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Hip Arthroscopy and Treatment of Acetabular Anteversion and Impingement

Since 1931, when its concept was introduced, hip arthroscopy has made slow progress. Recently it has allowed appreciation and comprehension of a variety of conditions previously unrecognised, poorly understood or underestimated. This way it has brought hope, especially to an evolving generation of young, high-demand patients and athletes who seek minimally invasive solutions to occasionally subtle but disabling symptoms.

The young adult with hip pain presents a clinical challenge posed by the non-specific symptomatology and subtle clinical or imaging findings paired with demanding lifestyles and the trend for joint preserving surgery. Recent developments in the diagnosis and treatment of hip pathologies have enabled the orthopaedic surgeon to offer a new range of effective solutions, where the role of hip arthroscopy is central.

The normal arthroscopic anatomy and its variations have now been described systematically. Arthroscopic technique is becoming standard and popular. The reported complication range of 0.5-5% is gradually being reduced due to the continuous advances in technique, instruments and surgeon training. Postoperative care and rehabilitation are becoming more specialised and efficient.

The diagnostic efficacy of modern imaging modalities together with the concept of femoroacetabular impingement have increased our insight into the multitude of arthroscopically treatable pathologies. A major advance came with the realisation of the potential for arthroscopic alteration of hip biomechanics, addressing femoroacetabular impingement (FAI) and acetabular version abnormalities. Overall the arthroscopic management of FAI has so far been encouraging allowing a growing interest to develop. There has been no evidence to date, suggesting superior outcomes of open to arthroscopic FAI treatment.

Slowly but steadily, hip arthroscopy has become an established tool. In the future it is expected to play an expanding, central role, especially in the treatment of young adult hip pathologies.


2. GENERAL INTRODUCTION

Since 1931, when its concept was introduced by Burman,1 hip arthroscopy has made slow progress, despite its theoretical advantages of minimal invasion, high diagnostic efficiency and shortened postoperative recovery or rehabilitation. Understandably, the deep containment of the femoral head, its sphericity, the limited distraction potential and the multiple neurovascular structures that surround the hip joint have posed difficulties in standardising a safe technique. The technique has a steep learning curve and requires a time-consuming, special distraction setup and specific education.

The evolution of hip arthroscopy goes hand in hand with the appreciation and comprehension of a variety of conditions previously unrecognised, poorly understood or underestimated. It is an especially attractive approach for an evolving generation of young, high-demand patients and athletes who seek minimally invasive solutions to occasionally subtle but disabling symptoms. As the characteristics of pathological conditions of the acetabular labrum, of joint surfaces, of the ligamentum teres or the synovium are unveiled, hip arthroscopy has taken the first step towards answering the question of how to improve and prolong hip function before the establishment of osteoarthritis. The variety of arthroscopically treatable pathologies further includes hip instability,3 septic arthritis,4 problems after total hip and resurfacing arthroplasty5,6 and extra-articular lesions.7,8

A major advance in the understanding of intraarticular hip conditions came with the arthroscopic attempt to alter of the three-dimensional biomechanics of the hip joint, addressing femoroacetabular impingement (FAI) and acetabular version. Klaue et al9 described the acetabular rim syndrome in a series of mostly young adult patients in 1991. They maintained it is secondary to hip dysplasia and a precursor of osteoarthritis. Effective treatment by peri-acetabular osteotomy and arthrotomy addressed the issues of hip orientation and the associated limbus tear. In 1993 Snow et al10 recognised anterior impingement in four patients with Legg-Calve-Perthes disease (LCPD) and treated it effectively by arthroscopic debridement and proximal femoral osteotomy. In 1999 Myers et al11 described anterior femoroacetabular impingement after Bernese peri-acetabular osteotomy and Reynolds et al12 described acetabular retroversion as a cause of hip pain and the associated posterior wall sign. Eijer et al13 in 2001 identified the association between malunion of femoral neck fractures and femoroacetabular impingement and Ganz et al14 reported on successful open decompression of FAI using the trochanteric flip osteotomy. Nevertheless the possible significant morbidity of a surgical dislocation of the femoral head has been the reason why arthroscopic techniques have been developed and initially applied especially in athletes.15-19 In 2002 Notzli et al20 attempted to quantify the femoral involvement in anterior impingement by means of the width of the femoral head-neck junction and the described alpha angle. The first report of arthroscopic treatment of FAI was seen in 2004.21

Since then a growing interest in arthroscopic FAI treatment has appeared. In 2005 Sampson22 published results for FAI comparable with those of open treatment. A report by Bardakos et al23 of the early outcome of treatment of cam-type FAI with the addition of arthroscopic femoral osteoplasty was encouraging.

Interestingly the theory that femoroacetabular impingement leads to osteoarthritis has been strongly supported by the concept described initially by Tonnis and Heinecke24 and formulated into an "integrated mechanical concept" by Ganz et al.24,25 They support that primary osteoarthritis can actually be secondary to "subtle developmental abnormalities" associated with FAI whereby the cam lesion produces acetabular delamination and acetabular retroversion and overcoverage produces pincer impingement and further damage. Early surgical intervention is recommended to avoid progression to osteoarthritis. Further elaboration of this theory by Bardakos and Villar26 has indicated the predictive value of the medial proximal femoral angle and the posterior wall sign on progression of FAI to osteoarthritis.

Finally the importance of acetabular anteversion has recently been taken into account with increasing appreciation in FAI surgery. Tonnis et al24 in their classical description of the "relationship of acetabular and femoral anteversion with osteoarthritis of the hip" emphasized the need to evaluate in detail any changes in anteversion. Abnormal combined anteversion, as depicted by the McKibbin instability index,27 is associated with alterations in range of rotation, pain and osteoarthritis. Acetabular and/or femoral osteotomy was the proposed solution. Together with the addition of the term 'acetabular retroversion' by Reynolds et al12 the issue of the three dimensional correction of acetabular version has been further elaborated since28 and associated with FAI29 and symptomatic acetabular labral tears.30

Overall the arthroscopic management of FAI has so far been encouraging. There has been no evidence to date, suggesting superior outcomes of open to arthroscopic FAI treatment.31


3. AETIOLOGY AND CLASSIFICATION

AETIOLOGY OF HIP PAIN IN THE YOUNG ADULT

The young adult with hip pain presents a clinical challenge posed by the non-specific symptomatology and subtle clinical or imaging findings paired with the demanding lifestyle of young people and the trend for joint preserving surgery. Recent developments in the diagnosis32-34 and treatment14,15,35-38 of hip pathologies have enabled hip arthroscopists to offer a new range of effective solutions. The multitude of painful hip pathologies includes:39-41

  1. Intra-articular

    2. Symptomatic acetabular labral tears,42 cam, pincer or mixed femoroacetabular impingement (FAI),43,44 chondral flaps or defects, avascular necrosis,44 degenerative osteoarthritis, loose bodies, post-traumatic intra-articular debris (fracture, dislocation, osteochondral injury),45 septic arthritis,46 chondrolysis,41 neoplasms and synovial abnormalities (PVNS, synovial osteochondromatosis),47 osteochondritis dissecans,48 ligamentum teres injuries49, Legg-Calvé-Perthes disease (LCPD) and slipped capital femoral epiphysis (SCFE).

  2. Extra-articular local

    3. Developmental dysplasia of the hip (DDH), bursitis,50 tendinitis (iliopsoas, adductor, abductor), gluteus medius and minimus tears,50 snapping hip syndrome (iliotibial band,50 iliopsoas41) stress fractures, neoplasms (e.g. osteoid osteoma) and local nerve entrapment.

  3. Extra-articular referred

    4. Gilmore's groin,51 inguinal or femoral hernia, spondyloarthropathy,52 ankylosing spondylitis52 and radiculopathy.

  4. Systemic

    5. Rheumatoid arthritis,53 Crystalline arthropathy (gout and pseudogout),48 Crohn's disease, psoriasis, Reiter's syndrome, corticosteroid use, sickle cell anaemia, psychosocial, alcoholism and systemic lupus erythematosus.

AETIOLOGY OF OSTEOARTHRITIS

Surgical attempts to treat the symptoms of the young adult hip have the ambition of decelerating the progress to osteoarthritis. This is based on Harris's theory of the developmental internal derangement of the hip.54 This theory describes the significance of intra-articular morphological characteristics, including the flattening and the "bump" of the femoral head, the pistol grip and hook deformity and the "intra-acetabular labrum". It also highlights the effect of different roentgenographic parameters such as the acetabular angle, acetabular roof, acetabular depth and centre-edge (CE) angle. Both the morphological and the roentgenographic parameters are associated with progression of mild SCFE and LCPD to osteoarthritis. Harris concludes that osteoarthritis of the hip may essentially be a secondary condition only.

The theory is now enhanced by the addition of the concept of femoroacetabular impingement,10,25,55 i.e. abnormal contact due to structural abnormalities of the acetabulum and/or the proximal femur. This offers a biomechanical explanation of early hip degeneration in young patients with "normal" hips.56-59 Kubiak-Langer et al mapped the usual location of the impingement zones and proposed the quantitative significance of the reduction in range of movement associated with impingement. The authors proposed that surgical treatment could be guided by the quantified severity of impingement.

However, the significance of osteoarthritis has been debated based on evidence that FAI is not always symptomatic. Wyss et al60 reported a 12% overlap in the range of internal rotation between symptomatic and asymptomatic patients based on positional MRI analysis. Moreover Yamamura et al61 reported that the Asian lifestyle often requires hip positions that cause impingement in spite of the low frequency of primary hip osteoarthritis in Japan and other Asian countries.

Recently Bardakos and Villar26 attempted to isolate the significant radiographic factors that predict progression of osteoarthritis in FAI. They proposed two predictors: the medial proximal femoral angle and the posterior wall sign. They concluded that, depending on the incidence of those two predictors, "a hip with cam impingement is not always destined for end-stage arthritic degeneration".

Three factors have been added to the concept of FAI: the femoral head-neck offset, femoral head sphericity and the acetabular version (decreased anteversion or true retroversion).24,55

CLASSIFICATIONS

Our perception of the pathologies of the young adult hip and their treatment necessitates common recognition of classifications. According to Ganz et al,56 femoroacetabular impingement is a dynamic, abnormal contact between the femoral head-neck junction and the acetabular rim, which can lead to acetabular cartilage damage and labral tears. It is classified as pincer-type due to acetabular overcoverage or retroversion,12,62 cam-type due to abnormality of anterolateral head-neck offset20,55,63 and a common mixed-type.64

Labral tears have been classified by Lage et al65 according to their aetiology as traumatic, degenerative, idiopathic and congenital. The authors also morphologically categorise them as radial flap tears, radial fibrillated, longitudinal peripheral or unstable labral tears. Ligamentum teres tears have been described as complete, partial or degenerate.49

It is also of relevance to note classify osteoarthritis. The Tönnis radiographic classification grades osteoarthritis (OA)24 from 0 to 3 (0= No signs of osteoarthritis; 1= Slight narrowing of joint space, slight lipping at joint margin, slight sclerosis of femoral head or acetabulum; 2=Small cysts in femoral head or acetabulum, increasing narrowing of joint space, moderate loss of sphericity of femoral head; 3=Large cysts, severe narrowing or obliteration of joint space, severe deformity of femoral head, avascular necrosis). Alternatively, the Outerbridge classification66 from 0 to 4 is used (0= normal, 1= softening and swelling of the cartilage; 2= fragmentation and fissuring in an area half an inch or less in diameter; 3= the same as grade 2 but an area more than half an inch in diameter is involved ; 4 there is erosion of cartilage down to bone).


4. ANATOMY AND BIOMECHANICS

ARTHROSCOPIC ANATOMY OF THE HIP

A systematic view and description of arthroscopic anatomy is sine qua non of a complete arthroscopy. Constructive though they are, personal interpretations of the orientation of lesions which abound in the literature are gradually being replaced by common, standard descriptions to avoid confusion. Few authors have looked into a systematic description of the normal intraarticular anatomy and its variations.1,67-70

Arthroscopic technique necessitates the descriptive division of the hip joint into a central and a peripheral compartment. The two are enclosed by the articular capsule and separated by the rim of the acetabulum.

The central compartment includes the acetabular and femoral joint surface. The femoral head and acetabulum are connected by the ligamentum teres and separated by the acetabular labrum and the transverse ligament. The peripheral compartment includes the part of the femoral articular surface that is not in articulation with the acetabular articular cartilage in different hip positions. It further includes the distal femoral head and neck surrounded by the capsule which clearly defines the zona orbicularis and medial and lateral synovial folds.

Central compartment

At the centre of the acetabular cavity the acetabular (cotyloid) fossa is identified. This extends inferiorly to the acetabular notch and is surrounded by the cartilaginous, horseshoe-shaped lunate surface. The transverse ligament bridges but doesn't seal the notch, therefore forming the inferior recess which should not be mistaken for a cartilaginous tear. The ligamentum teres originates from the posterior-inferior acetabular fossa which is lined by a dense connective tissue and covered for its lower two thirds by mobile adipose tissue, the pulvinar. The hyaline cartilage that clearly distinguishes the lunate surface from its surrounding structures is in peripheral continuity with the fibrocartilaginous labrum. It normally includes the stellate crease, an indentation corresponding to the anterior apex of the acetabular fossa which is deficient of hyaline cartilage and should not be mistaken for a pathological fissure. Santori and Villar69 described a transverse groove, running anteriorly from the acetabular fossa to the anterior margin of the acetabulum. The authors proposed that this iliopubic groove may represent an incomplete fusion of the iliac and pubic component of the triradiate region.

The acetabular labrum is a fibrocartilaginous structure of triangular cross-section, in perimetric continuity along the periphery of the lunate hyaline cartilage except from the margins of the acetabular fossa where it is separated by a distinct groove. Miller and Villar70 described a bifid posterior labrum; an anatomic variant that should not be mistaken for a labral tear. More often than not the normal labrum is in continuity with the transverse ligament. It is commonly inverted but it may often be everted or mobile. The adjacent peripheral synovium forms the perilabral sulcus.

The ligamentum teres extends from the posterior-inferior acetabular fossa to the femoral head fovea. It shows a banded appearance with occasional capillaries but no substantial vasculature is usually obvious on arthroscopy. Varying degrees of flexion and rotation facilitate visualisation and access to the ligamentum teres and the femoral head. This way it is estimated that approximately 80% of the articular surface of the femoral head may be visualised.

Topographically the acetabulum and labrum are commonly reported to consist of anterior (superior or inferior) and posterior (superior or inferior) quadrants. In addition, the clock-face method has often been utilised to describe areas of the acetabulum and femoral head. Recently Ilizaliturri et al71 have proposed a 6-zone method of geographic description of acetabular or femoral head pathology. The numerical order of the zones is unaffected by whether they describe right or left hips. The authors concluded that the method is more reproducible than the clock-face method.

Peripheral compartment

The structures identified external to the acetabular cavity but still inside the hip joint comprise the peripheral compartment. This is lined by the highly vascular articular capsule. Peripheral to the labrum, a perilabral sulcus, anterior and posterior gutters present as the margins of the hip joint. Medial and lateral synovial folds course longitudinally parallel to the femoral neck away from the acetabular margin on either side. Further distally, these are interrupted by a prominent transverse capsular condensation, the zona orbicularis. The area between the zona orbicularis and the medial synovial fold is in close proximity with the iliopsoas tendon. The head-neck junction including a significant part of the peripheral hyaline cartilage of the femoral head can be observed. Arthroscopy allows dynamic direct assessment of tracking at the level of the acetabular rim. This facilitates the diagnosis of femoroacetabular impingement and permits direct verification and documentation of the effect of arthroscopic impingement surgery.

THE VASCULARITY OF THE LABRUM

In a cadaveric study Kelly and Shapiro72 investigated the vascularity of the hip labrum in quest of regional differences in vascular penetration. They described the labrum as being relatively avascular, with increased vascularity at its capsular side and suggested possible implications in the healing potential of those labral tears which occur in the vascular compared to the inner, articular zone.

BIOMECHANICS

Hip contact stress is a quantity known to be affected by lateral coverage of the acetabulum in dysplasia. Daniel et al73 added the importance of the acetabular anteversion angle to lateral coverage of the acetabulum by comparing its impact on hip contact stress between normal and staircase walking. They suggested that acetabular anteversion should be considered in biomechanical evaluation of the hips, especially in the presence of dysplasia.

A finite element model as well as in vitro evidence by Ferguson et al74-76 supports the hypothesis that the labrum has a sealing effect by creating intra-articular hydrostatic fluid pressure and a limiting effect of the rate of cartilage layer consolidation. The direct implication is that labral pathology may contribute to early joint degeneration through the alteration of load transfer and the stresses at cartilage layer level.


5. DIAGNOSIS

HISTORY

Young adults often present with subtle and atypical discomfort and vague descriptions of the onset and progress of their pain. Diagnosis is often delayed as the patients remain active. However, a high index of suspicion of the multiple subtle intra and peri-articular pathologies can now be expected, as our diagnostic accuracy and therapeutic efficiency is recently being reinforced by non-invasive modalities and by arthroscopy.

The hip is a typical area where multiple, occasionally superimposed pathologies project. A detailed synopsis of the patient's symptom features is an essential first step towards the diagnosis. Special attention is paid to clues in identifying the anatomical origin of the complaint (intra-articular, extra-articular local, extra-articular referred or systemic). A so-called C-sign,77 whereby the patients touch their groin with their index finger and have their thumb at the greater trochanter, usually indicates intra-articular aetiology. Appearance of the discomfort after repetitive hip flexion as well as prolonged sitting is often seen with impingement. This may be associated with acute anterior inguinal pain and/or locking and catching indicating mechanical intra-articular sources such as labral tears, unstable articular cartilage or loose bodies.

Specific lateral hip pain (trochanteric) is not necessarily 'trochanteric bursitis'. It can be associated with muscle fatigue and a Trendelenburg sign, as in dysplastic hips. Occasionally it is combined with mechanical symptoms and or intra-articular snapping. It may also be part of extra-articular snapping syndromes, namely iliotibial band or iliopsoas tendinopathy. The combination of intra-articular and lateral hip pain is common.

Intra-articular pain often radiates down the thigh and may be superimposed with knee, lumbar and sacroiliac spine problems. Deterioration with coughing or sneezing may point towards hernias or lumbar disc prolapse as possible sources. Morning or post-inactivity stiffness may indicate osteoarthritic changes. Slow recovery from morning stiffness may indicate rheumatoid arthritis.

The degree to which pain interferes with the patient's normal activities is of critical importance. The level of possible incapacity at work, the desirable level of activity, the relation to sports and hobbies and the interference with other co-morbidities are crucial to the personal perception of pain and functional limitation. All these factors will determine and guide the therapeutic regime.

PHYSICAL EXAMINATION

Observation of gait for possible limping, antalgic or other pathological gait patterns can help differentiate between intrinsic hip and multiple other pathologies. The position in which the patient lies can indicate fixed-flexion deformity. Avoidance of significant hip flexion indicates possible femoro-acetabular impingement.

Palpation of the hip area differentiates between specific superficial or diffuse deep localisation of pain and is a clue for possible inflammation, abductor weakness and painful soft tissue lesions or hernias.

Assessment of leg length is important. Abductor strength is assessed by means of the Trendelenburg test and abductor testing against resistance in the lateral decubitus position. Fixed flexion deformity can be shown by the Thomas test.

Supine log-rolling allows assessment of intra-articular pain and its association with selective limitation of internal or external rotation. Assessment of range of movement is a very informative tool. Wyss et al have shown that "internal rotation can be used as a non-invasive tool to predict the risk of impingement".60 They found a strong correlation between internal rotation at 90 degrees of hip flexion and reduced space between bony contours, indicating impingement. Range of hip movement has been correlated with impingement and with its associated post-operative success.78

Femoroacetabular impingement can be more specifically assessed by means of provocative manoeuvres. The anterior impingement sign9 is defined as groin discomfort in passive flexion, adduction and internal rotation of the hip. Posterior-inferior impingement is underscored by the flexion-abduction-internal rotation (FABER) test. The test is positive when the affected hip combined movement is restricted compared to the contralateral healthy hip. The apprehension test of passive extension-adduction-external rotation is used to assess anterior hip stability and can be used to assess posterior FAI.

Snapping can usually be reproduced by the patients themselves and palpated by the examiner when it is related to the iliotibial band. Iliopsoas snapping79,80 or tendinitis can be elicited by active flexion against resistance.

IMAGING

Standard radiographic assessment includes an anteroposterior (AP) pelvic view (a weight-bearing view has been recommended to investigate dysplasia81), a cross-table lateral and/or frog-lateral views. Assessment of structural abnormalities is combined with evaluation of variations in the femoral and/or acetabular anatomy. Multiple radiographic measurements are informative in the diagnosis of structural hip abnormalities and crucial in the preoperative planning. Measurements specific to the investigation of FAI are the Alpha angle of Notzli20 and measurement of head-neck offset or sphericity. Asphericity is best shown by the Dunn view82 in 45 degrees of flexion or by a cross-table lateral view in internal rotation.

Interestingly AP or externally-rotated cross-table lateral views are likely to miss this deformity.83 In the assessment of acetabular retroversion it is of utmost significance to ensure the correct pelvic tilt and rotation is projected on the AP pelvic radiograph.84 Prerequisites of a correct pelvic tilt are two symmetrical obturator foramina, radiographic teardrops or iliac wings and a range of distance within 1-3 cm between the tip of the coccyx to the pubic symphysis.82 Alternatively, the average distance between the superior pubic symphysis and the sacrococcygeal junction has been measured to be 32.3mm in men and 47.3mm in women.84 Based on the correct pelvic tilt, acetabular retroversion can be assessed by the cross-over and posterior wall signs.12,62

Computed tomography (CT) is recommended to investigate for fracture fragments or loose bodies.85 Magnetic resonance imaging (MRI) is indicated for chronic hip pain, avascular necrosis, bone marrow oedema or muscle injuries and the anatomy of the femoral head-neck offset.20,55,86 Magnetic resonance arthrography (MRA) is indicated in the assessment of intra-articular hip pathologies.32-34,40 MRA signs of labral tears are 'labral blunting, absence, displacement, intra-substance contrast material and contrast material at the acetabular-labral junction'.87 Studies of the effectiveness and predictive value of MRA have documented the excellent positive predictive value with regards to labral tears and articular cartilage pathologies. However, the low negative predictive value of MRA emphasizes the need for arthroscopic diagnosis and treatment of such lesions, in case the clinical suspicion has not been confirmed by MRA.32

Finally ultrasound is very useful especially in the detection and differential diagnosis of peri-articular pathologies including bursitis, tendinitis, tendon ruptures, soft tissue tumours and lymphadenopathy, fluid collections etc. Ultrasound-guided hip injections definitely have a role in the differential diagnosis.88

LABORATORY

Analyses of blood, urine and synovial fluid are used to diagnose possible acute or chronic inflammation or infection. Standard investigations for inflammatory arthropathy and spondyloarthropathy need to be performed upon clinical suspicion.


6. INDICATIONS FOR SURGERY

Evidence supports arthroscopic treatment for many conditions. There are also indications where arthroscopy may prove beneficial due to its theoretical advantages and satisfactory early results. The array of indications2,89,90 is outlined below.

Common indications include symptomatic labral tears, femoroacetabular impingement (FAI), chondral lesions, loose bodies, osteochondritis dissecans, ligamentum teres injuries, iliopsoas bursitis and snapping hip syndrome.

Labral Tears are consistent arthroscopic findings when associated with a clear history of mechanical symptoms.91 There are few exceptions92,93 to the observation that labral tears most frequently occur at the anterior quadrant of the acetabulum2,65 and that they fail to heal with conservative treatment.58 Arthroscopy is excellent in diagnosing them as they can often be missed by other imaging methods including magnetic resonance arthrography (MRA).94 Arthroscopic treatment of symptomatic acetabular labral tears and possible associated instability is an effective and efficient method.42,48 Recent studies indicate that every attempt must be made to apply labrum-preserving surgery35,76,95-99 in order to produce satisfactory short and hopefully long-term results.

Labral disease is often associated with femoroacetabular impingement.100 In the last few years the question of whether we need to additionally correct the structural deformity during treatment of the labral pathology has arisen.101 FAI is of course a distinct pathology that is likely to predispose to osteoarthritis.102 The holistic approach to treat hip pain associated with FAI would be to address both the effect (e.g. a labral tear or cartilage delamination) as well as the cause (cam, pincer or mixed FAI with or without acetabular or femoral dysplasia or version abnormality). FAI has been treated successfully by surgical dislocation14,103 as well as arthroscopically assisted, "limited104-open" approaches.15,101,105 The arthroscopic approach decreases the postoperative morbidity and allows return to high-demand lifestyle, as is the case for athletes.17,23,31,106-111

Imaging of lesions of the articular surfaces of the femoral head and acetabulum is difficult. These lesions are often associated with other hip conditions. They are often found at the anterior aspect of the acetabulum in conjunction with labral tears.58 Interestingly the common pathogenetic mechanism involves the development of the so-called "watershed zone" or area of the "wave sign",17,57 an area of early subchondral delamination at the chondrolabral junction. Arthroscopy can offer early detection and treatment of chondral lesions by re-attachment of the watershed zone, radiofrequency probing of chondral splits, debridement of unstable flaps and microfracturing.112,113

Loose bodies are typically characterised by mechanical symptoms and are often not detected by radiographic studies.114 Upon clinical suspicion, computed tomography contrast enhancement has a high diagnostic efficacy.2 Arthroscopy offers a definitive diagnostic tool and a minimally invasive treatment of choice.45 It also typically applies in cases of primary synovial osteochondromatosis where it has been shown to provide satisfactory outcomes in at least 50% of cases47 in a minimally invasive approach suitable for the possible recurrences typical of this condition. Arthroscopy also allows a most accurate means of biopsying synovial abnormalities including pigmented villonodular synovitis (PVNS),115 crystalline arthropathies and autoimmune arthritis.

Patients with a ruptured ligamentum teres are likely to suffer pain and instability due to its possible biomechanical role.49,116 Tears have been classified as complete, partial or degenerate. Reported results following debridement have been satisfactory with isolated lesions but not in the case of associated intraarticular injuries.49

Arthroscopic bursectomy for recalcitrant trochanteric bursitis117 and iliopsoas release for bursitis or snapping hip syndrome48,118 has been reported to be a viable alternative to open surgical intervention.

Other described indications include avascular necrosis of the femoral head (to diagnose and treat possible associated mechanical symptoms),44,119 intra-articular debris following trauma2 and septic arthritis.120-123

Occasionally hip arthroscopy has been used to alleviate mechanical symptoms in mild to moderate osteoarthritis with less favourable results,119 to assist partial resurfacing procedures,90 to diagnose and treat the unsuccessful total hip or resurfacing arthroplasty124,125 and as a last resort in the investigation of intractable hip pain.126


7. PREOPERATIVE PREPARATION AND PLANNING

DECISION FOR ARTHROSCOPIC TREATMENT

Arthroscopy is our minimally-invasive weapon in the diagnosis of intra-articular and peri-articular pathologies. However, some intra-articular lesions detected by arthroscopy might only by a result of other structural hip abnormalities. Therefore, in order to treat such problems effectively a series of radiographic parameters26,127,128 needs to be assessed on x-rays and MRI or CT .

Routine preoperative assessment involves documentation of the radiographic grade of osteoarthritis according to Tönnis and Heinecke.24 Furthermore identified herniation pits129 are noted. The neck-shaft angle (124-136°),128 femoral antetorsion (retrotorsion is abnormal),130 Tönnis angle,24 acetabular index (<10°),24 Wiberg's centre-edge (CE) angle (20-40°),131,132 Sharp's angle133 and the femoral head extrusion index134 can be used to assess dysplasia. Coxa profunda is excluded by observation of the relation of the acetabular floor to the ilioischial line.103

With regards to FAI it is especially important to assess for possible morphological abnormalities of the proximal femur and acetabulum, including asphericity of the femoral head, head-neck offset and acetabular version. Asphericity is indicated by a 'pistol-grip deformity'135 or an abnormal a-angle of Notzli (women<50°, men<68°)20,136 which can be measured with the aid of 'Mose circles'.137 Version abnormalities are assessed by means of the cross-over (absent normally)12 and posterior wall (absent normally)12,62 signs. Recent evidence has underscored the significance of the medial proximal femoral angle (MPFA, normal range:80-89°)138 and the presence of the posterior wall sign in predicting progression of osteoarthritis in FAI.26 According to some authors, surgery for FAI has become a mainstay of treatment because conservative treatment is rarely successful.97,139

CHOICE OF SURGICAL TREATMENT

Based on the above radiographic data, we are faced with different surgical options.41 In structural abnormalities (developmental dysplasia of the hip (DDH), slipped capital femoral epiphysis (SCFE), Legg-Calvé-Perthes (LCPD) deformity or avascular necrosis) standard treatment may primarily include open surgery. However cam and/or pincer deformity in the absence of the above conditions is an indication for arthroscopic treatment with or without open osteoplasty.

Intra-articular hip pathologies which are not associated with structural bony abnormalities are clear indications for hip arthroscopic treatment. Arthroscopy has a role in treatment of lateral hip pathologies including trochanteric bursitis or snapping iliotibial band as well as of pain due to iliopsoas tendinopathy. The role of hip arthroscopy in the treatment of pronounced osteoarthritis (OA), inflammatory arthritis, chondrolysis and osteonecrosis is not yet clear.

ARTHROSCOPIC CONSIDERATIONS

Patient characteristics need to be taken into account. In the case of young athletes for example, one should bear in mind that it may be impossible for leg traction to produce adequate hip joint distraction. Another factor to consider in patient selection is morbid obesity which may be a contra-indication for hip arthroscopy simply because of the standard lengths of instruments available.

In all cases, availability of a 70 as well as a 30 degree arthroscope is essential to overcome individual difficulties and to gain maximal visualisation. Manual and power instruments need to be available, including various shaver blades and/or flexible radiofrequency probes. A hip-aiming system can be used. Chondral treatment options (microfracture treatment, chondroplasty, mosaic-plasty, partial-surface arthroplasty) should be kept open and the necessary kits of instruments or implants must be available. Rehabilitation starts with the pre-operative consultation and physiotherapy, including prospective documentation of outcome measures.


8. OPERATIVE TECHNIQUE

Patient

Three are the cornerstones of successful hip arthroscopy: positioning, positioning and positioning! There are two standard arthroscopic positions: the supine140 and the lateral.141 The supine position utilises a standard fracture table similar to positioning for hip fracture fixation, therefore familiar to theatre staff, minimising the need for specialised traction devices. Similarly familiar to most surgeons is the positioning of the image intensifier and orientation to the hip joint. The anterior portal is easily accessible. On the other hand the lateral position possibly offers easily reproducible bony landmarks and relative ease of applying the peri-trochanteric portals. In this article the author's preferred lateral position will be the basis of the technique description.

In the lateral position with the affected hip up, manual traction is applied through a purpose-built boot with a specialised hip distractor allowing controlled movement of the hip in all directions. A well-padded perineal post is applied at the affected proximal thigh rather than the perineum with the fulcrum allowing simultaneous abduction of the proximal femur when traction is applied. The final position is in 10-20° flexion, 20° abduction and neutral foot rotation. This allows a resultant distraction force roughly in line with the femoral neck.

Manual longitudinal traction is applied until evidence of an "inverted crescent" or "vacuum sign"142 on fluoroscopy signifies adequate negative intraarticular pressure created by joint distraction. A minimum 10-15 mm of distraction is required. The position is documented and marked and traction is released to allow prepping and draping. With the traction re-applied and the vacuum sign created the joint is distended with fluid through a 17G spinal needle positioned 2 cm proximal to the tip of the greater trochanter.

Central compartment

Similarly anterolateral and posterolateral paratrochanteric portals are made by use of needles, guide wires and annulated trocars. A 70° arthroscope is usually preferred to allow adequate visualisation but a 30° arthroscope may also be needed. A systematic arthroscopic examination of the central compartment follows. Initially debridement of labral tears or chondroplasty is done by means of arthroscopic shaving or radiofrequency ablation. Additional labral repair and microfractures may be appropriate.

Pincer or mixed type of FAI

Arthroscopic acetabular recession is used to suppress the augmented anterior acetabular coverage of the femoral head in pincer or mixed type FAI. The intraoperative questions that the surgeon is faced with are: to ignore a pincer lesion on the basis of a satisfactory cam osteoplasty; to recess the acetabular rim by performing osteoplasty without elevation of the labrum; or to perform a full-blown acetabular recession with elevation and re-attachment of the anterior labrum ?

Following careful recognition of the pincer lesion margins and elevation of the anterior labrum with an arthroscopy knife the anterior wall is recessed with an arthroscopy burr. Conservative acetabular osteoplasty is recommended to avoid instability. The labrum is reattached by means of suture anchors or fibrin glue. The degree of decreased acetabular anteversion or retroversion that may benefit from arthroscopic recession is unknown. Significant retroversion and/or associated acetabular or femoral dysplasia may be better candidates for extra-articular correction by means of osteotomies.

Peripheral compartment and cam type of FAI

Traction is released and the hip is flexed. This allows better visualisation and avoids the risk of neuroapraxia. A superior portal 4-5 cm superior to the greater trochanter is made under fluoroscopy as previously. A 30° viewing arthroscope is usually adequate for viewing this compartment. The anterolateral portal is also used. Examination of the peripheral compartment follows143. The impingement (cam) lesion extent is assessed by a dynamic examination in varying degrees of flexion and rotation. Successful femoral osteoplasty is completed by radiofrequency ablation of soft tissues and periosteum followed by bone burring and is confirmed by a second dynamic examination. Care is taken to avoid extending the excision posterior-lateral to the lateral synovial fold (risk of perforation of the lateral retinacular vessels) and doing a very extensive excision that could increase the risk of fracture.144 As a general rule of thumb a depth of 5mm is considered safe.


9. POSTOPERATIVE CARE AND REHABILITATION

Hip arthroscopy is a day-case procedure. Rehabilitation starts from the day of surgery. The aid of a dedicated hip physiotherapist is necessary. The patient is discharged with instructions to touch-weight bear for the first four days for comfort and for an additional period of up to 4-6 weeks in the case of microfractures, labral repair or acetabular recession. Full range of movement exercises are encouraged immediately and commencement of physiotherapy and low impact exercise is recommended from the first few days. The use of continuous passive movement (CPM) has been implemented by some.145 Different structured programs of physiotherapy can be followed, based on the pathology identified in the operating theatre and the aggressiveness of the surgical intervention.18,146 Return to sport is not advisable earlier than three months postoperatively. An average rehabilitation period of 3-4 months is expected. The patient is followed-up 6, 12 and 24 weeks postoperatively.

Following 'simple' hip arthroscopy (labral debridement only, removal of loose bodies, synovial biopsy) partial weight-bearing for only a few days may be recommended. Emphasis is given to range of movement and stretching exercises for the first five weeks. Hydrotherapy (swimming, walking) commence at 2 weeks. Cardiovascular exercise including stationary bike and stepper/cross trainer are gradually introduced from the second week and the intensity increased over the next two weeks. Intensive muscle strength and control exercises generally start from the second week. Dynamic/power/pleiometric exercises (lunges, jump lunges, box jumps, ski-type training) commence at 4 weeks. High-impact training is best avoided for the first 6 weeks.

In cases of labral repair or moderate femoral osteoplasty touch-weight-bearing for four weeks is recommended. Emphasis is given to range of movement and stretching exercises as well as hydrotherapy from the second week. Cardiovascular exercise is gradually introduced from the second week (stationary bike) and the intensity increases from the sixth week onwards (stepper/cross trainer). Intensive muscle strength and control exercises generally start from the second week but intensity is increased after the sixth week. Dynamic/power/pleiometric exercises commence at 6 weeks. High-impact training is best avoided for the first 8 weeks.

In case of chondral surgery and extensive femoroacetabular impingement and/or labral surgery touch-weight-bearing for four weeks is advised. Range of movement and stretching exercises as well as hydrotherapy start from the second week and become more intense after the fourth week. Cardiovascular exercise is gradually introduced from the third or fourth week (stationary bike) and the intensity increases from the sixth week onwards (stepper/cross trainer). Intensive muscle strength and control exercises generally start in 4-6 weeks. Dynamic/power/pleiometric exercises commence at 7-8 weeks. High-impact training is best avoided for eight weeks. In this group of patients there is a greater variety of response to physiotherapy which is individually tailored.


10. COMPLICATIONS

The generally reported complication rate of 0.5-5%2 is showing a trend towards reduction due to the continuous advances in technique, instruments and surgeon training. As hip arthroscopy evolves the reported complication rates within the same series have improved. The largest series of complications in the literature, quote overall complication rates of 1.4%147 (1054 patients included), 1.6%142 (640 patients), 3.8%148 (1000 patients) and 5%2 (1500 patients). Sampson148 reported significant improvement down to a recent complication rate of 0.5% in the last 500 patients from an initial 15% in the first 60 cases of the series reported.

Reported complications include neuroapraxia (lateral cutaneous nerve of the thigh,149-151 femoral,142 sciatic,141,152 pudendal nerve140,141,152-156) or rarely permanent nerve damage,151 portal bleeding or haematoma,142 instrument failure,142 trochanteric bursitis,142 vaginal tear142 or labial haematoma,153 myositis ossificans149 or heterotopic bone formation,43 reflex sympathetic dystrophy,155 abdominal pain,153 intra-abdominal fluid extravasation148,157 (followed by death due to cardiac arrest in one case of arthroscopy following acetabular fracture157), avascular necrosis,148 femoral neck fracture148 and infection142.

The majority of complications of hip arthroscopy are related to joint distraction2 and portal creation.90 Transient neuroapraxia is the most common injury2. Iatrogenic injuries that are difficult to quantify and probably under-reported158 but definitely related to outcome, include cartilage scuffing and damage of the labrum upon entry into the joint. Deep vein thrombosis or pulmonary embolism have not been reported in relation to hip arthroscopy.158

Few issues about complications related to arthroscopic treatment of femoroacetabular impingement (FAI) need to be addressed. First, extensive resection can theoretically predispose to fracture but the borders to suboptimal decompression are not clearly defined. One answer has been provided in the work of Mardones et al144 whose results are suggestive of an upper limit of resection at 30% of the anterolateral quadrant of the head-neck junction. Others have recommended an area of resection limited to 5-7mm in depth and 8-12 mm in width.18 Second, avascular necrosis is possible due to injury of the medial circumflex femoral artery upon excision of the cam lesion or upon lateral acetabular recession. This is a hypothetical concern as there has not been any reported relation with FAI. Respect to the principle of no capsular or bony resection posterior to the lateral synovial fold should be sufficient to minimize this risk.158 Finally, the concern that excessive anterior hip capsulotomy or capsulectomy or excessive bone removal during acetabular rim recession may result in hip instability has been raised158 but has not been formally reported in the literature.

Reports of complications from the larger series have shown that most complications are related to patient positioning, traction and fluid management. Emphasis needs to be placed on adequate padding and lateralisation of the perineal post and traction time limited to 2 hours.147,148,159 Favourable results have been reported for arthroscopic treatment of FAI but the literature is still limited and anecdotal.


11. SUMMARY

Modern advances in diagnosis and the trend for minimally invasive approaches in orthopaedics made apparent the need for soft tissue surgery of the hip joint. Hip surgeons are no longer content with merely excluding conditions that would set clear indications for arthrotomy, arthroplasty or osteotomy. However a large population of the patients that historically would be treated 'conservatively' can now be given hope that they may not have to sustain the morbidity of conservative treatment in their quest to postpone hip arthroplasty. Surgeons now have at their fingertips an impressive array of diagnoses and reassuringly effective, minimally invasive treatments that only hip arthroscopy can offer to hip patients.

Symptomatic acetabular labral tears, femoroacetabular impingement (FAI), chondral lesions, osteochondritis dissecans, ligamentum teres injuries, snapping hip syndrome, iliopsoas bursitis and loose bodies are now considered standard indications. Other indications include osteonecrosis, synovial abnormalities, crystalline arthropathy, infection and post-traumatic intra-articular debris. Finally arthroscopy has also been utilised following unsuccessful hip arthroplasty and hip trauma.

The evidence base supporting the effectiveness of the intervention has been reinforced with large retrospective and some prospective studies. Technical advances and standardization of portals have improved the efficiency and lowered the complication rate to as low as 1.4%. The addition of femoral and acetabular osteoplasty in the treatment of FAI has encouraging results. Controversy is being reduced in a fast steady pace although there are still relatively few long-term outcome studies.

An indication of the still relatively poor evidence base is the National Institute for Health and Clinical Excellence (NICE) guidance of 2007 in the UK which concluded that current evidence on safety and efficacy of arthroscopic femoro-acetabular surgery for hip impingement syndrome did not appear adequate for it to be used without special arrangements for consent and for audit and research. This of course is a valid point; however at this early stage it is of vital importance for the technique to become widespread and popular. With this aim societies of hip arthroscopy have recently been established. High quality courses and fellowships are being organised to make the new generations of surgeons more familiar with arthroscopic hip pathology. Long-term studies are establishing the standard indications, results and complications of the procedure.

As a result specialised surgeons in referral centres have started undertaking high-volume arthroscopic surgery and developing specialised teams. Subspecialty interests are being developed. For example specific experience may be gained in the paediatric population. Minimal invasion is expected to preserve vascularity and growth, hopefully minimizing the surgical risk of osteonecrosis in children. Paediatric indications include septic arthritis, labral disorders - developmental hip dysplasia, slipped capital femoral epiphysis and Legg-Calve-Perthes disease.

Another promising area of arthroscopic focus is that of sports injuries. The published results of hip arthroscopy are known to be excellent in elite athletes. This group of patients may be subject to a separate approach: arthroscopic surgery for timely return to previous levels of symptom-free activity, not necessarily delaying progress to osteoarthritis. In young patients arthroscopy could fulfil expectations of better quality of life and activity.

Finally based on previous experience with knee and shoulder arthroscopy, one can postulate that treatment of impingement or ligamentum teres lesions will become routine practice in the near future.

Overall the widespread use of hip arthroscopy will assist us in determining patient outcome and satisfaction. Results will then be stratified according to extent, grade etc. Further classification will promote better results. It would be no exaggeration to postulate that in the future early detection and treatment of hip pathology will shift the hospital elective hip admissions towards a higher degree of day case surgery. Whether timely arthroscopic surgery will make any difference to the logistics of hip arthroplasty is a fascinating question that only the future can answer.


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