The Journal of Foot & Ankle Surgery 54 (2015) 94–98

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The Fifth Metatarsal Base: Anatomic Evaluation Regarding Fracture Mechanism and Treatment Algorithms J. George DeVries, DPM, FACFAS 1, Erfan Taefi, BA 2, Bradly W. Bussewitz, DPM, FACFAS 3, Christopher F. Hyer, DPM, MS, FACFAS 4, Thomas H. Lee, MD 5 1

Attending Physician, BayCare Clinic, Orthopedic and Sports Medicine, Manitowoc, WI Student, Ripon College, Ripon, WI Attending Physician, Professional Foot and Ankle, Iowa City, IA 4 Fellowship Director, Advanced Foot and Ankle Surgical Fellowship, Orthopedic Foot and Ankle Center, Westerville, OH 5 Attending Physician, Orthopedic Foot and Ankle Center, Westerville, OH 2 3

a r t i c l e i n f o

a b s t r a c t

Level of Clinical Evidence: 5

Fractures occurring within the 1.5-cm proximal portion of the fifth metatarsal are commonly considered avulsion fractures. The exact mechanisms of such fractures are controversial. The present study focused on determining the likely mechanism of fracture according to the exact anatomy to allow for more successful treatment. The research sample included 10 frozen cadaveric specimens. The lateral band of the plantar fascia, peroneus brevis, and articular surface were identified and separated from their attachments, thereby splitting the fifth metatarsal base into zones A, B, and C. In zone A, the attachment of the plantar fascia was 6.6  2.2 mm from the inferior aspect, 9.5  2.9 mm from the proximal aspect, and 11.5  0.9 mm from the lateral aspect. In zone B, the attachment of the peroneus brevis was 12.0  2.2 mm from the inferior aspect, 10.2  2.2 mm from the proximal aspect, and 11.5  0.9 mm from the lateral aspect. Zone C was measured from the border of zone B and encompassed the articulation of the fifth metatarsal to the cuboid. We propose that fractures occurring in the most proximal end of the fifth metatarsal, zone A, are caused by a lateral band of plantar fascia and might be able to be treated conservatively by immobilization with weightbearing. We also propose that fractures occurring in zones B and C result from traumatic tension on peroneus brevis and might need to be treated with strict immobilization and non-weightbearing or open reduction internal fixation. Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved.

Keywords: avulsion fracture diaphyseal stress fifth metatarsal injury Jones fracture trauma

Among the fractures of the foot, the proximal portion of the fifth metatarsal is a common site (1). Fractures at this location can be divided into diaphyseal stress, Jones, and avulsion fractures. After the fracture of Sir Robert Jones in 1902, much research has been done on fractures that occur 1.5 cm from the base segment of the fifth metatarsal shaft (2). Less attention has been given to the avulsion fracture that occurs proximal to the Jones fracture. The cause of fifth metatarsal avulsion fractures has been widely studied; however, the exact mechanism of this fracture is controversial. Previously, the fracture was believed to be caused by contraction of the peroneus brevis tendon during hindfoot inversion (2,3). Others have argued that avulsion fractures are less likely to be caused by peroneus brevis tendon because the insertion of the tendon is more distal than the site of an avulsion fracture (4–6). Recent studies have Financial Disclosure: Cadaveric study made possible by DJO Global. Conflict of Interest: None reported. Address correspondence to: J. George DeVries, DPM, FACFAS, Orthopedic Foot and Ankle Center, 300 Polaris Parkway, Suite 2000, Westerville, OH 43082. E-mail address: [email protected] (J.G. DeVries).

shown that it is more likely that the lateral band of the plantar fascia is the cause of avulsion fractures, resulting from contraction of the short peroneal tendon during inversion and flexion of the forefoot (7,8). To more fully understand the fracture mechanism and subsequent treatment, we undertook a cadaveric study of the anatomy. Our hypothesis was that a better understanding of the exact local anatomy would help physicians to better understand the fracture mechanisms and patterns and could lead to evidence-based treatment plans. Materials and Methods Ten fresh-frozen adult below-the-knee cadaver limbs were obtained for the San Diego Cadaveric Anatomy Research Symposium. The demographic data included race. The right versus left leg was recorded, and the specimens were numbered 1 through 10. A lateral incision was taken to the fifth metatarsal. All distal soft tissue attachments were removed. Proximally, the lateral band of the plantar fascia and the peroneus brevis tendon were identified and cut several centimeters from their respective attachments on the fifth metatarsal base. The base was then disarticulated from the cuboid and fourth metatarsal and removed from the specimen. The specimen was then freed of any remaining soft tissue adherence, except for the peroneus brevis tendon and plantar fascia.

1067-2516/$ - see front matter Ó 2015 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2014.08.019

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Fig. 1. Fifth metatarsal from the lateral aspect showing overall length of the metatarsal from head to distal aspect of the articular surface and head to proximal aspect of the articular surface.

A digital caliper was used to measure the dimensions of the fifth metatarsal, peroneus brevis tendon, and plantar fascia. After measuring the soft tissue structures as they inserted on the base of the fifth metatarsal, they were dissected off the bone to perform additional measurements of the insertion and how it related to the local anatomy. The analysis of the data collected was performed using Excel (Microsoft, Redmond, WA).

Results Ten cadavers from unmatched limbs were used. All the specimens were skeletally mature. Of the 10 specimens, 5 were right and 5 were left; no information was available regarding the precise age or sex of the cadaver specimens. The overall length of the metatarsals, from the head to the tip of the tuberosity was 75.1  8.0 mm, and the length medially from the metatarsal head to the cuboid articulation was 69.7  6.7 mm. The base was in all cases triangular and was examined for the articulation with the cuboid bone, the attachment of the plantar fascia, and the insertion of the peroneus brevis tendon. The height of the base at the level of the cuboid articulation was 13.7  2.3 mm, and the width of the articulation was 15.2  2.4 mm. The height of the nonarticular base adjacent to the articulation was 12.4  1.7 mm, and the width of the nonarticular base was 11.5  0.9 mm (Figs. 1 and 2). All the findings are listed in the Table. The attachment of the plantar fascia was also described. The height of the soft tissue was measured as it attached to the fifth metatarsal and

was 7.2  2.1 mm. The plantar fascia was then removed and the attachment examined. The width of the attachment was 4.0  0.9 mm, and the height was 5.5  1.4 mm. The length of the attachment from posteriorly to anteriorly was 9.5  2.9 mm when measured from the lateral view. The shape in all cases was oval. When measured from the most inferior portion of the metatarsal base, the attachment went from 0.5  1.0 mm inferiorly to 6.0  2.0 mm superiorly. The distance from the lateral aspect of the articular surface to the medial most portion of the attachment was 6.9  1.9 mm (Figs. 3 and 4). The insertion of the peroneus brevis tendon was described in a similar fashion. The height of the soft tissue was again measured as it attached to the fifth metatarsal and was 6.9  1.8 mm. Similarly, the peroneus brevis tendon was detached and the insertion examined. The width and height of the insertion was 3.5  1.0 mm and 5.2  1.2 mm, respectively. The length was also measured, just as with the plantar fascia, and was 10.2  2.2 mm. The shape in all cases was again oval. When measured from the most inferior portion of the metatarsal base, the insertion increased from 6.7  2.6 mm inferiorly to 12.0  2.2 mm superiorly. The distance from the lateral aspect of the articular surface to the medial most portion of the insertion was 4.7  2.1 mm (Figs. 3 and 5). From these data, 3 zones of the tuberosity were identified. Zone A comprises the attachment of the plantar fascia only and is nonarticular. It measured 6.6  2.2 mm from the inferior aspect,

Fig. 2. Base of the metatarsal at the articulation with the cuboid. This particular specimen had significant crystal deposition on the articular surfaces. This demonstrates the measured dimensions of the articular surface with the cuboid and the nonarticular portion of the tuberosity.

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Table Anatomic study of base of fifth metatarsal, plantar fascia, and peroneus brevis tendon Specimen

1 2 3 4 5 6 7 8 9 10 Average SD

Fifth Metatarsal

Plantar Fascia

Length (mm)

Base Height (mm)

Base Width (mm)

Base Shape (mm)

Soft Tissue Height (mm)

Width (mm)

Shape (mm)

Inferior Border of PF to Inferior Metatarsal (mm)

Superior Border of PF to Inferior metatarsal (mm)

Articular Surface Medial Distance to PF (mm)

PF Length (mm)

Insertion Height (mm)

71.97 68.58 80.83 69.38 64.03 67.89 79.98 59.73 63.85 70.73 69.697 6.717921

14.05 14.73 16.46 9 14.78 12.08 17.07 12.91 12.22 13.98 13.728 2.331517

17 16.6 17.31 17.13 12.4 13.36 18.26 12.39 12.19 15.5 15.214 2.38072

Triangular Triangular Triangular Triangular Triangular Triangular Triangular Triangular Triangular Triangular

6.91 11.34 7.45 7.55 8.35 5.76 9.01 5.56 3.91 6.56 7.24 2.054486

2.95 4.5 4.82 4.38 2.99 3.47 5.6 3.94 2.72 4.13 3.95 0.92281

Oval Oval Oval Oval Oval Oval Oval Oval Oval Oval

0 2.93 0 0 1.98 0 0 0 0.32 0 0.523 1.04734638

5.69 11.19 5.32 6.01 5.96 3.9 6.82 4.61 4.73 5.62 5.985 2.0073711

6.2 4.57 7.32 7.3 7.18 5.73 9.51 5.09 5.51 10.66 6.907 1.939645

6.96 11.58 13.22 7.89 11.67 8.62 13.93 5.38 9.18 6.94 9.537 2.904659

5.69 8.26 5.32 6.01 3.98 3.9 6.82 4.61 4.41 5.62 5.462 1.355612

Abbreviations: PB, peroneus brevis; PF, plantar fascia; SD, standard deviation.

9.5  2.9 mm from the proximal aspect, and 11.5  0.9 mm from the lateral aspect. Zone B entails the attachment of the peroneus brevis tendon and is nonarticular. It measured 12.0  2.2 mm from the inferior aspect, 10.2  2.2 mm from the proximal aspect, and 11.5  0.9 mm from the lateral aspect. Zone C involved the articular surface of the fifth metatarsal–cuboid joint. It was measured from the border of zone B and encompasses the articulation of the fifth metatarsal to the cuboid (Figs. 6 and 7). Discussion The specific anatomy of the base of the fifth metatarsal is important for several conditions. The classic Jones fracture is a fracture 1.5 cm distal to the articular surface of the fifth metatarsal and is very well described (2). Tuberosity fractures have been much less well described. Controversy also exists regarding whether the peroneus brevis tendon or plantar fascia is more pertinent to fracture healing (5,9). Evidence has even shown that some avulsion injuries might not be visualized on traditional foot radiographs and additional projections could be needed to fully appreciate the fracture (10). Overall, avulsion fractures are less understood and have been studied less. From the cadaveric research we have performed, traumatic tension of the lateral plantar fascia is the anatomically logical cause of fractures to the most proximal end of the fifth digit, the area defined as zone A. Because of the limited motion allowed superficially and

Fig. 3. Inferior-lateral aspect of the base of the fifth metatarsal examining the attachments of the plantar fascia (toward the bottom) and the peroneus brevis tendon. The structures, as they attach on the fifth metatarsal and the attachment footprints, are demonstrated.

laterally by the plantar aponeurosis, the fracture should not be subject to significant dynamic force. This might allow for treatment consisting of immobilization with weightbearing (11). Alternatively, fractures occurring in zone B could be subject to the dynamic contraction of the peroneus brevis tendon. The peroneus brevis tendon applies force against the posterior surface of the lateral malleolus, which results in additional tension force after the fracture (9,11). To combat this force, treatment could benefit from strict immobilization and non-weightbearing or open reduction internal fixation. Fractures within zone C will be articular and are likely to be subjected to tension forces from the peroneus brevis tendon. Displaced fractures can be considered for open reduction internal fixation to help avoid the development of late arthritis. It might be possible to treat nondisplaced fractures with immobilization and non-weightbearing or open reduction internal fixation. Most of the published clinical data have favored nonoperative treatment of avulsion injuries to the fifth metatarsal base. Polzer et al (12) in 2012 published a meta-analysis of the classification and treatment of proximal fifth metatarsal fractures. They divided their findings into 3 zones, grouping all avulsion fractures into zone 1 and

Fig. 4. Base of the metatarsal at the articulation with the cuboid showing the attachment of the lateral band of the plantar fascia as it attaches on the tuberosity and its relationship to the metatarsal-cuboid articulation.

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Peroneus Brevis Soft Tissue Height (mm)

Width (mm)

Shape (mm)

Inferior Border of PB to Inferior Metatarsal (mm)

Superior Border of PB to Inferior Metatarsal (mm)

Articular Surface Medial Distance to PB (mm)

PB Length (mm)

Insertion Height (mm)

10.45 7.63 6.38 9.43 5.34 6.05 7.37 4.97 5.21 6.63 6.946 1.820148

4.35 4.82 2.48 3.31 3.55 2.62 4.64 2.64 2.3 4.11 3.482 0.952561

Oval Oval Oval Oval Oval Oval Oval Oval Oval Oval

8.68 8.85 7.32 5.33 5.19 6.42 11.68 4.06 2.62 6.52 6.667 2.616202

13.73 13.75 12.46 10.23 11.7 9.44 15.65 9.91 9.3 13.37 11.954 2.182757

5.32 1.13 6.94 7.51 5.11 3.31 6.81 4.36 4.78 1.98 4.725 2.111067

12.77 9.36 12.56 10.16 10.74 6.21 12.24 8.27 8.05 11.59 10.195 2.19935

5.05 4.9 5.14 4.9 6.51 3.02 3.97 5.85 6.68 6.85 5.287 1.22234792

classified Jones fractures as zone 2 and proximal diaphyseal stress fractures as zone 3. They recommended nonoperative treatment for all zone 1 fractures, regardless of comminution or intra-articular extension (12). This would include all zones described in the present study. A comparative study of the treatment of avulsion fractures in either a weightbearing cast or weightbearing boot was undertaken by Shahid et al (13) and published in 2013. No patients were treated with operative intervention. Although the investigators concluded that patients ultimately did better with a boot than with a cast, the patients required 6 to 12 weeks to return to driving and required an average of 35.8 days off work during their recovery. This extended recovery time was also reported by Egol et al (14) in 2007 when 52 patients were prospectively followed up for their avulsion fractures treated with a weightbearing surgical shoe. The average period off work was 22 days, and only 20.4% of the patients had returned to the preinjury activity level by 3 months. Other meta-analyses have also concluded that avulsion injuries are largely amenable to nonoperative

Fig. 5. Base of the metatarsal at the articulation with the cuboid highlighting the attachment of the peroneus brevis tendon as it attaches on the tuberosity and its relationship to the metatarsal-cuboid articulation.

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Total Length (head to nonarticular surface) (mm)

Nonarticular Height (mm)

Nonarticular Width (mm)

75.85 73.57 85.94 76.87 69.24 73.2 89.05 61.35 69.83 76.01 75.091 7.9844063

14.17 13.04 13.12 11.03 12.18 10.65 15.24 11.24 9.92 13.12 12.371 1.670672

12.85 11.55 11.26 11.21 11.68 10.63 11.99 10.58 10.2 13.07 11.502 0.942653

treatment, with surgery reserved for those classified as Jones fractures (15). No studies that we were able to find have divided avulsion injuries into specific categories such as were demonstrated in the present cadaveric study. If internal fixation is to be undertaken, the anatomy and mechanics should be considered. Previous data have explored various hardware configurations; however, most research has considered the strength of fixation using bench testing. Bicortical screw fixation (9,16,17), Kirschner wire tension banding (9,18), and hook plating have been described (19). Previous work on Jones fractures has demonstrated that either titanium or stainless steel can be used (20). When deciding on hardware, care must be taken to recognize the various “foot prints” of the desired hardware. Each type of hardware will have different needs. If the fixation will need to be more medial than 11.5 mm from the lateral surface of the tuberosity, wire fixation might be best to avoid intra-articular screw or plate placement. If the fracture is very small and lateral, a hook plate construct might be best because of its ability to grasp the most bone and soft tissue. Although the present investigation was useful in describing the anatomy and treatment considerations for fifth metatarsal avulsion fractures, the study had a number of weaknesses that must be addressed. First, the use of only 10 cadaveric specimens could be considered a small number. However, Theodorou et al (8) in 2003

Fig. 6. Lateral aspect of the fifth metatarsal base with zones A, B, and C schematically identified, highlighting the relationship of the anatomic structures.

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clinical correlations must be made to assess the value of these recommendations. However, the presented information should prove useful to foot and ankle surgeons when faced with these fractures.

References

Fig. 7. Base of the metatarsal at the articulation with the cuboid, with zones A, B, and C identified.

made several recommendations from only 2 cadaveric dissected models and 4 nondissected, but imaged, specimens. With a greater number of specimens, additional specification and more accurate measurements could be made. Second, although care was taken to perform the measurements in as consistent a method as possible, the specific differences inherent to each specimen and the lack of a controlled mounting jig might have introduced error into the measurements. Third, there was a lack of load testing of the various suggestions made by the cadaveric and anatomic considerations to hardware choice. Thus, what might make sense in a laboratory setting might not be practical clinically. Fourth, various other attachments, such as the adductor digiti quinit and the peroneus tertius, were not evaluated. Although their inclusion was initially discussed, owing to their inconsistent presence and location, these structures were not included in the study, but they could be clinically relevant. Finally, this was a cadaveric bench study, and clinical conclusions must always be drawn with the utmost care. From the cadaveric research findings in the present study, 3 zones of fracture pattern were identified at the fifth metatarsal tuberosity, and these were determined from the anatomic considerations for the mechanisms of injury. Zone A fractures do not appear to be subjected to dynamic tension forces. Zone B fractures likely are subjected to the dynamic tension force of the peroneus brevis, and the treatment chosen could be required to account for this muscle action. Zone C fractures involve the articular surface, and care should be taken to assess the articular surface. All the data and conclusions drawn must be tempered because our study was only a cadaveric study, and

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The fifth metatarsal base: anatomic evaluation regarding fracture mechanism and treatment algorithms.

Fractures occurring within the 1.5-cm proximal portion of the fifth metatarsal are commonly considered avulsion fractures. The exact mechanisms of suc...
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