Abstract
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This review focuses on the anatomic and radiographic characteristics of the pediatric proximal femur and the advantages and disadvantages of different protocols for the management of pediatric femoral neck fractures (PFNFs) in terms of fracture classification, reduction methods, reduction quality and fixation methods, with the goal of proposing an optimal treatment protocol for PFNFs to reduce the incidence of postoperative complications.
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The anatomic and radiographic characteristics of the pediatric proximal femur, including the presence of an active growth plate, an immature femoral calcar, greater trabecular density and plasticity and a relatively immature blood supply are very different from those of the adult proximal femur.
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Treatment protocols for PFNFs must differ from those for adult femoral neck fractures.
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PFNFs with posterior translation, and those with comminuted medial-posterior columns, are associated with a higher postoperative complication rate.
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This review suggests that the degree of damage to the nutrient vessels along the posterior femoral neck and the stability of the medial-posterior column of the femoral neck should be well assessed in patients with PFNFs for both classification and treatment purposes.
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Anatomic reduction through an anterior approach, placement of a small number of implants in the mid-inferior part of the femoral neck and additional external support are effective in reducing postoperative complications in patients with PFNFs.
Introduction
Pediatric femoral neck fractures (PFNFs) are very rare, accounting for approximately 0.3–0.5% of all pediatric fractures, and are caused mostly by high-energy trauma (1, 2, 3, 4). The complications of PFNFs including femoral head avascular necrosis (AVN) (20–29%), delayed union or nonunion (10–24%) and premature physeal closure (PPC) (20–62%) are relatively common and increase the risk of morbidity and the difficulty of management (1, 2, 5, 6, 7, 8, 9, 10, 11, 12, 13). Recent reports have indicated that complications of PFNFs are related not only to the anatomic and radiographic features of the fracture, such as the amount of displacement and the comminution of the medial-posterior column, but also to treatment, such as reduction and fixation methods (14, 15, 16, 17). However, the low incidence of PFNFs and the lack of clinical experience are responsible for the insufficient understanding of PFNFs and inappropriate treatment (1, 2, 3, 4). In addition, owing to the lack of pediatric orthopedic specialists and facilities worldwide, most PFNFs are treated by adult orthopedic surgeons, who often use adult treatment protocols for PFNFs (1, 2, 3, 4, 18, 19, 20, 21, 22, 23, 24). However, the anatomic and radiographic characteristics of the pediatric proximal femur, including the presence of an active growth plate, an immature femoral calcar, greater trabecular density and plasticity and a relatively immature blood supply vastly differ from those of the adult proximal femur (25, 26, 27, 28). Therefore, treatment protocols for PFNFs must differ from those for adult femoral neck fractures.
In addition, owing to the low incidence of PFNFs, the conclusions of most previous reports based on small samples are controversial and lack sufficient statistical power, resulting in a lack of consensus on the management protocol for such injuries (29). In recent years, owing to the increase in research on PFNFs based on large samples and progress of research on the anatomic and radiographic characteristics of the pediatric proximal femur, treatment protocols for PFNFs have gradually evolved. In particular, protocols that take into account the anatomic and radiographic characteristics of the pediatric proximal femur have been reported to be effective in reducing the postoperative complication rate of PFNFs, although these protocols have not been narratively reviewed (14, 15, 17, 30).
Therefore, on the basis of recent research advances, this review focuses on the anatomic and radiographic characteristics of the pediatric proximal femur and the advantages and disadvantages of different treatment protocols for PFNFs, from classification to surgery. In particular, the following questions will be addressed with the aim of revealing the optimal treatment protocol for PFNFs to therefore reduce the incidence of postoperative complications: i) which classification of PFNFs better reflects the anatomic and radiographic characteristics of the pediatric proximal femur? ii) Does open reduction of PFNFs increase the incidence of postoperative complications? iii) Why is high-quality anatomic reduction of PFNFs necessary? iv) How can internal fixation of PFNFs reduce the incidence of postoperative complications?
Literature search and article selection
In this narrative review, a literature search on the classification, treatment and complications of pediatric and adult femoral neck fractures and the anatomic and radiographic characteristics of the pediatric and adult proximal femur was conducted using the electronic PubMed database to address the four clinical questions proposed above.
Specifically, the literature on the treatment protocols for pediatric and adult femoral neck fractures was found by searching the database using keywords including ‘pediatric femoral neck fractures’ and ‘adult femoral neck fractures’. In addition, the anatomic and radiographic characteristics of the proximal femur were determined according to the literature obtained by searching the database using keywords including ‘anatomy of the proximal femur’, ‘blood supply of the proximal femur’, ‘medial circumflex femoral artery’, ‘biomechanics of the proximal femur’, ‘trabecular bone in children’, ‘femoral neck-shaft angle’, ‘femoral anteversion angle’ and ‘femoral calcar’.
Due to the low incidence of PFNFs and the limited statistical power of studies with small numbers of patients, the answers to the four clinical questions above were mainly based on studies with adequate statistical power, especially multicenter studies, meta-analyses, prospective studies and studies with large samples (1, 2, 3, 4).
Of the previous studies, only those that presented treatment protocols based on the anatomic and radiographic characteristics of the pediatric proximal femur were used to support the answers to the four clinical questions, including the advantages and disadvantages of different treatment protocols.
In addition, the proposed treatment protocols for PFNFs, from classification to surgery, were based on studies that discussed the anatomic and radiographic characteristics of the pediatric proximal femur in relation to PFNFs, which had adequate statistical power, and were therefore considered representative (5, 6, 14, 15, 17, 30).
Answers to the four clinical questions
Which classification of PFNFs better reflects the anatomic and radiographic characteristics of the pediatric proximal femur?
The role of fracture classification is to predict the outcome or risk of potential complications and to guide surgical treatment. The Delbet–Colonna classification, which divides PFNFs into four types according to fracture location (transepiphyseal, transcervical, cervicotrochanteric and intertrochanteric), has been used in clinical practice for about a century (31). However, its clinical significance has been questioned recently (7, 14, 32, 33). In particular, several studies have failed to identify which fracture subtype according to the Delbet–Colonna classification as a risk factor for postoperative complications, including AVN, delayed union or nonunion and PPC (7, 14, 32, 33). In addition, the Delbet-Colonna classification does not include a classification for other types of PFNFs, such as those involving the comminution of the medial-posterior column and those involving the passage of fracture lines through both the cervical and cervicotrochanteric or both the cervicotrochanteric and intertrochanteric portions of the femoral neck (31, 34). A number of recent studies have identified medial-posterior comminution as a risk factor for postoperative complications, including AVN and delayed union or nonunion, in surgically treated patients with PFNFs (15, 30, 32). In addition, the Delbet–Colonna classification does not evaluate the severity of displacement other than fracture location, which has been shown to be a risk factor for a higher incidence of AVN and delayed union or nonunion (6, 14, 32). Therefore, the Delbet–Colonna classification may not be sufficient for guiding the surgical strategy for patients with PFNFs.
The clinical significance of the Delbet–Colonna classification is limited by the similarity of the anatomic and radiographic characteristics of PFNFs located in different regions, especially for those classified as Delbet–Colonna type II and type III fractures. The femoral calcar, an important anatomic structure located within the medial-posterior portion of the proximal femoral medullary cavity, which is absent at birth, matures with weight gain and can effectively counteract the torsional and shear stresses generated by the femoral neck-shaft angle and anteversion angle during weight-bearing activities (Fig. 1) (25, 26, 27, 28, 35, 36, 37, 38); previous reports indicate that the bone trabecule within the femoral neck medullary cavity is not fully oriented until 16 years of age (25, 26, 27, 28, 35, 36, 37, 38). As a result, there was no significant difference in biomechanical stability between Delbet–Colonna type II and type III PFNFs due to the similar strength of the femoral calcar and trabecular bone within the transcervical and cervicotrochanteric portions of the femoral neck (25, 26, 27, 28, 35, 36, 37, 38). In addition, even the superior retinacular artery (SRA), which runs along the superior femoral neck and is a prominent source of blood supply to the femoral head, decreases in caliber and distance from the femoral neck surface as it approaches the femoral head (39, 40, 41, 42, 43); however, the Delbet–Colonna classification of PFNFs does not take into account the direction of fracture displacement or the degree of damage to the nutrient vessels, but only the location of the fracture, which limits the ability of the classification to estimate the risk of complications, especially in surgically treated patients (14, 32, 33, 44).
The femoral neck-shaft angle (A) and anteversion angle (B) show that the medial-posterior column (C) of the femoral neck is an important anatomical structure that carries loads during weight-bearing (red arrow), and thus that there is more biomechanical stability in PFNFs (D) without comminuted medial-posterior columns than in those with comminutions (E).
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
Several studies have shown that the complications of PFNFs are related mainly to the comminution of the medial-posterior column of the femoral neck and the destruction of the nutrient vessels running along the posterior part of the proximal femur (Figs 1 and 2) (15, 30, 32). The vascular network formed by the intersection of several branches of the medial circumflex femoral artery (MCFA) is located posteriorly along the neck of the femur and is the major source of blood supply to the femoral head, whereas the lateral circumflex femoral artery, located anteriorly, contributes very little to the femoral head blood supply (Fig. 2) (39, 40, 41, 42, 43). In addition, owing to the femoral neck-shaft angle and the anteversion angle of the proximal femur, the medial-posterior column of the proximal femur plays an important role in supporting loads during weight-bearing and resisting both torsional and shear stresses (Fig. 1) (35, 36, 37, 38). Furthermore, the location and function of the femoral calcar described above further illustrate the importance of the medial-posterior portion of the femoral neck (Fig. 1) (35, 36, 37, 38). Therefore, to effectively guide treatment and evaluate the prognosis of PFNFs, the optimization of the classification should improve the assessment of the degree of damage to the nutrient vessels along the posterior femoral neck and the stability of the medial-posterior column of the femoral neck (Figs 1 and 2).
The nutrient vessels (A) running along the posterior part of the proximal femur, which are susceptible to injury in PFNFs with posterior (POST) translation (B). ANT: anterior.
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
In this context, the classification of PFNFs recently proposed by Wang et al. is more consistent with the anatomic and radiographic characteristics of the pediatric proximal femur (Figs 3 and 4) (45). On the basis of the direction of displacement of the distal fracture fragment on the lateral radiograph and the presence of comminution of the medial-posterior femoral neck, this classification identifies five types of PFNFs: without anterior or posterior translation (type I), with anterior (type II) or posterior (type III) translation, with a comminuted medial-posterior column (type IV) and with subtrochanteric femoral fractures (type V) (Figs 3 and 4). Therefore, this novel classification better assesses potential damage to the nutrient vessels running along the posterior proximal femur and the stability of the medial-posterior femoral neck column (Figs 3 and 4) (45). Research has shown that the incidence of AVN in PFNFs with posterior translation is significantly higher than that in those with no translation or anterior translation (15). In particular, posterior displacement of more than 29% of the femoral neck width significantly increases the incidence of AVN (15). In addition, several studies have confirmed that PFNFs with a comminuted medial-posterior column are more prone to develop complications such as AVN, delayed union and nonunion because of the greater likelihood of damaging the MCFA network and failing to achieve sufficient fracture stability, resulting in a worse prognosis (15, 30, 32).
PFNF types according to the new classification system of Wang et al. (45), including type I (A) fractures without anterior (ANT) or posterior (POST) translation (not displaced), type II (B) fractures with anterior translation, type III (C) fractures with posterior translation, type IV (D) fractures with comminuted medial-posterior columns and type V (E) subtrochanteric fractures with any direction of displacement.
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
Radiographs of different types of PFNFs according to the new classification system reported by Wang et al. (45), including type I without translation, type II with anterior translation, type III with posterior translation, type IV with a medial-posterior comminution (white arrow) and type V with the subtrochanteric femoral fracture.
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
In conclusion, compared with the widely accepted Delbet–Colonna classification, the Wang et al. classification is better correlated with the anatomic and radiographic characteristics of the pediatric proximal femur and may be more appropriate and accurate for guiding the management of PFNFs (31, 45).
Does open reduction of PFNFs increase the incidence of postoperative complications?
Displaced PFNFs can be satisfactorily reduced with both closed and open reduction techniques (16, 46). Previous reports indicate that the quality of reduction is better with open reduction than with closed reduction, mainly due to the instability of proximal fracture fragments, potential soft tissue incarceration and hematoma formation between fracture fragments (16, 46). In addition, repeated attempts to successfully reduce the fracture with closed reduction may cause secondary damage to the blood supply to the femoral head and surrounding soft tissues. In contrast, open reduction can achieve better reduction quality because of direct visualization of the fracture fragments (16, 46). Currently, open reduction of PFNFs is performed mainly through anterior approaches such as the Smith–Peterson, Watson–Jones and direct anterior approaches (47, 48, 49, 50, 51, 52). Although the surgical approach that provides the best reduction quality is unknown, several reports have shown that the Smith–Peterson and direct anterior approaches might provide better reduction quality (47, 48, 51).
Numerous reports have shown that anatomic reduction of PFNFs is crucial for reducing the incidence of postoperative complications (Figs 5, 6, 7, 8) (14, 30, 32, 53). However, whether open reduction of PFNFs through an anterior incision will cause additional damage to the blood supply, bone fragment and soft tissues, thereby increasing the incidence of postoperative complications, has always been a concern for surgeons. Owing to the recent progress of research on PFNFs and proximal femoral blood vessels, open reduction of PFNFs has been increasingly recommended (14, 30, 32, 33, 43). Surgeons have increasingly reported that open reduction of PFNFs does not increase the incidence of AVN, delayed union or nonunion or PPC (5, 14, 30, 32, 54). Following single and multifactorial analyses, Wang et al. reported that the method of reduction of PFNFs was not a risk factor for AVN in 239 patients (14). Similar results were reported in a meta-analysis by AlKhatib et al. that included 230 PFNFs (54). In addition, a multicenter study revealed that the reduction method for PFNFs was not a risk factor for complications such as delayed union or nonunion (30, 32). A systematic review of 935 patients with PFNFs also reported similar results, with no significant difference in the rate of nonunion between PFNFs treated with open reduction and those treated with closed reduction (5). Furthermore, Wang et al. and Kong et al. reported that the method of reduction of PFNFs was not a risk factor for PPC (33, 55). In conclusion, open reduction provides high-quality reduction without increasing the incidence of postoperative complications in patients with PFNFs treated appropriately (5, 14, 30, 32, 54, 56).
Preoperative (A) and postoperative (B, C and D) radiographs of a 6-year-old girl with a unilateral displaced femoral neck fracture. Radiograph (B) taken on the second day after surgery shows that a ‘positive support reduction’ (white arrow) with the medial cortex of the proximal fracture fragment outside that of the distal fracture fragment was achieved after closed reduction and fixation with two large cannulated screws; radiographs (C and D) taken at the 16-month follow-up show the avascular necrosis of the femoral head and the premature closure of the proximal femoral physis of the injured side (C) in relation to those of the uninjured side (D).
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
Preoperative (A) and postoperative (B, C and D) radiographs of a 14-year-old boy with a unilateral displaced femoral neck fracture. Radiograph (B) taken on the second day after surgery shows that a ‘positive support reduction’ (white arrow) with the medial cortex of the proximal fracture fragment outside that of the distal fracture fragment has been achieved after closed reduction and three cannulated screws fixation; radiograph (C) taken at the 6-month follow-up shows delayed fracture union; radiograph (D) taken at the 7-month follow-up shows fracture union.
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
Preoperative (A) and postoperative (B, C and D) radiographs of a 4-year-old boy with a unilateral displaced femoral neck fracture. Radiograph (B) taken on the second day after surgery shows that ‘negative support reduction’ (white arrow) with the medial cortex of the proximal fracture fragment medial to that of the distal fracture fragment was achieved after open reduction and fixation with two cannulated screws; radiographs taken at the 13-month follow-up show avascular necrosis of the femoral head and premature closure of the proximal femoral physis of the injured side (C) in relation to those of the uninjured side (D).
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
Preoperative (A) and postoperative (B, C and D) radiographs of a 11-year-old boy with a unilateral displaced femoral neck fracture. Radiograph (B) taken on the second day after surgery shows that a nonanatomical reduction quality with residual displacement and angular deformity was achieved after open reduction with cannulated screws and plate and Kirschner fixation; radiographs taken at the 38-month follow-up show the avascular necrosis of the femoral head and neck and the narrow and short femoral neck deformity (C) when compared with those of the uninjured side (D).
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
The physiologic and anatomic characteristics of the pediatric proximal femur may elucidate the mechanism by which open reduction of PFNFs through the anterior approach has no effect on the incidence of postoperative complications. The branches of the MCFA mainly include the SRA, the inferior retinacular artery (IRA) and the anterior retinacular artery (ARA), which are located in the superior, inferior and anterior femoral neck, respectively (Fig. 9) (43, 57). The SRA and IRA are important sources of femoral head blood supply, but the ARA is usually smaller in caliber, has fewer anastomoses and is often absent (Fig. 9) (43, 57). Furthermore, compared with that of the tissues around the posterior proximal femur, the functional importance of the tissues around the anterior proximal femur is limited by the femoral neck-shaft angle and anteversion angle in children (Fig. 1) (58, 59, 60, 61). In addition, with the development of vascular imaging techniques, it has been reported that the nourishing vessels within the femoral neck are connected to the SRA and IRA, and that this vascular network supplies more blood to both the neck and head of the femur than the ARA does (Fig. 9) (43, 57). Therefore, open reduction of PFNFs through the anterior approach does not diminish the nutritional blood supply of the proximal femur and instead allows for better reduction quality. However, it should be performed carefully and soft tissues should be protected to minimize the risk of iatrogenic injury.
The vascular network (A) formed by the intersection of the nutrient vessels (black and white boxes in (A)) within the femoral neck, including the superior retinacular artery (SRA) with small caliber and fewer anastomoses to the nutrient vessels within the medullary cavity in the superior region (black box) and the inferior retinacular artery (IRA) with larger diameter and more anastomoses to the nutrient vessels within the medullary cavity in the inferior region (white box), which would be destroyed after bone fracture (B) and implant insertion (C).
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
Why is high-quality anatomic reduction of PFNFs necessary?
In 2013, Gotfried et al. first proposed the concept of ‘positive support reduction’, which refers to the quality of reduction of femoral neck fractures (Figs 10 and 11) (23). This concept is not characterized by ‘classic’ anatomic reduction quality with no residual displacement or angular deformity but is instead characterized by the presence of the medial cortex of the proximal fracture fragment outside that of the distal fracture fragment on anteroposterior (AP) radiographs (Figs 10 and 11). Conversely, ‘negative support reduction’ is described as the presence of the medial cortex of the proximal fracture fragment medial to that of the distal fracture fragment on AP radiographs (Figs 10 and 11). Gotfried et al. introduced this concept after following five adult patients with ‘positive support reduction’ of femoral neck fractures for 12 months and reported that none of the patients experienced secondary displacement, nonunion or AVN, hypothesizing that the prognosis of fractures subjected to ‘positive support reduction’ might be better than that of those subjected to ‘classic’ anatomic reduction (23). Many studies have shown that ‘positive support reduction’ is an acceptable treatment for femoral neck fractures in adults and has some advantages over ‘classic’ anatomic reduction, especially for fractures that are difficult to reduce with closed reduction (62, 63, 64, 65). A retrospective study of 46 adult femoral neck fractures revealed that there was no significant difference in the incidence of postoperative coxa vara, internal fixation failure, nonunion or AVN between patients (n = 16) who had ‘positive support reduction’ and those (n = 30) who had anatomic reduction (62). Zhao et al. and Huang et al. reported similar clinical results and opinions in that once ‘positive support reduction’ of adult femoral neck fractures was achieved, anatomic reduction was not necessary (63, 64). Wang et al. also reported that the promotion of osteogenesis and angiogenesis at fracture sites was the main reason for the good prognosis of femoral neck fractures with ‘positive support reduction’ (65).
Three types of reduction quality of surgically treated PFNFs on anteroposterior (AP) radiographs, including anatomic reduction quality (A) with no residual displacement or angular deformity, ‘positive support reduction’ (B) with the medial cortex of the proximal fracture fragment outside that of the distal fracture fragment and ‘negative support reduction’ (C) with the medial cortex of the proximal fracture fragment medial to that of the distal fracture fragment.
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
Different types of reduction quality of surgically treated PFNFs on anteroposterior radiographs, including anatomic reduction quality (A) with no residual displacement or angular deformity (red arrow), ‘positive support reduction’ (B) with the medial cortex of the proximal fracture fragment outside that of the distal fracture fragment (white arrow) and ‘negative support reduction’ (C) with the medial cortex of the proximal fracture fragment medial to that of the distal fracture fragment (yellow arrow).
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
On the basis of the anatomy of the proximal femur, the main reason why ‘positive support reduction’ is suitable for the treatment of adult femoral neck fractures is related to rigid femoral calcars present in adults (35, 36, 37, 38). When ‘positive support reduction’ is achieved, the femoral calcar, which is located in the medial-posterior part of the proximal femoral cavity, is connected with the posterior cortex, and thicker than the cortex, and can provide sufficient mechanical support to the medial cortex (28, 35, 36, 37, 38). On the other hand, in cases of ‘negative support reduction’, the lack of sufficient medial support leads to poorer fracture fragment stability, resulting in a higher incidence of postoperative complications (63, 64). In addition, the femoral neck-shaft angle and anteversion angle make the proximal fracture fragment susceptible to downward displacement under mechanical forces, following fracture site bone absorption (23, 66, 67). Therefore, there is a possibility of a transition from anatomic reduction to ‘negative support reduction’ (23, 66, 67). However, in fractures with ‘positive support reduction’, the medial cortex of the distal fragment may provide sufficient mechanical support for the proximal fragment even if the proximal fragment displaces downward following bone absorption (23, 63, 64, 66, 67).
Is ‘positive support reduction’ of PFNFs achievable? The answer is probably no (Figs 5 and 6). Several reports indicate that anatomic reduction rather than nonanatomic reduction of such fractures can effectively reduce the incidence of AVN, delayed union or nonunion in PFNFs patients (8, 14, 53, 68). A retrospective multicenter study of 103 PFNFs treated with closed reduction revealed that the incidence of AVN was lower in patients who underwent anatomic reduction than in those who underwent nonanatomic reduction (14). Stone et al., Shrader et al. and Morsy et al. also reported similar findings (8, 53, 68). In addition, the quality of reduction of PFNFs has also been correlated with the incidence of delayed union or nonunion (8, 16, 32, 68). Wang et al. evaluated the factors affecting the healing of PFNFs (n = 177) and reported that PFNFs subjected to anatomic reduction were more likely to heal with a lower incidence of delayed union or nonunion than those subjected to nonanatomic reduction (32). Morsy et al., Stone et al. and Song et al. also reported similar clinical outcomes (8, 16, 68).
The reason that ‘positive support reduction’ is more appropriate for treating adult femoral neck fractures than PFNFs is that the pediatric femoral calcar is relatively weak and not as rigid as the adult calcar because it is not fully mature (28, 35, 36, 37, 38). Therefore, in PFNFs with ‘positive support reduction’, the weak femoral calcar does not provide adequate medial mechanical support and the risks of further fracture displacement and coxa vara deformity increase (28, 35, 36, 37, 38). In addition, another reason is that the osteogenic ability of adults is inferior to that of children (69, 70, 71). Adult femoral neck fractures require more time to heal than PFNFs do and have an increased risk of fracture displacement due to fracture line bone resorption (32, 66, 67, 72, 73, 74); thus, ‘positive support reduction’ can provide long-term stability in surgically treated adult femoral neck fractures (32, 66, 67, 72, 73, 74). However, even in the presence of bone resorption at the fracture site, the superior osteogenic capacity of children can effectively prevent fracture displacement (32, 66, 67, 72, 73, 74). In addition, the use of casts or brace immobilization further improves fracture stability in children compared with adults, who, for obvious reasons, are not regularly immobilized with casts or braces postoperatively (Figs 12 and 13) (30, 75). Moreover, the greater body weight of adults places more shear stress on the fracture site as the affected limb is mobilized, which may further increase the risk of secondary displacement and nonunion (76, 77).
The optimal treatment protocol for PFNFs, including anatomic reduction (A), placement of a small number of smaller implants in the mid-inferior part of the femoral neck without the need for parallel insertion (A and B) and additional external support (C).
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
Preoperative (A) and postoperative (B, C and D) radiographs of a 6-year-old boy with a unilateral displaced femoral neck fracture. Radiograph (B) taken on the second day after surgery shows that an anatomical reduction quality was achieved after open reduction and internal fixation with two small-diameter cannulated screws inserted in the mid-inferior part of the femoral neck and cast immobilization; radiographs taken at the 15-month follow-up show the femoral head without avascular necrosis and the growth plate without premature closure and the femoral neck without narrow and short deformity (C) when compared with those of the uninjured side (D).
Citation: EFORT Open Reviews 10, 3; 10.1530/EOR-2024-0129
In summary, the differences in anatomic and radiographic characteristics between adults and children align with the differences in the goals of treatment for such fractures in adults and children. In particular, ‘positive support reduction’ is suitable for adult femoral neck fractures, whereas anatomic reduction is required for PFNFs (Figs 5, 6, 7, 8, 12 and 13).
How can internal fixation of PFNFs reduce the incidence of postoperative complications?
Internal fixation of PFNFs can effectively maintain the reduction quality and provide the mechanical stability required for fracture healing, especially for unstable, severely displaced fractures (17, 30). Besides the damage of nutrient vessels within femoral neck following bony break, distal-to-proximal insertion of hardware to fix such fractures also inevitably results in damage to the nourishing vessels within femoral neck, depending on the number, size and location of the fixators (Figs 5 and 9) (17, 78, 79). As mentioned above, the nutrient vessels within the medullary cavity are an important source of blood supply to the proximal femur, so the number, size and location of fixators can potentially increase the incidences of AVN, delayed union, nonunion and PPC (Figs 5 and 9) (39, 40, 41, 42, 43). In addition, the growth plate can be damaged if it is injured by the hardware used to fix the fracture (80, 81). Therefore, the goal of internal fixation for PFNFs should be to provide sufficient stability and reduce the postoperative complication rate as much as possible.
The types of fixators for PFNFs include the following: Kirschner wires, cannulated screws and screw and plate fixation (6, 14, 82). However, according to the reports published over the past two to three decades, cannulated screws and screw and plate fixation have been used more frequently than Kirschner wires (6, 14). In another retrospective study of PFNFs (n = 70), only six patients (8.6%) were treated with Kirschner wire fixation (6). In a multicenter retrospective study of 241 PFNFs, only seven cases (2.9%) were fixed with Kirschner wires, whereas the remaining 234 PFNFs (97.1%) were treated with cannulated screws (n = 193, 80.1%) or screw and plate fixations (n = 41, 17%) (14).
Previous reports have confirmed that for surgically treated PFNFs, hardware type is not a risk factor for AVN, delayed union, nonunion or PPC despite variations in the type of hardware used (6, 14, 32, 33, 82). Several reports have shown that threaded Kirschner wire fixation of PFNFs can achieve satisfactory results (83, 84). These results are attributed mainly to the large and densely distributed pediatric bone trabecule within the femoral neck medullary cavity (72, 73, 74). Therefore, the insertion of Kirschner wires or cannulated screws can effectively grasp the bone trabecule within the medullary cavity and thereby provide sufficient stabilization of PFNFs (6, 14).
The number and diameter of cannulated screws used to fix such fractures may compromise the blood supply from the medullary cavity (Figs 5 and 9) (17, 78, 79). Currently, two or three cannulated screws are commonly used to treat PFNFs instead of a single cannulated screw, which cannot effectively prevent rotational displacement of fracture fragments (17, 30). The greater the number and diameter of cannulated screws inserted into the medullary cavity of the femoral neck, the greater the potential damage to the nutrient vessels within the medullary cavity that supply the femoral head and the greater the risk of AVN (Figs 5 and 9) (17, 39, 43, 78, 79). Moreover, a multicenter study revealed that the incidence of AVN in PFNFs treated with three cannulated screws was significantly higher than that in those treated with two, and cannulated screws with diameters exceeding 16.5% of the width of the femoral head significantly increased the incidence of AVN (17). Lykke et al. and Razik et al. also reported similar results (78, 79).
In addition, the time required for union of PFNFs does not correlate with the number or diameter of the cannulated screws used to fix the fracture, although more cannulated screws with larger diameters may increase mechanical stability (30, 53, 85). Wang et al. reviewed 136 cases of surgically treated PFNFs and reported no significant difference in the time to union between PFNFs treated with two cannulated screws and those treated with three (30); they also reported that the diameter of the cannulated screw had no effect on the time to PFNF union (30). Shrader et al. and Pavone et al. also reported similar results (53, 85). In addition, owing to the limited space within the pediatric femoral neck, the difficulty of inserting three cannulated screws to fix the fracture is significantly greater than that of inserting two. Therefore, if anatomic reduction can be achieved, the placement of two small-diameter cannulated screws can provide sufficient mechanical stability for fracture union and reduce the AVN rate (17, 30, 53, 78, 85, 86).
On the other hand, three cannulated screws are generally used to treat such fractures in adults (87, 88, 89). This discrepancy with PFNFs might be due to the significant differences in the anatomic and physiologic characteristics of the proximal femur between adults and children (39, 43, 69, 70, 71). The nutrient vessels within the medullary cavity of the proximal femoral head and the proximal femur epiphysis do not fully interconnect until closure of the proximal femoral growth plate (Fig. 9) (39). Therefore, it is hypothesized that despite the destruction of the nutrient vessels in the medullary cavity after the insertion of a considerable amount of implants, the blood supply to the femoral head is still adequate because the vascular network of nutrient vessels connecting the inner and outer parts of the femoral neck is more developed in adults than in children (39, 43). In addition, the healing time for adult femoral neck fractures is longer than that for PFNFs because of the inferior osteogenic capacity in adults, so multiple cannulated screws with larger diameters can provide long-term mechanical stability in adults (69, 70, 71, 72, 73, 74).
The position of the hardware must be considered when treating PFNFs. As mentioned above, the medial column of the femoral neck plays a more important role than the lateral column in counteracting mechanical forces (Fig. 1) (35, 36, 37, 38). Therefore, when placed in the mid-medial part of the femoral neck, the implants can effectively improve the stability of the fracture fragments (Figs 12 and 13). Most importantly, the location of the SRA and IRA supports the strategy of placing cannulated screws in the mid-medial part of the femoral neck (Fig. 9) (39, 43). While the SRA is located closer to the superior cortex of the femoral neck and has a smaller diameter and fewer anastomoses to the nutrient vessels within the medullary cavity, the IRA is located further from the inferior cortex and has a larger diameter and more anastomoses to the nutrient vessels within the medullary cavity (Fig. 9). Therefore, owing to the presence of more vessels and anastomoses, the mid-inferior area of the medullary cavity is safer for implant insertion (Figs 9, 12, 13) (39, 43). In addition, multicenter studies have shown that implants located closer to the inferior cortex of the femoral neck on AP radiographs were associated with a lower postoperative AVN rate in patients with surgically treated PFNFs (15, 17). In conclusion, placing hardware in the mid-inferior part of the femoral neck may provide sufficient stability without compromising the blood supply to the proximal femur and femoral head (Figs 12 and 13).
In addition, owing to the numerous blood vessels distributed behind the femoral neck and the limited vascular contribution of the ARA to the proximal femur, it is not necessary to focus on the position of the cannulated screws on lateral radiographs because of the limited vascular damage of the anterior and posterior medullary cavities (Fig. 12) (39, 43). Several studies have shown that the position of cannulated screws on lateral radiographs is not a risk factor for AVN or delayed union or nonunion in PFNFs treated surgically (17, 30).
It is not necessary to place two cannulated screws parallel in PFNFs during surgery (Figs 12 and 13). Single-factor and multifactor analyses of the correlations between the number, size, position and angle between two cannulated screws and the complications of PFNFs revealed that the angle between two cannulated screws on AP or lateral radiographs is not a risk factor for AVN, delayed union or nonunion (17, 30). Lim et al. and Spangler et al. also reported similar results (90, 91). Regardless of the angle between two cannulated screws, the volume of implants placed in the medullary cavity is nearly the same; therefore, the corresponding degree of damage to the nutrient vessels within the medullary cavity is similar. Therefore, AVN rates and the time to fracture union in surgically treated PFNFs do not vary with the angle between two cannulated screws on AP or lateral radiographs (17, 30).
The threads of cannulated screws located within the proximal fragment allow for full compression of the fragments to improve stability (92, 93). However, in PFNFs with fracture lines closer to the proximal femur growth plate, it is difficult to fully compress the proximal fracture fragment without passing the implants through the growth plate; in addition, full compression may increase the risk of a coxa vara deformity, especially for PFNFs with a comminuted medial-posterior column (Figs 1 and 4). Therefore, the need for full compression between the fragments must be evaluated. Currently, there are few reports on this topic. Some researchers have reported that there is no significant difference in the time required to heal PFNFs between those that are fully compressed and those that are partially compressed with threads at the level of the fracture line (30). Furthermore, previous reports have indicated that Kirschner wires less than 2.0 mm in diameter passing through the growth plate do not cause growth disturbances (6, 14, 80, 81, 94); therefore, a 2.0 mm Kirschner wire through the growth plate could be considered to further improve mechanical stability, especially for unstable PFNFs (6, 14, 80, 81, 94).
Notably, the postoperative complications of surgery for PFNFs are related not only to the placement of the implants but also to the removal of the internal fixator, especially the timing of the removal of the implants (17, 95). According to a multicenter study of 71 PFNFs fixed with cannulated screws, 15.5% of the PFNFs developed or showed signs of worsening AVN of the femoral head or neck after implant removal, and more than 7 months of hardware retention after radiologic healing of PFNFs is associated with a significantly reduced incidence of this complication (95). Hahn et al. also recommend that metal removal should be performed 1 year after surgery in patients with PFNFs treated with cancellous screws (96). Other reports have noted that the earlier the implant is removed, the higher the risks of trabecular fracture and damage to the nutrient vessels within the medullary cavity (97, 98). This phenomenon is related primarily to the destruction of weak, newly formed trabecular bone and nutrient vessels within the medullary cavity during or after hardware removal. The implants shield most of the stress, so newly formed trabecular bone and nutrient vessels around the hardware are subjected to minimal mechanical stimulation, which induces osteogenesis and angiogenesis, during the short period of PFNF union (32, 99, 100, 101). Therefore, the bone strength and vascular network around the implants should be evaluated before hardware removal. Some studies have revealed that if the fixators do not cause complications such as pain or inflammation, they can be retained (102, 103). Currently, there are no reports on whether the long-term retention of implants can cause complications such as osteoporosis in patients with surgically treated PFNFs.
At present, there is no consensus on the optimal time to start weight bearing, which is associated with fewer complications in patients with surgically treated PFNFs. Similarly, the bone strength and vascular network around the implants should be considered before allowing weight-bearing and more intense physical activity. Given that more than 7 months of implant retention after radiographic healing of PFNFs can effectively prevent the occurrence and aggravation of AVN after hardware removal, we suggest delaying intense activity until 7 months after radiographic confirmation of a completely healed PFNF (95).
Notably, rigid external fixation is also crucial for reducing the incidence of postoperative complications in patients with PFNFs treated surgically (Figs 12 and 13) (30, 104, 105). Eberl et al. reported that the rate of secondary displacement of PFNFs treated with internal fixation without additional external support was as high as 54.5% (104). However, a study by Wang et al. revealed a postoperative reduction loss rate of only 0.7% when PFNFs were fixed with internal fixators and provided additional external support (30).
Overall, we propose that after anatomic reduction of PFNFs, two small-diameter cannulated screws in the mid-inferior column of the femoral neck and additional external support for 4–6 months after surgery can effectively maintain the reduction quality and reduce the occurrence of postoperative complications (Figs 12 and 13). For unstable PFNFs, a 2.0 mm Kirschner wire passing through the growth plate could be considered to further improve mechanical stability. Parallel placement of two cannulated screws and full compression of the fracture fragments are not necessary in the treatment of PFNFs (Figs 12 and 13).
Discussion
This narrative review reports the advantages and disadvantages of different treatment protocols for PFNFs in terms of fracture classification, reduction methods, reduction quality and fixation methods, and explains why the treatment protocols for PFNFs taking into account the anatomic and radiographic characteristics of the pediatric proximal femur are optimal and effective in reducing the incidence of postoperative complications.
The optimal classification of PFNFs is expected to predict prognosis and guide treatment. However, previous studies have shown that the Delbet–Colonna classification has limited clinical significance and is not a risk factor for several postoperative complications, including AVN, delayed union or non-union and PPC (7, 14, 31, 32, 33). Recently, numerous reports have shown that damage to the MCFA, which is located behind the proximal femur, and the lack of sufficient mechanical stability of the medial-posterior femoral neck column are responsible for the occurrence of postoperative complications in patients with surgically treated PFNFs (15, 17, 30, 32). Currently, the classification proposed by Wang et al., which classifies PFNFs according to the direction of displacement on lateral radiographs and the comminution of the medial-posterior column, better reflects the anatomic and radiographic characteristics of the pediatric proximal femur, and is more effective in predicting prognosis and guiding treatment than the Delbet–Colonna classification (31, 45).
Our current study recommends open reduction through an anterior approach as an excellent alternative when closed reduction fails to achieve anatomical reduction of PFNFs, as the rate of postoperative complications including AVN, delayed union or non-union and PPC was similar between patients treated with open and closed reduction (5, 6, 8, 14, 16, 54, 106). Such findings are supported by the frequent absence of the ARA, which is usually small in caliber and has few anastomoses; open reduction through an anterior approach would not reduce the nutritive blood supply to the proximal femur and would in fact achieve a better reduction quality (16, 43, 46).
In this regard, due to the immature femoral calcar, femoral neck-shaft angle and femoral anteversion angle in patients with PFNFs, the treatment protocols supporting anatomical reduction, placing implants in the mid-inferior region of the femoral neck and suggesting additional external support to provide sufficient mechanical stability have important clinical implications (15, 28, 35, 36, 37, 38, 104, 107, 108). On the other hand, several studies have shown that the nonanatomical reduction, the insufficient mechanical stability of the medial-posterior column and the absence of external mechanical support are risk factors for postoperative complications due to the lack of a suitable mechanically stable microenvironment (14, 15, 104, 107, 108). Therefore, an appropriate mechanical microenvironment is critical for the tissue repair and regeneration and is effective in reducing the incidence of postoperative complication of PFNFs treated surgically.
However, achieving adequate mechanical stability of surgically treated PFNFs should not result in excessive damage to the nutrient vessels within the medullary cavity, which is inevitable during hardware insertion (17, 78, 79). Studies have shown that increasing the number and size of hardware inserted significantly increases the AVN rate in surgically treated patients with PFNFs (17, 30); such findings may be explained by the fragile network of nutrient vessels and fewer anastomoses of vessels within and outside the femoral medullary cavity in children (39). In addition, due to the larger caliber and more anastomoses of the IRA than the SRA, hardware placement in the mid-inferior femoral neck not only reduces damage to the nutrient vessels within the medullary cavity, but also improves mechanical stability (15, 43).
Finally, bone strength and the vascular network around the hardware should be assessed well before weight bearing and hardware removal, as an inappropriate time to start weight bearing and an inappropriate time to remove hardware would contribute to the occurrence of complications after the healing process is complete (95, 96). According to previous studies, it should be recommended to delay heavy activity and hardware removal until 7 months after radiographic union of the PFNFs to avoid late complications, including AVN (95, 96).
Conclusion
In conclusion, the development of the PFNFs treatment protocol, including fracture classification, reduction methods, reduction quality and fixation methods, must consider the anatomic, physiologic and radiographic characteristics of the pediatric proximal femur. Among these, the open growth plates, immature femoral calcars, superior osteogenic capacity, increased number, density and flexibility of the bone trabecule and fewer anastomoses of vessels within and outside the femoral medullary cavity are unique to children; therefore, adult treatment protocols are not appropriate for PFNFs.
In addition, nutrient vessels, including the MCFA, SRA, IRA and nutrient vessels within the medullary cavity and the medial-posterior column of the femoral neck, are the most important anatomical structures that should be evaluated and protected as much as possible during surgical treatment (Figs 1, 9, 12, 13). Specifically, PFNFs without posterior translation, PFNFs without comminuted medial-posterior columns and PFNFs treated with anatomic reduction through an anterior approach, fixation with a small number of small-sized cannulated screws in the mid-inferior portions of the femoral neck and additional external support are associated with a lower complication rate (Figs 1, 2, 9, 12, 13).
Future prospects
However, there are still many unanswered questions, such as i) whether it is necessary to repair MCFA branches outside the medullary cavity or to use absorbable cannulated screws, which may potentially reduce damage to the intramedullary blood supply during hardware removal; ii) the optimal time to start weight bearing after complete healing of PFNFs; and iii) what training intensity is more appropriate to facilitate remodeling of new bone trabecule. In addition, it is extremely important to verify the accuracy of PFNFs treatment protocols based on the anatomic and radiographic characteristics of the proximal femur through prospective researches with large sample sizes. Furthermore, achieving high-quality anatomic reduction of PFNFs and placement of cannulated screws in the mid-inferior part of the femoral neck in children is crucial to reduce the incidence of postoperative complications; therefore, future studies should take full advantage of interdisciplinary collaboration, medical-engineering collaboration, including research and development of robots that can assist in anatomical reduction of PFNFs and precise placement of cannulated screws. Furthermore, based on the importance of nutrient vessels within the medullary cavity and the need for external support, future studies should also focus on the development of advanced fixation devices, such as cannulated screws with small diameters and good gripping force, cannulated screws with good biological properties, including osteogenesis and angiogenesis induction, and external devices with excellent breathability and stability. Adherence to such principles could further reduce the incidence of postoperative complications following surgical reduction and fixation of PFNFs.
Declaration of interest
The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the work.
Funding
This work was supported by China Postdoctoral Science Foundation (Certificate Number: 2024M762149).
Author contribution statement
W Wang, F Canavese and Z Xiong, jointly designed the study, conducted a thorough literature search and drafted the manuscript. S Chen and S He contributed substantially by preparing the figures, distilling the key findings from the literature, improving the clarity and fluency of the writing and making critical revisions to enhance the quality of the manuscript. In addition, S Tang provided expertise in the conceptualization of the study and assisted in the literature search.
Acknowledgements
We thank the following experts for their participation in this study: Antonio Andreacchio and GuoXin Nan.
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