الفهرس 
Anatomy of the knee jointOnly 14 pages are availabe for public view
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Abstract
Although intra-articular knee lesions are common, their correct diagnosis still a challenge ,MRI of the knee has become a reliable tool in the detection of knee injuries. Injuries to menisci and cruciate ligaments can be diagnosed on MRI with a high degree of sensitivity and specificity, but accuracy of MRI decreases in patients with multiple injuries .
Complete ACL tears usually cause considerable knee joint instability and reconstructive surgery is typically recommended. In contrast, a partial ACL tear can be treated with physical rehabilitation. Since reconstructive surgery involves significant remodelling, confirmation of the diagnosis is desirable before undertaking unnecessary surgery on patients with incomplete ACL tears.
Arthroscopic examination allows the diagnosis to be confirmed through direct visualisation and probing. Arthroscopies are invasive and require a skilled surgeon. MRI has become a popular and practical tool for the evaluation of ACL injuries with its high degree of accuracy and sensitivity as reported in the literature.
Arthroscopy is associated with several pitfalls, such as a thickened vestigial ligamentum mucosum, a scarred stump of a torn ligament, and an intact synovial sheath, Diagnosis of lesions located in the posterior horns, particularly, may be missed by arthroscopy
MRI is more sensitive in the diagnosis of the medial meniscus and that the specificity is higher for the lateral meniscus with a higher sensitivity for the lateral meniscus and a higher specificity for the medial meniscus.
The sensitivity for meniscal injuries decreased markedly in cases associated with ACL tears. This may be the cause of the low sensitivity detected in medial meniscal tears as most of the cases had associated ACL injuries. However, the sensitivity of the lateral meniscus was not affected
There are several other factors that may contribute to the discrepancy found between arthroscopic findings and MRI reports. The Arthroscopies allow reliable assessment of injury, but are invasive, expensive and require hospitalisation, anaesthesia and an experienced surgeon.
The overall rate of complications following arthroscopy include cellulitis, haemarthrosis, other effusions requiring arthrocentesis,vasovagal reactions, flare of crystal arthropatby, fluid extravasation, allergic reactions to skin preparation, and synovial sinus formation; most events.
Also arthroscopy is not capable of diagnosing important knee disorders as osteocondritis dessicans when the fragment is still in its place also PCL tears are easy to be missed by arthroscopy on other hand its diagnosis is very easy and accurate by MRI also all subchondral lesions are easily missed by arthroscopy collateral ligament are easily detected by MRI very difficult to be seen by arthroscopy
On the other hand MRI accuracy is also affected by factors interpretation of MRI may be influenced by imaging techniques and subjective bias of the reading radiologists. In older patients, false images of meniscal rupture (pseudotear) may be caused by meniscal degeneration, by scarring or by reactive changes around meniscal calcifications. In the absence of a frank meniscal rupture,MRI is not able to distinguish intrameniscal changes induced by trauma and chronic degeneration.
Few anatomical structures in the vicinity of the meniscus can be confused with a meniscal tear (e.g., the transverse geniculate ligament). Two structures, in particular, give an image of posterolateral meniscal pseudotear: the popliteal tendon and the central meniscofemoral attachment of the lateral meniscus. The magic angle phenomenon (due to the orientation of the meniscus fibers in the magnetic field) is another cause of increased signal in the posteromedial aspect of the lateral meniscus.MRI is the most appropriate screening tool before arthroscopy. It is preferable to diagnostic arthroscopy in most patients because it avoids the surgical risks . Also concerning the economic burden especially in a country like Egypt, MRI may decrease unjustified arthroscopies.
MRI as the primary diagnostic tool for internal knee derangements; however, arthroscopy should be done in cases where MRI findings do not agree with the clinical findings of the patients or in cases clinically diagnosed as complete ACL tears where reconstruction surgery is indicated.