1 Introduction

Due to the limited ability of supracondylar humeral fractures to remodel, malunion can result in permanent deformities such as cubitus varus or valgus.¹ Clinical and radiological evaluations of the quality of reduction in supracondylar fractures play a crucial role in preventing this outcome.² To assess sagittal deformity, radiographic parameters such as the Baumann angle, humero-ulna angle, shaft condylar angle (SCA), metaphyseal-diaphyseal angle, radial epiphyseal angle, and lateral capitellohumeral angle (LCHA) are commonly used.^3–5

The SCA and LCHA are measured on the lateral view of the elbow to assess sagittal deformity, with an average SCA value of 40° and an average LCHA value of 51° according to Shank et al.⁶ The reliability of both SCA and LCHA has been reported to be good.^7,8 The ability to determine the angle difference from the normal value makes both angles more useful than the anterior humeral line.^9,10

Gartland types two and three supracondylar humeral fractures are currently treated surgically^11–15 Although the goal of surgical fixation is to restore the SCA and minimize malunion, restricted ROM can still occur post-operatively due to soft tissue stiffness, immobilization, and healing-related processes. To date, no studies have investigated the relationship between SCA or LCHA and post-operative range of motion in surgically treated supracondylar fractures. Our study aims to validate the effectiveness of these parameters and establish a more precise correlation between the SCA, LCHA, and post-operative elbow range of motion. By doing so, we hope to reinforce the importance of these measurements in improving surgical outcomes and provide additional evidence to support their use in clinical practice.

2 Materials and methods

The study was registered in the Thai Clinical Trials Registry (TCTR20220430007) and received approval from the ethical committee of Srinakharinwirot University (SWUEC/E−374/2563). The procedures used in this study followed the principles of the Declaration of Helsinki. This was a prospective cohort study that was conducted at the HRH Princess Maha Chakri Sirindhorn Medical Center (MSMC), Srinakharinwirot University, between March 2020 and March 2023. The eligible patients were under the age of 11 with a closed supracondylar fracture of the humerus, of Gartland types two and three. Patients who refused surgical treatment, had open fractures, or had a history of arm or forearm injury prior to the supracondylar fracture, or who missed follow-up appointments, were excluded from the study. All patients underwent closed reduction and percutaneous pinning (CRPP) performed by a single pediatric orthopedic surgeon. This procedure involved the reduction of the fracture under fluoroscopic guidance followed by the insertion of percutaneous K-wires to stabilize the fracture.

Following the operation, patients were immobilized with a posterior long arm cast in 60-degree elbow flexion. All patients received the same post-operative protocol, including pain control, oral antibiotics, and wound care. The posterior long-arm cast was used for 3 weeks, and the K-wires were removed 4 weeks postoperatively. After K-wire removal at 4 weeks postoperatively, patients were instructed to begin range of motion exercises under the guidance of the pediatric orthopedist. The range of motion of the operated elbow and the non-operated elbow in flexion and extension were assessed using a goniometer 6 weeks after the operation by the pediatric orthopedist. The difference between the two sides was calculated. Anteroposterior and lateral x-ray elbow images were obtained.

The angle formed by the axis of the distal humerus shaft and the axis of the distal humeral condyle is known as the SCA (Fig. 1). An initial line was drawn through the anterior cortex of the humerus, and a second line was drawn at the proximal border of the capitellar ossification center. The LCHA was the anterior proximal corner of these two lines (Fig. 2). The pediatric orthopedist and an orthopedic resident measured the LCHA and SCA 6 weeks after the operation, and the measurements were redone 4 weeks later. The difference between the average values of each angle from normal (SCA of 40° and LCHA of 50°) was used to analyze the results.

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Fig. 1 Measurement of shaft condylar angle.

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Fig. 2 Measurement of lateral capitellohumeral angle.

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The sample size was calculated using Stata version 13.0 and a one-sample correlation test (Fisher RA., 1915 and Hulley SB et al., 2013). Previous research (Simanovsky et al., 2007) found a negative correlation (rho = −0.6903) between the shaft condylar angle and range of motion. As a result, 18 patients were needed in the current study to detect a significant correlation between groups with a p-value of 0.05 and a power (1-β) of 0.8.

3 Data analysis

Stata version 13.0 statistical software was used for data analysis (College Station, TX). Descriptive statistics were used to calculate the mean and standard deviation, and the Kruskal-Wallis test was used to determine the significance of the results. The significance of the elbow flexion and extension data was calculated using the independent t-test and the Mann-Whitney test. The Pearson product-moment correlation coefficient was used to calculate the correlation, and intraclass correlation coefficients were used to examine the intra-observer and inter-observer reliability of the LCHA and SCA (ICC). Statistical analysis was performed with a 95 % confidence interval (95%CI), and p-values less than 5 % were considered significant.

4 Results

A total of 44 patients were evaluated for eligibility, however, 8 of them did not return for follow-up after 6 weeks, resulting in 36 patients being assessed. Most of the patients were male, with a percentage of 72 %. The average age of the patients was 6.67 years, ranging from 4 to 10 years old. In 14 out of the 36 patients (39 %), the right side was involved, and in 22 cases (61 %). Preoperative findings based on Gartland classification revealed that among the 36 patients included in the study, 17 patients (47 %) had Gartland type 2A fractures, 5 patients (14 %) had Gartland type 2B fractures, and 14 patients (39 %) had Gartland type 3 fractures. No associated injury was found. The post-operative SCA measurements ranged from 25° to 59°, with a mean value of 38.5°. The post-operative LCHA measurements ranged from 30° to 78°, with a mean value of 52.3°.

The relationship between SCA, LCHA, and the range of motion was shown in Table 1. The results showed that SCA was significantly correlated with elbow flexion range of motion (Rho = 0.63; p < 0.05), however, it did not correlate with elbow extension range of motion (Rho = 0.25, p 0.32). Meanwhile, LCHA had no correlation with the range of motion in either flexion (Rho = 0.30, p 0.22) or extension (Rho = 0.33, p 0.18). The subgroup analysis revealed that a 7.65-degree difference in SCA from the normal value of 40° was associated with a significant difference in flexion angle (Mean difference = 7.25, p 0.05) (Fig. 3).

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Fig. 3 Subgroup analysis of SCA difference from the normal value at 40° in flexion angle.

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The intra-observer reliability for SCA was good for the orthopedics resident (ICC = 0.79, 95%CI = 0.61–0.97) and excellent for the pediatric orthopedist (ICC = 0.96, 95%CI = 0.93–1.00). The inter-observer reliability for SCA was also good (ICC = 0.63, 95 % confidence interval = 0.35–0.91). The intra-observer reliability for LCHA was excellent for both the orthopedics resident (ICC = 0.82, 95 % CI = 0.67–0.97) and the pediatric orthopedist (ICC = 0.98, 95 % CI = 0.95–1.00). The inter-observer reliability for LCHA was also excellent (ICC = 0.88, 95 % CI = 0.77–0.99).

5 Discussion

Supracondylar fractures are one of the most prevalent pediatric elbow fractures.¹⁶ It is crucial to achieve proper reduction of displaced supracondylar fractures to prevent postoperative issues, especially malunion, which can result in reduced elbow range of motion.¹⁷ According to a study by Sinikumpu et al., long-term consequences of pediatric supracondylar fractures include decreased elbow range of motion, particularly in Gartland types two and three.¹ There have been several reports of the SCA and LCHA being useful in the management of pediatric elbow injuries. Thanase et al. found that a loss of more than 18° of initial SCA and/or LCHA in Gartland type 2A fractures was a predictor of unstable fractures and an indication for pinning.¹⁸ Sukvanich et al. reported that SCA values less than 40° and LCHA values less than 50° were effective in diagnosing incomplete supracondylar fractures in lateral elbow films.¹⁹ According to Mulpruek et al., SCA can serve as a sagittal alignment reference during surgery to reduce displaced lateral condyle fractures in children. However, it is believed that the SCA is more closely related to supracondylar fractures than lateral condyle fractures. Lateral condyle fractures are intra-articular and can result in intra-articular stepping or malrotation and reduced postoperative range of motion. The displacement of the capitellum following a lateral condyle fracture has a direct impact on the SCA, but the SCA cannot identify capitellum malrotation. Thus, relying solely on SCA to predict the success of lateral condyle fracture treatment may be insufficient. Supracondylar fractures, on the other hand, occur extra-articularly and result in distal humerus extension, leading to a change in the center of elbow rotation and SCA. As a result, SCA should be more accurate in predicting postoperative range of motion in supracondylar fractures compared to lateral condyle fractures.

Inadequate reduction of supracondylar fractures can result in long-term functional deficits, leading to prolonged rehabilitation and potentially repeated visits to the clinic. While the anterior humeral line has traditionally been used to diagnose these fractures, it has been shown to be a poor predictor of functional outcomes. Therefore, we consider intraoperative measurement of the SCA to be a valuable parameter in the evaluation of reduction and optimizing patient outcomes. Although it can be challenging to measure, we think it's worth taking the time to do so, since every available parameter should be utilized to assess the reduction and ensure the best possible outcome. As Rashid et al. have pointed out, combining multiple radiographic parameters can give a more accurate assessment of reduction than any one measurement alone.²⁰ Therefore, we recommend that surgeons incorporate the SCA measurement into their intra-operative evaluation of supracondylar fractures to achieve the best possible outcomes for their patients.

While it is true that the most accurate way to determine the normal SCA for an individual patient is by measuring the contralateral uninjured SCA, we avoided additional radiation exposure to the children in our study. It's worth noting that using the average SCA value at 40° for analysis is a common practice in the literature and has been used in previous studies on SCA in children with supracondylar fractures.^18,19 We found that achieving an SCA within 7.65 degrees of the normal value significantly reduced elbow flexion deficits at 6 weeks post-operatively. Among the 36 patients in our study, 18 (50 %) achieved a post-operative SCA within 7.65 degrees of the normal value, which was associated with better recovery of elbow flexion. In contrast, the remaining 18 patients (50 %) with SCA values outside this range experienced greater flexion deficits. These findings highlight the importance of achieving a post-operative SCA close to the normal value during surgical reduction to minimize functional limitations and optimize recovery. After reducing the fracture, the intra-operative fluoroscope should be obtained and printed out for the assistant to measure the SCA while the surgeon maintains reduction. By measuring this angle before introducing the k-wire for internal fixation, the surgeon can employ SCA as intra-operative reduction guidance. Lee et al. developed a treatment-based classification of extension-type supracondylar humerus fractures based on Baumann's angle and SCA, and measured these angles immediately after surgery, one week later, and during follow-up visits four to five weeks later.²¹ However, we considered measuring the angles immediately after surgery impractical due to the k-wire and slab immobilization, so we used x-rays at 6 weeks to examine the SCA and LCHA.

In terms of reliability, our study showed that the SCA had good inter-observer and intra-observer reliability, which is consistent with previous research.^7,8 On the other hand, the LCHA demonstrated excellent inter- and intra-observer reliability, which was higher than in previous studies.^3,5 The experience level of the observer was found to be a significant factor affecting reliability, with non-medical personnel being the primary influencer.⁸ Intra-observer reliability was at least good for orthopedic residents and pediatric orthopedists, who use the SCA as guidance during surgery.

Our study has several limitations that should be considered when interpreting the results. Firstly, the follow-up duration was limited to 6 weeks post-surgery, which may not fully capture long-term outcomes. However, previous research by Wang et al. found that patients with supracondylar fractures achieved 90 % range of motion in extension, flexion, supination, and pronation directions within 6 weeks of treatment.²² Moreover, Nikolic et al. reported that bone remodeling for distal supracondylar humerus fractures is relatively low.²³ Therefore, we believe that the range of motion assessed at 6 weeks serves as a reliable early indicator of the final outcome, particularly given the plaster application duration of 3 weeks. However, we acknowledge that a longer follow-up period, such as 6–12 months, could provide more comprehensive insights into the recovery process. We plan to consider a longer follow-up period in future studies. Secondly, we used the average values reported in the literature as a reference for analysis, but the SCA and LCHA values may vary across different races and ages. Although we ensured that our patient population was homogenous in terms of ethnicity and age range to minimize variability, future studies should consider demographic-specific normal values of SCA and LCHA to enhance the accuracy of these measurements in different populations. Thirdly, our study's sample size is relatively small, which may limit the generalizability of our findings. However, we conducted a sample size calculation and found it to be adequate to ensure that our study contributes valuable data by reinforcing the importance of SCA and LCHA in the context of pediatric supracondylar humeral fractures. We aim to conduct larger, multicenter studies in the future to further validate our findings and contribute more significantly to the existing literature. Lastly, the absence of pre-operative SCA measurements limits our ability to directly compare alignment across the pre-operative, intra-operative, and post-operative stages. This gap restricts a thorough evaluation of the maintenance of reduction over time. Future studies should incorporate pre-operative measurements to gain a more comprehensive understanding of the relationship between fracture alignment and functional outcomes.

6 Conclusion

Our study has demonstrated a significant association between SCA and elbow flexion loss at 6 weeks post-operative in children with supracondylar humerus fractures. These findings emphasize the importance of evaluating SCA using intraoperative fluoroscopy and aiming for a value within 7.65 degrees of the normal range at 40 degrees of elbow flexion. By adopting this approach, surgeons can potentially improve outcomes and reduce post-operative elbow flexion deficits in these patients.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Patient consent

Informed consent was obtained from all individual participants included in the study. The study protocol was thoroughly explained to all participants, and written consent was obtained prior to their enrollment. For patients who were minors or unable to provide consent on their own, written consent was obtained from their legal guardians.

Ethical statement

This study was conducted in accordance with the principles outlined in the Declaration of Helsinki. Ethical approval was obtained from the Strategic Wisdom and Research Institute, the ethics committee of Srinakharinwirot University (SWUEC/E−374/2563). Informed consent was obtained from all individual participants included in the study prior to enrollment. For participants unable to provide consent, written consent was obtained from their legal guardians. Confidentiality of all participant data was strictly maintained throughout the research process.

Ethical approval

Approval was obtained from Strategic Wisdom and Research Institute, ethic committee of Srinakharinwirot University (SWUEC/E−374/2563).

Credit author statement

Pawaris Sukvanich: contributed to the study conception and design. Chanavee Jirapornkul: Material preparation, data collection and Formal analysis were performed by, The first draft of the manuscript was written by. Ronnachit Boonprasert: The first draft of the manuscript was written by. Pinkawas Kongmalai: contributed to the study conception and design, reviewed and edited on previous versions of the manuscript. All authors read and approved the final manuscript.

Consent to publish

The authors affirm that human research participants provided informed consent for publication of all data in the manuscript.

Availability of data and materials

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Funding

The research leading to these results received funding from Srinakharinwirot university. (Grant number 541/2563)