Bipolar lesions of the knee are associated with inferior clinical outcome following articular cartilage regeneration. A propensity score- matched analysis including 238 patients of the German Cartilage Registry (KnorpelRegister DGOU).

Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration for Tibiofemoral Bipolar Lesions Results in Promising Failure Rates: A Systematic Review. Arthrosc Sports Med Rehabil. 2021;3(4):e1227-e1235. Epub 20210624. doi: 10.1016/j.asmr.2021.03.020. PubMed PMID: 34430903; PubMed Central PMCID: PMC8365214.

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). Considering the lack of alternatives especially in young and active patients, there have been ongoing attempts of performing established CR procedures in the presence of BL with variable success rates (

Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration for Tibiofemoral Bipolar Lesions Results in Promising Failure Rates: A Systematic Review. Arthrosc Sports Med Rehabil. 2021;3(4):e1227-e1235. Epub 20210624. doi: 10.1016/j.asmr.2021.03.020. PubMed PMID: 34430903; PubMed Central PMCID: PMC8365214.

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Farr J.

Autologous chondrocyte implantation improves patellofemoral cartilage treatment outcomes.

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Peterson L, Vasiliadis HS, Brittberg M, Lindahl A. Autologous chondrocyte implantation: a long-term follow-up. Am J Sports Med. 2010;38(6):1117-1124. Epub 20100224. doi: 10.1177/0363546509357915. PubMed PMID: 20181804.

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Ossendorf C, Steinwachs MR, Kreuz PC, Osterhoff G, Lahm A, Ducommun PP, et al. Autologous chondrocyte implantation (ACI) for the treatment of large and complex cartilage lesions of the knee. Sports Med Arthrosc Rehabil Ther Technol. 2011;3:11. Epub 20110521. doi: 10.1186/1758-2555-3-11. PubMed PMID: 21599992; PubMed Central PMCID: PMC3114778.

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Vasiliadis HS, Lindahl A, Georgoulis AD, Peterson L. Malalignment and cartilage lesions in the patellofemoral joint treated with autologous chondrocyte implantation. Knee Surg Sports Traumatol Arthrosc. 2011;19(3):452-457. Epub 20100916. doi: 10.1007/s00167-010-1267-1. PubMed PMID: 20845030.

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). In a long-term follow-up study, Ogura et al. reported an overall survival rate of 79% ten years following ACI for the treatment of BL in the patellofemoral (PF) compartment (

Ogura T, Bryant T, Merkely G, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Patellofemoral Compartment: Clinical Outcomes at a Mean 9 Years' Follow-up. Am J Sports Med. 2019;47(4):837-846. Epub 20190213. doi: 10.1177/0363546518824600. PubMed PMID: 30758979.

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). The best survival rate was observed when concomitant tibial tubercle osteotomy was performed (

Ogura T, Bryant T, Merkely G, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Patellofemoral Compartment: Clinical Outcomes at a Mean 9 Years' Follow-up. Am J Sports Med. 2019;47(4):837-846. Epub 20190213. doi: 10.1177/0363546518824600. PubMed PMID: 30758979.

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). In another study including young patients with early knee OA, Minas et al. reported relevant clinical improvement and pain reduction five years after ACI (

18

Minas T, Gomoll AH, Solhpour S, Rosenberger R, Probst C, Bryant T. Autologous chondrocyte implantation for joint preservation in patients with early osteoarthritis. Clin Orthop Relat Res. 2010;468(1):147-157. Epub 20090804. doi: 10.1007/s11999-009-0998-0. PubMed PMID: 19653049; PubMed Central PMCID: PMC2795849.

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). Two recent systematic reviews concluded that CR procedures might even delay the need for secondary arthroplasty in patients with BL both in the tibiofemoral (TF) and PF compartments (

Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration for Tibiofemoral Bipolar Lesions Results in Promising Failure Rates: A Systematic Review. Arthrosc Sports Med Rehabil. 2021;3(4):e1227-e1235. Epub 20210624. doi: 10.1016/j.asmr.2021.03.020. PubMed PMID: 34430903; PubMed Central PMCID: PMC8365214.

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Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration of Bipolar Lesions Within the Patellofemoral Joint Delays Need for Arthroplasty: A Systematic Review of Rates of Failure. Arthrosc Sports Med Rehabil. 2021;3(4):e1189-e1197. Epub 20210614. doi: 10.1016/j.asmr.2021.02.001. PubMed PMID: 34430900; PubMed Central PMCID: PMC8365210.

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). Furthermore, a high percentage of subjective patient satisfaction was reported (

15

Ossendorf C, Steinwachs MR, Kreuz PC, Osterhoff G, Lahm A, Ducommun PP, et al. Autologous chondrocyte implantation (ACI) for the treatment of large and complex cartilage lesions of the knee. Sports Med Arthrosc Rehabil Ther Technol. 2011;3:11. Epub 20110521. doi: 10.1186/1758-2555-3-11. PubMed PMID: 21599992; PubMed Central PMCID: PMC3114778.

Google Scholar

,

Ogura T, Bryant T, Mosier BA, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Tibiofemoral Compartment. Am J Sports Med. 2018;46(6):1371-1381. Epub 20180313. doi: 10.1177/0363546518756977. PubMed PMID: 29533678.

Google Scholar

). However, the available evidence is predominantly based on case series with a considerable heterogeneity of study populations, concomitant procedures and reported outcome measures. In one of the rare studies including a control group, Hannon et al. concluded that femoral OCA for the treatment of bipolar TF lesions provided comparable clinical outcomes to OCA for isolated femoral lesions (

21

Hannon CP, Weber AE, Gitelis M, Meyer MA, Yanke AB, Cole BJ. Does Treatment of the Tibia Matter in Bipolar Chondral Defects of the Knee? Clinical Outcomes with Greater Than 2 Years Follow-up. Arthroscopy. 2018;34(4):1044-1051. Epub 20171128. doi: 10.1016/j.arthro.2017.09.040. PubMed PMID: 29195732.

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). Nevertheless, the inclusion of patients who underwent combined procedures, such as meniscus transplantation, complicates a precise assessment of the performance of CR for BL. To the best of our knowledge, there are only two case series reporting outcomes of CR for BL without concomitant procedures (

22

Torga Spak R
Teitge RA

Fresh osteochondral allografts for patellofemoral arthritis: long-term followup.

,

Yabumoto H, Nakagawa Y, Mukai S, Saji T. Osteochondral autograft transplantation for isolated patellofemoral osteoarthritis. Knee. 2017;24(6):1498-1503. Epub 20170930. doi: 10.1016/j.knee.2017.07.016. PubMed PMID: 28970117.

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). These studies reported a relief of symptoms and therefore a potential delay of secondary arthroplasty following osteochondral autograft transfer system (OATS) and OCA for PF OA in small case series of 7 and 12 patients, respectively (

22

Torga Spak R
Teitge RA

Fresh osteochondral allografts for patellofemoral arthritis: long-term followup.

,

Yabumoto H, Nakagawa Y, Mukai S, Saji T. Osteochondral autograft transplantation for isolated patellofemoral osteoarthritis. Knee. 2017;24(6):1498-1503. Epub 20170930. doi: 10.1016/j.knee.2017.07.016. PubMed PMID: 28970117.

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). In summary, while a few studies suggest reasonable clinical outcome, the available data is insufficient for a final conclusion. The purpose of the study was to determine if BL are associated with inferior clinical outcome following CR compared to UL. We hypothesized that patients with BL would show inferior clinical outcome following CR as compared to those with unipolar lesions (UL).

Methods

This study analyzed data from the German Cartilage Registry (KnorpelRegister DGOU) which is an observational multi-center registry of patients assigned for CR of the knee. The registry is conducted in accordance with the Declaration of Helsinki and registered at germanctr.de (DRKS00005617). The current study was approved by the Institutional Review Board of the Albert-Ludwigs-University Freiburg: EK-FR 105/13_130795).

We performed a registry-based, propensity-score matched analysis of patients who underwent CR for focal cartilage lesions of the knee. Propensity-score matching strives to match patients based on their propensity to exhibit a specific characteristic (e.g., bipolar cartilage lesion) by accounting for covariates that predict this characteristic. Participants were assessed by a board-certified orthopedic surgeon upon inclusion to the registry. Patients with lesions in the PF or TF compartment of the knee and available status of the opposing cartilage (OC, i.e., opposite to the index lesion) were included (Figure 1). Patients with concomitant procedures (i.e. osteotomy, ligament reconstruction, etc.) were excluded. Patients with a Kellgren-Lawrence-Score (KL) > 2 were not eligible for CR. Patients were stratified into two groups according to the lesion type of the OC. Lesions with intact OC were considered unipolar lesions (UL) and lesions with a full-thickness defect of the OC bipolar lesions (BL).

Figure thumbnail gr1 — Figure 1Flowchart demonstrating patient selection and matching. Knee Injury and Osteoarthritis Outcome Score (KOOS), Propensity Score Matching (PSM), Body-Mass-Index (BMI)
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Outcome Measures

The Knee Injury and Osteoarthritis Outcome Score (KOOS) at the time of surgery, as well as 6, 12, 24 and 36 months postoperatively served as primary outcome measure (

24

Roos EM, Lohmander LS. The Knee injury and Osteoarthritis Outcome Score (KOOS): from joint injury to osteoarthritis. Health Qual Life Outcomes. 2003;1:64. Epub 20031103. doi: 10.1186/1477-7525-1-64. PubMed PMID: 14613558; PubMed Central PMCID: PMC280702.

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Bekkers JE, de Windt TS, Raijmakers NJ, Dhert WJ, Saris DB. Validation of the Knee Injury and Osteoarthritis Outcome Score (KOOS) for the treatment of focal cartilage lesions. Osteoarthritis Cartilage. 2009;17(11):1434-1439. Epub 20090507. doi: 10.1016/j.joca.2009.04.019. PubMed PMID: 19454278.

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). First, we report overall KOOS and intergroup differences (Delta KOOS) as in previous studies (

26

Seiferth NL
Faber SO
Angele P
Kniffler H
Loer I
Schauf G
et al.

Effect of Previous Knee Surgery on Clinical Outcome After ACI for Knee Cartilage Defects: A Propensity Score-Matched Study Based on the German Cartilage Registry (KnorpelRegister DGOU).

,

27

Kim SJ, Shetty AA, Kurian NM, Ahmed S, Shetty N, Stelzeneder D, et al. Articular cartilage repair using autologous collagen-induced chondrogenesis (ACIC): a pragmatic and cost-effective enhancement of a traditional technique. Knee Surg Sports Traumatol Arthrosc. 2020;28(8):2598-2603. Epub 20200217. doi: 10.1007/s00167-020-05884-y. PubMed PMID: 32064573.

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).Differences in KOOS-subcomponents were then calculated in the further analysis. Secondary outcome measures inculded the clinical response rate which was defined as the percentage of patients reaching the minimal clinically important difference (MCID). The MCID for the overall KOOS was estimated to 10 based on recent literature (

28

Ogura T, Ackermann J, Barbieri Mestriner A, Merkely G, Gomoll AH. Minimal Clinically Important Differences and Substantial Clinical Benefit in Patient-Reported Outcome Measures after Autologous Chondrocyte Implantation. Cartilage. 2020;11(4):412-422. Epub 20180915. doi: 10.1177/1947603518799839. PubMed PMID: 30221977; PubMed Central PMCID: PMC7488950.

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). Furthermore, failure rates and time to failure were analyzed. CR failure was defined as any kind of revision surgery within the follow-up period.

Matching and Statistical Analysis

To reduce bias of potential confounders on clinical outcome, we performed a 1:1 nearest neighbor propensity score matching with replacement including UL and BL groups, based on the variables age, sex, body-mass-index (BMI), number of previous surgeries, lesion localization and lesion size. A matching tolerance of 0.00015 was determined to obtain groups with similar baseline characteristics. We applied prioritization for exact matching, without minimization of memory and with shuffling activated. Thereby, two groups including 119 patients with balanced baseline characteristics could be obtained (figure 1).

Kaplan-Meier survival-analysis was applied to compare the estimated mean time to failure between both groups, based on the prevalence and time of revision surgery (event) during the follow-up period. If no revision surgery was reported, the time of the last follow-up was noted.

Chi-square test was used to compare distribution of categorial variables (sex, number of previous surgeries category, lesion localization, failure rate) between the two groups according to lesion type (UL vs. BL). Unpaired t-tests were performed to compare continuous variables between UL and BL groups. Levene’s test was used to assess homoscedasticity. In case of heteroscedasticity, Welch’s test was used, and respective p-values reported accordingly.

We performed a post-hoc power analysis to determine the validity of our findings. At an estimated effect size of ω = .386, an available patient number of n = 131 at 24 months postoperatively and α set to .05, the calculated statistical power to detect an underlying difference regarding KOOS was 69.9%. At an estimated effect size of ω = .155, an available patient number of n = 212 and α set to .05, the calculated statistical power to detect an underlying difference of failure rates was 61.9%.

P-values < .05 were considered statistically significant. Bonferroni correction was applied to account for accumulation of alpha-errors within the KOOS sub-component analysis. The resulting adjusted level of significance was .01. All statistical analyses were performed in SPSS Version 27.0 (IBM, Armonk, USA) and G*Power 3.1 (Heinrich Heine Universität, Düsseldorf, Germany).

Results

Descriptive Analysis

Two groups, each consisting of 119 patients with similar baseline characteristics, were matched (Table 1). The mean age was 36.79 (11.41) with 54.2% male patients. The average BMI was 25.76 kg/m² which is almost within normal limits according to WHO criteria and is comparable to populations of previous studies (

Ogura T, Bryant T, Merkely G, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Patellofemoral Compartment: Clinical Outcomes at a Mean 9 Years' Follow-up. Am J Sports Med. 2019;47(4):837-846. Epub 20190213. doi: 10.1177/0363546518824600. PubMed PMID: 30758979.

Google Scholar

,

Ogura T, Bryant T, Mosier BA, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Tibiofemoral Compartment. Am J Sports Med. 2018;46(6):1371-1381. Epub 20180313. doi: 10.1177/0363546518756977. PubMed PMID: 29533678.

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). No significant inter-group differences were found regarding these baseline parameters. The mean follow-up time in the UL group was 25.79 (6-60) and 30.01 (6-60) months in the BL group (p = .090). The follow-up rate was 64.7% in the BL and 45.4% in the UL group at 24 months following CR and is within the range of previous registry-based studies (

29

Fauno P, Rahr-Wagner L, Lind M. Risk for Revision After Anterior Cruciate Ligament Reconstruction Is Higher Among Adolescents: Results From the Danish Registry of Knee Ligament Reconstruction. Orthop J Sports Med. 2014;2(10):2325967114552405. Epub 20141008. doi: 10.1177/2325967114552405. PubMed PMID: 26535272; PubMed Central PMCID: PMC4555549.

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Granan LP, Baste V, Engebretsen L, Inacio MC. Associations between inadequate knee function detected by KOOS and prospective graft failure in an anterior cruciate ligament-reconstructed knee. Knee Surg Sports Traumatol Arthrosc. 2015;23(4):1135-1140. Epub 20140312. doi: 10.1007/s00167-014-2925-5. PubMed PMID: 24619491.

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).

Table 1Patient baseline characteristics after matching

	UL (n = 119)	BL (n = 119)	P
Age (years)	37.87 (11.48)	35.71 (11.29)	.143
Gender m/f	53.78% male	54.62% male	.896
BMI (kg/m²)	26.25 (4.07)	25.76 (4.31)	.372
Lesion size (mm²)	355.43 (173.66)	385.66 (314.69)	.360
Lesion localization	PF		TF		PF		TF
	41.18%		58.82%		51.26%		48.74%		.119
No. of previous surgeries	0	1-2		>2	0	1-2		>2
	58.82%	40.34%		.84%	49.58%	48.74%		1.68%	.330

Unipolar (UL) and bipolar lesion (BL) groups, Body Mass Index (BMI), patellofemoral (PF), tibiofemoral (TF)

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Procedure Types

The most frequently applied CR procedure for the primary lesion was ACI with 63.0% and 46.2% for the UL and BL group, respectively (Table 5). Although the type of CR procedure was not included in the matching algorithm there were no significant differences regarding the distribution between groups (p = .169). In 69.8% (83/119) of the cases with bipolar cartilage lesions the opposing (secondary) lesion was treated simultaneously. ACI was also the most frequently performed procedure for treatment of the opposite lesion with 66.3%, followed by bone-marrow-stimulation in 13.3% of the cases.

Table 5Percentage type of articular cartilage regeneration regarding index lesion of matched groups

	UL (%)	BL (%)	P
ACI	57.6	44.5	.169
BMS	11.0	15.1
ACI + Bone Grafting	5.9	1.7
OCT	0.8	4.2
Matrix-BMS	1.7	1.7
Debridement	0.8	0.8
Other	12.7	18.5
More than one	9.3	13.4

Percentage of each type of articular cartilage regeneration procedure performed per group. Unipolar lesions (UL), bipolar lesions (BL), Autologous Chondrocyte Implantation (ACI), Bone Marrow Stimulation (BMS), Osteochondral Transfer (OCT),

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Clinical Outcome

Patients with BL had significantly worse overall KOOS at 24 months as compared to those with UL (p = .028). At all other follow-ups the difference of overall KOOS was not statistically significant, although patients with UL generally showed slightly higher KOOS, except at baseline (Table 2, Figure 2).

Table 2Mean KOOS scores at different follow-ups of matched groups

	N (unipolar/bipolar)	Unipolar	Bipolar	P
Baseline	119/119	54.55 (16.14)	58.18 (17.00)	.093
6 months	81/89	69.68 (15.43)	69.62 (16.43)	.979
12 months	67/93	73.33 (14.71)	68.59 (17.75)	.101
24 months	54/77	76.39 (14.96)	69.83 (18.83)	.028*
36 months	32/37	80.61 (10.48)	77.56 (13.70)	.310

Number of patients available at follow-up per group (n = unipolar/bipolar), Mean (SD), p-values are presented of t-tests for independent samples, p < .05 (*), Knee Injury and Osteoarthritis Outcome Score (KOOS)

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Figure thumbnail gr2 — Figure 2Overall KOOS of unipolar (UL) vs. bipolar lesions (BL) at baseline, 6 months (6m), 12 months (12m), 24 months (24m) and 36 months (36m) following articular cartilage regeneration. p < .05 (*), 95% CI (whiskers), mean (+)
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There was a significant difference of KOOS improvement between the UL and BL group at all follow-ups in favor of patients with UL (Table 3, Figure 3). The clinical response rate (percentage of patients reaching MCID) in the BL group did not show a significant difference at 12 months (53.8% vs. 65.7%, p = .131), but was significantly lower at 24 months (45.5% vs. 64.8%, p = .029).

Table 3Delta KOOS at different follow-ups of matched groups

	Unipolar (n = 119)	Bipolar (n = 119)	P
Baseline – 6 months	15.89 (16.01)	10.28 (15.17)	.020*
Baseline – 12 months	17.76 (16.40)	10.66 (16.00)	.007*
Baseline – 24 months	19.35 (16.62)	11.30 (13.97)	.003*
Baseline – 36 months	26.00 (16.12)	16.63 (17.29)	.024*

Mean (SD), p-values are presented of t-tests for independent samples, p < .05 (*), Knee Injury and Osteoarthritis Outcome Score (KOOS),

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Figure thumbnail gr3 — Figure 3Delta KOOS of unipolar (UL) vs. bipolar lesions (BL) at 6 months (6m), 12 months (12m), 24 months (24m), 36 months (36m) following articular cartilage regeneration, unipolar vs. bipolar lesions. p < .05 (*), 95% CI (whiskers), mean (+)
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Differences regarding KOOS sub-components were calculated at all follow-ups. Patients with BL had significantly worse symptoms at 12 months (67.30 [17.07] vs. 74.9 [15.42], p = .003) and 36 months (67.09 [15.94] vs. 78.01 [12.59], p = .001), as well as significantly worse pain at 24 months (70.71 [18.81] vs. 80.13 [14.78], p = .002) following CR. A complete overview of p-values regarding inter-group differences in KOOS sub-components is provided in Table 4. For the 12- and 24-months follow-up the differences of KOOS sub-components are visualized in Figure 4 and Figure 5.

Table 4KOOS sub-component analysis (unipolar vs. bipolar group)

	Pain	Symptoms	ADL	QoL	Sports/Rec
Baseline	.050	.605	.047	.248	.114
6 months	.232	.119	.333	.590	.632
12 months	.012	.003*	.809	.286	.130
24 months	.002*	.072	.126	.045	.074
36 months	.028	.001*	.118	.677	.161

P-values of unpaired t-tests regarding differences of KOOS sub-components between patients with unipolar (UL) and bipolar lesions (BL) in favor of UL. Adjusted level of significance α = .01, p < .01 (*), Knee Injury and Osteoarthritis Outcome Score (KOOS), Activities of Daily Living (ADL), Quality of Life (QoL), Sports and Recreational Activities (Sports/Rec)

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Figure thumbnail gr4 — Figure 4KOOS sub-components of unipolar (UL) vs. bipolar lesion (BL) groups at 12 months postoperatively. Activities of Daily Living (ADL), Quality of Life (QoL), Sports and Recreational Activities (Sports/Rec), p < .05 (*)
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Figure thumbnail gr5 — Figure 5KOOS sub-components of unipolar (UL) vs. bipolar lesion (BL) groups at 24 months postoperatively. Activities of Daily Living (ADL), Quality of Life (QoL), Sports and Recreational Activities (Sports/Rec), p < .05 (*)
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Failure Rates and Time to Failure

The overall CR failure rate in the present population was 6.1% (13/212). The failure rate in the BL group was higher at 8.2% (9/110) as compared to the UL group at 3.9% (4/98), however, this difference was statistically not significant (p = .256). The observed mean time to failure in the BL group was 17.44 (4.69) as compared to 32.33 (15.18) months in the UL group (p = .229). The estimated mean time to failure according to a Kaplan-Meier survival-analysis was 55.24 (1.52) months in the BL group and 57.70 (1.28) months in the UL group (p = .195).

Discussion

The most remarkable finding of our present study was that patients with BL demonstrated an ongoing clinical improvement following CR up to 36 months postoperatively. Despite a tendency towards inferior overall KOOS in the BL group, which was statistically significant at 24 months, the difference did not exceed the reported threshold of MCID at any follow-up (

28

Ogura T, Ackermann J, Barbieri Mestriner A, Merkely G, Gomoll AH. Minimal Clinically Important Differences and Substantial Clinical Benefit in Patient-Reported Outcome Measures after Autologous Chondrocyte Implantation. Cartilage. 2020;11(4):412-422. Epub 20180915. doi: 10.1177/1947603518799839. PubMed PMID: 30221977; PubMed Central PMCID: PMC7488950.

Google Scholar

). However, KOOS improvement from baseline was significantly lower in the BL group at all follow-ups.

Only a few studies reported on the average BL size which was between 5.2 and 5.3cm² in two studies on PF lesions and between 3.4 and 8.3cm² for TF lesions (

Ogura T, Bryant T, Merkely G, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Patellofemoral Compartment: Clinical Outcomes at a Mean 9 Years' Follow-up. Am J Sports Med. 2019;47(4):837-846. Epub 20190213. doi: 10.1177/0363546518824600. PubMed PMID: 30758979.

Google Scholar

,

Ogura T, Bryant T, Mosier BA, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Tibiofemoral Compartment. Am J Sports Med. 2018;46(6):1371-1381. Epub 20180313. doi: 10.1177/0363546518756977. PubMed PMID: 29533678.

Google Scholar

,

31

Jamali AA, Emmerson BC, Chung C, Convery FR, Bugbee WD. Fresh osteochondral allografts: results in the patellofemoral joint. Clin Orthop Relat Res. 2005;NA(437):176-185. doi: 10.1097/01.blo.0000165854.15579.85. PubMed PMID: 16056047.

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). At an average lesion size in the BL group of 4.2cm² for PF and 3.4cm² for TF lesions, patients in the present study had relatively small lesions. This is perhaps related to the various CR procedures included in the present study, in contrast to ACI and OCA, which are usually used for larger lesions and were exclusively performed in the referred studies.

Most of the available data is based on case series, with many studies suggesting that patients with BL benefit from surgery (

16

Vasiliadis HS, Lindahl A, Georgoulis AD, Peterson L. Malalignment and cartilage lesions in the patellofemoral joint treated with autologous chondrocyte implantation. Knee Surg Sports Traumatol Arthrosc. 2011;19(3):452-457. Epub 20100916. doi: 10.1007/s00167-010-1267-1. PubMed PMID: 20845030.

Google Scholar

,

Ogura T, Bryant T, Merkely G, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Patellofemoral Compartment: Clinical Outcomes at a Mean 9 Years' Follow-up. Am J Sports Med. 2019;47(4):837-846. Epub 20190213. doi: 10.1177/0363546518824600. PubMed PMID: 30758979.

Google Scholar

,

Ogura T, Bryant T, Mosier BA, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Tibiofemoral Compartment. Am J Sports Med. 2018;46(6):1371-1381. Epub 20180313. doi: 10.1177/0363546518756977. PubMed PMID: 29533678.

Google Scholar

,

Yabumoto H, Nakagawa Y, Mukai S, Saji T. Osteochondral autograft transplantation for isolated patellofemoral osteoarthritis. Knee. 2017;24(6):1498-1503. Epub 20170930. doi: 10.1016/j.knee.2017.07.016. PubMed PMID: 28970117.

Google Scholar

,

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Gomoll AH, Gillogly SD, Cole BJ, Farr J, Arnold R, Hussey K, et al. Autologous chondrocyte implantation in the patella: a multicenter experience. Am J Sports Med. 2014;42(5):1074-1081. Epub 20140304. doi: 10.1177/0363546514523927. PubMed PMID: 24595400.

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). In a recent review, Melugin et al. concluded that CR of BL can achieve short- and mid-term clinical improvement and is associated with a low rate of major complications (

33

Melugin HP, Bernard CD, Camp CL, Saris DBF, Krych AJ. Bipolar Cartilage Lesions of the Knee: A Systematic Review of Techniques, Outcomes, and Complications. Cartilage. 2021;13(1_suppl):17S-30S. Epub 20190616. doi: 10.1177/1947603519855761. PubMed PMID: 31204486; PubMed Central PMCID: PMC8808778.

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). Our analysis supports this finding, in that patients with BL demonstrated an ongoing clinical improvement up to 36 months following CR. Ogura et al. reported a 76% ACI graft survival and excellent patient satisfaction when grafts were retained, even at ten years following ACI for BL in the tibiofemoral compartment (

Ogura T, Bryant T, Mosier BA, Minas T. Autologous Chondrocyte Implantation for Bipolar Chondral Lesions in the Tibiofemoral Compartment. Am J Sports Med. 2018;46(6):1371-1381. Epub 20180313. doi: 10.1177/0363546518756977. PubMed PMID: 29533678.

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). Though, in most of the included cases concomitant osteotomy was performed which obscures the effect of ACI in these patients. Moreover, there was no control group. These are two issues that are frequently encountered in the available literature and underline the significance of the present study (

Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration for Tibiofemoral Bipolar Lesions Results in Promising Failure Rates: A Systematic Review. Arthrosc Sports Med Rehabil. 2021;3(4):e1227-e1235. Epub 20210624. doi: 10.1016/j.asmr.2021.03.020. PubMed PMID: 34430903; PubMed Central PMCID: PMC8365214.

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Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration of Bipolar Lesions Within the Patellofemoral Joint Delays Need for Arthroplasty: A Systematic Review of Rates of Failure. Arthrosc Sports Med Rehabil. 2021;3(4):e1189-e1197. Epub 20210614. doi: 10.1016/j.asmr.2021.02.001. PubMed PMID: 34430900; PubMed Central PMCID: PMC8365210.

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Melugin HP, Bernard CD, Camp CL, Saris DBF, Krych AJ. Bipolar Cartilage Lesions of the Knee: A Systematic Review of Techniques, Outcomes, and Complications. Cartilage. 2021;13(1_suppl):17S-30S. Epub 20190616. doi: 10.1177/1947603519855761. PubMed PMID: 31204486; PubMed Central PMCID: PMC8808778.

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).

Hannon et al. concluded that femoral OCA for the treatment of bipolar TF lesions provided comparable clinical outcomes to OCA for isolated femoral lesions, in one of the rare comparative studies (

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Hannon CP, Weber AE, Gitelis M, Meyer MA, Yanke AB, Cole BJ. Does Treatment of the Tibia Matter in Bipolar Chondral Defects of the Knee? Clinical Outcomes with Greater Than 2 Years Follow-up. Arthroscopy. 2018;34(4):1044-1051. Epub 20171128. doi: 10.1016/j.arthro.2017.09.040. PubMed PMID: 29195732.

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). Still, the significance of this finding is questionable as many of the included patients underwent concomitant lateral or medial meniscus transplant and patients with isolated femoral lesions were younger than those with BL. In our study, ACI was the most frequently applied procedure both in the PF and TF compartment, which complicates a direct comparison. Nevertheless, we think that our findings support the conclusion by Hannon et al., showing that the observed detrimental effect of BL on clinical outcome might not generally justify the exclusion of these patients from CR.

Delta KOOS demonstrated significantly lower improvement in the BL group at all follow-ups. The clinical response rate, which was defined as the percentage of patients reaching the threshold of MCID, was lower in the BL group with 53.8% and 45.5%, as compared to 65.7% and 64.8% in the UL group at 12 and 24 months, respectively. This discrepancy yielded statistical significance at 24 months and demonstrated compromised chances of gaining clinically relevant improvement for patients with BL, although average overall KOOS scores suggested a negligible difference. The overall low clinical response rate in the present study- even in the UL group- might be related to the heterogeneous types of CR procedures included. Nevertheless, these findings partly contradict the data reported by Minas et al. who found clinically relevant improvement in most patients undergoing ACI for early knee OA (

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Minas T, Gomoll AH, Solhpour S, Rosenberger R, Probst C, Bryant T. Autologous chondrocyte implantation for joint preservation in patients with early osteoarthritis. Clin Orthop Relat Res. 2010;468(1):147-157. Epub 20090804. doi: 10.1007/s11999-009-0998-0. PubMed PMID: 19653049; PubMed Central PMCID: PMC2795849.

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). However, concurrent correction of TF malalignment and patellar maltracking were performed in most of these cases. Hence, the comparability of data is limited.

The present data show a tendency towards higher failure rates in patients with BL as compared to UL. While there was no statistical significance, a post-hoc analysis demonstrated that this calculation was most likely underpowered to detect an underlying difference. It should also be mentioned that surgeons might be more likely to perform revision surgery in patients following CR of UL as compared to more complex injuries (i.e., BL), which must be considered when comparing the failure rates. Finally, the survival-analysis demonstrated an estimated time to failure of 4.6 years in the BL groups which compares well to the range of 2.7 to 8.9 years reported in the literature (

Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration for Tibiofemoral Bipolar Lesions Results in Promising Failure Rates: A Systematic Review. Arthrosc Sports Med Rehabil. 2021;3(4):e1227-e1235. Epub 20210624. doi: 10.1016/j.asmr.2021.03.020. PubMed PMID: 34430903; PubMed Central PMCID: PMC8365214.

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Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration of Bipolar Lesions Within the Patellofemoral Joint Delays Need for Arthroplasty: A Systematic Review of Rates of Failure. Arthrosc Sports Med Rehabil. 2021;3(4):e1189-e1197. Epub 20210614. doi: 10.1016/j.asmr.2021.02.001. PubMed PMID: 34430900; PubMed Central PMCID: PMC8365210.

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).

We managed to overcome considerable shortcomings of previous publications, which frequently included patients with combined procedures, were lacking control groups or had a very low case number (

Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration for Tibiofemoral Bipolar Lesions Results in Promising Failure Rates: A Systematic Review. Arthrosc Sports Med Rehabil. 2021;3(4):e1227-e1235. Epub 20210624. doi: 10.1016/j.asmr.2021.03.020. PubMed PMID: 34430903; PubMed Central PMCID: PMC8365214.

Google Scholar

,

Gowd AK, Weimer AE, Rider DE, Beck EC, Agarwalla A, O'Brien LK, et al. Cartilage Restoration of Bipolar Lesions Within the Patellofemoral Joint Delays Need for Arthroplasty: A Systematic Review of Rates of Failure. Arthrosc Sports Med Rehabil. 2021;3(4):e1189-e1197. Epub 20210614. doi: 10.1016/j.asmr.2021.02.001. PubMed PMID: 34430900; PubMed Central PMCID: PMC8365210.

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Torga Spak R
Teitge RA

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