Differentials
Anterior cruciate ligament tear
SIGNS / SYMPTOMS
Subluxation on twisting, turning, or pivoting; some patients can feel this coming on, while other patients are not able to feel it and may experience frequent falls due to their injury.
Positive Lachman's test, anterior drawer test, and pivot shift test on physical examination.
INVESTIGATIONS
MRI scan reveals ruptured anterior cruciate ligament (ACL) and disruption of ACL fibres, usually associated with bone bruising in acute setting.
Medial collateral ligament sprain
SIGNS / SYMPTOMS
True dynamic instability is rare, unless it is a complete tear or associated with other injuries. Tenderness over medial collateral ligament (MCL) course/insertion may be present. MCL stress testing reveals laxity and/or pain.
INVESTIGATIONS
MRI scan reveals fluid around or injury to MCL and differentiates between an isolated MCL injury and one combined with a meniscal tear.
Subsequent x-rays may reveal calcification along previously injured MCL (Pellegrini-Stieda's disease).
Posterior cruciate ligament sprain
SIGNS / SYMPTOMS
Patient is often able to continue activity but notes that the knee does not feel right.
Instability may be more subtle, with knee effusion typically small and less noticeable. In addition, the posterior drawer test is positive.
INVESTIGATIONS
MRI scan reveals disrupted posterior cruciate ligament and intact menisci.
Lateral collateral ligament sprain
SIGNS / SYMPTOMS
Local swelling is common, but significant effusion is rare. There is tenderness over the lateral collateral ligament (LCL) and/or bony insertion.
A complete tear often results in a palpable gap.[30]
INVESTIGATIONS
MRI reveals fluid around or disruption to the LCL and differentiates between an isolated LCL and one combined with a meniscal tear.
Osteochondritis dissecans
SIGNS / SYMPTOMS
A joint condition in which some parts of the joint cartilage and bone lose their blood supply due to an unknown aetiology, and may detach from the joint surface. Adolescents are commonly affected. May present with knee pain and swelling. Catching of the knee can occur, especially during or after sporting activity.
INVESTIGATIONS
X-ray or MRI scan of the affected knee will reveal the osteochondral lesion. MRI can be of particular use in detecting the early phase of the condition.
Osteochondral fracture
SIGNS / SYMPTOMS
Caused by a twisted knee, usually occurring during sporting activity. Presents with knee pain, swelling, and catching. The osteochondral fragment is detached. The medial femoral condyle is frequently involved.
INVESTIGATIONS
X-rays or other advanced imaging including CT scan or MRI may demonstrate the osteochondral fragment.
Medial synovial plica syndrome
SIGNS / SYMPTOMS
The synovial fold on the medial side of the knee is called the medial plica. This structure is sometimes exposed to direct injury or impingement between the patella and medial femoral condyle. It may also be injured in overuse syndromes. The injured medial plica causes irritation and inflammation of the knee presenting with knee swelling and pain usually in a medial distribution, although can involve the superior or lateral aspect of the knee.
INVESTIGATIONS
MRI scan usually confirms the diagnosis. However, arthroscopy may be necessary.
Osteoarthritis
SIGNS / SYMPTOMS
Degenerative meniscal tears are common in osteoarthritis (OA).
Patients with OA are usually aged >45 years and may present with activity-related joint pain, with either no morning joint-related stiffness or morning stiffness that lasts no longer than 30 minutes.[31]
INVESTIGATIONS
Diagnosis of OA is usually clinical.[31] There may be an absence of acute trauma in patient history.
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