Femoroacetabular Impingement Syndrome (FAI) with CAM Morphology: Pathophysiology, Diagnosis, Imaging, and Treatment

on


Introduction

Femoroacetabular impingement syndrome (FAI) with CAM morphology is increasingly recognized as a significant cause of hip pain, functional limitation, and early onset osteoarthritis in young and middle-aged adults. With advances in imaging modalities and clinical research, a more nuanced understanding of its pathophysiology, epidemiology, clinical features, diagnostic protocols, treatment strategies, and prognosis has emerged. This article aims to provide a comprehensive, evidence-based review of CAM-type FAI, enriched with illustrative figures, and optimized for academic and clinical readership.

Pathophysiology

FAI syndrome results from abnormal contact between the femoral head-neck junction and the acetabular rim during hip joint movement. CAM morphology refers to an aspherical femoral head, where a bony bump or convexity at the head-neck junction disrupts the smooth articulation. This deformity leads to shearing forces on the acetabular cartilage and labrum, resulting in progressive chondrolabral damage and early degenerative joint disease.

The underlying mechanisms involve:

  • Abnormal bone growth: Particularly at the proximal femoral physis during adolescence.

  • Microtrauma and repetitive stress: Especially in athletes engaged in high-impact sports (e.g., soccer, hockey).

  • Genetic predisposition: Several studies suggest familial aggregation, though genetic determinants remain under investigation.

Epidemiology

Epidemiological studies demonstrate that CAM morphology is relatively common in athletic populations:

  • Prevalence: 14–25% in the general population; higher (up to 60%) in athletes.

  • Gender differences: More common in males than females.

  • Age of onset: CAM lesions often form during adolescence due to physeal stress and remain asymptomatic until early adulthood.

Clinical Presentation

Patients with CAM-type FAI typically present with:

  • Symptoms: Gradual onset of groin pain exacerbated by hip flexion, prolonged sitting, or pivoting activities.

  • Functional limitations: Difficulty in sports, squatting, or climbing stairs.

  • Physical examination:

    • Positive impingement test (flexion-adduction-internal rotation, FADIR).

    • Restricted internal rotation and flexion.

Imaging Features

Accurate imaging is critical for diagnosis and surgical planning.

  • X-rays: Anteroposterior pelvis and lateral Dunn view reveal asphericity at the femoral head-neck junction.

  • MRI/MRA: Identifies chondrolabral injury, cartilage delamination, and bone marrow edema.

  • CT scans: Provide 3D reconstructions for surgical planning.

  • Alpha angle: Quantitative measure of CAM deformity; >55° indicates pathology.

Figures

[Figure 1] Axial bone window; 👉 Findings of decreased offset at the femoral head-neck junction on both sides.

[Figure 2]  Axial non-contrast; 👉 Check for femoral neck bumps and subtle deformations.

[Figure 3] Coronal bone window

[Figure 4] Coronal bone window; 👉 Irregular shading around the right acetabulum. os acetabuli

[Figure 5] [Figure 5] Coronal bone window; 👉 Deformity around the left acetabulum. os acetabuli

[Figure 6] Sagittal bone window; 👉 L5 isthmus defect

Differential Diagnosis

Conditions that mimic FAI include:

  • Hip dysplasia

  • Slipped capital femoral epiphysis (SCFE)

  • Osteoarthritis

  • Iliopsoas tendinitis

  • Stress fractures of the femoral neck

Diagnosis

Diagnosis is made by integrating clinical symptoms, physical examination, and imaging findings. A structured approach involves:

  1. History taking (pain, activity limitation).

  2. Clinical examination (impingement tests).

  3. Imaging confirmation with X-ray, MRI, or CT.

Treatment

Non-Surgical Management

  • Activity modification

  • NSAIDs and physiotherapy

  • Intra-articular corticosteroid injections (short-term relief)

Surgical Management

  • Arthroscopic CAM resection (femoral osteoplasty): Minimally invasive, high success rates.

  • Open surgical dislocation and osteoplasty: Reserved for complex cases.

  • Labral repair/reconstruction: Improves functional outcomes.

Prognosis

With early detection and appropriate management, outcomes are favorable. Arthroscopic surgery yields significant pain relief and functional improvement in most patients. However, delayed diagnosis may predispose patients to early hip osteoarthritis requiring total hip arthroplasty.

Quiz Section

Question 1: What imaging modality provides the best assessment of labral tears in CAM-type FAI?

A) X-ray

B) CT scan

C) MRI/MRA

D) Ultrasound

Question 2: Which physical examination test is most sensitive for diagnosing FAI?

A) Ober’s test

B) FABER test

C) FADIR test

D) Thomas test

Question 3: Which risk factor contributes most significantly to CAM morphology development?

A) Genetic inheritance

B) Obesity

C) High-impact adolescent sports

D) Vitamin D deficiency

Answer & Explanation

1. Answer: C) MRI/MRA. Explanation: MRI, particularly with arthrography, is the most sensitive for detecting labral and cartilage pathology.

2. Answer: C) FADIR test. Explanation: The flexion-adduction-internal rotation test is highly sensitive for reproducing impingement pain.

3. Answer: C) High-impact adolescent sports. Explanation: Physeal stress from intense sports during skeletal maturation strongly contributes to CAM lesion formation.

References

[1] Ganz, R., Parvizi, J., Beck, M., Leunig, M., Notzli, H., & Siebenrock, K. A. (2003). Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clinical Orthopaedics and Related Research, 417, 112-120. 

[2] Agricola, R., Bessems, J. H., Ginai, A. Z., Heijboer, M. P., van der Heijden, R. A., Verhaar, J. A., & Weinans, H. (2012). The development of CAM-type deformity in adolescent and young male soccer players. American Journal of Sports Medicine, 40(5), 1099-1106. 

[3] Clohisy, J. C., Baca, G., Beaule, P. E., Kim, Y. J., Larson, C. M., Millis, M. B., & Sierra, R. J. (2013). Descriptive epidemiology of femoroacetabular impingement. Clinical Orthopaedics and Related Research, 471(6), 1810-1816. 

[4] Nepple, J. J., Prather, H., Trousdale, R. T., et al. (2013). Clinical presentation of patients with symptomatic anterior hip impingement. Clinical Orthopaedics and Related Research, 471, 3743–3749. 

[5] Palmer, A. J., Ayyar Gupta, V., Fernquest, S., et al. (2019). Imaging of femoroacetabular impingement-current concepts. Journal of Clinical Orthopaedics and Trauma, 10(1), 16–26. 

[6] Domb, B. G., Lareau, J. M., Baydoun, H., Botser, I. B., Millis, M. B., & Yen, Y. M. (2013). Arthroscopic labral reconstruction is superior to labral debridement in the hip: a matched-pair controlled study. American Journal of Sports Medicine, 42(1), 122-130. 

[7] Kuhns, B. D., Weber, A. E., Levy, D. M., & Nho, S. J. (2016). Hip arthroscopy for femoroacetabular impingement syndrome: clinical outcomes with minimum five-year follow-up. Journal of Hip Preservation Surgery, 3(2), 87–93.

Comments

Post a Comment