Unable to completely straighten knee. Pain lateral side.

There is an bursal collection with synovial thickening between the posterior lateral femoral condyle and the iliotibial band. Synovial thickening is present. The iliotibial band itself is thickened. These findings are consistent with iliotibial band friction syndrome.

This is an overuse syndrome commonly seen in runners, and military personnel. Conservative therapy with rest, and ice, usually suffice. Surgery is indicated if, such as in this case, the bursa does not resolve, and there is significant limitation of movement.

It's caused by repetitive rubbing of the IT band with the posterior femoral condyle, and can be exacerbated by genu varum (absent in this case), limb length discrepancy, hip adductor weakness, and awkward running style.

Sonography is a useful adjunct to the study of IT band syndrome, but MRI elegantly demonstrates all the relevant pathology (author's bias).

A simple referral for imaging guided dry needle/lignocaine can often help the patient back on his way to full function.

Young man, post ACL-recon 8 years ago. Presents with joint locking. Cannot fully extend the knee. History of medial and lateral meniscus injuries.

It's a very nice meniscal ossicle. The atypical thing about it is that it's in the lateral meniscus (most of these ossicles are in the posterior horn of medial meniscus). The theory goes that these ossicles develop in damaged menisci, and have MR signal which follows underlying bone. The ossicle is usually triangular, and is surrounded by meniscus. See radiograph below.

Here's a good reference by Dr Harry Genant's team.

Ever seen a dislocated femoral tunnel screw?

Knee pain. Recent trauma.

What's that? There's tricompartmental osteoarthritis (osteophytes, subchondral cysts, cartilage defects). But, look at the popliteal neurovascular bundle. There's expansion and filling defects within the popliteal vein- in keeping with deep venous thrombosis. This is likely acute on chronic as the vein is expanded, but there are also "bands" extending out to the vein wall. Minimally increased T2 signal around the vein suggests thrombophlebitis.

72/male with TKR done about 9 months ago, recent minor trauma and this is the radiograph.

Fractured patella, post total knee replacement.

The reported incidence of patellar fracture after total knee replacement varies markedly, ranging from 0.5% to 3.8%. Most fractures present within a year of TKR, and in elderly patients, suggesting that there is underlying bone weakness. Technical factors are important and include patellofemoral malalignment, femoralor tibial component rotational malalignment, patellar devascularization,lateral retinacular release, and excessive or inadequate patellar resection. In this case, the patellar is shaved very thin.

Osteonecrosis of the patella is another consideration. The vascular network of the patella is at risk during total knee replacement surgery. Median parapatellar arthrotomy, fatpad removal, and lateral release all contribute to patellar devascularization.

A nice review of the topic can be found here.

- Thanks to Dr Ian Tsou for a very nice contribution.

MRIs of the knee follow. Appearance is characteristic off?

Osteonecrosis of the knee. But connoisseurs of the art will recognise that this is NOT spontaneous osteonecrosis, but secondary osteonecrosis because it involves both the medial and lateral aspects. Classic spontaneous osteonecrosis (SONK) involves one condyle/plateau (usually the medial), and is a diagnostic differential of osteoarthritis. Both may present with subchondral oedema, both are hot on bone scans, but cortical collapse is a sequelae of undiagnosed SONK- so be careful.

Thankfully, the treatment of SONK and osteoarthritis are somewhat similar: high tibial osteotomy, unicondylar replacement and others. Core decompression is performed in cases of high-probability SONK.

It's also worth noting the link between osteoporosis medications (bisphosphonates) with osteonecrosis.

Plain radiography: (Aglietti, modification of Koshino classification)
Stage I: Normal. MRI or bone scan positive.
Stage II: flattening of weightbearing surface of condyle.
Stage III: radiolucent area surrounded by sclerosis.
Stage IV: ring of sclerosis, subchondral bone collapse, sequestrum, fragment.
Stage V: Narrowing of joint space, osteophyte, femoral and/or tibial subchondral sclerosis.

Have a look below... note position of hardware.

It's a posterior cruciate ligament reconstruction! Your radiographic clues are the position of the endobutton and the locations of the tunnels. ACL recons have their endobuttons on the lateral femoral condyle. So, why replace the PCL?

The indications are pain, avulsed PCL with or without bony avulsion, locking or instability. Choice of graft material is the same as for ACL recons, and this one happens to be a hamstring graft. You may note the horizontal screw post used to secure the distal end of the graft. Care is taken to preserve the meniscofemoral ligaments during graft repair.

Intragraft signal intensity is raised mildly (i.e. less than fluid signal on T2-weighted images) within 1 year, and then gradually turns hypointense.

References:

Young Cheol Yoon, MD, Hye Won Chung, MD, Jin Hwan Ahn, MD. MR Imaging of Stable Posterior Cruciate Ligament Grafts in 21 Arthroscopically Proven Cases. Korean Journal of Radiology; 2007 October; 8(5):403-409            


Sherman PM, Sanders TG, Morrison WB, Schweitzer ME, Leis HT, Nusser CA. MR imaging of the posterior cruciate ligament graft: initial experience in 15 patients with clinical correlation. Radiology. 2001 Oct;221(1):191-8.

It's a patient with diabetes (type II), presenting with ankle pain. MRI obtained in sagittal plane- T1 (top row) and T2 fat sat (bottom row) sequences.

There are clearly fracture lines in the distal tibia, and also the calcaneal apophysis. The radiographs reveal osteopaenia, and these may represent insufficiency fractures.

However, note the incompletely images serpiginous lines in the distal tibial metaphysis! Those aren't fracture lines. They have a double line, which is charateristic for osteonecrosis. In diabetics, it's more common to get osteonecrosis around the knee (SONK- spontaneous osteonecrosis of the knee).