The ‘Floating Medial Meniscus’ Lesion in KD3M Knee Dislocations

Abstract

Introduction

An unusual meniscal tear involving avulsion of both anterior and posterior roots of the medial meniscus with extra-articular displacement of the meniscus in the medial soft-tissues has occasionally been observed in high energy knee dislocations. We have termed this tear pattern as a ‘floating medial meniscus’ lesion. This study aims to define this lesion, report its incidence, assess its impact on surgical timing, describe the repair technique, and evaluate healing rates and outcomes.

Materials and Methods

We retrospectively analysed a database of multiple ligament knee injury surgeries performed between 2008 and 2022 at a referral centre for complex knee injuries and identified cases with a floating medial meniscus lesion. The surgical procedure involved a combined arthroscopic and medial open approach that addressed the meniscus tear and ligament tears in one stage. Early intervention was defined as surgery within 3 weeks of injury. We evaluated injury characteristics, surgical challenges, and clinico-radiological outcomes at a minimum 2-year follow-up.

Results

Seven patients (all male, mean age 27.2 years) with floating medial meniscus lesions were identified from 341 knees with multiple ligament injuries. Five patients underwent early surgery, while two had delayed intervention. Preoperative MRI effectively identified the lesions. Early surgery facilitated easier meniscus identification, reduction, and repair, whereas delayed surgery posed challenges. At follow-up, all patients had regained a minimum 0 to 130 degrees knee range of motion, with no residual instability or pain. MRI confirmed healed meniscal roots, and the mean IKDC score was 89.5. There were two competitive elite athletes in this series and both returned to their previous level of sports.

Conclusion

Although floating medial meniscus lesions are daunting at presentation, they can be successfully repaired with a systematic surgical approach, resulting in satisfactory functional outcomes. Early surgery enables easier meniscus dissection, reduction and repair.

Introduction

High energy knee dislocations have the potential not only to disrupt multiple ligaments but also to cause complex meniscal tears not commonly encountered in non-dislocated knees [1, 2]. A particularly devastating injury pattern involves an avulsion of both the anterior and posterior roots of the medial meniscus associated with major disruption of the medial ligament complex and consequent extra-articular displacement of the medial meniscus in the medial soft-tissues. We have termed this unusual tear pattern as a ‘floating medial meniscus lesion’ (Fig. 1). This injury pattern remains largely unreported, and strategies to treat it have not been described.

Fig. 1.

Right knee KD3M injury with a ‘floating medial meniscus’ lesion. a–d MRI reveals the ACL and MCL tears. The sagittal cut demonstrates medial meniscus avulsion with tears at the anterior and posterior meniscal roots. The coronal cuts at the level of the tibial meniscal insertions demonstrate complete root tears, and at the level of the meniscal body reveal significant peripheral displacement of the medial meniscus with absence of the meniscus within the joint articulation. Note that the medial meniscus is attached to the avulsed capsule and meniscofemoral or coronary ligaments. e, f Arthroscopy images of the root tear along with cinch knot used to fix the meniscus

The purpose of this study was to define the floating medial meniscus lesion, report on its incidence, identify the impact of this particular tear pattern to surgical timing, describe the surgical technique for repair, and determine the healing rates and outcomes following repair.

Patients and Methods

Patients were included for this retrospective study from a prospectively gathered database at our institution which is a tertiary care referral centre for complex knee injuries. We identified knees with a floating medial meniscus lesion amongst patients with a history of reconstructive surgery for multiple ligament knee injury performed between 2008 and 2022 by a single surgeon. A floating medial meniscus lesion was defined as one which had a complete tear of the anterior and posterior roots with consequent extra-articular displacement of the meniscus into the disrupted medial ligament complex. We excluded patients with fracture dislocations and tibial condyle fractures who had associated medial meniscus avulsion injuries.

The surgical procedure involved a combined arthroscopic and medial open approach that addressed the meniscus tear and ligament tears in one stage (Fig. 2). We first performed the open medial exploration which allowed for meniscus reduction. This was especially useful for menisci that had flipped or everted with the peripherally attached and avulsed medial capsule. The medial arthrotomy prior to arthroscopy allowed accurate delineation of torn structures and layers devoid of fluid extravasation, and also ensured that subsequent arthroscopy did not cause fluid accumulation in the soft-tissues. The arthrotomy did hamper joint distention and clear visualisation during arthroscopy but was not significant enough to affect accurate ACL and PCL tunnel creation, or medial meniscus anterior and posterior root repair using a transtibial pull-out suture technique. Arthroscopy without fluid was sometimes employed in cases where visualisation was problematic or calf distention due to fluid extravasation was encountered.

Fig. 2.

Acute KD3M with floating medial meniscus. MRI reveals a bicruciate injury, b medial meniscus anterior and posterior root tears with “ghost sign”, c MCL tear with displaced medial meniscus floating in the soft-tissue hematoma. Note that the peripheral attachment of the meniscus to capsule and meniscofemoral ligament is intact. d Axial MRI image with medial extra-articular displacement of the medial meniscus. e A medial approach to the knee reveals tears of the superficial and deep MCL with the medial meniscus displaced in the medial soft-tissues. The capsular attachment of the meniscus is not torn. f The patient underwent a single stage multiple ligament reconstruction which included allograft reconstruction of the MCL and posterior oblique ligament. g Postoperative MRI two years following surgery reveals a healed medial meniscus with no extrusion

The detailed steps for meniscus repair involved careful dissection of the torn medial ligamentous structures so as to accurately delineate the medial meniscus. In each ‘floating meniscus’, both anterior and posterior roots were avulsed and the peripheral capsular attachment of the meniscus was intact. This resulted in extra-articular displacement and often eversion of the meniscus along with the torn and displaced medial ligamentous structures including the capsule and deep MCL. When surgery was performed early, the meniscus was easily identifiable floating within the hematoma in the medial soft-tissue structures. Delineation and dissection of the meniscus was demanding in the two cases with delayed surgery since soft-tissue planes were obliterated with early fibrotic organisation of the hematoma. Transtibial tunnels were then created at the anatomical sites of the posterior and anterior roots of medial meniscus. In the initial cases, these were of 4.5 mm diameter, in recent years these were of 3.7 mm. Cinch sutures were taken in the meniscus at the sites of anterior and posterior horns and the medial meniscus was then reduced within the medial compartment with delivery of the sutures within the trans-tibial tunnels. The sutures were tightened and tied over a button. Once meniscus repair was completed, the ACL, PCL, and MCL were addressed with repair or reconstruction. Although each patient underwent an individualised postoperative rehabilitation program, non-weight bearing for 6 weeks, and early initiation of knee range of motion was adhered to for all cases.

Injury characteristics using the Schenk classification [3], preoperative imaging, and operative reports were reviewed following patient consent. Clinical, functional and radiological outcome measures were determined at a minimum 2-year follow-up. Chronicity was evaluated to determine whether the time interval from injury to surgery contributed to surgical challenges in meniscal identification in the disrupted medial ligament complex and subsequent reduction to achieve an anatomical repair of the anterior and posterior roots. Early intervention was defined as less than 3 weeks between injury and surgery, whereas delayed intervention was more than 3 weeks after injury.

Results

From a database comprising 341 knees operated for multiple ligament knee injuries, of which 119 were KD3M type of injuries, we identified 7 patients who had a floating medial meniscus lesion. All patients were males with a mean age of 27.2 years (range 21–32 years). All 7 patients had a KD3M type of knee dislocation with significant tears of the anterior cruciate ligament, posterior cruciate ligament, and medial ligament complex. All seven patients sustained a high-velocity knee dislocation following a either a motor vehicular accident or fall from height. In five patients, the surgery was performed early (within 3 weeks following injury), whereas in two patients, the surgery was performed at 5 and 6 weeks following injury.

Preoperative MRI distinctively identified a floating medial meniscus lesion with certain classical features. The coronal cuts at the level of the tibial meniscal insertions demonstrated complete root or horn tears, and at the level of the meniscal body revealed significant peripheral displacement of the medial meniscus which was attached to the avulsed capsule and meniscofemoral or coronary ligaments. The axial cuts demonstrated absence of the medial meniscus within the tibiofemoral articulation and a significantly displaced meniscus within the hematoma associated with the medial ligament disruption. The sagittal cuts demonstrated a ‘ghost sign’ at the sites of the anterior and posterior meniscal roots with absence of the meniscus within the joint articulation.

An evaluation of the detailed surgical notes revealed that identification of the displaced or everted medial meniscus with reduction and anatomic repair was achieved without difficulty in the five patients who underwent surgical repair early, however, this step was extremely challenging in the two patients in whom a delayed surgical repair was performed (Fig. 3).

Fig. 3.

KD3M with “floating medial meniscus”—delayed presentation. a–d MRI images reveal tears of ACL, PCL, and MCL with extra-articular displacement of the medial meniscus. e Intraoperative image shows anterior and posterior root tears of medial meniscus with intact peripheral attachment to capsule

At the minimum 2-year follow-up, all 7 patients were ambulating without pain, had no residual instability symptoms, and had regained a minimum 0 to 130 degrees knee range of motion. Bilateral weight bearing radiographs revealed no significant difference in medial joint space between the affected and normal knees, with no evidence of degenerative changes. MRI revealed healed medial menisci roots, though some extrusion was noted in four patients. The mean IKDC score 2 years following surgery was 89.5 and ranged from 76 to 93. Two patients in this case series were competitive athletes (cricket and triathlon) and both returned to the same level of sports participation following surgery. This was achieved 14 and 17 months following surgery. No patient in this case series has undergone reoperation on his knee for any reason.

Discussion

The floating medial meniscus lesion is a traumatic avulsion of the medial meniscus with tears at both anterior and posterior roots along with extra-articular displacement within the disrupted medial ligamentous structures. It is an uncommon type of meniscus tear which occurs exclusively in KD3M type of injuries, and in this series was noted in 2% of knees operated for multiple ligament knee injuries (7 of 341), of which 119 were KD3M injuries. Early surgery enables easier dissection and identification of the displaced or everted medial meniscus and facilitates anatomic reduction and repair. The dissection and reduction was challenging in the two patients in whom delayed surgical repair was performed. Hence, we recommend that although delayed single stage multiple ligament reconstruction is a valid option in most KD3M injuries [4], we would not propose this approach if a ‘floating medial meniscus’ lesion is identified.

Restoration of meniscus anatomy is the key determinant in achieving a good functional result [5–7]. To accomplish this goal, it is important to attain an accurate reduction of the displaced meniscus, and firmly fix the avulsed roots to their insertion sites, whilst ensuring adequate knee stability with MCL and ACL repair or reconstruction. Unlike degenerative root tears [8], the healing rates for traumatic root avulsions are encouraging, and all seven patients revealed healed root repairs on MRI at minimum 2 years follow-up. Excellent outcomes scores with an ability to return to sports was also demonstrated and this was primarily due to a functional medial meniscus.

In conclusion, although a ‘floating medial meniscus’ lesion results from a severe traumatic avulsion and has an alarming appearance on MRI, if addressed early and with a systematic approach, anatomical repair is feasible and results in satisfactory healing with excellent functional outcomes.

Data availability

The data supporting the findings of this study may be made available upon request.

Declarations

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical standard statement

This article does not contain any studies with human or animal subjects performed by the any of the authors.

Informed consent

For this type of study informed consent is not required.