Schatzker Type IV Medial Tibial Plateau Fractures: A Computed Tomography–based Morphological Subclassification

Materials and Methods

This retrospective image study (radiographs, CT, and 3-D reconstruction), which received institutional review board approval, was conducted at a Level 1 trauma center. A total of 45 cases with Schatzker type IV tibial plateau fractures were retrieved from January 2007 to June 2013. After exclusion of patients younger than 18 years and those with inadequate imaging documentation (incomplete radiograph or CT images), 42 cases remained for the study. They included 27 men and 15 women, with an average age of 46 years (range, 21–65 years). The mechanism of injury was a traffic accident in 26 cases, a fall from a height in 11 cases, and simply a fall in 5 cases.

The authors defined Schatzker type IV tibial plateau fractures as AO/OTA 41 type B fractures (partial articular) with partial or total medial plateau involvement, leaving at least the anterolateral quadrant intact. This means that the anterolateral metaphyseal cortex is spared, and a small portion of the intact articular surface remains attached to the intact anterior cortex at the lateral condyle. Otherwise, the fracture is classified as a Schatzker type V fracture (bicondylar fracture, corresponding to 3 subgroups in AO/OTA 41C1) or Schatzker type VI (bicondylar fracture with metaphysis-diaphysis dissociation, corresponding to 6 subgroups in AO/OTA 41C2 and C3).2

On the basis of the 3-column classification of Luo et al9 and Zhu et al,10 the tibial plateau was further divided into 2 condyles and 4 articular plateau quadrants—the medial and lateral condyles and the anteromedial, anterolateral, posteromedial, and posterolateral quadrants (Figure 1).

Figure 1: Schematic drawing showing the 4 articular plateau quadrants of the tibial plateau: anterolateral (AL), posterolateral (PL), anteromedial (AM), and posteromedial (PM).

The images were viewed on clinical picture archiving and communication system (PACS) workstations by 2 orthopedic trauma resident surgeons (Y.-Q.Z, Q.L.), who first evaluated the images separately and then worked together to achieve a consensus. The fracture morphology was described on the basis of tibial plateau quadrant involvement, major fragment location, fracture type (split and/or depression), and fracture line orientation.

Results

In this new subclassification system, Schatzker type IV fractures are further divided into 2 groups according to the fracture line orientation and area involvement. Group 1 are the classic medial unicondylar fractures, composed of 5 subgroups: (1) anteromedial quadrant plateau fracture (oblique-coronal fracture line); (2) posteromedial quadrant plateau fracture (oblique-coronal fracture line); (3) partial sagittal medial plateau fracture (sagittal fracture line located medial to the intercondylar spines); (4) total medial plateau fracture (sagittal fracture line located within the intercondylar spines); and (5) comminuted medial plateau fracture (complex fracture line). Group 2 are the more complicated bicondylar variants, characterized by medial plateau fractures with lateral plateau extension and are divided into 3 subgroups, including (6) total medial condyle fracture with partial lateral plateau split (sagittal fracture line lateral to the intercondylar spines) (Figure 2), (7) total/subtotal medial condyle fracture with posterolateral plateau depression (Figure 3), and (8) posteromedial plateau fracture with posterolateral plateau depression (Figure 4).

Figure 2: Total medial condyle fracture with partial lateral plateau split en bloc. The fracture line runs in the sagittal direction through the lateral plateau; the medial plateau articular surface is intact. Schematic drawing showing the characteristics of the fracture pattern (A). Anteroposterior (B) and lateral (C) radiographs of a total medial condyle fracture with partial lateral plateau split fracture in sagittal orientation. The fracture spike is located in the medial aspect. Coronal computed tomography image showing that the split fracture line passes through the lateral tibial plateau (D). The articular medial plateau is intact.

Figure 3: Total/subtotal medial condyle split fracture with centroposterior impaction of the lateral plateau. Schematic drawing showing the characteristics of the fracture pattern (A). Anteroposterior (B) and lateral (C) radiographs of a total medial plateau split fracture associated with articular depression of the centroposterior-lateral plateau. The spike of the split medial fragment is located on the posterior aspect of the medial condyle. Axial computed tomography (CT) image showing total medial condyle split with centroposterior impaction of the lateral plateau, while the posterior cortex of the lateral plateau is intact (D). Coronal CT image showing substantial depression of the articular cartilage of the centroposterior lateral plateau (E). The anterolateral quadrant articular cartilage is left intact with the lateral plateau cortical bone. Three-dimensional reconstruction showing the fracture pattern and fragment anatomy (F).

Figure 4: Posteromedial condyle split fracture with posterior articular impaction of the lateral plateau. Schematic drawing showing the characteristics of the fracture pattern (A). Anteroposterior (B) and lateral (C) radiographs of a posteromedial plateau split fracture associated with articular depression of the posterolateral plateau. The spike of the split posteromedial fragment locates on the posterior aspect of the medial condyle. Axial computed tomography (CT) image showing a posteromedial condyle split fragment with posterolateral quadrant impaction (posterior bicondylar fractures) (D). The posterior cortex of the lateral plateau is broken. Posterior coronal CT image showing posteromedial plateau fragment and comminuted impaction of the posterolateral plateau (E). Three-dimensional reconstruction showing the fracture pattern and fragment anatomy (F).

A total of 42 patients were included in the study (Table). Twelve (29%) cases involved only the medial condyle, and 30 (71%) involved both the medial and lateral condyles. Twenty-nine (69%) cases demonstrated posterior coronal fractures. The most common pattern in this case series was the bicondylar posteromedial plateau fracture with posterolateral plateau quadrant depression (bicondylar posterior fractures: 14 cases, 33%). The second most common pattern was total/subtotal medial plateau fracture with posterolateral plateau depression (13 cases, 31%). Interestingly, the authors found the isolated unicondylar posteromedial quadrant plateau fracture to be uncommon (2 cases, 5%).

Table: Subclassification of Schatzker Type IV Tibial Plateau Fracture Patterns

The morphological characteristics of the fracture patterns are summarized in the Table.

Discussion

Historically, Schatzker type IV fractures referred to medial condyle fractures, which accounted for approximately 10% of all tibial plateau fractures.1,3,8 These were frequently attributed to a high-energy trauma and described as either split-wedge types or depressed and comminuted types. The fracture involvement area and fracture line orientation could be highly variable, and the medial articular surface may or may not have been violated. The fracture line could pass within the medial articular surface (Wahlquist type A) but typically passed more laterally through the intercondylar eminence (Wahlquist type B) or through the lateral tibial plateau (Wahlquist type C),4 separating the medial condyle from the remainder of the tibia.

With large medial condyle fractures, the medial collateral ligament and cruciate ligaments may stay attached (or partially attached) to the medial condyle, whereas the remaining lateral plateau and shaft are displaced laterally, away from the femur and medial plateau fragment, leading to a fracture-dislocation/subluxation pattern (Moore types I–II).5 These severe injuries include a risk of associated injuries, such as meniscus tears, ligament injuries, compartment syndromes, peroneal nerve injuries, and popliteal vascular injuries.8 Wahlquist et al4 found that the more the fracture line moved laterally, the greater the risk for these associated complications, especially compartment syndromes. Chan et al10 found a high incidence of associated anterior cruciate ligament injuries with posteromedial fracture patterns. Computed tomography scanning and 3-D reconstruction lead to an accurate understanding of the fracture anatomy and the pathological relationship of fracture fragments. In Schatzker type IV fractures, the fracture line may be a pure sagittal split but, more commonly, it is oblique to the frontal plane, resulting in an isolated coronal split with the apex of the fracture occurring posteromedially (posteromedial fragment) or in the more common split-depression fracture pattern (total/subtotal medial or posteromedial split with posterolateral depression). In the authors’ series, 27 (64%) cases had lateral plateau depression in the centroposterior area, and for the 16 posteromedial quadrant-shearing fractures, 14 (87.5%) were combined with posterolateral plateau quadrant depression. In a literature review,12–15 the authors found that the most commonly reported unicondylar posteromedial split fractures (or fracture-dislocations) were truly bicondylar posteromedial split with posterolateral depression fracture patterns (posterior bicondylar fractures: Group 2, subgroups 7 and 8). For example, in a recent morphological study of 75 cases of Schatzker type IV tibial plateau fractures, Yang et al16 found that 27 (84%) of 32 posteromedial fractures were characterized by a posteromedial plateau split with posterolateral plateau depression.

Carlson17 described posteromedial split with posterolateral depression fracture patterns as posterior bicondylar tibial plateau fractures. Weil et al15 and Doornberg et al18 classified these bicondylar fracture patterns as Schatzker type V or VI. Potocnik et al19 described this uniform injury pattern as posteromedial fracture-dislocation and noted 3 characteristics: (1) posteromedial tibial plateau split fracture, (2) posterocentral lateral tibial plateau depression fracture, and (3) avulsion fracture of the anterior cruciate ligament attachment from intercondylar eminence. This combination may be called a fracture triad of posterior bicondylar tibial plateau fractures.

In a clinical setting, it is critically important to recognize the extended complex variants of the classic unicondylar Schatzker type IV fractures, as they each require different approaches and treatment strategies. For fracture patterns in Group 1, surgical exposure is straightforward based on the fragment location, and plate fixation in buttress mode is the preferred treatment. For fracture patterns in Group 2 with a lateral plateau sagittal split (subgroup 6), a medial approach with a heavy buttress plate over the fragment spike is usually sufficient. For fracture patterns combined with centroposterior lateral plateau coronal depression (Group 2, subgroups 7 and 8), the operative strategies vary widely. They include a posterior midline incision,20 separate posteromedial and posterolateral incisions,21 an extensive anterior midline incision,22a large medial incision,19 or combined posteromedial and anterolateral dual incisions with intra-articular osteotomy,23,24and the use of arthroscopy assistance.25 The authors prefer to use a single inverted L-shaped posteromedial incision in the prone position.9,26,27,28 By retracting the medial gastrocnemius-soleus muscle laterally and elevating the popliteus muscle, both the medial and lateral posterior condyles are sufficiently exposed, facilitating direct fixation with a buttress plate (Figure 5).

Figure 5: A 56-year-old man with posterior bicondylar fractures of the right side treated with inverted L-shaped posteromedial approach with double plate fixation. Preoperative anteroposterior (A) and lateral (B) radiographs showing the fracture involvement. Axial computed tomography (CT) image demonstrating the fractured triad: posteromedial split, posterolateral depression, and anterior cruciate ligament attachment avulsion (C). The anterolateral plateau quadrant is intact. Three-dimensional reconstruction showing the bicondylar posterior fracture pattern and fragment anatomy (D). Intraoperative picture of inverted L-shaped posteromedial approach with dual plate fixation of the posterior bicondylar fractures (E). The posteromedial fragment was fixed with a T plate, and the posterolateral fracture was fixed with an oblique placed reconstruction plate. As the intraoperative manual test showed a stable knee joint, the avulsed anterior cruciate ligament fragment was not fixed further. Anteroposterior radiographs showing complete healing and axis alignment with anatomic reduction of joint surfaces 1 year after fracture (F). Lateral radiograph of healed plateau fracture showing restoration of plateau joint surfaces and position of hardware (G). Functional outcome at 1-year follow-up (H).

Conclusion

Based on 2-D and 3-D CT images, Schatzker type IV tibial plateau fractures are further classified into 2 groups: the classic medial plateau fractures (unicondylar) and the extended variants of medial condyle fractures associated with centroposterior impaction of the lateral plateau (bicondylar). This subclassification system may improve the understanding of fracture anatomy, preoperative treatment planning, the reduction and fixation strategy, and patient functional outcome.