SLR - February 2021 - Kevin N. Nguyen
Reference: Van Dijk PA, Breuking S, Guss D, Johnson H, DiGiovanni CW, Vopat B. Optimizing Surgery of Metaphyseal-Diaphyseal Fractures of the Fifth Metatarsal: A Cadaveric Study on Implications of Intramedullary Screw Position, Screw Parameters and Surrounding Anatomic Structures. Injury. 2020 Sept 25.Level of Evidence: 4
Scientific Literature Review
Reviewed By: Kevin N. Nguyen, DPM
Residency Program: Grant Medical Center – Columbus, OH
Podiatric Relevance: Fractures of the fifth metatarsal (MT5) metaphyseal-diaphyseal junction, better known as a “Jones” fracture, are common athletic foot injuries. These fractures can be problematic as the fracture occurs in an anatomic “watershed” region, resulting in poor healing. Intermedullary screw fixation has been shown to provide earlier return to sports. Effective insertion of said intramedullary screw may be complicated due to the curvilinear geometry of the MT5, as well as the surrounding soft tissue structures. The authors of this study aimed to define the relationship of the Jones fracture to the peroneal brevis (PB) and plantar fascia (PF) footprints. They also wanted to better describe the screw parameters and trajectory relative to the surrounding MT5 anatomy.
Methods: 22 fresh frozen cadavers were obtained and the MT5 was harvested from each cadaver with PB and PF identified, preserved, and severed several centimeters proximal to their insertions. The base of each MT5 was proximally disarticulated and removed from the specimen. Any remaining soft tissue adherence, except for the PB & PF, was dissected free from each MT5. To allow for accurate registration of the PB and PF footprints, a reference screw was placed at three positions; proximal in the middle of the articular surface (AS), the most distal tip of the MT5, and in the medial cortex. Each MT5 was then CT scanned to reconstruct a 3D model. Using the reference screws, the locations of PB, PF, and AS were digitized and mapped onto each 3D bone model.
In total, two traditional screw positions were defined: (1) an anatomically positioned screw (AP), which aimed to maximize screw length by following the intramedullary canal for as long as possible, and (2) a Clinically achievable screw (CA), which aimed to maximize screw length while entering the MT5 and not violating the 5th TMTJ or adjacent cuboid.
Results: In 21 unpaired MT5 specimen, calculated mean diameter of the canal was 4.3 millimeters. Three of 21 (14.3 percent) required the use of a 5.0 millimeter screw, whereas a majority (18/21) required a 4.5 millimeter screw. The PB insertion was oval shaped and located on the dorsal side of the MT5 base. The PF was also oval shaped but located on around the tip of the tuberosity. The AP screw did not compromise the footprints, but did require an intraarticular entry point. The CA screw entry points partially sacrificed the PB 62 percent and the PF 33 percent of the time, but were not intra-articular. The mean screw length was 64.2 percent of the bone or 48 +/- 5/8 millimeter.
Conclusions: It was found that the PB and PF footprints were found to frequently overlap at the Jones fracture site. These insertions are hypothesized as potential contributors to the Jones fracture injury mechanism and might also potentiate displacement or delay healing. Careful screw insertion was found to minimally compromise the surface area of the footprints. A CA screw with a length of approximately 2/3s the MT5 is desired as it maximizes the pull-out strength while avoiding cortical penetration or inadvertent fracture site distraction.