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. 2020 Sep 21;8(9):2325967120952415.
doi: 10.1177/2325967120952415. eCollection 2020 Sep.

Morphological Features of the Ulnar Collateral Ligament of the Elbow and Common Tendon of Flexor-Pronator Muscles

Masahiro Ikezu  1 , Mutsuaki Edama  1   2 , Kanta Matsuzawa  1 , Fumiya Kaneko  1 , Sohei Shimizu  1 , Ryo Hirabayashi  1 , Ikuo Kageyama  2
Affiliations

Morphological Features of the Ulnar Collateral Ligament of the Elbow and Common Tendon of Flexor-Pronator Muscles

Masahiro Ikezu et al. Orthop J Sports Med. .

Abstract

Background: The anterior bundle (AB) of the ulnar collateral ligament is the most important structure for valgus stabilization of the elbow. However, anatomic relationships among the AB, posterior bundle (PB) of the ulnar collateral ligament, and common tendon (CT) of the flexor-pronator muscles have not been fully clarified.

Purpose: To classify the AB, PB, and CT and to clarify their morphological features.

Study design: Descriptive laboratory study.

Methods: This investigation examined 56 arms from 31 embalmed Japanese cadavers. The CT investigation examined 34 arms from 23 embalmed Japanese cadavers with CTs remaining. Type classification was performed by focusing on positional relationships with surrounding structures. Morphological features measured were length, width, thickness, and footprint for the AB and PB and attachment length, thickness, and footprint for the CT.

Results: The AB was classified as type I (44 elbows; 78.6%), can be separated as a single bundle, or type II (12 elbows; 21.4%), cannot be separated from the PB and joint capsule. The PB was classified as type I (28 elbows; 50.0%), can be separated as a single bundle; type IIa (6 elbows; 10.7%), posterior edge cannot be separated; type IIb (7 elbows; 12.5%), anterior edge cannot be separated; or type III (15 elbows; 26.8%), cannot be separated from the joint capsule. The CT was classified as type I (18 elbows; 52.9%), can be separated from the AB, or type II (16 elbows; 47.1%), cannot be separated from the AB. Significant differences in frequencies of AB, PB, and CT types were identified between men and women. Morphological features were measured only for type I of each structure, and reliability was almost perfect.

Conclusion: These results suggest that the AB, PB, and CT each can be classified into an independent form and an unclear form. Presence of the unclear form was suggested as one factor contributing to morphological variation.

Clinical relevance: This study may provide basic information for clarifying functional roles of the AB, PB, and CT.

Keywords: anatomy; baseball; elbow; ulnar collateral ligament injury.

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Conflict of interest statement

One or more of the authors has declared the following potential conflict of interest or source of funding: This study was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI grant No. JP19K11358 and a grant-in-aid program from Niigata University of Health and Welfare. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Figures

Figure 1.
Figure 1.
Sites of measurement of morphological features (left side, medial view). (A) Dissections of the anterior bundle (AB), anterior common tendon (ACT), and posterior common tendon (PCT). D, distal; MEC, medial epicondyle of the humerus; P, proximal. (B) Measurement site of AB length and width. (C) Measurement site of AB thickness. (D) Measurement site of attachment length and thickness of the ACT and PCT. AB length (1); AB width (proximal site) (2); AB width (intermediate site) (3); AB width (distal site) (4); AB thickness (intermediate site) (5); ACT attachment length (6); PCT attachment length (7); ACT thickness (intermediate site) (8); PCT thickness (intermediate site) (9).
Figure 2.
Figure 2.
Measurement of the footprint using the MicroScribe system (left side, medial view). Anterior bundle (AB) origin (1); AB insertion (2); posterior bundle (PB) origin (3); PB insertion (4); anterior common tendon (ACT) and posterior common tendon (PCT) humeral attachment (5); ACT ulnar attachment (6); PCT ulnar attachment (7); humerus (8); ulna (9); radius (10). D, distal; P, proximal.
Figure 3.
Figure 3.
Classification of the anterior bundle (AB), posterior bundle (PB), and common tendon (CT) (left side, medial view). AB type I: The AB is located superficial to the PB and joint capsule and can be separated as a single bundle. AB type II: The AB is located in the same layer as the PB and joint capsule and cannot be separated from them. PB type I: The anterior and posterior edges of the PB are located on the surface of the joint capsule and can be separated as a single bundle. PB type IIa: The anterior edge of the PB can be separated from the joint capsule, but the posterior edge cannot. PB type IIb: The posterior edge of the PB can be separated from the joint capsule, but the anterior edge cannot. PB type III: The PB cannot be separated from the joint capsule. CT type I: The AB is located superficial to the anterior common tendon (ACT) and posterior common tendon (PCT), and the ligament and tendon can be separated from each other. CT type II: The AB is located in the same layer as and cannot be separated from the ACT and PCT. Anterior bundle (1); medial epicondyle of the humerus (2); sublime tubercle of the ulna (3); posterior bundle (4); anterior common tendon (5); posterior common tendon (6). D, distal; P, proximal.
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