Optimal orientation of implanted components in total hip arthroplasty with polyethylene on metal articulation

Establishing a range of motion boundary for total hip arthroplasty

“…A = cos f : cos r À sin f : sin a: sin r À sin f : cos a cos f : sin r + sin f : sin a: cos r sin f : cos r + cos f : sin a: sin r cos f : cos a sin f : sin r À cos f : sin a: cos r À cos a: sin r sin a cos a: cos r LEVEL Level walking [59] PIVOT Standing while turning the upper body away [6,21] ROLL Lying supine and rolling over, for example, when in bed [21] SQUAT 1 Squatting with feet flat [3] SQUAT 2 Squatting balancing on flexed toes [3] SSL Stand-sit-stand from a low seat (~40 cm high) [6,21] SSN Stand-sit-stand from a normal seat (~46 cm high) [6,21] STAIR Ascending and descending stairs [20] STOOP Standing then bending to retrieve an object from floor [6,21] SWING Swinging leg back and forth [21] TIE Sitting on a normal seat and bending to tie shoe laces [6,20] XLG Sitting on a normal seat while crossing legs [6,20] Using equation (1), when the body is posed in neutral, the knee centre position at the distal femur would lie on the femoral y-axis and have position vector, P = (0, 21, 0). To visualize the ROM of this knee centre, as a representation of the ROM of the hip joint, its position in 3D space for any given manoeuvre would be defined by equation (2).…”

“…For the referenced ADLs, key points were selected by identifying the points of maximum flexion/extension, abduction/adduction, and internal/ external rotation, and then recording the corresponding joint angles at this point in the two other anatomical planes [3,6,20,21,58,59]. The key points that represented the mean of the sample of cohorts measured were taken from the gait cycles.…”

Evaluation of range of motion restriction within the hip joint

“…An overly contained cup may lead to impingement between the neck of the femoral component and the rim of the acetabular cup during terminal motion of the hip. Such contact can create wear particles potentially leading to implant loosening [22, 41, 54]. Further motion beyond the impingement point causes subluxation of the femoral head until the joint dislocates [21, 27, 31].…”

“…Yoshimine and Ginbayashi [57] specified five factors that determine the range of motion which a THA can achieve, four of these are associated with prosthetic component orientation: (1) acetabular cup anteversion, (2) acetabular cup inclination, (3) femoral stem version and (4) femoral component neck axis away from the transverse plane which is dependent upon femoral stem varus–valgus within the femoral canal and femoral component neck-shaft angle [22, 53, 56]. A further orientation parameter has been defined by Renkawitz et al [36] which is significant in femoral components with a non-axis symmetric neck.…”

“…At present, specifications for an impingement free range motion outcome have been based on limits of pure joint motion of healthy individuals in the coronal, sagittal and transverse planes [11, 42, 54, 56], or from measuring joint rotations for specific activities of daily living [16, 19, 22, 31]. Other studies have used computer tomography (CT) scans of healthy bony anatomy to determine patient range of motion requirement [23, 46–49].…”