While stress injuries in general are a common occurrence in athletes, adductor insertion avulsion syndrome (AIAS) is a rare diagnosis along the stress injury spectrum. Analogous to shin splints, or medial tibial stress syndrome, AIAS is related to avulsion forces of the adductor muscles on the mid to proximal posteromedial femoral diaphysis resulting in periostitis and osseous stress reactions (1–5). This condition is most commonly seen in athletes and military personnel and also demonstrates a preponderance for the female population and those with short stature (1,3,5–7).
A 21-year-old healthy, right hand dominant, Division I collegiate female tennis player presented to the athletic training room with the complaint of left anterior thigh pain. She stated that the pain was most notable when landing from a serve, and she rated the pain as a 6/10. She denied pain in her left hip or knee and denied any previous history of hip or knee injuries. On examination, no swelling, ecchymosis, or gross deformities were noted. The range of motion in her bilateral hips and knees were within a normal range and pain-free. Manual muscle testing noted 4+/5 strength in bilateral hip flexion, knee flexion, and knee extension, while 4/5 strength was noted bilaterally with hip internal and external rotation. A four-view radiograph series of the left femur, including separate anteroposterior (AP) views of the proximal and distal femur, a lateral view, and an oblique view were ordered by the team physician. These images did not demonstrate any cortical defects, periosteal reaction, soft tissue swelling, or bony masses.
The athletic training staff provided the athlete with hip and core strengthening exercises and modified her weight room activities to avoid jumping and plyometric exercises. In the first 10 d, the athlete was noncompliant with performing the prescribed hip and core exercises. The athlete electively sat out the next tennis match but competed in a doubles match later that week. Following the match, the athlete reported worsening pain in the left thigh, which was exacerbated by walking. She was provided with crutches for ambulation and referred to the team physician for further evaluation.
At her evaluation in an outpatient orthopedic clinic, she denied any specific traumatic events and reported gradual onset of pain in the left thigh, which tended to be worse when participating in serving drills. The patient related the pain to jumping off of and landing on her left lower extremity. Per the coaches and athletic training staff, the athlete had an average jump height during her serve, and they did not note any specific abnormalities associated with her serve. She denied any pain at rest and was initially asymptomatic with walking and running but was now reporting pain with all weight-bearing activities including walking. The patient denied any other complaints. She reported having normal menstrual cycles and denied any history of stress fractures. She had been focusing solely on competitive tennis for 6 years and had been practicing with the tennis team for approximately 12 hr·wk−1. The athlete’s training also included full body resistance training for 1 hr twice per week, which included plyometric training.
Physical examination at that time revealed a well-appearing woman, in no acute distress. No erythema or ecchymosis was observed on visualization of the left thigh, and no increased warmth to touch was noted over the affected area. Tenderness to palpation was elicited along the medial aspect of the left femur without palpable mass or defect in the surrounding soft tissue. The patient had negative fulcrum and tuning fork tests, but had pain noted on the hop test. Pain was reproducible with resisted left hip flexion and adduction. The patient had normal, pain-free range of motion on internal and external rotation, with a negative flexed abduction external rotation (FABER) and flexed adduction internal rotation (FADIR) testing of the left hip. The left lower extremity was well perfused and neurologically intact.
Based on physical examination findings, it was suspected that the patient had a muscular strain of either the quadriceps or adductor group, but due to recent worsening of symptoms and pain present with walking, magnetic resonance imaging (MRI) was ordered to rule out a femoral stress reaction and expedite the patient’s return to competitive tennis. Magnetic resonance imaging of the left femur without contrast showed mild periosteal edema of the medial mid-femoral diaphysis with mild patchy marrow signal in the underlying femoral diaphysis (Figs. 1, 2). These findings were consistent with AIAS. Relative rest was recommended, and the patient was allowed to continue her tennis training as long as she remained asymptomatic.
The patient used crutches for 5 d, during which time she was restricted to ground-based abdominal workouts and stationary biking and remained asymptomatic with these activities. She was then able to return to full weight-bearing ambulation without issue. She was instructed to continue to avoid plyometric exercises over the following 2 wk, and gradually progressed thereafter under the supervision of the athletic training staff with emphasis placed on proper mechanics and core strengthening. The patient was then returned to full competition approximately 4 wk after initial presentation and completed the remainder of the season without recurrent symptoms.
Adductor insertion avulsion syndrome (thigh splints) is an overuse condition which develops because of repetitive microtrauma from tractional forces on the femoral diaphysis, which are related to forceful muscular contractions. These injuries are often associated with poor biomechanics and other risk factors including hip adductor weakness, hip adductor to abductor muscular imbalance, history of a previous groin injury, higher level of competitive play, and less sport-specific training (1,2,7,8). Our athlete in this case was noted to have a moderate drop into knee valgus during a single leg squat as well as hip adductor weakness which was noted to be 4-/5 on manual muscle testing, which may have contributed to her injury. Adductor insertion avulsion syndrome is an early finding along the stress injury spectrum, which may develop into a stress reaction or stress fracture if left untreated (1–6).
Radiographs may demonstrate periosteal reaction later in the injury process, but are usually unremarkable at earlier stages in the condition (1–3,5–7). The MRI findings often show increased signal intensity in a linear pattern along the cortex of the proximal to mid femoral diaphysis on T2-weighted sequences, consistent with periostitis and periosteal edema (2,3,5–7). Depending on the duration and severity of the condition, increased bone marrow signal intensity suggestive of stress reaction or stress fracture may be visualized. Stress fractures in the femoral diaphysis often present in an oblique orientation (1,6,7).
Nuclear bone scintigraphy also can be a useful imaging modality in AIAS, which can demonstrate abnormal elongated linear uptake along the medial cortex of the proximal third of the femur (2,3,5,7). Ultrasound also has been reported as a useful adjunct in the diagnosis of AIAS, although it requires an experienced ultrasonographer. Ultrasound may demonstrate cortical irregularities, hypoechoic soft tissue, and hyperemia in the affected region (3,5).
A broad differential diagnosis should always be considered by the clinician assessing a patient with presumed AIAS, as the clinical and imaging findings also can be associated with osteomyelitis, Ewing’s sarcoma, or osteoid osteoma (1–4,6,7). The absence of soft tissue masses, osseous destruction, and abnormal signal intensity on T1-weighted images opposes the diagnosis of infection or neoplasm (1,6).
When AIAS is suspected, it is reasonable to prescribe a trial of relative rest, which will typically lead to the resolution of symptoms within 1 to 2 months (1,3,5,6). The athlete may progress with activity as tolerated, focusing on core strengthening, flexibility, and improved biomechanics to avoid recurrence of symptoms. In patients with persistent or worsening symptoms, it would be recommended to pursue repeat advanced imaging, or even consider the possibility of performing a biopsy to rule out infection or neoplasm (3,4).
Although AIAS is an uncommon diagnosis, which may be underrecognized due to subtle findings on clinical examination and imaging, it should be considered in the differential diagnosis of an athlete with persistent medial thigh pain. As with most stress-related overuse injuries, AIAS typically resolves within a matter of 4 to 8 wk of rest and appropriate conservative treatment (1,3,5,6). Any lasting or worsening symptoms should prompt further investigation into more ominous disease processes (1–4,6,7).
The authors declare no conflict of interest and do not have any financial disclosures.
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