Purpose: Single-segment wedge osteotomy is classically proposed to correct for kyphosis subsequent to ankylosing spondylitits. We analysed the usefulness of this technique for other indications (revision procedures for flat back and deformed calluses of the lumbar spine) by studying the overall sagittal balance of the spine and tilt of the sacrum.

Material and methods: Between 1980 and 1999, we retained 68 patients with complet clinical and radiological data (37 patients with ankylosing spondylitis and 31 patients with “post-operative” flat back, including nine trauma cases and 22 degenerative spines). Opening osteotomy was performed in the first 19 patients and closure osteotomy in the next 49. The correction level was L2L3 in 26 patients and lower in 42. Digitalised lateral views of the entire spine were obtained at minimum follow-up of three years to measure:

- posterior displacement of T9 (between the vertical line and a line joining the geometric centre of T9 and the femoral heads (normal 11±5°),

Results and discussion: The overall angle of local correction was 44° and the correction of T9 displacement was 30.6°. For the low osteotomies, the local correction was 49° and the T9 displacement was +28° (−2° to +26°). Tilt of the sacrum varied from 4° to 7°. Tilt of the sacrum was influenced more and more for lower and lower osteotomies. T9 displacement stabilised between 12° and 26° (mean 19°) irrespective of the osteotomy level, although the angle of local correction was greater (up to 60°). This discordance was explained by adaptation of the pelvis. Seven patients developed secondary functional kyphosis (limited hip movement preventing the necessary adaptation to the overall correction of the sagittal balance).

Conclusion: Single-segment spinal osteotomy remains difficult but offers very important correction possibilities affecting the position of the trunk and adaptation of the pelvis. The level for the correction must be chosen with care because it conditions final adjustment and function consequences affecting the pelvis.

Purpose: The aim of this work was to evaluate the short- and long-term biocompatibility, tolerance and tissue response after implantation of an intersomatic bioresorbabled lumbar cage (Phusiline®).

Material and methods: Eighteen sheep were operated on in 1999; three animals were sacrificed for study at three, six, nine and twelve months after implantation. The cage was placed between two lumbar vertebrae and filled and covered with cancellous bone. Cerebrospinal fluid, lateroaortic lymph nodes, liver, spleen and kidney samples were taken after sacrifice. The spinal segment from L1 to S1 was removed with the surrounding ligaments and muscles for radiography, MRI, and CT scan. Histology sections were stained with Paragon. The pathology examination included: bone and cell density, degree of tissue differentiation in contact with the implant, remodeling and consolidation of the fusion, implant resorption and associated reactions. An epifluorescence study was performed to assess bone apposition. Reaction of tissue in contact with the implant or far from the implant (laterovertebral muscles, paravetebral lymph nodes, liver, kidney, spleen) were qualified histologically.

Results: At three months, there was no evidence of implant resorption; there was active formation of new bone around the implant. Implant resorption and osteointegration had started at six months and bone remodeling around the implant was increased. There were signs of bone fusion within and around the cage. Spondylodesis was effective at nine months with bone apposition. Implant resorption continued. Spondylodesis was confirmed. After nine and twelve months implantation, there was no sign of local or general intolerance. Degradation of the implants was visible after one month and appeared to be most marked at 12 months. Approximately 30% of the initial surfaced area of the implants had been resorbed at 12 months.

Conclusion: One year after implantation, the implant had not induced any sign of local intolerance (no sign of inflammation, necrosis, osteolysis). Fusion occurred within and around the case. This study will be pursued (two groups of three animals will be sacrificed at 24 and 36 months) and should confirm the long-term effectiveness of this technique.

Purpose: A significant increase in serum cobalt level has been reported after metal-on-metal total hip arthroplasty with wide individual variability related to activity level, mechanical conditions of the implant, and urinary elimination of cobalt. We studied serum cobalt levels over time to further analyse these factors.

Material and methods: The Metazul® prosthesis was implanted in 119 patients (72 men and 47 women, 12 bilateral implantations) (131 implants). We selected 50 patients (27 men and 23 women, mean age 53 years) who had two blood samples after the procedure allowing an assessment of the serum cobalt kinetics. Other chromium-cobalt implants, vitamin B12 intake, renal failure, or haematological disorders were recorded. An activity questionnaire was filled out by the patients at the time of the blood sample. Samples were drawn with a special kit to avoid metal contamination. The detection limit was 1 nmol/L (0.06 μg/L) with direct electrothermic atomic spectrometric absorption.

Results: In the overall series, serum cobalt level was 44 nmol/L for a physiological level in a control population of 4.28 nmol/L. The difference was significant (p < 0.0001) between the levels observed before surgery and after 18 months implantation. There was no significant correlation with the indication for arthroplasty, presence of dislocation or subdislocation, functional outcome or radiographic findings. Activity level the week before sampling did not influence the results. For the 50 cases evaluated longitudinally, four groups of patients could be identified. The first group (29 patients) had a serum cobalt level below 50 nmol/L over the entire study period. The second group (nine patients) had a level greater than 50 nmol/L followed by a decline ending with a final level below 50 nmol/L. In the third group (six patients) serum cobalt was greater than 50 nmol/L with no trend to a decline. In the fourth group (six patients) the cobalt levels were very high (greater than 150 nmol/L).

Discussion: The six patients in the fourth group were very particular. There were three patients with secondary bilateral implants with a late peak in serum cobalt, one with an impingement on the acetabular rim, one with renal failure, and one who had a very high level of physical activity. The first group had what appears to be a favourable course, similar to the second group where a stabilisation phenomenon could be operating. An explanation in the third group is difficult but could involve a third segment abrasion phenomenon.

Conclusion: Longitudinal analysis of serum cobalt levels provides more information than point measures in patients with metal-on-metal arthroplasties. Intercurrent mechanical phenomena can be detected; unexpected behaviour of the metal-on-metal junction can be suspected in certain patients.