Coracoid Process Fractures of the Scapula Treated by Baseplate Three-Column Glenoid Fixation: A Retrospective Study of 24 Patients

Background

Coracoid process (CP) fractures constitute 3% to 13% of scapular fractures and 5% of all shoulder fractures [1]. Many methods of treatment for coracoid fractures have been described. Of these, metallic screw fixation from the CP into the neck of the scapula is the standard surgical approach and is believed to be effective [2–4].

Moreover, many CP fractures are associated with fractures of the glenoid, scapular spine, and scapular neck/body [5,6]. These types of cases are extremely challenging for the orthopedic surgeon.

A new scapular bone stock consisting of a baseplate three-column glenoid construct has been described in recent years, which could be a surgically relevant technique in the fixation of these complex types of scapular fractures [7].

The purpose of this study was to introduce a modified fixation technique utilizing the “baseplate three-column glenoid construct” for CP fractures, including complex types with scapular neck/body or intra-articular glenoid fractures, and we also discuss the main characteristics of the technique. This retrospective study from a single center aimed to evaluate 24 patients with coracoid process fractures of the scapula treated by baseplate three-column glenoid fixation of the 3 columns attached to the glenoid, or the scapula-glenoid construct, which includes the base of the coracoid, the scapular spine, and the lateral/scapular pillar.

Material and Methods

PATIENTS IDENTIFICATION:

Twenty-four patients with CP fractures were treated from March 2018 to August 2020 in our hospital. Eleven patients (1 female, 10 male) with an average age of 50.2 years (range, 27 to 67 years) were placed in the modified technique group; the etiologies of the injuries were fall (4 cases), direct blow to shoulder (5 cases), and motor vehicle accident (2 cases). Thirteen patients (1 female, 12 male) with an average age of 47.7 years (range, 29 to 65 years) were in the conventional group; the etiologies of their injuries were fall (3 cases), direct blow to shoulder (2 cases), and motor vehicle accident (9 cases).

INDICATIONS:

All injuries were confirmed with shoulder X-rays. In addition, computed tomography (CT) scans were used to delineate the distribution and displacement of the fracture fragments. Indications for surgical fixation were the following: 1) ≥ 1-cm displacement on radiographic evaluation, 2) active patients requiring normal shoulder function and wishing to return to work sooner, 3) multi-trauma patients requiring function of the shoulder to mobilize.

TREATMENT METHODS:

All patients received general anesthesia and were placed in lateral or beach-chair position according to the surgical plan. An approximately 4-cm vertical incision was made through the Langer’s lines. Blunt dissection was then performed with an elevator from the tip of the CP down the cephalad slope. Under fluoroscopic guidance, a guidewire was inserted to the glenoid neck at the coracoid base anterior and lateral to the coracoid clavicle ligament with 30- to 40-degree medial angulation and 20- to 30-degree posterior angulation in the modified group (Figure 1). Fifteen medial angulations with 30 to 40 posterior angulations were used in the conventional group [8].

After the position and depth of the guide wire were confirmed, a 4.5-mm partially-threaded cannulated lag screw (Synthes, Paoli, Pennsylvania), 55 to 60 mm in the modified group and 30 to 60 mm in the conventional group, was inserted over the guide wire. The wound was then irrigated thoroughly and the soft tissues were closed in layers, then the arm was immobilized in a sling.

POSTOPERATIVE MANAGEMENT AND EVALUATION:

Pendulum shoulder exercises and active-assisted motions of the shoulder were initiated during the first 3 weeks after surgery. In the following 3 weeks, the focus shifted to achieving strength and resistance training beginning with 3 to 5 lb weights and advancing as tolerated. After 6 weeks, the patients were encouraged to have complete movement of the shoulder joint. Once full range of motion was achieved, the patient was instructed in performing a series of progressive resistance strengthening exercises for the rotator cuff, deltoid, and scapular stabilizing muscles.

Patients were followed up and functions of the shoulder joints were evaluated using the Constant-Murley shoulder outcome score [4]. Bone union and reduction position were confirmed with X-ray and CT scans.

STATISTICAL ANALYSIS:

The results are presented as mean±standard deviation (SD). Statistical evaluation of the data was carried out using SPSS Statistics for Windows, version 21.0 (IBM Corp., Armonk, NY, USA). The Mann-Whitney test was used for normally distributed data. The significant differences between variables were tested using the t test and Fisher’s exact test. P value <0.05 was considered to be statistically significant.

Results

In all patents, the surgical wounds healed with primary closure, and no infections or neurovascular injuries were observed. The patients were followed for a mean duration of 12 months (range: 10 to 16 months). In the modified group, 10 patients showed bone union with a mean time from surgery to union of 11 weeks (range: 8 to 16 weeks), and 1 patient had screw broken at 5 months from heavy manual labor and showed delayed union at 8 months (Figure 2). Five patients had incomplete reduction with up to 3 mm displacement. The mean Constant-Murley shoulder outcome score was 70.2±18.5 at last follow-up.

In the conventional group, 12 patients showed bone union with a mean time from surgery to union of 8 weeks (range: 6 to 10 weeks). Two patients had incomplete reduction with up to 3 mm displacement. The mean Constant-Murley shoulder outcome score was 73.9±13.2 at last follow-up. All patients returned to their previous occupations and levels of activity, and no loss of reduction or surgical revision occurred.

When comparing the 2 groups, we found the mean Constant-Murley shoulder outcome score did not differ significantly (P>0.05), nor did fracture malreduction (P>0.05) or bone union time (P=0.003). Furthermore, the average length of the screw in the modified group (56.8±3.4mm) was longer than that of the conventional group (41.6±8.7 mm) (P=0.002) (Table 1).

Discussion

The CP is an important structure for the attachment of the limb flexion muscles and ligaments, especially those stabilizing the clavicle [9]. Unstable CP fractures as part of multiple shoulder fractures are usually best treated by surgical fixation. Some complex types of CP fractures, including Eyres type IV, type V associated with comminuted fractures or glenoid neck (Miller type II and type III), or with extension to the inferior glenoid (Ideberg type V and type IV), are extremely challenging for the orthopedic surgeon. The fixation technique should be customized and selected based on the size of the fragment, the degree of comminution, and the extent of articular involvement to ensure adequate stabilization [8]. This retrospective study describes a “baseplate three-column glenoid construct” fixation technique used in simple and complex types of CP fractures with cannulated screws, which can be considered as a surgical option for patients with coracoid process fractures.

The parameters of scapular anatomy and the intact screw zone are essential for the fixation of CP fractures. The baseplate three-column glenoid construct is a supportive bony framework formed by the lateral scapular border, scapular spine, and the inferior coracoid pillar [7]. The junctional construct of baseplate three-column glenoid construct can be described as the center of the scapular bone stock, and the maximal length of coracoid fixation screw can be achieved from the superior coracoid pillar to the center of baseplate three-column glenoid construct.

The “baseplate three-column glenoid construct” fixation technique re-establishes a firm connection between the coracoid and the center of the scapula bone stock. This technique was successfully used in simple and complex types of CP fractures in this study, and the mean Constant-Murley score did not differ significantly (P>0.05) between groups at last follow-up.

There are several differences between the modified fixation method and the conventional technique (Table 2). In the conventional technique, the screw used to fix the CP to the scapular neck has a 15-degree medial angulation and 30- to 40-degree posterior angulation [8]; we utilized a screw with 30- to 40-degree medial angulation and 20- to 30-degree posterior angulation in the modified technique. The insertion site is at the anterior and lateral rim of the coracoid base with the modified technique, which could offer more working space, allowing more flexibility in surgical positioning in lateral or even supine positions.

The length of the screw used in the modified group varied between 55 and 60 mm, and the average length was longer than in the conventional group (P<0.01), as the latter varied between 30 and 60 mm. In the conventional technique, the CP was fixed to the scapular glenoid, and in the modified technique the longer screw was positioned in a zone in the baseplate three-column glenoid construct (Figures 3, 4), which is the most solid structure of the scapular frame and is resistant to comminuted fractures. Therefore, the modified technique could be used in most CP fractures, including complex fractures, avoiding additional posterior approach fixation with plates [10].

There are some limitations of this modified fixation method. Without exposing the fractured ends, complete anatomical reduction was difficult to achieve for the complex cases (5 cases). However, compared with the conventional group (2 cases), the fracture malreduction rate did not differ significantly (P>0.05). Previous studies have suggested that complete anatomic reduction of the coracoid process may not be necessary, as long as functional outcome is preserved [11]. The time for bone union was longer than that of the conventional group (P<0.05). However, 1 patient had a screw broken at 5 months from heavy manual labor and showed delayed union at 8 months. Further research is needed to verify our results. The main technical difficulty of the modified method lies in the risk of injuring the suprascapular nerve due to increased medial angulation. Previous studies have demonstrated that the nerve may be injured if the screw is placed with too much medial angulation [12]. In this study, the breakthrough point of the screw was medial to the spinoglenoid notch, with potential risk of suprascapular neurovascular damage [13]. Therefore, it is important to keep the guidewire in the construct of the superior coracoid pillar to the center of the baseplate three-column glenoid, a narrow “safe zone” to decrease the risk of neurovascular injury. Given the technical difficulty, this modified technique may be difficult for the novice surgeon. Fluoroscopic guidance is essential to ensure proper guidewire and screw placement in the “safe zone”.

The baseplate three-column glenoid construct fixation method provides a customized solution to the surgeon, but most cases in the modified group were combined with other fixation of the scapular components, which could influence the evaluation of the technique. Further clinical and biomechanical studies are required to support these results.

Conclusions

The findings from this retrospective study show that baseplate three-column glenoid fixation of the coracoid process is a good surgical option for coracoid process fractures. This technique can be considered as a surgical option for coracoid process fractures, but further studies are required to explore the efficacy of the modified technique.