Pain presented as lumbar-radiculalgia in 7 patients, pure lumbar pain in 2 patients and pure radiculalgia in 1 patient.

Arthrodesis was performed on the basis of hyperalgic discopathy. It involved the L4-L5 disc in 7 cases, T12-L1 in 1 case, L2-L3 in 1 case and L5-S1 in 1 case. This discopathy was secondary to isthmic lysis in 05 cases, to a vicious L1 malunion in 01 case and was of degenerative origin in 04 cases.

The mean time to progression was 16.5 months (range 3 months to 48 months).

All patients were operated on under general anesthesia with orotracheal intubation. The approach was posterior for all our patients. Bone graft was from the posterior ( Figure 1 ) crest in 9 patients. In one patient, the graft was prepared with grafts from the laminectomy.

All patients underwent single-level interbody fusion. It was done at L4-L5 in 70% of cases. A transpedicular osteotomy was performed for one patient. Posterior fixation was done using titanium screws and rods for all patients.

The number of levels set by the posterior instrumentation was unique for 7 patients, double for 2 patients and triple in one patient.

The average hospital stay was 17.7 days with extremes of 6 days and 41 days.

The comparison of the mean of the radicular and lumbar VAS in pre and post-operative period is shown in Table 1 .

Acute complications were observed in 4 patients (40%):

—minimal skin necrosis with delayed healing;

—subcutaneous infection of the surgical wound requiring revision in the operating theatre;

—dysuria lasting several weeks reported by the patient who underwent OTP with secondary normalisation;

—unilateral sensorimotor neurological deficit along the L5 pathway; the patient did not wish to undergo further surgery and presented with persistent steppage.

Functional scores

We used the Beaujon functional score ( Figure 2 ) and the Oswestry Disability Index (ODI) disability scale ( Figure 3 ).

The patient satisfaction index is reported in Table 2 .

All patients evaluated (9/10) had consolidated at the last follow-up without disassembly of the material, nor fracture of the screw or rod ( Figure 4 ). The average time to consolidation was 6.75 months with extremes of 3 and 12 months.

There were no variations in disc height in all patients.

The evaluation at follow-up also allows us to note a case of junctional kyphosis. This is the patient who has the greatest follow-up. He presented with lumbar pain with a positive Caddie sign.

We perform this procedure for advanced disc diseases such as spondylolisthesis by isthmic lysis, degenerative spondylolisthesis, degenerative disc diseases with disc crushing responsible for low back pain with radiculalgia. It can sometimes be a stenosis secondary to a discectomy or a vicious spinal cord injury. Some indications such as arthrodesis after discectomy or on discitis sequelae are much more controversial [2] [6] .

The posterior approach is the one we use to approach our patients. The incision is vertical following the spinous processes as reported in most studies unlike Lerat [3] who makes a transverse incision. This approach allows us through a small approach under the TCSC to access the posterior crest for harvesting the interbody graft. After discectomy and preparation of the vertebral endplates, the iliac grafts are inserted via the posterior approach with impaction by a graft extractor. This approach is simple and now allows ALIF [7] and TLIF to be performed after arthrectomy [3] .

There is an extracanal posterior approach [8] . This Wiltse approach allows:

The anterior and anterolateral approaches allow the disc to be distracted as much as possible, but they present a significant risk of vascular and nerve lesions [9] [10] .

Combined approaches are also reported in the literature. This is often an intersomatic route by lumbotomy or anterior route [11] associated with posterior pedicle fixation, sometimes by minimally invasive route.

The position of the graft that appears most valid for promoting bone consolidation is that where the graft is in compression and not subject to movement. This designates the center of movement located near the nucleus pulposis [2] . It therefore appears that intercorporeal grafts are the best placed from the point of view of consolidation.

The best grafts for obtaining good consolidation are therefore iliac grafts. This is a cancellous bone whose quality as a graft is recognized [2] [3] . It is notably used for intersomatic grafts of the cervical spine, during opening osteotomies of the limbs, during total hip arthroplasties. Autogenous iliac crest harvesting was hampered by donor site morbidity, with a reported complication rate of 2.8% to 39%, and long-term graft site pain persisting in 31% of patients [11] [12] .

We used iliac crest grafts for 9 of our 10 patients and a laminectomy chip graft. It was the latter patient who presented with PES paralysis due to migration of a fragment at the transverse foramen with probable compression on the nerve root. We impact the grafts interbody after their introduction, using a graft extractor. We put in the maximum amount of graft without trying to fill the disc. This is one of the differences between interbody arthrodesis and the prosthesis which seeks to occupy the disc as much as possible. Many surgeons have accepted the use of bone substitutes because they offer an excellent fusion rate in anterior procedures and avoid the morbidity of iliac grafts [13] .

The posterolateral graft is also widely used, such as in scoliosis or in posterolateral arthrodesis on low-grade spondylolisthesis. It is now used in discopathies in addition to intersomatic grafts to have a 360˚ circumferential fusion.

In intersomatic, modern arthrodesis is performed by cage. These cages allow consolidation via bone grafts introduced into them and around them, in the disc. They also allow the disc to be distracted as much as possible to free the nerve roots trapped at the transverse foramen. The appearance of the cage depends on the approach.

We used iliac crest grafts because at the time we did not yet have intervertebral cages.

ALIP is a safe technique that allows an interesting consolidation rate. We obtained consolidation in all our patients evaluated (9 out of 10), with variable delay (3 months to 12 months). Lerat [2] reports a consolidation rate of 28/29 for spondylolisthesis by isthmic lysis. Rubini [14] reports a consolidation rate of 19/20.

Arthrodesis by cage gives very good consolidation rates. Inamdar [15] obtained consolidation in all his patients (PLIF). This rate is 96% for Kapustka [10] (ALIF) or Craig Humphrey [16] .

Consolidation is achieved more easily as the number of grafted levels is reduced [17] . The use of autologous iliac graft seems to promote consolidation due to its high osteogenic capacity [18] - [20] .

Arthrodesis did not allow us to restore disc height. The use of the intersomatic cage seems to be the current standard for good distraction and good restoration of disc height and sagittal parameters. However, some authors [21] maintain that there is no correlation between restoration of disc height and clinical results.

We noted a clear decrease in pain intensity with a lumbar VAS of 1.75 to 5.63 and a radicular VAS of 1.38 versus 3.25. This trend is found in most series such as that of Boissière [11] and that of Fritzel [22] and Lee [23] . The posterior approach provides good stabilization with complete decompression [3] . This could explain the marked decrease in low back pain and radiculalgia. Short arthrodesis gives the best results [2] . All our patients benefited from a single level of arthrodesis.

Four patients kept low back pain of moderate to low intensity at the last follow-up. Inamdar [15] in his series found a percentage of 20% of postoperative low back pain.

On average, we noted a significant improvement in the ODI score and Beaujon score, with a postoperative gain of 3.2 points.

Some previous studies [21] [24] [25] have demonstrated the superiority of the clinical results of posterior interbody arthrodesis compared to other types of arthrodesis. Our good results could also be explained by the fact that our population is relatively young with an average age of less than 60 years as demonstrated by Lee [23] .

We obtained 87.5% of very satisfied and satisfied patients after surgery.

Spinal surgery is very prone to complications. Some of these complications can be life-threatening (vascular lesions) while others can be functionally hazardous (spinal cord and root lesions).

One of our patients presented with L5 paralysis, certainly due to migration of an intersomatic graft fragment into the transverse foramen. This patient did not want to repeat the surgical procedure for nerve decompression. This is why we preferred to use iliac grafts for the graft.

We had a case of dural breach. This breach was due to an exaggerated gap between the spinal cord and the root on the one hand and the forced passage of a large-caliber bone graft. The repair was done by a direct and watertight suture. This is a common complication of spinal surgery with an estimated rate of between 3% and 5%. The management of these breaches consists of a direct suture or a reinforced suture (muscle, fat). The use of products such as biological glue is increasingly frequent to reinforce and protect these sutures. It is then recommended not to drain or to drain in a rag. Infection of the surgical site was found in one of our patients. It was a persistent discharge from the iliac graft harvesting site. This is a serious complication with a mortality rate of up to 3%.