MPFL and chondral injury, as well as bone bruising, are common following primary LPD; the location of the injury can be different depending on skeletal maturity status. The MPFL and chondral injury findings were generally centered at the inferomedial aspect of the patella which suggests that injury to the medial patellotibial ligament (MPTL) is underappreciated.
and Hypothesis: The primary goal was to describe the injury patterns in a population of primary (first time) lateral patella dislocators (LPD). A secondary goal was to see if commonly held beliefs about injury patterns were observed in this population. These included:
(1) Patients with a greater number of underlying anatomic risk factors for patellofemoral instability will have less chondral damage.
(2) Skeletally immature patients have more MPFL patellar based lesions.
(3) Bone bruising infers higher forces and is associated with greater cartilage damage.
(4) Injury patterns in primary LPD are not different between the sexes.
A prospective study identifying patients presenting with LPD between 2008-2012. Inclusion criteria were:
1) A history and physical exam consistent with primary LPD
2) An MRI consistent with diagnosis without other significant ligamentous injury
A retrospective chart review was performed. On MRI, the severity and location of cartilage lesions, medial patellofemoral ligament (MPFL) injury, and bone bruising were noted. The data was analyzed by sex and skeletal maturity. Anatomic patellar instability risk factors, such as patella alta, trochlear dysplasia, and increased tibial tubercle trochlear groove distance were recorded and compared to the injury patterns.
This study involved 157 patients; 107 patients were skeletally mature. MPFL injury severity was complete rupture (N=69, 44%), partial (N=67, 43%), and none (N=21, 13%). All partial and complete tears involved the inferomedial aspect of the patella. MPFL injury location was isolated femoral (N=16, 10%), isolated patella (N=26, 17%), isolated mid-substance (0%), multiple locations (N=95, 61%), and none (N=20, 13%). Chondral injury location was patella (N=67, 43%), lateral femoral condyle (N=12%), multiple locations (N=53, 34%), and none (N=26, 17%). A majority (61%) of patellar chondral lesions were at its inferomedial aspect. Chondral injury severity was full thickness (N=81, 51.6%), partial thickness (N=50, 31.8%), and none (N=26, 16.6%). Bone bruising was most commonly a combination of patella and lateral femoral condyle lesions (80.9%).
Underlying anatomic patellar instability risk factors, as defined by MRI, did not predict MPFL, chondral damage, or bone bruising injury patterns. Skeletally immature patients had a greater risk of isolated patellar MPFL or chondral injury. No clear relationship was found between/across the location and/or severity of bone bruising, MPFL, or chondral injury. There was no clear relationship between sex and injury findings.
MPFL and chondral injury, as well as bone bruising, are common following primary LPD. The location of MPFL and chondral injury being centered at the inferomedial aspect of the patella suggests that injury to the medial patellotibial ligament (MPTL) is underappreciated. Underlying anatomic patellar instability risk factors do not predict injury patterns. Skeletal immaturity plays a role in the location of the injury pattern with isolated patellar MPFL/chondral injury being more common in the skeletally immature patient. Bone bruising does not mean greater cartilage damage, as assessed by MRI. Sex does not appear to be a factor in injury patterns after primary LPD.