Thursday, October 22, 2015

A Torn Meniscus and the Moon

The menisci of the knee are crescent-shaped pieces of cartilage which lie between the femur and tibia, and serve to cushion the weight of the body and reduce friction during movement. Here is a view of the menisci from above, looking down on the tibia, depicting the medial meniscus (blue arrows) and the lateral meniscus (green arrows):

You can see why these pieces of cartilage are called menisci, from the Greek "meniskos", or "lunar crescent". Consider the similarity to the crescent of the moon:

Images from a knee MRI of a 59 year old male, who heard a "pop" walking down some steps, and had subsequent knee pain:

This coronal T2 fatsat image identifies a torn medial meniscus, with an inferiorly displaced meniscal fragment (red arrow). There is a trace of marrow edema (yellow arrow) subjacent to the torn meniscus.

A series of sagittal images (medial to lateral) identifies the displaced meniscal fragment (red arrows) as well as the adjacent truncated undersurface of the meniscus (blue arrows):

An axial intermediate image also visualizes the displaced meniscal fragment:

A magnification of this axial view better shows the meniscal fragment (red arrows) underneath the posterior oblique ligament (green arrow):

Inferiorly displaced flap tears were first described in the radiology literature by Lecas et al. (AJR 2000; 174:161-164). More recently, McKnight et al. (Skel Rad 2010: 39:279-283) have described common patterns of displaced meniscal tears on MRI. They noted that meniscal fragments can be displaced inferiorly or superiorly, and displaced tears can affect both the medial and lateral meniscus. As noted by both authors, flap tears that are displaced peripherally can be overlooked at arthroscopy, as they are not immediately visible to the arthroscopist.

The patient in this case was taken to arthroscopy. In this arthroscopic image, we see the torn meniscus located between the femur and tibia. Note that the displaced meniscal fragment is not apparent:

The arthroscopist was alerted to the presence of the fragment by the preoperative MRI, and used a hook to probe the region in question:

This enabled the arthroscopist to deliver the displaced fragment back into the joint:

The displaced fragment was then resected, and the meniscus trimmed back to a stable rim.

This case illustrates the type of important information a preoperative MRI can provide to the orthopedic surgeon. This information enhances appropriate pre-operative planning, and maximizes the ability of the surgeon to provide optimal care to the patient.

Vic David MD

Friday, June 22, 2012

Golfing and Rib Pain


Golfing injuries— could anything be worse for the avid golfer? Taking a sport you love, and making it painful. Injuries are typically of the upper extremity, and include tendonitis and hook of the hamate fractures. Injuries of the torso are less common, but can also occur.

In this case, a 27-year-old golfer presented to his physician with upper back pain. Conventional radiographs revealed no abnormalities, and the patient was sent for an MRI.
A coronal STIR image reveals bone marrow edema in two adjacent ribs in posterior left hemithorax:

Corresponding abnormal signal is seen on a coronal T1 weighted image:

The findings are diagnostic of rib stress fractures, secondary to overzealous golfing. Goyal et al. described several pertinent features of rib stress fractures in golfers:

--> injury usually occurs in beginners who golf frequently.

--> patients present with vague discomfort of the upper back, which is often mistaken for muscle strain.

--> conventional radiographs may show rib fractures, but they are often normal. Bone scintigraphy shows a characteristic pattern of abnormal focal uptake in the medial aspect of one or more posterior upper ribs (usually the 2nd-7th ribs).

--> affected ribs are typically contralateral to the patient's dominant hand (but these injuries can also occur on the dominant hand side).

--> proposed mechanism is that inexperienced golfers repetitively strike the ground when they swing their club. This causes a forceful traction of the serratus anterior muscle, which consequently places stress on the ribs.

Stress fractures can occur in golfers in other locations, including the tibial diaphysis, proximal phalanx, sternum, ulnar diaphysis, and acromion. The hook of the hamate and ribs remain the most common location of stress fractures, however.

Watch your form, and happy golfing!

Vic David MD

Monday, May 14, 2012

Shape of the Sacroiliac Joint

Man with psoriasis

Systemic diseases can have osteoarticular manifestations. A classic set of diseases that can manifest in the region of the sacroiliac joint are the HLA-B27 spondyloarthropathies, which include ankylosing spondylitis, reactive arthritis, and psoriasis.

Part of the radiologic evaluation for these diseases can include studies of the sacroiliac (SI) joint. Conventional radiographs are typically obtained, but in some cases CT and MRI are also used. Ironically, the hardest one of these three exams to interpret accurately is the low tech X-ray. The non-tomographic nature of x-ray, overlapping bowel gas, and the curving nature of the SI joint all confound interpretation.

In this post, we will try to clarify the standard AP view of the pelvis, which visualizes the SI joint. The shape of the SI joint is worth noting:

This is an oblique view of the pelvis skeleton with the sacrum removed, viewed from the inside looking out. It depicts the origin of the iliacus muscle along the ilium (red outline) anteriorly. The articulation of the sacrum with the ilium is depicted in orange, outlined by the red arrows. (The blue arrows point out non-anatomic raised pins that hold the sacrum in place, and these pins should be ignored).

Note how the SI joint has a saddle-shape, with the anterior portion of the joint extending more superiorly than the posterior portion of the joint.

This photograph of the pelvis, with the sacrum removed, depicts the iliac side of the sacroiliac joint articulation (region outlined by the red arrows):

A series of CT images, posterior to anterior, show that the inferior edge of the posterior aspect of the SI joint (second frame) is just medial to the inferior edge of the anterior aspect of the joint (last frame):

If we put this information together, we can better understand the AP view of the pelvis:

Red arrows = posterior aspect of joint. Green arrows = anterior aspect of joint. In the area above the yellow arrow, we visualize only the anterosuperior aspect of the joint.

Armed with this knowledge, we can better evaluate the SI joint on x-ray, but this remains a challenging endeavor. Ultimately, some patients will need CT or MRI to better evaluate the complex anatomy in this region.

Vic David MD

Sunday, April 15, 2012

A Missing Mass in the Hand

 From by qthomasbower

Radiologists depend on two things to detect abnormalities that otherwise blend into the adjacent structures of the body: 1) abnormal contrast and 2) abnormal morphology. Not surprisingly, we are much better at detecting abnormalities when the pathology has differential contrast. When the abnormality is simply a variation in morphology, the detection rate falls.

In this case, a 17-year-old girl was sent to a hand surgeon because of a painful, bluish mass in the palm. She came to the appointment with an MRI scan, which was interpreted as normal. The clinical examination clearly revealed a palpable mass in the palm. Given the discrepancy between the MRI and clinical findings, the MRI scan was reviewed again.

In the area of clinical question, an axial T1-weighted image reveals a morphologic abnormality that is the same signal as muscle:

The mass is isointense to muscle on T2-weighted images:

Here is a comparison axial image from a normal patient. The normal flexor digitorum profundus (yellow arrow), flexor digitorum superficialis (green arrow) and lumbrical muscles (blue arrow) are identified:

The shape of the lesion in our patient is best seen on a coronal T1-weighted image, where a fusiform structure that is isointense to muscle is well-seen:

The MRI findings are diagnostic of an anomalous flexor digitorum superficialis (FDS) muscle. This is an uncommon accessory muscle that can present as a painful mass or pseudotumour within the palm. Stephens et al. (Can J Plast Surg, 15:44-46, 2007) described a similar case, and noted that there are three anomalies of the FDS that supplies the index finger:

1) Muscle belly originates in the forearm and extends distally into the carpal tunnel but not further into the palm.

2) Digastric form exhibiting continuity by way of a tendon between the palmar and forearm bellies. Patients with this form may present with a palmar mass or carpal tunnel syndrome.

3) Proximal tendon of the muscle attaches either to the base of the thenar eminence or the transverse carpal ligament.

If the anomalous muscle is causing symptoms (typically carpal tunnel syndrome or pain due to local pressure effects), then a total or partial resection can be performed.

Take away points from this case:

--> If a patient presents with a palpable mass, and you do not see anything on initial review of an MRI examination, consider the possibility of an anomalous muscle, especially in the hand and wrist, where anomalous muscles are relatively common. In other areas of the body, consider the possibility of a nonencapsulated lipoma or a fascial herniation, two other entities that are detected by morphologic changes, rather than by differential contrast

--> One of the strengths of MRI is the superb tissue contrast it offers. The vast majority of pathologic conditions will exhibit differential contrast, but strict reliance on tissue contrast to detect pathology will inevitably lead to a missed diagnosis. It is also important to consider morphologic disturbances, which can be much more subtle.

Vic David MD

Sunday, March 18, 2012

Fins and Pectoral Tears

 Photo by laprimadonna

"Pectoralis" is Latin for "of the breast", and is derived from pectus ("breast, chest"). The pectoral structures take on various forms in the branches of the tree of life. For example, in the water, fish use their pectoral fins to help control their direction during swimming. In cetaceans (e.g. dolphins) pectoral fins are similar to the skeletal structure of land mammals, with fingers and ball and socket joints.

In humans, the pectoralis major is the main muscle of the anterior chest:

As discussed before, tears of this muscle occur almost exclusively in males, as a rule. Rules are made to be broken, however...

In this case, a 53 year-old female complained of severe shoulder pain after moving furniture over the weekend. Her clinical examination was confusing, and she was sent for an MRI for further evaluation. The alert MRI technologist noted edema along the anterior shaft of the humerus: 

The MRI technologist then obtained additional axial images through the area in question, enabling visualization of a partial tear of the pectoralis major tendon at its humeral insertion:

An axial intermediate-weighted image better shows the anatomy of the partially torn pectoralis tendon (red arrow), the shaft of the humerus (yellow arrow), and the deltoid muscle (green arrows).

Tears of the pectoralis muscle and tendon are rare in women, and have been infrequently reported in the literature. In one example, a partial tear of the pectoralis major muscle masqueraded as a breast mass in an 87-year-old woman (Povoski and Spigos, Acta Radiologica 43, 615–616, 2002). The clinician may not consider this diagnosis. When edema is seen anterior to the proximal shaft of the humerus, additional axial MRI images should be obtained through the area, as in this case.

Vic David MD

Thursday, February 16, 2012

Jammed Finger

Photo by ToastyKen

A "jammed finger" is a common injury of the proximal interphalangeal (PIP) joint. It is an imprecise term, which subsumes a variety of injuries that are typically related to axial loading and hyperextension forces.

The injury results in swelling around the joint, reflecting soft tissue injury.

Photo by xadrian

Mild forces result in disruption of the volar plate, a collagenous structure that forms the floor of the joint. In this case, a 43 year old male suffered an injury to his finger two years ago, and reinjured his finger several weeks before he was sent for his MRI.

A sagittal T2 fatsat image reveals disruption of the volar plate of the PIP joint (red arrow) and dorsal subluxation of the middle phalanx (yellow arrow):

A sagittal intermediate image better depicts the torn, macerated volar plate:

Here is a normal volar plate, for comparison:

Volar plate injuries can be a pure soft tissue injury, but can also be associated with fractures at the attachment of the volar plate on the base of the middle phalanx. With more substantive force, there can be tears of the collateral ligament, and this can create joint instability.

Most volar plate tears are treated conservatively, with splinting and buddy taping. If an injury cannot be reduced, one should suspect interposition of soft tissue structures.  Fracture-dislocations that are unstable, exhibit persistent subluxation of the middle phalanx, or involve large portions of the articular surface should be referred for surgical fixation. 

Vic David MD

Tuesday, January 17, 2012

Bubbles in a Paralabral Cyst

Photo by Artolog
SLAP lesions and paralabral cysts are well-known lesions of the shoulder. Although classically associated with the throwing athlete, they can be seen with relatively sedentary patients as well. Any busy radiologist will see dozens on SLAP lesions every year, with some of these lesions harboring paralabral cysts.

In this case, a 38 year-old male with a history of a prior distal clavicular resection presented to his orthopedic surgeon with persistent shoulder pain. He was referred for an MR arthrogram, to elucidate the cause of his pain.

A coronal T2 fatsat image demonstrates a SLAP lesion (red arrow) as well as a large paralabral cyst (yellow arrows) that occupies the suprascapular and spinoglenoid notches:

An adjacent coronal image again depicts the SLAP lesion (red arrow), and also reveals an oval focus of decreased signal (green arrow) within the paralabral cyst:


A coronal T1 fatsat image demonstrates additional hypointense foci within the paralabral cyst (green arrows); the paralabral cyst (pink arrows) is primarily hypointense on this pulse sequence, but a portion of the cyst does fill with gadolinium (yellow arrow):


An axial intermediate image depicts the overall anatomy nicely, showing the posterosuperior component of the SLAP lesion (red arrow), paralabral cyst (yellow arrows) and hypointense material (green arrow) within the cyst:

What is the hypointense material within the cyst? Possible explanations include areas of calcification or air. A CT scan of the shoulder shows that the hypointense material is air within the paralabral cyst:

Tung et al. (AJR 174, 1707-1715, 2000) described the MRI features of shoulder paralabral cysts.  They observed that:

--> paralabral cysts are strongly associated with labral tears.

--> paralabral cysts can exert local mass effect, and cause a compressive neuropathy, typically affecting the suprascapular nerve.

--> prevailing theory is that these cysts form after the capsulolabral complex is torn or avulsed.

There are few reports of air in paralabral cysts in the literature. Lozano Calderon et al. recently reported a case of a paralabral cyst containing air in a middle-aged woman (Am J Orthop 38, E107-E109, 2009). Air can be more commonly seen in synovial cysts arising from spinal facet joints, but is an uncommon finding in shoulder paralabral cysts. The etiology of air formation in a paralabral cyst is unclear, although the mechanism of air formation in joints has been elucidated (Unsworth et al., Ann Rheum Dis 30, 348, 1971).

The differential diagnosis for hypointense material associated with a paralabral cyst is air, calcification, and prior surgery. Conventional radiographs and/or CT scan will reliably differentiate between these possibilities.

Vic David MD