Review Question - QID 4787

The patient underwent an osteochondral autograft transfer (OAT) with multiple plugs (also known as mosaicplasty) for a full-thickness chondral defect of the medial femoral condyle. The chondrocytes in the graft remain viable, the transferred cartilage heals, and biopsy reveals articular cartilage composed primarily of type II collagen.

Articular cartilage defects can be treated by a variety of methods including debridement, fixation of unstable osteochondral fragments, marrow stimulation techniques (microfracture, abrasion chondroplasty), cartilage replacement techniques (osteochondral autograft and allograft) and cellular techniques (autologous chondrocyte implantation). Osteochondral autograft transfer is performed by harvesting normal articular cartilage with underlying bone from lesser weightbearing areas (e.g. intercondylar notch) and transferring the graft to a recipient socket at the site of the chondral defect. Graft incorporation occurs by integration of the bony graft into the subchondral bone and healing of the overlying cartilage layer.

Hangody et al. reviewed the outcomes of autologous osteochondral mosaicplasty in professional athletes. They found successful outcomes similar to that of less athletic patients, despite a higher rate of preoperative osteoarthritic changes in the athletic population. The authors noted that histological evaluation revealed good graft incorporation in all 11 cases.

Alford et al. authored a two part Current Concepts article on cartilage restoration. They constructed an algorithm (Illustration A) highlighting many factors that impact treatment choice, including patient activity level and defect characteristics such as location and size. This algorithm also illustrates comorbidities (malalignment, ligament insufficiency) that warrant correction prior to addressing the chondral defect.

Figure A shows a full-thickness chondral defect (left) and subsequent osteochondral autograft transfer (right). Illustration A is a treatment algorithm for the management of chondral defects, as discussed above. Illustration B shows a microfracture procedure, a marrow stimulation technique resulting in fibrocartilage filling of the chondral defect. Illustration C shows an osteochondral allograft transplant, a cartilage replacement technique useful for large defects in which donor graft is obtained from a cadaver hemicondyle and transferred to a recipient socket at the site of the chondral defect. Illustration D shows the autologous chondrocyte implantation technique, a two-stage procedure consisting of 1. Cartilage biopsy for growth of autologous chondrocytes, and 2. Subsequent injection of autologous chondrocytes beneath a periosteal patch.

Incorrect Answers:
Answer 1: Type I collagen is more commonly found in reparative fibrocartilage (following microfracture), bone, ligaments and tendons. Biopsy in this patient would show articular cartilage composed of predominately type II collagen.
Answers 3, 4, 5: The transplanted chondrocytes and overlying articular cartilage remain viable. The cartilage is not used as a scaffold for new growth, nor is it replaced by fibrocartilage.