Isolated Patellar Chondromalacia Treated With Arthroscopic Chondroplasty Provides Significant Early Improvements in Patient‐Reported Outcomes

Abstract

Purpose

To report 1‐year patient‐reported outcomes in retrospectively reviewed patients who underwent isolated arthroscopic patellar chondroplasty and determine preoperative risk factors for not reaching the Knee Injury and Osteoarthritis Outcome Score (KOOS) Pain subscore patient acceptable symptom state (PASS) threshold.

Methods

From a surgeon's outcomes registry, patients who underwent isolated arthroscopic patellar chondroplasty were identified. Patients were asked to complete the KOOS, Single Assessment Numerical Evaluation, Pain Visual Analog Scale, Marx Activity Rating Scale, and Veterans RAND 12‐Item Health Survey preoperatively and at 3, 6, and 12 months postoperatively. Changes in patient‐reported outcomes over time were assessed with repeated‐measures analysis of variance. Additionally, we quantified the number of patients who met PASS thresholds for KOOS subscales 12 months postoperatively. To determine if patient demographic or surgical variables were predictive of a patient achieving KOOS Pain PASS, a binary logistic regression was done.

Results

Thirty‐nine patients with complete pre‐ and postoperative data were identified and included in the analyses (35 women/4 men, mean age = 31.4 years, mean body mass index = 26.5). Except for Veterans RAND 12‐Item Health Survey Mental Component Scores (P = .33) and Marx Activity Rating Scale scores (P = .11), all other outcome measures significantly improved from baseline to 3 months (P < .001), and results were maintained at 12 months. Most patients achieved KOOS PASS threshold scores at 12 months (Pain: 32/39 patients [82.1%], Symptoms: 24/39 [61.5%], Activities of Daily Living: 30/39 [76.9%], Sport and Recreation Function: 35/39 [89.7%], Knee‐Related Quality of Life: 29/39 [74.4%]). There were no significant preoperative predictive factors for reaching a KOOS Pain PASS threshold.

Conclusions

Isolated patellar chondroplasty provided significant early improvements in patient‐reported outcomes as early as 3 months after surgery, with the majority maintaining PASS at 12 months.

Level of Evidence

Level IV, retrospective case series.

Anterior knee pain is a common knee complaint, of which patellofemoral pain comprises a subset. Patellofemoral chondral lesions are a common finding in patients with anterior knee pain. ¹ Patellofemoral morphology is associated with patellar chondromalacia. ² , ³ The dynamic forces exerted on the patellofemoral articulation by the quadriceps are of critical importance in the treatment of patellofemoral pain. ⁴

Most patients with patellar chondromalacia, high and low grade, can be successfully treated with conservative measures, including activity modification, nonsteroidal anti‐inflammatories, physical therapy, or injections. However, in patients with isolated patellar chondromalacia who have not responded to conservative treatment, arthroscopic patellar chondroplasty can be offered.

Isolated arthroscopic patellar chondroplasty has historically been and remains controversial. ⁵ There is no evidence to suggest that chondroplasty itself will ultimately alter prognosis. Furthermore, removing or shaving down an aneural tissue, like articular cartilage, should theoretically not change pain response. ⁵ , ⁶ Articular cartilage fissuring seen on magnetic resonance imaging may represent either normal or abnormal cartilage, ⁷ which may or may not be symptomatic. Mechanical catching of undersurface patellar fissures and chondromalacia can lead to particulate debris and shear stresses that could induce pain in the knee. Patellofemoral crepitus may not be associated with pain, but painful catching or locking of the patellofemoral joint may represent a surgical indication.

The duration of symptom relief and improvement in patient‐reported outcomes (PROs) after undergoing an isolated patellar chondroplasty is not well understood. The purposes of this study were to report 1‐year PROs in retrospectively reviewed patients who underwent isolated arthroscopic patellar chondroplasty and determine preoperative risk factors for not reaching the Knee Injury and Osteoarthritis Outcome Score (KOOS) Pain subscore patient acceptable symptom state (PASS) threshold. We hypothesized that there would be significant improvements in pain and PROs at the 1‐year postoperative period.

METHODS

From a single surgeon's (E.G.M.) Institutional Review Board‐approved outcomes registry (IRB No. 2024P003333), patients who underwent isolated arthroscopic patellar chondroplasty between September 2012 and July 2023, after failing conservative treatment, were retrospectively reviewed and identified. These patients had trialed months of conservative treatment and self‐selected for surgical intervention; therefore, there was no control or comparison group. Patients were included in the study if they had undergone isolated arthroscopic patellar chondroplasty for a diagnosis of patellar chondromalacia and consented to obtaining PROs. Patients who underwent concomitant procedures or those who had incomplete 1‐year postoperative PROs were excluded. Patients undergoing trochlear chondroplasty at the time of patellar chondroplasty were also excluded (Figure 1).

FIGURE 1.

Flow diagram illustrating study cohort. (PROs, patient‐reported outcomes.)

Demographics and medical history, including smoking status and diabetes, were collected, and patellar Outerbridge grade was assessed intraoperatively. PROs included the following: KOOS comprised of 5 subscales which start with Pain, then Symptoms, followed by Activities of daily living (ADL), then Sport and recreation function (Sport), and finally Knee‐related quality of life (QOL); ⁸ Single Assessment Numerical Evaluation; ⁹ Pain Visual Analog Scale (Pain VAS); ¹⁰ Marx Activity Rating Scale (MARS); ¹¹ and Veterans RAND 12‐Item Health Survey (VR‐12) Mental Component Score (MCS) and Physical Component Score. ¹² These PROs were distributed at the preoperative time point, as well as postoperatively at 3, 6, 12, and 24 months. The primary outcome of this study was to investigate the PRO trend from baseline to 12 months.

Surgery and Postoperative Management

Patients were offered surgery after failing nonoperative treatment, including activity modification, nonsteroidal anti‐inflammatories, physical therapy for proximal muscle strengthening, and optional injection. All patients underwent elective outpatient surgery under general anesthesia without preoperative anesthetic block or tourniquet. Local anesthetic was infiltrated at the beginning and conclusion of the case. Diagnostic arthroscopy confirmed isolated patellar chondromalacia, and chondroplasty with an arthroscopic mechanical shaver was performed. Chondral flaps and loose, fibrillated cartilage were debrided, and the subchondral bone was protected (Figure 2). The goal of the surgery was to smooth unstable edges of patellar cartilage soft spots to reach a stable edge and rim and remove chondral flaps that could potentially induce mechanical symptoms. No marrow stimulation procedures or biological procedures were included. After surgery, patients were instructed to bear weight as tolerated and follow our standardized rehabilitation protocol.

FIGURE 2.

This figure depicts MRI and intraoperative images from a right knee. (A) Axial MRI showing chondromalacia and chondral fissure of the lateral patellar facet. Undersurface patellar chondral fissure with soft surrounding cartilage. (B) Sagittal MRI showing chondromalacia of the lateral patellar facet. (C) Intraoperative visualization of the chondral fissure seen on MRI. Patient in supine position, viewed from the standard anterolateral portal with the probe in the anteromedial portal. (D) On probing, the fissure is unstable. (E) The fissure extends deep and is surrounded by soft, abnormal cartilage. (F) Lesion after mechanical debridement. (MRI, magnetic resonance imaging.)

Statistical Methods

Changes in PROs over time were assessed with repeated‐measures analysis of variance. Additionally, we quantified the number of patients who met previously established PASS thresholds for KOOS subscales 12 months after surgery. ¹³ Repeated‐measures analysis of variance was performed to compare preoperative, 12‐month, and 24‐month results with Holm‐Bonferroni post hoc analyses to identify the location of significant differences. Eventually, a binary logistic regression was performed to determine if age, sex, body mass index, preoperative KOOS Pain score, and Outerbridge grade were predictive of patients achieving a KOOS Pain PASS threshold score at 12 months. No sex disaggregation was performed because of the small sample size. A P value of <.05 determined statistical significance, and SPSS Statistics 29 (IBM, Armonk, NY) was used to execute all analyses.

RESULTS

Between September 2012 and July 2023, a single surgeon (E.G.M.) performed 2133 knee arthroscopies. Within this cohort, there were 86 patients (4.0%) who underwent isolated patellar chondroplasty. A total of 47 patients were excluded for not completing PROs at 1 or more of the study time points, and the analyses were performed for 39 patients with complete preoperative, 3‐month, 6‐month, and 1‐year data (35 women/4 men, mean age = 31.4 years, mean body mass index = 26.5, Table 1). There were 4 patients with grade I chondromalacia, 23 patients with grade II chondromalacia, and 8 and 4 patients with grade III and IV chondromalacia, respectively (Table 1).

TABLE 1.

Demographic Information Regarding Patient Population

Characteristic	N (%), Mean (SD)
Age	31.4 (8.8)
Sex
Female	35
Male	4
BMI	26.5 (6.6)
Outerbridge grade
I	4
II	23
III	8
IV	4
Race
White	35
Black	2
Asian	0
Declined to specify	2
Ethnicity
Hispanic or Latino	0
Not Hispanic or Latino	39
Declined to specify	0
Smoker
Yes	1
No	38
Declined to specify	0
Diabetes diagnosis
Yes	0
No	39
Declined to specify	0

BMI, body mass index; N, total number of subjects in the cohort; SD, standard deviation.

Except for VR‐12 Mental Component Scores (P = .33) and MARS scores (P = .11), all other outcome measures significantly improved from baseline to 3 months (P < .001 for all variables; Table 2, Figure 3), and results were maintained at 12 months. Most patients achieved KOOS PASS threshold scores at 12 months (Pain: 32/39 patients [82.1%], Symptoms: 24/39 [61.5%], ADL: 30/39 [76.9%], Sport: 35/39 [89.7%], QOL: 29/39 [74.4%]; Table 3). Within the subset of patients with complete 2‐year results, PROs at 12 months were maintained at 24 months (Table 4).

TABLE 2.

Changes in PROs From Preoperative Baseline to Postoperative Time Points

Outcome Measure	Baseline	3 mo	6 mo	12 mo
Pain VAS	4.3 ± 1.9	1.8 ± 1.4*	1.7 ± 1.6*	1.6 ± 1.5*
KOOS Pain	58.4 ± 16.3	74.1 ± 14.1*	79.1 ± 13.8* , †	82.5 ± 14.6* , †
KOOS Symptom	59.3 ± 13.7	71.4 ± 16.4*	73.5 ± 15.3*	77.9 ± 14.3*
KOOS ADL	71.3 ± 17.5	85.2 ± 12.1*	88.3 ± 11.1*	90.5 ± 11.1*
KOOS Sport	29.7 ± 20.6	53.9 ± 22.1*	63.8 ± 22.5* , †	71.8 ± 22.0* , † , ‡
KOOS QOL	28.7 ± 15.5	54.3 ± 21.3*	56.4 ± 23.3*	62.7 ± 22.0* , †
SANE	37.5 ± 18.1	67.5 ± 19.4*	75.1 ± 18.2*	76.7 ± 17.5*
VR‐12 PCS	36.9 ± 8.9	Not assessed	45.6 ± 8.8*	48.2 ± 8.6*
VR‐12 MCS	55.0 ± 10.1	Not assessed	53.5 ± 8.3	53.4 ± 9.8
MARS	5.6 ± 5.2	Not assessed	Not assessed	4.3 ± 4.7

ADL, Activities of Daily Living; KOOS, Knee Injury and Osteoarthritis Score; MARS, Marx Activity Rating Scale; MCS, Mental Component Score; mo, months; PCS, Physical Component Score; PROs, patient‐reported outcomes; QOL, Knee‐Related Quality of Life; SANE, Single Assessment Numerical Evaluation; Sport, Sport and Recreation Function; VAS, visual analog scale; VR‐12, Veterans RAND 12‐Item Health Survey.

^∗Significantly different than baseline.

^†Significantly different from 3 months.

^‡Significantly different from 6 months.

FIGURE 3.

Change in KOOS and SANE scores during the first year after isolated patellar chondroplasty. (ADL, Activities of Daily Living; KOOS, Knee Injury and Osteoarthritis Outcome Score; mo, months; Preop, preoperative; QOL, Knee‐Related Quality of Life; SANE, Single Assessment Numerical Evaluation; Sport, Sport and Recreation Function.)

TABLE 3.

Proportion of Patients (%) Who Achieved Patient Acceptable Symptom State Threshold Scores at the Different Study Time Points

KOOS Subscale	Threshold Value	3 mo	6 mo	12 mo
Pain	72.2	24 (61.5%)	28 (71.8%)	32 (82.1%)
Symptom	71.5	22 (56.4%)	20 (51.3%)	24 (61.5%)
ADL	86.8	21 (53.8%)	24 (61.5%)	30 (76.9%)
Sport	43.8	28 (71.8%)	29 (74.4%)	35 (89.7%)
QOL	50	23 (59.0%)	24 (61.5%)	29 (74.4%)

ADL, Activities of Daily Living; KOOS, Knee Injury and Osteoarthritis Score; mo, months; QOL, Knee‐Related Quality of Life; Sport, Sport and Recreation Function.

TABLE 4.

Preoperative, 12‐Month, and 24‐Month PRO Scores for the Subset of Patients With Complete 2‐Year Follow‐Up

Patient‐Reported Outcome Measure	n	Preop	12 mo	24 mo	P Value *
Pain VAS	23	4.6 ± 1.7	1.7 ± 1.5	2.2 ± 2.1	.94
MARS	24	5.2 ± 5.6	3.6 ± 3.6	5.4 ± 4.4	‐
KOOS Pain	22	58.1 ± 15.9	81.3 ± 13.5	84.6 ± 10.4	.41
KOOS Symptom	22	58.9 ± 14.7	76.5 ± 13.8	79.1 ± 13.6	>.99
KOOS ADL	22	72.3 ± 18.1	89.0 ± 11.6	91.9 ± 9.1	.23
KOOS Sport	19	28.1 ± 21.9	69.5 ± 18.3	68.6 ± 19.9	>.99
KOOS QOL	22	28.7 ± 14.5	60.2 ± 21.6	64.5 ± 23.2	.92

ADL, Activities of Daily Living; ANOVA, analysis of variance; KOOS, Knee Injury and Osteoarthritis Score; MARS, Marx Activity Rating Scale; mo, months; Preop, preoperative; PRO, patient‐reported outcome; QOL, Knee‐Related Quality of Life; Sport, Sport and Recreation Function; VAS, visual analog scale.

^∗The repeated‐measures ANOVA was statistically significant for all variables with the exception of the MARS score (P = .11). P values reported in this table represent the pairwise comparisons of 12‐ and 24‐month results.

Pain VAS

Pain VAS scores significantly improved from baseline (4.3 ± 1.9) to 3 months (1.8 ± 1.4). After 3 months, there were no significant improvements in VAS pain scores at the 6‐ and 12‐month postoperative period (Table 2). Twenty‐three patients had complete Pain VAS scores up to 24 months postoperatively, and there was no significant difference between 1‐ and 2‐year scores (P = .94, Table 4). When subanalyzed by grade I and II versus grade III and IV chondromalacia, 77.8% of grade I/II patients met the Pain VAS PASS threshold versus 91.7% in grade III/IV patients.

KOOS Pain

Baseline KOOS Pain scores were 58.4 ± 16.3, which significantly improved to 74.1 ± 14.1 at 3 months. From 3 to 6 months, there was again a significant improvement to 79.1 ± 13.8, but significant difference was not observed between 6 and 12 months (82.5 ± 14.6, Table 2). Overall, 82.1% of patients reached the PASS threshold at 1 year (Table 3). None of the included variables were predictive of a patient's ability to achieve KOOS Pain PASS at 12 months (age, P = .29; sex, P = .13; body mass index, P = .25; preoperative KOOS Pain score, P = .08; Outerbridge grade, P = .26). KOOS Pain scores were not significantly different at 24 months postoperatively compared with 12 months postoperatively (n = 22, P = .41, Table 4).

KOOS Symptom

KOOS Symptom scores significantly improved from 59.3 ± 13.7 at baseline to 71.4 ± 16.4 at 3 months. Although KOOS Symptom scores continued to improve from 3 to 12 months (77.9 ± 14.3), the improvement did not meet statistical significance (Table 2). There were no significant differences in scores between 1 and 2 years postoperatively (n = 22, P > .99, Table 4).

Knee Injury and Osteoarthritis Outcome Score Activities of Daily Living

There was a significant improvement in KOOS ADL scores at 3 months after arthroscopic patellar chondroplasty (85.2 ± 12.1) compared with baseline (71.3 ± 17.5). There was no significant difference in improvements from 3 months up to 12 months (Table 2). Twenty‐two patients completed scores at 2 years postoperatively, and there were no significant differences compared with 1‐year results (P = .23, Table 4).

KOOS Sport

KOOS Sport scores showed significant improvement at all time points compared with the prior. Baseline scores of 29.7 ± 20.6 had increased to 71.8 ± 22.0 at 12 months (Table 2). There were no significant differences at 2 years compared with 1 year (n = 19, P > .99, Table 4).

Knee Injury and Osteoarthritis Outcome Score Knee‐Related Quality of Life

There were significant differences between baseline KOOS QOL scores (28.7 ± 15.5) and scores at 3 months (54.3 ± 21.3). At 12 months, there was again a significant increase (62.7 ± 22.0) compared with the 3‐month scores (Table 2). KOOS QOL scores were not significantly different at 1 and 2 years postoperatively (n = 22, P = .92, Table 4).

Single Assessment Numerical Evaluation

Single Assessment Numerical Evaluation scores showed a significant increase from 37.5 ± 18.1 at baseline to 67.5 ± 19.4 at 3 months. Additional score increases at 6 and 12 months were nonsignificant compared with the 3‐month interval (Table 2).

Veterans RAND 12‐Item Health Survey Physical Component Score

VR‐12 scores were not assessed at the 3‐month postoperative interval, but there were significant differences between the baseline (36.9 ± 8.9) and 6‐month time points (45.6 ± 8.8). These differences were maintained to 12 months postoperatively (48.2 ± 8.6, Table 2).

Veterans RAND 12‐Item Health Survey Mental Component Score

There were no significant differences between baseline, 6‐month, and 12‐month VR‐12 MCS scores (Table 2).

Marx Activity Rating Scale

MARS scores were assessed at baseline and 12 months postoperatively. Preoperative MARS scores decreased from 5.6 ± 5.2 at baseline to 4.3 ± 4.7 at 12 months (Table 2). Nevertheless, this decrease was not significant (P = .11, Table 4). At 2 years postoperatively, MARS scores remain unchanged compared with 1‐year scores (n = 24, Table 4).

DISCUSSION

This study found that patients with isolated patellar chondromalacia, without concomitant procedures, undergoing arthroscopic patellar chondroplasty reported significant improvements in PROs as early as 3 months after surgery, with KOOS subscale PASS thresholds at 12 months reaching 82.1% for Pain, 61.5% for Symptoms, 76.9% for ADL, 89.7% for Sport, and 74.4% for QOL. There were no significant preoperative predictive factors for reaching a KOOS Pain PASS threshold. For the patients with 2‐year follow‐up, the clinical improvements were sustained at that time threshold. In patients who have failed nonoperative treatment of patellar chondromalacia, arthroscopic patellar chondroplasty may be a surgical treatment option able to provide symptomatic relief.

In one of the first studies on the outcomes of arthroscopic patellar chondroplasty, Schonholtz and Ling retrospectively reviewed a cohort of 1083 arthroscopic knee procedures, of which only 41 knees (40 patients) had isolated patellar chondromalacia (3.8%). ⁵ Patient age varied widely from 21 to 76 years, and the average follow‐up was 40 months. In their sample, 10% of patients reported “excellent” results, 39% “good” results, 44% “fair” results, and 7% “poor” results. Overall, 78% of patients stated they would recommend the surgery or consider it again. However, Schonholtz and Ling used different PROs than the current study to determine patient improvement and satisfaction.

Arthroscopic debridement of symptomatic chondromalacia still has a place in the treatment algorithm of high‐grade cartilage lesions, ¹⁴ , ¹⁵ , ¹⁶ but few studies have investigated isolated arthroscopic patellar chondral debridement. Arthroscopic mechanical debridement remains an option for small, low‐grade lesions and may result in short‐term improvement in PROs. ¹⁷ Many early articles on arthroscopic patellar chondroplasty did not include PRO measures. ⁵ , ¹⁸ Federico and Reider in 1997, however, reported on 17 and 19 patients with isolated atraumatic and traumatic patellar chondromalacia, respectively, who underwent arthroscopic debridement and were assessed preoperatively and at the last follow‐up with the Patellofemoral Joint Evaluation Score. ¹⁹ Patients showed significant improvement at the final follow‐up, and patients with traumatic cause tended to fare better than those with atraumatic cause.

Our study followed all patients for up to 1 year postoperatively, and in these patients, we found high KOOS subscale PASS percentages. There were significant improvements in Pain VAS, KOOS subscale scores, Single Assessment Numerical Evaluation, and VR‐12 Physical Component Score at 12 months postoperatively. The only scores that did not reach statistical significance were the VR‐12 MCS and MARS scores, which assess patient mental state and the frequency with which a patient can complete cutting, pivoting, decelerating, and running exercises, respectively. Therefore, either arthroscopic patellar chondroplasty had no bearing on patients’ interpretation of their own mental well‐being based on the VR‐12 MCS results, the instrument was unable to identify a difference, or our study was improperly powered to determine a difference. MARS scores had decreased at 12 months compared with baseline measurements, and although this was not a significant difference in our study, a decreased score may indicate a decreased level or perception of the patient's level of running, cutting, decelerating, and pivoting exercises. Therefore, arthroscopic patellar chondroplasty did not alter patients’ ability to perform these activities at 1‐ or 2‐year follow‐up.

Patellofemoral biomechanics, an interplay of patellofemoral morphology, dynamic stabilization, gait, and femoral rotation, is complex and unique to each patient. Although this study was not designed to assess the cause of patellar chondromalacia, we must recognize that there are a host of underlying contributing factors and these lesions have the ability to progress. ²⁰ How mechanical chondroplasty affects the natural history of chondromalacia is poorly understood and highly debated. Mechanical chondroplasty not only removes damaged cartilage but also likely simultaneously sacrifices a percentage of healthy cartilage. The act of mechanical chondroplasty itself does not appear to induce chondrocyte death outside the zone of penetration, and the metabolic activity of chondrocytes quickly returns to normal. ²¹ Furthermore, the biologic implications and autoimmune response to fragmented cartilage are not well understood, but it is generally recognized that damaged cartilage propagates an inflammatory response within the knee. It remains unclear how mechanical chondroplasty modulates the immune response, and this is an avenue for future research.

What matters most to the patient, however, is how they feel and what they can do with their knee, and isolated arthroscopic patellar chondroplasty for the treatment of patellar chondromalacia appears to allow a subset of patients who have failed conservative treatment to achieve significantly improved PROs at 1 year postoperatively. For many, these results persist until 2 years postoperatively. The presentation of such findings should not be interpreted as advocacy for or against surgical treatment of patellar chondromalacia. The authors support, and regularly practice, an aggressive trial of conservative treatment for patellar chondromalacia, including lower extremity strength and conditioning with or without formal physical therapy, aerobic exercise, activity and lifestyle modifications, bracing in the appropriate context, nonsteroidal anti‐inflammatory medications, topical treatments, and injection therapy. However, in patients with isolated patellar chondromalacia, arthroscopic chondroplasty may represent a surgical option for patients for whom nonoperative treatment has failed to provide clinical relief.

Limitations

Limitations of this study include a small sample size. Additionally, the data for this study was retrospectively obtained from prospectively collected data from a single surgeon, and there is a possibility of inaccurate data collection inherently present in all retrospective studies. Furthermore, we excluded all patients with incomplete 1‐year follow‐up, and we were unable to determine if the severity of chondral lesion impacted postoperative outcomes because only 12 of our participants had either Outerbridge grade III or IV changes, although most patients, 27, had grade I or II changes. Finally, not all patellar chondral defects are created equal. We recognize that the location and size of the defects were not explicitly reported, which may lead to a generalization of the chondral defects treated in our study.

CONCLUSIONS

Isolated patellar chondroplasty provided significant early improvements in PROs as early as 3 months after surgery, with the majority maintaining PASS at 12 months.

DISCLOSURES

The authors (N.S., E.G.M.) declare the following financial interests/personal relationships which may be considered as potential competing interests: N.S. reports a relationship with Arthroscopy: The Journal of Arthroscopic & Related Surgery that includes: editorial board membership. E.G.M. reports a relationship with Arthrex that includes: speaking and lecture fees; and also reports a relationship with the American Academy of Orthopaedic Surgeons that includes serving on the board as second vice president. The other authors (K.Q., J.L.M., C.A.J.) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.