Abstract
Background
Proximal femoral unicameral bone cysts (UBCs) are challenging in children because the lesions occur in a weight-bearing region near the proximal femoral physis. This study describes outcomes after elastic stable intramedullary nailing-(ESIN)–based treatment and the indication-based use of selective transphyseal nail advancement.
Methods
We retrospectively reviewed consecutive skeletally immature patients with pathologically confirmed proximal femoral UBCs treated at 2 centers with curettage, high-speed burring, allogeneic bone grafting, and 2 titanium elastic nails. Minimum follow-up was 12 months. Outcomes included Ratliff and modified Neer status, recurrent or persistent cystic change, unplanned reoperation, complications, and growth-related radiographic findings.
Results
Thirty-eight patients were included: 31 underwent physeal-sparing ESIN, and 7 underwent selective transphyseal ESIN because physeal-sparing fixation provided insufficient proximal purchase. Median follow-up was 30.0 months. At the final follow-up, all patients had good Ratliff outcomes; modified Neer grade I was achieved in 26 patients (68.4%) and grade II in 12 (31.6%). Recurrent or persistent cystic change occurred in 9 patients, and 10 underwent unplanned reoperation. Among the 7 transphyseal cases, no clinically apparent progressive proximal femoral angular deformity or definite growth disturbance attributable to nail placement was identified during available follow-up.
Conclusions
ESIN-based management yielded satisfactory final outcomes. A physeal-sparing trajectory should remain preferred. Selective transphyseal advancement may provide proximal purchase in carefully selected juxtaphyseal lesions, but the small subgroup and absence of follow-up to skeletal maturity preclude conclusions regarding long-term physeal safety.
Key Concepts
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(1)
Elastic stable intramedullary nailing–based treatment produced good final clinical and radiographic outcomes in this high-risk pediatric proximal femoral unicameral bone cyst series.
-
(2)
A physeal-sparing nail trajectory should remain preferred when stable proximal purchase can be achieved.
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(3)
Selective transphyseal advancement may be considered when a juxtaphyseal lesion prevents secure physeal-sparing fixation.
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(4)
No definite growth disturbance attributable to nail passage was identified in 7 transphyseal cases during available follow-up.
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(5)
The small subgroup and lack of follow-up to skeletal maturity preclude conclusions about long-term physeal safety.
Level of Evidence
IV, Case Series
Keywords: Unicameral bone cyst, Proximal femur, Pediatric orthopaedics, Elastic stable intramedullary nailing, Physis
Introduction
Unicameral bone cysts (UBCs) are benign fluid-filled bone lesions that predominantly affect children and adolescents. Although many UBCs occur in the proximal humerus, proximal femoral lesions are clinically more challenging because they involve a weight-bearing region and may present with pain, impending fracture, or established pathologic fracture. In skeletally immature patients, treatment failure or insufficient structural support in this location may be followed by refracture, progressive deformity, limb length discrepancy, or other growth-related sequelae [[1], [2], [3], [4], [5]].
Several treatment strategies have been described for pediatric UBCs, including observation, injection-based procedures, decompression, curettage and grafting, and internal fixation [3,[6], [7], [8]]. For proximal femoral lesions at high risk of fracture, treatment must address both the biological cyst cavity and the mechanical vulnerability of the proximal femur. Elastic stable intramedullary nailing (ESIN) is a commonly used pediatric fixation method that can provide internal support through a relatively conservative intramedullary construct while also permitting decompression of the cyst cavity [[9], [10], [11], [12], [13], [14], [15]].
A specific technical dilemma occurs when a proximal femoral UBC is active and extends close to the proximal femoral physis. In such lesions, a physeal-sparing ESIN trajectory may leave the proximal nail tips too distal to provide secure purchase, particularly when residual proximal bone stock is limited or the lesion extends into the femoral neck. Conversely, intentional transphyseal nail advancement raises concern regarding physeal injury and subsequent growth disturbance. This balance between proximal fixation stability and physeal preservation is a practical issue in pediatric orthopaedic decision-making, but it remains insufficiently described in proximal femoral UBCs.
This study aimed to describe the clinical and radiographic outcomes of ESIN-based management for high-risk pediatric proximal femoral UBCs and to document the indications and short- to mid-term growth-related observations of selective transphyseal nail advancement in active juxtaphyseal lesions. The primary outcomes of interest were final Ratliff outcome, final modified Neer grade, recurrent or persistent cystic change, unplanned reoperation, recorded complications, and growth-related radiographic findings.
Materials and methods
Study design and reporting
This was a retrospective case series of skeletally immature patients with high-risk proximal femoral UBCs treated using an ESIN-based procedure at 2 tertiary pediatric orthopaedic centers. Institutional databases were reviewed for the period from January 2009 to December 2025. The study was reported in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology recommendations where applicable.
Patient selection
Institutional databases were reviewed to identify pediatric patients who underwent surgical treatment for proximal femoral UBCs during the study period. The analysis focused on ESIN trajectory, proximal purchase, and growth-related observations.
Patients were eligible if they met all of the following criteria: (1) pathologically confirmed UBC; (2) lesion located in the proximal femur; (3) skeletally immature status with an open proximal femoral physis at the time of surgery; (4) high-fracture-risk lesion or pathologic fracture at presentation; (5) treatment with curettage, high-speed burring, allogeneic bone grafting, and fixation with 2 titanium elastic nails; and (6) minimum postoperative follow-up of 12 months.
Patients were excluded if they had non-UBC pathology, inadequate clinical or radiographic documentation, inadequate pathological confirmation, or treatment with a non-ESIN construct. Non-ESIN constructs were excluded and were not used as a comparison group.
During the study period, 74 surgically treated pediatric proximal femoral UBCs were assessed. Thirty-six patients treated with non-ESIN constructs were excluded. The final ESIN-treated series included 38 eligible patients: 31 treated with physeal-sparing ESIN and 7 treated with selective transphyseal ESIN. The patient selection process is shown in Fig. 1.
Figure 1.
Patient flow diagram. During the study period, 74 surgically treated pediatric proximal femoral UBCs were assessed. Thirty-six patients treated with non-ESIN constructs were excluded because the present analysis focused on ESIN nail trajectory, proximal nail purchase, and growth-related observations after intramedullary fixation. The final ESIN-treated series included 38 eligible patients: 31 treated with physeal-sparing ESIN and 7 treated with selective transphyseal ESIN. ESIN, elastic stable intramedullary nailing; UBC, unicameral bone cyst.
Definitions and data collection
Demographic, clinical, operative, and follow-up data were extracted from medical records and serial radiographs. An active UBC was defined as a lesion located within 1 cm of the proximal femoral physeal edge [16,17]. Lesions were considered at high risk of fracture when the bone cyst index exceeded 3.5 or when the cyst occupied more than 85% of the diameter of the involved long bone [18,19]. All included lesions met one of these high-risk criteria or had already sustained a pathologic fracture at presentation.
Physeal-sparing ESIN was defined as proximal nail placement without crossing the proximal femoral physis. Selective transphyseal ESIN was defined as clear passage of at least one nail tip across the proximal femoral physis with definite entry into the epiphysis on intraoperative fluoroscopy and postoperative radiographs.
A growth disturbance was considered attributable to transphyseal nail placement only when serial clinical and radiographic findings demonstrated progressive deformity or limb length change anatomically consistent with injury to the crossed proximal femoral physis, without a more plausible alternative explanation such as lesion-related change, fracture-related remodeling, or nontransphyseal disease progression.
Surgical technique
All procedures were performed by pediatric orthopaedic surgeons under fluoroscopic guidance. Through an anterolateral approach, biopsy tissue was obtained for histopathological confirmation. A cortical window was created, the cyst was thoroughly curetted, and the cavity wall was additionally treated using a high-speed burr. The resulting defect was filled with allogeneic bone graft material.
Fixation was achieved with 2 retrograde titanium elastic nails according to standard ESIN principles. Nail diameter was selected according to patient age and medullary canal size, with balanced paired nails used whenever feasible [20].
Across both participating centers and throughout the 2009–2025 study period, the core surgical indications and operative technique remained consistent: curettage, high-speed burring, allogeneic bone grafting, and fixation with 2 titanium elastic nails. The only trajectory-specific variation was whether the nails remained physeal-sparing or crossed the proximal femoral physis, selected according to lesion location and the proximal purchase achievable intraoperatively.
A physeal-sparing trajectory was preferred whenever adequate proximal purchase and construct stability could be achieved without crossing the proximal femoral physis. Selective transphyseal advancement was reserved for active juxtaphyseal lesions when a physeal-sparing trajectory would leave the proximal nail tips too distal, when residual proximal bone stock was insufficient, or when a femoral neck lesion could not obtain adequate proximal purchase without crossing the physis. A schematic illustration of the 2 ESIN trajectories is shown in Fig. 2.
Figure 2.
Schematic illustration of physeal-sparing and selective transphyseal ESIN according to lesion proximity to the proximal femoral physeal edge. (A) When the lesion is more than 1 cm from the physeal edge and sufficient proximal bone stock is available, a physeal-sparing ESIN trajectory can usually be achieved. (B) For a lesion within 1 cm of the physeal edge, selective transphyseal advancement may be considered in carefully selected cases if a physeal-sparing trajectory cannot provide secure proximal purchase. ESIN, elastic stable intramedullary nailing.
Postoperative management and follow-up
Postoperatively, the affected limb was protected with either a hip spica cast or a brace for approximately 6 weeks. Progressive weight-bearing was then initiated according to radiographic appearance and clinical symptoms. Follow-up visits were generally scheduled at 6 weeks and at 3, 6, 9, and 12 months after surgery and annually thereafter when possible.
Standard radiographs were reviewed to assess fracture union when applicable, cyst healing, implant position, recurrent or persistent cystic change, and growth-related morphology. Implant removal was considered after radiographic consolidation of the lesion and/or fracture, when cortical reconstitution was judged sufficient and continued internal support was no longer necessary.
Radiographic and growth-related assessment
Radiographic healing was evaluated using the modified Neer classification [16,17]. The final clinical hip outcome was assessed using the Ratliff criteria [21].
Proximal femoral morphology was reviewed on available serial anteroposterior pelvic or hip radiographs, with attention to clinically apparent coxa vara, coxa valga, femoral-neck shortening, and gross neck-shaft angle abnormality. Formal neck-shaft angle measurement was not analyzed as a prespecified series-wide endpoint because standardized bilateral pelvic radiographs were not available for all patients. Pediatric neck-shaft angle varies with age, and conventional 2-dimensional radiographic measurements may be influenced by projection and positioning [22,23]. Therefore, growth-related morphology was summarized descriptively rather than used for formal comparative inference.
When physical examination suggested limb length discrepancy, standing full-length lower extremity radiographs were obtained for measurement.
Outcome measures
Outcomes of interest included final Ratliff outcome, final modified Neer radiographic status, recurrent or persistent cystic change during follow-up, implant removal, unplanned postindex reoperation, recorded complications, and growth-related observations in selective transphyseal cases.
Recurrent or persistent cystic change was defined as reappearance or persistence of a radiolucent cystic lesion at any point during follow-up after the index ESIN procedure, irrespective of the final modified Neer grade. Unplanned postindex reoperation was counted only when a subsequent surgical procedure was explicitly documented in the medical record.
Statistical analysis
Continuous variables are presented as medians with interquartile ranges (IQRs), and categorical variables are presented as numbers and percentages. Because selective transphyseal ESIN was used in a small, indication-based subset of active juxtaphyseal lesions, the analysis was primarily descriptive. No comparative efficacy or safety inference between physeal-sparing and selective transphyseal ESIN was attempted.
Because of the limited number of events and the strong relationship between lesion proximity to the physis and selective transphyseal nail advancement, multivariable modeling was not performed.
Results
Patient flow and baseline characteristics
Of 74 surgically treated pediatric proximal femoral UBCs assessed, 36 patients treated with non-ESIN constructs were excluded, leaving 38 eligible skeletally immature patients: 31 treated with physeal-sparing ESIN and 7 with selective transphyseal ESIN.
Baseline demographic and lesion characteristics are summarized descriptively in Table 1. The overall median age at surgery was 7.0 years (IQR, 4.9-8.7 years). Twenty-nine patients were boys, and 9 were girls. Sixteen patients had left-sided lesions. Twenty patients had active UBCs, defined as lesions located within 1 cm of the proximal femoral physeal edge, and 12 patients presented with a pathologic fracture. All 7 selective transphyseal cases were active juxtaphyseal lesions, reflecting the indication-based use of this trajectory when secure proximal purchase was judged insufficient with a physeal-sparing path.
Table 1.
Baseline demographic and lesion characteristics of the ESIN-treated series.
| Variable | Overall (n = 38) | Physeal-sparing ESIN (n = 31) | Selective transphyseal ESIN (n = 7) |
|---|---|---|---|
| Male sex, n (%) | 29 (76.3) | 23 (74.2) | 6 (85.7) |
| Left-sided lesion, n (%) | 16 (42.1) | 10 (32.3) | 6 (85.7) |
| Age at surgery, y, median (IQR) | 7.0 (4.9-8.7) | 7.0 (4.8-8.6) | 7.4 (5.3-9.4) |
| Active UBC, n (%) | 20 (52.6) | 13 (41.9) | 7 (100.0) |
| Pathologic fracture at presentation, n (%) | 12 (31.6) | 10 (32.3) | 2 (28.6) |
ESIN, elastic stable intramedullary nailing; IQR, interquartile range; UBC, unicameral bone cyst.
Data are presented as median (IQR) or n (%). Active UBC was defined as a lesion located within 1 cm of the proximal femoral physeal edge. All lesions were pathologically confirmed UBCs. All patients were included because they either presented with a pathologic fracture or met the prespecified radiographic high-risk criteria. Because selective transphyseal ESIN was used in a small, indication-based subset of active juxtaphyseal lesions, between-trajectory comparisons were interpreted descriptively.
Operative and follow-up outcomes
All patients underwent curettage, high-speed burring, allogeneic bone grafting, and fixation with 2 titanium elastic nails. Operative and follow-up outcomes are summarized descriptively in Table 2. The overall median follow-up duration was 30.0 months (IQR, 25.2-48.2 months), and the median age at the final follow-up was 10.1 years (IQR, 7.8-12.1 years).
Table 2.
Operative and follow-up outcomes of the ESIN-treated series.
| Variable | Overall (n = 38) | Physeal-sparing ESIN (n = 31) | Selective transphyseal ESIN (n = 7) |
|---|---|---|---|
| Nail diameter, mm, median (IQR) | 3.0 (2.5-3.0) | 3.0 (2.5-3.0) | 3.0 (2.8-3.5) |
| Follow-up duration, mo, median (IQR) | 30.0 (25.2-48.2) | 28.6 (24.1-44.8) | 37.6 (28.2-59.3) |
| Age at the final follow-up, y, median (IQR) | 10.1 (7.8-12.1) | 9.2 (7.5-11.8) | 11.6 (9.7-13.1) |
| Implant removed, n (%) | 31 (81.6) | 26 (83.9) | 5 (71.4) |
| Implant retention time, mo, median (IQR) | 23.2 (15.7-28.2) | 22.5 (14.8-27.7) | 28.3 (27.0-31.0) |
| Recurrent or persistent cystic change during follow-up, n (%) | 9 (23.7) | 7 (22.6) | 2 (28.6) |
| Unplanned postindex reoperation, n (%) | 10 (26.3) | 8 (25.8) | 2 (28.6) |
| Any recorded complication, n (%) | 5 (13.2) | 3 (9.7) | 2 (28.6) |
| Good Ratliff outcome at the final follow-up, n (%) | 38 (100.0) | 31 (100.0) | 7 (100.0) |
| Modified Neer grade I at the final follow-up, n (%) | 26 (68.4) | 21 (67.7) | 5 (71.4) |
| Modified Neer grade II at the final follow-up, n (%) | 12 (31.6) | 10 (32.3) | 2 (28.6) |
ESIN, elastic stable intramedullary nailing; IQR, interquartile range.
Data are presented as median (IQR) or n (%). Implant retention time was calculated only among patients who underwent implant removal. Unplanned postindex reoperation was counted only when a subsequent surgical procedure was explicitly documented in the medical record. Final modified Neer grades are presented separately. Because selective transphyseal ESIN was used in a small, indication-based subset, between-trajectory comparisons were interpreted descriptively.
Implant removal had been performed in 31 of 38 patients. Among patients who underwent implant removal, the median implant retention time was 23.2 months (IQR, 15.7-28.2 months). All pathologic fractures achieved radiographic union without documented nonunion. At the final follow-up, all patients had good Ratliff outcomes; modified Neer grade I was achieved in 26 patients (68.4%) and grade II in 12 (31.6%).
Recurrent or persistent cystic change was documented in 9 patients during follow-up, all of whom underwent unplanned repeat surgery for this finding. In total, unplanned postindex reoperation was documented in 10 patients: 9 repeat operations for recurrent or persistent cystic change and one conversion to plate fixation for postoperative instability with fracture.
Selective transphyseal cases and growth-related observations
Individual characteristics and follow-up observations of the 7 selective transphyseal ESIN cases are summarized in Table 3. All 7 lesions were active and juxtaphyseal. In each case, the nail tip or tips were intentionally advanced across the proximal femoral physis to obtain intraepiphyseal purchase when a physeal-sparing trajectory was judged insufficient for secure proximal fixation.
Table 3.
Individual characteristics and follow-up observations of the 7 selective transphyseal ESIN cases.
| Case | Baseline profile | Follow-up and implant status | Recurrent or persistent cystic change | Unplanned postindex reoperation | Other recorded complication | Attributable growth disturbance |
|---|---|---|---|---|---|---|
| 1 | Male; left side; age 5.4 y; no pathologic fracture; 2.5-mm nails | 28.2 mo; implant removed at 26.6 mo | No | No | None | No |
| 2 | Male; left side; age 9.0 y; no pathologic fracture; 3.0-mm nails | 60.1 mo; implant removed at 31.0 mo | No | No | Affected femur +1.3 cm | No |
| 3 | Male; left side; age 4.0 y; no pathologic fracture; 3.0-mm nails | 58.5 mo; implant in situ | Yes | Yes - repeat surgery for cystic change | Attempted implant removal was difficult; implant remained in situ | No |
| 4 | Male; left side; age 5.2 y; no pathologic fracture; 3.0-mm nails | 105.6 mo; implant removed at 93.4 mo | No | No | None | No |
| 5 | Male; right side; age 7.4 y; no pathologic fracture; 2.5-mm nails | 37.6 mo; implant removed at 27.0 mo | No | No | None | No |
| 6 | Male; left side; age 9.8 y; pathologic fracture; 4.0-mm nails | 30.0 mo; implant removed at 28.3 mo | No | No | None | No |
| 7 | Female; left side; age 9.8 y; pathologic fracture; 4.0-mm nails | 24.7 mo; implant in situ | Yes | Yes - repeat surgery for cystic change | None | No |
ESIN, elastic stable intramedullary nailing; UBC, unicameral bone cyst.
All 7 lesions were active UBCs located within 1 cm of the proximal femoral physeal edge. All 7 cases were treated with 2 titanium elastic nails, cortical windowing, curettage, high-speed burring, and allogeneic bone grafting. Recurrent or persistent cystic change was defined as reappearance or persistence of a radiolucent cystic lesion at any point during follow-up, irrespective of the final modified Neer grade. Cases 3 and 7 underwent unplanned repeat surgery for recurrent or persistent cystic change. In all 7 cases, the nail tip or tips were advanced across the proximal femoral physis into the epiphysis to obtain intraepiphyseal purchase. Attributable growth disturbance was defined as progressive deformity or limb length change anatomically consistent with injury to the crossed proximal femoral physis, without a more plausible alternative explanation.
Five patients in the overall series had recorded complications during follow-up. Three patients had clinically documented limb length discrepancy. One physeal-sparing case developed 2-cm shortening of the operated limb, accompanied by femoral neck shortening and suspected premature physeal closure. Another physeal-sparing case had a 2-cm-longer operated limb. In the selective transphyseal subgroup, one patient had a 1.3-cm-longer affected femur. None of these three limb length discrepancy cases underwent further surgery.
The remaining complications were postoperative instability with fracture requiring conversion to plate fixation in one physeal-sparing case and difficult attempted implant removal, with the implant left in situ, in one selective transphyseal case. Both selective transphyseal cases with recurrent or persistent cystic change (cases 3 and 7) underwent unplanned repeat surgery.
Qualitative review of available serial radiographs did not identify clinically apparent progressive coxa vara, coxa valga, femoral-neck shortening, or gross proximal femoral angular deformity among the selective transphyseal cases. After case-by-case review of clinical records and serial radiographs, no definite growth disturbance attributable to transphyseal nail placement was identified during available follow-up (see Figure 3, Figure 4).
Figure 3.
Representative case of physeal-sparing ESIN for a pediatric proximal femoral UBC. (A) Preoperative anteroposterior radiograph showing a proximal femoral UBC. (B) Early postoperative anteroposterior radiograph after curettage, high-speed burring, allogeneic bone grafting, and fixation with 2 titanium elastic nails; the proximal nail tips remained below the proximal femoral physis. (C) Interval follow-up radiograph showing progressive healing of the lesion with the implants in situ. (D, E) Final follow-up anteroposterior and lateral radiographs demonstrating radiographic healing of the cyst and maintained proximal femoral morphology. ESIN, elastic stable intramedullary nailing; UBC, unicameral bone cyst.
Figure 4.
Representative case of selective transphyseal ESIN for a pediatric proximal femoral UBC abutting the proximal femoral physis. (A) Preoperative anteroposterior radiograph showing a proximal femoral UBC close to the physeal edge. (B, C) Early postoperative anteroposterior and lateral radiographs after curettage, high-speed burring, allogeneic bone grafting, and fixation with 2 titanium elastic nails; the proximal nail tips were intentionally advanced across the physis to obtain intraepiphyseal purchase. (D, E) Follow-up anteroposterior and lateral radiographs demonstrating radiographic healing of the cyst with preserved proximal femoral contour. ESIN, elastic stable intramedullary nailing; UBC, unicameral bone cyst.
Discussion
This retrospective case series describes ESIN-based management of high-risk pediatric proximal femoral UBCs and documents the limited use of selective transphyseal nail advancement in active juxtaphyseal lesions. The final clinical and radiographic outcomes were satisfactory: All patients had good Ratliff outcomes; modified Neer grade I was achieved in 26 patients (68.4%) and grade II in 12 (31.6%). Selective transphyseal ESIN was used in 7 cases when physeal-sparing nail placement was judged insufficient to obtain secure proximal purchase. No definite growth disturbance attributable to transphyseal nail placement was identified during available follow-up. These findings should be interpreted as limited short- to mid-term observations rather than evidence of long-term physeal safety.
Proximal femoral UBCs are challenging because they affect a weight-bearing region and may compromise the femoral neck and intertrochanteric area. Treatment must therefore address both the cyst cavity and structural vulnerability. In this series, the standardized procedure combined cortical windowing, curettage, high-speed burring, allogeneic bone grafting, and flexible intramedullary fixation to promote healing while maintaining internal support.
The specific pediatric orthopaedic issue addressed by this study is nail trajectory decision-making in active juxtaphyseal lesions. When the cyst closely approaches the proximal femoral physis, a physeal-sparing ESIN trajectory may leave the proximal nail tips too distal, especially when residual proximal bone stock is limited or the lesion extends into the femoral neck. In such cases, inadequate proximal purchase may compromise construct stability. Selective transphyseal advancement was therefore used only when intraoperative fluoroscopy suggested that a physeal-sparing trajectory would not provide reliable proximal fixation. This should be regarded as a limited technical option for selected lesions, not as a routine strategy for proximal femoral UBCs.
Growth-related findings require cautious interpretation. The absence of clinically apparent progressive coxa vara, coxa valga, femoral-neck shortening, or gross proximal femoral angular deformity in the selective transphyseal subgroup is reassuring, but it is not definitive. Growth disturbance in proximal femoral UBCs may be influenced by the lesion itself, proximity to the physis, pathologic fracture, remodeling, and fixation strategy [[24], [25], [26], [27]]. In this series, limb length discrepancy was not confined to the selective transphyseal subgroup, and one physeal-sparing case developed shortening with femoral neck shortening and suspected premature physeal closure. Conversely, the selective transphyseal case with limb length discrepancy showed relative overgrowth of the affected femur. These observations do not support a simple assumption that all growth-related findings are attributable to transphyseal nail passage.
The rates of recurrent or persistent cystic change and unplanned reoperation should also be interpreted in context. This was not a mixed-location series of uncomplicated UBCs. All included lesions were in the proximal femur and were considered at high risk for fracture or had already fractured. Many lesions were active and close to the proximal femoral physis. Recurrent or persistent cystic change was counted whenever it was documented during follow-up, even if the final radiographic status was modified Neer grade I or II. Therefore, this interim radiographic event and the associated unplanned reoperations should not be interpreted as final treatment failure alone but rather as events occurring during longitudinal management of a high-risk proximal femoral series. Recent proximal-femur-specific studies have similarly emphasized that treatment failure, additional procedures, and limb length discrepancy remain relevant concerns in this anatomic location [[28], [29], [30], [31], [32], [33], [34]].
This study has several limitations. First, it was retrospective and descriptive. Second, selective transphyseal ESIN was used in only 7 patients, all selected on the basis of lesion anatomy and intraoperative fixation requirements. Therefore, no comparative efficacy or safety inference between physeal-sparing and selective transphyseal ESIN can be made. Third, not all patients had follow-up to skeletal maturity, which limits interpretation of growth-related outcomes. Fourth, standardized bilateral pelvic radiographs and standing full-length radiographs were not available in all patients; consequently, formal neck-shaft angle measurement was not analyzed as a series-wide endpoint, and subtle angular changes cannot be excluded. Finally, patients treated with non-ESIN constructs were outside the scope of this ESIN trajectory-focused analysis, so the findings cannot be generalized to plate fixation, injection-based treatment, or other strategies.
Despite these limitations, the study provides a practical description of ESIN-based treatment in high-risk proximal femoral UBCs. A physeal-sparing ESIN trajectory should remain preferred whenever stable proximal purchase can be achieved. Selective transphyseal advancement may be considered only in carefully selected active juxtaphyseal lesions when physeal-sparing fixation is mechanically insufficient. Continued follow-up toward skeletal maturity is necessary when this strategy is used.
Conclusions
ESIN-based treatment produced satisfactory final clinical and radiographic outcomes in this high-risk case series. Selective transphyseal nail advancement was used only when adequate proximal purchase could not be achieved with a physeal-sparing trajectory. No definite growth disturbance attributable to transphyseal nail placement was identified during available follow-up; however, the small, selected subgroup, lack of follow-up to skeletal maturity, and the absence of standardized series-wide morphometric assessment preclude conclusions regarding long-term physeal safety.
Additional links
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POSNA Study Guide: Unicameral Bone Cyst
Author contributions
Taichun Li: Writing – original draft, Visualization, Resources, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Jingmiao Wang: Writing – original draft, Visualization, Resources, Methodology, Investigation, Formal analysis, Data curation. Qin Zhang: Writing – review & editing, Resources, Investigation, Data curation. Hai Li: Writing – review & editing, Supervision, Project administration. Ziming Zhang: Writing – review & editing, Supervision, Project administration, Methodology, Conceptualization.
Ethics approval and consent
The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Shanghai Children’s Hospital, School of Medicine, Shanghai Jiao Tong University (Approval No. 2026R039-E01; approval date: 10 March 2026) and the Ethics Committee of Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine (Approval No. XHEC-D-2023-009; approval date: 16 January 2023). Patient consent for participation was waived for the Shanghai Children’s Hospital data because of the retrospective design and use of de-identified data. For the Xinhua Hospital data, patients had previously provided broad consent permitting research use of clinical data within the approved scope. Written informed consent for publication of the clinical data and radiographic images was obtained from the patients’ legal guardians.
Data availability
The data supporting the findings of this study are available from the corresponding authors upon reasonable request. The data are not publicly available because of institutional restrictions and patient privacy considerations.
Declaration of the use of generative AI and AI-assisted technologies in the writing process
During the preparation of this work, the authors used ChatGPT (OpenAI, San Francisco, CA, USA) to support English-language editing and journal-format adaptation. The tool was not used for data acquisition, statistical analysis, outcome adjudication, clinical interpretation, or generation of scientific references. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the article.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Declaration of competing interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Contributor Information
Hai Li, Email: lihai@shchildren.com.cn.
Ziming Zhang, Email: zhangziming@shchildren.com.cn.
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data supporting the findings of this study are available from the corresponding authors upon reasonable request. The data are not publicly available because of institutional restrictions and patient privacy considerations.