The floating knee: epidemiology, prognostic indicators & outcome following surgical management

The incidence of fractures resulting from motor vehicle accidents is on the rise. As a by-product of the horsepower race, high velocity accidents are now more common. Such accidents produce violent and complex injuries. Frequently, multiple fractures are produced in the same extremity, adding new dimensions to the problems of their management.

Floating Knee is the term applied to the flail knee joint segment resulting from a fracture of the shaft or adjacent metaphysis of the ipsilateral femur and tibia [1]. The fractures range from simple diaphyseal to complex articular types. This complex injury has increased in proportion to population growth, number of motor vehicles on the road, and high speed traffic. Although the exact incidence of the floating knee is not known, it is an uncommon injury. The largest series reported in the literature was of 222 patients over 11 years [2]. This injury is generally caused by high-energy trauma and the trauma to the soft tissues is often extensive. There also may be life-threatening injuries to the head, chest or abdomen and a high incidence of fat embolism. Management of this injury has been variously described in the literature [3–8].

The purpose of our study was to determine the outcome of patients after surgical management of the Floating Knee and identify prognostic factors for this injury.

This was a prospective study conducted at a tertiary care trauma centre after approval of the Research and Ethics committee over a 3 year period (1998 – 2001). All floating knee injuries that were managed surgically during the study period were included. Children and floating knee injuries managed conservatively were excluded from the study.

Our study included 29 patients with 29 floating knee injuries, 27 males and 2 females [Table 1]. Initial management involved resuscitation and haemodynamic stabilisation of the patient, splinting of the affected limb in a Thomas splint and a thorough secondary survey to identify other injuries. Radiographs of the chest, pelvis, affected lower limb including all its joints and other suspected bony injuries were done. Open fractures were classified according to Gustilo & Anderson's classification [9]. Initial wound toilet, tetanus immunisation and antibiotic therapy was initiated for open fractures. The floating knee injury was classified according to Blake & McBryde's Classification [10] [Table 2] [Figure 1, 2 &3].

Patients were observed closely to detect development of fat embolism. (Tachypnoea, confusion, tachycardia). If fat embolism was diagnosed, patients were managed in the surgical intensive care and surgical fixation of the fractures was postponed. Patients with associated chest or head injuries were managed appropriately prior to surgical stabilisation of the fractures. We inserted chest drains in patients with suspected haemothorax or pneumothorax. All patients with fluctuating conscious levels had a CT scan of the brain. If an intracranial haematoma or bleed was diagnosed, these patients were referred to the neurosurgery unit for further management. Surgical stabilisation of the fractures was delayed till the head injury is dealt with. Detection of abdominal injuries was by clinical assessment and ultrasonography. If there was a suspicion of intra-abdominal injury, an urgent CT scan was indicated. If significant abdominal injuries were detected, these took priority over surgical stabilisation of the fractures. In our study, we did not have any patients with significant abdominal trauma, intracranial haematoma or bleed.

Surgical management of both the fractures were done once patients were hemodynamically stable and fit to undergo surgery. The femur fracture was fixed prior to the tibia fracture. Intramedullary nailing of both fractures was the commonest method. Both the femur and tibia nails were inserted antegrade. When external fixation was used in open tibia fractures, this was the definitive management. Associated injuries that needed surgery were treated under the same anaesthesia. Knee ligament injuries were diagnosed by clinical assessment by the surgeon after surgical stabilisation of the fractures. Lachman's test and posterior drawer's test were used to clinically assess the anterior and posterior cruciate ligaments respectively. If a knee ligament injury was suspected, a diagnostic arthroscopy was performed under the same anaesthesia and primary ligament reconstruction done. Patellar bone-tendon-bone grafts were used for reconstruction of the torn cruciate ligaments.

Thromboprophylaxis was initiated in all patients in the post-operative period. Physiotherapy and mobilisation was started as soon as possible after surgery. Patients were followed up regularly till bony union (clinical and radiological). Functional assessment and final outcome was measured using the Karlstrom's criteria [11] after bony union [Table 3] [Figure 4 &5].

3 patients had contralateral femoral fractures and 4 had contralateral tibial fractures. 4 patients had associated humeral fractures and 1 patient had fractures of the forearm bones. 4 patients had tarsal/metatarsal fractures. All bony injuries that needed surgical stabilisation were managed during the same anaesthesia as for the surgical stabilisation of the floating knee.

3 patients sustained head injuries for which a CT scan of the brain was done. None of these patients had intracranial bleeds or haematomas that needed intervention by the neurosurgeons. All of these patients were diagnosed to have cerebral concussion. The initial assessment and management was neurological monitoring recording the pupil size and the Glasgow Coma Scale (GCS). These patients were operated only after their GCS was 15 and this delayed the time of initial surgery in all these patients by 2 – 3 days.

The complications encountered were knee stiffness in 4 patients, foot drop in 1 patient, delayed union of tibia in 2 patients and superficial infection in 2 patients. Nerve conduction study was done in the patient with foot drop which revealed an axonotmesis of the common peroneal nerve. The additional procedures were manipulation under anaesthesia for knee stiffness, dynamisation in one patient with delayed union and common peroneal nerve exploration in the patient with foot drop which revealed a partial nerve transection. Patients with delayed union needed dynamisation of the tibial nail and removal of external fixator and functional cast bracing of the fracture. These fractures went on to unite following these interventions. The superficial infections were related to pin sites of the external fixators which were managed by pin site care and antibiotics. The infection settled with this management. The average follow up was for 23.5 months (Range 21 – 26 months). In the assessment of end results after bony union according to the Karlstrom criteria the following results were obtained: Excellent – 15, Good – 9, Acceptable – 2 and Poor – 3.

When the knee joint is isolated partially or completely due to fracture of the femur and tibia the term "Floating Knee" is used [10]. Survivors of high-speed traffic accidents often have injuries to several of the parenchymal organs as well as multiple fractures. Careful evaluation of these injuries and resuscitation of the patient must precede the definitive management of specific fractures.

Hayes JT [5] suggested that automobile passengers with floating knee, braced their feet firmly against the sloping floor of the front seat just prior to the collision, their legs getting crumpled under the massive decelerating forces produced by the impact. Pedestrians were frequently catapulted some distance from the point of impact and were further injured by striking the pavement. In a study of 222 cases of floating knee by Fraser [2], all cases were involved in road traffic accidents.

Studies showed associated injuries like head injuries, chest injuries, abdominal injuries and injuries to other extremities. Most of the injuries to the head, chest and abdomen were life threatening. Adamson et al in their study encountered 71% major associated injuries with 21% vascular injuries [12]. The reported mortality rate ranged from 5% – 15%, reflecting the seriousness of the associated injuries [1]. Deliberate and careful examination of the patient must be carried out in order to determine whether a major intracranial, abdominal or thoracic injury is present. Such injuries should take precedence over extremity injuries in the priority of treatment.

There are plenty of studies in the literature detailing different management options for the Floating Knee. Hayes JT [5] opined that in a patient with multiple fractures in the same extremity, operative fixation of one or more of the fractures was valuable in the management of the entire limb. Ratcliff AH [8] found that internal fixation of both the fractures should be done wherever possible as these patients were less likely to develop knee stiffness or shortening and were in hospital and off work for less time than those treated conservatively. Omer GE [6] treated the Floating Knee by both conservative and operative fixation found that where internal fixation was done for both femoral and tibial fractures, the healing time was about 8 weeks earlier than the group managed conservatively. Behr JT [3] treated patients with the Floating knee by closed intramedullary nailing with Ender nails and achieved femoral union at an average of 10.3 weeks and tibial union at 18 weeks. Ostrum RF [7] treated patients with a retrograde femoral tibial intramedullary nail through a 4 cm medial parapatellar incision. The average time to union of the femoral fractures was 14.7 weeks and that for the tibial fractures was 23 weeks. They opined that this method was an excellent treatment option.

The general consensus in recent studies is that the best management for the Floating knee is surgical fixation of both the fractures with intramedullary nails. Dwyer used combined modalities of treatment with one fracture managed conservatively and the other surgically. They concluded that the treatment method for the tibia did not interfere with joint mobilisation [13]. Lundy recommended surgical stabilisation of the fractures for early mobilisation which produced the best results [14]. Theodoratus recommended intramedullary nailing as the best choice of treatment except for grade 3B & C open fractures [15]. Single incision technique for nailing of both the fractures have been recommended by several authors [7, 16, 17]. Rios J compared single incision versus traditional antegrade nailing of the fractures and found the former to have less surgical & anaesthesia time with reduced blood loss [17]. Shiedts found an increased incidence of fat embolism when both fractures were treated by reamed nails [18].

Szalay [19] demonstrated knee ligament laxity in 53% of patients while 18% complained of instability. Most of the patients with instability had a rupture of the anterior cruciate ligament with or without damage to other ligaments. They concluded that knee ligament injury was more common with floating knee injuries than with isolated femoral fractures and advocated careful assessment of the knee in all cases of fractures of the femur and floating knee injuries. Other studies [20] have showed that the incidence of knee ligament injuries in the floating knee was upto 50%, most of which were missed in the initial assessment. Meticulous examination of the knee at the time of injury is strongly advocated although the practicality of this method is questionable.

Our study showed a male predominance comparable to other studies. Most of the studies showed road traffic accidents as the only mode of injury. In our study, the most common mode of injury was road traffic accidents but two of our patients sustained their injury after a fall from height. This mode of injury for the Floating Knee has not been mentioned in the literature reviewed. The classification used by us was the one that was proposed by Robert Blake [10]. This was used as it took into account the injuries sustained at the hip or ankle of the affected side and helps one in planning the surgical procedure. The other classification system advocated by Fraser [2] includes intra-articular fractures at the knee but does not mention about injuries to the ipsilateral hip or ankle both of which can have implications on the surgical management of the Floating Knee. Our management consisted of treating both the femoral and tibial fractures surgically, most of them by intramedullary nailing using an interlocking nail. With this management, we found the fracture union time and functional recovery was better than the other surgical modalities. This was in accordance to studies by Gregory [4] and Ostrum RF [7] who had excellent results with fixation of both fractures by intra-medullary nailing. Both these authors used a retrograde nailing for the femur although in our study all the nailing was antegrade. Though no knee problems have been found when single incision technique is used [4, 7, 16] we feel that antegrade nailing allowed easier knee ligament reconstruction if needed as the femoral nail inserted retrograde would make knee ligament reconstruction technically difficult.

Intra-articular involvement of the fractures, higher skeletal injury scores and severity of soft tissue injuries are significant indicators of poor outcome results [21–23]. Hee suggested a preoperative scoring system which took into consideration the age, smoking status at time of injury, Injury severity scores, open fractures, segmental fractures and comminution to prognosticate the final outcome of these fractures [24].

The best results were seen when both fractures were treated by intramedullary nailing. We found that these patients returned to their normal level of activity earlier than when the fractures were treated with other modalities. Tibia fractures treated with external fixation had a longer union time probably related to the soft tissue injury and comminution at the initial injury. The 3 patients who had a poor outcome in our study were 2 patients with tibia plateau fractures who had knee stiffness and persisting pain in the knee while the other patient had a Grade 3B open tibia fracture treated by external fixation. This shows that the poor prognostic factors were related to the type of fracture (open or closed, intra-articular fractures, severe comminution). The associated injuries played a major role in the initial outcome of patients in our study with regards to delay in initial surgery, prolonged duration of surgery, anaesthetic exposure and delay in rehabilitation. From our study we found Floating knee injuries to be a group of complex injuries that needed careful assessment to detect poor prognostic factors (open, intra-articular, comminuted fractures) and associated injuries, surgical fixation of the fractures with thorough planning of surgeries and prolonged rehabilitation. Combination of all these would determine the ultimate outcome of these patients.

The Floating Knee is a complex injury with more than just ipsilateral fractures of the femur and tibia. The associated injuries and the type of fracture (open, intra-articular, comminution) are prognostic indicators of the initial and final outcome in patients. We recommend thorough initial assessment of patients with regards to life threatening associated injuries, surgical fixation of both fractures preferably by intramedullary nailing, knee ligament assessment to detect injuries and rigorous post-operative rehabilitation for a good final outcome.