Background

Subchondroplasty (SCP) is a progressively established procedure with chronic bone marrow lesion as a cause of pain being its main indication. It is a simple and safe procedure with little complications described. In this case we describe a relative indication for SCP following failed chondroplasty of a focal chondral defect due to a traumatic event shortly after the procedure.

Case presentation
A 49-year-old female was diagnosed with a focal chondral defect in the medial femoral condyle (figure 1). An arthroscopic nanofracture procedure was performed and the patient was supposed to keep the extremity non-weight bearing for 6 weeks after the surgery. 10 days after the procedure, the patient was attacked by wasps, reacted vigorously, jumped away and landed on the operated extremity. She felt a sudden pain that resolved only partially over next days. She was advised to be further non-bearing for 4 weeks with a progressive loading afterwards. A control MRI (figure 2) of the knee was performed 3 months after the initial procedure, showing a nice fibrocartilaginous tissue cap over the defect, but a significant subchondral bone insufficiency underneath it. Due to a persisting pain (VAS 7) and inappropriate subchondral bone remodeling, subchondroplasty of the medial femoral condyle was performed. After the procedure, the patient was non-weight bearing for 10 days followed by progressive loading, ROM and strength training. Significant improvement in pain (VAS 3 post-op) was seen at the 1-month follow-up, with a good range of motion and no swelling. A control MRI was performed 3 months after subchondroplasty revealing still present fibrocartilaginous tissue at the site of a chondral defect with partially remodeled subchondral bone (figure 3). At the 1-year follow-up, the patient is still satisfied with the treatment and is able live and work with only some minor restrictions.

Conclusion

Subchondroplasty is a procedure indicated in case of chronic bone marrow lesion, either as isolated or as a part of knee osteoarthritis. However, some out-of-the-box thinking may give rise to some other indications, such as one described in the case above. Limb unloading is one of the crucial steps in managing chondral defects with micro- or nanofracture. With failure to achieve that (ie. due to an injury early after the procedure), a subchondral bone marrow deficiency may occur where bone fails to remodel. As in the presented case, subchondroplasty is a viable option for restoring subchondral bone integrity after failed nanofracture procedure.