Geometrical restoration during total hip arthroplasty is related to change in gait pattern - a study based on computed tomography and three-dimensional gait analysis

A cohort of 75 individuals with unilateral primary hip osteoarthritis were recruited for this prospective intervention study. The study was part of a comprehensive study investigating different aspects of THA. The participants underwent THA between October 2009 and September 2011. Inclusion criteria were: < 75 years of age, primary unilateral osteoarthritis of the hip, ability to commit to the conditions of the study, including repeated CT and gait analysis evaluations. Exclusion criteria were: previous major orthopedic surgery in the lower limbs, other lower extremity joint pain or severe back pain, spinal deformities, rheumatoid arthritis, diabetes mellitus, neurologic disease, BMI > 40, and/or other conditions affecting walking ability. Participants were recruited from the THA waiting list at the department of orthopedics, Skåne University Hospital, Lund, Sweden. All enrolled participants provided written and verbal informed consent to participate in all parts of the study in accordance with the Declaration of Helsinki. The regional ethical review board at Lund University, Sweden, approved the study (Dnr:2009/369). Identifier number at ClinicalTrials.​gov: NCT01512550.

Participants were evaluated with low dose CT scans, 3D gait analysis, and patient-reported outcome measures within 1 month prior to THA and again 1 year postoperatively. Reasons for failure to follow-up and/or exclusion were: periprosthetic fracture (n = 1), inability to walk independently because of other conditions (n = 2), no preoperative CT (n = 2), no postoperative gait analysis (n = 1) or CT (n = 2), and THA of contralateral hip within 6 months (n = 2). Thus, 65 participants remained for this study and were included in the statistical analysis.

Two experienced hip surgeons performed the operations through a posterolateral approach using a cementless cup and stem (ABG II and Trident (Stryker Orthopedics, Mahwah, New Jersey, USA)). Based on preoperative 2D templating and CT measurements, geometrical restoration of FNA and GO was attempted with the contralateral hip as reference. Preoperative planning was based on calibrated digital plain radiographs using Sectra IDS7 PACS Orthopaedic PackageTM (Sectra AB, Linköping, Sweden).

Postoperative regimens allowed full weight-bearing immediately following surgery. After surgery, participants were encouraged to use an appropriate walking aid for 1 to 2 months to facilitate normal gait pattern and avoid limping. Participants participated in rehabilitation according to standard practice at the hospital and, thereafter, in a primary care setting of the patient’s choice.

In the current study, CT was performed using a low-dose technique, with an effective dose close to that of plain radiography [24], showing that even with increased image noise, excellent results can be achieved. This study was part of a comprehensive study project investigating different aspects of THA where all the added information that CT gives was essential. The project had approval from both ethical review board and the local the local radiation committee. An independent observer made all measurements on the pre- and postoperative 3D-CT data blinded to previous measurements, preoperative 2D templating, and the participants’ management. The pre- and postoperative 3D-CT data were assessed for lever arms (i.e., AO and FO) and rotatory positions of the hip and stems (i.e., FNA) using a CT based 3D templating software, Ortoma® Hip plan, version 1.0.0.26 (Ortoma, Gothenburg, Sweden). The 3D-analysis software produced repeatable measurements for GO, FO, AO, and FNA with near-perfect both inter- and intra-observer agreements [25]. The analyzed variables were FNA, GO, and the FO/AO quota on both sides. The following definitions for CT measurements were used: The long axis of the proximal femur was defined by the center of two best-fit intramedullary spheres, one on the distal level of the trochanter minor and the other 6 cm further down in the femoral shaft. True FO was defined as the perpendicular distance from the long axis of the proximal femur to the rotational center of the femoral head. We will refer to the intersection of the FO onto the proximal long axis of the femur as point A. The condylar plane was defined by the posterior subchondral joint surface of the medial and lateral femoral condyles projected proximally to point A. The FNA was defined as the angle between the condylar plane and the line between point A and the rotational center of the head of the femur. The symphysial plane was defined as a plane in the middle of the symphysis and perpendicular to the bi-ischial line. The AO was defined as the distance from the symphyseal plane to the rotational center of the femoral head. The GO was defined as the sum of the FO and AO (Fig. 1).

Three-dimensional gait analysis was conducted at the motion analysis laboratory in Lund, Sweden using a six camera Vicon MX40+ system (Vicon Motion Systems Ltd., UK) set at a capture frequency of 100 hz and one OR6–5 force plate (Advanced Mechanical Technologies inc, USA). Segment position of the trunk and pelvis, joint rotations of the hip and foot, external joint moments and time/distance parameters were calculated using the Plug-In-Gait model (Vicon Motion Systems Ltd., UK) [26]. Data were extracted for analysis using proCalc software (Vicon Motion Systems Ltd., UK). The following parameters from the gait analysis were selected based on an a priori hypotheses of their association with changes in the transverse plane (hip anteversion) and in the frontal plane (femoral, acetabular or global offsets): mean trunk obliquity in stance (°), mean pelvic obliquity and rotation in stance (°), mean hip rotation in single stance (°), mean foot progression in single stance (°), mean hip adduction moment in stance (Nmm/kg), and maximal hip adduction moment between initial contact and midstance (1st peak) and between midstance and foot-off (2nd peak) (Nmm/kg). The following time and distance parameters were included: walking speed (m/s) and time in single stance (s). To evaluate overall gait quality in the lower extremity, the Gait Deviation Index (GDI) was calculated for the operated side. The GDI is based on kinematics from the pelvis and the hip in all three planes, the knee and ankle in the sagittal plane and foot progression in the transversal plane [27]. GDI scores are interpreted as follows: a value of 100 or higher indicates a normal gait pattern, while each 10-point decrement below 100 indicates one standard deviation (SD) from normal gait (e.g., a GDI score of 80 indicates 2 SD from normal gait). Participants walked barefoot on a 10 m walkway and were instructed to walk in a self-selected speed. Enough trial walks were allowed for the participants to reach their customary gait pattern. Following this, three strides containing kinematic and kinetic data from each side were collected and subsequently analyzed. Gait parameters showed excellent intra-subject repeatability between strides and the statistical analysis was based on the mean of discrete values and variables from the three strides.

Pre- and 1 year postoperatively, all participants completed the hip disability and osteoarthritis outcome score (HOOS) [28] and the EuroQol- Five Dimensions EQ-5D [29]. HOOS is a joint-specific self-assessment questionnaire; reliable for assessing baseline function and change over time in individuals with hip osteoarthritis. The questionnaire is divided into five subscales, and each subscale generates a score ranging from 0 to 100, where 0 represents “worst” and 100 “best” [28]. In this study, the subscale for pain was used. EQ-5D is a generic, reliable questionnaire used to evaluate health-related quality of life. In this study, the patient-rated health VAS scale from EQ-5D, ranging from worst health 0 to perfect health 100, was used in the analysis [29].

Preoperative radiographs were collected according to standard procedures. Images were classified according to the modified Kellgren Lawrence grade ranging from 0 to 4, where 0 represents no osteoarthritis and 4 severe osteoarthritis [30].

To evaluate the differences between pre- and postoperative hip joint anatomy (CT measured) and variables derived from 3D gait analysis, a paired sample t-test was used. To evaluate differences between postoperative CT measures and reference values from the contralateral side, an independent t-test was used. The Wilcoxon’s signed-rank test was used for identifying pre and postoperative differences in HOOS pain and EQ. 5D VAS score.

Multiple linear regressions were performed to evaluate the relations between changes in joint anatomy (THA) and changes in gait pattern. Assumptions of linear relationship and multivariate normality were checked by scatterplots and by comparing the residuals vs. predicted values (i.e., the residuals had to be normally distributed around zero). In regression model 1, change in mean hip rotation in single stance was used as the dependent variable. Change in femoral neck anteversion, pelvic rotation, and walking speed between pre and post evaluations were included as independent variables. In regression model 2, change in max external hip adduction moment in the first 50% of stance was used as the dependent variable. Change in FO/AO quota, trunk obliquity, pelvic obliquity, and in walking speed between pre and post evaluations were included as independent variables. All variables were entered at the same time. Pain, subscale in HOOS, was initially included as an independent variable in both models but was excluded based on low response frequency (n = 55). However, pain was not a statistically significant variable in any model, and the results of the analyses were equivalent with pain excluded.

Compared to preoperative values, FNA angles changed equally in internal and external directions leading to a statistically non-significant change on group level (Fig. 2). Compared to preoperative values, the FO and FO/AO quota increased, while AO and GO decreased (Table 2). Postoperatively, compared to the contralateral side, FO had increased, and AO had decreased on the operated side while symmetry between sides were noted in FNA and GO (Table 2). The postoperative differences between sides in FO were distributed as follows: In 74% of the participants, the femoral offset of the operated side was within +/− 5 mm of the FO of the non-operated side. In 26%, the FO on the operated side was more than 5 mm longer than that of the non-operated side (increased FO > 5 mm). None of the participants had an FO which had decreased by more than 5 mm compared to the FO of the non-operated side (decreased FO > 5 mm).

After THA, the quality of overall gait pattern, walking speed, and time spent in single stance increased significantly (Table 3). On the operated side, hip rotation during gait changed equally in internal and external directions leading to a statistically non-significant change on group level (Fig. 2). On the operated side, the pelvis segment became more externally rotated, and the foot segment became less externally rotated during stance. External hip adduction moments increased significantly, and participants walked with less trunk obliquity (i.e., less lean over the operated side). Pelvic obliquity decreased on the operated side, indicating less Trendelenburg gait, however this was not statistically significant (Table 3).

The change in hip rotation during gait after THA was associated with change in FNA, in the same direction, and with pelvic rotation, in the opposite direction, but not with change in walking speed (Table 4).

The increase in hip adduction moment during gait was not associated with change in FO/AO quota but with less trunk lean and pelvic obliquity and an increase in walking speed (Table 4).