Introduction

Femoral shaft fractures are a quite common injury, with a reported incidence of 37.1 per 100,000 person-years in the USA [1]. This kind of injury commonly results from high-energy trauma—i.e., motor vehicle accidents, pedestrian accidents, sports injuries, and falls from a height—but they can also be caused by low-energy trauma, especially in older adults with osteoporotic bone [2].

Closed reduction with intramedullary nailing is currently the most used technique in the management of femoral shaft fractures, since it is associated to low non-union, delayed union, and infection rates and to a better functional outcome [2, 3].

Femoral shaft fractures with third fragments, classified as 32-B fracture type according to the Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association classification system (AO/OTA 32-B), account for 10–34% of all femoral shaft fractures [2, 4]. This injury pattern shows a high non-union rate which may reach 14% [5], since the presence of a third fragment makes the anatomical reduction of the fracture challenging, thus interfering with the bone healing [4, 6]. Non-union is defined, according to the Food and Drugs Administration (FDA), as a fractured bone that has not completely healed within 9 months of injury and that has not shown progression towards healing over three consecutive months on serial radiographs [7].

Lee et al. [3], in a retrospective cohort study on 64 femoral shaft fractures with third fragments managed with intramedullary nailing, have recently observed that non-union occurs more frequently in fractures with great third fragment size and high displacement degree. These authors depicted that the displacement degree has more influence on the union rate than the third fragment size.

The role of the displacement degree on the healing time of femoral shaft fractures with third fragments was also observed by An et al. [8]; thus, care should be taken to avoid an excessive displacement of the third fragment during the intramedullary nail implantation.

None of the previous studies, to the authors’ knowledge, however, has quantified how the third fragment features could increase the fracture healing time.

This retrospective study aims to evaluate the impact of the radiological features of the third fragment, evaluated on post-operative X-rays, on the outcome of AO/OTA type 32-B fractures managed with intramedullary nailing, to obtain an algorithm which could predict the fracture healing time.

Materials and methods

Selection of study population: inclusion/exclusion criteria

We retrospectively reviewed a series of 127 patients with femoral shaft fractures referred to our department between January 2009 and January 2016. Clinical and radiological data were obtained from our trauma database.

Inclusion criteria were type 32-B fracture according to AO/OTA classification system, minimum clinical and radiological 12-month follow-up, and surgical management with intramedullary nailing. Exclusion criteria were type 32-A or 32-C fractures according to AO/OTA classification system; surgical management with open reduction and internal fixation; concomitant ipsilateral femoral neck fracture; periprosthetic fractures; exposed fractures; history of infections or malignant neoplasms; osteoporosis, defined as lumbar or hip T score < 2.5; diabetes mellitus; and BMI > 35 kg/m2.

By applying the inclusion and exclusion criteria, 52 patients (33 male and 19 female, mean age 34.6 years old, range 21–58) were recruited for the current study. All the patients had undergone a clinical and radiographic follow-up at one, two, three, six, nine and 12 months post-operatively.

The patients were then divided into three groups according to the fracture healing time:

  • Group A: fracture healing occurred within six months (Fig. 1)

  • Group B: fracture healing occurred between six and 12 months

  • Group C: fracture non-union after 12 months

Fig. 1
figure 1

A group A clinical case: a post-operative X-ray and b 6-month follow-up X-ray

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Surgical management and post-operative care

The average time from trauma to surgery was about 42 hours (range 21–72 h). All the patients were treated by the same surgical team. The intramedullary nailing was always performed after the fracture reduction was obtained on a traction table; anterograde intramedullary reamed nails were used in all surgery. The distal screws were implanted in both static and dynamic holes. The mean length of post-operative hospital stay was eight days (range 6–14 days). Passive mobilization, i.e., static quadriceps exercises and passive mobilization of the knee with an electric motion device, started on post-operative day one. The patients observed a non-weight-bearing until the callus formation, but they were encouraged, under the supervision of a physiotherapist, to mobilize the hip and the knee progressively actively.

After the callus formation, partial weight bearing was authorized with a ten weight increase a week for six weeks.

Radiographic study

Post-operative anteroposterior (AP) and lateral (LL) femur X-rays were analyzed by two orthopaedic surgeons with more than five years of experience in lower limb surgery. On each X-ray, the following parameters (Figs. 2, 3, 4, and 5) were measured in AP view:

  • Third fragment angle (A): defined as the angle between a line parallel to the femoral diaphysis cortex and a line parallel to the third fragment cortex

  • Fracture gap (G): defined as the distance between the proximal diaphysis fragment and the distal one

  • Third fragment size (L): defined as the length of the major axis of the fragment

  • Mean third fragment displacement (M): defined as the perpendicular distance between the midpoint of the fragment and the nearest humeral shaft cortex

Fig. 2
figure 2

Third fragment angle (A): defined as the angle between a line parallel to the femoral diaphyseal cortex and a line parallel to the third fragment cortex

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Fig. 3
figure 3

Fracture gap (G): defined as the distance between the proximal diaphyseal fragment and the distal one

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Fig. 4
figure 4

Third fragment size (L): defined as the length of the major axis of the fragment

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Fig. 5
figure 5

Mean third fragment displacement (M): defined as the perpendicular distance between the midpoint of the fragment and the nearest femoral shaft cortex

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Other two orthopaedists evaluated the follow-up X-rays, performed at one, two, three, six, nine and 12 months post-operatively, in order to assess the correct intramedullary nail placement and the bone healing. The fracture was considered healed when a bone callus could be depicted in at least three bone cortices out of four in AP and LL views [9].

Statistical analysis

Statistical analysis was performed using STATA/MP 14 for Windows (Stata Corp LP, College Station, USA). The Shapiro-Wilk test was conducted to verify the normal distribution of the data.

One-way ANOVA (analysis of variance) was used to assess the differences between the three groups. Bonferroni multiple-comparison test was then executed to evaluate the differences between each group.

Pearson correlation test was performed to assess the association between the union time and the fracture gap, third fragment size, angle, and mean displacement. Logistic regression analysis was conducted to investigate the effects of the fracture gap and the third fragment size, angle, and mean displacement on the fracture union. The tests were two-tailed with a confidence level of 5%.

Results

Fifty-two patients (33 male and 19 female, mean age 34.6 years old, range 21–58) were recruited for the current study. In 28 patients out of 52 (53.85%), the fracture healing was observed at 6-month follow-up (group A); in 18 patients out of 52 (34.62%), the fracture healed within 12-months after trauma (group B); and in 6 patients out of 52 (11.54%), no fracture healing was observed at 12-month follow-up (group C). The main data of the study are summarized in Table 1.

Table 1 General data of the study
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Shapiro-Wilk test results are reported in Table 2: the radiological features of the third fragment showed a normal distribution.

Table 2 Normality investigation
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Table 3 shows the one-way ANOVA results and Table 4 summarizes the Bonferroni multiple-comparison test results: the mean third fragment size was significantly different in group A compared with group B (p = 0.0048) and group C (p = 0.0015); the mean third fragment displacement was significantly higher in group C, compared with group A (p = 0.0006), and group B (p = 0.0027) (Table 4).

Table 3 Radiological study: comparison between the three groups (one-way ANOVA)
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Table 4 Bonferroni multiple-comparison test
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Pearson correlation test is shown in Table 5: in group B, a positive correlation was found between the fracture healing time and the mean third fragment size (R = 0.594; p = 0.036); in group C, the fracture union time was positively related to the third fragment size (R = 0.689; p = 0.013) and the mean third fragment displacement (R = 0.7107; p = 0.006) (Table 5).

Table 5 Pearson correlation test
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The linear regression analysis results are summarized in Table 6: the impact of the third fragment size (X) on the fracture healing (Y) is summarized by the following equation:

$$ Y=2.290+0.0955\ X $$
(1)
Table 6 Linear regression analysis
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It could be noted that a femoral shaft fracture, treated with an intramedullary nail, needs about 69 days to heal; when a third fragment is present, the fracture healing time increases of about three days, every millimeter of the third fragment size enlargement.

The following equation describes the influence of the mean third fragment displacement (Z) on bone healing (Y):

$$ Y=3.739+0.6745\ Z $$
(2)

It could be argued that a femoral shaft fracture with a third fragment which is not displaced, after closed reduction with an intramedullary nail, needs about 112 days to heal; every millimeter of the third fragment displacement increases the fracture healing time of about 20 days.

Multiple regression analysis was finally conducted to evaluate the concomitant effect of the mean third fragment size (X) and the mean third fragment displacement (Z) on the healing of femoral shaft fractures with third fragments; thus, the following equation was obtained:

$$ Y=0.13+0.074\ X+0.501\ Z $$
(3)

From these data, we have proposed a prognostic algorithm which is shown in Fig. 6.

Fig. 6
figure 6

The prognostic algorithm

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Discussion

Femoral shaft fractures with third fragments are a quite common injury, accounting for about one third of all femoral fractures [2, 4]. Closed reduction and internal fixation with an intramedullary nail is widely considered as an appropriate management for femoral shaft fractures [3, 4, 10, 11]. Intramedullary nailing, indeed, could be performed through minimal accesses, respecting the soft tissue and the fracture hematoma, and the periosteal blood perfusion [3].

Despite all these advantages, delayed-union or non-union could develop even in femoral shaft fractures treated with intramedullary nailing, especially in comminuted fractures or in fractures with third fragments. Several studies have investigated the risk factors which could affect the healing time of this kind of injuries and the role of the dynamization of the nail [12,13,14]. Some authors affirm that chipping and lengthening over nailing technique for femoral shaft non-union may be the first choice of treatment in case of shortening more than 10 mm [15].

Lee et al. [3], in a retrospective study on 64 femoral shaft fractures with third fragments, have recently observed that the healing of femoral shaft fractures with third fragments is mainly affected by the third fragment degree of displacement and the third fragment size. Consequently, according to these authors, fractures with fragments 8 cm or longer or when the third fragment proximal displacement is 20 mm or greater or the distal displacement is 10 mm or greater, non-union is more frequent. An et al. also reported similar data [8], who confirmed that the degree of the third fragment displacement affects the fracture healing, so they suggest that during the intramedullary nail placement care should be taken to avoid an excessive third fragment displacement or angulation.

The current study aims to obtain an algorithm which could be useful in predicting the healing time of femoral shaft fractures on the basis of third fragment features, evaluated on a post-operative X-ray. For this purpose, we retrospectively reviewed a series of 52 patients with 32-B fracture type according to AO/OTA classification.

Our data show that the third fragment size and the mean third fragment displacement, evaluated on post-operative X-rays of femoral shaft fracture treated with intramedullary nailing, are the two key features, which could affect the fracture healing time. We found that a third fragment smaller than 40 mm is a predictive factor of fracture healing within six months, while in fractures with a third fragment bigger than 40 mm, the third fragment displacement is the primary factor which influences the fracture healing time. Indeed, a low third fragment displacement (< 12 mm) is a predictive factor of fracture healing within 12 months, while a third fragment displacement greater than 12 mm may predict a fracture non-union. Consequently, the aim of the closed reduction of 32-B fractures with an intramedullary nail is to minimize the third fragment dislocation, in order to shorten the fracture healing time.

The role of the third fragment displacement on the fracture healing time could be explained considering a high displacement may increase the movements between the fragments, also after the fracture fixation, thus slowing down the callus formation [3, 16, 17].

We remark that our data agree with the ones reported in other studies [3, 18]. As stated by Lee et al. [3], we also found that the third fragment displacement and its size are the two main factors that affect the fracture healing in patients with femoral shaft fractures.

Lin et al. [18], in a retrospective study in 50 patients with 32-B and 32-C fractures according to AO/OTA classification, observed that fractures non-union was more frequent when the third fragment displacement is greater than 10 mm; these authors also noticed that the third fragment shape could affect the fracture healing.

Our study, however, has the advantage of proposing a prognostic algorithm, which could help the physician in decision making, in the management of femoral shaft fractures.

This study has some limitations that could not be overcome. Even if all the data were collected in a blinded manner, the sample size is quite small. Thus, future studies with a more significant sample size are needed to confirm our data with higher statistical power. The retrospective nature of this study is another limitation; however, we are currently recruiting, at our Department, patients with femoral shaft fractures with third fragments in a prospective trial to finally validate the algorithm proposed.

Conclusions

Femoral shaft fractures with third fragments are an insidious fracture pattern. In this study, we have proposed a prognostic algorithm to predict the healing time of femoral shaft fractures treated with intramedullary nailing. Our data shows the third fragment size (cutoff 40 mm) is the leading parameter which influences the fracture healing within or in more than 6 months. The main third fragment displacement (cutoff 12 mm), on the other hand, impacts on the fracture delayed rather than absent healing.