Freiberg Disease

♦ INTRODUCTION

Freiberg disease is an avascular necrosis¹ affecting the second metatarsal head and, much less commonly, the third and fourth metatarsal heads² (Figure 10.1). The condition manifests in young adolescents, mainly women, and has a variable clinical course. It was first described by Albert H. Freiberg in 1914³ and later by Köhler in 1915; hence, it is also known as Köhler second disease.⁴

♦ PATHOGENESIS

The pathogenetic pattern seen in Freiberg disease is identical to that of avascular necrosis of the femoral head. Several theories have been proposed to explain the development of necrosis localized in the metatarsal heads; the two most widely accepted is as follows:

Vascular theory
Mechanical theory (microtraumas)

Figure 10.1 A, B. Anteroposterior (AP) and oblique radiographs of Freiberg disease.

Vascular and mechanical factors are closely related. Given the specific biomechanical characteristics of the foot, mechanical factors seem more likely, as the second metatarsal head is subject to greater mechanical demands during the normal gait cycle, reason why it was first referred to as Freiberg infraction.³,⁴ However, trauma itself could not reliably explain all cases.⁵

It is a degenerative process involving the epiphysis that results in osteonecrosis of the subchondral cancellous bone. By improving the biomechanical and vascular environment, the process can be altered in such a way as to restore normal physiology (followed by regeneration or recalcification).³ If not, the process continues to subchondral collapse and fragmentation of the joint surface.⁶

According to Gauthier,²,⁷ the necrosis progresses through five stages:

Stage 0: subchondral necrosis of the upper portion of the metatarsal head. The cartilage may be intact or slightly fractured.
Stage 1: subchondral necrosis progresses to a necrotic osteocartilaginous fragment. The hyaline cartilage remains intact.
Stage 2: deformation of the necrotic metatarsal head by crushing, accompanied by morphological abnormalities of the metatarsal neck.
Stage 3: tearing of the cartilage with detachment of the osteocartilaginous sequestrum, leaving the head completely deformed and flat, with a loose intra-articular body.
Stage 4: sequelae of the deformed head and metatarsophalangeal (MTP) arthrosis.

♦ PATIENT HISTORY AND PHYSICAL EXAMINATION

The individuals most affected range in age from adolescence through the second decade of life.³

Patients often present with complaints of activity-related forefoot pain. Walking alone is often enough to trigger pain³ at the central metatarsal heads, accompanied by claudication that disappears with rest. The patient sometimes may recall a minor trauma, although the onset is more commonly spontaneous with no known cause. Over time, pain becomes more persistent, and dorsal swelling over the injured joint may ultimately develop.

On physical examination, applying dorsoplantar pressure at the painful area easily localizes the affected metatarsal head (Figure 10.2). In early stages of the disease, MTP tenderness may be the only finding.³

Figure 10.2 Location of the tender spot typical of Freiberg’s.

Figure 10.3 Clinical image of a Freiberg case in the final stages with swelling at the dorsal aspect of the second metatarsophalangeal joint.

The subsequent phases are usually seen in middle-aged patients, who have pain at the metatarsal heads, swelling on the dorsal aspect of the forefoot (secondary to exostoses) (Figure 10.3), limited MTP movement, and often hammertoe deformity of the affected toe.

Laboratory Studies

Laboratory studies may be indicated to rule out other etiologies of pain or deformity,³ such as infectious, rheumatologic, and/or oncologic diseases.

Classification

Several staging schemes have been described. Nevertheless, the classification scheme developed by Smillie in 1967⁸ is the most commonly used (Table 10.1).³

♦ IMAGING STUDIES

Radiographs

Radiographs provide characteristic images according to the phase of bone necrosis. Weight-bearing anteroposterior (AP), oblique, and lateral radiographs of both feet should be performed. In the first phase, there are no imaging abnormalities, and oblique views may be especially useful for a full appreciation of subtle changes early in the disease³ (Figures 10.4 and 10.5).

Necrotic areas (osteopenia) gradually appear, alternating with areas of condensation (sclerosis) that progress to osseous sequestrum and joint deformity (like the pattern seen in Perthes disease of the hip) (Figures 10.6 and 10.7).

Nuclear Bone Scans and MRI

When Freiberg disease is suspected clinically despite relatively normal radiographs, nuclear bone scans can help to identify a vascular abnormality at the metatarsal head, although its value as a diagnostic or prognostic tool is still

debated.⁹ MRI may also prove useful in the early diagnostic stages¹⁰ (Figure 10.8).

Table 10.1 Stages of Freiberg Disease

Stage	Findings
I	Fissuring of the epiphysis as earliest sign. Radiographic changes may be so subtle that they are missed with routine radiographs.
II	Later central depression of the articular surface (subchondral cancellous bone is resorbed). The articular cartilage hinges on an intact plantar bridge.
III	Central depression, medial and lateral projections at the margins; the plantar hinge remains intact at its plantar isthmus.
IV	Central portion has sunk below the surface and is free of the plantar hinge (loose body). Fractures of the medial and lateral projections, over the central loose body.
V	Marked flattening and deformity of the metatarsal head with secondary degenerative changes. Central loose body may have been resorbed; metatarsal shaft becomes thickened and dense.