DePuy High Flex Knee Replacement Systems

Section Guide

DePuy Orthopaedics, one of the world’s largest knee-replacement manufacturers, markets two high-flex knee devices – the Sigma CR150 High-Flex Knee System and the Sigma RP-F Knee System. Both are part of DePuy’s P.F.C. (Press Fit Condylar) Sigma Revision Knee System line. The P.F.C. Sigma High Flex Knee Prosthesis is the only mobile-bearing, high-flex knee approved by the FDA.

As the name implies, the Sigma CR150 accommodates up to 150 degrees of flexion and is offered in both fixed and rotating platform options. In fixed-bearing implants, the top of the tibia (shinbone) is resurfaced with a metal tray or bearing, which is attached firmly in a fixed position. Once attached, the bearing can flex and extend but cannot rotate.

In addition, the Sigma CR150 is a cruciate-retaining knee replacement. That means the knee replacement surgery (arthroplasty) keeps the posterior cruciate ligament (the large ligament in the back of the knee that gives the knee the normal roll back when bending) intact, thus giving the knee more support.

DePuy Sigma CR 150 High Flex Knee Replacement

DePuy Sigma CR 150 High Flex Knee Replacement

Conversely, a mobile or rotating platform (RP) knee is designed to allow the bearing to twist and turn, letting the knee rotate up to 20 degrees as it bends. The Sigma CR150 high-flex implant includes an oxidatively stable polyethylene insert and a highly polished cobalt-chrome tray to help improve wear performance compared to the original Sigma polyethylene and forged titanium tray.

The Sigma RP-F Knee System is a rotating platform high-flex knee prosthesis based on the company’s original rotating

platform design. However, several differences in material, engineering and surgical technique allow the RP-F knee to flex up to 155 degrees.

The RP-F implant is thicker than the RP, has more reinforcements and increased contact areas, and is positioned differently. Also, the RP-F requires an additional 2-4 mm of bone tissue to be resected from the femoral condyles (the rounded prominence at the end of a bone) to accommodate the hardware and allow the greater knee flexion.

The Sigma RP-F Knee System is a rotating platform high-flex knee prosthesis based on the company’s original rotating platform design. However, several differences in material, engineering and surgical technique allow the RP-F knee to flex up to 155 degrees.

The RP-F implant is thicker than the RP, has more reinforcements and increased contact areas, and is positioned differently. Also, the RP-F requires an additional 2-4 mm of bone tissue to be resected from the femoral condyles (the rounded prominence at the end of a bone) to accommodate the hardware and allow the greater knee flexion.

Reasons Behind High-Flex Knee Systems

Flexion is the action of bending a joint, such as the elbow or knee. The opposite of flexion is extension, or straightening, of a joint, such as the elbow when a person is pointing or the knee when a person is standing.

Full extension is measured at an angle of 0 degrees. Full flexion rarely exceeds an angle of 165 degrees. For most activities of daily living, high knee flexion – greater than 130 degrees – is not necessary. For example, 70 degrees of knee flexion is necessary for a normal stride on level ground; 80-90 degrees is needed to go up and down most stairs; 105 degrees is needed to arise from a normal chair; and 120 degrees is enough to arise from a low sofa or toilet seat.

Typically, knee replacement patients cannot flex their knees beyond 110–115 degrees. This is because their postoperative range of motion (ROM) is dependent on several variables, including:

  • Surgical technique (for example, the alignment and placement of the implants, removal of bone and soft tissue that can interfere with flexion at the time of surgery, and balancing of the soft tissue with the new device)
  • The implant design (most contemporary TKA implants are not designed to permit flexion beyond 120 degrees)
  • Pain tolerance
  • The patient’s motivation for postoperative physical therapy.

Other factors that impact range of motion include a patient’s age, gender, body-mass index, history of previous surgery and the patient’s preoperative ROM.

Activities like gardening, playing golf, kneeling for prayer, sitting cross-legged or even climbing in and out of a bathtub involve motions that require up to 130-165 degrees of knee flexion. So over the past several years, various implant device manufacturers developed and marketed high-flexion knee replacements for patients who want more range of motion.

Originally designed for people who required more flexion in their professional, cultural and religious environments, especially in India and various Asian countries, high flexion designs are becoming an increasingly attractive option in Western nations. The age of patients undergoing knee replacements is declining, and the desire for greater ROM is increasing.

Studies of DePuy High-Flex Knee Replacements

DePuy Sigma RP-F Knee Implant

DePuy Sigma RP-F Knee Implant

Recent studies indicate that patients considering high-flex knee replacement should proceed with caution. While several clinical trials showed an improvement in knee flexion with high-flex implants, including the DePuy Sigma RP-F model, others revealed that for the average patient without any special demands, the additional knee flexion provided by the high-flex design made no significant difference in range of motion when compared to normal prosthetics.

Another study showed a greater potential of loosening around the femoral components because more femoral bone must be removed in high-flex replacement surgery. That can lead to requiring revision surgery because of progressive device loosening and pain.

The same study also found that the higher the flexion achieved (136 degrees compared to 125 degrees), the more likely patients were to experience loosening of the implant.

Side Effects from DePuy High-Flex Knee Replacements

With any knee arthroplasty, there is the potential of adverse events. These include:

  • Change in the position of the components
  • Loosening and/or instability of the implant
  • Tibial subsidence (the implant sinking into the softer bone tissue within the tibia)
  • Bending, cracking, fracture, deformation or wear of one or more of the components
  • Infection
  • Dislocation (slipping out) or subluxation (slipping out and back in) of the patella (the kneecap)
  • Flexion contracture (the inability of the knee to fully straighten)
  • Fractures of the femur (thighbone) or tibia (shinbone)

Symptoms that could indicate any one of the above problems or a possible failure of either the Sigma CR150 High-flex Knee System or Sigma RP-F Knee System include:

  • Swelling
  • A “loose” feeling in the knee joint
  • Difficulty walking or standing
  • Heat or warmth in the knee (normal for the first few months after knee surgery, but should not persist beyond)
  • A popping sensation or clicking noise in the knee
  • Pain beyond normal recovery period (may range from minor soreness to constant throbbing)

Knee Revision Surgery

Should a knee replacement fail for any reason, whether because of inept surgical technique or problems with product design or manufacture, revision surgery is usually required. Revision knee surgery is much more difficult and painful than initial implantation and is often complicated by bone loss.

It is estimated that about 22,000 knee revision operations are performed in the United States each year. More than half of them are done within two years of the patient’s original total knee replacement surgery.

There is no corporate or FDA recall of the DePuy High-Flex knee replacement products and no lawsuits against DePuy because of pain and suffering with the devices. However, several law firms that specialize in defective medical device litigation are investigating reports of alleged failures that might be tied to the design of DePuy’s P.F.C. Sigma High-Flex Knee systems.

If it is determined that the design of the Sigma CR150 High-flex Knee System or the Sigma RP-F Knee System contributed to complications following knee arthroplasty, patients may be entitled to receive compensation for their injuries. A patient who has experienced pain, loosening and/or difficulty in walking or bearing weight since his or her knee replacement surgery, or has had to undergo painful revision surgery because of knee replacement failure, of either the DePuy High-Flex or any other system, should investigate all available legal options.

 

Sources:

  1. “The P.F.C. Sigma RP-F Total Knee Arthroplasty: Designed for Improved Performance” by Amar S. Ranawat, MD, Sanjay K. Gupta, FRCS, MSc (Engin), FRCS (Orth) and Chitranjan S. Ranawat, MD. http://www.orthosupersite.com/view.aspx?rid=18367
  2.  http://www.zimmer.com
  3.  “High Flexion Knee Replacement” by Alampallam Venkatachalam. http://www.kneesforyou.com/highflexionkneereplacement.php
  4. http://www.depuy.com/healthcare-professionals/product-details/sigma-cr150-high-flex-knee-system
  5.  “High Flexion Total Knee Replacement” by Dr. William Barrett. http://www.valleymed.org/blogs/joint-replacement/index.php/2011/09/29/high-flexion-total-knee-replacement/
  6.  “Does High-Flexion Total Knee Arthroplasty Promote Early Loosening of the Femoral Component?” by J. Zelle, D. Janssen, J. Van Eijden, M. De Waal Malefijt and N. Verdonschot. Copyright © 2011 Orthopaedic Research Society. Source – http://www.ncbi.nlm.nih.gov/pubmed/21308756