Modified SHILLA Technique for Scoliosis Remodulates the Apex Vertebra

Sidebar Q&A: Avoiding complications associated with MAGEC rods for scoliosis.

Peer Reviewed

A modified SHILLA procedure demonstrates that active remodulation of the apex vertebra is possible in patients with scoliosis and may reduce the potential for loss of correction over time due to the crankshaft effect or distal migration (or adding-on) with the standard SHILLA technique, according to findings published in Global Spine Journal.

While growth guidance technique using SHILLA is a commonly used posterior-based growth friendly technique for curve correction and halting the progression of deformity in scoliosis and kyphoscoliosis, this procedure has limitations.

postoperative x-ray scoliosis; instrumentation and fusion deformity treatmentPostoperative x-ray demonstrates surgical treatment of scoliosis with instrumentation and fusion. Photo Credit and Source: Douglas Olivares, iStock.com.“The primary limitation of the traditional SHILLA technique is the loss of correction due to crankshafting, adding on, or distal migration,” explained lead author Aakash Agarwal, PhD, who is Director of Research at Spinal Balance Inc. and an Adjunct Professor of Bioengineering at University of Toledo. “Active apex correction (APC) aims to reduce this risk by adding an active component to the guided growth technique (ie, compression on the convex side). The secondary limitation is the need for osteotomies at the apex, which APC avoids as it seeks to let the concave sides of wedged vertebrae grow and not fuse.”

Active Apex Correction Explained

“This modified SHILLA procedure (APC), combines the principles of guided growth (traditional SHILLA) and remodulation (tethering, staples, etc),” Dr. Agarwal told SpineUniverse. “The technique simply consists of replacing the apical fusion (of traditional SHILLA) with unilateral compression (via pedicle screws or any other means) on the convex side. This compression is meant to halt the growth on convex side and thus allow the ratio of concave:convex height to increase overtime, which reduces wedging.”

The technique was conceptualized and developed by Alaaeldin Azmi Ahmad, MD.

The study involved 20 patients with either scoliosis or kyphoscoliosis, who underwent the modified SHILLA approach with APC applied. The most wedged vertebra was selected, along with a control vertebra that was similar in terms of dimensions. Pedicle screws were inserted into the convex sides of the vertebrae above and below the targeted wedged vertebra. Computed tomography was used to measure the convex and concave heights of the wedged and control vertebrae at the time of surgery and at minimum 8-month follow-up (with an average of 32 months follow-up).

Key Study Findings

A significant increase in the proportion of concave:convex ratio of 17% was found at follow-up in the wedged vertebra under apex compression (P=0.00014). In contrast, no lateral deviance in height was found in the control vertebra. The average increase in the concave end of wedged vertebra was 36%, of the convex side was 16%.

“The result of this study provides clinical evidence of reverse vertebral modulation at the apex of the curve in patients with scoliosis and kyphoscoliosis, when modifying the traditional SHILLA technique with APC,” Dr. Agarwal explained.

“During the period of follow-up period, no patient presented with loss of correction, although we must continue to follow them up,” Dr. Agarwal said. “The immediate benefits of the procedure were avoidance of risky osteotomies required to insert screws at the concave end of the apex, and more economical surgery (only two screws were used at the apex).”

Another study by Dr. Agarwal and colleagues demonstrated clinical equivalency between the APC and traditional growth rod systems in regard to correction.1,2 A higher complication rate with growth rods than APC.1,2

“However, traditional growth rods presented an obvious disadvantage because they require multiple surgeries to regularly distract the spine,” Dr. Agarwal said.

Future Directions in Scoliosis Surgery

“I believe we will be moving towards early (but minimally invasive) intervention of progressive scoliosis using remodulation,” Dr. Agarwal concluded. “Alongside surgical intervention, ability to nonsurgically intervene via bracing and specific exercises should remain a priority. These all fall under reverse modulation, and sooner we address a progressive curve, better the results would be.”

Source
Agarwal A, Aker L, Ahmad AA. Active Apex correction with guided growth technique for controlling spinal deformity in growing children: a modified SHILLA technique. Global Spine J. 2019; DOI: 10.1177/2192568219859836.

References
1. Agarwal A, Ahmad AA. Distraction-based growth rods fixation vs active apex correction: what do the correction parameters say? Spine J. 2019;19(9):S153.
2. Agarwal A, Aker L, Ahmad AA. Active apex correction (Modified SHILLA Technique) versus distraction-based growth rod fixation: What do the correction parameters say? Spine Surg Related Research. 2019; doi.org/10.22603/ssrr.2019-0045.

Sidebar Q&A: Avoiding Complications Associated With MAGEC Rods for Scoliosis

Dr. Agarwal and colleagues recently compared adverse events from MAGEC rods (MAGnetic Expansion Control System) for distraction-based correction of scoliosis with those of standard instrumentation for spinal fusion using US Food and Drug Administration Manufacturer and User Facility Device Experience (MAUDE) databases (Table). Below are key insights from the study shared by Dr. Agarwal.

How do the device-related adverse events of MAGEC rod usage compare with those of standard instrumentation used in spine surgery?

Dr. Agarwal: There is a growing number of distraction mechanism failures associated with MAGEC rods. The relatively high frequency of this failure event when compared to the top 5 failure modes associated with standard instrumentation usage in spinal fusion is a matter of great concern (Table).

Device-related adverse events with MAGEC rods vs standard instrumentation for spinal fusionSource: Aakash Agarwal, PhD, and SpineUniverse.com.

Your study found that distraction mechanism failure was the most common complication associated with MAGEC rod usage. Can you comment on ways to avoid these failures?

Dr. Agarwal: Better technical and clinical controls need to be set in place to avoid such adverse events, which lead to unplanned open surgeries. A higher distraction magnitude results in the generation of higher distraction forces, and this in combination with off-axis loading (exemplified by “growth marks”) result in wear and breakage of MAGEC rod components. Therefore, one method to reduce the propensity of such failures would be to apply minimum distraction at higher frequency, for example, 1.5–2.0 mm every month, instead of 4.5–6.0 mm every 3 months.1-5 This would also reduce tissue trauma and its effects, such as autofusion.6 Other technical methods to reduce attrition could include ceramic coating at wear generating surfaces.

Is there anything else you would like to tell our readers about this research?

Dr. Agarwal: The main benefit of the MAGEC rod is that it allows for the noninvasive distraction of the growth rods. This benefit is realized by a drastic reduction in the number of consecutive surgeries. It can also reduce growth rod fracture as I have described previously—ie, via shorter distraction magnitudes at shorter intervals.1-5 Along with reduction in growth rod fracture, the MAGEC rod has been shown to reduce autofusion, when following this principle of “shorter distraction magnitudes at short intervals.”6 However, to realize these benefits the distraction mechanism problems have to be fixed, and the surgical technique should adopt the practice of shorter distraction magnitude at shorter intervals.1-5

Source
Agarwal A, Kelkar A, Agarwal A, Jayaswal D, Jayaswa A, Shendge V. Device-related complications associated with Magec Rod Usage for distraction-based correction of scoliosis. Spine Surg Rel Res. 2019; https://doi.org/10.22603/ssrr.2019-0041.

References
1. Agarwal A, Agarwal AK, Jayaswal A, Goel V. Smaller interval distractions may reduce chances of growth rod breakage without impeding desired spinal growth: a finite element study. Spine Deformity. 2014;2(6):430-436.
2. Agarwal A, Jayaswal AK, Goel VK, Agarwal AK. Letter to the Editor concerning "Rod fracture and lengthening intervals in traditional growing rods: is there a relationship?" by P. Hosseini et al. Eur Spine J (2016). doi:10.1007/s00586-016-4786-8. Eur Spine J. 2017;26(6):1696-1697.
3. Agarwal A, Jayaswal A, Goel VK, Agarwal AK. Patient-specific distraction regimen to avoid growth-rod failure. Spine. 2018;43(4):E221-6.
4. Agarwal A, Agarwal AK, Jayaswal A, Goel VK. Outcomes of optimal distraction forces and frequencies in growth rod surgery for different types of scoliotic curves: an in silico and in vitro study. Spine Deform. 2017;5(1):18-26.
5. Agarwal A, Zakeri A, Agarwal AK, Jayaswal A, Goel VK. Distraction magnitude and frequency affects the outcome in juvenile idiopathic patients with growth rods: finite element study using a representative scoliotic spine model. Spine J. 2015;15(8):1848-1855.
6. Cheung JP, Bow C, Samartzis D, Kwan K, Cheung KM. Frequent small distractions with a magnetically controlled growing rod for early-onset scoliosis and avoidance of the law of diminishing returns. J Orthop Surg. 2016;24(3):332-337.

Disclosures
Dr. Agarwal is a Consultant/Independent Contractor for Spinal Balance Inc.; on the Editorial Board for Clinical Spine Surgery (Lippincott Williams & Wilkins, LLW), Spine (LLW); an advisory board member for the Center for Disruptive Musculoskeletal Innovation (CDMI); and, receives royalties from joimax, Paradigm Spine.

Updated on: 01/27/20
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Aakash Agarwal, PhD
Director of Research
Spinal Balance Inc.
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