Laura E. Thorp

Bone mineral density in the proximal tibia varies as a function of static alignment and knee adduction angular momentum in individuals with medial knee osteoarthritis

Based on the premise that bone mass and bone geometry are related to load history and that subchondral bone may play a role in osteoarthritis (OA), we sought to determine if static and dynamic markers of knee joint loads explain variance in the medial-to-lateral ratio of proximal tibial bone mineral density (BMD) in subjects with mild and moderate medial knee OA. We utilized two surrogate markers of dynamic load, the peak knee adduction moment and the knee adduction angular momentum, the latter being the time integral of the frontal plane knee joint moment. BMD for medial and lateral regions of the proximal tibial plateau and one distal region in the tibial shaft was measured in 84 symptomatic subjects with Kellgren and Lawrence radiographic OA grades of 2 or 3. Utilizing gait analysis, the peak knee adduction moment (the external adduction moment of greatest magnitude) and the time integral of the frontal plane knee joint moment (the angular momentum) over the entire stance phase as well as for each of the four subdivisions of stance were calculated. The BMD ratio was not significantly different in grade 2 (1.32 +/- 0.27) and grade 3 knees (1.47 +/- 0.40) (P = 0.215). BMD of the tibial shaft was not correlated with any loading parameter or static alignment. Of all the surrogate gait markers of dynamic load, the knee adduction angular momentum in terminal stance explained the most variance (20%) in the medial-to-lateral BMD ratio (adjusted r(2) = 0.196, P < 0.001). The knee adduction angular momentum for the entire stance phase explained 18% of the variance in the BMD ratio (adjusted r(2) = 0.178, P < 0.001), 10% more variance than explained by the overall peak knee adduction moment (adjusted r(2) = 0.081, P < 0.001). 18% of the variance in the BMD ratio was also explained by the knee alignment angle (adjusted r(2) = 0.183, P < 0.001), and the total explanatory power was increased to 22% when the knee adduction angular momentum in terminal stance was added (change in r(2) = 0.041, P < 0.05, total adjusted r(2) = 0.215, P < 0.001). The BMD ratio and its relationship to dynamic and static markers of loading were independent of height, weight, and the body mass index, demonstrating that both dynamic markers of knee loading as well as knee alignment explained variance in the tibial BMD ratio independent of body size.

Asymmetric loading and bone mineral density at the asymptomatic knees of patients with unilateral hip osteoarthritis

OBJECTIVE In patients with unilateral end-stage hip osteoarthritis (OA), the contralateral knee is known to be at greater risk for end-stage knee OA compared to the ipsilateral (i.e., same-side) knee. The contralateral knee is known to have increased dynamic joint loads compared to the ipsilateral knee. The present study was undertaken to examine patients who had unilateral hip OA but who did not have symptoms of knee OA, in order to detect early asymmetries in knee loading. METHODS Data on 62 patients with unilateral hip OA were evaluated. Patients underwent gait analyses of dynamic knee loads as well as dual x-ray absorptiometry for determination of bone mineral density (BMD) in both knees. Differences between knees were compared. RESULTS Peak dynamic knee loads were significantly higher at the contralateral knee compared to the ipsilateral knee (mean ± SD 2.46 ± 0.71 percent of body weight × height versus 2.23 ± 0.81 percent of body weight × height; P = 0.029). Similarly, medial compartment tibial BMD was significantly higher in the contralateral knee compared to the ipsilateral knee (mean ± SD 0.897 ± 0.208 gm/cm(2) versus 0.854 ± 0.206 gm/cm(2); P = 0.033). Interestingly, there was a direct correlation between the contralateral:ipsilateral dynamic knee load and contralateral:ipsilateral medial compartment tibial BMD (ρ = 0.287, P = 0.036). CONCLUSION The risk of developing progressive symptomatic OA in contralateral knees is higher compared to the risk in ipsilateral knees in patients with unilateral hip OA. The present study demonstrates that loading and structural asymmetries appear early in the disease course, while the knees are still asymptomatic. These early biomechanical asymmetries may have corresponding long-term consequences, providing further evidence for the potential role of loading in OA onset and progression.

Bridging the transfer gap: laboratory exercise combines clinical exposure and anatomy review

Objectives  One of the goals of medical education is to bridge the gap between basic science and clinical practice. Students acquire basic science knowledge during their pre‐clinical years, yet have limited opportunities to apply this knowledge clinically. This hands‐on laboratory exercise was designed to facilitate a review of anatomy in the context of select clinical procedures, highlighting the application of anatomical concepts in clinical practice.

Differences in Preferred Walking Speeds in a Gait Laboratory Compared With the Real World After Total Hip Replacement

OBJECTIVE To evaluate the relation between walking speeds measured in a gait laboratory and those measured in real-world settings (habitual speed) in subjects with total hip replacements (THRs) and control subjects. The secondary objective is to determine whether the relationship between gait laboratory and habitual speeds was affected by recovery time or related to clinical indices. DESIGN Cohort study. SETTING Academic medical center. PARTICIPANTS Experimental subjects (n=26) evaluated 3 weeks and 12 months after THR and control subjects (n=24). INTERVENTIONS None. MAIN OUTCOME MEASURES Walking speed measured in the gait laboratory, walking speed measured in the field by using activity monitors, Harris Hip Score (HHS), and the Western Ontario and McMaster Osteoarthritis Index (WOMAC). RESULTS Laboratory speeds were significantly faster than habitual speeds in all groups (P<.001), but the 2 correlated significantly. The laboratory versus habitual-speed difference was unaffected by recovery time within the THR group (P=.180) but was larger for control subjects (.32+/-.21m/s) than for THR subjects (.19+/-.15m/s 1 year after surgery). Habitual speed significantly correlated with total WOMAC scores and with WOMAC stiffness and function subscores 3 weeks after THR. The HHS weakly correlated with 3-week laboratory speed. No speed and clinical correlations were seen 1 year after THR. CONCLUSIONS Although subjects may exaggerate walking speeds in laboratory settings, laboratory-based data accurately reflect real-world activity. Setting affected speeds most in the control group. It is important to consider potential discrepancies between speeds walked in a laboratory versus in the real world when interpreting gait studies comparing 2 or more populations. Finally, analysis of these data suggests that clinical indices may more accurately reflect biomechanical function during early recovery after THR than after full recovery.

An Investigation of Alternating Group Dissections in Medical Gross Anatomy

Background: Reduction in contact hours has led to the use of more efficient teaching approaches in medical education, yet the efficacy of such approaches is often not fully investigated. Purpose: This work provides a detailed analysis of alternating group dissections with peer-teaching in Medical Anatomy (MA). Methods: MA I and II percentages of the alternating (ALT) and nonalternating (NALT) groups were compared, scores of ALT subgroups (A and B) were compared, and subgroup performance on practical exam questions was compared. Results: MA I and MA II percentages indicated no significant difference in median scores (pMAI = 0.581, pMAII = 0.223) between ALT and NALT. Subgroup analysis and assessment of question types showed that student performance and ability to identify a structure were not dependent on dissection group assignment. Conclusion: Alternating dissections offered students more unscheduled time for independent learning activities, such as studying or shadowing preceptors, and reduced student-to-cadaver and student-to-faculty ratios by 50%. Alternating dissections with peer teaching were not detrimental to student performance.

The Feasibility of Using Augmented Auditory Feedback From a Pressure Detecting Insole To Reduce the Knee Adduction Moment: a Proof of Concept Study

The objective of this work was to conduct a proof of concept study utilizing auditory feedback from a pressure-detecting shoe insole to shift plantar pressure medially in order to reduce the knee adduction moment (KAM). When compared with normal walking, 32 healthy subjects significantly reduced their peak KAM using feedback (p < 0.001). When compared with medial thrust gait, an established gait modification, walking with pressure-based feedback was equally effective at reducing the peak KAM, yet it successfully mitigated other potentially detrimental gait measures such as the peak knee flexion moment (KFM), knee internal rotation moment (KIrM), and a reduction in speed.

Activity Levels in Healthy Older Adults: Implications for Joint Arthroplasty

This work evaluated activity levels in a group of healthy older adults to establish a target activity level for adults of similar age after total joint arthroplasty (TJA). With the decreasing age of TJA patients, it is essential to have a reference for activity level in younger patients as activity level affects quality of life and implant design. 54 asymptomatic, healthy older adults with no clinical evidence of lower extremity OA participated. The main outcome measure, average daily step count, was measured using an accelerometer-based activity monitor. On average the group took 8813 ± 3611 steps per day, approximately 4000 more steps per day than has been previously reported in patients following total joint arthroplasty. The present work provides a reference for activity after joint arthroplasty which is relevant given the projected number of people under the age of 65 who will undergo joint arthroplasty in the coming years.

A reduction in the knee adduction moment with medial thrust gait is associated with a medial shift in center of plantar pressure

The knee adduction moment (KAM) is an established marker of compartmental load distribution across the tibiofemoral joint. Research suggests a link between the magnitude of the KAM and center of plantar pressure (COP) thus alterations in the two may be related. The objective of this study was to investigate whether the COP predictably shifts when the KAM is reduced through a gait adaptation. Twenty healthy adults underwent gait analysis walking with their normal gait pattern and with medial thrust gait, a gait adaptation known to significantly reduce the KAM. Simultaneous COP and 3-D kinetics were acquired to allow for a comparison of the change in COP to the change in the KAM. The COP was quantified by determining a customized medial-lateral pressure index (MLPI) which compares the COP tracing line during the first and second halves of stance to the longitudinal axis of the foot. Linear regressions assessing the association between the changes in KAM and MLPI indicated that 48.3% (p=0.001) of the variation in MLPI during the first half of stance can be explained by the KAM during the same period. A trend was observed between the association between the KAM and MLPI during the second half of stance (R(2)=0.16, p=0.080). Backwards elimination regression analysis was used to explore whether simultaneous consideration of the KAM and other potential confounding factors such as sagittal plane knee moments and speed explained variance in the MLPI during the first half of stance. Only the KAM exhibited explanatory power (β=0.695, p=0.001). During medial thrust gait, a reduction in the KAM was associated with a medial shift in the MLPI, and an increase in the KAM was associated with a lateral shift in the MLPI, especially in the first half of the stance phase. Together, these results demonstrate an inherent link between foot pressure and the KAM during medial thrust gait, and suggest that manipulating foot pressure may be a biomechanical mechanism for an intervention designed to improve loading conditions at the knee.