Introduction

In 1995, Ganz first described femoroacetabular impingement (FAI), and, in 1999, it was introduced into the English literature. Although the first case was pincer impingement as a result of acetabular overcoverage after a periacetabular osteotomy, further investigations by Professor Ganz and his group led to the recognition of a second type of impingement: cam impingement. This type of impingement is the result of loss of the femoral head–neck offset, which causes the joint to function like a mechanical cam device. The anatomy of cam impingement has been previously described as a pistol grip deformity or a tilt deformity (Figure 19-1). Many investigators have attributed this anatomy to subclinical slipped capital femoral epiphysis (SCFE), and certainly the residuals of an unreduced SCFE can result in cam impingement. Beaule and colleagues demonstrated in a computed-tomography–based study that cam impingement can occur without SCFE, which suggests that this condition is not the result of a subclinical SCFE. Wagner and colleagues demonstrated that the bone of the cam lesion is not reactive nor does it involve any inflammation; thus it is not likely the result of the impingement or arthritis. Because the deformity occurs at or near the femoral head physeal scar, it may be genetically predetermined or the result of stresses applied during development. Either way, this pistol grip deformity has been associated with premature osteoarthritis of the hip. It has also been suggested that cam impingement results in premature or idiopathic arthritis of the hip. However, Bardakos and Villar have shown that only two thirds of patients with cam impingement show radiographic progression of arthritis at 10-year follow up.

Figure 19–1 Cam impingement. A, Anteroposterior hip radiograph (cropped from an anteroposterior pelvic view) and B, lateral radiograph of a 19-year-old collegiate basketball player with cam-type impingement with a mild crossing sign. Notice the loss of offset at the femoral head–neck junction and the convexity of the anterior femoral neck.

The anatomy of cam impingement can frequently be seen among those patients with idiopathic arthritis, although this is still a controversial subject. The suggestion that impingement results in hip arthritis is also likely when studying the pathologic findings of symptomatic impingement patients without arthritis, particularly of those with labral tears and chondral lesions that are thought to progress to arthritis when untreated. The majority of patients in Ganz’s series had a combination of cam and pincer impingement, which has been confirmed in other published series as well as my own experience of several hundred patients with symptomatic FAI. Beck and colleagues found that the demographics and pathology do correlate with the different subtypes of impingements. Particularly, for those with isolated types of impingements, the cam type is the most common (17%). It tends to occur in 19-year-old males, whereas those with isolated pincer impingement are 40-year-old active females. For those with isolated cam impingement, the common pathologic findings initially are focal, deep chondral delamination lesions (anterolaterally and extending about 1 cm from the acetabular edge) (Figure 19-2). At first the labrum is intact, but it eventually separates from the acetabular articular cartilage edge before degenerating. The labrum often separates from the acetabulum and the articular cartilage, and the articular cartilage delaminates from the bony acetabulum (Figure 19-3). Alternatively, those with pincer impingement tend to have intrasubstance crushing of the labrum, and the articular cartilage damage extends only a couple of millimeters from the acetabular edge (Figure 19-4). Although the greatest depth of penetration of articular cartilage damage in pincer impingement is also anterolateral, the damage tends to be more global and to extend around the circumference of the acetabulum. In addition, there is often posterior acetabular (62%) and femoral head (31%) articular cartilage damage as a result of the contrecoup phenomenon of the femoral head levering against the anterior acetabulum as the patient tries to obtain hip motion, which results in shearing forces posteriorly (see Figure 19-4). It has been my experience that one type of impingement will predominate the intra-articular pathologic findings.

Figure 19–2 Arthroscopic view of the chondral delamination of the acetabulum associated with cam impingement.

Figure 19–3 A, Schematic representation of the pathophysiology of joint damage with cam impingement. The cam lesion slides underneath the labrum, thereby resulting in a labral chondral separation and the detachment of the labrum from the underlying acetabulum. This occurs anterolaterally. The articular cartilage is then abutted, which results in the delamination of the cartilage from the underlying bone. B, A close-up of the region of interest where the impringement occurs.

Figure 19–4 Schematic representation of the pathophysiology of joint damage as a result of pincer impingement. The overcoverage of the acetabulum results in the crushing of the labrum against the femoral neck. This may occasionally result in the notching of the femoral neck. There is some articular cartilage damage, although this is shallower than that seen with cam impingement. With continued motion, the femoral neck levers against the acetabulum. This results in posteroinferior subluxation of the femoral head and causes posterior femoral head and acetabular articular cartilage damage.

Although the overall goal of restoring the femoral head–neck offset to relieve the abutment is the same, there is controversy with regard to the approach to be taken to address the cam lesion. Beck and colleagues found that the restoration of the femoral head–neck complex can be most reliably performed through an open approach with a trochanteric osteotomy and surgical dislocation. Although the open approach to this problem is beyond the scope of this chapter, Ganz and colleagues stated that the hip arthroscopy “technique is difficult. Simultaneous assessment of movement of the hip and debridement is not possible.” Furthermore, it has been suggested that the open approach, which is the gold standard, allows one to see the entire femoral head and the head–neck junction and thus allows for the use of templates to standardize the resection. This, in combination with the potential for complications of hip arthroscopy such as “nerve traction palsies, foot or perineal pressure sores, and iatrogenic damage to the articular cartilage of the joint,” has led many to believe that arthroscopy is limited with regard to its usefulness. However, advances in hip arthroscopy and particularly in peripheral compartment arthroscopy without traction have enhanced the ability to arthroscopically observe impingement dynamically during arthroscopic osteoplasty of the femoral head–neck junction. It has also been suggested that the “constrained hip renders access to the underlying cause of impingement technically challenging, if not impossible.” However, Sussman and colleagues performed a cadaveric comparison of open and arthroscopic techniques for cam impingement. With the use of subtraction computed tomography, those authors demonstrated that the accuracy and precision of arthroscopic osteoplasty approach that of open osteoplasty. They did report that the time for resection was faster with the open technique, although the time required to create the approach (e.g., trochanteric osteotomy, surgical dislocation) was not included. Those who perform the femoral osteoplasty or cheilectomy arthroscopically prefer this technique, because open surgical dislocation involves prolonged postoperative hospitalization (up to a week as compared with outpatient arthroscopic surgery), significant blood loss, a risk of trochanteric nonunion, and prolonged limited weight bearing (up to 12 weeks of crutch use as compared with 0 to 6 weeks). In addition, it is quite easy to see the entire central compartment arthroscopically as compared with the open surgical dislocation.

Indications

Although some believe that FAI results in arthritis and thus that surgery should be performed to prevent the arthritis, that has not been the approach used in our practice, because there is no evidence at this point that arthritis can be prevented. I certainly believe that having the anatomy of impingement does put the patient at risk for chondral injury, labral injury, and, potentially, arthritis. However, on the basis of my experience with patients who are more than 60 to 70 years old with the anatomy of FAI but no evidence of arthritis or hip symptoms in combination with my extensive experience of cadaveric research involving specimens 80 to 90 years old with the anatomy of obvious cam and combined impingement without evidence of arthritis, I have concluded that not everyone with the anatomy of FAI will develop osteoarthritis (Figure 19-5). It is my belief that the anatomy of FAI does put patients at potential risk for joint damage. However, it likely requires the individual to be involved in activities that require greater hip range of motion with or without pivoting (e.g., martial arts, soccer, running, golf) to result in impingement. After the tissues start breaking down, patients develop symptoms, because the labrum is a structure that is richly innervated. It is as soon as patients have confirmed intra-articular pain that surgery is indicated. Intra-articular anesthetic guided by fluoroscopy or ultrasound and that is given by itself or with contrast when performing magnetic resonance arthrography is a useful diagnostic test to confirm that the joint is the source of pain. Thus, the goal of surgery is to relieve intra-articular hip pain that is the result of impingement.

Figure 19–5 Photograph of a cadaveric specimen from an 85-year-old patient. Notice the obvious cam lesion and the lack of arthritic change.

Jäger and colleagues demonstrated that there is no role for physical therapy in the treatment of FAI. Their finding is not unexpected, because the bony problem will not resolve with physical therapy. Furthermore, the structures that are injured have limited if any capacity to heal spontaneously. That being said, conservative management consists of activity modification (particularly the avoidance of extremes of motion and of flexion and internal rotation particularly) and nonsteroidal anti-inflammatory medications.

The pathologies that need to be addressed include labral pathology and chondral lesions in addition to the underlying bony cause. Nearly 90% of patients who undergo hip arthroscopy for labral tears have associated bony pathology. It has been shown that those undergoing hip arthroscopy for labral tears in which the FAI was not addressed had poorer results than those without FAI. Thus, addressing intra-articular pathology without addressing the underlying cause will be less likely to result in a good outcome. Although magnetic resonance imaging is not as good as one would hope for identifying chondral damage, Johnston and colleagues found that those patients with symptomatic cam impingement and an alpha angle of more than 62 degrees are at increased risk for chondral injury. As a result, all patients undergoing surgery for intra-articular damage (e.g., symptomatic labral tears, chondral lesions) who have the anatomy of FAI should have the bony impingement treated at the same time.

Thus, indications for surgery include the following:

History and physical examination

Those patients with FAI generally describe an insidious onset of groin aching or pain. Although the condition is frequently confused with hip tendonitis or other problems, patients will often note difficulty putting on or taking off their socks and shoes. The pain is usually described as being in the groin, the inguinal region, or deep inside the joint. The pain may be worsened with activities, particularly running and other impact types of activities. Sitting (especially in low seats or chairs) for prolonged periods of time may also result in pain, and there is frequently pain when arising from a seated position. Patients with cam impingement may also have pain when squatting, cutting, or pivoting or when making sudden stops and starts. Stair climbing may also be problematic for patients with impingement. Patients may note the limited hip range of motion, particularly during flexion, adduction, and internal rotation. If the patient has an associated labral tear or a chondral flap, there may be an acute onset of symptoms as well as mechanical symptoms (e.g., locking, catching). It is not uncommon for patients to complain of hip or groin pain for years.

It is also not uncommon for patients to have had other surgeries that may not have relieved their symptoms. This may be the result of radiating symptoms or the fact that cam impingement results in limited hip range of motion. The limited motion within the femoroacetabular joint may put stress on other structures, which may result in pain or injury in these remote locations as athletic patients try to get motion to perform their activities, such as the pubic symphysis (osteitis pubis), the sacroiliac joint (sacroiliac joint dysfunction), the lower back (strains, herniated disc), and the abdominal musculature (sports hernia/athletic pubalgia). As such, several patients have been successfully treated with arthroscopic FAI in my practice (and in other practices) who have had previous laparoscopy, laparotomy, inguinal hernia repair, athletic pubalgia surgery, osteitis pubis injections and surgery, orchiectomy, oophorectomy, lumbar spine injections, decompressions, diskectomies, and lumbar spine fusion.

Although a complete discussion of the evaluation of the hip is beyond the scope of this chapter, a brief discussion of the general concepts is appropriate. First, evaluation includes the inspection of the gait and of the skin around the hip. Patients are assessed for hip weakness and tightness with the use of the Trendelenburg and Ober tests. Hip range of motion is assessed while the patient is supine. Evaluation of hip adduction and abduction, as well as internal and external rotation, should be performed in hip flexion and extension. Also, hip motions evaluated include flexion, extension, and flexion contracture. There is usually limited hip internal rotation, particularly when the hip is in flexion, among patients with impingement. Furthermore, patients frequently have pain when the hip is flexed to 90 degrees, adducted, and internally rotated; this is known as the impingement test (Figure 19-6). The labral stress test and the resisted straight-leg raise are tests that commonly result in hip pain among patients with labral tears and symptomatic impingement (Figure 19-7). These tests are often positive among patients with both cam and pincer types of FAI, and they may also be positive among patients with other sources of intra-articular hip pain.

Figure 19–6 Impingement test. The hip is flexed to 90 degrees, adducted, and internally rotated. The test is positive if pain is elicited. However, this test is not positive only in cases of femoroacetabular impingement.

Figure 19–7 The labral stress test: A, The supine patient’s hip is brought to the position of flexion, abduction, and external rotation and B, then brought into extension, adduction, and internal rotation.

Imaging and diagnostic tests

Plain radiographs are extremely valuable for the assessment of patients with hip pain that is the result of hip impingement. The standard imaging series for patients with hip pain includes an anteroposterior pelvic view with the coccyx centered 1 cm to 3 cm above the pubic symphysis and a true cross-table lateral radiograph (Figure 19-8). A frog-leg lateral view will demonstrate a lateral projection of the proximal femur and thus can be used for cam impingement assessment; however, this is not a lateral view of the acetabulum, so it has limited usefulness (see Figure 19-8, B). A cross-table lateral view, a Dunn view, and a modified Dunn view are true lateral views of the hip that can provide more information about the acetabulum (see Figure 19-8, C). The femoral head is generally symmetric, particularly the head–neck offset. A loss of the sphericity of the femoral head–neck region may be consistent with cam impingement (see Figure 19-8, A through C). This can be seen as a flattening of the concave surface of the lateral femoral neck and the appearance that the femoral head is not centered over the femoral neck. Leunig and colleagues demonstrated that, for patients with hip dysplasia, the apex of the femoral head is approximately 1 cm beyond the low point of the femoral neck, whereas in patients with impingement this distance was only 3 mm. In some situations, there may be a bump on the anterolateral surface of the femoral neck that may project beyond the femoral head or have a sharp transition or even a hook appearance at the head–neck junction. The alpha angle was originally described by Notzli and colleagues to quantify the head–neck offset on radially generated axial magnetic resonance imaging cuts of the femoral neck and head. These authors demonstrated that, in their normal population, the alpha angle averaged 42 degrees, whereas in those patients with impingement, this angle averaged 74 degrees. Most surgeons use 50 degrees or 55 degrees as their cutoff point for defining cam impingement. This angle has also been used when evaluating plain radiographs and computed tomography scans, although it has not been validated for these modalities. Additional plain radiographs may demonstrate a short femoral neck or a femoral neck–shaft angle that is varus, which may result in cam-type impingement. Untreated or residual deformity from SCFE or Legg-Calvé-Perthes disease may be seen on plain films, and this may result in cam impingement. Pincer impingement may also be seen on plain radiographs in association with coxa profunda, protrusio, retroversion, or relative retroversion of the superior acetabulum and arthritic changes.

Figure 19–8 Plain radiographs: anteroposterior pelvic and lateral views of a 22-year-old professional football player with cam impingement. A, Anteroposterior radiograph of the pelvis that demonstrates cam impingement. B, The frog-leg lateral view also shows the loss of the femoral head–neck offset. However, this view is not a lateral view of the acetabulum but only of the proximal femur. C, A true lateral view (this time of a collegiate lacrosse player). A Dunn view, or a modified Dunn lateral view may also be obtained.

Computed tomography scans, particularly three-dimensional ones, are particularly useful for demonstrating the bony anatomy associated with cam impingement (Figure 19-9). Magnetic resonance imaging, particularly magnetic resonance arthrography, is beneficial for demonstrating the cam lesion by allowing for a way to measure the alpha angle and to demonstrate labral tears, edema, or cysts within the femoral neck (these are often seen with impingement); this type of imaging can occasionally demonstrate chondral lesions (Figure 19-10). Local anesthetic is usually introduced with the contrast used for magnetic resonance arthrography to determine whether the pain is temporarily relieved within the joint, which confirms the source of pain as being intra-articular.

Figure 19–9 Representative three-dimensional computed tomography scans of 3 patients: A, a 40-year-old recreational athlete; B and C, a 35-year-old world-class triathlete; and D, a 27-year-old recreational softball player. These images demonstrate the loss of the offset at the femoral head–neck junction, thus showing the usefulness of this type of scan for the identification of the extent of the cam lesion. Figure D also demonstrates an acetabular rim fracture seen with combined cam and pincer FAI.