Background: Patellofemoral instability (PFI) is a common problem with various anatomic risk factors identified, including patella alta as one of the most powerful predictors. Given that the medial patellofemoral ligament (MPFL) is the primary soft tissue stabilizer of the patella, a common procedure to treat recurrent patellar instability is MPFL reconstruction. The aim of this study is to examine the relationship between MPFL reconstruction and patellar height. We hypothesize that after reconstruction, patellar instability patients would have demonstrable reduction in patella height and patella alta correction.
Methods: Patient records were queried for patients who underwent MPFL reconstruction for recurrent patellar instability. Patient and operative demographics were collected. We measured Insall-Salvati ratio (ISR), Caton Deschamps index (CDI), and Blackburne-Peel ratio (BPR) in all patients at various time points. The height indices were compared across the preoperative, immediately postoperative, and 6-month time points in a pairwise fashion using paired-sample t-tests. Further subgroup analysis of patients (n=27) with elevated preoperative Caton Deschamps Index (defined as >1.3) was completed.
Results: The final cohort was 103 patients. There was a significant difference between pre- and postoperative ISR (P<0.001) and at 6-month follow up (P<0.001), between preoperative CDI and the 6-month follow-up (P<0.0010), and between the postoperative and preoperative CDI (P<0.001). There was also a difference between preoperative and postoperative BPR (P<0.001), as well as between the preoperative and 6-month follow-up BPR (P=0.002). Twenty-seven patients had an initial CDI greater than 1.3. Differences were observed between pre- and postoperative mean CDI (P=0.001) and at 6-month follow-up (P=0.006), between both postoperative and 6-month ISR (both P<0.001), and preoperative mean BPR and the postoperative (P=0.004) and 6-month mean BPR (P=0.027).
Conclusions: Patients with pre-existing patella alta and recurrent patella dislocations who undergo isolated MPFL reconstruction have decreased patella alta at their 6-month follow-up as measured by ISR, CDI, and BPR. Patients without patella alta do not demonstrate statistically significant differences after their MPFL reconstruction.
Level of evidence: III (retrospective comparative study).
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