#MiniTeach: An Uncommon Case of Patella Dislocation
"A 12 year old boy presents with a history of his knee giving way while playing football and looking funny. As he got up, the knee felt that it popped back."
He says that this has happened a couple of times before and that sometimes his knee clicks or gives way. Today he’s come in because the knee is swollen. He’s able to mobilise with a good range of movement and there’s a small effusion. There is no bony tenderness.
His dad says that there’s strong family history of problems with the knees on his side of the family. He says that many members of the family have funny looking fingernails too. His dad shows you his fingernails and they appear ridged and abnormally shaped.
1. Should the X-ray have been taken? What does it show?
The Ottowa knee rules were originally derived to look specifically for fractures in the adult population. They have been validated for use in older children, so could be applied here.
Fractures are not the only reason to do X-rays and so if there is concern regarding other pathology (such as abnormal bone growth or structure), an X-ray may still be warranted.
The X-ray shows a small and misshapen patella.
2. What's the likely diagnosis?
Nail-patella syndrome, which is also known as Fong disease, Hereditary onycho osteodystrophy (HOOD), Osterriecher-Turner syndrome, or Turner-Keiser syndrome.
3. What are the genetics of this condition?
It’s an autosomal dominantly inherited condition, which affects 1/50,000 individuals. The gene mutation is LMXiB on chromosome 9.
4. What other organs can be affected?
Almost any, but the big ones to look out for are bone and joint abnormalities (they often have knee and elbow problems), renal involvement and glaucoma from late adolescence.
5. How should the knee injury be managed?
It sounds as though he has had a patella dislocation that has spontaneously reduced. He should have a cricket pad splint and be referred to orthopaedics.
6. What long term follow up should patients have in this condition?
They should have their urine checked every year for blood and protein and start having yearly checks for glaucoma from adolescence.
