MRI of a painful carpal boss: variations at the extensor carpi radialis brevis insertion and imaging findings in regional traumatic and overuse injuries

Mika T Nevalainen,Johannes B Roedl,William B Morrison,Adam C Zoga

doi:10.1007/s00256-018-3136-9

Abstract

ObjectiveTo report patterns of MRI findings involving carpal boss and extensor carpi radialis brevis (ECRB) tendon insertion in individuals with overuse-related or post-traumatic wrist pain.Materials and MethodsEighty-four MRI cases with carpal bossing between December 2006 and June 2015 were analyzed by two fellowship-trained musculoskeletal radiologists. The following MRI findings were reviewed: type of carpal bossing (bony prominence, partial coalition, os styloideum), insertion of ECRB tendon (to the 3rd metacarpal, to carpal boss or to both), bone marrow edema (BME), insertion site, and tenosynovitis/tendinosis of ECRB tendon. Clinical information on wrist pain was available on 68 patients.ResultsFused carpal bossing was detected in 21%, partial coalition in 35%, and os styloideum in 44% of the cases. Regional BME was observed in 64% of the cases. When BME specifically at the carpal boss was assessed, 78% of stable and 50% of unstable bosses showed BME (p = 0.035). ECRB tendon inserted on a carpal boss in 20%, on the 3rd metacarpal bone in 35%, and on both sites in 45% of the cases. As BME at the carpal boss was assessed, BME was detected at the respective insertion sites in 71%, 35%, and 66% of the cases (p = 0.015). Dorsal wrist pain was associated with BME as 75% of the patients had regional BME in the vicinity of the carpal boss (p = 0.006).ConclusionA spectrum ranging from complete fusion of a boss to an entirely unfused os styloideum exists with a variable ECRB insertional anatomy. BME at the carpal boss is a consistent MRI finding.

Highlights

Carpal boss is defined as a bony protuberance on the dorsal base of the 3rd metacarpal bone on the quadrangular jointSkeletal Radiol (2019) 48:1079–1085 carpal boss might be more likely to be on the dominant hand of an individual in their early 30s [3, 4, 6]
84 cases with carpal bossing were identified at magnetic resonance imaging (MRI): fully fused carpal bossing was logged in 21% (18 out of 84), partial coalitions in 35% (29 out of 84), and an non-united os styloideum in 44% of subjects (37 out of 84; Fig. 1)
The painful carpal boss is a well-published clinical syndrome, little work has examined the relationship between biomechanical avulsive forces at the extensor carpi radialis brevis (ECRB) insertion and symptoms/ anatomical variations

Summary

Introduction

Carpal boss is defined as a bony protuberance on the dorsal base of the 3rd metacarpal bone on the quadrangular jointSkeletal Radiol (2019) 48:1079–1085 carpal boss might be more likely to be on the dominant hand of an individual in their early 30s [3, 4, 6]. Regional soft-tissue anatomy, is complex and the extensor carpi radialis brevis (ECRB) tendon generally inserts on the base of the 3rd metacarpal, in close proximity to a carpal boss. We noted several cases of symptomatic carpal boss that had clinical and MRI findings indicating stress or avulsive injury at the ECRB insertion [10]. We hypothesized that osseous and soft-tissue anatomical variations at and around a carpal boss might contribute to pain syndromes at the dorsum of the wrist, and that recognition of these variations might contribute to improved treatment planning. We set out to systematically categorize anatomical variations at the ECRB insertion and the carpal boss, and to describe the patterns of MRI findings associated with the painful carpal boss, including types of os styloideum and the relationship of the ECRB tendon insertion with osseous anatomy

Methods

Results

Conclusion