Adductor Strain

The hip adductors are a powerful muscle group. They consist of the adductor magnus, minimus, brevis, and longus. The gracilis and pectineus muscles also are included. All of the adductor muscles are innervated by the obturator nerve (L2-L4) except the pectineus, which is innervated by the femoral nerve (L2-L4). The adductor magnus also is innervated by the tibial nerve (L4-S3). ^{[5, 6, 7]}

The origins and insertions of each of the hip adductors are noted below:

• Adductor magnus/minimus: origin is the inferior pubic ramus/ischial tuberosity; insertion, linea aspera/adductor tubercle

• Adductor brevis: origin is the inferior pubic ramus; insertion, linea aspera/pectineal line

• Adductor longus: origin is the anterior pubic ramus; insertion, linea aspera

• Gracilis: origin is the inferior symphysis/pubic arch; insertion, proximal medial tibia

• Pectineus: origin is the pectineal line of pubis; insertion, pectineal line of femur

The musculotendinous junction is thought to be the most common site of injury in a muscle strain. Studies in muscle physiology demonstrate that the sarcomeres near the junction are less elastic than those found at the central portion of the muscle. ^[8]

The adductor tendons have a small insertion area that attaches to the periosteum-free bone. This transitional zone is characterized by a poor blood supply and rich nerve supply, explaining the high level of perceived pain and poor healing characteristics of adductor strains.

The musculotendinous junction is likely to be vulnerable to indirect muscle injury that results from excessive force. Muscle strain injury has been characterized as occurring in response to forcible stretching of a muscle, most commonly while the muscle is activated. When the muscle is activated, muscle strain injury occurs, most often during eccentric (lengthening) contraction.

Injury to the hip adductors most commonly occurs following forced push-off (side-to-side motion). An extreme amount of stress is placed on the adductor tendons when, because of the athlete's momentum, a large amount of force is applied to one side in the sagittal plane and the adductor muscles must contract rapidly to shift the force to the opposite direction.

Rapid adduction of the hip against an abduction force (eg, changing direction suddenly in tennis), acute forced abduction that puts an unusual stretch on the tendon (eg, a rugby tackle), and a sudden acceleration in sprinting are the most common mechanisms of injury. Jumping is involved to a lesser extent than abduction and is associated more commonly with hip flexor strains. Overstretching of the adductor tendons is a much less common cause. ^{[9, 10, 11]}

Failure to stretch the adductor muscles properly puts them at increased risk for injury. Weakness of the adductor muscles is a common problem that puts these muscles at increased risk for injury, as the load to failure is much less in weaker muscles.

A systematic literature review by Ryan et al indicated that for participants in field-based sports, those who have sustained a groin/hip injury are at the greatest risk for future injuries of this type. The report, based on seven high-quality studies, identified 11 significant risk factors for groin/hip injuries in field-based sports. In addition to previous injury, the next most prominent risk factors were older age and weak adductor muscles. ^[12]

Similarly, a prospective cohort study by Mosler et al indicated that in male professional soccer players, the risk of groin injuries is increased in relation to previous groin injuries and abnormally high or low eccentric adduction strength. The investigators found that the hazard ratio (HR) for hip/groin injury is raised to 1.8 when previous hip/groin injuries have occurred and to 1.6 in association with higher than normal eccentric adductor strength. Additionally, lower than normal eccentric adductor strength is linked to an HR of 1.7 specifically for adductor-related injuries. However, the study also found that these factors are not strongly enough associated with likelihood of injury to identify whether a specific individual is at risk of injury. ^[13]

A study of 110 male athletes with sports-related acute groin pain (66% of whom had adductor injuries) found that change of direction was the most common cause of the injury in most sports (31%), although in soccer, kicking was the most frequent mechanism (40%). Of adductor injuries, imaging showed the adductor longus to be involved in more than 90% of cases. ^[14]

Muscle strain is the most frequent injury observed in sports. Up to 30% of office visits in a primary care sports medicine practice are attributed to muscle strain. As with other musculotendinous injuries, increased age is related to elevated risk for strains due to reduced elasticity of connective tissue.

Scandinavian soccer studies have reported groin injury rates of 10-18 injuries per 100 soccer players each year. Lovell studied 189 cases of chronic groin pain in which he attributed 30% to adductor injuries. ^[15] The Renstrom and Peterson study found the adductor longus was responsible for 62% of groin injuries. ^[16] Injuries to the groin account for 5% of all soccer injuries and 2.5% of karate injuries.

An epidemiologic study by Eckard et al reported that among student athletes in the National Collegiate Athletic Association (NCAA), for the 2009/2010-2014/2015 academic years, 1.29 hip adductor strains occurred per 10,000 athlete-exposures (AEs), including 1.71 per 10,000 AEs in men and 1.15 per 10,000 AEs in women. ^[17]

Sex

According to a literature review by Orchard, moderate evidence suggests that among men and women playing the same sport, the risk of groin injury is greater in males. ^[18]

Improper management of acute adductor strains or returning to play before pain-free sport-specific activities can be performed may lead to chronic injury. According Renstrom and Peterson, 42% of athletes with groin muscle-tendon injuries could not return to physical activity after more than 20 weeks following the initial injury. ^[16] This prolonged length of time seems to indicate the importance of proper management of these injuries in the acute stage.

In a study of 81 adult male athletes, Serner et al reported that following acute adductor injury, a longer period before return to sport is most strongly predicted by palpation pain at the proximal adductor longus insertion, a palpable defect, and/or, as found on MRI, a bone-tendon junction injury. ^[19]

Another study by Serner et al found that in adult male athletes with acute adductor injury who were treated with a supervised, standardized, criteria-based exercise rehabilitation program, the period of time for return to sport did not statistically differ between those with an MRI-based grade 0, I, or II injury. It took a median 13 days for the athletes with grade 0-II injuries to achieve a clinically pain-free state, while controlled sports training for these individuals was completed in a median 17 days, and a return to full team training took place in a median 18 days. Athletes with a grade III injury (complete tear/avulsion) reached these milestones in a median 55, 68, and 78 days, respectively. ^[20]

An additional study by Serner and colleagues found that in male athletes with acute adductor injuries, progress gained through rehabilitation was only roughly revealed through repeated measures of adductor strength, flexibility, and palpation pain. The investigators reported that measurements involving the extent of palpation pain, the bent-knee fall-out test, hip abduction range of motion, and eccentric hip adduction strength could not “define a precise recovery point during rehabilitation.” ^[21]

The patient needs to be educated on proper treatment following an acute groin injury. PRICE (protection, rest, ice, compression, and elevation) needs to be emphasized to ensure that swelling is reduced. In the acute stage, inform patients to avoid activities that may be harmful and to promote increased blood flow to the adductor muscles by use of hot packs, hot showers, or massage. The athletic trainer and/or physical therapist should instruct the patient in proper exercises to rehabilitate the adductor muscles and enable the patient to return safely to participation in a sport or activity.

As is the case in many injuries involving athletes, outside influence on the physician to return the athlete to play before being medically ready can be a problem. The best interest of the player must take precedence in this situation. Returning players with an adductor injury to their sport too quickly can have a detrimental effect on a future career. Adductor injuries have a tendency to become chronic when not properly treated.

For excellent patient education resources, visit the Sports Injury Center, as well as Muscle Strain.