Of Conventional TKR Surgeries
Recently, there has been much debate on how the overall mechanical alignment in TKR will affect the durability of the implant. In most studies, it has been discovered that component alignment does play a very important role in the clinical outcomes following TKR. In a review of 3,152 TKR surgeries by Berend et al, it has been demonstrated that a tibial varus alignment tends to increase the odds of implant failure by approximately 17 times.
Most surgeons are still using the conventional method of aiming for a neutral mechanical axis in TKR. The most common approach is to use an extramedullary tibial alignment guide and an intramedullary femoral alignment guide to perform distal femur and proximal tibial bone cuts, perpendicular to their mechanical axes. Sadly, this conventional method has a limited degree of accuracy.
Computer-assisted navigation of surgical tools is engineered to improve the accuracy and alignment of TKR surgeries. This technology assists the surgeon in precisely aligning knee implants to each patient’s unique anatomy, providing a personalised fit and a truly tailored TKR, and thereby decreasing the need for revision surgery.
Numerous studies have shown computer-assisted navigation can increase the accuracy of bone cuts in the coronal (frontal) and sagittal (vertical) planes.
In a meta-analysis of 29 studies comparing computer-assisted surgery (CAS) to conventional techniques in TKR by Mason et al, the CAS group achieved 90.4% success in achieving a femoral varus/valgus alignment within 2° of perpendicular to the femoral mechanical axis, as compared to 65.9% in the conventional group, and 95.2% success in achieving a tibial varus/valgus alignment within 2° of perpendicular to the tibial mechanical axis, as compared to 79.7% in the conventional group.
Another meta-analysis by Brett et al in 2013 shows that TKR performed with computer-assisted navigation is more likely to be within 3° of ideal mechanical alignment (87.1% versus 73.7% in the conventional group). Navigated TKRs have a significantly higher increase in Knee Society Score at three-month follow-up (68.5 versus 58.1) and at 12-32 month follow-up (53.1 versus 45.8).
Therefore, computer-assisted navigation in TKR provides more accurate alignment and superior functional outcomes within a short period of follow-up.
Although the technique is clinically proven to be a better option, the computer-assisted TKR surgery has yet to be widely accepted due to several challenges. There are concerns with the previous navigation system that requires a steep learning curve to master the surgical technique, a longer operative time, additional surgical incision and external pin fixation. On top of that, there is also concern with the increased capital and operating cost.
A New Computer System
The emergence of modern technology has produced newer navigation systems that are able to overcome the above-mentioned shortcomings. One of these new devices is made up of small electronic pods, which are essentially mini-computers with Bluetooth-like technology similar to those used in smartphones.
These electronic pods snap onto conventional instruments used in TKR surgeries. By simply moving the knee to different positions during a surgery, the device registers the anatomic axis of the leg unique to the patient, which guides each bone cut.
The device also allows the surgeon to verify each surgical step, such as bone cuts and overall alignment, in real time. This reduces mechanical errors during surgery and helps the surgeon place the knee implant in a more accurate alignment.
Overall, this small and portable device is more user-friendly and saves operative time. It saves cost as expensive pre-operative imaging like CT scans and MRIs are not necessary. This new device, about two inches wide, is the only piece of equipment needed to guide surgeons, and therefore large consoles in the previous computer-assisted systems are no longer required.
More importantly, this new procedure has no need for external pin fixation, which is known to cause post-operative stress fracture of the long bones. In conclusion, TKR surgery is a safe and effective procedure to relieve pain, correct bone deformity and help patients resume normal activities.
Ever since the first TKR surgery was performed in 1968, the procedure has been refined and improved with surgical materials and modern techniques. Now, TKR is one of the most successful procedures in treating knee arthritis.
> Dr Wong Him Yau is a consultant orthopaedic surgeon. This article is courtesy of Quill Orthopaedic. The information provided is for educational purposes only and should not be considered as medical advice. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this column. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.