A deformidade da pelve Cam é um fator de risco para a dor no quadril?

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Incidence of Hip Pain in a Prospective Cohort of Asymptomatic Volunteers: Is the Cam Deformity a Risk Factor for Hip Pain?

Vickas Khanna, Anthony Caragianis, Gina DiPrimio, Kawan Rakhra and Paul E. BeaulĂŠ Am J Sports Med 2014 42: 793 originally published online January 30, 2014 DOI: 10.1177/0363546513518417 The online version of this article can be found at: http://ajs.sagepub.com/content/42/4/793 Published by: http://www.sagepublications.com

On behalf of: American Orthopaedic Society for Sports Medicine

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In-Depth

Incidence of Hip Pain in a Prospective Cohort of Asymptomatic Volunteers Is the Cam Deformity a Risk Factor for Hip Pain?

Vickas Khanna,* MD, FRCSC, Anthony Caragianis,* BSc, Gina DiPrimio,y MD, FRCPC, Kawan Rakhra,y MD, FRCPC, and Paul E. Beaule´,*z MD, FRCSC Investigation performed at The Ottawa Hospital, University of Ottawa, Ottawa, Ontario, Canada Background: Although cam-type femoroacetabular impingement is commonly associated with labral chondral damage and hip pain, a large proportion of asymptomatic individuals will have this deformity.

Purpose: To determine the incidence of hip pain in a prospective cohort of volunteers who had undergone magnetic resonance imaging (MRI) of their hips.

Study Design: Case control study; Level of evidence, 3.

Methods: A total of 200 asymptomatic volunteers who underwent an MRI of both hips were followed for a mean time of 4.4 years (range, 4.01-4.95 years). Thirty were lost to follow-up, leaving 170 individuals (77 males, 93 females) with a mean age of 29.5 years (range, 25.7-54.5 years). All patients were blinded to the results of their MRI. All completed a follow-up questionnaire inquiring about the presence of hip pain or a history of hip pain lasting longer than 6 weeks since the original MRI. Each patient was asked to draw where the pain was on a body diagram.

Results: Eleven patients (5 males, 6 females; 6.5% of sample; mean age, 29.9 years; range, 25.7-45.6 years) reported hip pain, of which 3 (1 male, 2 females) had bilateral pain for a total of 14 hips. Seven of the 14 painful hips had a cam-type deformity at the time of the initial MRI versus 37 of the 318 nonpainful hips (P = .0002). This gave a relative risk of 4.3 (95% confidence interval [CI], 2.3-7.8) of developing hip pain if cam deformity was present. Those 14 painful hips had a significantly greater alpha angle at the radial 1:30 clock position than did those who did not develop pain with a cam deformity: 61.5! (range, 57.3!-65.7!) versus 57.9! (range, 56.9!-59.1!), respectively (P = .05). A significantly greater proportion of patients (12%) with limited internal rotation !20! (versus 2.7% with internal rotation .20!) went on to develop hip pain (P = .009; relative risk = 3.1 [95% CI, 1.6-6.0]).

Conclusion: The presence of a cam deformity represents a significant risk factor for the development of hip pain. An elevated alpha angle at the 1:30 clock position and decreased internal rotation are associated with an increased risk of developing hip pain. However, not all patients with a cam deformity develop hip pain, and further research is needed to better define those at greater risk of developing degenerative symptoms.

Keywords: hip deformity; cam; pain; internal rotation.

et al,10 with cam-type impingement being more common than pincer type, with 80% having the deformity bilaterally, especially in males. A growing body of evidence suggests that FAI is not a benign condition but may in fact be the leading cause of degenerative hip arthritis, which had previously been attributed to idiopathic osteoarthritis.13,22,32 The mechanism by which cam- and pincer-type deformities can initiate degenerative changes of the hip is thought to be related to the abnormal/premature femoral and acetabular abutment. These abnormal contact points generate shear forces at the level of the labrum and cartilage, resulting in tearing of the labrum and delamination/abrasion of the acetabular cartilage, which are precursors to hip arthritis.6,31,33 Recent studies have shown the prevalence of this deformity in the general population to be approximately 15%,11,12 with males being 5 times more likely to have

Femoroacetabular impingement (FAI) results from osseous deformities of the femoral head-neck junction and/or the acetabulum, leading to cartilage damage within the hip joint. There are 2 forms of FAI as identified by Ganz z Address correspondence to Paul E. Beaule´, MD, FRCSC, Division of Orthopedic Surgery, University of Ottawa, 501 Smyth Road, CCW 1646, Ottawa, ON, Canada K1H 8L6 (e-mail: pbeaule@ottawahospital.on.ca). *Division of Orthopaedic Surgery, University of Ottawa, Ottawa, Ontario, Canada. y Department of Medical Imaging, University of Ottawa, Ottawa, Ontario, Canada.

The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.

The American Journal of Sports Medicine, Vol. 42, No. 4 DOI: 10.1177/0363546513518417 " 2014 The Author(s)

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this deformity.26 Cam deformity has also been shown to be present in over 50% of male collegiate football players as well as a high percentage of professional soccer players.15 While a relationship between FAI and osteoarthritis has been identified, and a large number of patients are being treated for intra-articular pathologic changes related to cam-type deformity, it is unclear if the mere presence of a cam deformity is solely responsible for the onset of hip symptoms.2,3 More importantly, the natural history of this deformity in the previously asymptomatic individual is relatively unknown and is important to establish if we are to consider screening programs and early intervention for this condition as well as to establish treatment guidelines for patients with intra-articular cartilage hip damage.

In a previous study12 we reported the prevalence of camtype deformity in a cohort of 200 asymptomatic patients, and the purpose of this study is to identify the incidence of hip pain in this patient cohort and to identify whether a cam deformity and its severity as quantified by the alpha angle is a risk factor for the development of hip pain.

MATERIALS AND METHODS This study is a midterm follow-up of our initial report on the prevalence of cam-type deformity on magnetic resonance imaging (MRI)12 in 200 healthy volunteers. Methodology of patient recruitment and MRI protocol were previously described.8 In summary, patients were selected based on a strict set of inclusion criteria, including age younger than 50 years, no prior hip surgery or posttraumatic deformity, no arthritis in any joint, no contraindication to MRI, and perhaps most central to this current study, no history of hip or groin pain. Participation in the study was voluntary, and patients were not compensated. Patients were primarily recruited from our health care institution and were employees or affiliates at the institution comprising various employments. The main method of recruitment was via a letter appealing for volunteers that provided background information on the topic of femoroacetabular impingement, an outline of the goals of the study, as well as the inclusion criteria. Range of motion of their hips in the supine position, as well as presence or absence of impingement, was recorded.

All participants previously recruited were recontacted via mail, e-mail, telephone, fax, or family doctor and asked to complete a questionnaire asking if they (1) currently had hip pain for longer than 6 weeks and/or (2) experienced any hip pain lasting longer than 6 weeks since the time of their MRI. They were asked to circle a yes or no response, and in the case of a yes response, they were asked to indicate the location of the pain on a body diagram (Figure 1). Patients were blinded as to the results of their MRI. Alpha angle measurements were done both at the axial oblique (3-o’clock position) and at the radial 1:30 clock position,23,24,29 with an alpha angle .50.5! considered positive for cam-type deformity.5,20,22 Some recent reports30 suggest that an alpha angle "60! at the 1:30 clock position is an optimal cutoff point for cam-type deformity with greater specificity, so a secondary analysis of our data was performed with this more stringent criteria.

Figure 1. Illustration of free body diagram sent to participants asking them to circle area of hip pain. The X points to areas considered positive for hip pain.

Descriptive statistics were used to summarize patients’ demographic and baseline characteristics. Categorical variables were reported as count and percentages and continuous variables as mean and 95% confidence intervals (CI).

The comparison of patient characteristics, including sex, internal rotation, and presence of impingement sign between groups, was done using chi-square test for categorical variables. Differences in mean alpha angles between groups were compared using Student t test. A P value of .05 was considered for statistical significance; all tests were 2-sided.

RESULTS Of the 200 original participants, 172 were recontacted. Of these 172 patients, 2 refused to complete the follow-up questionnaire, leaving 170 for analysis, giving us an 85% followup. When comparing those lost to follow-up to our remaining cohort, the only difference was a smaller alpha angle in the group lost to follow-up group at both the 3-o’clock and 1:30 positions (P = .004 and .04, respectively) (Table 1).

For the 170 patients, the average age was 29.5 years (range, 25.7-54.5 years), with 77 males and 93 females.

Eleven of these patients (5 males, 6 females; 6.5% of sample; mean age, 29.9 years; range, 25.7-45.6 years) reported at least 1 episode of hip pain lasting longer than 6 weeks, of which 3 (1 male, 2 females) had bilateral pain for a total of 14 hips. Seven of the 14 hips (50%) with a history of hip pain had a cam-type deformity (a angle .50.5!) at the time of the original MRI, whereas 37 of the 318 nonpainful hips (11.6%) had a cam deformity (P = .0002), giving a relative risk of 4.3 (95% CI, 2.3-7.8) of developing hip pain with the presence of a cam deformity. The 14 hips with pain had a significantly higher alpha angle than the remaining 318 hips at both the 3-o’clock position: 44.1!

(95% CI, 40.8!-46.7!) versus 40.9! (95% CI, 40.1!-41.7!)

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TABLE 1 Comparison of Group Lost to Follow-up Versus Group With Follow-upa Group Lost to Follow-up (n = 30)

Group With Follow-up (n = 170)

12 (40):18 (60) 29.3 (24.2-38.4)

77 (45):93 (55) 29.5 (25.7-54.5)

.91

38.3 (36.9-39.6) 48.0 (46.3-49.8o) 12 (20)

41.1 (40.3-41.9) 50.4 (49.5-51.3) 44 (25.8)

.004b .04b .15

Males:females, n (%) Age, y, mean (range) a angle, deg, mean (95% CI) At 3:00 At 1:30 Hips with a angle .50.5! on original MRI, n (%)

P Value

a

CI, confidence interval; MRI, magnetic resonance imaging.

Statistically significant difference.

b

TABLE 2 Comparison of Follow-up Group With Hip Pain Versus Follow-up Group Without Hip Paina Group With Hip Pain (n = 11)

Group Without Hip Pain (n = 159)

14 5 (45):6 (55) 29.9 (25.7-45.6)

318 72 (45%):87 (55) 29.4 (25.8-54.5)

.78

44.1 54.4 7 6

40.9 50.9 37 30

.03b .01b .0002b .001b

Hips, n Males:females, n (%) Age, y, mean (range) a angle, deg, mean (95% CI) At 3:00 At 1:30 Hips with a angle .50.5! at 1:30 and/or 3:00, n (%) Hips with a angle .60! at 1:30, n (%)

(40.8-46.7) (50.0-58.9) (50) (42.8)

(40.1-41.7) (49.2-51.0) (11.6) (9.4)

P Value

a

CI, confidence interval.

Statistically significant difference.

b

TABLE 3 Comparison of Cam 1 (a angle .50.5!) Follow-up Groups With and Without Hip Paina

Hips, n Males:females, n (%) Age, y, mean (range) a angle, deg, mean (95% CI) At 3:00 At 1:30

Follow-up Group With Hip Pain

Follow-up Group Without Hip Pain

P Value

7 4 (57):3 (43) 29.8 (24.4-35.1)

37 20 (54):17 (46) 29.4 (27.9-38.8)

.85

46.9 (43.0-50.7) 61.5 (57.3-65.7)

45.2 (43.9-46.6) 57.9 (56.9-59.1)

0.47 0.05b

a

CI, confidence interval.

Statistically significant difference.

b

(P = .03) and the 1:30 position: 54.4! (95% CI, 50.0!-58.9!) versus 50.9! (95% CI, 49.2!-51.0!) (P = .01) (Table 2). Of 7 of 44 hips with a cam deformity that developed hip pain, the alpha angle was significantly higher at the 1:30 position: 61.5! (95% CI, 57.3!-65.7!) versus 57.9! (95% CI, 56.9!-59.1!)

(P = .05) but not at the 3-o’clock position (Table 3).

When an alpha angle "60! at the 1:30 position was applied as a cutoff, 6 of 14 painful hips (42.8%) were found to have cam deformities on initial MRI, versus 30 of the 318 nonpainful hips (9.4%) found to have cam deformities (P = .001). Relative risk of developing hip pain if a large cam deformity is present is 4.5 (95% CI, 2.3-9.1) (Table 2).

When looking at internal rotation, a significantly greater percentage of patients with internal rotation (IR) !20! went on to develop hip pain compared with those with .20! of IR: 12% (6/50 hips) versus 2.7% (8/290 hips), respectively (P = .009). Individuals with IR !20! had a relative risk of 3.1 (95% CI, 1.6-6.0) of developing

hip pain. Presence of an impingement sign or patient sex were not significant risk factors for development of hip pain (P = .99).

DISCUSSION Management of intra-articular hip injury by means of hip arthroscopy has grown exponentially in the past decade.21 And although arthroscopic treatment originally focused on debridement of the labral/chondral damage, our understanding of the role of subtle osseous abnormalities of the femoral head-neck junction and/or acetabulum as a cause of the lesions13,22,32 has shifted the focus of patient evaluation to identification and correction of these abnormalities. Ganz et al10 recognized and described these abnormalities as femoroacetabular impingement, which is now a leading indication for arthroscopy of the

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hip.8,9,28 With that, aggressive correction or undercorrection are now being reported as negatively affecting clinical outcome,19 with significant complications such as femoral neck fracture and hip instability18,25 associated with overcorrection. Consequently, gaining a better understanding on the role of these bony deformities in leading to hip symptomatology and cartilage damage is critical in guiding surgical management as well as patient counseling.

In our current study, 11 of the 170 participants (6.5%) went on to develop hip pain, with 3 having bilateral hip pain with an equal distribution between male and females.

Seven of these 14 hips had cam-type deformity at the time of the original MRI (defined as an a angle .50.5!), with cam deformity representing a relative risk of 4.3 of developing hip pain. This relationship was maintained even when more rigid criteria for the definition of the cam deformity (ie, a angle "60! at the 1:30 clock position) was utilized. Consequently, the presence of cam-type deformity represents a significant risk factor for the development of hip pain, which is consistent with other studies in regard to the development of intra-articular hip pathologic changes.2,7,27 In a recent study of professional football prospects, an increased alpha angle was the only predictor of groin pain in players with cam-type deformity, with an alpha angle greater than 60! associated with a painful hip in over 20% of the players.17 Similarly, when looking at patients with bilateral cam-type deformity, Allen et al2 found that hips with an alpha angle .60! had an odds ratio of 2.59 of being painful compared with the other hips. In a more detailed analysis27 using more sensitive MRI sequences of 244 male volunteers, the 67 individuals with cam-type deformity had thinner cartilage (–0.19 mm), with an odds ratio of 2.7 for labral tears and 2.9 for impingement pits. Unfortunately, the MRI sequence used in our study was a fast spin sequence geared at morphological assessment of the hip joint and not sensitive enough to delineate acetabular and/or labral damage.

With the original publication of the alpha angle by Notzli,22 the 3-o’clock position has been used to determine the presence of cam-type deformity using an alpha angle .50.5! as a cutoff value. Having said that, our study failed to find a difference in alpha angle values at the 3-o’clock position in differentiating hips at risk of developing pain, whereas the alpha angle at the 1:30 clock position was significantly higher in the symptomatic hips: 61.5! versus 57.9!, respectively. These findings are consistent with the recent work of Rakhra et al24 and Pfirrmann et al,23 in which they demonstrated the increased sensitivity and specificity of the 1:30 clock position compared with the 3-o’clock position in detecting the cam deformity. More specifically, using a cutoff angle of 60! at the 1:30 position, Pfirrmann23 reported a sensitivity and specificity of 76% and 74.5% in diagnosing symptomatic femoroacetabular impingement. Finally, while the vast majority of studies have shown a higher incidence of cam-type deformity in males,12,15,26 we did not find sex as a risk factor for the development of hip pain.

Some limitations to this study include that 15% of patients were lost to follow-up, despite an extensive effort to contact all of the original 200 patients. Having said that, over 80% follow-up in this younger patient age group is quite acceptable. More importantly, when comparing those lost to follow-up to the rest of the cohort, the only

difference was less than a 3! alpha angle value at both the 3-o’clock and 1:30 positions. Another limitation of the study is a limited follow-up period of just over 4 years. As the natural history of FAI remains relatively unknown, it is unclear whether a prolonged period of follow-up could have led to increasing or decreasing rates of hip pain in either group.

Finally, the study is limited by a self-reported pain questionnaire and diagram for the assessment of hip pain where the extra- or intra-articular source of the hip cannot be independently verified. However, 2 recent studies showed that a patient questionnaire and pain diagram reporting hip pain matched both clinical and radiographic findings of hip disease.7,14 More specifically, a cross-sectional populationbased study from 2005 on 2935 subjects compared groups reporting hip pain using either a pain diagram or answering questions specifically about hip pain. The groups were compared with a control group without hip pain for several clinical indices of hip disease, including range of motion limitations and radiographic changes. The investigators concluded that a patient questionnaire and pain diagram reporting hip pain matched both clinical and radiographic findings of hip disease.7 Similarly, a study of 4151 patients found a significant association between a self-reported questionnaire on hip pain and radiographic joint space loss of less than or equal to 2 millimeters in both sexes.14 The presence of decreased internal rotation at the time of initial assessment was also identified as a risk factor for the subsequent development of pain. We found that patients with internal rotation \20! had approximately 3 times more likelihood of developing hip pain versus those patients with greater than 20! of internal rotation. This finding correlated directly to our 2010 study,12 which found patients with decreased internal rotation were more likely to have a cam lesion, and with the 2012 CHECK study,1 which found that individuals with a severe cam-type deformity and decreased internal rotation were predisposed to developing rapid onset end-stage arthritis.

Given the incidence of cam deformities in the hips that went on to develop pain, this link between decreased internal rotation and the development of hip pain was not an unexpected finding. The loss of flexion and internal rotation is a readily described finding with cam-type FAI.6,10,13,22,32 However, the cam lesion itself may not be solely responsible for loss of internal rotation, chondrolabral injury, and subsequent pain development. As concluded by Lamontagne et al,16 other bony morphologic abnormalities such as acetabular retroversion, loss of pelvic pitch, and decreased femoral anteversion may also serve as limiters to range of motion of the hip and ultimately pathologic damage to the cartilage, resulting in pain. Similarly, some studies are reporting that there may be other structural aspects of the hip joint that produce impingement, leading to the development of osteoarthritis and subsequently the development of hip pain.

For instance, Bardokos and Villar3 in 2009 reported that a varus proximal femoral neck with greater trochanter overgrowth, measured using the modified anatomic proximal femoral angle (MPFA), was more predictive of osteoarthritis development secondary to impingement than an elevated alpha angle. However, assessment of the MPFA or other (non–cam deformity) bony abnormalities for

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a possible association with hip pain development was beyond the scope of this paper.

From our original 2010 study, 56 hips (14%) were found to have evidence of cam-type deformity, and follow-up was achieved for 44 of those hips. However, after 4 years only 7 of those hips (15.9%) went on to become painful. This suggests that in isolation alone, a cam lesion in an asymptomatic patient is not a strong indication for surgical intervention.

Similar to our recommendations from the 2010 study, we caution that a radiographic finding alone is not sufficient criteria for the diagnosis of FAI. As shown, only a small percentage of these patients go on to develop clinically relevant hip pain, and it remains unclear as to whether the cam lesion was solely the cause of their pain. As discussed, other possible factors for hip pain and arthritis development include genetics,29 severity of deformity,2,27 and an associated bony deformity.2,3,6 Thus, in a patient with a radiographically identified cam lesion but who is otherwise asymptomatic, we would suggest clinical follow-up and surgical intervention only if the patient develops persistent hip pain and has physical examination findings consistent with impingement, and additional imaging is performed to assess cartilage, soft tissue, and osseous structures of the hip.4 Scan the QR code with your smartphone to view the In-Depth podcast associated with this article or visit http://ajsm.sagepub.com/site//misc/Index/ Podcasts.xhtml.

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3. Bardakos NV, Villar RN. Predictors of progression of osteoarthritis in femoroacetabular impingement. A radiological study with a minimum of ten years follow-up. J Bone Joint Surg Br. 2009;94:162-169.

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23. Pfirrmann CW, Mengiardi B, Dora C, Kalberer F, Zanetti M, Hodler J. Cam and pincer femoroacetabular impingement: characteristic MR arthrographic findings in 50 patients. Radiology. 2006;240:778-785.

24. Rakhra K, Sheikh AM, Allen DJ, Beaule PE. Comparison of MRI alpha angle measurement planes in femoroacetabular impingement. Clin Orthop Relat Res. 2009;467:660-665.

25. Ranawat AS, McClincy M, Sekiya JK. Anterior dislocation of the hip after arthroscopy in a patient with capsular laxity of the hip. A case report. J Bone Joint Surg Am. 2009;91:192-197.

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