Blocking Pins Instead of Blocking Screws in the Treatment of Distal Tibial Fractures with Intramedullary Nail

Background: Distal tibial fractures have a high risk of malalignment when treated with intramedullary nails. The use of blocking screws can aid in achieving satisfactory alignment. The aim of this study was to compare the clinical and radiographic outcomes of temporary blocking pins with those of blocking screws for distal tibial fractures. Methods: From June 2011 through November 2018, a total of 90 patients with distal tibial fractures were enrolled in this prospective randomized controlled study. The patients were randomly received either blocking pins or blocking screws reduction during nailing. After reduction, 5 points at the distal fragment were effectively fixed. Results: The operating time in the BP group was 73.77±6.25 min, which was significantly shorter than 80.05±8.51 min in the BS group (P<0.001). The time to healing in the BP group was shorter than that in the BS group (18.52±4.57 vs. 21.51±3.17 weeks; P=0.001). The coronal and sagittal plane deformities at any time points were comparable (all P0.05). During the 12-month follow-up period, patients had an average change in the coronal plane of 1.34 degrees in the BP group and 1.00 degrees in the BS group (P=0.120), as well as an average change in the sagittal plane of 1.09 degrees and 0.81 degrees (P=0.110), respectively. Malunion was seen in two patients (5%) in the BP group and one patient (2%) in the BS group ( P0.05). Conclusion: The blocking pins can help achieve satisfactory alignment for distal tibial fractures during nailing. Intramedullary nails without blocking screws can afford adequate stability to maintain the reduction during the healing process when an effective five-point anchoring fixation is achieved.


Introduction
Modern intramedullary nail (IMN) technique is the standard treatment for long bone fractures [1,2], which can provide favorable reduction and stabilization. However, it is difficult to achieve good reduction if nail does not properly fit in the larger canal of distal diametaphyseal and metaphyseal segments [3][4][5]. In order to achieve a satisfactory reduction, multiple techniques including manual traction, percutaneous clamping, external fixation and temporary unicortical plating have been proposed. The blocking screws(BS), introduced by kretek [6], attempted to provide improved 3 reduction and stabilization by narrowing the canal available for nail placement and directing nail to the desired position [6][7][8]. Then, the BS was left in place to maintain the achieved reduction [8][9][10][11][12].
Compared to other methods, the BS could provide a more predictable reduction [6,13]. As long as the screw is in the correct position, the reduction is generally satisfactory, which is just like an equation.
The clinical practices of BS in proximal and distal tibial fractures and distal femur fractures have been well reported [8][9][10][11]. Nevertheless, the complications related to the BS might compromise the operative outcomes, including screw breakage, iatrogenic bone splitting, adjacent soft tissue irritation, and higher risk of hardware removal. Wang et al [14] used Kirschner wire instead of BS to treat 9 tibial (proximal or distal) metaphyseal fractures, and obtained the improved alignment and functional outcomes. Poyanlı et al [15] used temporary K-wires instead of BS to treat 7 distal femoral, 2 proximal tibial, and 4 distal tibial diametaphyseal fractures, and 12 of 13 fractures achieved successful alignment and maintain it to fracture union. However, the evidences supporting K-wires in place of BS remain insufficient and it remains a controversy whether it is necessary to retain the BS after achieving the reduction.
We established a protocol of blocking pins (BP) augmented with 5-point anchoring fixation in place of BS in IMN fixation of distal third tibial fractures. The BP is a 3.0 mm diameter steinmann pin, which is used during reduction and removed after fixation of distal inter-locking screws. We designed this prospective randomized controlled trial and the aim was to assess clinical and radiographic outcomes of distal tibial fractures treated following this protocol. We hypothesize that BP can achieve the same reduction and maintain it until the fracture union.

Materials And Methods
This was a prospective study. The protocol and informed consent forms were reviewed and approved by the Institutional Review Board (IRB) of the 3rd Hospital of Hebei Medical University, Shijiazhuang, PR China. All patients participating in this study signed the written informed consent. The study was conducted in accordance with the Declaration of Helsinki.

Patients
From June 2011 through November 2018, a consecutive cohort of patients aged eighteen years or 4 older who had a definite diagnosis of an acute fracture of the distal 1/3 tibia with indications for treatment with IMN were enrolled. Exclusion criteria were as follows: AO/OTA 43 fractures, open   fractures, pathological fractures, multiple fractures or preexisting diseases affecting activities of the   ipsilateral lower limbs. Based on a sequence number randomly generated by a computer, patients were randomized into the BP group or the BS group. A plaster splint was used as a temporary fixation to reduce swelling in each patient.

Surgical Technique
Under general anesthesia or epidural anesthesia, patients were placed on a radiolucent table in a supine position. The lateral malleolus fracture was plated when it was less than 6cm from the fibula tip. If any, accompanying posterior malleolus fracture was reduced in a closed manner, and fixated with annulated screws, prior to nailing [16]. A trans-patellar tendon approach was used with the knee in a flexed position. Percutaneous manipulation was performed to obtain and maintain an approximate reduction. A guidewire was introduced into the fracture site prior to reaming. A 3.0 mm smooth Steinmann pin was used as a BP. "Concave side" principle [6] and "Acute angle" principle [13] were followed to reduce the lateral displacement and angular displacement respectively. The location of BP is 6.0-7.0 mm from the center of the canal, approximately one-third of the canal diameter in the AP view, and 2.0 cm from the fracture line [13]. If necessary, a second pin was inserted from the medial to lateral direction to correct deformity in the sagittal plane, namely, biplanar modifier. The ball-tipped guidewire was then inserted at the correct side. The critical techniques included the central placement of the ball-tipped guidewire in the distal fragment and reaching a subchondral level, approximately 5.0 mm from the articular surface. The nail was inserted to a subchondral level after sequential reaming. The position of BP could be corrected until a satisfactory reduction was achieved. Thereafter, the proximal end of the nail was locked with two cross static locking screws, and the distal end of the IMN was locked with two parallel transverse interlocking screws. In the BP group, the pin was removed after fixation of distal interlocking screws.
Alternatively, the pin was replaced with a screw in the BS group. All procedures were performed under fluoroscopic control. 5 We categorized fractures into two types according to the positional relationship of the main fragments. Type 1 is defined as a fracture that the dominant deformity is lateral displacement and the angle between the proximal and distal axis is less than 20°in the AP view. The majority of this type fractures are AO type A fractures. Type 2 is a type of fracture that the dominant deformity is angulation with the angle between the proximal and distal axis being above 20°in the AP view. The majority of this type fractures are AO type B and type C fractures. For type 1 fracture, we followed the "acute angle" principle, proposed by Hannah et al [13] to place the BP or screw in the acute angle of the metaphyseal (distal) segment. For type 2 fracture, we followed the "concave side" principle, advocated by Krettek et al [6], to place the BP or BS in the concave side of the metaphyseal (distal) segment. Special emphasis should be placed on achieving adequate visualization of each process on the distal segments in both planes until fixation of distal interlocking screws.
All the operations were performed by three senior trauma surgeons specialized in IMN.
The parameters including age, sex, smoking, diabetes, injury characteristics, articular involvement, AO/OTA classification, interval from initial injury to surgery, intraoperative blood loss, number of BP or BS, and operating time were recorded among BP and BS group ( Table 1).

Postoperative management
The same postoperative protocol was used in all patients. After 24 h of the operation, patients were advised to begin an early, active, full range of motion of the ankle and knee joints within the limits of their comfort. Gradually, weight-bearing was permitted based on the signs of fracture callus visualized on postoperative radiographs. Standard anteroposterior and lateral radiographs were taken every month until fracture healing, then taken every three months to evaluate potential complications.

Outcomes Evaluation
Fracture union was defined as full weight-bearing without pain and bridging callus of 3 or 4 cortices on x-rays. Failure to achieve this at 6 months was defined as delayed union, and failure to achieve this at 9 months was defined as nonunion [17]. Coronal and sagittal alignments were evaluated using technique described by Freedman and Johnson [18]. Varus and recurvatum angulation were expressed as negative values, and valgus and antecurvatum as positive values. Satisfactory reduction and alignment is defined as less than 5° angulation in both planes. Leg length and rotational angulation were not measured. The quality of fracture reduction, fracture union time, alignment at 6 and 12 months and loss of reduction at 12 months were recorded. Unplanned secondary surgery and complications (including wound dehiscence, infection, soft tissue irritation, and malunion/delayed union/nonunion) were recorded. The American Orthopaedic Foot and Ankle Society (AOFAS) scoring system [19] was used to evaluate the functional outcome at the last follow-up examination (≥ 12 months).

Statistical Analysis
The data were analyzed with the use of SPSS software 25.0 (SPSS, IBM, Armonk, NY, USA ). The continuous data were expressed as mean and standard deviation or median and range, and were evaluated using Student-t test or Mann Whitney U test. Categorical data were expressed as number and percentage, and were evaluated using Chi-square test or Fisher exact test. P values less than 0.05 were considered to represent a significant difference.

Results
During the study period, a total of 90 patients sustaining a distal tibial fracture were enrolled. Of them, 46 (51%) patients were randomized to the BP group and 44 (49%) to the BS group, with a mean age of 45.6 years and 42.3 years, respectively. During follow-up period, 3 patients, 2 in the BP group and 1 in the BS group were lost, leaving 87 patients for data analysis. The age, gender, side of injury, smoking, diabetes, mechanism of injury, AO/OTA classification, the interval between injury and surgery and follow-up period of patients in both groups were summarized in Table 1, all of which were significantly comparable between the BP and BS group. All patients underwent closed reduction and IMN fixation.
The average intraoperative blood loss was 87.32 mL in the BP group and 96.26 mL in the BS group (p = 0.126). The average operating time of the BP group was significantly shorter than that of the BS group (73.77 vs. 80.05 min, p < 0.001). Six patients (4 in BP group vs.2 in BS group, P = 0.676) who had concomitant posterior malleolus fractures underwent closed reduction and were treated with 7 percutaneous lag screw fixation before the placement of IMN. Five distal fibula fractures (2 in BP group vs. 3 in BS group, P = 0.676) were plated to increase the ankle stability. In the BP group, 41 fractures were reduced with one BP, and 3 fractures with two. In the BS group, 42 fractures were reduced with one BS, and 1 fracture with two (p = 0.713). Surgical characteristics were summarized in Table 2.
The average coronal plane deformities immediately after surgery, at 6 months and 12 months after surgery were 1.09 degree, 1.91 degrees, and 2.11 degrees in the BP group, as well as 0.72 degree,  Table 4.
One typical case is shown in Fig. 1.

Discussion 8
This study investigated the clinical and radiographic outcomes of BP compared to BS in treatment of distal tibial fractures with IMN. The hypothesis of the current study was confirmed that BP could achieve similarly improved reduction and maintain it until the fracture union. There was no significant difference in deformities and angular changes of both coronal and sagittal planes between groups, but the BP group required shorter operating time and fracture union time.
IMN is more acceptable in the treatment of distal tibial fracture due to the minimized soft tissue dissection, protection of extraosseous blood supply, and superiority in axial loading [20,21]. Some studies have reported that it potentially increased the risk of deformity healing [21][22][23][24][25][26][27]. This deformity may originate from an insufficient initial reduction or later loss of reduction. BS can help to achieve satisfactory initial reduction by narrowing the canal available for nail placement [6,7,28]. In order to pursue a better result, BP were used to replace BS in this study. Both groups of patients were reduced by BP, and successful reductions were achieved in all fractures without intraoperative adverse events, consistent with other reported results [6,12]. To achieve a satisfactory reduction, it is important to adhere to the placement principles mentioned in surgical technique, more important to have a standard entry point and a centered end point [29]. Otherwise, there may be eccentric reaming and deformities after nailing.
When satisfactory initial reduction is achieved, does the IMN alone provide sufficient mechanical strength to maintain stability without loss of reduction? De Giacomo and Tornetta [17] treated 117 distal tibia fractures with a standard IMN (2 medial-lateral distal interlocking screws), and the malalignment rate was 2%. In their study, no significant loss of reduction (average change of 0.9 degrees in both the coronal and sagittal planes) was observed after surgery, which was consistent with our results. In the present study, all patients in the BP group were fixed with a standard IMN after reduction, and the average loss of reduction in coronal and sagittal plane at 1 year after surgery was 1.34 and 1.09 degrees, respectively. Collinge et al [30] used percutaneous clamping to reduce tibial fractures and after a satisfactory reduction all fractures were fixed with a traditional IMN. In their study, only one patient had a notable loss of reduction, where alignment changed from anatomic to acceptable. Stedtfeld et al [8] proposed three-point fixation of the short fragment ( isthmus, the blocking screw, and the nail tip ), which could achieve a good axial alignment when the nail was in the central position. In order to achieve the maximum mechanical strength of the IMN, the five metalbone contact points at the distal fragment must be effectively fixed (picture 1). Our 5-point anchoring fixation is a strengthened combinational fixation than the simple nail tip fixation( Fig. 1-i), which can maintain the reduction and stability of the IMN. IMN was generally placed to the subchondral level, about 5 mm to the articular surface which is the solidest area of the metaphysis [20]. This is just like 97 min, p < 0.001) was significantly longer than that of the BP group.

10
The BP, a 3.0-mm-diameter Steinmann pin, has the following advantages. Firstly, the smooth surface reduces friction and the probability of damage to metal equipment. Secondly, more elastic and proper compromises can be made when the nail is inserted without iatrogenic fracture Thirdly, it is easy to control and adjust the position. Fourthly, direct extraction can shorten the operation time, reduce costs, and avoid the prominent irritation to the adjacent soft tissue. We select a 3.0-mm-diameter Steinmann pin, because the thinner one is too soft and the thicker one is more destructive and prone to producing a new iatrogenic fracture. In this study, the Steinmann pin was used to assist reduction in both groups, and no intraoperative adverse events occurred. Two patients in the BS group underwent removal of the BS due to soft tissue irritation.
The use of BS is an ideal technique to decrease the incidence of mal-alignment in treatment of tibial fractures with displacement [6]. In this study, satisfactory reduction and radiographic alignment within five degrees were achieved for all patients as shown by immediate postoperative radiographs.
The union rates and complications were not different between groups, indicating that the outcomes were not affected by replacing the screw with a pin. Following the removal of the BP during surgery, satisfactory reduction and stability were maintained. There was no statistically significant difference between the two groups in loss of alignment, although 3 patients developed malunion. The reason for 1st malunion in the BP group was that the bone around the distal locking screws was damaged during drilling, and no obvious reasons for the other 2 cases. Therefore, if an effective 5-point fixation cannot be achieved during locking of the distal fragment, surgeons should consider placing BS to increase stability. Two patients underwent removal of BS due to soft tissue irritation although there is no statistical difference in rate of soft tissue irritation. The BP group did not have such a risk, and this difference may be reflected in future large-scale studies.

Conclusion
The blocking pins can help achieve satisfactory alignment for distal tibial fractures during nailing.
Intramedullary nails without blocking screws can afford adequate stability to maintain the reduction during the healing process when an effective five-point anchoring fixation is achieved.

Consent for publication
Written informed consent was obtained from each patients' parents for the publication of this study and the accompanying images.

Availability of data and materials
The datasets generated and/or analyzed during the current study are not in public but are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests

Funding support
This study was supported by Talent training plan of hebei province in 2013(A2013003043). The funders had no effect on the study design, data collection and publication of the manuscript.

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Hannah A, Aboelmagd T, Yip G, Hull P: A novel technique for accurate Poller