Ceramic acetabular cups for hip endoprostheses. 7: How do position of the center of rotation and the CCD angle of the shaft modify range of motion and impingement?]

The range of motion (ROM) of total hip prostheses is influenced by a number of parameters. An insufficient ROM may cause impingement, which may result in subluxation, dislocation or material failure of the prostheses. In a three-dimensional CAD simulation, the position of the centre of rotation and the CCD angle of the stem were investigated. Displacement of the centre of rotation of the femoral head may be due to wear (PE cups) or to the design of the prosthesis (ceramic cups). Stems of widely differing design have been developed and implanted. The results of the present study demonstrate that the ROM is clearly reduced by increasing penetration of the femoral head. At an inclination angle of 45 degrees, a depth of penetration of 2 mm restricts flexion by about 15 degrees, and a depth of penetration of 3 mm by about 30 degrees. At smaller angles of inclination the ROM is reduced and flexion and abduction are associated with an increased risk of impingement. With steeper acetabular cup inclinations, the risk of impingement decreases, but dislocation, the risk of rim fractures (ceramic cups), and wear and penetration rates (PE cups) increase. The CCD angle of the stem should be oriented to the anatomical situation. At high CCD angles (> 135 degrees), flexion is clearly limited, in particular when there is penetration of the femoral head. For modern total hip arthroplasty, prosthetic systems characterised by precise positioning of components, minimum wear, slightly recessed inserts, and appropriate CCD angles should be used.     

A kinematic model for calculating cup alignment error during total hip arthroplasty

Reduced range of motion, prosthetic impingement, and joint dislocation can all result from misalignment of the acetabular component (i.e. cup alignment) in patients undergoing total hip arthroplasty. Most methods for acetabular component alignment are designed to provide 45-50 degrees abduction and 15-25 degrees of operative anteversion (also known as flexion) with respect to the anterior pelvic plane coordinate system. Yet in most cases, this coordinate system is not assigned properly, due to differences in patient anatomy and improper positioning in the operating room. This misalignment can result in an error in the cup alignment, which can cause the above-mentioned consequences. This work presents a complete mathematical formulation for the analysis of the inaccuracies related to the anterior pelvic plane axes (APPA) definition and their effect on final cup orientation. We do this by introducing a method taken from Kinematics of Mechanisms, and by representing the errors in the APPA as three concurrent axes of rotation, followed by the version and abduction rotations which are defined relative to the previous rotations. We also present a sensitivity analysis of the results by introducing differential changes between sequential coordinate frames, which simulates the errors in the APPA and their effect on cup orientation. Finally, we demonstrate a computational method which provides corrected version and abduction angles to achieve the desired cup orientation, given that the actual measurement errors are known.     

Method for the evaluation of factors influencing the dislocation stability of total hip endoprotheses]

Dislocation of the artificial joint is a serious complication of total hip replacement. Various factors with an influence on dislocation stability were determined clinically. Our goal was to develop a method for evaluating experimentally the parameters implant design, position and the load situation for their influence on joint stability. With the newly developed testing device the range of motion to impingement and to dislocation can be determined at different implant positions. In addition, the rotational moments on subluxation, i.e. the "levering out" of the femoral head, can be determined. By way of example several hip implants were examined during movements associated with dislocation, e.g. (internal-)rotation in 90 degrees flexion and 0 degrees adduction as well as with (external-)rotation in combination with 10 degrees extension and 15 degrees adduction. Irrespective of implant design and position, the following movement phases can be differentiated: undisturbed motion, impingement, subluxation and, finally, complete dislocation of the head. On the basis of the range of motion of the specific phases, the moments occurring and the direction of dislocation, different implant systems can be compared. In this study the influence of the head diameter on the dislocation stability of the hip endoprosthesis is shown. With the aid of the model presented herein, a data set showing the most favourable and/or most dislocation stable implant position can be acquired for different combinations of the implant components. Additionally, useful information for implant design can be deduced and applied to new developments and/or modifications of existing implant components.     

Ceramic cups for hip endoprostheses. 6: Cup design, inclination and antetorsion angle modify range of motion and impingement]

The present investigation focuses on total hip replacement using ceramic acetabular components. The relationship between the position of the cup and the range of motion (ROM) was investigated. A limited range of motion may cause impingement, which is defined as contact between the femoral neck and the rim of the acetabular cup. Impingement may result in wear, chipping, fracture or dislocation of the femoral head. Joint movements were simulated in a three-dimensional CAD program. The results obtained underscore the importance of correct positioning and design of the cup for achieving a ROM as close to the physiological situation as possible. With ceramic cups, the inclination angle should not be more than 45 degrees, and the antetorsion angle between 10 and 15 degrees. If the cup is too vertical, the risk of dislocation and fracture of the ceramic increases. If, on the other hand, the angle of inclination is too small, flexion and abduction will be greatly limited. The study shows that acetabular components with non-recessed ceramic inserts should not be used. Slight recession of the insert helps to avoid impingement. The ROM is reduced and the risk of impingement appreciably increased when mushroom-shaped femoral heads (XL heads) or ceramic inserts protected by a polyethylene ring are used.     

On the estimation of joint kinematics during gait.

In gait analysis, the concepts of Euler and helical (screw) angles are used to define the three-dimensional relative joint angular motion of lower extremities. Reliable estimation of joint angular motion depends on the accurate definition and construction of embedded axes within each body segment. In this paper, using sensitivity analysis, we quantify the effects of uncertainties in the definition and construction of embedded axes on the estimation of joint angular motion during gait. Using representative hip and knee motion data from normal subjects and cerebral palsy patients, the flexion-extension axis is analytically perturbed +/- 15 degrees in 5 degrees steps from a reference position, and the joint angles are recomputed for both Euler and helical angle definitions. For the Euler model, hip and knee flexion angles are relatively unaffected while the ab/adduction and rotation angles are significantly affected throughout the gait cycle. An error of 15 degrees in the definition of flexion-extension axis gives rise to maximum errors of 8 and 12 degrees for the ab/adduction angle, and 10-15 degrees for the rotation angles at the hip and knee, respectively. Furthermore, the magnitude of errors in ab/adduction and rotation angles are a function of the flexion angle. The errors for the ab/adduction angles increase with increasing flexion angle and for the rotation angle, decrease with increasing flexion angle. In cerebral palsy patients with flexed knee pattern of gait, this will result in distorted estimation of ab/adduction and rotation. For the helical model, similar results are obtained for the helical angle and associated direction cosines.(ABSTRACT TRUNCATED AT 250 WORDS)     

A mathematical formula to calculate the theoretical range of motion for total hip replacement

The reduced range of motion (ROM) resulting from total hip replacement (THR) leads to frequent prosthetic impingement, which may restrict activities of daily living and cause subluxation and dislocation. Therefore, to know the ROM of THR is very important in clinical situations and in the design of prostheses. THR involves a pure ball and socket joint. We created a mathematical formula to calculate the theoretical ROM of THR limited by the prosthetic impingement. The ROM of THR is governed by the following five factors, (1) The prosthetic ROM (oscillation angle: obtained from company data), (2) cup abduction (3) cup anterior opening, (4) the angle of the femoral neck component from the horizontal plane, and (5) the femoral neck anteversion. The last 4 factors are able to be obtained from anterior-posterior, axial X-rays and CT of the patient's THR. The objective was to create mathematical formulas that could accurately and quickly calculate the ROM of THR. By entering the five values into a computer programmed with the formulas, one could obtain the ROM for the THR. This reveals the effect on ROM of the oscillation angle and the interaction of ROM with cup abduction, anterior opening and neck anteversion. Furthermore this readily would enable a clinical evaluation of the possibility of postoperative dislocation and help in postoperative rehabilitation. The calculated numerical values of ROM by these mathematical formulas were successfully compared with the ROMs obtained from 3-dimensional computer graphics (3D-CG).     

Relationship between hip and knee strength and knee valgus during a single leg squat

The purpose of this study was to determine the relationship between hip and knee strength, and valgus knee motion during a single leg squat. Thirty healthy adults (15 men, 15 women) stood on their preferred foot, squatted to approximately 60 deg of knee flexion, and returned to the standing position. Frontal plane knee motion was evaluated using 3-D motion analysis. During Session 2, isokinetic (60 deg/sec) concentric and eccentric hip (abduction/adduction, flexion/extension, and internal/external rotation) and knee (flexion/extension) strength was evaluated. The results demonstrated that hip abduction (r2=0.13), knee flexion (r2=0.18), and knee extension (r2=0.14) peak torque were significant predictors of frontal plane knee motion. Significant negative correlations showed that individuals with greater hip abduction (r=-0.37), knee flexion (r=-0.43), and knee extension (r=-0.37) peak torque exhibited less motion toward the valgus direction. Men exhibited significantly greater absolute peak torque for all motions, excluding eccentric internal rotation. When normalized to body mass, men demonstrated significantly greater strength than women for concentric hip adduction and flexion, knee flexion and extension, and eccentric hip extension. The major findings demonstrate a significant role of hip muscle strength in the control of frontal plane knee motion.     

The safe-zones for combined cup and neck anteversions that fulfill the essential range of motion and their optimum combination in total hip replacements

Reduction of the range of motion (ROM) until prosthetic impingement of a total hip replacement may lead to frequent impingement, subluxation and dislocation especially for patients with good hip movement. The ROM until prosthetic impingement can be calculated using the technical ROM (theta) and the cup and neck positions by a previously created mathematical formula. A larger (theta) with proper cup and neck positions results in a larger ROM. However there was only one paper written in English, which revealed the optimum theoretical combination of cup and neck anteversions. ROM of more than 110 degrees flexion, 30 degrees internal-rotation at 90 degrees flexion, 30 degrees extension and 40 degrees external-rotation were defined as the criteria for essential ROM for ADL. The safe-zones for combined cup anteversion (betaanat) and neck anteversion (b) were defined as the areas that fulfill all the criteria of ROM without prosthetic impingement. The safe-zones were created for 35 degrees , 45 degrees and 55 degrees cup abductions (alpha) and for 120 degrees and 135 degrees (theta). The safe-zones for combined (betaanat) and (b) were much larger for a 135 degrees (theta) than a 120 degrees (theta). Their safe-zones showed that (b) should be reduced if (betaanat) is increased and choosing a lower (alpha) requires that the sum of (betaanat) and (b) should be higher and vice versa. A (theta) of more than 135 degrees is recommended as it further increases the size of the safe-zone and provides a larger ROM, and the optimum values of combined cup and neck anteversions can be estimated by the formula: (alpha) + (betaanat) + 0.77(b) = 84.3.     

The influence of the oscillation angle and the neck anteversion of the prosthesis on the cup safe-zone that fulfills the criteria for range of motion in total hip replacements. The required oscillation angle for an acceptable cup safe-zone

A normal hip joint has more than 120 degrees flexion. The reduced range of motion (ROM) of total hip arthroplast leads to frequent prosthetic impingement, subluxation and dislocation. Prosthetic impingement may be more serious for metal-on-metal and ceramic-on-ceramic total hip prosthesis (THP). A larger oscillation angle of THP (OsA) and proper cup and neck positions make a larger theoretical ROM of a patient's artificial hip joint. But what OsA is required and what range of cup positions is kinetically accepted are not clearly understood. A ROM of more than 120 degrees flexion, 45 degrees internal-rotation at 90 degrees flexion, 30 degrees extension and 40 degrees external-rotation was defined as severe criteria for an acceptable ROM. Theoretical cup safe-zones were created that fulfill the severe criteria of ROM for (OsA=110 degrees , 120 degrees , 135 degrees ) by the mathematical formulas. The size of the cup safe-zone mainly depends on the size of the OsA. There is no cup safe-zone for 110 degrees OsA, an extremely small safe-zone for 120 degrees OsA and an acceptable safe-zone for 135 degrees OsA. Each THP has its own OsA, because OsA is the function of head and neck diameter and cup design. More than 135 degrees OsA enlarges the safe-zone of the prosthetic position, so it extends the acceptable range of error that surgeons cannot avoid completely. However, few THPs with more than 135 degrees OsA are currently clinically available. Both surgeons and manufacturers must realize that OsA is as essential as cup and neck orientations for ROM.     

Kinematics,kinetics, and finite element analysis of commonplace maneuvers at risk for total hip dislocation

Dislocation remains a disturbingly frequent complication of total hip arthroplasty (THA). Over the past several years, increasingly rigorous biomechanical approaches have been developed for studying dislocation, both experimentally and computationally. Realism of the input motion challenge data has lagged behind most other aspects of this body of work, and anterior dislocation maneuvers remain unstudied. To enhance realism of biomechanical studies of dislocation, motion data are here reported for ten THA-aged subjects, each repeatedly performing seven maneuvers known to be dislocation-prone. An optoelectronic motion tracking system and a recessed force plate captured the kinematics and ground reaction forces of these maneuvers. Using an established inverse dynamics model to estimate hip joint loading, 354 motion trials were evaluated using an existing finite element model of THA dislocation. Worst-case-scenario THA constructs were simulated (22 mm femoral head, acetabular cup orientations at the limit of the accepted safe zone), in order to deliberately induce impingement and dislocation. The results showed a high incidence of computationally predicted dislocation for all movements studied, but also that risk was very maneuver-dependent, with patients being six times more likely to dislocate from a low-sit-to-stand maneuver than from stooping. These new motion data hopefully will help facilitate systematic efforts to reduce the incidence of dislocation.     

A Novel Approach for Dynamic Testing of Total Hip Dislocation under Physiological Conditions

Constant high rates of dislocation-related complications of total hip replacements (THRs) show that contributing factors like implant position and design, soft tissue condition and dynamics of physiological motions have not yet been fully understood. As in vivo measurements of excessive motions are not possible due to ethical objections, a comprehensive approach is proposed which is capable of testing THR stability under dynamic, reproducible and physiological conditions. The approach is based on a hardware-in-the-loop (HiL) simulation where a robotic physical setup interacts with a computational musculoskeletal model based on inverse dynamics. A major objective of this work was the validation of the HiL test system against in vivo data derived from patients with instrumented THRs. Moreover, the impact of certain test conditions, such as joint lubrication, implant position, load level in terms of body mass and removal of muscle structures, was evaluated within several HiL simulations. The outcomes for a normal sitting down and standing up maneuver revealed good agreement in trend and magnitude compared with in vivo measured hip joint forces. For a deep maneuver with femoral adduction, lubrication was shown to cause less friction torques than under dry conditions. Similarly, it could be demonstrated that less cup anteversion and inclination lead to earlier impingement in flexion motion including pelvic tilt for selected combinations of cup and stem positions. Reducing body mass did not influence impingement-free range of motion and dislocation behavior; however, higher resisting torques were observed under higher loads. Muscle removal emulating a posterior surgical approach indicated alterations in THR loading and the instability process in contrast to a reference case with intact musculature. Based on the presented data, it can be concluded that the HiL test system is able to reproduce comparable joint dynamics as present in THR patients.     

A novel acetabular alignment guide for THR using selective anatomic landmarks on the pelvis

This paper presents a novel approach for acetabular alignment during the implant of a prosthetic hip joint in a natural pelvis. The alignment instrument uses selective anatomic bony landmarks on the pelvis, which are accessible in surgery, to guide the placement of the acetabular component in the appropriate orientation. A closed form solution, involving both a forward and reverse analysis, is presented to relate the parameters of the device with the abduction and anteversion angles. Using mathematical models, this device should allow the surgeon to place the acetabular component with an orientation between 10.9 degrees and 19.1 degrees anteversion and 35.7 degrees and 44.3 degrees abduction with 95% confidence in a male/left specimen for the commonly accepted target of 15 degrees anteversion and 40 degrees abduction. This device is currently being used successfully by one of the authors in THR surgery.     

Importance of maintaining the basic stress pathway above the acetabular dome during acetabular reconstruction

The basic stress pathway above the acetabular dome is important for the maintenance of implant stability in press-fit acetabular reconstruction of total hip arthroplasty. However, information on the basic stress pathway and its impact factors remains unclear. The objective of this study was to investigate the effects of the orientations and positions of the acetabular component on the basic stress pathway. The basic stress pathway above the acetabular dome was defined as two parts: 3D basic trabecular bone stress distribution and quantified basic cortical bone stress level, using two subject-specific finite element normal hip models. The effects were then analysed by generating 32 reconstructed acetabular cases with different cup abduction and anteversion angles within a range of 35–50° and 10–25°, respectively, and 12 cases with different hip centre heights within a range of 0–15 mm above the acetabular dome. The 3D trabecular stress distribution decreased remarkably in all cases, while the 80% of the basic cortical bone stress level was maintained in cases when the acetabular component was positioned at 10° or 15° anteversion and 40° or 45° abduction angles. The basic stress pathway above the acetabular dome was disturbed when the superior displacement of the hip centre exceeded 5 mm above the anatomical hip centre. Positioning the acetabular component correctly contributes to maintain the stress balance between the acetabular cup and the bone during acetabular reconstruction, thus helping restore the normal hip biomechanics and preserve the stability of the implants.     

Test–retest reliability of cardinal plane isokinetic hip torque and EMG

The objective of the present study was to establish test–retest reliability of isokinetic hip torque and prime mover electromyogram (EMG) through the three cardinal planes of motion. Thirteen healthy young adults participated in two experimental sessions, separated by approximately one week. During each session, isokinetic hip torque was evaluated on the Biodex Isokinetic Dynamometer at a velocity of 60 deg/s. Subjects performed three maximal-effort concentric and eccentric contractions, separately, for right and left hip abduction/adduction, flexion/extension, and internal/external rotation. Surface EMGs were sampled from the gluteus maximus, gluteus medius, adductor, medial and lateral hamstring, and rectus femoris muscles during all contractions. Intraclass correlation coefficients (ICC – 2,1) and standard errors of measurement (SEM) were calculated for peak torque for each movement direction and contraction mode, while ICCs were only computed for the EMG data. Motions that demonstrated high torque reliability included concentric hip abduction (right and left), flexion (right and left), extension (right) and internal rotation (right and left), and eccentric hip abduction (left), adduction (left), flexion (right), and extension (right and left) (ICC range = 0.81–0.91). Motions with moderate torque reliability included concentric hip adduction (right), extension (left), internal rotation (left), and external rotation (right), and eccentric hip abduction and adduction (right), flexion (left), internal rotation (right and left), and external rotation (right and left) (ICC range = 0.49–0.79). The majority of the EMG sampled muscles (n = 12 and n = 11 for concentric and eccentric contractions, respectively) demonstrated high reliability (ICC = 0.81–0.95). Instances of low, or unacceptable, EMG reliability values occurred for the medial hamstring muscle of the left leg (both contraction modes) and the adductor muscle of the right leg during eccentric internal rotation. The major finding revealed high and moderate levels of between-day reliability of isokinetic hip peak torque and prime mover EMG. It is recommended that the day-to-day variability estimates concomitant with acceptable levels of reliability be considered when attempting to objectify intervention effects on hip muscle performance.     

Dual-task and anticipation impact lower limb biomechanics during a single-leg cut with body borne load

This study quantified how a dual cognitive task impacts lower limb biomechanics during anticipated and unanticipated single-leg cuts with body borne load. Twenty-four males performed anticipated and unanticipated cuts with and without a dual cognitive task with three load conditions: no load (∼6 kg), medium load (15% of BW), and heavy load (30% of BW). Lower limb biomechanics were submitted to a repeated measures linear mixed model to test the main and interaction effects of load, anticipation, and dual task. With body borne load, participants increased peak stance (PS) hip flexion (p = .004) and hip internal rotation (p = .001) angle, and PS hip flexion (p = .001) and internal rotation (p = .018), and knee flexion (p = .016) and abduction (p = .001) moments. With the dual task, participants decreased PS knee flexion angle (p < .001) and hip flexion moment (p = .027), and increased PS knee external rotation angle (p = .034). During the unanticipated cut, participants increased PS hip (p = .040) and knee flexion angle (p < .001), and decreased PS hip adduction (p = .001), and knee abduction (p = .005) and external rotation (p = .026) moments. Adding body borne load produces lower limb biomechanical adaptations thought to increase risk of musculoskeletal injury, but neither anticipation nor dual task exaggerated those biomechanical adaptations. With a dual task, participants adopted biomechanics known to increase injury risk; whereas, participants used lower limb biomechanics thought to decrease injury risk during unanticipated cuts.     

Development and Physical Validation of a Finite Element Model of Total Hip Dislocation

Component-on-component impingement, followed by levering of the femoral head, is a common mode of dislocation in total hip arthroplasty. While there have been many registry-based studies of dislocation incidence, confounding factors and sources of variability in the clinical domain make it difficult to identify specific parameter influences. A three dimensional nonlinear finite element model has been developed for the purpose of studying the dislocation event, to allow determination of how individual factors such as component design and clinical implantation position affect the propensity for dislocation. Also, a laboratory testing apparatus was constructed to provide physical validation of the computational model. The finite element model correctly predicted the range of motion observed in the physical apparatus to within 1%, and predicted the peak resisting moment to within 2.5%. Under even a light joint load of 200 N, the von Mises stresses developed in the polyethylene insert reached 13 MPa, and the contact stresses rose to as high as 30 MPa. These deleterious elevations occurred not only at the site of neck impingement, but also at the site of head egress from the liner.     

Non-invasive assessment of soft-tissue artifact and its effect on knee joint kinematics during functional activity

The soft-tissue interface between skin-mounted markers and the underlying bones poses a major limitation to accurate, non-invasive measurement of joint kinematics. The aim of this study was twofold: first, to quantify lower limb soft-tissue artifact in young healthy subjects during functional activity; and second, to determine the effect of soft-tissue artifact on the calculation of knee joint kinematics. Subject-specific bone models generated from magnetic resonance imaging (MRI) were used in conjunction with X-ray images obtained from single-plane fluoroscopy to determine three-dimensional knee joint kinematics for four separate tasks: open-chain knee flexion, hip axial rotation, level walking, and a step-up. Knee joint kinematics was derived using the anatomical frames from the MRI-based, 3D bone models together with the data from video motion capture and X-ray fluoroscopy. Soft-tissue artifact was defined as the degree of movement of each marker in the anteroposterior, proximodistal and mediolateral directions of the corresponding anatomical frame. A number of different skin-marker clusters (total of 180) were used to calculate knee joint rotations, and the results were compared against those obtained from fluoroscopy. Although a consistent pattern of soft-tissue artifact was found for each task across all subjects, the magnitudes of soft-tissue artifact were subject-, task- and location-dependent. Soft-tissue artifact for the thigh markers was substantially greater than that for the shank markers. Markers positioned in the vicinity of the knee joint showed considerable movement, with root mean square errors as high as 29.3 mm. The maximum root mean square errors for calculating knee joint rotations occurred for the open-chain knee flexion task and were 24.3°, 17.8° and 14.5° for flexion, internal–external rotation and abduction–adduction, respectively. The present results on soft-tissue artifact, based on fluoroscopic measurements in healthy adult subjects, may be helpful in developing location- and direction-specific weighting factors for use in global optimization algorithms aimed at minimizing the effects of soft-tissue artifact on calculations of knee joint rotations.     

Magnetic resonance imaging of the erector spinae muscles in Duchenne muscular dystrophy: implication for scoliotic deformities

Background

In patients with structural idiopathic scoliosis the body asymmetries involve the pelvis and the lower limbs; they are included in many theories debating the pathogenesis of idiopathic scoliosis.

Methods

Hip joint range of motion was studied in 158 adolescent girls, aged 10–18 years (mean 14.2 ± 2.0) with structural idiopathic scoliosis of 20–83° of Cobb angle (mean 43.0° ± 14.5°) and compared to 57 controls, sex and age matched. Hip range of rotation was examined in prone position, the pelvis level controlled with an inclinometer; hip adduction was tested in five different positions.

Results

In girls with structural scoliosis the symmetry of hip rotation was less frequent (p = 0.0047), the difference between left and right hip range of internal rotation was significantly higher (p = 0.0013), and the static rotational offset of the pelvis, calculated from the mid-points of rotation, revealed significantly greater (p = 0.0092) than in healthy controls. The detected asymmetries comprised no limitation of hip range of motion, but a transposition of the sector of motion, mainly towards internal rotation in one hip and external rotation in the opposite hip. The data failed to demonstrate the curve type, the Cobb angle, the angle of trunk rotation or the curve progression factor to be related to the hip joint asymmetrical range of motion.

Conclusion

Numerous asymmetries around the hip were detected, most of them were expressed equally in scoliotics and in controls. Pathogenic implications concern producing a "torsional offset" of muscles patterns of activation around the spine in adolescent girls with structural idiopathic scoliosis during gait.     

Hip contact stress during normal and staircase walking: the influence of acetabular anteversion angle and lateral coverage of the acetabulum

Hip contact stress is considered to be an important biomechanical factor related to development of coxarthrosis. The effect of the lateral coverage of the acetabulum on the hip contact stress has been demonstrated in several studies of hip dysplasia, whereas the effect of the anterior anteversion remains unclear. Therefore, the joint hip contact stress during normal level walking and staircase walking, in normal and dysplastic hips, for small and large acetabular anteversion angle was computed. For small acetabular anteversion angle, the hip contact stress is slightly increased (less than 15%) in staircase walking when compared with normal walking. In hips with large angle of acetabular anteversion, walking downstairs significantly increases the maximal peak contact stress (70% in normal hips and 115% in dysplastic hips) whereas walking upstairs decreases the peak contact stress (4% in normal hips and 34% in dysplastic hips) in comparison to normal walking. Based on the presented results, we suggest that the acetabular anteversion should be considered in biomechanical evaluation of the hips, especially when the lateral coverage of the acetabulum is small.