A Jones fracture is a fracture of the proximal part of the fifth metatarsal bone of the foot. Sir Robert Jones, British surgeon, sustained an acute fracture at the base of the fifth metatarsal bone while dancing, so the bone was named after him. The Jones fracture occurs at the metaphyseal diaphysis junction and it extends into the intermetatarsal joint proximal to the metatarsalcuboid joint. There are joints at the base of the 5th metatarsal bone. One joint articulates with the cuboid bone and the second joint articulates with the 4th metatarsal. The Jones fracture occurs about 1 1/2 cm distal to the tuberosity of the 5th metatarsal bone.
The metatarsal bone is divided into the head, neck, shaft, and tuberosity. Jones fractures of the proximal fifth metatarsal occur in the watershed area within 1.5cm of the tuberosity. The area where the Jones fracture occurs is an area of limited blood supply. There are multiple metaphyseal arteries and the nutrient artery with intramedullary branches provides retrograde blood flow to the proximal fifth metatarsal. A fracture distal to the tuberosity will disrupt the nutrient artery supply resulting in relative avascularity. The Peronius Tertius tendon is inserted into the dorsal metaphysis of the 5th metatarsal. The Peroneus Brevis tendon is inserted into the tuberosity of the 5th metatarsal. When a Jones fracture occurs, the tendons will pull the fracture apart and prevent healing. A fracture of the proximal 5th metatarsal bone could be mistaken for a sprain because sprains are common on this side of the foot.
There are three types of fractures at the proximal fifth metatarsal:
Zone I: tuberosity avulsion fracture
Zone II: Jones fracture
Zone III: stress fracture
Zone I avulsion fractures (pseudo Jones fracture). Peroneus Brevis insertion site-conservative treatment. Zone II Jones fractures are acute fractures that occur at the metaphyseal-diaphyseal junction and involve the 4th and 5th metatarsal articulation. Zone III stress fractures are chronic fractures that occur distal to the 4th and 5th metatarsal articulation and may be associated with cavovarus foot deformities. It is important not to mistake an abnormal growth plate injury with a fracture of the proximal 5th metatarsal. The growth plate is usually present between the ages of 9-14 years of age and is parallel and lateral to the metatarsal. X-rays will show the fracture and its location. An acute Jones fracture will have sharp margins with no intramedullary sclerosis. A stress fracture will have a wide fracture line with medullar sclerosis.
Treatment for nondisplaced fractures include a boot or cast. The patient will be nonweightbearing for 6-8 weeks. Approximately 75% will heal. The patient may be given additional vitamin D and calcium. Patients that have displaced fractures or are athletes, a screw fixation of the fracture is a popular treatment method. In the lateral view, the canal appears to be straight and narrow. In the AP view, the 5th metatarsal appears to be curved (lateral bow). A lateral bow of the 5th metatarsal may cause complications during surgery. There is vulnerability at the midshaft for perforation of the medial cortex. The canal is narrower in the dorsal plantar dimension, which is narrow in the lateral view. The point of entry for the wire or the screw is not centered. The 5th metatarsalcuboid joint blocks the proximal canal projection and this situation can cause complications. The projection of the canal will be inside the metatarsal cuboid joint and this point of entry should be avoided. Each patient’s metatarsal should be evaluated individually for proper screw selection. During surgery and screw placement, the surgeon should drill parallel with the shaft in the lateral plane and avoid the plantar direction, as well as the sural nerve. The physician will probably need to use at least a 4.5 mm cancellous screw; some will use a 5.0 mm. The diameter of the screw depends on the width of the canal. With a smaller screw, the fixation will be unstable. A larger screw may displace the fracture. A tap may be used to determine the appropriate size of the screw needed. The screw must cross the fracture site. The appropriate length of the screw that should be used is usually around 40-50 mm. Failure of the procedure of screw fixation is attributed to poor blood supply or return of the athlete to activity before complete radiographic union.
