The Lisfranc joint is broadly defined to include the metatarsocuneiform, intermetatarsal, intercuneiform, and metatarsocuboid joints, and is also referred to as the Lisfranc joint complex [10, 11]. Myerson was the first to propose the three-column theory for the Lisfranc joint [12], which has since greatly assisted in the staging and treatment of Lisfranc fracture-dislocation. Anatomically, the Lisfranc joint is involved in the formation of the medial longitudinal arch (medial and intermediate columns), the lateral longitudinal arch (lateral column), and the transverse arch (Lisfranc complex), which play important roles in weight-bearing and the gait cycle [13]. Lisfranc joint injuries often present as simple Lisfranc joint dislocations or fracture dislocations [14]. In recent years, the incidence of Lisfranc injuries has been increasing annually with the rapid development of the transportation and construction industries [10, 15]. The Lisfranc joint is a major component of the foot arch. Once injured, the transverse and longitudinal arches of the foot are often destroyed. Without timely or standardized treatment, patients will experience discomfort while walking, chronic pain, foot deformity, traumatic arthritis, and other complications, which have serious impacts on weight bearing and gait [12, 16]. The seven patients in the present cohort were clearly diagnosed with high-energy injuries with varying degrees of joint dislocation and ligamentous injuries, all of which required surgical treatment. Numerous studies have shown that open reduction internal fixation results in better clinical outcomes than closed reduction and plaster fixation [17–19]. Common methods of fixation include Kirschner pins, screws, transarticular plates, and external fixation frames [5, 20, 21]. Kirschner pin fixation is prone to breakage and loosening, which may lead to loss of reduction. Screw fixation is associated with damage to the articular surface, increasing the likelihood of postoperative traumatic arthritis. In addition, screw fatigue fractures may occur with excessive delays of screw removal. Plate fixation is effective but involves excessive intraoperative detachment of soft tissues [4, 5, 22]. In this study, a Ni-Ti shape memory alloy nail angle fixator developed by our group was used for the treatment of fresh Lisfranc fracture-dislocation. Effective fixation and satisfactory recovery of foot function was achieved for all seven patients.
4.1 Design features of the Ni-Ti shape memory alloy nail angle fixator
These included (1) a hollow-body design that was convenient for observing whether fixation resulted in reduction of the intra-articular space, in addition to reducing the compressive surface of the fixator body on the periosteum and soft tissues; (2) four fixation arms that allowed fixation of the 1st and 2nd metatarsals and the 1st and 2nd cuneiform bones, which not only enabled fixation of the tarsometatarsal joints, but also played a role in fixing the intermetatarsal joints and intertarsal joints, reducing the need for Lisfranc screws; (3) the initial design of the four fixation corners included an inward angle, which fixed the bone at a normal vertical angle at a lower temperature (martensitic state), and the four fixation arms returned to the initial design when the temperature of the martensite completely disappeared to pressurize the fracture and the joints [8]; (4) we designed different sizes and types of the nail angle fixator so that they can be selected for different situations, making fixation convenient.
4.2 Advantages of the Ni-Ti shape memory alloy nail angle fixator for Lisfranc fracture-dislocation
The advantages of the Ni-Ti shape memory alloy nail angle fixator include (1) simplicity of operation and wide a range of applications. Lisfranc fracture-dislocations of all Myerson types can be fixed with the Ni-Ti shape memory alloy nail angle fixator, and all are amenable to standard surgical procedures. The current consensus [10, 15] is that strong internal fixation is required for the medial and intermediate columns, and flexible fixation with Kirschner pins for the lateral columns. For Myerson A, B, and C fractures, the four fixation arms of the fixator meet these requirements as long as the 1st and 2nd sequences are fixed. A typical Hardcastle incision is made, and the four fixator arms are used to fixate the metatarsals and cuneiform bones in the 1st and 2nd sequences. Because of the presence of a stable interosseous ligament between the 2nd and 3rd metatarsals and the 3rd and 4th metatarsals, it has been concluded that fixation of the 2nd and 4th sequences is possible without the need to fixate the 3rd sequence of the central column. The supplementary incision between the 3rd and 4th metatarsals can be decided on a case-by-case basis as it is primarily used to reposition the 3rd metatarsocuneiform joint and fixate the posterolateral column. Percutaneous Kirschner pin fixation of the posterolateral column can be used if percutaneous repositioning is satisfactory. In our type A case, we used a nail angle fixator for fixation of sequences 1 and 2, and a percutaneous Kirschner needle for flexible fixation of the posterolateral column, while no internal fixation was used for sequence 3. In addition, we added Lisfranc screw fixation in this case but not in the other cases. The results confirmed that the shape memory alloy nail angle fixator can completely replace Lisfranc screw fixation. (2) This internal fixation is reliable and does not require postoperative plaster fixation so rehabilitation training can be started as early as possible for functional recovery. (3) Standardization of surgery and simplicity of operation. This fixation simplifies complex surgeries, involves fewer surgical complications, and can be performed at most primary hospitals. All seven patients in this group achieved anatomical joint reduction, good functional recovery, and significant pain improvement over the follow-up period.
4.3 Surgical practice points and considerations for Ni-Ti shape memory alloy nail angle fixator for Lisfranc fracture-dislocation
There are many surgical practice points and considerations for the Ni-Ti shape memory alloy nail angle fixator. (1) The surgical incision, which is located at the base of the 1st and 2nd metatarsals, centered on the metatarsophalangeal joint, and about 1.5 cm in length. It exposes only the periarticular area but does not excessively strip the periosteum and subcutaneous tissues; (2) after visualization of the joints and debriding the intra-articular tissues, the joints were reduced and reset. The order of reduction was the 2nd metatarsophalangeal joint, followed by the 1st metatarsophalangeal joint. These joints were temporarily fixed with Kirschner pins after reduction. If the 3rd metatarsocuneiform joint and the lateral column need to be reduced, percutaneous Kirschner pin fixation can be performed first, and then an auxiliary incision between the 3rd and 4th metatarsals can be made if fluoroscopy indicates that joint reduction would be difficult; (3) fixation of the nail angle fixator can be performed after satisfactory reduction of all joints, confirmed by fluoroscopy. First, the test mold of the nail angle fixator was selected and placed on the dorsal side of the 1st and 2nd metatarsocuneiform joints. After determining the appropriate size and adjusting the position, holes were drilled with a drill bit in the guide holes on the four corners of the test molds. Next, the four fixation arms of the deformation-formed nail angle fixator were driven into the bone. Finally, warm water was used to return the fixator to its pre-memory form and provide fixation to the joints.
In conclusion, the Ni-Ti memory alloy nail angle fixator for the treatment of Lisfranc fracture-dislocation is a simple procedure with good fixation, satisfactory recovery of postoperative foot function, effective pain relief, and few surgical complications, thereby ensuring a degree of clinical efficacy. The shortcomings of the present study are that it was a single-center retrospective study and lacks large-sample clinical data. In the future, a large-sample, multi-center, prospective study should be conducted to further validate clinical efficacy.