Segond fracture presents as an avulsion fracture of the lateral tibial border, but his presence is an indicative sign of intra-articular injury. According to the previous literature11,12, the probability of Segond fracture combined with ACL injury is 75% -100%, and the probability of accompanied by meniscus injury is 66% -75%. In this study, 35 cases of Segond fracture were combined with ACL injury, and 20 cases (57.1%) were combined with meniscus injury, which was slightly lower than the results reported in the literature. This study found that the indicative effect of Segond fracture on timely detection of combined injuries in the knee joint cannot be ignored. In addition to repairing the intra-articular injuries, more attention should be paid to the anterolateral structural stability of the knee joint. For patients with higher pivot shift grade, reconstruction of ALL may be considered.
Anterolateral complex (ALC) injury of the knee is a secondary injury to ACL injury of the knee. The ALL in the ALC is considered to provide an important limitation for knee joint rotational stability, and Segond fracture is also considered to be an avulsion fracture of tibial attachment of the ALL12-14. However, there are also some studies that oppose this viewpoint. Brockmeyer et al.15 found that the osteofascial layer of the iliotibial tract (ITT) in the ALC also has a high attachment rate (41.1%-52.1%) in Segond fracture slices, and a large proportion of Segond fractures have ALL and ITT coattachment. When comparing the structural characteristics of the ALL and ITT of cadaveric knee joints, Rahnemai et al.16 found that the ALL was at least 4 times lower than the ITT in stiffness and ultimate load, while the ultimate elongation was 2 times higher, indicating that the ALL seemed unlikely to play an important role in providing joint stability. The ITT, as the main constraint for intratibial rotation, was more likely to be the cause of Segond fracture. In addition, studies17,18 have pointed out that the ITT is the main structure for maintaining anterolateral rotational stability in the 30°-90° flexion state of the knee, while the ALL has a smaller rotational stability at those angles. We believe that the ALL starts from the lateral epicondyle of the femur and ends at the midpoint of the line between the Gerdy tubercle and the fibula head. Because of its oblique shape, the ALL is more horizontal than the ITT and has a certain limiting force in the horizontal direction. When the pivot shift occurs, the knee joint flexion ranged from 20 to 30, and the tibia rotates around the medial collateral ligament. The ALL has a greater torque than the centre of rotation, which limits the internal rotation of the tibia to a certain extent and can provide a part of the stress to prevent anterior dislocation of the tibia relative to the femur.
The lateral meniscus (LM) tear, a common injury incidental to ACL rupture, also has a high incidence in the formation of Segond fractures19. Meniscal tears are usually caused by compression of the femoral condyle against the meniscus when the knee is twisted or excessively flexed. It is worth noting that although the injury mechanism of Segond fracture is controversial, it is closely related to excessive internal rotation of the tibia, and both conditions have similarities in their injury mechanism. Claes et al.3 found that the ALL was tightly connected to 1/3 of the LM body, causing the ALL to separate into two fibrous bands: the meniscal femoral portion (inserted across the femur to the lateral meniscus) and the meniscal tibial portion (extending from the lateral meniscus to the tibial insertion). Corbo et al.20 observed that although the histological properties were relatively similar, the separated inferior meniscal fibres were stronger and harder than the superior meniscal fibres and speculated that the ALL inferior meniscal fibres might provide greater anterolateral rotational stability in ACL-deficient knees due to their greater stretchability. However, Burkhart et al.21 found that there was no significant difference in axial movement or tibiofemoral rotation between superior meniscal slices and inferior meniscal slices of the ALL in a study of isolated knee joints. Although the relationship between the ALL and the LM is unclear, Segond fractures have been identified in clinical studies as a high-risk factor for LM tearing. Sulaiman et al.11 showed that Segond fractures significantly increased the risk of lateral meniscus tear, and the incidence of LM tear in patients with Segond fracture (49.1%) was higher than in patients without Segond fracture (32.6%) among patients with ACL tear. In addition, Byrne et al.22 studied 9 cases of ACL tears with Segond fractures and found that 4 of 9 patients had LM tears. In our study, 17 of 35 Segond patients (48.6%) were complicated with LM injury, and all preoperative physical examinations were positive for a high degree of pivot shift (2+ or 3+). There are still 5 patients with LM injury who have a positive pivot shift 1 degree after two years follow-up after surgery. We speculate that the Segond fracture may be associated with residual axial migration postoperatively, but it is unclear whether it was caused by the ALL injury affecting the integrity and stability of the LM.
Previous studies6,7,23 confirmed that ACL reconstruction combined with external tendon fixation of the ALL joint has achieved good clinical results in long-term follow-up and that postoperative patients perform well in terms of clinical function and imaging. Nonetheless, several scholars24,25 have pointed out that compared with simple ACL reconstruction, ACL reconstruction combined with ALL reconstruction does not show a significant advantage in improving residual axial movement and may even lead to an excessive pronation constraint of the knee join. Based on the clinical results, we believe that the ALL injury caused by Segond fracture may affect the stability of the anterolateral structure of the knee joint. Segond fracture patients with higher pivot shift grade may have residual axial migration after surgery, so ALL reconstruction surgery may be considered.
The present study has the following limitations. As a retrospective study, this investigation has an inherent confounding bias and a single-centre research design, which leads to patient selection bias. In screening patients, the inclusion of patients with avulsion fractures in the study based only on X-ray and CT data may leave out patients with ALL injury but no avulsion fracture formation. Although the pivot shift tests were all performed by the same senior researcher with the patients under anaesthesia, the results were obtained from qualitative observations and thus were affected by the subjective operation and assessment by the researcher. Therefore, the quantitative pivot shift test might be a more appropriate evaluation method26. In addition, there was no ALL ligament reconstruction group, so it is difficult to evaluate whether the postoperative effect in patients with Segond fracture and ALL reconstruction is better than that of patients with avulsion fracture treated conservatively. Finally, the relatively short follow-up time is also a deficiency of this study, as only two years of follow-up could not be used to assess potential degenerative changes.