Original article Microinstability of the hip: a previously unrecognized pathology Ioanna Bolia 1 The role of the hip joint capsule has gained par - Jorge Chahla 1 ticular research interest during the last years, and Renato Locks 1 its repair or reconstruction during hip arthro - Karen Briggs 1 scopy is considered necessary in order to avoid Marc J. Philippon 1,2 iatrogenic hip microinstability. Various capsular closure/plication techniques have been devel - oped towards this direction with encouraging re - 1 Steadman Philippon Research Institute, Colorado, USA sults. 2 The Steadman Clinic, Colorado, USA Level of evidence: V. KEY WORDS: hip arthroscopy, hip microinstability, hip Corresponding author: dysplasia. Marc J. Philippon, MD Steadman Philippon Research Institute The Steadman Clinic Introduction 181 West Meadow Drive, Suite 400 Vail, Colorado 81657, USA The native hip is a particularly constrained joint with a E-mail: [email protected] powerful suction seal that is imperative for optimal 1,2 function of the joint . The hip capsule is one of the most important static stabilizers of the hip joint 3 and Summary disruption or debridement of the capsule during hip arthroscopy is a potential contributor to postoperative Background : Hip microinstability is an estab - iatrogenic hip instability. Therefore, hip surgeons must lished diagnosis; however, its occurrence is still be thoughtful of hip capsule management as hip debated by many physicians. Diagnosis of hip mi - arthroscopic procedures are increasing exponentially 4. croinstability is often challenging, due to a lack of Unlike other joints in the anatomy, hip instability is specific signs or symptoms, and patients may re - generally defined as extra-physiologic hip motion that main undiagnosed for long periods. This may lead causes pain with or without symptoms of hip joint in - to early manifestation of degenerative joint dis - stability 5. This entity is not well defined, as no objec - ease. Consequently, careful patient and family tive criteria has been proposed to characterize hip history must be obtained and diagnostic imaging microinstability 6. should follow. After a thorough clinical evaluation The source of pain and symptoms are subtle anatom - of the patient with suspected hip microinstability, ic abnormalities and in most cases are associated the physician should focus on how to improve with a repetitive movement generally involving rota - symptoms and functionality in daily and sports tions and axial load 6. Alternatively, ligamentous laxity activities. or muscle weakness can also mimic hip microinstabil - Purpose : The purpose of this review article was ity 7. As a result of the altered biomechanics between to give a current update regarding this diagnosis the femoral head and the acetabulum, the surround - and to provide a complete diagnostic approach in ing structures such as the labrum, the capsule and order to effectively treat hip microinstability. the cartilage may be at risk. Symptoms related to this Methods : We reviewed the literature on the diag - pathology are persistent groin pain, tendinitis from nosis, the non-operative and operative indica - dynamic stabilizer overload or pistoning of the tions for the treatment of this complex and often femoroacetabular joint. misdiagnosed pathology. Iatrogenic microinstability is a significant cause for Conclusion : Conservative treatment is consid - failure of hip arthroscopy and a growing cause of re - ered the best initial approach, though, surgical in - vision hip arthroscopy. Therefore, awareness of this tervention should be considered if symptoms per - pathology is vital for the surgeon in order to avoid un - sist or other hip pathology exists. Successful sur - necessary insult to the capsule or the labrum during gical intervention, such as hip arthroscopy, hip arthroscopy and thus impede future iatrogenic should focus on restoring the normal anatomy of pathology. The purpose of this article was to review the hip joint in order to regain its functionality. the most relevant data from anatomy and biomechan - 354 Muscles, Ligaments and Tendons Journal 2016;6 (3):354-360 Hip microinstability ics for diagnosis and treatment of this pathology. sule to the distractive stability of the hip in the afore - This article submits to the ethical standards of the mentioned six labral states 1. They found that a dis - journal 8. traction level of 1-2 mm labrum was the most impor - tant hip stabilizer, whereas in greater distraction states, the contribution of the capsule to hip stability Anatomy and Biomechanics started to increase. In addition, the partial labral tear decreased the distractive stability of the joint while The bony part of the hip joint consists of the acetabu - the labral reconstruction procedure significantly im - lum and the femoral head that are placed together to proved it. Consequently, a relationship between labral create a “ball and socket” mechanism in order to pathology and hip microinstability seems to exist and serve the mobility and stability properties of the hip the contribution of the capsule to the hip joint stability joint. As a result, the femoral head receives 170° cov - cannot be ignored. When loading forces are applied erage from the acetabular surface that creates a qua - to the hip joint, the labrum is considered to have a si-hemisphere 7. More specifically, its posterior cover - protecting role by distributing those stresses 13 . The age is greater than the anterior, due to the acetabular presence of nociceptors and proprioceptors 14 in the tilt in the coronal plane (48°) as well as in the sagittal labrum are responsible for the sensory information plane (21°) 9. The femoral neck is inclined superiorly transferred from the hip joint to the CNS, supporting 130° relative to the femoral shaft and is also 10° an - the coordination of movements that may affect the teverted relative to the femoral transcondylar axis 7. joint stability. In order to standardize the anatomical approach to the acetabulum during the hip arthroscopy procedure, Philippon et al. established a reproducible method to The Hip Capsule arthroscopically localize the anatomical landmarks on the acetabulum 10 . According to their model, the 3:00 The hip capsule is composed of both longitudinal and position on the clock face corresponds to the superior circular fibers. The longitudinal component is 60% re - margin of the psoas U that can be easily located as inforced 5 owing to the existence of the three stabiliza - well as the stellate crease at 12 o’clock. tion ligaments externally; the iliofemoral, the pub - Apart from the bones, the stability of this joint is ofemoral and the ischiofemoral ligaments. At the in - based on the soft tissue components that mainly in - ner side of the capsule the circular fibers define the clude the labrum, the capsule, the static hip stabiliz - zona orbicularis, which encircles mainly the femoral ers (ligamentum teres and capsular ligaments) as neck, and its thickness increases while moving from well as the dynamic hip stabilizers (muscles). the anteroinferior (1.3 mm) to the posterosuperior part (4 mm) 15 . A pericapsular recess of the proximal hip capsule (5 The Acetabular Labrum mm proximal and medial to the acetabular rim) 15 may be an useful anatomical pearl in MRI assessment of The labrum is an avascular structure made of fibro - the capsular elasticity 16 . Biomechanically, the cap - cartilage, which runs along the acetabular rim, being sule seems to offer in the distractional stability of the continuous with the transverse acetabular ligament at hip joint at 3-5 mm of distraction as reported by Nep - the site of the acetabular fossa 11 . In addition, a transi - ple et al. 2014 1. tional zone of calcified cartilage (1-2 mm) connects the labrum with the acetabular articular cartilage 12 . The labrum provides stability to the hip joint by in - Static Hip Stabilizers creasing the acetabular volume by 20% and the ac - etabular surface area by 25% approximately 12 . Iliofemoral, Pubofemoral, Ischiofemoral Ligament The presence of the labrum increases the intraarticu - The iliofemoral ligament, the strongest ligament of lar negative hydrostatic fluid pressure contributing to the body 5, has its acetabular origin at the 1: 26 posi - the “suction cup”, preventing the leak of fluid from the tion using the clock face system 17 . Its lateral arm fol - central compartment 5. In a study of eight cadaveric lows a horizontal route along the neck of the femur to hips, Philippon et al. 2 underlined the role of the ac - insert at the anterior greater trochanteric crest, etabular labrum in the hip fluid seal by measuring the whereas the medial arm inserts distally at the in - intra-articular fluid pressurization in six different hip tertrochanteric line 18 . The ischiofemoral ligament joint states including the intact state, labral tear, originates at 10:15 clock position on the acetabulum 17 labral repair (looped vs through the tissue sutures), and follows a spiral route to insert at the base of the partial and complete resection as well as the recon - greater trochanter 19 . The pubofemoral ligament aris - struction with iliotibial band state. They reported that es at the 4:44 clock position on the acetabular rim 17 partial labral tears decrease the pressurization effect and blends with the medial arm of iliofemoral liga - of the hip fluid seal and that the through-the-tissue ment, lacking a femoral attachment site 5. type labral repair can achieve superior results in the According to the contribution of the aforementioned restoration of fluid pressure compared with the ligaments to hip joint stability, Martin et al. hypothe - looped type. Moreover, the same researchers studied sized that the grade of restriction of the rotational hip the contribution of the labrum as well as the hip cap - movements that each of those ligaments offered, was Muscles, Ligaments and Tendons Journal 2016;6 (3):354-360 355 I. Bolia et al. alternating with the range of motion 18 . On a cadaveric the absence of other hip joint pathology.