Intra-articular ganglion cysts of the knee have reported prevalence ranging from 0.2% to 1.3%, detected on knee MRI images, and 0.6%, on knee arthroscopy.3–5
first described the ACL ganglion cyst during a routine autopsy in 1924. In the early 1990s only a few sporadic cases were found in the literature;1 7–11
thus, widespread use of MRI and arthroscopy, owing to increasing the number of cases, is a more recent development in this discpline.12
The pathogenesis of the ganglion cysts remains unclear; nevertheless, probable causative factors include herniation of the synovium into surrounding tissue, connective tissue degeneration after trauma, ectopia of the synovial tissue or proliferation of the pluripotential mesenchymal stem cells.2 5 8
In the instant case, however, the patient had a history of trauma and he presented with clinical features of internal derangement of the knee as the ACL was ruptured; the pain that he experienced limited the range of motions otherwise possible in a sound knee, espeically the loss of 15-degree knee flexion and was one of the main symptoms of the damage.
Krudwig et al9
reported 85 cases of intra-articular ganglion cysts of which nine were symptomatic and 76 were asymptomatic. Symptoms of intra-articular ganglion cysts vary according to their size and location, including pain, joint line tenderness, palpable mass, clicky sound, mechanical knee symptoms such as limitation of extension or flexion. Cysts of the ACL limit extension of joints; on the other hand, cysts of the PCL tend to limit the flexion of knee joint in particular, and in such cases, symptoms may worsen with increased physical activities, for example, running, jumping, standing for long time and squatting.
Ganglion cysts are differentiated from pigmented villo – nodular synovitis, fibroma, synovial sarcoma, myxoma, haemangioma, synovial chondromatosis, synovial proliferation, aneurysm and intra-articular lipoma.2
MRI and arthroscopy are the usual tools for diagnosing intra-articular ACL cysts; thus, the clinical diagnosis of such cases may be difficult due to their rare occurrence.11
Although final diagnoses depend on pathological examination of the excised specimen, arthroscopy provides direct visualisation of the lesion; in our patient arthroscopy revealed a complete tear of the ACL with detachment of the ligament from its femoral attachment. The patient underwent ACL reconstruction with double-bundle rigidfix technique, during which a cyst within the PCL was detected; it was ovoid, 1 cm by 1.5 cm in diameter, thin walled, transparent and well demarcated and was the main cause of the loss of 15-degree knee flexion.
Asymptomatic cysts need to be treated and excised; otherwise, they may become symptomatic later. Arthroscopic resection, debridement and excision are the treatments of choice for ganglion cysts as the rate of recurrence is remote.13 14
Brown and Dandy14
found that 95% of their patients had good or excellent results after arthroscopic excision. No recurrence was reported. Other treatments include ultrasound; CT-guided needle aspiration has also been reported to be successful, but reports indicate the possibility of recurrence of symptoms.
Nokes et al15
reported treating two cases of ganglion cysts: in both cases, ganglion cysts of the PCL of the knee were aspirated using CT-guided fine-needle and syringe holder, in order to avoid the popliteal vessels; both patients had relief from pain and had no recurrence of the ganglia after the follow-up at 2 years. Recurrence is unlikely if the ganglion cyst is treated by arthroscopic excision.14 16
- Diagnosis of intra-articular ganglion cysts should be considered significant in cases of internal derangement of the knee, and gaining awareness of any history of trauma arising out of patient's past ailments or injury is equally important, as diagnosis may later reveal it to be the leading cause for cyst formation.
- Clinical picture of ganglion cysts of the knee may mimic ligamentous and menscical injuries.
- Arthroscopic resection is the treatment of choice, given the absence of symptoms recurrence post-surgery.