In joint arthroplasty and in knee replacement in particular, the currently used patient assessment scores like KSS, are characterized by subjective ceiling effects. To monitor patients accurately in time, objective function assessment is required which is impossible with the classic scores. A single time point comparison study showed that an acceleration based gait test is reliable to analyze gait and to distinguish between knee pathologies. How-ever the use of an accelerometer to monitor functional changes over time is never reported before and will be investigated in this study. A representative group of 29 TKP patients (11 men, mean age 72yrs, weight 85kg, height 1.68m) operated for osteoarthritis receiving unilateral TKP (Stryker Scorpio) were monitored for 3 months. Classic scores (ROM, KSS, WOMAC, VAS, PDI) and the gait test was performed pre, 2 and 6 weeks and 3 months postoperative. Gait was analyzed using a triaxial accelerometer fixed to the sacrum while walking 6 times 20meters at preferred speed. Movement parameters like step frequency, step time, step length, speed and up/down displacement were calculated based on a peak detection algorithm. The gait test was compared with the classic scores using Pearson correlation. The paired t-test was used to investigate the changes after surgery (p<
0.05). Significant correlations were shown between all classic scores and all movement parameters (except up/down displacement and step length). The function KSS and PDI showed significant correlations with most gait parameters, while all Womac scores did not. Two weeks after surgery, the classic scores reached the preoperative scores. For instance function KSS was 57.21 preoperative and reached a score of 59.75 at 2 weeks postoperative. No significant changes were shown between preoperative and 2 weeks postoperative for the VAS, KSS and PDI. In contrast all gait parameters were significantly impaired at 2 weeks postoperative (step time of 0.63s) compared to preoperative (step time of 0.72s) and reached the preoperative functional abilities only at 6 week follow up or still later (step time of 0.64s). Between the 2nd and 6th week postoperative, significant changes were shown in all classic scores, ROM and in speed, up/down displacement. After 6 weeks postoperative KSS, PDI, ROM and the frequency improved significantly. The correlations between all movement parameters and function KSS and PDI indicates that these scores are more function based due to inclusion of objective function measures like ROM, while the Womac contains only questions about ADLs. According to the classic scales, patients show at 2 weeks similar skills as preoperative, while the gait test shows that patients are performing less at 2 weeks and reach the pre operative ability at 6 weeks. This suggest that the addition of the gait test give more information about the functional changes a patient experiences after surgery.
Femoral neck fracture is a serious complication in hip resurfacing arthroplasty and reducing its risk is a major challenge. From a biomechanical point of view changing the geometrical characteristics in surgery could affect the stresses in the femoral neck. We analysed standing AP X-rays of 85 randomly selected patients having pain in the pelvic region in order to gain better understanding of the geometrical influences. Patients were selected on age, weight, pelvis visibility and no deformations of the proximal femur. A variety of geometrical characteristics has been measured and analysed using the two-sided t-test. A significant difference was found between men and women, which was compared to previous publications in order to verify the measurement method. Statistical indication could not be found for leg-dominancy influencing geometrical dimensions. This is not mentioned in literature, but it is mentioned that the BMC and BMD differs between the legs. Several linear relations have been found between geometrical characteristics and demographics. The average head-neck ratio for both left and right was about 1.4 and the ratio of the abductor moment arm and body moment arm was about 2.1. The linear relation between femoral head diameter and femoral neck diameter indicates that the femoral component should be chosen according to the natural head diameter. The ratio between the abductor arm and body arm in combination with the bodyweight determines the static stresses in the femoral neck and can be changed in surgery by altering the hip axis length and neck shaft angle.
In joint arthroplasty the currently used patient assessment scores suffer from subjectivity, a low ceiling effect and pain dominance. These effects mask functional differences which are important for today’s demanding patients. Functional assessment tools are needed which can objectively monitor patient outcome. This study investigates whether an acceleration based gait test is able to assess TKR patients. A cohort of 24 patients (11m, 13f) operated for osteoarthritis receiving unilateral TKR (Stryker Scorpio) were monitored for 3 months post-operative. Classic scores including subscores (KSS, Womac, VAS, PDI) and a gait test were measured pre-operative, at 2 weeks, 6 weeks and 3 months post-operative. Gait was analyzed using a triaxial accelerometer fixed to the sacrum while walking 6 times a 20m distance at preferred speed. Movement parameters like step frequency, step time, step number, vertical displacement, asymmetry and irregularity were calculated based on a peak detection algorithm. All classic scores were significantly intercorrelated (e.g. KSS and Womac, R=−0.73) indicating a degree of redundancy. Significant correlations were shown between several gait parameters and the KSS, PDI and VAS. Most correlations between gait parameters and a classical score were found for the KSS function subscore indicating it as the most objective functional assessement amongst the classic scores. In contrast Womac did not correlate with any gait parameter. This lack WOMAC capturing objective function was reported before using functional tests. The classic scales and the gait test cover different dimensions of surgical outcome supporting their combined use to follow up patients The accelerometer based gait test is clinically valid for the follow-up of TKR patients.
To clinically diagnose and postoperatively monitor the younger or more demanding orthopaedic patients it becomes increasingly important to measure function beyond the capacity of classic scores suffering from subjectivity, pain dominance and ceiling effects. This study investigates whether a stair climbing test with accelerometer derived motion parameters in a group of healthy subjects is clinically feasible and valid to distinguish between demographic differences. The ascending and descending of stairs (preferred speed, no handrails) was measured in 46 healthy subjects (19m/27f, no orthopaedic pathology) using a triaxial accelerometer attached with a belt to the sacrum. The study group was divided in two age groups: young group (15m/16f; age: 25 [21–38]) and old group (4m/11f; age: 67 [54–74]). Motion parameters were derived by acceleration peak detection algorithms based on step times: tup, tdown, tup-tdown,, step irregularity: irrup, irrdown and asymmetry: asymup, asymdown. Step times were slightly higher ascending (tup=606ms) than descending (tdown=575ms, p<
0.05). The step time difference between ascending and descending (tup-tdown=31ms) showed a significant difference between the young (47ms) and elderly (−7ms). All subjects with descending times ≥20ms slower than ascending (6/46) were elderly. Irregularity and asymmetry were similar between stepping direction and age groups. Asymmetry identified the dominant leg with equal or faster steps than the non-dominant leg in 43/46 cases. Motion parameters were not correlated to gender, height or BMI. Slower step times down than up seem a promising parameter to detect general or bilateral orthopaedic pathologies. Asymmetry identifying the dominant leg shall detect unilateral pathologies. The accelerometer assessed stair test seems suitable for routine clinical follow-up complementing classic scores.
At 8-years the wear rate was significantly (p<
0.01) lower for Duration [0.088 ± 0.03 mm/yr (0.02–0.14)] than conventional PE [0.142 ± 0.07 mm/yr (0.05–0.31)]. This reduction (−38%) compared well to the simulator (−45%) and did not change over time (−33% at 5-years). Radiolucencies and signs of osteolysis were also less in the Duration group (n.s.).
The annual wear rates were compared and intra-observer variability was calculated as the difference between both measurements (precision). The average time it takes to measure one image (without format conversions) was documented and practicality of daily clinical use was evaluated.
The precision was (mean +/− SD): Martell = 1.74+/−1.53, Hyperview = 0.36 +/−0.92, Pro-X = 0.10+/−0.11 Roman = 0.08 +/−0.08. The average measuring time per image was: Martell = 94s, Hyperview = 94s, Pro-X = 92s Roman = 158s.
Proximal bone resorption occurred in 27% (R1) or 34% (R7) which is lower than the values reported for the ABG-I stem (R1: 48%, R7: 45%). Bone resorption was significantly higher with tight than non-tight mid-stem fit (69% vs 27%, p=0.04). The same trend was true for tight distal fit (56% vs 37%). Cancellous densifications were frequent at mid-stem level (R2: 83%, R6:88%) but much less distally (R3: 44%, R5:25%). No influence of fit &
fill was measured. Cortical densifications were noted in 16% (ABG-I 15%) overall with a higher proportion measured for tight distal fit (25%) than loose distal fit (6%, p=0.07). A similar observation was made for cortical thickening (11% overall, tight:non-tight=16%:6%). Pedestal formation (17% overall) was more likely with a non-tight proximal fit (23% vs 12%) and mid-stem fit (20% vs 8%) A proximal tight fit was achieved more frequently with normal (55%) and stovepipe femora (50%) than champagne flute femora which had the highest proportion of tight distal fit (85%).
As LTP occurred with non-tight fit it seems that elastic mismatch is not the main cause. Less proximal bone resorption and less distal densifications confirm the design changes from ABG-I to ABG-II.
Patients were clinically assessed for 2 years using the Knee Society Score (KSS). At final follow-up patients were assessed once using two accelerometer based motion tests (Dynaport Knee Test and Minimod Gait Test; McRoberts, Netherlands). The knee score is composed of four sub scores (Locomotion, Rise &
Descend, Transfers, Lift &
Move). The gait test records walking parameters such as step frequency, length and speed plus various parameters of step asymmetry, irregularity and efficiency. Statistical analysis was performed using the van Elteren’s test (KSS data) and a stratified regression analysis (Dynaport and Minimod data)
The Dynaport knee test showed a significant functional advantage for patella resurfacing (RS=44.1+/−12.1, NR=39.7+/−19.2, p=0.04). The sub score Rise &
Descend showed the largest advantage for patella resurfacing (RS=44.7, NR=39.7, p=0.04). The other sub scores also favored resurfacing but were not significant. The Minimod Gait test favoured RS in most parameters but at non-significant levels.
The advantage of patella resurfacing may be less due to pain relief but due to a functional benefit during demanding motion tasks for which standard clinical scores and low demanding tests do not account for sufficiently and objectively enough. We recommend complementing the classic evaluation tools with demanding functional tests.
Three cross sections were cut from the metaphyseal femur and surrounding bone proximal to Gruen zones 2 and 6 (regions with HA coating). The three sections were A (proximal), B (mid-part) and C (distal). Sections were prepared using the Donath technique and then paragon stained for quantitative histomorphometry using an Axioskop microscope (Carl Zeiss, Germany) with image analysing (SAMBA, France). For each segment the total implant perimeter, percentage of implant perimeter covered by bone and the total percentage of residual HA coating were measured. Bone implant contact was defined as direct ongrowth of bone to the coating or the titanium surface.
Bone ongrowth ranged between 18%–56% and was independent of the time in-vivo. Bone ongrowth was most strongly correlated to patient age with younger patients having significantly higher bone ongrowth (p=0.001). Bone ongrowth was correlated with HA-resorption only in the most proximal zone A (p=0.001) with lower ongrowth associated with lower levels of residual HA. However, HA resorption was not significantly correlated with patient age. HA resorption was significantly higher most proximally with less residual HA (13.0%) than mid-stem (22.6%, p=0.05) and distal (28.1%, p=0.05). Metaphyseal stem level and bone ongrowth were not significantly correlated in this manner.
Bone ongrowth but not HA resorption was strongly correlated to patient age indicating that the bone remodelling process is more affected by individual bone health than it can be stimulated by HA coating. HA resorption increased significantly from the distal to mid-stem and the most proximal coating level in the same way as stress shielding and thus osteoclastic stimulation goes up.
This study confirms that the Vancouver classification and the modified algorithm for the management of PPF are a simple,reproducible classification system also for the uncemented treatment modality. Conservative treatment is a valid option in case of a stable implant, while in case of a loose implant surgical intervention is mandatory.
For the ABG-I cup the literature review gave survival rates between 59%–97% after 8–10 years. In our own study cup survival was 97.4% at 10 years. Looking at PE-wear, the literature gave average wear rates ranging from 0.24 to 0.32mm/year, values clearly above the wear rate boundary of 0.10–0.15mm/year usually considered as critical. In our own study augmented PE-wear (>
0.15mm/year) was noted in 23.6% of all implants. The majority (77%) of these implants were from patients younger than 70 years although this group only represented 57% of the total. The revision rates at 10 years reflect a similar trend with values much higher for patients below 70 years (2.8%) than above(4.9%).