The blood supply of femoral head after surface hip replacement
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The blood supply of femoral head is precarious. It is in jeopardy with every trauma to the femoral head and /or neck, for example with the fracture of the femoral neck.
Recent studies also demonstrated that the blood supply of femoral head is damaged during the preparation (chamfering) of the femoral head to receive the metallic shell (Steffen 2005).
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The blood supply to the femoral head comes through branches of a large artery that encircles the base of the femoral neck. This artery is therefore called circumflex artery. Because the circumflex artery lies a considerable distance from the femoral head, the branches nourishing the femoral head have a rather long distance to pass to reach the femoral head.
The branches pass first through the deep muscles and ligaments around the hip joint and then pass along the whole length of the surface of the femoral neck unprotected. At the border between the femoral neck and the femoral head these branches then submerge under the surface of the femoral head and nourish the soft spongy bone tissue there. |
| Picture: Blood supply of a normal femoral head. Click on the icon for a full size picture |
There is also some blood supply to the femoral head through special ligament (ligamentum teres) to the centre of the femoral head in children and adolescents; this supply is without importance in adults with osteoarthritic hips and is thus omitted from the figure.
Dangers for blood supply of femoral head during replacement surgery
The round femoral head must be made fit for the cylindrical hole in the femoral shell. The surgeon chisels off the harder surface layer off the femoral head and chamfers the remaining soft bone tissue into a cylindrical form.
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During this stage of operation there is a great risk that the unprotected arteries that submerge just at the border between the femoral head and the femoral neck may be disrupted by chiseling and carving into the neck. Equally great is the risk that these arteries will be damaged when the surgeon prepares the access route to the hip joint. When the surgeon divides the muscles and ligaments to have access to the hip joint there is a risk that he may damage the branches of the nourishing vessels that pass through these tissues.
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| Picture: Damage to blood vessels of femoral head during surgery. Click on the icon for a full size picture |
The spongy bone tissue of the chamfered femoral head that is partially or entirely without blood supply will die. Then it depends on the extent of the bone tissue death what happens with the surface replacement device (shell) attached to the dead bone tissue.
In the majority of patients the circulation in the hip joint after surface replacement will be successively restored. Studies demonstrated that one year after surface replacement surgery there is adequate circulation in the replaced hip in the majority of patients.
But in a small minority of the patients the circulation in the femoral head will not recover. These patients are then at risk for two major complications: a) fracture of the femoral neck and b) loosening of the replacement shell.
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References:
Steffen RT et al.: The effect of hip resurfacing on oxygen concentration in the femoral head. J Bone Joint Surg-Br 2005; 87-B: 1468-74