In this study, the distal radius fractures were divided into three types: 1, 2, and 3, based on CT. Each type was divided into three subtypes. The patients included in our hospital were followed up. There was no significant statistical difference in each type of DASH, PRWE, and VAS scores. The main reasons were as followed. First, it was a selection bias of the included patients. This study included inpatients for inpatient surgery without including outpatient conservative treatment. Some inpatient data were inadequate. Second, the wrist joint was a functional joint rather than a weight-bearing joint. There was little impact on the patient's daily functional requirements about the loss of the smaller range of the wrist joint. Therefore, the DASH, PRWE scores were low, which reflected the subjective functional outcome of a patient. However, the observer consistency evaluation results of the new typing system were more significant than 0.9, and according to the Landis and Koch standards, they were utterly credible. Moreover, the intra-observer repeatability results of the 123 classification were unrelated to the observer's experience.
Requirements for an ideal classification system
A practical and widely accepted classification was characterized by the following characteristics: 1. Better observer-consistent results. 2. Characteristics of fractures can be accurately understood and described, the fracture injury mechanism can be reproduced, preoperative plans were formulated, treatment guidance was provided, and possible complications were accurately judged for clinicians. Moreover, it can be used as a credible “common language” for clinicians in different countries and regions. 3. It was comprehensive and easy to remember. Based on the above characteristics and requirements, we established an ideal 123 classification of CT-based distal radius fractures.
Insufficient research on current conventional classification systems
At present, the observer-consistent results of the AO / OTA classification were entirely credible or basically credible in individual studies[11]. The majority of studies reported observations of AO / OTA group, Frykman type, Fernández type, and Universal type were moderately reliable or below[6, 7, 12–21]. All the above classifications were based on ordinary understandable film classification. The number and shape of fracture lines in the joint and the direction of fracture block displacement were diagnosed by CT. It was helpful to the classification understanding and a surgical plan. However, was it possible to improve observer-consistent results? At present, there were only two studies on whether the increase of CT examination can improve the observer consensus results of AO / OTA typing, Frykman typing, Fernández typing, and Universal typing [22, 23]. The results of both studies were different. In 2014, research by Arealis and others indicated that adding CT examinations can help senior doctors to formulate treatment plans, but it cannot improve the observer-consistent results of AO / OTA, Fernández, and Universal classification[22]. In 2017, Kleinlugtenbelt et al. reported that except Frykman typing, the addition of CT + 2D examination could improve the repeatability within the observer of AO / OTA classification, Fernández typing, and Universal classification than using plain X-ray films alone, and it cannot improve all Inter-observer reliability of classification[23]. Our study found that adding CT + 2D examination did not improve observer-consistent results for Frykman classification, Fernández classification, and Universal classification. However, a noticeable improvement was in the observer consensus results of AO / OTA classification and AO / OTA grouping.
Recent Research on New Typing System for Distal Radius
In view of the low reproducibility of the classification of distal radius fractures, Bellott et al. proposed an IDEAL classification method based on epidemiological and imaging factors[24]. According to the patient's age, epidemiological factors of trauma energy, degree of bone mass displacement, joint integrity, and imageology factors with injuries, scores were classified. A score of 0–1 was a stable fracture, and conservative treatment was adopted. A score of 2–3 was a potentially unstable fracture and K-needle, external fixation or internal fixation was used. A score of 4–5 was a complex fracture that required multiple methods and bone grafting[24]. Kapppa between observers of IDEAL classification = 0.595, and Kapppa within observers = 0.771. Yi Lu et al. described a morphological typing and grading system specifically for Barton fractures[25]. It was divided into four types by the research team: classic Bartong fracture, ulnar Bartong fracture, radialis Bartong fracture, comminuted Bartong fracture, and the inter-observer reliability and intra-observer repeatability scores were 0.71–0.80 and 0.68–0.88 [25].
A majority of literature pays attention to the radialis wrist joint, while the distal radioulnar joint was ignored. Frykman's study indicated that the fracture line involved the inferior ulnar radial joint in 19% of cases[2]. Malunion of the distal radioulnar and weak line of force can lead to chronic pain and weaken of the wrist. Jupiter et al. found that distal radioulnar joint mismatch gradually developed arthritis, with varying degrees of wrist pain in 33% of patients[26]. Later, some scholars were classified according to the situation of sigmoid notch. Rozental et al. included imaging data of 20 intra-articular fractures. 13 (65%) intra-articular fracture lines extended to the sigmoid notch in CT data[27]. By the sigmoid notch image data analyzation, all cases were divided into three types, type 1 was the complete sigmoid notch, type 2 was fracture line involving sigmoid notch but no displacement, and type 3 was fracture line involving B The notch is shifted. Nakanishi et al. classified intra-articular fractures of the distal radius into type 3 and 5 subtypes based on the number of fracture lines involving the sigmoid notch and the degree of displacement of the fractured mass[28]. Their study found that sigmoid fractures were presented in 83% of cases of intra-articular fractures and that sigmoid fractures were comminuted in 34%[28]. The application of 3D-CT provided accurate judgment of the sigmoid notch damage and a basis for surgical strategy. Hintringer et al. combined the biomechanical foundation of the distal radius, a new classification based on CT has been proposed[29].
Theoretical basis and a basis for the 123 classification system
The theoretical basis for the establishment of the 123 classification system is based on the characteristics of the fracture line of the articular surface of the distal radius fracture, the bone ligament unit theory, the three-column classification of Rikli and Regazzoni[30] and the four-part classification of Melone and many other theoretical studies[31, 32].
There are many ligament attachment points around the articular surface of the distal radius, and the fracture line often occurs between the ligament attachment areas with a certain regularity. Increasing evidence suggests that even if the distal radial articular surface was a comminuted fracture, the ligament attachment points around the articular surface remain intact [33, 34]. It is reproducible about the distribution of articular surface fracture lines in the distal radius[35, 36]. In 2011 and 2013, Gregory's team successively studied the relationship between the attachment of the ligament around the distal radius and the position of intra-articular fractures [35]. In this study, the periphery of the distal radius was divided into 11 regions (Fig. 11). The following regions are easily affected: the familiar site of the fracture was in the center of the sigmoid notch (inter-ligamentary region 10), the short radiolunate ligament, SRL), long radiolunate ligament (LRL) (ligament area 2), the dorsal center of the scaphoid fossa (ligament area 6), LRL (ligamentous area 3), and ulnar side of the dorsal scaphoid fossa ( Ligament area 7). The following areas are less involved: dorsal ulnar radial ligament attachment (ligament area 9), palmaris ulnar radialis ligament attachment (ligament area 11), SRL attachment (ligament area 1), radialis scaphoid ligament attachment (ligament area) 4), the radialis the scaphoid fossa (ligament area 5), and the dorsal radiaisl wrist ligament attachment (ligament area 8)[35]. Fractures are more likely to occur in areas 2, 6, 10 than other areas, and there are significant statistical differences. Some scholars carried out atlas analysis of 40 cases of intra-articular fractures of the distal radius, and found that the characteristics of the horizontally oriented fracture line, which are the fracture line started from the base of the radial styloid process and extends horizontally along the scaphoid fossa and the lunar fossa to the sigmoid Trace middle[32].
The three-column typing theory of Rikli and Regazzoni emphasizes the importance of the intermediolateral column. It consists of sigmoid notches and lunar fossa. When the wrist joint is under axial stress, the intermediate column load is higher than 50% of the axial pressure[30]. At the 0 ° position of the wrist joint, the matching area of the sigmoid notch and the ulnar head's articular surface is the largest. When the forearm is pronated or supinated, the matching area of the two decreases. At the junction of the sigmoid notch of the triangular fibrocartilage origin and the lunar fossa, the stops are widely attached to the triangular bone, the hook bone, etc., forming a stable structure of the lower ulnar radius and the ulnar side of the carpal bone[27]. If the fracture line involves the sigmoid notch, the distal radioulnar joint will be damaged, which changes the biomechanics and movement trajectory of the wrist and forearm. Post-traumatic sigmoid notch healing due to steps or gaps may cause wrist pain, instability, or loss of range of motion[28]. Therefore, it is particularly important to emphasize the reduction of the intermediolateral column. Among them, restoring the anatomical structure of the Distal radioulnar joint, especially the anatomical reduction of the sigmoid notch, is very important.
Melone focuses on and supplements the classification of the carpal surface of the distal radius. This classification emphasizes the importance of lunar fossa and its clinical prognosis, and include the formation mechanism of die-punch fractures analyzation. This classification benefits to identify surgical indications for intra-articular fractures and guide of intraoperative reduction and fixation, but it is useless in classifying extra-articular fractures. It is difficult to judge the four characteristic fracture blocks of the distal radius and the die-punch bone blocks based on X-rays alone without extensive experience. There is no satisfactory result on the observer consistency study of Melone typing. Melone classification includes five types based on the dorsal medial bone mass on the articular surface, the medial volar bone mass, the radial styloid bone mass, and the radial shaft. There may be some differences and variations in the four parts of the articular surface of the distal radius according to our judgment, in which the dorsal part of the scaphoid fossa and the lunar fossa are collectively summarized in the dorsal part of the 123 classification. Based on many studies on the characteristics of the fracture of the radial surface of the articular surface and the fracture of the articular surface, this study found that the dorsal part of the scaphoid fossa and the lunar fossa could be damaged at the same time due to the back extension of the wrist, was also verified in the analysis of patient imageology data [32–35].
Significance of 123 classification system for incision selection, reduction, and fixation
Because there is a stable radial wrist ligament between the lunar bone and the palamris or dorsal part, subluxation of the wrist joint is in 1-D and 1-V fracture. In this case, it should be fixed firmly by surgery. For 1-D fractures, the dorsal approach is preferred for reduction and fixation. If Henry approach is chosen, it will not only increase the difficulty of restoration but also may result in poor restoration and fixation strength due to failure to reset, particularly in lateral collapse. The dorsal approach uses a straight incision between the third and fourth extensor compartments, placing the steel plate in the fourth extensor compartment.
Similarly, 1-V fracture require a palmaris approach for reduction and fixation. If a dorsal approach is chosen, it will not only increase the difficulty of reduction but may also lead to poor restoration. When the palmaris part and the dorsal part are involved at the same time, the palmar approach is preferred for reset. For cases where the dorsal part cannot be reset through the palmar approach, a dorsal approach can be selected to assist in reset.
Rikli et al. confirmed in vitro studies that during regular wrist movements, the lunare fossa and radial sigmoid notch were subjected to > 50% axial pressure[37]. The level of CT can be used to intuitively and accurately determine the number of fracture lines passing through the lunare fossa. When the fracture line of the radial sigmoid notch passes, the radial sigmoid notch should be reduced and fixed first to avoid the abnormal healing of the radial sigmoid notch. While restoring the anatomical restoration and stable fixation of the sigmoid notch, it is necessary to take into account the stable fixation of the palmar and dorsal columns to avoid secondary displacement caused by a weak reset or poor fixation of the palmaris or dorsal columns. A slight subluxation of the near-wrist carpal bones, thereby ensuring the restoration of the kinematics of the wrist joints.
Taken together, there are theoretically and practically significant for selecting incisions, guiding the reduction of the fracture block, and placing the steel plate about judging the damage of the three parts by correctly understanding the fracture type and the displacement direction of the fracture block by visually analyzing the three planes of the CT.
Advantages and disadvantages of the 123 classification system
This study is a retrospective study. All the included cases originated from inpatients, severe fractures in many patients. It is inevitable on case selection bias and statistical bias. Besides, the number of cases of some types is small due to incomplete image data of some patients, and the included research subjects are mainly inpatients; of course, some types may indeed be due to the small number of cases in the clinic, further verification is necessary. The larger sample size is necessary for practice and validation in the future. At the same time, more retrospective and prospective studies are necessary to verify the effectiveness of the 123 classification system in order to help better the surgeon understand the type of fracture in clinical work, and then formulate a surgical plan to obtain the desired results and judge the prognosis. Moreover, no control group treated non-operatively exists, constitutes another weakness of this study. Last, we could not exclude residual confounding by unmeasured or unknown confounders.
However, the CT-based 123 typing system provides a new classification idea. Based on the advantages of CT classification, the number of fracture lines, and the direction of bone mass displacement can be intuitively judged, which has a unique advantage for understanding fracture types and making surgical plans. At the same time, it benefits to improve the accuracy of typing, so it has better observer consistency. Besides, the 123 typing system is comprehensive and easy to remember. Of course, the traditional and conventional X-ray examinations cannot be replaced, and have certain reference functions for CT typing.