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What is it?

  • Recent concept. Common cause of hip pain in young adults.
  • Proposed to be one of the causes of arthritis of the hip at younger age.

What are the mechanisms?

  • Cam impingement (bony bump at the head neck junction damages the labrum and cartilage with flexion)
  • Pincer impingement (over-coverage of the acetabular wall – the labrum gets pinched between the acetabulum and femoral neck and gets damaged)

What are the symptoms?

  • FAI usually presents in active young adults with slow onset of deep groin pain that may start after a minor trauma. During the initial stages of the disease, the pain is intermittent and may be exacerbated by excessive demand on the hip, such as from athletic activities including deep flexion of the hip or prolonged walking. The pain also may present after sitting for a prolonged period.
  • Mechanical symptoms from the hip such as painful locking or giving way are common presenting feature if labral tear is present.

Whom does it affect?

  • Cam impingement – more common in young active males (M:F 14:1, age range 21-51, mean 32)
  • Pincer impingement – More common in middle-aged active females (M:F 1:3, age range 40-57, mean 40)

           (Tannast M, Siebenrock KA, Anderson SE. Femoroacetabular Impingement: Radiographic                        Diagnosis—What the Radiologist Should Know AJR 2007; 188:1540-1552.)

  • Often many have mixed type of impingement

What are the clinical signs?

  • Anterior Impingement test – Hip is flexed to 90 degrees. Hip then passively flexed further, adducted and internal rotation – Positive if it reproduces the pain similar to that experienced by the patient.
  • Posterior impingement (uncommon) – The hip is passively hyperextended by hanging the leg over the end of the couch while keeping the opposite limb in neutral position. Pain is reproduced if passive external rotation of the extended leg.

 Differential diagnosis of hip pain in young adults

  • Acetabular dysplasia                                                   
  • Avascular necrosis
  • Snapping iliopsoas tendon
  • Arthritis
  • Non hip causes like inguinal hernia etc.,

How do we investigate?

  • Plain radiographs

Cam impingement: Bump over the anterolateral aspect of the femoral neck. Often obvious only in the horizontal beam lateral – hence the need to do both AP pelvis Xray and horizontal beam lateral when impingement syndrome is suspected. Various measurements like alpha angle etc.,

Pincer impingement: Cross over sign in standardised AP pelvis Xray – due to overcoverage of the anterior acetabular wall.

  • MRI arthrogram – evaluates cartilage damage and labral tear. Also may show pathology like avascular necrosis.


  • Nonsurgical:

An initial trial of nonsurgical treatment, which may include activity modification including restriction of athletic activities, and nonsteroidal anti-inflammatory medications. Physical therapy with an emphasis on improving passive range of motion or stretching may be counterproductive and exacerbate the symptoms.

  • Surgical treatment:

    1. Through open dislocation of the hip

    2. Combined arthroscopy and mini-open approach

    3. Arthroscopic treatment


  • Encouraging early results for symptomatic improvement in recent literature.
  • Less optimal result when there is large area of cartilage damage or presence of early arthritis
  • Still an evolving concept
  • No long term studies are available to show that surgical treatment can prevent the progression of arthritis

Hip impingement is a recently recognised condition which can cause hip pain in young adults. Essentially in this condition, the clearance between the ball (femoral head) and the cup (socket) of the hip joint is less than adequate. Often this is due to an abnormal shape of the ball of the hip joint (CAM impingement) or over coverage of the cup of the hip joint (Pincer impingement). Often it is due to a combination of both factors. Hip impingement can also occur if the socket is deeper than normal and also if there is joint laxity allowing abnormal movement. Hip impingement can lead to damage to labrum (could be considered like a soft tissue bumper for the hip joint) and subsequently the articular cartilage (surface lining of the hip joint) can get damaged leading to arthritis in young adults.

In a normal hip, the “ball” moves inside the cup without any restriction (impingement).

CAM impingement can occur when the shape of ball of the hip joint is not a sphere and more like a rugby ball on one side or with a “impingement bump” on one side. This leads to less clearance and with repetitive bending movements of the hip the labrum (a special cartilage at the rim of the cup of the hip joint) and the articular cartilage (surface lining of the hip joint) gradually get damaged.

Pincer impingement occurs when there is over coverage of the cup of the hip joint and this leads to impingement.  With repetitive bending movements of the hip, the labrum gets damaged initially followed by the articular cartilage.

Progressive damage to the cartilage can gradually lead to arthritis of the hip in young adults.


The most common symptom in hip impingement is pain in the region of the groin (front of the hip joint). It may start following a minor injury or often without any injury. The pain increases with activities which involve bending of the hip joint. Activities which increase the pain include sitting for a prolonged period, getting up from a seated position, getting in and out of the car, walking up and down slopes, climbing stairs, getting in and out of the bath tub, squatting, heavy work including push/pull, carrying heavy objects, putting on shoes and socks, twisting etc., Sporting activities may also be affected. While many of the above symptoms can also be present in patients with hip arthritis, the arthritic pain also increases with activities like walking and sometimes there may be pain even at rest. The patients with impingement can also have a sensation of the hip coming out of the hip joint and also a feeling of clicking sensation. This can be due to a labral tear although in some patients this could be due to dysplasia (shallow cup).


While the preliminary diagnosis of hip impingement is based on the symptoms and the clinical finding on examination, further radiological investigation including plain x-rays and MRI scan and /or CT scan would be required.

X-rays showing CAM type impingement

X-rays showing the removal of the CAM (bump) from the femoral head

X-ray showing relatively normal looking hip but closer inspection
reveal calcification in the labral area and impingement cyst
suggesting possible impingement.


X-ray showing cross-over sign suggesting pincer impingement
(“figure of 8” sign, shaded area representing the overcoverage
of the acetabulum)

CT scan with 3 D reconstruction showing
CAM type impingement (shaded in green for

MR arthrogram showing labral tear
and impingement cyst

The following are some relevant selected scientific references:


1.Femoroacetabular impingement syndrome: an under recognized cause of hip pain and premature osteoarthritis?

J Rheumatol. 2010 Jul;37(7):1395-404.

Reid GD, Reid CG, Widmer N, Munk PL.

Department of Medicine,University of British Columbia, Vancouver, British Columbia, Canada.

Abstract: Acetabular dysplasia is well recognized as a potential predisposing factor to the development of hip osteoarthritis (OA). In the orthopedic literature, other dysmorphic and orientation abnormalities of the femoral head, femoral head-neck junction, and the acetabulum have been reported, with increasing frequency in recent years, under the term femoroacetabular impingement syndrome (FAI). The studies have shown a clear association of these structural anomalies with patients’ symptoms and signs, radiographic and pathologic abnormalities, and the development of degenerative hip arthritis. FAI is now believed to be a very important predisposing factor for the development of degenerative hip arthritis, particularly in younger adults. Although the results of longterm studies are awaited, the hope is that early surgical intervention in patients with FAI will change the course or prevent the development of hip OA. It is well documented that early recognition of potential FAI surgical candidates, before OA is advanced, determines the postsurgical outcome. FAI has not been reported in the rheumatology literature, but since patients with FAI likely often initially present to rheumatology clinics for assessment of hip pain, it is important for rheumatologists to be aware of this condition and refer to orthopedics when appropriate. The objective of this review is to provide an outline of the basic concepts of FAI, including clinical presentation and radiographic findings, so that rheumatologists become more familiar with this important emerging entity.


2. Efficacy of Surgery for Femoroacetabular Impingement: A Systematic Review.

Am J Sports Med. 2010 May 20. [Epub ahead of print]

Ng VY, Arora N, Best TM, Pan X, Ellis TJ.

The Ohio State University.

Abstract: BACKGROUND: Recent case studies on the surgical treatment of femoroacetabular impingement (FAI) have introduced a large amount of clinical data. However, there has been no clear consensus on its efficacy. HYPOTHESIS: The current literature can be clarified to address 4 questions: (1) Does treatment for FAI succeed in improving symptoms? (2) In which subset of patients should treatment for FAI be avoided? (3) Is labral refixation superior to simple resection? (4) Does treatment for FAI alter the natural progression of osteoarthritis in this group of typically young patients? STUDY DESIGN: Systematic review. METHODS: Twenty-three reports of case studies on the surgical treatment of FAI were identified and a systematic review was conducted. Data from each study were collected to answer each of the 4 focus questions. RESULTS: This review of 970 cases included 1 level II evidence trial, 2 level III studies, and 20 level IV studies. Based on patient outcome scores and effect size, all studies demonstrated improvement of patient symptoms. Up to 30% of patients will eventually require total hip arthroplasty; those patients with Outerbridge grade III or IV cartilage damage seen intraoperatively or with preoperative radiographs showing greater than Tonnis grade I osteoarthritis will have worse outcomes with treatment for FAI. Only 2 studies directly compared labral refixation with labral debridement. Several studies reported postoperative osteoarthritis findings; only a minority of these patients had progression of their osteoarthritis. CONCLUSION: Surgical treatment for FAI reliably improves patient symptoms in the majority of patients without advanced osteoarthritis or chondral damage. Early evidence supports labral refixation. It is too soon to predict whether progression of osteoarthritis is delayed. CLINICAL RELEVANCE: These results may be used to help predict the outcome of surgical treatment of FAI in different patient populations and to assess the need for labral refixation.


3. Combined hip arthroscopy and limited open osteochondroplasty for anterior femoroacetabular impingement.

J Bone Joint Surg Am. 2010 Jul;92(8):1697-706.

Clohisy JC, Zebala LP, Nepple JJ, Pashos G.

Department of Orthopaedic Surgery, Washington University School of Medicine, Barnes-Jewish Hospital, St. Louis, MO 63110, USA.  

Abstract: BACKGROUND: A variety of surgical techniques have been introduced for the treatment of femoroacetabular impingement, but clinical outcome studies of less-invasive treatment with a minimum duration of follow-up of two years are limited. The purpose of this study was to evaluate the early clinical and radiographic outcomes of combined hip arthroscopy and limited open osteochondroplasty of the femoral head-neck junction for the treatment of cam femoroacetabular impingement. METHODS: We performed a retrospective review of our first thirty-five patients (thirty-five hips) in whom cam femoroacetabular impingement had been treated with combined hip arthroscopy and limited open osteochondroplasty. Thirty-five patients (twenty-eight men and seven women) with an average age of thirty-four years and a minimum duration of follow-up of two years were analyzed. The modified Harris hip score was utilized to assess hip function. The Tönnis osteoarthritis grade and the alpha angle were determined to assess osteoarthritis progression and deformity correction, respectively. RESULTS: The average modified Harris hip score improved from 63.8 points preoperatively to 87.4 points at the time of the last follow-up. Twenty-nine (83%) of the thirty-five patients had at least a 10-point improvement in the Harris hip score, and 71% had a score of >80 points. The average alpha angle was reduced from 58.6 degrees preoperatively to 37.1 degrees at the time of follow-up when measured on cross-table lateral radiographs, from 63.9 degrees to 37.8 degrees when measured on frog-leg lateral radiographs, and from 63.1 degrees to 44.8 degrees when measured on anteroposterior radiographs. Two patients had osteoarthritis progression from Tönnis grade 0 to grade 1. Minor complications included one superficial wound infection, one deep vein thrombosis, and four cases of asymptomatic Brooker grade-I heterotopic ossification. There were no femoral neck fractures or cases of femoral head osteonecrosis, and no hip was converted to an arthroplasty. CONCLUSIONS: Early results indicate that combined hip arthroscopy and limited open osteochondroplasty of the femoral head-neck junction is a safe and effective treatment for femoroacetabular impingement. In our small series, most patients had symptomatic relief, improved hip function, and enhanced activity after two years of follow-up.


4. Open treatment of femoroacetabular impingement is associated with clinical improvement and low complication rate at short-term followup.

Clin Orthop Relat Res. 2010 Feb;468(2):504-10.

Peters CL, Schabel K, Anderson L, Erickson J.

Department of Orthopaedic Surgery, University of Utah School of Medicine, 590 Wakara Way, Salt Lake City, UT 84108, USA.

Abstract: BACKGROUND: Since the modern description of femoroacetabular impingement (FAI) a decade ago, surgical treatment has become increasingly common. Although the ability of open treatment of FAI to relieve pain and improve function has been demonstrated in a number of retrospective studies, questions remain regarding predictability of clinical outcome, the factors associated with clinical failure, and the complications associated with treatment. QUESTIONS/PURPOSES: We therefore described the change in clinical pain and function after open treatment, determined whether failure of treatment and progression of osteoarthritis was associated with Outerbridge Grade IV hyaline cartilage injury, and described the associated complications. METHODS: We retrospectively reviewed all 94 patients (96 hips) (55 males and 39 females; mean age, 28 years) who underwent surgical dislocation for femoroacetabular impingement between 2000 and 2008. Seventy-two of the 96 hips had acetabular articular cartilage lesions treated with a variety of methods, most commonly resection of damaged hyaline cartilage and labral advancement. Patients were followed for a minimum of 18 months (mean, 26 months; range, 18-96 months). RESULTS: Mean Harris hip scores improved from 67 to 91 at final followup. Six of the 96 hips (6%) were converted to arthroplasty or had worse Harris hip score after surgical recovery. Four of these six had Outerbridge Grade IV acetabular cartilage lesions and two had Legg-Calvé-Perthes disease or slipped capital epiphysis deformities. Two hips (2%) had refixation of the greater trochanter. CONCLUSIONS: At short-term followup, open treatment for femoroacetabular impingement in hips without substantial acetabular hyaline cartilage damage reduced pain and improved function with a low complication rate. Treatment of Outerbridge Grade IV acetabular cartilage delamination remains the major challenge. LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.


5. Combined arthroscopic and modified open approach for cam femoroacetabular impingement: a preliminary experience.

Arthroscopy. 2009 Apr;25(4):392-9.

Lincoln M, Johnston K, Muldoon M, Santore R.

Orthopedic Medical Group, San Diego, California 92123, USA.

Abstract: PURPOSE: We report our case series of patients undergoing surgical treatment (femoral osteoplasty) for symptomatic cam femoroacetabular impingement (FAI). Clinical results using a modified Heuter anterior approach combined with adjunctive hip arthroscopy are presented. METHODS: A chart review of 16 hips (14 consecutive patients) was conducted. Radiographic parameters (alpha angle, head-neck offset, and Tönnis grade) were compared preoperatively and postoperatively. Clinical features (range of motion, provocative testing, and Harris hip score) were assessed. RESULTS: At 2.0 years, mean hip flexion improved from 94.1 degrees to 110.0 degrees (P < .01) and internal rotation from 7.1 degrees to 12.3 degrees (P = .02). The mean alpha angle improved from 64.5 degrees to 43.3 degrees (P < .01), whereas the mean femoral head-neck offset improved from 1.9 to 9.6 mm (P < .01). The mean Harris hip score improved from 63.8 to 76.1 (P = .01). No deterioration in overall radiographic Tönnis grades was present at last follow-up. CONCLUSIONS: The combination of hip arthroscopy with a limited anterior approach (Heuter) is a useful technique for patients with cam or cam-dominant FAI lesions. We believe the limited anterior approach with open osteoplasty presents a reasonable alternative to arthroscopic methods of osteoplasty with minimal drawbacks in the event that total hip arthroplasty is indicated in the future. LEVEL OF EVIDENCE: Level IV, therapeutic case series.


6. Arthroscopic femoroplasty in the management of cam-type femoroacetabular impingement.

Clin Orthop Relat Res. 2009 Mar;467(3):739-46. Byrd JW, Jones KS.

Nashville Sports Medicine Foundation, 2011 Church Street, Suite 100, Nashville, TN 37203, USA.

Abstract: Cam-type femoroacetabular impingement is a recognized cause of intraarticular pathology and secondary osteoarthritis in young adults. Arthroscopy is reportedly useful to treat selected hip abnormalities and has been proposed as a method of correcting underlying impingement. We report the outcomes of arthroscopic management of cam-type femoroacetabular impingement. We prospectively assessed all 200 patients (207 hips) who underwent arthroscopic correction of cam impingement from December 2003 to October 2007, using a modified Harris hip score. The minimum followup was 12 months (mean, 16 months; range, 12-24 months); no patients were lost to followup. The average age was 33 years with 138 men and 62 women. One hundred and fifty-eight patients (163 hips) underwent correction of cam impingement (femoroplasty) alone while 42 patients (44 hips) underwent concomitant correction of pincer impingement. The average increase in Harris hip score was 20 points; 0.5% converted to THA. We had a 1.5% complication rate. The short-term outcomes of arthroscopic treatment of cam-type femoroacetabular impingement are comparable to published reports for open methods with the advantage of a less invasive approach.


7. Femoroacetabular impingement treatment using arthroscopy and anterior approach.

Clin Orthop Relat Res. 2009 Mar;467(3):747-52. Laude F, Sariali E, Nogier A.

CMC Paris V, 36 boulevard saint Marcel, 75005, Paris, France.

Abstract: Femoroacetabular impingement (FAI) has been identified as a common cause of hip pain in young adults. However, treatment is not well standardized. We retrospectively reviewed 97 patients (100 hips) who underwent osteochondroplasty of the femoral head-neck for FAI using a mini-open anterior Hueter approach with arthroscopic assistance. The mean age of the patients was 33.4 years. The labrum was refixed in 40 hips, partially excised in 39 cases, completely excised in 14 cases, and left intact in seven. Six patients were lost to followup, leaving 91 (94 hips) with a minimum followup of 28.6 months (mean, 58.3 months; range, 28.6-104.4 months). We assessed patients clinically using the nonarthritic hip score (NAHS). One patient had a femoral neck fracture 3 weeks postoperatively. At the last followup, the mean NAHS score increased by 29.1 points (54.8 +/- 12 preoperatively to 83.9 +/- 16 points at last followup). Eleven hips developed osteoarthritis and subsequently had total hip arthroplasty. The best results were obtained in patients younger than 40 years old with a 0 Tönnis grade. Refixation of the labrum did not correlate with a higher NAHS score (87 +/- 11 with refixation versus 82 +/- 19 points without) at the last followup. The technique for FAI treatment allowed direct visualization of the anterior femoral head-neck junction while avoiding surgical dislocation, had a low complication rate, and improved functional scores.

As the condition (hip impingement) is only being recently recognized as a cause of hip pain which can progress to hip arthritis  in young adults, the treatment strategies are still evolving. In the initial stages, it would be appropriate to consider conservative treatment including physiotherapy, painkillers and activity modification.

If the symptoms persist, it would be appropriate to consider surgical option. When Ganz initially suggested this condition as a cause of hip pain, he advised surgery using a technique known as “surgical dislocation” of the hip. In this exposure, the hip joint is completely exposed (see picture below). While this still may be needed in some cases, the  surgical exposure is extensive and carries certain morbidities including non-union of the trochanteric fragment.

Exposure of the femoral head with Ganz “surgical dislocation” of the hip
(the picture also shows the bony bump the so called “CAM  lesion” to be excised)

Hip arthroscopy is a technically more challenging procedure when compared with a knee arthroscopy.  However, with the advances in the technique of hip arthroscopy and instrumentation, treatment strategies are also evolving which makes it possible for at least some impingement pathologies to be treated entirely through hip arthroscopy.

CAM impingement resection through hip arthroscopy

Whatever the surgical technique may be, the treatment essentially entails creating better clearance for the ball of the hip joint.  The bump in the anterolateral aspect of the ball is removed and/or the over covered part of the acetabulum is excised.  The labral tear is often debrided but in some cases, the labrum could be repaired.

While studies have shown that many patients gain short term improvement in their symptoms, the symptom relief is not universal. One of the main negative predictors of symptoms relief is presence of arthritic changes or damage to the surface lining of the hip joint.  

At this stage, there is lack of data to say whether surgical treatment of hip impingement can delay or prevent the progression to hip arthritis.