vendex and Hip-Dislocation

Alternative bearings allow for the increased utilization of large femoral heads in total hip arthroplasty. This study demonstrated the effect of increasing femoral head size on the force required for dislocation during intraoperative assessment. Using a standard posterior approach, 10 cadaver hips underwent total hip arthroplasty; components were implanted in a standard fashion. The extremity was attached to a custom jig to replicate intraoperative assessment (internal rotation with 90° of hip flexion/neutral adduction). This range of motion (ROM) was repeated in triplicate using femoral head sizes of 28mm, 32mm, 36mm, 40mm, and 44mm. The ROM to dislocation (degrees) and torque (N*m) required were recorded. With increasing head sizes, there was a significant increase in torque required for dislocation (p<0.0001). The least square means torques (N*m) for each femoral head size (28-44mm) were 2.07, 2.15, 2.42, 2.74, and 3.65N*m. The corresponding least square means ROMs prior to dislocation were 43.5°, 46.2°, 50.8°, 54.3°, and 59.5°. There was a significant difference in ROM between nonadjacent head sizes (i.e., 28mm and 44mm) (p<0.0001). Total hip implant stability is multifactorial. Increasing femoral head size may confer stability during intraoperative assessment by increasing both the ROM prior to dislocation and the force required for dislocation.

Topics: Arthroplasty, Replacement, Hip; Cadaver; Femur Head; Hip Dislocation; Hip Joint; Hip Prosthesis; Humans; Prosthesis Design; Range of Motion, Articular; Torque

Dislocation is a serious potential complication of total hip replacement. Previous studies have proposed a newly developed total hip structure that meets the required oscillation angle of 120°, for which the chamfer on the acetabular liner rim was designed to enable the neck to impinge on the chamfer over a large area after impingement occurs. This study adopted the finite element method to further analyse the torque limits leading to dislocation and the contact stresses at the impingement and egress sites of the liner during subluxation. The compressive stress-strain curve for ultra-high molecular weight polyethylene is nonlinear. The results reveal that an adequate chamfer angle of the acetabular cup liner can significantly increase dislocation torque and decrease contact stress on the liner rim. By means of the new design, when the head-neck ratio (HNR) is 2.5 or 3.0, the maximum torque value that a 36-mm head can withstand is 1.38 (8.7 Nm/6.3 Nm) or 1.47 (8.4 Nm/5.7 Nm) times that of a 22-mm head, while the maximum stress of a 36-mm head is 0.41 (14.58 MPa/35.73 MPa) or 0.70 (33.71 MPa/47.90 MPa) times that of a 22-mm head. When the head diameters are identical, the dislocation torque of the HNR = 2.5 structure is slightly greater than that of the HNR = 3.0 structure (3.3-10.5%); thus, the newly developed structure can disperse contact stress, and the structure of a large head with a low HNR exhibits a higher dislocation torque value and lower stress.

Topics: Femur Head; Finite Element Analysis; Hip Dislocation; Hip Prosthesis; Humans; Nonlinear Dynamics; Stress, Mechanical; Torque

Reported rates of dislocation in hip hemiarthroplasty (HA) for the treatment of intra-capsular fractures of the hip, range between 1% and 10%. HA is frequently performed through a direct lateral surgical approach. The aim of this study is to determine the contribution of the anterior capsule to the stability of a cemented HA through a direct lateral approach. A total of five whole-body cadavers were thawed at room temperature, providing ten hip joints for investigation. A Thompson HA was cemented in place via a direct lateral approach. The cadavers were then positioned supine, both knee joints were disarticulated and a digital torque wrench was attached to the femur using a circular frame with three half pins. The wrench applied an external rotation force with the hip in extension to allow the hip to dislocate anteriorly. Each hip was dislocated twice; once with a capsular repair and once without repairing the capsule. Stratified sampling ensured the order in which this was performed was alternated for the paired hips on each cadaver. Comparing peak torque force in hips with the capsule repaired and peak torque force in hips without repair of the capsule, revealed a significant difference between the 'capsule repaired' (mean 22.96 Nm, standard deviation (sd) 4.61) and the 'capsule not repaired' group (mean 5.6 Nm, sd 2.81) (p < 0.001). Capsular repair may help reduce the risk of hip dislocation following HA.

Topics: Aged; Aged, 80 and over; Cadaver; Hemiarthroplasty; Hip Dislocation; Hip Fractures; Humans; Joint Capsule; Joint Instability; Sensitivity and Specificity; Torque

Fragility hip fractures are increasingly common and hemiarthroplasty is one of the standard treatments. Although a common surgery, it should be performed with great caution because of the poor premorbid and bone quality in this demographic. Intra-operative fractures can occur while attempting press fit of the femoral implant. However; vigilance often steps down once the implant is secured and the hip reduced. This case report reminds surgeons that a large amount of torque can be transmitted during intra-operative positioning, such as during an attempt of hip dislocation. This torque, in addition to the risk factor of osteoporotic bone, can result in iatrogenic fractures. Published literature regarding management of an intra-operative fracture while the prosthetic hip is still reduced is lacking. The authors propose that temporary prophylactic cerclage wiring is a prudent and safe procedure prior to hip dislocation.

Topics: Aged, 80 and over; Bone Wires; Female; Femoral Neck Fractures; Hemiarthroplasty; Hip Dislocation; Humans; Intraoperative Complications; Male; Osteoporotic Fractures; Periprosthetic Fractures; Prosthesis Failure; Risk Factors; Torque

Several studies have investigated walking characteristics in hip dysplasia patients, but so far none have described all hip rotational degrees of freedom during the whole gait cycle. This descriptive study reports 3D joint angles and torques, and furthermore extends previous studies with muscle and joint contact forces in 32 hip dysplasia patients and 32 matching controls.. 3D motion capture data from walking and standing trials were analysed. Hip, knee, ankle and pelvis angles were calculated with inverse kinematics for both standing and walking trials. Hip, knee and ankle torques were calculated with inverse dynamics, while hip muscle and joint contact forces were calculated with static optimisation for the walking trials.. No differences were found between the two groups while standing. While walking, patients showed decreased hip extension, increased ankle pronation and increased hip abduction and external rotation torques. Furthermore, hip muscle forces were generally lower and shifted to more posteriorly situated muscles, while the hip joint contact force was lower and directed more superiorly.. During walking, patients showed lower and more superiorly directed hip joint contact force, which might alleviate pain from an antero-superiorly degenerated joint.

Topics: Adolescent; Adult; Ankle Joint; Biomechanical Phenomena; Case-Control Studies; Female; Gait; Hip Dislocation; Hip Joint; Humans; Knee Joint; Male; Middle Aged; Muscle, Skeletal; Range of Motion, Articular; Rotation; Torque; Walking; Young Adult

This study investigated the rotational response of the hip with different repairs of posterior structures after using the posterior approach in total hip replacement. Five groups were tested: (1) the normal hip without a replacement, (2) the normal hip with a vented capsule, (3) no repair of the capsule and external rotators after total hip replacement, (4) repair of only the piriformis tendon, and (5) repair of the capsule and external rotators as a flap of tissue (capsule, piriformis, obturator internus, gemellae, and quadratus) to the posterior aspect of the greater trochanter. Hemipelvis cadaveric specimens were attached to a joint testing device for testing at full extension, 30 degree, 60 degree and 90 degree hip flexion as internal and external rotation was applied to the femur and the load deflection curves were recorded. Specimens after total hip replacement were externally rotated in full extension until dislocation occurred and the maximum torque was recorded. Each specimen then was rotated internally at 90 degree flexion to the point of dislocation and the maximum torque was recorded for comparison as well. The posterior approach had significantly decreased internal rotational support with no repair or only piriformis repair. When the capsule and external rotators were repaired, a more normal load deflection curve resulted when comparing the full repair group with the normal hip. Significantly higher torque was needed to dislocate the hip in flexion when a full posterior repair was done, and most specimens dislocated in flexion without complete failure of the repair.

Topics: Arthroplasty, Replacement, Hip; Femur; Hip Dislocation; Hip Joint; Humans; Range of Motion, Articular; Torque; Weight-Bearing

After total hip replacement an insufficient range of motion (ROM) can lead to contact between femoral neck and rim of the cup (= impingement) causing dislocation and consecutive material failure. The purpose of this study was to analyse the influence of different wear couples on the ROM and stability against dislocation. By means of a special testing device the ROM until impingement, the ROM until dislocation as well as the resisting moment against levering the head out of the cup were experimentally determined. Various total hip systems with cup inserts made of ceramic and polyethylene were comparatively examined in different implant positions. Maximum resisting moment as well as the ROM until impingement and dislocation were clearly influenced by the implant position. Furthermore, the stability against dislocation was affected by design parameters, whereas in the case of appropriate implant position differing wear couples (metal-on-polyethylene vs. ceramic-on-ceramic) had a minor impact. However, as shown by tests under lubricant conditions, ceramic-on-ceramic couples provided less dislocation stability in unfavourable implant position in comparison to metal-on-polyethylene. Therefore, ceramic-on-ceramic couples should only be applied in the case of optimised implant orientation preventing impingement and dislocation with subsequent material failure like chipping off or breakage.

Topics: Ceramics; Equipment Failure Analysis; Friction; Hip Dislocation; Hip Joint; Hip Prosthesis; Humans; Joint Instability; Materials Testing; Metals; Polyethylene; Prosthesis Failure; Range of Motion, Articular; Torque

Reports indicate that constrained acetabular cups may reduce range of motion and catastrophically fail, although the biomechanics of dislocation have not been reported. We measured the available motion in 6 constrained cups (from 2 manufacturers) when anatomically placed in cadaver pelves. We measured the torque and rotation necessary to dislocate the hip. Range of motion was measured using a custom jig and revealed a functional range of motion with all cup positions. Extension was limited to 0 degrees with anteversion of 11 degrees to 29 degrees. Thus, anteversion of <10 degrees is recommended. Torque and rotation to produce dislocation was 7 ft-pounds and 11 ft-pounds and 82 degrees and 72 degrees, for each manufacturer. Torques were reduced with subsequent dislocations. We recommend consideration of polyethylene replacement if dislocation occurs. Dislocation occurred at the ball-polyethylene interface without catastrophic failure.

Topics: Acetabulum; Analysis of Variance; Biomechanical Phenomena; Cadaver; Hip Dislocation; Hip Prosthesis; Humans; Prosthesis Design; Prosthesis Failure; Risk Factors; Rotation; Torque

One treatment strategy for recurrent dislocation after total hip arthroplasty is the use of a constrained acetabular component. A major drawback of currently available constrained components is the limited range of motion (ROM). We present a novel constrained component that employs a monopolar, highly cross-linked polyethylene liner with cutouts oriented to allow increased ROM, while maintaining constraint against dislocation. ROM and lever-out tests comparing this novel design with a conventional constrained component showed that the cutaway monopolar component allowed ROM substantially greater than a currently available design. The lever-out torque for the cutaway monopolar constrained component was 243% higher than the conventional constrained component. This novel constrained acetabular component offers promise for providing excellent constraint against dislocation, while maintaining a wide ROM.

Topics: Acetabulum; Arthroplasty, Replacement, Hip; Hip Dislocation; Hip Prosthesis; Humans; Polyethylenes; Postoperative Complications; Prosthesis Design; Prosthesis Failure; Range of Motion, Articular; Torque

Topics: Congenital Abnormalities; Hip Dislocation; Hip Dislocation, Congenital; Hip Joint; Humans; Osteotomy; Torque