Diagnostic Ultrasound of the Hamstring Muscle Group
In some sports, the hamstrings injuries represent the most common non contact injury (Opar, 2012). They are especially common in Australian football, American football, rugby, soccer and sprinting. Acute hamstring injuries represent a spectrum of strains (grade 1) to full thickness tears (grade 3) all of which may be sonographically evident. More chronic or subacute injuries may involve proximal or distal tendinopathies, pes anserine bursitis or ischial bursitis. Hamstring injuries are associated with lost time from training, competition and diminished athletic performance (Verrall, 2006). They also result in financial loss for the athletes and organization (Woods, 2002). They are most commonly characterized by posterior thigh pain and the athlete can often describe the specific step or jump when the injury occurred.
Introduction
Image 1: Anatomy of the hamstring muscles (adopted from Balius et al 2019)
It is important to properly understand the anatomy prior to any sonographic evaluation. The hamstring is composed of three muscle groups: the semimembranosus (SM), semitendinosus (ST), and biceps femoris (BF) muscles. All three muscle groups arise from the ischial tuberosity with the exception being the short head of the biceps femoris originating from the linea aspera of the femur. The hamstring muscles split proximal to the popliteal fossa. The SM and ST attach on the medial side of the tibia while the BF attaches laterally to the head of the fibula. The proximal muscle mass of the hamstrings is composed of the BF laterally and ST medially while the SM increases in mass more distally.
The long head of BF is approximately 6-9 cm long, a part of which is the so-called ‘free tendon’ which is about 5 cm in length (Balius, 2019). The ST has a ridge in the middle, separating it into two seperate muscle units with separate innervations of the sciatic nerve. The proximal aponeurosis of BF and ST form the conjoint tendon, which is one of the most susceptible anatomy areas and sonographically significant for this reason. The sciatic nerve courses along the BF.
The hamstring is a diarthrodial muscle group, meaning it crosses both the hip and the knee. At the hip, the hamstrings are responsible for hip extension. At the knee, they muscle groups are responsible for knee flexion. With the knee in flexion, the SM and ST can provide some medial rotation while the BF can provide some lateral rotation of the knee.
Ultrasound
The patient is evaluated in the prone position. In most patients, the linear (superficial) probe is ideal and should be adequate, however you may need to switch to either curved or phased array probe for patients with more significant muscle mass or adipose tissue. Views should be obtained in short and long axes. Dynamic scanning should be performed. Comparison to the contralateral limb should be considered as a reference.
In general, it is important to be systematic in your approach to a sonographic hamstring evaluation when possible. Jacobson recommends starting at the triangular section of the SM and moving laterally (Jacobson, 2012) while Bianchi eta suggest identifying the same section and moving distally (Bianchi, 2007). Other approaches have also been suggested. Although none are likely “best” or “correct”, the key is identifying your landmarks in a structured manner and this brief review will present one such approach. Note that ultrasound of the posterior thigh is challenging and requires practice. This overview is meant to outline some of the basic views and structures sonographers should be looking for but is not a comprehensive review of the entirety of structures and findings.
Proximal Thigh/ Origin
Image 2. Ultrasound of proximal Thigh. Structures of interest: Ischial tuberosity and bursa, muscles (BF, SM, ST), ST tendon, sciatic nerve (SCN), conjoint tendon (adopted from Balius et al, 2019)
The starting landmark is typically the ischial tuberosity. The ischial bursa typically appears with a hypoechoic line overlying the ischial tuberosity. The ST sits above the ischial tuberosity, with the long head of BF more laterally. The conjoint tendon is easily found between the BF and the SM and can be considered a reference area if disoriented. The sciatic nerve (SCN) may be seen posterior to the BF. The conjoint tendon (superficial), lies over the medial SM and lateral SCN forming the triangle of cohen. Glute Max is overlying the majority of the structures.
Mid-Proximal Thigh
Image 3. Ultrasound of mid proximal thigh. Structures of interest: BF long head, ST muscle, SM tendon, SCN (adopted from Balius et al, 2019)
Probe is moving distally and medially. SM is visualized to increase in size moving distally and become oval in shape, while ST decreases. SM is superficial and lateral to ST. Adductor Magnus is also visualized deep to these structures. The probe can be moved medially to find BF and SCN.
Distal Lateral Thigh
Image 4. Ultrasound of distal lateral thigh. Structures of interest: BF long head, ST muscle, SM tendon, SCN (adopted from Balius et al, 2019)
Moving distally, the sciatic nerve can be used as a reference point. The short head of BF will come into focus, which distinguishes proximal and distal hamstring injuries.
Distal Medial Thigh
Image 5. Distal medial thigh. Structures of interest: ST, SM (adopted from balius et al, 2019)
Along the medial side, the ST and SM can be visualized as they move towards the medial tibia. The SM becomes increasingly prominent. The gracilis and sartorius muscles may be visualized as the insert into the pes anserine along with ST.
Read more: http://wikism.org/Hamstring_Strain
REFERENCES
[1] Opar, David, Morgan Williams, and Anthony Shield. “Hamstring strain injuries: Factors that lead to injury and re-injury [accepted manuscript].” (2012).
[2] Balius, Ramon, et al. “Sonographic landmarks in hamstring muscles.” Skeletal radiology (2019): 1-9.
[3] Jacobson JA. Chapter 6: Hip and thigh ultrasound. In: Fundamentals of musculoskeletal ultrasound. Philadelphia: Elsevier Saunders; 2012. p. 223–83.
[4] Bianchi S, Martinoli C. Chapter 13: Thigh. In: Bianchi S, Martinoli C, editors. Ultrasound of the Musculoskeletal System. Berlin Heidelberg: Springer-Verlag; 2007. p. 611–36.
[5] Verrall GM, Kalairajah Y, Slavotinek JP, et al. Assessment of player performance following return to sport after hamstring muscle strain injury. J Sci Med Sport 2006 May; 9 (1-2): 87–90
[6] Woods C, Hawkins R, Hulse M, et al. The Football Association Medical Research Programme: an audit of injuries in professional football-analysis of preseason injuries. Br J Sports Med 2002 Dec; 36 (6): 436–41
Dr Mederical Hall US video: https://www.youtube.com/watch?v=-aPqbpS8VAE
