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Original article

Comparison of initial efficacy between single and dual growing rods in treatment of early onset scoliosis

ZHAO, Yu; QIU, Gui-xing; WANG, Yi-peng; ZHANG, Jian-guo; SHEN, Jian-xiong; LI, Shu-gang; ZHAO, Hong; JIANG, Yu; LI, Ye

Editor(s): HAO, Xiu-yuan

Author Information
doi: 10.3760/cma.j.issn.0366-6999.2012.16.012
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Abstract

Early onset scoliosis (EOS) refers to patients developing scoliosis before the age of 5 years.1 EOS is characterized by a young onset with severe deformity and rapid exacerbation and poses significant challenges for orthopedic treatment strategies. Traditional standard brace correction results are often unsatisfactory, with possible failure, which leaves surgical intervention as the only feasible option for treatment. Most of the standard surgical treatments include internal fixation with bone graft fusion. However, despite achieving good spine stability, this procedure is unsuitable for infants and young adolescents, as the spinal fixation and fusion stunts the child's growth, as well as affects and restricts the development of organs, such as the lungs, heart, and other vital organs, within the chest cavity. Growing rods are now considered an efficient surgical consideration in the treatment of EOS.2,3 These rods control spine deformity at an early age, reduce the severity of scoliosis, and still allow sufficient spinal growth through the use of either single or dual growing rods. Currently, there are few reports comparing the efficacy and differences observed between single and dual growing rod correction treatments. Here, we retrospectively analyzed 25 growing rod EOS surgical cases, assessing initial efficacy and correction results.

METHODS

Patient information

Between November 2002 and May 2010, 25 patients with EOS were admitted in our hospital for growing rod scoliosis surgical treatment. Twenty-four were diagnosed with congenital scoliosis and one with neuromuscular scoliosis. Most of the patients were female and under the age of 10 years at the time of surgical treatment (Table 1). All the patients were positive candidates and fulfilled the following surgical indications and criteria: scoliosis Cobb's angle >40° or annual exacerbation >5°. Patients were divided into single or dual growing rod groups according to their individual conditions: six in the single growing rod group and 19 in the dual growing rods group (of which four single rod cases and two dual rod cases underwent the final spine fusion procedure). All patients who underwent growing rod treatment later returned for growing rod distraction. Distraction is often performed when patients exhibit scoliosis exacerbation of 15°-20°; thus, distraction allows for spinal lengthening. All surgeries were performed by the same surgical group.

Table 1
Table 1:
Basic clinical information

The Ethics Committee of Peking Union Medical College Hospital approved the study protocol, and informed consent was obtained from the parents of all patients.

Surgical method

All patients underwent general anesthesia with endotracheal intubation, and were placed in a prone position on a cushioned surgical table. After approximating the location of the superior and inferior vertebrae to be fixed, a posterior midline incision was made, according to standard methods, to expose the spinal process, vertebral endplate, articular process, and pedicles of each vertebra. Irrespective of whether a single or dual growing rod procedure was to be performed, pediatric articular hooks or pedicle screws were used to form a “bud” for both the upper and lower vertebral fixations. A pre-curved metal rod was subcutaneously inserted under the fascia, and connected to the articular hooks and pedicle screws of upper vertebral sections. A paired pre-curved metal rod was inserted in the same manner and linked with the lower vertebral sections. A growth valve or domino connector was used to connect the ipsilateral rods that were distracted and tightened with a screw nut. On the scoliotic side, at the level of the lower fixation, both autologous spinous process bone grafting and allogeneic bone grafting were performed. A drainage tube was inserted and the incision was sutured.

The wound drainage tube was removed 24-48 hours after surgery and patients were instructed to wear a brace for 8-10 weeks. Regular follow-up visits and examinations were performed, normally at 3-6 month intervals. At 6-12 months, patients returned for a growing rod distraction surgical procedure; in cases where a longer rod was required, rod replacement was performed.

Data collection and radiographic analysis

All patients were closely monitored and all clinical information, including patient gender, age during first surgical procedure, surgery duration, bleeding volume, and post-surgical complications were recorded. All patients received standard radiological examinations of anteroposterior X-rays, Cobb's angle measurements of scoliosis and kyphosis, pre-surgical and post-surgical angular measurements, and measurements to determine the change in the angle degree. These values were used to calculate the correction rate required, using surgical correction (%)=(correction angle/pre-surgical scoliosis (kyphosis) angle) × 100%. In addition, pre- and post-surgical C7-S1 distances were measured. All surgical procedures were performed by the same surgical team.

Statistical analysis

SPSS 13.0 software (SPSS Inc., IL, USA) was used to identify the mean and standard deviation in each of the parameters measured. A complete randomization of the group sample test analysis was used to determine the standard deviation and difference. P <0.05 was defined as statistically significant.

RESULTS

Basic clinical information

Twenty-five patients assigned into single or dual growing rod groups were assessed for 12-89 months, with an average of 31.9 months follow-up. In the single growing rod group, three cases used ISOLA series coupling connectors (ISOLA, DePuy Spine Inc., USA) and three cases used CDH parallel coupling connectors (Medtronic Inc., USA). In the dual growing rods group, nine cases used ISOLA series coupling connectors and 10 cases used parallel connectors, of whom nine used CDH and one used TSRH instrumentation (Medtronic Inc., USA, Table 1).

Surgical situation

The average time for the single growing rod surgery was (3.1±0.4) hours (2.5-3.7 hours) and the average time for dual growing rods surgery was (3.4±0.7) hours (2.5-4.8 hours), with no statistical difference observed (P=0.287, t=-1.090). Similarly, the average single rod surgical bleeding volume was (137±84) ml (70-300 ml) and the average dual growing rods surgical bleeding volume was (143±66) ml (50-300 ml), with no significant difference observed (P=0.845, t=-0.198).

Radiographic data and information

There were no statistical differences in pre-surgical coronal and sagittal Cobb's angles and post-surgical sagittal angles between the patients in the single growing rod group and the dual growing rods group (Table 2). However, a significant difference was observed in the initial coronal correction rate, with an average of (35.0±10.2)% for the single growing rod group (24%-51%), and an average of (52.0±13.3)% for the dual growing rod group (30%-75%) (P=0.007, t=-2.991). Likewise, a significant difference was observed for measurements of the C7-S1 height, with an average of (2.4±1.1) cm, (1-3 cm) for the single growing rod group and an average of (4.0±1.2) cm (2-6 cm) in the dual growing rods group (P=0.011, t=-2.772).

Table 2
Table 2:
Pre- and post-surgical measurements for both surgical groups

Figures 1 and 2 shows a representative patient who underwent either a single or dual growing rod corrective surgery, respectively.

Figure 1.
Figure 1.:
Single growing rod case of a 7-year-old female EOS patient (1A) who underwent surgery in September 2002 (1B). During a follow-up in July 2007, lower pedicle screw distraction was identified (1C), and in June of 2008, the patient underwent revision surgery (1D). Finally, the patient underwent scoliosis correction with Moss Miami internal fixation and bone graft fusion at the age of 13 years (1E).Figure 2. Dual growing rod case of a 2-year-old female patient with congenital scoliosis (2A) who underwent correction surgery in October 2001 (2B), followed by intermittent regular distraction procedures over the next 6-12 months. The last distraction procedure was performed in December 2009 (2C).

Complications

There were no initial complications after surgery observed in the single growing rod group, but one case of post-surgical infection in the dual growing rods group that recovered following wound debridement. Up until this retrospective analysis, there was one case of a broken rod and two cases of pedicle screw loosening in the single rod group. In the dual rods group, there were nine incidences of complication including one broken rod, six cases with hook or pedicle screw distraction and loosening, and two cases of wound infection.

DISCUSSION

The concept of EOS was first proposed and introduced by Dickson1 in 1985 who defined EOS as the onset of scoliosis before the age of 5 years. This age represents the peak age for development of the human pulmonary system, where lung capacity can already be 30% of the adult capacity. Thus, for children under 5 years, scoliosis and other spinal deformities may severely impact the proper development of the cardio-pulmonary system.2–6

In the past, the treatment of EOS involved hard-braces and pipes formed by plaster casts, with unsatisfactory results. Unlike the surgical treatment of adolescent and adult patients with scoliosis, surgical treatment in young EOS patients hinder and often limit spinal height and the body-limb ratio, as well as affect the development of the chest cavity and the capacity and functioning of the heart and lungs. In 1962, Harrington7 developed an adjustable and expandable retraction instrumentation which allowed simultaneous spine growth through intervention. However, he proposed that, for scoliotic children less than 10 years of age, the apparatus alone should suffice, without fusion. Based on Harrington's non-fusion concept, the growing rod technique gradually developed. Over the years, various different internal fixation devices have been developed, such as articular hooks, pedicle hooks, pedicle screws, and various user-friendly growing rods, connectors, and links. The division of growing rods into an upper and lower rod, using a joint connector to link the two rods is a further modification of the technique that now permits distraction to increase the spine length.

Initially, the growing rod technique began with single rod fixation. Blackemore and colleagues8 retrospectively analyzed 29 cases using an ISOLA single growing rod with and without apical fusion to treat pediatric scoliosis. Of these 29 cases, 18 cases did not undergo apical fusion, with an average pre-surgical Cobb's angle of 72° and a post-surgical angle of 49°. The incidence of post-surgical complication was 24%, including broken rods, hook dislocation, and skin infections. Later, a study by Mineiro and Weinstein9 concluded that the single growing rod technique in spine fixation is a weak consideration for scoliosis treatment, with a high rate of rod breakage and poor correction as well as rod preservation rate.

In 2000, Akbarnia et al10 proposed a dual growing rod technique, using a Tandem connector to link two correction rods in the internal fixation system. In following studies,11 they retrospectively analyzed 23 cases using the dual growing rod system. The results showed that the pre-surgical Cobb's angle decreased from an average of 82° to 38° after surgery. In addition, the T1-S1 height increased from the pre-surgical average of 23.01 cm to a post-surgical average of 28.00 cm. However, the incidence of post-surgical complications was still high at 48%, with two cases of infection, two cases of broken rods, two cases of dislocated hooks, and five cases of pedicle screw loosening.

Currently, there are limited studies comparing the single and dual growing rod techniques. However, the existing literature12 indicates that the dual growing rod technique allows for better clinical results and a stronger correction, with structure stability and cosmesis as compared to the single rod technique. In addition, there appears to be a lower incidence of hook dislocations, broken rods, and infection.

In our study, we observed no significant differences in intra-operative bleeding volume between the single and dual growing rod groups, but a longer, though not significant, operative time for the dual growing rod surgical procedure. However, bleeding and surgical time may be related to the surgeon's skill and gradual improvement in the application of the technique. We identified significant improvement in the coronal correction in the dual growing rod group that is comparable to the findings in the literature. We also observed no significant difference in sagittal correction between the two groups. By analytical reasoning, we could presume a two-dimensional correction structure, as proposed by Harrington, with correction achieved by an axial distraction that does not affect the sagittal correction, and instead distends and increases the kyphosis apex of the inter-vertebral disc space. Technical reasoning, on the other hand, suggests that if dual growing rods allow for stronger distraction, then kyphosis correction should be achieved; however, instead, distraction increases the space between two vertebrae, resulting in a kyphotic increase. In accordance with other literature, our study indicated a significant increase in the C7-S1 height in the dual growing rod group, with this increase directly related to growing rod distraction.

Compared to other studies,11,12 the complication rate in our study was also above 40%. Due to a small sample size, and most cases resulting with spine fusion, we were unable to determine the significance of the complication rate and the difference between the surgical groups. The main complications included screw and hook dislocation and loosening, broken rods, infection with hook dislocation, and pedicle screw loosening and broken rods associated with increased point stress of internal fixation instrumentation. Klemme et al13 reported 33 internal fixation-related complications from a cohort of 25 patients (incidence rate of 37%), with 21 cases of hook dislocation and 11 cases of broken rods.

Mineiro and Weinstein9 indicated that rod breakage is related to rod curvature, bending, the number of times extended, scoliosis flexibility, and patient age, rather than the design of the rod. Post-surgical infection is related to subcutaneous rod insertion and increased dermal tension, as well as direct stress tension caused by the rod. Thus, various surgeons now suggest rod placement in the muscular layer. However, due to the regularity of repeated surgical procedures, wound incision infection rates are high, and surgeons need to take prophylactic and precautionary measures. In addition, prevention of the insertion of connectors in the kyphotic range to prevent direct pressure and physical stress to the spine and avoidance of creating incisions directly above the connector surface should be carefully considered.

There are two major limitations to our study: (1) our study was not a randomized controlled study, with a small sample size and (2) we reviewed patients after a short follow-up period, and did not compare the final surgical results. With the improvement and development of the growing rod technique in the treatment of scoliosis correction, further detailed analyses and observations are required.

EOS treatment is relatively challenging, and the ideal EOS surgical procedure will neither hinder nor affect the natural growth of the spine while simultaneously preventing further development of scoliosis. This non-fusion correction technique is now the most widely used means of scoliosis correction surgery and our preliminary short-term follow-up results suggest that the dual growing rod technique is superior over the single rod technique; however, further studies with a large sample size and long-term follow-up are needed to reveal the effect of growing rod surgery on EOS.

REFERENCES

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3. Li QY, Zhang JG, Qiu GX, Wang YP, Shen JX, Zhao Y, et al. Primary effect of dual growing rod technique for the treatment of severe scoliosis in young children. Chin Med J 2010; 123: 151-155.
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7. Harrington PR. Treatment of scoliosis. Correction and internal fixation by spine instrumentation. J Bone Joint Surg Am 1962; 44-A: 591-610.
8. Blakemore LC, Scoles PV, Poe-Kochert C, Thompson GH. Submuscular Isola rod with or without limited apical fusion in the management of severe spinal deformities in young children: preliminary report. Spine (Phila Pa 1976) 2001; 26: 2044-2048.
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11. Akbarnia BA, Marks DS, Boachie-Adjei O, Thompson AG, Asher MA. Dual growing rod technique for the treatment of progressive early-onset scoliosis: a multicenter study. Spine (Phila Pa 1976) 2005; 30: S46-S57.
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13. Klemme WR, Denis F, Winter RB, Lonstein JW, Koop SE. Spinal instrumentation without fusion for progressive scoliosis in young children. J Pediatr Orthop 1997; 17: 734-742.
Keywords:

single growing rod; dual growing rod; early onset scoliosis

© 2012 Chinese Medical Association