Fernstrom, Nachemson and Harmon are long gone now.
Ulf Fernstrom, M.D., died a couple decades ago. Alf Nachemson, M.D. in 2006. Paul H. Harmon, M.D., long before that. But the ‘Ball’—the implant they invented, manufactured, declared war over and implanted in about 100 patients—finally made it to an FDA panel meeting. Fifty-seven years after it was first implanted in a human.
The panel convened its meeting on December 12, 2013 to consider the use of spinal spheres…and a stair climbing wheelchair. Almost no one attended. In fact it was the shortest Panel meeting in recent memory. Done before lunch.
Twice the panel’s chair (John Kelly, M.D., associate professor, orthopedic surgery, Hospital of the University of Pennsylvania’s Sports Medicine Center, Philadelphia) said, “ok, we all agree, that does it” before the FDA staff said they still had to answer a couple of questions on the agenda.
At one point panel member Bernard A. Pfeiffer, M.D., looked out at the comparatively empty room and commented that no one from industry was around. He asked if that was a sign that spheres had come and gone for industry.
The panel’s industry representative said she spoke to a number of the companies and none were marketing spheres currently. Although, if the FDA had any guidance, they were all ears.
In the panel’s view Fernstrom’s ball exists somewhere in spine’s rear-view mirror. Far, far back. As one panel member said: “It’s come and gone (replaced by cages) and I don’t want it back.”
Well, sort of.
The Old Academic Brawl
Fernstrom and Nachemson were Swedish contemporaries. Alf Nachemson was a research assistant for Dr. Carl Hirsch at Uppsala University, Sweden’s first University. Ulf Fernstrom was a surgeon.
Both Fernstrom and Nachemson invented an intervertebral implant and each implant reflected the respective professional focus of the two physicians.
Alf Nachemson was the lab rat and believed strongly that any implant in the spine disc must mimic the elastic properties of the anatomic disc. His doctoral thesis analyzed the loads and stresses of the spinal disc as derived from detailed studies of cadaveric specimens (Rydevik et al., 2007). Many of today’s principles of biomechanic behavior of the spine originated from Nachemson’s work and remain, to this day, highly influential.
Ulf Fernstrom was a surgeon and looked for a more basic solution. Building on the work of Harmon, he came up with a stainless steel ball to implant into the intervertebral disc space. Its purpose was to restore disc articulation and spacing. Two purposes. One implant.
Nachemson was appalled that Fernstrom was actually implanting such a rigid construct into a living human spine. A solid-rigid ball had zero elastic properties. Nachemson’s alternative was a silicone ball—which would ultimately fail every cadaveric test (Szpalski et al., 2002).
Fernstrom Balls
Beginning in the late 1950s, Fernstrom implanted 191 of his “Fernstrom Balls” in 101 patients. It was an attempt to achieve arthroplasty in the spine and to create center of rotation that was mobile. President John F. Kennedy is rumored to have been a Fernstrom Ball patient.
Ironically, given Nachemson’s focus on biomechanics, X-rays of two- and three-level Fernstrom Ball implants show that the alignment of the spine with the Fernstrom Balls tended to be very good.
The Fernstrom Balls were implanted with minimal disruption to the structures of the spine, including the ligamenture. Later Dr. McKenzie from Alberta, Canada, began implanting the Fernstrom Ball. Interestingly enough, he had two of them implanted in himself.
The Evidence
At a spine meeting five years ago, Art Steffee, M.D., founder of AcroMed Corporation and one of the pioneers of modern spine surgery, shared photos of a patient who’d had the Fernstrom Balls for 35 years and was doing fine.
Reitz and Joubert looked at 75 cervical disc arthroplasties performed with the Fernstrom Ball in 32 patients and reported that at the one year point they had not detected either neurological complications or subluxations of the Balls. In two cases they did find intrusion into adjacent bone, but the clinical results remained excellent in both cases. The authors cautioned about the need for a two-year follow-up period before a final assessment of this surgical technique could be made.
A 2012 study (Eur Spine J. 2012 Mar;21(3):443-8. doi: 10.1007/s00586-011-2040-y. Epub 2011 Oct 19. The Fernstrom ball revisited. Siemionow KB, Hu X, Lieberman IH) reported on four patients who underwent cobalt-chrome sphere implantation and later presented with symptoms of sphere subsidence. All four patients presented with low back pain and/or lower extremity pain, and some with weakness. Imaging demonstrated that all patients had a loss of disc space height with sphere subsidence. Three patients underwent sphere removal, anterior interbody fusion using femoral ring allograft and posterior pedicle or facet screw fixation. In the fourth patient, the sphere was subsided into both the L5 and S1 endplates prohibiting removal.
“The Rape of the Spine”
Dr. Nachemson called the use of the Fernstrom Balls “The Rape of the Spine” and, in the course of authoring more than 400 studies and articles became the dominant critic of spinal fusions and spinal arthroplasty.
His co-author on some of these studies was Richard Deyo, M.D., of the University of Washington. Among his other accomplishments, Dr. Deyo petitioned the Center for Medicare and Medicaid services to deny coverage for the first spinal arthroplasty system approved by the FDA—the Charité.
Two Camps – Elastomeric vs. Rigid Implant
In terms of technical and service characteristics, the spine sphere only has to be mobile.
By contrast, Nachemson’s elastomeric implant had to have three functions: mobility, elasticity and shock absorbing.
Over time, both designs added new components to try to correct perceived failures of each.
Nachemson’s silicone balls were placed between two metal vertebral plates forming a sandwich structure.
Fernstrom’s rigid sphere morphed into lateral versions of the ball-and-socket joint which echoed the success of Sir John Charnley’s hip articulating prosthesis in the late 1960s.
The Charité disc, for example, is the natural extension of Fernstrom’s solid joint articulating and load bearing surfaces (although not shock absorbing—strictly motion preserving). In 1982 in Charité Hospital at the University of East Berlin, surgeons Kurt Schelznack, M.D., and Karin Büuttner-Janz, M.D., developed the design of the SB Charité, the first artificial disc to be implanted commercially in France in 1989.
In 1986, Waldemar Link, a West German orthopedic implant manufacturer joined the project. Charité was approved for U.S. commercial sale in 2004. Since then 10 other joint articulating intervertebral designs have emerged. Two were approved by the FDA for commercialization in the U.S. Only one remains on the market—the ProDisc.
Discs based on Nachemson’s mimetic theories were much slower to reach the market. One of the strongest U.S. projects came from AcroMed (purchased by DePuy, now a JNJ company) and that was the AcroFlex disc project. AcroFlex was an elastomeric ball sandwiched between two metal plates. It was tested in human trials in 1988-1989, 1993-1994 and 1998-2000. All failed.
Other elastomeric intervertebral implants were developed over the years but none ever made it to market.
FDA’s Housecleaning
Since 2005, four manufacturers have submitted 510(k) applications to clear their sphere devices. The companies and their respective spheres are Medtronic, Inc.’s Satellite Spinal System, Biomet Spine’s Spinal Stabilization Sphere System, Interbody Innovation LLPs’ Spinal Spheres and PEEK Spinal Spheres and Life Spine’s Spinal Sphere System.
At the December 2013 panel meeting, Constance Soves, Ph.D., a member of the FDA’s Review Team, said “We could not identify any reports specifically describing spinal sphere devices for use in intervertebral fusion procedures. Consequently, we could not obtain any valid scientific evidence regarding the safety and effectiveness of spinal sphere devices when used for intervertebral body procedures based on this review.”
Apparently spinal spheres had been marketed for use in intervertebral body fusion procedures before passage in 1976 of the Medical Device Amendment rules for 510(k) clearances. In effect, spinal spheres had been grandfathered in as intervertebral body fusion devices.
The FDA noted the inherent contradiction of clearing for fusion a device (the ball) which is intended for use as a non-fusion device.
Still, the FDA was doing a little housecleaning and asked the Panel to recommend reclassifying spinal spheres as Class III devices. Which the Panel did.
To help put the nail in the 510(k) pathway for spheres, the FDA staff reported that their search of the Manufacturer and User Facility Device Experience (MAUDE) database search up to June 30, uncovered 21 unique medical device reports (MDR) on the spheres. Of those cases, 16 resulted in removal/revision, 10 of pain and 6 of neurological impairment.
So, the Fernstrom Ball will live on as Pro-Disc, Charité and every other metal-on-metal ball and socket motion preserving spinal implant. Fittingly, among the practitioners.
As for Nachemson’s mimetic theories—they also live on in the academic literature and from podiums throughout the world. Among the theoreticians.
