Classification of Acetabular Cartilage Lesions Claudio Mella, MD Acetabular cartilage lesions are frequently found during hip arthroscopy. The arthroscopic view offers an exceptional perspective to assess cartilage injuries especially in their early stages. We know that articular cartilage damage occurs progressively up to the development of hip osteoarthritis requiring joint replacement. Numerous studies have shown that advanced cartilage damage is an indicator of a bad prognosis when performing hip arthroscopy. It is important to identify before surgery patients with advanced cartilage damage that are not candidates for a hip preservation procedure (hip arthroscopy). In addition to clinical evaluation, Radiology is very useful to estimate the degree of arthritis (Tönnis Classification); narrowing of joint space (<2 mm) advanced chondral damage. Magnetic Resonance Imaging (MRI) is also useful for assessing cartilage damage. The formation of subchondral cysts and acetabular bone edema are signs of poor prognosis corresponding to significant damage of the articular cartilage. Nowadays there are advanced techniques to determine with more accuracy the damage of the articular cartilage prior to a possible hip arthroscopy (T-2 Mapping, G-Gemric). However, arthroscopic vision is considered more accurate to assess acetabular cartilage damage, especially in early stages. For a correct evaluation of these different stages of chondral damage, a proper classification is necessary to describe these lesions in a simple and reproducible manner. Several classifications exist to assess the cartilage damage in other joints, which also have been used in the hip (Outerbridge, ICRS). However, the hip has special conditions that make it different from other joints. It is exceptional that these lesions occur secondary to a trauma with a normal hip anatomy. They mostly occur secondary to a mechanical overload resulting from a pre-existing deformity as hip dysplasia or femoroacetabular impingement (FAI). These pathological forces on the cartilage of the acetabulum (overload, shearing forces) occur initial in the peripheral portion of the acetabulum. Femoral cartilage damage occurs in more advanced stages of the disease as a sign of osteoarthritis of the hip. Lesions identified during arthroscopy can vary greatly from the earliest stages to the most advanced. The progression of the chondral damage in the hip is relatively systematic. The following questions always arise, regardless of the type of lesion found during the arthroscopy: Is the injury reparable? What kind of repair is recommended? What is the prognosis and risk factor of developing osteoarthritis? To answer these questions we need a classification that allows the surgeon to guide the
treatment, including prognostic factors, permitting also to compare the results of various cartilage repair techniques. To classify the cartilage damage of the hip, topographic, morphological or physiopathology factors of the articular damage can be considered. Topographic classification: Classification of Ilizaliturri et al: From the topographical point of view, the classification of Ilizaliturri et al. is the most common classification used. It divides the acetabulum area in 6 geographic zones, using the acetabular fossa and ligamentum teres as reference. In this classification, zone 2 (anterior/lateral) and zone 3 (lateral) are areas where the acetabular cartilage damage occurs more frequently (anterior and lateral zone) corresponding to the zone of the mechanical impact in patients with FAI or the mechanical overload in cases of dysplasia. Zone system - Ilizaliturri et al. Arthroscopy 2008 Anterior Right Hip Acetabulum Acetabular Fossa Posterior Morphologic classifications: Outerbridge Classification This classification is probably the most frecuently used to classify Outerbridge Classification Grade 1 Softening or edema the chondral damage in different Grade 2 Fragmentation /tear < 0.5 inches joints. It was initially created to Grade 3 Fragmentation /tear > 0.5 inches classify the chondral damage of Grade 4 Erosion of cartilage down to bone the knee and first published in 1961. It distinguishes 4 degrees of chondral damage, where grade 1 is an initial lesion characterized by softening or chondromalacia and grade 4 is the most advanced lesion with full thickness damage of the cartilage with exposed subchondral bone. The
classification is based on the depth of chondral damage, considering it as an isolated lesion. It has the advantages of being simple to apply and is used to classify chondral lesions in other orthopedic fields. The disadvantage is that it is not designed specifically for the hip and don t include different pathophysiology considerations of acetabular cartilage damage. Another disadvantage is the difficult distinction between grades 2 and 3 to quantify the extent of the fragmentation of the acetabular cartilage. M. Beck classification This classification, M. Beck - Classification published by M Beck Grade 1 Malacia; roughering of surface, fibrilation in 2004, is also based on the Grade 2 Debonding, loss of fixation to the subchondral morphology and bone; macroscopically sound cartilage, carpet depth of the phenomenon chondral damage as an isolated lesion in Grade 3 Cleavage, loss of fixation to the subchondral bone; the acetabulum. It frayed edges, thinning of the cartilage, flap distinguishes 4 degrees of Grade 4 Full thickness defect progression of the lesions, where grade 1 is Chondromalacia or Cartilage Fibrillation and grade 4 is a full-thickness injury (similar to the Outerbridge classification). As an intermediate stage, degree 2 is described as debonding or loss of chondral fixation but with an intact cartilage surface (wave sign) unlike grade 3 where there is already loss of fixation and thinning of the cartilage and formation of a chondral flap. This classification has the advantage that it was created specifically for the hip, based on the damage occurring in cases of FAI. A potential disadvantage is that it was developed based on macroscopic findings in open surgery (surgical dislocation) that nowadays can be considered equivalent to arthroscopic vision.
Konan / Haddad classification This classification, published in 2011 by Konan et. al, describes chondral lesions in 4 degrees based on the arthroscopic vision and morphology of the damage. It also considers pathophysiologic factors of FAI (its relationship with the chondrolabral junction) and its extension from the chondrolabral junction towards the central or loading area of the acetabulum. The loss of chondral fixation to the subchondral bone (wave sign) is classified as Grade 1; Grade 2 correspond to a clear separation of the chondrolabral junction, the articular cartilage Konan / Haddad Classification Morphology Grade 1 Wave sign, loss of fixation of subchondral bone Grade 2 Grade 3 Grade 4 Extention Grade A Grade B Grade C Cleavage tear, obvious separation at the Chondolabral junction, but arthroscopic probing of the tear shows adherence of the articular cartilage to the underlying bone with no evidence of delamination Delamination, macroscopic debonding of the cartilage from the acetabular bone Exposed bone < 1/3 Distance from acetabular rim to the fossa 1/3 to 2/3 of this distance > 2/3 of this distance remains attached to the bone (this is one of the most common injuries found during arthroscopy in cases of FAI). Grade 3 is the delamination and detachment of the acetabular cartilage (chondral flap formation) starting at the chondrolabral junction; grade 4 is the full-thickness injury with exposed subchondral bone. Each of these groups can be supplemented by the name A, B and C depending on their extension from the chondrolabral union to the central part of the acetabulum. Grade A is an injury at <1/3 distance from the chondrolabral junction and the acetabular fossa; Grade B is an injury from 1/3 to 2/3 distance and Grade C is an injury with > 2/3 distance to the acetabular fossa. Thus, in addition to the description of the morphology and depth of the lesion, it describes its extension in the joint space. Given these considerations, this classification must be considered as one of the most comprehensive classifications to assess acetabular cartilage damage, especially in patients with Fermoroacetabular Impingement. It can also be a good basis for generating algorithms to treat chondral injuries. Lastly, the extension of lesions in the acetabulum, aside from their depth, can also be considered an important prognostic factor, which is not considered by the aforementioned classifications. A disadvantage of this classification is that it has not been used and validated in a bigger number of cases or utilized in scientific papers after its publication.
T. Sampson classification T. Sampson and his group have also proposed a classification for acetabular articular cartilage lesions in an effort to create an algorithm for treatment. He includes in his classification not only the type of chondral damage as mentioned in the Outerbridge and Beck Classification. He includes also the size of the lesion and the condition of the labrocartilage junction, which is essential to decide the best option for treatment. Thomas Sampson Classification AC 0 = No Damage AC 1 = Softening, no wave sign AC 1w = Softening with wave sign; intact cartilage union AC 1wTj = AC 1wD = AC 1wTjD= Softening with wave sign, and torn labrocartilage junction Softening with wave sign; intact labrocartilage junction with delamination Softening with wave sign; torn labrocartilage junction with delamination AC 2 = Fibrillation AC 2Tj = Fibrillation with torn labrocartilage junction AC 3 = Exposed bone small area < 1 cm 2 AC 4 = Exposed bone large area > 1 cm 2 Abbreviations: A, acetabulum; C, cartilage defects; D, with delamination; Tj, Torn labrocartilage junction; w, with wave sign. An ideal classification, which should be simple and reproducible, should consider the depth of the lesions and their location and extension in the acetabulum. It should be a guide to select the best treatment option and should offer a prognostic factor for our patients. The acetabular cartilage lesions secondary to hip impingement generally follow a typical pattern. Impact injuries begin in the peripheral portion near the chondrolabral junction with a detachment of the cartilage from the subchondral bone. This produce the chondromalacia or the so-called wave sign represented by grades 1
of Outerbridge, Beck and Konan/Haddad. Subsequently, the chondrolabral junction is separated (Konan/Haddad Grade 2). As the lesion progresses, the cartilage detaches from the chondrolabral junction towards the central part of the acetabulum, generating a flap of variable depth or thickness (Outerbridge 2-3, Beck 2-3 Konan/Haddad 3). At the end of all classifications are the full-thickness lesions with exposure of the subchondral bone, equivalent to Grade 4 of the three classifications described. Considering that the extent of the lesion towards the central part of the acetabulum is a relevant factor in assessing articular damage, the Konan/Haddad Classification should be considered as the most complete classification to assess the acetabular cartilage damage with hip arthroscopy. Beyond the clinical utility, a good classification of chondral damage must be easy to use and reproducible. In a recent publication of our work group by Amenabar et al, the interobserver and intraobserver reliability of these 3 aforementioned classifications was examined (Outerbridge, Beck and Konan/Haddad) for arthroscopic assessment of acetabular cartilage damage. A prospective multicenter study was made to assess chondral damage in patients with femoroacetabular impingement with evidence of chondral damage during arthroscopy. Four experienced surgeons in hip arthroscopy assessed the obtained images from 2 hospitals of 2 different countries. They categorized each lesion in 2 separate assessments (with a 4 months interval) according to Outerbridge, Beck, and Konan/Haddad classifications. The conclusion was that the Konan/Haddad classification had the best interobserver reliability without presenting significant differences in the intraobserver reliability in these 3 classifications. Based on the aforementioned considerations and the results of this study, the Konan/Haddad classification should be considered as having the greatest current clinical utility for the classification of cartilage lesions of the acetabulum. Final Thoughts: The acetabular cartilage lesions are considered a relevant prognostic factor when performing a hip arthroscopy. Their correct classification allows choosing the optimal treatment of the chondral injury. There are several options available to treat these lesions during the hip arthroscopy combining micro fractures with different complementary biological treatments. However, beyond effectiveness treating the focal chondral lesion in the acetabulum, the hip presents other related factors, which will significantly influence the long-term results. Unlike the knee, in which chondral injuries occur often due to traumatic injuries but leave a healthy remaining cartilage, the remaining cartilage in the hip often have some degree of diffuse damage (thinning, cracking, etc.) without an effective option for arthroscopic treatment. On the other hand, proper correction of the underlying bone deformity (impingement, hip dysplasia) will be essential in the long-term prognosis of the hip treated by hip arthroscopy.
Arthroscopic vision will be the best tool to properly classify acetabular cartilage injuries allowing a direct palpation of the lesion and the chondrolabral junction in addition to the visual assessment. An ideal and hip-specific classification should consider various factors such as the depth of the lesion, its location, its extension towards the loading area of the acetabulum and its relationship with the chondrolabral junction. Such a classification would unify criteria to describe acetabular cartilage lesions helping to create an algorithm for an effective treatment and having also a prognostic value for the patients. References Amenabar T, Piriz J, Mella C, Hetaimish B, O Donnel J. Reliability of 3 Different Arthroscopic Classifications for Chondral Damage of the Acetabulum. Arthroscopy Vol 31, No 8 2015 pp 1492 1496 Beck M, Kalhor M, Leunig M et al. Hip morphology influences the pattern of damage to the acetabular cartilage: Femoroacetabular impingement as a cause of early osteoartritis of the hip. J Bone Joint Surg Br 2005;87:1012-1018 El Bitar Y, Lindner D, Jackson T, Domb B. Joint-preserving Surgical Options for Management of Chondral Injuries of the Hip. Journal of the American Academy of Orthopaedic Surgeons January 2014, Vol 22, No 1 Ilizaliturri VM Jr, Byrd JW, Sampson TG, et al. A geographic zone method to describe intra-articular pathology in hip arthroscopy: cadaveric study and preliminary report. Arthroscopy 2008;24(5):534 9. Konan S, Rayan F, Meermans G, Witt J, Haddad FS. Validation of the classification system for acetabular chondral lesions identified at arthroscopy in patients with femoroacetabular impingement. J Bone Joint Surg Br 2011; 93: 332-336 Marquez-Lara A, Mannava S, Howse E, Stone A, Stubbs A. Arthroscopic Management of Hip Chondral Defects: A Systematic Review of the Literaure. Arthroscopy, 2016: Article in Press Outerbridge RE. The etiology of condromalacia patellae. J Bone Joint Surg Br 1961; 43:752-757 Sampson T. Arthrocopic Treatment for Chondral Lesions of the Hip. Clin Sports Med 30 (2011) 331 348