Changes in pelvic position has been shown to affect acetabular coverage of the femoral head in total hip arthroplasty (THA) and may contribute to complications such as impingement, dislocation, or early wear. Understanding the kinematic changes of these positions during functional activities may help surgeons reach a consensus regarding stable hip mechanics and ideal implant positioning in THA. Therefore, in this study, we aimed to evaluate the following in patients who had unilateral hip OA: 1) dynamic changes; and 2) variability; in the following pelvic position parameters: A) tilt; B) obliquity; and C) rotation standing position to walking. This same data was also collected from a control cohort of normal subjects with non-arthritic hip joints. Data from both cohorts were then compared.
This study analyzed 50 patients who had unilateral osteoarthritis of the hip. There were 27 men and 23 women who had a mean age of 59 years, a mean height of 173 cm (range, 152 to 200 cm), a mean weight of 84 kg (range, 31.5 to 125 kg), and a mean body mass index (BMI) of 28 kg/m2 [range, 13 to 43 kg/m2). In addition, a cohort of 19 healthy subjects with matching demographics (11 men and 9 women, mean age; 64, mean height; 168 cm, mean weight; 88 kg, mean BMI; 30 kg/m2) served as a control group. Joint marker sets were used for analysis and specific markers were used to assess pelvic position of the participants. In each cohort, mean pelvic tilt, obliquity, and rotation values in standing position, as well as mean minimum and maximum values in walking position were collected and compared. Dynamic change from standing to walking was calculated in both cohorts and then compared. Variability was demonstrated by comparing a graphic representation of individual values from both cohorts.
In hip OA patients, wide dynamic changes were demonstrated in pelvic tilt, obliquity, and rotation when going from a standing to a walking position (pelvic tilt; mean standing +8°, [range, -5° to +32°], walking range -13.5° to +33°, obliquity; mean standing +0.4°, [range, -8° to 7°], walking range -14° to +10°, rotation; mean standing -1.5° [range, -16 to +10°], and walking range -28° to +13°). In the non-arthritic cohort, narrower ranges of dynamic changes were recorded (pelvic tilt; mean standing +7°, [range, +4.35° to +9.81°], walking range +4.35° to +9.81°, obliquity; mean standing +0.66° , [range, -0.35° to 1.67°], walking range [-2.8° to 5.1°], rotation; standing mean +0.5° [range, -1.16° to +2.16°], and walking range [-6.8° to +5.1°]). When both cohorts were compared, the hip OA cohort had a three- to four-folds increase in dynamic change relative to the non-arthritic group, and in pelvic tilt, obliquity, and rotation (pelvic tilt; 38.5° vs. 9.3°, obliquity; 23.6° vs. 7.24°, rotation; 39.5° vs. 11.4). In addition, marked variability in pelvic position was also demonstrated when walking ranges of all three parameters for hip OA patients were compared to the non-arthritic subjects.
This study utilized a novel and innovative approach to analyze the dynamic changes and variability in pelvic position parameters in patients with hip OA in comparison to non-arthritic matching subjects. Hip OA patients showed marked changes in pelvic tilt, obliquity, and rotation when going from standing to walking. Non-arthritic subjects exhibited much less noticeable changes in all three parameters. When dynamic changes in both cohorts were compared, hip OA patients had a three- to four-folds increase relative to the non-arthritic group with marked variability in walking ranges. These findings may have implications on the acetabular spatial orientation and highlight the need for individual planning when undertaking THA to account for the dynamic changes in pelvic position parameters during functional activities.