Extra Bone Creates Early Contact in the Hip Joint FAI occurs when the shape of the femoral head or acetabulum causes bone to contact bone before the joint reaches its normal end of range. In a normal hip, the femoral head (a smooth sphere) rotates freely within the acetabulum (a smooth cup) through a wide arc of movement. In FAI, extra bone on one or both surfaces reduces the available arc. The femur hits the socket rim prematurely, pinching the labrum (the cartilage ring lining the socket) between the bony surfaces (Griffin et al., 2016). Three types of FAI: Cam type: Extra bone on the femoral head creates a bump that jams against the socket rim during flexion and internal rotation. Cam is more common in males and athletic populations. The bump is typically on the anterolateral femoral head. Pincer type: Extra bone on the acetabular rim (socket) creates overcoverage that contacts the femoral neck during movement. Pincer is more common in females. The overcoverage restricts range in all directions but particularly flexion and internal rotation. Mixed type: Both cam and pincer morphology present simultaneously. Mixed type is the most common presentation in symptomatic patients. The critical fact: FAI morphology is present in 37-55% of the general population on imaging. Most people with FAI morphology have zero symptoms. The morphology alone does not cause pain. Symptoms develop when the impingement occurs repeatedly under load (deep squatting, aggressive stretching, sports with hip demands). Having FAI morphology does not mean your hip is broken. Having FAI morphology means your hip has a specific shape that limits range in specific directions. How FAI Restricts Specific Movements Deep hip flexion is the most commonly restricted movement. During flexion (bringing the knee toward the chest), the femoral neck approaches the anterior socket rim. With cam morphology, the bump on the femoral head contacts the rim prematurely. With pincer morphology, the overcoverage reaches the femoral neck prematurely. The result: a hard stop with a pinching sensation in the front of the hip at 90-100 degrees of flexion instead of the normal 120-130 degrees. Internal rotation is restricted in cam morphology. As the hip rotates internally, the cam bump rotates toward the anterior socket. The bump contacts the rim, producing the characteristic pinch. Many cam patients have less than 15 degrees of internal rotation compared to the normal 35-45 degrees. This restriction affects squatting, sitting cross-legged, and any movement requiring the knee to cross midline. Combined positions are worst. Flexion plus internal rotation plus adduction (the FADIR test position) produces maximal impingement. This combined position occurs during deep squatting, sitting in low chairs, hip flexor stretches with rotation, and the front leg of a split. These positions force the cam bump directly into the socket rim with maximum contact area. Hip Mobility Exercises That Work Around FAI JME 116 Hip external rotation is typically the least restricted direction in FAI because external rotation moves the cam bump away from the socket rim rather than into it. Building maximum external rotation range creates functional mobility for daily activities and sports without provoking impingement. 8 repetitions per side with controlled holds at end range. JME 111 Hip extension mobility opens the front of the hip without the deep flexion that provokes impingement. Extension stretches the anterior capsule and hip flexors, which often tighten reactively around an impinging hip. Improved extension reduces the anterior hip tightness that amplifies impingement symptoms during daily activities. 8 repetitions per side. JME 112 Hip circles at mid-range (not end-range) maintain joint capsule health and lubrication without forcing the impingement position. Keep the circles within a comfortable range where no pinching occurs. The goal is nourishing the joint cartilage with movement, not pushing into the restricted zone. 10 circles each direction, each hip. JME 119 Hip abduction is often well-tolerated in FAI because the movement opens the joint space rather than compressing it. Building abduction range provides lateral mobility that compensates for the flexion and rotation limitations. 10 repetitions per side. Start your 14-day free trial for hip mobility programming designed around individual joint limitations. Supporting Exercises for FAI Management JME 89 Low back mobility prevents the lumbar spine from compensating for restricted hip flexion. When the hip does not flex fully, the pelvis tilts posteriorly and the lumbar spine flexes to compensate. This compensation pattern produces low back pain alongside the hip limitation. Maintaining low back mobility breaks the compensation cycle. 8 repetitions. JME 150 Thoracic rotation prevents the trunk from compensating for restricted hip rotation. FAI limits internal rotation, forcing the trunk to rotate more during activities like turning and reaching. Thoracic mobility absorbs the rotational demand that the hip no longer provides. 8 repetitions per direction. JME 167 Knee mobility ensures the knee does not absorb compensatory stress from restricted hip range. When the hip does not flex or rotate adequately, the knee takes excessive rotational and flexion demands during squatting and stairs. Maintaining knee health prevents the downstream effects of FAI from producing secondary problems. 8 repetitions per side. JME 232 Ankle mobility prevents the full kinetic chain from compensating for hip restriction. Limited ankle dorsiflexion combined with limited hip flexion creates a double restriction that severely limits squatting depth and stair descent. Maintaining ankle mobility ensures the lower extremity functions optimally despite the hip limitation. 10 repetitions per side. Manage your hip mobility with simplmobility's joint-specific programming for every level. Training Modifications for FAI Squat modifications: Widen your stance and turn your toes out 15-30 degrees. This externally rotates the femur, moving the cam bump away from the socket rim during squat descent. Limit depth to where the hip feels comfortable without pinching. Box squats at a controlled depth prevent the reflexive drop into the impingement zone. Hip-width squats with toes forward are the worst position for FAI because this demands maximum flexion with the cam in its most vulnerable orientation. Stretching modifications: Avoid deep pigeon pose, deep frog stretch, and aggressive split training if they provoke anterior hip pinching. Replace with the individual rotation and extension exercises above. Stretching into impingement does not improve range. Stretching into impingement damages the labrum incrementally with each session. Exercise selection: Favor hip hinge movements (deadlifts, RDLs) over deep squat movements. Hinge movements load the hip in extension and posterior chain engagement, avoiding the deep flexion that provokes impingement. Single-leg work with controlled depth (step-ups, lunges to comfortable depth) maintains hip strength without impingement. Does FAI require surgery? Most FAI is managed successfully without surgery. Exercise modification, hip strengthening (particularly gluteal strengthening to optimize femoral head centering), and avoiding impingement-provoking positions resolve symptoms in the majority of patients. Surgery (hip arthroscopy to shave the extra bone) is reserved for patients who fail 3-6 months of conservative management and have confirmed labral damage contributing to symptoms. Surgery does not create normal hip anatomy. Surgery reduces the extra bone to decrease impingement frequency (Griffin et al., 2016). Will FAI get worse over time? The bone morphology does not change (the extra bone stays). Symptoms fluctuate based on activity level and how well you manage positions. Repeated impingement damages the labrum progressively, so managing positions is important for long-term joint health. Strengthening the hip stabilizers (glutes, deep rotators) optimizes how the femoral head sits in the socket, reducing impingement frequency even though the morphology remains. How is FAI diagnosed? Clinical diagnosis starts with the FADIR test (flexion, adduction, internal rotation combined): if this position reproduces the anterior hip pinch, FAI is likely. X-ray confirms the bone morphology (cam bump, pincer overcoverage). MRI arthrogram shows labral tears if present. Not everyone with symptoms needs imaging. Clinical testing guides management. Imaging confirms diagnosis when conservative management fails or surgery is being considered. References Griffin, D. R., et al. (2016). The Warwick Agreement on femoroacetabular impingement syndrome (FAI syndrome). British Journal of Sports Medicine, 50(19), 1169-1176. PubMed Frank, J. M., et al. (2015). Prevalence of femoroacetabular impingement imaging findings in asymptomatic volunteers. Arthroscopy, 31(6), 1199-1204. PubMed