John C. Clohisy
DEFINITION
Anterior femoroacetabular impingement encompasses a category of structural hip disorders that are characterized by abnormal abutment of the anterolateral femoral head–neck junction against the acetabular rim–labral complex.
Repetitive anterolateral impingement produces acetabular articular cartilage delamination, labral disease, and, eventually, secondary osteoarthritis.
ANATOMY
Understanding the pathoanatomy of hip impingement disorders is essential to establishing an accurate diagnosis and selecting an optimal surgical treatment strategy.
Structural impingement disease can be primarily femoralbased (ie, “cam” impingement) or primarily acetabular-based (ie, “pincer” impingement) (FIG 1).2,12,17
Combined cam and pincer impingement deformities are common,2 and are characterized by abnormal anatomy of both the proximal femur and the acetabulum.
Deformities of the proximal femur that produce impingement disease include reduced femoral head–neck offset, an aspherical femoral head, slipped capital femoral epiphysis, Perthes abnormalities, and femoral neck malunion.
The common impingement deformities on the acetabular side include acetabular retroversion, coxa profunda, and protrusio acetabulum.
PATHOGENESIS
Impingement deformities of the proximal femur or acetabulum, or both, produce an abnormal mechanical environment that initiates and sustains hip joint degeneration.12,17,22
Mechanical impingement is most pronounced with hip flexion alone or hip flexion and combined internal rotation.
Recurrent impingement of the anterolateral femoral head–neck junction with the acetabular rim–labral complex initiates a detrimental cascade of biologic events.
Osseous impingement leads variously to delamination of the articular cartilage of the acetabular rim, labral degeneration, posteroinferior acetabular articular disease (due to levering of the femoral head from anterior impingement), and anterolateral femoral head–neck junction chondral disease.
This constellation of intra-articular disease worsens with time and is a common cause of secondary osteoarthritis.12,17,22
NATURAL HISTORY
The natural history of anterior femoroacetabular impingement has not been clearly defined.
Radiographic studies have demonstrated an association between structural impingement deformities and secondary osteoarthritis,1,15,22 but authentic natural history data are lacking.
The consensus is that the prognosis of symptomatic impingement disorders is poor, and that these diseases commonly result in secondary osteoarthritis.
Future natural history studies will add substantially to improved understanding of these disorders.
PATIENT HISTORY AND PHYSICAL FINDINGS
Patients with anterior femoroacetabular impingement commonly present with activity-related anterior inguinal (groin) pain. Associated lateral and posterior hip pain are common.
Symptoms are variable and may include a combination of aching pain with intermittent episodes of sharp or stabbing pain.
FIG 1 • Patterns of anterior femoroacetabular impingement disease. The reduced clearance during joint motion leads to repetitive abutment between the proximal femur and the anterior acetabular rim. Cam impingement is caused by reduced femoral head and neck offset, pincer impingement by overcoverage of the femoral head by the acetabulum, and combined cam and pincer impingement by both reduced head and neck offset and excessive anterior overcoverage.
Mechanical symptoms of locking and catching also may be problematic, presumably from labral disease or unstable articular cartilage flaps.4
Difficulty with daily activities, including prolonged walking, prolonged sitting, raising from a seated position, and pivoting, is common.
High-demand athletic activities, including running, cutting, pivoting, and repetitive hip flexion (eg, soccer), often exacerabate symptoms.
Any history of hip trauma, childhood hip disease, previous surgeries, and previous treatments should be determined.
The patient's age, activity level, and overall health, and the impact of hip dysfunction on his or her quality of life are obtained.
Physical examination should include assessment of overall health, conditioning, and body habitus.
Previous surgical scars are inspected to clarify the nature of previous procedures and to facilitate preoperative planning.
Observation of sitting posture, gait, palpation of the hip, abductor strength testing, careful hip range of motion assessment, and specific provocative tests are performed.
Anterior femoroacetabular impingement commonly elicits discomfort in an erect sitting position.
A level pelvis in the single-legged stance is normal. Dropping of the contralateral hemipelvis indicates abductor weakness of the symptomatic hip. Abductor weakness is common in patients with early intra-articular hip disease and impingement.
Hip flexion commonly is restricted to 100 degrees or less in impingement disorders. Internal rotation in flexion is frequently restricted to 0 to 10 degrees.
The gait pattern over short distances and abductor strength usually are normal in early stages of disease.
A limp and mild abductor weakness may develop as labral disease and joint degeneration progress.
Hip range-of-motion testing should be performed carefully with stabilization of the pelvis to accurately define motion endpoints. Passive hip flexion motion and internal rotation at 90 degrees of flexion are restricted. Hip discomfort often is reproduced at the endpoints of passive motion.
The anterior impingement test and Patrick's test are sensitive maneuvers to detect intrinsic hip disease and usually reproduce hip symptoms in patients with anterior femoroacetabular impingement.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Plain radiographs include a supine anteroposterior (AP) view of the pelvis, cross-table lateral view with the extremity in 15 degrees of internal rotation, and a frog-leg lateral view.9,18,20
The structural parameters of the hip are assessed on all radiographic views.
The acetabular inclination, femoral head coverage, and acetabular version (FIG 2C–E) are determined from the AP view of the pelvis. Joint space narrowing, periarticular cysts, and labral ossification also are noted.
The lateral views are examined to assess femoral head sphericity and femoral head–neck offset.
These projections best visualize the anterior and anterolateral femoral head–neck deformity that characterizes cam impingement disease.
FIG 2 • Radiographic assessment of acetabular version. A. Drawing of an AP view of the hemipelvis showing a hip with normal version. Note the near parallel orientation of the anterior and posterior (dashed line) acetabular walls. There is no crossover, and the lines converge at the superolateral aspect of the acetabulum. B. Drawing of a hip with acetabular retroversion. The “crossover” sign, which has been previously described as an indicator of acetabular retroversion, is present. The anterior aspect of the acetabular rim projects lateral to the posterior aspect of the rim (dashed line) at the most proximal aspect of the acetabulum. C–E. Preoperative radiographs from a 19-year-old football player with left hip pain and cam impingement. C. In this case, the patient has relatively normal acetabular version, femoral head coverage, and acetabular inclination on AP view. D. On the frog-leg lateral view, an anterolateral prominence is noted at the femoral head–neck junction (arrow). E. On the cross-table lateral view, there is a mild decreased offset from the anterior aspect of the femoral head to the anterior aspect of the femoral neck (arrow). (A,B: Adapted from Espinosa N, et al. Treatment of femoro-acetabular impingement: preliminary results of labral fixation. J Bone Joint Surg Am 2006;88A:925–935.)
An MR arthrogram (MRA) of the hip is obtained on all patients with suspected impingement and associated intraarticular disease.
The contour of the femoral head–neck junction,16 labral disease, and associated articular cartilage disease are all inspected.
The MRI also facilitates exclusion of other uncommon disorders, including stress fracture, osteonecrosis of the femoral head, neoplasm, and infection.
CT scanning of the hip can be useful in identifying and characterizing the extent of osseous impingement lesions.
The contour of the femoral head–neck junction and the extent of femoral-sided disease can be appreciated in detail.
Version of the acetabulum and associated osseous abnormalities of the acetabular rim also can be assessed in detail.
The CT scan complements other imaging modalities and can impact surgical decision making.
DIFFERENTIAL DIAGNOSIS
Isolated intra-articular hip disease (eg, synovitis, labral tear, chondral disease, loose body) in the abscence of an impingement disorder4
Mild hip dysplasia (joint instability)
Extra-articular disorders (eg, lumbar spine disease, bursitis, inguinal hernia)
NONOPERATIVE MANAGEMENT
Nonoperative management for the treatment of anterior femoroacetabular impingement has not been rigorously investigated or documented in the literature.
Consensus is developing that hip impingement disease is common, and that definitive treatment should address the underlying pathomechanics of the joint.
The benefit of nonoperative treatment has not been established for joints that are relatively healthy with no or mild degenerative changes.
Activity restrictions, physical therapy, anti-inflammatory medicines, and intra-articular cortisone injections can be considered as potential nonoperative treatment options. Nevertheless, the efficacy of these treatment modalities over time has not been proven.
Physical therapy should not emphasize improving hip range of motion and should avoid aggressive maneuvers to gain hip flexion and internal rotation motion, because these will irritate the hip.
Anti-inflammatory medicines may reduce discomfort derived from labral disease and structural impingement.
Activity restriction may alleviate symptoms in some patients. Athletes involved in repetitive hip flexion activities may experience significant relief of discomfort if they refrain from their sport.
Patients with symptomatic femoroacetabular impingement who desire to maintain high activity levels often fail nonoperative management and desire surgical intervention.
For patients with moderate to advanced degenerative disease, the nonoperative modalities listed can be considered as temporizing therapies before joint arthroplasty.
SURGICAL MANAGEMENT
Surgical management of hip impingement disease continues to evolve, and various surgical techniques are now available for joint reconstruction,6 including surgical dislocation of the hip,11 combined hip arthroscopy and limited open decompression,7 and purely arthoscopic decompression techniques.14
The fundamental goal of surgery, independent of the technique selected, is to address the structural impingement lesions and the associated intra-articular disease elements (eg, labrum, articular cartilage).
We prefer surgical dislocation of the hip for cases with nonfocal impingement problems or severe deformities and for those cases requiring acetabular rim trimming with labral repair, eg, hips with a nonfocal femoral head deformity or circumferential pincer impingement.
For hips with focal, cam-type anterior femoroacetabular impingement, the less-invasive surgical techniques may have distinct advantages. In such cases, we use hip arthroscopy to precisely address the intra-articular disease (eg, labrum, articular cartilage), followed by a limited open osteochondroplasty to correct the femoral-sided impingement deformity.
Preoperative Planning
The patient history and physical examination findings are reviewed.
All preoperative radiographs plus the MRA and CT scan (if obtained) are evaluated. The size and location of the impingement lesion or lesions is determined. The status of the acetabular labrum and articular cartilage should be assessed on the MRA.
Restriction of hip flexion motion and internal rotation in flexion is noted, because these clinical parameters should be improved with recontouring of the anterolateral femoral head–neck junction.
It is very important that the surgeon determine whether the impingement lesion is a cam, pincer, or a combined campincer deformity, because the characteristics of the specific deformity will impact the surgical planning and treatment.
In our practice, hip arthroscopy and limited open osteochondroplasty of the femoral head–neck junction are used primarily for the treatment of cam-type impingement and associated intra-articular disease.
Positioning
Spinal or general anesthesia with muscle relaxation is preferred.
The patient is positioned supine on a radiolucent fracture table with lower-extremity traction attachments (FIG 3).5
The feet and ankles are well padded and firmly stabilized within the traction boots. The perineal post is heavily padded to prevent pudendal nerve palsy.
FIG 3 • Surgical positioning and operating room set-up. The patient is positioned supine on a radiolucent fracture table. The hip arthroscopy is performed first followed by the limited open osteochondroplasty of the femoral head–neck junction.
The operative hip initially is positioned in neutral flexion– extension and slight (0 to 10 degrees) abduction. The operative lower extremity is internally rotated 15 to 20 degrees.
The contralateral hip is flexed about 15 degrees and abducted 10 to 20 degrees, and minor traction is applied to stabilize the pelvis.
The ipsilateral upper extremity is positioned over the chest.
Traction is applied to the operative hip to achieve 8 to 10 mm of joint distraction, which is confirmed with fluoroscopy. Traction is released during preparation and draping of the hip.
TECHNIQUES
HIP ARTHROSCOPY PORTALS
Hip arthroscopy is perfomed via the anterior, anterolateral, and posterolateral portals with the patient in the supine position5 (TECH FIG 1A). The limited open osteochondroplasty of the femoral head–neck junction also is performed in the supine position. This surgical incision uses the Smith-Peterson interval to access the anterior hip joint.19
The open incision is 8 to 10 cm long and extends from the anterosuperior iliac spine distally to incorporate the anterior arthroscopic portal (TECH FIG 1B).
A cannulated hip arthroscopy system is used for portal placement.
The anterolateral portal is established first with fluoroscopic guidance.
The joint is entered distal to the labrum and superior to the femoral head. A 70-degree arthroscopic lens is inserted and used to directly visualize placement of the anterior and posterolateral portals (TECH FIG 1C, D).
The anterior portal should be established with specific care to avoid injury to the lateral femoral cutaneous nerve.
A superficial skin incision is made, and the soft tissues are then spread with a hemostat down to the hip capsule.
The cannula sheath is advanced through the subcutaneous tissue to the hip capsule, and the trocar is advanced into the joint.
Diagnostic evaluation of the central compartment is performed with both a 70- and 30-degree arthroscope. This enables excellent visualization of the femoral head and acetabulum.
Most arthroscopy is done with the arthroscope in the anterolateral portal, but the anterior and posterolateral portals are used for comprehensive joint inspection.
TECH FIG 1 • A. The anterior, anterolateral, and posterolateral arthroscopic portal positions are demonstrated with respect to the greater trochanter and anterior superior iliac spine (ASIS). B. The hip joint is distracted 8 to 10 mm, and the anterolateral portal is established first. C,D. The posterolateral (C) and anterior portals are then placed under direct visualization with a 70-degree arthroscope positioned in the anterolateral portal (D).
HIP ARTHROSCOPY FOR LABRAL AND CHONDRAL DISEASE
The anterior and superolateral labrum is carefully inspected and probed (TECH FIG 2A).
If a labral tear is identified, the labrum is débrided back to the stable labral remnant.
The débridement is performed with a combination of an arthroscopic shaver and radio-frequency chisel.
Care is taken to be conservative in not resecting excessive labral tissue.
In most cases, the capsular attachment of the labrum remains stable and should not be excised.
Labral repair is an option in selected cases, but our initial experience has focused on partial labral resection (TECH FIG 2B).
The articular cartilage is assessed, specifically along the anterior and superolateral rim of the acetabulum.
Unstable flaps of articular cartilage should be removed with a mechanical shaver.
If full-thickness delaminated flaps are present, they are débrided back to a stable articular cartilage remnant (TECH FIG 2C). Care is taken to avoid central propagation of the delaminated articular flaps.
TECH FIG 2 • Arthroscopic treatment of intra-articular disease. A. The anterior and superolateral labrum are inspected and probed. Labral disease commonly involves this region of the acetabular rim and often includes a degenerative, intraarticular tear with an intact capsular attachment. B. Partial labral resection is performed, and the adjacent articular cartilage is examined. C–E. Unstable articular cartilage flaps are débrided (C), and exposed subchondral bone is treated with a microfracture technique (D,E).
When subchondral bone is exposed, microfracture treatment is performed (TECH FIG 2D,E).
Associated synovitis is ablated.
When arthroscopic evaluation and treatment of intraarticular disease is completed, the instruments are removed and the traction is released.
LIMITED OPEN OSTOECHONDROPLASTY
Surgical Approach
The patient is maintained in a supine position and an 8- to 10-cm incision is made extending from the lateral aspect of the anterior superior iliac spine distally to incorporate the anterior arthroscopic portal incision (TECH FIG 3A).
The dissection is carried through the subcutaneous tissue to the fascia of the tensor fascia lata muscle (TECH FIG 3B). Care is taken to bring the subcutaneous dissection slightly lateral to avoid the lateral femoral cutaneous nerve.
The fascia of the tensor muscle is incised over the muscle belly, and the tensor fascia muscle is reflected laterally. The medial soft tissue flap, including the sartorius, is reflected medially. The underlying rectus tendon is identified.
The direct and indirect heads of the rectus are released and reflected distally to allow wide access to the hip and wide exposure of the femoral head–neck junction (TECH FIG 3C, D).
TECH FIG 3 • Osteochondroplasty surgical approach. A. The anterior incision (8–10 cm) is started at the lateral aspect of the anterosuperior spine and extended distally to incorporate the anterior arthroscopic portal incision. B. The dissection is carried through the subcutaneous tissue to the underlying fascia of the tensor fascia lata (TFL) muscle. The fascia is incised, and the tensor muscle belly is reflected laterally. The sartorius is reflected medially. C. This enables exposure of the direct (pictured) and indirect heads of the rectus femoris tendon. D. Both heads of the rectus tendon are released, exposing the underlying iliocapsularis muscle over the anterior hip joint capsule. The iliocapsularis is reflected distally and medially. The plane between the hip capsule and overlying iliopsoas muscle is developed medially.
TECH FIG 3 • E. The anterior hip capsule is then identified and a capital I–type arthrotomy made. F. The retractors are placed intraarticularly, and exposure of the anterolateral head-neck junction is obtained.
After release of the rectus, the soft tissue and iliocapsularis muscle fibers are stripped from the anterior hip capsule. A cobra retractor is placed medially between the psoas muscle and the anterior hip capsule, and a right angle narrow-deep retractor is placed laterally.
A capital “I”-shaped arthrotomy is made, and the retractors are moved intra-articularly to displace the medial and lateral capsular flaps and provide access to the femoral head and neck (TECH FIG 3E, F).
The foot is then removed from traction and positioned on the radiolucent table to allow unrestricted motion of the lower extremity and wide access to the femoral head–neck junction.
The joint is inspected with specific attention to the femoral head–neck junction.
Femoral Head–Neck Recontouring
The lower extremity is brought up into a figure 4 position, which enables excellent visualization of the anteromedial head–neck junction.
This region of the proximal femur commonly has normal offset in the face of reduced anterolateral head–neck junction offset. Thus, the anteromedial neck contour may be used as a template for the anterolateral osteochondral resection.
Articular cartilage discoloration, the presence of chondromalacia, or evidence of an impingement trough (indentation) also is observed at the anterolateral femoral head–neck junction (TECH FIG 4A). The osteochondroplasty is started proximal to the area of suspected impingement.
A combination of ½- and ¼-inch curved osteotomes is used to perform the recontrouring of the femoral head and neck (TECH FIG 4B). The osteochondroplasty is beveled inferiorly to prevent delamination of the preserved femoral head articular cartilage.
The depth of the osteochondroplasty ranges from 5 to 10 mm, depending on the severity of the deformity. The resection usually involves the majority of the anterolateral femoral head–neck junction, and may expand to cover more than 180 degrees of the femoral head–neck circumference.
Lower extremity positioning with internal and external rotation greatly enhances the extent of visualization and allows safe recontouring under direct vision.
Care is taken not to extend into the posterolateral femoral neck, because this area contains the terminal branches of the deep branch of the medial femoral circumflex artery.13
After the femoral head has been recontoured, the resection is assessed by direct visualization and palpation through the arthrotomy. Anterior femoroacetabular impingement is examined dynamically by palpation through the arthrotomy while moving the hip into flexion and combined flexion–internal rotation.
If palpation identifies residual impingement, then the resection is refined to remove the impinging structures at the femoral head–neck junction or the femoral neck.
TECH FIG 4 • Femoral head–neck recontouring. The anterolateral femoral head–neck junction is inspected. A. Care is taken to observe any irregularity in the articular catilage, discoloration of the articular cartilage, and impingement trough or indentation. B. The osteochondroplasty and recontouring of the anterolateral femoral head–neck junction are performed using ½- and ¼-inch curved osteotomes. C. After the osteochondroplasty is completed and inspected by direct physical examination and fluoroscopy, the osteochondroplasty bony bed is treated with bone wax.
Fluoroscopic examination is performed after completion of femoral head recontouring to confirm sphericity and adequate osteochondral resection. The head is visualized in extension with neutral rotation and external rotation. The hip is then examined in a frog-leg lateral position to better visualize the anterolateral head–neck junction. Varying degrees of flexion and internal–external rotation permit excellent assessment of the osteochondroplasty.
After recontouring of the femoral head–neck junction is complete, the osteochondroplasty bed is treated with bone wax (TECH FIG 4C).
CLOSURE
The longitudinal capsulotomy incision is approximated with absorbable suture. The superomedial and superolateral capsular flaps are also reapproximated. The inferior capsular flaps do not require repair.
The direct and indirect heads of the rectus tendon are repaired with nonabsorbable sutures (TECH FIG 5).
The fascia, subcutaneous tissue, and skin are closed in standard fashion.
TECH FIG 5 • The hip joint capsule and overlying rectus tendons are repaired.
FIG 4 • AP pelvis and frog-leg lateral views after hip arthroscopy and limited anterior osteochondroplaty of the femoral head–neck junction. A. The AP pelvis view shows enhanced offset at the lateral femoral head–neck junction (arrow). B. The frog-leg lateral view clearly shows improved femoral head–neck offset (arrow) anteriorly and improved sphericity of the femoral head compared to preoperative x-rays (see Fig 2C–E). At 2-year follow-up, this patient had no symptoms and no activity restrictions.
POSTOPERATIVE CARE
Postoperative radiographs are obtained to verify the recontouring of the femoral head–neck junction and to document the integrity of the proximal femur (FIG 4).
Patients are treated with one aspirin two times a day for 6 weeks for deep venous thrombosis prophylaxis, and with indomethacin, 75 mg per day for 6 weeks, to prevent heterotopic ossification.
Patients are toe-touch weight bearing for 4 weeks and then progress to full weight bearing. Gentle physical therapy is started the day after surgery. Therapy focuses on gentle range of motion and progressive strengthening within the patient's comfort zone.
Continous passive motion is used for 4 to 6 hours per day for 2 to 4 weeks.
The patient may return to normal daily activities as tolerated 4 weeks after surgery and may return to contact sports or running 6 months after surgery.
OUTCOMES
Documentation of clinical outcomes for surgical treatment of hip impingement disease is limited.3,8,10,14,21
Early to mid-term results are now available for treament with surgical dislocation of the hip and are encouraging for most patients.3,10,21
Reported clinical outcomes with less invasive impingement techniques are limited.8,14
Our experience with hip arthroscopy and combined limited open osteochondroplasty has been encouraging. Analysis of our first 23 consecutive cases demonstrated good or excellent clinical results in 22 of the 23 hips at a mean 18 months of follow-up.8
COMPLICATIONS
Neurovascular injury
Deep venous thrombosis
Heterotopic ossification
Femoral neck fracture
Infection
Articular cartilage scuffing
Arthroscopic instrument breakage
REFERENCES
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3. Beck M, Leunig M, Parvizi J, et al. Anterior femoroacetabular impingement: part II. Midterm results of surgical treatment. Clin Orthop Relat Res 2004;418:67–73.
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