L. Humphreys

Gait kinematics of age-stratified hip replacement patients—A large scale, long-term follow-up study

Three-dimensional gait analysis data from 134 patients attending routine 10-year post-operative review clinics is presented. Patients were divided into five age groups-54-64 years, 65-69 years, 70-74 years, 75-79 years and over 80 years. A group of 10 normal elderly subjects was also tested. All age groups displayed reduced range of hip flexion/extension, range of knee flexion extension, maximum hip extension and range of hip abduction/adduction and reduced velocity and step length compared to the normal elderly group. However, there was no difference in gait kinematics between the age groups. Patients over 80 years of age displayed significantly reduced range of sagittal plane ankle motion, but this is unlikely to be secondary to hip joint restriction and more likely due to reduced walking speed associated with very elderly subjects. This study reveals that even the youngest hip replacement patients do not attain normal gait kinematics 10-year post-operatively and that muscle atrophy and residual stiffness may influence patient kinematics many years post-operation.

Test-retest reliability of a 1-min walk test in children with bilateral spastic cerebral palsy (BSCP).

The test-retest reliability of a 1-min walk test at a childs maximum walking speed was assessed in children with bilateral spastic cerebral palsy (BSCP). Twelve male and five female children (age range 3-18 years, mean age 12 years 8 months) participated in the study. Children were classified as GMFCS level I (n=5), level II (n=8) and level III (n=4). Results showed that for walk tests performed on different days, distances varied by no more than 13.1m (for 95% of participants) and that a practice walk was vital for reducing systematic bias. The intraclass correlation coefficient was 0.94. A 1-min walk test is a reliable method of assessing function in children with CP but care must be taken when interpreting changes in individual patient data.

Wear paths produced by individual hip-replacement patients--a large-scale, long-term follow-up study.

Wear particle accumulation is one of the main contributors to osteolysis and implant failure in hip replacements. Altered kinematics produce significant differences in wear rates of hip replacements in simulator studies due to varying degrees of multidirectional motion. Gait analysis data from 153 hip-replacement patients 10-years post-operation were used to model two- and three-dimensional wear paths for each patient. Wear paths were quantified in two dimensions using aspect ratios and in three dimensions using the surface areas of the wear paths, with wear-path surface area correlating poorly with aspect ratio. The average aspect ratio of the patients wear paths was 3.97 (standard deviation=1.38), ranging from 2.13 to 10.86. Sixty percent of patients displayed aspect ratios between 2.50 and 3.99. However, 13% of patients displayed wear paths with aspect ratios >5.5, which indicates reduced multidirectional motion. The majority of total hip replacement (THR) patients display gait kinematics which produce multidirectional wear paths, but a significant minority display more linear paths.

The influence of wear paths produced by hip replacement patients during normal walking on wear rates.

Variation in wear paths is known to greatly affect wear rates in vitro, with multidirectional paths producing much greater wear than unidirectional paths. This study investigated the relationship between multidirectional motion at the hip joint, as measured by aspect ratio, sliding distance, and wear rate for 164 hip replacements. Kinematic input from three‐dimensional gait analysis was used to determine the wear paths. Activity cycles were determined for a subgroup of 100 patients using a pedometer study, and the relationship between annual sliding distance and wear rate was analyzed. Poor correlations were found between both aspect ratio and sliding distance and wear rate for the larger group and between annual sliding distance and wear rate for the subgroup. However, patients who experienced a wear rate <0.08 mm/year showed a strong positive correlation between the combination of sliding distance, activity levels, and aspect ratio and wear rate (adjusted r2 = 55.4%). This group may represent those patients who experience conditions that most closely match those that prevail in simulator and laboratory tests. Although the shape of wear paths, their sliding distance, and the number of articulation cycles at the hip joint affect wear rates in simulator studies, this relationship was not seen in this clinical study. Other factors such as lubrication, loading conditions and roughness of the femoral head may influence the wear rate.

Surgical versus Ponseti approach for the management of CTEV: a comparative study.

Background: Results from a comparative study of Ponseti versus surgical management for congenital talipes equino varus (CTEV), using historically managed patients, are presented. No bias existed in terms of management choice or participants recruited. Methods: Twenty-three surgically treated children (31 club feet; mean age 9.1 y) and 29 treated by the Ponseti technique (42 club feet; mean age 6.5 y) agreed to participate in the study. Twenty-six typically developing children (mean age 7.9 y) were also recruited as a control group. A physical examination and 3-dimensional gait analyses were carried out on all participants, and each child and his/her parent also, independently, completed the Oxford Ankle Foot Questionnaire (OxAFQ). Results: The Ponseti group underwent fewer joint-invasive procedures than the surgical group. Passive range of dorsiflexion and plantarflexion were significantly less in the CTEV groups when compared with the control group (P<0.001), and plantarflexion was also significantly less in the surgical than in the Ponseti group (P<0.05). The bimalleolar axis was found to be significantly less in the CTEV groups than in the control group (P<0.001) and also significantly less in the surgical than in the Ponseti group (P<0.05). The gait deviation index, a gait score based on kinematics, showed a more normal gait pattern in the Ponseti group compared with the surgical group (P<0.001). The CTEV groups did not differ significantly from each other in terms of ankle sagittal and transverse plane kinematics or kinetics, but foot progression angle for the Ponseti group was external, whereas that for the surgical group was internal. The Ponseti group also scored higher than the surgical group in terms of patient satisfaction, with significantly better parent-rated OxAFQ scores in the “emotional” and “school and play” domains. Conclusions: The adoption of the Ponseti technique has resulted in fewer and less-invasive operations for our CTEV population, with accompanying improvement in the overall gait pattern (gait deviation index) and parent satisfaction (OxAFQ). Level of Evidence: Level III.

Activity Levels and Polyethylene Wear of Patients 10 years Post Hip Replacement

BACKGROUND Wear of the acetabular cup and implant loosening in total hip arthroplasty are thought to be affected by individual patient activity levels. METHODS Activity levels of 100 patients with unilateral primary hip replacements were measured using a digital pedometer 10-years post-operatively. FINDINGS Activity rates of hip replacement patients 10 years post surgery were found to fall with increasing age strata, with the age group 70-74 years showing significantly reduced activity rates compared to the 55-64 years age group and the age group greater than 80 years showing significantly reduced activity rates compared to both the 55-64 years age group and the 65-69 years age group. However, a clear correlation between age and activity was not found. Acetabular cup wear showed no relationship with patient activity levels. INTERPRETATION Progressive reduction in activity levels with more elderly hip replacement patients may inform long term planning of hip arthroplasty and implant choice.

Pelvic orientation for total hip arthroplasty in lateral decubitus: can it be accurately measured?

Introduction During total hip arthroplasty (THA), accurately predicting acetabular cup orientation remains a key challenge, in great part because of uncertainty about pelvic orientation. This pilot study aimed to develop and validate a technique to measure pelvic orientation; establish its accuracy in the location of anatomical landmarks and subsequently; investigate if limb movement during a simulated surgical procedure alters pelvic orientation. Methods The developed technique measured 3-D orientation of an isolated Sawbone pelvis, it was then implemented to measure pelvic orientation in lateral decubitus with post-THA patients (n = 20) using a motion capture system. Results Orientation of the isolated Sawbone pelvis was accurately measured, demonstrated by high correlations with angular data from a coordinate measurement machine; R-squared values close to 1 for all pelvic axes. When applied to volunteer subjects, largest movements occurred about the longitudinal pelvic axis; internal and external pelvic rotation. Rotations about the anteroposterior axis, which directly affect inclination angles, showed >75% of participants had movement within ±5° of neutral, 0°. Conclusions The technique accurately measured orientation of the isolated bony pelvis. This was not the case in a simulated theatre environment. Soft tissue landmarks were difficult to palpate repeatedly. These findings have direct clinical relevance, landmark registration in lateral decubitus is a potential source of error, contributing here to large ranges in measured movement. Surgeons must be aware that present techniques using bony landmarks to reference pelvic orientation for cup implantation, both computer-based and mechanical, may not be sufficiently accurate.