Ultrasound imaging and guided injection for an overlooked medial patellar retinaculum tear
Journal
American Journal of Physical Medicine and Rehabilitation
Journal Volume
99
Journal Issue
4
Pages
E58
Date Issued
2020
Author(s)
Abstract
A 19-yr-old elite tennis player had right anterior inferior knee pain whenever he played tennis for more than 10 mins. He stated that the symptom had developed after a knee sprain 3 mos ago. He had received physical therapy for 1 mo with a likely diagnosis of patellar tendinopathy, but the improvement was minimal. As the pain during running and jumping (7/10 on visual analog scale) had made his sport play difficult, he was referred for an ultrasound (US) evaluation. The prescanning physical examination revealed a tender point medial to the patellar tendon, which became more painful while the patella was pushed laterally. US imaging revealed a normal patellar tendon. The medial patellar retinaculum (MPR), a hyperechoic fibrillary structure bridging the patellar tendon and the proximal tibia, also appeared intact at its cranial part (Fig. 1A). However, when the transducer was moved over the tender spot, we identified a hypoechoic slit piercing the lateral attachment of the MPR (Figs. 1B, C). Increased power Doppler signals were observed inside the lesion. With the diagnosis of MPR tear, the patient was given a US-guided perilesional injection using 4 mL 25% dextrose (Fig. 1D). After two injections, he described complete symptom relief and the follow-up US imaging revealed a significant decrease in the hypervascularity and gap width regarding the previously mentioned lesion.FIGURE 1: Ultrasound imaging of the MPR (black arrowheads) (A). A hypoechoic gap (white arrows) is seen at the lateral attachment of the MPR in the short- (B) and long-axis (C) imaging. Ultrasound-guided dextrose prolotherapy for the MPR tear (D). PT, patellar tendon; white arrowheads, needle.The MPR can be divided into two layers. The superficial layer is derived from the fascial extension of the vastus medialis muscle, sartorius muscle, and medial collateral ligament, whereas the deep layer receives fibers from the medial patellar femoral ligament.1 The patella and patellar tendon serve as the lateral border of the MPR, whereas it attaches medially onto the medial tibial condyle. The MPR stabilizes the patella, preventing it from lateral subluxation. In our case, we believe that the MPR was injured during internal rotation of the femur as the tibia externally rotated. Dextrose prolotherapy has been proven useful for treating tendinopathies and osteoarthritis.2 Our case has also shown its potential in promoting fascial repair. Of additional note, the use of US imaging/guidance was not only beneficial for the prompt diagnosis of MPR tear but also avoided any damage to the overlying infrapatellar branch of the saphenous nerve.3 In conclusion, this case highlights an overlooked cause of anterior knee pain in sport injuries and the importance of US in the differential diagnosis and guided interventions for MPR tears.
Publisher
Lippincott Williams and Wilkins
Type
note