Hip Impingement


The hip joint is formed by the thigh bone that presents as a narrow neck and a round ball (femoral head) to a socket on the side of the pelvis (acetabulum). The normal shape of the ball and the socket allow close contact through adequate range of motion. The end point for hip movement in any direction is usually from the jamming of the head neck junction against the rim of the socket.

As we all need to bend the hip forwards more than in any other direction, the normal socket and ball are turned forwards allowing more motion to bend the hip forward before they jam. Due to congenital and developmental factors, the size, shape, or orientation of the ball and the socket may not be ideal, and can cause limitation of hip motion from premature jamming. Most active people do not feel the jamming initially and force their hips beyond the possible range to continue their activities. Decreased hip motion without pain is a form of hip stiffness. Painful limitation of motion from jamming of the hip is impingement (Femoroacetabular Impingement).

Repetitive forceful jamming of the ball against the socket wall is the most common cause of hip labral tears. Continued jamming can cause further damage to the joint cartilage and lead to arthritis at a young age. Repetitive jamming can also thicken the ball and the socket and lead to jamming at lesser range of hip motion. This condition does not cause significant pain in the early stages when treatment can prevent arthritis.

The modern concepts of Femoro-Acetabular Impingement (FAI) were described by Professor Reinhold Ganz from Switzerland in the early nineties. This jamming causes the more common type of impingement with decreased range of motion. Impingement from out of round femoral head can occur even with good range of motion. Hip impingement explains the previously unknown causes of hip pain and premature arthritis in young adults.

Pubic symphysis irregularity is commonly associated with stiff hips, even sacroiliac pain and lumbar pain can be associated with FAI. Athletic pubalgia, Sports hernia, rectus abdominal strain, adductor muscle strain, avulsion fractures of the pelvis are well known associations too.

Diagnosis of Impingement can be made confidently by clinical examination by an experienced healthcare provider. Occasionally, local anesthetic injection into the hip joint may be used to confirm that the pain is coming from the hip joint. The morphology of the femur and acetabulum can be understood well on plain radiographs to guide treatment most of the times. Computed tomography (CT) is occasionally needed to see the bones better. Magnetic Resonance Imaging (MRI) may show labral tear and damage, but it is better used to rule out confounding pathology.

Current Treatment Options

FAI risk factors are very common in asymptomatic hips. So the condition should be diagnosed clinically. Unfortunately, not everyone has a lot of pain while the hip is accumulating damage. We do not treat hip stiffness without any pain.

The current treatment options for this condition are limited to simple observation or surgical intervention. There are no known medications to correct the impingement and stretching of the joint with physiotherapy can cause more damage. However, physiotherapy to strengthen core and hip muscles and posture improvement can decrease pain. Surgery is an excellent option if pain persists and the surgeon can safely identify and correct the bony abnormalities without causing further damage. This can be done with arthroscopic, open, or combined techniques based on experience and feasibility. Any hip with adequate femoral and acetabular cartilage can be relieved of impingement. Labral and cartilage tears can be shaven, repaired, or reconstructed. Acetabular socket can be reduced, enlarged, or reoriented. The femoral head can be made rounder by removing the bump and larger heads can be made smaller. Femoral necks can be created or lengthened. Femoral shaft to neck alignment can be changed in all planes. Please read the sections on hip arthroscopy, mini open, and surgical dislocation approaches and individual techniques for more details.

Femoroacetabular Impingement for health care providers

Definition – Femoroacetabular impingement is a pathomechanism of hip pain and damage from morphological variations of the femur, acetabulum, or both during normal movements of the hip joint.

Types of Impingement

Clinically, hip impingement is often obvious and occurs with less than required movement in one or more directions from the bony block called Type 1 impingement. The bony block signifies that the end range of FIR is from bones jamming in the front and not from posterior contracture, effusion, or guarding. At this point the head neck junction is pinching the labrum and acetabulum. If there is no pain in other directions and the FIR end point causes pain, I cannot think of any other cause except FAI. This is Type 1 or Clinically obvious FAI. Decreased range of motion without pain is hip stiffness. Impingement requires some degree of pain. Impingement in the front is known to cause posterior damage from instability called Contre Coup damage from FAI induced instability. This instability can increase motion in some Type 1 hips making them appear like Type 2 hips.

Impingement with adequate range of motion is less obvious and less common and is called Type 2 Impingement.

A – Extra-articular impingement is from bony prominences pinching the intervening soft tissues and causing pain. i. Anterior Inferior Iliac Spine (AIIS) impingement against the femoral neck in straight flexion. ii. Greater trochanter(GT) impingement against the ilium in flexion and abduction and against the ischium in external rotation. iii. Lesser trochanter (LT) impingement against the ischium.

AIIS and GT impingement are Type 1 and LT impingement is often type 2

B – Intra-articular impingement can be anterior, anterolateral, posterior, or global i. Cam type – always from asphericity of the head causing chondral debonding. ii. Pincer type – often acetabulur, can be femoral causes pinching of the labrum. iii. SCFE type – causes pincer and abrasion of the labrum and acetabular cartilage iv. Foveal type – pinching of Ligamentum Teres between the head and acetabulum. v. Mixed type

Most Cam and all pincer hips are Type 1. A few cam and most foveal hips are Type 2. Cam and pincer impingement can be confirmed only by the labral and acetabular cartilage damage patterns seen during surgery

Clinical features

The diagnosis of FAI is suspected by excluding conditions of the back and pelvis that refer pain to the hip and non-mechanical hip conditions like tumors, infections, and synovial diseases. The diagnosis can be made with reasonable certainty with good clinical exam.

Symptoms – Pain is the most common complaint. Groin or lateral hip pain suggest hip problems, but pain referred to the thigh and knee is not uncommon. Groin pain is not specific to hip problems and other causes of groin pain need exclusion. Patellofemoral pain and knee tenderness, hip adductor tendinitis, hamstring strains, gluteal enthesopathy, sacroiliac strain, low back pain, osteitis pubis, abdominal muscle strain, and sports hernia are often associated and may be caused by hip impingement.  There are no tests to prove this causation at this time. Clicking, popping, and locking are not uncommon. Flexion activities like sitting in low seats, getting in and out of a car, ice hockey goal keeping are expected causes of pain, but pain only with running and sports is not uncommon.

Signs  Station & Gait are not effected unless there is severe deformity or irritation of the hip joint. Tenderness of strained periarticular tissues secondary to impingement is known, but actual tenderness of the hip joint is uncommon.  Range of motion and pain provoking tests are more useful.

  1. SLR – tests for posterior instability in addition to testing for sciatica and hamstring tightness.
  2. Straight Flexion causes pain in the groin from AAIS impingement or inflamed labrum.
  3. Anterior Impingement sign / Flexion-adduction-Internal rotation (FADDIR) causing groin pain is very sensitive for hip pathology, but not specific. FADDIR can also elicit posterior apprehension.
  4. Flexion Internal rotation (FIR) range is very useful. Internal rotation at 90 degrees of flexion improves the utility of FADDIR. Healthy FIR is 20-30 degrees. Decreased FIR with reproducible pain with a bony block and without pain in other directions is very specific for anterior FAI regardless of the cause of that impingement. FADDIR pain with increased FIR can be from containing cam or from anterior dysplasia
  5. Flexion External Rotation (FER) is often pain less and it is limited only with several deformity or incongruity.
  6. Flexion Abduction External rotation (FABER) stresses the sacroiliac joint and can cause groin pain from labral irritation. Decreased FABER range with lateral pain suggests anterolateral cam impingement.
  7. Posterior impingement / Extension Adduction External rotation (EADER) elicits posterior impingement and anterior apprehension.


A good Pelvis AP view shows most of the details of acetabular and femoral morphology. Lateral view at different angles shows different parts of the femoral head and neck contour. Acetabular over coverage, coxa vara, coxa breva, coxa plana, cam morphology and version abnormalities are known causes of impingement and can be seen directly or interpreted well on plain films.

Computed tomography shows femoral morphology the best, but it is rarely required.

MRI scan shows the soft tissues well and rules out other pathology like AVN and tumors, shows labral tears sometimes and damage when it is advanced. Circumferential alpha angle measurements are best done on radial sequences. MRI can differentiate between borderline dysplasia and cam damage as the cause of pain based on the labral size. Lack of labral hypertrophy goes against dysplasia. The surgeon has to obtain all the tests required to make an accurate assessment and to rule out other pathology. FAI risk factors on imaging are very common in hips which do not have impingement or stiffness.  No imaging finding is diagnostic of FAI before damage patterns are established. So, the diagnosis should be made clinically and correlated with imaging to suggest treatment.

Ultrasonography in experienced hand can evaluate the labrum, capsule, and tendons of the hip and document impingement and hip snapping.

Image guided intra-articular local anesthetic injection can be diagnostic in localizing the origin of the pain to the hip, therapeutic to relieve pain, and prognostic to suggest the expected pain relief from surgical intervention.

There were a few unsuccessful attempts made to develop a scale or a score of impingement risk by quantifying and adding up all the risk factors. We found that in Type 1 anterior FAI without FAI induced instability, FIR is a good measure that adds up the clinical effects of all the risk factors.


The goal of treatment is to relieve pain and prevent further damage. This is often accomplished by correcting the shape, size, or version deviation from ideal morphology. Sometimes, the treatment can be simpler by obtaining compensatory overcorrection of some aspect of the morphology. FAI with decreased range of motion (Type 1) requires both improvement of range of motion and correction of the potential causes of the hip pain. FAI with good range of motion needs only correction of the morphological variation that is the likely cause of hip pain. 70-90% of active children develop radiographic risk factors without symptoms. Today, there is no role for prophylactic treatment because we do not know how many and who develop FAI and arthritis.

It is reasonable to treat all FAI conservatively for a few months just to make sure that we are not operating based on one-time hip pain. As much as I rely on clinical exam and FIR, it is subjective and repeating the exam a few times decreases errors. Nonop treatment is limited to improving core and hip strength and decrease lumbar lordosis if possible. Increased lordosis aggravates FAI and any decrease with muscle strengthening can help to a small extent. Lordosis is a function of pelvic incidence and usually cannot be changed without surgery. Physical therapy should not try to improve hip movement because stretching the hip usually aggravates impingement. Activity modification usually decreases pain.

Surgical treatment

The surgical treatment of FAI is correction of all the potential causes of pain and to provide adequate range of impingement free motion in a hip that has good cartilage space and good prognosis.  Correction of the bony cause of the impingement should not cause or unmask articular incongruity, hip instability or abductor dysfunction. Multiple bony causes may need multiple procedures to optimize the hip morphology. Labral tears are often caused by FAI and treatment of labral tears alone without correcting the causative morphology is likely to fail.  Labral tears can be debrided, repaired, or reconstructed based on the quality of the tissue that remains after correction of the bony cause.

Type 1 FAI needs correction of the impinging structures and increase in FIR. Most hips need impingement free range of motion especially FIR (90 degree Flexion Internal Rotation) of 20-30 to remain pain-free. Obese and inactive people may get away with less and people like contortionists need a lot more. 

Type 2 needs only correction of impinging structures. Clinically, I have diagnosed a few children with idiopathic FAI between 5-10 years of age. Radio graphically, both the head and acetabulum are not fully ossified at that age. Femoral derotation osteotomy is a reversible compensation to any invisible intra articular deformity for this group. I have done idiopathic cam osteoplasty in 12 year olds and osteoplasty for correction of cam morphology from AVN and SCFE in children as young as 7.

AIIS impingement can be treated with arthroscopic or open AIIS resection.

GT impingement responds well to distal transfer of GT along with relative neck lengthening.

LT impingement can be treated with arthroscopic LT resection or open LT resection or distal transfer.

Foveal impingement corrects well with varus intertrochanteric osteotomy. Often needs relative neck lengthening before the varus osteotomy.

Cam and pincer should be intraop diagnoses based on labral and acetabular damage seen during open or arthroscopic surgery. Pure cam impingement does not damage the labrum initially. Labral crushing is pincer damage. Cam is always from the femur, but pincer can be from acetabular or femoral abnormalities. Cam or pincer should not influence what you do to the labrum. The labrum requires repair only if it is already unstable or you make it unstable with rim trimming.

Type 1 Cam & Pincer impingement requires increased FIR and cam osteoplasty.  Cam osteoplasty does not always improve FIR. Rim trimming always does. Each millimeter of rim removed increases FIR by 2-3 degrees.  If FIR cannot be improved to +20-30 degrees safely with arthroscopy alone or the bony cause requires an extra –articular procedure, additional femoral and acetabular osteotomies can be performed with open incisions. Surgical dislocation approach allows comprehensive correction of the proximal femur and acetabular morphology.

Type 2 Cam impingement requires only cam osteoplasty regardless of the acetabular morphology unless the labrum shows pincer damage.