TDR implants for the lumbar spine are currently most 2- or 3-piece devices with a purely mechanical function that provide/restore mobility. Lately interest is growing on non-mechanical implants that could possibly provide/restore mobility, but also produce counterforces on mobility as in healthy discs. No previous comparison between these two concepts has been performed, neither on clinical outcome, neither on specific differences on facet-joint load and wear.

A total of 250 patients are to be enrolled and treated. Inclusion criteria is unbearable pain and dysfunction from degenerative disc disease (DDD) that at one or two segments in the lover lumbar spine, that has not responded positively from at least one year of conservative treatment (that is combination of intense physical training and drugs).

Patients with DDD below L3 vertebra are divided I three groups:

1. One segment DDD appropriate for treatment with TDR.
2. Two segments DDD appropriate for treatment with TDR.
3. One segment DDD appropriate for treatment with TDR and one segment DDD not appropriate for treatment with TDR, that will be treated with anterior fusion (ALIF) at the same surgical procedure, called "hybrids". Within all three groups there will be an equal randomization between the two prosthesis types.

Clinical outcome will be evaluated from questionnaires sent out to patients after 12- and 24 months and 5- and 10 years after surgery. The questionnaire are the currently used ones from the Swedish Spine Registry (SweSpine) including VAS leg/back, EuroQol ,GA and ODI. Complications will be registered continuously and facet-joint load/health will be examined from flex-ext x-rays at 1 and 2 years. At the 2-year check up a 3D-CT will be performed to further evaluate the facet joints and their load under flex-ext.

Inclusion Criteria:

• Incapacitating pain from DDD (both clinical and radiological) in one or two segments below the L3 vertebra, were at least one segment is suitable for TDR treatment.
• Patient with more than one year of pain, that has during this period made a prolonged and adequate conservative program.

-Patient between 20 and 55 years of age. -

-Patient able to understand written and spoken Swedish.

Exclusion Criteria:

• Patient does not accept to be part of the study.
• Three or more segments suspected to be symptomatic.
• Earlier vertebral fracture, tumour, infection or fusion in the lumbar spine. -Substantial scoliosis/deformity.
• Need for posterior decompression.
• Pregnancy, psychiatric illness or drug abuse. -Patient does not understand written and spoken Swedish and can thus not take part in information and answer questionnaires.

-Patient residing outside Sweden and thus is not covered with SweSpine. -