Femoroacetabular impingement (FAI) can occur when osseous abnormalities of the femur or acetabulum are coupled with vigorous or terminal motion of the hip.1 Abnormalities can be of the proximal femoral head (cam type), of the acetabular rim (pincer type), or a combination of both, which is seen most commonly. The movement of the femoral head within the acetabulum is limited in FAI, potentially resulting in injury to the labrum and cartilage of the hip joint and leading to early osteoarthritis of the hip joint.1–5
Because the impingement is often elicited by flexion and internal rotation of the hip, FAI commonly presents in young athletes playing football, soccer, or hockey.2 Although it can be asymptomatic,3 FAI is a major cause of hip and groin pain while also restricting the range of motion of the hip, decreasing athletic performance, and lowering quality of life in these patients.1,2 However, the hip joint is not the only affected structure in FAI patients—other structural abnormalities, such as hip flexor dysfunction2,3 and osteitis pubis,4 have been shown to be associated with FAI. The kinetic chain principle dictates that several anatomic links are activated in sequence to generate force. For the hip, the spine, pubis, core musculature, hamstrings, and pubic symphysis are inextricably linked and aid in human locomotion. An impairment of one kinetic chain element will translate to increasing stress at adjacent segments. A commonly cited example of kinetic chain breakdown leading to “downstream dysfunction” is the relationship of shoulder capsular tightness and subsequent heightened risk of elbow injury.6
Although numerous associations between FAI and other hip girdle pathologies have been reported,2–4,7 there is currently a lack of literature relating FAI to hamstring tendon pathology. The 2 entities may be related because, as mentioned, they are part of the lower extremity kinetic chain. Second, they are both commonly found in young, active athletes and are elicited by the same sorts of motions, namely repeated acceleration and deceleration of the leg during activity.2,7,8 Finally, the decreased range of motion of the hip may cause “downstream” stress on the hamstring muscles during the act of running and pivoting. Therefore, the authors explored magnetic resonance imaging (MRI) and magnetic resonance arthrography (MRA) sequences of patients with known FAI to determine if there was an increased incidence of hamstring tendon pathology in these patients compared with age-matched controls. This information could be useful in identifying subclinical or subtle hamstring tendon pathology in FAI patients.
Materials and Methods
Patient data for the current study were gathered from an original patient search that was aimed at evaluating for an association between FAI and osteitis pubis in a retrospective cohort study, as demonstrated by Phillips et al.5 After institutional review board approval was obtained, patients with FAI were identified via a search through a radiology database within the authors' large, academic health institution. The search was limited to MRAs and MRIs from January 1, 2000, to October 22, 2013, and included the terms “FAI,” “femoroacetabular impingement,” “pincer,” and “cam.” This initial search yielded 203 radiographic reports. One of the authors (N.T.) read these reports and excluded those that did not meet the study criteria. Patients who were at least 18 years old, had a diagnosis of FAI based on MRA or MRI (1.5 T), and had available radiologic images that provided adequate assessment of the hip joint were included. Patients with previous hip surgery or no actual report of FAI were excluded (Figure 1).
Flowchart of the search and selection process for the radiology report adapted from Phillips et al.5 Abbreviations: FAI, femoroacetabular impingement; MR, magnetic resonance; PACS, Picture Archiving and Communication System (Intellispace PACS; Phillips, Amsterdam, The Netherlands).
A total of 93 patients met the criteria for MRI review. Images were reviewed in the Picture Archiving and Communication System (Intellispace PACS; Phillips, Amsterdam, The Netherlands) by a fellowship-trained musculoskeletal radiologist (V.K.) and a musculoskeletal fellow (A.L.G.) to confirm the presence of FAI and further exclude patients with underlying hip dysplasia or severe osteoarthritis. One criterion used to determine the presence of FAI was an alpha angle greater than 55° in cases for which an axial-oblique sequence was available. In addition, other characteristics were used to make a final decision about the diagnosis of cam-type FAI, including an osseous bump at the anterolateral head–neck junction (Figure 2), synovial herniation pits, labral tears, cartilage lesions, subchondral cysts, and subchondral bone marrow edema (Figure 3). Pincer morphology was identified when there was an increase in coverage of the anterior aspect of the femoral head due to acetabular retroversion (a posteriorly oriented acetabulum) that was seen on the axial-oblique MRIs of the hip. Additionally, the presence of a cross-over sign, whereby the anterior acetabulum overlaps the posterior wall, was used to determine pincer morphology.
Radiograph of a 48-year-old man showing bilateral cam-type morphology (single arrows) and superior joint space loss indicating cartilage loss on the right (double arrows).
Coronal fat-saturated proton density magnetic resonance image of the right hip showing a large region of cartilage loss with subchondral edema (arrow) and a labral tear (arrowhead).
Of the 49 patients with FAI who met criteria for the original study, 9 were excluded from analysis for the current study because of poor signal-to-noise ratio on imaging, exclusion of hamstring tendon on radiographic images, unavailable radiographic images, or an inability of the reviewing radiologists to reach consensus regarding the presence or absence of hamstring tendon pathology.5
A group of age-matched controls without radiographic evidence of FAI was identified through the same radiology database. Similar to the FAI patient cohort, subjects were originally evaluated for the presence of osteitis pubis.9 The search included all MRIs of the pelvis from January 1, 2010, to March 11, 2013. The first 47 reports that matched the age distribution and sex of the study patients, as well as all inclusion criteria except the presence of FAI, were included as control subjects. Most of the female controls had had MRIs completed for gynecological indications, whereas most males had been assessed for inflammatory bowel disease or malignancy. Of the 47 subjects in the original control cohort, 2 were excluded from analysis for the current study because of the discovery of a previous injury to the left ischium and an inability to reach consensus.
For the current study, patients in each cohort were evaluated for signs of hamstring tendon pathology (in the same leg affected by FAI) by 2 fellowship-trained musculoskeletal radiologists. Each radiologist separately evaluated the images for hamstring tendon pathology. The radiologists were not blinded to whether the patients had previous FAI or were controls. For cases in which there was a discrepancy, the 2 radiologists reviewed the images together and attempted to reach a consensus. Images were reviewed for signs of pathology, including tendon thickening, intermediate signal changes, partial tears (Figure 4), tears at the origin, or bone marrow edema. Most of the injuries seen involved partial-thickness tears, tendon thickening, and intermediate signal changes. Because of the generally mild degree of abnormalities, hamstring tendon pathology was simply classified as normal or abnormal. Fisher's exact test was used to assess for a statistically significant difference in the occurrence of hamstring tendon pathology in the FAI patient cohort compared with the age-matched controls. In addition, an odds ratio was calculated between the 2 groups to further evaluate for an association between hamstring tendon pathology and FAI. Finally, each subject with FAI was evaluated for osteoarthritis of the hip using the Tonnis classification system, which allowed the authors to evaluate for any association between osteoarthritis of the hip and hamstring tendon pathology.
Axial (A) and coronal (B) fat-saturated proton density magnetic resonance images of the right hip showing small partial tears of the hamstring tendon (arrows).
After inclusion and exclusion criteria were considered, a total of 40 confirmed FAI cases (37 cam type and 3 pincer type) and 45 control cases were included in the analysis. For assessment of hamstring tendon pathology within the FAI patient cohort, MRA (n=17) and MRI (n=23) were the imaging modalities available. Magnetic resonance images were used for the 45 age-matched controls.
The mean age of the patients with FAI (n=40) and the aged-matched controls (n=45) was 35.36 years (range, 20–59 years) and 35.16 years (range, 20–57 years), respectively, yielding a difference that was not statistically significant (P=.9260) (Table 1). Within the FAI patient cohort, 28 (70%) of 40 patients were men and 12 (30%) of 40 patients were women. Of the control cases, 30 (66.67%) of 45 patients were men and 15 (33.33%) of 45 patients were women. The average alpha angle for the FAI patients was 63.79°. Consistent concurrent pathologies noted within the FAI cohort were labral tears (32 of 40, 80%), cartilage lesions (23 of 40, 57.5%), subchondral cysts (18 of 40, 45%), osteophytes (14 of 40, 35%), bone marrow edema (9 of 40, 22.5%), and synovial herniation pits (9 of 40, 22.5%).
Demographics of the 2 Groups
Eleven patients within the FAI cohort (n=40) had confirmed bilateral FAI. For these cases, each side was evaluated as an independent subject in relation to the ipsilateral hip; thus, 40 cases yielded 51 individual subjects. Similarly, in the control cohort, the authors evaluated each side as an individual subject; that is, each hamstring was evaluated independently in each control subject. This methodology was consistent with the authors' hypothesis that FAI affects primarily the ipsilateral kinetic chain, thus predisposing to pathology in the ipsilateral hamstrings.
The authors found a statistically significant increase in the occurrence of hamstring tendon pathology in the FAI patient cohort compared with the age-matched controls (Table 2). Within the FAI patient cohort (51 subjects from 40 patients), the prevalence of hamstring tendon pathology was 41.18% (21 of 51), compared with 7.78% (7 of 90) among the age-matched controls (90 subjects from 45 patients) (P<.001). The odds ratio for hamstring tendon pathology in a subject with confirmed FAI vs control subjects was 8.30 (95% confidence interval, 3.20–21.5), indicating a significant increase in the prevalence of hamstring tendon pathology among subjects with FAI (P<.001).
Hamstring Pathology in the 2 Groups
Regarding osteoarthritis of the hip and hamstring tendon pathology, there does not appear to be a correlation between severity of osteoarthritis per Tonnis grade and the incidence of tendon pathology (Table 3). Subjects with no signs of osteoarthritis (Tonnis grade 0) had the greatest proportion of hamstring tendon pathology (52.6%), followed by Tonnis grade 4 (44.4%), Tonnis grade 1 (33.3%), and Tonnis grade 2 (28.6%). Only 1 subject was graded as Tonnis 3. This subject did not have evidence of hamstring tendon pathology (0%).
Severity of Osteoarthritis of the Hip per Tonnis Grade and the Incidence of Hamstring Tendon Pathology
Femoroacetabular impingement has been associated with other musculoskeletal pathologies, such as osteitis pubis5 and weaker hip flexors and abductor muscles.1 Decreased absolute tensor fascia lata activity on electromyography has also been noted.1 Although an exact mechanism has not been fully elucidated, it has been suggested that FAI causes restricted range of motion in the hip joint,2,4,10 leading to alterations in the kinetic chain and causing increased stress on adjacent links in the lower limb. However, to the current authors' knowledge, there is a lack of data on the association between FAI and hamstring tendon pathology. Therefore, the current authors used a database of MRI and MRA images of patients with known FAI and age-matched controls to determine if FAI was associated with an increased incidence of hamstring tendon pathology. The authors found that while 21 of 51 FAI patients had evidence of hamstring tendon injury on imaging, only 7 of the 90 age-matched controls did, yielding a statistically significant difference (P<.001). Although patients with severe osteoarthritis of the hip were excluded from the study, the authors did include patients with less severe osteoarthritis, which makes this variable a potential confounder in assessing for the relationship between FAI and hamstring tendon pathology. However, the authors' analysis did not reveal any particular trend related to the presence or severity of osteoarthritis of the hip and hamstring tendon pathology in their subjects with FAI (Table 3), which reduces the authors' concern for any confounding between hip osteoarthritis and hamstring tendon pathology. However, the authors think that the current study was not sufficiently powered to fully evaluate for such an association, which should thus be an objective of future studies.
The current findings support a kinetic chain theory of the hip and lower extremity. Femoroacetabular impingement has already been associated with deficits in the pubic symphysis5 and the hip flexors,2,3 presumably due to added load to these structures because of restricted hip motion. Through a similar mechanism, the hamstring would be subject to an increased load because of the restriction in hip motion the cam and pincer lesions place on the movement of the femoral head.1 The current authors' result is further evidence of a kinetic chain phenomenon, where decreased motion of one joint has a direct effect on the function and movement of an adjacent joint. Remarkably, altered range of motion of the hip has been shown to increase shoulder and elbow injuries in throwers.9 Therefore, any sort of impairment of hip function could dramatically affect the stress the hamstring tendon realizes during locomotion and pivoting activities.
Clinically, it is significant that hamstring tendon injury can occur with greater frequency in patients with FAI, and clinicians can provide better anticipatory guidance for patients in terms of return to play. It may also lead to more directed rehabilitation efforts—patients working to recover from FAI injury may benefit from doing hamstring-strengthening exercises as well. Finally, the current findings add to the growing body of literature of the wide association of FAI on other joints and muscles, including the pubic symphysis, the hip flexors, and now the hamstring tendon. In recalcitrant cases of recurrent hamstring injury, FAI should be sought and recognized as a potential risk factor. This may lead physicians to treat FAI more aggressively on initial presentation to avoid strain on other joints and tendons.
This study had several limitations. First, male patients made up 66% of the study population, indicating an uneven sex distribution. Additionally, because the mean age was 35 years, the findings may not reflect the correlation of FAI and hamstring tendon pathology in young or elderly populations. Because there were 131 cases of FAI, the study's power is limited. Because the diagnosis of hamstring tendon pathology was made on imaging only, the clinical significance of the imaging abnormality is not known. Adding follow-up in future studies to determine the degree of clinical impairment caused by the imaging findings would be valuable. Also, several hamstring imaging findings were used to identify hamstring tendon pathology, including both tendinosis and tears of the hamstring tendon. All of the findings were grouped together as hamstring tendon abnormality rather than stratified by type or degree of severity of the lesion. Finally, the radiologists were not blinded to which patients had FAI and which patients were the controls, although 2 independent fellowship-trained musculoskeletal radiologists read the radiographs to minimize bias. The study also carries the limitations that accompany a retrospective study.
Ultimately, in this study, patients with known FAI were more likely to have hamstring tendon abnormalities compared with age-matched controls. This finding may be evidence of a kinetic chain, where limited motion of the hip stresses the hamstring tendon and leads to injury. Clinically, it may be important to consider hamstring tendon pathology when treating patients with FAI.
- Leunig M, Beaulé PE, Ganz R. The concept of femoroacetabular impingement: current status and future perspectives. Clin Orthop Relat Res. 2009; 467(3):616–622. doi:10.1007/s11999-008-0646-0 [CrossRef]
- Diamond LE, Dobson FL, Bennell KL, Wrigley TV, Hodges PW, Hinman RS. Physical impairments and activity limitations in people with femoroacetabular impingement: a systematic review. Br J Sports Med. 2015; 49(4):230–242. doi:10.1136/bjsports-2013-093340 [CrossRef]
- Frank JM, Harris JD, Erickson BJ, et al. Prevalence of femoroacetabular impingement imaging findings in asymptomatic volunteers: a systematic review. Arthroscopy. 2015; 31(6):1199–1204. doi:10.1016/j.arthro.2014.11.042 [CrossRef]
- Kaplan KM, Shah MR, Youm T. Femoroacetabular impingement: diagnosis and treatment. Bull NYU Hosp Jt Dis. 2010; 68(2):70–75.
- Phillips E, Khoury V, Wilmot A, Kelly JD IV, . Correlation between cam-type femoroacetabular impingement and radiographic osteitis pubis. Orthopedics. 2016; 39(3):e417–e422. doi:10.3928/01477447-20160404-03 [CrossRef]
- Garrison JC, Cole MA, Conway JE, Macko MJ, Thigpen C, Shanley E. Shoulder range of motion deficits in baseball players with an ulnar collateral ligament tear. Am J Sports Med. 2012; 40(11):2597–2603. doi:10.1177/0363546512459175 [CrossRef]
- Woods C, Hawkins RD, Maltby S, et al. The Football Association Medical Research Programme: an audit of injuries in professional football. Analysis of hamstring injuries. Br J Sports Med. 2004; 38(1):36–41. doi:10.1136/bjsm.2002.002352 [CrossRef]
- Hamming MG, Philippon MJ, Rasmussen MT, et al. Structural properties of the intact proximal hamstring origin and evaluation of varying avulsion repair techniques: an in vitro biomechanical analysis. Am J Sports Med. 2015; 43(3):721–728. doi:10.1177/0363546514560878 [CrossRef]
- Laudner K, Wong R, Onuki T, Lynall R, Meister K. The relationship between clinically measured hip rotational motion and shoulder biomechanics during the pitching motion. J Sci Med Sport. 2015; 18(5):581–584. doi:10.1016/j.jsams.2014.07.011 [CrossRef]
- Sierra RJ, Trousdale RT, Ganz R, Leunig M. Hip disease in the young, active patient: evaluation and nonarthroplasty surgical options. J Am Acad Orthop Surg. 2008; 16(12):689–703. doi:10.5435/00124635-200812000-00002 [CrossRef]
Demographics of the 2 Groups
|Age, mean±SD, y||35.36±10.11||35.16±10.15||.9260|
|Sex, No. (%)|
| Male||28 (70)||30 (66.67)|
| Female||12 (30)||15 (33.33)|
Hamstring Pathology in the 2 Groups
|Normal Hamstrings||Abnormal Hamstrings||Total|
|Femoroacetabular impingement patients||30 (58.82)||21 (41.18)||51||<.001|
|Controls||83 (92.22)||7 (7.78)||90|
Severity of Osteoarthritis of the Hip per Tonnis Grade and the Incidence of Hamstring Tendon Pathology
|Tonnis Grade||No. of Subjects||No. With Hamstring Tendon Pathology||Percent With Hamstring Tendon Pathology|