Does Ligamentous Laxity Protect Against Chondral Injury in Patients with Patellofemoral Instability?

OBJECTIVES: Hypermobility may be a risk factor for musculoskeletal injuries during sports participation. However, we have seen a low incidence of chondral injuries requiring treatment in patients undergoing medial patellofemoral ligament (MPFL) reconstruction for patellofemoral instability. It is unknown if patients with ligamentous laxity, who are at an increased risk for patellofemoral instability, are somewhat protected from chondral injury. We hypothesize in patients undergoing MPFL reconstruction for patellofemoral instability, patients with ligamentous laxity will be less likely to have chondral defects requiring surgical intervention. METHODS: 171 patients (32 male, 139 female) average age 22 years (range 11-57) with patellofemoral instability were rated with the Beighton-Horan (BH) scale for constitutional ligamentous laxity (0-9). Preoperative MRIs were evaluated (chondral injury present/absent, size of chondral injury, Outerbridge grade) and intra-operative arthroscopic findings noted (chondral injury present/absent, size of chondral injury, Outerbridge grade, surgical intervention yes/no, type of surgical intervention) of 79 non-lax (BH<6) and 92 ligamentously lax patients (BH≥6) (LAX) undergoing MPFL reconstruction. Anatomic measurements were documented for each patient including: tibial tubercle-trochlear groove (TT-TG) distance, Caton-Deschamps (C/D) ratio for patellar height, and the Dejour classification of trochlear dysplasia. Surgical interventions included chondroplasty, microfracture, particulated juvenile cartilage implantation (DeNovo, Zimmer, Warsaw, IN), osteochondral fracture fixation or osteochondral allograft transplantation (OATS). RESULTS: 58/171 (33.9%) required a surgical intervention for a chondral defect: chondroplasty 29/58 (50%), microfracture 16/58 (27.6%), particulated juvenile cartilage implantation 18/58 (31%), osteochondral fracture fixation 2/58 (3.5%), and OATS 2/58 (3.5%). There was no difference in the proportion of additional procedures in LAX vs. non-lax (p=0.475). There was no difference in the proportion of patellar chondral injuries sustained (LAX 29.3% vs. non-lax 45.7%) (p=0.538) but LAX patients had a lower proportion of patellar grade IV chondral injury compared to non-lax (p=0.026). There was no difference in the proportion of femoral chondral injuries sustained (LAX 13.1% vs. non-lax 26.4%) (p=0.073) but LAX patients had a lower proportion of femoral grade IV chondral injury compared to non-lax (p=0.023). There was no association of chondral injury with trochlear morphology (p=0.843), patellar height (p=0.303), TT-TG (p=0.874), number of instability events (p=0.878), age at time of surgery (p=0.482), and contact vs. non-contact mechanism of injury (p=0.772). CONCLUSION: LAX patients had a lower proportion of severe patellar and femoral cartilage injuries. There was no significant difference in the proportions of injuries, however there were 2x the proportion of femoral chondral injuries and 1.5x the proportion of patellar chondral injuries in non-lax vs. LAX, which is clinically significant.