Anterior cruciate ligament deficiency (ACLD) affects the performance of walking in some patients (non-copers) while copers are able to minimize the effects via proper musculoskeletal compensations. Since many daily activities are more challenging than level walking, e.g., obstacle-crossing, it is not clear whether copers are able to cope with such a challenging task. A successful and safe obstacle-crossing requires not only sufficient foot clearance of the swing limb, but also the stability of the body provided mainly by the stance limb. Failure to meet these demands may lead to falls owing to loss of balance or tripping over obstacles. The purpose of the current study was to identify the motor deficits and/or biomechanical strategies in coper and non-coper ACLD patients when crossing obstacles of different heights for a better function assessment.

Ten coper and ten non-coper ACLD patients were recruited in the current study. The non-coper ACLD subjects were those who had not been able to return to their pre-injury level activities, had at least once giving way during the last six months and their Lysholm knee scale was less than 70 [1]. Each subject walked and crossed obstacles of heights of 10%, 20% and 30% of their leg lengths at a self-selected pace. Kinematic and kinetic data were measured with a 7-camera motion analysis system (Vicon, Oxford Metrics, U.K.) and two force plates (AMTI, U.S.A.). The leading and trailing toe clearances were calculated as the vertical distances between the toe markers and the obstacle when the toe was directly above the obstacle. Joint angles of both limbs, and joint moments of the stance limb, were calculated. Peak extensor moments at the knee during stance phase and the corresponding joint angles were extracted for statistical analysis. A 3 by 2, 2-way mixed-model analysis of variance with one between-subject factor (group) and one within-subject factor (obstacle height) was performed (α=0.05). SAS version 9.2 was used for all statistical analysis.

Compared with the copers, significantly reduced leading and trailing toe clearances were found in the non-coper group (P<0.05). The non-copers showed significantly decreased peak extensor moments (P<0.05) and flexion angle at the affected knee during the stance phase before leading limb crossing (P<0.05).

Distinctive gait patterns were identified in coper and non-coper patients with unilateral anterior cruciate ligament deficiency during obstacle crossing. During the stance phase before the un-affected leading limb crossing, the non-copers showed significantly reduced flexion and peak extensor moments at the affected knee (i.e., quadriceps avoidance), primarily owing to the impaired stability at the affected knee. The significantly reduced leading and trailing toe clearances in the non-coper group indicate that the non-coper ACLD patients are at a higher risk of tripping over the obstacle, and may have difficulty in regaining balance owing to the unstable ACLD knee. Advanced rehabilitation program or reconstruction of the ACL is suggested for the non-coper group.

Identification of gait deviations and compensations in patients with total hip arthroplasty (THA) is important for the management of their fall risks. To prevent collapse of the lower limbs while balancing and supporting the body, proper combinations of joint moments are necessary. However, hip muscles affected by THA may compromise the sharing of load and thus the whole body balance. The current study aimed to quantify the control of body support in patients with THA in terms of the total support moment (Ms) and contributions of individual joint moments to Ms during walking.

Six patients who underwent unilateral THA via an anterolateral approach for at least six months at the time of the gait experiment, and six age- and gender-matched healthy controls were recruited. Twenty-eight infrared retro-reflected markers were placed on specific landmarks of the pelvis-leg apparatus to track the motion of the segments during walking. Kinematic and kinetic data were measured using an 8-camera motion analysis system (Vicon, Oxford Metrics, U.K.) and two force plates (AMTI, U.S.A.). The Ms of a limb was calculated as the sum of the net extensor moments at the hip, knee and ankle during stance phase. The contributions of the hip, knee and ankle to the first and second peaks of Ms (Ms1 and Ms2) were calculated by dividing the joint moment value by the corresponding peak values of Ms. Independent t-tests were performed to compare between groups at a significance level set at α=0.05 using SAS version 9.2 (SAS Institute Inc., NC, USA).

No significant differences in Ms1 and Ms2 were found between the THA group and normal controls (P >0.05). However, compared to the healthy controls, significantly increased hip and ankle contributions but decreased knee contributions to Ms1, and significantly increased hip contributions but decreased ankle contributions to Ms2 were found in the THA group.

Similar Ms1 and Ms2 between groups indicates that the lower limbs in the THA group were able to provide normal body supports. However, this was achieved via an altered contributions of the hip, knee and ankle. Hip and knee extensors play important roles in supporting the body when the Ms1 occurs during early stance of walking. In the THA group, greater hip and ankle contributions but lesser knee contributions for the Ms1 indicates that the function of hip extensors were not affected but compensatory mechanisms of the knee and ankle were found. For the Ms2, hip flexor and ankle plantarflexors are important for supporting the body during late stance. Decreased hip flexor (i.e., greater hip extensor contributions) and ankle plantarflexor moments in the THA patients suggests that the hip flexors and ankle plantarflexor muscles were affected by THA surgery. Hip muscles affected by the THA may compromise the sharing of load at the hip and thus the whole body balance. Further postoperative rehabilitation is suggested for the patients following THA. Further studies on the effects of different surgical approaches on the support moments is needed for improving treatment plans.

Subtalar arthrodesis known as talocalcaneal fusion is an end-stage treatment for adult hind foot pathologies. The goal of the arthrodesis is to restrict the relative motion between bones of the subtalar joints, aiming to reduce pain and improve function for the patient. However, the change of the subtalar structures through the fusion is considered a disturbance to the joint biomechanics, which have been suggested to affect the biomechanics of the adjacent joints. However, no quantitative data are available to document this phenomenon. The purpose of the current study was to quantify the effects of subtalar arthrodesis on the laxity and stiffness of the talocrural joint in vitro using a robot-based joint testing system (RJTS) during anterioposterior (A/P) drawer test.

Six fresh frozen ankle specimens were used in this study. The lateral tissues of the specimens were removed but the anterior and posterior talofibular ligaments and calcaneofibular ligament were kept intact. A/P drawer tests were performed on each of the specimens at neutral position, 5° and 10° of dorsiflexion, and 5?and 10?of plantarflexion using a robot-based joint testing system (RJTS), before and after subtalar arthrodesis. The RJTS enabled unconstrained A/P drawer testing at the prescribed ankle position while keeping the proximal/distal and lateral/medial forces, and varus/valgus and internal/external moments to be zero. This was achieved via a force-position hybrid control method with force and moment control, which has been shown to be more accurate than other existing force-position hybrid control methods. The target A/P force applied during the A/P drawer test was 100N in both anterior and posterior directions. The stiffness and laxity were calculated from the measured force and displacement data. The anterior and posterior stiffness of the talocrural joint were defined as the slope beyond 30% of the target A/P force, and the peak displacements quantified the laxity of the joint. Comparisons of laxity and stiffness between the intact and fusion ankle specimens were performed using Wilcoxon signed rank test (SPSS 19.0, IBM, USA) and a significance level of 0.05 was set.

Subtalar arthrodesis did not lead to significant changes in the stiffness and laxity in both anterior and posterior directions (P>0.05). The mean anterior stiffness before arthrodesis was 9.54±1.17 N/mm and was 10.35±2.40 N/mm after arthrodesis. The mean anterior displacements before and after arthrodesis were 9.68±0.94 mm and 8.97±1.42 mm, respectively.

Subtalar arthrodesis did not show significant effects on the A/P laxity and stiffness of the talocrural joint in both anterior and posterior directions. This may imply that the motion of the subtalar joints do not have significant effects on the A/P stability of the talocrural joint, which is the main joint of the ankle complex. This agrees with the anatomical roles of the subtalar joints which provide mainly the varus/valgus motions for the ankle complex. The current study provides a basis for further studies needed to evaluate the effects subtalar arthrodesis on the varus/valgus stability.

Summary Statement

The current study introduced the effects of projection errors on ankle morphological measurements using CT-based simulated radiographs by correlation analysis between 2D/3D dimensions and reliability analysis with randomised perturbations while measuring planar parameters on radiographs.