Title: Osteotomies about the Hip for the Prevention and Treatment of Osteoarthrosis
Reference: Millis, Murphy, Poss, Instructional Course Lectures, 1996
– the finite lifespan of arthroplasty makes osteotomy a consideration, particularly in the young patient.
Points of Interest
Many joints degenerate for MECHANICAL reasons – elevated joint contact pressure seems to be related directly to the onset of degeneration of articular cartilage. Osteoarthritis begins when the magnitude of UNIT LOAD experience by the joint exceeds the tolerance level of the articular cartilage and subchondral bone.
Most OA Of the hip is secondary to some pre-existing anatomic deformity – primary OA caused by biological failure of articular cartilage in the absence of any mechanical derangement is RARE.
Aronson – 474 patients with end-stage OA – 76% had some disorder (dysplasia, Perthes, slip)
Average unit load of articular cartilage: 25kg/cm2 (remarkably consistent among species)
The sourcil in normal hips has a symmetric density, reflecting a nice distribution of forces. In dysplastic hips, the sourcil becomes eccentric, with increased density laterally and anteriorly.
Varus osteotomy: seeks to restore congruency (and therefore decrease unit load); seeks to decrease muscle forces about the hip by elevating and lateralizing the GT and by medializing the abductors and the psoas.
Valgus osteotomy: seeks to increase congruency and to transfer the center or rotation of the hip from the superior aspect of the acetabulum towards the medial aspect.
Ideal patient for reconstructive osteotomy: young, good range of motion, minimal symptoms, good function, congruent surfaces with minor degenerative changes if any.
Patients who have an osteotomy usually neither gain nor lose overall motion of the hip. Contractures do not necessarily represent a contraindication to a realignment osteotomy as long as the patient has a pain-free flexion/extension arc of at least 80o.
The false profile view is taken with the patient standing, the pelvis pointing 25o towards the beam, with the ipsilateral foot and knee lying perpendicular to the beam. Provides a true lateral radiograph of the acetabulum. This is good for showing subtle acetabular dysplasia with anterior coverage defect.
Examination of the hip under fluoro may be helpful in determining the incongruity of the joint.
Selecting the site of osteotomy
– if CE angle