Explorative study of the sensitivity and specificity of the pronator quadratus fat pad sign as a predictor of subtle wrist fractures

F Fallahi,P Jennings,Gail Jefferson,H Jafari,R Read

doi:10.1007/s00256-012-1451-0

Abstract

ObjectiveTo investigate the value of post-traumatic pronator quadratus (PQ) fat pad sign as a reliable predictor of subtle wrist fractures.Materials and methodsThis was a prospective study of 68 patients undergoing X-ray for traumatic wrist injuries and subsequent MRI. The reliability of a positive PQ fat pad sign on X-ray, defined as either raised, interrupted or obliterated, was evaluated in detection of subtle wrist fractures.ResultsOut of 68 patients, 28 had a positive PQ sign without any obvious bony injuries on plain radiographs; of these, the PQ fat pad was obliterated in 11, disrupted in 12, and raised in five cases. Fractures defined as cortical interruption or trabecular fractures were revealed in 13/28 (46 %) patients with a positive PQ sign but only in 7/40 (18 %) patients with a negative sign. With regards to different types of abnormal PQ fat planes, fractures were present in 7/12 patients with a disrupted plane (58 %), 6/11 patients with an obliterated plane (54 %), and none of the patients with a raised plane. The overall sensitivity and specificity of a positive PQ sign in the prediction of occult wrist fractures were 65 and 69 %, respectively.ConclusionsOur findings indicate that a positive pronator quadratus (PQ) fat pad sign is not a reliable predictor of subtle fractures of the wrist, although we believe that it is a useful radiographic sign in justifying MRI for further clarification of possible joint abnormalities including occult fracture and cortex interruption.

Highlights

The pronator fat pad is a small fat plane at the volar aspect of the distal forearm
With regards to different types of abnormal pronator quadratus (PQ) fat planes, fractures were present in 7/12 patients with a disrupted plane (58 %), 6/11 patients with an obliterated plane (54 %), and none of the patients with a raised plane
Our findings indicate that a positive pronator quadratus (PQ) fat pad sign is not a reliable predictor of subtle fractures of the wrist, we believe that it is a useful radiographic sign in justifying magnetic resonance imaging (MRI) for further clarification of possible joint abnormalities including occult fracture and cortex interruption

Summary

Introduction

The pronator fat pad is a small fat plane at the volar aspect of the distal forearm. A fracture of the distal forearm can displace this and create a radiologically “positive” fat pad sign (Fig. 1).The pronator quadratus (PQ) fat pad (FP) sign was first described in 1963 by MacEwan who observed an altered FP sign in 295 of 300 patients with fractures at the level of PQ attachment [1]. The pronator fat pad is a small fat plane at the volar aspect of the distal forearm. A fracture of the distal forearm can displace this and create a radiologically “positive” fat pad sign (Fig. 1). The pronator quadratus (PQ) fat pad (FP) sign was first described in 1963 by MacEwan who observed an altered FP sign in 295 of 300 patients with fractures at the level of PQ attachment [1]. Zammit-Maempell et al [4] measured the pronator value (maximum distance between the pronator fat line and the distal radius) in 1,453 patients with wrist injury and reported a statistically significant increased pronator value in fractures of the distal forearm. The pronator FP was abnormal in only 51 % of forearm fractures. Sasaki and Sugioka [5] classified the radiological appearances of the PQ sign into four types ranging from an undisplaced straight or gently convex curve to an absent soft-tissue shadow

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