[The DIAM spinal stabilisation system to treat degenerative disease of the lumbosacral spine]

L Hrabálek, J Machác, M Vaverka
Acta Chirurgiae Orthopaedicae et Traumatologiae Cechoslovaca 2009, 76 (5): 417-23

PURPOSE OF THE STUDY: Each dynamic stabilisation should preserve motion at the operated segment as well as reduce a load on the disc and intervertebral joints. One of the methods to achieve this is the implantation of interspinous spacers between lumbar spinous processes. In this study, the patients treated with the DIAM interspinous spacer (Medtronic, USA) were prospective- ly followed up with the aim to evaluate clinical outcomes and post-operative complications.

MATERIAL: Patients with a degenerative disease of the lumbosacral spine were indicated for the operation. They suffered from axial pain with signs of nerve root involvement due to disc hernia, foraminal stenosis or disc herniation recurrence A total of 68 patients aged 23 to 75 (average age, 50.01) years, including 39 men (average age, 50.44) and 29 women (average age, 49.45), were followed up for 1 to 3 years and evaluated.

METHODS: All patients underwent a standard pre-operative clinical and neurological examination. Each patient assessed pain intensity using a Visual Analogue Scale (VAS) and, with an Oswestry Disability Index (ODI) questionnaire, evaluated their functional state. In the case of disc hernia or disc herniation recurrence, a sequester was removed; for foraminal stenosis, foraminotomy and partial medial facetectomy was performed. After this decompression of nerve structures, a spacer was implanted. Follow-up included clinical and neurological examination at 6 weeks, 6 months and 1 - 3 years post-operative- ly. At 6 months and between 1 and 3 years after surgery, pain intensity and functional outcome using VAS and ODI assessments were measured by the patients, and antero-posterior and lateral skiagrams of the lumbosacral spine were made. The X-ray examination was made to reveal a potential implant dislocation. The VAS and ODI values at 1-3 post-operative years were compared with those before surgery and the results were statistically analysed. The surgeon evaluated the outcomes at 1-3 years of follow-up according to the Odom criteria.

RESULTS: The average ODI of the group was 60.44 % before and 21.85 % after surgery, which showed an improvement by 63.85%. The average VAS was 7.18 points before and 2.10 points after surgery, showing an improvement by 70.75 %. A comparison of the pre- and post-operative results showed, in the average ODI differences of 38.24 % and 39.44 % in women and men, respectively; and in the average VAS value, 5.00 in women and 5.19 in men. The results evaluated according to indication for surgery were as follows: in patients with disc hernia, the difference in ODI was 39.62 % on average, and in VAS it was 5.42 points on average. In patients with disc herniation recurrence, the differences between pre- and post-operative average values were 41.50 % for ODI and 5.00 points for VAS. In patients treated for foraminal stenosis, these differences were 39.79 % for ODI and 5.18 points for VAS. The results for the level treated showed that at L5/S1 the average difference for ODI was 46.75 % and 4.50 points for VAS ; at L4/5 it was 35.52 % for ODI and 5.12 for VAS; at L3/4 it was 48.00 % for ODI and 5.78 for VAS; and at L2/3 it was 39.00 % for ODI and 4.50 for VAS.The results related to the method of nerve root decompression included the average differences of 40.00 % in ODI and 5.17 in VAS for removal of a disc sequester; and average differences of 32.89 % in ODI and 4.78 in VAS for foraminotomy and partial medial facetectomy. The results evaluated for the duration of pre-operative complaints were as follows: surgery by 3 months, average ODI, 44, 53 % and average VAS, 5.25; surgery between 3 and 6 months, average ODI, 37.65 % and average VAS, 4.71; and surgery after 6 months, average ODI, 35.60 % and average VAS, 5.28. The Odom criteria showed results as excellent in 41 %, good in 51.5 % and fair in 7.5 % of the patients. No poor result was recorded. There were no early complications such as haematoma, wound seroma or deep subfascial infection, and no implant dis- location. One patient had to undergo repeat surgery for subcutaneous infection without affecting the implant. Until the end of the study, no signs of herniation recurrence at the segment stabilised with a Diam interspinous spacer had been found.

DISCUSSION: The fact that none of the patients in this study required revision surgery or had a recurrence of disc herniation provides evidence for the effectiveness of the DIAM interspinous spacer.This also suggests that the implant protects the whole operated spinal segment, i.e., both intervertebral joints and discs, from being overloaded. Lesser mechanical stress applied to intervertebral facets may slow down degenerative processes and reduce their signs.

CONCLUSIONS: The implantation of a DIAM interspinous spacer is a less invasive and safe method of dynamic stabilisation of the spi- ne without intra- or post-operative complications that is well tolerated by the patient. At 3-year follow-up the patients reported improvement in their functional state, as measured with an ODI, by 64 % on the average. Their axial and nerve root pain was reduced by 71 % on the average. All patients showed improved clinical conditions and the outcomes were evaluated as excellent in 41 %, good in 51 % and fair in 7.5 % of the patients. The results of implantation were not significantly related to age, gender, operative indications, operated lumbosacral level, method of nerve root decompression or duration of pre-operative problems. No patient treated by the DIAM spacer had any recurrence of disc herniation.

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