Introduction
FAI is a disorder resulting from abnormal contact between the acetabulum and proximal femur [2, 7, 10, 25, 29]. This disorder can result in labral-chondral injury and eventual osteoarthritic changes in the hip [2, 7, 10, 25, 29]. Numerous studies show the presence of OA negatively impacts improvements in pain and function after hip arthroscopy and nonarthroplasty open hip surgery [2, 4, 8, 13, 14, 17, 18, 23, 25, 27, 29-32, 35]. However, the majority of these studies predate resection of FAI impingement lesions [4, 8, 13, 17, 18, 23, 27, 35], or are limited to small numbers [2, 14, 25, 32]. These studies also lack well-defined predictors of improved function or failure rates after managing FAI in the presence of OA. One study reported that, in the presence of OA, simple arthroscopic labral and chondral débridement resulted in less improvement in pain scores in hips with FAI compared with hips without FAI [18]. However, whether resection of FAI impingement lesions, in addition to management of labral and chondral disorders, leads to improved pain and function in the setting of OA remains unclear. Additionally, the degree of degenerative changes and associated preoperative findings that make functional improvements after arthroscopic FAI correction unlikely are not well defined.
The purposes of our study were to (1) determine whether pain and function improved after resection of FAI impingement lesions in patients with preoperative radiographic joint space narrowing, (2) compare pain, function, and failure rates in patients undergoing FAI correction without and with preoperative radiographic joint space narrowing, and (3) determine whether any preoperative factors independently predicted pain, function, or failure rates after surgical management of FAI in the presence of radiographic OA.
Patients and Materials
Between September 2004 and April 2008, 618 hip arthroscopies were performed on 585 patients by the senior author (CML); of these, 296 patients (319 hips) underwent arthroscopic management of FAI. The preoperative diagnosis of FAI was made based on plain radiographs (Table 1). We included all patients who met the radiographic criteria for FAI and had arthroscopic FAI correction during the study period. All patients had preoperative AP pelvic radiographs of both hips, and 45° modified Dunn, cross-table lateral, and false profile views of the affected hip. Cam-type impingement was present when there was asphericity of the femoral head neck junction (alpha angle > 50°) on AP and or lateral radiographs as previously described [26]. Pincer impingement was evaluated on a well-centered AP pelvis radiograph with 0 cm to 2 cm between the pubic symphysis and coccyx. Pincer impingement was present if there was evidence for acetabular retroversion, focal anterior acetabular overcoverage, coxa profunda, or protrusio acetabula [19]. Three-dimensional CT was used to further characterize and define the degree and extent of FAI. IRB approval was obtained before conducting this study. The indications for arthroscopic treatment of FAI were: (1) radiographic evidence of FAI, (2) clinical examination consistent with hip pain, (3) a failed conservative treatment regimen consisting of a period of relative rest, activity modification, NSAIDS, and core strengthening with avoidance of deep hip flexion weight training, and (4) temporary relief of pain with an intraarticular anesthetic injection. The indications for surgery of FAI in the presence of radiographic OA included: (1) the above named criteria plus, (2) lack of lasting relief after at least one corticosteroid injection, (3) predominance of sharp mechanical pain with activity, and (4) rest or night pain that was tolerable by the patient. Patients with radiographic OA and intolerable aching pain, especially at night, were not deemed appropriate candidates for hip arthroscopy, and were referred for possible hip arthroplasty. Among the 296 patients (319 hips) who underwent arthroscopic management of FAI, 210 (227 hips) had a minimum 12-month followup (mean, 27 months; range, 12-60 months). One hundred fifty-four patients (169 hips) had a Tönnis Grade 0 to Grade 1 change preoperatively (Group FAI), and 56 patients (58 hips) had a Tönnis Grade 2 or Grade 3 change preoperatively (Group FAI-OA). Of the 56 patients (58 hips) in group FAI-OA, 34 (36 hips) had mild to moderate joint space narrowing (< 50% narrowing or > 2 mm joint space), and 22 (22 hips) had advanced joint space narrowing (> 50% narrowing or ≤ 2 mm joint space). There were 88 males and 81 females in Group FAI with a mean age of 31.8 years (range, 14-61 years), and a mean followup of 25 months (range, 12-60 months). There were 45 males and 13 females in Group FAI-OA with a mean age of 44.7 years (range, 24-64 years), and a mean followup of 30 months (range, 12-60 months). We did not recall any patients specifically for this study; all data were obtained from medical records and radiographs.
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Table 1: FAI classification
One of us (CML) evaluated all radiographs preoperatively. OA was graded using the Tönnis classification [33, 34]. Patients with no or only slight joint space narrowing (Tönnis Grades 0-1) were defined as Group FAI. Patients with definite joint space narrowing (Tönnis Grades 2-3) were defined as Group FAI-OA. As Tönnis Grade 2 ranges from mild to near complete joint space narrowing, we performed an additional evaluation of joint space narrowing. Joint space narrowing was graded by measuring the narrowest distance between the femoral head and acetabulum at the lateral sourcil, middle sourcil, and above the level of the fovea with a digital caliper (IMPAX, AGFA, Mortsel, Belgium) and Imagecast RIS/PACS (UMCET, Miami, FL, USA) on nonweightbearing AP hip radiographs, as previously described [11, 16, 31]. Prior studies reported acceptable repeatability of measurements (r = 0.90) using this technique, and that a joint space of 2 mm or less correlated with OA and symptoms [16, 31]. If the contralateral hip or prior radiographs revealed a well-maintained joint space, we recorded the percentage of joint space narrowing. We defined mild to moderate joint space narrowing as less than 50% joint space narrowing, or greater than 2 mm joint space remaining in all portions of the femoroacetabular joint when current or prior radiographs lacked a hip with normal joint space. We defined advanced joint space narrowing as greater than 50% narrowing, or 2 mm or less of joint space remaining in any portion of the femoroacetabular joint when current or prior radiographs with normal joint space were not available for comparison (Fig. 1).
Fig. 1A-B:
Preoperative AP radiographs show (A) a patient with FAI without substantial degenerative changes (Group FAI), and (B) a patient with FAI and advanced focal joint space narrowing (Group FAI-OA) superiorly with a large femoral head-neck impingement cyst (arrow).
We performed the surgery with the patient in the supine position using a previously technique described [20, 21]. For all cases, we used the anterolateral and midanterior portals. We also established a posterolateral portal if posterior rim resection was required. A central compartment arthroscopy was performed first and then a capsulotomy from the midanterior portal to the anterolateral portal. For pincer-type impingement, a labral takedown was performed with an arthroscopic knife, and then performed a rim resection with a motorized burr. Partial thickness acetabular chondral and femoral lesions were debrided with a shaver and full-thickness chondral lesions were treated with microfracture if contained. Containment was defined as a lesion with relatively healthy surrounding articular cartilage or a peripheral lesion with subchondral bone that did not contact the opposing articulating surface (nonengaging lesion) through ROM after release of traction. Hips with bipolar and engaging Grade 4 lesions were not appropriate for microfracture. The labrum either was débrided or refixed/repaired with suture anchors, depending on the quality of labral tissue. We then released traction and flexed the hip approximately 40°. If a cam lesion was present, a femoral resection was performed, with care taken to identify and protect the lateral retinacular vessels. We performed the cam resection in varying degrees of hip flexion and extension to access the entire anteroinferior to superoposterior femoral head neck junction as necessary. The extent of rim resection and femoral resection osteoplasty performed was based on preoperative plain radiographs and 3-D CT, an intraoperative fluoroscopic evaluation as described previously [22], and intraoperative dynamic assessment (Fig. 2).
Fig. 2A-D:
Preoperative and postoperative radiographs show the management of pincer and cam-type FAI. (A) A preoperative radiograph of a 25-year-old woman shows bilateral pincer-type FAI secondary to global overcoverage and labral ossification (arrows). (B) Her postoperative radiograph is shown after left hip global rim resection (arrow). (C) A preoperative lateral radiograph shows a 20-year-old man with cam-type FAI (arrow). (D) His postoperative radiograph shows improved head-neck offset after femoral resection osteoplasty (arrow).
There was a greater percentage of labral repair/refixation in Group FAI and a greater percentage of microfracture in Group FAI-OA (Table 1). The senior author (CML) intraoperatively graded articular cartilage damage for the acetabulum and femoral head with direct observation and probing of the articular surfaces [28]. A probe was used to assess for articular cartilage softening, evaluate for the presence and depth of fissuring and fibrillation, and identify chondral flaps and presence of exposed subchondral bone [28]. Articular cartilage damage for the acetabulum and femoral head was graded using a modification of the Outerbridge classification [24, 28]: Grade 0 indicated intact articular cartilage; Grade 1 was chondral softening; Grade 2 was superficial ulceration, fissuring, or fibrillation involving less than 50% of the depth of the articular surface; Grade 3 was ulceration, fissuring, or fibrillation involving greater than 50% of the depth of the articular cartilage; and Grade 4 was full-thickness chondral wear with exposure of subchondral bone. This differs from the original Outerbridge classification which describes Grade 2 lesions as partial thickness lesions not reaching subchondral bone or less than 1.5 cm in diameter and Grade 3 lesions as fissures reaching subchondral bone or greater than 1.5 cm in diameter [28].
We prospectively measured outcomes using the modified HHS, SF-12 score, and pain score on a VAS preoperatively and postoperatively at 6 weeks, 3 months, 6 months, 1 year, and yearly thereafter. To identify possible predictors of improvements and failures for group FAI-OA, the senior author (CML) and an orthopaedic fellow (MT) recorded preoperative symptoms; mechanical/sharp versus aching pain (minimal to none versus definitely present), duration of symptoms (months), age (years), gender, and ROM (degrees measured with a goniometer for flexion, extension, internal, and external rotation) from each patient’s medical records. The above findings were included routinely in all preoperative records.
MR images were examined and graded by one of three independent musculoskeletal radiologists (HMF, CRG, AEC) using the same modification of the Outerbridge classification [24, 28] we used to assess intraoperative articular cartilage damage. A prior study evaluating this grading system for hip articular cartilage found agreement between MRI and arthroscopy within one grade of 89% for femoral head and 86% for acetabular articular cartilage [24]. In addition, interobserver agreement for MRI grading yielded a kappa of .8 for the femoral head and .7 for the acetabular articular cartilage [24]. Grade 3 or 4 chondromalacia was seen intraoperatively on the acetabulum for 66% of patients in Group FAI and 98% of patients in Group FAI-OA (Table 2).
Table 2: Intraoperative chondromalacia (Outerbridge classification)
Failure was defined as a modified HHS of less than 70 or conversion to hip arthroplasty. Using independent samples t-test, we determined differences in clinical scores between patients with FAI and FAI-OA, and between patients separated into two independent groups. Paired samples t-tests were used to assess differences in scores from preoperative to mean last followup in groups. We determined the differences in failure rates between groups of three or more by using Kruskal-Wallis one way ANOVAs, while one-way ANOVAs and post hoc t-tests were used to assess differences in clinical scores. To determine independent predictors of failure rate and functional outcome scoring within the FAI-OA group, binary logistic regression and multiple linear regression models were constructed. In creating our regression models, the number of parameters that were included in each model was based on the effective sample size (m), and m/10 used as the ratio for reliable models. This method was used to generate a model as complex as the data would allow without overfitting the data, as described in Dunn et al. [6] and Harrell [12]. To limit the number of parameters used, five variables were chosen that were considered to be the most relevant to our study: joint space narrowing, MRI chondral grade, intraoperative chondral grade, symptoms of aching, and duration of symptoms. To limit the effect of long-term attrition, patients who dropped out (THA) were assigned a score one point lower (rounded to the nearest whole number) than the minimum score at mean last followup for the specific group in question. By following procedural precedent set by Byrd and Jones [4], this avoided the exclusion of patients who dropped out, which could cause the results to appear falsely superior. Statistical analysis was performed using SPSS (Version 16.0 for Windows, SPSS Inc, Chicago, IL, USA).
Results
Patients with preoperative radiographic joint space narrowing (Group FAI-OA) had improved mean HHSs at 1 year postoperatively compared with preoperative scores (p = 0.008). However, there were no improvements in HHS beyond 1 year postoperatively (p = 0.45, 2-year score; p = 0.99, 3-year score) and no improvements at mean last followup (p = 0.28). There were no improvements in SF-12 scores (p = 0.22) at any time postoperatively compared with preoperative scores for Group-FAI-OA. VAS pain scores, however, were improved (p < 0.001) at last followup compared with preoperative scores. The failure rate for Group FAI-OA at last followup was 52%.
A comparison of patients with preoperative radiographic joint space narrowing (Group FAI-OA) to those without preoperative joint space narrowing (Group FAI) revealed that Group FAI had better (p < 0.001) mean HHSs at last followup compared with Group FAI-OA: 88 versus 67. The failure rate was lower (p < 0.001) at last followup for Group FAI compared with Group FAI-OA: 12% versus 52%. The overall improvement from preoperative to mean last followup outcomes scoring for Group FAI was 22.8 points (HHS), 20.9 points (SF-12), and 4.5 points (VAS), compared with 3.7 points (HHS), 4.3 points (SF-12), and 2.6 points (VAS) for Group FAI-OA. Although Group FAI maintained improved (p < 0.001) mean HHSs at mean last followup, we observed no improvements (p = 0.45, 2 years; p = 0.99, 3 years) beyond 1 year postoperatively in Group FAI-OA (Fig. 3).
Fig. 3:
This graph shows the mean HHS at each time for Group FAI and Group FAI-OA. p Values are placed directly above each group’s bar at different times (* = p < .001). Each p value corresponds to improvement in the HHS between that individual bar and the preoperative value.
We further evaluated the FAI-OA group to find independent predictors of HHSs and failure rates (Tables 3-5). Increasing preoperative joint space narrowing was an independent predictor for failure and lower HHSs (Tables 4, 5). There was a 12% failure rate for Group FAI, 33% failure rate with mild to moderate preoperative joint space narrowing (< 50% joint space narrowing or > 2 mm joint space), and 82% failure rate with advanced preoperative joint space narrowing (> 50% joint space narrowing or ≤ 2 mm joint space) at last followup (p < 0.001) (Fig. 4). Patients with slight or no preoperative joint space narrowing (Group FAI) and mild to moderate preoperative joint space narrowing maintained improved HHSs (p < 0.001 and p = 0.023, respectively) throughout the study period (Fig. 5). In contrast, patients with advanced preoperative joint space narrowing lacked improvements in HHS (p > 0.05) at any time postoperatively (Fig. 5). At mean last followup, hip arthroplasty was performed in one hip (one patient, 0.6%) in Group FAI, eight hips (eight patients, 22.2%) with mild to moderate preoperative joint space narrowing, and 12 hips (12 patients, 57.1%) with advanced preoperative joint space narrowing. Using binary logistic regression analysis, increasing radiographic joint space narrowing (p = 0.014) and greater duration of symptoms preoperatively (p = 0.015) were independent predictors of higher failure rates (Table 4). Multiple linear regression analysis revealed that increasing radiographic joint space narrowing preoperatively (p = 0.001), increasing MRI chondral grade preoperatively (p = 0.019), and greater duration of symptoms preoperatively (p = 0.014) were independent predictors for lower HHSs (Table 5). Eighteen patients (18 hips) had complications (8%) and there were no differences between groups for any complication (p > 0.05). Four patients (four hips) were treated with a course of antibiotics for superficial wound infection. Three patients (three hips) had small areas of pericapsular heterotopic bone and none were symptomatic. Revision hip arthroscopies for adhesions and inadequately addressed FAI were performed for 10 patients (10 hips), and one patient (one hip) had continued discomfort attributed to injury to the lateral femoral cutaneous nerve.
Table 3: Prevalence of preoperative and intraoperative variables for Group FAI-OA
Table 4: Predictors of increased failure rate
Table 5: Predictors of decreased Harris hip scores
Fig. 4:
This graph shows the mean failure rates at each time for Groups FAI (Tönnis Grades 0-1), mild to moderate OA (< 50% joint space narrowing or > 2 mm joint space remaining), and advanced OA (> 50% joint space narrowing or < 2 mm joint space remaining). p Values are placed directly above the each group’s bar at different times (* = p < .001). Each p value corresponds to improvement in failure rates between that individual bar and the preoperative value.
Fig. 5:
The graph shows the mean HHS for Groups FAI (Tönnis Grades 0-1), mild to moderate OA (< 50% joint space narrowing or > 2 mm joint space remaining), and advanced OA (> 50% joint space narrowing or < 2 mm joint space remaining). p Values are placed directly above the each group’s bar at different times (* = p < .001). Each p value corresponds to improvement in HHS between that individual bar and the preoperative value.
Discussion
Studies show that the presence of OA negatively impacts outcomes after hip arthroscopy and nonarthroplasty open hip surgery [2, 4, 8, 13, 14, 17, 18, 23, 25, 27, 29-32, 35]. However, most studies predate FAI correction, are limited to small numbers, or lack well-defined independent predictors of improved function or failure rates after managing FAI in the presence of OA. The first purpose of this study was to clarify whether pain and function improved after resection of FAI impingement lesions in patients with preoperative radiographic joint space narrowing. The second purpose was to compare pain, function, and failure rates of patients with preoperative radiographic joint space narrowing with those of a cohort of patients undergoing FAI correction with no or only slight preoperative radiographic joint space narrowing. The final purpose was to identify whether there were any preoperative independent predictors of pain, function, or failure rates after surgical management of FAI in the presence of radiographic OA.
We acknowledge several limitations to our study. First, we had short-term followup. It is likely that with further followup, outcomes in patients with established OA will continue to deteriorate. Second, the treating surgeon evaluated the preoperative plain radiographs, not an independent observer which could lead to observer bias. However, he assigned the Tönnis grade before surgery, and evaluated joint space narrowing on blinded radiographs, without the knowledge of eventual outcomes in this study. Finally, as there was no control group of patients with FAI-OA that continued nonoperative treatment, we cannot truly evaluate the effectiveness of surgery in comparison to conservative management. However, conservative treatment options had failed or had been exhausted in all of the patients with radiographic OA, and many of the patients had contemplated hip arthroplasty.
Our study revealed that arthroscopic management of FAI with preoperative joint space narrowing, including resection of FAI impingement lesions, resulted in improved HHSs at 1 year postoperatively. There was no improvement, however, for HHSs beyond 1 year compared with preoperative scores. SF-12 scores were not improved postoperatively compared with preoperative scores at any time after surgery for Group FAI-OA. VAS pain scores, however, were significantly improved throughout the study for patients in Group FAI-OA. This may not be surprising as VAS scores do not take into account the use of oral pain medications and limitations in activity to manage continued functional disability that was indicated by lack of improvement after 1 year for functional scores. The failure rate for all patients in Group FAI-OA was 52%. There is only one study that specifically evaluated the results of arthroscopic FAI correction in the setting of OA [14] (Table 6). Similar to our study, Horisberger et al. reported a 60% (12 patients) failure rate using non-arthritic hip score (NAHS) in 20 patients with radiographic OA (Tonnis Grades 1-3) at a mean last followup of 3 years [14]. Most studies evaluating hip arthroscopy in the setting of OA predate FAI bony resections [4, 8, 13, 17, 18, 23, 27, 35] (Table 6). Margheritini and Villar [23] evaluated 133 patients with hip OA who underwent hip arthroscopy and reported a 39% failure rate at a mean followup of 18 months using the HHS. Walton et al. [35] reported 72% poor results at a minimum 4 months followup using the classification of Farjo et al. [8] in a cohort of 39 patients with OA who underwent hip arthroscopy. Byrd and Jones [4] evaluated 50 patients with a minimum of 10 years followup; 14 of these patients had preoperative radiographic OA. Modified HHSs revealed that 50% (seven hips) of patients with OA were improved at 2 years, 36% (five hips) were improved at 5 years, and 79% (11 hips) had undergone THAs by 10 years minimum followup [4].
Table 6: Literature review of failure rates and predictors of failures
When compared with a cohort of patients without preoperative radiographic joint space narrowing, patients with preoperative joint space narrowing had less improvements in HSS, SF-12, and VAS scores and a higher failure rate (12 versus 52%, respectively) at last followup of 27 months. There are no arthroscopic studies that specifically evaluate patients after FAI correction in the presence of radiographic joint space narrowing compared with a cohort without radiographic OA. Philippon et al. reported that less than 2 mm joint space preoperatively was predictive of poorer HSSs in a cohort of patients who underwent FAI correction with a minimum of 2 years followup [31]. Studies reporting open surgical approaches for FAI also suggest higher failure rates for patients with preoperative OA, but sample sizes of patients with radiographic OA typically have been small [1, 2, 5, 7, 9, 10, 25, 29, 30] (Table 6).
We found that a greater degree of joint space narrowing was an independent predictor of poorer scores and higher failure rates. Patients without significant preoperative joint space narrowing and those with mild to moderate preoperative joint space narrowing had improved scores at each time throughout the study (up to 3 years followup). In contrast, patients with advanced joint space narrowing did not improve at any time throughout the study period and had a failure rate of 82%. In addition, we found that a greater duration of symptoms preoperatively was an independent predictor of poorer scores and higher failure rates, and increasing MRI chondral grade was an independent predictor of poorer scores (Tables 3-5). Two prior studies report increased failure rates with greater degrees of intraoperative chondral disorders in the presence of preoperative radiographic OA [8, 35]. In addition, Margheritini and Villar [23] found that greater age was predictive of a poorer HHS for patients with OA undergoing hip arthroscopy. The remainder of studies evaluating surgery in patients with radiographic OA either did not evaluate for other predictors of improvement or failures, or had a small sample size of patients with radiographic OA that limited the ability to make any relevant conclusions [1-5, 7-10, 13, 15, 17, 18, 25, 27, 29-32] (Table 6).
Based on this study, FAI correction in the presence of milder degrees (< 50% or > 2 mm joint space remaining) of preoperative radiographic joint space narrowing results in improvements in pain and function at short-term followup, and might be considered for younger patients with primarily intermittent, mechanical pain of shorter duration with appropriate expectations. Patients with advanced radiographic joint space narrowing lacked any improvement postoperatively, and are better served with continued conservative care and eventual hip arthroplasty.
Acknowledgments
We thank Hollis M. Fritz MD, Cooper R. Gundry MD, and Andrew E. Cooperman MD for assistance in grading MRI chondral changes.
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