CamCT focal pincerMRI coronal




Femoro-acetabular impingement (FAI)

- abnormal contact between the femoral head neck junction and the acetabular rim

- causes pain secondary to labral and chondral lesions






Mixed - CAM and Pincer


Cam impingement

- abnormal femoral head morphology at head neck junction

- loss of sphericity

- typically anterolateral


Pincer impingement


a. Global

- overcoverage of femoral head

- profunda, protrusio

- acetabular retroversion / relative anterior rim overcoverage


b. focal

- os acetabuli

- focal acetabular lesion


CT focal pincerLarge os acetabuli



- combination of pincer and Cam impingement


Hip CT Anterior Cam LesionOs acetabuli




Hack et al JBJS Am 2010

- MRI of bilateral hips in 200 asymptomatic people

- 14% had Cam deformity in at least one hip

- 80% men, 20% women


Gao et al J Orthop Surg Res 2021

- MRI of 125 hips in 70 asymptomatic patients

- 53% of hips had a labral tear




Developmental / sports

- increased incidence of Cam in hockey / basketball / football / soccer

- suggests changes to femoral epiphysis with certain athletic pursuits


Pediatric hip disease / SUFE


Acetabular retroversion

- posteriorly orientated acetabular opening

- relative prominence of anterior rim


Coxa profunda (deep socket) / Protrusio




Groin pain

- with activity

- with flexion


C shaped pain

- patient uses hand to grip anterior and posterior hip




FADIR (Flexion-adduction Internal Rotation)


FABER (Flexion-abduction External Rotation)




True AP


Coccyx and symphysis pubis within 1-2cm of each other 

- exclude osteoarthritis

- pincer

- dysplasia

- retroversion / crossover sign

- os acetabuli / ossification labrum

- bony prominence junction anterolateral head and neck - Cam


PincerPincer lateral

Bilateral pincer


Ossified labrumOssified labrum
Ossified labrum


Os 1Os 2

Os acetabuli


45 and 90 degree Dunn view


Look for Cam morphology


Dunn view 1Dunn view cam

Small Cam on Dunn view                                       Large anterior Cam on Dunn view


Alpha angle



- centered in the center of the femoral head (best fit circle)

- formed by two lines

- one line center of the femoral neck axis

- a line where the femoral head leaves a best-fit circle

- higher alpha angle with Cam lesion


Alpha 2Alpha 1


Alpha 2Alpha 1

Alpha < 55 degrees                                                   Alpha > 55 degrees


Barrientos et al J Hip Preserv Surg 2016

- 38 patients with Cam versus 108 control

- CT scans

- mean 48+/-5 degrees in controls

- mean 67+/-12 degrees in patients with symptomatic Cam


Kowalczuk et al Sports Med Arthrosc Rev 2015

- systematic review

- Cam lesions with elevated alpha angles predispose to development of OA


Lateral centre edge angle (LCEA)



- vertical line drawn from the center of the femoral head

- line from the center of the femoral head to the lateral acetabular rim

- normal 20 - 40 degrees

- dysplasia < 20 degrees

- profunda > 40 degrees


Protrusio 1Protrusio 2

Increased LCEA in profunda




Labral tears


Best seen on coronal MRI


MRI coronal Mri labral MRI labrum 2


Saied et al BMC Musculoskeletal Disorders 2017

- systematic review

- labral tears: MRI sensitivity 86% and specificity 83%

- chondral lesions: MRI sensitivity 87% and specificity 72%

- labral tears: MRA sensitivity 91% and specificity 58%

- chondral lesions: MRA sensitivity 75% and specificity 79%


Hip MRI Anterior CAMMRI anterior cam

MRI alpha angle




Cam impingement


Hip Cam CT Sagittalcam CT


Hip CT Cam 3DHIp Cam CT 3D 3




CT focal pincer

Focal pincer


Os acetabuli


Os acetabuliLarge os acetabuli


Subspine impingement


Subspine Impingement 1Subspine impingement 2

Enlarged AIIS likely from old partial avulsion




Hip arthroscopy OAOA with Cam < 2 mm joint spaceFemoral head osteophytes


Tonnis Grade

Grade 0 No sign of arthritis
Grade 1 Sclerosis, slight narrowing of joint space
Grade 2 Cyst, moderate narrowing of joint space, loss sphericity of femoral head
Grade 3 Severe narrowing or obliteration of joint space

TonnisTonnis Grade 0Tonnis grade 2

Tonnis grade 0                            Tonnis grade 1                                 Tonnis grade 1


Outcomes of hip arthroscopy and mild OA


Ruzbarsky et al AJSM 2023

- 2 year follow up of hip arthroscopy

- < 2 mm joint space 16% conversion to THA

- preserved joint space 2% conversion to THA


Skendzel et al AJSM 2014

- 5 year follow up of hip arthroscopy

- < 2mm joint space versus > 2 mm joint space

- 86% with joint space < 2mm had THA at 5 years

- 16% with preserve joint space had THA at 5 years


Fenn et al AJSM 2024

- 62 Tonnis grade 0 versus 31 Tonnis grade 1

- minimum 10 year follow up

- 5% THA grade 0 versus 26% THA grade 1




Kowalczuk et al Sports Med Arthros Rev 2015

- systematic review

- Cam impingement and elevate alpha angles predispose to OA


Pelvic tilt / acetabular retroversion




Acetabular retroversion causes anterior overcoverage

Likely due to rotational abnormality of the hemipelvis


Xray diagnosis


1.  Crossover sign - crossover of the anterior and posterior acetabular wall

2.  Positive ischial spine sign - intrapelvic protrusion of the ischial spine

3.  Positive posterior wall sign - the posterior wall runs medial to the femoral head center


Cross over signCross over

Crossover sign - anterior wall in red, posterior wall in black


Alter et al AJSM 2022

- CT versus xray for measurement of retroversion

- crossover sign and ischial spine sign not reliable


CT / MRI  diagnosis


CT acetabular versionAcetabular version


Acetabular version < 15 degrees between B and C

- affected by pelvic tilt and obliquity

- Line A: posterior acetabular walls

- Line B: posterior to anterior acetabular walls

- Line C: perpendicular to line A


Acetabular version 1Acetabular version 2

Normal acetabular version > 15 degrees


Acetabular version 1Acetabular version 2

Reduced acetabular version < 15 degrees




Arthroscopy acetabular rim trim

Periacetabular Osteotomy (PAO)


Zurmuhle et al CORR 2017

- surgical treatment of acetabular retroversion

- 67 hips undergoing PAO and 57 underwent rim trimming

- no difference in outcomes at 5 years

- 80% 10 year survival for PAO, and 23% survival at 10 years for rim trim




Borderline Dysplasia

- LCEA 18 - 25 degrees


Lee et al Arthroscopy 2023

- systematic review of hip arthroscopy in borderline dysplasia

- 6 articles and 400 studies

- at minimum 5 years follow up, 70% achieved MCID in at least one outcome


Nonoperative management




Probst et al J Orthop Sports Phys Therapy 2023

- meta-analysis of 16 studies of non-arthritic hip pain

- overall response rate to nonoperative treatment was 54%

- physiotherapy improved outcomes by average of 11 points on 100 point scale




Takla et al J Orthop 2023

- systematic review of 7 studies and 600 patients

- some association between responsiveness to injections and good outcomes after hip arthroscopy


Operative management


Operative versus nonoperative treatment


Dwyer et al Arthroscopy 2020

- meta-analysis of 3 RCTs and 650 patients

- improved outcomes with operative intervention


Griffin et al Lancet 2018

- 348 patients randomized to surgery v personalized hip therapy

- 1 year follow up, significant improvements in hip arthroscopy group

- mean iHOT-33 scores had improved from 39·2 to 58·8 for hip arthroscopy group

- mean iHOT-33 35·6 to 49·7 in the personalised hip therapy group


Operative outcomes


Levy et al Arthroscopy 2016

- systematic review of 91 studies and 10,000 hips

- > 90% met MCID

- 88% achieved PASS for mHHS but 25 - 30% for HOS

- 6% revision rate hip arthroscopy

- 6% THA


Factors associated with outcomes


Sogbein et al Orthop J Sports Med 2019

- systematic review of 39 studies and 9000 hips

- male, Tonnis grade 0, younger age, BMI < 25 and relief with intra-articular injections associated with good outcomes

- female, > 45, < 2 mm joint space, increase LCEA and labral debridement associated with poorer outcomes


Labrum Repair v Debridement


Su et al Arthroscopy 2024

- 76 labral repairs matched to 76 labral debridement controls

- significant improvement in both groups

- no signficant difference between groups


Wirries et al Arthroscopy 2024

- German registry

- 963 labral repair versus 673 labral debridement

- no difference in outcome

- at 5 years > 90% arthroplasty free survival in both groups

- outcomes and THA influenced by cartilage status at time of surgery


Cam Resection


de Sa et al KSSTA 2014

- systematic review

- correction postoperative alpha angle associated with improved outcomes


Lansdown et al AJSM 2018

- 707 patients

- postoperative alpha angle associated with outcome


Capsular repair


Dasari et al Orthop J Sports Med 2023

- systematic review of capsular closure

- superior outcomes with complete capsular closure