MRI analysis of the chondral surface following deepening trochleoplasty for patellofemoral instability

Background

The incidence of patellofemoral instability is 5.8 per 100,000 in the general population, rising to 29–43 per 100,000 in adolescents. Up to 85% of recurrent instability is associated with trochlea dysplasia. The Dejour sulcus deepening trochleoplasty can be used to effectively treat patellofemoral instability, however the effect on patellofemoral cartilage and survival of the osteochondral flap is not known. The aim of the study was to determine changes in the patellofemoral articular surface in the early postoperative period with MRI analysis.

Patients and methods

MRI analysis of a single-surgeon series, retrospective review of 61 sulcus deepening trochleoplasties between 2014 and 2022, of which 40 had a postoperative MRI and were assessed – including 26 women (65%) and 22 (55%) right knees. Trochleoplasty was performed in conjunction with medial reefing and lateral release in 26 patients (65%), in conjunction with MPFL reconstruction alone in 12 (30%), and in conjunction with MPFL reconstruction and tibial tubercle osteotomy in 2 (5%). Preoperative and postoperative MRIs were assessed for articular cartilage loss, percentage of full thickness cartilage loss as well as volume and number of bone marrow lesions using a modified version of the MRI osteoarthritis knee score (MOAKS).

Results

Mean age at operation was 25.3 years (SD: 7.3). The modal number of comorbidities was zero, and no patient had diabetes or was taking immunosuppressive medication. Mean time between preoperative MRI and trochleoplasty was 8.7 months (SD: 6.9). Mean time between trochleoplasty and postoperative MRI was 19.9 months (SD 14.9). There were further episodes of symptomatic instability in 8 (20%) of patients. In all anatomical subregions (medial and lateral patellar, medial and lateral trochlear groove) there was a significant increase in articular cartilage loss between pre- and post-operative MRIs (p < 0.001). There was a significant decrease in the volume and number of bone marrow lesions (BMLs) in the medial patella only, with static or nonsignificant increases in the lateral patella and medial trochlear groove, and significant increases in the number and volume of BMLs in the lateral trochlea (p < 0.001). MOAK grade 1 was seen in at least one anatomical subregion in every patient post-operatively and there was progression in MOAK grade in all subregions. Progression in MOAK grade was seen in the medial patella in 20 patients (50%), lateral patella in 18 patients (45%), medial trochlea in 22 patients (45%) and lateral trochlea in 31 patients (78%).

Discussion and conclusion

Whilst patellofemoral osteoarthritis is common post trochleoplasty, the history of its development is not clear. Few studies report cartilage condition post-surgery. Authors in the only other MRI study found no change in cartilage condition at a mean of 64-months. A small case series of histological samples taken from trochleoplasty patients during subsequent arthroscopy also found normal cartilage and a healing osteochondral flap. Our study evaluated the entire patellofemoral surface using MRI and found that patellofemoral articular cartilage loss was seen in at least one anatomical subregion in every patient post-operatively, with progression in chondral damage seen in between 45% and 78% of anatomical subregions.

Level of evidence

IV; observational cohort study