A fifteen-year-old obese girl (weight, 113 kg; height, 167 cm; body-mass index, 40.5 kg/m2) injured her right knee after falling over a friend's leg while playing at school. On initial evaluation at an outside institution, she was noted to have posterior dislocation of the right knee (Figs. 1-A and 1-B) and no pulse in the involved extremity. The knee was reduced with traction, but the limb remained pulseless. The patient was transferred to the regional pediatric level-I trauma hospital for treatment. Decreased sensation and motor weakness in both the superficial and the deep peroneal distribution were noted, and she was taken to the operating room immediately. Examination under anesthesia revealed a high-grade injury involving the posterior cruciate ligament, lateral collateral ligament, and posterolateral corner. A bridging external fixator was applied for stabilization of the tibiofemoral joint. Intraoperative angiography demonstrated complete blockage at the popliteal fossa, which was treated with a saphenous vein graft. Because the total ischemic time was approximately seven to eight hours, four compartment fasciotomies were performed. Posterior and anterior tibial artery pulses were weak but present during the Doppler evaluation at the conclusion of the procedure.
The patient was admitted for continued evaluation. During her hospital stay, she was noted to have persistent swelling of the involved lower extremity. Duplex ultrasonography of the lower extremity revealed a popliteal deep venous thrombosis, for which Coumadin (warfarin) therapy was started. Within the first week, a surveillance ankle-brachial index test and a duplex ultrasound test showed insufficient filling of the distal popliteal artery and decreased blood flow. The patient was again brought to the operating room, where she underwent a thrombectomy and arterial graft revision.
Surgery resulted in improved perfusion and pulses, and the patient was discharged three weeks after the injury. The follow-up care was complicated by the need for extended negative-pressure wound therapy to assist in the healing process of the fasciotomy wounds. Skin grafts were successfully placed seven weeks after the injury, and these healed over a six-week period without further complication. On vascular follow-up six months after the injury, the arterial graft exhibited worsening stenosis and required angioplasty. At the one-year follow-up, the arterial graft continued to exhibit stenosis; however, no additional surgery was recommended because the patient had a perfused extremity that was not causing claudication or pain at rest.
It was elected to keep the external fixator on for three months until the wounds were completely healed. The patient progressed to functional daily activities four months later, although her activity level was minimal and primarily involved walking. On subsequent knee examinations, a grade-II posterior drawer sign of the posterior cruciate ligament was noted, with the lateral collateral ligament-posterolateral corner complex showing slight opening in full extension. Additionally, an opening of 1 cm was observed when varus stress was applied to the lower limb with the knee positioned in 30° of flexion. Rotational assessment was difficult because of the size of the extremity. At the one-year follow-up visit, the peroneal nerve abnormalities had resolved, and the patient reported that the knee was still stable and functional. Because of her low baseline activity level and lack of subjective instability, she elected not to pursue any further surgical repair.
Obesity counseling for this patient was first discussed during her inpatient stay. The mechanism of injury and its association with obesity were discussed with the patient and her mother. After the patient's wounds had healed and she was bearing weight on the injured extremity, she was referred to a wellness center for a formal evaluation and to receive counseling with regard to nutrition, exercise, and behavior management. At the time of final follow-up, although the patient was still overweight, she and her mother continued to be active in a nutrition and exercise program.
Body-mass index, expressed as weight in kilograms divided by height in meters squared (kg/m2), is commonly used to identify obesity among adults. It is also used to identify children who are overweight or at risk of becoming overweight1. According to the U.S. Centers for Disease Control growth charts for the year 2000, an adolescent is considered to be overweight when his or her body-mass index value is at or above the 95th percentile4. With this defining criterion, it has become apparent that childhood and adolescent obesity was relatively stable from the 1960s through the 1980s but has nearly doubled since that time1. With such statistics, events such as low-velocity traumatic injuries may become more common, as evidenced by emerging cases discovered within the last twenty years.
The literature contains multiple case reports documenting multiligamentous knee injuries in obese patients due to ground-level falls3,5-8. The injuries in six of the seven patients in those studies were complicated by nerve and/or vascular injuries, and three of the seven patients subsequently required an amputation. These studies also highlight some of the potential problems with rehabilitation in obese patients, including prolonged hospitalizations and recovery times as well as difficulty finding properly sized rehabilitation equipment.
Hagino et al.2 reviewed the cases of seven morbidly obese individuals (body-mass index >35 kg/m2) who all sustained a popliteal vascular injury after a knee dislocation, hypothesizing that limb salvage would be complicated by obesity-related medical illnesses, technically challenging operative repair, and poor rehabilitation potential. All patients exhibited arterial avulsion and thrombosis, requiring operative repair. Despite patent grafts in all patients, two patients required above-the-knee amputation. Obesity-related complications included deep wound infections in three patients, diabetic ketoacidosis in two patients, and cor pulmonale in one patient. The authors concluded that morbid obesity is a risk factor for spontaneous knee dislocation along with additional operative challenges and unusual postoperative complications.
Peltola et al.9, in a retrospective study of knee dislocations treated at a level-I trauma center over a ninety-month time span, evaluated the prevalence and cause of knee dislocations in patients with normal or increased body-mass indices. Of twenty-four patients, eleven had body-mass indices that were >25, and two of those eleven patients were morbidly obese (body-mass index >40). Nine of the eleven overweight patients had sustained a knee dislocation due to low-energy trauma (a ground-level fall), whereas the other two patients had sustained a knee dislocation while participating in a sport. Of the remaining thirteen patients with body-mass indices of =25, only one had a knee dislocation that was due to a simple fall, whereas the mechanism of injury in the other twelve patients was either a motor-vehicle accident or a sports injury.
A recent review by Johnson et al.10 provides a summary of the vascular injury risks that can be associated with ligamentous injuries of the knee. Twaddle et al.11 reported vascular injuries in 15% of patients who had a low-velocity injury, although all of these injuries were associated with sports and were not ground-level falls associated with obesity. Although the exact prevalence of arterial injury is not well documented, Johnson et al.10 commented that the overall popliteal artery injury rate was 23% and 32%, respectively, of all patients in the two largest studies on knee dislocation12,13.
It is important to note the timing of revascularization in the case of our patient. Early recognition of the pulseless extremity is paramount, and, in the case of our patient, recognition at the outside institution allowed for salvage of the lower extremity. Green and Allen12 reported an 87% salvage rate of the extremity when revascularization occurred within eight hours after the injury. In contrast, there was an amputation rate of 85% when revascularization was attempted more than eight hours after the injury.
Current literature would suggest that obesity is a risk factor for unusual complications after a low-velocity knee dislocation. Low-velocity knee dislocations occur infrequently, yet the increasing number of reported cases may indicate that this injury is becoming more common. It is well known that the obesity epidemic is increasing at a substantial rate for adults, and we are now seeing the effect of this epidemic on our adolescent population. A search of the current literature revealed three reported cases of low-velocity knee dislocations in obese, young individuals (ages nineteen, twenty-two, and twenty-six years)3,7,8.
Obesity-related disorders in pediatric orthopaedics include slipped capital femoral epiphysis, Blount disease, and femoral retroversion. As the proportion of overweight adolescents increases, we need to be aware of the associated orthopaedic problems that can occur in these individuals. Injuries that were once thought to occur only as a result of high-velocity accidents are now being seen after simple ground-level falls. Obesity complicates the entire process of patient care. Some difficulties include compromised vasculature, longer rehabilitation, slower healing time, and unavailability of properly sized, necessary equipment2,5,14. More importantly, obesity may cause other comorbid health concerns at the time of injury or later in life. A study done by Brown et al. evaluated the posttraumatic outcomes in obese children and adolescents at an urban, level-I trauma center from 1998 to 200314. Although there was no significant difference in mortality, obese children had more complications, including sepsis, wound infections, postoperative fistulas, increased days on ventilator support, and longer stays in the intensive care unit. Furthermore, obese children may have preexisting comorbid conditions such as asthma, insulin resistance, and even cardiovascular disease, all of which further complicate outcomes after injury14.
The case of our patient highlights the association of obesity and low-velocity knee dislocations and helps to raise awareness of the fact that obesity is increasing in the adolescent population. A knee dislocation such as the one presented in this case report may be just the beginning of a lifetime of obesity-related health problems. Until we address the issues that are causing obesity in our youth, those in the orthopaedic and pediatric arena must be aware of the injuries that may occur.