Background context: Cauda equina following a prosthetic Disc nucleus replacement has never been reported. Purpose: To describe a case of Cauda equina following migration of the Prosthetic disc nucleus and possible cause. Study design: Case report and review of literature. Patient Sample: Case report. Outcome measures: 2 patients. Report of presenting symptoms and review of radiographs. Method/description: A 24-year-old man presented with progressively worsening pain radiating down his right leg and low back pain. His MRI scan showed a disc bulge at L4/5 for which we underwent decompression and discetomy. 4 months later he presented again with same symptoms. MRI imaging showed a disc prolapse at L4/5. He underwent a revision decompression discectomy and a prosthetic disc nucleus replacement. On the 4th postoperative day he complained of urinary retention and was unable to move his right ankle with loss of sphincter tone. The plain radiographs showed that the prosthetic disc nucleus had migrated posteriorly. He was immediately taken to theatre, which showed posterior migration of the prosthetic disc nucleus compressing the theca and displacing the nerve root. The prosthetic disc nucleus was removed from the space relieving the tension of the nerve root and the theca. Conclusions: Migration of Prosthetic disc nucleus can lead to cauda equina and this needs to be explained to the patient as possible risk factor. The angle of the vertebrae has to be measured before selecting a patient. If angle below 5 degree it is a high risk patient

Objective: To determine the success of the Anterior Lateral transPsoatic Approach (ALPA) for implanting the PDN disc nucleus prosthesis.

Design: Eight patients were implanted with the PDN device via the ALPA technique. After making a 4cm incision in the lateral-abdominal area, the peritoneum was accessed and followed medially towards the lumbar spine, where a blunt-dissection technique through the psoas muscle was used to reach the disc. The anulus was then incised, and the nucleus material was removed before inserting the PDN device into the vacated disc cavity.

Subjects: Five female and three male patients, all with moderate degenerative disc disease, were implanted. Average age was 44.5 years (+/− 8.3). Seven patients were implanted at L4–L5 and one at L2–L3. These eight subjects were followed for twelve months.

Outcome measures: Improvements in Oswestry scores and disc-height measurements were considered indicative of implant success.

Results: Oswestry scores improved from a preoperative mean of 33.8 (+/− 15.1) to a postoperative mean of 10.0 (+/− 11.1), and disc height increased from a preoperative mean of 8.6mm (+/−2.4) to 9.4mm (+/− 2.3) postoperatively.

Conclusion: The ALPA technique facilitates implantation of the PDN device, with excellent clinical results.

The clinical and radiological outcome of 34 patients who were treated with PDN-Solo and PDN-Solo XL devices for symptomatic degenerative lumbar discs is described.

34 patients had PDNs implanted in their lumbar spines between September 2002 and August 2004. Suitable patients, with proven discogenic back pain, who failed at least six months of conservative treatment, were fully consented prior to surgery. The approach was retroperitoneal in all cases except at L5/S1 when it was transperitoneal. The primary clinical outcome measure was the Low Back Outcome Score (LBOS). X-rays were taken at these follow-up points to assess the integrity and effectiveness of the implants.

36 operations were performed in 15 males and 19 females (including 2 early revision PDNs). All patients were between 20 and 65 years old, with a mean age of 42. 17 patients were treated with PDN alone and 17 with PDN as an adjunct to an interbody fusion.

There were 10 device related complications, two being amenable to early PDN revision and six requiring revision to fusion. Two patients remain symptom-free.

According to the LBOS, only 19 of 29 patients who have not been revised to fusion have had successful outcomes (65.5% of unrevised patients, 56% of all patients). Final follow-up x-rays show that when the PDN remains intact the disc space height is very similar to its neighbours. If the device has dissociated, the disc is narrowed.

Fifty years after lumbar disc nucleus replacement was first attempted by Fernstrom, the success rate is no higher and the reasons for revision are the same. Clearly there has to be a major improvement in this technology before it can be widely adopted. Until such a time as that improvement has occurred, we cannot recommend this device as a treatment for back pain.

Introduction: Europe has no equivalent of the US Food and Drug Administration (FDA). As a result, spinal implants can be adopted into clinical use in Europe earlier than in the US with a lesser regulatory burden. This may benefit patients, but if a device fails due to design changes that are not fully evaluated, outcomes can be compromised. The classic example in the past was the Capital Hip. If Europe had an equivalent to the FDA, oversight of implant design and design changes might prevent such occurrences. The Prosthetic Disc Nucleus (PDN) is an implant designed to replace the nucleus of the lumbar disc in early stage symptomatic disc degeneration. The PDN originally was a paired device. Due to technical difficulties encountered by surgeons these were converted to a single implant (PDN Solo range). Mechanical testing suggested the new device would function as well as the original paired device. However, the implant was introduced into clinical practice, outside of the US, without any clinical evaluation. Study Design: Prospective cohort study with 3 to 5 year clinical and radiological follow-up. Objective of Study: To review the outcome of PDN Solo implanted anteriorly in the lumbar spine, define the mode of failure and describe revision strategies. Patients and Methods: PDN Solo was used in 35 patients from September 2002 to January 2005 with a median follow-up of 49 months. Patients with discogenic back pain causing significant disability were offered nucleus replacement after an extensive process of consent. The approach was anterior retroperitoneal with the exception of L5/S1 which was transperitoneal. 17 patients were treated with PDN alone and 18 with a PDN to treat a degenerate level adjacent to an interbody fusion. Outcome measures were the Low Back Outcome Score and a Patient Satisfaction Evaluation. Results: 14 patients have needed PDN revision. The mean time to failure was 16.5 months. There were three early extrusions, two replaced with PDNs and one converted to a fusion. Revision procedures included seven conversions to STALIF, two circumferential fusions and five posterolateral fusions. Four more unrevised patients were identified as clinical failures. The total failure rate was therefore 51.4%. In patients with a successful outcome there was a 33 point improvement in the mean LBOS score. In all cases of failure the PDN jacket became disrupted with concomitant fragmentation of the hydrogel core. Conclusions: Modification of the paired PDN to a single device was introduced outside the US without any clinical evaluation. In the US, the original PDN and the Solo version failed to gain regulatory approval and following the failure of the Solo it has been redesigned again. This study raises questions regarding implant design, testing and approval considering that more than 4500 PDN replacements have been carried out worldwide since 1996. Do these events call for a European equivalent to the FDA?