###### Abstract  
The present study analysed current rehabilitation protocols to investigate whether there is a standard for early rehabilitation after microfracturing (MFX), matrix-assisted cartilage transplantation (MACT), and osteochondral at autograft transfer (OATS) of the knee joint in clinical routine, and if rehabilitation protocols differ in the repair technique used or the localization of the cartilage defect. The evaluation included rehabilitation criteria such as weight-bearing, range of motion, use of an orthosis, motion therapy, and rehabilitation training during the early rehabilitation phase after MFX, MACT, and OATS of the femorotbial and retropotellar joint space. We analysed 153 rehabilitation protocols after cartilage repair of the knee joint, including 137 protocols for after repair of the main weight-bearing (femorotbial) area and 16 for after retropatellar cartilage repair. Most of the protocols differed significantly according to the location of the repair and the procedure performed. Our findings indicate that full weight-bearing can be achieved significantly faster after MFX (5.6 weeks) and OATS (5.3 weeks) than after MACT of the main weight-bearing zone (6.6 weeks, \(p<0.001\)). In addition, after retropatellar cartilage repair, patients are allowed full weight-bearing after 2.1 weeks compared to the main weight-bearing zone (5.3-6.6 weeks; \(p<0.001\)). No standardized rehabilitation recommendations have been established. The present study shows that rehabilitation needs to be adjusted to the surgical technique and the location of the defect zone, and further investigation is warranted to establish standardized rehabilitation protocols after cartilage repair of the knee joint. p 2021 11 8873 2021 2  
[PERSON] et al. (2018) [6] showed an improvement in all patient-reported outcomes after microfracturing of the knee joint after a mean follow-up of 5.7 years. However, according to [PERSON] et al. (2009) [7] the improvement worsens after 5 years when compared to the 2 year mark for MACT. This indicates a comparative advantage of MACT, especially regarding long-term outcome. It is therefore better suited for younger patients [8]. [PERSON] et al. (2018) [9] also reported that improvements in daily life activities lasted significantly longer in MACI (using autologous cultured chondrocytes on porcine collagen membrane) than MFX. [PERSON] et al. (2012) [10] compared all three repair techniques (MFX, MACT, OATS) for similar defect size and location and showed that all three procedures led to similar improvement in functional outcome scores at 5 year follow-up. For osteochondral allograft, [PERSON] et al. (2016) [11] reported an improvement in all scores (Knee Society Function Score, Knee Society Knee Score, Lyshlm Score) in 75% of patients after a long-term follow-up 12.3 years post-surgery. Cartilage repair surgery is well-established. It is commonly performed and yields good clinical results. However, the early stages of post-surgical rehabilitation have not been thoroughly investigated. Evidence-based rehabilitation protocols are needed because the regeneration of cartilaginous tissue is challenging and limited. On the one hand, early weight-bearing and shear forces from a progressive release of ROM might endanger the outcome of the surgical procedure by inducing apoptosis of the chondrocytes [12; 13]. On the other hand in vitro studies have demonstrated that physiological contact forces produced by, for example, continuous passive motion therapy (CPM) or partial weight-bearing enable cartilaginous tissue to enhance chondrogenic differentiation [14; 15]. Additionally, even healthy joint cartilage reacts to the restriction of weight bearing by atrophy [16]. Therefore, rehabilitation after cartilage repair of the knee joint must be performed with caution and must be balanced between restriction and progression of rehabilitation criteria such as weight bearing and ROM.