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COVER ARTICLE Urgent Care 2 (1):16, 2007 JD, 19, arrives, limping, at an urgent care clinic. His right foot is so painful that he can’t put any weight on it. A college basketball player, JD fell a couple of hours ago after jumping to block a shot. His medical history is unremarkable, although he tells the physician that his foot hurts occasionally—after practice, for example, and sometimes when he steps off a curb. Clinical evaluation reveals moderate swelling and bruising over the dorsolateral foot and ankle. Maximum pinpoint tenderness is noted along the lateral border of the foot overlying the proximal fifth metatarsal but not over the lateral ankle complex. Range of motion in the ankle joint is not painful, but JD is guarding when the clinician tries moving the subtalar and midfoot joints. ANATOMY OF THE FIFTH METATARSAL We’ll come back to JD later, but let’s review the anatomy of the fifth metatarsal first. Then we’ll take a closer look at tuberosity and Jones fractures. The fifth metatarsal bone comprises a head, neck, shaft, base, and tuberosity. The tuberosity (also called the styloid process) protrudes in a lateral and slightly plantar direction from the base of the bone. The proximal fifth metatarsal serves as an insertion site for several tendinous and fascial attachments (see illustration below). The peroneus brevis inserts over a fairly broad, fan-shaped area on the dorsolateral aspect of the tuberosity, while the peroneus tertius inserts on the dorsal surface of the proximal diaphysis (shaft) distal to the tuberosity. Finally, the lateral band of the plantar aponeurosis inserts on the plantar aspect of the tuberosity. It extends toward the toes from the medial process of the calcaneal tuberosity and gives attachment to the short flexor muscle of the toes.
The base of the fifth metatarsal articulates proximally with the cuboid and laterally with the base of the fourth metatarsal. The fifth metatarsal is relatively mobile, compared with the second and third metatarsals, which are relatively fixed. It possesses its own axis of motion, with a triplanar pronation/supination axis that moves independently of the central three rays. The location of its axis dictates that this bone moves more freely in the direction of inversion-eversion and plantarflexion-dorsiflexion, with little abduction or adduction. Blood supply—or lack thereof—is an important factor in the comparative healing of tuberosity and Jones fractures. The intraosseous blood supply to the tuberosity arises from numerous metaphyseal vessels in a random pattern. The proximal diaphysis, on the other hand, is supplied by the nutrient artery, which gives rise to intramedullary branches in a longitudinal pattern. These two blood supplies converge at the region of the metaphyseal/diaphyseal junction, creating an area of relative avascularity. Therefore, fractures in the tuberosity benefit from a rich vascularity that facilitates healing, whereas Jones fractures are plagued by poor blood supply and delayed healing. TUBEROSITY FRACTURES Fractures of the fifth metatarsal tuberosity almost always present as an acute injury, with pain, swelling, and bruising along the lateral arch. The patient finds it painful to put weight on the foot. The cause is often an inversion mechanism of injury, similar to what would be expected with an ankle sprain. Because of this mechanism, the fifth metatarsal base should always be evaluated in patients presenting with a history of inversion ankle sprain. Anteroposterior, lateral, and oblique radiographs should be performed on any patient with acute lateral midfoot pain. It was originally thought that a tuberosity fracture occurred due to avulsion by the peroneus brevis tendon. However, a cadaveric study by Richli and Rosenthal instead implicated the lateral band of the plantar aponeurosis. This theory is supported by the fact that such fractures rarely become displaced. If the peroneus brevis were the cause of injury, more displacement would be expected with continued muscle contracture. Tuberosity fractures are typically transverse or slightly oblique, involving all or part of the styloid process (see image below). They may be either extra-articular or intra-articular. Fortunately, research suggests that articular involvement does not lead to post-traumatic arthrosis. In one retrospective study, all avulsion tuberosity fractures healed uneventfully or went on to asymptomatic nonunion within five weeks regardless of the method of treatment. Therefore, the vast majority of these injuries can be treated with several layers of soft casting and a stiff-soled surgical shoe, with full weight-bearing as tolerated. Patients may also transition to a supportive sneaker when they can tolerate it.
Typically, union is obvious on x-rays by eight weeks. It should be noted that four to six weeks after the injury, it is common to see widening of the fracture line with early evidence of trabeculation. However, even without full union, patients are usually asymptomatic. Very rarely, a displaced fragment causes symptoms, making it necessary to perform open reduction and fixation or to remove the fragment. JONES FRACTURES Jones fractures have a much poorer prognosis than do tuberosity fractures, so it is important to recognize this type of fracture in time to prevent healing problems, if possible. Named in 1902 for Sir Robert Jones, who sustained the injury while dancing, the fracture occurs at the proximal metaphyseal-diaphyseal junction (see images below). Whereas tuberosity fractures are associated with inversion, Jones fractures appear to be caused by vertical and mediolateral forces concentrated over the bone. (Jones described his injury as occurring when he placed weight on the outer side of his foot with his heel off the ground—he was dancing around a maypole.)
While a Jones fracture can be acute, more often it involves a stress component. One study found that maximum stress is concentrated in the proximal diaphyseal region, corresponding to the location of Jones fractures. This stress theory is also supported by the fact that many patients report having had pain in the lateral midfoot for weeks, and that the injury appears to be more frequent among athletes (both amateur and professional), suggesting a repetitive pattern of trauma. Finally, there has been a reported association between Jones fractures and cavus (high-arched) foot types and metatarsus adductus, which places added pressure along the lateral midfoot. determining treatment Because of the relative avascularity of this region, and possibly because of the stress nature of most of these injuries, Jones fractures are fraught with delayed healing. In fact, one study reported that union was delayed in 67% of 23 fractures treated nonoperatively, and another found a 25% incidence of nonunion among 20 cases. The Torg system classifies Jones fractures as type 1, 2, or 3, according to radiographic appearance. A type 1 fracture is defined as an acute fracture on a chronic process, characterized by a plantar-based fracture line and an absence of intramedullary sclerosis. A type 2 fracture involves delayed union, in which there is a widening fracture line and evidence of intramedullary sclerosis. A type 3 fracture shows a true nonunion with complete obliteration of the medullary canal. Surgery is needed for type 2 and 3 Jones fractures, with curettage of any sclerotic bone, inlay bone grafting, and rigid fixation, but type 1 fractures are traditionally treated conservatively with strict non-weight-bearing immobilization in a short leg cast for six to eight weeks. This regimen is usually appropriate for the sedentary, inactive patient, or for patients not considered to be good candidates for surgery. But one study showed that although 72% of acute Jones fractures healed with non-weight-bearing immobilization, it took an average of 21 weeks—a considerable issue for younger or more athletic patients. Moreover, refracture is common even after initial healing. According to one study, one third of patients treated nonsurgically developed refractures. The researchers concluded that as many as half of the fractures treated by casting do not heal primarily or they refracture even after osseous union is documented. These suboptimal results increasingly have led many to advocate surgery for the young or active patient. Most surgeons perform percutaneous intramedullary screw fixation. Researchers have reported much faster unions—and thus much earlier returns to activity—ranging from 7 to 10 weeks. External fixation is an alternative that may help patients return to activity even sooner. Patients are kept non-weight-bearing during the initial healing period of four weeks, with guarded transition to weight-bearing in a surgical shoe as tolerated. External bone stimulation may be added to either conservative or surgical management. Surgical management does not necessarily guarantee against refracture, and patients must be warned of this possibility. returning to our patient JD, our injured basketball player, was found to have grossly intact neurovascular status. Anteroposterior, lateral, and oblique radiographs of the right foot and ankle showed a transverse incomplete fracture line at the proximal metaphyseal-diaphyseal junction of the fifth metatarsal consistent with a Jones fracture. No disruption of the tarsometatarsal joint complex was noted and ankle views showed no fracture or dislocation. Initial treatment consisted of a modified below-knee compression dressing and posterior splint. JD was given crutches and instructed to keep the foot elevated and iced. He was given a prescription for hydrocodone for pain. At follow-up three days later, JD’s clinical team talked with him and his parents about the treatment options of prolonged cast immobilization versus surgery. Given his athletic activities, JD opted for surgery, with application of an external fixator to optimize his chances for an earlier return to playing sports. Under intravenous sedation and local anesthesia, with ankle tourniquet hemostasis, a mini-external fixator was applied using intraoperative fluoroscopic guidance. The fixator was maintained for four weeks, at which time JD was switched to a short leg cast with minimal toe-touch weight-bearing. After two weeks in a stiff-soled sneaker, he was able to put full weight on his foot and nine weeks after the injury, he was back playing basketball. He’s still pain- and refracture-free 23 months later. age matters In the growing child, the tuberosity originates as a secondary ossification center (apophysis) that appears in girls between ages 9 and 11 and in boys between ages 11 and 14. The time between the appearance of this ossification center and its complete union to the shaft is usually two years. Therefore, in adolescents, it’s important to differentiate between a true fracture and the apophysis. Children may present with dull, aching pain along the lateral midfoot that worsens with activity. Bilateral radiographs are helpful in comparing the symmetry of the physis and apophysis in these cases. The following radiographic features can also help differentiate a normal physeal line from a fracture: • Physeal line extends almost parallel to the long axis of the shaft. • Physeal line does not extend proximally into the metatarsocuboid joint or into the fourth to fifth intermetatarsal articulation. It’s also important to bear in mind that two accessory ossicles are occasionally found near the base of the fifth metatarsal and may become painful from repetitive overuse or by direct impact. The os peroneum, with a reported incidence of 15%, is located within the peroneus longus tendon at the lateral border of the cuboid (see image below). The os vesalianum, located next to the tuberosity, is much less frequent, found in only approximately 1 of 1000 radiographs. It has been noted that avulsion fractures appear to have “scalloped” edges, while symptomatic accessory ossicles have a smooth appearance.
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