**5. TDR surgery**

The typical diseased lumbar segment considered for artificial disc technologies at L4-L5 or L5-S1 has advanced degenerative disc disease with loss of vertical height and lordosis, dehydration changes, adjacent Modic endplate changes, and little motion on dynamic studies (see Figure 1). The natural progression of degenerative disease disc limits the joint mobility and this biomechanical fact places more forces on the adjacent levels then in the normal situation. The artificial lumbar disc, by restoring normal motion, height, and lordosis, will decrease the forces on the adjacent levels. Thus, theoretically, levels adjacent to a dynamically stabilized level may have beneficial effects compared to the natural history of the unoperated degenerative state. Clearly some patients will benefit from the decreased force on the adjacent vertebral level(s) following a dynamic stabilization (arthroplasty) compared to a static stabilization (fusion). Estimates of the rate and groups of patients at maximum benefit will need to await long-term clinical follow up studies with lumbar arthroplasty devices similar to the hip and knee arthroplasty registries. Also, although a dynamically stabilized level can be converted to a fusion, a fused level cannot be converted to a dynamic joint. Thus, artificial technology can be thought of as a definitive procedure for the vast majority of patients that can be converted to a fusion if the pain and functional goals are not met or degenerative changes occur in the posterior elements and the arthrodesis level is believed to be the pain generator.

Lumbar Spinal Arthroplasty: Clinical Experience 527

Fig. 2. Five years results from the Charité FDA IDE prospective randomized study. 2a. ODI.

2b. VAS.

Fig. 1. Typical radiographies for a TDR patient. 1a. Pre-operative MRI. 1b. Post-operative A-P radiography. 1c. Post-operative lateral radiography.

Fig. 1. Typical radiographies for a TDR patient. 1a. Pre-operative MRI. 1b. Post-operative A-

P radiography. 1c. Post-operative lateral radiography.

Fig. 2. Five years results from the Charité FDA IDE prospective randomized study. 2a. ODI. 2b. VAS.

Lumbar Spinal Arthroplasty: Clinical Experience 529

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