Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA
There are at least seven bones with very important blood supply which are the talus,navicular,scaphoid,lunate,5th metatarsal,proximal femoral head and proximal humerus.Fracture in these bones or dislocation of their joints can lead to interruption in this peculiar blood supply causing the threat of death of the bone which is known as the avascular necrosis of bone. It may also cause delay in healing of the bone or non-union of the fractures.Fractures in these areas usually result from trauma or stress related injuries.Speaking about the talus first,the most important blood supply comes from the artery of the tarsal canal.The artery of the tarsal canal arises from the posterior tibial artery.The deltoid branch also arises from the posterior tibial artery.It is essential to be aware that the deltoid branch of the artery of the tarsal canal is the only remaining artery in displaced fractures of the talar neck.Fracture of the talar neck will interrupt the blood supply and cause non-union of the fracture or Avascular Necrosis of bone.The more displacement of the fracture, the more likely that the fracture will develop non-union and the bone will develop avascular necrosis.The Hawkins sign is a subchondral radiolucent line that is seen in the dome of the talus on X-rays.It is more commonly seen on the medial side and on the mortise view.The Hawkins sign is usually seen at 6 weeks after injury.This means that there is resorption of the subchondral bone because there is vascularity. Death of the bone hasn’t yet taken place, thus presence of Hawkin’s sign is a good prognostic factor.
Talking about the 5th metatarsal bone.If the fracture occurs in the watershed area of the blood supply of the bone,then non-union may occur.Fracture distal to the tuberosity will disturb the nutrient artery blood supply which causes relative avascularity. Interruption of the blood supply causes non-union and delayed union.There are 3 types of fractures at the proximal 5th metatarsal.The fracture in zone-1 is called tuberosity avulsion fracture, in zone-2 Jone’s fracture and that in zone-3 stress fracture.It is called Jone’s fracture when it occurs at the level of articulation of the 4th and 5th metatarsals.Treatment of Jone’s fracture is non weight bearing with cast or intramedullary screw fixation,the later being the majority choice and it is usually done in athletes and active individuals.If the fracture occurs distal to the 4th-5th metatarsal articulation, the fracture occurs mostly due to stress and won’t heal very well without some form of fixation.If the fracture occurs in the rich area of the tuberosity which is proximal,then this fracture will heal(pseudo-Jone’s fracture).Non-union of fractures in zone-2 occur in upto 30% of cases.In zone-3 fractures, always check the foot for cavovarus deformity which can be very subtle.
Next,coming to the scaphoid whose blood supply is very tenuous and unique,it’s main blood supply comes from the dorsal branch of the radial artery. Scaphoid fractures can lead to non-union and avascular necrosis due to interruption of its blood supply. Avascular necrosis is best seen in MRI which is also useful for diagnosing occult fractures.The more proximal the fracture ,the morely likely it is to develop AVN owing to the retrograde circulation. AVN of the proximal 5th of scaphoid occurs in 100% of cases when it is fractured at that level. Next ,we have the navicular bone fractures which are rare but popular because its blood supply is unique. Branches of the dorsalis pedis artery supply the dorsum of the navicular bone while the medial plantar branch of the posterior tibial artery supplies the plantar surface of the bone.The navicular tuberosity receives it’s blood supply from an anastomosis between these 2 vessels.The area where a stress fracture may occur is avascular which for the navicular bone is the central 1/3rd.There is a risk for developing non-union, delayed union and AVN when stress fractures occur in this area of the navicular bone. Navicular fractures are always treated initially with a non-weight bearing cast.
Speaking of the femoral head vascularity,the medial femoral circumflex artery is the main blood supply of the femoral head.Damage to the MFCA due to trauma,fractures or dislocations may lead to AVN of the femoral head whose risk will increase with the delay in reduction of a dislocated hip. AVN occurs due to the interruption in the terminal branches of the MFCA.
For the humeral head, there are 2 important arteries which are the anterior and posterior humeral circumflex arteries.The arcuate artery is still one of the primary blood supply to the humeral head.However,recent studies suggest that the posterior humeral circumflex artery provides the main blood supply of the humeral head and it is a controversial topic. AVN of the humeral head usually occurs in 4 part fractures.Fractures or dislocations of the head also result in AVN. AVN may also be a result of a disrupted medial hinge.A short calcar segment can also lead to AVN. The vascularity of the articular segment is more likely to be preserved if greater than 8 mm of calcar remains attached to the articular segment.
Avascular necrosis of the lunate bone is called Keinbock’s disease.It is usually associated with a negative ulnar variance that will lead to increased stress on the lunate area.The ‘I’ pattern of blood supply of the lunate bone is associated with the greatest risk of AVN of the bone. Kienbock’s disease may also be caused by repetitive trauma.Initially the condition seems like a wrist sprain but gradually if it is not recognised and treated early,it leads the collapse of the lunate bone and arthritis of the wrist.MRI is useful in the early diagnosis of this disease.Shortening osteotomy of the radius is the main procedure used to treat when the condition is symptomatic and in stage-2 and also when the patient has a negative ulnar variance.
Always informative