Influence of coracoglenoid space on scapular neck fracture stability: biomechanical study

Abstract

Background: The anatomical variation of the coracoglenoid space has the potential to influence the stability of scapular neck fractures. This paper aimed to investigate the mechanical mechanism underlying the influence of different coracoglenoid space types on scapular neck fractures by morphometric analysis and biomechanical experiments.

Methods: The morphology of 68 dried scapulae (left: 36; right: 32) was studied. Two variables, the length of the coracoglenoid distance (CGD) and the coracoglenoid notch (CGN), were measured. The distribution of CGN/CGD × 100% was used to identify the morphology of the coracoglenoid space. Each specimen was tested for failure under static axial compression loading. The average failure load, stiffness, and energy were calculated.

Results: Two coracoglenoid space types were identified. The incidence of Type I (''hook'' shape) was 53%, and that of Type II (''square bracket'' shape) was 47%. The CGD and CGN were significantly higher for type I than type II (13.81 ± 0.74 mm vs. 11.50 ± 1.03 mm, P < 0.05; 4.74 ± 0.45 mm vs. 2.61 ± 0.45 mm, P < 0.05). The average maximum failure load of the two types was 1270.82 ± 318.85 N and 1529.18 ± 467.29 N, respectively (P = 0.011). The stiffness and energy were significantly higher for type II than type I (896.75 ± 281.14 N/mm vs. 692.91 ± 217.95 N/mm, P = 0.001; 2100.38 ± 649.54 N × mm vs. 1712.71 ± 626.02 N × mm, P = 0.015).

Conclusions: There was great interindividual variation in the anatomical morphology of the coracoglenoid space. Type I (hook-like) spaces bore lower forces, were less stiff, and bore less energy, which may constitute an anatomical predisposition to scapular neck fractures.

Keywords: Biomechanics; Coracoglenoid space; Fractures; Scapular neck.

Fig. 1

Measurement of morphological parameters of the coracoglenoid space. a Coracoglenoid distance (orange arrow), lateral view of the right scapula. b Coracoglenoid notch (orange arrow), posterolateral view of the right scapula

Fig. 2

Biomechanical axial compression test setup. The test specimen was loaded in the material testing machine

Fig. 3

Typical load–displacement curves of the two types after increasing the load in the static axial compression test. The triangular symbol represents the maximum failure load

Fig. 4

Distribution of the coracoglenoid space. CGN: coracoglenoid notch; CGD: coracoglenoid distance

Fig. 5

Configuration of the two coracoglenoid space type. View from the posterosuperior of the right scapula. a Type I (‘‘hook’’ shape). b Type II (‘‘square bracket’’ shape)

Fig. 6

Normal distribution diagrams of two types of measurement parameters. CGN: coracoglenoid notch; CGD: coracoglenoid distance

Fig. 7

Diagram of fracture under axial load to failure. a anterior–superior view of acromion. b posterior-inferior view of acromion. The proximal fracture line started at the scapular notch area (black arrow), it ran into the spinoglenoidal notch distally (white arrow)

Fig. 8

Biomechanical parameters of the two different types under axial loading. a Failure stiffness. b Failure load. c Failure energy