Introduction

Cartilage injuries are said to frequently lead to incomplete defect-regeneration due to the limited healing properties of hyaline cartilage (Gomoll AH, Minas T. 2014). As a pre-arthrotic deformity, this failure of restoration often results in progressive degeneration of the affected joint and a continous function impairment (Shapiro F et al.1993, Steinwachs MR et al 2008). Arthroscopic one step microfracture is the most common technique for cartilage repairs worldwide (Steadman JR et al. 2002, Kreuz PC et al. 2006, Mithoefer K et al. 2009). This method induces the formation of a repair tissue yet carries insufficient biomechanical features as well as an inadequate long-term weight-bearing capacity (Kreuz PC et al. 2006, Mithoefer K et al. 2009). Firstly, more extended injury of the subchondral bone caused by the use of V-shaped top of microfracture instruments is considered to be causative. Secondly, the shallow depth of perforation (3 mm) achieved by these devices only allows very restricted access to the subchondral pool of stem cells with poorly developed cell differentiation characteristics (Chen H et al. 2011). This restriction becomes very apparent with the hypertrophic formation of bone within the defective region and may be circumstantial evidence for spontaneous osteogenic stem cell differentiation (Caplan AI 2007, Shive MS et al. 2014). Persistent bone marrow edema as a manifestation of the mechanical insufficiency of the injured subchondral bone, in combination with the biomechanical restrictions of fibrocartilage, are the main reasons for the histologically and clinically evident problems of this method (Gomoll AH, Minas T.2014, Steinwachs MR et al 2008). Multiple studies show the limited successful outcomes of MFx for patients >40 with large >3-4cm² defects. Seeking clarity regarding the efficacy of MFx, a recent Cochrane review of Gracitelli GC et al. 2016 examined the evidence from randomized trials comparing MFx to other treatment options. The conclusion was that the currently available evidence is not enough to determine whether mosaicplasty, allograft transplantation, or MFx is better for treating cartilage defects in adults. The long-term results of MFx established a failure rate of about 25% at 10 years requiring an additional intervention.

The Autologous Matrix Induced Chondrogenesis (AMIC®) technique involves the debridement of the cartilage lesion, the classic MFx procedure with ale and the coverage of the lesion site by the collagen membrane Chondro-Gide® plus fibrin. This technique has been used to complete the MFx-cartilage repair process in several joints (knee, hip, talus and metatarsal) so far. Although two recent studies on the use of AMIC® for the repair of articular cartilage defects have been published recently (Gao L et al.2017, Shaikh N et al. 2017). These papers do not exclusively address the knee joint, but rather refer to all three major joints where AMIC® is used (hip, knee, talus). In our meta-analysis (Steinwachs M et al ICRS 2019) the AMIC® procedure significantly improved the clinical status and functional scoring versus preoperative values. Evidence was obtained in a non-selected patient population, corresponding to real-life treatment of knee chondral and osteochondral defects

Content

The idea for a modification of AMIC technology is based on new biological findings related to the tissue healing cascade. Experimental data of the utilization of K-Wire instead of ale for bone marrow stimulation was able to claim superiority in comparison to the conventional microfracture technique (Chen H et al. 2011). Experimental studies with PRGF-Endoret® demonstrate significant stimulation of angiogenesis, stem cell migration, cell proliferation, reduced inflammation and enhanced paracrine cell activity combined with antimicrobial activities in different tissues (Anitua E et al. 2007, Andia I et al. 2012). In addition, PRGF can avoid the activation of the NF-κB pathway, thus reducing the inflammatory and catabolic responses (Jia J et al. 2018). Clinical and experimental data show that the additional use of PRGF (Endoret®) enhances the biological tissue regeneration in bone and cartilage naturally (Filderado G et al. 2011, Anitua E et al 2013). Nowadays, the treatment scarcely addresses subchondral bone as one of the most relevant factors for the outcome of cartilage repair. Based on these new findings we have developed a new AMIC® technique with an enhanced approach to bone marrow stimulation employing tapered 1.5 mm K-Wires with a perforation depth of 1 - 1.5 cm and the subchondral injection of activated autologous PRGF® (Endoret®) in combination with a PRGF derived fibrin clot loaded ChondroGide® collagen membrane (Biological-Enhanced-AMIC;“BE-AMIC”) as a treatment option for symptomatic full-thickness cartilage lesions (> 2 cm²) with bone marrow edema. Initial clinical and MRI data show encouraging results.