A large collar increases neck resorption in total hip replacement. 204 hips evaluated during 5 years

Proximal femoral anatomy and collared stems in hip arthroplasty: is a single collar size sufficient?

Background

Even if the benefits of collars are unclear, they remain widely used, in several femoral stem designs. This study aimed to determine whether collar size should be proportional to hip dimensions and morphology. The hypothesis was that the collar should be larger for greater stem sizes and for varus femoral necks.

Methods

Computed Tomography scans of 204 healthy hips were digitally analysed and manually templated to determine principle dimensions, appropriate stem size and model, as well as cortical distance at the femoral calcar (ideal collar size).

Results

Univariable analysis revealed that cortical distance was moderately correlated with mediolateral offset (r = 0.572; p < 0.0001) and stem model (r = 0.520; p < 0.0001). Cortical distance was weakly correlated with head diameter (r = 0.399; p < 0.0001), stem size (r = 0.200; p = 0.017), and patient gender (r = 0.361; p < 0.0001). Multivariable analysis confirmed that stem model (p < 0.0001) and head diameter (p = 0.0162) are directly correlated to cortical distance.

Conclusion

We found that cortical distance along the femoral calcar is directly correlated with the model of the stem implanted (‘standard’ or ‘varus’) and with the head diameter. This cortical distance indicates optimal collar size, which would grant maximum calcar coverage without prosthetic overhang. Collar size should be proportional to the size of the operated hip, and should be larger for ‘varus’ stem models than for ‘standard’ stem models.

High failure rates of the Spectron EF stem at a minimum of 10 year's follow-up

We prospectively followed 112 hips, undergoing THA with a Spectron EF stem. At mean follow-up of 11.2years, 21 patients had died. We obtained radiological follow-up in 99% and clinical follow-up in 100% of the surviving 91 hips. Fifty-four percent demonstrated osteolysis in at least one Gruen zone. Twenty-two hips required revision for all causes, with a further five stems radiologically loose. With endpoint being stem revision for aseptic loosening or radiological failure, survivorship at 11years was 0.783. We believe the addition of a rougher surface finish has contributed to the high levels of osteolysis and stem failure seen with the Spectron EF.

The biomechanical effect of the collar of a femoral stem on total hip arthroplasty

To investigate the biomechanical effect of collars, finite element analyses are carried out through two hip joints that are implanted using collared and collarless stems, respectively, and an intact hip joint model. For the analyses, the sacrum, coxal bone, and the cancellous and cortical bones of a femur are modelled using finite elements based on X-ray computed tomographic images taken from a 27-year-old woman. From the results, it is found that a collar with perfect calcar contact prevents stem subsidence and decreases the proximal-lateral gap and the lateral stem tilting. Therefore, it can impart reasonable biomechanical stability for total hip arthroplasty. However, its low load transmission ability and increased stem tilting effect due to the imperfect contact between the collar and the calcar are found to be serious problems that need to be solved. Results of clinical follow-up are presented for supporting the computational results.

Cement collar and longitudinal groove: the effects on mechanical stability with aseptic loosening in Müller straight-stem implants

INTRODUCTION

The Müller straight-stem prosthesis (GS-77), in contrast to the Müller SL prosthesis (SL-88), is equipped with a cement collar and longitudinal grooves. Comparative observation of these prostheses suggests that cement collars protect against rapid subsidence and that longitudinal grooves prevent premature formation of a varus tilting deformity.

METHOD

Because loosening is often observed in the titanium-alloy models of these implants, this retrospective study focused on these models. Differences based on other parameters known to affect mechanical performance were minimized by careful selection: the use of lateralizing implants, patient population characteristics (gender distribution, age, BMI, activity level), and consistency of prosthetic size (10). The comparability of the bending stiffness of both implants in corresponding sizes was verified using finite element method calculations.

RESULTS

Up to the time of revision, 17 GS-77 and 33 SL-88 implants were compared for the amounts of subsidence and prosthetic tilting. Standardized follow-up films were contrasted and radiographically measured. At the time of revision, the GS-77 implants showed subsidence of 4.8 (+/-3.7) mm and the SL-88 implants 8.2 (+/-5.1) mm (p = 0.012). Leaving apart 3 cases with an extreme situation tilting of the GS-77 implants, with 1.2 (+/-0.9) degrees , averaged only two-thirds that of the SL-88 implants, with 1.9 (+/-1.1(p = 0.032). These results support the hypothesis that the cement collar of the Müller straight-stem prosthesis protects against rapid subsidence occurring with aseptic loosening of the implant. The longitudinal grooves appear to counter the development of varus tilting.

The design features of cemented femoral hip implants

We undertook a review of the literature relating to the two basic stem designs in use in cemented hip replacement, namely loaded tapers or force-closed femoral stems, and the composite beam or shape-closed designs. The associated stem fixation theory as understood from in vitro studies and finite element modelling were examined with reference to the survivorship results for each of the concepts of fixation.

It is clear that both design principles are capable of producing successful long-term results, providing that their specific requirements of stem metallurgy, shape and surface finish, preparation of the bone and handling of the cement are observed.

Three-dimensional computed cementless custom femoral stems in young patients: midterm followup

We prospectively evaluated the results of our custom cementless femoral stems to ascertain whether this technology produced reasonable clinical function, complication rates, and loosening rates at midterm. Fifty-seven consecutive patients had surgery in 62 hips for primary osteoarthritis at a mean age of 57 years using a three-dimensional computed custom cementless stem. Patients were reviewed at a mean followup of 94.9 months. At review, the mean Harris hip score was 98.8 points (range, 84-100) compared with 61.1 (range, 28-78) points preoperatively. No patient complained of thigh pain. No migration or subsidence was observed. All stems were considered stable according to the radiographic criteria defined by Engh et al. There were no dislocations, no infections, and no reoperations. Our results are comparable with published results from clinical and radiologic points of view. Two problems remain unsolved: the price of a custom stem is twice as expensive as a standard stem; and we need longer term results before definitely recommending this technology as a reasonable alternative to current arthroplasties in younger patients. The data support the continued exploration of this technology with controlled clinical followup.

LEVEL OF EVIDENCE

Therapeutic study, Level II-1 (prospective cohort study). See the Guidelines to Authors for a complete description of levels of evidence.

Radiological findings and clinical results of 102 thrust-plate femoral hip prostheses: a follow-up of 2 to 8 years

We report the radiological and clinical outcome of 102 consecutive femoral hip arthroplasty we prospectively followed up in 84 patients using the third generation of the thrust-plate prosthesis with a mean period of follow-up of 58 (range, 26-100) months. Four implants were revised: 2 because of an infection and 2 because of aseptic loosening. The thrust-plate prosthesis, which allows preservation of part of the femoral neck, was used in younger patients, 80% were younger than 60 years. In 95 implants, contact was maintained between thrust plate and underlying bone, and in only 3 instances, without any clinical manifestation, did the bone retract from the thrust plate to the extent that a gap appeared. The extent of radiologically evident bone contact with the flat surface of the thrust plate, as a consequence of the bone remodeling behavior, is described and retrospectively classified. The average Harris hip score increased from 51 points preoperatively to 96 points postoperatively at the last follow-up. Survivorship analysis according to Kaplan-Meier showed a survival rate of 98% after 6 years, with no further losses up to the end of the 8-year follow-up period.

A conical-collared intramedullary stem can improve stress transfer and limit micromotion

OBJECTIVE

The objective of this study was to quantify the effect of collar geometry on stress transfer and micromotion in idealized models of a cementless implant having an intramedullary stem.

BACKGROUND

Intramedullary stems exist on several types of orthopaedic implants, including the femoral component of hip arthroplasties and segmental replacements used in the surgical treatment of a tumor or trauma in the diaphysis of a long bone.

METHODS

Using three-dimensional finite element analysis, we compared four idealized, straight-stemmed, axisymmetric prostheses: flat-collared (0 degrees), conical-collared (30 degrees and 60 degrees), and collarless tapered (80 degrees). We simulated axial and non-axial (20 degrees oblique) loads as well as non-ingrown and ingrown interface conditions.

RESULTS

Without bone ingrowth, stress transfer to bone adjacent to the collar increased with collar angle. Micromotion at the distal stem increased moderately with collar angle from 0 degrees through 60 degrees, then increased markedly from 60 degrees to 80 degrees. With simulated bony ingrowth, the effect of the collar was greatly reduced.

CONCLUSIONS

The results of this study suggest that the selection of collar angle represents a tradeoff between initial stress transfer and micromotion. Stems with conical collar angles in the range of 30-60 degrees can provide increased stress transfer compared to a flat collar design and reduced micromotion compared to a collarless tapered design.

Collarless polished tapered stem: clinical and radiological follow-up over 5 years

The clinical and radiologic outcome of a cemented, polished, tapered stem (CPT), implanted using contemporary cementing techniques in 108 consecutive operated hips in 100 patients (68 women and 32 men, aged 19 to 83 years at the time of surgery [mean, 65 years]) was assessed after >5 years. The Harris hip scores were good or excellent in 96% of the patients. Stem subsidence measured by the computer-assisted method described by Braud and Freeman was at a mean rate of 0.44 mm/y, 1.08 mm during the first year, and stabilizing to a mean total of 2.18 mm at >5 years. Subsidence was related inversely to the completeness of the cement mantle but did not correlate with the clinical or radiologic outcome. This study confirms that collarless, polished, tapered stems subside within the cement mantle but without loosening and that the CPT performs at least as well as the Exeter stem.

Hip arthroplasty with a collared straight cobalt-chrome femoral stem using second-generation cementing technique: a 10-year-average follow-up study

Clinical and radiographic results of 116 patients who had undergone 132 hip arthroplasties at our institution from 1983 to 1988 with a collared cemented straight cobalt-chrome femoral stem using second-generation cementing technique were reviewed. Twenty hips in 20 patients who were part of the original cohort were lost to follow-up. Mean age at the time of surgery was 68.2 years. Mean radiographic follow-up was 9.6 years with a minimum follow-up of 5 years. Ten-year survivorship of the component was 96.5% with revision considered as an endpoint and 94.2% with either revision or radiographic loosening considered the endpoint. Three implants (2.3%) were revised for aseptic loosening at a mean of 8.1 years after implantation. One implant (0.8%) was revised for septic loosening at 10.5 years after surgery. Of the implants not revised, 1 showed evidence of circumferential bone-cement radiolucencies, and 1 had radiolucencies at the implant-cement interface. Five of the surviving femoral components (5.0%) showed focal areas of cystic osteolysis, and proximal femoral bone resorption under the collar was seen in 32 patients (31.7%). There were no cases of cement fracture or stem subsidence. The biomechanical and material properties of this stem combined with second-generation cementing technique look promising for long-term survivorship.

The Charnley versus the Spectron hip prosthesis: radiographic evaluation of a randomized, prospective study of 2 different hip implants

A total of 410 hips were randomized to treatment with either a Charnley (206 hips) or a Spectron (204 hips) total hip arthroplasty. The patients were operated on by a standardized procedure using a contemporary cementing technique and were followed after 1, 3, 5 to 6, and 10 years. The postoperative radiographs showed a significantly increased rate of malalignment and consequently low grade of cement mantle quality of the Charnley stem compared to the Spectron. No differences concerning cement mantle quality or positioning were found between the Charnley ogee cup and the metal-backed Spectron. Evaluation of the follow-up radiographs revealed 10 loose Charnley stems and 1 loose Spectron stem and 4 loose Charnley ogee cups and 23 loose Spectron metal-backed cups. The differences of revision rate for the femoral and acetabular components of the 2 prostheses were significant (P = .03, Charnley femoral component more frequent; P = .03, Spectron acetabular component more frequent). The radiographic evaluation strengthened this disparity. Poor wear characteristics of the metal-backed Spectron cup are perhaps the main reason for the highly significant difference in mechanical failure rate between the 2 cups. We therefore propose that metal-backing of cemented cups should be avoided, at least when combined with larger femoral heads. The difficulty in positioning the Charnley stem with an adequate cement mantle, especially in the absence of trochanteric osteotomy, might explain the inferior Charnley stem longevity in this study.