Expandable Cages and Minimal Invasive Approaches to the Thoracolumbar Spine for Anterior Column Reconstruction

Fig. 13.1
Twenty-seven-year-old female, L3 burst fracture 4 months before, neurologically intact. Anterior column mechanical incompetence is seen in lateral view standing X-ray (a) and CT scan (b). Reconstruction is made by expandable cage and plating to neutralize share forces due to trunk rotational movements (c and d)


Fig. 13.2
Same case as in Fig. 13.1. Intraoperative X-ray imaging (a) and clinical view (b) of the left retroperitoneal minimal invasive transpsoas approach. A 7 cm incision allows exposing L3 vertebral body and half of the adjacent vertebra to perform an L2–L4 anterior fusion. Abdominal muscles are splitted along their fibres to reduce the risk for late laparocele

13.5 Preoperative Planning

In recent trauma, MRI can give information on the spinal canal encroachment and spinal cord and, most important, on the posterior longitudinal ligament complex (PLC) integrity [15]. Other basic information required are anterior gap longitudinal extension (to be measured on CT scan 2D reconstruction images both along the posterior and anterior wall lines), local kyphosis and scoliosis if present, and superior and inferior adjacent end plates size. From the abovementioned data depends the implant size although these data are not enough to move in the operatory room. Surgical strategy also relies on multiple further aspects that strongly influence type of surgery, approach, and implant choice. The most important factors are presence of fixed or flexible deformity and previous surgery, with or without posterior instrumentation, and the previously mentioned PLC integrity. Anterior column reconstruction (ACR) alone is feasible in case of no deformity or corrigible deformity; therefore preoperative planning, in ancient trauma, must include flexion-extension and lateral bending X-rays. If incorrigible kyphosis depends on anterior ligament shortening or anterior bone bridging (new callus formation), then ACR only can be still considered, but surgical strategy will include anterior ligament release or bone bridging excision. In these cases, the anterior aspect of the vertebral column needs to be exposed at the chosen level. This can be done by moving in front the major vessels by blunt dissection after ligating and cutting the segmental arteries and veins. Posterior fusion (spontaneous or surgical, with or without instrumentation) and fixed deformity together are a contraindication to ACR alone, and posterior osteotomy (and/or hardware revision) should be considered instead. ACR will follow in case an anterior gap is left after posterior correction (Fig. 13.3). As the cage body is generally smaller compared to its end plates, then a complete corpectomy is generally unnecessary, and the surgeon can leave a bone shell in the front and in the contralateral side to protect the major vascular structures from unwanted injuries. On the other hand, disk removal and vertebral end plate preparation should be impeccable. The surgeono must take care not to break the bone surface during this step to ensure the largest contact between bone and cage end plates and favoring fusion. Expandable cages are very helpful in correcting local kyphosis via anterior approach nevertheless, the risk of cage subsidence through the vertebral end plates during this maneuver is high, especially if the patient bone stoke is not satisfactory. Accordingly, preoperative dual X-ray absorptiometry scan is strongly suggested in adult patients before a kyphosis correction by ACR, and this procedure should be considered in any case hazardous in female older than 50 and male older than 60. In such cases, vertebral body augmentation by cement ingjection can be achieved during the anterior approach, before cage expansion, reducing the risk for vertebral endplates failure. Relevance of PLC in surgical planning will be discussed later (Sect. 13.6.5).


Fig. 13.3
Flowchart showing surgical pathway in case of posttraumatic anterior column incompetence with and without local kyphosis

13.6 Choosing the Right Instrumentation

13.6.1 Expandable Cages

Cage dimension is defined during the preoperative workup but must be confirmed by direct measurement of the anterior gap in the operatory room, and then the cage body is filled by bone graft ore bone substitute. Cage end plates size should be as close as possible to that of the adjacent vertebra’s to provide the largest contact surface and leave enough room for additive bone grafting. As the epiphyseal ring is considered the strongest part of the end plate, a direct contact between the cage and this aspect of the vertebra is desirable. Recently, end plates in the shape of the XLIF cages (larger than the vertebral end plate on the coronal plane) have become available on the market and can be helpful in osteoporotic patient as they always provide a direct contact with epiphyseal rings at least at the lateral aspects of the vertebral body (Fig. 13.1). Cage length, before its expansions, should be no more than 3–4 mm shorter than the gap to fill to have at least 1 cm of lengthening available. This is to achieve adequate primary stability through preloading after cage expansion. Angulated end plates are fixed on the cage before its insertion and its final angle (sum of the two end plates angles) should perfectly match the adjacent end plates inclination, if no correction is required (Figs. 13.4 and 13.5). Conversely, if we intend to correct a kyphotic deformity, then we will consider the sagittal angle we want to obtain. Cage expansion is generally achieved by a mechanical apparatus that, for safety reasons, is self-limiting once a certain pressure against the end plates is achieved. Once the cage location is considered satisfactory, then it can be released from its holder, and the expansion mechanism is finally locked by a safety screw. Hydraulic expansion mechanism is also available and allows the surgeon to check pressure continuously through a manometer. On the other hand, these systems are more complicated and sometimes more expensive. No matter the type of mechanism one would choose the most important point is that, once opened, the cage must be very ease to engage with the proper cage holder, to re-collapse and relocate in a different position, as this eventuality is common during surgery. Cages with variable angle end plates are also available and can be placed in the gap with loose end plates and then expanded to enable the best contact with the adjacent surfaces. The further step consists in locking the end plate angle and further lengthens the cage to obtain primary stability through preloading.


Fig. 13.4
S1 fracture and L5 burst fracture in a 27-year-old male seen in sagittal (a) and coronal (b) CT reconstruction. Emergency treatment consisted of posterior decompression and lumboiliac fixation is seen on lateral (c) and AP (d) standard X-rays


Fig. 13.5
Same case as in Fig. 13.4. Standard X-rays showing anterior reconstruction by expandable cage with angulated end plates completed 4 months after trauma, once sacral fracture is healed (a and b). Iliac screws are substituted by sacral screws 3 months later (c and d)

13.6.2 Titanium Mesh

As no internal mechanism is enclosed, they provide the largest space to receive bone graft thus improving chances for fusion. Furthermore, they are cheap as their cost is five to six times less compared to the previous type. On the other hand, they need to be cut manually during the surgical procedure; the contact surface is minor and occurs through residual spikes coming from the mesh pattern manual cut. Cage handling must be careful as those spikes may hurt o.r. staff hands during the surgical maneuvers. An internal titanium ring can generally be placed inside both extremities of the cage (at least in the largest diameter ones) to improve stiffness and contact surface. For this reason and because an effective preloading cannot be obtained during surgery, primary stability in stand-alone ACR is inadequate and not advisable. Vice versa, in case of ACR following posterior surgery not requiring sagittal correction, they remain a viable and economic option.

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Feb 8, 2018 | Posted by in ORTHOPEDIC | Comments Off on Expandable Cages and Minimal Invasive Approaches to the Thoracolumbar Spine for Anterior Column Reconstruction
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