Growing rods in meningomyelocele lead to increased risk for complications in comparison with fusion; a retrospective study of 30 patients treated for at the University Hospital of Uppsala

Coronal and sagittal imbalance of the spine is a prevalent sequela in patients with meningomyelocele (MMC) and is either developmental in nature or as a result of a coexisting malformation (e.g., hemivertebrae) [1]. Spine surgery for meningomyelocele (MMC) is usually performed electively with the exceptions of postnatal MMC closure and perhaps decompressive upper cervical laminectomy in case of Chiari II malformations [2, 3]. Patients with scoliosis, which is defined as having a Cobb angle of more than 20° [4], may need spinal fusion surgery if the curve is greater than 40–50° at skeletal maturity. Otherwise, skeletally immature patients with curve rigidity [1, 5], tethered spinal cord, suboptimal sitting balance, patients requiring the use of upper limbs for balance, or patients with deteriorated pulmonary function and marked pelvic obliquity are all candidates for operation [6]. Another indication for operative treatment is rigid lumbar and thoracolumbar kyphosis causing recalcitrant skin ulcerations at the gibbus site [7].

Both posterior lateral fixation (PLF) and anterior spinal fixation are common surgical practices [8, 9]. Although pelvic obliquity can be addressed satisfactorily with sacropelvic sparring PLF and tautochronous anterior fixation [10], inclusion of the sacrum and pelvis in the fusion confers superior correction results; this can be done with S1 screws, Galveston technique, iliac screws, sacral alar fixation (S2) screws [11]. In order to strengthen the construct, a horizontal rod can bridge both sides of the pelvis with the sacrum in a “segmental T-assembly” [12].

Because patients with MMC are typically young in age, growing systems (fusionless surgery) offer advantages in terms of preservation of spinal growth. The main drawback of growing systems such as growing rods and vertical expandable prosthetic titanium ribs (VEPTR) is that they require additional surgeries for lengthening, exposing the patient to surgical and anesthesia risks [13]. A retrospective study by Bess et al. from 2010 [14] showed that 18% of the patients that received double growing rods experienced wound complications, while the risk for complications increased with each additional surgery by 24%. Implant problems such as loosening/breakage or implant prominence manifested in 34% of the patients. The growth guidance technique (Shilla^®) [15] alleviates the need of repetitive lengthening surgeries, and even though the infection rates are different between different growth systems, the overall complication rate is similar [16]. Other disadvantages of the fusionless surgery is the stiffening of the spine (law of diminishing returns), where the Cobb angle stops improving after approximately three years of treatment [17] and the crankshaft phenomenon which is a progressive deformity, despite fusion due to remaining growth potential of the spine [18]. On the other hand, definitive fusion surgery seems to mitigate some of these risks. Standalone posterior fusions in MMC have a reported infection rate 7% [19, 20], rod breakage 20% [20], while putting screws at the apex of the curves hinders the development of the crankshaft phenomenon [12]. In a single-surgeon retrospective study of 12 non-ambulatory MMC cases of anterolateral fusion with a 6-mm titanium rod [21], there were no delayed complications in the form of pseudarthrosis, rod breakage and deep wound infections, achieving satisfactory curve correction and improved quality of life.

In this retrospective analysis, we are presenting a review of the treatment of MMC cases in our institution, from 2008 to 2020. Particular focus was given in complications, reoperations rate and correction in relation to fusion or fusionless techniques and although this is a descriptive study, it concerns a rare patient group.

The majority of the cases presented in this study consists of patients treated with guiding rods (McCarthy Dunn technique and Shilla^®). Kyphectomy was performed when needed, with fusion and PLF (Werner Fackler technique). In the fusion cases, the pelvis was routinely included for a better correction of pelvic obliquity and due to the lack of any muscle tone caudal to the lesion.

Thirty patients with MMC that underwent spine surgery at the University hospital of Uppsala from 2008 to 2020 were included in this study. The study was approved by the regional committee for research and ethics (DNR 2019–02345). The patients were sub-grouped in those that were operated on with growing rods (n = 18) versus definitive fixation at index surgery (n = 12), and in those that underwent osteotomy (n = 9) versus no osteotomy (n = 21). Osteotomy was either pedicle subtraction osteotomy (PSO) or vertebral column resection (VCR). Differences between the means were compared with the Mann–Whitney test and paired student t-test. R studio [22] was used for graph design and statistics. The results are expressed as mean (± SD) unless stated otherwise.

The purpose of spine surgery in MMC is to address the patients’ postural problems, primarily while sitting in the wheelchair. High Cobb values are an indication for surgery as well, as high-grade scoliosis is not compatible with life [10].

A generally acceptable practice for younger children is the use of growing systems instead of definitive fixation, in order to avoid stunting trunk growth [23]. In our series, 33% (10/30 patients) developed a postoperative infection, 10% (3/10) was superficial wound infection that went on remission with oral antibiotics, while 23% was deep wound infection that necessitated revision surgeries. It has been advocated that growing systems do not significantly increase complication rates in comparison with fusions [19], as long posterior instrumentations are also thought to be coupled with increased risk for postoperative infections [21, 24]. In the present retrospective study, growing rods increased the number of major surgeries by 25% in comparison to definitive fusion, a difference that was statistically significant. A complication that led to early surgery also led to a 100% increase in the number of major operations per patient. A 2021 study by Johnston et al. [25]of patients with early-onset scoliosis raised questions about the validity of relying solely on the thoracic spine height threshold (18 cm) as an effective measure for treatment outcomes. It was shown that residual curves of ≥ 50 degrees, and not the age at index surgery (< 5 or ≥ 5 years) nor the thoracic height were correlated with worse pulmonary function tests. Thus, a case can be made that the function in children with MMC may not be affected, in spite of limited vital capacity, and for that reason definite fusion might be an option even in younger age.

Out of the 12 MMC patients that underwent definitive posterior fusion, 7 (58%) were fused to the sacrum in order to better address the correction of their deformity, which also been shown to improve the patients’ sitting ability [24]. It has been suggested however that if acceptable deformity correction is achievable, ending the construct at L4 allows for better mobility of the patients in their wheelchairs [21]. In Araujo’s [26] retrospective study from 2021 of MMC patients with a standalone posterior fusion, they achieved a mean Cobb angle correction of 47 degrees in 34 patients (mean 102 degrees preoperatively and 55 degrees postoperatively). In our current series, we achieved an average correction of 47 degrees, from 69 degrees preoperative to 22 degrees postoperatively. In the 9 patients that kyphosis was addressed, we achieved a correction of 92% [from 66,2 (± 42,5) degrees preoperatively, to 5,6 (± 30,8) degrees]. Concordantly, in a retrospective study of 30 MMC patients from Özcan et al. [27], treated with growing rods, a 96% correction of the kyphotic deformity was reported, from a mean 115 degrees preoperative to 5,1 postoperatively.

The group that underwent osteotomy or VCR did not have a statistically significant difference from the non-osteotomy group, in regard neither to major reoperations nor in the amount of bleeding. To that might have contributed the development of our surgical technique, the use of tranexamic acid and pedicle screw navigation system that have been evolved and are now routinely used in our institution. These findings are in accordance with the literature, whereby blood loss and operative time have not been clearly coupled with higher risk for infection [26]. In accordance with these previous findings, we did not find a correlation between blood loss and infection.

Growing systems led to a significantly higher number of major reoperations compared to final fusions. Complications that led to early surgery were associated to a higher number of major reoperations. Osteotomy or VCR was not correlated with the amount of perioperative blood loss, nor the number of major reoperations. The patients’ postural problems improved after surgery and they were satisfied, despite complications such as revision surgeries. The option of choosing a system for definitive fusion should be strongly considered, especially in patients close to adolescence because the significantly lower risk of developing complications. In our patient group, the oldest patients that underwent correction with growing rods were two 10-year-old patients, while the youngest three patients that underwent correction with fusion were one 10 years old, one 11 years old and a one 12 years old. There were totally 12 patients that were fused (median of 13.5 and a 0.25, 0.75 IQR of 12.7 and 14.2 years, respectively). Thus, 10 years of age might represent a gray zone for definitive fusion, however, if the patient is in urgent need of surgery and is from 11 to 12 years old, then deformity correction with fusion could be appropriate.