Outcomes by BMI Following Arthroscopic Management of Symptomatic Discoid Lateral Meniscus in Children and Adolescents: A Retrospective Cohort Study With a Minimum 5-Year Follow-Up

Abstract

Background:

While it is well established that obesity alters knee biomechanics, its long-term effects on outcomes following arthroscopic management of discoid lateral meniscus (DLM) remain poorly understood.

Purpose:

To investigate the relationship between body mass index (BMI) and outcomes following arthroscopic treatment of symptomatic children/adolescents with DLM.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

A retrospective review was conducted at a single institution to analyze pediatric and adolescent patients (age range 6-20 years) who underwent arthroscopic treatment for symptomatic DLM with a minimum 5-year follow-up. The cohort was divided into 2 groups based on patients’ BMI: <85th percentile (normal weight) and ≥85th percentile (overweight/obese). Patients underwent either isolated saucerization or saucerization and meniscus repair based on the presence of meniscal instability confirmed intraoperatively. Demographics, clinical presentation, arthroscopic findings and management, complications, rates of return to activity, and patient-reported outcomes (PROs) were collected. PRO measures were interpreted using established instrument-specific thresholds to define clinically acceptable or excellent outcomes. Wilcoxon rank-sum tests were used to compare postoperative PROs between normal-weight and overweight/obese patients.

Results:

Of the 36 patients included, 14 (38.89%) had a BMI <85th percentile and 22 (61.11%) had a BMI ≥85th percentile. No statistically significant differences were found between cohorts for demographics, clinical presentation, meniscus pathology, and surgical technique. PROs were considered acceptable to excellent in both groups after the 5-year follow-up. Comparison between normal-weight and overweight groups demonstrated no significant differences between PROs: Tegner Lysholm (95.00 vs 85.50; P = .974), Pediatric International Knee Documentation Committee (93.00 vs 90.83; P = .536), Knee injury and Osteoarthritis Outcome Score (KOOS)–Symptom (92.26 vs 82.14; P = .586), KOOS-Pain (93.30 vs 87.50; P = .824), KOOS–Activities of Daily Living (98.86 vs 97.73; P = .674), KOOS-Sport (96.43 vs 96.43; P = .755), and KOOS–Quality of Life (87.50 vs 79.16; P = .160). Overall reoperation rate was 8.3%, and 97.2% of patients returned to preinjury levels of activity.

Conclusion:

Overweight/obese pediatric and adolescent patients have comparable acceptable to excellent outcomes to patients who are normal weight at least 5 years following arthroscopic treatment for symptomatic DLM, demonstrating reliable 5-year outcomes regardless of BMI. Weight-related factors should not deter surgical management of overweight or obese patients with symptomatic DLM.

Obesity is a global issue with increasing prevalence, and in the United States, childhood obesity rates have more than tripled since the 1960s and now affect 1 in 5 children.^10,40,48 Obesity is defined by excessive adipose accumulation and is commonly assessed using body mass index (BMI); in pediatrics, BMI is age and sex adjusted (≥85th percentile BMI = overweight, ≥95th percentile BMI = obese). ²⁴ Children with obesity are at greater risk for numerous comorbidities, including asthma, type 2 diabetes, hypertension, metabolic dysfunction–associated steatotic liver disease, and poor mental health outcomes.^4,18,36,44

Obesity affects musculoskeletal development and is associated with slipped capital femoral epiphysis, Blount disease, and altered scoliosis progression. ²⁹ Increased body mass in children correlates with advanced bone age and higher fracture rates despite greater bone mineral density.^12,13,30,34 In the knee, obesity alters biomechanics and kinematics, increasing risk of intra-articular injuries.^26,38 Accordingly, higher BMI has been linked with more frequent complex meniscal tears and concomitant cruciate ligament injuries.^32,35,37,49 However, prior studies examining BMI and outcomes in discoid lateral meniscus (DLM) have been conflicting, with some reporting poorer patient-reported outcomes (PROs) and more cartilage lesions, while others found no association.

DLM is a congenital anatomic variant of the meniscus characterized by a thickened body and disc-like shape. ⁴⁷ Patients with DLM are more prone to instability and tearing due to factors such as increased thickness, abnormal capsular attachments, and histopathologic changes, including poor vascularity and collagen disorganization.^3,7,41 The impact of obesity on DLM presentation and outcomes has been mixed in the literature. Following arthroscopic treatment of symptomatic DLM, BMI has been associated with poorer PROs and an increase in concomitant articular cartilage lesions.^14,45,46 In contrast, other studies have found no association between BMI and clinical outcomes or meniscal extrusion risk in patients with DLM.^23,25 Nonetheless, few studies have investigated the long-term relationship between BMI and outcomes following surgical management of symptomatic DLM.^45,46 The study investigates the relationship between BMI and outcomes of symptomatic pediatric patients with DLM following arthroscopic management, with a minimum 5-year follow-up.

Methods

After receiving institutional review board (IRB #2020-12484; Reference #121491) approval, a retrospective cohort study was conducted at a single academic institution (January 1, 2012, to August 4, 2022). Patients were included if they were <21 years old on the date of surgery, had ≥5 years of follow-up, and underwent arthroscopic treatment for symptomatic DLM. During the study period, 62 patients underwent arthroscopic management of symptomatic DLM. A total of 26 patients had not yet reached 5 years postoperatively and were therefore excluded, leaving 36 patients who met the inclusion criterion of a minimum 5-year clinical follow-up.

Patients were categorized as normal weight (BMI <85th percentile) or overweight/obese (BMI ≥85th percentile) based on age- and sex-specific BMI percentiles at the time of surgery, as defined by the 2022 Centers for Disease Control and Prevention extended BMI-for-age growth charts. ¹⁶ Demographics, including age, sex, ethnicity, Child Opportunity Index 3.0 (COI), and insurance status, were collected from chart review. Skeletal maturity was determined via knee radiographs obtained preoperatively to assess physeal status according to the technique described by Dekhne et al. ¹¹ A review of clinical presentations focused on documented mechanical symptoms, such as locking and catching, and preoperative range of motion (with a focus on extension deficit) was measured by comparing the difference to the contralateral side.

Diagnostic arthroscopy was performed in a standard fashion to evaluate meniscal stability (peripheral rim instability [PRI]) and identify tears. Stable discoid lateral menisci underwent isolated saucerization, while unstable menisci were treated with saucerization and repair. The goal of saucerization was to achieve a residual meniscal rim of at least 8 mm. Posterior PRI was repaired using an all-inside technique (Fast-Fix Flex Meniscal Repair System; Smith & Nephew), and anterior PRI was stabilized with an outside-in technique without implants, as described by Chahla et al. ⁹ All repairs followed the same rehabilitation protocol, including protected weightbearing with a brace locked in extension and early passive range of motion for 6 weeks, followed by progressive strengthening and proprioceptive exercises.

At the 6-month postoperative visit, readiness to return to sports was systematically evaluated. Clinical criteria for clearance included absence of pain, restoration of full range of motion, and completion of a structured rehabilitation program with formal clearance from the treating physical therapist. Functional readiness was assessed through the ability to perform sport-specific activities as well as standardized functional tests, including single-leg squatting and the single-hop test.

All 36 patients had a minimum 5-year clinical follow-up, defined as either an in-person clinic visit or a structured telephone interview. Among these, 22 patients (61.1%) completed standardized PRO instruments at or beyond 5 years postoperatively. The PROs collected included the Tegner Lysholm score, the Pediatric International Knee Documentation Committee (Pedi-IKDC) subjective knee evaluation form, and the Knee injury and Osteoarthritis Outcome Score (KOOS) for Children (KOOS-Child). These instruments have been validated in the literature and measure various aspects of knee function and patient satisfaction.^{5,6,22,27,31,42} Higher scores indicate better outcomes across all PROs. PRO measures were interpreted using established scoring thresholds for each instrument to define clinically acceptable or excellent outcomes (see Table 2 legend for thresholds). These instruments were completed electronically through EPIC during office visits or by telephone, as part of routine research procedures.

Table 2.

Postoperative Patient-Reported Outcome Scores Based on Body Mass Index ^a

Postoperative PRO Scores (n = 22)		BMI		P Value
	Median (IQR)	<85th Percentile (n = 9)	≥85th Percentile (n = 13)
Tegner Lysholm	86.00 (79.50-100.00)	95.00 (81.00-100.00)	85.50 (79.00-100.00)	.974
Pedi-IKDC	92.00 (62.20-96.91)	93.00 (87.38-99.14)	90.83 (60.60-96.29)	.536
KOOS Child Symptom	89.28 (69.43-100.00)	92.26 (83.03-100.00)	82.14 (67.86-100.00)	.586
KOOS Child Pain	92.86 (78.12-100.00)	93.30 (78.91-100.00)	87.50 (78.12-100.00)	.824
KOOS Child ADL	97.73 (80.91-100.00)	98.86 (85.23-100.00)	97.73 (80.00-100.00)	.674
KOOS Child Sport	96.43 (59.82-100.00)	96.43 (78.57-100.00)	96.43 (53.57-100.00)	.755
KOOS Child QOL	79.58 (48.96-91.00)	87.50 (70.83-100.00)	79.16 (33.33-87.50)	.16

^aPostoperative PRO scores at ≥5 years based on BMI. BMI percentile thresholds are age and sex adjusted according to the Centers for Disease Control and Prevention BMI-for-age growth charts. For clinical interpretation: Lysholm scores ≥84 indicate good to excellent outcomes and ≥95 excellent; Pedi-IKDC scores >90 are generally considered near-normal function; KOOS-Child subscale scores ≥75 are typically regarded as clinically acceptable (Patient Acceptable Symptom State threshold). Scores are reported as medians with interquartile ranges (IQR). ADL, activities of daily living; BMI, body mass index; KOOS, Knee injury and Osteoarthritis Outcome Score; Pedi-IKDC, Pediatric International Knee Documentation Committee; PRO, patient-reported outcome; QOL, quality of life.

The remaining 14 patients (38.9%) either declined or were unable to complete the formal PRO questionnaires. To ensure consistent long-term documentation across all contacted patients, these individuals were interviewed by telephone and completed a brief structured functional survey modeled after the Single Assessment Numeric Evaluation. ²⁸ During this standardized interview, patients were asked about pain or mechanical symptoms in the operated knee, any additional surgery on the operated knee, their ability to return to activities or sports and type of activity, their perceived knee function compared with the contralateral knee from 0% (worst) to 100% (completely normal), and their satisfaction with the surgical result on a 0% to 100% scale. This approach ensured that all 36 patients contributed long-term clinical data, with 22 providing complete PROs and 14 providing structured interview responses.

Data were presented as means and standard deviations or medians and interquartile ranges for continuous variables and frequencies and percentages for categorical variables. Demographic differences and weight status were assessed using t tests or Wilcoxon rank-sum tests for continuous variables and chi-square or Fisher exact tests for categorical variables. Wilcoxon rank-sum tests compared PROs between the 2 groups. All statistical analyses were performed using R (version 4.2.1; R Foundation for Statistical Computing). P values of <.05 were considered statistically significant.

Results

In total, 36 met the inclusion criterion of a minimum 5-year clinical follow-up and were included in the analysis (Figure 1). These patients had a mean age at surgery of 13.31 ± 3.82 years, 55.6% were male, 72.2% identified as Hispanic and/or Latino/a, and 83.3% had public insurance. The mean COI was 31.06 ± 30.03, and the average duration of follow-up was 8.08 years (range, 5.03-11.50 years).

Figure 1.

Patient flowchart illustrates the patient selection process for the study.

BMI group classification was determined using age- and sex-specific percentiles at the time of surgery, resulting in 14 patients (38.9%) in the normal-weight group and 22 patients (61.1%) in the overweight/obese group. The total cohort had a median BMI of 23.31 (IQR, 19.34-29.11) and a median BMI percentile of 93.00 (IQR, 64.50-97.00). In the normal-weight group, the median BMI (18.57 vs 27.85; P < .001) and BMI percentile (56.00th vs 95.50th; P < .001) were significantly lower than in the overweight/obese group. There were no significant differences between groups for age, sex, ethnicity, COI, insurance status, skeletal maturity, or length of follow-up (Table 1).

Table 1.

Patient Demographics and Characteristics Based on Body Mass Index ^a

Patient Demographics and Characteristics (N = 36)		BMI
		<85th Percentile (n = 14)	≥85th Percentile (n = 22)	P Value
BMI, median (IQR), kg/m2	23.31 (19.34-29.11)	18.57 (15.98-20.95)	27.85 (25.38-30.09)		<.001
BMI percentile	93.00 (64.50, 97.00)	56.00 (50.25-66.50)	95.50 (93.25-97.00)	<.001
Age at surgery, mean ± SD, y	13.31 ± 3.82	12.07 ± 3.97	14.09 ± 3.60	.124
Sex				.117
Male	20 (55.6)	5 (35.7)	15 (68.2)
Female	16 (44.4)	9 (64.3)	7 (31.8)
Ethnicity				.641
Not Hispanic and/or Latino/a	10 (27.8)	5 (35.7)	5 (22.7)
Hispanic and/or Latino/a	26 (72.2)	9 (64.3)	17 (77.3)
Total COI National Rank	31.06 (30.03)	41.00 (32.98)	24.73 (26.87)	.114
Insurance status				.878
Private	6 (16.7)	3 (21.4)	3 (13.6)
Public	30 (83.3)	11 (78.6)	19 (86.4)
Skeletal maturity				.117
Immature	16 (44.4)	9 (64.3)	7 (31.8)
Mature	20 (55.6)	5 (35.7)	15 (68.2)
Follow-up, y	8.08 (5.96-8.92)	8.09 (6.58-8.40)	7.83 (5.90-9.14)	.538
Mechanical symptoms				>.99
Yes	20 (55.6)	8 (57.1)	12 (54.5)
No	16 (44.4)	6 (42.9)	10 (45.5)
Stability				.196
Stable	19 (52.8)	5 (35.7)	14 (63.6)
Unstable	17 (47.2)	9 (64.3)	8 (36.4)
Chondral lesion				.952
No	32 (88.9)	13 (92.9)	19 (86.4)
Yes	4 (11.1)	1 (7.1)	3 (13.6)
Anterior cruciate ligament injury				>.99
No	33 (91.7)	13 (92.9)	20 (90.9)
Yes	3 (8.3)	1 (7.1)	2 (9.1)
Arthroscopic findings				.621
No tear	7 (19.4)	2 (14.3)	5 (22.7)
Posterior horn and/or body	13 (36.1)	4 (28.6)	9 (40.9)
Anterior horn	9 (25.0)	5 (35.7)	4 (18.2)
Posterior and anterior horn	7 (19.4)	3 (21.4)	4 (18.2)
Arthroscopic management				.349
Saucerization	19 (52.8)	5 (35.7)	14 (63.6)
Posterior repair	2 (5.6)	1 (7.1)	1 (4.5)
Anterior repair	8 (22.2)	5 (35.7)	3 (13.6)
Posterior and anterior repair	7 (19.4)	3 (21.4)	4 (18.2)
Repeat surgery				.680
No	33 (91.7)	12 (85.7)	21 (95.5)
Yes	3 (8.3)	2 (14.3)	1 (4.5)
Return to activity				>.99
No	1 (2.8)	0 (0.0)	1 (4.5)
Yes	35 (97.2)	14 (100.0)	21 (95.5)

^aValues are presented as number (%) unless otherwise indicated. BMI percentile thresholds are age and sex adjusted according to the Centers for Disease Control and Prevention BMI-for-age growth charts. BMI, body mass index; COI, Child Opportunity Index 3.0.

All 36 patients had at least 5 years of clinical follow-up, defined as either an in-person visit or a structured telephone interview. Among these, 22 patients (61.1%) completed standardized PRO questionnaires at a minimum of 5 years postoperatively, while 14 patients (38.9%) declined or did not complete formal PRO forms but provided structured interview responses as described in the Methods. This ensured long-term functional data were available for all patients.

There were no statistically significant differences between BMI groups with respect to preoperative mechanical symptoms (P > .99), intraoperative meniscal stability on probing (P = .196), presence of a chondral lesion (P = .952), concomitant anterior cruciate ligament injury (P > .99), arthroscopic findings (P = .621), or rates of meniscal repair (P = .349) (Table 1).

Among the 22 patients (61%) who completed postoperative PROs after a minimum 5-year follow-up (9 normal weight, 13 overweight/obese), median Tegner Lysholm scores were 95.00 and 85.50, respectively, corresponding to excellent and acceptable categories. Median Pedi-IKDC scores for both cohorts were classified as excellent (93.00 vs 90.83), and all KOOS-Child subscores exceeded the 75.00 threshold for clinically acceptable outcomes. There were no statistically significant differences between normal-weight and overweight/obese groups for the Tegner Lysholm (95.00 vs 85.50; P = .974), Pedi-IKDC (93.00 vs 90.83; P = .536), KOOS-Symptom (92.26 vs 82.14; P = .586), KOOS-Pain (93.30 vs 87.50; P = .824), KOOS–Activities of Daily Living (98.86 vs 97.73; P = .674), KOOS-Sport (96.43 vs 96.43; P = .755), or KOOS–Quality of Life (87.50 vs 79.16; P = .160) scores (Table 2).

Among the 14 patients who did not complete standardized PROs (5 normal weight, 9 overweight/obese), chart review and telephone interview demonstrated that 13 were cleared to return to sport based on the clinical criteria described in the Methods, with 90% to 100% satisfaction based on the Single Assessment Numeric Evaluation score, and 1 patient did not achieve full clearance. This individual was reported to have 80% knee function compared with the contralateral side. For the remaining 13 patients without PROs, chart review and phone interview indicated successful return to activity.

At final follow-up, 35 of 36 patients (97.2%) achieved the clinical criteria for return to full activity. The single patient who did not meet these criteria was in the overweight/obese group; however, there was no statistically significant difference in return-to-activity rates between BMI cohorts (P > .99) (Table 1).

The overall reoperation rate was 8.3% (3 of 36 patients), with 2 patients in the normal-weight group and 1 in the overweight/obese group (P = .680). The first normal-weight patient had recurrent knee pain and swelling 427 days after the initial surgery; arthroscopy revealed a new horizontal cleavage tear at a different location than the original, which had healed successfully. The second normal-weight patient underwent reoperation 2398 days after the initial procedure for drilling of an osteochondral lesion following a new twisting injury, unrelated to the prior operation. The overweight/obese patient required reoperation 517 days postoperatively after sustaining a fall on ice that resulted in a retear of the meniscus.

Discussion

The main finding of this study is that pediatric and adolescent patients with symptomatic DLM who are overweight/obese have comparable acceptable to excellent postoperative outcomes to normal-weight peers at the ≥5-year follow-up after arthroscopic management with a low complication rate (8.3%). These findings support arthroscopic management of DLM as reliable and associated with favorable outcomes regardless of BMI, with an average 8-year follow-up.

Prior studies have investigated the role of BMI on outcomes in patients with DLM. Our findings were consistent with a retrospective review of 73 DLM knees by Lee et al, ²³ which found that BMI did not affect long-term clinical outcomes, including Lysholm knee scores and reoperation rates. Our reoperation rate was lower (8.3% vs 32.9%), and our median postoperative Tegner Lysholm score (86; IQR, 79.50-100.0) was greater than their reported mean postoperative Lysholm score (84.2 ± 14). These differences may be, in part, due to the longer follow-up period (mean follow-up 10.0 vs 8.08 years) and differing patient population: the Lee et al ²³ study took place in Korea with an older patient population (mean 22.2 vs 13.31 years) and a lower mean BMI compared to our patients’ BMI (22.2 vs 24.46 kg/m²). Additionally, our study had incomplete follow-up of PROs, which may also contribute to the differences observed. These factors highlight the importance of our study to investigate this question in a diverse patient population, which in our case focused on a predominantly Hispanic/Latino/a pediatric population in the United States.

Additional studies report associations between BMI and outcomes in patients with DLM in populations varying from ours. Yang et al ⁴⁵ conducted 2 studies in China to determine factors influencing postoperative outcomes in patients with DLM. The first study reviewed 502 patients with DLM at a minimum 5-year follow-up and found on multivariate analysis that BMI <18.5 kg/m² was associated with a better IKDC score compared to patients with a BMI ≥25 kg/m², although no differences in IKDC scores were found between patients with a BMI ranging from 18.5 to 25 kg/m² and patients with a BMI ≥25 kg/m². The median postoperative IKDC score of that study’s total cohort was 87.4 (IQR, 14.6) compared to our median of 92.00 (IQR, 62.20-96.91). The second study, performed on the same cohort, found that BMI was inversely correlated with Ikeuchi grade, indicating that poorer outcomes were linked to a higher BMI. ⁴⁶ In comparison to the cohort used by Yang et al, ⁴⁵ our total cohort had fewer patients (36 vs 502) but a longer median follow-up (8.08 vs 6.3 years), and our patients were younger (age at surgery 13.31 years vs age of symptom onset 32.0 years) and more frequently male (55.6% vs 29.7%). These factors may support the different findings between our study and that of Yang et al. ⁴⁶ In addition, Mochizuki et al ²⁵ sought to determine risk factors for postoperative lateral meniscus extrusion in patients with DLM and found that median BMI did not differ between patients with and without extrusion. This study’s findings parallel our findings by showing that BMI may not influence a postoperative outcome in patients with DLM. In our cohort, we also observed a low reoperation rate, with an average follow-up of 8 years after discoid meniscus saucerization with or without repair. Based on our findings, weight-related factors should not deter surgical management of overweight or obese symptomatic patients with DLM.

Within our overweight/obese cohort, the median BMI was at the 95.50th percentile (IQR, 93.25th-97.00th percentile), which demonstrates that most patients in this cohort met the category of obesity (≥95th percentile) rather than overweight (85th-95th percentile). Compared to other studies investigating the role of obesity in patients with DLM, our patient population has a higher prevalence of overweight/obese patients at a rate of nearly two-thirds^15,45,46 and highlights the importance of exploring the role of obesity specifically in our patient population.

This study has several limitations. First, our sample size, including the number of patients with available PROs, was relatively small, reflecting the rarity of symptomatic discoid lateral meniscus requiring surgical intervention and the challenges of obtaining long-term follow-up.^1,8,19,33,39 This may have limited the statistical power of our analyses, and nonsignificant findings should therefore be interpreted with caution, as clinically meaningful differences may not have been detected. Thus, the lack of statistically significant differences in reoperation rates and PROs may reflect a type II error rather than true equivalence between groups. Second, incomplete follow-up of PROs may introduce bias and limit the generalizability of our results; in particular, our low complication rate compared with the literature may be partially explained by loss to follow-up. Third, radiographic parameters such as hip/knee/ankle angle were not consistently available across the cohort, precluding reliable inclusion of these measures, although all patients were clinically documented as having a neutral mechanical axis. In addition, while the surgical goal of saucerization was to achieve a residual meniscal rim of at least 8 mm, we were unable to quantify the exact rim size postoperatively for every patient. Furthermore, the absence of preoperative PROs limited our ability to calculate the minimal clinically important difference, and BMI was only recorded at the time of surgery and not at final follow-up, which may introduce misclassification, as patient body composition could have changed over the course of the study. Although BMI is a convenient and widely available metric, it does not distinguish adiposity from muscle mass. Other anthropometric measures, such as waist circumference, waist-to-hip ratio, or body composition via dual-energy x-ray absorptiometry, have been shown to more accurately reflect risk in other surgical populations.^2,17,20,21 Accordingly, our results should be interpreted as exploratory and hypothesis-generating, and confirmation in larger, multicenter studies is warranted. Despite these limitations, our study contributes meaningful data by providing an average 8-year follow-up, demonstrating low reoperation rates, and suggesting that weight-related factors should not deter surgical management of overweight or obese symptomatic patients with DLM. ⁴³

We demonstrate that overweight/obese pediatric and adolescent patients have comparable good to excellent outcomes to patients who are normal weight, with a minimum 5-year follow-up (average 8 years), following arthroscopic treatment for symptomatic DLM with a low complication rate (8.3%). Our findings suggest that weight-related factors should not deter surgical management of overweight or obese symptomatic patients with DLM.