Assessment of the mechanical stability of the knee is a critically important part of the assessment of the patient with a tibial plateau fracture. Mediolateral stability of the knee has proven to play an extremely important role in the outcome of tibial plateau fractures. This is a clinical assessment done in the patient with a tibial plateau fracture; the fully extended knee is stressed into varus and valgus from its resting position. More than a 10° increase in either varus or valgus compared with the normal contralateral knee on this clinical assessment is considered a positive test for instability. A positive result on this test may occur in two situations: (1) where the medial or lateral collateral ligaments have been torn as part of the injury; and (2) where the fracture pattern and displacement allows the lateral femoral condyle to extend into the lateral tibial plateau on valgus stress (Fig 2). Either of these two occurrences produces the clinical finding of mediolateral instability, which has been correlated with poor outcomes. Doing this test in a patient who has sustained a tibial plateau fracture may cause significant pain; injection of local anesthetic into the knee or performance of some sort of regional block may be considered before doing this important evaluation.
Numerous studies have indicated the critical importance of normal mediolateral stability to a good outcome after a tibial plateau fracture. Delamarter et al10 reported the results of 39 patients with tibial plateau fractures and ligamentous injuries; 19 of the patients had operative repair of the ligaments at the time of fracture stabilization. Results were better in the group that had ligament repair. The authors concluded that instability is a major cause of unacceptable results in tibial plateau fractures. Rasmussen20 reported that patients with knees stable on clinical examination (< 10° angulation on manual testing with the knee in full extension) had an incidence of arthrosis of 17%, whereas the incidence was 46% in those with knees unstable to clinical examination. Honkonen12 observed that 69% of patients with more than 10° varus and valgus laxity had OA at followup. Lansinger et al14 reported that varus instability and valgus instability of the knee on clinical examination were necessary to a poor clinical outcome and that, in the absence of instability, articular incongruity greater than 10 mm was well tolerated.
These studies provide strong evidence that mediolateral stability of the knee is critical to a good outcome after tibial plateau fractures. The presence of varus or valgus instability of the knee more than 10° greater than the normal side is an indication for surgical treatment in a patient with a tibial plateau fracture. Appropriate reduction and stabilization of the tibial plateau fracture should result in restoration of mediolateral stability to the knee.
Radiographic Assessment of Injury Severity
Appropriate radiographic assessment of a tibial plateau fracture is critical to understanding the injury, formulating a treatment plan, and counseling the patient as to the expected long-term outcome. Routine radiographic assessment of a tibial plateau fracture consists of AP and lateral views of the proximal tibia. Anteroposterior and lateral views of the knee on 17-inch radiographic cassettes generally are satisfactory, but some fracture patterns may necessitate obtaining full-length radiographs of the tibia. Radiographs of the knee on 12-inch cassettes never are sufficient for adequate evaluation of a tibial plateau fracture. Some physicians recommend obtaining oblique views of the proximal tibia as part of the routine assessment of these injuries, but this recommendation has become less frequent now that CT scanning is in wide use in evaluating these injuries. For complex, high-energy injuries, AP and lateral radiographs of the knee after the application of traction (usually with an external fixator spanning the knee) can provide a great deal of additional information about the fracture pattern and can be helpful in planning treatment (Fig 3).
Although most tibial plateau fractures can be characterized adequately on plain radiographs, an axial CT scan of the proximal tibia is useful in complex fracture patterns, and some surgeons recommend they be obtained in all cases. The CT scan will provide the greatest amount of information if it is obtained after the application of a spanning external fixator in complex injuries. Newer spiral CT technology has enabled the CT scan data to be reconstructed in any plane, allowing high quality sagittal and coronal reconstructions of the fractured tibia. Some newer software systems even allow the construction of a three-dimensional computer image of the proximal tibia, which can be rotated in any plane by the physician, using a computer workstation.
Radiographic classification systems for fractures have been the hallmark of injury severity assessment in orthopaedics. Classification schemes are intended to group fractures that are similar in their mechanism of injury and fracture pattern and, as such, require a similar approach in their treatment. Classification systems also are intended to identify fractures that have a similar prognosis. There are two commonly-used classification schemes for tibial plateau fractures: the Schatzker classification and the Orthopaedic Trauma Association (OTA) classification system. The most widely used and accepted classification of tibial plateau fractures in North America is that proposed by Schatzker21 and Schatzker et al.22 This scheme addresses with greater precision the regional idiosyncrasies of tibial plateau fractures. In general, the six numeric fracture categories indicate increasing severity, reflecting not only an increased energy imparted to the bone at the time of injury but also an increasingly worse prognosis.4Figure 4 shows the Schatzker classification system, and the six types of fracture, in order of increasing severity.
The OTA classification system is unique because it applies to all long bones, rather than only to one bone or fracture location.18 It classifies fractures in such a way that they are organized in an ascending order of severity. Therefore, Type A fractures generally are less severe than Type B fractures, and Type C fractures have the greatest severity. When this classification is applied to fractures of the tibial plateau, extraarticular fractures are Type A. Partial articular fractures (Type B) are those in which part of the articular surface remains in contact with the diaphysis. Complete articular fractures (Type C) are those in which the articular surface has lost all connection to the diaphysis. The OTA classification further divides the fracture types into groups and subgroups. Figure 5 shows the OTA fracture classification for tibial plateau fractures.
Inherent to both of these fracture classifications schemes are radiographic assessments that are used to differentiate one fracture type from another. These assessments include determining the presence and location of fracture lines, judging the amount of displacement and comminution, and judging fracture stability. Classically, these assessments have been used to guide treatment and determine prognosis of patients with fractures.
Fracture classification systems have come under scrutiny because they have been shown to have suboptimal interobserver reliability and intraobserver reproducibility.1–3 One study of tibial plateau fractures tried to identify the fracture characteristics that could be assessed reliably by analysis of plain radiographs of tibial plateau fractures.17 Observers made assessments based on the radiographs of 56 tibial plateau fractures, of which 38 also had CT scans. The reliability of the assessments varied widely, as measured by the kappa statistic. Determining the location of fracture lines had the greatest reliability (kappa = 0.68), whereas the subjective assessments of fracture stability and energy showed the poorest reliability (kappa = 0.37 and 0.29, respectively). The addition of a CT scan improved the reliability of most assessments, but not to a statistically significant degree. Intraclass correlation coefficients (ICC) for determining maximal articular depression and condylar widening were 0.66 and 0.72, respectively. The 95% confidence interval for assessing maximal articular depression was ± 12 mm, whereas it was ± 9 mm for assessing maximal condylar widening. This study showed that the reliability of fracture classification is limited by raters’ abilities to agree on basic radiographic assessments, and that we cannot assume that even the most basic radiographic assessments can be done with high interobserver reliability. Furthermore, quantitative measures have wide tolerance limits and, therefore, probably cannot be used reproducibly to classify fractures or make treatment decisions. Another study by Carman et a16 showed tolerance limits of ± 10° in measuring Cobb angles on radiographs of patients with scoliosis. In a study measuring the articular congruity of healed distal radial fractures on plain radiographs, a 95% confidence interval of ± 3 mm was identified, when the range of articular congruity measurements was only 4 mm.7
It has been hypothesized that CT scans would improve rater agreement because the fracture lines and details are more clearly shown on these images. Previous studies, however, have shown that CT scans did not improve interobserver agreement for the classification of proximal humeral or pelvic ring fractures.3,14 Studies of proximal and distal tibial fractures showed that viewing CT scans did not result in statistically significant improvement in interobserver agreement.16,17 Chan et al8 evaluated the interobserver and the intraobserver agreement for treatment plan and fracture classification of tibial plateau fractures using plain radiographs alone and with CT scans. The mean kappa coefficient for formulating treatment plan increased from 0.58–0.71 after the addition of CT scans. The mean kappa coefficient for fracture classification, however, was unchanged after addition of CT scans. These studies indicate that viewing the CT scans rarely changed a rater’s categorical assessment of articular displacement or fracture stability. Therefore, the value of a CT scan seems to be greatest in facilitating preoperative planning, rather than for classifying the fracture.
A recent study showed the impact of MRI scanning on the interobserver reliability of classification of tibial plateau fractures according to the Schatzker classification system.24 Three orthopaedic trauma surgeons classified tibial plateau fractures first with plain radiographs, and then with either the addition of a CT and an MRI scan. Kappa values averaged 0.68 with plain radiographs alone, 0.73 with the addition of a CT scan, and 0.85 with addition of an MRI scan. No statistical analysis was reported to indicate whether the addition of CT and MRI information resulted in a statistically significant improvement in reliability.
Assessing Severity of Injury to Articular Cartilage
Injury to the bone of the tibial plateau is necessarily accompanied by injury to the overlying articular cartilage. The injury to the articular cartilage is a critical and significant contributor to the overall severity of the injury, but we currently have almost no means for assessing the severity of injury to the articular cartilage. Plain radiographs and CT scans provide very little information to assess the injury to the articular cartilage. Articular cartilage injury clearly can affect outcome, as evidenced by a study documenting poor outcomes after osteochondritis dissecans and other chondral injuries15 and various animal studies on the outcomes of impact loading of articular cartilage.15
The basic science evidence that shows that cartilage injury can lead to articular cartilage degeneration is corroborated in clinical studies. Taken together, information in the literature indicates that the severity of injury to the articular surface during fracture has an important bearing on outcome and the eventual development of posttraumatic OA. A better understanding of the impaction injury to the articular cartilage and the prognosis of such injury will be critical to improving our assessment and understanding of severe intraarticular fractures.15 Unfortunately, there currently are no imaging modalities that have been validated to indicate to the clinician the extent of injury to the cartilage of the articular surface, and/or the potential for repair, or the risk of posttraumatic degeneration of the articular cartilage.
Correlation between Injury Severity and Outcome
The severity of the articular injury is linked to the quality of the reduction achieved after treatment. That is, fractures with greater amounts of displacement and comminution tend to have less satisfactory reductions after treatment than do more simple fractures. It also is clear that fractures with more comminution lead to less satisfactory clinical outcomes. It is important to be able to meaningfully separate the effects of articular reduction from those of comminution. Ignoring this issue is similar to ignoring an important known comorbidity in any medical trial.
To characterize the link between comminution and the quality of reduction achieved, rank order methodology has been used to examine fractures of the tibial plafond.9 Clinicians ranked a series of radiographs of fractures for the severity of the injury putting them in order from worst to best. The same clinicians separately ranked the radiographs taken after reduction for quality of the reduction. There was a high degree of correlation between the injury ranks and the reduction ranks. The fractures that were judged to be the most comminuted were considered to have the worst reductions and, alternatively, the fractures that the investigators thought were the least comminuted had the best reductions. In these experiments, the investigators were not able to substantially separate these two linked variables. Although no similar studies have been done for tibial plateau fractures, there is no reason to think that the results of this study would not be applicable to the tibial plateau.
Assessment of injury severity is an integral component of the care of the patient with orthopaedic injuries. Devising ways to reliably quantify injury severity, and to make a predictive link between injury severity and outcome have been difficult. Patient factors must be taken into consideration in determining the treatment of any fracture: there are no objective rules here, but the surgeon should consider nonoperative care in each case where patient factors seem to make the risks of surgery outweigh the benefits. Mediolateral knee instability is a major cause of poor outcomes after tibial plateau fractures. The presence of this clinical finding is an indication for surgical reduction and fracture stabilization. Radiographic fracture classification systems are important in understanding fractures and planning treatment, but have shown disappointing interobserver reliability. We cannot assume that even the most basic radiographic assessments can be done with high interobserver reliability. The addition of modalities such as a CT scan in evaluating tibial plateau fractures seems to be greatest in facilitating preoperative planning, rather than for improving fracture classification. Soft tissue classifications for tibial plateau fractures have not been studied for reliability. Until the results of such studies are published, the surgeon should be cautious about inferring a linkage between extent of soft tissue injury and outcome.
Although the severity of injury to the articular cartilage has an important bearing on outcome and the eventual development of posttraumatic OA, there currently are no validated modalities to measure the extent of injury to the articular cartilage or the risk of posttraumatic degeneration. It is unknown whether posttraumatic arthritis arises predominantly from inadequacy of articular reduction, from severe, irreversible injury to articular cartilage, or from a combination of the two. A better understanding of the links between injury severity and outcomes is needed: this should include the development of more sophisticated methodologies that undergo rigorous validation.
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24. Reference not available.