1JollyClinics, Kaohsiung, Taiwan
2Department of Radiology, Taichung Veterans General Hospital, Taichung, Taiwan
A 62-year-old woman complained about anterior medial knee pulsating pain and soreness for months after suddenly standing up with a “pop” sound at her left posterior knee. She was injected with intraosseous platelet-rich plasma (PRP) after magnetic resonance imaging (MRI) showed bone marrow edema in the anterior intercondylar area of tibia (Figure 1). However, her symptoms persisted even after the treatment.
Ultrasound examination just below the medial gastrocnemius muscle, between the popliteal artery and the semimembranosus muscle and above the oblique popliteal ligament, revealed a calcifi ed loose body at the posterior knee region of the patient (Figure 2). Scans of the loose body showed the inferior medial genicular nerve and accompanying artery crossing the loose body and then proceeding laterally and inferiorly to her medial condyle of the tibia. The loose body also appeared on MRI (Figure 1).
The calcified loose body was assumed compressing the inferior medial genicular nerve, considering the pulsating pain she reported. A diagnostic hydrodissection was performed to separate the inferior medial genicular nerve from the calcifi cation (Figure 3). Hydrodissection by 5% dextrose was performed to release the nervi nervorum or vasa nervorum compression for compressive neuropathy . After this treatment, the patient reported 70% pain relief and sound sleep. Ultrasound-guided barbotage of the calcifi cation, a technique previously used by Niazi and Hetta  in shoulder calcifi cation tendinitis, was then conducted (Figure 4).
The inferior genicular nerve arises from the tibial nerve at the popliteal region just below the area where the tibial nerve gives the motor branch to the medial gastrocnemius muscle. This nerve travels laterally below the medial gastrocnemius muscle and semimembranosus muscle and proceeds lower to the medial condyle of the tibia. The inferior genicular nerve conducts sensory distribution to the inferomedial and anteromedial parts of the joint capsule and the tibia periosteum. Some fibers from the infrapatellar branch of the saphenous nerve supply the cutaneous layer, but some variants have fi bers to the anteromedial part of the joint capsule . The lesions along the inferior genicular nerve may cause nerve compression and medial knee pain (Figure 5).
Figure 1. Magnetic Resonance Imaging (MRI)
(A) Sagittal proton-density-weighted fat-suppressed MRI of the left knee in this 62-year-old woman shows bone marrow edema in the anterior intercon-
dylar area of tibia, (B) horizontal tear of the posterior horn of the medial meniscus, and (C) ganglion cyst and calciﬁed loose body in the posterior knee.
Figure 2. Posterior Knee Loose Body
(A) Transverse view. (B) Longitudinal inferior medial genicular
nerve (IMGN) from the tibial nerve.
Abbreviations: MC, medial condyle; MG, medial gastrocnemius; N.MG, nerve to the medial gastrocnemius; OPL, oblique popliteal ligament; PA, popliteal artery; SemiM, semimembranosus muscle; SemiMt, semimembranosus tendon; TN, tibial nerve.
Figure 4. Treatment
(A) Ganglion cyst like aspirate, the loose body may be a meniscal cyst or posterior cruciate ligament ganglion origin. (B, C) Calciﬁed aspirated. (D) Echo Guide image with an 18-inch needle.
Intra-articular loose bodies could present as synovial chondromatosis, which may develop as a consequence of other joint diseases, such as degenerative joint disease, osteochondritis dissecans, neurotrophic arthritis, tuberculosis arthritis, and osteochondral fractures. This condition is common among adults between 40 and 60 years of age. Those chondral foci are detached from the synovium and form intra-articular loose bodies. Bilgili et al.  studied the localization features of secondary chondromatosis and found that the most easily observed area is posterior to the posterior cruciate ligament (PCL) region. The presence and number of secondary chondromatosis increase in patients with a high degree of osteoarthritis and meniscal injury.
However, the sesamoid bone must be considered in the differential diagnosis. Samuels reviewed the patellar sesamoid bones, namely, patelloid, lunula, fabella, parafi bula, and cyamella . On the basis of position, a cyamella posterior to the PCL and inferior to the popliteus was highly suspected. However, differentiating between the two is diffi cult without histological evidence. Nevertheless, the ganglion cyst beside the loose body was aspirated, and triamcinolone was injected at the fi rst visit of the patient. Its origin was hypothesized to be pathological.
In conclusion, medial knee pain is common in clinical practice. Bone marrow edema can be treated through intraosseous injection with PRP or bone marrow aspirate concentrate. However, if the clinical symptoms showed no improvement even after the treatment, other causes of medial knee pain must be considered. The inferior medial genicular nerve can be entrapped by a cystic, osteochondral, tendon, or ligamentous lesion near this area. Complete ultrasound tracing can be performed from the tibial nerve to the distal end to evaluate this nerve.
For the ultrasound video please refer to this link: https://reurl.cc/X46jy3.
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