Minimally Invasive Surgery Transpedicular Intrabody Cage Technique for the Management of Kummell Disease

Discussion

The incidence of vertebral compression fractures has been gradually increasing in South Korea due to an aging population and unique social and environmental factors.1 One of the complications of vertebral compression fractures is the development of avascular necrosis, which results in failure of fracture healing. This is also known as Kummell disease. While previously thought to be rare, there are increasing reports of Kummell disease in the literature. This condition causes 3 issues: (1) significant pain and functional disability due to instability at the fracture site, (2) kyphotic deformity, and (3) possible neurological compromise.2–4 The preferred treatment should ideally address all the issues that are presented by the patient.

The ideal treatment for Kummell disease remains controversial and therefore should be individualized according to the patient’s issues and preferences. Several treatment methods have been proposed for the management of Kummell disease. Vertebroplasty is a widely accepted minimally invasive procedure in the treatment of OVCFs, with many authors reporting successful outcomes even for patients with Kummell disease.3,6,7 However, cement leakage and loss of correction are common complications after vertebroplasty, with a greater incidence of cement leakage (75%) and recollapse of the vertebra in compression fractures complicated by osteonecrosis.8,9 Furthermore, there is evidence of progressive recollapse and worsening clinical outcomes over 2 years after vertebroplasty in such fractures.10 In a study by Heo et al, the kyphotic angle (SA) improved after vertebroplasty from 13.51° to 8.54°, but at 2 years after vertebroplasty, it returned to 13.62°.10 In comparison, the SA in our study improved from 15.2° to 1.2° postoperatively, and at 12 months, there was only a slight deterioration to 3.6°. The SA in our study is likely to be maintained in the long term as there is radiological confirmation (either CT or radiographs) of fracture union at the level of pathology. In another study by Ha et al, the ODI and VAS scores of patients with Kummell disease remained elevated at 48.5 and 4.5 points, respectively, despite vertebroplasty. Those patients had progressively poorer ODI and VAS scores of 55.4 and 5.9 points at the final follow-up, although it did not reach statistical significance.9 In our study, the ODI and VAS scores decreased significantly and remained low at 22.9 and 2.3 points at 12-month follow-up. Therefore, vertebroplasty might not provide the desired improvement in clinical outcomes or maintain its results in the long term.

In patients with neurological compromise, surgical treatment is preferred to decompress the spinal canal and stabilize the spine. Various surgical techniques have been proposed, ranging from the anterior approach alone, the combination of anterior and posterior approaches, to the posterior approach alone.11 Anterior approaches offer excellent reconstruction of the anterior spinal column and correction of the kyphotic deformity. However, 20% of patients still required posterior instrumentation due to the progression of kyphosis and early implant failure.12 Furthermore, most spine surgeons may not be familiar with anterior approaches because they are less commonly performed or an access surgeon may be required.

Both posterior long- and short-segment fusions have been utilized successfully to treat Kummell disease. In a meta-analysis by Yu et al, the authors concluded that both treatment methods are equally effective clinically, but short-segment fusions are inferior to longer constructs in maintaining their correction of kyphosis over time. None of the studies included in the meta-analysis described the insertion of an intrabody cage, while some studies performed vertebroplasty at the fracture site with posterior fusion.13 We believe that the addition of an intrabody cage provides increased stability and anterior column support, further augmenting the correction of the kyphotic deformity.

The insertion of intrabody cages in the treatment of Kummell disease had been reported in the literature previously.11,14,15 All studies reported good clinical outcomes and excellent correction of deformity, but all of the techniques were performed using an open surgical approach. To our knowledge, only 1 other article by Park et al described a similar technique.16 This is the first case series describing the treatment of Kummell disease using percutaneous or minimally invasive transpedicular insertion of an intrabody cage. In this study, we offer clinical outcomes and radiological results of at least 12 months to support the feasibility of this technique.

The MISTIC technique is an evolution of previous open techniques described by other authors and has several advantages. First, this minimally invasive surgical technique helps to avoid wide exposure-related complications, such as back muscle injury, bleeding, infection, and postoperative pain.17 Furthermore, the shorter operative time places less physiological stress on patients who are elderly or frail. This approach is also familiar to most spine surgeons, and the implants used are widely available.

Second, the intrabody cage offers the restoration of vertebral body height with anterior column support. There was only a mild reduction in the SA, AH, and BH at the final follow-up, and there were no cases of cage migration. The PEEK cage was filled with DBM and allograft, which promotes fracture union through its osteoconduction and osteoinduction properties. Additionally, this technique allows for the insertion of a pedicle screw at the fractured vertebra (intermediate screw) contralaterally, and this has been shown to improve biomechanical stability and reduce implant failures.18

There are several limitations of this study and technique. First, no fusion was performed at the instrumented levels. Although fracture union was achieved in all patients and the implants remained stable at the 12-month follow-up, there is a possibility that the pedicle screws may cut out or loosen over time due to motion at the unfused levels. However, this surgery aims to promote union of the fracture by using the instrumentation as an internal brace, and the implants can be removed once union is achieved. This allows for motion preservation but at the cost of requiring another surgery to remove the implants.

Second, there was no control group in this study and no comparisons were made between the MISTIC technique and other techniques. Thus, we are unable to prove that this technique provides significant advantages over existing techniques. However, it is well established that minimally invasive techniques lead to less blood loss and fewer complications, and this study’s technique provides some of the benefits associated with minimally invasive surgery.19

In addition, this technique alone may not be suitable for patients with neurological deficits, although the intrabody cage does allow for indirect decompression of the spinal canal through ligamentotaxis of the posterior longitudinal ligament (PLL) and correction of the focal kyphosis. By increasing the vertebral height, the PLL becomes taut, which reduces the retropulsed fragments caused by the fracture while correction of the kyphosis reduces the tenting and compression of the spinal cord. This principle is illustrated by Li et al, who showed that the reduction of the fracture alone is sufficient to decompress the spinal canal and therefore lead to neurological improvements.11 However, in our study, manual reduction of the fracture was not performed because we excluded patients with neurological deficits. For such patients, it may be possible to combine the MISTIC technique with manual reduction to eliminate the need for direct decompression.

Finally, this is a small study consisting of 20 patients with a short follow-up of less than 2 years. Although none of our patients had complications from this procedure, possible complications such as implant breakage, cage migration, nonunion, hematoma, and infection may occur. Larger studies are necessary to detect rare or uncommon complications such as adjacent segment fractures, major vessel injuries, major organ injuries, and others. Longer follow-up is necessary to detect loosening of the implants as no fusion was performed, and this may eventually lead to instrumentation failure or implant cut-out. Because this is a novel technique, further studies are also required to define the ideal indications and contraindications for this technique. Patients with single-level Kummell disease and without neurological deficits appear to be suitable candidates for the MISTIC technique.