Current literature often confuses or fails to correctly describe the limbus and the neolimbus. An orthopaedic dictionary [7
] from 1994 incorrectly defines the limbus as “a fibrous, resilient, sharp-edged, crescent-shaped tissue attached to the bony rim of the acetabulum and the transverse acetabular ligament. Its free edge cups around the head of the femur to increase the stability of the hip joint. Also known as the Acetabular Labrum.” This is the definition of the labrum, not the limbus.
In the chapter describing the normal anatomy of the developing acetabulum from the textbook of Tönnis’ et al., the authors describe the “labrum” or “acetabular labrum” that has “come to be preferred over the older terms ‘limbus’ and limbus articularis’” [21
]. However, rather than an evolution of a term, this probably represents confusion of the limbus - a pathologic structure seen in dysplastic hips - with the labrum, a normal structure.
Wheeless’ Textbook of Orthopaedics [24
], an online orthopaedic reference popular with orthopaedic surgical residents, refers to the “inverted neolimbus” as a “rare type of obstruction in DDH,” and a “lip of hypertrophied fibrocartilage” that “may be infolded or everted.” This would be an accurate description of the limbus not the neolimbus.
In a 2002 article discussing complications of failed open reductions in DDH, Chmielewski and Albinana [3
] describe that osteonecrosis (ON) can occur secondary to increased pressure against the posterior acetabular rim as well as the neolimbus, referencing an article by Morcuende et al. [13
] among others. However, Morcuende et al. actually state that it is the increased pressure against the posterior part of the acetabular rim as well as the limbus that may lead to ON [13
Whether the comment by Chmielewski and Albinana [3
] is a correction or a mistake, however, is not clear, since the referenced article by Morcuende et al. [13
] itself does not consistently define the terms limbus and neolimbus correctly. For instance, these authors classify the “neolimbus” into three types, depending on whether it was inverted, everted, or neither. They also use the term “inverted neolimbus” three times. These authors must mean “limbus” and “inverted limbus” instead, as it is the fibrous, hypertrophied labrum (or limbus) and not the small ridge of acetabular cartilage (or neolimbus) that is able to invert and evert. Therefore, when they report that pressure of the limbus on the lateral physis of the femoral head may be responsible for ON, it is not clear whether they actually mean limbus or neolimbus. Probably either one could, at least in theory, be responsible.
Similarly, a 2005 article by Angliss et al. [1
] describes an “inverted neolimbus” as a poor prognostic factor in the open reduction of DDH. These authors mean “inverted limbus,” as this is the entity with the potential to block reduction. An English text refers to the neolimbus as a block to reduction and discusses the possibility of radialization of this structure [14
]; again substituting the term neolimbus for limbus (which according to some authors is the structure that may benefit from radialization).
Clearly the terms are often confused for one another in modern textbooks and peer-reviewed literature. It is therefore imperative these terms be clarified and used correctly in order to avoid confusion, especially since the presentation and management of these two entities are so different.
The limbus and the neolimbus are both important pathologic structures that occur in developmental dysplasia of the hip. Most accurately, the neolimbus represents a hypertrophic ridge of acetabular articular cartilage whereas the limbus is a hypertrophic labrum with fibrous and fibrocartilaginous overgrowth. The use of the term “inverted neolimbus” is not accurate and should be replaced with the term “inverted limbus.”
The neolimbus may at times cause the palpable “click” heard on clinical exam. It is not an obstruction to reduction and will spontaneously resolve assuming quick diagnosis and proper reduction. The neolimbus should never be excised.
The limbus can also resolve spontaneously in a reduced hip or can invert and cause obstruction to concentric reduction. There has been debate about its removal, although current reports argue that excision should be avoided.
Both the limbus and the neolimbus have been proposed as potentially causing or contributing to ON, though due to the confusion of terms in the literature it is not clear which of the two structures is being proposed as the offender. Most likely, both the limbus and the neolimbus are potential causes of ON due to pressure on the lateral femoral head and physis when the hip is positioned in forced abduction.
In conclusion, limbus and neolimbus are important terms for clinicians managing DDH. The hopeful future correct use of these terms in the literature and discussions will help clarify the surgical management of DDH.