Freiberg's infraction is a condition
specific to the lesser metatarsal heads, most commonly the second
metatarsal. Also known as avascular necrosis, or AVN, this
condition results in a focal loss of blood supply to the metatarsal
head. Freiberg's infraction occurs at the metaphysis of the metatarsal bone.
The metaphysis
in the region where the primary or nutrient artery of the bone supplies
the distal metatarsal. Loss of blood supply to the metaphysis
(infraction) results in collapse of the metatarsal
head.
Freiberg first described this condition
in 1914. He believed that the condition was secondary to trauma
which resulted in a collapse of the bone. Other authors have
speculated about the cause of this localized phenomenon and have
suggested origins that are consistent with other forms of AVN including
steroid use, fat embolism, hypercoagulability and chronic overloading of
the bone. Most authors agree that Freiberg's infraction is due to trauma.
Freiberg's Infraction is most commonly seen in women and has an onset
during the second decade of life.
X-rays can confirm the diagnosis and show
a progressive flattening of the metatarsal head. Thickening of the
bone beneath the cartilage of the
metatarsal head is evident and
represents diffuse micro-fractures of the bone. Several
radiographic classifications have been described with the most
accepted being that described by Katcherian.
Katcherian
Classification of Radiographic Levels of Freiberg's Infraction
Level A Fissures (micro-fractures) noted in
the epiphysis or most distal segment of the metatarsal
Level B Increased evidence of fissures with
slight bone resorption
Level C Continued evidence of fissures with
collapse of the central portion of the metatarsal head
Level D Continuation of fracture and
collapse with free floating bone on the medial and lateral
margins of the joint
Level E Complete collapse of the metatarsal
head
Treatment of Freiberg's Infraction
Treatment of Freiberg's infraction tends to
vary based upon the degree of degenerative change in the cartilage and
the level of collapse of the subchondral bone. Casting may be used in the
early levels to decrease the tendency of the distal bone to
collapse. Long term pain control can be achieved by stiffening the shoe with
a carbon
plate and anterior rocker sole shoe. Steroid injections may help to relieve pain and reduce
inflammation of the joint capsule.
Surgical correction may include simple
debridement of the joint with revision of the cartilage. Tip-up
osteotomies of the metatarsal are used to deflect the eroded cartilage
away from the joint space bringing new cartilage from the bottom of the
joint into the central aspect of the joint.
Autogenous osteo-articular transfers can be used to restore the
surface cartilage of the metatarsal head. Graft sources can include the
lateral condyle of the knee or the dorsal surface of the 1st metatarsal head.
Synthetic graft plugs are also available. The advantage of a synthetic
graft is that there is no donor site that may require healing. The
disadvantage of synthetic plugs is that their surface does not typically
contour to meet the normal contours of the metatarsal head. Synthetic
grafts also have a lower induction capacity for vascular and osseus ingrowth.
Osteo-articular transfers, or what are commonly called OAT's
procedures can accomplish two things. First, they can restore normal
surface cartilage. Second, graft placement addresses the avascular bone of
the metatarsal head. The graft provides the structure for new vascular
ingrowth into what has become dense, avascular bone. Many doctors will
also employ a technique called drilling of the bone to initiate vascular
ingrowth.
Joint implants have
also been used with marginal success. Joint implants are reserved
for cases where the majority of surface cartilage of both the metatarsal head
and base of the proximal phalanx is eroded. Two types of implants are used, a
hinged total joint replacement and a metallic metatarsal head replacement. The goal of implant
arthroplasty in cases of Freiberg's infraction is two fold. First is to
restore pain free range of motion. Second is to preserve weight bearing of
the plantar metatarsal head. Excessive resection of the metatarsal can
result in shortening and altered weight bearing characteristics of the bottom of
the foot.
The long term success of the treatment of
Freiberg's infraction varies. Active patients, such as athletes
tend to have greater residual disability.
