Current concepts of traumatic elbow instability are developing at a rapid pace. Recent trends include a shift in interest from the medial to the lateral side of the elbow; from the ligamentous to the osseous and articular contributions to stability; and from consideration of the component parts of the injury (e.g. radial head, coronoid process) to an appreciation of the importance of the overall pattern of injury.1 The Orthopaedic Hand Service at the Massachusetts General Hospital has a long-standing interest in elbow trauma and has made a number of recent contributions to the field.

From Medial to Lateral

          Since Morrey and colleagues published their cadaver studies2, 3, the anterior band of the medial collateral ligament has been considered one of the most important stabilizers of the elbow. Their data suggest that the medial collateral ligament is the primary stabilizer of the elbow under a valgus stress, with the radial head playing a less important, secondary role.3 According to clinical experience, it may be more appropriate to consider the functions of the medial collateral ligament and radial head as overlapping and complimentary rather than hierarchical. A person with either an attenuated medial collateral ligament or an absent radial head can have difficulty performing activities that place a vigorous valgus stress on the elbow such as throwing, but usually has little difficulty with normal daily activities. On the other hand, when the medial collateral ligament and radial head are injured simultaneously, the elbow can become very unstable and prone to subluxation or dislocation.

From Ligamentous to Osseous/Articular Structures

          Most posterior dislocations of the elbow without associated fracture are stable after closed reduction.7 This inherent stability has led many to emphasize the primacy of the osseous and articular contributions to stability. This concept is influencing the treatment of fracture-dislocations of the elbow. If the osseous anatomy is restored, it is argued, then it should be possible to treat the elbow as if it were a simple dislocation, allowing gentle active mobilization in the immediate post-operative period without having to repair the ligaments.1, 8

          The importance of the radial head to the stability of the elbow with ligament damage has been demonstrated in the laboratory and clinical settings.2, 3, 9, 10 Contact between the radial head and capitellum provides stability under valgus stress and an anterior buttress against posterior subluxation or dislocation of the ulnohumeral joint. It also maintains tension in the lateral collateral ligament complex. In the past, resection of the radial head was advocated for comminuted fractures, even in the face ligament injury of the elbow. Currently, most elbow authorities recommend repair or prosthetic replacement of the radial head when the ligamentous stabilizers of the forearm or elbow have been injured.1 Comminuted fractures of the radial head are often associated with such ligament damage.11

          Unfortunately, the ideal radial head prosthesis has yet to be developed. Stiffer metal prostheses have become more popular after laboratory studies suggested the inadequacy of prostheses made of silicone rubber. However, there are a number of drawbacks to current metal prostheses. First of all, the stem size of one popular design is too large to fit into the radial neck of a large percentage of healthy adults.12 Secondly, there is concern that the stiff metal prosthesis can cause painful wear of the capitellum. Removal of a metal prosthesis is very difficult, and often requires that the origin of the lateral collateral ligament be released so that the elbow can be subluxated. Finally, current prostheses cannot account for the situation in which fragmentation extends below the radial head, into the radial neck. In this situation, restoration of radiocapitellar contact may require an osteoarticular allograft or other bone graft.13

          Very little data have been published on the treatment of coronoid fractures of the ulna. Regan and Morrey suggested that fragments representing less that 50% of the height of the coronoid process were relatively inconsequential, but that larger fragments require internal fixation.14 Their analysis did not account for the overall pattern of the injury associated with the fracture of the coronoid.

From Component Parts to Overall Patterns of Injury

          When we reviewed the elbow fracture-dislocations at the Massachusetts General Hospital and Beth-Israel Deaconess Hospitals we found that elbow fracture-dislocations occurred in a limited number of distinct injury patterns. The patterns were predictive of complications and overall prognosis and helped guide treatment.15 One major distinction was between injuries that represented true dislocation of the ulnohumeral joint - i.e., complete loss of apposition of the articular surfaces (Figure 1) - and those in which the trochlear notch of the ulna was disrupted by fracture, but the articular surfaces remained apposed. (Figures 2, 3) Nearly all of the olecranon fracture-dislocations were disruptions rather than true dislocations of the ulnohumeral joint.

          Large coronoid fractures - fractures representing more than 50% of the height of the coronoid - occurred almost exclusively in olecranon-fracture dislocation pattern injuries. Such injuries can either be anterior or posterior in direction. The ligamentous stabilizers are probably at least partially spared in these disruption type injuries and the key to a good result is anatomic restoration of the normal contour and dimensions of the trochlear notch of the ulna.16-18 Anatomic reduction of large coronoid fractures is central to this goal and also restores proper tension in the anterior band of the medial collateral ligament, which inserts at its base.18 In posterior olecranon fracture-dislocations, one must be aware of the potential for posterolateral rotatory instability of the ulnohumeral joint as a result of injury to the lateral collateral ligament complex.17 When such instability occurs, it is important to confirm restoration of the alignment of the trochlear notch of the ulna, and to consider repair or replacement of the radial head and reattachment of the origin of the lateral ligamentous complex to the lateral epicondyle.

          Small coronoid fractures - fractures representing less than 50% of the height of the coronoid, but more than a small fleck - are usually associated with posterior dislocation of the ulnohumeral joint and fracture of the radial head. This combination of injuries has been referred to as the terrible triad due to its propensity for recurrent dislocation, chronic instability, and poor functional results.19 It is therefore not suprising that our data suggest that smaller coronoid fractures lead to unsatisfactory results more often than the larger fractures that are usually surgically repaired. The best method of treating terrible triad type fracture-dislocations of the elbow remains uncertain. In particular, it seems that there might be a role for internal fixation of small coronoid fractures associated with posterior elbow dislocation and fracture of the radial head, but it is possible that repair of the radial head and lateral collateral ligament complex might be sufficient in many cases. Recent biomechanical data support clinical observations that even small coronoid fractures may destabilize the elbow.20, 21 The surgeon is pressed to decide early on whether or not to fix the coronoid fracture because access to the coronoid is best prior to repair of the radial head and lateral collateral ligament complex. If repair of the radial head and lateral ligaments alone proves inadequate, these repairs would have to be taken down to regain access for repair of the coronoid.

Conclusions

          There has been an amazing coalescence among surgeons interested in traumatic elbow instability with many of the concepts outlined above being widely agreed upon. There are many areas of continued uncertainty, and much potential for improvement in the treatment of patients with fracture-dislocations of the elbow.

David Ring, MD is a Resident in the Harvard Combined Orthopaedic Residency Program

Jesse B. Jupiter, MD is Chief of the Hand Surgery Service; Massachusetts General Hospital; and Professor of Orthopaedic Surgery at Harvard Medical School

Address correspondence to:
Jesse B. Jupiter, MD; ACC 527; 15 Parkman St.; Boston, MA 02114.
e-mail: jjupiter1@partners.org