Evidence suggests that hip pain may affect up to 15% of the population at any given time (8,9,29). The underlying cause of hip pain is multifactorial, with most conditions having a defined clinical presentation inclusive of both aggravating and alleviating factors. Of the various diagnoses implicated in the etiology of hip pain, femoral acetabular impingement (FAI) has gained considerable attention in the orthopedic and sports medicine professions. The interest in FAI is in part owing to its prevalence among young active adults and well-known prearthritis association (4,11,13). Irrespective of the architectural changes present with the diagnosis itself, individuals with FAI are encouraged to participate in safe and pain-free exercise as a means of mitigating impairments and pursuing fitness attributes.
At some point, strength and conditioning professionals will encounter clients diagnosed with FAI. In these circumstances, the provision of an appropriate training program would seem to be contingent on an awareness of the condition, clinical profile, and biomechanical implications for exercise. Moreover, an understanding of FAI and its clinical presentation provides the strength and conditioning professional with cognitive tools necessary for interdisciplinary communication, and in some cases where a diagnosis may not be established, insight to determine the need for referral to a qualified health care practitioner. Although diagnosis and treatment does not fall within the purview of strength and conditioning professionals, an awareness of high-risk activities known to perpetuate the condition, as well as relevant lower extremity exercise modifications, would seemingly serve useful for providing a safe and effective training program.
The primary purpose of this article is to provide the strength and conditioning professional with insight into the structural pathology, clinical presentation, and impairments ascribed to FAI. In addition, we sought to provide exercise-based modifications that consider impairments associated with FAI and factors responsible for symptom provocation. Accordingly, this article provides insight into the client profile, provocating factors, common impairments, and practical exercise-based modifications specific to FAI. Recommendations are presented in an effort to allay the impairment sequela and promote safe and purposeful training. It is beyond the scope and intent of this article to provide content intended to diagnose or treat FAI, as this should be determined by a qualified health care professional.
There are 3 types of FAI described in the orthopedic literature, which include cam, pincer, and mixed cam-pincer. In cam type impingement, the femoral head is abnormally shaped (nonspherical) (Figure 1A). The nonspherical shape generally appears as extra bone on the anterior aspect (front) of the femoral neck-head junction (shaded in blue, Figure 1A). The altered boney architecture may impinge the labrum and acetabular rim with certain hip positions, such as internal rotation, adduction (crossing legs), or high hip flexion angles as seen with a deep squat (5,22). Figure 1B illustrates the morphological differences seen with a cam deformity (right hip), as compared with a normal left hip from an axial perspective (view from overhead). Although the illustration itself does not depict impingement, one can easily identify the different morphology present in the right hip with a cam presentation. Cam impingement is a known etiological risk factor for injuries to the labrum, femoral head, and acetabular rim (7,24). Cam impingement is prevalent in young males primarily and has a predilection for athletic individuals (5).
The pincer type of impingement is caused by an abnormally shaped or retroverted (surface is rotated backward) acetabular rim (7,24). The abnormal shape, commonly referred to as “overcoverage,” presents structurally as a prominent anterosuperior (front) acetabular rim. This overcoverage, as seen in Figure 2A (shaded in blue), may contact the femoral neck during routine activities creating an impingement that can lead to joint damage (e.g., labral and chondral injuries) (7,24). Specifically, the prominent acetabular rim that defines a pincer deformity may create impingement with certain hip positions that require hip flexion (5), such as a squat (Figure 2B and 2C). As seen in Figure 2B, limited space is present between the pincer deformity on the acetabulum (shaded blue) and proximal femur. Thus, impingement is likely if the squat depth increased or if abnormal movement patterns were present (e.g., hip adduction). In Figure 2C, the squat angle exceeds 90°, which is more likely to cause impingement. Note the hips are slightly abducted to avoid impingement. The pincer type FAI is most prevalent in middle age women, and the impingement itself results primarily in labral damage with only minor involvement to the acetabular rim (18,28). A comparison between the structural morphology of a normal hip as seen in Figure 3 and Figures 1A and 2A illustrates the pathological changes and differences in the boney architecture that occurs with FAI. Finally, mixed cam-pincer impingement occurs when both a cam and pincer deformity are present. Younger males seem to be most susceptible to the mixed cam-pincer impingement (16). Figure 4A illustrates a lateral visualization of the architectural changes associated with a mixed cam-pincer presentation. The structural changes present in Figure 4A are most appreciated when compared with a normal hip in the same visualization plane (Figure 4B).
Although the literature is predominantly focused on structural FAI, impingement is not limited to individuals with morphological changes. Improper movement patterns, such as hip adduction or internal rotation, during loaded flexion (e.g., squat) as seen in Figure 5 place the boney structures of the hip in close approximation, which may incite impingement type symptoms. Similarly, athletic activities requiring extreme range of motion (e.g., gymnastics or ballet) may provoke impingement symptoms in a morphologically normal hip. One could reasonably assert that a normal hip subjected to compulsory end-range positioning or abnormal movement patterns would develop structural changes and ensuing pathology. Moreover, impact type activities in combination with excessive range of motion or abnormal positioning may trigger previously occult FAI, causing these individuals to become symptomatic (5). Therefore, an awareness of the condition and its biomechanical attributes may prevent inappropriate exercise prescription that would otherwise perpetuate the condition.
In a morphologically normal hip, the acetabulum and femoral head articulate as a ball and socket joint to allow unobstructed motion in 3 planes. Movement is achieved through muscle activity, which controls the direction of motion, as well as arthrokinematic movement within the joint. Generally speaking, arthrokinematic movement is the normal gliding that occurs to maintain the femoral head position within the acetabulum. Theoretically, without arthrokinematic movement, the femoral head would be expected to roll off the acetabulum. Figures 3 and 4B illustrate the normal ball and socket configuration of the hip. In the normal hip, end-range mobility is expected to occur without obstruction or restriction, as the joint is designed for unimpeded movement throughout a majority of activities. Unlike individuals with normal hip morphology, those with FAI experience impeded (e.g., obstructed) hip mobility as a result of altered boney architecture.
As previously stated, FAI is caused by morphological changes at either the acetabulum or femoral head-neck junction. These structural changes from an “overbearing” acetabulum (pincer) or an abnormally shaped femoral head (cam) directly impair movement and are responsible for impairments and ensuing pathology. Generally speaking, the anatomical region of the hip joint affected by FAI (cam or pincer) is most often anterior and superior in location with respect to the hip joint as illustrated in Figure 4A. Thus, specific movements (Table 1), which are known to approximate the anterior and superior regions of the hip, are more likely to be aggravating factors. The specific motion loss and degree of pain is variable, based on the extent of structural change, as well as activity demands (e.g., athletic versus sedentary). Although FAI may be an incidental finding in some, it does have the potential to cause considerable secondary joint damage and accelerate osteoarthritic changes.
The importance of recognizing the presentation of FAI extends well beyond the clinical setting. To this point, as it relates to exercise prescription, a lack of awareness or neglecting the condition may lead to joint damage and worsening of symptoms. Although certain clients may have an established diagnosis and present after formal rehabilitation, others may only be cognizant of hip pain with certain exercises or positions. Thus, an awareness of the more common signs and symptoms of FAI may provide the strength and conditioning professional with an opportunity to appropriately modify the exercise prescription. Although it is neither expected nor practical for strength and conditioning professionals to diagnose FAI, an awareness of the condition and its presentation may help with recognition and directing an appropriate referral to a medical practitioner.
The onset of symptoms from FAI is variable and thought to be cumulative or microtraumatic in nature. Clients with FAI often report pain and discomfort in the periarticular hip and groin region when provocation occurs. When prompted to identify the location of pain, these individuals will often exhibit a “C” sign (5) (Figure 6A and 6B) and describe a deep joint pain. On occasion, symptoms may travel (refer) to the anterior or medial thigh (5,21). Clients with FAI may also note audible sounds, such as popping and clicking or even a sense of instability or catching of the hip (5,21,23), which may be the result of a coexisting labral tear or chondral injury. Although a detailed discussion of labral tears is beyond the scope of this article, it should be noted that such injuries often occur as a consequence of FAI. In most cases, symptoms from FAI are aggravated by end-range hip flexion (deep squat), internal rotation (pivoting or turning toward affected hip), and adduction (crossing legs) (1,5,10,12,17,21,28). Moreover, performing dynamic activities with poor lower extremity control (e.g., hip adduction and internal rotation during squat) may also be a provocating source of pain among those with FAI due to the abnormal contact of the femur and acetabulum from this position. From an anatomical perspective, combined hip flexion, adduction, and internal rotation (FADIR) accentuate premature contact between the boney prominence of the femoral head-neck and acetabular prominence (to a greater degree than individual motions) and would most likely be intolerable.
It has been postulated that individuals with FAI often exhibit either a swayback posture or a pronounced anterior pelvic tilt (19–21,26). From a postural perspective, a pronounced anterior pelvic tilt or a swayback would seemingly provoke symptoms from FAI, albeit for different reasons (19,20). Although both conditions are associated with an increased lordosis (hyperlordosis) and seem similar, they are distinctly different. A swayback posture consists of an increased lumbar lordosis with a neutral positioned pelvis and an extended hip joint (Figure 7). With this posture, the line of gravity is shifted posteriorly of the hip joint (note the pelvis/hip is pushed forward with respect to the femur), and it has been suggested that this posture may result in a disuse atrophy and weakness of the gluteal muscles (15). Moreover, a swayback posture is associated with a pronounced thoracic kyphosis as seen in Figure 7. With significant weakness, the gluteal musculature may not properly function to control lower extremity alignment while performing dynamic activities, such as running, jumping (23), or squatting. Failure to control lower extremity alignment may be identified by adduction and internal rotation during the land or flexion component of the squat (Figure 5). It should be noted that posture is not the only factor that may lead to improper function of the gluteal musculature. Individuals with FAI may attempt to compensate for the injured or painful joint. This compensatory response, combined with pain from improper exercise form or positioning, could indeed lead to changes in muscle activity (6,14). In fact, evidence suggests that these individuals may have hip abductor and external rotator weakness of up to 22 and 18%, respectively, when compared with asymptomatic controls (6,14). Thus, it is seemingly important for the individual with FAI to maintain strength and endurance of the gluteal musculature given its role in hip abduction and external rotation (3).
Comparatively, when the pelvis is anteriorly tilted with a hyperlordosis, an approximation between the femoral neck and anterior-superior acetabulum occurs as a result of the hip assuming a mildly flexed position. Thus, a pronounced anterior pelvic tilt with hyperlordosis (Figure 8) would seemingly be a provocative factor leading to or aggravating existing FAI. What constitutes a hyperlordosis is debatable, however, evidence suggests that in young adults, a lordosis of 32° is normal (27). Although it is beyond the scope of this article to describe measurement techniques for evaluating a lumbar lordosis, procedures have been described in the literature using both bubble inclinometer and smart phone applications (27). Moreover, Reynolds et al. (26) suggest that as the pelvis is rotated anteriorly, the functional retroversion of the acetabulum is greater, which can lead to an increased likelihood of impingement occurring at the acetabular rim with activities. Although an exaggerated anterior pelvic tilt combined with end range hip flexion (e.g., deep squats) would cause impingement in a normal hip, the symptoms experienced and mobility obstruction would be more pronounced among those with FAI. Given the relationship between structural impingement and a pronounced anterior pelvic tilt and the potential association between a swayback and gluteal muscle performance, it seems reasonable to promote a more natural postural positioning among these individuals as seen in Figure 9. Moreover, evidence exists to suggest that correction of a swayback posture has a benefit in terms of reduced pain and increased performance among individuals with hip pathology (19,20).
Individuals with FAI have been shown to demonstrate decreased hip range of motion, increased hip pain while performing physical activities, and reduced overall athletic performance (10,25). From a mobility perspective, hip flexion, adduction, and internal rotation will be limited as a result of FAI (3,5,28,32). It is also important to note that insufficient arthrokinematic posterior glide of the femur (on the acetabulum) during hip flexion or internal rotation can be an aggravating factor, as it theoretically positions the femoral head anteriorly in closer approximation to the acetabulum. One might surmise that individuals with FAI may tend to avoid positions of provocation, such as flexion and internal rotation. Avoidance of such motions could theoretically lead to reduced arthrokinematic mobility (posterior glide) and stiffness from adaptive shortening. Stiffness of the hip extensors and posterior joint structures, as well as hyperlaxity of anterior joint structures, may result in excessive anterior glide of the femoral head, based on the femoral head taking the path of least resistance. Excessive anterior glide with posterior stiffness during certain movements, such as flexion, would impair normal movement patterns subsequently fostering premature impingement (17,21).
Individuals with FAI often report pain with prolonged sitting, deep squatting, stair climbing, and athletic activities requiring greater ranges of mobility or movement into end-range positions (17). With squatting, there is no specific range that constitutes “deep,” as it pertains to FAI, particularly as each client may have a different “structural” degree of FAI. Furthermore, poor lower extremity control, such as seen in squatting with hips adducting and internally rotated, will accentuate symptoms as a result of premature FAI. Moreover, specific stretching activities that require end-range flexion with or without internal rotation and adduction may place the hip in an impinged position and subsequently produce pain. Figure 10 illustrates a commonly used piriformis stretch that places the hip in the FADIR position known to promote FAI.
In high-demand sports involving cutting or sprinting, 88% of athletes with FAI reported moderate or total inability to perform the task due to mobility limitations (25). It could be postulated that the loss of mobility is the result of impingement or pain. In addition, squatting, especially at an increased depth, instigates pain provocation of the areas (of the hip) affected by FAI (17,21). In a study by Lamontagne et al. (17), participants with cam type impingement had decreased maximal squat depths compared with asymptomatic participants due to limited sagittal pelvic motion. Although deep squatting is a component of everyday activities, such as getting in and out of cars and tying shoes, it nevertheless places the hip in a position of impingement when FAI is present. Furthermore, other activities may provoke and perpetuate FAI, such as sitting in a low chair, which closely reproduces the movements of a squat. Sagittal plane activities, such as straight walking or jogging, may be tolerated in individuals with FAI, but running may be problematic, as it requires an increased range of motion demand at the hip. It is important to also note that running on an incline may warrant caution and should potentially be avoided as this causes more hip flexion and increases the likelihood of reproducing pain (21). “W” sitting (Figure 11) is also a position that can be detrimental, as it combines the motions of hip flexion and internal rotation, leading to FAI (12). Finally, rotation of the torso toward the symptomatic side during cutting or agility activities may be provocative for individuals with FAI, as it places the hip in internal rotation.
The aforementioned activities and positions represent more common movements and activities known to perpetuate the symptoms of FAI. Although these activities cannot be strictly avoided, most are amenable to modification, which may include at minimum avoiding compulsory performance and restricting movement to preimpingement thresholds. Without early recognition and proper management, FAI can lead to more serious pathology and accelerate the progression of hip osteoarthrosis (4,7,24).
EXERCISE AND ACTIVITY MODIFICATIONS
For individuals with FAI, modifications to exercise form to avoid painful hip positions may serve useful regarding alleviating symptoms, impairments, and the progression to more serious pathology (4,5,12,23,28). Unfortunately, a paucity of research trials exist to support what might be considered the ideal nonoperative management of clients with FAI. Despite uncertainty regarding the most efficacious management strategy, an awareness of the anatomical and biomechanical attributes associated with FAI provides insight into plausible management strategies.
From an evidence-based perspective, case reports and commentary exist to describe both interventions and modifications. Interventions, such as resistance training, manual therapy, taping, and stretching, have been described with a central theme of restoring normal hip strength and mobility while avoiding positions known to provoke impingement (5,12,21,23,25,30,31). Although manual therapy and taping have been described in the literature, their inclusion is beyond the scope of this article. Readers seeking a more detailed discussion of nonoperative interventions for FAI are encouraged to read the systematic review by Wall et al. (30). The intent of this article is to provide exercise-based modifications and positional changes that would positively affect FAI. Specifically, the exercise and activity modifications presented in this article are aimed to promote pain-free participation in athletic and fitness endeavors. It is recommended that strength and conditioning professionals require clients to seek medical clearance before initiating any exercises or modifications when a diagnosis of FAI has been established. Furthermore, in cases where FAI may be suspected, clients should be referred to a qualified medical professional before participation in any exercise routine.
The emphasis of a resistance training regimen for individuals with FAI should focus on strengthening of the hip external rotators, abductors, and extensors. These muscle groups not only provide dynamic stability while performing activities, such as squatting and jumping, but also help prevent undesirable positions and faulty biomechanics known to exacerbate FAI. The ascribed benefit is essentially due to their ability to dynamically control the hip and avoid the provocation positions (23). Essentially, strengthening the gluteal musculature with extension, abduction, and external rotation movements may serve to improve lower extremity alignment and positioning (e.g., prevention of adduction and internal rotation) during activities, such as squatting, running, and jumping. Although resistance training efforts for the gluteal musculature are likely to serve a preventative role, global hip strengthening must be approached with caution, as overzealous or end-range strengthening of the hip flexors, adductors, and internal rotators may perpetuate signs and symptoms of FAI.
For those individuals who are symptomatic, gluteus medius and maximus strengthening may begin in non–weight-bearing open-kinetic chain positions, with exercise technique being the primary objective as these muscle groups may be weak due to the client's posture (15,21). Examples of non–weight-bearing exercises targeting the hip extensors and abductors include but are not limited to prone hip extension, side lying abduction with external rotation, and clamshells. Clamshells and side-lying hip abduction exercises are reasonably performed by individuals at varying fitness levels and can be modified to prevent unnecessary hip adduction. For example, clamshells can be modified by applying a pillow or large towel roll in between the client's legs to decrease hip adduction during the exercise (Figure 12). A drawback of these exercises is that although they may be easily adaptable to a majority of clients, they have a lower recruitment level of the gluteal musculature when compared with alternate exercises (2).
Boren et al. (2) investigated muscle recruitment of the gluteus maximus and medius (Table 2) among asymptomatic participants and reported the top 3 exercises that maximally recruit both the gluteus medius and maximus. These 3 exercises included the (a) front plank with hip extension, (b) side plank abduction with dominant leg up, and (c) side plank abduction with dominant leg down. The side plank with hip abduction and front plank with hip extension are shown in Figure 13A and 13B, respectively.
Closed-chain exercises should also be incorporated into an exercise plan to model functional activities. These types of activities often require squatting, a common complaint among individuals with FAI as a result of both depth and, in some cases, poor lower extremity alignment or positioning as seen in Figure 5. Individuals with FAI are advised to avoid repetitive or compulsory deep squatting without modifications. Performing a squat with the hip abducted and externally rotated (Figure 14) is a viable alternative, as it decreases impingement of the femur and acetabulum (12). Squatting can also be modified by limiting hip flexion to 45° to protect the joint from impingement encountered with greater amounts of flexion (5). These recommendations regarding squatting would theoretically apply to similar exercises, such as the leg press, lunge, or hack squat.
Given the biomechanical association between an increased lumbar lordosis-anterior pelvic tilt and FAI, it would seem reasonable to incorporate postural awareness aimed at achieving a more natural lordosis or neutral posture. It is important to note that the lumbar spines natural curvature is a lordosis; thus, changes or recommendations should be centered on avoiding an excessive lordotic curvature and maintaining a more natural anterior tilt (Figure 9). Theoretically, it would not be unreasonable to teach clients with FAI to perform gluteus maximus squeezes (contraction) during provocative activities, such as squatting or lunging. Performing a gluteal squeeze has been reported to maximally activate the gluteus maximus with a reported 81% maximum voluntary isometric contraction (2). Moreover, an isometric gluteal squeeze would potentially serve to improve lower extremity control (reduce compensatory hip internal rotation) and reduce ones lordosis by way of the contractile line of action.
Aerobic training may be modified, as it is another potential area of concern for individuals with FAI. Although walking and jogging in a linear (straight) pattern may not reproduce pain, running and sprinting may be intolerable for individuals with FAI (21,25). Cycling should be modified if possible, as it involves compulsory hip flexion often combined with internal rotation, both of which can lead to impingement at the hip. If unavoidable, elevating the bicycle seat and slightly externally rotating or abducting the legs can aid in avoiding the combined positions of provocation (12).
Prolonged sitting, especially in a low chair or with hip flexed, or “W” sitting are common positions that can aggravate symptoms among individuals with FAI. “W” sitting, which is more common among young children, should be avoided in all circumstances, as it promotes abnormal contact leading to impingement among other impairments. Prolonged sitting is another position that can be modified to allow for more comfort for individuals with FAI. Specifically, it is recommended to lean back or recline the seat to decrease hip flexion if prolonged sitting is unavoidable (12). Moreover, sitting with the legs crossed should be avoided, as it combines hip flexion and adduction.
The demands imposed on the hip as a result of athletic activities or exercise that would otherwise be tolerated in a normal hip may lead to injury, impairment, and discomfort among individuals with FAI. The consequence of neglecting signs and symptoms of FAI may ultimately lead to breakdown of the acetabular labrum, as well as delamination and failure of the articular cartilage (5). Strength and conditioning professionals will have to contend with FAI at some point in their careers, as the condition itself has a higher predilection for athletic individuals. With this being stated, recognition and awareness of the condition itself is a requisite skill set necessary to understand the appropriate activity modifications. Furthermore, an awareness of signs and symptoms pathognomonic of FAI would serve useful as a means of recognizing the need for a referral to a qualified medical professional.
The forefront of conservative management for FAI resides in prevention. Modifying activity levels and avoiding positions known to accentuate impingement is paramount to decelerating the progression of FAI. Specific modifications include avoiding end-range hip flexion, internal rotation and adduction past midline. From an exercise perspective, avoiding both deep squats and cycling with a low seat are recommended, as well as stretching activities that require provocative positioning. Modifications, such as raising the seat during cycling and avoiding incline treadmill activities, would inarguably be reasonable. Moreover, abducting and externally rotating the hip during flexion-based activities, such as squatting or leg press, would serve to prevent impingement as well.
From a functional perspective, restricting the duration of sitting would be indicated, as would avoiding “W” sitting or crossed-leg sitting. Outside of modifications, exercises designed to correct an excessive lordosis or anterior pelvic tilt, as well as gluteal strengthening, are recommended. Although the recommendations provided in this article are based on existing evidence and biomechanical plausibility, one must recognize the individual variability among clients. In cases where pain or symptoms increase or an obvious decline in mobility or performance is recognized, a prompt referral to a qualified medical professional is indicated.
The authors thank Betsy Kreymer for providing the illustrations and pictures.
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