Elbow dislocations occur in approximately 6 out of every 100,000 people during their lifetime. The elbow is the second most commonly dislocated joint in the adult upper limb.1 Dislocations constitute 10% to 25% of all injuries to the elbow, and are most prevalent in young adults.2 Isolated coronoid fractures are uncommon and are usually associated with injuries to the collateral ligaments.3 Although the coronoid is considered one of the primary stabilizers of the elbow, there are only limited clinical and biomechanical studies investigating these injuries. Interest in the coronoid has recently increased due to the recognized importance of anteromedial coronoid facet fractures.
The elbow is composed of three articulations:
- Ulnohumeral joint
- Radiocapitellar joint
- Proximal radioulnar joint
The ulnohumeral joint, along with the LCL and MCL, is considered a primary stabilizer of the elbow.4,5 The coronoid makes up the distal aspect of the ulnohumeral joint and articulates with the trochlea. It consists of an anterior coronoid process and an anteromedial facet. The anterior coronoid process provides attachments for the anterior capsule and the brachialis muscle, and acts as a buttress to posteriorly directed forces, thereby resisting posterior ulnohumeral displacement.6 Biomechanical studies have shown that 50% of the coronoid is required to provide normal kinematics and posterior and varus stability.7
The anteromedial facet has a medial projection, making it susceptible to injury during an elbow dislocation,8 and it has been reported to provide posteromedial stability of the ulnohumeral joint^.9^ Fractures of the anteromedial facet have been linked to posteromedial rotational instability (PMRI) of the elbow. and if untreated. are thought to rapidly lead to posttraumatic arthritis.10-14 A recent biomechanical study demonstrated that small anteromedial coronoid fractures affect elbow kinematics.9 This study suggested that internal fixation of anteromedial coronoid facet fractures larger than 2.5 mm should be considered and that LCL repair alone is insufficient to restore kinematics in most patients with this injury.
The LCL consists of the lateral ulnar collateral ligament (LUCL), the radial collateral ligament (RCL), and the annular ligament (AL). The LUCL originates on the lateral epicondyle and inserts onto the supinator crest of the proximal ulna. The LCL is considered the primary soft tissue stabilizer of varus angulation and posterolateral rotation.15
The MCL consists of three distinct bundles: anterior, posterior and transverse. The anterior bundle is considered the most important ligamentous stabilizer against valgus stress, PMRI, and internal rotation of the ulna. It originates on the medial epicondyle and inserts onto the sublime tubercle, which is located on the anteromedial base of the coronoid process. The posteromedial bundle of the MCL has been shown to contribute to varus and internal rotational stability of the elbow.16
Regan and Morrey17 classified coronoid fractures into three types (1-3) based on height in the coronal plane:
- Type 1 fractures involve the anterior tip of the coronoid.
- Type 2 fractures involve up to 50% of the coronoid height.
- Type 3 fractures are fractures involving more than 50% of the coronoid height.
This classification system continues to be useful and is commonly employed clinically. However, it does not consider fractures that occur in the sagittal plane, particularly those involving the anteromedial facet of the coronoid.
O’ Driscoll et al11 introduced a more comprehensive classification that includes the anteromedial facet and is based on anatomical location, fracture size, and mechanism of injury (Figure 1):
- Type 1 fractures involve the tip of the coronoid process and are divided into two subtypes based on size of the fracture: subtype I fractures, smaller than 2 mm, and subtype II fractures, larger than 2 mm.
- Type 2 fractures involve the anteromedial facet and are divided, based on anatomical location, into three subtypes: subtype I, involving the rim; subtype II, involving the rim and the tip; and subtype III, involving the rim and the sublime tubercle with or without the tip.
- Basal coronoid fractures make up Type 3 fractures, involve at least 50% of the height of the coronoid, and are divided into two subtypes, depending on whether the fracture involves the base of the olecranon.
Figure 1. O’Driscoll Coronoid Fracture Classification. Type 1 fractures involve the tip (A). Type 2 fractures involve the anteromedial facet of the coronoid and are subdivided into three subtypes: subtype I involves the rim, subtype II involves the rim and tip, and subtype III involves the rim and sublime tubercle with or without the tip (B). Type 3 fractures involve the base and body of the coronoid (C).
Anteromedial coronoid (AMC) fractures (O’Driscoll type 2) are thought to occur by falling on an outstretched arm, with the forearm in pronation, and varus/posteromedial rotation with axial loading through the elbow. These fractures are commonly accompanied by injuries to the LCL and posterior bundle of the MCL. The trochlea causes a shear or depression fracture of the anteromedial facet of the coronoid. Injury to the anterior bundle of the MCL can also occur with AMC fractures, particularly with subtype III. The combined ligamentous and osseous injury can result in PMRI, articular incongruity, alteration in joint contact patterns, and arthrosis.11
A detailed neurovascular examination must be performed before and after reduction of a dislocated elbow. The shoulder and wrist (particularly the DRUJ) should be evaluated for associated injury. Although rare, compartment syndrome and vascular injury can occur and should be ruled out.
Radiographic signs of these fractures are often subtle, such as loss of a parallel medial ulnohumeral joint line, or varus mal-alignment. A double crescent sign, which represents a depressed anteromedial facet of the coronoid, may be seen on a lateral radiograph (Figure 2).11 The radiocapitellar joint can also be widened with a LCL injury. Computed tomography (CT) is recommended, with a low threshold, if there are any clinical or radiographic concerns.18 CT can clarify fracture patterns, identify osteochondral fragments within the joint and assist in selecting the surgical approach and type of internal fixation.
Figure 2. AP and lateral radiographs of a left elbow. The double arch sign can be seen on the lateral view (solid white arrows). The AP view clearly demonstrates an anteromedial coronoid fracture involving the rim and sublime tubercle (Type 2, subtype III).
The literature on AMC fractures is very limited, and the exact treatment indications and optimal surgical techniques and fixation have not yet been established. Currently, recommendations are based on a single biomechanical study,9 a small clinical series,10 and expert opinion.13,14,19 Internal fixation of AMC fractures and collateral ligament repair are recommended to avoid rapid degeneration of the ulnohumeral joint.10,18 Based on biomechanical evidence, internal fixation of AMC facet fractures larger than 2.5 mm should be considered, as isolated repair of the LCL will not restore kinematics in the majority of patients with this injury. It may be possible to manage small (2.5 mm) subtype I AMC fractures, with an intact MCL, non-operatively using a strict rehabilitation protocol.
A posterior incision is recommended for the surgical treatment of anteromedial coronoid fractures to allow access to both the medial and lateral sides of the elbow. A medial fasciocutaneus flap should be developed, followed by the identification and release of the ulnar nerve. A Taylor approach, through the bed of the ulnar nerve (between the heads of flexor carpi ulnaris), provides the most complete exposure to the anteromedial coronoid, the sublime tubercle, and the MCL. If necessary, this approach can be extended proximally by releasing the flexor-pronator muscle origin off the supracondylar ridge and reflecting the anterior capsule off the humerus. The most difficult aspect of this approach is preserving the origin of the MCL on the medial epicondyle and the insertion on the sublime tubercle. An injured MCL should be repaired.
While the optimal fixation of anteromedial coronoid fractures has not yet been determined, buttress plate or screw fixation has been suggested. Once the coronoid is secured, the LCL should be repaired through either an anterolateral EDC split or posterolateral Kocher approach. To restore stability, reestablishing the isometric origin of the LCL on the lateral epicondyle is essential. Non-comminuted AMC fractures involving the rim and tip can be addressed with arthroscopic-assisted percutaneous fixation. However, this method requires considerable expertise with elbow arthroscopy and clinical studies are needed to determine the efficacy, safety, and applicability of this technique. An important potential advantage of arthroscopic fixation is that it avoids the extensive anteromedial dissection required to access the coronoid.
Reports on the outcomes of anteromedial coronoid fractures are very limited. Doornberg and Ring10 reported a retrospective review of 67 coronoid fracture dislocations of the elbow. Eleven of those patients developed varus posteromedial instability, all of which were associated with anteromedial facet fractures of the coronoid. In a second study, Doornberg and Ring reported on 18 patients with AMC fractures with an average follow-up of 26 months. Of these, six patients had malalignment of the anteromedial facet, and all developed varus subluxation, arthrosis of the elbow, and fair or poor function. The remaining 12 patients, treated with stable anatomical fixation of the AMC, had a good or excellent functional result. Based on these two studies and other case reports, repair of the LCL and ORIF of anteromedial coronoid fracture are recommended, as well as repair of the MCL when necessary.
Unrecognized or untreated AMC fractures can have devastating outcomes and can potentially result in career-ending injuries. For this reason, it is important to have a high level of suspicion for these fractures. CT should be considered for most if not all of these injuries. Further research is required to determine the outcome of non-operative and operative management. Treatment indications, protocols, and optimal surgical techniques for AMC fractures have not yet been established. Preoperative planning, proficient knowledge of elbow anatomy, and patience are required for successful treatment of these difficult injuries.
- Morrey BF. The elbow and its disorders. 3rd ed. Philadelphia: Saunders; 2000.
- Josefsson PO, Nilsson BE. Incidence of elbow dislocation. Acta Orthop Scand 1986 Dec;57(6):537-8.
- Hildebrand KA, Patterson SD, King GJ. Acute elbow dislocations: simple and complex. [Review] [68 refs]. Orthopedic Clinics of North America 1999 Jan;30(1):63-79.
- Morrey BF, An KN. Stability of the elbow: osseous constraints. Journal of Shoulder & Elbow Surgery 2005 Jan;14(1 Suppl S):174S-8S.
- O'Driscoll SW, Jupiter JB, King GJ, Hotchkiss RN, Morrey BF. The unstable elbow. [Review] [64 refs]. Instructional Course Lectures 2001;50:89-102.
- Regan W, Morrey B. Fractures of the coronoid process of the ulna. Journal of Bone & Joint Surgery - American Volume 1989 Oct;71(9):1348-54.
- Beingessner DM, Dunning CE, Stacpoole RA, Johnson JA, King GJ. The effect of coronoid fractures on elbow kinematics and stability. Clin Biomech (Bristol , Avon ) 2007 Feb;22(2):183-90.
- Doornberg JN, de Jong IM, Lindenhovius AL, Ring D. The anteromedial facet of the coronoid process of the ulna. J Shoulder Elbow Surg 2007 May 16;16(5).
- Pollock JW, Brownhill J, Ferreira L, et al. The effect of anteromedial facet fractures of the coronoid and lateral collateral ligament injury on elbow stability and kinematics. Journal of Bone & Joint Surgery - American Volume 2009 Jun;91(6):1448-58.
- Doornberg J., Ring D. Fracture of the Anteromedial Facet of The Coronoid Process. Journal of Bone and Joint Surgery 2006 Jan 10;88A(10):2216-30.
- O'Driscoll SW, Jupiter JB, Cohen MS, Ring D, McKee MD. Difficult elbow fractures: pearls and pitfalls. [Review] [91 refs]. Instructional Course Lectures 2003;52:113-34.
- Ring D. Fractures of the coronoid process of the ulna. [Review] [34 refs]. Journal of Hand Surgery - American Volume 2006 Dec;31(10):1679-89.
- Sanchez-Sotelo J, O'Driscoll SW, Morrey BF. Medial oblique compression fracture of the coronoid process of the ulna. Journal of Shoulder & Elbow Surgery 2005 Jan;14(1):60-4.
- Sanchez-Sotelo J, O'Driscoll SW, Morrey BF. Anteromedial fracture of the coronoid process of the ulna. Journal of Shoulder & Elbow Surgery 2006 Sep;15(5):e5-e8.
- Dunning CE, Zarzour ZD, Patterson SD, Johnson JA, King GJ. Ligamentous stabilizers against posterolateral rotatory instability of the elbow. J Bone Joint Surg Am 2001 Dec;83-A(12):1823-8.
- Pollock JW, Brownhill J, Ferreira LM, McDonald CP, Johnson JA, King GJ. Effect of the posterior bundle of the medial collateral ligament on elbow stability. J Hand Surg Am 2009 Jan;34(1):116-23.
- Regan W, Morrey BF. Classification and treatment of coronoid process fractures. Orthopedics 1992 Jul;15(7):845-8.
- Doornberg JN, Ring D. Coronoid fracture patterns. Journal of Hand Surgery - American Volume 2006 Jan;31(1):45-52.
- Cohen MS. Fractures of the coronoid process. [Review] [12 refs]. Hand Clinics 2004 Nov;20(4):443-53.
Reprinted with permission from the Summer 2010 issue of COA Bulletin