Total Disc Replacement

History

LTDR

LTDR came before CTDR in historical context. In 1960, Fernstrom performed the initial implantation of the first LTDR, which took the shape of a steel ball. The procedure was conducted using an anterior approach.

At first, the outcomes appeared promising, but over time, it became evident that the ball settling into the subchondral bone led to disappointing long-term results. Schellnack and Buttner implanted the SB Charité® prosthesis in the early 1980s. This prosthesis comprised two chromium-cobalt plates and a mobile polyethylene core.

In France, David and Lemaire regularly used the three successive models [1–3] of this prosthesis. In 1989, Marnay described the ProDisc-L®, which featured plates with a central titanium stem. Following that time, numerous diverse LTDR designs have been introduced to the market.

CTDR

In 1962, Fernstrom faced similar challenges with his prosthesis in CTDR (cervical total disc replacement) as he did with LTDR (lumbar total disc replacement). The Prestige® prosthesis, a metal-metal design screwed into the vertebral bodies with a stabilization crest, was not developed until 1989-1991. It was only in 1995 that Bryan started regularly utilizing the CTDR named after him. Under the supervision of Goffin and Pointillart, numerous multicenter studies followed the first implantation in Europe in 2000. Subsequently, a wide variety of CTDR designs have been introduced to the market.

Biomechanicals

Artificial disc replacements (TDRs) consist of bearing surfaces specifically engineered to endure load without fracturing, minimize friction and wear, and preserve the range of motion for as long as feasible. The assessment is based on wear and motion tests conducted under varying loads and movements. A lifespan of 30 to 50 years is deemed equivalent to the successful completion of 30 to 50 million cycles.
Materials:

• Metals and alloys, including:
  • stainless steel alloys,
  • titanium and titanium alloys
  • cobalt alloys
• Ceramics, known for their increased wear resistance but reduced ductility, tend to be more fragile in nature.
• For the nucleus positioned between the metal plates, high molecular weight polyethylene, such as UHMWPE (ultrahigh molecular weight
• polyethylene), is employed.

TDR models are categorized based on factors such as anchorage, surface and friction couple, constrained or unconstrained design, location of the center of movement, and compatibility with MRI scans.

The surface coating facilitates osseointegration and may be composed of materials such as hydroxyapatite, tricalcium phosphate, porous titanium, or chromium-cobalt.

Anchorage, referring to the contact between the implant and the vertebral plates, can be accomplished using a stem, screw, or macro-texture. In the case of constrained TDRs, stronger anchorage is necessary due to the higher transmission of forces to the vertebral plates. To safeguard the plates from potential mechanical stress, the Bryan CTDR incorporates highly mobile plates.

Friction Couples

• metal/polyethylene
• metal/metal
• ceramic/polyethylen
• ceramic/ceramic

Among the various friction bearings used in arthroplasty, the metal/polyethylene combination is the oldest and well-established, particularly in hip replacements. This combination serves as a reference point, but it is worth noting that the polyethylene debris particles produced in this setting are relatively large in size.

Metal-metal couples and, to an even greater extent, ceramic-ceramic couples generate minimal amounts of debris, which are also smaller in size. This characteristic greatly reduces the risk of inflammation associated with the presence of debris.

Indications

CTDRs and LTDRs have different indications and can be used in young patients with various clinical signs. LTDRs are typically recommended for severe low back pain, while CTDRs are often performed alongside decompression surgery. Hybrid procedures, combining TDR with fusion, may be conducted in both cervical and lumbar regions.

Lumbar

TDR is primarily indicated for chronic low back pain that does not respond to conservative treatment. Clinical assessment involves evaluating pain levels, functional impairment, and overall health. Factors associated with poor prognosis include prolonged symptom duration, severity of the condition, and psychological factors.

Radiographs and MRI help assess spinal alignment, disc pathology, and muscle degeneration. Vascular exploration and discography may be considered in certain cases. Previous discal surgery is a common indication, while conditions like malalignment and osteoporosis are contraindications for LTDR.

Cervical

The primary indication for CTDR is the presence of soft hernia leading to cervical radiculopathy or myelopathy that is resistant to treatment. The assessment process includes evaluating pain levels, functional impairment, and myelopathy scores. Surgical interventions for this condition may involve either discectomy or arthrodesis.

The suitability of CTDR for cases of osteophytic hard discal hernia and myelopathy caused by cervical osteoarthritis is a subject of ongoing debate. Certain factors serve as contraindications for CTDR, including prior cervical surgery, posterior joint osteoarthritis, ligament ossification, hyperostosis, instability, osteoporosis, and the presence of infectious or neoplastic conditions.

Surgical Techniques

Both LTDR and CTDR employ an anterior approach, albeit with distinct techniques. Anterior cervical disc procedures involve cervicotomy, leading to a lateral inclination of the trachea-bronchial axis. LTDR presents difficulties due to the close proximity of major blood vessels at specific lumbar levels.

LTDR

Throughout the procedure, the patient is positioned in the “French position” with legs apart and a bladder catheter inserted. The surgical field extends from the xyphoid region to the pubis, ensuring clear visibility of the iliac crests.

To minimize risks, the retroperitoneal approach is preferred over other options, reducing potential harm to the superior hypogastric plexus. Careful attention is given to controlling the median sacral vessels, and the disc is completely removed up to the dorsal longitudinal ligament.

Anchoring of the prosthesis is performed after thorough preparation of the vertebral plates, with precise centering being critical for optimal mechanical functioning.

The height of the LTDR varies depending on the specific level and the patient’s size. In some cases, oblique prostheses may be utilized to prevent undue traction on blood vessels. Vessel exposure can be challenging and may require the expertise of a skilled vascular surgeon. Although the lateral transpsoas approach is an alternative that avoids vessel dissection, it has not yet been fully validated.

CTDR

CTDR, much like LTDR, utilizes techniques similar to the implantation of an intersomatic cage. Before the procedure, careful planning is done, taking into account the dimensions of the disc and vertebral bodies.

During the surgery, the patient is positioned in dorsal decubitus with slight forward inclination, guided by fluoroscopy. Cervicotomy can be performed horizontally or vertically, depending on the number of levels involved. Discectomy includes the sectioning of the dorsal longitudinal ligament, and the use of an intersomatic distractor aids in exposing the discal space.

The specific resection techniques employed depend on the type of hernia. The height of the CTDR is determined by neighboring discs, taking into consideration factors such as postoperative neck pain and the preservation of range of motion. Postoperative recovery is usually uncomplicated, with no requirement for a cervical collar following CTDR.

TDR has proven to be as effective as fusion procedures. LTDR indications have diminished due to uncertain outcomes, except for specific cases like inflammatory single-discopathy. CTDR is a reasonable option for young patients with cervical disc herniation.

The procedure preserves preoperative range of motion and reduces involvement of adjacent segments. However, long-term follow-up is needed to confirm the advantages of TDR over fusion.