Floating Knee

Updated: Nov 22, 2022
Author: Srinivasa Vidyadhara, MBBS, DNB, MS(Orth), DNB(Orth), FNB(SpineSurg), MNAMS; Chief Editor: Thomas M DeBerardino, MD, FAAOS, FAOA 


Practice Essentials

Floating knee is a flail knee joint resulting from fractures of the shafts or adjacent metaphyses of the femur and ipsilateral tibia.[1, 2]  Blake and McBryde initially described this injury, which is generally caused by high-energy trauma.[3]  Local trauma to the soft tissues is often extensive, and life-threatening injuries to the head, chest, or abdomen may also be present.[4]

An initial evaluation to determine the extent of a patient's injuries is of critical importance. This evaluation should be followed by an appropriate sequence of emergency diagnostic and therapeutic measures.

Isolated fractures in stable patients can be treated acutely. (See Treatment.) By contrast, temporary stabilization of the fractures with external fixation is indicated for unstable patients or those in extremis. When the patient's physiologic state is stabilized, conversion to internal fixation is desirable. In adults, all floating knee injuries must be addressed with early anatomic reconstruction and stable surgical stabilization of both fractures. In children, especially those younger than 10 years, treatment of ipsilateral femoral and tibial fractures has been controversial. 

Relatively little is recorded in the English-language literature on the subject of ipsilateral fracture of the femur and tibia. The complication rate associated with floating knee injuries remains high, regardless of the treatment regimen used. Infection, nonunion, malunion, and stiffness of the knee are all common. These complications can lead to functional impairment and frequently cause unsatisfactory results.


Floating knee injuries may include a combination of diaphyseal, metaphyseal, and intra-articular fractures (see the image below).[5]  This combination of fractures is less common in the pediatric population than in adults. However, epiphyseal injury can adversely affect open growth plates, predisposing a child to limb-length discrepancy and angular deformities.

Floating knee injury. Floating knee injury.



Blake and McBryde used the terms true (or type I) injury and variant (or type II) injury to classify the floating-knee fracture pattern, as follows[3] :

  • Type I is a pure diaphyseal fracture of the femur and tibia
  • Type II is a fracture that extends into the  kneehip, or  ankle joint [6]

Fraser et al classified floating knee injuries in a similar way by analyzing knee involvement (see the image below)[7] :

  • Type I is the same as the true injury Blake and McBryde described, with extra-articular fractures of both bones
  • Type II is subdivided into three subtypes: type IIa, which involves femoral shaft and tibial plateau fractures; type IIb, which includes fractures of the distal femur and the shaft of the tibia; and type IIc, which indicates fractures of the distal femur and tibial plateau
Fraser classification of floating knee injuries. Fraser classification of floating knee injuries.

In both of these classification systems, type II fractures with intra-articular involvement have been linked with higher complication rates and poorer functional results than those observed with type I injuries.


In children, floating knee injuries are classified according to the Bohn-Durbin or Letts classification systems.

In the Bohn-Durbin classification, floating knee injuries are described as follows:

  • Type I - Double-shaft pattern of fracture
  • Type II - Juxta-articular pattern
  • Type III - Epiphyseal

The Bohn-Durbin system does not account for open fractures and cannot be used to predict complications and prognoses.

Unacceptable findings are femoral union in a position of greater than 30° anterior angulation, 15° valgus angulation, and 5° posterior or varus angulation, or greater than 2 cm of shortening. Tibial malunion is defined as greater than 5° angulation in any plane or greater than 1 cm of shortening. Rotational malunion is defined as any internal rotational deformity exceeding findings on the unaffected side or greater than 20° external rotation of the extremity, as detected during walking or standing.

Letts et al designed a classification system in which they recognized diaphyseal, metaphyseal, or epiphyseal knee fractures (types A, B, C) and also open fractures (types D and E) (see the image below). The drawback of this system is that it does not indicate how to classify patients with epiphyseal separation in the distal femur and tibia or how to describe the location of open fractures in the epiphysis, metaphysis, or diaphysis.[8]

Letts and Vincent classification system for floati Letts and Vincent classification system for floating knee injuries in children.


Road traffic accidents are the most common mechanisms of trauma, followed by gunshot wounds and falls from heights.


This severe injury appears to be increasing in frequency. A male preponderance is observed, particularly in young adults 20-30 years of age.


The criteria Karlstrom and Olerud established are widely accepted for evaluating functional outcomes in adults.[9, 10]  The following data are recorded and characterized as excellent, good, acceptable, or poor (see the image below):

  • Subjective symptoms from the thigh or leg
  • Subjective symptoms from the knee or ankle joint
  • Walking ability
  • Participation in work and sports
  • Angulation and/or rotational deformity
  • Shortening
  • Restricted mobility of the hip, knee, or ankle joint
Karlstrom and Olerud's criteria for assessing func Karlstrom and Olerud's criteria for assessing functional outcomes after a floating knee injury.

Using the criteria of Karlstrom and Olerud,[9, 10, 11]  most authors of published series have described excellent-to-good results in as many as 65% of surgically treated patients. After conservative treatment, success rates decrease to 29%. The complication rate is associated with fracture type (open fracture), Fraser type IIc, tibial plateau, and distal tibia.[12, 13, 14]

In children, subjective outcomes of floating knee injuries can be evaluated according to the criteria described by Yue et al,[15]  as follows:

  • Excellent - No complaints or limitations secondary to the injury to the extremity
  • Good - Occasional minor pain in the extremity or a decreased ability to participate in athletic activities
  • Fair - Intermittent moderate pain in the extremity but with the ability to perform all activities of daily living (ADLs) and most recreational activities
  • Poor - Constant pain in the extremity and an inability to perform ADLs because of the injury to the extremity

Good-to-excellent results have been reported with both conservative and surgical methods in children. Fixation of one or two fractures in children aged 9 years or younger offers superior results and minimizes the incidence of long-term dysfunction of the extremity.

Regarding intra-articular (type II) injuries, good or excellent results have been reported in 24% of patients. The difficulty in obtaining satisfactory function after type II injuries may result from severe injuries to the soft tissue, damage to the knee joint, and/or the complexities of achieving stable reconstruction.

Apart from knee involvement and open type III femoral fractures, other significant factors that affect functional outcomes after floating knee injuries are the following[11] :

  • Involvement of the knee joint
  • Severity of soft-tissue injury in the tibia
  • Fixation time after injury in the tibia
  • AO fracture grade in the femur and tibia
  • Fixation time after injury in the femur and severity of open femoral fractures


History and Physical Examination

Floating knee injuries must be included in assessment and treatment protocols for patients with polytrauma.

Damage to the vessels (mainly the popliteal and posterior tibial arteries) and lesions of the nerves (eg, peroneal nerve) are common. Vascular injury is common and may be limb-threatening if not recognized and addressed. Often, the vascular injury is to the anterior tibial artery and does not result in ischemia and is not treated with vascular repair or reconstruction. However, vascular status must be assessed and addressed as appropriate. Traction usually causes neurapraxia, which often resolves, but complete resolution cannot always be anticipated.

The incidence of open fractures is high, approaching 50-70%, at one or both fracture sites. The most common combination is a closed femoral fracture with an open tibial fracture.

A well-documented finding is injury to the knee ligaments that occur in association with ipsilateral femoral and tibial fractures. Anterolateral rotatory instability is the most common pattern of instability. Knee ligament injury is not always suspected, and joint swelling due to hemarthrosis should not be mistaken for a sympathetic effusion. The ipsilateral femoral and tibial shaft fractures and knee ligament injury appear to be part of a continuum of combined injuries resulting from complex, high-energy forces.[16]

In skeletally immature patients, floating knee is uncommon. Few studies of this injury have been conducted in children. Data from available studies have shown that findings observed in children are comparable to those in adults in terms of the mechanism of fracture, the incidence of associated major injuries, and the complexity of treatment.



Imaging Studies

Imaging modalities that may be helpful include plain radiography, magnetic resonance imaging (MRI), and computed tomography (CT).

Obtain anteroposterior (AP) and lateral radiographs of the femur and tibia, including views of the joint above and below. Order radiographs showing the pelvis and both hips. Obtain AP and lateral views of the affected knee.

MRI of the knee joint is advocated in patients with suspected injuries to the intra- or extra-articular ligaments. MRI findings may in help in planning management of ligamentous injuries.

CT scans of the metaphyseal fractures may be useful for understanding the three-dimensional configuration of the fracture fragments.

In addition, generalized radiologic screening of suspected skeletal injuries may be undertaken.

None of the investigations should hinder surgical management in emergency situations. In these circumstances, intraoperative examination under anesthesia after stabilization of the fractures may be more appropriate.



Approach Considerations

Patients with ipsilateral femoral and tibial fractures present after high-energy trauma.[17, 18] These injuries are associated with an increased risk of morbidity and mortality. Involvement of the knee joint, severe trauma to the soft tissues, fracture comminution, and open fractures are associated with increased complication rates resulting in worsened functional outcomes.

Isolated fractures in stable patients can be treated acutely. By contrast, temporary stabilization of the fractures with external fixation is indicated for unstable patients or those in extremis, according to the concepts of damage-control orthopedics. When the patient's physiologic state is stabilized, conversion to internal fixation is desirable (see the image below).

Treatment protocol for floating knee injuries. Ex- Treatment protocol for floating knee injuries. Ex-Fix = external fixation; IM = intramedullary; ORIF = open reduction and internal fixation.

In adults, all floating knee injuries must be addressed with early anatomic reconstruction and stable surgical stabilization of both fractures. The goal is to facilitate early joint mobilization.

In children, especially those younger than 10 years, treatment of ipsilateral femoral and tibial fractures is controversial. When the physis is involved, the possibility of leg-length discrepancy must always be considered.

Medical Therapy


Early reports favored a nonsurgical approach to one or both fractures in a floating knee because of the unavailability of internal fixation. High infection rates and lack of knowledge of posttraumatic critical care further delayed the acceptance of internal fixation in this tough clinical situation. However, conservative methods entailed considerable risks of fracture-related shortening and angulation, with delays in fracture union and return to normal activities. (See the image below.) Consequently, nonsurgical methods fell from favor and were gradually replaced by internal fixation.

Conservative management of the femur in an ipsilat Conservative management of the femur in an ipsilateral injury of this type is likely to result in malunion of the femoral fracture and shortening.


Nonsurgical treatment for children consists of skeletal traction for the femoral fracture with closed reduction and casting or splinting for the tibial fracture. A hip spica cast is applied when sufficient femoral healing has occurred.[19, 20]

The incidence of complications of fracture healing is high in older children treated with conservative methods. Malunion, nonunion, refracture, and limb-length discrepancy have been documented in almost 50% of patients receiving closed treatment.[8]

Surgical Therapy


Most surgeons currently recommend aggressive treatment with early stabilization of both fractures, integrated with a multisystem approach that emphasizes early mobilization of the patient to facilitate better care and quicker recovery.[21, 10, 19, 20, 22, 23, 24]  (See the image below.)

Early joint mobilization determines the patient's Early joint mobilization determines the patient's functional outcome after treatment of floating knee injuries. Nailing of both the tibial and the femoral fractures, as shown, is the best method for enabling early mobilization.

At present, the use of intramedullary nails on either side of the knee joint is the best modality for fracture management. An antegrade technique is usually employed when the nails are applied. The procedure is performed after adequate resuscitation and physiologic stabilization is accomplished. Resuscitation and stabilization are of particular importance in patients with a high Injury Severity Score (ISS) due to associated injuries.

If immediate intramedullary nailing is not possible, a spanning external fixator can be applied to stabilize the entire limb. This fixator can be replaced with internal fixation when the patient's general condition is stable, when neurovascular lesions and soft-tissue coverage are managed, or both.

The technique of antegrade nailing does have drawbacks, such as difficulties in positioning the patient, the need for two incisions, prolonged anesthesia and surgical time, and an inability to perform other surgical procedures at the same time.

To overcome these concerns, retrograde intramedullary nailing of the femur with antegrade nailing of the tibia through the same incision has been proposed as an alternative. The fracture of the femoral shaft is always addressed first, for the following two reasons:

  • First, stabilization of the femur permits mobilization of the patient without traction if the patient has decompensation during the operation that necessitates abandonment of the second procedure; the extremity with the tibial fracture can be placed in a splint or cast, or an external fixator can be applied quickly
  • Second, stabilization of the femoral shaft fracture allows the surgeon to flex the knee sufficiently to access the starting point in the proximal tibia; in addition, it provides a stable proximal limb for support

When the fracture pattern involves the metaphyseal region of the tibia or femur with or without intra-articular extension, stabilization can be achieved by using locking plates. Plate fixation can offer anatomic reduction of the articular surface; this method allows  rigorous mobilization and maximizes the functional outcome.

The nailing of a proximal femoral fracture and a less invasive stabilization system for distal femur (LISS-DF) fixation of a distal one could be a reliable and effective approach to handle ipsilateral concomitant fractures of a proximal extracapsular and distal femur.[25]

Early diagnosis of ligamentous injuries is essential to facilitate appropriate rehabilitation. Conservative treatment is preferred for an isolated injury to the medial collateral ligament. If necessary, reconstruction of anterior or posterior cruciate ligament tears may be delayed until union of the fractures occurs. Injuries to the posterolateral corner and avulsion fractures of the cruciate ligaments from either the femur or the tibia should be repaired at the time of the initial procedure or in the early postoperative period.


Most authors suggest operative treatment of at least the femoral fracture in patients older than 10 years. Surgical treatment reduces complications, hospital stays, and the time to unsupported walking. Therefore, many authors recommend surgical treatment for both the femoral fracture and the tibial fracture in all age groups.[19, 20, 22, 23]

Even in patients younger than 9 years, at least one fracture must be rigidly fixed. With the advent of newer pediatric fracture treatment methods, including flexible nail fixation of pediatric femur fractures, fixation of the femur fracture should be performed. This allows mobilization of the patient and patient discharge whether the tibia is also surgically stabilized or is treated closed.

A single-center retrospective study by Navarro Vergara et al (N = 25) evaluated surgical treatment of floating knee in pediatric patients.[26]  Of the 25 cases, 19 were resolved with surgery on at least one of the fractures, and six were managed with simultaneous orthopedic treatment of both. Outcomes were excellent in 15 cases, good in three, fair in five, and poor in one. Complications occurred in eight cases, of which five were associated with limb discrepancy and three with functional limitations of the knee; nonunion of the distal tibia was noted in one case.

Postoperative Care

Early joint mobilization is the key to success. Early weightbearing may be helpful in patients with diaphyseal fractures, and delayed weightbearing is preferred for those with intra-articular or metaphyseal fractures.


Delayed union, nonunion, malunion, and stiffness of the knee are more prevalent in patients with the floating-knee combination of fractures than in patients with isolated femoral or tibial fractures.[10, 20, 27]

For patients in general, factors such as older age, an increased number of pack-years of cigarettes smoked at the time of injury, a high ISS, and the presence of open and comminuted fractures adversely affect the bony union time and the reoperation rate.[28]

Complications unique to children

In the pediatric population, open growth plates present an additional dynamic factor that leads to complications unique to children. Examples of such complications include overgrowth of the bone after a fracture and premature closure of the ipsilateral physis, genu valgum, and physeal arrest.

Mean overgrowths of the femur and tibia are 1.4 and 1.1 cm, respectively. The incidence of leg-length discrepancy is increased in patients younger than 9 years and in those treated nonoperatively. However, subjective limps and length discrepancies of the lower extremities can occur regardless of the type of fracture, the extent of soft-tissue injury, or the treatment method.

Pediatric patients and their parents must be informed of these possible outcomes and counseled. Patients should be followed up until they reach skeletal maturity to monitor for signs of these complications.


The incidence of infection and the incidence of osteomyelitis are relatively high in floating knee injuries, especially in patients with open or type II fracture patterns. Strategies that have led to the eradication of infections in most cases include meticulous debridement, continuous suction and irrigation drainage, and use of polymethylmethacrylate beads or sticks impregnated with antibiotics.

Knee stiffness

Delayed rehabilitation and associated injuries around the knee result in limitation of knee movement.