Commonly missed fractures

Knee pain

A 36 year old lady presents with left knee pain after slipping on ice. She now has severe knee pain with mild swelling, and is unable to weight bear. Triage nurses have given her codeine and paracetamol, but examination is still difficult due to pain. She is very tender along the joint line particularly medially, and cannot flex or extend her knee. She is sent for an Xray:

Lateral knee X-ray

AP knee X-ray

1. What does the X-ray show?2. Can you see a fracture?3. Does she need further imaging?

The lateral knee x-ray shows a lipohaemarthrosis. When there is an intraarticular fracture, fat and blood can from the bone marrow into the joint. The fat is less dense than blood, so it forms 2 layers. Lipohaemarthroses occur in approximately 40% of all intraarticular fractures of the knee, and are usually due to a minimally displaced tibial plateau fracture.

CT showing lipohaemarthrosis.

2. There is no fracture seen on the AP or lateral Xray. Lipohaemarthrosis may be the only sign of intraarticular fracture.

3. CT is indicated to further evaluate. In this patient, a CT left knee showed a minimally displaced medial tibial platueau fracture. She was reviewed by Orthopaedics, who advised her to wear a zimmer splint and not to weightbear. She was discharged home with appropriate analgesia and follow up with the Orthopaedic Consultant in fracture clinc.

Fat

Blood

Femur

Elbow pain

A 40 year old man fell off his bicycle and landed on left elbow. He got straight back up and cycled home. Over the following day he had gradually increasing pain and swelling of his elbow. On examination, there was a small joint effusion, no bony tenderness and limited flexion to 45 degrees.

Lateral elbow X-ray

AP elbow X-ray

1. What do the X-rays show?2. What is the treatment?

1. The lateral X-ray shows a displaced anterior fat pad and a visible posterior fat pad. The AP X-ray shows a haemarthrosis and an intraarticular radial head fracture.

This is the fat pad sign. Fat pads are intra-articular but extra-synovial. When there is a joint effusion or haemarthrosis, the fat pads are displaced. On a normal Xray, the anterior fat pad can be visible, however a displaced anterior fat pad, the “SAIL sign”, is abnormal and can indicate an occult frature. A visible posterior fat pad is always abnormal. In adults, the commonest fracture causing the fat pad sign is a radial head fracture. In children it is usually a supracondylar fracture.

Elbow joint effusion causing displacement of anterior fat pad and visible posterior fat pad.

2. This radial head fracture is non displaced, and therefore will heal well with immobilisation. He was discharged home in a sling and advised to not use his arm, with Orthopaedic follow up in fracture clinic.

If there is displacement of the fracture fragment, the fragment needs to be reduced and fixated with a plate or screws in theatres. This is important to reduce the risk of stiffness, reduced function, deformity and post-traumatic arthritis.