Recently, femoroacetabular impingement has been recognised as a cause of early osteoarthritis. There are two mechanisms of impingement: 1) cam impingement caused by a non-spherical head and 2) pincer impingement caused by excessive acetabular cover. We hypothesised that both mechanisms result in different patterns of articular damage. Of 302 analysed hips only 26 had an isolated cam and 16 an isolated pincer impingement. Cam impingement caused damage to the anterosuperior acetabular cartilage with separation between the labrum and cartilage. During flexion, the cartilage was sheared off the bone by the non-spherical femoral head while the labrum remained untouched. In pincer impingement, the cartilage damage was located circumferentially and included only a narrow strip. During movement the labrum is crushed between the acetabular rim and the femoral neck causing degeneration and ossification. Both cam and pincer impingement lead to osteoarthritis of the hip. Labral damage indicates ongoing impingement and rarely occurs alone.

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The high prevalence of juxta-articular fibrocystic changes at the anterosuperior femoral neck and their spatial relation to the impingement site suggest an association and possible causal relationship between these alterations and FAI.

Capsular and pericapsular vessels that contribute to the blood supply of the acetabulum run on the posterior and posterolateral surface of the capsule. The dominant blood supply to the femoral head comes from vessels that approach the joint posteriorly and penetrate the joint near the femoral attachment of the capsule.

The purpose of this cadaveric study was to clearly define the blood supply to the femoral head to help further reduce the incidence of iatrogenic avascular necrosis (AVN). Thirty-five hips of twenty-eight fresh cadavers were injected with colored silicone. Anterior and posterior dissection was performed to assess the vessels contributing to femoral head vascularity. The medial femoral circumflex artery (MFCA) was found to be the main blood supply to the hip in twenty-nine specimens; the inferior gluteal artery (IGA) was found to be the main blood supply in six. The MFCA consistently provided at least one smaller-calibre inferomedial retinacular artery. The foveal artery provided no significant vascular contribution in any specimen. The quantity and calibre of superior retinacular vessels demonstrated their dominance in head vascularity, although inferior retinacular arteries were consistently present. To reduce the risk of iatrogenic AVN, branches of both the IGA and MFCA traversing the interval between the quadratus femoris and piriformis muscles must be protected during surgery. Since all intracapsular vessels penetrated the capsule near its distal attachment, distal capsulotomy carries a significantly higher risk of AVN than proximal capsulotomy, particularly posterolaterally and inferomedially.

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The acetabular labrum receives its blood supply from radial branches of a periacetabular periosteal vascular ring that traverses the osseolabral junction on its capsular side and continues toward the labrum's free edge. The hip capsule, the synovial lining, and the osseous acetabular rim do not appear to provide substantial contributions to the labral blood supply.

The modified Smith-Petersen and Kocher-Langenbeck approaches were used to expose the lateral cutaneous nerve of the thigh and the femoral, obturator and sciatic nerves in order to study the risk of injury to these structures during the dissection, osteotomy, and acetabular reorientation stages of a Bernese peri-acetabular osteotomy. Injury of the lateral cutaneous nerve of thigh was less likely to occur if an osteotomy of the anterior superior iliac spine had been carried out before exposing the hip. The obturator nerve was likely to be injured during unprotected osteotomy of the pubis if the far cortex was penetrated by > 5 mm. This could be avoided by inclining the osteotome 45° medially and performing the osteotomy at least 2 cm medial to the iliopectineal eminence. The sciatic nerve could be injured during the first and last stages of the osteotomy if the osteotome perforated the lateral cortex of ischium and the ilio-ischial junction by > 10 mm. The femoral nerve could be stretched or entrapped during osteotomy of the pubis if there was significant rotational or linear displacement of the acetabulum. Anterior or medial displacement of < 2 cm and lateral tilt (retroversion) of < 30° were safe margins. The combination of retroversion and anterior displacement could increase tension on the nerve. Strict observation of anatomical details, proper handling of the osteotomes and careful manipulation of the acetabular fragment reduce the neurological complications of Bernese peri-acetabular osteotomy.