The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 94, Issue 11

Scientific Articles | June 06, 2012

Activity Levels Are Higher After Osteochondral Autograft Transfer Mosaicplasty Than After Microfracture for Articular Cartilage Defects of the Knee: A Retrospective Comparative Study

Aaron J. Krych, MD¹; Heather W. Harnly, MD²; Scott A. Rodeo, MD³; Riley J. Williams, III, MD³

¹ Department of Orthopedic Surgery, Mayo Clinic, 200 First Street S.W., Rochester, MN 55905. E-mail address: krych.aaron@mayo.edu
² Pediatric Orthopedic Associates, 585 Cranbury Road, East Brunswick, NJ 08816
³ Cartilage Study Group, Institute for Cartilage Repair, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021

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Investigation performed at the Hospital for Special Surgery, New York, NYA commentary by James L. Carey, MD, MPH, is linked to the online version of this article at jbjs.org.

Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

J Bone Joint Surg Am, 2012 Jun 06;94(11):971-978. doi: 10.2106/JBJS.K.00815

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Abstract

Background:

There is limited information regarding direct comparisons of the outcome of osteochondral autograft transfer (OAT) mosaicplasty and microfracture for the treatment of isolated articular cartilage defects of the knee. The purpose of this retrospective comparative study was to compare the general health outcomes, knee function, and Marx Activity Rating Scale scores for patients treated with OAT or microfracture for symptomatic chondral defects of the femoral condyles or trochlea. We hypothesized that the patients in the two treatment groups would have similar clinical outcomes at intermediate-term follow-up.

Methods:

Ninety-six patients with full-thickness cartilage defects of the femoral condyles or trochlea were treated with either OAT mosaicplasty (n = 48) or microfracture (n = 48). The average age of the patients (thirty-two male and sixteen female in each group) at the time of surgery was 29.7 years in the OAT group and 32.5 years in the microfracture group. Patients were prospectively evaluated at baseline and at one, two, three, and five years postoperatively with use of validated clinical outcome measures including the Short Form-36 (SF-36) physical component, International Knee Documentation Committee (IKDC), Knee Outcome Survey activities of daily living, and Marx Activity Rating Scale instruments. Comparisons between outcomes before and after treatment or between outcomes after microfracture and mosaicplasty were made with use of two-tailed tests.

Results:

At the time of the latest follow-up, both groups demonstrated significant increases in SF-36 physical component, Knee Outcome Survey activities of daily living, and IKDC scores compared with baseline. These scores did not differ significantly between the two groups at any of the follow-up time points. However, the OAT group demonstrated a significantly greater improvement in the Marx Activity Rating Scale scores from baseline to the two-year (p = 0.001), three-year (p = 0.03), and five-year (p = 0.02) time points compared with the microfracture group.

Conclusions:

In the present retrospective comparative study, the hypothesis that patients treated with microfracture or OAT mosaicplasty for symptomatic articular cartilage defects of the femoral condyles or trochlea would have similar clinical outcomes at intermediate-term follow-up was affirmed for general health outcome and for knee function. However, patients treated with OAT mosaicplasty maintained a superior level of athletic activity compared with those treated with microfracture.

Level of Evidence:

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

Injured articular cartilage has a limited ability to regenerate and full-thickness lesions may contribute to premature development of osteoarthritis¹, although the natural history of these cartilage lesions remains largely unknown. Surgical options for patients for whom nonoperative management of symptomatic articular cartilage defects has been unsuccessful include palliative, reparative, and restorative methods², with the treatment algorithm and surgical indications for each procedure continuing to evolve^3-5.

Microfracture is the most common marrow-stimulation technique performed in the United States, with over 25,000 procedures annually⁶. The goal of this procedure is to breach the subchondral bone and to promote stem cells, growth factors, and platelets to flow from the marrow, creating a fibrin clot that will eventually remodel into fibrocartilage to fill the defect. Because of its single-stage technical simplicity, limited invasiveness, and low cost, microfracture has become a popular treatment option for articular cartilage lesions, and it has been reported to be 90% successful in relieving pain at two to five years postoperatively^7-12. However, the primary limitation of microfracture treatment is the fact that healing is with mature fibrocartilage that contains predominantly type-I collagen, with only small amounts of type-II collagen^13,14, resulting in a deficiency in durability compared with articular cartilage¹⁵.

Osteochondral autograft transfer (OAT) mosaicplasty involves the transfer of a healthy osteochondral plug from an area of the knee that bears little weight to a small or medium-sized focal chondral or osteochondral defect^16,17. This technique has the advantages of resurfacing the defect with normal hyaline cartilage¹⁸, requiring only a single-stage procedure, and being of relatively low cost. Short-term studies of the mosaicplasty technique have demonstrated good to excellent clinical results at one to five years of follow-up¹⁸. However, this technique has the disadvantages of leaving an articular cartilage defect in another location in the treated knee¹⁹, of usually being performed by means of an open arthrotomy, and of being more technically demanding than microfracture. To our knowledge, only one study has directly compared the outcomes of microfracture and mosaicplasty-type OAT²⁰.

We designed a retrospective comparative study of microfracture and OAT mosaicplasty for the treatment of symptomatic full-thickness articular cartilage defects of the femoral condyles or trochlea of the knee to test the hypothesis that patients would have similar clinical outcomes with either treatment at short to intermediate-term follow-up. The purpose of this study was to determine whether (1) the clinical outcome was similar between patients treated with microfracture and OAT, as measured with use of the Short Form-36 (SF-36) physical component scale; (2) knee function was similar between patients treated with microfracture and OAT, as measured with use of the activities of daily living scale of the Knee Outcome Survey and the International Knee Documentation Committee (IKDC) score; and (3) the activity level was similar between patients treated with microfracture and OAT, as measured with use of the Marx Activity Rating Scale score.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

In 1999, our institution implemented a prospective registry dedicated to the tracking of patient outcomes after articular cartilage repair and reconstruction procedures. The institutional review board approved the registry, and all patients provided informed consent before participation. Patients included in the registry were evaluated preoperatively and were prospectively followed at one, two, three, and five years postoperatively.

Inclusion Criteria

The inclusion criteria were (1) skeletal maturity, (2) a single symptomatic cartilage lesion of the medial condyle, lateral condyle, or trochlea of the femur that was classified as Outerbridge²¹ grade III or IV at the time of the initial arthroscopy and did not involve substantial bone loss, and (3) a lesion area of 1 to 6 cm². To be eligible for analysis, patients were required to have a minimum of two years of follow-up. Exclusion criteria were generalized osteoarthritis, osteonecrosis, lower extremity malalignment, ligamentous instability or concomitant stabilization procedures involving more than one ligament, inflammatory arthritis, and an age of less than fifteen years or more than fifty years.

Patients

Our institutional cartilage registry was used to match each patient in the OAT group with a control patient who had received microfracture treatment. The matching was performed on the basis of sex and the location and size of the chondral defect. The only factor that differed between the microfracture group and the OAT group was the treatment of the cartilage lesion. A total of ninety-six patients were analyzed; forty-eight were treated with microfracture and forty-eight with OAT mosaicplasty.

Thirty-two patients (67%) in each group were male and sixteen were female. The average patient age at the time of surgery was 32.5 years (range, fifteen to forty-six years) in the microfracture group compared with 29.7 years (range, fifteen to forty-nine years) in the OAT group. The mean body mass index (BMI) of the patients was 25.5 kg/m² (range, 21 to 31 kg/m²) in the microfracture group compared with 25.2 kg/m² (range, 18 to 36 kg/m²) in the OAT group. Both groups included twenty-seven chondral lesions of the medial femoral condyle, sixteen of the lateral femoral condyle, and five of the trochlea. The mean size of the chondral defect was 2.55 cm² (range, 1.00 to 6.25 cm²) in the microfracture group compared with 2.65 cm² (range, 1.00 to 6.25 cm²) in the OAT group. In the microfracture group, the etiology of the chondral defect was chronic or atraumatic in twenty-three patients, traumatic in twenty-two, and osteochondritis dissecans in three. In the OAT group, the etiology was traumatic in twenty patients, osteochondritis dissecans in fifteen, and chronic or atraumatic in thirteen. No patient in the microfracture group had undergone a previous cartilage procedure; sixteen patients in the OAT group had previously undergone an unsuccessful microfracture procedure.

Surgical Technique

Only surgeons who were well trained and experienced with both the microfracture and the mosaicplasty technique performed the surgical procedures in this study. A diagnostic arthroscopy was performed in all patients to identify any additional intra-articular abnormality.

Microfracture of the isolated femoral cartilage lesion was performed according to the method described by Steadman et al.²² and Mithoefer et al.¹⁰. This method included debridement of the cartilage lesion to stable cartilage margins, careful removal of the calcified cartilage layer, and micropenetration of the subchondral bone with use of commercially available pick instruments (ConMed Linvatec, Largo, Florida). Subchondral bone bridges 3 to 4 mm wide were carefully maintained between the microfracture holes to ensure that the integrity and function of the subchondral bone plate were preserved. Release of blood and marrow fat droplets from the microfracture holes was confirmed by eliminating the pressure of the arthroscopic pump. Concomitant procedures in this group included three meniscal repairs involving the affected compartment, three arthroscopic partial meniscectomies involving the affected compartment, and one lateral retinacular release.

Mosaicplasty of the isolated femoral cartilage lesion was performed according to the method described by Hangody et al.¹⁶. This method included debridement of the defect to stable cartilage margins. A parapatellar arthrotomy was made either medially or laterally, depending on which location allowed the best visualization of the lesion. The patella was not everted in any patient. Donor osteochondral plugs were harvested by hand with use of commercially available instruments (Arthrex, Naples, Florida). All plugs were harvested from either the superolateral margin of the trochlea or the notch area, as Simonian et al. determined that contact pressures are lowest in this area²³. The plug diameters ranged from 6 to 10 mm, and the typical plug depth was 8 to 10 mm. The mean number of plugs transferred was 2.7 (range, one to ten, with only two patients having more than five plugs). Osteochondral plugs were placed flush with the surrounding normal articular cartilage in a manner that recreated the normal condylar architecture. When multiple plugs were used, each successive plug was completely inserted before the core of bone from the next donor site was removed. Concomitant procedures in this group included one meniscal repair in the affected compartment, five arthroscopic partial meniscectomies in the affected compartment, and one lateral retinacular release.

Patients in both groups had the same postoperative rehabilitation schedule. For patients with a lesion of the medial or the lateral femoral condyle, continuous passive motion from 0° to 60° was started in the recovery room, and the range of motion was gradually increased until full passive motion was achieved; continuous passive motion was continued for six hours per day for six weeks, and weight-bearing was permitted after six weeks. Patients with a trochlear lesion were permitted to bear weight as tolerated with the knee in full extension, although active flexion was limited to 0° to 20°; continuous passive motion from 0° to 80° was used for six hours per day for six weeks²⁴. A return to regular activities was generally achieved in both groups at six to eight months postoperatively.

Assessment of Clinical Outcomes

The general health outcome for each patient was assessed with use of the physical component of the SF-36 (version 1.0)²⁵, which has the ability to evaluate general physical well-being. Patients were assessed preoperatively and at one, two, three, and five years postoperatively.

Knee function was assessed with use of the IKDC subjective knee score and the activities of daily living scale of the Knee Outcome Survey. The IKDC score is a reliable and valid knee-specific measure of symptoms and function²⁶. Although it was originally designed for the assessment of ligament disruption, the IKDC instrument has been shown to provide a good overall measure of knee-related disability in patients who have undergone a cartilage regeneration procedure²⁷. The activities of daily living scale of the Knee Outcome Survey has been shown to have high reliability, validity, and responsiveness²⁸. Patients were assessed preoperatively and at one, two, three, and five years postoperatively with use of both of these instruments.

The patient activity level was assessed with use of the Marx Activity Rating Scale for disorders of the knee²⁹. Patients were assessed preoperatively and at one, two, three, and five years postoperatively.

An independent observer performed postoperative data collection for all clinical outcome instruments. These knee-specific outcome instruments have been validated previously, and they have been used previously for prospective evaluation of the repair of articular cartilage of the knee^{11,12,28,30-32}.

Statistical Methods

A power calculation performed before the study indicated that thirty-five patients per group would be required to demonstrate differences in the SF-36, IKDC, Knee Outcome Survey activities of daily living, and Marx Activity Rating Scale scores between the two groups with an effect size of 0.8, an alpha level of 0.05, and a beta level of 95%^33,34. Descriptive analyses of baseline patient characteristics were performed with use of means and standard deviations for continuous variables and frequencies and percentages for discrete variables. Comparisons of baseline patient characteristics between the microfracture and mosaicplasty groups were conducted with use of independent-sample t tests for continuous variables and chi-square or Fisher exact tests for categorical variables.

Changes in the subjective patient outcome scores (SF-36, Knee Outcome Survey activities of daily living, IKDC, and Marx Activity Rating Scale) over time in each group were assessed with use of paired t tests comparing each postoperative time point with the baseline. Differences between the mean outcomes in the two procedure groups at each time point were then evaluated to determine whether they were significant.

Two-tailed tests were used for all statistical analyses. Bonferroni adjustment of the p value threshold for significance was performed to avoid the increase in the chance of type-I error that would otherwise result from performing multiple comparisons. Thus, the required p value was adjusted from 0.05 to 0.013 to account for comparisons at multiple time points. All analyses were performed with use of SPSS software (version 18.0; SPSS, Chicago, Illinois).

Source of Funding

There was no external funding source for this study.

Results

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

Sixty-one patients treated with OAT mosaicplasty between 1999 and 2009 met the inclusion criteria, and forty-eight had at least two years of follow-up (a follow-up rate of 79%). The mean duration of follow-up was 4.4 years (range, two to ten years) in the microfracture group and 3.1 years (range, two to ten years) in the OAT group. Patient demographics, chondral defects, and baseline clinical scores in the two groups were similar at the time of surgery (Table I).

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TABLE I Similarity of Baseline Characteristics Between the Two Groups*

	Microfracture Group	OAT Group	P Value
Patient characteristics
Sex (male:female)	32:16	32:16	†
Age‡(yr)	32.5 (15-46)	29.7 (15-49)	0.19
Body mass index‡(kg/m2)	25.5 (21-31)	25.2 (18-36)	0.75
Lesion characteristics
Location (no.)			†
Medial femoral condyle	27	27
Lateral femoral condyle	16	16
Trochlea	5	5
Size‡(cm2)	2.55 (1.00-6.25)	2.65 (1.00-6.25)	0.77†
Baseline clinical scores§
SF-36 physical	40.5 (9.8)	39.4 (9.5)	0.60
KOS activities of dailyliving	64.1 (16.8)	63.6 (18.8)	0.90
IKDC subjective	49.7 (15.8)	43.7 (15.8)	0.15
Marx Activity Rating Scale	7.3 (5.4)	6.4 (6.4)	0.49

*OAT = osteochondral autograft transfer, SF-36 = Short Form-36, KOS = Knee Outcome Survey, and IKDC = International Knee Documentation Committee.
†Matched variables.
‡Values are given as the mean, with the range in parentheses.
§Values are given as the mean, with the standard deviation in parentheses.

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TABLE I Similarity of Baseline Characteristics Between the Two Groups*

	Microfracture Group	OAT Group	P Value
Patient characteristics
Sex (male:female)	32:16	32:16	†
Age‡(yr)	32.5 (15-46)	29.7 (15-49)	0.19
Body mass index‡(kg/m2)	25.5 (21-31)	25.2 (18-36)	0.75
Lesion characteristics
Location (no.)			†
Medial femoral condyle	27	27
Lateral femoral condyle	16	16
Trochlea	5	5
Size‡(cm2)	2.55 (1.00-6.25)	2.65 (1.00-6.25)	0.77†
Baseline clinical scores§
SF-36 physical	40.5 (9.8)	39.4 (9.5)	0.60
KOS activities of dailyliving	64.1 (16.8)	63.6 (18.8)	0.90
IKDC subjective	49.7 (15.8)	43.7 (15.8)	0.15
Marx Activity Rating Scale	7.3 (5.4)	6.4 (6.4)	0.49

General Health Outcome

The mean SF-36 physical component improved significantly from baseline to one, two, three, and five years postoperatively in both the microfracture group and the OAT group (p < 0.01 for all). The score did not differ significantly between the groups at any of the time points (Fig. 1).

Fig. 1

The Short Form-36 physical component score improved significantly from baseline in both groups and was similar in the two groups. The error bars represent the standard deviation. OAT = osteochondral autograft transfer, and MFX = microfracture.

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Knee Function

The Knee Outcome Survey activities of daily living score and the IKDC score improved significantly from baseline to one, two, three, and five years postoperatively in both groups (p < 0.01 for all). The Knee Outcome Survey score (Fig. 2) and the IKDC score (Fig. 3) did not differ significantly between the groups at any of the time points.

Fig. 2

The Knee Outcome Survey activities of daily living score improved significantly from baseline in both groups and was similar in the two groups. The error bars represent the standard deviation. OAT = osteochondral autograft transfer, and MFX = microfracture.

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Fig. 3

The IKDC subjective score improved significantly from baseline in both groups and was similar in the two groups. The error bars represent the standard deviation. OAT = osteochondral autograft transfer, and MFX = microfracture.

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Activity Level

The Marx Activity Rating Scale score in the microfracture group declined from baseline (mean and standard deviation, 7.3 ± 5.4) to the one-year (4.11 ± 1.05, p = 0.02), two-year (3.71 ± 1.64, p < 0.01), three-year (2.91 ± 2.12, p = 0.02), and five-year (2.89 ± 2.5, p = 0.02) time points. In contrast, the score in the OAT group remained similar to the baseline value (6.4 ± 6.4) at the one-year (5.21 ± 2.3, p = 0.49), two-year (7.29 ± 1.24, p = 0.28), three-year (7.75 ± 2.24, p = 0.63), and five-year (8.55 ± 2.31, p = 0.22) time points. The score in the OAT group was better than that in the microfracture group at two (p = 0.001), three (p = 0.03), and five (p = 0.02) years postoperatively (Fig. 4).

Fig. 4

The Marx Activity Rating Scale score was superior in the OAT group compared with the microfracture group. The error bars represent the standard deviation. OAT = osteochondral autograft transfer, and MFX = microfracture.

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Discussion

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

Injuries involving the articular cartilage of the knee are a therapeutic challenge, and the best method to treat full-thickness articular cartilage defects has not been determined. As more clinical evidence regarding outcomes accumulates, treatment algorithms and surgical indications for each procedure continue to evolve^3-5. In the present retrospective comparative study, our hypothesis that patients treated with microfracture or OAT mosaicplasty for symptomatic chondral defects of the femoral condyles or trochlea would have similar clinical outcomes at intermediate-term follow-up was affirmed for general health outcome and for knee function. However, patients who had undergone OAT mosaicplasty maintained a higher level of athletic activity compared with patients who had undergone microfracture.

The limitations of our study include the lack of randomization, the short to intermediate-term duration of follow-up, and the absence of magnetic resonance imaging (MRI) data. Despite the lack of randomization, the two patient groups had similar demographics and baseline scores. BMI and age at the time of surgery, which have been shown to influence outcome after microfracture^10,35, were similar in the two groups. To our knowledge, this study is the largest comparative study to date of these two single-stage treatments for articular cartilage defects, and it was adequately powered to detect a modest clinical difference. As with any retrospective study, selection bias could have influenced the results. For example, surgeons at our institution are more likely to recommend OAT treatment rather than microfracture for osteochondritis dissecans lesions with accompanying bone loss, as reflected by the greater number of osteochondritis dissecans lesions in the OAT group. Therefore, it is possible that the superior activity scores in the OAT group resulted because primary cartilage repair procedures for osteochondritis dissecans lesions fare better than repairs for lesions with other etiologies^20,36. In the current series, however, five of the patients in the OAT group who had osteochondritis dissecans lesions had previously undergone an unsuccessful microfracture procedure. This introduces two additional variables, previous surgery and a longer interval between injury and surgery, that have been shown previously to be negative predictors of return to sports^35,37.

Although this study lacks long-term data, we clearly demonstrated a declining activity level in the microfracture group compared with the OAT mosaicplasty group, and the activity level in the microfracture group is unlikely to increase with longer follow-up and may decrease even further^8-10,38.

Although we did not review imaging data in this study, the defect fill grade on MRI has previously been shown to be associated with knee function scores after microfracture¹⁰. Similarly, the MOCART (magnetic resonance observation of cartilage repair tissue) score has been shown to be significantly associated with objective and subjective scores after OAT mosaicplasty³⁹.

Patients in both groups had similar, significant improvements in general health outcome. This improvement may be due in large part to the young age and relative fitness of the patients in both of the groups in this study. In a prospective cohort study of forty-eight patients treated with microfracture, a lower BMI was correlated with a higher SF-36 physical component score¹⁰. In addition, younger patient age was associated with better outcome after microfracture^35,36 and after OAT mosaicplasty³⁶.

In the only other comparative study of these procedures, Gudas et al. randomized sixty patients with a mean age of 24.3 years to treatment with either microfracture or OAT mosaicplasty²⁰. At a mean of 37.1 months of follow-up, both groups had significant clinical improvement, as measured with the modified Hospital for Special Surgery (HSS) and International Cartilage Repair Society (ICRS) scores, but the results were significantly better in the mosaicplasty group (96% good or excellent results compared with 52% in the microfracture group). No general health outcomes were assessed. The main limitation of the study by Gudas et al. was the fact that almost one-half of the chondral defects in that series were due to osteochondritis dissecans and the amount of bone loss was not documented. OAT mosaicplasty, which transfers bone and cartilage, restores joint congruity better than microfracture does if lesions involve substantial bone loss. In addition, many osteochondritis dissecans lesions are located adjacent to the intercondylar notch at the lateral aspect of the medial femoral condyle, and these represent uncontained lesions for which microfracture is not recommended^10,11,22.

In the present series, only three chondral defects in the microfracture group were due to osteochondritis dissecans and all three were contained defects with minimal bone loss; this may account for the better results after microfracture in the present series compared with the study by Gudas et al. It is important to note that the defects included in the study by Gudas et al. were 1 to 4 cm² in size, whereas the present study included lesions up to 6 cm². Although Gudas et al.³⁶ and Hangody et al.¹⁶ recommended treatment with osteochondral autograft for defects between 1 and 4 cm² in size, it is unclear whether 4 or 6 cm² defines the upper threshold for OAT mosaicplasty. Certainly, donor site morbidity increases for 8 to 9-cm² lesions⁴⁰, and OAT is contraindicated for these large lesions.

In the current study, we demonstrated improvement in knee function after both microfracture and OAT mosaicplasty. In the long-term study by Steadman et al., which involved a cohort of seventy-one knees treated with microfracture, the mean Lysholm score improved from 59 before surgery to 89 at a mean of eleven years of follow-up¹². The greatest improvement occurred in the first year after surgery, but improvement continued for two to three years postoperatively. In contrast, other studies of microfracture have shown deterioration of results over time^8-10,38. Hangody et al. reported good to excellent results in 92% of patients with femoral condyle lesions treated with mosaicplasty¹⁷. Other clinical studies have reported significant improvements in pain and activity level in approximately 85% of knees treated with OAT^41,42. More recently, Chow et al. retrospectively reviewed the two to five-year results after mosaicplasty and showed that the Lysholm score and the IKDC score improved significantly in almost 85% of the patients⁴³. However, slight to severe degenerative changes at the recipient site have been reported in up to 17% of patients after OAT mosaicplasty⁴⁴.

In the present retrospective comparative study, athletic activity scores were significantly higher for patients treated with OAT mosaicplasty compared with patients treated with microfracture. Similarly, Gudas et al. found a higher rate of return to sports in the mosaicplasty group (93%) than in the microfracture group (52%) in their prospective randomized study²⁰. In another study, histological analysis of OAT grafts demonstrated consistent survival of the transplanted hyaline cartilage and deep matrix integration of the transplanted cartilage to the surrounding tissue at the recipient site¹⁸. In contrast, mature fibrocartilage produced by healing after microfracture is predominantly type-I collagen, with only small amounts of type-II collagen^13,14, and thus lacks the strength of articular cartilage¹⁵.

Although most clinical studies of the outcome after microfracture in the knee indicate improvement in knee function in 70% to 90% of patients, a decline in the activity level over time is often reported^9,11,12. Gobbi et al. used microfracture to treat chondral lesions in fifty-three athletes with a mean age of thirty-eight years. They found that the initial improvement from baseline in the treated athletes was followed by a decline in sports participation over time⁸. Similarly, Mithoefer et al. found that only 44% of athletes were able to regularly participate in high-impact, pivoting sports after microfracture³⁵. Blevins et al. assessed the functional and arthroscopically visible improvement in a group of forty-eight highly competitive athletes and 188 recreational athletes after microfracture; significant improvements from the time of microfracture to the time of final follow-up at three years were demonstrated⁷. However, there was no comparison group in that study. In the current series, activity scores were lower in the microfracture group than in the OAT group even though the two groups had similar knee symptoms at baseline; we attribute this to the likelihood that patients modified their activity level to one that provided satisfactory knee function and comfort. Lower-demand activities cause fewer knee symptoms, and activity modification is one of very few recommendations for nonoperative alleviation of knee symptoms that has a grade of A and a level of evidence of I⁴⁵.

In conclusion, in this retrospective comparative study of patients with symptomatic chondral defects of the femoral condyles or trochlea, we demonstrated that both OAT mosaicplasty and microfracture resulted in significantly improved general health outcomes and knee function at intermediate-term follow-up compared with the preoperative baseline. However, patients treated with OAT mosaicplasty achieved higher activity levels postoperatively compared with patients treated with microfracture.

Acknowledgements

Introduction | Materials and Methods | Results | Discussion | Acknowledgements

Note: The other members of the Cartilage Study Group include Russell F. Warren, MD, Jo A. Hannafin, MD, Robert Marx, MD, Answorth A. Allen, MD, Thomas Wickiewicz, MD, and Hollis Potter, MD. The authors thank Joseph Nguyen, MPH, of the Hospital for Special Surgery Division of Epidemiology and Biostatistics, for his skill and expertise in performing the statistical analysis for this manuscript.

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Topics

articular cartilage ; transplantation, autologous ; osteochondral lesions of the knee

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Aaron J. Krych, Heather W. Harnly, Scott A. Rodeo, Riley J. Williams, III; Activity Levels Are Higher After Osteochondral Autograft Transfer Mosaicplasty Than After Microfracture for Articular Cartilage Defects of the KneeA Retrospective Comparative Study. The Journal of Bone & Joint Surgery. 2012 Jun;94(11):971-978.

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