Acceptable outcomes for isolated medial patellofemoral ligament reconstruction despite using higher thresholds for patella alta and regardless the value of tibial tubercle-trochlear groove distance and the degree of trochlear dysplasia-An international multicenter study.

INTRODUCTION

When planning surgery for treatment of recurrent patellar instability, one of the questions of interest is how far the indications for an isolated medial patellofemoral ligament (MPFL) reconstruction can be extended. This international multicenter study followed the outcomes of patients undergoing isolated MPFL reconstruction using higher thresholds for patella alta and tibial tubercle-trochlear groove (TT-TG) distance imaging measurements than in the current literature and in common practice algorithms.

METHODS

One hundred ninety-nine patients from five countries (USA, Australia, Finland, Japan and Chile) were enrolled. All underwent an isolated MPFL reconstruction. The decision to perform additional stabilization surgery such as a tibial tubercle osteotomy was left to the discretion of the individual surgeon. Patients having additional bony surgery were not included. The guiding principle was a TT-TG distance up to 24 ​mm on magnetic resonance imaging (MRI) and a Caton-Deschamps index (CDI) or Insall-Salvati index (ISI) up to 1.4 were not considered to be an automatic indication for a tibial tubercle osteotomy. Patient-reported outcome measures (PROMs; Norwich Patellar Instability, Marx Activity, and the Knee injury and Osteoarthritis Outcome Score (KOOS) uality of ife scores) were recorded preoperatively and the same PROMS and reinjury (patellar re-dislocation) were recorded at 1 and 2 years, postoperatively.

RESULTS

Sixty-six percent of patients were female and the mean age at surgery was 21 (standard deviation [SD]: 7.4) years. The CDI ranged from 0.7 to 1.7 with a mean of 1.1 (SD: 0.15); 7 ​% patients had a CDI of 1.4 or more. The ISI ranged from 0.7 to 1.9 with a mean of 1.3 (SD: 0.21); 44 ​% patients had an ISI ≥1.4. The TT-TG distance ranged from 4.0 to 29.0 ​mm (mean: 15 ​mm, SD: 4.4 ​mm); 3 ​% patients had a TT-TG distance ≥24 ​mm. Fourteen percent had no trochlear dysplasia, while 51 ​% had Dejour type A dysplasia; the remaining 35 ​% had types B to D dysplasia. Fourteen percent of patients had a J-sign on the affected side. The re-dislocation rate was 2 ​% at 2 years. There were more re-dislocations when the CDI was ≥1.4 compared to when it was <1.4 (p ​= ​0.04). There were no differences in re-dislocation rates based on an ISI threshold of ≥1.4, a TT-TG distance threshold of ≥24 ​mm, or on the grade of trochlear dysplasia (Dejour B, C, or D).

CONCLUSION

Based on the data of this case series, isolated MPFL reconstruction in the setting of increased thresholds for patella alta height and regardless of the value of TT-TG distance and the degree of trochlear dysplasia resulted in a low overall rate of patellar re-dislocation. This finding supports the concept of using higher threshold values for patella alta and TT-TG distance than previously suggested when deciding what surgical intervention is appropriate for a patient with recurrent patellar dislocation, but always in the context of the whole clinical scenario.

LEVEL OF EVIDENCE: III.