1
ACL Ganglion Cyst
1.1
Background
Anterior cruciate ligament (ACL) ganglion cyst is a microtraumatic pathology that has been found to be associated with insidious onset of chronic knee pain in athletes. This condition may present as a limitation in knee range of motion (ROM) due to pain or mechanical blocking [ ]. A ganglion cyst contains a mucin-rich fluid surrounded by a pseudomembrane.
These cysts are difficult to diagnose clinically as they are not palpable. The incidence of intraarticular ganglia cyst of the knee has been reported to range from 0.20% to 1.33% on knee magnetic resonance imaging (MRI) and 0.6%–2% on knee arthroscopy [ , ]. Almost 62% of them are located on the ACL. Other frequent locations are knee collateral ligaments and posterior cruciate ligament. ACL ganglion cyst coexists with ACL mucoid degeneration in about 35% of cases ( Fig. 8.1 ).
The mean age of patients with ACL ganglion has been reported to be 39 years old [ ], although isolated cases in children aged between 2 and 12 years old have been reported in the literature [ , ]. Male preponderance has been reported and no genetic predisposition has been described [ ].
The exact pathogenesis of ACL ganglion cyst is still controversial. Theories proposing to explain this condition include mucinous degeneration of connective tissue mediated by the local release of hyaluronic acid, displacement of synovial tissue during embryogenesis, and herniation of synovium into a defect of the surrounding tissue [ , ]. There are no fixed groups of symptoms that are pathognomonic of this condition and it is often discovered incidentally on MRI or knee arthroscopy while investigating painful and stiff knees.
MRI remains the gold standard imaging technique for evaluating an ACL ganglion cyst [ , ].
The treatment is essentially arthroscopic with excellent results [ ].
1.2
Clinical Study
1.2.1
Symptoms
There are no specific groups of symptoms that are used to diagnose ACL ganglion cyst. These lesions should be suspected in patients with chronic knee pain and limitations in knee ROM.
Isolated ACL ganglion that is alone responsible for knee symptoms without any concomitant intraarticular pathology is regarded as “symptomatic,” while incidentally detected ACL ganglion cysts associated with other knee lesions are classified as “asymptomatic” and are not necessarily responsible for the painful symptoms.
The most common presentation is chronic knee pain of insidious onset. This pain is worsened by extreme knee movements. Duration of symptoms can range from weeks-to-months and sometimes years [ ]. Mechanical locking, clicking sensation, and stiffness also occur frequently. A ganglion cyst that is located anteriorly to the tibial attachment results in extension limitation, while a cyst that is located posteriorly produces flexion limitation [ , ]. There is commonly no history of knee instability.
These symptoms are mostly of spontaneous onset without a history of trauma. When trauma is reported, it is usually minor and of little significance.
1.2.2
Physical examination
The clinical examination may reveal knee joint effusion [ ].
Joint line tenderness can be present on palpation of the medial and lateral aspects of the knee [ , ].
Limping and decreased gait speed can be observed and are related to pain intensity [ ].
Active and passive knee ROM can have a certain limitation [ , ].
The ACL stability tests such as the anterior drawer test ( Fig. 8.2 ), Lachman test ( Fig. 8.3 ), and pivot shift Tests ( Fig. 8.4 ) are negative.
1.3
Differential Diagnosis
1.3.1
Popliteal cysts
The patient usually presents with posterior knee pain and a limitation in knee ROM can be found on physical examination.
1.3.2
Knee bursitis
The patient will usually complain of local pain, tenderness, or swelling in the site of the affected bursae.
1.4
Imaging
1.4.1
Conventional X-rays
There are no specific signs of ACL ganglion cyst on conventional X-rays.
1.4.2
CT scan and arthrography
Both of these radiological examinations are specific, but they are of low diagnostic value because of their lack of sensitivity.
1.4.3
Magnetic resonance imaging
MRI scan is the gold standard investigation because of its multiplanar capability, superior identification, and morphologic interpretation of synovial tissue and ability to detect other intraarticular pathologies. It is sensitive, specific, noninvasive, and useful in planning operative treatment.
An ACL ganglion cyst appears as a fusiform or rounded structure. This structure is surrounded by a clear boundary extending along the course of the ligament. ACL ganglion cyst shows as hypointense signals on T1-weighted images and as hyperintense signals on T2-weighted images ( Fig. 8.5 ).
Bergin defined MRI diagnostic criteria for ACL ganglion cyst [ ]. Fluid signal in the substance of the ligament with at least two of the three following criteria have to be present in order to be able to retain the diagnosis.
- 1
Mass effect on normal ACL fibers
- 2
Ligament signal stronger than joint fluid
- 3
Lobulated aspect with definite margins
Associated internal lesions such as meniscal tear and articular cartilage damage have been reported in 22%–50% of patients [ ].
1.5
Treatment
1.5.1
Conservative management
1.5.1.1
Medical treatment
Pain killers and nonsteroidal antiinflammatory drugs (NSAIDs) may be indicated by clinicians and can play a role in reducing the perceived pain. Pain response to these treatments is only partial.
1.5.1.2
Rehabilitation
A well-conducted rehabilitation program should be undertaken by the patients before and after surgery.
Such program should focus on pain management and gain in ROM while maintaining the flexibility of lower limb muscles.
Strengthening programs for the lower extremities play a role in pain management before surgery and are essential after surgical management in order to facilitate recovery.
1.5.2
Procedures
Computed tomography (CT) scan and an ultrasound (US)-guided aspiration have been tried with excellent results [ ]. This procedure is reported to provide instant relief of pain and improvement in ROM. However, there are concerns about the possibility of recurrence since it is impossible to completely remove the sac of the cyst. To the best of our knowledge, no recurrence has been reported after percutaneous treatment. Another drawback of this method is the inability to address associated intraarticular pathologies. This method may only be considered in select cases of symptomatic ACL ganglion cysts. Campagnolo [ ] reported the use of CT scan aspiration in athletes. An 18-gauge needle was used and local anesthetic was given to the patients. A resolution of the pain and the locking sensation of the knee was observed almost immediately.
1.5.3
Surgical treatment
Arthroscopic decompression with debridement of the cyst is the treatment of choice for instant relief of pain, improvement in ROM, and return to play.
At arthroscopy, ACL ganglion cyst appears as a cystic mass with defined margin on the ligament.
Arthroscopy allows complete excision of the cyst, along with diagnosis and treatment of other associated intraarticular knee disorders. No recurrence of symptoms or cyst on MRI postarthroscopic excision has been reported in the literature with five years as the longest follow-up [ , ].
2
ACL Mucoid Degeneration
2.1
Background
ACL mucoid degeneration is an uncommon knee overuse injury in athletes. The pathogenesis, the prevalence, and the association with other intraarticular knee structural damage are still poorly estimated.
This condition often presents with progressive knee pain, restriction in ROM without a significant history of trauma, and without knee instability.
It is characterized by degeneration of collagen fibers of the ligament and deposition of new glycosaminoglycans [ ].
With the use of MRI to evaluate the painful knee joint conditions, ACL mucoid degeneration is increasingly being diagnosed incidentally. The prevalence of this condition on MRI of the knee is about 4.3% and the median age of diagnosis is 43 years old [ ].
The pathogenesis of ACL mucoid degeneration is still unclear, but previous knee injury, ganglion cyst, and the degenerative process leading to the loss of synovial lining of the ACL have been suggested [ ].
It was also reported that ACL mucoid degeneration might be due to repeated microtrauma. However, in older patients, it could be due to progressive degenerative ACL lesion with a concomitant meniscal lesion.
Treatment is mainly surgical.
2.2
Clinical Study
2.2.1
Symptoms
Insidious onset of chronic knee pain located behind the patella is the most common complaint [ , ].
Symptoms can last weeks to months.
Pain may limit the movements of the knee in maximal degrees of flexion or extension. There is usually no history of significant trauma, and when present, it is normally minor. Pain and limitation in ROM have been attributed to both increased volume and tension within the ligament [ ].
Locking and grinding sensations may be present.
2.2.2
Physical examination
Clinical examination may show limitation of ROM, joint line tenderness, and joint swelling. A positive grinding test of the meniscus may be present in case of concomitant meniscus injury [ ].
The Lachman test, anterior drawer test, and pivot shift test for ACL integrity are usually negative.
These clinical features, however, are not pathognomonic for ACL mucoid degeneration as they are common presentations of internal knee derangement. However, they should raise suspicion and prompt further evaluation with MRI especially if the symptoms are nonspecific and resistant to NSAIDs and physiotherapy.
2.3
Differential Diagnosis
ACL mucoid degeneration can be mistakenly diagnosed as ACL rupture on MRI.
2.4
Imaging
2.4.1
Standard X-rays
Conventional X-rays will reveal potentially associated osteoarthritic changes, but they do not have any specific role in the diagnosis of ACL mucoid degeneration.
2.4.2
Magnetic resonance imaging
MRI is the main radiological investigation in the diagnosis of ACL mucoid degeneration. The MRI features of ACL mucoid degeneration are abnormal thickening of the ACL, an increased intraligamentous signal on all sequences (intermediate signal intensity on T1-weighted images, high signal intensity on T2-weighted images, and proton density weighted images) and maintenance of normal orientation and continuity of the ligament ( Fig. 8.6 ).
