Effect of Decompression Range on Decompression Limit of Cervical Laminoplasty

Effect of Decompression Range on Decompression Limit of Cervical Laminoplasty

Cervical posterior decompression surgery is a common procedure used to treat multilevel cervical compressive myelopathy (CCM). The primary mechanism of this surgery involves relieving ventral compression indirectly by inducing a backward shift of the spinal cord. However, this indirect decompression is inherently limited. Understanding the decompression limit and the factors that influence it is crucial for optimizing surgical outcomes. This study aimed to evaluate the decompression limit of posterior cervical surgeries and determine the effect of the decompression range on this limit.

The study retrospectively reviewed data from 129 patients who underwent cervical open-door laminoplasty between 2008 and 2012. Patients were grouped based on the range of decompression: C4–C7 (n = 11), C3–C6 (n = 61), C3–C7 (n = 32), and C2–C7 (n = 25). The decompression at each spinal level was categorized into three types based on its location relative to the decompression range: external decompression (ED), internal decompression (ID), and central decompression (CD). ED was achieved at levels immediately external to the decompression range margin, ID at levels immediately internal to the margin, and CD at levels located centrally, far from the margins. The vertebral–cord distance (VCD) was used to evaluate the decompression limit. Post-operative magnetic resonance imaging (MRI) was used to measure the C2–C7 angle and VCD, and these measurements were compared among the groups.

The study found no significant kyphosis in cervical curvature among the groups, and the C2–C7 angles did not significantly differ. The VCD at a specific level depended on the decompression type, following the pattern ED < ID < CD. The decompression type of a level was influenced by the decompression range, and for a given magnitude of the ventral compressive factor, the probability of residual compression was lower in groups with larger VCDs at that level.

The decompression type at each level varied with the decompression range. For example, at the C3/4 level, the decompression type changed from ED in the C4–C7 group to ID in the C3–C6 and C3–C7 groups, and to CD in the C2–C7 group. This change in decompression type was associated with a significant increase in the decompression limit, as reflected by the VCD. The study concluded that the decompression range affected the decompression limit by changing the decompression type at a particular level. Central decompression provided the maximal decompression limit for a given level, and no greater decompression could be achieved by further expanding the decompression range.

The relationship between the ventral magnitude of the compressive factor (MCF) and the probability of post-operative residual compression was also studied. At a given level, the probability of residual compression increased with an increase in MCF for each decompression range. However, the rate of increase in residual compression probability was different between groups with significantly different VCDs. For example, at the C3/4 level, when the MCF increased from 5 mm to 9 mm, the residual compression probability increased from 12.82% to 95.56% in the C3–C7 group, while it increased from 0.76% to 56.70% in the C2–C7 group. For a given MCF, the residual compression probability was lower in the group with a larger VCD at the same level.

The study highlighted that the backward shift of the spinal cord, often used to evaluate the indirect decompression limit, does not always correlate with good clinical outcomes. The measured backward shift (MBS) is affected by the ventral compressive factor, leading to an underestimation of the decompression limit. The theoretical backward shift (TBS) represents the true indirect decompression limit but cannot be measured directly in clinical practice. Therefore, the VCD was proposed as a more accurate parameter for evaluating the decompression limit.

The clinical significance of the decompression limit was emphasized, as adequate decompression is crucial for satisfactory neurological recovery. Previous studies have shown that patients with adequate decompression have higher neurological recovery rates compared to those with residual compression. The study suggested that by predicting the decompression limit pre-operatively and understanding the factors that influence it, the risk of residual post-operative compression could be minimized.

The study also discussed the differences between its findings and those of previous studies. While the K-line method synthesizes cervical alignment and the size of the compressive mass, it does not consider the effect of the decompression range. The study quantitatively analyzed the decompression limits for each level from C2/3 to C6/7, allowing for a more precise selection of the decompression range based on the magnitude of the ventral compressive mass.

In conclusion, the study demonstrated that the VCD is an ideal parameter for evaluating the decompression limit of posterior cervical surgeries. The decompression limit for a specific cervical level within the C2–C7 range is related to the decompression type at that level, following the pattern ED < ID < CD. Central decompression provides the maximum decompression limit for a given level, and no greater decompressive effect can be achieved by further expanding the decompression range. A reasonable range of decompression can be pre-operatively selected based on the relationship between the compressive mass and the estimated decompression limit, thereby optimizing surgical outcomes.

doi.org/10.1097/CM9.0000000000000730

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