Total Disc Arthroplasty

In the first half of the 20th century, spinal fusion procedures were introduced for the treatment of spinal infections.^1,2 In the second half of the 20th century, the indications for spinal fusion were widened, and soon included the treatment of deformities, fractures and tumours.^3–5 Between 1970 and 1980, spinal instrumentation systems were developed. These implants allowed the intraoperative correction of spinal curvature and restoration of disc and foraminal height.^6,7 Therefore, spinal instrumented fusion procedures became more and more popular. In addition, the more rapid post-operative mobilisation of patients reduced the number of complications caused by long-term hospitalisation.⁸ After the establishment of spinal fusion as a standard surgical procedure, it began to be used for the treatment of degenerative or post-operative changes of the spine. ^9,10 Spinal fusion is now accepted worldwide as a standard surgical procedure for the treatment of degenerative changes of the spine, such as spondylolisthesis, lumbar scoliosis, post-discectomy syndromes or adjacent-segment disease.^11–13 However, the disadvantages of instrumented spinal fusion for degenerative changes of the spine, such as iatrogenic soft-tissue damage caused by the approach, the number of complications and adverse side effects, as well as the consequences of the immobilisation of previously mobile spinal segments, have been reported more frequently as this type of surgery has become more widely used.^8,14–17 In particular, the risk of adjacent-segment disease has become an important factor in spinal instrumented fusion procedures. ¹⁵ In addition, the expectations of patients and surgeons regarding the clinical outcome of the surgery have increased, leading to demands for further surgical options.¹⁸ Therefore, in the last two decades, new techniques and implants for the degenerative lumbar spine have been developed as an alternative to spinal fusion. The most promising of these methods seems to be the lumbar total disc arthroplasty (TDA).

Diagnostics and Imaging
Low-back pain (LBP) is the most common cause of disability in the Caucasian population. The lifetime incidence of LBP is reported to be between 70 and 80%. The treatment of LBP accounts for approximately 1.15% of total public healthcare.¹⁹ In the US, annual healthcare costs related to LBP exceed US$50 billion. ²⁰ Although many of these complaints can be treated conservatively, a growing number of cases are failing with conservative management; surgical procedures may be a treatment option for these cases. There are some surgical options available for degenerative disc disease, such as open or microsurgical discectomies, nucleotomies, chemical and thermal nucleolysis and spinal instrumented fusion procedures. However, the long-term outcome of these procedures is far from optimal.²¹ Nowadays, TDA has become a treatment option for some of these patients. Ideal patients for TDA typically present with LBP without sciatica. The pain increases in flexion and typically there is pain after periods of inactivity, such as in the morning.²² However, discogenic pain can manifest in various ways.²³

Radiological evaluation is required to determine the affected level. Plain radiographs as well as flexion and extension films are required to show the range of motion (ROM) of the spinal segments. In addition, they might show a slight loss of disc height at the affected level. Computed tomography (CT) provides no additional information and is therefore unnecessary. The first changes in a degenerative disc might be seen in a magnetic resonance imaging (MRI) scan. The first degenerative sign in MRI is the black disc in the T2-weighted sequence. Initially, the centre of the nucleus loses its ability to absorb water and becomes dehydrated.²⁴ The presence of a high intensity zone correlates significantly with the presence of grade 4 annular disruption and with reproduction of the patient’s pain, with high specificity and moderate sensitivity. Furthermore, the positive predictive value for a severely disrupted, symptomatic disc has been shown to be 86%, demonstrating that this is a useful diagnostic tool to determine discogenic pain.²⁵ On a T2-weighted MRI scan, this signal appears to be more intense than the nucleus and is surrounded by a low-intensity black area. Degenerated discs are also associated with endplate changes, known as Modic signs. ²⁶ It has been reported that Modic type 2 signs are seen in 71% of cases of LBP. ²⁷