Imaging Quiz Answer: A Swollen, Painful Elbow
Jane T. Servi, MD, Robert J. Johnson, MDTHE PHYSICIAN AND SPORTSMEDICINE - VOL 24 - NO. 9 - SEPTEMBER 96
The lateral radiograph of the right elbow (figure 2) demonstrates anterior and posterior fat-pad signs: displacement of the anterior and posterior elbow fat pads because of expansion of the synovial capsule. Accumulation or leakage of intracapsular fluid into the intra-articular space is responsible for displacing the fat pads. There is no obvious fracture. After x-ray, the presumed diagnosis was nondisplaced fracture of the radial head.
A positive fat-pad sign reflects a response to an intra-articular disease process--such as occult fracture of the olecranon, radial head, or coronoid process. Other causes of the fat-pad sign include intra-articular blood from trauma (such as a spontaneously reduced dislocation) or hemophilia; transudates from rheumatoid, crystal, synovial, or neuropathic arthropathies; and exudates from infection and neoplasia.
Elbow trauma, including fracture, is most commonly sustained during a fall onto an outstretched arm, which often occurs in sports settings. Fractures and other trauma occur rarely with forced manipulation of the elbow, as with this patient.
Norell (1) first associated a radiographic posterior fat-pad sign with elbow trauma in 1954. His theory that a posterior fat-pad sign would be present with various arthropathies was later confirmed. Bledsoe and Izenstark (2) described the anterior fat-pad sign in 1959.
The anterior fat pad is a summation of the radial and coronoid fat pads. The shape is determined by the brachial muscle in extension and by intrinsic surface tension, bone, capsule, and intra-articular volume in flexion. The shape of the posterior fat pad, located in the olecranon fossa, is determined by the triceps tendon and anconeus muscle during flexion. The posterior fat pad is more mobile in extension, and the shape is defined by surface tension, bone, capsule, and intra-articular volume.
Standard x-rays of the elbow include an anteroposterior view with the elbow extended and a true lateral view with the elbow flexed to 90° and the forearm neutral. The fat pads are best visualized in the lateral view.
In a positive anterior fat-pad sign, the fat pad is displaced ventrally and superiorly, changing the inferior margin from convex to concave. This configuration, an exaggeration of its normal appearance, resembles a ship's sail ("sail sign"). A false-negative anterior fat-pad sign can be seen with insufficient effusion, poor positioning, extracapsular fracture, and capsular rupture.
When the posterior fat-pad sign is positive, the extension of the synovial capsule with the elbow in 90° of flexion displaces the fat pad superiorly and dorsally. A false-positive posterior fat-pad sign can occur with the elbow in extension and is caused by olecranon process displacement and posterior capsule laxity. A paradoxical positive posterior fat-pad sign can occur with extra-articular processes. Neoplasia or hemorrhage from a supracondylar humeral fracture may elevate the periosteum and displace the proximal half of the posterior fat pad dorsally.
Traumatic elbow injuries without evident fracture that result in a positive fat-pad sign may be treated conservatively with a sling, ice, gentle range-of-motion exercises, and analgesics as needed. Follow-up x-ray, especially an oblique view, may demonstrate a fracture of the radial head.
This patient was treated with a sling, ice, analgesics, and gentle range-of-motion exercises. She returned for re-evaluation 5 days postinjury and had decreased effusion and increased range of motion, but continued pain with valgus stress. She was asked to return for re-examination 5 days later, with a plan to obtain an oblique radiograph if she did not continue to demonstrate improvement. However, the patient did not keep her appointment and attempts to arrange follow-up evaluation were unsuccessful.
The key to treatment is to closely monitor pain, range of motion, and strength. Failure to resolve pain and regain range of motion and strength may indicate the need for further evaluation.
Dr Servi is a former sports medicine fellow and Dr Johnson is director of Primary Care Sports Medicine at Hennepin County Medical Center in Minneapolis. Dr Servi is a member and Dr Johnson is a fellow of the American College of Sports Medicine. Dr Johnson is an editorial board member of The Physician and Sportsmedicine. Address correspondence to Robert J. Johnson, MD, Hennepin County Medical Center, Family Medical Center, 5 W Lake St, Minneapolis, MN 55408.
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