MRI but not arthroscopy accurately diagnoses femoral MPFL injury in first-time patellar dislocations

Abstract

Purpose: The purpose of this study was to investigate whether the femoral part of the medial patellofemoral ligament (MPFL) and its injury can be accurately assessed by standard knee arthroscopy in first-time patellar dislocations or whether preoperative MRI is required to determine injury location in patients where primary MPFL repair is attempted.

Methods: Twelve patients with acute first-time dislocations and MRI-based injury of the femoral MPFL and ten patients with recurrent patellar dislocations underwent knee arthroscopy with the use of a 30-degree optic and standard antero-medial and antero-lateral portals. The femoral origin was marked with a cannula under lateral fluoroscopy. Arthroscopic findings of the location of the native femoral MPFL and its injury were compared to the results of MRI and mini-open exploration.

Results: In acute cases, the average time from primary patellar dislocation to MRI evaluation was 3 days (1-9 days), and the average time from MRI to surgery was 8 days (3-20 days). The native femoral origin of the MPFL was not visible in any of the chronic cases during arthroscopy. In addition, in all acute cases, arthroscopy failed to directly visualize injury of the femoral MPFL (0 of 12), but mini-open exploration confirmed injury in 11 of 12 patients. This means that arthroscopy was less accurate than MRI for the diagnosis of femoral MPFL injury (P < 0.05).

Conclusion: The results of this study indicate the limitations of knee arthroscopy in identifying the femoral disruption of the MPFL, a crucial injury that occurs in patellar dislocations. Thus, if a primary MPFL repair is planned, determination of the site of repair should be based on the preoperative MRI.

Level of evidence: Diagnostic study of non-consecutive patients, Level III.

Figures

Fig. 1

The femoral origin of the MPFL (red circle) was determined under lateral fluoroscopy according to the method described by Schoettle et al. [14] and was marked with a cannula (arrow)

Fig. 2

The appearance of a complete femoral MPFL injury with retraction of the MPFL fibres anteriorly (thick arrow) and surrounding oedema (small arrows) in a 25-year-old woman 5 days after primary patellar dislocation

Fig. 3

The appearance of a combined injury of the MPFL with tear, surrounding oedema near the adductor tubercle and discontinuity at the patellar insertion (arrows) in a 14-year-old girl 2 days after primary patellar dislocation

Fig. 4

Arthroscopic appearance of the medial recessus in a 25-year-old woman with an MRI-based complete disruption of the MPFL (please see Fig. 2) 20 days after patellar dislocation. The synovial tissue is intact with some blood residues and haematoma shining through the synovial membrane. The MPFL injury is not directly visible

Fig. 5

Arthroscopic appearance of the medial recessus in a 13-year-old girl 9 days after primary patellar dislocation (a). After transection of the synovial membrane, haematomas became obvious in projections of the femoral MPFL (b), and partial tearing and stretching of the MPFL (arrows) were confirmed by mini-open exploration (c)

Fig. 6

MRI shows combined injury of the MPFL with tear, surrounding oedema near the adductor tubercle and discontinuity at the patellar insertion (arrows) in a 13-year-old girl 3 days after primary patellar dislocation (a). Arthroscopy discovered haematoma at the patellar margin (b), but mini-open exploration could not confirm a substantial disruption of the medial ligamentous complex