Abstract
Introduction
The smiley face rod method is an effective treatment for symptomatic terminal-stage spondylolysis. However, the risk factors for treatment failure are unknown. We investigated the association of pars defect type with the treatment outcomes of this method.
Methods
We retrospectively examined data from 34 patients (18.0±6.7 years) with terminal-stage spondylolysis who underwent surgery using the smiley face rod method. The mean follow-up period was 44.9±21.4 months. The patients were divided into 2 groups: pars defect without bone atrophy or sclerosis (group A; 18 patients), and with bone atrophy and sclerosis (group B; 16 patients). We evaluated and compared the visual analog scale (VAS) score for back pain, bone union rate, and time to return to preinjury athletics level between the groups. Fisher exact and paired t tests were used to compare the variables between groups. The VAS score between the groups was compared using a 2-factor repeated-measures analysis of variance.
Results
Within groups, the VAS score was significantly different over time (p<0.001). The VAS scores between groups were not significantly different. Patients in group A had a significantly higher bone union rate per pars at 6 months (group A, 65.7%; and group B, 37.5%, p=0.028) and 24 months after surgery (group A, 97.1%; and group B, 75.0%, p=0.011). All patients returned to their respective sports, and no significant differences were observed in the time to return to preinjury athletics level between the groups (p=0.055).
Conclusions
The type of pars defect are associated with bone union after the smiley face rod method, but have little effect on postoperative symptoms.
Keywords: Lumbar spondylolysis, smiley face rod method, direct repair of pars interarticularis, surgical outcome, pars defect type
Introduction
Lumbar spondylolysis is a bone defect of the vertebral pars interarticularis and constitutes a comparatively common condition that causes back pain in young patients. In patients with spondylolysis who do not have pseudoarthrosis, conservative treatment, including physical therapy, activity modification, and bracing, are considered the primary forms of treatment and result in a successful bone union in many of these patients1,2). Surgical management may be required in those with pseudoarthrosis spondylolysis, which is not expected to progress to bone union, and when symptomatic spondylolysis fails to respond to conservative treatment3) and affects the quality of life of young patients, particularly athletes4).
The smiley face rod method of direct repair and intrasegmental fusion was first reported in 1999 by Gillet and Petit, who called it the “V-rod method”5). This method became known as the so called “smiley face rod method”6). Ulibarri et al. reported that biomechanical evaluation of this method showed excellent stability of a spondylolysis defect compared with other types of direct repair surgery7). The smiley face rod method can produce promising results, has the possibility of repairing grade-1 spondylolisthesis, and the implant can be removed after the bone union8). However, bone union cannot be achieved in some patients. Generally, the size of the bone defect is an independent risk factor for nonunion9,10). Atrophic nonunion refers to an inadequate or poorly vascularized mesenchymal tissue with very limited potential for successful healing of the bone union11). In patients with spondylolysis, sclerotic or atrophic changes in the pars defect may associated with nonunion after direct repair surgery12). However, it remains unclear whether surgical outcomes of smiley face rod methods differ according to the type of pars defect.
Herein, we hypothesized that the type of pars defect in spondylolysis is associated with the outcomes of surgical treatment with the smiley face rod method. In the present study, we examined the association of the type of pars defects in patients with pseudoarthrosis spondylolysis with surgical outcomes, such as bone union and symptoms.
Materials and Methods
The present study was conducted with the approval of our local institutional research ethics committee, which approved the study protocol. All patients were informed about the study in writing and provided their documented informed consent in compliance with the Declaration of Helsinki and its contemporary amendments.
In a comparative retrospective study, we included data from 38 consecutive patients with pseudoarthrosis spondylolysis who underwent direct repairs of the pars interarticularis using the smiley face rod method between October 2014 and December 2020. The inclusion criteria were: (1) chronic back pain with or without neurological symptoms of lower extremities. (2) Lumbar spine spondylolysis was diagnosed using X-ray imaging, computed tomography (CT), and magnetic resonance imaging (MRI) that corresponded to clinical manifestations and a pars block was performed to determine whether the pain was caused by lumbar spondylolysis, using lidocaine as a local anesthetic13,14). We conducted a single block test for diagnostic purposes before surgery. However, for treatment, multiple blocks were occasionally performed. Diagnostic pars block was considered effective when patients had symptomatic pain relief for at least 60 min after the block15,16). (3) For pseudoarthrosis, an MRI showing the absence of bone marrow edema with CT indicating bone defect was considered. (4) Refractory to conservative treatments, including medication, brace, and physical therapy. (5) A follow-up of at least 12 months. The exclusion criteria constituted: (1) lumbar spine fractures, infection, or tumors; (2) patients who had undergone other spinal surgery, including for cases of recurrence; (3) imaging findings showed severe segmental degeneration disease or lumbar instability, which are consistent with the symptoms and signs. Finally, three patients were lost to follow-up, one was a recurrent case, and ultimately data from 34 patients were investigated. The mean age of the patients was 18.0±6.7 years, 23 were male, and 11 were female. The mean follow-up period after surgery was 44.9±21.4 months. The following were investigated in each patient: level of injury, laterality, sports category, duration of conservative treatment, spina bifida occulta, Meyerding grade of spondylolisthesis17), disc degeneration according to the Pfirrmann classification18), which evaluates disc degeneration in the involved segments, intraoperative blood loss, operative time, length of hospital stays, and complications. The surgical procedure was the smiley face rod method, as previously reported8), which was performed using pedicle screw insertion with the Weinstein method, and a bone graft was harvested from the iliac crest (Fig. 1).
Figure 1.
The smiley face rod method uses a bent rod and pedicle screws. (A) Frontal plane, (B) lateral plane.
We categorized the pars defect based on the axial CT12) as follows: type I (line type), in which the gap is almost hairline; type II (intermediate type) shows a clear bone gap with no signs of bone atrophy or sclerosis at the edge of the bony defect; type III (sclerosis type) shows an enlarged bony gap with manifestations of bone atrophy and sclerosis. We defined atrophy as a defect with a depression in the defect line that causes the defect to expand and the edge to become asymmetrical. In the present study, patients with types I and II were included in group A; and type III was included in group B (Fig. 2). We evaluated the maximum width of the gap of the bone defect in each group. Intra- and interobserver errors in the type of spondylolysis were calculated for all 34 vertebrae. The intraobserver variability was determined by comparing results with those after a 3-month interval. Two experienced orthopedic surgeons blinded to the surgical conditions analyzed the results.
Figure 2.
CT classification of lumbar spondylolysis. (A) Type I (line type), (B) type II (intermediate type), and (C) type III (sclerosis type). Types I and II were included in group A; and type III was included in group B.
CT, computed tomography
Primary outcome
The primary outcome was the visual analog scale (VAS) score for back pain, which was evaluated before surgery, and 3, 6, 12, and 24 months after surgery. The evaluation included determining whether there was a significant difference in VAS between the two groups, and whether there was any postoperative improvement. In each group, we examined whether there was a significant improvement at 3, 6, 12, and 24 months after surgery.
Secondary outcome
The secondary outcomes were time to return to preinjury athletics level and the rate of bone union. We allowed patients to resume sports as long as the pain had at least improved and the trunk and back muscles were sufficiently actively exercised and stable. The rate of bone union was examined per patient and pars. According to the follow-up plan, postoperative CT was obtained 6, 12, 18, and 24 months after surgery. Two criteria were examined to assess bone union in the pars interarticularis. First, whether there was a disappearance of the hypodense area and trabecular bone formation. Second, whether there was bone continuity in both the pars interarticularis and the bone graft, as evidenced by reconstructed sagittal and axial CT images. Nonunion was defined when the bone defect or a clear zone existed. A representative case of bone union and nonunion postoperatively is shown in Fig. 3, 4. The bone union rate was calculated at the various follow-up times, and we evaluated the difference in back pain postoperatively and compared the pain score between the group with bone union and the group with nonunion.
Figure 3.
Representative case of bone union postoperatively.
A case of union in a 15-year-old boy is shown. (A, B) Preoperative CT images showing a bilateral pars defect at L4, classified as type II, group A. (C, D) Follow-up CT images showing bony continuity at the pars defect in the axial and sagittal plane at 12 months postoperatively.
CT, computed tomography
Figure 4.
Representative case of bone nonunion postoperatively.
A case of nonunion in a 15-year-old boy is shown. (A, B) Preoperative CT images showing a bilateral pars defect at L5, classified as type III, group B. (C, D) Bone defect at the pars in axial and sagittal CT images at 24 months postoperatively.
CT, computed tomography
Statistical analysis
Descriptive statistics for qualitative data are expressed as numbers and percentages, whereas quantitative data are expressed as mean and standard deviation. Fisher's exact test was used for categorical variables, and a paired t test for continuous variables when comparing the groups. VAS score for back pain between the groups was analyzed using a two-factor analysis of variance (ANOVA).
Differences were considered significant when p<0.05. All statistical analyses were performed with Prism9 statistical package (GraphPad Software, USA) and EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria, http://www.R-project.org/, version 4.1.1). More precisely, we used a modified version of R commander designed to add statistical functions frequently used in biostatistics19).
Results
Patient demographic data are shown in Table 1. Based on CT classification, there were 18 patients in group A and 16 in group B. The maximum width of the gap of the bone defect in group A was 2.5±1.4 mm, and in group B was 4.7±1.6 mm. The reliability of measurements for intraobserver and interobserver in the type of spondylolysis were determined as κ=0.900 and κ=0.755, respectively. There were significant differences in operative time (164.2±25.9 min vs. 187.4±29.4 min, p=0.020) (Table 2).
Table 1.
Patient Demographic Data.
| Characteristics | Value (range) |
|---|---|
| Age (years) | 18.0±6.7 (12-43) |
| Sex (male:female) | 23:11 |
| Level | |
| L4 | 1 |
| L5 | 33 |
| Laterality | |
| Unilateral | 1 |
| Bilateral | 33 |
| Sport category | |
| Soccer | 7 |
| Baseball | 7 |
| Basketball | 4 |
| Judo | 3 |
| Volleyball | 3 |
| Rugby | 2 |
| Others | 6 |
| None | 2 |
| Duration of conservative treatment (months) | 11.7±9.6 (3-40) |
| Follow-up (months) | 44.9±21.4 (12-89) |
Value is equivalent to sample size except for where otherwise noted.
Table 2.
Comparison between Groups A and B.
| Group A (n=18) | Group B (n=16) | p | |
|---|---|---|---|
| Age (years) | 17.1±6.7 | 19.1±7.0 | 0.398 |
| Sex, male (%) | 13 (72.2) | 10 (62.5) | 0.717 |
| Spina bifida occulta (%) | 9 (50.0) | 5 (31.2) | 0.315 |
| Pfirrmann classification (%) | |||
| 1 | 3 (16.7) | 7 (43.8) | 0.063 |
| 2 | 7 (38.9) | 1 (6.2) | |
| 3 | 7 (38.9) | 5 (31.2) | |
| 4 | 1 (5.6) | 3 (18.8) | |
| 5 | 0 | 0 | |
| Meyerding classification (%) | |||
| 0 | 15 (83.3) | 9 (56.2) | 0.134 |
| 1 | 3 (16.7) | 7 (43.8) | |
| Operative time (min) | 164.2±25.9 | 187.4±29.4 | 0.020* |
| Blood loss (mL) | 56.6±55.1 | 46.6±34.7 | 0.538 |
| Length of hospital stay (days) | 8.7±1.6 | 8.9±1.8 | 0.647 |
*Statistically significant difference.
Group A, types I and II; Group B, type III.
Comparison of VAS score for back pain
The VAS score for back pain was only evaluated in the subsets of patients we could follow up postoperatively. So, at 3 months, 33 patients; 6 months, 32 patients; 12 months, 28 patients; and 24 months, 22 patients. There were significant differences in VAS scores over time (p<0.001) within the groups. No significant differences between groups (p=0.19) were found for VAS score (Fig. 5). In group A, compared with preoperative levels (43.3±26.6), the mean VAS for back pain was improved at 3 months (15.8±20.5, p=0.0091), 6 months (17.4±29.4, p=0.019), 12 months (3.3±19.7, p=0.0013), and 24 months (10.0±16.1, p=0.0089). In group B, compared with preoperative levels (52.8±29.8), the mean VAS for back pain was improved at 3 months (19.7±22.0, p<0.001), 6 months (34.1±31.3, p=0.095), 12 months (20.3±23.7, p<0.001), and 24 months (15.0±16.3, p<0.001).
Figure 5.
VAS score for back pain.
Repeated-measures analysis of variance was used to compare the VAS score for back pain preoperatively, and 3, 6, 12, and 24 months after surgery. The VAS score changes were significant over time (p<0.05). Data are presented as means ± SD.
VAS, visual analog scale; Group A, types I and II; Group B, type III; pre-op, preoperatively; SD, standard deviation
Time to return to preinjury level athletics
All 32 patients, except for two who were not engaged in athletics before surgery, were able to resume preinjury athletics level after surgery. In groups A and B, the average times required to resume preinjury athletics level were 5.7±1.1 and 6.9±2.3 months, respectively. We found no significant difference between groups (p=0.055) for time to resume preinjury athletics level.
Bone union
The overall bone union rate was 79.4% (27 patients) at 24 months after surgery. The bone union rate per patient in groups A and B is shown in Table 3. The union rates per patient were significantly different between the groups at 24 months after surgery (94.4% and 62.5%, p=0.035).
Table 3.
Spondylolysis Union Rate (per Patient) According to CT Classification.
| Time (postop) | Group A (n=18) n (%) | Group B (n=16) n (%) | p |
|---|---|---|---|
| 6 months | 10 (55.6) | 4 (25.0) | 0.092 |
| 12 months | 14 (77.8) | 9 (56.2) | 0.274 |
| 18 months | 15 (83.3) | 10 (62.5) | 0.250 |
| 24 months | 17 (94.4) | 10 (62.5) | 0.035* |
*Statistically significant difference.
CT, computed tomography; Postop, postoperatively; Group A, types I and II; Group B, type III.
The bone union rate per pars is shown in Table 4. The union rates per pars were significantly different between groups at 6 months (65.7% and 37.5%, p=0.028) and 24 months after surgery (97.1% and 75.0%, p=0.011).
Table 4.
Spondylolysis Union Rate (per Pars) According to CT Classification.
| Time (postop) | Group A (n=35) n (%) | Group B (n=32) n (%) | p |
|---|---|---|---|
| 6 months | 23 (65.7) | 12 (37.5) | 0.028* |
| 12 months | 29 (82.9) | 22 (68.8) | 0.252 |
| 18 months | 31 (88.6) | 23 (71.9) | 0.123 |
| 24 months | 34 (97.1) | 24 (75.0) | 0.011* |
*Statistically significant difference.
CT, computed tomography; Postop, postoperatively; Group A, types I and II; Group B, type III.
We found no significant difference in the VAS scores for back pain between union and nonunion groups at 6, 12, and 24 months postoperatively (Table 5).
Table 5.
Difference between Bone Union and Nonunion Groups with Respect to Back Pain at 6, 12, and 24 Months Postoperatively.
| VAS score for back pain ± SD | |||
|---|---|---|---|
| Time (postop) | Union group | Nonunion group | p |
| 6 months | 22.4 ± 26.9 (n=14) | 27.2 ± 33.7 (n=20) | 0.670 |
| 12 months | 9.5 ± 17.8 (n=23) | 20.6 ± 25.1 (n=11) | 0.189 |
| 24 months | 11.1 ± 16.0 (n=27) | 20.0 ± 26.5 (n=7) | 0.415 |
Postop, postoperative; VAS, visual analog scale (score range 0-100); SD, standard deviation
Complications
There were no intraoperative complications, such as cerebrospinal fluid leakage or nerve injury, and no postoperative complications related to infection. There was one patient with reoperation in group B. This patient underwent the smiley face rod method for bilateral L5 lesions, which did not achieve bone union. Moreover, the patient had bilateral L3 recurrent spondylolysis, which resulted in pseudoarthrosis. Twelve months after the first surgery, the patient underwent a second surgery with the smiley face rod method in both L3 and L5 lesions, resulting in bone union 12 months later.
Discussion
We have shown that the VAS score improves in patients who underwent the smile face rod method for pseudoarthrosis spondylolysis. Furthermore, there were no significant differences in VAS score between the deferent defect of gaps. In addition, we found that the bone union rates after the smiley face rod method were significantly different depending on the type of pars defect, whether per patient or pars. To our knowledge, this is the first study to evaluate clinical outcomes of the smiley face rod method associated with the pars type defect. Our results suggested that the defect of pars sclerosis is associated with bone nonunion, but has little effect on postoperative symptoms.
We found the presence of sclerosis in the spondylolysis defect is associated with the bone union rate after surgery, and high bone union rates were observed in group A. The smiley face rod methods provide more stiffness and rigidity to the pars than other methods20,21), such as those using tension band principles22), which allows greater compression of the pedicle screw holding the lamina toward the isthmus of the pars. The smiley face rod method has been used successfully to fuse fracture sites of the pars interarticularis, and the average VAS score has improved postoperatively23). In addition, a cancellous autograft from the iliac crest is a suitable void filler for treating bone defects. It provides osteoconductive, osteoinductive, and osteogenic factors24). The postoperative bone union rate using the smiley face rod method is around 80%25). In the present study, the overall bone union rate at 24 months after surgery was 79.4%, as consistent with past reports. However, when the pars defect was of a sclerosis or atrophy type, the rate was lower at 62.5%. The bone union rate was poor when the pars defect was of the sclerosis type, although the smiley face rod method provides biomechanically and biologically favorable conditions. Intervertebral fusion is another method that can increase the rate of bone union. However, it is not an easy choice for young patients due to the risk of adjacent intervertebral disorders26). In this series, many patients have returned to competition even without bone union, which is not necessarily a poor short-term outcome. However, if bone union is not achieved, implant failure5,27) and residual pain5,28) may occur in the long term. In the present study, the pars defect was of a sclerosis or atrophy type, which may be an unfavorable condition for bone union. Therefore, careful selection of treatment strategies in patients with preoperative defects of the gap with sclerosis or atrophy is necessary. Moreover, because the defect has a fatigue fracture mechanism, we think the time for bone union may be longer than for a normal acute fracture, and long-term results warrant investigation.
We found that the pars defect in spondylolysis is not associated with a reduction in VAS scores. Our results suggested that even if the pars defect is of the sclerosis type, which is unfavorable for bone union, surgery can improve symptoms and allow the patient to return to competition. There is a report that synovitis around the defect of the pars and facet site causes pain29). In this report, the patient underwent a surgical curettage and bone grafting in the same area, which may also have improved symptoms. Although this was a short-term evaluation, in patients with a large sclerosis gap defect, bone union may not always be achieved, but improvement in symptoms is expected.
There are some limitations to the present study. First, the sample size was small, which might have caused data bias or lack of power; the strength of evidence of observational studies for evaluating outcomes is not high. Second, the study might have intervention and selection biases, especially with regard to the VAS score evaluation, because it is not an assessment of all patients. Third, the present study did not evaluate hamstring tightness and its relationship to bone fusion. The tightness of the hamstring should be evaluated quantitatively. Fourth, although a pars block was used for the diagnosis, it is difficult to distinguish pain from the pars from pain originating from the facet joints. Pseudoarthrotic pars defects may communicate with adjoining facet joints, and inflammatory events in the pseudoarthrotic pars defects or adjoining facet joints, or both, could be the source of back pain in terminal-stage spondylolysis29). It is difficult to distinguish accurately between pars or facet joint-derived pain, and the pars block may also affect the facet joint. Moreover, because some patients have disc degeneration and spondylolisthesis preoperatively, postoperative pain assessment is difficult due to these confounding factors. However, although patients with these factors have been excluded in previous reports12,22), they had good outcomes in the present study. Multiple regression analysis, including these factors with a larger number of patients, is needed. Furthermore, the defect gap was not evaluated as a continuous variable and was evaluated only qualitatively. However, the intraclass correlation coefficient is high, and this is, to our knowledge, the first study to evaluate the defect gap and postoperative outcomes. Finally, the long-term prognosis of cases in which bone union was not achieved is unknown, and additional studies are required to determine their long-term prognosis.
Conclusion
We showed that the bone union rates were significantly associated with the type of pars defect in patients with pseudoarthrosis spondylolysis treated with smiley face rod methods, and improvement of VAS score was not. Our study suggested that a postoperative bone union may be difficult to achieve for athletic patients with a large sclerosis gap defect. Nevertheless, there is a possibility of improving symptoms and returning the patient to athletics.
Conflicts of Interest: The authors declare that there are no relevant conflicts of interest.
Sources of Funding: None.
Author Contributions: Shun Okuwaki wrote and prepared the manuscript, and Masaki Tatsumura, Hisanori Gamada, and Reo Asai participated in the study design and data analysis. All authors have reviewed and approved the final manuscript.
Ethics Approval and Consent to Participate: Ethical approval was obtained from the institutional ethics committee of Mito Kyodo General Hospital (application No. 22-11).
All methods were carried out in accordance with relevant guidelines and regulations Informed consent was obtained from all participants in this study.
Consent for Publication: Not applicable
Availability of Data and Materials: The study data and details of materials used may be made available upon reasonable request by sending an e-mail to the corresponding author.
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