As far as we can judge, there are very few studies on the long-term results of surgical correction of juvenile kyphosis, while both the treatment strategy and the outcomes seem to be ambiguous.
Apparently, the first study of this kind was published by Soo et al.  in 2002. The authors evaluated the outcomes of three strategies used for treating 63 patients: observation and exercise, bracing, and surgical correction using Harrington compression rods following anterior release. The results were followed up for 14 (10–28) years. The main examination methods were radiography and surveys using a questionnaire designed by the authors. The kyphotic curves in patients of the three subgroups were 57°, 64°, and 73° before surgery, and 57°, 51°, and 59°, respectively, at the end of the follow-up. About half of the achieved correction (20 out of 37 cases) was lost in the surgery group. The achieved kyphotic curvatures were almost identical in the three subgroups by the end of the follow-up period.
The questionnaire results demonstrated no differences in the following parameters between the patents: marital status, general health, educational level, work status, pain degree, and functional capacity. There was no relationship with the treatment mode, as well as type and degree of the kyphotic curve. Patients of the brace and surgery subgroups noted the greatest improvement in their self-image among other participants, attributing it to the treatment. The lowest functional level was observed in patients with deformities of ˃ 70° by the end of the follow-up.
The authors conclude that careful selection of the method for treating patients with Scheuermann’s disease should be based on age, deformity type, and pain severity.
In 2009, Denis et al. . investigated the frequency and risk factors for the development of junctional kyphosis after surgical correction of kyphotic deformities due to Scheuermann’s disease. The authors analyzed the results of the treatment of 67 patients who were operated on at least five years ago (mean follow-up, 73 months). A total of 15 individuals underwent one-stage posterior intervention; 52 patients were treated by two-stage surgery. Traditional definitions were used to identify junctional kyphosis. PJK was considered if the proximal junctional angle between the cranial endplates of the UIV and the vertebra two levels cranial to it was ˃ 10° or increased by at least 10° after surgery compared to the baseline. Distal junctional kyphosis was determined by the angle between the caudal endplates of the LIV and the vertebra located one level caudal to it. The authors managed to reduce kyphosis from 78° to 45° and almost completely preserve it: the curve angle was 49° at final follow-up. PJK developed in 20 patients (30 %). The frequency of PJK was 8 % if the proximal end vertebra in the curvature was included in the fusion and 63 % if it was not. The authors mention damage to the ligamentum flavum by a hook or a sublaminar wire as the second most important cause of PJK. PJK development is associated with neither the baseline kyphosis magnitude nor the achieved correction rate. DJK was detected in eight patients (12 %), with seven of them sharing the same feature: the first lordotic disc was not included in the fusion. No correlation between the instrumentation type used and the frequency of junctional kyphosis was noted.
In 2016, Graat et al.  published the long-term outcomes of surgeries for Scheuermann’s kyphosis in 29 patients. The postoperative follow-up was 18 (14–21) years. Posterior approach was used in 13 cases; combined (anterior–posterior) procedure was carried out in 16 individuals. The initial Cobb angle (82°) was reduced to 69° after surgery by the end of the follow-up. Unfortunately, the authors present radiography data for the general group only and do not differentiate them depending on the surgical approach used (one-/two-stage). They only mention that the combined and posterior approaches reduced the curvature by 27 and 17 %, respectively, while not considering the difference to be statistically significant. The number of PJK cases increased with the duration of postoperative follow-up: there were nine (31 %) patients during the first year after surgery, 12 (43 %) individuals in the period of eight years after surgery, and 15 (53 %) cases by the end of the follow-up period. The upper end vertebra was fused in eight patients (four PJK cases) and not included in the instrumentation in 19 individuals (11 PJK cases). No revision surgeries for PJK were performed. There were no reported cases of DJK. Implant-associated complications were observed in 20 patients (69 %) and distributed approximately equally between the two subgroups. Implants were removed in seven individuals; a solid bone fusion was visually confirmed in all of the cases. The correction loss was 5° after implant removal. HRQoL was assessed using the Oswestry Disability Index, Visual Analog Score Pain (SF-36), and EQ-5d. A total of 21 (72 %) out of 29 patients were satisfied with the treatment outcome and would be willing to undergo the same treatment again if they had a similar condition, while the remaining 23 (79 %) participants recommended the procedure to others. The authors consider the radiographic results of surgical treatment as “disappointing”. However, they also reasonably correlate them with the data of clinical studies indicating high functional activity of patients for many years after surgery even with a high incidence of postoperative pain. In addition, the patients who underwent the combined surgical treatment demonstrated better functional results than those subjected to posterior fusion only. Despite the ambiguity of the obtained results, the authors note that the outcomes are better than in case of natural disease course, as far as it can be judged from the literature.
In 2019, Chang Ju Hwang et al.  published the results of all-pedicle-screw fixation in individuals with kyphosis of various etiologies, including Scheuermann’s disease. Juvenile kyphosis was diagnosed in 15 out of 43 patients. The mean postoperative follow-up was 5.8 (5–9.7) years for these 15 individuals. The average age of the patients with Scheuermann’s disease was 19.1 years. Vertebral column resection was conducted in 11 cases in order to increase the mobility of the spinal deformity. The authors chose the length of the instrumented fusion based on the following principles: the number of vertebra involved in fusion should be symmetrical both above and below the kyphosis apex, provided that the disc located cranial to the UIV is lordotic. Kyphosis was 91° at baseline, 48.1° immediately after surgery, and 49.9° at the end of the follow-up, i.e. the average correction rate was only 1.8°. Complications included two cases of PJK, one screw pullout, and one case of signal loss during spinal neuromonitoring, which were followed by complete recovery. Evaluation of the quality of life (ODI and SRS-30) showed significant improvement in all domains.
Our data confirm that the combined approach has no advantages over the use of one type of instrumentation. Furthermore, posterior intervention made it possible to obtain a slightly larger correction and its better preservation.The rate of junctional kyphosis was significant in the group we studied: 48.8 % for PJK and 39.5 % for DJK. Moreover, the overwhelming majority of the cases were asymptomatic and did not require reoperation. Spinal fusion was successfully extended to the cranium in only two PJK cases with kyphosis reaching 90°, which can be interpreted as proximal junctional failure (PJF). PJK usually develops when UIV is excluded from the fusion, but the differences are insignificant. According to our data, the rate of the major curve correction is not a risk factor for PJK. As for the distal end of the fusion, adverse changes in the disc caudal to the LIV occur immediately after surgery and further deteriorate. As far as we can judge, choosing SSV as the LIV seems reasonable.
We did not find any literature data on the effect of ID on the outcome of juvenile kyphosis correction. According to our data, an increase in ID due to a gradual transition from hook to pedicle crew fixation is accompanied by growth in the achieved deformity correction and yields more stable results.
We used the SRS-24 questionnaire and noted improvement for all the seven domains, although it was not statistically significant in all cases. The consent to have the same surgery if required increased from 82 to 86 %.
One of the main drawbacks of our work is the relatively small number of patients included in the study. Only 43 out of 152 participants with more than five-year follow-up considered it necessary and possible to undergo examination after the end of the follow-up period. Firstly, it can be explained by the distant clinic location relative to the patient and, hence, the high trip cost. Secondly, this can be also due to the alleged fact that the patients did not consider it necessary to undergo another examination in the absence of complaints. We also did not present any data on changes in the spinal and pelvic parameters. This is because the clinic lacked the opportunity to perform radiography with inclusion of the femoral heads for a significant period. Hence, we are unable to present the pelvic incidence and pelvic tilt parameter values. We considered it wrong to present the results of changes in the sacral slope only in the absence of other parameters.