Positional Screw Effect in the Treatment of Humeral Shaft Fractures Using a Minimally Invasive Plate Osteosynthesis Technique

Abstract

Background

This study compares the difference in the clinical and radiologic outcomes when minimally invasive plate osteosynthesis (MIPO) technique is performed with or without using a positional screw in the treatment of humeral shaft fractures.

Methods

From January 2010 to January 2021, a retrospective study was conducted on a total of 63 patients who underwent the MIPO technique for the treatment of humeral shaft fractures. We divided these patients into 2 groups: in group I, patients underwent MIPO without a positional screw; in group II, patients underwent MIPO with a positional screw. We compared functional outcomes including the American Shoulder and Elbow Surgeons score, University of California at Los Angeles score, Simple Shoulder Test, range of motion before and after surgery, operation time, blood loss, and complications. And we compared radiologic outcomes including pre- and postoperative anteroposterior (AP) and lateral displacement of the fracture and union time on plain radiographs.

Results

The average patient age was 64.6 ± 15.1 years (range, 25–88 years). Group I consisted of 30 patients (10 men and 20 women), and group II consisted of 33 patients (11 men and 22 women). Between the 2 groups, there was no statistically significant difference in sex, body mass index, functional scores, AP and lateral displacement of the fracture on postoperative x-ray, operation time, and blood loss. In group II, a faster bony union was obtained than that in group I (4.6 vs. 6.4 months). Complications included 2 cases of transient radial nerve palsy in both groups and metallic failures (2 in group I and 1 in group II).

Conclusions

When performing MIPO for humeral shaft fractures, adding a positional screw could be more stabilizing than bridge plating without a positional screw, leading to faster bony union. A positional screw might help control interfragmentary movement without inhibiting essential interfragmentary movement for fracture healing.

In long bone fractures, a minimally invasive plate osteosynthesis (MIPO) technique is an atraumatic procedure that does not involve opening the fracture site directly, helping to preserve the blood supply to the soft and hard tissues.¹⁾ This procedure was commonly used to treat fractures of the distal femur, proximal and distal tibia, and forearm. Currently, the MIPO technique is widely used in the treatment of humeral shaft fractures.²,³,⁴⁾

The MIPO technique preserves soft issues by avoiding the destruction of the surrounding local vasculature and early callus by eliminating the need to directly open the fracture. In the AO Principles of Fracture Management (3rd edition), open reduction and internal fixation is an anatomical reduction and rigid internal fixation technique, but the MIPO technique provides relative stability by bridging the fracture site using a locking plate. Secondary bone healing can be achieved by obtaining relative stability and a certain degree of interventional movement. However, MIPO is a closed method, which sometimes requires allowing alignment, rotation, and angulation to occur.⁵,⁶⁾

Some surgeons use the screws to reduce the interfragmentary gap. When a interfragmentary screw was used with the MIPO technique to treat the distal tibia, the initial callus formation appeared faster and the union rate was significantly higher after 1 year.⁷⁾ The authors described these screws as appositional screws that approximate 2 main fragments in the closed method guided by fluoroscopy. Another author described these screws as positional screws rather than appositional screws. In a distal femur fracture with a simple fracture pattern, using positional screws to sustain the reduced interfragmentary gap resulted in a more rapid union by reducing the fracture gap.⁸⁾

The purpose of this study was to compare the clinical and radiological outcomes of patients after the MIPO technique and using a locking plate with or without positional screws for long comminuted, wedged, or spiral humeral shaft fractures. We hypothesized that the use of positional screws would reduce nonunion and shorten bone union time.

METHODS

Institutional Review Board approval was obtained with the requirement to collect consent from participants waived due to the retrospective nature of the study (The Catholic University of Korea, Daejeon St. Mary’s Hospital; IRB No. DC17RESI0067).

Study Patients

Adult patients aged 18 years or older who received MIPO for humeral shaft fractures from January 2010 to April 2021 were included in the study. This retrospective study was conducted at a single center and surgeries were performed by a single surgeon (JHJ). We divided these patients into groups I and II. Group I was defined as a group of patients who underwent MIPO through proximal and distal incisions without a positional screw for the treatment of humeral shaft fractures (Fig. 1). In group II, a positional screw was used in the fracture area during the MIPO technique for the treatment of humeral shaft fractures (Fig. 2).

Fig. 1. A 63-year-old woman with a humeral shaft fracture (AO classification 12B1) caused by a fall injury. Preoperative x-ray (A) and preoperative computed tomography scan (B). After undergoing minimally invasive plate osteosynthesis without the use of a positional screw, an immediate postoperative x-ray confirmed that the anteroposterior (C) and lateral (D) displacement had been corrected compared to the preoperative status.

Fig. 2. A 60-year-old woman with a humeral shaft fracture (AO classification 12C1). Preoperative x-ray (A) and preoperative computed tomography scan (B). (C) Postoperative x-ray after minimally invasive plate osteosynthesis with a positional screw (red arrow). (D, E) At postoperative 6 months, there was callus formation seen on x-ray.

Positional Screw

During general MIPO surgery, screws are not inserted into the fracture site, and only the proximal and distal main bone fragments are fixed. In the case of MIPO surgery for humerus fractures, screws in the proximal bone fragment are fixed only to the proximal part of the axillary nerve. If there is a wedged fragment, comminuted fracture, or long spiral fracture, the working length becomes longer. A screw inserted to reduce the working length without causing excessive soft-tissue damage at the fracture site was defined as a “positional screw.” The positional screw is inserted by fixing the wedged bone fragment or the comminuted bone fragment to the main bone fragment. In the case of a long spiral fracture, interfragmentary fixation is performed on the 2 main fragments, but compression is not applied, and they are inserted through in situ fixation without any procedure for interfragmentary compression such as overdrilling after fracture reduction and fixation are completed (Fig. 3).

Fig. 3. The positional screw (red screw) is inserted by fixing the wedged bone fragment (A) or the comminuted bone fragment (B) to the main bone fragment. In the case of a long spiral fracture, interfragmentary fixation (C) is performed on the 2 main fragments, but compression is not applied, and they are inserted through in situ fixation after fracture reduction and fixation are completed.

Surgical Technique

Under general anesthesia, a beach chair position was used and the patient was then placed on a conventional table in the supine position. A lateral deltoid-split approach proximally and an intermuscular approach between brachialis and brachioradialis distally were performed. A skin incision was made beginning at the anterolateral tip of the acromion extending approximately 5 cm distal. The skin, subcutaneous tissue, fascia, and deltoid muscle were dissected to partially expose the greater tuberosity. The axillary nerve was not formally exposed but identified by finger dissection and elevation of the deltoid muscle from the proximal humerus.

A long PHILOS (Proximal Humeral Internal Locking System, Synthes) plate was inserted through the created tunnel from proximal to distal along the lateral surface of the humerus and beneath the axillary nerve after reduction was performed using a combination of direct and indirect reduction maneuver. When performing MIPO, a distal incision was applied based on the fracture site. The length of the plate was adjusted to the fracture site and the location of the distal incision was determined under fluoroscopy. If the fracture was confined to the proximal part of the humeral shaft, no radial nerve exploration was performed and the distal incision was confined to the middle humerus. If the distal end of the humeral fracture was located in the mid or distal humerus, the distal incision was used to more easily find the radial nerve. After identifying the radial nerve between the brachialis and brachioradialis in the distal incision, the plate was inserted through the submuscular tunnel, and internal fixation was performed from the proximal incision to the distal incision.

When using a positional screw, after inserting the plate, an additional skin incision where the positional screw was used, and the comminuted or wedged bone fragment was reduced using a Hohmann retractor and a Steinmann pin and temporarily fixed with a 2.0-mm Steinmann pin at the cortical screw hole of the plate (Fig. 4). Reduction of the entire fracture was performed, and proximal and distal screws were fixed. Finally, the temporary Steinmann pin was removed and fixed in the same position with a 3.5-mm cortical screw. In case of long spiral fracture, it was inserted in the center of the fracture range after proximal and distal screws were fixed.

Fig. 4. When performing minimally invasive plate osteosynthesis with a positional screw, an additional, minimal incision was made for a positional screw.

Evaluation

We measured fracture displacement on anteroposterior and lateral plain radiographs before and after surgery (Fig. 5). We evaluated the patients every month until bony union was observed and obtained plain radiographs of the anteroposterior, lateral, and both oblique views at every follow-up. Radiologic union was defined as the presence of a tricortical or greater bridging callus. We reviewed the complications, range of motion (ROM), preoperative and postoperative displacement, amount of bleeding, and subsequent operations on every patient’s chart. We measured the ROM at 3 months, 6 months, and 1 year postoperatively. We measured clinical scores at 6 months and 1 year, including the American Shoulder and Elbow Surgeons (ASES) score, University of California at Los Angeles (UCLA) score, and Simple Shoulder Test (SST) score.

Fig. 5. Fracture displacement (yellow lines) was measured on preoperative anteroposterior (A) and lateral (B) and postoperative anteroposterior (C) and lateral (D) plain radiographs.

Data Analysis

Data were analyzed using SAS version 9.2 (SAS institute), and p < 0.05 was considered statistically significant for all analysis. Continuous variables were described using mean and standard deviation if normally distributed. Differences between study groups were assessed using independent t-test for continuous variables and chi-square test or Fisher exact test for binary variables. Statistical significance was set at p < 0.05 with 95% CIs.

RESULTS

Patient Demographics

A total of 63 patients underwent the MIPO technique for the treatment of humeral shaft fractures from January 2010 to April 2021. Group I consisted of 30 patients (10 men and 20 women), and group II consisted of 33 patients (11 men and 22 women). All these humeral shaft fractures were included in AO classification 12A, 12B, and 12C. There were 21 men and 42 women. The average patient age was 64.6 ± 15.1 years, ranging from 25 to 88 years (Table 1). There were no significant differences in the preoperative displacement of the fractures, injury mechanism, and fractures type (Table 2).

Table 1. Comparison of the Patient Demographics.

Variable	Group I (MIPO without positional screw, n = 30)	Group II (MIPO with positional screw, n = 33)	p-value
Age (yr)	62 ± 16 (25–88)	67 ± 14 (35–88)	0.136
Sex (male : female)	10 : 20	11 : 22	0.934
BMI (kg/m2)	26.6 ± 5.1	23.7 ± 3.6	0.062
Operating site (right : left)	16 : 14	15 : 17	0.545
Fracture type (AO classification)	A1, 15; B1, 3; B3, 3; C1, 2; C2, 7	A1, 19; B1, 4; B3, 3; C1, 3; C2, 3; C3, 1	-

Values are presented as mean ± SD (range) or mean ± SD.

MIPO: minimally invasive plate osteosynthesis, BMI: body mass index, SD: standard deviation.

Table 2. Comparison of the Preoperative Displacement, Injury Mechanism, and Fracture Type.

Variable		Group I (MIPO without positional screw, n = 30)	Group II (MIPO with positional screw, n = 33)	p-value
Preoperative AP displacement (mm)		13.1 ± 7.6	15.0 ± 10.1	0.593
Preoperative lateral displacement (mm)		11.7 ± 8.0	11.8 ± 7.9	0.755
Injury mechanism				-
	Fall	15	19
	Traffic accident	13	11
	Work	1	2
	Blunt trauma	1	1
Fracture (closed : open)		29 : 1	32 : 1	0.223

Values are presented as mean ± standard deviation.

MIPO: minimally invasive plate osteosynthesis, AP: anteroposterior.

Outcomes

There were no significant differences in the postoperative displacement of the fractures, operation time, and blood loss between the 2 groups (Table 3). There were no significant differences in the ROM and clinical scores such as the ASES score, UCLA score, and SST score (Table 4). Bony union time was significantly different (p = 0.024) with an average duration of 6.4 months in group II (no positional screw) and 4.6 months in group I (positional screw). Both groups had 2 cases of transient radial nerve palsy. The transient symptoms improved without any sequelae within 3 months. There were no cases of infection. In group I, 2 metallic failures (distal screw breakage) occurred. There was also 1 case of a delayed union that took more than 9 months to occur in group II. A metal failure was found in group II.

Table 3. Comparison of the Postoperative Displacement, Operation Time, Blood Loss, and Time to Bony Union.

Variable	Group I (MIPO without positional screw, n = 30)	Group II (MIPO with positional screw, n = 33)	p-value
Postoperative AP displacement (mm)	3.81 ± 5.18 (0–11.5)	3.43 ± 2.51 (0–10.5)	0.732
Postoperative lateral displacement (mm)	3.18 ± 2.59 (0–10.9)	3.96 ± 2.95 (0.3–10.7)	0.330
Operation time (min)	93 ± 21 (60–150)	99.3 ± 24.8 (60–156)	0.182
Blood loss (mL)	114 ± 91 (20–550)	154 ± 140 (20–500)	0.297
Bony union (mo)	6.4 ± 2.1 (3–11)	4.6 ± 1.2 (2–7)	0.024

Values are presented as mean ± standard deviation (range).

MIPO: minimally invasive plate osteosynthesis, AP: anteroposterior.

Table 4. Comparison of the Clinical Outcomes at the Final Follow-up.

Variable	Group I (MIPO without positional screw, n = 30)	Group II (MIPO with positional screw, n = 33)	p-value
Postoperative FF	142.2 ± 14.8 (90–160)	143.0 ± 16.0 (120–160)	0.261
Postoperative abduction	139.2 ± 15.5 (90–150)	140.0 ± 13.7 (120–160)	0.153
Postoperative ER	41.9 ± 22.0 (10–80)	34.0 ± 11.4 (20–60)	0.152
Postoperative IR	T10 (L2–T5)	T12 (L3–T9)	0.094
UCLA score	29.4 ± 5.0 (14–35)	29.8 ± 3.3 (16–35)	0.471
ASES score	83.0 ± 17.8 (28–100)	83.5 ± 13.1 (40–100)	0.947
SST	7.8 ± 2.0 (2–11)	8.0 ± 3.0 (3–12)	0.948

Values are presented as mean ± standard deviation (range).

MIPO: minimally invasive plate osteosynthesis, FF: forward flexion, ER: external rotation, IR: internal rotation, UCLA: University of California at Los Angeles, ASES: Shoulder and Elbow Surgeons, SST: Simple Shoulder Test.

DISCUSSION

Our study showed that there were no significant differences in postoperative clinical outcomes between the 2 groups. We hypothesized that inserting a positional screw would reduce fracture nonunion and shorten bone union time. The bony union time was significantly reduced when a positional screw was added during the MIPO technique; however, there was no difference in the incidence of nonunion.

In previous studies, it was difficult to reduce the gap between fracture fragments during the MIPO technique, and some gap inevitably remained.¹,⁹⁾ Accurate anatomical reduction is not necessary to close the fracture gap during MIPO. However, malalignment and malunion have been reported in fracture fixation using indirect reduction and the MIPO technique,⁵,¹⁰,¹¹,¹²,¹³⁾ and thus, reducing the fracture gap could help prevent these complications. Chung et al.⁸⁾ reported that when the fracture gap was reduced using an interfragmentary screw in MIPO treatment of distal femur fractures, complications such as malunion and nonunion were reduced, and the period of bony union decreased. In our study, the period of bony union was shortened when the positional screw was used during MIPO.

For successful surgery, protection of radial nerves is imperative. The location of the axillary nerve is very predictable as it crosses the lateral aspect of the proximal humerus (6.3 ± 0.5 cm below the acromion).¹⁴⁾ Therefore, the safe zone of the PHILOS plate for proximal screw insertion was respected, using only the 6 most proximal holes as described by previous studies.¹⁵,¹⁶⁾ The screw for the proximal fragment is fixed to the proximal portion of the axillary nerve, and when the location of the fracture is in the mid-shaft of humerus, the working length, which is the distance between the first screws at each side of the fracture, is increased.¹⁷,¹⁸⁾ Axial stiffness and torsional rigidity are mainly influenced by the working length of the plate construct. An increase in the plate working length is accompanied by a rise in interfragmentary movements (notably interfragmentary shear) and this may extend to a point where sufficient stabilization is no longer achieved, causing fracture healing disturbances.¹⁹,²⁰⁾ In the current study, when a positional screw was used, the working length was reduced, possibility reducing instability that can inhibit fracture healing. Mardian et al. reported a significant increase in interfragmentary movements when the working length exceeded 62 mm.²¹⁾ If the working length is more than 62 mm and the fracture gap is large, the use of a positional screw is expected to be helpful, and further biomechanical research is needed.

With the MIPO technique, interfragmentary movement due to relative stability promotes secondary bone healing. However, it is difficult to adjust the interfragmentary gap due to the closed method of the MIPO technique. It takes a considerable length of time for bone with a gap that is too large to heal.¹⁾ A gap can be rigidly fixed with a lag screw and an anatomic locking plate to reduce the interfragmentary gap, but this method results in soft-tissue damage due to the open technique. To reduce the working length, we added a small, additional incision and used a positional screw. Compared to the conventional MIPO technique, this method interferes with bone healing by injuring soft tissue and reducing interfragmentary movement. However, in our study, considering that the initial callus formation time was shorter in the interventional group, the positive effect of reducing the working length may outweigh these disadvantages. These findings were also consistent with the distal tibia and distal femur.⁷,⁸⁾

There was concern that limiting motion between the fragments and the relatively rigid configuration of MIPO may inhibit callus formation. However, insertion of the positional screw did not completely eliminate the movement between the 2 fragments because in the closed method, the positional screw has limited contact area and compression force compared to that in the conventional lag screw fixation.

In this study, we confirmed that the union rate was not significantly different and the time to initial callus formation and radiologic union was shorter in the positional screw group. This is consistent with the results of previous studies on appositional screw use during MIPO for lower extremity fractures.⁷⁾ It should be clearly noted that the positional screw used in this study is not used for fracture reduction, but rather the screw is inserted after proper reduction of the fracture.

The current study has several limitations. First, this is a retrospective study. The allocation of treatment was not random. Thus, a selection bias may be present in this study. However, consecutively admitted patients were included to reduce the selection bias. In the early periods of this study, we did not use a positional screw in the MIPO technique, and in the late period of this study, we preferred the use of the positional screw in the MIPO technique. Second, there were few patients with short-term follow-up periods in this study, and a larger number of patients with longer follow-up periods are needed. Third, there might be some bias in the evaluation of radiologic outcomes. As the positional screw was visible with radiography, the authors were able to choose the preferred outcomes. To reduce this bias, a surgeon who did not know the role of the positional screw was asked to evaluate the callus formation in the follow-up radiographs.

When performing MIPO for humeral shaft fractures, adding a positional screw could be more stabilizing than bridge plating without a positional screw, leading to faster bony union. A positional screw might help control interfragmentary movement without inhibiting essential interfragmentary movement for fracture healing.