Summary
Isolated MPFL reconstruction had a low rate of recurrent patellar instability and it appears that an increase in the previously reported thresholds for when to add a bony procedure to an MPFL reconstruction can result in successful outcomes in some patients.
Abstract
Background
In treating recurrent patellar instability, one of the questions of interest is how far the indications for an isolated MPFL reconstruction can be extended. This ISAKOS-sponsored multi-center study followed the outcomes of patients undergoing isolated MPFL reconstruction using higher thresholds than widely accepted for additional surgery for patella alta and tibial tubercle trochlear groove (TT-TG) distance.
Methods
199 patients from 5 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, but patients having additional surgery were not included. The guiding principle was a TT-TG distance up to 24 mm on MRI and a Caton-Deschamps index (CDI) up to 1.4 were not considered to be an indication for a tibial tubercle osteotomy. Rates of further patellar dislocation and PROMs (Norwich Patellar Instability, Marx Activity and KOOS QOL scores) were recorded preoperatively and at 1 and 2 years.
Results
66% patients were female, 89% had a non-contact injury originally, and13% had a positive family history of patellar instability. The mean age at surgery was 21 (SD: 7.4).
TT-TG distance ranged from 4.0 to 29.0mm with a mean 15.1 (SD: 4.4). CDI ranged from 0.7 to 1.7 with a mean 1.1 (SD: 0.2). Only 14% had no trochlear dysplasia and 45% had Dejour B-D dysplasia. 27/199 (14%) had a J-sign on the affected side.
The re-dislocation rate at 12 months was 2%. and this increased to 4% at 2 years.
The mean preoperative Norwich Patellar Instability score was 36.5 (SD: 23.7). This improved to 25.5 (SD: 23.4) at 1 year and was similar (mean: 24.8, SD:6.20) at 2 years (p<0.0001)
The mean preoperative Marx activity score was 7.7 (SD: 6.4) and did not change significantly at 1 year (mean: 6.8, SD: 5.6) or at 2 years (mean:7.2, SD: 5.7).
The mean preoperative KOOS QOL score was 32.1 (SD:21.2). This improved to 69.8 (SD:23.5) at 1 year and was similar (mean:73.2, SD:21.6) at 2 years: (p<0.0001).
Discussion
The re-dislocation rate and PROMs indicated satisfactory outcomes in this patient cohort. However, the project has highlighted the practical difficulties of addressing the question of how far the indications for isolated MPFL reconstruction can be extended as patients undergoing any bony procedure were automatically excluded and the thresholds for an additional procedure were at the individual surgeons’ discretion. In addition, the re-dislocation rate was low, thereby precluding a useful comparison between recurrent dislocators and patients who had no further instability episodes. Nonetheless, the fact that patients with a CDI of up to 1.7, a TT-TG of up to 29mm, or Dejour D trochlear dysplasia were included, does suggest that an increase in the previously reported thresholds for when to add a bony procedure to an MPFLR can result in successful outcomes in some patients.