Impact of antagonistic muscle co-contraction on in vivo knee contact forces.

BACKGROUND: The onset and progression of osteoarthritis, but also the wear and loosening of the components of an artificial joint, are commonly associated with mechanical overloading of the structures. Knowledge of the mechanical forces acting at the joints, together with an understanding of the key factors that can alter them, are critical to develop effective treatments for restoring joint function. While static anatomy is usually the clinical focus, less is known about the impact of dynamic factors, such as individual muscle recruitment, on joint contact forces. METHODS: In this study, instrumented knee implants provided accurate in vivo tibio-femoral contact forces in a unique cohort of 9 patients, which were used as input for subject specific musculoskeletal models, to quantify the individual muscle forces during walking and stair negotiation. RESULTS: Even between patients with a very similar self-selected gait speed, the total tibio-femoral peak forces varied 1.7-fold, but had only weak correlation with static alignment (varus/valgus). In some patients, muscle co-contraction of quadriceps and gastrocnemii during walking added up to 1 bodyweight (~ 50%) to the peak tibio-femoral contact force during late stance. The greatest impact of co-contraction was observed in the late stance phase of stair ascent, with an increase of the peak tibio-femoral contact force by up to 1.7 bodyweight (66%). CONCLUSIONS: Treatment of diseased and failed joints should therefore not only be restricted to anatomical reconstruction of static limb axes alignment. The dynamic activation of muscles, as a key modifier of lower limb biomechanics, should also be taken into account and thus also represents a promising target for restoring function, patient mobility, and preventing future joint failure. TRIAL REGISTRATION: German Clinical Trials Register: ID: DRKS00000606 , date: 05.11.2010.

A comprehensive assessment of the musculoskeletal system: The CAMS-Knee data set.

Combined knowledge of the functional kinematics and kinetics of the human body is critical for understanding a wide range of biomechanical processes including musculoskeletal adaptation, injury mechanics, and orthopaedic treatment outcome, but also for validation of musculoskeletal models. Until now, however, no datasets that include internal loading conditions (kinetics), synchronized with advanced kinematic analyses in multiple subjects have been available. Our goal was to provide such datasets and thereby foster a new understanding of how in vivo knee joint movement and contact forces are interlinked - and thereby impact biomechanical interpretation of any new knee replacement design. In this collaborative study, we have created unique kinematic and kinetic datasets of the lower limb musculoskeletal system for worldwide dissemination by assessing a unique cohort of 6 subjects with instrumented knee implants (Charité - Universitätsmedizin Berlin) synchronized with a moving fluoroscope (ETH Zürich) and other measurement techniques (including whole body kinematics, ground reaction forces, video data, and electromyography data) for multiple complete cycles of 5 activities of daily living. Maximal tibio-femoral joint contact forces during walking (mean peak 2.74 BW), sit-to-stand (2.73 BW), stand-to-sit (2.57 BW), squats (2.64 BW), stair descent (3.38 BW), and ramp descent (3.39 BW) were observed. Internal rotation of the tibia ranged from 3° external to 9.3° internal. The greatest range of anterio-posterior translation was measured during stair descent (medial 9.3 ±â€¯1.0 mm, lateral 7.5 ±â€¯1.6 mm), and the lowest during stand-to-sit (medial 4.5 ±â€¯1.1 mm, lateral 3.7 ±â€¯1.4 mm). The complete and comprehensive datasets will soon be made available online for public use in biomechanical and orthopaedic research and development.

Medial and lateral foot loading and its effect on knee joint loading.

BACKGROUND: The medial knee contact force may be lowered by modified foot loading to prevent the progression of unilateral gonarthrosis but the real effects of such gait modifications are unknown. This study investigates how walking with a more medial or lateral rollover of the foot influences the in vivo measured knee contact forces. METHODS: Five subjects with telemeterized knee implants walked on a treadmill with pronounced lateral or medial foot loading. Acoustic feedback of peak foot pressure was used to facilitate the weight bearing shift. The resultant contact force, Fres, the medial contact force, Fmed, and the force distribution Fmed/Fres across the tibial plateau were computed from the measured joint contact loads. FINDINGS: During lateral foot loading, the two maxima of Fres during the stance phase, Peak 1 and Peak 2, increased by an average of 20% and 12%, respectively. The force distribution was changed by only -3%/+2%. As a result, Fmed increased by +16%/+17%. Medial foot loading, on the other hand, changed Fres only slightly, but decreased the distribution by -18%/-11%. This led to average reductions of Fmed by -18%/-18%. The reductions were realized by kinematic adaptations, such as increases of ankle eversion, step width and foot progression angle. INTERPRETATION: Medial foot loading consistently reduced the medial knee compartment, and may be a helpful gait modification for patients with pronounced medial gonarthrosis. The increase of Fmed during lateral foot loading was most likely caused by muscular co-contractions. Long-term training may lead to more efficient gait and reduce co-contractions.

Spinal loads during post-operative physiotherapeutic exercises.

After spinal surgery, physiotherapeutic exercises are performed to achieve a rapid return to normal life. One important aim of treatment is to regain muscle strength, but it is known that muscle forces increase the spinal loads to potentially hazardous levels. It has not yet been clarified which exercises cause high spinal forces and thus endanger the surgical outcome. The loads on vertebral body replacements were measured in 5 patients during eleven physiotherapeutic exercises, performed in the supine, prone, or lateral position or on all fours (kneeling on the hands and knees). Low resultant forces on the vertebral body replacement were measured for the following exercises: lifting one straight leg in the supine position, abduction of the leg in the lateral position, outstretching one leg in the all-fours position, and hollowing the back in the all-fours position. From the biomechanical point of view, these exercises can be performed shortly after surgery. Implant forces similar or even greater than those for walking were measured during: lifting both legs, lifting the pelvis in the supine position, outstretching one arm with or without simultaneously outstretching the contralateral leg in the all-fours position, and arching the back in the all-fours position. These exercises should not be performed shortly after spine surgery.

In vivo hip joint loading during post-operative physiotherapeutic exercises.

INTRODUCTION: After hip surgery, it is the orthopedist's decision to allow full weight bearing to prevent complications or to prescribe partial weight bearing for bone ingrowth or fracture consolidation. While most loading conditions in the hip joint during activities of daily living are known, it remains unclear how demanding physiotherapeutic exercises are. Recommendations for clinical rehabilitation have been established, but these guidelines vary and have not been scientifically confirmed. The aim of this study was to provide a basis for practical recommendations by determining the hip joint contact forces and moments that act during physiotherapeutic activities. METHODS: Joint contact loads were telemetrically measured in 6 patients using instrumented hip endoprostheses. The resultant hip contact force, the torque around the implant stem, and the bending moment in the neck were determined for 13 common physiotherapeutic exercises, classified as weight bearing, isometric, long lever arm, or dynamic exercises, and compared to the loads during walking. RESULTS: With peak values up to 441%BW, weight bearing exercises caused the highest forces among all exercises; in some patients they exceeded those during walking. During voluntary isometric contractions, the peak loads ranged widely and potentially reached high levels, depending on the intensity of the contraction. Long lever arms and dynamic exercises caused loads that were distributed around 50% of those during walking. CONCLUSION: Weight bearing exercises should be avoided or handled cautiously within the early post-operative period. The hip joint loads during isometric exercises depend strongly on the contraction intensity. Nonetheless, most physiotherapeutic exercises seem to be non-hazardous when considering the load magnitudes, even though the loads were much higher than expected. When deciding between partial and full weight bearing, physicians should consider the loads relative to those caused by activities of daily living.

In vivo hip joint loads during three methods of walking with forearm crutches.

BACKGROUND: Patients with osteoarthritis, joint implants or fractures use crutches in order to reduce lower limb loading. However, insufficient information exists on how much the loading is then in fact reduced. This situation was studied by using seven patients who had instrumented hip implants. METHODS: Part I: To investigate the effectiveness of forearm crutches, crutch and hip joint contact forces were measured in seven patients with instrumented hip prostheses. Additionally, the bending moments in the implant neck and torsion around its stem were determined. Reductions of peak loads during 3, 4, and 2-point gaits were compared with loads present when walking without crutches. Part II: This examines joint load reduction during a 4-point gait from one to 12 weeks post-operatively. FINDINGS: Part I: During a 3, 4, and 2-point gait, the joint force was 17, 12, and 13% lower than it was while walking without crutches. The corresponding reductions of the bending moment were 16, 11, and 12%, while the maximum torque decreased by 19, 21, and 10%. Part II: The reductions of contact forces in comparison with walking without crutches were highest during the first 4 weeks after surgery. One and 4 weeks post-operatively, the force maximum was 21 and 8% lower than it was after 3 months. When compared with the initial values of the 1st week, crutch forces decreased by 28% in the 4th week and by 38% in the 3rd month. INTERPRETATION: Average reductions of the joint load by more than 20% are achieved only during the first 4 post-operative weeks. Because fractures are in most cases relatively stable after 6 weeks, and bone ingrowth into implant interfaces is nearly finished after this time, a single crutch and a 2-point gait can be prescribed during the 5th and 6th post-operative week.

Terminally differentiated CD8⁺ T cells negatively affect bone regeneration in humans.

There is growing evidence that adaptive immunity contributes to endogenous regeneration processes: For example, endogenous bone fracture repair is modulated by T cells even in the absence of infection. Because delayed or incomplete fracture healing is associated with poor long-term outcomes and high socioeconomic costs, we investigated the relationship between an individual's immune reactivity and healing outcome. Our study revealed that delayed fracture healing significantly correlated with enhanced levels of terminally differentiated CD8(+) effector memory T (TEMRA) cells (CD3(+)CD8(+)CD11a(++)CD28(-)CD57(+) T cells) in peripheral blood. This difference was long lasting, reflecting rather the individual's immune profile in response to lifelong antigen exposure than a post-fracture reaction. Moreover, CD8(+) TEMRA cells were enriched in fracture hematoma; these cells were the major producers of interferon-γ/tumor necrosis factor-α, which inhibit osteogenic differentiation and survival of human mesenchymal stromal cells. Accordingly, depletion of CD8(+) T cells in a mouse osteotomy model resulted in enhanced endogenous fracture regeneration, whereas a transfer of CD8(+) T cells impaired the healing process. Our data demonstrate the high impact of the individual adaptive immune profile on endogenous bone regeneration. Quantification of CD8(+) TEMRA cells represents a potential marker for the prognosis of the healing outcome and opens new opportunities for early and targeted intervention strategies.

The direct lateral approach: impact on gait patterns, foot progression angle and pain in comparison with a minimally invasive anterolateral approach.

INTRODUCTION: Minimally invasive total hip arthroplasty has been successfully introduced in the past decade. Nevertheless, standard approaches such as the direct lateral approach are still commonly used in orthopaedic surgery due to easy handling, good intra-operative overview and low complication rates. However, a frequent occurrence of fatty atrophy within the anterior third of the gluteus medius muscle has been demonstrated when using the modified direct-lateral approach (mDL), which may be associated with a reduction in function, limitation of internal leg rotation, gait disorders and pain. The question addressed in this study is whether mDL-approach leads to unfavourable changes in foot progression angle (FPA), gait and to more postoperative pain compared with a minimally invasive anterolateral approach (ALMI). METHODS: Thirty patients with primary osteoarthritis of the hip were recruited for this study. All subjects received an uncemented THA (Alloclassic-Zweymüller stem, Allofit Cup, FA Zimmer), 15 through an ALMI-approach and 15 via the mDL-approach. Gait analyses were performed both preoperatively and 3 months after surgery to measure FPA, step length, stance duration, cadence and walking speed. Additionally, the Harris-Hip Score, pain according to the visual analogue scale and the Trendelenburg sign were evaluated. RESULTS: No influence of the surgical approach could be observed on the gait patterns or FPA. Furthermore, neither increased external rotation of the limb nor restriction of internal rotation during walking could be established. Pain and Harris-Hip Score did not diVer significantly between the two groups. CONCLUSION: In comparison with an ALMI approach, the mDL approach did not lead to a change in FPA postoperatively. No detrimental effect could be found on the gait pattern or pain after surgery. Based on these measurements, the minimally invasive anterolateral approach did not appear to provide functional benefits in outcome over the mDL approach. Consequently, both surgical approaches seem to be equally applicable approaches with good to very good functional results.