Clinical Outcomes of Arthroscopic Loose-Body Removal and Synovectomy for Knee Synovial Chondromatosis: Comparable Results in Patients With and Without Concomitant Chondral Lesions

Abstract

Background:

Arthroscopic loose-body removal and synovectomy are recommended for the treatment of knee synovial chondromatosis (SC). However, there are limited data on clinical outcomes and survivorship after arthroscopic treatment for knee SC.

Purposes/Hypothesis:

The purpose was to evaluate the clinical outcomes and survivorship of arthroscopic loose-body removal and synovectomy in patients with knee SC, as well as to investigate the potential effect of concomitant chondral lesions on these outcomes. It was hypothesized that arthroscopic treatment for knee SC could yield satisfactory clinical outcomes, with concomitant chondral lesions negatively affecting clinical efficacy.

Study Design:

Case series; Level of evidence, 4.

Methods:

A consecutive cohort of patients diagnosed with knee SC and treated with arthroscopy between 2016 and 2022 was included in the study. Patient-reported outcomes (PROs) were collected preoperatively and at the final follow-up, including the Knee injury and Osteoarthritis Outcome Score, the subjective International Knee Documentation Committee (IKDC) score, the Lysholm score, and the visual analog scale for pain score. Data on arthroscopic findings, patient satisfaction, complications, and survivorship rates were also documented. The percentage of patients achieving the minimal clinically important difference (MCID) was calculated. Clinical outcomes were then compared between patients with and without chondral lesions identified during arthroscopy.

Results:

A total of 51 patients (54 knees) were included in the study, with a mean age at surgery of 42.3 ± 14.7 years and a mean follow-up period of 5.6 years. All PROs showed significant improvements at the final follow-up (P < .001), with >90% of patients achieving the MCID. Six knees (11.1%) experienced symptomatic recurrence confirmed by magnetic resonance imaging, and 3 knees (5.6%) underwent reoperation. The survivorship rates free from recurrence and reoperation were 85.1% and 93.9% at 8 years, respectively. At the final follow-up, no significant differences were found between knees with (n = 32) and without (n = 22) chondral lesions in all postoperative scores and survivorship rate.

Conclusion:

Arthroscopic treatment for knee SC yields favorable clinical outcomes with symptom relief and functional improvement. However, there remains a risk of recurrence and the need for reoperation. Additionally, patients with concomitant chondral lesions could achieve clinical outcomes and survivorship comparable to those of patients without chondral lesions.

Keywords

synovial chondromatosis knee arthroscopy chondral lesion

Synovial chondromatosis (SC) is a rare, benign process that most commonly affects the knee joint.^12,29 It is characterized by the metaplasia of the synovial membrane into chondrocytes, leading to the formation of cartilaginous nodules.^3,14 These nodules can detach from the synovium, resulting in multiple intra-articular loose bodies,¹⁸ which in turn cause symptoms including pain, swelling, locking, stiffness, giving away, and palpable loose bodies.¹⁹ Treatment for knee SC typically involves the removal of loose bodies and synovectomy with the primary aim of symptom relief, performed either arthroscopically or through open surgery.^4,6,17 Compared with traditional open surgery, arthroscopic treatment offers favorable clinical outcomes, including less invasiveness, lower morbidity, and faster recovery.¹² However, the risk of recurrence and the need for reoperation persist.^4,6,14 Previous studies on the clinical outcomes and survivorship of arthroscopic treatment for knee SC have been limited to small case series and case reports,^{2,4,6,17,18,25,29} highlighting the need for larger series with longer follow-up periods to comprehensively assess the prognosis of this treatment.

The diagnosis of SC is often delayed,¹⁵ leading to chondral lesions and subsequent degenerative changes.¹ This may result from both mechanical injuries caused by the loose bodies and the disruption of the nutritional mechanisms of the articular cartilage.²⁴ Dorfmann et al⁶ noted that the cartilage status of the tibiofemoral joint might correlate with clinical outcomes and potentially influence prognosis. However, limited data are available regarding whether concomitant chondral lesions affect the clinical efficacy and survivorship of arthroscopic treatment for knee SC.

The purpose of the present study was to evaluate the clinical outcomes and survivorship of arthroscopic loose-body removal and synovectomy in patients with knee SC, as well as to investigate the potential effect of concomitant chondral lesions on these outcomes. It was hypothesized that arthroscopic treatment for knee SC could yield satisfactory clinical outcomes, with concomitant chondral lesions negatively affecting clinical efficacy.

Methods

Patient Selection

After approval of the institutional review board (M2024707), a retrospective study was carried out among patients with knee SC at our institution. Patients with a confirmed diagnosis of SC treated by arthroscopy between June 2016 and June 2022 were eligible for inclusion. The diagnosis of SC was based on a thorough medical history of symptoms, physical examination, magnetic resonance imaging (MRI), intraoperative sighting, and postoperative pathology confirmation. Exclusion criteria were as follows: (1) combined patellar dislocation, (2) combined knee ligament injuries, (3) severe degenerative changes (Kellgrene-Lawrence grade ≥3), and (4) <2 years of follow-up.

Surgical Procedure

All patients underwent arthroscopic examination in the same institution using a consistent surgical technique performed by a team of 5 senior surgeons (Y.Y., Jian.W., H.W., C.W., and X.G.) with >15 years of experience in knee arthroscopy. Under spinal anesthesia, routine arthroscopic inspection was performed. Anterior knee arthroscopy was performed via the anteromedial, anterolateral, and suprapatellar portals. Posterior knee arthroscopy was performed through the coaxial posteromedial and posterolateral portals.^12,27 Using a standard supine approach, loose-body removal and synovectomy were performed in an orderly fashion. The loose bodies were removed by a hemostat, and the inflamed synovium was resected by an arthroscopic shaver. Ablation was utilized to facilitate the separation of synovium and surrounding tissues. In addition to loose-body removal and synovectomy, meniscal injuries were treated with meniscal suture, partial meniscectomy, or meniscectomy depending on the position and degree of injury. Furthermore, chondral lesions were treated with arthroscopic debridement, which involved the removal of damaged and unstable cartilage fragments from the articular surface. Patients underwent a computed tomography (CT) or MRI examination within 3 days postoperatively to confirm that the loose bodies were thoroughly removed.

Rehabilitation Protocol

All patients followed the standardized postoperative rehabilitation protocol. On the first day after surgery, patients were encouraged to engage in quadriceps strengthening exercises, straight-leg raises, patellar movements, and ankle pump exercises. Partial weightbearing exercises for restoring range of motion and promoting regular gait were introduced from day 3 to week 6. Weightbearing muscle strength exercises and dynamic balance training began at week 6. Patients gradually resumed activities and sports based on their tolerance.

Evaluation Methods

Patient characteristics, including age, sex, body mass index (BMI), affected side, and duration of symptoms, were retrieved from medical records at the time of inclusion. Surgical data were also obtained. Intraoperatively, the number of loose bodies and the presence of synovial hypertrophy were meticulously documented. The stage of SC was evaluated according to the classification by Milgram.¹⁵ Additionally, concomitant meniscal and chondral lesions were carefully recorded. The location of meniscal injury was specified, and the cartilage status was assessed in accordance with the International Cartilage Regeneration & Joint Preservation Society (ICRS) scale.¹³ Chondral lesions were defined as ICRS grade 3 or 4.¹¹

Knee radiography and CT were performed preoperatively to preliminarily locate loose bodies. MRI examinations were performed preoperatively using a Signa HDxt 3.0-T magnetic resonance scanner (GE HealthCare) to confirm the diagnosis. Patients who experienced recurrent clinical symptoms were advised to undergo MRI examinations to confirm the presence of recurrence.

Patient-reported outcomes (PROs) including the Knee injury and Osteoarthritis Outcome Score (KOOS),²¹ the subjective International Knee Documentation Committee (IKDC) score,⁷ the Lysholm score,²³ and the visual analog scale (VAS) for pain score were used to assess knee function preoperatively and at the final follow-up. The KOOS consists of 5 separately scored subscales: Symptoms, Pain, Activities of Daily Living (ADL), Sport and Recreation Function (Sport/Rec), and Knee-related Quality of Life (QoL).²⁰ Postoperative scores were collected via telephone at the final follow-up. Preoperative scores were obtained from original medical records and verified through telephone interviews, during which patients recalled their initial symptoms. The percentage of patients achieving the minimal clinically important difference (MCID) was calculated. MCID cutoff values for the KOOS, IKDC score, Lysholm score, and VAS score were calculated using a distribution-based method proposed by Norman et al,¹⁶ with the MCID cutoff set to half the standard deviation of the preoperative outcome scores in the cohort.

Data regarding patient satisfaction, postoperative complications, and survivorship were documented. Patient satisfaction with surgical outcomes (0-10, where 10 represents highly satisfied) was collected at the final follow-up. Survivorship was evaluated based on clinical and objective evaluations. Recurrence was defined as the reappearance of clinical symptoms in conjunction with MRI evidence of newly formed loose bodies. Reoperations included any subsequent surgical procedures, such as secondary lesion excision via arthroscopy or open surgery, and conversion to total knee arthroplasty (TKA).

Statistical Analysis

All data were analyzed using SPSS Statistics (Version 26.0; IBM Corp). Continuous parameters are presented as mean ± standard deviation (range). Categorial variables are presented as the number of observations and percentage. Comparisons between pre- and postoperative scores were evaluated using paired-sample t tests for normally distributed statistics and the Wilcoxon signed-rank test when normality was absent, as determined by the Shapiro-Wilk normality test. Chi-square and Fisher exact tests were used in evaluation of categorial variables. Survivorship rates free from recurrence and reoperation were independently assessed using the Kaplan-Meier analysis. Kendall tau-b correlation analysis was performed to assess the association between patients’ characteristics and recurrence. Comparisons between patients with and without chondral lesions were evaluated using the independent t test and Mann-Whitney U test. Statistical power was considered given the fixed available sample size. Based on an alpha level of .05 and 2-tailed hypothesis testing, a sample of 54 knees was sufficient to provide 95% statistical power. The level of statistical significance was set at a P value <.05.

Results

A total of 60 patients met the inclusion criteria. Eight patients were excluded for the reasons outlined in Figure 1. Of the 52 eligible patients, 1 (1.9%) was lost to follow-up despite attempts to contact him through telephone. Finally, 51 patients (54 knees) were included in this study. Detailed patient characteristics are presented in Table 1. The mean age at surgery was 42.3 ± 14.7 years (range, 12-70 years), with a mean follow-up time of 5.6 years (range, 2.7-8.3 years). Preoperatively, 9 patients (17.6%) had a history of preceding trauma, and 6 patients (11.8%) had previously undergone arthroscopic treatment for SC. The stage of SC and the detailed pathological changes were carefully recorded during arthroscopic inspection and retrieved from medical records (Table 1). All patients had synovial hypertrophy alone with loose bodies. Additionally, details of concomitant meniscal and chondral lesions are presented in Tables 2 and 3. Among the knees with meniscal pathology, 5 were treated with meniscal suture, 16 with partial meniscectomy, and 2 with meniscectomy. Thorough arthroscopy and immediate postoperative CT or MRI examination showed that no patients with residual loose bodies were observed.

Figure 1.

Flowchart for inclusion and exclusion of patients. SC, synovial chondromatosis.

Table 1

Patient Characteristics (54 Knees) ^a

	Value
Age at time of surgery, y	42.3 ± 14.7 (12-70)
Sex
Male	26 (48.1)
Female	28 (51.9)
BMI at time of surgery, kg/m²	26.0 ± 3.7 (15.6-35.4)
Side affected
Right	28 (51.9)
Left	26 (48.1)
Duration of symptoms, mo	42.1 ± 44.1 (2-240)
Follow-up time, y	5.6 ± 1.7 (2.7-8.3)
Milgram stage
2	28 (51.9)
3	26 (48.1)
No. of loose bodies under arthroscopy
<10	11 (20.4)
10-20	26 (48.1)
>20	17 (31.5)

Data are presented as mean ± SD (range) or No. of knees (%). BMI, body mass index.

Table 2

Concomitant Meniscal Lesions and Treatments (54 Knees)

	No. of Knees (%)
Meniscal lesions
No meniscal injury	31 (57.4)
Medial	7 (13.0)
Lateral	14 (25.9)
Both	2 (3.7)
Treatment of meniscal lesions
Meniscal suture	5 (9.3)
Partial meniscectomy	16 (29.6)
Meniscectomy	2 (3.7)

Table 3

Concomitant Chondral Lesions (54 Knees) ^a

ICRS Grade	No. of Knees (%)
Patellar
1	2 (3.7)
2	10 (18.5)
3	11 (20.4)
4	11 (20.4)
Trochlea
1	2 (3.7)
2	5 (9.3)
3	11 (20.4)
4	15 (27.8)
Medial femoral condyle
1	2 (3.7)
2	12 (22.2)
3	7 (13.0)
4	7 (13.0)
Medial tibial plateau
1	4 (7.4)
2	12 (22.2)
3	8 (14.8)
4	2 (3.7)
Lateral femoral condyle
1	1 (1.9)
2	11 (20.4)
3	5 (9.3)
4	7 (13.0)
Lateral tibial plateau
1	1 (1.9)
2	16 (29.6)
3	10 (18.5)
4	5 (9.3)

ICRS, International Cartilage Regeneration & Joint Preservation Society.

Clinical Outcomes

At a mean follow-up of 5.1 years (range, 2.1-7.7 years), all PROs showed significant improvements from baseline preoperative scores (all P < .001) (Table 4 and Figure 2). All patients reported being satisfied or extremely satisfied with their outcomes, with a mean satisfaction score of 9.4 (range, 7-10). According to the preoperative PROs, the MCIDs were respectively calculated to be 5.8 for KOOS Pain, 5.0 for KOOS Symptoms, 4.5 for KOOS ADL, 6.6 for KOOS Sport/Rec, 6.6 for KOOS QoL, 4.5 for IKDC score, 5.2 for Lysholm score, and 0.5 for VAS score. The percentages of knees achieving these MCIDs are presented in Table 4.

Table 4

Pre- and Postoperative PRO (54 Knees) ^a

PROs	Preoperative ^b	Final Follow-up ^b	P Value	MCID, %
KOOS
Pain	71.0 ± 11.6	92.8 ± 6.9	<.001	90.7
Symptoms	72.2 ± 10.0	92.9 ± 6.7	<.001	96.3
ADL	82.7 ± 9.0	96.9 ± 3.8	<.001	90.7
Sport/Rec	45.2 ± 13.2	72.8 ± 16.8	<.001	94.4
QoL	29.8 ± 13.2	83.5 ± 13.9	<.001	98.1
Subjective IKDC	43.8 ± 9.1	74.8 ± 12.0	<.001	98.1
Lysholm	59.1 ± 10.4	89.8 ± 7.5	<.001	100
VAS	5 (3-7)	1 (0-4)	<.001	100

All scores showed significant improvements at the final follow-up (P < .001). ADL, Activities of Daily Living; IKDC, International Knee Documentation Committee; KOOS, Knee injury and Osteoarthritis Outcome Score; MCID, minimal clinically important difference; PRO, patient-reported outcome; QoL, Knee-related Quality of Life; Sport/Rec, Sport and Recreation Function; VAS, visual analog scale.

Data are presented as mean ± SD or median (range).

Figure 2.

Knee injury and Osteoarthritis Outcome Score (KOOS) profile. ADL, Activities of Daily Living; QoL, Knee-related Quality of Life; Sport/Rec, Sport and Recreation Function.

Complications and Survivorship

No infections or thromboembolic complications were observed after surgery. Recurrence occurred in 6 knees (11.1%), with a mean recurrence time of 3.6 years (range, 1.0-5.1 years). However, only 3 (5.6%) of these knees underwent reoperation to excise the recurrent lesions, with 2 undergoing a secondary arthroscopic procedure and 1 undergoing open surgery. No conversions to TKA were identified. The remaining patients with recurrence chose not to undergo a second operation because they had milder symptoms. Kaplan-Meier survivorship analysis revealed that the survivorship rates free from recurrence and reoperation were 85.1% and 93.9% at 8 years, respectively (Figure 3). The detailed characteristics of patients with recurrence, along with their PROs at 3 time points—before the initial surgery, before the secondary surgery, and at the final follow-up—are presented in Table 5. Correlation analysis revealed that a shorter duration of symptoms before surgery (r = −0.246; P = .035) and a lower preoperative KOOS ADL (r = −0.289; P = .012) were weakly associated with recurrence. However, no significant correlations were observed between recurrence and age, sex, BMI, follow-up duration, previous knee surgery history, or other preoperative PROs.

Figure 3.

Kaplan-Meier survival curve with 95% confidence interval: overall survival rate. (A) The endpoint was defined as the reappearance of clinical symptoms in conjunction with magnetic resonance imaging evidence of newly formed loose bodies. (B) The endpoint was defined as reoperations due to recurrence.

Table 5

Characteristics and Outcome Assessments in Patients Experiencing Recurrence ^a

	Case 1	Case 2	Case 3	Case 4	Case 5	Case 6
Age at surgery, y	48	34	48	32	43	42
Sex	M	M	M	M	F	M
BMI, kg/m²	30.1	23.7	29.1	25.0	26.3	28.1
Duration of symptoms, mo	12	7	6	12	36	12
Follow-up time, y	7.6	4.8	2.7	7.1	7.1	6.8
Previous surgery	No	No	Yes	No	Yes	No
Revision surgery	Yes	Yes	Yes	No	No	No
KOOS
Preop	60.7	68.5	46.0	53.0	46.2	54.2
Pre-reop	61.6	72.8	51.8	—	—	—
Postop	96.2	82.5	74.9	89.5	72.7	92.7
IKDC
Preop	37.9	57.5	26.4	36.8	35.6	39.1
Pre-reop	32.2	56.3	29.9	—	—	—
Postop	88.5	62.1	51.7	86.2	57.5	75.9
Lysholm
Preop	56	66	54	38	50	61
Pre-reop	52	70	52	—	—	—
Postop	95	75	72	95	75	86
VAS
Preop	6	4	7	6	6	4
Pre-reop	6	4	6	—	—	—
Postop	1	2	4	3	4	2

BMI, body mass index; F, female; IKDC, International Knee Documentation Committee; KOOS, Knee injury and Osteoarthritis Outcome Score; M, male; preop, preoperative; pre-reop, pre-reoperative; postop, postoperative; VAS, visual analog scale; dashes indicate not applicable.

Effect of Chondral Lesions on Outcomes

No significant differences were found between patients with and without chondral lesions in terms of sex, BMI, and follow-up time. However, patients with chondral lesions were significantly older (P < .001) and had a longer duration of symptoms (P = .002). Both groups demonstrated significant improvements when comparing the pre- and postoperative scores of the IKDC, Lysholm, VAS, and all KOOS subscales (all P < .01) (Table 6). No significant differences were found between patients with and without chondral lesions in all postoperative scores and survivorship rate. According to the MCID analysis, no significant differences between groups were observed for the percentage of patients who achieved the MCID postoperatively in all clinical scores (Table 7).

Table 6

Comparison of Clinical Outcomes Between Patients With and Without Chondral Lesions ^a

	With Chondral Lesions (n = 32)	Without Chondral Lesions (n = 22)	P Value
Age at time of surgery, y	48.0 ± 14.1	34.1 ± 11.4	<.001
Male/female sex, n	13:19	13:9	.182
BMI, kg/m²	26.3 ± 9.0	25.5 ± 4.6	.421
Symptom onset, mo	55.9 (2-240)	22.0 (2-60)	.002
Follow-up time, y	5.3 ± 2.7	6.0 ± 3.0	.168
Preoperative PROs
KOOS
Pain	72.1 ± 12.9	69.3 ± 9.6	.387
Symptoms	70.8 ± 9.5	74.2 ± 10.5	.081
ADL	82.4 ± 9.1	83.1 ± 8.9	.798
Sport/Rec	41.4 ± 13.4	50.7 ± 10.9	.010
QoL	30.9 ± 12.9	28.1 ± 13.9	.461
IKDC score	43.5 ± 9.1	44.3 ± 9.2	.726
Lysholm score	57.5 ± 11.1	61.5 ± 9.0	.167
VAS score	4.9 (3-7)	4.9 (3-7)	.855
Postoperative PROs
KOOS
Pain	93.4 ± 6.6	91.9 ± 7.5	.427
Symptoms	92.5 ± 7.0	93.5 ± 6.4	.659
ADL	95.8 ± 19.1	98.5 ± 3.2	.055
Sport/Rec	69.5 ± 18.6	77.5 ± 12.7	.067
QoL	85.5 ± 13.9	80.4 ± 13.7	.081
IKDC score	73.2 ± 13.2	77.0 ± 9.9	.266
Lysholm score	90.0 ± 7.9	89.5 ± 7.2	.798
VAS score	1.3 (0-4)	1.7 (0-4)	.323
Δ PROs
KOOS
Pain	21.3 ± 13.1	22.6 ± 9.4	.682
Symptoms	21.8 ± 7.8	19.3 ± 8.7	.283
ADL	13.4 ± 8.5	15.4 ± 8.6	.438
Sport/Rec	28.1 ± 17.0	26.8 ± 12.7	.936
QoL	54.7 ± 16.6	52.3 ± 18.8	.620
IKDC score	29.8 ± 13.4	32.6 ± 9.9	.402
Lysholm score	32.5 ± 12.3	28.0 ± 10.1	.159
VAS score	3.6 (1-6)	3.2 (1-5)	.232
Recurrence, n (%)	2 (6.3)	4 (18.2)	.211

Data are presented as mean ± SD or median (range) unless otherwise indicated. Bold P values indicate statistically significant differences between groups (P < .05). ADL, Activities of Daily Living; BMI, body mass index; IKDC, International Knee Documentation Committee; KOOS, Knee injury and Osteoarthritis Outcome Score; QoL, Knee-related Quality of Life; Sport/Rec, Sport and Recreation Function; VAS, visual analog scale.

Table 7

MCID Analysis of Outcome Measures Between Patients With and Without Chondral Lesions ^a

	Δ (Postoperative PRO – Preoperative PRO) ≥ MCID, %
PROs	With Chondral Lesions (n = 32)	Without Chondral Lesions (n = 22)	P Value
KOOS
Pain	87.5	95.5	.638
Symptoms	96.9	95.5	>.999
ADL	90.6	90.9	>.999
Sport/Rec	96.9	90.9	.560
QoL	100	95.5	.407
IKDC score	96.9	100	>.999
Lysholm score	100	100	>.999
VAS score	100	100	>.999

ADL, Activities of Daily Living; IKDC, International Knee Documentation Committee; KOOS, Knee injury and Osteoarthritis Outcome Score; MCID, minimal clinically important difference; PRO, patient-reported outcome; QoL, Knee-related Quality of Life; Sport/Rec, Sport and Recreation Function; VAS visual analog scale.

Discussion

The most important finding of this study was that arthroscopic treatment for knee SC could achieve satisfactory clinical outcomes at a mean follow-up time of 5.6 years. Arthroscopic treatment was proved to be a valuable option for patients with SC, offering symptom relief and functional improvement. However, there remained a risk of recurrence and reoperations. Additionally, patients with concomitant chondral lesions were found to achieve clinical outcomes and survivorship comparable to those of patients without chondral lesions.

Treatment for knee SC generally involves removal of loose bodies combined with synovectomy, performed either arthroscopically or through open surgery.^4,6,17,27 The traditional open procedure requires an extensive approach, which may lead to persistent joint stiffness and prolonged rehabilitation.⁴ As a result, arthroscopic treatment has become the preferred option for surgeons, offering advantages including less invasiveness, lower morbidity, and faster recovery.^4,6,12 Despite the limited number of patients previously reported in the literature, the efficacy of arthroscopic treatment for SC has been reported to be good to excellent in short- to midterm follow-ups.^4,6,17 The present study aligns with these findings, demonstrating that arthroscopic treatment for knee SC achieves satisfactory mid- to long-term clinical outcomes, as measured by PROs.

Although arthroscopic treatment has been recognized for producing satisfactory clinical outcomes in knee SC, survivorship remains a concern. The recurrence rate after arthroscopic treatment varied in previous studies. Maurice et al¹⁴ reported a recurrence rate of 13.5% in 37 cases of SC at a mean follow-up time of 7 years postoperation. Coolican and Dandy⁴ found that 3 of 18 patients (16.7%) required a second arthroscopic treatment, while Dorfmann et al⁶ reported that 3 of 32 patients (9.4%) needed reoperations for recurrence. In the present study, recurrence was observed in 6 patients (11.1%), with a mean recurrence time of 3.6 years. Of these, only 3 (5.6%) underwent reoperations to excise the recurrent lesions, while the others chose not to undergo a second operation because they had milder symptoms. The survivorship rates free from recurrence and reoperations were 85.1% and 93.9% at 8 years, respectively, which have not been previously reported in the literature. The cause of recurrence remains unclear, and few studies have investigated the factors associated with survivorship. Synovectomy has been recommended along with loose-body removal because the recurrence rate is higher with loose-body removal alone.^4,17 Incomplete synovectomy and inadequate removal of loose bodies during arthroscopy also demonstrate a negative effect on survivorship and clinical outcomes.^5,30 In the present study, shorter duration of symptoms before surgery and lower preoperative KOOS ADL values showed a weak association with recurrence, indicating that patients who experienced recurrence tended to have worse preoperative conditions, more severe symptoms, and shorter tolerance for symptom duration. However, further research in larger cohorts is necessary to better evaluate the risk factors for recurrence and to uncover its underlying causes and mechanisms.

Early diagnosis and treatment of SC are crucial to prevent the occurrence of concomitant lesions.⁸ In the knee, loose bodies typically originate from diseased synovium in the anterior compartment, including the suprapatellar pouch, infrapatellar fat pad, and anterior interval. However, synovial disease can also be diffuse and involve the posterior compartment, which increases the difficulty of surgical treatment.^10,28 Additionally, altered mechanical pressure and subsequent biochemical changes of the synovial fluid in the condition of SC can lead to chondral lesions and progressive degenerative changes over an extended period, significantly limiting management options.¹ However, the diagnosis of SC is often delayed. In the present study, the mean duration between symptom onset and surgery was 42.1 months, which falls within the range of 36 to 54 months reported in previous studies.^14,22

Although the exact cause of SC remains unclear, the destructive pathology of the knee has been documented.^9,26 A delay in diagnosis may lead to cartilage wear, resulting from both mechanical injuries caused by the loose bodies and disruption of the nutrition mechanism of the articular cartilage.²⁴ In the present study, a subset of patients had SC and concomitant chondral lesions observed under arthroscopy. To our knowledge, limited studies have evaluated the potential effects of the presence of chondral lesions. Dorfmann et al⁶ reported that the condition of the tibiofemoral joint cartilage appears to have a correlation with the outcomes. Given the potential influence of concurrent chondral lesions on prognosis, the present study compared the clinical outcomes between patients with and without chondral lesions. Contrary to previous literature, patients with chondral lesions showed comparable outcomes in PROs, MCID, and survivorship rate, despite being significantly older and having a longer duration in symptoms preoperatively. In this study, concomitant chondral lesions were treated with debridement, yielding favorable clinical outcomes. However, the long-term effects of the progression of chondral lesions need to be further investigated in cohorts with extended follow-up.

To our knowledge, this study provides a detailed analysis of mid- to long-term clinical outcomes after arthroscopic treatment for knee SC with a relatively large sample size. The findings indicate that patients with knee SC could benefit from arthroscopic treatment, regardless of the presence of concomitant chondral lesions. These findings may assist surgeons in counseling patients with SC on the expected outcomes of arthroscopic treatment, particularly in cases involving chondral lesions.

Limitations

This study has several limitations. First, because of its retrospective design and reliance on chart review, potential selection, recall, and documentation biases were inevitable. Second, the operations were performed by 5 surgeons, which could potentially affect procedural consistency. However, all surgeons were part of the same team specializing in knee arthroscopy for at least 15 years. Third, patients did not undergo scheduled follow-up MRI studies at predefined intervals, which limited our ability to regularly assess radiological outcomes. Consequently, the true rate of disease recurrence remains unknown. This limitation was primarily due to patients achieving good clinical outcomes and the challenges posed by long travel distances from their residences to the hospital. Future large-scale, long-term prospective studies are needed to further investigate the clinical efficacy of arthroscopic treatment for knee SC and to identify potential risk factors affecting clinical outcomes and survivorship.

Conclusion

Footnotes

Final revision submitted January 12, 2025; accepted March 17, 2025.

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.

Ethical approval for this study was obtained from Peking University Third Hospital Medical Science Research Ethics Committee (M2024707).

ORCID iDs

Zhuohan Cao

Cheng Wang

Jianquan Wang

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