Essex-Lopresti—When Do All Three Levels Require Attention?

History

Although the eponym for forearm longitudinal instability is known as Essex-Lopresti, Dr. Peter Essex-Lopresti was not the first person who reported the injury. It was first described by Brockman in 1931. Curr and Coe later reported on a case of a dislocation “on both ends of the radius” 15 years later in 1946. However, in a case report by Dr. Essex-Lopresti in 1951, he correctly identified forearm instability as part of the injury constellation after his first patient had severe radial impingement following a radial head excision. It was his observation that expanded the diagnosis from a proximal radius injury and distal radioulnar joint (DRUJ) dislocation to include the disruption of the interosseous membrane (IOM). He predicted that preventing proximal migration by maintaining radial length was paramount for healing of the IOM and DRUJ, and therefore a successful recovery.

Anatomy and Biomechanics

In one sense, the forearm can be visualized as a bicondylar joint with the proximal radioulnar joint and DRUJ as the condyles and the IOM as the cruciate ligament. The three levels are interdependent. Thus an injury at one level has a high likelihood of a reciprocal injury at the other two levels. The radius travels like a bucket handle around the ulna in pronation and supination.

Hennequin, a French anatomist, first characterized the IOM as a ligament in 1894. Subsequently, more detailed histologic studies have confirmed that the structural arrangement of the collagen and its biomechanical behavior is that of a ligament and not just a membrane that separates the flexor and extensor compartments. ^, Microscopically, the IOM can be divided into three sections: (1) proximally with the proximal oblique cord (known as the ligament of Weitbrecht) and the dorsal oblique accessory cord ; (2) centrally, the major central band and variable accessory bands; and (3) distally, the distal oblique bundle (DOB) as seen in Fig. 56.1 .

The central band is the largest component and the major IOM stabilizer to axial stability. It is stout with an average width of 1.1 cm. Its origin begins at 7.7 cm from the radial head and spans obliquely at an angle of 21 degrees to the ulna axis to insert on the ulna 13.7 mm from the olecranon tip. Noda localized the origin of the central band to 60% of the radial length and 33% of the ulnar length ( Fig. 56.2 ). In a biomechanical study, Pfaeffle confirmed that the modulus of elasticity and the ultimate tensile strength was similar to that of the patellar tendon. The central band plays a major role in the longitudinal load transfer of the wrist to the elbow and of the radius to the ulna. It also helps to maintain transverse forearm stability.

The DOB is a short ligament that runs from the proximal ulnar border of the pronator quadratus distally toward the sigmoid notch on the radius. It is a major stabilizer of the DRUJ and adds support to axial and transverse stability. The role of the proximal IOM ligaments is yet to be fully defined; currently, they are felt to play a role in stabilizing the proximal radioulnar joint similar to the role of the DOB distally. Werner and colleagues calculated the contributions of the various portions of IOM to transverse stability: proximal 18%, central band 25%, and DOB 31%.

The IOM has four primary functions: (1) transmit load from the wrist to the elbow, (2) transfer load from the radius to the ulna, (3) maintain forearm stability, and (4) help maintain DRUJ stability. In a cadaveric study by Birkbeck et al., axial forces in supination through the distal radius and distal ulna are 68% and 32%, respectively. The force is then translated through the IOM to equilibrate, resulting in 51% at the proximal radius and 49% at the proximal ulna. However, when the IOM was divided, there was no load transfer within the forearm, and the proximal radiocapitellar joint experienced significantly larger amount of force than the proximal ulna ( Fig. 56.3 ).

Pathomechanics

Essex-Lopresti injuries result from an axial force to the upper extremity. Reports in the literature range from high-energy motor vehicle accidents to low-energy falls from height. ^, The differing amount of force required to create this injury leads to varying severities and presentations. The position of the forearm influences the injury pattern as well. In a cadaveric study by McGinley, the authors noted that Essex-Lopresti injuries occurred more frequently when the forearm was pronated at an average 70 ± 25 degrees, while isolated radial head fractures and both bone forearm fractures occurred in less pronation.

Many studies have evaluated the strength of the central band to identify the force needed to disrupt it. ^{, , ,} Wegmann applied 210 J to cadaveric specimen forearms while filming with a high-speed video. He reported that with increasing longitudinal force, the central band failed first, followed by radial head fracture and then the triangular fibrocartilage complex (TFCC). However, these in vitro models neither evaluate the role of the accessory structures (such as the TFCC and the distal oblique ligament) nor explain the incompetence of the central band that can occur after radial head excision. In one cadaver study, the strength of the central and accessory bands was tested with a slow force application and revealed a biphasic failure.

The two common scenarios are the acute presentation recognized at the time of initial injury and the chronic presentation, which occurs over time and only after the radial head is excised.

The primary stabilizer to axial instability is the radial head and thus preservation of the radial head is the first line of treatment. When the radial head is not salvageable and removed, the secondary restraints, that is, the central band and the DRUJ stabilizers, become critical. The early literature debated the relative contributions of these secondary restraints. Hotchkiss showed that with radial head excision, the IOM contributes to 71% of axial load stability compared to only 8% in the TFCC. He also noted that for the radius to migrate proximally >2 mm, the TFCC must also be disrupted. Other studies emphasized the role of the DRUJ stabilizers. Skahen, using a three-space tracking system and a differential variable reluctance transducer (DVRT) strain gauge attached to the central band, concluded that the central band and the distal DRUJ stabilizers were of equal importance in preventing axial migration of the radius.