Locking compression plate distal ulna hook plate fixation versus intramedullary screw fixation for displaced avulsion fifth Metatarsal Base fractures: a comparative retrospective cohort study

The base of fifth metatarsal was defined as the proximal 1.5 cm of the shaft distal to its articular surface. Fifth metatarsal base fractures (FMBFs) were the most common type of the fifth metatarsal fractures [1]. The fracture typically occurred when an adduction force was applied to the forefoot with the ankle plantarflexed. The base was usually divided anatomically into three zones [2] (its tuberosity, meta-diaphyseal junction and proximal shaft). Fractures in zone 1 were the most familiar ones which comprised about 93% of all the proximal fifth metatarsal fractures [1]. In our study, displaced avulsion FMBFs were defined as the displaced fractures in zone 1 [3, 4] (Fig. 1).

Most un-displaced avulsion FMBFs can be treated with conservative treatment [3, 5]. Non-weight-bearing with cast immobilization has been the main treatment of this injury [5, 6]. However, this injury often was a source of lost work productivity and associated with nonunion rates of 7% to 28% [2]. Fractures displaced more than 2 mm frequently required surgical treatment to achieve anatomic reduction of the articular surface, early weight-bearing and restoration of peroneus longus and brevis tendons [2]. Surgery treatment of displaced avulsion FMBFs was challenging because of its subcutaneous location, comminuted fracture, its attachment of peroneus longus and brevis muscles and its weight-bearing function [3, 7]. Intramedullary screw (IMS) fixation was wildly used in FMBFs [7‐9] (Fig. 2). Previous studies showed that the screw was larger in both diameter and length the better [10]. However, the comminuted or small displaced avulsion FMBFs were difficulty to treat with large IMS and function outcomes following IMS remained unsatisfactory because of late weight-bearing [11]. Meanwhile, the IMS was associated with many complications, including lateral gapping, distraction of the fracture site and mal-reduction of the fractures [10, 12].

The Locking Compression Plate (LCP) distal ulna hook plate fixation was a novel alternative fixation method [13, 14] (Fig. 2). In addition, case series with LCP distal ulna hook plate fixation had shown improved clinical outcomes [14]. The purpose of this retrospective cohort study was to determine if LCP distal ulna hook plate fixation resulted in improved outcomes compared to the IMS fixation.

18 patients treated with IMS and 25 patients treated with LCP distal ulna hook plate fixation were included in the study. All the raw data was in the Additional file 1. The two cohorts had similar baseline characteristics, including mean age (39.89 and 34.36 years, p = 0.4575), gender distribution (27.78% and 60.00% male, p = 0.5226), and smoking rates (38.89% and 48.00%, p = 0.5528) (Table 1). For both cohorts, the surgery time was significantly less in patients with LCP distal ulna hook plate fixation cohort (40.94 and 53.5 min, p < 0.001). Time for partial weight-bearing (3.67 and 5.36 weeks, p < 0.001), full weight-bearing (6.52 and 8.48 weeks, p < 0.001), and bony union (7.49 and 9.64 weeks, p = 0.0053) was significantly less in patients with LCP distal ulna hook plate fixation cohort compared to IMS cohort. There was no significant difference in the time for return to daily life (12 and 12.52 weeks, p = 0.4192), pain scores before surgery (7.72 and 8, p = 0.2432), pain scores at 3 (4.61 and 4.64, p = 0.9072), 6 (3.56 and 3.68, p = 0.4589), 9 (2.39 and 2.68, p = 0.0856), and 12 weeks (0.44 and 0.52, p = 0.6346) after surgery, AOFAS before surgery (43.61 and 44.24, p = 0.4554), AOFAS at 3 (74.17 and 74.16, p = 0.9931), 6 months (76.67 and 76.6, p = 0.7879) after surgery between the two cohorts. While, the AOFAS scores at 9 (82.06 and 78.64, p < 0.0001), 12 months (93.56 and 87.8, p < 0.0001) after surgery were significantly higher in patients with LCP distal ulna hook plate fixation cohort (Table 2). One patient immigrates to Canada, we missed the follow up. There was no significant difference in the complications after surgery between the two cohorts.

The main finding of this study is the efficacity of the fixation using a LCP distal ulna hook plate for a novel approach. There were only 4 studies studied the plate in the treatment of FMBFs [13, 15‐17]. Three studies had evaluated the results of surgical treatment of zones I and II FMBFs using a mini-hook plate [13, 15, 16]. The fourth investigated the biomechanical comparison of IMS versus Low-Profile Plate fixation of a jones fracture [17]. There has been no previous comparison study investigating pain and functional outcome following treatment with LCP distal ulna hook plate and IMS, and our study is the first comparative retrospective cohort study to compare LCP distal ulna hook plate and IMS in displace evulsion FMBFs. Our finding showed that LCP distal ulna hook plate fixation as an alternative fixation method was better therapy for the displaced avulsion FMBFs than IMS fixation. LCP distal ulna hook plate fixation had a short surgery time and improved functional performance.

FMBFs can be challenging because of its subcutaneous location [18]. IMS as a precuneus technical was widely used in clinic and accepted as the standard of surgical treatment of these fractures [12]. Meanwhile, the screw system was developed, allowing surgeons to choose among 4.5-, 5.5-, and 6.5-mm solid stainless steel screws. However, it was difficulty to fix the small avulsion fractures with screws and there were several complications associated with them, such as irritability of screws head, injury of peripheral nerve, bone nonunion because of small diameter, and secondary fractures because of large diameter [12]. Alternatively, LCP distal ulna hook plate may be a good choice. This plate has several advantages: (1) the fifth metatarsal tuberosity can be grasped tightly by the plate hook to maintain the stability of the peroneal tendons adhesion; (2) as a checkered plate, the re-displaced of fractures can be reduced. Joint surface collapse can be prevented by the support function of this plate; (3) this plate had good histocompatibility; (4) the fifth metatarsal’s bending curvature fitted to the LCP distal ulna hook plate; and (5) low profile, obtuse edge and polishing surface can reduce the irritability of the soft tissue [17]. Vorlat, Achtergael and Haentjens reported that the most significant predictor of a poor functional outcome after these injuries was a prolonged period of non-weight-bearing [19]. The advantage functional outcome of LCP distal ulna hook plate was related to the early weight-bearing.

The retrospective cohort design of this study has several strengths. All cases were performed by a single senior surgeon (ZHF) using the same surgical approach, and all functional outcome evaluations were completed by a single senior physical therapist (SJZ) for precision. In addition, complications in both groups minimal. Limitations of this study include only twelve months of outcomes postoperatively, the total number of patients were small, and the radiographic evaluation was incomplete. Nowadays, we are focus on the effectively of the fifth metatarsal fractures anatomy plate.

This study suggests that the use of LCP distal ulna hook plate fixation improves patients’ outcomes postoperatively.