The impact of the CCD-angle on range of motion and cup positioning in total hip arthroplasty

Optimal orientation of implanted components in total hip arthroplasty with polyethylene on metal articulation

BACKGROUND

In many studies related to the total hip arthroplasty, it has been found that incorrect alignment of the total hip component is one of the major factors influencing mechanical failures. Although various recommendations for cup orientation have been presented, there were few studies that seek to determine a proper orientation of the implants based on the human motion data. The objective of this study is to determine an optimum orientation of the hip implant considering various daily activities.

METHODS

Firstly, the cup orientations free of impingement were calculated for a given set of implant geometric parameters and the required range of motion for daily activities measured in 10 subjects. Next, the optimum values for the cup orientation and stem anteversion avoiding impingement and minimizing cup wear were determined for the proposed motion criteria.

FINDINGS

Different cup orientation was obtained as optimum for each combination of the neck angles (40 degrees and 50 degrees) and oscillation angles (120 degrees and 135 degrees). The corresponding optimum stem anteversion was also different when different neck angle was used.

INTERPRETATION

As the margin for the impingement-free orientation of the cup was small, the optimum cup orientation and stem anteversion should be adopted specific for each combination of the neck angle and oscillation angle.

Containment versus impingement: finding a compromise for cup placement in total hip arthroplasty

Recommendations for cup containment and impingement may provide conflicting directions for component orientation in total hip arthroplasty. For optimal containment, the cup is positioned with respect to the acetabular bone, resulting in coincidence of the rim of the cup and the acetabulum. This results in good coverage and symmetric load transfer, leading to good long-term stability, but occasionally necessitates more abduction of the cup than that recommended by the safe zone. On the other hand, placement of the cup for an optimal range of motion would lead to only partial containment, with a higher risk of component loosening and revision. The most effective compromise is to use a prosthesis that has a large safe zone, realised by a high head-to-neck ratio, and orienting the cup such that a good containment is achieved and the safe zone is respected. Computer navigation or smart aiming devices may help to find the best relative orientation.

Factors affecting hip range of motion in surface replacement arthroplasty

BACKGROUND

Surface replacement arthroplasty aims to re-create normal hip biomechanics; however the pathoanathomy of the hip, prosthetic component design, surgical technique and other factors may have a significant impact on the range of motion restoration attained following surface replacement arthroplasty. However, there is paucity of information on the effect of such factors.

METHODS

A computerized three-dimensional hip model was created from preoperative computerized tomography images of a patient who was scheduled for a surface replacement arthroplasty. The effects of the femoral component size, translation and orientation on the range of motion were analysed as was the effect of increasing the seating depth and modification of the version of the acetabular component.

FINDINGS

Increasing the femoral component size led to global improvement in range of motion while translation increased range of motion in one direction but reduced it in the opposite direction. Change in the femoral component orientation had minimal effects on range of motion in comparison to the effect of changes in the version of the acetabular component. Increasing the seating depth of the acetabulum only caused reduced range of motion in internal rotation in 90 degrees flexion.

INTERPRETATION

To restore hip range of motion, surgeons performing surface replacement arthroplasty should aim to reproduce the natural femoral head-neck offset. Although increasing the femoral component size may achieve this, more acetabular bone will be resected. Knowing the specific zones of impingement of each arc of movement, selective translation of the femoral component or femoral neck osteoplasty can restore femoral neck offset in more critical areas without affecting acetabular bone stock. Over deepening of the acetabulum or leaving rim osteophytes should also be avoided to prevent impingement.

Anatomic hip range of motion after implantation during total hip arthroplasty as measured by a navigation system

Simulation of prosthetic impingement is important for preventing complications after total hip arthroplasty (THA). Although the anatomical hip range of motion (ROM) in patients after THA is an essential parameter for these simulations, previous simulation studies substituted various clinical hip ROMs for the anatomical hip ROM. Using a navigation system, anatomical hip ROM was accurately assessed after implantation during primary THA in 30 patients. We found that the hip could be passively moved to 113 degrees of flexion, 34 degrees of extension, 46 degrees of abduction, 75 degrees of internal rotation, and 36 degrees of external rotation. Almost all reference hip ROMs used in previous simulations were smaller than these values. Therefore, wider hip ROM values should be used as parameters for such simulations.

Alteration of the hip joint centre during acetabular reaming

Change of the hip joint centre location during preparation of the acetabular cavity for the acetabular component can affect the outcome of total hip arthroplasty. Deviations from the preoperative geometry can compromise an otherwise successful operation with regard to hip dislocations, leg length inequality and range of motion of the hip joint. Eighteen acetabula from pelvic specimens were measured before and after acetabular reaming to determine the change of hip centre location. Two different acetabular reamers were applied to the acetabular cavity: a chamfered reamer intended for minimal invasive hip surgery (MIS) and a conventional hemispherical reamer. An optical 3D scanning system created 3D models of the cavities prior to and after the reaming procedure. The two 3D models were merged into a single 3D model and displacements in all three dimensions were calculated The results showed no significant difference between MIS and conventional reaming with regard to transition vector length (p=0.9). The mean length of the transition vector was 3.6 mm (SD. 2.4 mm). Our findings suggest that the alteration of the hip centre location is not influenced by the changes made to the MIS reamers in comparison with conventional reamers. In comparison with previous studies the drift of the hip centre caused by the acetabular reaming is reduced due to new reaming techniques and prosthesis designs.