Reinjury rates after acute hamstring injuries are reported to range from 14% to 63% within the same playing season or up to 2 years after the initial injury. Despite relatively high reinjury risk after hamstring injuries, there is a lack of exact knowledge about their severity, location, and timing. Thus far, the location and severity, in terms of the radiological extent, and the timing of MRI-confirmed reinjuries compared with MRI-confirmed index injuries have not been described.
The purposes of this descriptive study were to investigate the location, radiological severity, and timing of reinjuries on MRI compared with the index injury.
Between January 2011 and June 2014, athletes with acute onset of posterior thigh pain were consecutively recruited. Within 5 days after injury, the treating sports medicine physician performed standardized comprehensive patient history taking and clinical examinations, including pain with hamstring range of motion testing, pain with manual muscle resistance testing, active slump test, and pain with palpation. MRI scans of the hamstring muscle were obtained from the ischial tuberosity to the knee using a 1.5-T magnet system with a body matrix coil. A single experienced radiologist with >10 years of experience within musculoskeletal radiology assessed and scored the MRI scans and determined the localization and extent of the injury using a standardized scoring form. The number of days until registered return to sports (RTS) was provided by the club medical staff was registered.
Reinjury was defined as acute posterior thigh pain occurring during training or competition in the same leg as the index injury within 1 year after RTS from the index injury, confirmed by clinical evaluation and MRI showing increased signal intensity on fluid-sensitive sequence. MRI examinations were reviewed and scored by the same radiologist using the same scoring form as for the index injury, while he was blinded for the index injury scorings. To determine the location of the reinjury, axial and coronal views of the index injury and reinjury were directly compared on PDw-FS–weighted images and scored as (1) same muscle and same location within the muscle, (2) same muscle but other location within the muscle, and (3) different muscle.
A total of 180 athletes with a clinical diagnosis of acute hamstring injury were included in the study. Nineteen reinjuries were included in the analysis. The athletes who sustained a reinjury were football (n = 18) or futsal (n = 1) players, with a mean age of 26 ± 5 years, weight of 75 ± 8 kg, and height of 179 ± 7 cm.
The median time to RTS after the index injury was 19 days (range, 5-37 days). The median time between the index injury and reinjury was 60 days (range, 20-316) and the median time between RTS after the index injury and the reinjury was 24 days (range, 4-311). More than 50% of reinjuries occurred within the first 25 days (4 weeks) after RTS from the index injury (n = 10) and 70% of reinjuries occurred within 100 days. In the first 6 weeks (42 days) after the index injury, all of the reinjuries occurred in the same location as the index injury.
The biceps femoris muscle was the most commonly injured muscle and was involved in 95% of index injuries (n = 18) and 79% of reinjuries (n = 15). Of the 19 reinjuries, 79% occurred in the same muscle and same location within the muscle as the index injury. The most common anatomic location within the muscle was the musculotendinous junction (n = 13; 68.4%), followed by the conjoint tendon (n = 4) and muscle belly (n = 2).
MRI severity grading revealed that 73.6% of reinjuries showed similar severity or were more severe than the index injury. Of the more severe reinjuries (37%), all occurred in the same location as the index injury. The reinjuries with more extensive craniocaudal length and greater extent of edema occurred earlier after the index injury.
The authors concluded that the majority of hamstring reinjuries occurr in the same location as the index injury, and these reinjuries happened relatively early after RTS and with a radiological greater extent. The findings suggest that although the athletes were clinically recovered after their index injury and were cleared for RTS, biological and/or functional healing of the index injury might not be fully completed, leading to a reinjury at the index injury site. Specific exercise programs focusing on reinjury prevention initiated after RTS from the index injury are therefore highly recommended.