A Novel Method for Internal Fixation of Fifth Metatarsal Tuberosity Avulsion Fractures

Background: The purpose of this study is to introduce a novel technique of xation with a suture anchor combined with a headless cannulated screw. Patients and Methods: Ninepatients with fth metatarsal tuberosity avulsion fractures were recruited and surgically treated witha suture anchor combined with headless cannulated screw xation. Those patients were seen for follow-up visits monthly. Clinical and radiological outcomes were evaluated after surgery, at 4, 6 and 8 weeks, and monthly thereafter. The functional outcome was graded using the American Orthopedic Foot and Ankle Society (AOFAS) midfoot scoring system at the nal follow-up visit. Results: The mean interval to bone union observed radiologically was 5.6 weeks (range 4–8 weeks). No case of delayed union/nonunion or refracture was detected. No screw migration or implant breakage occurred. The mean interval to daily living activities was 8.2 (range 6 to 12) weeks after surgery.The mean AOFASscore improved from 30.8 (range 10 to 45) points preoperatively to 92.3 (range 87 to 98) points at the nal follow-up visit. Conclusions:


Introduction
The fth metatarsal basal fracture, rst described by Sir Robert Jones, [1] is the most common of the metatarsal fractures and is classi ed into 3 zones by Lawrence and Botte. [2] Zone I is a proximal avulsion fracture. Zone II is a fracture between the metaphysic and diaphysis, including articulation with the fourth metatarsal. Zone III is a proximal diaphyseal fracture. Zones I and II are fractures due to acute injury, whereas Zone III fractures are usually pathologic stress fractures. Fifth metatarsal tuberosity avulsion fractures (Zone I) were the most familiar fractures, accounting for approximately 93% of all fth metatarsal fractures. [2] Although undisplaced fth metatarsal tuberosity avulsion fractures (Zone I) usually respond well to conservative treatment, such as a walking cast, [3] investigators have shown that undisplaced Zone I fractures can require ≤ 12 weeks for bone union. [4] In addition, for acute fractures in athletic or active patients and fractures with displacements of > 2 mm, delayed union, painful nonunion and refracture have been reported. [5][6][7][8] Operative xation is recommended for displaced fth metatarsal tuberosity avulsion fractures and can decrease the delayed union/nonunion rates associated with these fractures. [9] However, several studies have reported failure after xation with screws. Wright [10] found that failure seemed to be correlated with the fracture dimensions, as an increased length and width raised the failure rate (a combination of refracture and nonunion) up to 5% in athletic patients. Granata [11] reported a 7.3% failure rate after surgical treatment, mainly due to refractures. Therefore, other methods for xation have been developed to achieve better stability and a lower rate of complications. Kirschner wire xation combined with a tension band [12] or ulna hook plate [13] has been used with similar outcomes. There have been many studies regarding fth metatarsal basal fracture; however the most appropriate surgical treatment remains controversial.
This report describes and discusses a novel method for internal xation of fth metatarsal tuberosity avulsion fractures via a combination of a suture anchor combined with a headless cannulated screw.

Patients and Methods
Nine patients who sustained displaced fth metatarsal tuberosity avulsion fractures were recruited and surgically treated with a suture anchor combined with a headless cannulated screw xation form January 2017 to September 2018.
The study protocol and consent forms were approved by our institutional review board. All patients provided written informed consent for the present study and were informed that the necessary data and photographs would be submitted for publication without patient identi cation.
Those patients were seen for follow-up visits every 4 weeks, and clinical and radiological outcomes were evaluated. They were followed up for a mean of 11.8 (range 8 to 16) months. Of the 9 patients, 6 were male and 3 were female. Their mean age was 37.9 (range 18 to 55) years. All patients had sustained displaced fth metatarsal tuberosity avulsion fractures. Radiographs were obtained after surgery, at 4, 6 and 8 weeks, and monthly thereafter. The functional outcome was graded using the American Orthopedic Foot and Ankle Society (AOFAS) midfoot scoring system preoperatively and at the nal follow-up visit.

Surgical technique
The operation was performed in the supine position after anesthesia induction. Intraoperative uoroscopic imaging was used to guarantee appropriate drilling position, depth and guide wire placement. After sterile draping and prepping of the surgical site, a 3 cm long longitudinal incision was implemented on the lateral border of the fth metatarsal bone, parallel to the plantar surface. The entry point for the anchor was created at the distal metatarsal shaft, 1 cm past the fracture site and perpendicular to the metatarsal shaft. Next, a suture anchor (2.8 mm, Smith & Nephew, Andover, USA) was inserted into the fth metatarsal fracture shaft. Once the suture anchor was completely inserted, the sutures were released from the anchor. The two groups of suture threads were then sewn into the soft tissue sleeve of the proximal fragments and the termination of the peroneus brevis tendon. Reduction was veri ed under direct vision before knotting the rst group of sutures ( Fig. 1). A guide wire was inserted perpendicular to the fracture line at the tip of the fth metatarsal basal part. A second guide needle was implanted to prevent rotation of the fracture fragment. The placement of the guide wire and the reduction of the fracture were con rmed under uoroscopic imaging. Then, through the rst guide wire, a cannulated drill was advanced down the medullary canal and passed through the fracture site. A headless cannulated screw (2.4 mm × 14 mm, Osteomed, Addison, USA) was then placed into the intramedullary canal and advanced until compression was obtained. The placement of the headless cannulated screw and the reduction of fracture were con rmed again under uoroscopic imaging. Then, the other suture was knotted to strengthen the xation. The incision was closed using sutures after irrigating the wounds.
The postoperative protocol consisted of non-weight-bearing restrictions and crutches for 4 weeks. The radiographs were examined for evidence of fracture healing, implant failure or migration, and fragmentation of the distal fth metatarsal. Radiographic fracture healing was de ned as any evidence of normalization of the medullary or obliteration of the fracture lines. Gradual weightbearing was allowed until the radiographs revealed evidence of union. All patients were allowed to return to full activity when they were clinically asymptomatic and had demonstrated radiographic union.

Results
The present study has demonstrated that good clinical and radiological outcomes can be achieved for displaced fth metatarsal tuberosity avulsion fractures treated with a suture anchor combined with headless cannulated screw (Fig. 2).
A total of 9 patients, 3 females and 6 males, were treated from January 2017 to September 2018. The average age was 37.9 years at the time of injury (range 18 to 55). Eight patients sustained twisting injuries during sport activity, and 1 patient sustained a crushing injury from a wheel rolling over the foot.
All patients had sustained displaced fth metatarsal tuberosity avulsion fractures.
The mean follow-up period was 11.8 (range 8 to 16) months. The average time to fracture healing observed radiologically was 5.6 weeks (range 4-8 weeks

Discussion
There have been many studies regarding fth metatarsal basal fracture; however, the most appropriate surgical treatment remains to be controversial. The mechanism of fracture has been described as a large directed force applied to the forefoot while the ankle is plantar exed. [2] Because the fth metatarsal has the widest motive range compared to other metatarsals, while the base is tightly xed by ligamentous connections, fth metatarsal tuberosity avulsion fractures will occasionally result in displacement and carry a risk of delayed union/nonunion. [14] The different arterial supply to the proximal diaphysis and the base of the fth metatarsal create a potential relative avascularity region, resulting in poor prognosis for fracture healing. [15] Initially, most fth metatarsal tuberosity avulsion fractures of the fth metatarsal were treated with immobilization and non-weight-bearing approaches, such as walking cast or bandaging. [4] However, conservative treatments exhibit a high rate of delayed union/nonunion. It has been reported that 8 of 44 patients managed nonsurgically required subsequent surgical intervention due to delayed union, while no delayed union occurred in the surgical group. [16] It has also been reported that the mean time to return to activity was 7.9 weeks in the surgical group compared to 15 weeks in the non-surgical group. [3] Various methods for surgical management have been reported, including tension band wiring [12,17,18]; ulna hook plates, [19] crossed Kirschner wires, [20] intramedullary screw xation [5] and suture anchor. [21] Tension band wiring xation has become a well-documented surgical management for the treatment of patients with sustained acute fth metatarsal fractures. [18] This technique used 1.6/1.8 mm intramedullary Kirschner wires implanted longitudinally in the metatarsal bone from the tuberosity. One of the Kirschner wires engaged the medial cortex 2 to 3 cm distal to the fracture. A optimal tension band wire (0.6 to 1 mm in diameter) was implanted again 1-2 cm distal to the fracture and around the K-wires in gure-8 format. [17] However, hardware fatigue was the main problem of xation with tension band wiring, especially in athletic patients. Fixation needed to be removed due to this problem. Pain and paresthesia over the insertion point were also reported. [12] A case of stress fracture of the fth metatarsal base caused by tension band wiring was reported. They described a 26-years-old athlete who sustained a stress fracture after surgery while the initial fracture had already healed, they believed that the Kirschner wires ware a stress contributor and that they should be removed within 6 to 12 months after bone union. [22] Direct compression at the fracture site was limited when treated with tension band wiring.
In addition, intramedullary screws have long been used to treat fth metatarsal base fractures. The most frequently used screw was 4.0/4.5 mm screw to provide fracture site compression. Biomechanical studies have been carried out to indicate that there is no signi cant difference between 4.0 mm and 4.5 mm screws. [5] An isolated intramedullary screw had poor resistance to dorsal exion forces; it resulted in a high risk of implant breakage or micromotion of the fracture site, and caused pain due to stimulation of the surrounding soft tissues. [23] To improve the compression at the fracture site, researchers are inclined to use a thicker screw, even though it can disintegrate the fracture fragment. We used 2.4 mm diameter screws to effectively prevent iatrogenic fracture fragmentation. The suture sewn into the peroneus brevis tendon can act as a tension band, a substitute for reduction that can effectively reduce the risk of iatrogenic fracture fragmentation and enhance the resistance to dorsal exion forces. The compression at the fracture site provided by the isolated tension band or screw is imitated. The lateral traction engendered by the tension band can be transmitted to the fracture site by the screw to strengthen the compression. Enhanced compression and good reduction can shorten the fracture healing time. The mean interval to union of fractures has been reported to be 5.3 to 7.8 weeks [24,25]; our result of 5.6 weeks is similar to that in the rst study. [24] However, the differences were not statistically signi cant.
The creation of a suture anchor combined with a headless cannulated screw allows minimal insalivation to soft tissue, which is useful for preserving the blood supply to fractures that have already been proved hypovascularized. The procedure is more likely to reduce the risk of delayed union/nonunion by protecting and preserving the blood supply compared to other more aggressive interventions. To the best of our knowledge, the present study is the rst to report displaced fth metatarsal tuberosity avulsion fractures treated successfully with a suture anchor combined with a headless cannulated screw. The concept of this technique is to combine the reduction of the suture and the direct compression of the screw. This new approach has not yet been widely used clinically; however, it has been shown to be effective and reliable. Biomechanically tested and contrastive studies need to be carried out to prove its superiority compared to other techniques.
The limitation of the present study is the small sample size and lack of contrast. We intend to launch a contrastive study to de ne the difference between this new technique and other techniques in the future. Another limitation of this technique is the higher expense of using a suture anchor combined with a headless cannulated screw.
It is highly recommended that this technique should be used in athletic and active patients. This is because of their requirements of better function and higher biomechanical stress on the fracture site, and an isolated intramedullary screw will raise the possibility of failure of xation. Therefore, it is credible to use a combination of a suture anchor and headless cannulated screw to achieve a more stable coalescence. Fixation with a suture anchor combined with a headless cannulated screw is an effective surgical management for acute displaced fth metatarsal tuberosity avulsion fractures. Furthermore, delayed union/nonunion of fth metatarsal fractures may be another indication due to its advanced biological requirement.

Conclusions
Displaced fth metatarsal tuberosity avulsion fractures are common. The most appropriate surgical treatment remains controversial. We have illustrated a novel method of internal xation of displaced fth metatarsal fractures with a combination of a suture anchor and headless a cannulated screw. We believe it is a reliable technique with good outcomes and can potentially allow for early bone union.

Declarations
Funding: Con icts of interest: The authors have no personal nancial or institutional interest in the materials or methods described in this paper.
Ethical Approval: The study received ethical approval from the Institutional Review Board of Shanghai Tenth People's Hospital a liated to Tongji University.

Consent to participate:
Written informed consent was obtained from all patients before surgical treatment including the fact that the data may be included in future publications.

Consent for publication:
Written informed consent for publication was obtained from all participants.
Availability of data and material: The data used to support the ndings of this study and the datasets used and/or analyzed during the present study are available from the corresponding author upon request.

Authors' contributions:
Lei Zhang and Chunlin Zhang contributed the central idea; Taicheng Zhan analysed most of the data, and wrote the initial draft of the paper. The remaining authors contributed to carrying out additional analyses and nalizing this paper.