A Lisfranc joint injury is defined as a bony or ligamentous injury which involves the tarsometatarsal joint of the midfoot. Failure to achieve stable fixation during surgery for a Lisfranc joint injury leads to subtle instability that causes dysfunction and posttraumatic osteoarthritis.^1,2) Most authors agree that fracture or dislocation of the Lisfranc joint causes midfoot instability, which requires surgical treatment involving open reduction and internal fixation.³⁾ Before surgery, instability can be confirmed through weight bearing radiograph and abduction stress radiograph. When instability is unclear, tests such as magnetic resonance imaging may be helpful for diagnosis. However, there is no reported method to check if the instability has been resolved through proper fixation during the surgery. The purpose of the present report was to introduce a test that evaluates joint instability dynamically during open reduction of the Lisfranc joint and checks the stability after fixation.

The protocol of this study was reviewed and approved by the Institutional Review Board. The patient was placed in the supine position and the Esmarch tourniquet was placed above ankle level. We made a dorsomedial incision between the first and the second metatarsals. The medial dorsal cuta-neous branch of the superficial peroneal nerve was identified and protected. This incision allows visualization, debridement, reduction, and stabilization of the Lisfranc joint. The Freer test suggested by us uses a Freer elevator (width 5 mm, thickness 1 mm) that is inserted into the interosseous area between the medial cuneiform and the second metatarsal base (Fig. 1). The surgeon applies a twisting force to the Freer elevator to widen the space between the medial cuneiform and second metatarsal base. The twisting motion applies a distraction force on the Lisfranc joint, directly stressing the Lisfranc ligament. It can be considered as instability of Lisfranc joint when the Freer elevator in the thin side is twisted more than 90 degree on the wide side. It allows the determi-nation of the necessity of fixation by immediately checking the dynamic instability caused by rupture of the Lisfranc ligamentous complex (Fig. 2). After removing the fibrous tissues that interfere with reduction, anatomic reduction can be performed by percutaneously inserted large bone reduction forceps. Subsequently, the Freer elevator can be inserted into the space between the medial cuneiform and second metatarsal base, and twisted to confirm stable reduction (Fig. 3). In the present case, A 4.0 mm cannulated screw was inserted from the medial cuneiform into the second metatarsal base to hold the Lisfranc ligament in an anatomic position for healing. This screw effectively secured the keystone of the arch. After fixation of the Lisfranc joint, the stability of the fixation could be tested by twisting motion with the freer elevator (Fig. 4). A 2-mm thick Freer elevator easily enters the space between the medial cuneiform and second metatarsal base. Inability to twist the Freer elevator denotes firm fixation.

Figure 1. The Freer elevator is inserted into the interosseous area between the medial cuneiform and the second metatarsal.

Figure 2. A twisting force is applied to the Freer elevator, attempting to separate the first and second metatarsals.

Figure 3. A twisting force is applied to the Freer elevator to check for stability after redudction with bone reduction forceps.

Figure 4. After fixation of the Lisfranc joint, the stability of the fixation can be tested by trying the twisting motion with the inserted Freer elevator.

After the surgery, the patient was instructed to perform non-weight bearing activities for 2 weeks while wearing a short leg splint. After 2 weeks, sutures were removed and a short leg cast could be worn. Non-weight bearing activities were advised for another 2 weeks. Short leg cast can be replaced with postoperative shoes, and tolerable weight bearing can be started 4 weeks after the surgery. Full weight bearing was started at 6 weeks after the surgery, and postoperative shoes were worn until 8 weeks after the surgery.

The Lisfranc joint complex is a very elaborate structure. The proximal part of the metatarsal bone and the cross-section of the cuneiform have an inverted triangular shape, forming a Roman arch with inherent stability that prevents the collapse of the structure.⁴⁾ Particularly, the base of the second metatarsal bone is sandwiched between the medial and the lateral cuneiform bones, and is located at the top of the Roman arch, functioning as a keystone. It serves as a reference point for treatment of all Lisfranc joint injuries.⁵⁾

The complexity of the Lisfranc joint complex results in limitations in the diagnosis of Lisfranc joint injuries through physical examinations and simple radiographs. The probability of improper diagnosis at the first radiographic examination is approximately 20%.⁶⁾ Inadequate diagnosis and treatment lead to foot deformity, persistent instability, degenerative arthritis, and dysfunction including limping gait.¹⁾ For displaced or unstable Lisfranc injuries, recently reported series support the importance of achieving and maintaining anatomic reduction. Routine direct joint visualization allows for a more reliable reduction and anatomic internal fixation of larger osteochondral fragments, or excision of smaller interposed fragments. It is critical to ensure that there is no instability during the surgery after adequate reduction and fixation between the second metatarsal base and the medial cuneiform. If proper stability is not achieved, long-term discomfort and functional deterioration may result after the surgery.^7,8) We developed the Freer test to check for instability dynamically during open surgery and to check whether stability was maintained after fixation. The Freer test has the advantage of an easy approach with or without the C-arm and dynamic visualization of the Lisfranc joint.

Nevertheless, our test also has some limitations. Iatrogenic injury could occur during the twisting motion of the Freer elevator inserted into the joint. No comparison was performed with the findings in the preoperative examination. Thus, prospective studies regarding the accuracy of this test are needed.

In conclusion, the Freer test could be considered a valuable test in open surgery for the a Lisfranc joint injury.

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