Preoperative predictors of outcome in the arthroscopic treatment of femoroacetabular impingement

Arash Nabavi1, caroline M. Olwill1, ian a. Harris2

  • The Sydney Bone and Joint Clinic, Sydney - Australia
  • Ingham Institute for Applied Medical Research, South Western Sydney Clinical School, UNSW, Australia


Aims: The aim of this study was to establish preoperative factors associated with a good outcome in the surgical treatment of femoroacetabular impingement.

Methods: A prospective study including 253 consecutive patients (280 hips) was carried out. We defined a "good" score as one which had either a 20 point improvement from preoperative to 12 months postoperative follow-up, or a score of over 80 points at 12-month follow-up in either the Non Arthritic Hip Score (NAHS) or Modified Harris Hip Score (MHHS). We analysed 9 potential predictors of 12-month postoperative outcome: patient age, gender, BMI, surgery type (primary/revision), preoperative anxiety level, preoperative labrochondral damage, operative side, patients belonging to the armed forces and patients being treated under the workers compensation scheme. We used logistic regression (multivariable, adjusted) and, Fisher's exact test and student t test (bivariate, unadjusted) to analyse the data.

Results: A strong association between workers' compensation status and not achieving a good outcome follow- ing arthroscopic surgery for femoroacetabular impingement (odds ratio 3.84, 95% CI, 0.13-0.51, P < 0.0001) was found. A negative effect on postoperative outcome was also observed with increased BMI, although this association was modest (odds ratio 1.06, 95% CI, 0.87-0.99 p = 0.03). Patients with a higher preoperative score did better at 12 months than the rest of the cohort.

Conclusions: The data from this study may be useful for both patient and physician to consider when deciding on a suitable treatment in potential surgical candidates suffering from femoroacetabular impingement.

Keywords: Femoroacetabular impingement, Hip arthroscopy, Outcomes


Arthroscopic treatment of femoroacetabular impingement (FAI) is an area that has received increasing interest in recent years (1). The main aim of surgical intervention in FAI patients is to improve pain. Added benefits may include increasing a patient's range of movement, avoiding further destruction of the joint and allowing a patient to return to their previous functional and athletic activities (2, 3).

However, although arthroscopic intervention in FAI is becoming more widespread, preoperative factors that may affect patients' postoperative outcome have yet to be ex- plored. These factors have been examined more extensively in in other areas of hip surgery such as total hip arthroplasty where several preoperative factors have been linked to postoperative patient dissatisfaction. They include increased age, patient comorbidities, lower socioeconomic status, female gender, higher preoperative pain and mental anxiety (4-7).

The primary objective of this study was to identify preoperative predictors of outcome in the arthroscopic treatment of FAI.

Materials and methods

At our institution data is collected prospectively on all patients undergoing hip arthroscopy. Patient reported outcome scores in this study include the modified Harris hip score (MHHS), the non-arthritic hip score (NAHS) and EQ5D-3L score. These scores were collected preoperatively and at 3, 12 and 24 months follow-up.

A "good" score was defined as one which had either a 20 point improvement from preoperative to 12 month postoperative follow-up or a score of over 80 points at 12 month follow up in either the MHHS or NAHS (8-10). Available data on minimal clinically important difference (MCID) was taken into consideration to determine a suitable "good" outcome cut-off score. MCID may be defined as the minimum difference in treatment outcome that is considered important to the patient. A recent prospective single centre cohort study examined a consecutive series of FAI patients to determine the MCID in MHHS in patients treated with arthroscopic labral repair and femoral osteoplasty. They found the MCID for MHHS at 12 months was 20 points (11). In addition, an- other recent study examining the value of arthroscopic acetabular labral debridement in patients forty five years and older used a previous study on validated MCID in HHS to provide a reference MHHS value (12, 13). They reasoned that as MHHS is a modified version of the HHS, the MCID may be assumed to be similar to that described for HHS. In this case, an MCID was defined as an 8% change from baseline HHS (12, 13). Our cut-off limit of 20 points is well in excess of this value. There is currently no validated MCID value for the NAHS. Based on data from our clinical practice along with surgeon experience a 20 point improvement from baseline was considered a reasonable approximation for a "good" outcome in this questionnaire.

Patients who underwent hip arthroscopy for symptomatic FAI at our clinic between September 2006 and January 2014 were included in the study. A total of 9 potential predictors of 12 month postoperative outcome were analysed. They included patient age, gender, BMI, surgery type (primary or revision), preoperative anxiety level, preoperative labrochondral damage, operative side (left or right hip), patient belonging to the armed forces and patients being treated under the workers' compensation scheme.

When examining whether preoperative labral and chondral damage present may influence outcome. We performed a review of patients preoperative MRI scans where available (82% of cohort). We divided them into 2 groups based on preoperative MRI findings; 1) no to minor labrochondral damage; and 2) moderate to severe labrochondral damage. In total 68% displayed no to minor labrochondral damage and 32% displayed moderate to severe labrochondral damage. The criteria for the 1st group was that no labral tear or an undisplaced labral tear without chondral delamination was seen on MRI. For the 2nd group, a displaced labral tear and/or the presence of chondral delamination was present on MRI.

The exclusion criterion was an inability to complete the MHHS or NAHS questionnaire. There were 253 consecutive patients (280 treated hips) with a mean age of 39 (49% female) included in the study. All hip arthroscopy procedures were performed by a single orthopaedic surgeon (AN). Demographic data collected for all participants is displayed in Table I.

We used logistic regression (multivariable, adjusted), Fischer 's exact test and student t-test (bivariate, unadjusted) to analyse the data. Logistic regression gave adjusted odds ratios for each variable, with "outcome" as the dependent variable. Results were expressed as adjusted odds ratios (OR) with a 95% confidence interval (CI). p < 0.05 was regarded statistically significant. Analyses were carried out using SPSS version 7 (R Foundation for Stat Comp, Vienna, Austria).

Table I: Comparison of Patient Demographics in "Good" and "Poor" Outcome groups

  "Good" Outcome
"Poor" Outcome
Gender 111 Male
105 Female
30 Male
34 Female
Primary/Revision 200 Primary
16 Revision
56 Primary
8 Revision
(Mean in years)
38.9 38.9
BMI 26.73 29.06
Preop MHHS 60.03 53.4


Being a workers' compensation patient significantly increased the risk of not achieving a "good" outcome (odds ratio 3.84, 95% CI, 0.13-0.51, p < 0.0001). Preoperative and 12 month postoperative MHHS and NAHS were analysed in the workers' compensation subgroup and compared to the rest of the study population. In the workers' compensation group, preoperative MHHS was 47 compared to 67 in the non-workers compensation group. This difference was found to be very statistically significant (p < 0.0001). Similarly, in the NAHS preoperative workers compensation scores (NAHS: 40) were significantly lower (p < 0.0001) than the rest of the co- hort (NAHS: 59).

At 12 months post-op, non-workers compensation patient scores were also higher in both the NAH and MHH scores. Statistically significant differences from preoperative to 12 month follow up was found in both the NAHS and MHHS (p < 0.0001).

From preoperative to 12 months, workers' compensation patients improved 19 points in MHHS compared to non-workers' compensation patients who improved by 23. When looking at the NAHS improvements in both groups were identical with both workers compensation and non-workers' compensation patients improving by a total of 21 points from preoperative to 12-month post-op assessment.

Having an elevated BMI also significantly increased a patients' risk of not achieving a "good" postoperative outcome (odds ratio 1.06, 95% CI, 0.87-0.99 p = 0.03) (Tab. II).

The mean preoperative Harris hip score in the "good" out- come group was 60.03 (SD ± 20.87, 95% CI, 57-63) compared to a mean preoperative Harris Hip Score of 53.46 (SD ± 19.36, 95% CI, 49-58) in the rest of the cohort. Patients with a high preoperative Harris Hip Score had greater odds of achieving a "good" outcome (p = 0.02).

The adjusted analysis for the nine parameters is provided in Table II.


To our knowledge this study provides the first analysis of potential preoperative predictors of outcome in the arthroscopic treatment of FAI. Our findings confirm that overall, patients undergoing arthroscopic surgery for the treatment

Table II - Logistic Regression and Odds Ratio values for the 9 Parameters of Outcome measured

  Odd Ratio 95% Confidence
p value
Workers' Compensation 3.84 0.13-0.51 < 0.0001
BMI 1.06 0.87-0.99 0.03
Armed Forces 3.55 0.44 - 28.63 0.23
Gender 1.28 0.66-2.47 0.45
Surgery Type 1.7 0.60-5.06 0.29
Age 1.01 0.98-1.04 0.32
Operative Side 1.06 0.54-2.05 0.86
Preoperative Anxiety
0.64 0.32-1.28 0.21
Preoperative Labrochondral
1.50 0.68-3.33 0.31

of FAI can expect a good result. Preoperative predictors for not achieving a good outcome following arthroscopic surgery for FAI include those who are workers' compensation patients and those patients who present with an elevated BMI.

Similar findings were reported in other areas such as joint replacement. Liljensoe et al found an association between preoperative Body Mass Index (BMI) and impaired clinical outcome following knee arthroplasty using patient reported short form 36 (SF-36) and the American Knee Society Score (KSS) as outcome measures (14). Furthermore, Naylor et al established an association between obesity and many SF-36 domains when looking at 12-month follow-up after joint replacement surgery (15). This information may be useful for advising patients prior to surgery that losing weight preoperatively may have a beneficial effect on their 12-month postoperative outcome. Further large scale studies will be needed to confirm our findings for FAI.

Although a statistically significant difference was not found, a trend towards having a "good" outcome was observed in the armed forces group, which may be linked to higher levels of motivation within this group. This is however only speculative. We also found no association between labrochondral damage and postoperative outcome. It therefore appears that following osteoplasty, patient outcome is not influenced by the extent of preoperative labrochondral damage present.

Although the workers' compensation group has shown significant improvement from preoperative to 12 months, the difference between the means in the MHHS is 4 points less than the non-workers' compensation cohort. When look- ing at 12-month postoperative MHHS it is interesting to note that although workers' compensation patients scores are lower than the non-workers' compensation group, workers' compensation 12-month scores are significantly higher than their preoperative scores (p < 0.0001) suggesting that although this group may not have an outcome which is equal to their non-workers' compensation counterparts, having surgery is still a worthwhile endeavour for these patients. Similar findings were observed by Stake et al. In their matched pair controlled study, workers' compensation patients were found to have significantly lower preoperative patient reported outcome scores compared to a control group (16). As seen in our study, they also had lower postoperative scores but did benefit from the surgery overall.

In addition, Carreon et al found significantly lower improvement in mean change in both the Oswestry Disability Index (ODI) and short form-36 (SF-36) outcome measures they examined in lumbar fusion patients comparing workers' compensation patients with a case-matched control group (17). Interestingly, a study by Cuff et al examining patient outcomes following rotator cuff repair surgery in workers' compensation patients found that when poor results are observed in workers' compensation cohorts it is usually due to postoperative non-compliance (18). Postoperative non-compliance was not taken into consideration in this study. However, it may be interesting to examine this factor in studies in the future.

A recent study examining patient satisfaction in total knee replacement patients found that the primary cause of patient satisfaction is having their preoperative expectations fulfilled (19). This information may be useful in advising patients on their outcome. From our experience a workers' compensation patient will not have the same outcome as a non-workers' compensation patient and both patient and physician should therefore taper their expectations accordingly.

There are a number of limitations to this study. Injuries that patients included in the study may have sustained during the 12-month follow-up period were not accounted for. Furthermore, patient comorbidities, which may have impacted on patient outcomes, were not taken into consideration. A power analysis was not performed for the study, 'lost to follow-up' patients are unaccounted for, we have a relatively small study group size and short follow-up period of only 12 months. However, the short postoperative follow-up focuses the outcome measures on preoperative factors by reducing the influence of postoperative factors.

In conclusion, this study found a strong association between workers' compensation status and not achieving a good outcome following arthroscopic surgery for FAI. A negative effect on postoperative outcome was also observed with increased BMI.


Financial support: None.
Conflict of interest: None.


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