Minimally Invasive Operative Treatment of Proximal Fifth Metatarsal Fractures

Kathryn L. Williams

Robert B. Anderson

INDICATIONS

Proximal fractures of the fifth metatarsal are classified into three types based on anatomy and radiographic appearance. A zone I fracture occurs on the lateral aspect of the tuberosity, extending proximally into the metatarsocuboid joint, and represents an avulsion of the tuberosity. Zone II fractures, referred to as Jones fractures, include fractures that involve the metaphyseal-diaphyseal junction and begin laterally in the distal part of the tuberosity and extend obliquely and proximally into the medial cortex at the fourth and fifth metatarsal base articulation. Zone III fractures are distal to the fourth and fifth metatarsal base articulation and involve the proximal metatarsal shaft (Fig. 28-1).¹^, ²^, ³ Torg further classified the proximal diaphyseal fractures into three subtypes based on the age of the fracture and radiographic appearance. Type I fractures are acute with no intramedullary sclerosis, type II are delayed unions and have a widened fracture line with intramedullary sclerosis, and type III are nonunions, the medullary canal obliterated.³

The fracture type is important as the location of the fracture can have implications in ability to heal secondary to the blood supply of the fifth metatarsal. The watershed area present at the metaphyseal-diaphyseal junction creates an avascular zone, which can increase the risk of delayed union or nonunion (Fig. 28-2).⁴^, ⁵^, ⁶

In cases where surgical intervention is indicated, minimally invasive techniques for proximal fifth metatarsal fractures can be utilized. Typically this is best suited for athletes with acute type II Jones and Type III metaphyseal/diaphyseal fractures. Nonathletes with these fracture patterns can usually be managed with 6 to 8 weeks of non-weight-bearing cast immobilization. However, if there is little or no callous formation at the fracture site after this initial treatment, surgical treatment with minimally invasive techniques can still be pursued (Fig. 28-3A, B).

There is a subset of patients in whom initial surgical treatment should be considered. This includes not only athletes but also those patients with a refracture or postural abnormalities. Quill⁷ reported high rates of delayed union, nonunion, and re-fracture in athletes treated nonoperatively, with up to a 50% nonunion or refracture rate and recommended intramedullary screw fixation in all Jones fractures. Josefsson⁸ reported that 25% of patients with Jones fractures treated nonoperatively needed further surgical management for delayed union/refracture. Surgical treatment has been shown to decrease healing time. Clapper⁹ reported a 100% union for seven Jones fractures treated operatively with a healing time of 12.1 weeks compared with 21.2 weeks for those treated with casting. Further studies also support early surgical treatment of acute Jones fractures in elite or high-performance athlete.¹⁰^, ¹¹^, ¹²^, ¹³

The presence of prodromal pain prior to the presentation of an acute proximal diaphyseal fracture, the absence of prior treatment and radiographic evidence of a stress phenomenon indicates an etiology involving repetitive stress and a lower chance for successful healing with nonoperative treatment. Healing rates of 100% have been reported in proximal diaphyseal stress fractures using percutaneous screw fixation.¹⁰^, ¹¹^, ¹²^, ¹³

Percutaneous or minimally invasive operative treatment of fifth metatarsal base fractures is not indicated for treatment of Zone I (avulsion fractures), as these types have a high union rate with nonoperative treatment.⁹ It is also not indicated for those fractures that are localized to the distal half of the fifth metatarsal as these are best treated nonoperatively or with plate osteosynthesis.

In summary, minimally invasive operative treatment using percutaneous insertion of an intramedullary screw for fixation of proximal fifth metatarsal fractures is indicated for the treatment of acute Jones fractures in the elite or high-performance athlete, the patient with a diaphyseal stress fracture and radiographic evidence of nonunion or delayed union, and the informed nonathlete who prefers surgery rather than the risk development of a nonunion or refracture with nonsurgical treatment.

PATIENT POSITIONING

Surgery is performed as an outpatient and can be done with either a regional or general anesthetic. An Esmarch bandage placed at the midcalf level suffices as a tourniquet. General anesthesia is used if the surgeon desires a thigh tourniquet or bone marrow aspirate/graft from the iliac crest. The patient is positioned on a standard operating room table in the supine position. A radiolucent table may be used but is not necessary. The patient is positioned at the distal end of the table and a bump
is placed under the ipsilateral hip in order to internally rotate the operative extremity. The patient’s entire body is moved as far to the operative side of the table as safely possible so that the starting point can be accessed without obstruction. The ipsilateral knee must be able to be flexed in order to place the foot plantigrade on the edge of the fluoroscopy unit or the operating room table. A mini C-arm is essential and the physician should confirm that true oblique, AP, and lateral views of the fifth metatarsal can be obtained before prepping and draping the extremity.

Figure 28-1. The three anatomic zones of the proximal fifth metatarsal.

If general anesthesia is used, a nonsterile tourniquet may be placed high on the thigh of the operative leg. As mentioned previously, a sterile Esmarch tourniquet may be applied either with general anesthesia or with an ankle/popliteal block and sedation. This latter method is our preference for most patients. The foot is prepped to the level of the midtibia or knee and draped using an extremity drape. The iliac crest is also prepped and draped if bone marrow aspirate or autologous bone graft is to be harvested. The surgeon stands on the injured side of the patient to access the lateral foot and the assistant or scrub tech stands at the foot of the bed. The mini C-arm is positioned on the injured side and brought in at an approximately 45-degree angle to allow for access to all three views of the foot (Fig. 28-4).

Figure 28-2. Illustration of the vascular supply to the proximal fifth metatarsal demonstrating the avascular (watershed) zone in the metaphyseal-diaphyseal region.

SURGICAL APPROACH

The base of the fifth metatarsal is palpated and drawn out with a surgical marker on the lateral foot for anatomic reference. In order to estimate the axial alignment, a Kirschner wire can be laid over the top of the fifth metatarsal and fluoroscopic images taken in the oblique plane. Using a surgical pen, a line can drawn on the skin along the wire proximal to the base. The axial alignment can also be visualized with fluoroscopy and the guidewire inserted in line with the fifth metatarsal shaft. A 1- to 2-cm longitudinal incision is made in line with the metatarsal approximately 2 cm from the base (Fig. 28-5A, B). Blunt dissection is done to protect terminal branches of the sural nerve, and should be protected during drilling and screw insertion to prevent injury and the potential for a painful neuroma. The peroneus brevis tendon may be encountered but usually lies superior to the insertion site of the screw. The soft tissues are carefully and bluntly spread in line with the incision down to the level of the bone to allow for insertion of the guidewire.

Figure 28-3. A, B: Oblique and lateral radiographs of a type II nonunion of the fifth metatarsal base.

REDUCTION TECHNIQUES AND FIXATION

A formal reduction is not usually needed as the correct placement of the Kirschner wire, tap and partially threaded screw allows for indirect reduction of the fracture. However, there is a definite order of steps that must be carried out to achieve appropriate placement of the screw and fracture alignment.