Characteristics and pattern distributions of anterior talofibular ligament injuries

To the Editor: Ankle sprains are some of the most common emergency injuries from trauma. Due to the particularity of its anatomy, most sprains of the ankle are due to injuries of the lateral collateral ligaments, of which 80% are tears or ruptures of the anterior talofibular ligament (ATFL).[1] If the treatment is not appropriate, the injury will affect the patient's work and life in the long term, and the patient can even develop chronic ankle instability (CAI), increasing the treatment duration and resulting in higher economic burdens on the patients and the medical insurance system. Regarding the clinical epidemiology of ATFL injuries, at present, most research is focused on the exploration of the incidence, pathogenic causes, and treatment methods, but not enough attention has been given to individualized factors and the associated injuries. In addition, the guidance effect of the findings of these studies on clinical practice is limited. To the best of our knowledge, there have been no clinical epidemiological studies on ATFL injuries in ward patients in China. Therefore, this study retrospectively analyzed the clinical data of all patients with ATFL injuries in the Sports Medicine Center of the Southwest Hospital of Army Military Medical University from July 2007 to December 2020. The goal was to understand the characteristics and pattern distributions of ATFL injuries to provide a basis for their prevention, early diagnosis, and treatment. This study was approved by the Ethics Committee of The First Affiliated Hospital of Army Medical University (KY 2021026). In terms of the ages of the 360 patients, 239 patients (66.4%) were aged 18 to 40 years, with fewer patients in younger and older age groups. A total of 118 patients (32.8%) were in the acute injury stage (within 1 month). Over time, the number of visits decreased, especially 1 to 3 months after the injuries, which had the lowest proportion of patients (40 patients, 11.1%); after 12 months, however, the number of visits increased significantly (89 patients, 24.7%). In terms of the cause of the injuries, sprains were the most common, with 184 patients (51.1%), of whom 131 developed the sprain while walking on flat ground, accounting for 71.2% of the total sprains. This was followed by sports injuries, experienced by 118 patients (32.8%), and training injuries were also relatively common, accounting for 10.0% (36 patients). Eight patients (2.2%) were injured by traffic accidents and heavy objects, and the other patients had no obvious causes (14 patients, 3.9%). Associated injuries were more common in patients with ATFL injuries, and osteochondral lesions of the talus (OLT) (83 patients, 23.1%) were the most common, followed by calcaneofibular ligament (CFL) injuries in 41 patients (11.4%). Injuries of other ligaments around the ankle (triangular ligament/inferior tibiofibular syndesmosis ligament/posterior talofibular ligament/bifurcation ligament) were rare, accounting for 7.2% (26 patients) of the total patients. The numbers of avulsion fractures and midsubstance injuries were counted, and both injuries were analyzed and compared by patient-specific factors. There was no significant difference in the incidence of midsubstance injuries (183 patients, 50.8%) vs. avulsion fractures (177 patients, 49.2%). Among the patients with avulsion fractures, with the exception of 9 who had avulsions of the insertion of the talus, the remaining 168 patients had an avulsion fracture of the fibular insertion. There was no statistically significant difference in sex, side of the injured limb, cause of injuries, or time of visit after the injury between patients with avulsion fractures and patients with midsubstance injuries [Table 1]. Descriptive statistics were calculated for demographic data, and Pearson's χ2 test or Fisher's exact test was used to compare categorical variables. Analyses were performed using the SPSS 22.0 software package (SPSS Inc., Chicago, IL, USA). P values <0.05 were considered statistically significant. Table 1 - Distribution of patients with ATFL injuries (n [%]). Items Cases (n = 360) Avulsion (n = 177) Midsubstance (n = 183) χ 2 P value Sex 0.946 0.379 Female 129 59 (45.7) 70 (54.3) Male 231 118 (51.1) 113 (48.9) Side 2.082 0.165 Left 149 80 (53.7) 69 (46.3) Right 211 97 (46.0) 114 (54.0) Age 22.532 <0.001 <18 years 44 28 (63.6) 16 (36.4) 18–30 years 164 94 (57.3) 70 (42.7) 31–40 years 75 28 (37.3) 47 (62.7) 41–50 years 39 13 (33.3) 26 (66.7) 51–60 years 29 13 (44.8) 16 (55.2) ≥61 years 9 1 (11.1) 8 (88.9) History 7.428 0.115 Acute-phase 118 67 (56.8) 51 (43.2) Subacute-phase 40 17 (42.5) 23 (57.5) Early-phase 47 27 (57.4) 20 (42.6) Middle-phase 66 28 (42.4) 38 (57.6) Chronic-phase 89 38 (42.7) 51 (57.3) Cause 6.455 0.091 Training 36 22 (61.1) 14 (38.9) Sports 118 60 (50.8) 58 (49.2) Sprains 184 89 (48.4) 95 (51.6) Others 22 6 (27.3) 16 (72.7) Associated injures 24.580 0.002 IM 59 23 (39.0) 36 (61.0) OLT 83 35 (42.2) 48 (57.8) CAI 73 25 (34.2) 48 (65.8) CFL 41 30 (73.2) 11 (26.8) TA 33 8 (24.2) 25 (75.8) TS 24 10 (41.7) 14 (58.3) OLI 26 9 (34.6) 17 (65.4) LB 10 3 (30.0) 7 (70.0) TT 11 6 (54.5) 5 (45.5) The data are expressed as numbers and percentages, and each value was analyzed by the χ2 test. All theoretical numbers T ≥ 5 and total sample size n ≥ 40 were analyzed with the Pearson χ2 test. For T < 5 but T ≥ 1 and n ≥ 40, we used the continuity-corrected χ2 test. If there was a theoretical number T < 1 or n < 40, we used Fisher's exact test. P < 0.05 indicated statistical significance. ATFL: Anterior talofibular ligament; CAI: Chronic ankle instability; CFL: Calcaneofibular ligament; IM: Impingement lesion; LB: Loose body; OLI: Other ligament injury; OLT: Osteochondral lesion of the talus; TA: Traumatic arthritis; TS: Traumatic synovitis; TT: Tendon tenosynovitis. From the perspective of injury mechanism, the ATFL injuries mostly occurred in the ankle in the plantar flexion and varus positions. At the time of the injury, an excessive foot varus was combined with an external rotation of the leg. Moreover, since its middle section crosses the talus body and the bony ridges of the neck junction, the ATFL suffers the most tension. An analysis of injury factors highlighted sprains, sports injuries, and training injuries as the main factors for ATFL injuries. Additionally, congenital diseases such as tarsal fusion and arthrochalasis were rare injury factors. The primary factor in the injuries was the presence of a sprain, including sprains from walking and falls, with the former dominating. Anatomical studies have shown that after an ATFL injury, constant varus trauma often simultaneously damages other adjacent structures, including bones and soft tissues, such as the CFL and the OLT. In this study, 235 patients had comorbidities and complications of the ATFL injury, accounting for 65.3% of all patients, which is consistent with the results of other studies.[2] Associated injuries were common. Because of an incomplete diagnosis, untimely treatment, or improper treatment methods, later stages of the injury might be complicated with impingement lesions, traumatic arthritis, and loose bodies. Among them, 73 patients eventually developed CAI (20.3%). Further understanding of the reasons behind the high incidence of CAI and the importance of possible combined injuries can lead to fewer disagreements regarding the best treatment methods, which are more important than the actual reported data. In the diagnosis of ATFL injuries, particular attention should be paid to whether there is a combined injury of the CFL, which is an important structure for maintaining the posterolateral stability of the ankle joint and subtalar joint. According to previous results, 11.4% of patients with an ATFL injury will have a CFL injury, but it is often missed clinically. Previous studies have focused on the ankle joint. However, patients with lateral ankle instabilities included numerous patients with subtalar joint instabilities. Considering the stabilizing effect of the CFL on the subtalar joint, some of these patients with lateral ankle instability could have subtalar joint instability. Among 73 patients with ankle instability in this study, 60 (two with subtalar joint instability) were treated by surgery, and the remaining 13 patients were considered to have functional instability and improved after conservative treatment. This study presented two types of injuries: avulsion fractures and midsubstance injuries, and the treatment of the two differed significantly. In contrast to the conservative outcome for substantial injuries, conservative treatment for avulsion fractures is often unsatisfactory. Statistically, 171 avulsion fractures were treated surgically, two patients did not pursue surgery due to personal reasons, and only 3 patients were treated conservatively. Surgery was performed for 132 patients for midsubstance injuries, 7 patients declined surgery due to personal reasons, and the remaining 44 patients chose conservative treatment. Diallo[3] showed that the rate of surgery was significantly higher in avulsion fractures than in midsubstance injuries, which is consistent with the results presented here. The reason might be that when the injury is an avulsion fracture, stretching of the ATFL and CFL made healing of the avulsed bone more difficult. Relaxation of the lateral fibulotalocalcaneal ligament (LFTCL) complex is unable to prevent excessive valgus deformity of the talus, eventually leading to CAI. The results in this article suggest that the incidence of avulsion fractures is basically equal to that of midsubstance injuries, which is consistent with previous studies.[4] Kumai et al[5] studied the histology and immunohistochemistry of the ATFL in ankle sprains. Near the articular surface of the talus, “encircling” fibrocartilage structures dispersed the stress around the ligament insertion, and the bone density was greater than that on the fibular side. Therefore, the talus side was the strongest. Our results are consistent with the above results: only 9 of the 177 entry avulsion fractures were talar. Through the comparison between patients with midsubstance injuries and avulsion fractures, it was found that except for the difference in age, there was no significant difference in the causes of injury or other factors. The rate of avulsion fractures in patients aged <18 years and those aged 18 to 30 years was significantly higher than that in patients with midsubstance injuries, yet the opposite trend was observed in patients aged >30 years. There was a significant difference in the associated injuries between the two groups, and the probability of associated injuries was higher in the patients who had midsubstance injuries than in the patients who had avulsion fractures, which could be related to more trauma in the injury. This should remind doctors that comprehensive injury in patients with midsubstance injuries might be more serious. The latest biomechanical tests showed that there was no systematic difference in ultimate failure load or stiffness between different types of injuries,[6] which further proves that the two types of injuries were essentially the same, and the difference might be due to the different ages of the patients and the amount of trauma that caused the injury. Studies have found that the physical properties of the ligaments were closely related to the quality and quantity of cross-linking within and between collagen molecules: in patients aged <20 years, the quality and quantity of the cross-linking increase with age, and the tensile strength of the ligaments increases.[7] At the age of 20 years, when the ligaments mature and the patient is at an older age, the mechanical properties of collagen are balanced, the amount of collagen begins to decrease, and the strength and rigidity of the tissue begins to decrease. Siegler et al[8] studied cadaver specimens, and when he tested them with a low strain rate, there were more avulsion fractures, while testing at a high strain rate led to more midsubstance injuries. The complete bone-ligament-bone complex had a typical viscoelasticity. When the load was rapidly increased, the bone had higher strain rate sensitivity and became strong and hard. When the load was slowly increased, the weakest part was the midsubstance part of the ligament, and the local strain near it was significantly higher than that of the ligament insertion. Compared with midsubstance injuries, avulsion fractures were less responsive to conservative treatment and were more likely to result in non-sunion. The risk of repeated sprain and subsequent ankle instability in patients receiving conservative treatment should be understood because the longer the presence of the avulsion fracture, the more negative effects will appear on the ankle, and the treatment effect will not be as desirable as that from timely surgical treatment. In short, the type of ligament injury was an important reference factor before the operation because the surgical method (repair or reconstruction) was different due to the need for the ligament to be reconnected to the bone or ligament. The results of this study indicated a high incidence of associated injuries in patients with ATFL injuries. With a high suspicion of possible associated injuries, there was a higher awareness of injury and probability of injury, which helped more accurately diagnose and improve the treatment of ankle sprains. This also allowed for more individualized rehabilitation, which might lead to more consistent outcomes between the conservative and surgical treatment of patients with ATFL injuries and avoid the development of CAI as much as possible. Funding This study is supported by the grant from the National Natural Science Foundation (No. 82072516). Conflicts of interest None.