➢ A high level of activity at a young age, certain repetitive mechanical forces (such as those inherent to ice hockey), congenital or acquired coxa vara, and pediatric conditions such slipped capital femoral epiphysis and Legg-Calvé-Perthes disease are associated with the development of cam-type deformity of the hip.
➢ Cam deformity is present in the majority of cases of femoroacetabular impingement and is usually located at the anterior or anterolateral head-neck junction.
➢ Six radiographic views of the hip (anteroposterior and false-profile radiographs of the pelvis, cross-table and frog-leg lateral radiographs of the proximal part of the femur, and 45° and 90° Dunn lateral radiographs of the hip) should be made for accurate characterization of cam morphology for preoperative planning and can be repeated intraoperatively for the assessment of correction. Computed tomography (CT) scans, including three-dimensional reconstructions, can provide valuable information for preoperative planning.
➢ For larger cam deformities, a T-capsulotomy in line with the iliofemoral ligament may be performed and then repaired side-to-side to avoid iatrogenic hip instability and abnormal kinematics.
➢ While long-term outcome data are not available to show whether arthroscopic hip osteoplasty for the treatment of femoroacetabular impingement prevents the development of degenerative changes, short and intermediate-term outcome data have shown improvements in terms of pain, motion, and overall function.
Arthroscopic treatment of hip disorders is an area of growing interest in the United States, with increasing numbers of operations being performed and an increasing presence of fellowship programs for training in hip preservation1-3. Femoroacetabular impingement has been implicated as one of the most common causes of osteoarthritis of the nondysplastic hip when abnormal contact mechanics result in degeneration of chondrolabral soft tissues in the hip joint4-9. Structural deformities include loss of femoral head-neck offset and/or sphericity (cam-type lesion), acetabular overcoverage (pincer-type lesion), and combined deformities of both the proximal part of the femur and the acetabulum (combined/mixed lesion), which are more common than isolated deformities4. The pathophysiology, evaluation, and arthroscopic treatment of abnormality in the peripheral compartment will be discussed below.
Mechanism of Injury and Etiology
While the exact etiology of abnormal bone morphology is unknown, several related conditions that are known to alter normal proximal femoral anatomy (e.g., slipped capital femoral epiphysis, Legg-Calvé-Perthes disease, congenital or acquired coxa vara, and osteonecrosis) have been implicated in the development of femoroacetabular impingement10-13. However, patients with these conditions make up a minority of patients with secondary femoroacetabular impingement as the majority of patients with symptomatic primary femoroacetabular impingement do not report a history of hip conditions or hip surgery14. In an attempt to elucidate the overall prevalence of radiographic evidence of cam-type deformity, Hack et al.15 evaluated magnetic resonance imaging (MRI) scans of the hips of 200 asymptomatic male and female volunteers and found cam-type morphology in 14% of the individuals. Male sex and decreased internal rotation of the hip were associated with an increased α angle and cam-type morphology. The α angle is the angle created between two lines from the center of the femoral head through the middle of the femoral neck and through a point where the contour of the femoral head-neck junction exceeds the radius of the femoral head16.
A number of investigations have been performed to assess possible risk factors for the development of cam-type deformity17. A high level of activity is one risk factor that has been implicated to affect the developing physis and has been shown to be associated with radiographic findings of cam-type deformity. In the study by Agricola et al., cam-type deformity (α angle, >60°) was found in 26% of eighty-nine high-level youth soccer players, compared with 17% of ninety-two nonathletic controls, with the soccer players having substantially increased rates of anterosuperior flattening and prominence on radiographs18. Siebenrock et al.19 reported similar findings in a study in which seventy-two hips in thirty-seven male basketball players were compared with seventy-six hips in thirty-eight age-matched volunteers who had not participated in sporting activities at a high level. The average maximum α angle was 61° in the athletes, compared with 47° in the nonathletic controls. In the study by Philippon et al.20, in which sixty-one asymptomatic youth hockey players were compared with asymptomatic youth skiers (controls), the hockey players were found to be 4.5 times more likely to have an α angle of ≥55°. The authors concluded that repetitive mechanical forces inherent to ice hockey likely enhanced the development of an osseous overgrowth leading to cam-type femoroacetabular impingement20.
More recently, changes that occur in the proximal part of the femur during growth and physeal closure have been evaluated as a possible etiology in the development of cam-type osseous deformity21. Numerous studies evaluating hips longitudinally before and after physeal closure in both active and non-active patients have demonstrated an increased prevalence of cam-type morphology after physeal closure of the proximal part of the femur and have implicated high activity levels during that time as a risk factor for the development of cam deformity22-24. Carsen et al.25, in a cross-sectional study of eighty-eight hips, found increased α angles after physeal closure as compared with prior to physeal closure. The authors reported that cam-type deformity developed in patients with higher activity levels and concluded that increased activity is a likely risk factor in the development of cam-type femoroacetabular impingement.
Labral injury has been found to be strongly associated with corresponding osseous morphological deformities26,27. Hip pain and soft-tissue damage can occur because of abnormal bone geometry, supraphysiological hip motion, or both. The abnormal stress and contact between the acetabular rim and the femoral head during terminal motion of the hip precipitate chondrolabral injury9,26-30. Cam-type deformities are very common in patients with femoroacetabular impingement as both isolated and mixed deformities. In a recent large multicenter study, 92% of 1076 patients undergoing surgical intervention for the treatment of femoroacetabular impingement had a cam deformity30. Although the morphology of cam-type deformities varies widely from patient to patient, the most common deformity is located at the anterior or anterolateral head-neck junction4. Other variants of cam-type deformity exist, including purely anterior deformities, deformities with posterosuperior extension, and deformities with distal extension and loss of offset to the intertrochanteric line. Other secondary cam-type abnormalities related to sequelae of conditions such as slipped capital femoral epiphysis also have been well described and present additional challenges of abnormal head tilt and neck retroversion10-13. Radiographic examples of each variant are shown in Figure 1.
Other extra-articular abnormalities can predispose patients to symptomatic femoroacetabular impingement. As discussed in our previous report on pincer-type impingement31 (http://reviews.jbjs.org/content/3/8/e4), focal or global acetabular overcoverage (retroversion, profunda, protrusio, etc.) can lead to early contact between the acetabular rim and the femur. Similarly, alterations in proximal femoral geometry leading to early contact between the acetabulum and the femoral head can cause impingement even in the absence of a cam-type lesion. Relative or absolute femoral retroversion has been implicated as a risk factor that has a detrimental effect on hip range of motion and possibly predisposes patients to hip impingement9,27,32,33. Conversely, Siebenrock et al.34 evaluated the computed tomography (CT) scans of thirteen hips with coxa valga and increased femoral anteversion and found a higher prevalence of impingement in the anteroinferior part of the femur and posteroinferior part of the acetabulum.
History and Symptoms
Obtaining a comprehensive musculoskeletal history and assessment of symptoms is the first step in diagnosing femoroacetabular impingement. Patients often complain of pain deep in the groin that is generally exacerbated with activities requiring hip flexion. Sitting pain, start-up pain when rising from prolonged sitting such as in a car, and pain with squatting activities are commonly present. When symptoms are severe, patients may report a limp or pain with simple activities such as walking.
Physical Examination Findings
A thorough and complete physical examination is critical to help confirm the diagnosis of femoroacetabular impingement, to assess the severity of symptoms and physical limitations, and to determine the presence of concomitant or confounding disease processes. Gait, skin condition, hip range of motion, strength, provocative tests, and neurological function should be assessed. Range-of-motion limitations, especially limitation of internal rotation, have been found to be strongly associated with the presence of cam-type deformities35-37. However, the actual cause of range-of-motion limitations can often be multifactorial and even extra-articular in nature33. When present, asymmetric loss of motion in symptomatic hips can be a helpful but not necessarily reliable indicator because of the frequent presence of bilateral hip disease38. Provocative tests to assess for intra-articular sources of hip impingement can include the anterior impingement test (e.g., the flexion, adduction, and internal rotation [FADIR] test)39; the flexion, abduction, and external rotation (FABER) test40; the straight flexion impingement test41; and the resisted hip flexion test (Stinchfield test)40. The anterior impingement test serves to bring the cam deformity of the anterolateral head-neck junction up against the acetabular rim and is positive if it recreates the symptoms described by the patient. It is one of the key findings associated with cam-type femoroacetabular impingement. The straight flexion impingement test, which can be used to identify subspine impingement, is discussed in our previous article on pincer-type impingement31 (http://reviews.jbjs.org/content/3/8/e4), However, the main difference between the straight flexion and anterior impingement tests during a physical examination is the addition of adduction and internal rotation to a ≥90° flexed hip in the latter provocative maneuver. In cases of severe impingement and inflammation, a simple log roll test may reproduce pain as well. Clinical work performed by numerous authors, including Klaue et al.39 and Martin et al.40,42, has shown moderate levels of reliability and sensitivity and low levels of specificity.
Because of the relatively high prevalence of radiographic femoroacetabular impingement in asymptomatic patients15,43-46, the use of abnormal radiographs alone as an indication for surgery is inappropriate. Rather, radiographic findings should be utilized in conjunction with clinical history and examination findings that are consistent with symptomatic hip impingement. The proximal part of the femur can be evaluated with radiographs and/or three-dimensional (3D) studies such as CT scanning or MRI. Determining the location, morphology, and extent of cam-type deformity is important for surgical planning purposes such as calculating the pre-planned areas and amount of resection as well as ensuring that the deformity is amenable to arthroscopic treatment. Large, complex deformities of the proximal part of the femur or areas of deformity that extend far posteriorly behind the retinacular vessels may be more safely treated with open dislocation or combined techniques47,48. Additionally, radiographs should be carefully assessed for degenerative joint disease as hips with even moderate degenerative changes are poorer candidates for arthroscopic surgery49,50. Commonly used radiographs include anteroposterior and false-profile radiographs of the pelvis, cross-table and frog-leg lateral radiographs of the proximal part of the femur, and 45° and 90° Dunn lateral radiographs of the hip51-58. The two Dunn lateral radiographic views of the hip are the best views for assessing the cam deformity in the classic anterosuperior and anterolateral portions of the femoral head-neck junction. The 90° Dunn radiograph is made with the patient supine on the x-ray table and the symptomatic hip flexed 90° and abducted 20° while in a position of neutral rotation. The beam is then directed at a point midway between the anterior superior iliac spine and the pubic symphysis. The 45° Dunn view is made in a similar fashion, with hip flexion of 45°52. The anteroposterior view is used to assess the presence of cam deformities with posterosuperior extension, whereas the frog-leg and cross-table lateral views are better for evaluating deformities that are primarily located in the anterior aspect of the head-neck junction. The false-profile view allows for assessment of anterior acetabular coverage as well as posterior joint congruity. The false-profile radiograph is made with the patient standing with the symptomatic hip against the cassette and the pelvis rotated 65° in relation to the wall. The foot on the same side as the symptomatic hip should be positioned so that it is parallel to the cassette. The central beam is then centered on the femoral head59. Table I further outlines the utility of the radiographic views when assessing the proximal part of the femur.
Three-dimensional CT imaging has become an increasingly utilized tool to characterize proximal femoral morphology for both diagnostic confirmation and preoperative planning (Fig. 2)60. Additional advantages include assessment of femoral version and neck-shaft angles and characterization of cam morphology with a high level of accuracy and detail. Heyworth et al.61 found a higher correlation between 3D-CT scan findings and arthroscopic findings when used for the evaluation of cam-type lesions as compared with pincer lesions. In the setting of obvious osseous abnormalities on radiographs, chondrolabral abnormality would be expected to be present in the setting of associated deformity. MRI offers additional utility to characterize the chondral status of the joint, to demonstrate soft-tissue abnormality or injury, and to identify other occult causes of hip pain, including stress reaction, tumor, or fracture62.
In a clinical scenario in which the patient history, physical examination findings, and radiographic findings are contradictory or inconclusive for making a clear diagnosis of femoroacetabular impingement of the hip, a diagnostic injection may be a useful adjunct63. This procedure can often be performed with fluoroscopic or ultrasonographic guidance to introduce local anesthetic and/or corticosteroid medications directly into the hip joint. Improvement of symptoms has been found to correlate highly with intraoperative and radiographic findings of hip impingement62,64.
Although there is limited evidence-based information regarding the nonoperative treatment of femoroacetabular impingement, the general approach to treatment includes activity modification, oral anti-inflammatory medications, physical therapy, injections, and the use of walking aids. Recent studies on the benefits of intra-articular injections in patients with femoroacetabular impingement demonstrated limited reduction in pain at six weeks after cortisone injections but sustained reduction in pain at twelve months after injection with hyaluronic acid65,66. It is not clear if physical therapy can improve range of motion or hip kinematics, but it has been suggested that improvement in flexibility and adjustment in pelvic tilt or obliquity may help to alleviate functional impingement despite the lack of change in pathoanatomy67,68.
The arthroscopic treatment of cam-type deformities is focused on ensuring adequate resection of the abnormal bone that is thought to impinge against the acetabulum and to restore the normal contour of the proximal part of the femur. These goals must be achieved while avoiding injury to neurovascular structures around the hip, including the perfusing retinacular vessels. Care must also be exercised to avoid an inadequate resection, overzealous resection, and iatrogenic labral or chondral injury48,69-78.
Working in the peripheral compartment allows discontinuing the use of traction on the involved extremity. The hip should be freely flexed and rotated as necessary to bring the anatomic areas of focus into an easily visualized and accessible position. External rotation can bring an anterior deformity into view, whereas internal rotation and relative extension can make a posterosuperior deformity more accessible (Fig. 3). As discussed in our previous article on pincer-type impingement31 (http://reviews.jbjs.org/content/3/8/e4), an interportal capsulotomy connecting the anterolateral portal with one of the working anterior portals of choice can greatly facilitate visualization and access to correct the deformity. Depending on the resection technique utilized and how far distal from the femoral neck the cam deformity extends, an additional distal anterolateral portal may be created for instrumentation to access the distal portion of the femoral neck with the arthroscopic burr (Fig. 4).
The areas of the head-neck junction to be addressed and the depth of resection required to restore the normal head-neck contour should be planned preoperatively on the basis of radiographs and should be verified intraoperatively under direct arthroscopic visualization. Several resection techniques exist, but most commonly a large-radius (5.5-mm) arthroscopic burr is used to perform the decompression. Care should be taken to avoid excessive resection in one area of the femur, which can increase the risk of iatrogenic femoral neck fracture. The risk of this technical error is increased when the entire cam deformity is not well visualized or accessed or when the surgeon relies solely on fluoroscopic images to guide the resection in an errant plane. Wijdicks et al.79 performed an in vitro study and suggested that a cam resection with cortical notching of ≥4 mm markedly increased the risk of iatrogenic fracture during biomechanical testing. A combination of hip and knee flexion brings the suspected area of deformity into view arthroscopically, and the position and rotation of the leg should be continually adjusted during the resection to maintain visualization of and access to the entire cam deformity. The use of large, broad strokes can help to create a gentle sloping transition from a convex shape of the femoral head into a concave shape of the femoral neck, a potentially important anatomic parameter to maintain the suction seal of the joint through most of the functional range of motion of the hip. Posterior deformities of the proximal part of the femur pose further challenges to the surgeon because of difficulties with access and visualization as well as the proximity of retinacular vessels. Positioning the hip in relative extension and internal rotation can facilitate visualization and access. The arthroscope or switching sticks may be utilized to retract and protect the capsule and vessels when working on that area of the femur. Additionally, care must be exercised to retract the capsule in order to preserve stability and to facilitate later repair (Fig. 5). Intraoperative fluoroscopy should be utilized if there is any concern about overcorrection or undercorrection of the deformity during arthroscopic resection and to confirm satisfactory correction after resection of the cam deformity in all planes.
Managing the Capsule
The capsule can be retracted distally with the camera and burr to access the proximal portion of the head-neck junction. Flexion and external rotation of the involved extremity can facilitate access to the anterior portion of the head-neck junction, whereas relative extension, internal rotation, and abduction can facilitate more lateral and posterosuperior cam instrumentation. For larger deformities, a T-capsulotomy may be performed to better access the distal part of the femoral neck and the posterosuperior portion of the femoral head-neck junction69,80. With this technique, the fibers are divided in line with the iliofemoral ligament, and medial and lateral capsular flaps are retracted and protected for later closure (Fig. 6). Early techniques involved a more aggressive capsulectomy during hip arthroscopy, especially in severely tight hips with large deformities, in which access and visualization are difficult. Some surgeons have adopted repair of the medial and lateral flaps of the T-capsulotomy, whereas others have argued for repair of the interportal capsulotomy in addition to the T-capsulotomy to possibly reduce the risk of revision surgery and to improve outcomes after arthroscopic hip surgery81. At this time, many surgeons advocate capsular repair after capsulotomy to decrease the risk of iatrogenic hip instability and abnormal kinematics69,80,82,83.
Short-term outcomes after arthroscopic treatment of cam-type deformities of the proximal part of the femur generally have been reported to be good to excellent, with success rates ranging from 67% to as high as 98% regardless of patient population, outcome measure utilized, arthroscopic technique, and activity level8,70,74,84-92. Bardakos et al.85 and Nepple et al.86 reported improved outcomes after both hip arthroscopy and limited open surgery when osseous deformities were thoroughly corrected. Improved range of motion of the hip also has been documented after surgical correction of osseous deformities29,93,94. Bedi et al.93 found substantial improvements in terms of both hip flexion and internal rotation after surgical correction of cam deformities that were evaluated with 3D CT reconstructions. Despite the favorable outcomes that have been reported in the short and intermediate term, long-term follow-up and outcome studies are necessary to assess the efficacy of arthroscopic treatment for femoroacetabular impingement in altering the natural history and progression of degenerative changes8,95.
Hip disease in the peripheral compartment is commonly encountered in patients with femoroacetabular impingement. The mechanism of injury and the etiology of development of cam-type deformities are not completely understood, but the resulting pathophysiology is a common cause of pain, dysfunction, and limited range of motion in the hip. Assessing the presenting symptoms, physical examination findings, and radiographic studies can help to confirm the presence of symptomatic cam-type deformities and the diagnosis of hip impingement. For patients with peripheral compartment deformities that may be amenable to arthroscopic intervention, careful surgical planning and attention to intraoperative principles and goals can lead to favorable outcomes after surgery and can result in improvements in terms of pain, motion, and function. Long-term outcome studies are needed to validate the efficacy of arthroscopic treatment of peripheral compartment hip disease.
Source of Funding: There was no source of funding for the present study.
Investigation performed at the Sports Medicine and Shoulder Service, Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
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