Cam-Type Femoroacetabular Impingement

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CHAPTER 4 Cam-Type Femoroacetabular Impingement

Surgical correction of various hip impingement problems was described even early in the last century.¹^,² In 1975, Harris and coauthors described the pistol grip deformity of the femoral head observed in association with early-onset osteoarthritis.³ In 1998, we described arthroscopic correction of impingement caused by post-traumatic osteophytes and also reported an arthroscopic technique of cheilectomy for femoral protuberances associated with Legg-Calvé-Perthes disease.⁴^,⁵ However, it was Myers, Ganz, Lavigne and colleagues⁶^–⁸ who formulated the concept of femoroacetabular impingement, describing pincer, cam, and combined types. Subsequently, we have reported arthroscopic methods for correcting this disorder.⁹^–¹¹

We have identified a bimodal population of patients with cam-type femoroacetabular impingement (FAI).¹¹ One is the typical middle-aged patient (average age, 43 years, with a 1.9:1 male-to-female ratio) who presents with early-onset osteoarthritis. The second population is much younger, with an even greater male preponderance (average age, 20 years, with 3.1:1 male-to-female ratio) and most (70%) are involved in athletic activities. These are active individuals who have pushed their hip beyond its diminished physiologic limits and have sustained substantial joint breakdown at a young age.

ANATOMY AND PATHOANATOMY

Cam-type FAI refers to the cam effect created by a nonspherical femoral head. During flexion, the prominence of the out-of-round portion rotates into the acetabulum, engaging against its surface and resulting in delamination and failure of the acetabular articular cartilage (Fig. 4-1). Early in the disease process, the labrum is relatively preserved but, with time, it begins to sustain secondary damage.

FIGURE 4-1 A, Cam impingement occurs with hip flexion as the bony prominence of the nonspherical portion of the femoral head (cam lesion) glides under the labrum. engaging the edge of the articular cartilage and resulting in progressive delamination. B, Initially, the labrum is relatively preserved, but secondary failure occurs over time (arrow).

Cam impingement is classically attributed to a slipped capital femoral epiphysis, resulting in a bony prominence of the anterior and anterolateral head-neck junction. However, the most common cause is the pistol grip deformity, attributed to a developmental abnormality of the capital physis during growth. The exact cause is unclear; it may represent premature asymmetrical closure of the physis; it has been postulated that this could be caused by late separation of the common proximal femoral growth plate that forms the physis of the greater trochanter and femoral head.¹²

Femoroacetabular impingement is still incompletely understood. The pathomechanics explain the observations of secondary joint pathology caused by the impingement. However, some individuals with impingement shaped hips may never become symptomatic as a result of secondary damage. Thus, it is possible to have impingement morphology without impingement pathology. The arthroscope has become invaluable in the treatment algorithm for patients with FAI. Arthroscopic observations on the secondary articular and labral damage associated with pathologic impingement dictate the need for correcting the underlying bony abnormalities.

HISTORY AND PHYSICAL EXAMINATION

Patients with cam impingement have typical hip joint–type symptoms.¹³ The onset may be gradual or associated with an acute episode, which is the culmination of altered wear developing over a protracted period of time. Patients with cam impingement usually have reduced joint motion, which can result in other secondary disorders. Athletes compensate with increased pelvic motion, often resulting in problems with athletic pubalgia.¹⁴ More stress is placed on the lumbar spine, resulting in concomitant lumbar disease.

Pain with flexion, adduction, and internal rotation is almost uniformly present and is referred to as the impingement test (Fig. 4-2).⁷ However, in our experience, this maneuver is uncomfortable for most irritable hips, regardless of the underlying cause, and thus is not specific for impingement. Laterally based cam lesions may result in painful abduction or external rotation (Fig. 4-3). Internal rotation of the flexed hip is usually diminished, but may be preserved in some patients (Fig. 4-4). Limited range of motion may be present bilaterally because the morphologic variation is often present in both hips.

FIGURE 4-2 The impingement test is performed by provoking pain with flexion, adduction, and internal rotation of the symptomatic hip.

FIGURE 4-3 Abduction and external rotation may elicit pain with laterally based cam lesions.

FIGURE 4-4 Internal rotation is checked with the hip in a 90-degree flexed position.

DIAGNOSTIC IMAGING

Radiographs are essential for the routine evaluation of impingement. A well-centered anteroposterior (AP) pelvis x-ray is important for assessing the acetabular indices of pincer impingement, but also allows observations on the cam lesion comparing both hips (Fig. 4-5).¹⁵ The epicenter and shape of the cam lesion are variable. Thus, although the 40-degree Dunn view has been reported as the best image, we have found that no single lateral radiographic view is reliable for optimally assessing the cam lesion in all cases (Fig. 4-6).¹⁶ Sometimes, the cam lesion is more anteriorly based and sometimes more lateral. The characteristic feature is loss of sphericity of the femoral head. The alpha angle has been described to quantitate this observation (Fig. 4-7).¹⁷ However, imaging will underinterpret this measurement unless it catches the maximal location of the cam lesion. Also, no studies have shown a significant correlation between the amount of correction of the alpha angle and the results of surgery, indicating that there may be other factors at play.

FIGURE 4-5 A properly centered AP radiograph must be controlled for rotation and tilt. Proper rotation is confirmed by alignment of the coccyx over the symphysis pubic (vertical line). Proper tilt is controlled by maintaining the distance between the tip of the coccyx and the superior border of the symphysis pubis at 1 to 2 cm.

FIGURE 4-6 The frog-leg lateral radiograph is convenient because it is simple to carry out and is reproducible. The cam lesion (arrow) is evident as the convex abnormality at the head-neck junction where there should normally be a concave slope of the femoral neck.

FIGURE 4-7 The alpha angle is used to quantitate the severity of the cam lesion. A circle is placed over the femoral head. The alpha angle is formed by a line along the axis of the femoral neck (1) and a line (2) from the center of the femoral head to the point where the head diverges outside the circle (arrow).

Magnetic resonance imaging (MRI) and gadolinium arthrography with MRI (MRA) aid in assessing secondary damage to the articular cartilage and labrum associated with cam impingement.¹⁸ These studies are better at detecting labral pathology but reveal the severity of articular involvement less often. The alpha angle can again be recorded, but is still variable, depending on whether the cross-sectional images catch the maximal location of the cam lesion.

Computed tomography (CT) with three-dimensional reconstruction provides great clarity in evaluating the shape, size, and location of the cam lesion. This is valuable for the arthroscopic management of this condition. Exposure of the abnormal bone is simplified by knowing its exact appearance.

INDICATIONS AND CONTRAINDICATIONS

The indication for hip arthroscopy is imaging evidence of intra-articular pathology amenable to arthroscopic intervention, or sometimes recalcitrant hip pain that remains refractory to efforts at conservative treatment. It must be kept in mind that imaging studies may often underestimate the severity of intra-articular pathology. Correction of an accompanying cam lesion has been performed, when present, especially when there was arthroscopic evidence that it was responsible for the concomitant joint pathology. This secondary joint damage is best characterized by failure of the anterolateral acetabular articular surface. The failure is most typically represented by articular delamination with the peel-back mechanism, but earlier in the disease process may be characterized by deep, closed, grade I articular blistering, referred to as the wave sign.¹⁹

It is our opinion that radiographic findings of impingement, in the absence of clinical findings of a joint problem, are not solely an indication for arthroscopy. Some individuals with impingement morphology may function for decades without developing secondary joint damage and symptoms. For some, it is unclear when, or if, they will develop problems warranting surgical intervention. For example, many individuals may present with symptoms in one hip when radiographic findings of impingement are present in both. Although intervention in the asymptomatic joint would not be appropriate, it is important to educate the patient about warn ing signs of progressive joint damage. It is a clinical challenge in the decision not to intercede too early or too late. In our experience, 93% of patients undergoing arthroscopy for cam impingement demonstrate Grade III or IV articular damage, reflecting that the disease process is already substantially advanced at the time of intervention.¹¹

Contraindications include advanced disease states, such as grade III Tonnis changes, and sometimes there are patients who do not have reasonable expectations of what can be accomplished with the procedure.²⁰ Because the success of the operation is ultimately dictated by the patient’s impressions, it may be important to modulate the patient’s goals. Also, in the presence of secondary degenerative disease, the potential advantages of a joint-preserving procedure must be weighed against the high level of satisfaction associated with arthroplasty procedures.

TREATMENT

Conservative Management

Conservative management begins with an emphasis on early recognition of the underlying impingement disorder. The mainstay of treatment is identifying and modifying offending activities that precipitate symptoms. Some individuals can modify their lifestyles and stabilize the process for years. Efforts can be made to optimize mobility of the joint, but these are only modestly effective because motion is limited by the bony architecture, which cannot be corrected with manual techniques. Decompensatory disorders are those secondary problems that develop as individuals struggle to compensate for the chronic limitations imposed by the impingement. A conservative strategy must include assessment and treatment of the secondary problems, which can contribute substantially to the patient’s symptoms.

For patients with degenerative disease, treatment may be lifestyle modifications to keep the symptoms manageable. For athletes pushing the joint beyond its diminished physiologic limitations, a specific program becomes more important. Optimizing core strength can aid in regaining the athlete’s ability to compensate properly. Loading of a flexed hip can be particularly destructive in the presence of impingement; thus, repetitive training activities such as squats and lunges should be avoided or modified to limit hip flexion.

Surgical Technique

The procedure begins with arthroscopy of the central compartment to assess for the pathology associated with cam impingement. This is carried out with the standard supine three-portal technique that has been well described in the literature (Fig. 4-8).²¹^–²³ The characteristic feature of pathologic cam impingement is articular failure of the anterolateral acetabulum. The femoral head remains well preserved until late in the disease course. Early stages of the disease are characterized by closed grade I chondral blistering, which sometimes must be distinguished from normal articular softening. Our experience has been that most patients already have grade III or IV acetabular changes by the time of surgical intervention.¹¹ The articular surface is seen to separate or peel away from its attachment to the labrum (see Fig. 4-16D); this is caused by the shear effect of the cam lesion. The labrum may be relatively well preserved but, with time, progressive fragmentation occurs. Often, the damaged articular surface of the labrum can be selectively débrided, preserving the capsular margin and potentially some of its labral seal function. If there is good-quality tissue that has been detached, repair can be performed with suture anchors. In cases of combined impingement with concomitant pincer lesions, the acetabulum is reshaped, either by takedown and subsequent refixation of the labrum or by débridement when the labral damage is advanced. The articular pathology is addressed with chondroplasty and microfracture as dictated by its severity.

FIGURE 4-8 A, The site of the anterior portal coincides with the intersection of a sagittal line drawn distally from the anterior superior iliac spine and a transverse line across the superior margin of the greater trochanter. The direction of this portal courses approximately 45 degrees cephalad and 30 degrees toward the midline. The anterolateral and posterolateral portals are positioned directly over the superior aspect of the trochanter at its anterior and posterior borders. B, The relationship of the major neurovascular structures to the three standard portals is illustrated. The femoral artery and nerve lie well medial to the anterior portal. The sciatic nerve lies posterior to the posterolateral portal. The lateral femoral cutaneous nerve lies close to the anterior portal. Injury to this structure is avoided by using proper portal placement. The anterolateral portal is established first because it lies most centrally in the safe zone for arthroscopy. (A courtesy of Smith & Nephew Endoscopy, Andover, Mass.)

After completing arthroscopy of the central compartment, the cam lesion is addressed from the peripheral compartment. A capsulotomy is created by connecting the anterior and anterolateral portals (Fig. 4-9). The posterolateral portal can be removed and the anterior and anterolateral cannulas are backed out of the central compartment. The traction is released and the hip is flexed approximately 35 degrees. As the hip is flexed under arthroscopic visualization, the line of demarcation between healthy femoral cartilage and abnormal fibrocartilage that covers the cam lesion can usually be identified.

FIGURE 4-9 A capsulotomy is performed by connecting the anterior and anterolateral portals (dotted line). This is geographically located adjacent to the area of the cam lesion. This capsulotomy is necessary so that the instruments can pass freely from the central to the peripheral compartment as traction is released and the hip is flexed.

A cephalad anterolateral portal is established approximately 5 cm above the anterolateral portal, entering through the capsulotomy that has already been established. These proximal and distal anterolateral portals work well for accessing and addressing the cam lesion (Fig. 4-10). The anterior portal can be removed or maintained if it is needed for better access to the medial side of the femoral neck.

FIGURE 4-10 With the hip flexed, the anterolateral portal is now positioned along the neck of the femur. A cephalad (proximal) anterolateral portal has been placed. These two portals allow access to the entirety of the cam lesion in most cases. Their position also allows an unhindered view with the c-arm.

Most of the work for performing the recontouring of the cam lesion (femoroplasty) lies in the soft tissue preparation. This includes capsular débridement, as necessary, to ensure complete visualization of the lesion and then removal of the fibrocartilage and scar that cover the abnormal bone (Fig. 4-11). With the hip flexed, the proximal portal provides better access for the lateral and posterior portion, whereas the distal portal is more anterior relative to the joint and provides the best access for the anterior part of the lesion. The lateral synovial fold is identified as the arthroscopic landmark for the retinacular vessels, and care is taken to preserve this structure during the recontouring (Fig. 4-12). Switching between the portals is important for full appreciation of the three-dimensional anatomy of the recontouring.

FIGURE 4-11 The right hip is viewed from the anterolateral portal. A, The cam lesion is identified, covered in fibrocartilage (asterisk). B, An arthroscopic curette is used to denude the abnormal bone. C, The area to be excised has been fully exposed. The soft tissue preparation aids in precisely defining the margins to be excised.

FIGURE 4-12 Viewed laterally, underneath the area of the lateral capsulotomy, the lateral synovial fold (arrows) is identified along the lateral base of the neck, representing the arthroscopic landmarks of the lateral retinacular vessels.

Once the bone has been fully exposed, recontouring is performed with a spherical burr. The goal is to remove the abnormal bone identified on the preoperative CT scan and re-create the normal concave relationship that should exist where the femoral neck meets the articular edge of the femoral head. It is best to begin by creating the line and depth of resection at the articular margin. The resection is then extended distally, tapering with the normal portion of the femoral head (Figs. 4-13 and 4-14). We recommend beginning the resection at the lateral posterior limit of the cam lesion, with the arthroscope in the more distal portal and instrumentation in the more proximal portal. The posterior extent of the resection is usually the most difficult; the resection is also the most critical to avoid notching the tensile surface of the femoral neck, and particular attention must be given to avoiding and preserving the lateral retinacular vessels. Then, switching the arthroscope to the proximal portal, the burr is introduced distally and the reshaping is completed along the anterior head and neck junction. Finally, attention is given to ensure that all bone debris is removed as thoroughly as possible to lessen the likelihood of developing heterotopic ossification. The quality of the recontouring is assessed and preservation of the lateral retinacular vessels is confirmed (Fig. 4-15).

FIGURE 4-13 The arthroscope is in the more distal (anterolateral) portal, with the instrumentation placed from the proximal portal. A, Bony resection is begun at the articular margin. B, The resection is then carried distally, re-creating the normal concave relationship.

FIGURE 4-14 The arthroscope is now in the proximal portal with the instrumentation introduced distally. A, The line of resection is continued along the anterior articular border of the bump. B, The recontouring is completed.

FIGURE 4-15 The arthroscope has been returned to the distal portal for final survey. A, viewing medially; B, viewing laterally; C, confirming preservation of the lateral retinacular vessels (arrows).

Closure of the capsulotomy is not routinely performed. In cases in which instability might be a potential concern, such as dysplasia, the capsulotomy is limited and suture closure could be considered.

PEARLS& PITFALLS

• Be certain of the clinical relevance of the cam lesion. Radiographic evidence of cam morphology may often be encountered as an incidental finding. Make sure that the clinical findings indicate a hip problem and that the arthroscopic findings indicate pathology secondary to cam impingement.

• Make sure to complete the capsulotomy. A modest capsulotomy is necessary to mobilize the instruments adequately as they are moved from the central compartment with distraction to the peripheral compartment without distraction

• Fully expose the entirety of the cam lesion before beginning resection. Make sure to know the margins and amount of bone to be resected. This is important to avoid inadequate or excessive resection.

• Avoid reliance on fluoroscopic imaging in the absence of complete arthroscopic visualization during resection. This can result in erroneous bony resection.

• The first and most tedious step is the soft tissue preparation to expose the bone that needs to be resected. Bony resection should then proceed smoothly. Starting and stopping for added soft tissue exposure increases the risk of improper resection.

• Know the location of the lateral retinacular vessels. If in doubt, identify the vessels before beginning bony resection.

• Proper recontouring should entail a minimal risk for femoral neck fracture, but modest postoperative precautions are necessary. Weight bearing should be protected at least until good motor control of the hip musculature has been regained.

• Have a plan for assessing the amount of bone to remove whether this is based on visual templating of the abnormal bone from three-dimensional CT scans or on the intraoperative ROM to assess the adequacy of decompression. Note that the exact amount of bone to be removed, and the optimal method for assessing this, have not been defined. Inadequate or excessive resection are both problematic.

Case Reports

Case 1

A 20-year-old hockey player was evaluated, with a 4-year history of worsening right groin pain. Examination revealed diminished internal rotation of both hips (10 degrees). Forced flexion, adduction, and internal rotation of the right hip re-created the characteristic pain that he experienced with activities (Fig. 4-16).

FIGURE 4-16 Images of a 20-year-old hockey player with a 4-year history of right hip pain. A, AP radiograph is unremarkable. B, Frog-leg lateral radiograph demonstrates a morphologic variant with bony buildup at the anterior femoral head-neck junction (arrow) characteristic of cam impingement. C, Three-dimensional CT scan further defines the extent of the bony lesion (arrows). D, Viewing from the anterolateral portal, the probe introduced anteriorly displaces an area of articular delamination from the anterolateral acetabulum. This is characteristic of the peel-back mechanism created by the bony lesion shearing the articular surface during hip flexion. E, Viewed from the peripheral compartment, the bony lesion is identified (asterisk) immediately below the free edge of the acetabular labrum (L). F, The lesion has been excised, re-creating the normal concave relationship of the femoral head-neck junction immediately adjacent to the articular surface (arrows). Posteriorly, resection is limited to the midportion of the lateral neck to avoid compromising blood supply to the femoral head from the lateral retinacular vessels. G, A postoperative three-dimensional CT scan illustrates the extent of bony resection.

Case 2

A 38-year-old woman presented with a 3-year history of progressively worsening pain and loss of motion of both hips, right worse than left. Symptoms were initially precipitated by horseback riding, but have now become troublesome with daily activities. Examination revealed an antalgic gait. Range of motion was restricted in both hips (35 degrees external rotation, 5 degrees internal rotation), with pain at all end ranges (Fig. 4-17).

FIGURE 4-17 Images of a 38-year-old woman with progressive pain and loss of motion of the right hip. A, AP radiograph demonstrates acquired bony buildup and osteophyte formation on the lateral femoral head (arrow). B, Frog-leg lateral radiograph further defines the bony buildup on the anterior femoral head (arrow). C, Three-dimensional CT scan further defines the femoral head osteophyte (asterisk) and anterior acetabular lesion (arrows). D, Arthroscopy of the central weight-bearing surface of the joint demonstrates good articular preservation of both the acetabulum (A) and femoral head (FH), with some reactive synovitis within the fossa (S). E, The anterior acetabular osteophyte is excised. F, Viewed peripherally, the femoral head has been recontoured showing the edge of the femoral articular surface (white arrows) and the labrum (black arrows). G, Postoperative three-dimensional CT scan demonstrates the extent of bony recontouring of both the acetabulum and femoral head.

Case 3

A 15-year-old level 10 female gymnast presented with a 6-month history of left hip pain unresponsive to conservative treatment, including a protracted period of rest. Examination revealed a 20-degree loss of motion of the left hip compared with the right, with pain re-created on flexion, adduction, and internal rotation (Fig. 4-18).

FIGURE 4-18 Images of a 15-year-old female gymnast with pain and reduced internal rotation of the left hip. A, AP pelvic radiograph demonstrates a crossover sign of the left hip with an associated os acetabulum (arrow). B, Frog-leg lateral view illustrates asymmetrical cam lesion (arrow) present in the left hip and not the right. C, Three-dimensional CT scan further defines the pincer lesion with os acetabulum (arrow) and cam lesion (asterisk). D, Viewed from the anterolateral portal, the pincer lesion and os acetabulum (asterisk) are exposed, with the labrum being sharply released with an arthroscopic knife. E, The acetabular fragment has been removed and the rim trimmed with anchors placed for repair of the labrum. F, Viewed from the periphery, the cam lesion is identified (asterisk) covered in fibrocartilage. G, The cam lesion has been excised, re-creating the normal concave contour of the head-neck junction adjacent to the site of labral refixation.

POSTOPERATIVE PROTOCOL

Rehabilitation

Formal supervised physical therapy begins within 1 or 2 days following surgery. An emphasis is on optimizing ROM, with early implementation of closed-chain joint stabilization and core strengthening exercises. The patient is allowed to bear weight as tolerated but crutches are used for 4 weeks as a precautionary measure to protect the femoroplasty site against any awkward twisting episodes. Once normal muscle tone and response patterns have been regained, these will adequately protect the joint from normal forces. Impact loading is avoided for 3 months while the bone fully remodels. The rehabilitation protocol is modified for microfracture by keeping the patient on strict, protected, weight-bearing status for 2 months. The patient is allowed to place the weight of the leg on the ground, which provides optimal neutralization of forces across the joint. Also, if a labral repair has been performed, excessive flexion and external rotation are avoided for the first 4 weeks.

A formal structured rehabilitation protocol is continued for 3 months. For athletes, functional progression is then advanced as tolerated. Although some athletes may resume unrestricted activities quickly, usually it is anticipated that another 1 to 3 months are necessary for full participation.

OUTCOMES

We have reported on 200 patients (207 hips) with 100% follow-up at 1 to 2 years.¹¹ The average age was 33 years (range, 13 to 63 years). There were 138 males and 62 females, with 120 right and 87 left hips, and 163 patients underwent femoroplasty to correct cam impingement alone, whereas 44 patients underwent femoroplasty combined with correction of associated pincer impingement. Overall, the average improvement was 20 points (preoperative, 66; preoperative, 86). Using the Harris classification, 83% were improved, with 83% good and excellent results Viewing the results over time (see Fig. 4-8), continued improvement was noted throughout the first year, with results maintained in those with 2-year follow up. Most had Outerbridge grade IV (107) or grade III (83) articular damage on at least one side of the joint, and 58 underwent microfracture, with an average 20-point improvement (preoperative, 65; postoperative, 85). Comparing the results of cam and combined lesions, the results were comparable, with 20- versus 19-point improvement. The cam patients tended to be slightly younger, with an average age of 33 versus 35 years for combined lesions. A bimodal age distribution was identified, with a peak at age 20 and a second peak at age 43 years; 94 (45%) were sports-related. For those patients younger than 30 (N = 88), 62 (70%) were associated with athletic activities; after the third decade (N = 119), only 30 (25%) were associated with athletics. The under 30 group was also more male-dominated, with a male-to-female ratio of 3.1:1 compared with the over 30 group, with a male-to-female ratio of 1.9:1. One patient (0.5%) was converted to a total hip arthroplasty whereas 3 patients underwent a second arthroscopic procedure. There were three complications, but none were significant. There was one each of a transient neuropraxia of the pudendal nerve and lateral femoral cutaneous nerve, which resolved uneventfully. One patient was incidentally noted to have developed heterotopic ossification within the capsule, which did not preclude a successful outcome.

In a more recent review, we identified a cohort of 163 athletes with cam-type FAI (141 isolated, 22 combined with pincer), in which there was a 100% minimum 1-year follow-up. The average age was 29 years, with 119 men and 44 women. There were 18 professional, 49 intercollegiate, and 96 high school or recreational athletes. The average improvement was 22 points (preoperative, 71; postoperative, 93), with 89% of professional and 90% of intercollegiate athletes returning to their previous level of athletic competition.

Other authors have reported outcomes of arthroscopic management of FAI specifically in regard to correction of the cam lesion. Ilizaliturri and colleagues have reported improvement in 16 of 19 patients (84%), with a minimum 2-year follow-up.²⁴ Bardakos and associates²⁵ have reported on femoral osteoplasty in 24 patients with 1-year follow-up compared with a control group in which arthroscopic débridement was performed without excising the impingement lesion. The modified Harris hip score was better in the study group (83) compared with the control group (77), and there was a significantly higher proportion of good to excellent results in the study group (83%) compared with the control group (60%). Brunner and coworkers²⁶ have reported on 45 athletically active individuals; 31 (69%) were able to resume their activities, with an average 2.4-year follow-up.