Hamstring muscle strain injury caused by isokinetic testing.

The patient was a 25-year-old (height: 183 cm, weight: 86 kg) professional rugby league winger. He had suffered a recurrent episode of a left hamstring (biceps femoris) injury at a training drill late in the season (Day 0). This occurred suddenly while changing direction at pace. The player felt the degree of pain when injured to be very similar to his previous episode earlier in the season, which had taken 2 weeks to resolve. The initial clinical signs were consistent with a routine low-grade hamstring strain, with local tenderness in the midlateral hamstring and moderately decreased stretch and power on the left side compared with the right. He was ruled out for a scheduled match on Day 1. On Days 2–3 the player did not undertake any running activity and was treated with physiotherapy and ice. Over this period the player was pain free on walking. On the morning of Day 4, the player had an MRI scan that confirmed a grade 1 strain of the left biceps femoris muscle (Figure 1). The length of the right hamstring was visualized by the scan and was normal. On the afternoon of Day 4, the player underwent a concentric and eccentric bilateral isokinetic strength test using a KinCom dynamometer (Chattecx; Chattanooga, TN, U.S.A.). He had no previous experience with using this machine. The initial protocol was to test endurance and was performed in a seated position with a slow acceleration phase. There were 15 repetitions bilaterally of knee extension and then flexion at 180° per second. He completed this section of the test, but felt mild pain when testing his left hamstring and mild-to-moderate pain when testing his right hamstring muscle. He had not previously injured the right hamstring. Due to the pain, he did not undergo a maximal peak torque test that was planned to follow. After the test he felt pain on walking in both hamstring muscles and felt as though the test may have worsened his left hamstring strain and also caused a similar injury in his right hamstring muscle. The results of the testing are detailed in Table 1. On day 5, examination revealed very similar findings in the right and left hamstring muscle, with local tenderness, slightly reduced stretch, reduced power on clinical examination, and pain on resisted contraction. He continued physiotherapy treatment and ice, but was not prescribed nonsteroidal antiinflammatory drugs (NSAIDs). At this stage, the diagnosis was resolving left hamstring strain and probable muscle soreness in the right hamstring following the isokinetic testing. On day 7 the player attempted a light jog and felt sore in both hamstring muscles. Because of this symptom, he was told not to attempt further running and was ruled out of the weekend’s match, scheduled for day 10. On day 14 the player underwent an MRI scan, which showed signs of the original left hamstring strain with signal intensity that was markedly reduced. It also showed an unexpected finding of a strain of the right hamstring muscle of much greater signal intensity than the left side (Figure 2). The right hamstring strain involved 20% of the cross-sectional area of the semitendinosus muscle over a distance of 10 cm. On day 17 (17 days after the left hamstring injury and 13 days after the right hamstring injury) he successfully played a match, and had no further incidence of hamstring injury for the remainder of the season.