Outcomes of Hip Arthroscopic Surgery in Patients With Tönnis Grade 1 Osteoarthritis With a Minimum 2-Year Follow-up

Abstract

Background:

There are limited studies on the effect of mild osteoarthritis (OA) on outcomes of hip arthroscopic surgery.

Purpose:

To conduct a matched-pair analysis with a minimum 2-year follow-up to evaluate outcomes after hip arthroscopic surgery in patients with Tönnis grade 1 OA.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

Data were prospectively collected on patients who underwent hip arthroscopic surgery between April 2008 and December 2012. Patients were excluded if they had previous hip conditions. The remaining patients were divided into either Tönnis 0 or 1 grade OA groups and were matched in a 1-to-1 ratio according to age within 5 years, sex, body mass index category, labral treatment, and capsular treatment. Four patient-reported outcome (PRO) scores, as well as the visual analog scale (VAS) score for pain, patient satisfaction, and rates of revision arthroscopic surgery and conversion to total hip arthroplasty (THA), were recorded.

Results:

A total of 1412 hip arthroscopic procedures were performed during the study period, of which 1036 met the inclusion criteria and 892 (86.1%) had 2-year follow-up. There were 738 and 154 patients with Tönnis grade 0 and 1, respectively; 93 patients were matched in each group. The Tönnis grade 0 group had a mean follow up of 28.7 months (range, 23.5-67.9 months), and the Tönnis grade 1 group had a mean follow up of 31.5 months (range, 23.6-63.5 months). Both groups demonstrated a significant improvement in all PROs and the VAS at a minimum 2-year follow-up. For the Tönnis grade 0 group, the improvements (in points) in the PROs were as follows: modified Harris Hip Score (mHHS), 15.51; Nonarthritic Hip Score (NAHS), 20.65; Hip Outcome Score–Activities of Daily Living (HOS-ADL), 16.83; and Hip Outcome Score–Sport-Specific Subscale (HOS-SSS), 20.91. The VAS score for the Tönnis grade 0 group decreased by 2.82 points. For the Tönnis grade 1 group, the improvements (in points) in the PROs were as follows: mHHS, 19.52; NAHS, 20.96; HOS-ADL, 18.20; and HOS-SSS, 21.61. The VAS score for the Tönnis grade 1 group decreased by 2.84 points. No significant difference was found between the mean change in PROs, VAS, or patient satisfaction between the groups (P > .05). There was no significant difference in subsequent rates for revision arthroscopic surgery or conversion to THA between the groups (P = .3 and .6, respectively). The rates for revision arthroscopic surgery and conversion to THA were 9.68% and 9.68%, respectively, in the Tönnis grade 0 group and 5.38% and 11.83%, respectively, in the Tönnis grade 1 group.

Conclusion:

At 2-year follow-up, patients with Tönnis grade 1 OA had improved outcomes after hip arthroscopic surgery, with no significant difference compared with a matched control group of patients with Tönnis grade 0 OA. However, further studies are underway to determine if the results of the Tönnis grade 1 cohort will deteriorate over longer term follow-up.

Keywords

hip arthroscopic surgery hip arthroscopic surgery and osteoarthritis conversion to THA after hip arthroscopic surgery patient-reported outcome scores Tönnis grade

Osteoarthritis (OA) can adversely affect outcomes of arthroscopic hip preservation procedures.^4,24,34 The threshold of OA at which hip arthroscopic surgery may have clinical benefit is not clearly defined, although broad categories do exist.⁶ Research is required to determine the role of arthroscopic surgery in improving pain and function and delaying eventual total hip arthroplasty (THA) in patients with mild OA.^13,21

Several measures and grading symptoms have been used to quantify the amount of hip OA preoperatively.^5,14,37 Two common measures on plain radiographs are lateral joint space³⁴ and Tönnis grade (Table 1).³⁹ Lateral joint space of less than 2 mm has been associated with poorer outcomes after hip arthroscopic surgery.³⁴ A recent review by Domb et al⁶ reported that patients with Tönnis grade ≥2 have been shown to have poorer outcomes after hip arthroscopic surgery. However, many of these studies did not have control groups for comparison. Those studies with a nonarthritic arm did not control for important confounding factors such as age, sex, and arthroscopic treatment.

Table 1

Tönnis Grades for Osteoarthritis

Grade	Description
0	No signs of osteoarthritis
1	Increased sclerosis of the head and acetabulum, slight joint-space narrowing, and slight lipping at the joint margins
2	Small cysts in the head or acetabulum, moderate joint-space narrowing, and moderate loss of sphericity of the head
3	Large cysts in the head or acetabulum, joint-space obliteration or severe joint-space narrowing, severe deformity of the femoral head, and evidence of necrosis

The purpose of this study was to conduct a matched-pair analysis with a minimum 2-year follow-up to evaluate outcomes in patients with Tönnis grade 1 OA using a control group with Tönnis grade 0 OA.

Methods

Patient Selection and Matching Criteria

Institutional review board approval was obtained for this study, and data were prospectively collected on all patients who underwent hip arthroscopic surgery during the study period from April 2008 to December 2012. The inclusion criteria were all patients who underwent primary hip arthroscopic surgery for symptomatic intra-articular hip disorders refractory to nonoperative management with a Tönnis grade recorded on preoperative radiographs. The Tönnis grade was measured on 2 separate occasions to determine intrarater reliability. The same examiner carried out the measurements 1 week apart. Patients were excluded if they had previous hip conditions such as avascular necrosis, Legg-Calvé-Perthes disease, slipped capital femoral epiphysis, inflammatory arthritis, or hip fractures. Patients were matched in a 1-to-1 ratio according to age within 5 years, sex, and body mass index (BMI) category (≤25/>25 kg/m² and ≤30/>30 kg/m²). Patients were also matched for labral treatment (repair, debridement, or reconstruction) and capsular treatment (closure or no closure).

Radiological Evaluation

Radiographic views included an anteroposterior (AP) pelvic view, a 45° Dunn view,³ and a false-profile view.²⁵ Measurements were made including the acetabular inclination using the method described by Jessel et al,¹⁹ anterior center-edge angle (ACEA), lateral center-edge angle (LCEA) of Wiberg,⁴² presence of an ischial spine sign,⁴⁰ crossover sign,⁴¹ and alpha angle (Dunn view).³ Coxa profunda was defined on the AP pelvic view as the ilioischial line lateral to the medial border of the teardrop.¹² The size of the crossover sign was quantified according to its percentage from the acetabulum diameter. All measurements were taken by the same orthopaedic surgeon (B.G.D.) using a picture archiving and communication system (PACS) computer program and were repeated at a separate time interval to determine intrarater reliability. Magnetic resonance arthrography was used to diagnose intra-articular injuries such as labral tears, increased signal within the ligamentum teres, and loose bodies.

Surgical Technique

All hip arthroscopic procedures were performed under general anesthesia in the supine position using a traction table and well-padded perineal post. Intraoperative diagnoses and procedures performed in the central, peripheral, and peritrochanteric compartments were recorded. As a general treatment algorithm, pincer impingement was treated with acetabuloplasty, and cam impingement was treated with femoroplasty. Labral lesions were debrided, repaired, or reconstructed with an autograft or allograft depending on the size and available labral tissue for repair. Iliopsoas release was performed in patients with symptomatic internal snapping or an iliopsoas impingement sign⁷ on the labrum. The capsule was repaired routinely except in patients in whom a release was considered to be therapeutic, such as patients with stiff hips or thickened capsules. Postoperative rehabilitation was tailored to the specific intraoperative procedure performed but typically consisted of placing patients in an X-Act ROM brace (DJO Global) and crutches with toe-touch weightbearing for 2 weeks. Physical therapy was begun as early as postoperative day 1 to begin passive range of motion with either continuous passive motion or a stationary bicycle.

Patient-Reported Outcomes

Patients were assessed prospectively before surgery, 3 months after surgery, and yearly thereafter with 4 patient-reported outcomes (PROs): the modified Harris Hip Score (mHHS), Nonarthritic Hip Score (NAHS), Hip Outcome Score–Sport-Specific Subscale (HOS-SSS), and Hip Outcome Score–Activities of Daily Living (HOS-ADL). Patients were also instructed to rate their pain using a 10-point visual analog scale (VAS), with 0 being no pain and 10 being the worst pain that the patient can imagine, and were asked to rate their satisfaction with surgery out of 10, with 10 being completely satisfied and 0 being not satisfied with surgery, at each of the above follow-up periods. The incidence of revision arthroscopic surgery and conversion to THA were recorded for each of the Tönnis grades.

Statistical Analysis

Statistical analysis was performed using Microsoft Office Excel 2007. Normal data distribution was checked by a test for the equality of variance. An a priori power analysis was performed to estimate the number of patients needed for the study to have adequate power. On the basis of a previous study,⁸ a difference of 10 points in the mHHS was considered significant. Hence, with an estimated SD of 15, the effect size for the 2-tailed Student t test (Cohen d) was 0.67; thus, to obtain a power of 80% or higher, with P < .05 and a 2-tailed hypothesis, the study required a minimum of 37 patients in each group to achieve statistical significance. An unpaired and paired t test was used to test for differences in means for numerical data between the groups and chi-square analysis for categorical data. Values of P < .05 were considered statistically significant. Intrarater reliability of radiographic measurements was determined using the method of Bartko² for measuring a rater’s self-consistency. The intraclass correlation coefficient was found to be >0.89 for Tönnis grade measurements.

Results

Patient Demographics

During the study period, 1412 hip arthroscopic procedures were performed, and 1036 hip arthroscopic procedures met the inclusion criteria. Of these, 892 (86.1%) had a minimum 2-year follow-up (Figure 1). There were 738 patients with Tönnis grade 0 and 154 patients with Tönnis grade 1. The chi-square analysis revealed no significant difference with respect to the incidence of revision arthroscopic surgery or subsequent THA between the 2 groups (Table 2 and Figure 2). A total of 93 patients in each of the Tönnis 0 and 1 groups were matched according to the above criteria. The demographic characteristics of each group are shown in Table 2. There was no significant difference with respect to age, sex, or BMI. The Tönnis grade 1 group had a significantly higher number of left-sided operations. The Tönnis grade 1 group also had a significantly longer mean follow-up, with a difference of 2.8 months. However, the minimum follow-up in both groups was 24 months. Nine and 11 patients, respectively, required subsequent THA, and 9 and 5 patients, respectively, required subsequent revision arthroscopic surgery in the Tönnis grade 0 and 1 groups. There was no significant difference between the groups with respect to the mean time to THA or revision arthroscopic surgery.

Figure 1.

Flowchart of the matching process.

Table 2

Patient Demographics and Secondary Procedures Performed^a

	Tönnis Grade 0 Group	Tönnis Grade 1 Group	P Value
Patients eligible for study, n	738	154
Patients matched, n	93	93
Sex, female:male, n	45:48	45:48	>.999
Side affected, right:left, n	58:35	44:49	.040
Age at surgery, y	41.2 (15.5-63.9)	41.3 (15.0-63.3)	>.999
Body mass index, kg/cm²	26.0 (17.7-37.9)	26.5 (18.5-48.7)	.500
Follow-up time, mo	28.7 (23.5-67.9)	31.5 (23.6-63.5)	.030
Conversion to THA, n (%)	9 (9.68)	11 (11.83)	.600
Time to THA, mo	22.4 (9.9-32.6)	32.1 (3.5-58.1)	.200
Revision arthroscopic surgery, n (%)	9 (9.68)	5 (5.38)	.300
Time to revision arthroscopic surgery, mo	26.5 (0.9-53.3)	25.1 (3.7-49.7)	.900

Values are reported as mean (range) unless otherwise indicated. THA, total hip arthroplasty.

Figure 2.

Percentage of procedures that required revision arthroscopic surgery or total hip arthroplasty (THA) for the Tönnis grade 0 and 1 groups. There was no significant difference between the groups with respect to the incidence of revision arthroscopic surgery or THA.

Radiological Findings

Table 3 shows the radiological findings within each of the 2 groups. There was no significant difference between the groups with respect to preoperative radiological markers of acetabular coverage: LCEA, ACEA, and acetabular inclination. There was also no significant difference between the groups with respect to the percentage of crossover sign between the anterior and posterior walls of the acetabulum, which is a radiological marker of acetabular retroversion. Both groups had a significant reduction in the mean of all the above-measured acetabular radiological markers postoperatively except acetabular inclination, which was increased, but there was no significant difference between the groups. The Tönnis grade 1 group had a significantly larger mean alpha angle preoperatively of 63.8° compared with 60.0° in the Tönnis grade 0 group. Both groups had a significantly reduced mean alpha angle postoperatively. The Tönnis grade 0 group had a significantly lower postoperative alpha angle.

Table 3

Preoperative and Postoperative Acetabular and Femoral Radiological Indices Measured in the Study Cohorts^a

	Tönnis Grade 0 Group			Tönnis Grade 1 Group			P Value Between Groups
	Preoperative	Postoperative	P Value	Preoperative	Postoperative	P Value	Preoperative	Postoperative
Crossover sign, %	11.8 ± 15.3 (0 to 60)	7.8 ± 14.0 (0 to 55)	<.0001	10.0 ± 15.1 (0 to 50)	5.3 ± 12.9 (0 to 60)	.0002	.4000	.2000
LCEA, deg	31.8 ± 7.1 (18 to 54)	28.8 ± 4.8 (15 to 41)	<.0001	30.5 ± 6.5 (15 to 50)	28.0 ± 5.4 (15 to 40)	<.0001	.2000	.3000
ACEA, deg	32.4 ± 7.3 (16 to 50)	29.8 ± 6.2 (16 to 48)	<.0001	31.6 ± 8.6 (15 to 51)	30.4 ± 8.7 (12 to 65)	<.0001	.6000	.6000
Acetabular inclination, deg	3.5 ± 4.9 (−11 to 18)	4.5 ± 3.9 (−5 to 16)	.0040	4.3 ± 4.6 (−9 to 18)	5.5 ± 4.0 (−4 to 18)	<.0001	.3000	.0900
Alpha angle, deg	60.0 ± 10.6 (39 to 86)	42.2 ± 7.4 (29 to 72)	<.0001	63.8 ± 13.6 (35 to 104)	47.8 ± 11.6 (32 to 92)	<.0001	.0400	.0002

Values are reported as mean ± SD (range). ACEA, anterior center-edge angle; LCEA, lateral center-edge angle.

Intraoperative Diagnoses and Procedures Performed

Table 4 shows the intraoperative diagnoses within each group. There were no significant differences between the groups with respect to the type of labral tear, according to the classification of Seldes et al.³⁸ The Tönnis grade 1 group had a significantly higher percentage of patients with an acetabular labral articular disruption (ALAD)²⁹ grade 4 defect compared with the Tönnis grade 0 group. With respect to Outerbridge defects,³² the Tönnis grade 1 group had significantly higher grade 4 acetabular defects and grade 2 femoral head defects. The incidence of ligamentum teres tears was not significantly different between the 2 groups. With respect to arthroscopic procedures performed (Table 5), a significant difference was only observed with the Tönnis grade 0 group having a significantly higher rate of iliopsoas release (36.56%) compared with the Tonnis grade 1 group (22.58%).

Table 4

Intraoperative Diagnoses in the Study Cohorts^a

Intraoperative Diagnosis^b	Tönnis Grade 0 Group	Tönnis Grade 1 Group	P Value Between Groups
Seldes tear type
1	39 (41.94)	36 (38.71)	.7000
2	26 (27.96)	28 (30.11)	.7000
1 and 2	28 (30.11)	29 (31.18)	.9000
Acetabular chondral lesion (ALAD grade)
0	16 (17.20)	25 (26.88)	.1000
1	18 (19.35)	12 (12.90)	.2000
2	27 (29.03)	20 (21.51)	.3000
3	29 (31.18)	20 (21.51)	.1000
4	3 (3.23)	15 (16.13)	.0030
Acetabular chondral lesion (Outerbridge grade)
0	8 (8.60)	3 (3.23)	.1000
1	23 (24.73)	15 (16.13)	.2000
2	31 (33.33)	23 (24.73)	.2000
3	17 (18.28)	15 (16.13)	.7000
4	7 (7.53)	29 (31.18)	<.0001
Femoral head chondral lesion (Outerbridge grade)
0	58 (62.37)	47 (50.54)	.0500
1	0 (0)	3 (3.23)	.3000
2	3 (3.23)	12 (12.90)	.0200
3	5 (5.38)	11 (11.83)	.1000
4	12 (12.90)	14 (15.05)	.8000
Ligamentum teres tear
Intact	42 (45.16)	37 (39.78)	.5000
Torn	51 (54.84)	56 (60.22)	.2000

Values are reported as n (%). ALAD, acetabular labral articular disruption.

Not recorded: ALAD grade 1 (n = 1), acetabular Outerbridge grade 0 (n = 7) and grade 1 (n = 8), femoral Outerbridge grade 0 (n =15) and grade 1 (n = 6).

Table 5

Arthroscopic Procedures Performed^a

Procedure	Tönnis Grade 0 Group	Tönnis Grade 1 Group	P Value Between Groups
Labral treatment
Repair	47 (50.54)	47 (50.54)	>.99
Debridement	45 (48.39)	45 (48.39)	>.99
Reconstruction	1 (1.08)	1 (1.08)	.50
Capsular treatment
Repair	17 (18.28)	17 (18.28)	>.99
Release	76 (81.72)	75 (80.65)	>.99
Acetabuloplasty	72 (77.42)	72 (77.42)	>.99
Acetabular microfracture	13 (13.98)	16 (17.20)	.50
Acetabular chondroplasty	21 (22.58)	29 (31.18)	.20
Acetabular subchondral cyst removal	3 (3.23)	1 (1.08)	.60
Femoral osteoplasty	78 (83.87)	71 (76.34)	.20
Femoral head microfracture	0 (0)	2 (2.15)	.50
Femoral head chondroplasty	11 (11.83)	9 (9.68)	.60
Femoral subchondral cyst removal	3 (3.23)	1 (1.08)	.60
Notchplasty	5 (5.38)	4 (4.30)	>.99
Subspine decompression	0 (0)	1 (1.08)	>.99
Ligamentum teres treatment	42 (45.16)	51 (54.84)	.20
Iliopsoas release	34 (36.56)	21 (22.58)	.04
Loose body removal	15 (16.13)	22 (23.66)	.20

Values are reported as n (%).

Outcomes

Table 6 shows the mean preoperative and latest postoperative PRO and VAS scores for both groups. There was a significant improvement in the mean scores of all PROs. There was no significant difference between the groups with respect to the change in PRO and VAS scores (Figures 3 and 4). Patient satisfaction was 7.42 and 7.71 for the Tönnis grade 0 and 1 groups, respectively.

Table 6

Patient-Reported Outcome Scores^a

	Tönnis Grade 0 Group				Tönnis Grade 1 Group
Outcome Measure	Preoperative	Postoperative	Change	P Value	Preoperative	Postoperative	Change	P Value
mHHS	59.32	74.83	15.51	<.001	59.44	78.96	19.52	<.001
NAHS	55.97	76.62	20.65	<.001	56.82	77.78	20.96	<.001
HOS-ADL	61.97	78.80	16.83	<.001	62.49	80.69	18.20	<.001
HOS-SSS	40.02	60.93	20.91	<.001	39.68	61.29	21.61	<.001
VAS	5.97	3.15	−2.82	<.001	6.09	3.25	−2.84	<.001
Satisfaction		7.42				7.71

Preoperative and postoperative values are reported as the mean. HOS-ADL, Hip Outcome Score–Activities of Daily Living; HOS-SSS, Hip Outcome Score–Sport-Specific Subscale; mHHS, modified Harris Hip Score; NAHS, Nonarthritic Hip Score; VAS, visual analog scale.

Figure 3.

Change in mean patient-reported outcome (PRO) scores for the Tönnis grade 0 and 1 cohorts. There was no statistical significance for change in any of the PRO scores. HOS-ADL, Hip Outcome Score–Activities of Daily Living; HOS-SSS, Hip Outcome Score–Sport-Specific Subscale; mHHS, modified Harris Hip Score; NAHS, Nonarthritic Hip Score.

Figure 4.

Change in mean patient-reported outcome scores for the Tönnis grade 0 and 1 cohorts. There was no statistical significance for change in the visual analog scale (VAS) score.

Discussion

This study evaluated minimum 2-year outcomes of hip arthroscopic surgery in patients with Tönnis grade 1 OA using a matched cohort of patients with Tönnis grade 0 OA. Patients were matched to minimize the confounding effects of age, sex, BMI, and arthroscopic treatment. Both groups demonstrated a significant improvement in PRO and VAS scores. No significant difference was found between the mean change in PRO, VAS, and patient satisfaction results between the groups at latest follow-up. There was no significant difference in subsequent rates for revision arthroscopic surgery or conversion to THA. The results of the study suggest that patients with minor grades of radiological OA demonstrate improvement with hip arthroscopic surgery that is not significantly different from that of a matched cohort of Tönnis grade 0 at 2-year follow-up.

Studies have shown that the presence of OA can adversely affect outcomes after hip arthroscopic surgery and open preservation surgery.^31,33 This is related to the limited efficacy of non-THA treatment options to treat OA.^20,23,27 Hip arthroscopic surgery can effectively restore the labral seal and address impingement, but patients may continue to experience symptoms associated with their OA.^30,35,36,43 This is reflected by the higher conversion rate to total hip replacement associated with moderate degrees of OA, as defined by a joint space of less than 2 mm or Tönnis grade ≥2.^{6,11,13,14,28,34} However, the results of the current study suggest that minor degrees of arthritis, as defined by a Tönnis grade ≤1, have less of an effect on the outcomes of hip arthroscopic surgery. This finding may relate to labral injuries and impingement being the predominant causes of disability in this patient population compared with chondropathies.

There have been several systematic reviews on the effects of OA on the outcomes of hip arthroscopic surgery.^6,14,20 The most recent of these reviews is by Domb et al,⁶ who identified 13 articles written in the English language that reported on the outcomes of hip arthroscopic surgery in OA with a sample size of ≥10. Only 4 of the 13 articles commented on grade 1 OA, of which 3 reported on either PROs or conversion to THA.^11,13,15,22 Gedouin et al¹¹ reported on the results of the arthroscopic treatment of femoroacetabular impingement in 101 patients with a mean 10-month follow-up: 65 with Tönnis grade 0 and 36 with Tönnis grade 1. Patients with grade 1 OA had significantly lower Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and satisfaction scores than those with no OA. Furthermore, 5 patients underwent conversion to THA at a mean of 12 months. Haviv and O’Donnell¹³ reported on 564 patients with OA treated with hip arthroscopic surgery. No PROs were recorded in the study, and the conversion rate to THA was 16%. However, patients with Tönnis grade 1, younger age, and multiple arthroscopic procedures had a longer time to THA. Horisberger et al¹⁵ reported on the results of 105 hip arthroscopic procedures in which 1 patient had Tönnis grade 0, 76 had Tönnis grade 1, and 28 patients had Tönnis grade 2 arthritis. The conversion rate to THA was 6% in the Tönnis grade 1 group compared with 64% in the Tönnis grade 2 group. They also reported that the NAHS was negatively correlated with THA. The 11.83% conversion rate to THA in the current study is in concordance with the above results in the literature. This rate was not significantly different from that of the Tönnis grade 0 group. One possible explanation for this is that the matched-pair design of the current study minimizes the effect of confounding factors such as age, which may influence the decision to convert to THA.

The current study reported an incidence of iliopsoas release of 22.58% to 36.56%. This is higher than that generally reported in the literature.⁷ This may be a reflection of the controversies that exist regarding the indications and efficacy of iliopsoas release. Although there have been reports of moderate success with release of the iliopsoas tendon for painful internal snapping of the hip,^16-18 there have also been reports of the recurrence of symptoms¹⁰ and the development of hip instability.¹ The latter has been theorized to relate to the important anterior dynamic stabilization function of the iliopsoas tendon.¹⁰ However, it is the opinion of the senior author (B.G.D.) that a pathological iliopsoas tendon is an important contributory pain trigger that can safely be lengthened with appropriate restoration of other soft tissue stabilizers such as the hip capsule.^7,9 Further research could provide the indications and technique for the management of a pathological iliopsoas tendon.

One of the strengths of this study was the matched-pair design. The matched-pair format minimizes the effects of age, sex, BMI, and difference in arthroscopic procedures performed on outcomes. Age and arthroscopic procedures have been shown to be major influences on outcomes after hip arthroscopic surgery, and hence, controlling for them strengthens the comparative analysis between the groups.⁴ The prospective collection of clinical data is another major strength of the study. PROs are useful tools for measuring clinical outcomes. The use of multiple scores allows researchers to look for consistency in patient reporting and to overcome ceiling effects that can occur. There is limited evidence for the use of a single score in hip arthroscopic surgery. Hence, multiple scores may better delineate surgical outcomes.²⁶

There were limitations of the study. Although the matched-pair analysis allows the control of several important confounding factors, there are still several factors that could not be controlled. These include intra-articular diagnoses. However, there was no significant difference in outcomes despite the Tönnis grade 1 group having a higher proportion of ALAD grade 4 and femoral head grade 4 chondral defects. Other important factors such as acetabular version and femoral cam size were not matched and may potentially affect outcomes, but these are independent of the Tönnis grade. One of the other limitations pertains to the length of follow-up. This study involved a minimum 2-year follow-up, and it is unknown whether the improvement demonstrated will persist over time. Longer term study of this patient population is currently underway at our institution.

Conclusion

At 2-year follow-up, patients with Tönnis grade 1 OA had improved outcomes after hip arthroscopic surgery, with no significant difference compared with a matched control group of Tönnis grade 0 OA. However, further studies are underway to determine if the results of the Tönnis grade 1 cohort will deteriorate over longer follow-up.

Footnotes

One or more of the authors has declared the following potential conflict of interest or source of funding: B.G.D. reports personal fees and other support from Arthrex, other support from Breg, other support from ATI, personal fees and other support from Pacira, personal fees and other support from Stryker MAKO Surgical, personal fees from Orthomerica, personal fees from DJO Global, and personal fees from Amplitude, outside the submitted work; he is also a board member of the American Hip Institute, which funds research and is the institution where the study was performed. The American Hip Institute receives support from Arthex, Breg, ATI, Pacira, and Stryker MAKO Surgical, but no direct or indirect funding was received for this study.

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