Diagnosis Index

•  Cases 1-10
• Cases 11-20

Case 52 Diagnosis: ACL Disruption with Segond fracture and partial MCL tear

The most typical mechanism of ACL disruption is a pivot shift injury where a valgus stress is placed on a flexed knee with the femur internally rotated. This yields a classic edema pattern of the posterior lateral tibial plateau and the sulcus terminalis of the lateral condyle. The sulcus of the lateral condyle when deeper than 1.5 mm indicates an ACL tear and can at times be identified on radiographs. A Segond fracture is an avulsion injury of the lateral joint capsule. The mechanism of injury relates to internal rotation of the tibia with a varus moment imparted to the knee. It has a high association (75-100%) with ACL injuries as well as of the menisci. Given that in this case there was additionally, an MCL injury, one can see the often complex mechanisms yielding injury patterns of the knee.

Case 51 Diagnosis: ALPSA

ALPSA or anterior labral periosteal sleeve avulaion is a Bankart variant or variant of an anteroinferor labral tear frequently seen in the setting of an anterior translational event (subluxation or dislocation). The ALPSA has a stripped but intact scapular periosteum allowing medial displacement of the labrum, which is important for the surgeon to be aware of preoperatively. Specific mention was made of the intact IGHL to make clear the absence of a HAGL lesion (humeral avulsion of the glenohumeral ligament). This lesion to most necessitates the need for an open instead of arthroscopic repair. The posterolateral impaction represents a classic Hill Sachs lesion that when large may necessitate soft tissue or bony grafting. The small avulsion of the anterior glenoid represents a very small bony Bankart lesion. Again, when this lesion becomes large it may necessitate bony augmentation to help prevent recurrent subluxation/dislocation.

Case 50 Diagnosis: Calcium hydroxyapatite

Calcium hydroxyapatite (CH) can deposit in and around tendons, bursae, or less commonly about a joint. This deposition may be referred to as calcium hydroxyapatite deposition disease but more commonly as calcific tendinosis or calcific tendonitits. The CH can cause a marked inflammatory response as is seen in this case and may involve the soft tissues and/or bone. In the bone, this may yield erosive change and when deposited in the joint may lead to joint destruction. CH’s typical appearance on radiographs is a cloud like, amorphous density lacking architecture (no cortical/medullary differentiation). On MRI, it shows low signal intensity on all pulse sequences, and when painful, typically is associated with a marked amount of surrounding edema/inflammatory change.

Case 49 Diagnosis: Lipoma Arborescens

Lipoma arborescens is a benign, intra-articular process that results in fatty deposition in the synovium. It is most typically seen in the setting of a long standing arthrosis. Classically associated with rheumatoid arthritis and inflammatory arthropathies, it can be seen as in this case, in the setting of bland, degenerative osteoarthritis. Intra-articular masses are exceedingly rare and this entity should not be confused with a synovial hemangioma, synovial chondroma, or synovial chondrosarcoma. In addition, when viewing studies, frequently, fat insinuates about a knee joint effusion but is not intra-articular. This can be particularly confusing when viewing only one plane but is frequently confirmed when evaluating all planes of imaging.

Case 48 Diagnosis: Infantile or Congenital Coxa Vara(CCV)

Infantile or congenital coxa vara results from abnormal maturation of the proximal femoral physis that causes decreased ossification, weakening of the bone, and subsequent coxa vara.  Classically, as in this case, there is a Y shaped confiiguration of the proximal femoral physis and a focus of ossification inferomedially. Patients typically present from the time they start walking up to about 6 years of age and present with a limp.

There is often a mild limb length discrepancy of 2-4 cm as is seen in this case.  If necessary, a valgus osteotomy is performed.  Osteotomy is indicated for a Hillgenreiner epiphyseal angle (HEA) of > 60 degrees or an HEA of 45-60 degrees with increasing coxa vara.  In distinction, to proximal femoral focal dysplasia (PFFD), the varus deformity in CCV is at the level of the physis and not subtrochanteric as in PFFD. Also, in PFFD, there is typically a more pronounced limb length discrepancy.

Case 47 Diagnosis: Sprengel's Deformity

Sprengel’s deformity is a congenital deformity yielding an elevation and medial rotation of the scapula related to a failure of the normal caudal migration of the scapula. In approximately 30% of the deformities, an omovertebral bone is present that extends from the posterior elements of the cervical spine to the native scapula. This may be connected directly to the scapula by osseous bridging or by non-osseous (cartilage or fibrous tissue) bridging as in this case. The deformity is most typically seen  in the setting of a Klippel Feil (KF) syndrome where there is fusion of two or more cervical vertebrae. KF often has associated other vertebral anomalies, a webbed neck,  cervical ribs,  and cardiac/pulmonary/renal/ and GI anomalies.

Case 46 Diagnosis: Sportsman's Hernia.

A confusing and poorly named entity thought originally to be related to an inguinal hernia given pain in the inguinal region.  The entity has subsequently been shown to represent a disruption of the rectus adductor aponeurosis.  This entity may be seen in the setting of other causes of athletic pubalgia such as osteitis pubis, manifest by edema and cysts extending anteriorly to posteriorly about the pubic symphysis, as well as adducor muscle injuries.  A sign previously described on arthrography is employed on MRI which is the secondary cleft sign. This represents a disruption of the pubic symphysis capsule as it blends with the rectus adductor aponeurosis.

Recently described are two typical patterns of sportsman’s hernia. The one is more lateral at the rectus/adductor aponeurosis and is associated with asymmetric pubic edema, an ipsilateral secondary cleft, and injury of the rectus and adductor. The other pattern is centered more at the pubic symphysis with bilateral secondary clefts and typically with a breech of the rectus but not often extending into the adductor longus. This case represents more of the second type of process, centered at the pubic symphysis, but with a clear tear of the adductor. Therefore, there likely is a continuum or spectrum across these two typical patterns.

Case 45 Diagnosis: Posterior hip subluxation with acetabular fracture and displaced labrum.

Posterior translation events of the hip are typically associated with high speed motor vehicle accidents where the flexed knee impacts the dashboard with a flexed hip driving the femoral head posteriorly. This can yield fractures of the posterior acetabulum, femoral head, and potential injury to the sciatic nerve. Gaining increased recognition is that athletes may sustain posterior subluxations either related to a flexed knee impacting the ground with a flexed hip, blow from behind while on all four limbs, or impaction of the foot on the ground with an extended leg and locked knee transmitting force posteriorly to the hip.

As compared to a dislocation, the subluxation event results from a less amount of force imparted to the hip and has a more subtle clinical and radiographic presentation. As seen in this case, there is often a posterior wall or lip fracture of the acetabulum. Often a joint effusion or hemarthrosis is seen and injury is seen of the anterior and posterior joint capsules. Missed diagnosis and particularly with displaced tissue into the joint may predispose to further translational events and long term instability. Additional morbidity includes the risk of avascular necrosis and potential for premature degenerative joint disease.

Case 44 Diagnosis: Transient Lateral Patellar Dislocation.

Transient lateral patellar dislocation (LPD) is a well documented injury caused by internal rotation of the femur on a fixed tibia with flexion of the knee and firing of the quadriceps mechanism. This leads to a laterally imparted force on the patella. With relocation of the patella, impaction fractures are seen of the anterior aspect of the lateral femoral condyle and the medial patellar facet. Positioning of the impaction along the central to inferior aspect of the medial patella relates to the degree of flexion of the patella at the time of injury. Along the medial aspect of the knee is a documented trilaminar structure that supports the medial aspect of the knee but with the medial patellofemoral ligament being the key stabilizer along the medial aspect of the knee. The disruption of the MPFL may be at the patellar, midsubstance, or femoral attachment. Often, as in this case force is transmitted through the entire ligament yielding diffuse injury. Recently, direct MPFL reconstruction has become a more routine procedure for some of these patients. Underlying osseous architecture is a known predisposition for recurrent LPD including trochlear hypoplasia, patella alta, patella tilt, elevated quadriceps angles, and others. Treatment often relates to reconstituting normal osseous relationships to help prevent recurrent LPD and subsequent early cartilage loss. In this case, the additional OCD of the medial condyle is not a classic finding although often MCL and medial meniscal injuries are seen in the setting of LPD.

Case 43 Diagnosis: Spondyloepiphyseal Dysplasia (SED).

SED is an inherited dysplasia that involves the ends of the bones or epiphyses and the spine. It comes in two variants, congenita ( present at birth) and tarda which has a normal appearance at birth and then develops at 4 years of age and older. Given the underlying dysplasia there is premature osteoarthritis which in this patient may have been neglected. In the spine, there is typically a hypoplastic dens which leads to spinal instability and as in this patient leads to fusion to help prevent a catastrophic event. The presence of an os odontoideum or non fused tip of the dens may be seen but is not as typically present.

The vertebral bodies are decreased in height and at times may be completely flat yielding platyspondyly. Ovoid or trapezoidal bodies in the pediatric patient typically than yield vertebrae in the adult with decreased height, increased AP diameter, and end plate irregularities as seen here. Severe stenosis or C1/C2 kinking may be found as compared to the typical cervicomedullary kinking found in achondroplasia. In this patient, no myelopathic symptoms were present, astonishingly so. Imaging of the other appendicular structures would have shown mutliple areas of epiphyseal dysplasia and advanced arthrosis.

Case 42 Diagnosis: Loosening of femoral component in THA.

In the setting of potential loosening of a component in joint arthroplasty, evaluation at the multiple interfaces (bone/prosthesis/cement) is of great consequence and requires close scrutiny. Frequently described evidence of loosening is greater than 2mm lucencies propagating among multiple Gruen zones (especially beyond those of the periarticular zones of 1,7,8,15). On arthography, propagation beyond the intertrochanteric line is often frequently used as an indicator of loosening. These findings do require correlation with clinical history and physical exam.

As a means to obviate the need for percutaneous intervention, MRI protocols have been developed over the last decade to accurately asses for loosening without joint injection/aspiration. The accuracy of this modality has been validated multiple times in the literature. As a way to improve this, new prototype pulse sequences, as shown here, are being fabricated to reduce susceptibility artifact at metal/tissue interfaces as to allow even better interpretation. This is particularly important in the setting of markedly ferrous components as used in metal on metal constructs that produce a tremendous amount of susceptibility artifact.

Case 41 Diagnosis: Ankle syndesmotic and deltoid ligament tears with Maissoneuve fracture.

Maissoneuve fracture is a proximal fibular fracture typically seen in the setting of an external rotation injury yielding a diruption of the syndesmotic complex, propagating into the interosseous ligament, and then extending into the fracture of the proximal fibula.  Often seen in association with a medial malleolar fracture or disruption of the deltoid ligament rendering an unstable ankle.  The deltoid ligament disruption can be identified directly on the MRI or by the widening of the medial clear space beyond 4-5mm.  As the ankle has been rendered unstable, fixation is then required.

Case 40 Diagnosis: Serous atrophy/gelatinous transformation of marrow with superimposed, post traumatic olecranon bursitis.

In the setting of anorexia or cachexia, the body will use whatever fat stores are available for survival. As such, the fat from marrow can be replaced with an interstitial infiltration of a ground gelatinous substance (acidic mucopolysaccharides). In addition, the intra-peritoneal fat and subcutaneous fat are also utilized. This yields the appearance seen in this case. The marrow in this situation has a much higher T2 signal related to the deposited gelatinous substance. The T1 signal is low but may not be as low as expected related to the underlying nature of the mucopoysaccharides. This condition is also referred to as serous atrophy of the marrow or starvation marrow.

There is no association with the post traumatic bursitis but that is what led the patient to seek medical attention. These patients are however, at times pancytopenic related to the abnormality of the underlying marrow and at times this will require medical attention. In younger women, a triad of eating disorder, amenorrhea, and osteoporosis/stress fractures is a well known triad also known as the female athletic triad. Awareness of this condition may help prevent further health problems.

Case 39 Diagnosis: Bisphosphonate Associated Subtrochanteric Stress Fractures

Bisphosphonate treatment has become a mainstay in the treatment of osteoporosis. More recently PTH analogs have also gained increasing favor. Bisphosphonates work by inhibiting osteoclast activity and inducing apoptosis so that bone is not resorbed. Although extremely useful in patients with osteoporosis to help prevent fractures, adverse reactions do occur.

The most well known is avascular necrosis of the jaw which is associated with high dose intravenous treatment in the cancer patient. In the orthopedic community, bisphosphonate treament has been associated with subtrochanteric stress fractures and frank, complete fractures. It is postulated that microfractures occur and because of the decreased bone turnover from the bisphosphonate treatment, healing can not occur and these atypical fractures subsequently propagate. There occurrence is however markedly decreased compared to hip fractures and the benefit of treatment is thought to outweigh the risks. That being said, these fractures are difficult to treat and can require subsequent surgery.

Case 38 Diagnosis:

Gout is an arthropathy based on urate crystal deposition. The deposition is typically in a juxta-articular location but may also be within tendons particularly within certain tendons such as the Achilles or knee extensor mechanism. On radiographs, gout produces classically juxta-articular erosions with well defined margins or overhanging edges related to the long standing process and subsequent bone repair. The soft tissue mass or tophus may become dense or frankly calcified related to dystrophic calcification

On MRI, the lesions are classically defined as having low signal intensity on all pulse sequences, but as seen in this example, mild hyperintensity may be encountered. The overall constellation of findings must be taken into account to make the diagnosis. In this case, the soft tissue mass of the left hand was resected and urate crystals were identified via microscopic analysis.

Case 37 Diagnosis: Ollier’s Disease with malignant transformation

A non-hereditary condition of multiple enchondroma or enchondromatosis yielding expansion and deformity of the bone and often rendering short bones or limb length discrepancies. At times the lesions are pedunculated, simulating osteochondroma and referred to as enchondroma protuberans. Lesions tend to predominate in the long bones as well as within the metacarpals/metatarsals. Lesions in the flat bones are not as common. In childhood, lesions are subject to fracture and in adulthood there is an increased risk of malignant transformation. After a child has reached skeletal maturity, the lesions should no longer grow. Continued growth with destruction of the underlying bone indicates malignant transformation which is said to occur in up to 30% of individuals. Typically, malignant transformation is to a chondrosarcoma. Lesions are treated with excision and patients are closely monitored for potential malignant transformation as in this case.

Case 36 Diagnosis: CPPD Arthropathy

Calcium pyrophosphate dihydrate arthropathy (CPPD) is a type of CPPD crystal deposition disease. The CPPD crystals can be deposited in fibrocartilage such as menisci, the TFCC, or pubic symphysis; hyaline cartilage; synovial membrame/synovial fluid; and in tendons and ligaments. The crystals may be seen in the setting of an asymptomatic patient or may yield joint damage leading to an arthropathy similar to degenerative joint disease (DJD) but with distinctive features.

As compared to DJD, large subchondral cysts often predominate and can become so large as to yield pathologic fractures as in this case. In addition, the distribution of joints tends to be somewhat different with increased proclivity in CPPD arthropahty for the wrist and MCP joints as again seen in this case. Although DJD and CPPD arthropathy both heavily affect the knee, in CPPD there is often isolated or severe patellofemoral disease or lateral compartment disease.

Case 35 Diagnosis: ASIS avulsion and posttraumatic subiliacus bursitis

Avulsion injuries at the apophyses are common in the athletic, skeletally immature patient. As the apophyseal plate is less able to sustain load than tendons, the apophyseal plate tends to be the site of failure in the skelletally immature patient. In the pelvis, multiple apophyses are present particularly with injury often seen at the ASIS, anterior inferior iliac spine, ischial tuberosity, and lesser trochanter. Although not discussed in the literature, anecdotally reported are avulsion injuries of the subiliacus muscle yielding posttraumatic bursitis in the skeletally immature patient. This may be similar to abdominal and gluteal muscle injuries sustained at the iliac crest in the skeletally mature patient.

Case 34 Diagnosis: DRUJ Instability

DRUJ (distal radioulnar joint) instability is a complex pathology related to the triangular fibrocartilage complex and particularly the volar and dorsal radioulnar ligaments (vrul and drul). With pronation, the drul will tighten with subsequent “dorsal displacement of the ulna” and with supination the vrul will tighten with subsequent “ volar displacement of the ulna”. With hyperpronation, there is a checkrein via the vrul, but in extreme circumstances this will fail. Failure of the vrul will lead to a persistent posterior positioning of the ulna in a neutral position.

With pronation there may be exaggeration of the posterior positioning or as seen in this case, the loss of competency of the vrul prevents adequate tightening to have the ulna move volarly with supination. Subsequently, the ulna will remain somewhat more posteriorly positioned than the contralateral side. The same pathology, but involving the drul, would occur in a hypersupination injury. The vrul and drul converge at the proximal ulnar attachments and hence all of these structures must be evaluated when assesing for DRUJ instability.

Case 33 Diagnosis: Distal Biceps Rupture

Distal avulsion of the biceps tendon from the radial tuberosity typically occurs in middle aged men who participate in weight lifting. The mechanism is typically eccentric contraction against the flexed elbow where the patient feels a snap or tearing sensation followed by soft tissue swelling at the level of the humerus. The soft tissue swelling relates to muscle retraction as well as soft tissue injury and given the prominence is often identified as a “Popeye” sign. Without repair, the injury can result in prominent weakness of flexion and supination.

Case 32 Diagnosis:

FAI relates to a mismatch at the hip joint either along the femoral side or the acetabular side. Patients typically present with pain exacerbated by certain motions, particularly those related to flexion and internal rotation. Cam lesions involve the femoral side and relate to a loss of the anterior femoral head neck offset. Bone and subchondral cysts form at this location causing subsequent degeneration of the anterorsuperior labrum and early cartilage loss.

The pincer lesions relate to ossification along the acetabular side leading to overcoverage of the femoral head. Although anterosuperior labral degeneration is seen, cartilage wear is often found at a contre-coup location of the posterior inferior acetabulum. Pincer pathology is also implicated in the setting of coxa profunda and focal retroversion of the acetabulum. In order to help prevent early degeneration of the hip joint, progression of degeneration, and alleviate patient’s pain surgeons, using new arthroscopic techniques, are able to debride the bone and labrum and restore normal architecture to the hip joint.

Case 31 Diagnosis:

Stress fractures can either be insufficiency fractures or overuse fractures. Previously, a case had demonstrated an insufficiency fracture where abnormal bone had fractured in the setting of normal load. The overuse injury is increased load transmitted to normal bone relating in a stress fracture. One of the classic overuse injuries is of the calcaneus with other bones such as the tibia and distal femur often frequently involved.

The lesion of the distal tibia is an incidental non-ossifying fibroma. The lesion is sclerotic as it has healed. It demonstrates classic features of a metaphyseal, eccentric lesion that is well demarcated and not aggressive nature.

Case 30 Diagnosis:

Facet joints are synovial joints that undergo the same degenerative processes as other joints and inflammatory processes as other joints.  Synovial cysts emanate from multiple joints and in the facet joints of the lumbar spine they can cause mass effect on adjacent, critical neural structures. Most common is that the cysts cause compression of the thecal sac, traversing nerve roots, or of the proximal nerve roots. In this circumstance, somewhat less common, the cyst is causing compression of the nerve root in the neural foramen extending to the exit zone of the neural foramen.

Case 29 Diagnosis: Insufficiency Fracture

Stress fractures are typically related to repetitive force applied to bone. They are typically classified as overuse where there is increased load transmitted to normal bone or insufficiency fractures where there is normal load transmitted to abnormal bone. Insufficiency fractures are frequently seen in the setting of osteoporosis, either postmenopausal, senile, or related to other factors. In the pelvis, the classic sites for insufficiency fractures are the sacral ala, superior acetabulum, pubic symphysis, superior/inferior pubic rami, and the subcapital femoral neck.

Stress fractures can be diagnosed on radiographs by either a thin lucent line in the cortex typically perpendicular to the long axis of the bone, periosteal bone or cortical thickening, or by bands of sclerosis in the medullary cavity. The sensitivity of MRI is vastly superior to radiographs and allows earlier establishment of a diagnosis. On MRI, the fracture line is seen as a low signal band typically surrounded by a prominent amount of increased T2 weighted signal representing marrow edema. Alternative means of diagnosis are on a bone scan where focal, typically oval or band like areas of increased radiotracer uptake are seen at the fracture site.

In this case, there is a clear stress fracture at the superior acetabulum. The low signal band at the femoral neck and mild edema pattern at this location likely represent sequelae of a more remote stress fracture.

Case 28 Diagnosis:

Injuries of the pectoralis major tendon occur as a result of typical eccentric contraction and are seen particularly with lifting as in weight lifting. The muscle has three heads with a clavicular, sternal, and a small abdominal head. The tendon has a complex, bilaminar attachment to the lateral aspect of the intertubercular groove with a superior clavicular and inferior sternal head. Partial tears typically occur at the myotendinous junction and more frequently involve the sternal head. Complete tears occur more frequently at the tendon attachment on the proximal humerus. As the injury occurs at the tendon bone interface, these complete tears frequently produce edema directly about the proximal humerus.

Case 27 Diagnosis:

Periprosthetic left femur fracture eliciting a small adjacent fluid collection containing post traumatic/synovial debris. Additional sacral alar insufficiency fracture.

In the older patient population the presence of osteoporosis makes the bone more predisposed to insufficency type stress fractures. These fractures occur when normal stress is transmitted to abnormal and in this case weakened bone. In this case the patient recalls focal trauma but at times a defined, inciting event is difficult to recall.

Evaluation of arthoplasties is limited for various reasons in different modalities. Radiographs as in this case may show radiolucency which may represent stress shielding or a focal area of osteolysis. Bone scans are often helpful to locate the site of abnormality but are frequently non-specific. Given the intensity and focal nature of the uptake in this case, the findings would be most consistent with a fracture. MRI is hampered by field inhomogeneity, difference in magnetization, and mismapping artifacts yielding areas of signal void and spurious high signal. Multiple technical parameters are employed to overcome these limitations. The linear bands representing fractures and the surrounding edema and fluid collection can be difficult to perceive and quite subtle.

Case 26 Diagnosis: Rheumatoid Arthritis

Rheumatoid arthritis is an inflammatory arthropathy that yields synovial proliferation and synovitis, accounting for the dense synovitis seen on the MRI. Inflammation leads to erosion of bone as well as cartilage loss, accounting for the joint space loss and articular findings seen well on both the CT and MRI. Rheumatoid is a diffuse process and, as such, typically involves joints in a symmetric pattern with uniform joint space narrowing.

This uniform joint space narrowing is what leads to the concentric or axial type narrowing seen of the hip joints in rheumatoid arthritis. The finding of protrusio is not unique to rheumatoid but is related to the joint remodeling often seen in inflammatory arthorpathies. Although strictly diagnosed via medial displacement of the acetabular line relative to the ilioischial line, an easier substitute is the femoral head crossing the ilioischial line.

Case 25 Diagnosis: Hemophilia

Hemophilia is a classically X-linked recessive disease affecting men where there is deficiency of a clotting factor (Factor VIII or IX) that  leads to repetitive episodes of bleeding into the joint or hemarthrosis with subsequent hemosiderin deposition and synovial proliferation. This in turn leads to erosion of the cartilage, subchondral cystic change, and hemophilic arthropathy. Secondary degenerative changes are frequently seen as well.

This underlying pathology accounts for the findings on the MRI of the thickened synovium, subchondral cysts, and bony erosions. The extensive cartilage loss is seen well particularly on the axial images of the current case. The blooming artifact or exaggerated low signal within the synovium relates to the physics in the acquisition of the gradient echo sequence and is seen in the presence of particularly pigment or hemosiderin and to a lesser degree calcification. Hemophilia has a proclivity to affect the hinge joints (elbow, ankle, and knee) secondary to the tendency for hemarthrosis in these joints.

Case 24 Diagnosis: Gaucher's Disease

Gaucher’s disease is a lysosomal storage disorder where the patient lacks the enzyme gluococerbrosidase that leads to accumulation of glucocerebroside within the lysosomes of macrophages. These Gaucher cells tend to deposit in the organs of the reticuloendothelial system such as the liver, spleen, and bone marrow. Accumulation in the bone marrow leads to osteopenia, or foci, of radiolucency, which can also predispose to fracture.

Gaucher’s also predisposes to bone infarcts, which can be seen in the medullary space or ends of the bone. Accumulation within the marrow can also cause expansion of the bone yielding an Erlenmeyer flask deformity. H-shaped vertebrae are thought to be secondary to an ischemic growth disturbance at the central portion of the chondro-osseous junction.

Replacement of the marrow tends to yield low signal T1 and low signal T2 marrow, but this may be patchy in appearance. Areas of increased T2 signal may be seen in the setting of infarction and a more “active marrow process” such as ongoing ischemia.

Case 23 Findings/Diagnosis: Lunatotriquetral Ligament Disruption with VISI

Radiographs and MR images demonstrate a volar flexion of the lunate on sagittal/lateral views and an abnormal triangular configuration of the lunate on the frontal radiograph.  MR images demonstrate a lack of the normal low signal intensity lunatotriquetral ligament and a high signal, granulation tissue is interposed at the site of the previous ligament.  Axial images demonstrate the high signal of the lunotriquetral interval spanning from dorsal to volar.

The lunatotriquetal (LT) ligament is one of the main intrinsic ligaments of the wrist along with the scapholunate (SL) ligament. The LT ligament is a complex structure with the volar fibers providing the majority of functional stability. In the setting of a lunatotriquetral ligament injury, a volar intercalated segment instability can sometimes be yielded. The proximal row of the wrist functions as a synchronous. The assesment of volar intercalated segment instability is provided on a sagittal or lateral image by evaluating the capitolunate and scapholunate angles. The normal capitolunate angle of 0 to 20 degrees is increased and the scapholunate angle of 30 to 60 degrees is decreased secondary to the palmar angulation of the lunate. On the contrary, DISI abnormality yields an increase in both the scapholunate and capitolunate angles.

Case 22 Finding/Diagnosis: Meniscal Tear

Multiple planes of imaging demonstrate a displaced lateral meniscal tear with the posterior horn and body displaced into the intercondylar notch. This is in the setting of a long standing ACL disruption with anterior translation of the tibia and focal scarring at the synovial reflection of the ACL or a so called cyclops lesion.

Discussion:
Tears oriented along the longitudingal axis of the meniscus may displace either into the intercondylar notch, anteriorly, or both. Meniscal fragments displaced into the intercondylar notch are rare on the lateral side because of the ACL. In the setting of a disrupted ACL, the meniscal tissue may displace into the intercondylar notch as in this case. About the ACL is a synovial reflection accounting for its intracapsular, extrasynovial position. In the setting typically of ACL reconstruction, there may be prominent focal scar tissue at the reflection yielding a block to extension. The arthroscopist sees this as a focal nodular density similar to the one eyed cyclops; hence the term cyclops lesion. Although not as common, a similar focal fibroproliferative process can occur in the setting of a long standing ACL tear without previous reconstruction as in this case.

Case 21 Diagnosis: Intermetatarsal Bursitis

In the forefoot, where the digital nerves traverse the deep transverse metatarsal ligament, there is often entrapment with fibrosis. This leads to a Morton’s neuroma. However, also at this location is the intermetatarsal bursa, which usually contains a minimal amount of fluid. With irritation of the nerve or directly of the bursae, an increasing amount of fluid may yield a pathological intermetatarsal bursitis. This may contain synovitis, as is seen in this case. Intemetatarsal bursitis is frequently seen with an underlying Morton’s neuroma, but may be seen in isolation, also as seen in this case.