[The human knee-joint as a biomechanical problem (author's transl)]

The impact of transfemoral socket adduction on pelvic and trunk stabilization during level walking - A biomechanical study

BACKGROUND

It is common practice to align transfemoral prosthetic sockets in adduction, due to the physiologic, adducted femoral alignment in unimpaired legs. An adducted femoral and socket alignment helps tightening hip abductors to stabilize the pelvis and reduce pelvic and trunk related compensatory movements.

RESEARCH QUESTION

How do different socket adduction conditions (SAC) of transfemoral sockets affect pelvic and trunk stabilization during level ground walking in the frontal plane?

METHODS

Seven persons with transfemoral amputation with medium residual limb length participated in this study. The prosthetic alignment in the sagittal plane was performed according to established recommendations. SAC varied (0°, 3°, 6°, 9°). Kinematic and kinetic parameters were recorded in a gait laboratory with a 12-camera optoelectronic system and two piezoelectric force plates embedded in a 12-m walkway. The measurements were performed during level ground walking with self-selected comfortable gait speed.

RESULTS

In the frontal plane, nearly all investigated kinematic and kinetic parameters showed a strong correlation with the SAC. The pelvis was raised on the contralateral side throughout the gait cycle with increasing SAC. During the prosthetic side stance phase, the mean shoulder obliquity and mean lateral trunk lean to the prosthetic side tended to be reduced with increased SAC. Prosthetic side hip abduction moment decreased with increasing SAC.

SIGNIFICANCE

The results confirm that transfemoral SAC contributes to pelvic stabilization and reduced compensatory movements of the pelvis and trunk. Transfemoral SAC of 6 ± 1° for bench alignment seems adequate for amputees with medium residual limb length. However, the optimum value for the individual patient may differ slightly.

Biomechanical analysis of stair ascent in persons with Chopart amputation

BACKGROUND

Compared to walking on level ground, ascending stairs requires a large range of motion not only of the hip and knee joint, but also of the ankle joint. The prosthesis often worn by persons with partial foot amputation largely prevents the ankle motion needed during stair ascent.

OBJECTIVES

Aim of this study was to assess subjects with a Chopart amputation utilizing a clamshell device during stair ascent to identify potential biomechanical deficits.

STUDY DESIGN

Cross-sectional study with reference group.

METHODS

Six subjects with unilateral Chopart amputation and 17 unimpaired subjects underwent three-dimensional motion analysis while ascending stairs in a step-over-step manner.

RESULTS

During weight acceptance, the involved side showed increased external hip-flexing and reduced knee-flexing moments and the sound side a higher ankle power than in the control group. The sound side showed higher external knee-flexing, dorsi-flexing, and hip-adducting moments than the controls during weight acceptance.

CONCLUSION

The mechanism observed on the involved side differs from that in controls, but is comparable to the mechanisms used by subjects with transtibial amputation reported in the literature. However, compensatory movements on the sound side take place at the ankle and knee joint, differing from subjects with more proximal amputations.

CLINICAL RELEVANCE

This study underpins the importance of adequate foot leverage and ankle function in cases of partial foot amputation, particularly in transfer situations such as stair ascent. If ankle range of motion is adequate, prosthetic/orthotic devices combining shank leverage with a hinged spring mechanism at the ankle may be promising.

Designs and performance of three new microprocessor-controlled knee joints

A crossover design study with a small group of subjects was used to evaluate the performance of three microprocessor-controlled exoprosthetic knee joints (MPKs): C-Leg 4, Plié 3 and Rheo Knee 3. Given that the mechanical designs and control algorithms of the joints determine the user outcome, the influence of these inherent differences on the functional characteristics was investigated in this study. The knee joints were evaluated during level-ground walking at different velocities in a motion analysis laboratory. Additionally, technical analyses using patents, technical documentations and X-ray computed tomography (CT) for each knee joint were performed. The technical analyses showed that only C-Leg 4 and Rheo Knee 3 allow microprocessor-controlled adaptation of the joint resistances for different gait velocities. Furthermore, Plié 3 is not able to provide stance extension damping. The biomechanical results showed that only if a knee joint adapts flexion and extension resistances by the microprocessor all known advantages of MPKs can become apparent. But not all users may benefit from the examined functions: e.g. a good accommodation to fast walking speeds or comfortable stance phase flexion. Hence, a detailed comparison of user demands and performance of the designated knee joint is mandatory to ensure a maximum in user outcome.

Knee-ankle-foot orthosis with powered knee for support in the elderly

A prototype of a powered knee orthotic device was developed to determine whether fractional external torque and power support to the knee relieves the biomechanical loads and reduces the muscular demand for a subject performing sit-to-stand movements. With this demonstrator, consisting of the subsystems actuation, kinematics, sensors, and control, all relevant sensor data can be acquired and full control is maintained over actuator parameters. A series-elastic actuator based on a direct current motor provides up to 30 Nm torque to the knee via a hinge joint with an additional sliding degree of freedom. For reasons of feasibility under everyday conditions, user intention is monitored by employing a noninvasive, nonsticking muscle activity sensor to replace electromyographic sensors, which require skin preparation. Furthermore, foot plates with force sensors have been developed and included to derive ground reaction forces. The actual knee torque needed to provide the desired support is based on an inverse dynamics model using ground reaction forces signals and leg kinematics. A control algorithm including disturbance feed forward has been implemented. A demonstration experiment with two subjects showed that 23 % of moment support in fact leads to a similar reduction in activation of the main knee extensor muscle.

Stair ascent with an innovative microprocessor-controlled exoprosthetic knee joint

Climbing stairs can pose a major challenge for above-knee amputees as a result of compromised motor performance and limitations to prosthetic design. A new, innovative microprocessor-controlled prosthetic knee joint, the Genium, incorporates a function that allows an above-knee amputee to climb stairs step over step. To execute this function, a number of different sensors and complex switching algorithms were integrated into the prosthetic knee joint. The function is intuitive for the user. A biomechanical study was conducted to assess objective gait measurements and calculate joint kinematics and kinetics as subjects ascended stairs. Results demonstrated that climbing stairs step over step is more biomechanically efficient for an amputee using the Genium prosthetic knee than the previously possible conventional method where the extended prosthesis is trailed as the amputee executes one or two steps at a time. There is a natural amount of stress on the residual musculoskeletal system, and it has been shown that the healthy contralateral side supports the movements of the amputated side. The mechanical power that the healthy contralateral knee joint needs to generate during the extension phase is also reduced. Similarly, there is near normal loading of the hip joint on the amputated side.

Collateral ligament length change patterns after joint line elevation may not explain midflexion instability following TKA

Midflexion instability (MFI) after TKA is a phenomenon often described as varus-valgus instability between 30° and 45° knee flexion. The exact mechanisms causing MFI remain unclear, but elevation of the joint line (JLE) may be one possible cause. In an in silico approach using 4 subject specific musculoskeletal models, the length change patterns of the collateral ligaments during knee flexion (relative to the extended knee) were calculated for the anatomically reconstructed joints as well as for JLEs of 5 and 10mm. Analysis of the distance between the ligaments' attachment sites (DA) in midflexion revealed a relative decrease in DA magnitude after JLE for both collateral ligaments in comparison to the anatomically reconstructed knee. This finding suggests that JLE could contribute to MFI. However, the anterior ligament regions also experienced a DA increase (MCL) or only a slight DA decrease (LCL) for each JLE simulated. From this perspective, the anterior ligament portions are unlikely to slacken in midflexion and JLE is unlikely to contribute greatly to MFI. In conclusion, our findings did not support the idea that JLE is a major contributor to midflexion instability for this particular ultra-congruent implant design.

Kinematics and kinetics with an adaptive ankle foot system during stair ambulation of transtibial amputees

Conventional prosthetic feet cannot adapt to specific conditions such as walking on stairs or ramps. Amputees are therefore forced to compensate their prosthetic deficits by modifying the kinematics and kinetics of their lower limbs. The Proprio-Foot (Ossur) intends to reduce these compensation mechanisms by automatically increasing dorsiflexion during stair ambulation thanks to an adaptive microprocessor-controlled ankle. The present investigation proposes to analyze the biomechanical effects of the dorsiflexion adaptation in transtibial (TT) amputees during stair ambulation. Sixteen TT amputees and sixteen healthy controls underwent conventional 3D gait analysis. Kinematics and kinetics of the lower limbs were compared during stair ascent and descent performed by patients with the prosthetic foot set to a neutral ankle angle and with an adapted dorsiflexion ankle angle of 4 degrees . Norm distance as well as minimum and maximal values of sagittal kinematics and kinetics were calculated for comparisons between patients and control subjects. For both stair ascent and descent, an improvement of the knee kinematics and kinetics could particularly be noticed on the involved side with an increase of the knee flexion and an increase of the knee moment during stance. Therefore, despite its additional weight compared to a conventional prosthetic ankle, the Proprio-Foot should be beneficial to active TT amputees whose knee musculature strength does not constitute a handicap.

Tibiofemoral joint contact forces and knee kinematics during squatting

Axial tibiofemoral joint contact forces were non-invasively determined for two high range of motion (high flexion) squatting activities. An electromagnetic motion tracking system and a non-conductive force platform were used to collect kinematic and kinetic data. An innovative scaling method was used to model subject-specific muscle group moment arms. One subject attained a peak axial tibiofemoral joint contact force of 49.7 N/kg during squatting at 149.9 degrees knee flexion. Average joint angles and average axial joint contact forces were calculated for each of the activities in order to facilitate a comparison with stair climbing data. Compared to stair climbing, the maximum average joint contact forces during the squatting activities occurred at significantly higher flexion angles (p<0.05.) The relative simplicity of the method makes it useful for application to large subject groups from diverse regions. The results of this study can be applied to the diagnosis and treatment of pathologies, and to the development of high range of motion (ROM) knee replacements.

Biomechanical analysis of stair ambulation in lower limb amputees

Lower extremity amputees have to cope with many activities in everyday life that are substantially more difficult than walking on level ground, and such demands require a high degree of functionality from their prosthetic components. The present study is a biomechanical evaluation (kinematics, kinetics and EMG) of stair ascent and descent in a group of eight transtibial amputees (mean (standard deviation): age 51(14) years, height 176(7)cm, mass 88(19)kg); a group of 12 transfemoral amputees (age 37(8) years, height 182(7)cm, mass 83(7)kg) fitted with the electronically controlled C-LEG knee joint system; and a group of 12 able bodied persons (age 30(10) years, height 174(12)cm, mass 69(12)kg). During stair descent the transfemoral amputees presented a strong reduction of the prosthetic ankle moments (0.11Nm/kg) compared to transtibial amputees (0.93Nm/kg) and control subjects (1.26Nm/kg). Loading of the prosthetic knee joint in the transfemoral amputees more closely resembles the loading seen in the control population when compared to transtibial amputees (mean maximum flexion moment: controls 1.31Nm/kg, transfemoral amputees 1.00Nm/kg, transtibial amputees 0.50Nm/kg). Overload of the contralateral limb is more prominent in the transfemoral amputee than in the transtibial amputee. During stair ascent, the transtibial amputee presents a significant reduction of the knee flexion moment compared to the controls (mean maximum flexion moment: transtibial amputees 0.28Nm/kg, controls 1.31Nm/kg). These differences correlate with a change in the muscle activity of the knee extensor and hamstring muscles. The results also show adaptations in motor strategies during stair negotiation, for those with the partial loss of a lower limb due to the functional limits of current prosthetic components. The present data may contribute to a further enhancement of the efficiency of prosthetic feet and knee joints.

Changes of meniscal interhorn distances: an in vivo magnetic resonance imaging study

The aim of this study was to evaluate the changes of the internal (IID) and external meniscal interhorn distance (EID) of the medial and the lateral meniscus under loading. Sagittal magnetic resonance images of 15 knees were studied. The medial and lateral meniscus were examined with the knee at 0 degrees and 30 degrees of flexion, under no load, with load equal to 50% of body weight and with load equal to 100% of body weight. Under no load, the mean IID was 19.9 mm for the medial meniscus and 12.3 mm for the lateral meniscus and the mean EID was 44.6 mm for the medial meniscus and 34.4 mm for the lateral meniscus. Under load equal to 50% and 100% of patient's body weight, there was a significant increase in both distances (p<0.05). Under constant loading, flexion of the knee from 0 degrees to 30 degrees , decreased the EID of both menisci. In conclusion, loading increases both IID and EID. Knee position affects only the EID. The quality of magnetic resonance images may affect the reliability of such measurements.

Effects of sagittal plane prosthetic alignment on standing trans-tibial amputee knee loads

The influence of sagittal plane prosthetic alignment changes on loads applied to the ispilateral knee was investigated using 5 transtibial amputee subjects. The goal was to determine which prosthetic alignment results in the most energy efficient standing and also minimises stresses on knee structures during standing. The electromyogram, the external mechanical loading of the prosthetic leg and the amputees' posture were recorded for a wide range of prosthetic alignments. The EMG of the vastus lateralis and biceps femoris muscles was measured bilaterally; the EMG of the gastrocnemius muscle was measured only on the contralateral side. The distance between the anatomical knee centre and each individual's load line, as determined by the Otto Bock "L.A.S.A.R. Posture" alignment system, was used as a measure of the mechanical load applied to the knee joint. Prosthetic alignment has almost no influence on muscle activity of the contralateral lower limb during static standing. On the other hand, prosthetic alignment has a significant influence on the load applied to the amputee's ipsilateral knee joint. The external knee moments applied to the knee ligaments and knee muscles on the amputated side change systematically in response to different plantar flexion or dorsiflexion angles of the prosthetic ankle-foot. During standing the extensor muscles stabilise the limb by contracting if the load line is located less than 15 mm anterior to the anatomical knee centre. The biceps femoris muscle appears to have little or no protective function against hyperextension during standing even if large external knee extension moments are caused by excessive plantar flexion. Such extreme alignments significantly increase the stresses on knee ligaments and the posterior knee capsule. When prosthetic sagittal plane alignment is altered, the trans-tibial amputee compensates by balancing the upper part of the body over the centre of pressure of the prosthetic foot. Biomechanically optimal alignment of the trans-tibial prosthesis occurs when the individual load line is approximately 15 mm anterior to the anatomical knee centre, permitting a comfortable, energy efficient standing and minimising the mechanical loading on the knee structures.

A new biomechanical method for determination of static prosthetic alignment

A new static alignment method for trans-tibial prostheses is suggested using the individual load line as a reference. Standing posture and static alignment of 18 experienced trans-tibial prosthetic users with good walking ability were determined and compared with 20 healthy persons. The individual load line was defined by means of the new Otto Bock alignment system "L.A.S.A.R. Posture". The sagittal standing posture of trans-tibial amputees and non-amputees differs. Normally only a prosthesis worn by the trans-tibial amputee and dynamically aligned over an extended period of time satisfies biomechanical rules of alignment. In contrast, prostheses aligned during one session in the traditional subjective manner seem to lack any recognizable biomechanical systematics. Initial results suggest the knee centre should be 10 to 30mm behind the load line, depending on patient's weight. This knee position is independent on the type of prosthetic foot.

An integrated procedure to assess knee-joint kinematics and kinetics during gait using an optoelectric system and standardized X-rays

This paper describes a 3-D gait analysis system, which combines optoelectric motion tracking and a standardized X-ray procedure, to calculate the net knee-joint forces and moments of a normal subject group during walking. The optoelectric system collects kinematic data from infra-red LED markers placed at selected skin surface locations and projecting probes attached to the lower limb. A standardized X-ray procedure is used to move surface markers into their designated bony landmarks based on individual bone structure, which reduces the error caused by uncertainty of skin-surface marker locations. Based on moved-in marker information, different joint coordinate systems are proposed for kinematic and kinetic analysis of the knee joint. Normalized data of knee angles, net reaction forces and net moments from 35 young, normal subjects are presented.