Femoroacetabular Impingement

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Introduction

Femoroacetabular impingement (FAI) syndrome is a motion-related clinical disorder of the hip involving premature contact between the acetabulum and the proximal femur and which results in particular symptoms, clinical signs and imaging findings.

Clinically Relevant Anatomy

File:Interactive hip - hip - L5F1.jpg

© Primal Pictures

The hip (acetabulofemoral joint) is a synovial joint formed by articulation between the femur and acetabulum of the pelvis. The head of the femur is covered by Type II collagen (hyaline cartilage) and proteoglycan. The acetabulum is the concave portion of the ball and socket joint. The acetabulum has a ring of fibrocartilage called the labrum that deepens the acetabulum and improves stability of the hip joint. For a more detailed review of the anatomy of the hip, please see the Hip Anatomy article.

Mechanism of Injury / Pathological Process

FAI syndrome is associated with key variations in morphology of the hip joint. Cam morphology describes a flattening or convexity of the femoral head neck junction. Pincer morphology describes "overcoverage" of the femoral head by the acetabulum in which the acetabular rim is extended beyond the typical amount, either in one focal area or more generally across the acetabular rim. It is possible for cam and pincer morphologies to be present at the same time (need ref). It is important to note that these morphologies are thought to be present in many people, including those without hip symptoms, thus the isolated presence of either cam or pincer morphology is insufficient for a diagnosis of FAI syndrome.

Both cam and pincher impingement typically result in cartilage delamination and labral lesions. Either cam or pincher impingement can cause significant disability with athletic activities and/or ADL’s.

Pathological Process CAM Type FAI

• Abnormal morphology of the anterior femoral head–neck junction.
• Prominence of the femoral head-neck junction in the anterior/anterosuperior portion of the proximal femur is known as the “pistol grip deformity"
• Younger males. 
• Prominence femoral head-neck junctions produces intermittent and consistent stress (the cam effect) on the associated articular cartilage.
• The shear forces cause damage to both the acetabular labrum and the articular cartilage of the femoral head and acetabulum.

Pathological Process PINCER Type FAI

• Abnormal acetabulum contacting a normal femur.
• Usually presents in elderly women.
• This can be due to increased acetabular anteversion or coxa profunda.
• Acquired causes can be acetabular protrusion or post-surgical prominent anterosuperior acetabulum.
• Acetabular retroversion: may be seen as a result of trauma or as part of acetabular dysplasia (either in isolation or part of a complex).
• The acetabular labrum is the first structure to be effected.
• The repetitive impact results in degeneration of the labrum with intrasubstance ganglion formation or ossification of the acetabular rim.
• Ossification can lead to further deepening of the acetabulum and therefore more overcoverage of the femoral head by the acetabulum.
• When cartilage lesions do occur with pincer impingement they are typically focal and involve small areas of the acetabular rim.

Clinical Presentation

In the Warwick Agreement on FAI syndrome published in 2016, the authors note that a particular triad of symptoms, clinical findings and imaging findings are required for a diagnosis of FAI.

Symptoms

• The primary symptom reported with this condition is hip or groin pain related to certain movements or positions
• Pain may also be reported in the thigh, back or buttock
• Additional symptoms such as stiffness, restricted ROM, clicking, catching, locking or giving way may be reported

Clinical Findings

• As per the Warwick Agreement from 2016, there is no single clinical sign that will indicate a diagnosis of FAI
• Various pain-provocation hip impingement tests are used clinically but flexion adduction internal rotation (FADIR) is the most commonly used test and is sensitive but not specific
• Hip ROM is often restricted, most commonly internal rotation with the hip flexed

Imaging Findings

• AP x-rays of the pelvis and lateral x-rays of the femoral neck are recommended initially for suspected FAI syndrome. These views can provide general information relating to the hips as well as specific information related to cam or pincer morphologies or other potential sources of the patient's pain
• If further assessment is required (e.g. for better appreciation of 3D morphology of the hip or for associated cartilage and labral lesions), cross-sectional imaging (CT or MR arthrogram) is recommended

Clinical Findings

• Estimated prevalence: 10-15%
• Onset of hip pain usually in the young 20-40 y/o, usually unilateral
• CAM type: Male:Female 14:1 (avg age: 32).
• Pincer type: Male:Female 1:3 and usually middle age women (avg age: 40)
• Present with groin pain with hip rotation, in sitting position, or during/after sports
• Typically aware of limited hip mobility long before sx.

Clinical Examination

• Loss of internal rotation out of proportion to the loss of range of movement at other positional extremes.
• Osteoarthosis will usually produce a universal limited range of motion.
• A grinding and popping sensation can be felt when the femur is externally rotated when the hip is maximally abducted
• Restricted range of motion, particularly flexion and internal rotation
• Positive impingement test: for anterior femoroacetabular impingement if forced internal
• rotation/adduction in 90 degrees of flexion reproduces pain.
• For posterior impingement: painful forced external rotation in full extension with legs hanging off the end of table and uninvolved leg flexed.
• Drehmann’s sign: unavoidable passive external rotation while performing hip flexion.

Differential Diagnosis

Acute hip pain due to tumour, infection, septic arthritis, osteomyelitis, fracture and avascular necrosis are all "red flag" conditions that should be ruled out.

Outcome Measures

international Hip Outcome Tool (iHOT)

Hip and Groin Outcome Score (HAGOS)

Hip Outcome Score (HOS)

Harris Hip Score (HHS) 

Non-arthritic Hip Score 

Management / Interventions

Researchers are still trying to ascertain the best approach to managing this condition. To date, hip arthroscopy has commonly been utilized but early reports tend to be limited to cohort-level and also typically showed only short-term benefits. In The Warwick Agreement on FAI syndrome which was published in 2016, the authors stated that "[t]here is currently no high-level evidence to support the choice of a definitive treatment for FAI syndrome" therefore all options should be considered for each patient and an approach should be selected based on a shared decision-making process.

Surgical Management

Surgical management for Femoroacetabular Impingment.

Surgery with Post-Operative Physiotherapy Programme

The addition of a physiotherapist-prescribed rehabilitation program following arthroscopy was found to improve primary outcomes (International Hip Outcome Tool and sport subscale of the Hip Outcome Scale) to a clinically-relevant degree at 14 weeks post-surgery compared to a control group who followed a self-management program with general guidance from their surgeon. In the same study, the results at 24 weeks were inconclusive due to the small sample size. Physical outcomes were not evaluated in this study.

Subjects in the physiotherapy treatment group attended one pre-operative and six post-operative 30-minute sessions with a physiotherapist. The post-op visits were two weeks apart on average, ending at 12 weeks. Treatment during these sessions consisted of education, manual therapy (mandatory release of key trigger points, optional lumbar mobilisation) and, starting at 6-8 weeks post-surgery, functional and sport-specific drills. Training within the patient's normal sport environment started at 10-12 weeks post-surgery. In addition, these patients performed a daily home exercise program (see exercise sheet below) and an unsupervised gym and aquatic programme (pool walking, stationary bike, cross-trainer and eventually swimming and lower body resistance) at least twice per week. The full treatment protocol can be viewed here. The home exercise sheets provided to patients in the physiotherapy group can be viewed here in PDF format.The return to sport guidelines provided to the treating physiotherapists can be viewed here in PDF format.

Conservative Management

Mansell et al 2018

In a randomized controlled trial, Mansell et al (2018) compared patient outcomes for surgical intervention versus physiotherapy. The group of subjects was 58.8% male with a mean age of 30.1 years. Eligible subjects had to have a diagnosis of FAI and/or labral tear and also report pain in the anterior hip or groin, have pain with the FADIR test (passive flexion, adduction, internal rotation), have pain reproduced with passive or active flexion and experience pain relief with an intra-articular injection. Outcomes were the Hip Outcome Score (including daily activity and sport subscales), International Hip Outcome Tool, Global Rating of Change and return to work. The surgical procedure included a possible combination of labral repair or debridement, trimming of the acetabular rim and/or femoroplasty, as determined by the surgeon. The physiotherapy protocol was tailored to each subject based on a standardized assessment conducted by a physiotherapist. The program could consist of manual therapy, motor control exercises and mobility/stretching exercises as follows;

• Manual Therapy: Hip Extension in Standing MWM, Hip Distraction during Internal Rotation MWM, Loaded Lateral Hip Distraction MWM, Loaded Internal Rotation, Lateral Glide in External Rotation, Long Axis Hip Distraction
• Motor Control Exercises: Reverse Lunge with Front Ball Tap, Isolateral Romanian Deadlift with Dowel, Lateral Step-Down with Heel Hover, Side Plank, Seated Isometric Hip Flexion, Supine Hip Flexion with Theraband.
• Mobility Exercises: Kneeling Internal Rotation Self-Mobilization with Lateral Distraction, Half-Kneel FABER Self-Mobilization, Quadruped Rock Self-Mobilization with Lateral Distraction, Prone Figure-4 Self-Mobilization, ITB Soft Tissue Self-Mobilization on Foam Roll, Quadriceps Soft Tissue Self-Mobilization on Foam Roll, Piriformis/Glut Min Self Myofascial Release on Ball, Standing Figure-4 Stretch, Kneeling Tri-Planar Mobilizations

Please note that the above program has been described in detail in the authors' supplemental files here.

At the two year follow-up, there was no statistically significant difference in outcomes found between the surgical and non-surgical groups and on average, subjects in both groups reported no improvement in their condition. There was a high crossover rate from subjects from the physiotherapy group to the surgery group. Complications from surgery were low. Fifteen percent of patients went on to have additional surgeries and 11.4% of patients were diagnosed with hip osteoarthritis by the two year follow-up. Need to study factors predicting success from surgical and nonsurgical outcomes e.g. type of surgery, baseline imaging findings, reasons for crossovers, extent of degeneration present . Could also look more at optimal timing, dosing and choice of exercise program. Also consider patient expectations - may be unwilling to try conservative options - need for better education - natural differences in morphology vs abnormalities, high rate of conversion to total hip arthroplasty within two years of arthroscopic surgery of the hip, joint degeneration may not progress beyond what is typical in a morphollogically normal hip.

Prognosis

Patients treated for symptomatic FAI syndrome frequently report improvement in their symptoms and are able to return to their usual activities. However, the long-term prognosis is not known, nor is it known if treatment of FAI syndrome prevents the development of hip OA. According to the authors in the Warwick Agreement, symptoms of FAI syndrome will probably worsen if no treatment is provided.

Resources

The Warwick Agreement on FAI Syndrome 2016 http://bjsm.bmj.com/content/50/19/1169

http://blog.evidenceinmotion.com/evidence/files/Tanzer-ClinOrthopRelRes-2004-HipPainLabralTearOA.pdf

http://www.hss.edu/conditions_Hip-Mobility-Arthroscopy-Patient's-Guide-Femoro-Acetabular-Impingement.asp

Presentations

Evidence Based Treatment of the Hip: FAI This presentation, created by Bridgit Finley as part of the Evidence In Motion OMPT Fellowship in 2012, discusses the evidence based treatment for the hip and specifically for femoral-acetabular impingement. View the presentation