What is the history of knee replacement devices?

In 1973, Zimmer Holdings, Inc. introduced the first metal and plastic knee replacement device. Since 1995, more than 1.45 million knee systems have been implanted in patients in the United States. In 2009 alone, domestic sales aone totaled more than a billion dollars. To date, Zimmer remains the most successful manufacturer, primarily because of its popular “NexGen” models.
There are several different members of this family of devices, each of which has distinct qualities appropriate for specific patient situations:

  • The NexGen CR knee and NexGen CR-Flex knee where introduced to offer increased amounts of flexion to patients. Flexion is described as the ability to bend at the knee. Generally, about 90 degrees of knee flexion is required to go up and down stairs, and between 90 and 110 degrees of flexion is required to sit and stand. Zimmer NexGen CR offers up to 120 degrees of flexion, while NexGen CR-Flex offers as much as 155 degrees of flexion.
  • Zimmer also has “Legacy Posterior Stabilized” devices such as the NexGen LPS and LPS-Flex knee replacement models. Both of these LPS models provide thickened posterior condyles for patients with weak posterior cruciate ligaments. A condyle is a rounded projection at the end of a bone that anchors muscles and ligaments and articulates with another bone to form a joint that flexes and bends – in this case, a joint between the femur and the tibia.

Recent evidence indicates that these NexGen knee replacement models can fail to adhere to a patient’s bones, whether the device is cemented into place or not. There are also documented failures of Zimmer’s Gender Solutions High-Flex Knee, made especially to fit the anatomical shape of a woman’s knee, and in knee replacement devices implanted using Zimmer’s Minimally Invasive Solution (MIS) system, which involves smaller incisions and less blood loss, and can mean shorter rehabilitation time for the patient.

When a patient’s knee replacement fails to adhere to the bone in which it was implanted, catastrophic damage can result, requiring extensive revision surgery to repair the damage and replace the knee. Zimmer’s posture has remained primarily one of denial. Unfortunately, there are no independent sources of corroboration when disputes arise about the safety of orthopedic devices – because no one tracks their performance. Zimmer’s FDA approval was gained through a fast-track process known as 510k, which does not require medical device manufacturers to prove safety or efficacy prior to marketing a product. Human trials are not required although some manufacturers do perform them.

The NexGen Complete Knee Solution was approved by the FDA in 1995 without studies affirming the device’s safety or effectiveness. The NexGen LPS-Flex knee was approved in 1999 and the NexGen CR-Flex knee in 2003 – both by the same fast-track process.
Dr. Richard A. Berger, who designed artificial joints for Zimmer for years and trained hundreds of surgeons to use Zimmer products, went public with a study that suggested Zimmer’s NexGen knees were failing prematurely. At a joint conference of the American Academy of Orthopaedic Surgeons and the American Association of Orthopaedic Surgeons, Dr. Berger and his colleagues presented results of their investigation of 146 Zimmer NexGen knee devices implanted in 2005. The study showed that within a year of implanting, 36% of the NexGen knees in Dr. Berger’s study loosened, and 9.3% of these cases required revisions surgery.

Additional studies in recent years have revealed that the Zimmer NexGen knee replacements, especially those implanted using the MIS technique advanced by Zimmer, have failed prematurely and have required revision surgery:

  • In 2008, adverse event reports began to surface in the FDA’s database of knee pain, polyethylene wear, and variance in the sizes of implant components.
  • In 2009, Robert L. Barrack, MD, published in the Journal of Arthroplasty results of his study of 237 first-time revisions of total knee replacement surgeries. 18.6% of the revisions involved Zimmer’s MIS system. He found that failures occurred in a shorter time among patients who had undergone MIS compared to patients with standard knee arthroscopy. Dr. Barrack concluded that, “High prevalence of MIS failures occurring within 24 months is disturbing and warrants further investigation.”
  • The January 2011 Journal of Arthroplasty published results of a study by Jared R.H. Foran, MD, and colleagues, which included 460 patients with implants containing NexGen MIS tibial components. Dr. Foran and his colleagues noted substantial early loosening of devices and radiographic (x-ray) signs of device failure. The authors discontinued their use of the MIS system pending determination of the etiology (causation) of the high failure rate.

In June 2009, the FDA issued a Class 2 recall of the Zimmer NexGen Legacy (LSD) knee. Your Class 2 recalls indicate that a medical device is “potentially dangerous.” This was the first of a list of recalls of Zimmer NexGen knee implants:

  •  June 25, 2009 Class 2 Recall, Legacy Knee: Implant surface not polished adequately, causing wear and possible polyethylene debris.
  • June 30, 2009 Class 2 Recall, Natural Knee System Modular Cemented Tibial Baseplate: Tibial spacer does not affix to distal (outer) surface of the base plate, as intended.
  • July 6, 2009 Class 2 Recall, Zimmer Femoral System: Threads on screw incomplete/non-functional.
  • November 13, 2009 Class 2 Recall, Gender Solutions Natural Knee Flex System: Surgeons may have difficulty inserting the polyethylene into tibial baseplate, resulting in damage to the device.
  • September 13, 2010, Class 2 Recall, NexGen MIS Tibial Components: Locking screws and stem extensions are associated with loosening of device, requiring revision surgery.
  • December 2, 2010 Class 2 Recall, NexGen LPS and LPS Flex Gender Femoral Components: Nonconforming internal CAM radius. (A cam is a rotating piece to allow movement from rotary to linear motion.)
  • April 14, 2011 Class 2 Recall, Posterior Referencing Sizer: Black coating break down with possible effect on surgical sites.

Many medical experts have concluded that the problems with Zimmer NexGen knee replacement products stem from the high flexion of these devices, which puts higher pressure on the knee; cementless insertion, which results in initial instability; and the MIS system, which does not give the surgeon a good view of the knee and often results in poor fixation of the device. A number of patients who have suffered pain, infection, and/or revision have filed lawsuits against Zimmer, which have been consolidated as mass torts at federal and state levels for discovery purposes.