Longitudinal Assessment of Clinical Outcomes After Arthroscopic Treatment for Hip Synovial Chondromatosis and the Effect of Residual Loose Bodies: Minimum 4-Year and 8-Year Follow-up

Abstract

Background:

Arthroscopic treatment is recommended for hip synovial chondromatosis. However, evidence regarding long-term clinical outcomes is limited.

Purpose:

To evaluate long-term patient-reported outcomes (PROs) and survival, and to determine the potential effect of residual loose bodies, as evaluated by immediate postoperative computed tomography (CT), on clinical outcomes.

Study Design:

Case series; Level of evidence, 4.

Methods:

A consecutive cohort of patients undergoing arthroscopic treatment and diagnosed with synovial chondromatosis between March 2010 and May 2015 were included in the study. Preoperative radiography, CT, and magnetic resonance imaging were performed. Preoperative, midterm (minimum of 4 years), and long-term (minimum of 8 years) PROs were collected for visual analog scale for pain, modified Harris Hip Score (mHHS), Non-Arthritic Hip Score (NAHS), and 12-item international Hip Outcome Tool (iHOT-12). The percentages achieving minimal clinically important difference (MCID) were calculated. PROs and survival were compared between patients with and without residual loose bodies evident on immediate postoperative CT scan.

Results:

A total of 28 patients (20% of patients were lost to follow-up) were included in the study with a mean follow-up period of 104.9 months (range, 96-139 months). PROs including visual analog scale for pain (preoperative, 3.8 ± 1.2; midterm, 0.9 ± 1.7; long-term, 0.8 ± 1.4), mHHS (preoperative, 66.4 ± 14.4; midterm, 92.8 ± 12.3; long-term, 93.5 ± 10.5), NAHS (preoperative, 45.2 ± 16.2; midterm, 81.8 ± 15.3; long-term, 83.1 ± 12.9), and iHOT-12 (preoperative, 48.4 ± 15.6; midterm, 69.3 ± 11.7; long-term, 72.7 ± 11.4) were improved at both midterm and long-term follow-up (all with P < .001). In total, 27 (96.4%), 28 (100%), and 26 (92.9%) patients achieved MCID for mHHS, NAHS and iHOT-12, respectively, at the long-term follow-up. No significant difference was found in any of the PROs and the rate of achieving MCID between midterm and long-term follow-up (all with P > .05). One patient (3.6%) underwent revision surgery. Among the 23 patients who had loose bodies on preoperative CT or radiographs, 14 patients (60.9%) with residual loose bodies evident on immediate postoperative CT demonstrated lower NAHS (P = .045) and iHOT-12 (P = .037) scores but a comparable survival (P > .05) at long-term follow-up compared with those who did not have loose bodies.

Conclusion:

Arthroscopic treatment for hip synovial chondromatosis achieved satisfactory long-term clinical outcomes with strong survival. Most patients maintained or improved their overall functional status between midterm and long-term follow-up. Furthermore, patients with residual loose bodies had less favorable clinical outcomes, although the survival rate was comparable.

Keywords

hip joint synovial chondromatosis hip arthroscopy

Synovial chondromatosis (SC) is a benign disease that commonly affects the knee, hip, elbow, and hand joints.² SC is characterized as metaplasia of the synovial membrane and formation of multiple calcified nodules.¹⁶ Although the cause of hip SC is unknown, the condition often presents with hip pain, mechanical locking, and stiffness.²⁷ If SC is untreated, joint deterioration and secondary osteoarthritis could arise and patients would eventually require total hip arthroplasty (THA).⁶

To relieve symptoms and preserve hip function, surgical intervention including loose body removal and synovectomy is recommended.²⁴ Compared with conventional open surgery, arthroscopic treatment can achieve favorable clinical outcomes with less invasiveness and faster recovery.¹¹ However, current studies primarily consist of short-term to midterm follow-up with limited long-term evidence to establish the prolonged efficacy of arthroscopic treatment.^{1,11,13,15,27} Recurrence is also a concern after arthroscopic surgery due to the difficulties of complete removal of loose bodies and synovectomy when using an arthroscopic technique.¹² The percentage of recurrence identified by a combination of clinical symptoms and imaging findings was systematically reported to be 7.1%, with 85.7% of those patients undergoing subsequent surgery (revision surgery or conversion to THA).⁷ Therefore, determining the dynamic changes in functional status and survival at short- and long-term follow-up after hip arthroscopy and exploring the effect of residual loose bodies on clinical outcomes could provide valuable information for orthopaedic surgeons in treating SC.

The purposes of the present study were (1) to evaluate short- and long-term patient-reported outcomes (PROs), the rate of achieving minimal clinically important difference (MCID) of each PRO, and survival after arthroscopic treatment for patients with SC and (2) to determine the potential effect of residual loose bodies on clinical outcomes. It was hypothesized that arthroscopic treatment could achieve satisfactory midterm and long-term PROs with strong survival and that residual loose bodies might negatively affect clinical outcomes.

Methods

Patient Selection

After institutional review board approval was granted, data were retrospectively collected for a consecutive cohort of patients who underwent hip arthroscopy between March 2010 and May 2015 at our institution. Patients diagnosed with postoperative hip SC were included to assess their eligibility.

Patients were excluded if they had (1) history of previous hip surgery, (2) severe hip osteoarthritis (Tönnis grade >1), (3) history of autoimmune disease, (4) avascular necrosis, or (5) Legg-Calve-Perthes disease.

Surgical Technique

We divided the hip synovia of both the peripheral and the central compartments into 7 regions as described by Tian et al.²⁵ As shown in Figure 1, hip synovia were separated into region 1, medial capsular recess; region 2, anterior capsular recess; region 3, lateral capsular recess; region 4, posteroinferior recess; region 5, posterosuperior recess; region 6, perilabrum; and region 7, acetabular fossa.

Two senior surgeons (Y.X. and J.W.) with >10 years of experience in hip arthroscopy performed all operations using a standard supine approach²⁵ with the patient on a traction table (Smith & Nephew). Arthroscopic inspection, loose body removal, and synovectomy were performed in order from the peripheral compartment to the central compartment. Both shaver and ablation techniques were used during the procedure, with the shaver being primarily applied for synovectomy. Ablation was used to facilitate the separation of synovium and surrounding tissues as well as to prevent bleeding. The proximal midanterior portal (PMAP) and the midanterior portal (MAP) were established first. With PMAP as the viewing portal and MAP as the working portal, the arthroscopic inspection was started at the medial capsular recess (region 1) and anterior capsular recess (region 2) without traction. The hip was gradually flexed and internally rotated for synovectomy and loose body removal. Switching the viewing portal to the MAP, and using the PMAP and the anterolateral portal (AL) as working portals while keeping the hip in flexion and neutral position, the surgeons performed synovectomy and loose body removal at the lateral capsular recess (region 3). After traction was applied, an extended incision was made through the AL portal along the posteroinferior rim of the zona orbicularis. With the MAP as the viewing portal and the AL as the working portal, synovectomy and loose body removal were performed at the posterior site (region 4 and 5).

After managing the peripheral compartment, the surgeons moved the arthroscope into the central compartment, using the AL as the viewing portal and the MAP as the working portal. In addition to removing loose bodies and synovectomy (region 6 and 7), the surgeons performed labral debridement or repair according to the condition of the labrum. Acetabular and femoral head cartilage was evaluated according to the Outerbridge classification,²² and chondroplasty was performed for partial-thickness cartilage lesions and chondral flaps. If a cam lesion in the head-neck junction or acetabular overcoverage was identified, femoral or acetabular osteoplasty was performed. The capsule was routinely repaired. Loose bodies and synovia were evaluated using the classification of Milgram¹⁸ and sent for pathological examination.

Rehabilitation Protocol

A standardized rehabilitation protocol was implemented for all patients. Isometric contractions and passive range of motion exercises were initiated on days 1 to 2 after surgery. Partial weightbearing exercises to restore range of motion and promote regular gait were introduced from day 3 to week 3, followed by full weightbearing walking at week 4. Full weightbearing muscle strength exercises and dynamic balance training began at week 6. Patients gradually resumed activities and returned to sports based on their tolerance.

Data Collection

Patient characteristics including age at surgery, sex, affected side, height, weight, body mass index (BMI), and duration of symptoms were collected.

Hip radiography and computed tomography (CT) were performed preoperatively to preliminarily locate loose bodies. The alpha angle, lateral center-edge angle (LCEA), Tönnis grade, and joint space were collected using methods described in previous studies.^10,14,17,23 Hip magnetic resonance imaging (MRI) examinations were performed preoperatively using a 3.0-T magnetic resonance scanner (Magnetom Trio with TIM system; Siemens Healthcare) to confirm the diagnosis and evaluate the condition of the labrum, cartilage, and hip muscles. All patients underwent hip radiography and CT on the day after surgery so we could evaluate the presence of residual loose bodies.

PROs, including visual analog scale (VAS) for pain, modified Harris Hip Score (mHHS), Non-Arthritic Hip Score (NAHS), and 12-item international Hip Outcome Tool (iHOT-12), were used to assess hip function for all patients.^4,5,9 The PROs were collected for all patients preoperatively, and PROs and survival at a minimum of 4-year (midterm) and 8-year (long-term) follow-up. Survival was defined as the absence of revision surgery or conversion to THA. Patients were contacted directly by phone or at outpatient clinic. Cutoff values for the MCIDs of the mHHS, NAHS, and iHOT-12 were calculated using a distribution-based method originally proposed by Norman et al,²¹ in which the MCID cutoff was set to half the standard deviation of the preoperative outcome scores of the cohort.

Statistical Analysis

All the data were analyzed using IBM SPSS Statistics 27.0 (SPSS Inc). The Kolmogorov-Smirnov test was performed first to check for normal distributions. The Wilcoxon signed-rank test was applied for the skewed variables, and paired t test was applied for the normally distributed variables to compare the longitudinal PROs. The Fisher exact test was used to compare the categorical variables between groups. Mann-Whitney U test and independent t test were used to compare the skewed variables and normally distributed variables between patients with and without residual loose bodies. Statistical significance was considered when P < .05.

Results

As shown in Figure 2, a total of 28 patients were included in the present study, after 20% of patients were lost to follow-up. Patients’ characteristics are listed in Table 1. The mean age at which patients underwent surgery was 37.2 years (range, 14-59 years). Most of the patients were men (67.9%). Eleven patients had SC on the left side and 17 patients had SC on the right side. The mean BMI of patients was 24.1 (range, 18.8-32.1). The mean duration from the appearance of symptoms to surgery was 41 months (range, 3-120 months). The mean follow-up period was 104.9 months (range, 96-139 months).

Table 1

Patient Characteristics^a (N = 28)

Characteristic	Value
Age, y	37.2 ± 11.7 (14-59)
Sex
Male	19 (67.9)
Female	9 (32.1)
Side
Left	11 (39.3)
Right	17 (60.7)
Height, cm	170.6 ± 7.3 (155-185)
Weight, kg	71.3 ± 14.2 (47-110)
Body mass index	24.1 ± 3.5 (18.8-32.1)
Duration of symptoms, mo	41.0 ± 33.1 (3-120)
Follow-up period, mo	104.9 ± 12.8 (96-139)

Values are expressed as mean ± SD (range) or n (%) of hips.

As shown in Table 2, loose bodies were observed on radiographs of 14 patients (50.0%), on CT scans of 23 patients (82.1%), and on MRI scans of 26 patients (92.9%). The mean alpha angle was 50.0° (range, 44.7°-69.7°). All patients had synovial hypertrophy. The mean LCEA was 34.7° (range, 27.2°-48.6°). Twelve patients (42.9%) had Tönnis grade 0, and 16 patients (57.1%) had Tönnis grade 1. The mean joint space was 4.1 mm (range, 2.5-6.3 mm).

Table 2

Preoperative Radiographic Findings^a (N = 28)

Radiographic Finding	Value
Loose bodies present on radiographs	14 (50.0)
Loose bodies present on computed tomography	23 (82.1)
Loose bodies present on magnetic resonance imaging	26 (92.9)
Synovial hypertrophy	28 (100)
Alpha angle, deg	50.0 ± 9.3 (44.7-69.7)
Lateral center-edge angle, deg	34.7 ± 9.3 (27.2-48.6)
Tönnis grade
0	12 (42.9)
1	16 (57.1)
Joint space, mm	4.1 ± 0.9 (2.5-6.3)

Values are expressed as mean ± SD (range) or n (%) of hips.

As shown in Table 3, under arthroscopic inspection, 16 patients (57.1%) had SC of Milgram stage 2, and 12 patients (42.9%) had SC of Milgram stage 3. In total, 26 patients (92.9%) had loose bodies at the peripheral compartment and 27 patients (96.4%) had loose bodies at the central compartment. Most of the loose bodies in the central compartment were observed in the acetabular fossa. Fewer than 10 loose bodies were observed in 5 patients (17.9%), whereas 8 patients (28.6%) had between 10 and 100 loose bodies and 15 patients (53.5%) had >100 loose bodies. Twelve patients (42.9%) had labral injury and received debridement or labral repair. Concerning acetabular cartilage lesion, Outerbridge grade 1 was observed in 4 patients (14.3%), grade 2 was observed in 5 patients (17.9%), and grade 3 was observed in 4 patients (14.3%). As for femoral head cartilage lesion, Outerbridge grade 1 was observed in 4 patients (14.3%), grade 2 was observed in 1 patient (3.6%), and grade 3 was observed in 1 patient (3.6%).

Table 3

Arthroscopic Findings (N = 28)

Arthroscopic Finding	No. (%) of Hips
Milgram stage
Stage 2	16 (57.1)
Stage 3	12 (42.9)
Location of loose bodies
Peripheral compartment	26 (92.9)
Central compartment	27 (96.4)
No. of loose bodies
<10	5 (17.9)
10-100	8 (28.6)
>100	15 (53.5)
Synovial hypertrophy	28 (100)
Labral injury	12 (42.9)
Cam-type impingement	8 (28.6)
Pincer-type impingement	2 (7.1)
Acetabular cartilage Outerbridge classification
Grade 0	15 (53.6)
Grade 1	4 (14.3)
Grade 2	5 (17.9)
Grade 3	4 (14.3)
Grade 4	0
Femoral head cartilage Outerbridge classification
Grade 0	22 (78.5)
Grade 1	4 (14.3)
Grade 2	1 (3.6)
Grade 3	1 (3.6)
Grade 4	0

As shown in Table 4, patients presented significant improvement in VAS, mHHS, NAHS, and iHOT-12 at midterm and long-term follow-up compared with the preoperative assessment (all with P < .001). No significant difference was found in any of the PROs between midterm and long-term follow-up periods (all with P > .05). One patient (a 44-year-old woman), who had persistent hip pain and increased number of loose bodies on CT (findings considered to indicate recurrence), underwent revision surgery 17 months after primary arthroscopy. No patient underwent conversion to THA during the follow-up period. According to the preoperative PROs, the MCIDs of mHHS, NAHS, and iHOT-12 were 7.2, 8.1, and 7.8, respectively. Table 5 shows that 26 patients (92.9%) achieved MCID of all PROs at midterm follow-up. Further, 27 (96.4%), 28 (100%), and 26 (92.9%) patients achieved MCID of mHHS, NAHS, and iHOT-12, respectively, at the long-term follow-up. No significant difference was found between the percentages of patients achieving MCIDs of PROs at midterm and long term (all with P > .05). A total of 25 patients (89.2%) maintained their status or demonstrated improvement in achieving MCIDs across all PROs from midterm to long-term follow-up.

Table 4

Patient-Reported Outcomes (PROs)^a (N = 28)

	Preoperative	Midterm, 4 y	P ^b	Long-term, 8 y	P ^c	P ^d
VAS	3.8 ± 1.2	0.9 ± 1.7	<.001	0.8 ± 1.4	<.001	.689
mHHS	66.4 ± 14.4	92.8 ± 12.3	<.001	93.5 ± 10.5	<.001	.273
NAHS	45.2 ± 16.2	81.8 ± 15.3	<.001	83.1 ± 12.9	<.001	.502
iHOT-12	48.4 ± 15.6	69.3 ± 11.7	<.001	72.7 ± 11.4	<.001	.158

Values are presented as mean ± SD. Boldface indicates statistically significant difference (P < .05). iHOT-12, 12-item international Hip Outcome Tool; mHHS, modified Harris Hip Score; NAHS, Non-Arthritic Hip Score; VAS, visual analog scale for pain.

P value comparing preoperative and midterm PROs.

P value comparing preoperative and long-term PROs.

P value comparing midterm and long-term PROs.

Table 5

Achievement of Minimal Clinically Important Difference^a (N = 28)

	Midterm, 4 y	Long-term, 8 y	P
mHHS	26 (92.9)	27 (96.4)	≥.999
NAHS	26 (92.9)	28 (100)	.491
iHOT-12	26 (92.9)	26 (92.9)	≥.999

Values are presented as n (%) of hips. iHOT-12, 12-item international Hip Outcome Tool; mHHS, modified Harris Hip Score; NAHS, Non-Arthritic Hip Score.

Of the 23 patients who had loose bodies on preoperative CT scan, all had a decreased number of loose bodies on the immediate postoperative CT scan (postoperative: 13.1 ± 2.8 vs preoperative: 53.2 ± 11.4; P < .001). However, residual loose bodies were observed in 14 patients (60.9%) on the day after surgery. As shown in Table 6, most of the residual bodies were located at the posterior region and central compartment on postoperative CT scan. One patient with residual loose bodies underwent revision surgery. Several loose bodies were observed at the posteroinferior capsule and the labral-chondral transition area under arthroscopy.

Table 6

Location and Number of Residual Loose Bodies (n = 14)

	No. (%) of Hips	No. of Loose Bodies^a
Region 1	3 (21.4)	1.6 ± 3.4 (0-10)
Region 2	3 (21.4)	0.7 ± 1.7 (0-6)
Region 3	4 (28.6)	1.2 ± 2.2 (0-6)
Region 4	10 (71.4)	6.1 ± 5.9 (0-15)
Region 5	8 (57.1)	3.9 ± 4.4 (0-15)
Region 6	8 (57.1)	1.8 ± 1.9 (0-6)
Region 7	6 (42.9)	0.9 ± 1.1 (0-3)
Subcutaneous area	2 (14.3)	0.6 ± 1.5 (0-5)

Presented as mean ± SD (range).

As shown in Table 7, no significant differences were found in age, BMI, and preoperative PROs (all with P > .05) between patients with and without residual loose bodies. Patients with residual loose bodies had a larger initial number of loose bodies (P = .024) and lower NAHS (P = .045) and iHOT-12 (P = .037) at long-term follow-up. No significant difference was found in the rate of revision surgery between the 2 groups (P = .609).

Table 7

Comparison of Long-term Clinical Outcomes Between Patients With and Without Residual Loose Bodies^a (n = 23)

	With Residual Loose Bodies (n = 14)	Without Residual Loose Bodies (n = 9)	P
Age, y	37.4 ± 13.5	35.4 ± 5.3	.692
Body mass index	24.7 ± 3.0	23.8 ± 3.7	.533
Initial number of loose bodies	77.8 ± 58.1	30.8 ± 24.9	.024
Pre-VAS	3.6 ± 1.1	3.8 ± 0.7	.617
Post-VAS	1.1 ± 1.7	0.3 ± 0.7	.139
Pre-mHHS	65.5 ± 11.2	71.4 ± 9.0	.198
Post-mHHS	91.1 ± 12.9	97.7 ± 3.2	.089
Pre-NAHS	44.3 ± 18.4	49.4 ± 7.6	.133
Post-NAHS	79.2 ± 15.9	89.6 ± 6.6	.045
Pre-iHOT-12	48.0 ± 9.9	52.2 ± 6.8	.239
Post-iHOT-12	69.9 ± 14.0	78.8 ± 3.6	.037
Revision, n (%)	1 (7.1)	0	.609

Values are presented as mean ± SD unless otherwise noted. Boldface indicates statistically significant difference between groups (P < .05). iHOT-12, 12-item international Hip Outcome Tool; mHHS, modified Harris Hip Score; NAHS, Non-Arthritic Hip Score; Pre, preoperative; Post, postoperative.

The comparison of baseline characteristics, PROs, and rate of revision surgery between patients with and without femoroacetabular impingement (FAI) is presented in Appendix Table A1 (available in the online version of this article). A comparison between patients with and without chondral lesion is presented in Appendix Table A2. A comparison was also performed among patients without labral tear and those who underwent labral debridement and repair, as shown in Appendix Table A3. Patient age, BMI, preoperative and postoperative PROs, and rate of revision surgery did not demonstrate any significant difference in any of the comparisons (all with P > .05).

Discussion

The primary finding of this study was that arthroscopic treatment for hip SC achieved satisfactory long-term clinical outcomes with strong survival. Most of our patients maintained or improved their overall functional status between midterm and long-term follow-up. Furthermore, patients with residual loose bodies had less favorable clinical outcomes.

Hip SC is a relatively rare, benign synovial disease that initially presents with hip pain and symptoms including locking, swelling, crepitus, stiffness, and decreased range of motion, which are frequently unrelieved by nonoperative treatment.² Previous literature reported that the incidence of SC was about 2 to 4 times higher in men than in women, with an age range of 20 to 40 years at the time of presentation.^7,24 Similarly, the majority of participants in the present study were men (67.9%), and the mean age of the sample was 37.2 years.

Although the cause of SC is not recognized, the destructive pathology of the hip has been well-documented. Milgram¹⁹ divided SC into 3 stages. In stage 1, metaplasia occurs in the synovial membrane without the presence of loose bodies. In stage 2, progressive metaplasia results in the detachment of loose bodies partially surrounded by the synovial membrane. In stage 3, metaplastic activity of the synovial membrane is restrained and multiple loose bodies can be observed within the joint. Altered mechanical pressure and subsequent biochemical changes of the synovial fluid in the condition of SC will finally result in cartilage deterioration and progressive arthritic changes over an extended period.^2,7,24 Therefore, timely diagnosis and surgical intervention of SC can limit the damage and delay the degeneration of the hip joint. However, the diagnosis of SC is often delayed. In the present study, the mean duration between symptom onset and surgery was 41 months, and a range of 38 to 61 months was reported in previous studies.^{1,11,13,15,27} Regarding the nonspecific hip pain and symptoms, it was challenging to differentiate SC from pigmented villonodular synovitis and other osseous deformities with similar presentations, such as FAI and developmental dysplasia of the hip.^1,16

In the present study, a subset of patients presented concurrent SC and FAI on radiography and under arthroscopy, which was similar to findings of previous studies.^1,26,27 FAI is an abnormal contact between the proximal aspect of the femur and the acetabulum that results in hip pain, causing intra-articular pathologies such as labral tears and chondral lesions.^1,16 Although idiopathic anatomic abnormalities of the femoral neck and the acetabulum are the most common causes of cam- and pincer-type impingement, respectively, various factors have been proposed as causes of secondary FAI. Abolghasemian et al¹ suggested that SC may contribute to the development of cam-type impingement and subsequent FAI. Synovial inflammation at an early stage of SC and subsequent interposition of loose bodies were suggested to be the potential mechanisms underlying FAI. However, whether FAI was primary or secondary to SC could not be determined. Although the correlation between cam-type impingement and SC requires further study, simultaneous treatment of FAI and related intra-articular lesions resulted in good outcomes and low rate of revision surgery.^1,26,27 Given the potential influence of FAI features, chondral lesions, and different treatments for labral tear on study results, we compared the clinical outcomes across those variables and found no significant difference. Therefore, patients should be informed of the necessity of more extensive surgery to treat FAI and other intra-articular lesions in addition to SC, as they can also expect favorable clinical outcomes comparable to those of patients without these concomitant conditions.

Radiological examinations are useful tools in the diagnosis of SC in stage 2 and 3. Radiographs can reveal multiple intra-articular calcifications of similar size and shape distributed throughout the joint with typical “ring and arc” chondroid mineralization; CT imaging can optimally present the calcified intra-articular fragments and extrinsic bone erosion; and MRI findings may reflect loose bodies in early stage with variable signals depending on the degree of mineralization.²⁰ In a literature review, Startzman et al²⁴ found that 104 of 190 patients (55%) showed radiographic changes on preoperative radiographs and 86 of 108 patients (80%) showed MRI abnormalities. In the present study, loose bodies were detected on CT and MRI scans in most cases, with a prevalence rate of 82.1% and 92.9%, respectively, highlighting the diagnostic value of thorough preoperative radiological evaluations.

Surgical intervention, through either open or arthroscopic removal of loose bodies and synovectomy, is recommended for patients with hip SC.²⁴ Traditionally, open surgery has been considered the gold standard for SC due to the superior access to the hip joint and larger operative field to remove all of the loose bodies and perform complete synovectomy.¹ However, open surgery carries risks such as avascular necrosis of the femoral head and iatrogenic femoral neck fracture associated with hip dislocation, as well as prolonged rehabilitation.¹¹ Therefore, arthroscopic treatment has become the first choice for surgeons to treat hip SC, with advantages of perioperative care, rehabilitation, and reduced complications. However, arthroscopic synovectomy requires an advanced technique. It was reported that incomplete synovectomy and removal of loose bodies during the primary arthroscopic procedure had a close relation to recurrence.⁸ Therefore, we have developed a standardized protocol to maximize the removal of loose bodies and synovium.²⁵ Applying this technique in the current study, we found that 14 of 23 patients (60.8%) had residual loose bodies, which was lower than 7 of 9 (77.8%) patients reported by Lee et al.¹² Most of the residual loose bodies presented at the posterior capsule and posterior acetabular fossa on CT, areas that pose challenges for arthroscopic access. Extended incision of the lateroposterior joint capsule could also cause migration of loose bodies to outside of the joint, such as to the obturator externus and subcutaneous area. We found that more preoperative loose bodies were observed in patients with residual loose bodies. Surgeons should exercise caution when performing hip arthroscopy in cases where a large number of initial loose bodies, particularly in the posterior region, are observed on preoperative imaging. In these cases, open surgery may be considered the optimal approach for achieving comprehensive removal of loose bodies and synovectomy.

Recently, the efficacy of arthroscopic treatment for hip SC was investigated and reported to be good to excellent at short term to midterm.^{1,11,13,15,27} In the present study, we found that most patients achieved satisfactory midterm and long-term clinical outcomes. Most of the patients (89.2%) maintained or improved their status of achieving clinical thresholds for all the PROs, and we found no difference in the overall clinical outcomes between midterm and long-term assessments, which demonstrated the persistent efficacy of arthroscopy. Furthermore, it was reasonable to anticipate favorable long-term outcomes when patients exhibited good midterm results.

Only 1 patient (7.1%) with residual loose bodies underwent revision surgery, which occurred at 17 months after the primary surgery. No patient underwent revision surgery or conversion to THA at the interval between midterm and long-term follow-up. In a systematic review, de Sa et al⁷ found that the recurrence rate after arthroscopic treatment was about 7.6%, and 85.7% of patients underwent subsequent surgery. The only reported factor related to recurrence was older age. Considering that different stages of SC entail different metaplastic activity, Boyer and Dorfmann³ investigated the association between Milgram stage and recurrence rate in open surgical procedures. However, it was found that patients with both active disease (stages 1 and 2) and quiescent disease (stage 3) had a comparable recurrence rate.

The presence of loose bodies poses a potential risk of malignant transformation into chondrosarcoma and consequent negative effect on hip function.²⁷ Therefore, concern regarding the necessity of reoperation due to residual loose bodies has been addressed. Lee et al¹² reported that 7 patients with residual loose bodies showed improvement of PROs, including VAS (from 5.4 to 4.0), mHHS (from 80.4 to 90.1), University of California, Los Angeles, score (from 4.4 to 4.8), and Western Ontario and McMaster Universities Osteoarthritis Index score (from 24.2 to 14.6), with no recurrence at a mean follow-up of 3.8 years. However, a control group was not included in their study, which may preclude drawing precise conclusion. To further determine the effect of incomplete removal, we compared long-term PROs between patients with and without residual loose bodies. Although patients with residual loose bodies had less favorable long-term PROs compared with patients without, the survival rate did not show a statistical difference. We cannot draw a conclusion about the necessity of performing revision surgery solely for the removal of residual loose bodies, and further investigation is required to determine the specific location of residual bodies related to recurrence and sufficient extent of removal to prevent recurrence. However, surgeons can offer critical context to patients regarding the technical difficulties and the possibility of dissatisfaction with outcomes after surgery.

Limitations

Several limitations of our study must be acknowledged. Due to the retrospective nature of the study, selection and recall biases were inevitable. The sample size was relatively small and had a high rate of loss to follow-up. Given the difference in postoperative iHOT-12 scores between the groups, a total sample size of 40 was required to provide a power of 0.8 when alpha was set to .05. The clinical outcomes and clinical significance of the comparison between patients with and without residual loose bodies need to be validated through further investigation involving a larger sample size and longer follow-up period. Not all of the patients underwent CT or MRI during the outpatient follow-up, and thus we were unable to assess whether patients had radiological recurrence. The surgical technique used in the present study necessitates extensive expertise. Therefore, caution should be exercised in generalizing the outcomes to the entire population of SC patients.

Conclusion

Arthroscopic treatment for hip SC achieved satisfactory long-term clinical outcomes with strong survival. Most patients maintained or improved their overall functional status between midterm and long-term follow-up. Furthermore, patients with residual loose bodies had less favorable clinical outcomes than patients without residual loose bodies, although the survival rate was comparable.

Supplemental Material

sj-pdf-1-ajs-10.1177_03635465241260354 – Supplemental material for Longitudinal Assessment of Clinical Outcomes After Arthroscopic Treatment for Hip Synovial Chondromatosis and the Effect of Residual Loose Bodies: Minimum 4-Year and 8-Year Follow-up

Supplemental material, sj-pdf-1-ajs-10.1177_03635465241260354 for Longitudinal Assessment of Clinical Outcomes After Arthroscopic Treatment for Hip Synovial Chondromatosis and the Effect of Residual Loose Bodies: Minimum 4-Year and 8-Year Follow-up by Yichuan Zhu, Guanying Gao, Shuo Luan, Kesheng Wu, Hongli Wang, Yanni Zhang, Xin Zhang, Jianquan Wang and Yan Xu in The American Journal of Sports Medicine

Footnotes

Submitted October 9, 2023; accepted April 25, 2024.

The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

ORCID iD

Jianquan Wang

References

Abolghasemian

Gharanizadeh

Kuzyk

, et al. Hips with synovial chondromatosis may display the features of femoroacetabular impingement. J Bone Joint Surg Am. 2014;96(2):e11.

Adelani

Wupperman

Holt

. Benign synovial disorders. J Am Acad Orthop Surg. 2008;16(5):268-275.

Boyer

Dorfmann

. Arthroscopy in primary synovial chondromatosis of the hip: description and outcome of treatment. J Bone Joint Surg Br. 2008;90(3):314-318.

Byrd

. Hip arthroscopy: patient assessment and indications. Instr Course Lect. 2003;52:711-719.

Christensen

Althausen

Mittleman

Lee

McCarthy

. The nonarthritic hip score: reliable and validated. Clin Orthop Relat Res. 2003;406:75-83.

Crotty

Monu

Pope

Jr.

Synovial osteochondromatosis. Radiol Clin North Am. 1996;34(2):327-342.

de Sa

Horner

MacDonald

, et al. Arthroscopic surgery for synovial chondromatosis of the hip: a systematic review of rates and predisposing factors for recurrence. Arthroscopy. 2014;30(11): 1499-1504.e1492.

Doward

Troxell

Fredericson

. Synovial chondromatosis in an elite cyclist: a case report. Arch Phys Med Rehabil. 2006;87(6): 860-865.

Griffin

Parsons

Mohtadi

Safran

; Multicenter Arthroscopy of the Hip Outcomes Research Network. A short version of the International Hip Outcome Tool (iHOT-12) for use in routine clinical practice. Arthroscopy. 2012;28(5):611-616.

10.

Hiza

Dierckman

Guanche

, et al. Reliability of the Tönnis classification and its correlation with magnetic resonance imaging and intraoperative chondral damage. Arthroscopy. 2019;35(2):403-408.

11.

Lee

Kang

Lee

Kim

Hwang

. Arthroscopic treatment of synovial chondromatosis of the hip. Am J Sports Med. 2012; 40(6):1412-1418.

12.

Lee

Moon

Kim

, et al. Remaining loose bodies after arthroscopic surgery including extensive capsulectomy for synovial chondromatosis of the hip. Clin Orthop Surg. 2018;10(4):393-397.

13.

Liu

, et al. Arthroscopic treatment of synovial chondromatosis of hip joint. J Orthop Surg Res. 2020;15(1):405.

14.

Mansor

Perets

Domb

. In search of the spherical femoroplasty: cam overresection leads to inferior functional scores before and after revision hip arthroscopic surgery. Am J Sports Med. 2018;46(9):2061-2071.

15.

Marchie

Panuncialman

McCarthy

. Efficacy of hip arthroscopy in the management of synovial chondromatosis. Am J Sports Med. 2011;39(suppl):126S-131S.

16.

Maurice

Crone

Watt

. Synovial chondromatosis. J Bone Joint Surg Br. 1988;70(5):807-811.

17.

Megerian

Strony

Mengers

, et al. Use of anatomic radiographic horizons for the lateral center-edge angle in the classification of hip dysplasia. Am J Sports Med. 2022;50(13):3610-3616.

18.

Milgram

. Synovial osteochondromatosis: a histopathological study of thirty cases. J Bone Joint Surg Am. 1977;59(6):792-801.

19.

Milgram

. The classification of loose bodies in human joints. Clin Orthop Relat Res. 1977;124:282-291.

20.

Murphey

Vidal

Fanburg-Smith

Gajewski

. Imaging of synovial chondromatosis with radiologic-pathologic correlation. Radiographics. 2007;27(5):1465-1488.

21.

Norman

Sloan

Wyrwich

. Interpretation of changes in health-related quality of life: the remarkable universality of half a standard deviation. Med Care. 2003;41(5):582-592.

22.

Outerbridge

. The etiology of chondromalacia patellae. J Bone Joint Surg Br. 1961;43:752-757.

23.

Reis

Nahal-Said

Ravaud

Dougados

Amor

. Are radiological joint space widths of normal hips asymmetrical? Ann Rheum Dis. 1999;58(4):246-249.

24.

Startzman

Collins

Carreira

. A systematic literature review of synovial chondromatosis and pigmented villonodular synovitis of the hip. Phys Sportsmed. 2016;44(4):425-431.

25.

Tian

Gao

Dong

, et al. Arthroscopic synovectomy of the hip joint: the regional surgical technique. Arthrosc Tech. 2022;11(7): e1181-e1187.

26.

Zhang

Gao

Wang

. Clinical outcomes after arthroscopic treatment of synovial chondromatosis in the hip. Cartilage. 2021; 13(1)(suppl):1324S-1330S.

27.

Zini

Longo

de Benedetto

, et al. Arthroscopic management of primary synovial chondromatosis of the hip. Arthroscopy. 2013;29(3):420-426.

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

0.09 MB