Hip Arthroscopy

Hip arthroscopy is a minimally invasive surgical technique for diagnosing and treating intra-articular and periarticular hip pathology. The primary indication is femoroacetabular impingement (FAI) with its associated labral tears, though the indications continue to expand.

Morphology is not disease. Cam and pincer shapes are common in people who have no symptoms at all: a systematic review of 2114 asymptomatic hips found cam morphology in 37% overall, 54.8% in athletes against 23.1% in the general population (Frank 2015). That is why the Warwick Agreement (2016) defines FAI syndrome as symptoms plus signs plus imaging findings; imaging morphology alone is not a diagnosis.

Who. Symptomatic FAI presents in athletes and active individuals, typically aged 20-45. Cam is more common in young athletic males, pincer in middle-aged females, and mixed morphology is the most common pattern overall. The high-risk sports load the hip in flexion and include ice hockey, football, martial arts, ballet and Australian Rules football.

Natural history. Untreated FAI leads to progressive cartilage damage and eventual osteoarthritis.

Indications for hip arthroscopy.

• Femoroacetabular impingement (cam, pincer or mixed)
• Labral tears
• Chondral lesions (debridement, microfracture)
• Ligamentum teres tears
• Loose bodies
• Synovial disorders (PVNS, synovial chondromatosis)
• Hip instability (capsular plication)
• Iliopsoas tendon release

The joint. The hip is a ball-and-socket joint with inherent bony stability, enhanced by the acetabular labrum, the capsule and the ligaments. The femoral head is covered by hyaline cartilage except at the fovea, where the ligamentum teres attaches.

The labrum. A fibrocartilaginous ring attached to the acetabular rim, it deepens the acetabulum by 21% and increases its surface area by 28%, and it creates the suction seal that gives the joint its stability. Its blood supply comes from the superior gluteal, inferior gluteal and obturator vessels and is better peripherally than centrally, which is worth remembering when a repair is planned.

Capsule and ligaments.

• Iliofemoral ligament (Y-ligament of Bigelow): the strongest, lying anteriorly
• Pubofemoral ligament: inferior, limits abduction
• Ischiofemoral ligament: posterior, limits internal rotation
• Zona orbicularis: circular fibres around the femoral neck

Neurovascular structures.

• Femoral neurovascular bundle: anterior, protected by iliopsoas, and rarely injured
• Lateral femoral cutaneous nerve: crosses 1-2cm distal and medial to the ASIS
• Superior gluteal nerve: exits above piriformis
• Sciatic nerve: posterior

The two compartments. The arthroscopist works in two spaces, and both need assessing. The central compartment is entered only under traction and holds the labrum, the acetabular cartilage, the ligamentum teres and the femoral head. The peripheral compartment needs no traction and holds the head-neck junction, the medial synovial fold and the zona orbicularis.

Cam morphology. The femoral side. An abnormal bump at the head-neck junction, most often anterosuperior, results from a developmental abnormality during skeletal maturation. During flexion and internal rotation the abnormal convexity shears against the labrum and cartilage, and the pattern of damage is an outside-in abrasion of the acetabular cartilage.

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Pincer morphology. The acetabular side. Overcoverage of the femoral head may be global (coxa profunda or protrusio acetabuli) or focal (retroversion of the superior acetabulum). The rim inflicts a crush injury on the labrum, with contrecoup cartilage damage on the posterior acetabulum.

Three patterns. FAI is classified by which side of the joint carries the abnormal bone. Cam is femoral-based, the aspherical head-neck junction; pincer is acetabular-based, the overcoverage; mixed has both components and is the most common presentation, at approximately 80% of cases. Treating one component in isolation leads to failure, so the intra-operative assessment has to cover both.

Labral tears (Seldes).

• Type 1: detachment of the labrum from the acetabular cartilage, the most common
• Type 2: a cleavage plane within the labral substance

Cartilage damage (Beck).

• Grade 0: normal cartilage
• Grade 1: softening (malacia)
• Grade 2: partial-thickness defect
• Grade 3: full-thickness defect
• Grade 4: exposed subchondral bone

The presentation. A young athletic patient with activity-related groin pain of insidious onset, typically present for more than 3 months, worse with prolonged sitting, pivoting and hip flexion, and often accompanied by clicking, catching or giving way. The symptoms to listen for:

• Deep anterior groin pain, shown as the C-sign: the patient cups a hand over the greater trochanter
• Pain with prolonged sitting, the theatre sign
• Pain with hip flexion activities such as squatting and stairs
• Mechanical symptoms: clicking, catching, locking

The history that changes the plan. Age at onset. Sport participation, with hockey, soccer and dance particularly high-risk. Prior treatments and the response to them. Mechanical symptoms, which suggest labral pathology. Night pain, which suggests more severe pathology or an alternative diagnosis.

Examination. Watch the gait for a Trendelenburg or antalgic pattern, note any pelvic obliquity or limb-length difference, and look for a hip flexion contracture. Measure flexion, extension, abduction, adduction, internal and external rotation and compare each with the other side; FAI typically shows decreased internal rotation in flexion.

Provocative tests.

• FADIR (flexion-adduction-internal rotation), the anterior impingement test: supine with hip and knee at 90° of flexion, then passive adduction and internal rotation. Positive if it reproduces the patient's groin pain. The most sensitive test for FAI, at approximately 95%, but specificity is only approximately 50%, so it must be correlated with imaging
• FABER (flexion-abduction-external rotation), the Patrick test: positive if it reproduces groin pain or motion is limited; can indicate labral or sacroiliac joint pathology
• Stinchfield test: a resisted straight-leg raise reproduces groin pain; suggests intra-articular pathology
• Log roll: passive internal and external rotation with the hip extended; pain suggests intra-articular pathology

Differential diagnosis. Because morphology is so often silent (Frank 2015), FAI syndrome is a clinical diagnosis of exclusion as much as of inclusion. Actively exclude the mimics before attributing pain to impingement.

Radiographs. The AP pelvis is the essential initial view, and it can only be read if it is positioned properly, with the coccyx 1-3cm above the symphysis; on it, assess the centre-edge angle, the crossover sign and the posterior wall sign. A lateral view, cross-table lateral (Dunn view) or frog-leg lateral, is where the alpha angle and the head-neck offset are assessed.

The measurements.

• Alpha angle, on an axial view (cross-table lateral radiograph or axial MRI): the angle between the femoral neck axis and the point where the head-neck junction exceeds the radius of the head. Normal is less than 50°; cam morphology is greater than 55°
• Centre-edge (CE) angle, on the AP pelvis: the angle between a vertical line through the femoral head centre and a line to the lateral acetabular edge. Normal is 25-40°; pincer is greater than 40°
• Crossover sign: the anterior and posterior acetabular walls cross before the lateral edge in a figure-of-8 pattern, indicating focal retroversion

MRI. Standard MRI evaluates the labrum, the cartilage and the periarticular soft tissues, and axial oblique views are the best for measuring the alpha angle. MR arthrogram is the gold standard for labral pathology: intra-articular gadolinium improves labral tear detection, with a sensitivity greater than 90%. Radial MRI, a series of views radiating from the femoral neck axis, is best for comprehensive assessment of where the cam lesion lies.

CT. 3D CT provides excellent bony detail of cam and pincer morphology and is useful for surgical planning; low-dose protocols reduce the radiation.

Diagnostic injection. Intra-articular local anaesthetic under fluoroscopic guidance can confirm an intra-articular source of pain. Greater than 50% relief suggests intra-articular pathology and predicts a good surgical outcome.

Who. Non-operative treatment is the choice for:

• Mild symptoms with minimal functional limitation
• Patient preference
• Significant osteoarthritis, a relative contraindication to arthroscopy
• Medical contraindications to surgery
• Initial management while the diagnosis is being confirmed

Algorithm

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Diagnosis. A positive FADIR test with anterior groin pain in a young active patient, correlated with cam or pincer morphology on imaging and an MR arthrogram to assess the labrum, then confirmed by the injection response.

Candidacy. The good candidate is typically aged 18-50, has a preserved joint space of greater than 2mm with minimal to moderate osteoarthritis (Tönnis 0-1), has failed 3-6 months of conservative management, and has a positive impingement test with pain relief from injection. That last combination, a positive impingement test with a positive injection, is the group with the best outcomes. The poor candidate has any of:

• Advanced osteoarthritis (Tönnis greater than 2)
• Severe joint space narrowing (less than 2mm) with arthritis, where arthroplasty is the consideration
• Significant dysplasia
• Inflammatory arthritis
• Expectations that are unlikely to be met

Planning. Identify the cam location on radial MRI or 3D CT, assess the extent of any pincer morphology, plan the labral management (repair versus debridement), assess the cartilage and decide on capsular management. The decisions that are made on the day are the extent of osteochondroplasty needed, labral repair versus reconstruction, microfracture for cartilage lesions and capsular plication for instability.

Positioning. Supine on a fracture table is the most common: a well-padded perineal post, the operative limb in a traction boot, and the other limb on a padded post or abducted in a leg holder. The position is familiar, fluoroscopy is easier and anterior access is better; the price is the pressure of the perineal post. Lateral positioning on a dedicated hip arthroscopy table, operative hip up and traction applied through a foot attachment, has no perineal post (less nerve risk) and gravity assists visualisation, but it is unfamiliar to some surgeons and requires the specialised table.

Traction. Typically 25-50lbs of force is needed. Apply longitudinal traction, then internal rotation to break the vacuum seal, and confirm at least 6mm of distraction on fluoroscopy. The target is to be off traction inside 60 minutes: in the 1615-hip series complications rose significantly beyond 60 minutes, and pudendal neurapraxia tracked traction time directly (61.5 versus 43.8 minutes). If the case is running long, release traction and continue in the peripheral compartment, which needs none; cam resection, capsular work and peritrochanteric access are all done off traction. Two hours is the point beyond which serious injury should be expected, not a permission.

Portals. Three standard portals:

• Anterolateral (AL): the primary viewing portal, 1cm anterior and superior to the tip of the greater trochanter
• Anterior: the primary working portal, at the intersection of a horizontal line from the ASIS and a vertical line from the greater trochanter
• Posterolateral (PL): 1cm posterior and superior to the greater trochanter, for supplementary viewing and working

Establish them under fluoroscopic guidance with an air arthrogram, confirm the trajectory with a spinal needle, and after the skin incision use blunt trocar insertion to avoid nerve injury.

The sequence.

1. Position the patient, supine or lateral
2. Apply traction
3. Establish the portals under fluoroscopy
4. Central compartment work first: labrum, cartilage
5. Release traction
6. Peripheral compartment work: cam resection
7. Dynamic assessment of impingement-free range of motion

Central compartment procedures.

• Labral repair: suture anchors for peripheral labral tears
• Labral debridement: for tears that cannot be repaired
• Acetabular rim trimming: for pincer lesions
• Microfracture: for focal cartilage defects
• Ligamentum teres debridement: for symptomatic tears
• Loose body removal

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Peripheral compartment procedures.

• Osteochondroplasty: resection of the cam lesion to restore the head-neck offset
• Capsulotomy management: repair or plication as needed
• Iliopsoas release: for a symptomatic internal snapping hip

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Capsular management. Access to the central compartment requires dividing the iliofemoral ligament. An interportal capsulotomy, a transverse cut connecting the anterolateral and anterior portals, is the basic exposure; a T-capsulotomy adds a longitudinal limb down the femoral neck for wider peripheral-compartment and cam access, at the cost of dividing more of the ligament.

Why closure matters. The iliofemoral ligament is the primary anterior stabiliser of the hip, so an unrepaired capsulotomy, especially a T-capsulotomy, can produce anterior microinstability, a recognised cause of persistent pain and failure and of the rare frank dislocation after hip arthroscopy. Routine capsular closure or plication is increasingly advocated, and the evidence and consensus most strongly support closure in the higher-risk hips where capsular competence is critical: borderline dysplasia, ligamentous laxity or hypermobility, and revision surgery. In the normal, well-covered hip the benefit of routine closure over selective closure is still debated, but most hip-preservation surgeons now repair the capsule.

The numbers. In the largest prospective multicentre series (Larson 2016, 1615 hips) the overall complication rate was 8.3%, with mostly low-grade events; the rates below are from that series unless stated otherwise.

Nerves. The single most important modifiable factor is traction, and the time threshold and the pudendal timing data are in the traction paragraph above. The lateral femoral cutaneous nerve is the most commonly affected nerve overall; pudendal (perineal) numbness is less common.

Other complications.

• Fluid extravasation: risk of abdominal compartment syndrome with prolonged cases (no extra-abdominal extravasation observed in the 1615-hip series)
• Femoral neck fracture or stress fracture: 0.1%; the risk comes from excessive osteochondroplasty, so avoid resecting more than about 30% of the neck circumference
• Instability: from excessive rim trimming or an unrepaired capsulotomy (no iatrogenic instability in the 1615-hip series); the impingement correction has to be balanced against preserving stability
• Iatrogenic chondral injury: 1.2%; iatrogenic labral puncture: 0.9%
• Heterotopic ossification: 0.8%; NSAID prophylaxis reduces the incidence
• Avascular necrosis: rare (none in the 1615-hip series), associated with damage to the lateral epiphyseal vessels
• Superficial portal infection: 1.1%
• DVT 0.1% and PE 0.1%: standard risk-stratified VTE prophylaxis

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By procedure. The generic protocol is adjusted to what was done in the joint.

Short term. At 2 years 85-90% of patients are satisfied. 80-90% return to sport, 70-80% at the same level. Pain scores improve significantly, by 70-80%, and the modified Harris Hip Score improves in 85% or more.

The cartilage decides the long term. The Beck grade of the cartilage predicts both the early result and whether the hip is still the patient's own at 10 years.

Prognostic factors. Age under 40, minimal osteoarthritis, a preserved joint space, labral repair rather than debridement and a positive pre-operative injection response all favour a good result. Advanced osteoarthritis, a joint space under 2mm, full-thickness cartilage loss, age over 50 and significant acetabular dysplasia are the unfavourable factors.

Global epidemiology. FAI morphology is common and frequently asymptomatic, so imaging must always be correlated with symptoms and signs. A PRISMA systematic review of 2114 asymptomatic hips (mean age 25 years) found asymptomatic cam morphology in 37% overall - 54.8% in athletes versus 23.1% in the general population - and the mean alpha angle in asymptomatic hips was 54° (Frank 2015). This is the single most important framing fact: morphology alone is not disease.

The diagnosis is a triad, not a radiograph. The 2016 Warwick Agreement (international consensus, 25 endorsing societies) introduced the term FAI syndrome, requiring symptoms + clinical signs + imaging findings together. Imaging morphology without symptoms is not FAI syndrome and should not be treated (Warwick 2016).

Guidance side by side

Patient selection drives outcome (global, evidence-led). Across health systems the same predictors apply: preserved joint space (2mm or more) and labral repair predict better results, while advanced arthritis (Tönnis 2 or more) and joint space less than 2mm predict failure and conversion to total hip replacement (Philippon 2009). The decisive modifiable intra-operative safety factor is traction - time greater than 60 minutes raises the complication rate (Larson 2016).

Registries and practice variation. Hip arthroscopy is a hip-preservation rather than an arthroplasty procedure, so it is not captured by the major joint replacement registries (NJR England & Wales, AOANJRR Australia, AJRR USA, SHAR Sweden). These registries are nonetheless relevant downstream: a meaningful minority of arthroscopy patients with pre-existing chondral wear later convert to total hip arthroplasty, and registry analyses are used to compare outcomes of THA after prior hip arthroscopy. Volume and access vary widely - arthroscopy is concentrated in high-resource centres with fluoroscopy and traction tables and a learning curve effect on complications, whereas in many regions open surgical hip dislocation or non-operative care predominate. FAI syndrome is recognised worldwide in flexion-loading sports (football/soccer, ice hockey, Australian Rules football, dance, martial arts), reflecting the higher cam prevalence seen in athletes.

Borderline dysplasia. A centre-edge angle of 20-25° is borderline. Such a hip may benefit from arthroscopy if there is an FAI component, but the failure rate is higher than in non-dysplastic hips, and where the dysplasia is significant a periacetabular osteotomy (PAO) should be considered instead.

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Revision arthroscopy. Success rates are lower than for primary surgery, at 60-70%. The most common reasons for failure are inadequate cam resection, a missed pincer and an untreated labral tear, and revision does better when there is a clear, identifiable pathology to address.

Adolescents. Arthroscopy may be considered in skeletally mature adolescents, and the physes must be confirmed closed before any aggressive osteochondroplasty.

Labral reconstruction. Indicated when the labrum is deficient and cannot be repaired. The options are iliotibial band autograft, tensor fascia lata and allograft; it is an emerging technique with promising early results.