In 1953, Ralph Bingham Cloward, M.D., Professor of Neurosurgery at the University of Hawaii and the only neurosurgeon in the territory of Hawaii, described in his seminal Journal of Neurosurgery paper, a way to remove blocks of bone from a patient’s pelvis and use that bone as an intervertebral spacer.
His objective was to de-compress the spinal canal thus relieving pressure on the nerves in the spinal canal. Aging, trauma, or other causes can degenerate the spacing and curves of the spine in such a way that the spinal canal narrows, and its nerves are impinged. That can create excruciating pain and, in the very worst cases, paralysis or death in patients.
Before Cloward, the few surgeons who would even attempt a surgical intervention of the spine would try to open up the canal and then instigate a fusion of bone at the affected site by scraping and cutting bone fragments (decorticating) from other sections of the spine (dorsal and lateral structures) and packing that living bone around the diseased spine segment.
While that approach could fuse vertebral segments, it could not also stabilize the spine. Cloward’s approach could.
Today, Cloward is most revered for articulating three of the most important concepts of modern spine surgery:
- The importance of, at the time, an underappreciated location in the spine—the space between the vertebrae.
- The importance of implanting a structural support.
- The importance of combining biologic processes with structure when attempting to fuse the spine.
Today, we refer to Cloward’s procedure as a posterior lumbar interbody fusion (PLIF).
Spine surgery, in 1953, was not a recognized specialty in orthopedics. So Cloward’s paper resonated with the few surgeons who were courageous enough to attempt spine surgery.
Cloward procedure was, by today’s standards, crude and rife with complication risk. He entered the patient’s body from the back, worked his way through the large muscles and arteries, removed the collapsed intervertebral disc—then, in a second procedure, cut blocks of bone from the patient’s pelvic bone—and implanted those bone blocks into the space he created between the spine discs.
The most common complications from Cloward’s procedure were excessive blood loss, dural injury, nerve root damage, graft extrusion, and inflammation of the membranes that cover the nerves (arachnoiditis).
It would be two decades before Cloward’s great lessons would be re-invigorated by way of a new intervertebral body spacer material—metal.
Using Metal as an Inter-Vertebral Spacer
Fernstrom, Nachemson, and Harmon are long gone now.
Ulf Fernstrom, M.D., died three 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, M.D., Ph.D. 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, M.D. 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 a 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 the Castellvi Spine around 2007, 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 interverbal, motion preserving disc for example, was a 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 Büttner-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. Over the next few years, a dozen other articulating intervertebral body implants were developed—the vast majority of which never made it to market.
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.
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 prodisc, 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.
The Bagby Basket
George Bagby, M.D., who was about 25 years younger than Cloward, grew up in 1930s Minnesota, where he accompanied his veterinarian stepfather on his rounds to visit local farmers. At first, Bagby thought he’d also become a veterinarian. Then World War II and, later, the Korean War broke out.
“Although I was interested in the veterinary field, thoughts of World War II changed me to thinking that caring for humans would be of greater use to the world,” remembered Dr. Bagby many years later. Bagby’s own military service was as a surgeon in the Korean War.
Bagby’s interest in veterinary medicine was rekindled in the 1980s when, by way of a providential conversation with his colleagues at the Washington State University in Pullman, Washington, he heard of degenerative spine disease—in horses.
“In speaking to veterinary friends at Washington State University (WSU) I heard about wobbler’s syndrome, a condition where the cervical spine encroaches on the spinal cord. I was disturbed to learn that horses afflicted with this problem were most often euthanized.”
Bagby, using Cloward’s principles as a starting point, developed a method for inserting a bone spacer between the horse’s collapsed cervical discs.
“Using instrumentation that I had utilized on my patients; I drilled a hole between two vertebrae and then filled it with the bone dowel. We had some great initial success, and the WSU veterinary staff has gone on to perfect my techniques. A number of the horses that would have otherwise been killed have gone on to great success in the racing arena.”
Famously, Bagby and the WSU team treated the legendary Triple Crown Winner, Seattle Slew, with the new procedure. Seattle Slew was walking sideways because his collapsed vertebrae were putting pressure on this spinal cord. So, Dr. Barrie Grant of WSU and Dr. George Bagby inserted a threaded titanium implant which contained bone graft harvested from the horse using a drilling and tapping technique, into the affected cervical disc space of the famed racehorse.
Over the next few months, not only did the implant maintain space in the cervical spine, relieving pain, but bone began to grow through the walls of the Bagby basket to form dense, healthy bone which then prevented excessive movement (stabilized) of the cervical spine.
To this day, that is referred to as the Seattle Slew Implant. Seattle Slew lived for two more years post-surgery and, according to his owners, Karen and Mickey Taylor, went on to breed 60 mares over the remaining years.
The key members of the WSU team that perfected the Seattle Slew implant were Dr. Pamela (Wagner) von Matthiessen and Dr. Barrie Grant and, of course, Dr. George Bagby.
In 1984, Bagby presented his experience applying, in effect, the Cloward procedure but with a threaded metal tube, rather than a block of bone, to the North American Spine Society (NASS). Among the members of the audience that day was a Stillwater, Minnesota-based spine surgeon named Stephen Kuslich.
As it turned out, Bagby, who had trained as an orthopedic surgeon at the Mayo Clinic in Rochester, Minnesota, and, for four years after World War II, practiced in Cannon Falls, Minnesota, was aware of Kuslich and the two men formed a working bond over Bagby’s metal basket.
Kuslich had a number of innovative ideas for converting Bagby’s basket into an implant for the human spine.
In 1987, the two men presented their new design at the North American Spine Society meeting in Banff, Alberta.
This new design was a threaded, hollow, titanium cylinder—more solid than the Bagby Basket—and was renamed the Bagby and Kuslich, or BAK, cage. Based to a large extent on the audience reaction at that 1987 NASS meeting (“We received strong acceptance and because of Dr. Kuslich’s leadership,” remembered Bagby many years later), the two men decided to start a company to bring their new spinal implant to market.
