Osteochondroma represents the most common bone tumor and is a developmental lesion rather than a true neoplasm. It constitutes 20%-50% of all benign bone tumors and 10%-15% of all bone tumors. Its radiologic features are often pathognomonic and identically reflect its pathologic appearance. Osteochondromas are composed of cortical and medullary bone with an overlying hyaline cartilage cap and must demonstrate continuity with the underlying parent bone cortex and medullary canal. Osteochondromas may be solitary or multiple, the latter being associated with the autosomal dominant syndrome, hereditary multiple exostoses (HME). Complications associated with osteochondromas are more frequent with HME and include deformity (cosmetic and osseous), fracture, vascular compromise, neurologic sequelae, overlying bursa formation, and malignant transformation. Malignant transformation is seen in 1% of solitary osteochondromas and in 3%-5% of patients with HME. Continued lesion growth and a hyaline cartilage cap greater than 1.5 cm in thickness, after skeletal maturity, suggest malignant transformation. Variants of osteochondroma include subungual exostosis, dysplasia epiphysealis hemimelica, turret and traction exostoses, bizarre parosteal osteochondromatous proliferation, and florid reactive periostitis. Recognition of the radiologic spectrum of appearances of osteochondroma and its variants usually allows prospective diagnosis and differentiation of the numerous potential complications, thus helping guide therapy and improving patient management.

In the last several years, many employers have decided to automatically enroll their new employees in the company 401(k) plan. Using several years of administrative data from three large firms, we analyze the impact of automatic enrollment on 401(k) participation rates, savings behavior, and asset accumulation. We find that although employees can opt out of the 401(k) plan, few choose to do so. As a result, automatic enrollment has a dramatic impact on retirement savings behavior: 401(k) participation rates at all three firms exceed 85%, but participants tend to anchor at a low default savings rate and in a conservative default investment vehicle. We find that initially, about 80% of participants accept both the default savings rate (2% or 3% for our three companies) and the default investment fund (a stable value or money market fund). Even after three years, half of the plan participants subject to automatic enrollment continue to contribute at the default rate and invest their contributions exclusively in the default fund. The effects of automatic enrollment on asset accumulation are not straightforward. While higher participation rates promote wealth accumulation, the low default savings rate and the conservative default investment fund undercut accumulation. In our sample, these two effects are roughly offsetting on average. However, automatic enrollment does increase saving in the lower tail of the savings distribution by dramatically reducing the fraction of employees who do not participate in the 401(k) plan.

This paper summarizes the empirical evidence on how defaults impact retirement savings outcomes. After outlining the salient features of the various sources of retirement income in the U.S., the paper presents the empirical evidence on how defaults impact retirement savings outcomes at all stages of the savings lifecycle, including savings plan participation, savings rates, asset allocation, and post-retirement savings distributions. The paper then discusses why defaults have such a tremendous impact on savings outcomes. The paper concludes with a discussion of the role of public policy towards retirement saving when defaults matter.

Defaults can have a dramatic influence on consumer decisions. We identify an overlooked but practical alternative to defaults: requiring individuals to make an explicit choice for themselves. We study such "active decisions" in the context of 401(k) saving. We find that compelling new hires to make active decisions about 401(k) enrollment raises the initial fraction that enroll by 28 percentage points relative to a standard opt-in enrollment procedure, producing a savings distribution three months after hire that would take three years to achieve under standard enrollment. We also present a model of 401(k) enrollment and characterize the optimal enrollment regime. Active decisions are optimal when consumers have a strong propensity to procrastinate and savings preferences that are highly heterogeneous. Naive beliefs about future time-inconsistency strengthen the normative appeal of the active-decision enrollment regime. However, financial illiteracy favors default enrollment over active decision enrollment.

We thank Hewitt Associates for their help in providing the data. We are particularly grateful to Lori Lucas and Jim McGhee, two of our many contacts at Hewitt. We also thank James Poterba and Olivia Mitchell for comments. Choi acknowledges financial support from a National Science Foundation Graduate Research Fellowship. Laibson and Madrian acknowledge financial support from the National Institute on Aging (R01-AG-16605 and R29-AG-013020 respectively). Laibson also acknowledges financial support from the MacArthur Foundation and the Sloan Foundation. The views expressed herein are those of the authors and not necessarily those of the National Bureau of Economic Research.