The pathogenesis of hip pain is usually seen in elderly patients with hip osteoarthritis. Traditionally, the pathogenesis emphasizes the degenerative changes in the articular cartilage and other joint structures due to decades of excessive axial loading on the joint, which leads to joint pain. However, it is true that some middle-aged and young people who exercise regularly also present with hip pain, which is not satisfactorily explained by the traditional pathogenesis, because these young patients have normal bone structure and intra-articular pressure on the surface of the hip joint. In recent years, a study by Ganz et al. found that femoroacetabular impingement syndrome (FAI) is the main cause of hip pain in young and middle-aged people, and therefore may offer some hope for the diagnosis and treatment of hip disorders. In this paper, we will give a comprehensive and systematic description of FAI in terms of basic concepts, pathogenesis, clinical typing, clinical manifestations, imaging manifestations, diagnosis, treatment and prospect.
I. Basic concepts
As early as 1999, Prof. Ganz and colleagues reported the phenomenon of femoroacetabular impingement as one of the complications after acetabular osteotomy, and scholars have reported on this phenomenon one after another since then. In 2003, Ganz et al. formally proposed the concept of FAI and defined and described it systematically: femoroacetabular impingement syndrome (FAI) refers to the hip joint with altered morphology, namely. an anatomical abnormality of the femur and/or acetabulum, where an abnormal collision of the proximal femur and acetabular rim occurs at the end of hip motion, which leads to damage to the acetabular glenoid labrum and/or adjacent acetabular cartilage, resulting in hip pain symptoms, which are mainly characterized by pain in the inguinal region (especially painful during joint hip flexion and internal rotation), and limited internal rotation during hip flexion. If the impingement factor is not detected and removed, early damage to the acetabular labrum and/or adjacent acetabular cartilage can continue to develop and eventually lead to joint degeneration.
II. Anatomy of the hip joint
To better understand the collision mechanism of FAI, we first provide a systematic review of the anatomy of the hip joint: the hip joint consists of the acetabulum and the femoral head, which is surrounded by a tough acetabular labrum that adds depth and closely encircles the femoral head, the joint capsule that encircles the joint from the periphery, and the articular cartilage that covers the bone joints. These anatomical components of the hip joint are described in detail below.
1.Acetabulum
The acetabulum is composed of three parts: the iliac body forms the roof of the socket, accounting for 2/5 of the socket area; the sciatic body forms the posterior wall and bottom of the socket, accounting for 2/5 of the socket area; and the pubic bone body forms the anterior wall of the socket, accounting for 1/5 of the socket area, which will heal together after about 20 years of age to form a solid bony structure. The acetabulum is low anteriorly and elevated posteriorly, with a deep and wide notch in the lower part, with transverse ligaments passing through and closing it, forming a hemispherical fossa surrounded by a labial glenoid rim formed by cartilaginous tissue, increasing the depth of the acetabulum and making it more than half the size of the sphere. The top of the acetabulum is the main weight-bearing area, thick and solid, and the posterior part is also thicker to enhance joint stability. The articular surface is semilunar in shape and covered by hyaline cartilage, and the bottom extends to the acetabular notch as the acetabular fossa, which is occupied by the femoral head ligament and is a non-articular part without cartilage. Morphological changes in the acetabulum, such as developmental deformities, acetabular retroversion, and acetabular invagination, can lead to the creation of an impingement ground.
2.Acetabular lip
The acetabular lip is a ring of fibrocartilage attached to the edge of the acetabulum, deepening the depth of the acetabulum, and the part of it that crosses the acetabular notch is called the transverse acetabular ligament, forming a complete ring; the cut of the acetabular lip is triangular, with the base attached to the edge of the acetabulum and the tip being the free edge; the lip narrows the acetabular cavity, thus hugging the femoral head; the transverse acetabular ligament is part of the acetabular lip, but does not contain chondrocytes, and its flat and strong fibers cross the The transverse acetabular ligament is part of the acetabular labrum but does not contain cartilage cells. The acetabular labrum is clamped between bony structures such as the femoral neck and is worn down and degenerated, which is an important cause of hip pain in patients with FAI.
3.Femoral head
The femoral head is round in shape, accounting for about 2/3 of the entire circle, covered mainly by articular cartilage, with the edge forming the labrum of the glenoid; under the cartilage is the bone plate shell, with a small fossa slightly behind the top, where the femoral head ligament is attached; the femoral neck is slightly inclined forward, thin in the middle, with the greater trochanter on the outside and the lesser trochanter on the inside, where multiple groups of muscles are attached; the femoral spur is on the inside of the femoral stem and neck combined with the inside back, a longitudinal row composed of multiple layers of dense bone The femur is eccentric in weight-bearing, and the femoral spur plays an important role in reinforcing the part of the femur that is subject to large forces. A wide spreading prominent femoral neck or an anterolateral shortened craniocervical junction are important anatomical factors that cause FAI.
4.Joint capsule
It is attached to the acetabular rim and transverse acetabular ligament on the proximal side, and ends at the intertrochanteric line on the distal side and at the middle and outer l/3 of the femoral neck on the posterior side, and is composed of superficial longitudinal fibers and deep transverse fibers. The transverse fibers form a tough whorl around the femoral neck, and the joint capsule is reinforced by ligaments on the outside and synovial membrane on the inside, which plays the role of support, heat dissipation and friction reduction; synovial fluid exists in the joint cavity, which is the nutrient fluid of the articular cartilage and lubricating fluid of joint movement.
5.Articular cartilage
In the synovial joint, the joint of bone is covered with a layer of 1-5mm thick transparent cartilage, which is an isolated tissue without blood vessels, nerves and lymphatic vessels after maturation. The articular cartilage is thickest in the center of the cartilage of the spherical articular surface of the femoral head, and the acetabular cartilage is also thicker. The articular cartilage plays a role in transmitting the load and expanding the compressive stress point, and it can reduce friction and consumption when moving, and its elasticity plays a role in shock absorption. The articular cartilage is capable of repairing after injury, with superficial mild injuries being repaired by chondrocyte regeneration and larger injuries being repaired by connective tissue.
III. Pathogenesis
The pathogenesis of FAI has not yet been confirmed by research. Of course, FAI can also occur in people with normal or near-normal hip anatomy but with an excessive range of motion of the hip joint that is beyond its physiological function and exhibits clinical symptoms.
A wide protruding femoral neck or shortened anterolateral craniocervical junction results in a narrow joint space, which leads to repetitive contact between the femoral neck and acetabular rim, and this contact directly causes a number of changes including anterior hip pain, wear and tear degeneration of the acetabular glenoid labrum, and damage to the acetabular articular cartilage.
Morphologic changes in the acetabulum such as developmental deformities, acetabular retroversion, and acetabular invagination can also lead to impingement. Posterior tilt of the acetabulum leads to the formation of a protrusion on the anterolateral aspect of the acetabular rim, and the hip joint encounters an obstacle in flexion and internal rotation, leading to femoroacetabular impingement. Posterior tilt can be caused by a defect in the posterior acetabular wall or secondary to excessive anterior acetabular wall coverage due to a misaligned acetabular development, or both, but it is often the former that causes impingement to occur. Acetabular invagination deepens the acetabulum, resulting in a relatively short femoral neck and a relative excess of cartilage surrounding the covering femoral head. when the range of motion of the femur increases, the proximal femur clamps on the corresponding acetabular rim, resulting in cartilage injury at the corresponding site. lavigne et al. showed that the incidence of femoral acetabular impingement was significantly higher in those with an overly deep acetabulum compared to those with a normal acetabulum. ezoe et al. observed through several surgical procedures demonstrated that removal of the anterior overlying acetabular rim relieved the collision and resulted in a significant reduction in pain.
Several studies have shown that FAI can cause progressive degenerative processes and early osteoarthritis in the hip joint.
IV. Clinical typing
There are three different types of FAI.
1.Cam impingement
It is usually present in men who exercise frequently, and it usually consists of the non-spherical part of the femoral head or the wide spreading protruding deformed femoral neck squeezing, colliding and shearing the acetabular cartilage and acetabular lip during flexion and internal rotation, and the shearing force causes the acetabular lip to be damaged from the surface to the inside and torn from the acetabulum, and the damage to the acetabular cartilage usually occurs in the anterior upper part of the acetabulum.
2.Clamp impact
It usually exists in middle-aged women who prefer to be active, and it usually consists of abnormal contact between the femoral neck junction and the acetabular rim. Repeated impingement contact leads to degeneration of the acetabular labrum, which further causes internal cystic degeneration of the acetabulum as well as peri-acetabular labral ossification and acetabular deepening. This chronic injury is often located in a narrow, elongated area around the acetabular cartilage. The degeneration around the acetabular labrum is usually manifested in the form of ossification.
3. Cam clamp impingement
In a study of 149 hips by Beck et al, they found that only 26 hips had cam impingement alone and 16 hips had clamp impingement alone. The study showed that cam impingement and clamp impingement rarely occurred independently, and most cases of FAI were a composite of these two mechanisms, and classified this composite as cam clamp impingement.
V. Histologic and pathologic features
FAI is characterized histologically by mild chronic irritation of the acetabular labrum where the fracture occurs and triggers a deformation response. A study of 25 patients with FAI symptoms showed that there was no difference in the histopathological characteristics of the acetabular labrum between cam impingement and clamp impingement.
VI. Clinical manifestations
1. Symptoms
Patients with femoroacetabular impingement syndrome are mostly young adults who enjoy sports and usually have a slow onset after a minor trauma or do not have a history of old trauma. In the initial stage of the disease, patients usually complain of intermittent chronic pain in the groin area, accompanied by limited hip movement, which is aggravated by excessive hip movement (e.g., sports or prolonged walking) or prolonged sitting. As the disease progresses, there may also be pain in the low back, sacroiliac joint, hip or greater trochanter, but the pain is usually not below the knee joint level.
2.Signs
Usually the hip joint is restricted in movement, especially in flexion and internal rotation. The positive rate of impingement test is up to 95%.
(1) If the impingement occurs in the anterolateral acetabulum, the anterior impingement test should be performed, specifically by: the patient is in the supine position, when the hip joint is passively flexed close to 90° and internally rotated. Flexion and internal rotation result in the femoral neck and acetabular rim coming close together. The additional internal rotational stress causes shear forces on the glenoid labrum and produces severe pain when there is cartilage damage, glenoid labral damage, or both.
(2) If the impingement occurs posteriorly under the acetabulum, a posterior impingement test should be performed with the patient supine on the side of the bed and with the affected limb dangling off the end of the bed, thus extending the hip joint. External rotation in the extended position produces deep groin pain indicating postero-inferior impingement.
A positive impingement test correlates closely with the acetabular rim damage seen on modern MRI tomography of the hip.
VII. Imaging manifestations
1.X-ray presentation
Standardized anteroposterior pelvic radiographs should be taken routinely in all patients with suspected FAI, and a good anteroposterior pelvic radiograph is one in which the tip of the coccyx points toward the pubic symphysis and the distance between the two is 1-2 cm. The abnormalities usually observed include: bony protrusion of the anterosuperior border of the femoral head and neck joint, hip hypertelorism, acetabular protrusion, acetabular labral ossification, acetabular retroversion, etc. In addition, there is shortening of the eccentric distance, internal and external hip There are also shortened eccentric distances, internal and external hip rotation and subtle hip dysplasia. These abnormalities can affect the acetabulum and proximal femur, leading to impingement, and there are some characteristic indicators on radiographs that can confirm abnormal acetabular and femoral changes. The eccentric distance is the distance between the parallel femoral neck tangent line and the anterior femoral head tangent line on a horizontal radiograph. The definition of posterior acetabular tilt can be made on the anterior-posterior pelvic radiographs, i.e., the projection of the anterior and posterior walls of the normal acetabulum is in a non-intersecting “herringbone” shape, and the projection of the posterior wall should be more lateral than the projection of the anterior wall, while the projection of the anterior and posterior walls of the posteriorly tilted acetabulum is in an intersecting “X” shape. “In a retrospective analysis, Peelle et al. found that 49% of patients had at least one of these imaging changes, and further studies confirmed that patients with pain and a central lateral rim angle of less than 16°, or an anterolateral protrusion, or an eccentric distance of less than 9 mm, or an acetabular If there is a posterior tilt, surgery can be considered.
2.3DCT performance
Edward et al. reported that 3D CT scans of FAI patients were performed from the acetabulum to the lesser trochanter, with the femoral neck axis as the central axis of rotation, and the so-called femoral neck axis was determined by two pelvic bases: the femoral head centroid and the narrowest part of the femoral neck. 3D CT could detect a reduced anterolateral offset at the femoral head-neck junction and a bony protrusion at the anterosuperior border of the femoral head-neck joint.
3.MRI performance
MRI has a high sensitivity and specificity for the detection of acetabular glenoid labrum and cartilage fractures, but for those cases where the articular cartilage is only fractured but not displaced, the detection rate is still high. However, the detection rate of articular cartilage with only fractures but no dislocation should be improved.
VIII. Diagnosis
Middle-aged people without a history of old trauma but with typical clinical symptoms of hip osteoarthritis, such as pain in the groin area, and young people who exercise frequently, the pain may worsen after activity or after prolonged sitting, and the patient may also present with limited hip inversion and/or flexion and internal rotation; a positive anterior-posterior impingement test and typical imaging changes such as X-ray, 3DCT, and MRI can diagnose FAI.
IX. Treatment
The treatment of FAI is divided into non-surgical treatment and surgical treatment, and surgical treatment includes hip arthrocentesis and hip arthroscopy.
1.Non-surgical treatment
Lavigne and others have recommended some non-surgical treatment methods: mainly including modification of hip movement, i.e. avoiding excessive hip flexion and reducing the amount of movement to reduce hip impingement; application of non-steroidal anti-inflammatory drugs to reduce joint inflammatory irritation. Non-surgical treatment can only temporarily relieve the pain symptoms and cannot lift the impingement factor, so it cannot stop the continuous progress of joint degeneration.
2.Hip arthrotomy surgery treatment
The surgical treatment of FAI is described by Ganz et al. The patient is placed in the lateral position and a Gibson approach is taken to enter the hip joint through a lateral hip incision and dislocate it forward. A Z-shaped incision is made outside the joint capsule to fully expose the hip joint and allow detailed visualization of the structures of the hip joint. This approach allows for a 360° view of the femoral head and acetabular labrum, so that all factors contributing to impingement and lesions in each area can be identified. The surgical management of the FAI is then based on the findings. In the case of “cam impingement”, the procedure consists mainly of removing any non-spherical elements of the femoral head, i.e., “femoral osteotomy”, and removing the widely spreading protruding femoral neck, i.e., “femoral neck osteotomy”. “For “clamping impingement”, the surgery mainly consists of removing the bony flank of the acetabular rim, and if there is an acetabular labral tear or If the acetabular lip is detached from the acetabulum, the detached acetabular lip can be sutured in place after cleaning the acetabulum. If the impingement is caused by morphological abnormalities of the acetabulum (e.g. posterior tilt of the acetabulum, acetabular invagination, etc.), a circumferential acetabular osteotomy can be performed to restore the normal shape of the acetabulum as much as possible. After each step of resection, the hip joint should be repositioned and repeatedly checked for the absence of impingement within the range of motion of the hip joint, and if impingement is still present, the excess bone may be resected again. Whenever deemed necessary, anterior rotor, femoral neck, or inter-rotor osteotomy is performed to improve bone removal and reduce impingement, provided excessive resection is avoided. The osteotomy is fixed intraoperatively with screws, and drains are rarely left in place because little dead space is left. Postoperatively, low molecular heparin is routinely used to prevent deep vein thrombosis. For complete healing of the rotor osteotomy site, weight bearing and hip flexion angles greater than 70 degrees and excessive abduction or adduction should be avoided. Continuous passive motion (CPM) functional exercise (hip flexion angle less than 70 degrees) should be performed on the first day after surgery to prevent joint adhesions, and normal activities and functions of the hip joint can be restored in about 6 to 8 weeks.
3.Hip arthroscopy treatment
Hip arthroscopy mainly includes the examination and treatment of the central and peripheral compartments of the hip joint. The central compartment includes the acetabular lip and all structures in the central part of the acetabulum; the peripheral compartment includes the structures on the outside of the acetabular lip but still inside the joint capsule, such as the femoral head, femoral neck, synovial folds and the joint capsule itself. With the patient in the lateral or supine position, an image-enhanced monitor ensures safe access of the guidewire and trocar into the joint, and the procedure is usually performed using the anterolateral and anterolateral approaches, with an additional posterolateral approach if necessary. Intraoperatively, the central chamber can detect characteristic lesions including anterolateral tears of the acetabular labrum and anterior degeneration of the acetabular cartilage, while performing the necessary debridement. Even though the long-term effects cannot be determined at this time, some acetabular labral tears should be repaired arthroscopically. The peripheral compartment allows for the identification and resection of osteoid at the femoral head-neck junction, and the lateral portion of the acetabular labrum can be repaired and its peripheral osteoid removed under complete visualization.
X. Prospects
Espinosa et al. performed a retrospective analysis of 52 patients (60 hips) with FAI who underwent acetabular labrum revision, divided into 2 groups according to the surgical approach. At the follow-up of 1 and 2 years after surgery, it was found that the recovery of joint function and quality of life of patients in group 2 were significantly better than those in group 1, and the incidence of arthritis on imaging was also significantly less than that in group 1; therefore, it was concluded that the surgical approach of preserving the acetabular labrum as much as possible showed superiority in terms of clinical efficacy and imaging performance.
Murphy et al. conducted a retrospective study of 23 patients (23 hips) with FAI who underwent femoral osteotomy. The results showed that none of the 23 patients developed femoral head necrosis; 15 of them had significant outcomes without secondary surgery; one patient underwent hip arthroscopy again for recurrent acetabular labral tear; and the remaining 7 patients eventually underwent total hip revision. Of the 7 patients who underwent total hip revision, 4 had significant outcomes for a period of time (6.4 to 9.5 years) after femoral osteotomy, with progression occurring later; only 3 had insignificant outcomes early after osteotomy, but it must be noted that these 3 patients already had hip disease other than FAI before surgery, 1 of which was osteoarthritis and the other 2 The other two cases were congenital acetabular dysplasia. Therefore, they concluded that femoral osteotomy based on careful screening of patients with FAI is safe and efficacious.
The early results of hip arthroscopic exploration and treatment for FAI are remarkable and have the advantage of rapid postoperative recovery of the patient. A retrospective study of 158 patients treated with hip arthroscopy showed that most patients experienced a 50% reduction in hip pain at 3 months, a 75% reduction at 5 months, and a 95% reduction at 1 year. This result is comparable to the efficacy of hip arthroscopy. Early correction with hip arthroscopy may increase hip pain in patients with FAI, but long-term observational studies are necessary to determine whether this procedure will prevent joint degeneration early in the course of the disease.