Osborne Retinaculum

Dynamic US of the elbow can be used to help demonstrate abnormal dislocation of the ulnar nerve, with or without snapping triceps syndrome. This finding typically occurs in the cubital tunnel, an osteofibrous tunnel formed by a groove between the olecranon and the medial epicondyle and bridged by the Osborn retinaculum. As described in Chapter 8, dynamic scanning during full elbow flexion can allow continual depiction of the intermittent dislo-... 

The anconeus epitrochlearis is a small accessory muscle (prevalence ranging from 1% to 34%) that forms the roof of the cubital tunnel, replacing the Osborne retinaculum and joins the posterior aspect of the medial epicondyle with the medial aspect of the olecranon.. This muscle is often bilateral and can cause ulnar neuropathy by occupying space within the cubital tunnel and decreasing its free volume during full elbow flexion. Somewhat equivalent to the anconeus epitrochlearis, an anomalous myotendinous junction of the triceps may also be prominent over the posteromedial side of the cubital tunnel (see Sect. 8.5.4.S). 

Fig. 8.64a,b. Snapping triceps syndrome. Schematic drawings of the posterior aspect of the elbow in a extension and b 90° flexion demonstrate the ulnar nerve (arrows) as it passes through the cubital tunnel and a prominent medial head (mh) of the triceps muscle (tin). Note the absence of the Osborne retinaculum when compared with Fig. 8.7c. With elbow flexion, the medial edge of the triceps (arrowheads) and the ulnar nerve move anterior to the tip of the epicondyle. T, distal triceps tendon /c , flexor carpi ulnaris...

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