Introduction

The viscoelastic cervical disk prosthesis CP-ESP is an innovative one-piece deformable but cohesive interbody spacer. It is an evolution of the LP-ESP lumbar disk implanted since 2006. The implant provides 6 full degrees of freedom including shock absorption. The design allows a limitation for rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion. It thus differs substantially from current prostheses.

This study reports the clinical results of a prospective observational study series of 89 patients who are representative of the current use of the ESP implant since 2012.

The radiological results are focused on the evolution of the mean center of rotation (MCR) as an additional information to the range of motion (ROM) for the evaluation of the quality of spine movement.

Introduction

The viscoelastic cervical disk prosthesis ESP is an innovative one-piece deformable but cohesive interbody spacer. It is an evolution of the LP ESP lumbar disk implanted since 2006. CP ESP provides 6 full degrees of freedom about the 3 axes including shock absorption. The prosthesis geometry allows limited rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion (figure 1)

It thus differs substantially from current prostheses. This study reports the results of a prospective series of 49 patients who are representative of the current use of the ESP implant since 2012.

Current total disc prostheses are 2- or 3-pieces devices, including 1 or 2 bearing surfaces, and providing 3 or 5 degrees of freedom but with no, or very little, resistance. The ESP^® is a one-piece deformable implant made of silicon and polycarbonate polyurethane elastomer securely fixed to titanium endplates. It allows limited rotation and translation with elastic return. This cushion without fixed rotation center achieves 6 degrees of freedom including shock absorption. An earlier attempt to use elastomers (Acroflex^®) failed clinically due to the polymer. This highlights the need for accurate in-vitro fatigue testing and clinical evaluations.

In-vitro fatigue testing with more than 40 millions cycles were performed on different samples for compression, flexion-extension bending, lateral bending, torsion and shear. A prospective trial was initiated in 2004 for L3L4, L4L5 and L5S1 levels. Total disc replacements have been performed in 153 lumbar levels through extra-peritoneal mini-invasive anterior approach.

After in-vitro testing, microscopic examination showed that the polymer core remained unchanged without evidence of cracking or other degradation. Gravimetric analysis revealed insignificant changes in weight. The geometrical characteristics and the cohesion of the implants remained stable. After 3 years clinical experience, there was no device related complication, except one early revision for a post-traumatic implant migration. VAS and ODI scores improvements were equivalent to other published series.

In-vitro fatigue testing and short term results of the innovative ESP^® prosthesis demonstrate the reliability of the concept. The results are equivalent to other series with conventional implants.

Purpose of the study: The endoscopic transforaminal approach to the lumbar disc proposed by A.T. Yeung has achieved world-wide acceptance. The Yeung endoscopic spinal system (YESS) used with a specific instrument set enables direct magnified optical control of discectomy performed under local anesthesia and neurolepanalgesia in the outpatient setting. We began our experience in 2003 and report here the results obtained in a consecutive series of 100 patients reviewed retrospectively.

Material and methods: The inclusion criteria were patients with lumbar disc herniation-related lumbosciatic or crural pain non-responsive to well conducted medical care (including epidural or periradicular injections) for at least three months. The patients also had to display a concordant clinical and radiographic picture with confirmation of the symptomatic level by discography. Exclusion criteria were: excluded herniation with a fragment which had migrated into the canal; caudia equina syndrome; lower limb paralysis with muscle force scored less than 3; advanced-stage degernerative central bony stenosis affecting the clinical expression; pregnancy. The levels treated were: L3–L4 (n=6), L4–L5 (n=72), and L5–S1 (n=22). Herniation was forminal and extraforaminal in 53 cases, posterolateral in 31, and median in 16. There was an associated constitutional central stenosis in ten cases and in thirteen others, herniation was a recurrence after conventional surgery.

Results: One hundred patients were reviewed at mean 18 months (range 12–34 months) follow-up. There were no serious neurological, vascular, or infectious complications. According to the McNab criteria outcome was good for 71 cases, fair for 16 and poor for 13 with 11 requiring revision with conventional surgery. Patients with foraminal and extraforminal herniation accounted for more than half of our series and responded best to treatment (84.9% good outcome) compared with posterolateral herniation (48%) (p< 0.05). Patients with median herniation had an intermediary outcome (68% good results). The least satisfactory outcome was observed at the L5–S1 level (63% fair and poor outcome), but the difference did not reach statistical significance compared with the higher levels. In patients with recurrent herniation after conventional surgery, there were four cases of failure.

Discussion: These results are less satisfactory than those found in the literature. This might be explained by the less satisfactory outcome obtained with posterolateral herniations, probably because more than halve had migrated, generally above the plane of the disc, which in our experience cannot be accessed via the transforaminal approach. In addition, comparison of our first 50 cases with the last 50 showed an improvement in outcome to a mean 82%, expressing a learning curve for this type of technique. The most frequent error early in our experience was to insert the working endoscopic canula too anteriorly compared with the disc. The point of insertion must be very lateral determined by the discography in order to enter at least 30° posterior to the posterior part of the disc. Progressive fine-tuning of patient selection also helped improve outcome. YESS improves the work of the intradiscal instruments which can be control by direct view, explaining the the better results compared with the older mechanical or automatic (blind) methods. YESS is a very effective alternative to chemonucleolysis since papaine is no longer available. Compared with other endoscopic techniques for disectomy via an interlaminar approach, YESS offers the possibility of treatment patients in an outpatient setting with a local anesthesia. In addition the quality of the visual control of the foramen is better. These methods can be used in association with intradiscal Holmium-Yag laser which can also be applied to the bony walls of the foramen for a widening foraminoplasty. This transformainal endoscopic approach also offers a way to perform an exclusively foraminoscopic spondylodesis using an intersomatic cage.

Conclusion: YESS is an excellent technique for non-migrated subligament posterolateral foraminal and extraforaminal herniations where conventional access to the foramen is known to be very difficult.

Purpose of the study: The surgical treatment of degenerative lumbar stenosis associated with degenerative lumbar spondylolithesis (DLSP) is generally treated by decompression of the neurological structures combined with fusion. Results have been superior compared with decompression alone. We opted for decompression combined with stabilization without fusion using the Dynesys® in order to limit the morbidity related to instrumented fusion in older patients and to avoid the progressive aggravation of the lithesis.

Material and methods: This was a prospective series of 25 patients with symptomatic DLSP. Inclusion criteria were: saccoradiculographic confirmed degenerative stenosis of the canal associated with static anteroposterior intervertebral translation measuring at least 3 cm in the upright position irrespective of the degree of displacement demonstrated on the stress images. Incomplete reduction of the anteroposterior translation in extension, osteoporosis, associated deformity in the frontal plane were not considered to be contraindications for Dynesys® instrumentation. Exclusion criteria were: complete uni- or bilateral arthrectomy, history of lumbar surgery involving the olisthesic level. The series included 19 women and 6 men, mean age 71 years (range 53–83). All 25 cases involved the L4–L5 level. Twelve single level (L4–L5) and 13 two level (L3–L5) instrumentations were performed. All patients had a CT scan and saccoradiculography and 12 had an MRI. Pre- and postoperative stress images were obtained using the Putto protocol. Whole spine weight-bearing images were also obtained to study pelvic and sagittal parameters before and after surgery. The Beaujon classification was determined at minimum 12 months follow-up (mean follow-up 22 months, range 12–48 months).

Results: Outcome was very good in 72% of patients (relative gain > 70%) and good in 28% (relative gain 40–70%). There were no fair or poor results (100% good or very good results). There were two complications: on patient whose preoperative crural paresia worsened before complete recovery and on neuroaggressive pedicular screw which had no later consequence. The radiologic study revealed four case with an antelisthesis reduction but generally the displacement persisted and did not worsen over time. The stress films confirmed the presence of residual mobility of the instrumented level when the disc height remained sufficient. A lucent line around a screw was found in two cases with no clinical expression. After instrumentation with the Dynesys®, sagittal tilt at T9 due to accentuated lordosis below the instrumentation was observed, even in cases with an spine unbalanced anteriorly.

Discussion: This prospective study can be validly compared with another prospective study we performed in 1999 in which we compared the outcome after isolated canal decompression for DLSP with that after decompression combined with fusion. Using the same evaluation criteria, the results after fusion in a comparable population (18 patients) were similar to those observed in the present study where good and very good outcome was achieved in 88% of patients. Stabilization with Dynesys® provides results at least as good as arthrodesis with lesser perioperative morbidity.

Conclusion: In our opinion, it would be rational to propose this method for DLSP patients aged less than 65 years with a self-reducible predominantly angular displacement and satisfactory disc height. This context (group 3)occurs for pelvi with a small sacral slope and incidence, and minimal lordosis adapted to the pelvic parameters. Dynesys® is a palliative alternative to fusion for more advanced DLSP with anterior imbalance when fusion would technically difficult to correct for the kyphosis or with in a patient with significant surgical risk. Longer follow-up would be needd to confirm these good results over time and to demonstrate that Dynesys® «protects» the adjacent levels against degeneration (stenosis, destabilization).