Ultra-low-velocity knee dislocations

Reports of low-velocity knee dislocations have focused primarily on dislocations occurring during athletic competition. The authors identified a subset of patients with low-velocity knee dislocations that occurred during activities of daily living, such as stepping off a curb, stepping off a stair, or simply falling while walking (ultra-low-velocity dislocations).

Ultra-low-velocity knee dislocations are common in obese individuals and are associated with more complications than high-velocity knee dislocations.

Case series; Level of evidence, 4.

A review of records identified 17 patients with knee dislocations that occurred during daily activities. All 17 were clinically obese, with an average body mass index (BMI) of 48 (BMI <25 is normal; ≥40 is severe obesity). Ligament injuries occurred in all 17 patients, neurologic injuries in 7, and popliteal artery injuries in 7. Thirteen (76.4%) of the 17 dislocations were anterior, 2 (11.8%) were posterior, and 2 (11.8%) were lateral. All dislocations were reduced closed and stabilized with splints, crossed pins, or external fixation; ligament reconstructions were done in 8 patients and popliteal artery repairs in 7. Above-knee amputations were required in 2 patients with vascular repairs because of tissue ischemia; 1 patient died from cardiac arrest 7 days after injury; and 3 were lost to follow-up. Of the 11 remaining patients, 6 had ligament reconstructions and 5 did not.

Four standardized knee scoring systems (International Knee Documentation Committee [IKDC], Hospital for Special Surgery [HSS], Lysholm, Tegner) were used to evaluate outcome at an average follow-up of 28.5 months. Although scores were low in all patients, those with ligamentous reconstruction had better outcomes ("fair": 74 ± 22) than those without reconstruction ("poor": 21 ± 8.5), with a statistically significant (P = .013) difference in HSS scores. Lysholm scores also were higher in those with reconstruction (average 67) than in those without (average 53), but the difference was not statistically significant (P = .45).

These results indicate that (1) neurovascular injuries are frequent with these ultra-low-velocity dislocations in severely obese patients, (2) the likelihood of combined neurovascular injury tends to increase as BMI increases, and (3) surgical ligament reconstruction with emphasis on posterolateral corner repair appears to improve outcomes.