The Knee Dislocation Classification System Is Simple, Reproducible, and Allows Communication among Surgeons

We read the article titled “Multiple Ligament Knee Injuries: Does the Knee Dislocation Classification Predict the Type of Surgical Management?” by Maxwell et al with interest.[1] We applaud the authors for investigating if the knee dislocation (KD) type predicted surgical treatment. However, as developers of this classification system,[2] [3] we wanted to point out several issues with this article.

• The KD classification was designed to help surgeons classify KDs, not for all multiple ligament knee injuries. The KD is defined as either clinical or radiographic evidence of a dislocation or tears of both cruciate ligaments. KD-I injuries (a single cruciate ligament injury with radiographic evidence of a dislocation) are rare injuries. The vast majority of single cruciate ligament injuries with a torn collateral ligament (anterior cruciate ligament [ACL]/medial collateral ligament [MCL], ACL/posterior cruciate ligament [PLC], PCL/MCL, and PCL/PLC) are not KDs. While all KDs are multiligament knee injuries (MLKIs), the majority of MLKIs are not KDs. This is an important distinction because the incidence of neurovascular injury is significant in KDs but is extremely rare in other single cruciate ligament injuries. We would predict that the vast majority of the 121 “KD-I” in this study are not true KDs.

• In the KD classification, only complete ligament injuries are included. Diagnosis of a complete ligament injury is made by physical examination, imaging and confirmed at the time of surgery. We have noticed in these severe injuries that increased signal on MRI is frequently seen in collateral ligaments that have no significant laxity when examined under anesthesia. The authors included “high-grade” partial injuries in this study and noted that the grade of injury was predictive of surgical treatment. The classification system uses examination and complete injury as a determinant of needing surgical management.

• In our original description, the addition of KD-V was meant to include large periarticular fracture fragments (e.g., femoral or tibial condylar fractures) that contained the attachment of at least one major knee ligament. Avulsion fractures such as tendinous rim fractures of the tibial plateau, etc. are not classified as a KD-V. Given the high number of KD-V injuries in this study, the authors should specify their criteria for classifying an injury as a KD-V.

• The KD classification was originally developed to improve communication between physicians and to help with surgical planning (surgical incisions, number, and type of grafts required, etc.). Prior to its development, most clinicians used the position classification developed by Kennedy. The position classification system missed the approximately 50% of KDs that present reduced.[3] Furthermore, describing a dislocation as anterior, posterior, lateral, or rotatory did not give any information as to which ligaments were torn or required surgical treatment. As noted by the authors, the timing of surgical treatment of the injured knee ligaments is often based more on associated injuries than on the KD classification. Additionally, different surgeons have different approaches to these injuries regarding surgical timing, staging versus single surgery, and ligament repair versus reconstruction. We have noted in our practice that KD-IV injuries are grossly unstable and frequently may benefit from placement of an external fixator.[4] [5]

• Finally, although the KD classification is not designed to be predictive of management strategy, Everhart et al showed that the KD classification is predictive of outcomes.[6] Cook et al also demonstrated higher failure rates with KD-IV injuries and greater stiffness with acute surgical treatment of KD injuries greater than KD-III.[7]

To summarize, we feel that the KD classification is a simple and reproducible classification system for complex knee injuries (specifically KDs) that allows communication between physicians, accurate surgical planning, and is predictive of outcomes.

Publication History

Received: 14 September 2020

Accepted: 05 October 2020

Article published online:
12 November 2020

• References

• 1 Maxwell GT, Warth RJ, Amin A. et al. Multiple ligament knee injuries: does the knee dislocation classification predict the type of surgical management?. J Knee Surg 2020; DOI: 10.1055/s-0039-1695739.
• 2 Walker DN, Hardison R, Schenck RC. A baker's dozen of knee dislocations. Am J Knee Surg 1994; 7 (03) 117-124
• 3 Wascher DC, Dvirnak PC, DeCoster TA. Knee dislocation: initial assessment and implications for treatment. J Orthop Trauma 1997; 11 (07) 525-529
• 4 Richter DL, Bankhead CP, Wascher DC, Treme GP, Veitch A, Schenck Jr RC. Knee dislocation (KD) IV injuries of the knee: presentation, treatment, and outcomes. Clin Sports Med 2019; 38 (02) 247-260
• 5 Schenck Jr RC, Richter DL, Wascher DC. Knee dislocations: lessons learned from 20-year follow-up. Orthop J Sports Med 2014; 2 (05) 2325967114534387
• 6 Everhart JS, Du A, Chalasani R, Kirven JC, Magnussen RA, Flanigan DC. Return to work or sport after multiligament knee injury: a systematic review of 21 studies and 524 patients. Arthroscopy 2018; 34 (05) 1708-1716
• 7 Cook S, Ridley TJ, McCarthy MA. et al. Surgical treatment of multiligament knee injuries. Knee Surg Sports Traumatol Arthrosc 2015; 23 (10) 2983-2991