Knee Cartilage Repair: Prognostic Factors Vary by Outcome

Key Takeaways

• Among adults undergoing knee cartilage repair for focal defects or osteoarthritis-associated lesions, no baseline prognostic factor was consistently established across procedures and outcomes.
• Increasing age was associated with less favorable outcomes after isolated marrow stimulation in two adjusted analyses, both at high risk of bias.
• Cell-based repair and osteochondral allograft studies identified outcome-specific candidate associations rather than shared predictors.
• Most prognosis-specific analyses were judged at high risk of bias, and none at low risk.

For patients with knee cartilage lesions, the prognostic meaning of age, lesion features, or preoperative function may depend on the disease setting, repair procedure, and outcome measured. Focal defects and osteoarthritis-associated lesions present different clinical contexts, while surgical approaches differ in their indications and repair mechanisms. Whether baseline characteristics carry comparable prognostic meaning across these settings remains uncertain.

Adults undergoing knee cartilage repair for focal defects or osteoarthritis-associated lesions were the focus of a systematic review of original English-language studies reporting quantitative associations between baseline factors and postoperative outcomes. Eligible patients were at least 18 years old. Investigators searched PubMed, Embase, the Cochrane Library, and Google Scholar from inception through August 29, 2026, and checked backward and forward citations. Two reviewers independently screened reports, extracted data, and assessed bias with the quality in prognosis studies (QUIPS) tool. Findings were organized by disease setting, primary procedure, factor, outcome, and follow-up; adjusted estimates took priority, and overlapping estimates were not treated as independent within identical association strata. Heterogeneous contexts and effect measures precluded meta-analysis.

Across 31 included reports, sample sizes summed to 13,022, not a count of distinct patients because cohorts overlapped or may have overlapped. Of 37 QUIPS study–analysis units, 29 were at high risk of bias, eight at moderate risk, and none at low risk. After autologous chondrocyte implantation (ACI) or matrix-induced autologous chondrocyte implantation (MACI), candidate associations involving age, sex, body mass index (BMI), baseline status, defect features, prior treatment, and manufacturing measures varied by outcome. For osteochondral allograft (OCA), adjusted failure models identified age, BMI, diagnosis, and graft area as candidates, whereas bony realignment related to salvage surgery. Clinical-threshold models and machine-learning rankings provided different kinds of evidence from adjusted failure models.

After isolated marrow stimulation, increasing age was associated with lower achievement of the minimal clinically important difference (MCID) at 24 months (odds ratio 0.61) and the patient acceptable symptom state (PASS) (odds ratio 0.86). A separate adjusted analysis linked increasing age to less long-term Lysholm improvement (standardized B −0.299). Both adjusted analyses were at high risk of bias, and confidence intervals for these age estimates were not reported. Lesion-size findings varied by endpoint and follow-up. In osteoarthritis-associated mesenchymal stromal cell (MSC) implantation, older age and bipolar kissing lesions were linked to long-term failure in one adjusted analysis. Stromal vascular fraction (SVF) estimates were imprecise, and some cohorts overlapped.

Residual confounding, inconsistent adjustment, incomplete precision reporting, and variation in factor definitions, indications, procedures, outcomes, and follow-up limit comparisons. Final status, change from baseline, MCID or PASS achievement, structural findings, and failure are distinct outcomes; reaching an improvement threshold does not necessarily indicate better final function. Cohort overlap limits independent replication. The authors did not pool effects or assign formal certainty grades, and parts of the classification and QUIPS appraisal framework were added after protocol registration. Differences between procedure-specific findings do not establish that a baseline factor has different effects under different procedures.

For prognosis after knee cartilage repair, the authors concluded that candidate associations apply to specific disease, procedure, outcome, and follow-up contexts. The evidence establishes neither universal baseline cutoffs nor differences in prognostic effects between procedures.

Clinician Questions

Can microfracture plus bone marrow aspirate concentrate findings be attributed to microfracture alone after knee cartilage repair?

Only a subset of a primary microfracture cohort received bone marrow aspirate concentrate. Investigators classified cohort-wide baseline-factor associations as mixed microfracture with or without augmentation, not as specific to microfracture alone; they considered the unadjusted augmented-versus-nonaugmented comparison separately.

Is postoperative MRI defect fill a baseline predictor of knee cartilage-repair outcomes?

Magnetic resonance imaging (MRI) defect fill measured after repair is a post-treatment measurement, not a baseline prognostic factor. Investigators retained associations involving postoperative fill only as post-treatment correlations and excluded them from the baseline prognostic-factor synthesis.

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