Biplane Fractures of the Distal Femur: A Proposed Computed Tomography-Based Classification and Surgical Management

Introduction

Distal femur fractures represent <1% of all fractures ^[1,2]. These fractures are frequently comminuted and have intra-articular involvement ^[3]. Principles of management of distal articular femur fractures are similar to those of any other articular fracture, i.e., to achieve anatomical reduction of the fracture fragments while providing rigid fixation to allow early functional mobilization ^[3]. Management of periarticular fractures requires a careful understanding of fracture characteristics and proper pre-operative planning ^[4]. Management of combined distal femoral intercondylar fractures along with coronal plane fractures has received very little attention in the past ^[5]. Proper pre-operative imaging of these injuries may assist in the planning of surgical approaches and the selection of implants ^[6].

The present AO-OTA classification is a radiograph-based classification system. The presence of multiple fragments and the orientation of the fragments are now simplified with the use of computed tomography ^[6]. The presence of combined sagittal and coronal plane fractures of either or both condyles necessitates that it be classified as AO-OTA type 33 C3 or multifragmentary articular type ^[5]. A single category 33 C 3 does not provide adequate information about the degree of articular comminution and cannot predict the functional outcome. Similarly, B3 represents all types of coronal plane or Hoffa’s fractures. However, a combined unicondylar sagittal fracture associated with a coronal plane fracture of the same condyle cannot be categorized according to the AO-OTA classification. Thus, we feel that there is a necessity for a new CT-based classification system for distal articular femur fractures, which can predict the severity, assist in the planning of surgical approaches, aid in implant selection, and suggest the functional outcome. The proposed CT-based classification is described (See Table 1) and its implications for the surgical management of biplanar articular fractures have been discussed in this article (Table 2 and Fig. 1).

In this study, we have included only the biplanar distal femoral articular fractures and evaluated the fixation techniques and functional outcomes in these patients. The degree of metaphyseal comminution should be considered separately, as the restoration of the articular surface is essential, irrespective of the degree of metaphyseal comminution. Accordingly, we have graded the degree of metaphyseal comminution separately.

Materials and Methods

This study was conducted at the Department of Orthopedics between May 2018 and June 2023. A total of 50 patients with distal articular biplanar femur fractures were included in our study. Pre-operative CT evaluation was done in all patients. Demographic details and the mechanism of injury were documented for all the patients. Surgical planning, including the approach and implant selection, was made based upon the proposed classification (Fig. 1). The suggested classification is as follows. Type A and B are uniplanar fractures but, for the sake of completeness, have been included in the picture. Types C, D, and E are biplanar fractures with increasing degree of comminution. Type C represents a 2-part fracture with combined coronal and sagittal fractures in one condyle. C-L and C-M have been used to represent the medial and lateral condyles. In type C fractures, there is metaphyseal continuity in the other condyle. Type D represents a 3-part fracture with combined sagittal and coronal fractures in one condyle, whereas the other condyle has a uniplanar fracture. Terminologies D-L and D-M are used to suggest the biplanar involvement of the lateral or medial condyle, whereas D and C suggest that there is a distal femur fracture associated with a bicondylar Hoffa’s fracture. Type E represents a 4-part fracture, wherein there is a combined coronal and sagittal fracture in both condyles. Type F suggests a comminuted fracture.

The metaphyseal comminution was graded as M0 if there was no comminution. M1 and M2 represent moderate and severe comminution, respectively, and M3 suggests comminution with bone loss.

Intraoperative photographs were also taken to confirm the CT findings. Postoperatively, patients were reviewed once every 15 days, and radiographs were repeated every 30 days. All the patients were followed up regularly for 6 months. Fracture healing time, post-operative complications, and Knee Society Scores were recorded in all patients.

Interobserver and intraobserver reliability for the classification was also assessed. To assess the interobserver reliability, five orthopedic consultants with more than 6 years of clinical experience and one radiologist were contacted. Each consultant received five randomly selected radiographs, CT images, and intra-operative photographs of different patients and was asked to classify them according to the above classification. The same exercise was repeated after an interval of 4 weeks to assess the intraobserver reliability.

Results

Fifty patients with biplanar distal articular fractures were included in our study. Road traffic accidents with a head-on collision were the most common mode of injury. Eight patients had a compound wound. Four patients had other associated fractures. Anterior cruciate ligament and posterior cruciate ligament avulsions were present in three patients.

The mean age was 35 years. The male-to-female ratio in our study was 5:1. The most common fracture type was D, followed by C, E, and F, respectively. ROM in each group of fractures was recorded at every follow-up. Patients with C- and D-type fractures had a good range of motion of more than 100°. While the patients who suffered type E and type F fractures had an average range of motion of <80°. One patient who suffered from a type E fracture and had a grade IIIB compound injury developed wound infection, which subsided with secondary debridement and cement bead placement. Two patients who had M3-type metaphyseal fractures required secondary bone grafting after 6 weeks. One patient of with a type D3M3 had a 1.5 cm shortening, which was managed with a shoe raise. Two patients had a significant post-operative varus deformity, and one had a valgus deformity. One patient had non-union and was lost to follow-up. The clinical and radiological representative pictures are shown in Fig. 2.

The interobserver agreement was 87.5%, and the intraobserver agreement was 100%. The chance-corrected and weighted kappa statistics for observer agreement, both for inter-observer and intra-observer variability, demonstrated satisfactory repeatability of the classification system.

Discussion

Various classification systems have been described in the literature ^[7,8]. The most commonly used classification system for distal femur fractures is the AO OTA classification ^[9]. In this classification, the distal femur fractures are broadly classified into type A, B, and C, corresponding to extra-articular, partially intra-articular, and fully intra-articular ^[9]. Each group is further subclassified into three types based on the pattern of the fracture and degree of comminution. Type B1 involves sagittal split of the Lateral condyle; B2 involves sagittal split of the medial condyle, and type B3 represents a coronal plane fracture known as a Hoffa’s fracture. Type C is subclassified into C1 (simple articular, simple metaphyseal), C2 (simple articular, multifragmentary metaphyseal), and C3 (multifragmentary articular and metaphyseal).

The above classification is simple, valid, and provides a good picture of the severity of the distal femur fractures. However, it is an X-ray-based classification. The inability of the AO system in classifying biplane fractures has been well explained by Nork et al. ^[5]. In their study, they found that associated coronal plane fractures were found in 38% of the distal femoral intra-articular fractures. All these combined fractures have to be invariably labeled as C3 type or multifragmentary articular fractures. The term multifragmentary is very subjective. What actually accounts for multifragmentary is not understood by the classification. The C3 type is further subclassified into C3.1, C3.2, and C3.3. However, all these subtypes focus on metaphyseal comminution and not articular fragments. A detailed CT-based evaluation irrespective of the degree of metaphyseal comminution is essential in all intra-articular fractures. CT will not only help in the proper identification of fracture fragments, but it will also help in planning the surgery and implant selection. Moreover, we found it difficult to classify a few fractures using the AO OTA system. One example is a combined sagittal and coronal plane fracture of an isolated medial or lateral condyle.

Although there is a consensus in the literature regarding the validity of AO OTA classification for distal femur fractures, there are a few studies that highlight the problems with it. Elsoe et al. conducted a population-based epidemiological study of distal femur fractures among Danish patients ^[10]. They found that approximately 10 % of the total distal femur fractures could not be classified using the AO Classification. They have subclassified this group as the Missing AO group. Similarly, Agrawal and Kiyawat conducted a study on the management of complex distal femur fractures ^[11]. The inability of the AO classification system to classify these fractures is very evident by the fact that they have used two sub-classifications for extra-articular and intra-articular parts of the same fracture. Bagaria et al. proposed a new classification system for the coronal plane fractures of the distal femur ^[12]. They have suggested a separate subclass for combined coronal and sagittal fracture of the femoral condyle, which could not be classified by the AO system. These studies highlight the necessity of a CT-based classification system.

Based upon these needs, we have described a classification system which is CT-based and provides a complete description of the articular fragments. This classification is based upon the planes of the fracture lines. Type A is a uniplanar sagittal fracture, and type B is a uniplanar coronal fracture. Type C, D, E, and F represent biplanar fractures with increasing grades of comminution. This classification system helps us in deciding the approach to the fracture and also helps in prognostication of fractures as well. Fractures with increasing degrees of articular comminution have less post-operative ROM, and there are increased chances of arthritis; e.g., type C has a better prognosis than type F. A metaphyseal fracture classification system is also added to the articular fracture classification. M1 is simple, M2 is comminuted, and M3 is associated with bone loss. A description of the applicability of the classification in terms of approach, surgical planning, implant selection, and prognosis is provided in Table 3.

Conclusion

Thus, we conclude that this CT-based classification system is a focused tool to assess the degree of severity of the articular comminution, plan our approach to the fracture, decide the implants necessary, and grade the prognosis. Simultaneously, this classification provides an addition to the metaphyseal comminution, which can be written together. In spite of being very elaborate, it is easy to reciprocate and communicate.

Clinical Message

This classification helps young surgeons who have little experience to understand the pattern of fracture, plan for fixation of the fragments, determine the types of implants needed, anticipate intraoperative difficulties, and be ready with armamentarium.

References

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About the Authors

• 

  Mohammed Sadiq

• 

  Sharon Rose Neerudi

• 

  Rohith Reddy Kasam

• 

  Kothalanka Udaya Kumar

• 

  Koribilli Sai Pradeep

• 

  Anudeep Manne