MRI and Knee Dislocations
ABSTRACT & COMMENTARY
Synopsis: The dislocated knee is a complex injury with multiple ligamentous tears and associated injuries. Examination under anesthesia is the most accurate manner to define functional integrity of ligamentous injuries in a dislocated knee, but the role of magnetic resonance imaging is still being defined.
Source: Lonner JH, et al. Comparison of magnetic resonance imaging with operative findings in acute traumatic dislocations of the adult knee. J Orthop Trauma 2000;14(3):183-186.
Knee dislocations are injuries that have great interest for both sports medicine and trauma orthopaedic surgeons. These injuries are complex, require careful evaluation and management, and can have significant complications. In one series, more than 20% of patients eventually diagnosed with a dislocated knee were found to have a reduced tibio-femoral joint at the time of presentation, thus other studies have been considered for optimal diagnosis and management. Lonner and colleagues describe their experience with knee dislocations in an attempt to identify the accuracy of magnetic resonance imaging (MRI) in the evaluation of soft tissue injuries as compared to clinical examination under anesthesia (EUA). Lonner et al used a retrospective analysis of 48 patients between 1986 and 1996 in which a cohort of 10 patients undergoing preoperative MRI, EUA, and operative exploration was identified.
The researchers found clinical examination to be the critical step in evaluating the functional integrity of ligamentous injuries in a knee dislocation. EUA neared 100% accuracy in functional evaluation; however, EUA was uncertain in two of five patients with a posterolateral corner injury requiring open exploration for definitive evaluation. However, it is unclear if the surgeons were blinded from the MRI and possibly the preoperative information influenced the results of the EUA. MRI accuracy ranged from 80-100%, with diagnosis of the lateral meniscus, MCL, and PCL at 100%. The accuracy of diagnosis of the posterolateral corner was 90%. Lonner et al concluded that MRI is useful for defining the presence of ligamentous injuries in knee dislocations. However, clinical examination was more accurate. Lonner et al noted that all injuries underwent operative exploration between one and two weeks postinjury; hence, they felt that an MRI was most useful for orthopaedic surgeons inexperienced in treating acute knee dislocations. Nonetheless, Lonner et al note that MRI may be helpful in the operative management of the acutely dislocated knee, particularly if an autograft is being considered for surgical reconstruction.
Comment by Robert C. Schenck, Jr., MD, Tom DeCoster, MD, & Dan Wascher, MD
This retrospective review is useful for the practicing sports medicine specialist as it clearly identifies the key point in decision making for the evaluation and treatment of knee dislocations, namely examination under anesthesia. Knee dislocations present in a variety of ligamentous combinations and energy mechanisms (high—motor vehicular trauma, and low—sporting injuries). In our experience, identifying what ligaments are torn is much more useful than identifying the joint position (ie., anterior, posterior, etc.) of the tibio-femoral joint. As in any ligamentous evaluation of the knee, examination under anesthesia is imperative preoperatively and should be part of any arthroscopic or open surgical reconstruction. We agree with Lonner et al on the importance of EUA in the diagnosis and surgical decision making in the dislocated knee.
However, we still find MRI useful under several situations in the evaluation and treatment of the dislocated knee. We agree that the radiographic study is not the best way to functionally evaluate ligamentous injuries. MRI frequently complements what is found at the time of EUA, and as reported by Reddy et al and Yu et al, determination of midsubstance vs. avulsion injuries of the ligaments can only be determined with preoperative MRI or surgical exploration.1,2 In our experience, we find that MRI is very important for preoperative decision making by more accurately defining:
• site and morphology of ligament injury (avulsions vs midsubstance tears);
• timing of surgical reconstruction by identifying avulsions that are best operated on early (3-5 days);
• meniscal tears or chondral injuries (which may be more readily treated with an arthroscopic approach;
• associated injuries, especially the condition of potential autograft tissues (patellar tendon, hamstrings) which may be considered for reconstruction/augmentation;
• collateral injuries, facilitating the surgical dissection by localizing the area of collateral ligament injury (proximal vs distal vs midsubstance).
Open ligament repair is the standard of treatment in knee dislocations.3 However, several researchers delay surgical repair with range of motion followed by arthroscopic simultaneous bicruciate reconstructions.4,5 In such plans, MRI could identify an avulsion injury that would be best treated with early, open repair. In summary, EUA is the key to functional evaluation of knee ligaments; nonetheless, MR imaging has other benefits in the evaluation and treatment of the dislocated knee and still can be recommended. In contrast to Lonner et al, we believe MRI can play an integral supplemental role in effective evaluation of patients with knee dislocations in 2000.
Dr. DeCoster is Professor and Division Head, Orthopaedic Trauma Service, Department of Orthopaedics and Rehabilitation, University of New Mexico Health Sciences Center, Albuquerque, NM. Dr. Wascher is Associate Professor, Division of Sports Medicine, Department of Orthopaedics and Rehabilitation, University of New Mexico Health Sciences Center, Albuquerque, NM.
References
1. Reddy PK, et al. The role of magnetic resonance imaging in evaluation of the cruciate ligaments in knee dislocations. Orthopaedics 2000;19(2):165-169.
2. Yu JS, et al. Complete dislocation of the knee: Spectrum of associated soft-tissue injuries depicted by MR imaging. Am J Roentgenol 1995;164:135-139.
3. Schenck RC Jr., et al. Knee dislocations. Instr Course Lect 1999;48:515-522.
4. Wascher DC, et al. Knee dislocation: Initial assessment and implications for treatment. J Orthop Trauma 1997;11(7):525-529.
5. Wascher DC, et al. Reconstruction of the anterior and posterior cruciate ligaments after knee dislocation. Results using fresh-frozen nonirradiated allografts. Am J Sports Med 1999;27(2):189-196.
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