CASE REPORT
A 16-year-old man presented to Fujairah Hospital in March 2004 with pain in his right knee joint for the previous 8 months. He was serving in the military and engaged in regular heavy physical activity. He had mildly twisted his right knee joint one year earlier and had been treated with anti-inflammatory medications. He recovered well and continued with his regular activities.
On presentation, the patient had difficulty bending his right knee. He had no history of locking or giving way of the knee, but had pain on standing. On clinical examination, there was mild wasting of the quadriceps muscle, some swelling of the right knee joint, and local tenderness over the medial joint line. The range of movement of his knee was full, with no loss of extension, but the terminal knee flexion (the final 10 to 15 degrees) was painful. McMurray's test was negative, and the collateral and cruciate ligaments were clinically stable. The patellar articular surface was not tender, and patellar movements were normal. The cause of his pain was presumed to be due to internal derangement of the knee, probably caused by a mild meniscal injury.
Magnetic resonance imaging (MRI) of the right knee showed a moderate amount of loculated fluid in the intercondylar fossa, with septations. The radiologist interpreted the MRI as a cyst involving the posterior horn of the medial meniscus. The swelling extended in front of the anterior cruciate ligament (ACL), in between the ACL and the posterior cruciate ligament (PCL), and further extended posterior to the PCL (Fig 1).
The patient underwent arthroscopy of his right knee joint under general anaesthesia through the standard anteromedial and anterolateral portals. The posterior portal was once considered an option while planning the procedure. As we were able to visualise the swelling clearly and were also able to excise a major part of it through the anterior portals, a further posterior approach was not considered.
During the procedure, the cyst was visualised well; it was located in front of the ACL and partially within the ACL close to the femoral attachment. It was ovoid in shape measuring about 15 mm in diameter. The cyst was well demarcated and its origin from the ACL was clearly visualised (Fig. 2). It was transparent and freely mobile. There were no adhesions or signs of inflammation surrounding the swelling. The cyst was thin-walled and easily punctured by the probe. The wall of the cyst lying posterior to the PCL was broken by the probe, and approximately three quarters of the cyst and its wall were excised.
A diagnosis of a cyst arising from the ACL was made. The medial and lateral menisci were normal.
Transparent gelatinous fluid came out of the cyst when it was punctured. The major portion of the cyst wall was resected using the arthroscopy resector. The area around the ACL was probed, and all the septa were broken. The knee was then put through a full range of motion. All other structures within the knee joint were found to be normal.
The cyst wall was sent for histopathological examination. The postoperative course was uneventful. The patient was mobilised in hospital and discharged home the next day. The histopathology report showed greyish-white membranous bits measuring 1.3x0.6x0.3 cm. Microscopic sections showed lobulated fibro-fatty tissue covered superficially by flattened synovial cells. A confluent area of fibrinoid/hyaline change of the stroma was observed, as well as a moderate infiltration by mononuclear leukocytes. Multinucleated giant cells were not seen. All these features were suggestive of a ganglion cyst.
The patient was followed up in an orthopaedic out-patient regularly. At the final follow-up of postoperative 6 months, the patient did not have any complaints and the follow-up MRI showed no signs of any residual cyst (Fig. 3).
Clinical features
Intra-articular swellings such as ganglion cysts may present with pain and/or limitation of the movements of the joint. These may be due to mechanical blocking effects. Some patients present with a clicking sensation and interference during extreme flexion and extension movement. Cysts anterior to ACL tend to limit extension, whereas those posterior to the PCL tend to limit flexion. There maybe joint line tenderness and retropatellar pain. Ganglion cysts may present as palpable masses around the knee joint. Symptoms may grow worse with activity, especially running, jumping, or squatting. The duration of symptoms may last from a few weeks to as long as 5 years. The symptoms are non-specific, and investigations are needed to diagnose the lesion, which usually be found incidentally during MRI or arthroscopy.
Ganglion cysts are differentiated from pigmented villo-nodular synovitis, fibroma, haemangioma, synovial sarcoma, synovial proliferation, myxoma, synovial chondromatosis, aneurysm, and intraarticular lipoma.1
Investigations
MRI and arthroscopy are the usual tools for diagnosing ACL cysts. MRI is the most sensitive, specific, accurate, and non-invasive method for diagnosing these lesions. It can also detect other intra-articular lesions. The ganglion cysts are usually ovoid and well circumscribed on MRI. They have homogeneously low signal intensity on Tl-weighted images and high signal intensity on T2-weighted images. They can extend towards the joint line and around the knee joint. MRI is also useful in detecting any associated internal derangement of the knee, such as ACL or meniscal tears. Other diagnostic modalities such as ultrasound, computed tomography (CT), and arthrography have also been used.
Treatment
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. Other treatment methods include ultrasound-, CT-, and arthroscopic-guided needle aspiration, but these are usually associated with a higher rate of recurrence.
DISCUSSION
Caan first described the ACL ganglion cyst during a routine autopsy in 1924. In the early 1990s, only a few sporadic cases and one main case report were found in the literature.2-12 With widespread use of MRI and arthroscopy in daily practice, an increasing number of cases have been discovered.
Ganglion is a cystic swelling that usually arises close to the tendons or joints. Most often it is encountered over the dorsum of the hand, but it can occur in any part of the body. Its occurrence inside a joint is very rare. The incidence of finding intraarticular cystic masses is 1.3% by MRI and 0.6% during arthroscopy. They may be single or multiple,13 as well as unilateral or bilateral.14 The cysts could be ganglia or synovial cysts. The term ganglion cyst is used to include both lesions. The common site for cystic lesions inside the knee joint is the ACL, followed by PCL, then menisci, especially the medial meniscus. Other rare sites of occurrence are at the infrapatellar fat pad, medial plica, from a subchondral cyst, popliteus tendon, from chondral fractures or subchondral bone cysts. They may arise from alar folds that cover either the infrapatellar fat pad15 or the cruciate ligaments. The cysts of the cruciate ligaments can distend outside along the fibres (anterior to the ACL and posterior to the PCL), between the 2 cruciate ligaments (intercruciate distension-as in our case), or interspersing within the fibres. Nearly two thirds of all ganglion cysts originate from the ACL. They usually arise from tibial insertion. In our case, it was from the substance of the ACL close to the femoral attachment. Meniscal cysts arise both from anterior and posterior horns. Cystic lesions posterior to PCL require additional portals such as posteromedial and posterolateral portals for access during arthroscopy. Intra-ligamentous ganglion cysts are detectable by intra-fibrous probing during surgery, which yields an outflow of whitish or yellowish gelatinous material. The shape of ganglion cysts could be fusiform, spindleshaped, rounded, ovoid, and well-demarcated outlines with a normal size of 5 to 30 mm, rarely up to 40 mm in diameter. They appear uni- or multi-locular and are usually found alone in each knee.16
The cause of ganglion cyst may be due to synovial tissue herniation, connective tissue degeneration after trauma, mucin deterioration of connective tissue, ectopia of synovial tissue, or proliferation of pluripotential mesenchymal stem cells. Patients may have a history of knee trauma.
The clinical features may suggest internal derangement of the knee. Pain is the most common symptom. There are often fusiform swellings on MRI examination. Intra-articular ganglion cysts can be symptomatic or asymptomatic. Krudwig et al.16 reported 85 cases of intra-articular ganglion cysts, of which 9 were symptomatic and 76 were asymptomatic. All the 9 symptomatic patients had no history of trauma. The definite history of trauma in our patient is a significant finding. The possible aetiology may be connective tissue degeneration or re-activation of dormant ectopic synovial tissue in the joint following the trauma.
Brown and Dandy3 found that 95% of their patients had good or excellent results after arthroscopic excision of ganglionic cysts. No recurrence after arthroscopic excision was reported. Intra-articular ganglia of the knee have also been reported to be successfully treated with CT-guided aspiration. Nokes et al.17 aspirated 2 ganglion cysts of the PCL of the knee with an 18-gauge needle and syringe holder, using CT guidance to avoid the popliteal vessels. Thick straw-coloured gelatinous material was aspirated. Both patients had relief of pain and had no recurrence of the ganglia 2 years after surgery. Recurrence is unlikely if the ganglion cyst is treated by excision during arthroscopy.18
CONCLUSION
Diagnosis of intra-articular ganglion cysts should be considered in cases of internal derangement of the knee. Trauma can incite changes in ectopic dormant synovial tissue and lead to cyst formation. These intra-articular ganglion cysts can mimic meniscal tears. Elderly patients may present with pain and tenderness over the joint line, suggestive of intraarticular degenerative lesion. Clinical diagnosis of such cases may be difficult because of their rare occurrence. MRI is helpful in diagnosis and depicting the size and location of the cyst. Arthroscopic resection is the treatment of choice. Slight damage to the wall may result in wall collapse and disappearance of the cyst. All the septa should be ruptured to prevent possible recurrence. Recurrence is very rare following complete resection but can occur after aspiration.
ACKNOWLEDGEMENTS
We wish to thank Dr Kavya Dinakar for her assistance in preparing this manuscript, Dr Mohammed Haroon for interpreting the MRI, Mr Shakeeb Mohammed for preparing the pictures, and Dr Issac Olude for interpreting the histopathological slides.
© 2005 Western Pacific Orthopaedic Association Provided by ProQuest LLC. All Rights Reserved.
Source: Journal of Orthopaedic Surgery
