These are displaced, truly subcapital fractures. The fracture line follows the border of the articular cartilage. As these fractures are intracapsular, the blood supply to the femoral head is disrupted in most cases.
X-rays are taken in two planes at 90° to one another. The lateral view is obtained by taking the so-called cross-table view. If this is of good quality, it will allow the surgeon to assess the degree of retroversion and the degree of fragmentation of the posterior cortex.
The Pauwels classification can best be determined intraoperatively, once traction is applied, and the fracture is reduced. After this, choice of fixation is easier. On an AP fluoroscopic view, assess the inclination of the fracture line. Pauwels type I is a fracture with <30º from the horizontal. Type II is 30º-70º from the horizontal. Type III is >70º from the horizontal.
The blood supply of the femoral head
The vascular anatomy varies, but in 60% of patients the medial and lateral femoral circumflex arteries originate from the profunda femoris artery (1).
Most of the blood supply of the femoral head comes from the medial femoral circumflex artery (2), which gives rise to three or four branches, the retinacular vessels. These run posteriorly and superiorly along the femoral neck in a synovial reflection until they reach the cartilaginous border of the head. The obturator artery gives rise to the vessels within the ligamentum teres (3). An ascending branch of the medial femoral circumflex artery (4) supplies the greater trochanter. The medial and lateral circumflex arteries may anastomose but the principal blood supply of the head originates from the medial circumflex and its branches.