TOTAL DISC ARTHROPLASTY

Centre of artifical disc
=
Centre of nucleus
=
2mm dorsal of sagittal verteblar midline

DEFINITION
Total disc arthroplasty (TDA functional disc replacement) is an operation where the painful degenerated disc is removed and replaced by an artificial mobile disc that mimics the movement of a normal disc. In thus way mobility in the motion segment is retained in comparison with fusion operations where mobility is lost.

INTRODUCTION:

Spine surgeons operate patients suffering from degenerative lumbar disc disease when they are not responding to good conservative treatment, or when they develop severe and progressive neurological symptoms e.g., weakness and sensation loss in their legs, and or loss of urinary continence and bowel function.

THREE OPERATION METHODS

1) Decompression procedures –where the neural canal and foraminae are cleared from impinging disc material, hypertrophied bone and ligaments or sinovial cysts from the facet joints. The operation can some times be follow by:
2) Fusion procedures-where the affected disc space is obliterated with bone or cages, the facet joints immobilised with bone graft. Immobilisation is often enhanced by pedicle screws insertion
3) Disc replacement operations (TDA, functional disc replacement, and mobile discs). With the operation, we want to retain movement over a prolonged period and keep the degeneration in the adjacent levels (above and below the device) at a minimum.

HISTORY OF THE FIRST ARTHROPLASTIC DISC

On the 19th September 1984 Dr Buttner Janz and co workers implanted the first artificial disc in a patient and it was called the “SB Charite Modular Type Disc Prosthesis” after the inventors and the site of its development and implantation (S=Kurt Schellnack, B= Karin Buttner-Janz, and Charitè - the Orthopaedic Hospital in Berlin.

Karen Buttner Janz


Given the anatomy and the kinematics of the spine, the inventors tried over a period of decades to restore stability while preserving motion.
Hjalmar Link, known for artificial hip prosthesis took over the development and very soon, the Charite mark 2 and later mark 3 were developed.

J P Lamaire

Lamaire from Dijon, one of the most prominent spine surgeons, implanted a large number Charitès and published the results of the first 100 cases with 10-year follow-up. Six independent observers examined these cases. The subsequent publication in “Rachis”, a French publication, can be regarded as the masterpiece on long-term follow up on artificial disc prosthesis.

Another prominent surgeon Thierry David, with regard to implantation of Charite who, at the 5th International Meeting on Advanced Spine Techniques, presented 132 patients, with long-term follow up with 85% excellent result.

Thiery Marnet from Mont Pellier invented the “Prodisc and performed the first clinical studies with success.

Where the nineteen hundreds ended with pedicle screw and anterior cage fusions the new millennium started with artificial disc arthroplasty and non-fusion technology, as alternate methods of treatment for degenerated disc disease.

Thiery David

RATIONALE AND GOALS OF THE ARTIFICIAL DISCS

1. To retain movement in the lumbar spine as opposed to fusion procedures that stiffened up the back. Motion how ever should be maintained over a prolonged period (decades).
2. Slow down the “normal” degeneration in adjacent level – (i.e. the level above or below the affected or degenerated level) - and not accelerate it as in fusion procedures.

INDICATIONS FOR OPERATIONS IN DDD (degenerative disc disease)

(When do we operate patients with degenerated disc disease?)

1. When patients suffering from degenerative disc disease (DDD) do not respond to good conservative treatment or deteriorate during treatment.
2. Consistent debilitating pain necessitates excessive use of pain medication.
3. Neurological deficit not responding to treatment (e.g. progressive leg weakness and sensation loss, urinary and bowel sphincter loss)
4. Painful degenerative scoliosis - abnormal curvature of the spine with imbalance and progressive neurological symptoms and signs. Artificial discs must not be inserted in scoliosis patients unless the curvature has been corrected, or a curve less than 11º on coronal plane

All other operation procedures will be dealt with in articles on the SA Spine web pages

INDICATIONS FOR TOTAL DISC ARTHROPLASTY (adopted FDA criteria)

(When do we insert a mobile disc?)

1. Age 18 to 60 years of age suffering from disabling backache, due to degenerative disc disease, or lumbar spondylosis. Objective evidence of DDD by CT or MRI is required, followed by positive provocative discogram. The discogram must demonstrate concordant pain reproduction and utilize at least one control level
2. Female patients over age of 50 or males over the age of 60 or and heavy smokers must have a BMD test (bone mineral density) to establish bone quality, prior to TDA.
3. Adjacent level pathology above a fusion seems to be an ideal indication for TDA
4. Chronic backache and radiculopathy with a contained disc on MRI.

CONTRA INDICATIONS

There are three basic biomechanical contraindications to TDA

1. Isthmic spondylolithesis (defects in the facet joints that produce abnormal sliding of the upper vertebra on the lower one).
2. Prior resection of the facet joints during laminectomies and decompression operations that will also lead to excessive sliding movement
3. Extreme lumbar kyphosis (hunchback)

Other contra-indications are

4. OSTEOPOROSIS (exclusion when BMD is more than 1 standard deviation below the norm for their age.
5. Bone diseases and malignancy
6. Metal allergies
7. Arachnoiditis (Burning legs is a warning sign)
8. Scoliosis more than 11º on coronal plane using the Cobb method
9. Tumours or infections of the vertebra
10. Pregnancy
11. Psychosocial disorders (Waddell> 3/5)
12. Post traumatic fracture or vertebral body wedging or when fracture in the thoraco-lumbar area causes abnormal kyphosis

RELATIVE CONTRA INDICATION

1. Obesity BMI > 40% i.e. (Weight in Kg ÷ Height x 100)
2. Heavy smokers and alcohol drinkers should have BMD test.
3. Marked facet joint degeneration
4. Low grade spondylolithesis without spondylolysis (grade 1)
5. Endplate abnormalities (the concave endplates) or interoseous
discus rupture
6. Mid. sagital stenosis < 8 mm on CT or MRI (severe spinal canal
narrowing)

DISC REPLACEMENTS CAN BE DIVIDED INTO:

1. Total disc replacements.(syn: Total disc arthroplasty, TDA)
Almost the whole disc is removed except the posterior part of the annulus and replaced by artificial device.
2. Posterior facet arthroplasty. (PFA)
Only the facet joints are removed and replaced by artificial devices (still in experimental phase)
3. Combination of anterior and posterior (experimental phase)
4. Nucleus replacement i.e. only the central soft part of the disc removed and replaced with artificial material or cultured cells. Cells taken from the nucleus of the patient’s disc during discectomy and cultured in the laboratory can later be re- implanted in the pathological disc space or a degenerated adjacent level disc (still in the experimental stage).
Other nucleus replacement devices are PDN, Sinux, etc.

TOTAL DISC ARTHROPLASTY DEVICES CONSIST OF:


Courtesy of Waldemar Link GMBH
1) Two metal end plates usually Cobalt-Molybdenum with special coating that will adhere to the vertebral end plates and eventually fuse with it. Some have keels other spikes on the metal end plates that facilitate stability and fusion of the plates to the vertebral end plate surfaces)
2) A central core (see pictures) made of either high molecular weighted poli-ethylene or metal, which forms the point or surface of rotation. It is
responsible for motion.

There is a lot of controversy regarding whether the core should consist of polyethylene or metal. Polyethylene has been used in arthroplasty for many years, and not withstanding osteolysis in a small % of patients polyethylene is still be used in hip arthroplasty.

Up to the present day, very few cases of osteolysis have been reported in disc arthroplasty. The possible reasons for this is that the disc is not a Synovial joint like the hip where the stress is far greater than that of the disc. Lemaire in his 10-year follow-up of more than 100 cases reported no osteolysis or loosening of the disc end plates.

APPROACHES:

Artificial disc are inserted though a mini laporotomy or small abdominal skin incision with an extra peritoneal approach i.e. moving the gut in the peritoneum sac over to the right side in the abdominal cavity. In thus way we avoid the complications of a transperitoneal abdominal operation, like adhesions, obstruction etc. Only in rare cases will a transperitoneal approach be used, usually when revision operations are being performed.
Sympathetic chain and the pre sacral nerve injury may result retrograde
ejaculation in the male patient – (sperms ejected backwards into the bladder during sexual intercourse). With care, how ever, this complication should be less than 1%.
Care should be taken to avoid injury to the left ureter.
A right retroperitoneal approach can some times also being used.

INSERTIONS TECHNIQUES

Different techniques are being used to insert the different TDA devices in the correct position, usually in the axis of rotation of the interspace (disc space).
Thorough decompression of the spinal canal after disc removal is necessary. All disc material and osteophytes (bony growths) in the spinal canal and nerve root openings or foramens should be removed before insertion of the device.
A surgeon, often a vascular surgeon, will be on the surgical team. Usually small veins can cause excessive bleeding. Under normal circumstances, the blood loss should not be more than 100- 200 mils per operation. The obese patient or the massive muscular patient can bleed more profusely.
Patients on aspirin derivates or anti coagulants should give full details to the spine surgeon and the anaesthesiologist well in advance of the operation, as these drugs can lead to excessive bleeding, and special precautions be taken prior to surgery.
Often a physician will also be part of the team to take care of the general post-operative condition, especially when the patient has heart, lung or kidney problems.

COMPLICATIONS

Complication rates are usually low and compare favourable with anterior cage fusion procedures.

Complications can be classified in 2 categories:

Immediate Complications During or Immediately after Implantation

1. Postoperative bleeding, deep venous thrombosis, pulmonary embolism and infection. Special care are being taken to avoid and treat these complications
2. Ureter injuries - already mentioned
3. Retrograde ejaculation as above
4. Postoperative leg pain may be present in 10% of cases. Usually this is transient and should disappear within 2 weeks after the operation.

If not, special investigation should be performed to rule out:

a. Inappropriate decompression
b. Fracture of the end plate
c. Post operative bleeding in the spinal canal
d. Over distraction of the interspace

5. Bad placement. Proper placement is essential within the axis of rotation. Minor off centre placement can be tolerated without any severe adverse effects. However, placement of more than 4 mm off target will often lead to leg pain, scoliosis and increased wear. Care should be taken for proper placement, as these devices must remain functional over prolonged periods.
Centring of the prosthesis is sometimes difficult during the operation specifically when double prosthesis are inserted. Although fluoroscopy is used, slight abnormalities of the spines and or the pedicles can make it very difficult for optimum placing.
Sometimes the patient may have a good clinical result but radiographically the disc is in a sub-optimal position. Revision operations in these cases should rather be avoided.

6. Subsidence: Part of the device sinks into the vertebral endplate. This can cause severe backache and salvage surgery is some times necessary. Either fusion procedure with pedicle screws or revision of the interspace with cage fusion and plate fixation performed. Osteoporosis is often the reason for subsidence and low bone mineral density (BMD) must be ruled out before the operation.
Revision surgery is best performed within 2 weeks after insertion, as post- operative fibrosis after 2 weeks makes revision surgery more difficult, with an increased complication rate.

Long Term Complications after Implantation

These complications are often related to poor implant positioning and techniques:

1. Heterotopic ossification or abnormal bone growth around the prosthesis that eventually leads to insufficient mobility and fusion. Causes are:
i Low bone mineral density or osteoporosis that leads to
subsidence.
ii Severe degenerated facet joints with poor mobility pre-op or “Locked Facet Joints”.
2. Scoliosis due to uni-lateral facet joint arthritis not detected pre-operatively or with asymmetric placement. Arthritis can develop in one of the facet joints
3. Inserting the device anterior to the axis of rotation can lead to loading of the facet joints and arthritis which undoubtedly will cause backache.

DEVICES BEING USED IN RSA

You might come across the following trademark lumbar devices when going through the web pages:

1. Charitè SB
2. Prodisc
3. Maverick
4. Kineflex or Centurion (South African)
5. Mobidisc
6. Flexicore


Courtesy of Waldemar Link GMBH
Three part SB Charite Invertebral Disc
Maverick functional disc prosthesis
Kineflex or Centurion
Mobidisc
Prodisc II prothesis

Many new devices will be introduced in future. All of these devices will be tested in the laboratories and CE (European) and FDA (American) clinical trials will be performed before being released on the open market for surgery.

RESULTS:

Dr Buttner-Janz has inserted Charitè since 1982. We can imagine the problems that arose, because at that stage the devices were very primitive and no dedicated tools available and even the abdominal approaches were not adapted for the procedure.

TDA started in the eighties and the following long-term follow up results are available

1. T.David from the policlinique de Bois Bernard-France reported at the close of 1998 that 1,700 S B Charite disc prostheses had been implanted since 1989 and he reviewed the first 85 patients with a follow- up period of five years. Depending on age, the results were excellent to good in 63%-78%. The younger patients were doing better than the older patients.

2. Lemaire et al reported in CLINICAL ORTHOPAEDICS AND RELATED RESEARCH No 337 April1997 that in a series 105 patients with a follow-up of 51 months. Seventy nine percent of patients have excellent results and 87% returned to work.

3. Thierry Marnet the inventor of Prodisc inserted the device for a period exceeding 10 years with good to excellent clinical results.

4. The FDA (American) Clinical Trials short term follow up shows that, as far as the over all recovery is concerned (ODI and Visual Analogue scales), TDA seems to be just as good and even better than fusion procedures

The Charitè artificial disc has been approved by the FDA.

The Prodisc and Maverick are in advanced stage of evaluation and should be approved shortly.

Flexicore, Kineflex (South African) and Mobidisc are being evaluated by the FDA.

WHAT DOES FDA APPROVAL MEAN?

All devices (and also medication) will, after extensive laboratory testing, be subjected to primate / animal studies before being inserted into or used in patients
Usually after the initial stages, multi centres over the world will start on controlled trials on patients, before the device or medicine is released for general application. Some South African surgeons are also included in performing some of these trials.
Eventually, after extensive studies and data, and the device seem to be accepted, then the FDA controlled randomized studies are performed to finally evaluate the product.
FDA approval is the ultimate and usually final stage of approval

REHABILITATION AFTER TOTAL DISC ARTHROPLASTY

Rehabilitation is an integral and important step in eventually returning the patient to normal life and activities and sending him back to his pre-morbid work environment.
As some patients suffered from back problems for prolonged periods before being referred for surgery, we often find abnormal behavioural patterns when standing and walking used by the patients to ease his pain. These abnormal patterns of behaviour must be recognized before the operation and should be addressed by the physical therapist in the postoperative period.
As mobility is the goal, no braces or soft braces are given post operatively.
Patients are usually ambulant after 2 days.
They may also suffer from ileus (abdominal distension) shortly after surgery but this usually clears up within a day or two.
The physical therapist will attend to the patient shortly after the operation to evaluate for abnormal neurology and start with respiratory and leg movement exercises.
As the operation is performed in the immediate vicinity of the vessels, it is important that peripheral pulses be examined and any abnormality reported to the surgeon.
Different surgeons will have different postoperative protocols but all will have in common:

1. Early initiation of motion as the success of the operation depends on it.
2. Motion in the first 3 weeks is basically in flexion with only slight extension up to the straightened position.
3. Extension and lateral flexion (sideways bending only after 3 weeks.
4. No lumbar rotation for 3-6 weeks.
5. Extension of the back beyond neutral position only after 6 weeks. Over extension should must be avoided.
6. Limit abdominal exercises until 6 weeks after operation.
7. Return to sport and high-level activity only after consulting your surgeon and only three to six months postoperatively depending on the kind of physical activity.
8. Always ensure proper posture and limit weight lifting to avoid abnormal stress on the prosthesis.
9. Neutral spine position may be individualized and modifications may be necessary to make the patient comfortable

CONCLUSION

TDA is an alternative treatment in the early stages of painful degenerated disc disease where mobility is retained, in comparison to fusion operations where mobility is lost.
The technical aspects of the operation should be precise with minimal trauma to the tissue. The prosthesis should be inserted in the optimal position for long-term survival
There is a steep learning curve for the surgeons and O R personal to ensure optimal success of the prostheses.
The initial results seem to be just as good as the fusion results with fewer complications, and retention of mobility. We also hope that the prosthetic devices when compared to fusion procedures would at least not aggravate adjacent level pathology.
Revision surgery should be kept to a minimum as the complication rate rises steeply in re-do surgery

© Copyright of the South African Spine Society