KINEMATIC ALIGNMENT: THE CURRENT TREND IN TOTAL KNEE REPLACEMENT

by | Oct 4, 2022 | Orthopaedic Updates | 0 comments

A total knee replacement surgery involves not only the implant that will replace your natural knee but also the technique that your surgeon applies.

AN ORIENTATION

For the last 50 years, surgeons followed a “neutral mechanical” technique for total knee replacements introduced by Insall, Ranawat, and Freeman in the 1970s with further development to a “universal instrument system” by David Hungerford in the 1980s. For the next 30 years, mechanical alignment became the standard for total knee replacements. Mechanical alignment for knee replacement has a critical place in the development of surgery, and as a surgical technique. The mechanical technique is based on measuring towards a straight knee post-operative, namely as if a straight line passes through the center of the hip, knee, and ankle. Figure 1 illustrates the mechanical axis of the thighbone (femur) and shinbone (tibia). Yet, over the last decade, alignment systems evolved to take into account the fact that our lower limbs all align differently and people with neutral knees, do not have 100 percent straight knees. Figure 2 illustrates that some of us have a neutral alignment, some bowlegged, and others knock knees. Understanding the unique structure of everyone is imperative for successful knee replacement outcomes.  

Figure 1: The mechanical axis of the thighbone (femur) and shinbone (tibia).

Figure 2: Different alignments of the knee: neutral (normal), bowlegged, and knock knees.

WHY THE MOVE TO KINEMATIC ALIGNMENT?

Orthopaedic surgeons worldwide see a rise in patients requiring knee replacements, largely due to obesity and osteoarthritis. Equally, an increase in knee replacements prompted more research on improved methods and better outcomes for patients.  Globally the number of women with osteoarthritis is rising. More women in their 40s seek joint replacements, many due to overexercising because of too many group classes or long runs after a lapse in physical activity. Whereas the high demand for a joint replacement among younger people is weight gain. Continually evaluating and evolving knee replacement techniques will improve the outcomes for patients.

WHAT IS KINEMATIC KNEE ALIGNMENT FOR KNEE REPLACEMENT?

The orientation referred to the mechanical alignment that works towards the straight alignment of the knee post-operative by determining a straight line through the center of the hip, knee, and ankle (Figure 1 HKA). Yet, the angles of the knees vary widely between individuals. In most patients, the hip-knee-ankle angle is not zero (or 180 degrees depending on how you measure it). Different alignments create different tensions or stability in the soft tissue that holds our knees together. In this continuous research for advancement in total knee replacement, Steve Howell (an orthopaedic surgeon and professor of biomedical engineering at the University of California, Davis) devised a 3D technique to enhance the positioning of the orthopaedic implants that form the new knee. Using Howell’s kinematic alignment, the implants are customised according to the patient’s limb and knee alignment, relieving the undesired after-effects of mechanical alignment.  In 2018 while in Sacramento, orthopaedic surgeon Hannes Jonker observed and learned from Dr Howell, the great pioneer of Kinematic Alignment. Dr Hannes Jonker’s Kinematic Alignment Total Knee Replacement procedure in Potchefstroom represents a great advancement in knee replacement surgery within the region.

HOW DOES KINEMATIC ALIGNMENT WORK?

The human knee aligns along three axes, each with a specific function. The first axis controls bending and straightening (flexion-extension); the second axis moves the kneecap (patella), and the third axis rotates the shinbone (tibia) in relation to the thigh bone (femur). Kinematic alignment takes all three of these axes into account. During the surgery, while the surgeon tests the implant for range of motion, he/she examines the three axes to ensure they are well-balanced. If the surgeon finds any tightness or looseness, he or she will make adjustments to the bone and implant as needed, ensuring that the implant mirrors the patient’s natural anatomy.

HOW DOES THE ORTHOPAEDIC SURGEON DETERMINE THE ALIGNMENT?

Surgeons plan the kinematic alignment with the aid of a pre-operative MRI/CT scan, but also have specialised instruments and measuring devices to plan if an MRI/CT is not possible before surgery. To ensure accuracy in knee replacement, they measure each cut of bone to the millimeter.

GENERAL: A CLOSER LOOK AT THE KNEE JOINT

As a hinge joint, the knee allows bones to move forward and backward, but there is limited motion in other directions (think of a door hinge). Hinge joints are complex and contain many different muscles and tissues. The knee comprises three main bones: the femur (thigh bone), the tibia (shinbone), and the patella (kneecap). Healthy knees have a coat of cartilage to absorb shock and help them move smoothly. In arthritic knees, the cartilage becomes eroded and rough. Inflammation, stiffness, and pain result from bone-on-bone contact as the cartilage breaks down. The most common causes of knee pain are arthritis and overuse injuries. An informed decision about knee replacement requires thoughtful consideration as well as an understanding of the procedure and recovery process. It may be time to discuss joint replacement surgery with your doctor if your knee pain or arthritis isn’t relieved by non-invasive treatments such as medication or physical therapy. A knee replacement may be a good option if you experience severe knee pain that interferes with your everyday activities such as walking, running, climbing stairs, or sitting in a chair.

IN CONCLUSION

Kinematic alignment in total knee reconstruction key points: The Kinematic Alignment technique is the current trend in total knee replacement technique, developed by Dr Steven Howell (Adjunct Professor of Biomedical Engineering at the University of California, Davis).

  • Most patients qualify for kinematic implantation.
  • Most primary implant designs are suitable for Kinematic Alignment.
  • The Kinematic Alignment technique is reliable.
  • The outcome of Kinematic Alignment implantation is high prosthetic joint function.
  • The lifespan of the component will improve because of the improvement in knee biomechanics.
  • The development of new implant designs might be on its way to adapting to Kinematic Alignment implantation.

PRECAUTIONS & DISCLAIMERS

Every patient is unique, and everyone’s results will differ. Surgery involves risks and recovery times. Consult your doctor to verify if joint replacement surgery is the appropriate treatment for you. Some factors influencing individual results after surgery include age, weight, and prior activity level. There are some patients that may not go through surgery.  Only a physician may inform you if a product and associated procedure are appropriate/suitable for you and your conditions. Please consult your doctor for ample information on benefits, risks, and outcomes.  

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