MCQs – Hip Recon 4

MCQs-Hip recon 4
intensity line can be found within this line – this is believed to represent hypervascular granulation tissue and is called the double-line sign.” Note that the “double line sign” is seen on T2 images.

– the safest zone to put a screw into the acetabulum is posterosuperior; avoid anterosuperior (ext. iliac vessels), anteroinferior (obturator artery) and if possible the posteroinferior (sciatic notch)

– acetabular protusio is seen with rheumatoids, Pagets, Marfans, homocystinuria (looks like Paget’s). It is not seen in neurofibromatosis.

– Indications for Chiari – coxa magna with lateral extrusion of the head.

– in DDH, the Chiari is a salvage operation that hopes to both medialize the hip, and improve the weightbearing surface via metaplasia of the capsule

– the purpose of doing an osteotomy for surgical treatment of OA is to medialize the joint reaction forces around the hip

– in an adult with untreated DDH, a poorly formed pseudoacetabulum from mild subluxation is worse than a high riding dislocation that articulates in a well formed pseudoacetabulum.

– in a young adult with asymptomatic high riding dislocated hips – do nothing.

– in osteoporosis of the hips, the last trabeculae to be lost are the primary compressive

– when planning a varus osteotomy of the hip, if the patient has limited ABDUCTION, be worried. By doing the varus osteotomy, you adduct their femur relative to the proximal fragment – if they have limited abduction, they’ll never be able to abduct their femur much past midline

– conversely, when planning a valgus osteotomy of the hip, if the patient has limited ADDUCTION, again, be worried. By doing the valgus osteotomy, you are abducting their femur relative to their proximal fragment. If they have limited adduction, their leg will be stuck out in abduction, and they wont be able to bring it to midline – this’ll piss them off just a tad.

In terms of thinking about varus and valgus osteotomies of the hip

– In general: varus osteotomy increases the lever arm of the abductors (and may ever so slightly decrease the lever arm of the body weight by medializing the contact point of the hip) – the force of the abductors is less, and hence, the joint reaction force (the vector sum of the body weight force and the abductor force) is LESS.

– the problem is that the abductor muscles are shortened, and may be shortened to the point where they are ineffective at holding up the GT – results in a limp! You may have to rectify this by advancing their trochanter. It also increases the prominence of the GT because it has been lateralized.

– In general: valgus osteotomy, you decrease the lever arm of the abductors (and may ever so slightly increase the lever arm of the body weight by lateralizing the contact point of the hip) – the force of the abductors is more, and hence, the joint reaction force (the vector sum of the body weight force and abductor force) is MORE.

The thing to remember though is that the osteotomies are done not just for joint biomechanics, but also to increase joint surface contact and thus decrease unit load on the cartilage. Often, when the head loses its sphericity and extrudes laterally abit (Perthes, AVN), the weightbearing characteristics of the joint can be improved with a valgus osteotomy. If the weightbearing is happening primarily along the superolateral aspect of the joint, a valgus osteotomy may medialize the primary point of weightbearing, thus DECREASING the moment arm of the body weight. By bringing inferior osteophytes to articulate with one another, you may decrease the unit load on the remaining cartilage and thus have less pain.

Some Hip Trauma

– subtrochanteric fractures have the highest incidence of complication because of medial buttress comminution

– the main blood supply for healing a femoral neck fracture in adults is ?lateral epiphyseal

– iliopsoas can be interposed in the joint after a posterior hip dislocation

– Pipken I type fractures do not necessarily have to be treated