Hip Impingement Case Presentations and Discussion

Archival Presentation Notice: This article modernizes the multimedia presentation “Hip Impingement Case Presentations and Discussion” originally presented by Robert T. Trousdale, MD (Professor of Orthopedic Surgery, Mayo Clinic, Rochester, MN). The historical Flash lecture has been reconstructed into the synchronized video slide presentation above, with the original file preserved in the digital archives (hip_impingement_and_dysplasia_case_presentation.swf).

1. High-Yield Summary

Femoroacetabular impingement (FAI) syndrome is a motion-dependent clinical entity characterized by abnormal contact between the proximal femur and the acetabular rim, predisposing to chondrolabral injury and progressive secondary osteoarthritis:

• Dual Pathomechanical Paradigms: FAI presents as cam deformity (aspherical femoral head-neck junction exerting shear stress on the anterosuperior chondrolabral transition zone), pincer deformity (focal or global acetabular overcoverage causing linear compression, rim crushing, and secondary labral ossification), or most commonly a mixed morphology (86% of operative cases).
• The Dysplasia-Impingement Overlap: Acetabular dysplasia (lateral center-edge angle <20°) and structural impingement frequently coexist. In shallow sockets, compensatory anterior labral hypertrophy can progress to ossification, creating functional secondary impingement on an inherently unstable, undercovered joint where isolated rim trimming induces catastrophic destabilization.
• Diagnostic Triad (Warwick Criteria): Diagnosis mandates the confluence of characteristic patient symptoms (persistent anterior groin or deep hip pain with the “C-sign”), reproducible physical exam signs (pain upon flexion, adduction, and internal rotation [FADIR]), and definitive concordant imaging findings (alpha angle >55°, crossover sign, lateral center-edge angle >40°, or herniation pit).
• Preservation Strategy & Procedural Selection: First-line care begins with nonoperative rehabilitation focusing on core and pelvic biomechanics. When nonoperative care fails, joint-preserving surgery aims to restore spherical head-neck offset and correct rim overcoverage via minimally invasive hip arthroscopy, surgical hip dislocation (Ganz trochanteric flip osteotomy), or periacetabular osteotomy (PAO) for structural dysplasia.
• Critical Prognostic Determinant: Preservation surgery succeeds only when pre-existing articular cartilage remains viable. Tönnis grade ≥2 osteoarthritis or joint space narrowing <2 mm correlates with high failure and rapid conversion to total hip arthroplasty (THA).

2. Applied Surgical Anatomy & Danger Zones

Femoroacetabular Joint Architecture & The Labral Seal

The native hip joint is a deeply constrained ball-and-socket synovial articulation. The acetabular labrum is a triangular fibrocartilaginous ring anchored to the bony acetabular rim via a calcified transition zone, continuous with the transverse acetabular ligament inferiorly. The labrum deepens the acetabulum by approximately 21% and expands the volume capacity by 28%. Biomechanically, it acts as a fluid-tight suction seal, preventing direct cartilage-to-cartilage contact by sustaining high interstitial fluid pressurization, minimizing joint friction, and distributing compressive joint loads across the articular cartilage.

Vascular Anatomy & Preservation of Femoral Head Perfusion

The primary vascular supply to the femoral head originates from the deep branch of the medial circumflex femoral artery (MCFA). The deep branch travels posterior to the obturator externus tendon and anterior to the gemelli and obturator internus muscles. Upon crossing the posterior capsule, it pierces the periosteum near the superior gemellus insertion to produce 2 to 4 subsynovial ascending retinacular arteries (predominantly the lateral retinacular arterial group) along the posterosuperior aspect of the femoral neck. In surgical approaches to the femoral neck (both open surgical dislocation and arthroscopic cam resection), the posterosuperior retinacular vessels must be rigorously safeguarded between the 10:30 and 1:30 clock-face positions. Dissection posterior to the 12 o’clock position on the femoral neck creates an immediate hazard of avascular necrosis (AVN).

Surgical Approaches, Internervous Planes & Neurovascular Hazards

Three primary operative windows exist for accessing the femoroacetabular joint:

• Open Surgical Hip Dislocation (Ganz Technique): Utilizes a digastric trochanteric flip osteotomy. The internervous plane lies between the tensor fasciae latae (superior gluteal nerve) and the gluteus maximus (inferior gluteal nerve). The deep branch of the MCFA is directly protected by maintaining the integrity of the obturator externus muscle and its tendon attached to the trochanteric fossa. The sciatic nerve courses 1 to 2 cm posterior to the posterior acetabular rim and must be protected without uncalibrated retractor pressure.
• Hip Arthroscopy (Anterolateral Portal): Placed 1 cm superior and 1 cm anterior to the tip of the greater trochanter; pierces the gluteus medius. Endangers the superior gluteal nerve if placed >4 cm proximal to the trochanteric tip.
• Hip Arthroscopy (Mid-Anterior Portal): Establishes triangulation. Endangers the lateral femoral cutaneous nerve (LFCN), specifically its branching anterior divisions, which typically pass within 2 to 10 mm of the portal trajectory.
• Hip Arthroscopy (Distal Anterolateral Accessory Portal): Used for femoral cam osteochondroplasty and suture anchor placement; passes distal to the femoral nerve trunk which lies safely medial to the rectus femoris and iliopsoas.
• Direct Anterior Approach (Smith-Petersen / Hueter Interval): Utilizes the true internervous plane between the sartorius/rectus femoris (femoral nerve) and tensor fasciae latae (superior gluteal nerve). Key danger zones include the LFCN crossing the sartorius and the ascending branch of the lateral circumflex femoral artery (“the red canine”), which requires early electrocautery or ligation.

3. Pathogenesis & Biomechanical Mechanics

Cam Deformity Biomechanics: Outside-In Shearing Delamination

Cam morphology consists of an aspherical prominence or lost waistline at the femoral head-neck junction, most frequently situated along the anterosuperior to anterolateral quadrant. During deep terminal flexion coupled with internal rotation, this nonspherical osseous bump acts as a rigid wedge forced into the congruent spherical acetabular socket. This delivers substantial normal and shear stresses directly across the chondrolabral junction. Because the hyaline cartilage of the acetabulum is anchored to the underlying subchondral bone plate, cyclic shear stress cleaves the cartilage from the subchondral tidemark—a phenomenon termed “outside-in chondrolabral delamination.” The overlying labrum is gradually undermined, displaced laterally, and torn from its base.

Pincer Deformity Biomechanics: Linear Compaction & Labral Ossification

Pincer morphology is characterized by localized or generalized acetabular overcoverage. Focal pincer impingement stems from cranial acetabular retroversion (deficient posterior wall relative to prominent anterior rim). Global pincer impingement occurs in coxa profunda or protrusio acetabuli. During motion, the normal, spherical femoral neck impacts against the excessive acetabular rim. The labrum functions as the initial shock-absorbing bumper, undergoing direct compressive crushing, interstitial degeneration, cystic mucoid transformation, and progressive secondary dystrophic ossification. This bony apposition further deepens the rim, compounding the mechanical block. Furthermore, the femoral head is driven in a levered fashion against the posteroinferior acetabulum, producing a secondary “contrecoup” cartilage lesion.

The Dysplasia-Impingement Overlap Dilemma

A classic diagnostic and therapeutic dilemma highlighted in complex case presentations is the confluence of hip dysplasia and impingement. In patients with developmental dysplasia of the hip (DDH; lateral center-edge angle <20°), deficient structural bony coverage results in excessive contact stress on the superolateral rim. To compensate for uncontained joint loads, the anterior and superolateral labrum undergoes marked reactive hypertrophy. Over years of chronic micro-instability and excessive shear loading, this hypertrophic labrum calcifies and ossifies. Patients often present clinically with classic anterior impingement symptoms upon terminal flexion and internal rotation. If a surgeon misidentifies this presentation as primary pincer impingement and performs arthroscopic labral debridement and rim resection, the residual bony socket is rendered critically deficient, triggering acute iatrogenic dislocation or accelerated catastrophic joint collapse.

4. Natural History & Epidemiology

Femoroacetabular impingement is recognized as a principal mechanical etiology driving secondary hip osteoarthritis in non-dysplastic hips. Epidemiological analyses establish that asymptomatic cam morphology occurs in 15% to 25% of the general population, with a predilection for young, active males (up to 60%–70% in elite soccer, ice hockey, and basketball athletes). Cam development is linked to high-impact athletic loading during the adolescent growth spurt, where mechanical stress across an open proximal femoral physis triggers reactive bony apposition at the anterolateral head-neck junction.

Untreated symptomatic FAI follows a predictable path of joint degeneration. Chronic repetitive abutment progresses from asymptomatic chondral softening and subtle labral fraying to extensive chondrolabral separation, subchondral cyst formation (herniation pits), and progressive full-thickness chondral loss. Long-term prospective natural history investigations demonstrate that an alpha angle >65° confers a 3- to 4-fold elevated relative risk for developing radiographic osteoarthritis and necessitating total hip arthroplasty within 10 to 15 years.

5. Clinical Presentation

Clinical History

Patients typically present between the ages of 15 and 50 years with an insidious onset of anterior groin pain, frequently described using the classic “C-sign” (cupping the hand above the greater trochanter with the thumb resting posteriorly and fingers extending into the anterior groin). Pain is exacerbated by prolonged sitting, entering or exiting low automobiles, pivoting athletic activities, and squats. Mechanical symptoms such as clicking, catching, locking, or sharp giving-way episodes indicate unstable chondral flaps or displaced labral tears. Radiation down the anterior thigh to the knee or into the buttock is common, frequently causing diagnostic confusion with lumbar radiculopathy, adductor tendinopathy, athletic pubalgia (“sports hernia”), or sacroiliac joint pathology.

Physical Examination & Provocative Testing

Physical examination must follow an orderly, systematic protocol comparing the affected hip to the contralateral asymptomatic side:

• Passive Range of Motion: Marked restriction in passive internal rotation in 90° of flexion (often 30° in the normal contralateral hip) is the hallmark physical exam finding of cam-type impingement.
• FADIR Test (Flexion, Adduction, Internal Rotation): Passive flexion to 90°, adduction to 20°, and forced internal rotation. Positive finding: Reproduction of sharp anterior groin pain. Sensitivity: 95%–99%; Specificity: 10%–25% (highly sensitive screening test; negative test effectively rules out intra-articular impingement).
• FABER Test (Flexion, Abduction, External Rotation / Patrick’s Test): Measurement of distance from the lateral knee to the examination table. Positive finding: Pain elicited in the anterior hip indicates intra-articular pathology; posterior pain localizes to the sacroiliac joint. Sensitivity: 82%; Specificity: 25%.
• Posterior Rim Impingement Test: Passive hip hyperextension, abduction, and external rotation with the patient supine at the end of the examination table. Positive finding: Deep posterior or groin pain indicating posterosuperior pincer impingement or contrecoup abutment.
• Log Roll Test: Gentle passive internal and external rotation of the lower extremity in full extension. Positive finding: Pain or palpable clicking reflecting isolated synovitis or capsular irritation without loading the extra-articular muscle envelope.
• Anterior Apprehension Test: Extension and external rotation. Subjective apprehension or sensation of subluxation alerts the clinician to underlying acetabular dysplasia or capsular hyperlaxity rather than isolated FAI.

6. Imaging and Diagnostic Studies

Plain Radiographic Evaluation

High-quality plain radiography remains the mandatory first-line diagnostic modality. The standard radiographic series comprises:

• Standardized AP Pelvis (LCEA of Wiberg): Angle between a vertical line dropped through the center of the femoral head and a line extending to the lateral acetabular margin. Normal: 25°–39°; Dysplasia: 40°.
• Standardized AP Pelvis (Tönnis Angle): Angle of the sclerotic acetabular weight-bearing roof (sourcil) relative to the horizontal teardrop line. Normal: 0°–10°; Dysplasia: >10°; Overcoverage: <0°.
• Standardized AP Pelvis (Crossover Sign): Projection of the anterior acetabular wall rim lateral to the posterior wall rim in the superior cranial third of the socket, confirming cranial acetabular retroversion.
• Standardized AP Pelvis (Posterior Wall Sign): The posterior wall line passes medial to the center of the femoral head, demonstrating posterior wall deficiency.
• Standardized AP Pelvis (Ischial Spine Sign): Projection of the ischial spine into the pelvic cavity on AP view, secondary confirmation of hemipelvic retroversion.
• Dunn 45° or 90° Projection: Hip flexed 45° or 90°, abducted 20°, neutral rotation. The most sensitive projection for identifying anterosuperior cam lesions and quantifying the alpha angle.
• Cross-Table Lateral (True Lateral): Evaluates anterior head-neck offset and detects herniation pits without distortion from internal rotation.
• False-Profile View (Lequesne): Standing view at 65° angle to the cassette. Evaluates anterior center-edge angle (ACEA) to detect isolated anterior dysplasia (40°).

Advanced Imaging: MRA & Computed Tomography

Magnetic resonance arthrography (MRA) with intra-articular gadolinium or high-resolution 3.0-Tesla non-contrast MRI is the gold standard for visualizing soft-tissue intra-articular pathology. Key diagnostic targets include: chondrolabral transition zone signal alteration; base-of-labrum tears (frequently anterosuperior); acetabular cartilage delamination (seen as a thin line of fluid tracking beneath intact-appearing articular cartilage); subchondral herniation pits (lucency in the anterosuperior neck secondary to elevated intra-articular pressure); and secondary paralabral cysts.

Computed tomography (CT) with 3D multiplanar reconstructions provides definitive osseous characterization. CT scans are critical for calculating radial alpha angles around the entire 360° clock-face of the femoral head-neck junction, measuring true femoral anteversion, assessing global 3D acetabular version (eliminating errors from pelvic tilt), and mapping resection volumes prior to osteochondroplasty.

7. Classification Systems

Validated classifications direct clinical staging and surgical indications in femoroacetabular impingement and concurrent hip preservation pathology:

8. Treatment Algorithms & Surgical Indications

Nonoperative Management

First-line therapy for FAI syndrome requires a minimum of 3 to 6 months of comprehensive nonoperative care. Protocol components include:

• Activity Modification: Avoidance of extreme terminal flexion, internal rotation, deep squats, and high-impact repetitive pivoting.
• Targeted Physiotherapy (FASHIoN / UK FAI Protocol): Core stability conditioning, gluteus medius/maximus neuromuscular retraining, pelvic posture re-education, and anterior hip capsule stretching without impinging maneuvers.
• Diagnostic and Therapeutic Intra-Articular Injections: Fluoroscopically or ultrasound-guided intra-articular injection of 1% lidocaine/bupivacaine and 40 mg triamcinolone. Relief of >80% of pain during the anesthetic window confirms an intra-articular pain generator, distinguishing intra-articular FAI from athletic pubalgia or spine pathology.

Operative Interventions & Goals of Surgery

The primary objectives of operative management are: (1) fully decompress bony impingement conflicts by eliminating the cam asphericity and trimming excessive pincer rims; (2) preserve and repair the acetabular labrum to restore the hydrodynamic suction seal; (3) stabilize and address chondral lesions; and (4) preserve vascularity to the femoral head while avoiding joint instability.

• Hip Arthroscopy: The contemporary gold standard for primary cam, focal pincer, and chondrolabral pathology. Arthroscopic labral repair using knotless suture anchors and rim trimming (recessing the bony rim while preserving the labrum) followed by dynamic fluoroscopic assessment of cam osteochondroplasty. Capsular closure is mandatory to prevent iatrogenic micro-instability.
• Open Surgical Hip Dislocation (Ganz Technique): The reference standard for complex, multidirectional pathology, circumferential 360° cam lesions, severe slipped capital femoral epiphysis (SCFE) deformity, deep coxa protrusio, and cases requiring complex labral reconstruction or femoral neck osteotomy. Provides complete 360° exposure of the head-neck junction and acetabulum with verified preservation of the deep branch of the MCFA.
• Periacetabular Osteotomy (Bernese PAO): Indicated in true acetabular dysplasia (LCEA <20°) with secondary impingement or cranial retroversion requiring reverse rotation. Reorients the acetabulum while maintaining an intact posterior column and vascularized pelvic blood supply.

Operative Indications

• Persistent, debilitating groin pain unresponsive to ≥3 months of targeted physical therapy.
• Positive provocative physical examination (FADIR test).
• Concordant radiographic signs: Alpha angle >55°, LCEA >40°, crossover sign >20%, or subchondral herniation pit.
• Preserved joint space: Minimum ≥2 mm uniform joint space on standing radiographs.
• Tönnis grade 0 or 1.

Absolute Contraindications

• Advanced osteoarthritis (Tönnis grade ≥2 or joint space <2 mm).
• Frank acetabular dysplasia (LCEA <20°) without concurrent reorientation osteotomy (isolated rim trimming will precipitate dislocation).
• Severe osteopenia or active joint infection.

9. Outcomes & Long-Term Prognosis

Modern joint preservation delivers statistically significant and clinically meaningful improvements across validated patient-reported outcome measures (PROMs), including the International Hip Outcome Tool (iHOT-33), modified Harris Hip Score (mHHS), and Hip Outcome Score-Sports Subscale (HOS-SSS). In properly selected patients without advanced chondropathy, successful clinical outcomes and return to sports exceed 85% to 90% at 2- to 5-year follow-up.

In high-level athletic cohorts, return-to-play timelines average 6 to 9 months postoperatively. Long-term survivorship analyses demonstrate that preserved joint space (>2 mm) and intact acetabular cartilage (Beck grade 0–1) predict 10-year survivorship free of total hip arthroplasty exceeding 90%. Conversely, patients undergoing arthroscopic or open intervention with pre-existing full-thickness chondral loss (Outerbridge grade IV / Beck grade 3–4) demonstrate a 30% to 50% rate of conversion to THA within 3 to 5 years.

10. Complications & Risk Mitigation

Complications following surgical management of FAI are categorized by procedural timing and anatomical tier:

11. Pearls and Pitfalls

Precision execution requires vigilance across every diagnostic and operative phase:

• The Anterior Dysplasia Trap: Never rely exclusively on the AP pelvis radiograph to clear a patient for isolated pincer rim trimming. Always obtain a false-profile view to measure the anterior center-edge angle (ACEA). If anterior coverage is deficient (ACEA <20°), trimming the anterior rim will destabilize the hip and trigger rapid anterosuperior subluxation.
• Dynamic Arthroscopic Assessment: Following cam osteochondroplasty, always release joint traction, rotate the C-arm to obtain true profile views, and physically manipulate the hip through 90° of flexion, 20° of adduction, and 30° of internal rotation. Directly visualize the head-neck junction entering the acetabulum to confirm that no residual bony abutment persists.
• Avoid the 30% Neck Resection Rule: Never resect greater than 30% of the femoral neck diameter during cam osteochondroplasty. Biomechanical investigations demonstrate that resecting beyond 30% creates a dramatic stress riser that reduces torsional resistance and triggers spontaneous femoral neck fracture under physiological walking loads.
• Preserve the Labral Suction Seal: Debridement of the labrum should be strictly reserved for completely macerated, unfixable fibrocartilaginous tissue. Whenever viable, the labrum must be mobilized, the underlying rim trimmed, and the labrum anatomically refixed to the rim using suture anchors to maintain the critical synovial fluid seal.
• Mandatory Capsular Repair: In every hip arthroscopy where an interportal or T-capsulotomy is performed, routine anatomical capsular repair using braided non-absorbable sutures is mandatory. Unrepaired capsulotomies induce iatrogenic anterior micro-instability, progressive synovitis, and poor clinical outcome scores.

12. Clinical Controversies

Several fundamental controversies continue to shape academic discourse in hip preservation:

• Hip Arthroscopy vs. Open Surgical Dislocation: While hip arthroscopy has largely superseded open surgery due to reduced soft-tissue morbidity and faster immediate recovery, open surgical dislocation remains the undisputed benchmark for complex proximal femoral dysmorphism (e.g., severe post-Perthes deformity, retroversion of the femoral neck, or large circumferential pistol-grip deformities). Comparative randomized trials confirm equivalent short-term clinical outcomes in standard anterosuperior FAI, with arthroscopy demonstrating lower early complication rates.
• Management of Borderline Dysplasia (LCEA 20°–25°): Debate persists regarding whether patients with borderline dysplasia and concomitant cam impingement should undergo isolated hip arthroscopy (with labral preservation and tight capsular plication) versus periacetabular osteotomy (PAO). Contemporary evidence emphasizes that arthroscopy in borderline dysplastic hips with concurrent capsular laxity carries higher failure rates unless rigorous capsular shift/plication is performed.
• Labral Repair vs. Labral Reconstruction: In cases of severe chronic labral ossification, hypoplasia (<3 mm), or complex multi-segment degeneration, primary repair cannot re-establish an effective suction seal. Emerging clinical series support primary or revision labral reconstruction using iliotibial band or semitendinosus autograft/allograft, showing comparable PROMs to native labral repair.
• Asymptomatic Cam Morphology: With cam lesions detected in up to 25% of asymptomatic young athletes, universal consensus opposes prophylactic surgical resection in the absence of clinical symptoms or reproducible physical findings. Longitudinal surveillance remains the recommended standard of care.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Schmaranzer F, Kheterpal AB, Bredella MA. Best Practices: Hip Femoroacetabular Impingement. AJR Am J Roentgenol. 2021. doi:10.2214/AJR.20.22783 [Level I: Systematic Review / Meta-Analysis]
• Zingg PO, Ulbrich EJ, Buehler TC et al. Surgical hip dislocation versus hip arthroscopy for femoroacetabular impingement: clinical and morphological short-term results. Arch Orthop Trauma Surg. 2013. doi:10.1007/s00402-012-1616-2 [Level I: Randomized Controlled Trial]
• Zhang D, Chen L, Wang G. Hip arthroscopy versus open surgical dislocation for femoroacetabular impingement: A systematic review and meta-analysis. Medicine (Baltimore). 2016. doi:10.1097/MD.0000000000005122 [Level I: Systematic Review / Meta-Analysis]
• Martín Beck, Morteza Kalhor, Michael Leunig et al. Hip morphology influences the pattern of damage to the acetabular cartilage. Journal of Bone and Joint Surgery – British Volume. 2005. doi:10.1302/0301-620x.87b7.15203 [Level IV (Prognostic / Case Series): Seminal Conceptual / Observational Study]
• Reinhold Ganz, Michael Leunig, Katharina Leunig-Ganz et al. The Etiology of Osteoarthritis of the Hip. Clinical Orthopaedics and Related Research. 2008. doi:10.1007/s11999-007-0060-z [Level IV (Prognostic / Case Series): Seminal Conceptual / Observational Study]

15. Master Class Pro-Tip

When evaluating a patient with groin pain whose radiographs demonstrate both an ossified acetabular labrum and a shallow acetabular socket, the paramount clinical pearl is to recognize that the ossified labrum represents nature’s attempt to stabilize an inherently dysplastic hip. Measuring the lateral center-edge angle exclusively to the lateral edge of the ossified labrum artificially masks the underlying structural deficiency. The true bony acetabular coverage must be calculated from the original subchondral sclerotic sourcil, ignoring the ossified labral ring. Resecting the ossified rim under the mistaken assumption of isolated pincer impingement strips the joint of its critical load-bearing support, precipitating rapid joint space collapse. If the true bony LCEA is less than 20°, the patient requires a redirectional periacetabular osteotomy (PAO) with secondary intra-articular clearance, rather than isolated rim debridement.

Master Class Surgical Pearl: Diagnostic Trap of the Ossified Labrum in Acetabular Dysplasia