Collarless Prosthesis Research Articles

Iliopsoas Tendonitis Caused by Overhang of a Collared Femoral Prosthesis

Pain after total hip arthroplasty can be due to a variety of causes, one of the less common being iliopsoas tendonitis. We report an unusual case of iliopsoas tendonitis caused by overhang of the femoral calcar by a collared femoral prosthesis resulting in impingement on the iliopsoas tendon. An ultrasound-guided corticosteroid and local anesthetic diagnostic injection to the site of impingement confirmed the diagnosis with temporary symptom relief. Revision of the femoral stem to a collarless prosthesis resulted in immediate and complete resolution of symptoms.

COMPARISON OF POLYETHYLENE WEAR ON THE BASIS OF FEMORAL HEAD PENETRATION RELATIVE TO THE ACETABULUM IN TOTAL HIP ARTHROPLASTY.

Polyethylene wear at the bearing surface of total hip prostheses can result in an inflammatory response that leads to periprosthetic osteolysis and aseptic loosening. Studies have demonstrated a reduction in wear in polyethylene with a more highly cross-linked molecular structure. The purpose of this study was to compare polyethylene wear on the basis of femoral head penetration in total hip prostheses with cross-linked polyethylene (XLPE) with those of standard polyethylene (non-XLPE). Femoral head penetration was evaluated in 74 patients. All hips were cemented stems with polished collarless prostheses and 28 mm CoCr femoral heads. Acetabular components were cementless hemispherical sockets with either XLPE or non-XLPE. The arthroplasties were performed because of degenerative joint disease in 54 hips, avascular necrosis in 8 hips, hip fracture in 4 hips, RA in 3 hips, psoriasis in 2 hips, AS in 1 hip, RA/AVN in 1 hip, and RA/fx in 1 hip. Linear polyethyelene wear was measured using the Livermore technique on standardized anteroposterior pelvic radiographs. The relationships between femoral head penetration (FHP) and implant material, gender, patient weight, and socket inclination were examined. Overall, the mean difference in FHP during the first year was not statistically significant when XLPE was compared with non-XLPE (p = .54). However, the comparison of FHP after the first year found that the FHP was lower for XLPE (p = .04). There were no significant differences in comparing FHP both during and after the first year by material and gender. The observed FHP for non-XLPE was greater than for XLPE both during and after the first year in males but only after the first year in females; however, the difference was not significant. Age has a significant negative relationship with FHP during the first year. The correlation between socket inclination and FHP was weak and not statistically significant (Rxy = .12, p = .307). These findings suggest that steady-state wear rates may be less in XLPE compared with non-XLPE after bedding-in has occurred in the first year. Bedding-in is a slow, plastic deformation in the direction of prevailing stress of the polyethylene and/or settling in of the liner. Radiographic methods for the assessment of polyethylene wear on the basis of femoral head penetration must be further developed to differentiate between plastic deformation of the polyethylene and actual polyethylene wear.

FEMORAL COMPONENT REVISION USING IMPACTED MORSELLISED CANCELLOUS GRAFT

We have tested the axial and torsional stability of femoral components after revision arthroplasty in a cadaver model, using impacted morsellised cancellous graft and cement. Each one of six matched pairs of fresh frozen human femora had either a primary or a revision prosthesis cemented in place. For the ‘revision’ experiments, all cancellous bone was removed from the proximal femur which was then over-reamed to create a smooth-walled cortical shell. An MTS servohydraulic test frame was used to apply axial and torsional loads to each specimen through the prosthetic femoral heads with the femur submerged in isotonic saline solution at 37°C. The mean subsidence was 0.27 ± 0.17 mm for the primary and 0.52 ± 0.30 mm for the revision groups. The difference was statistically significant (p < 0.025), but the mean subsidence was < 1 mm in both groups. The mean maximum torque before failure was 42.9 ± 26.9 N-m for the primary and 34.8± 20.7 N-m for the revision groups. This difference was not statistically significant (p > 0.015). Based on our results we suggest that revision of the femoral component using morsellised cancellous graft followed by cementing with a collarless prosthesis with a polished tapered stem restores the integrity of the proximal femur and provides immediate stability of the implant.

Three-dimensional embedded strain gauge analysis of the effect of collared versus collarless prostheses on cement mantle stresses in a femoral model of a total hip replacement

Experimental and finite element analyses have attributed considerable significance to the role of the prosthetic collar in load transfer to the proximal femur; however, some clinical evidence suggests that collar/calcar contact is unnecessary and detrimental. This study investigates the effects of collared versus collarless prostheses on cement mantle stresses in a model analysis of the proximal femur. Three-dimensional embedded strain gauging is used in a three-times full-size model of an implanted left femur. Tensor stresses in the cement mantle are derived for a collarless Exeter™ stem, a small and a large medial-collared stem and a full-collared prosthesis. Results show that the collar causes an increase in proximal-medial compressive longitudinal stresses, with other proximal stresses significantly reduced. Subsidence of the stem in the cement mantle is prevented, inducing unfavourable pivoting of the prosthesis about the calcar into varus. The collar type produces only minor additional effects in the mechanism of load transfer. The analysis suggests that collars may inhibit the prosthesis from attaining long-term secondary stability, by preventing the stem subsidence evident with cemented collarless implants. Derived stresses also illustrate the considerable variation in the mechanism of load transfer between collared and collarless prostheses in both the proximal and distal regions.

Alterations in femoral strain, micromotion, cortical geometry, cortical porosity, and bony ingrowth in uncemented collared and collarless prostheses in the dog

The effects of a collared femoral endoprosthesis in uncemented total hip arthroplasty were evaluated in 12 dogs. This experimental study compared the biomechanic and histologic responses between collared and collarless femoral prostheses 4 months after implantation. Implant stability (micromotion) and cortical surface strain were evaluated immediately and 4 months after implantation in a simulated postoperative condition, whereas bone ingrowth, cortical porosity, and cortical remodeling were assessed after 4 months only. There were no significant differences in implant stability or cortical surface strains when the collared and collarless groups were compared acutely or after 4 months ( P > .05). There were also no significant differences in percent fill, bony ingrowth, or cortical geometry after 4 months ( P > .05). There was a significant increase in cortical porosity measured from the proximal femur after 4 months for both the collared ( P = .0002) and collarless groups ( P = .009) and when both groups were compared (collarless, 8.2% and collared, 5.8%; P = .03). The results suggest that a collar may be beneficial in decreasing the cortical remodeling that occurs in the proximal femoral cortex after implantation of an uncemented total hip arthroplasty.

The effect of the medial collar in total hip arthroplasty with porous-coated components inserted without cement. An in vivo canine study.

We performed an in vivo study in a canine model to compare the results of the use of a porous-coated collared femoral component with those of the use of a porous-coated collarless femoral component in total hip arthroplasties without cement. Our study focused on the comparative proximal strain pattern, bone ingrowth, and cortical porosity of the two types of prostheses. We used a trochanteric wire marker to measure subsidence. The use of the limb was assessed with gait analysis. Twelve weeks after the operation, the collarless components had significantly greater bone ingrowth proximally (p = 0.003) and were associated with significantly lower cortical porosity (p = 0.006). There were no differences between the groups with regard to either axial or hoop strain. While the group that had a collarless prosthesis had significantly less proximal-medial radiolucency (p = 0.03), there were no differences between the groups with regard to subsidence.

A Prospective Randomized Study of a Collar Versus a Collarless Femoral Prosthesis

A prospective, randomized study of 44 collared versus 40 collarless cemented HD-2 total hip arthroplasties (THAs) was performed in 84 patients. Seventy patients were examined at an average of 4.6 years after surgery. Five hips have required, or are scheduled to have, revision arthroplasty: two with collared prostheses and three with collarless prostheses. Good collar contact with the proximal medial femur was achieved in 47% of the collared prostheses. No patient with good contact has required or is scheduled to have revision hip surgery. Radiolucent lines were greater in both frequency and width in Gruen Zones 2 and 7 in patients with a collarless prosthesis. Loss of endosteal height of the femoral neck was 3.5 mm in patients with collarless prostheses and 1.7 mm in patients with collared prostheses. Loss in height of the femoral neck was 2.6 mm in patients with collared prostheses with poor bone contact and 0.7 mm in patients with collared prostheses with good bone contact. The mean preoperative and postoperative Harris hip scores for the collarless group and for the collared group were not statistically different. There were no statistically significant differences in acetabular position, the incidence of acetabular radiolucent lines, or femoral subsidence between patients treated with collared or collarless prostheses. This study demonstrates that it is possible to stress the proximal medial portion of the femur with a collared prosthesis. Furthermore, a significant increase is identified in both the frequency and width of radiolucent lines in patients with collarless prostheses in Zones 2 and 7.(ABSTRACT TRUNCATED AT 250 WORDS)

Design Optimization of a Prosthesis Stem Reinforcing Shell in Total Hip Arthroplasty

The use of a perforated, titanium funicular shell to support the proximal femoral cortex in total hip arthroplasty was evaluated with the aid of both analytical and numerical techniques. The principal interactions between the femoral cortex, the metal shell, the implant stem and the acrylic bone cement were modeled using beam on elastic foundations theory and two-dimensional elasticity theory. Subsequent formulation of this model as a nonlinear design optimization problem enabled the determination of the dimensions of the implant and reinforcing shell which minimized an objective function based on a simplified material failure criterion. Two cases were examined, each with two cervico-diaphyseal angles: case A: with a rigid contact between a proximal prosthesis collar and the calcar femorale and case B: no collar contact (a collarless prosthesis or post-operative loosening). Case A achieved an optimal solution at a stem diameter 11-23 percent of the cortex inner diameter, a stem length to diameter ratio of 12-40, shell diameter 22-53 percent and thickness 0.2-7.2 percent of the cortex inner diameter and thickness, respectively. Case B achieved an optimal solution at a stem diameter 67-92 percent of the cortex inner diameter, length to diameter ratio of 4-6, and no shell. In case A the collar support makes the type of internal fixation unimportant, while in the more realistic case B, the shell is not recommended.

New design of hip prosthesis using carbon fibre reinforced composite

We present a new design for a hip prosthesis using polyethylene-hydroxyapatite, a composite material with layered stiffness and good bone compatibility. In order to overcome the low stiffness of the matrix, carbon fibre reinforcement is suggested. This new collarless prosthesis was designed to give maximum stiffness at the core and lower stiffness at the bone-implant interface. For this design a 2D finite element analysis was undertaken; its results were compared with those for a titanium alloy prosthesis. The effect of the variation in the collar stiffness was also analysed.

An experimental investigation in the dog into the mode of osseous integration of total joint implants.

An uncemented scaled down version of the Mueller SLS femoral component was inserted into 30 dogs. The material (Protasul 100), geometry, and finish were identical to those designed for clinical use. Half of the prostheses inserted were fitted out with a modular collar to improve stability. Initial stability was achieved through press fit which was made possible by the special modification of the surface area and external configuration of the prosthesis. The function of the prosthesis was assessed through clinical assessment and force plate gait analysis. This was correlated with the degree of osseous integration which was evaluated on the basis of regular radiological examinations, and at post mortem by microradiography of the serially sectioned undecalcified femurs, and histological examination of selected sections under regular and ultraviolet light. The animals were sacrificed at 4, 8, and 12 months. Force plate gait analysis revealed that all animals walked with a normal gait by the 4th post-operative month. Evaluation revealed that 29/30 femoral prostheses became successfully integrated. The prostheses without the collar were less stable and most achieved stability only by incorporation of the distal tip of the prostheses in bone and the remainder in dense fibrous tissue. The prostheses with the collar were stable and achieved without fail full bony integration. The stability was provided by appositional growth of bone which came into direct contact with the implant over the proximal 1/3 and the distal 1/3 without an intervening fibrous membrane. Despite failure of full integration of the collarless prostheses clinically and by force plate analyses the two groups were indistinguishable.(ABSTRACT TRUNCATED AT 250 WORDS)