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What is the diagnosis?

Left hamstring origin avulsion

• Pearl: The semimembranosus originates from the superolateral facet of the ischial tuberosity (Image 2). The semitendinosus and long head of the biceps femoris form a common tendon origin that is attached at the superomedial facet of the ischial tuberosity, called the conjoint tendon [1]. Acute proximal hamstring tendon injuries can include avulsion or complete or partial tearing; these should be differentiated from chronic degenerative tears, proximal hamstring tendinopathy, and tearing within the muscle body [2,3].

Image 2. MR hip bilateral w/o contrast, labeled to demonstrate injury compared to normal on contralateral side. Case courtesy of Dai Roberts, Radiopaedia.org, rID: 78009

What is the mechanism of injury?

Injury to the hamstring origins most commonly occurs when forcible hamstring contraction results in excessive eccentric overload to the hamstring, typically an event with forced hip flexion and the knee extended. Before fusion of the ischial apophysis, this sudden forcible contraction most often will cause avulsion of the apophysis itself.

• Pearl: In a skeletally mature patient in which the apophysis has fused, the avulsion is more likely to occur at the interface between the tendon and bone, and ischial avulsion fractures are rare [2, 4-6].

What physical exam findings are expected?

Examination typically reveals tenderness and ecchymoses to the posterior hip and posterior proximal thigh. There will likely be weakness to resisted knee flexion [6].

Which imaging modalities can be used?

Plain radiographs of the pelvis and lateral hip should be used initially, particularly in younger patients, to look for avulsion fractures.

• Pearl: If x-ray imaging is normal and there is still concern for significant hamstring injury, MRI is then needed to visualize tendinous injury [6]. This can be done on an outpatient basis.

What is the initial management and next steps? Should Orthopedics be involved?

In the ED, unless there is concern for rapidly expanding hematoma or other acute complications, management generally consists of pain control and patients can be advised to modify activity as necessary for pain level and use ice and NSAIDs. It is recommended to obtain Orthopedic Surgery follow up, as a proximal avulsion is generally a surgical indication, especially in higher level athletes. Delay of repair makes the surgical procedure more technically challenging and may produce worse functional outcomes [3]. Data has shown nonoperative treatment results in a lower rate of return to play, reduced functional ability, and lower patient satisfaction scores [1,2]. However, research comparing outcomes between operative and nonoperative management is lacking, and shared decision making is an appropriate strategy [7].