A CT scan protocol for the detection of radiographic loosening of the glenoid component after total shoulder arthroplasty

Background and purpose

It is difficult to evaluate glenoid component periprosthetic radiolucencies in total shoulder arthroplasties (TSAs) using plain radiographs. This study was performed to evaluate whether computed tomography (CT) using a specific patient position in the CT scanner provides a better method for assessing radiolucencies in TSA.

Methods

Following TSA, 11 patients were CT scanned in a lateral decubitus position with maximum forward flexion, which aligns the glenoid orientation with the axis of the CT scanner. Follow-up CT scanning is part of our routine patient care. Glenoid component periprosthetic lucency was assessed according to the Molé score and it was compared to routine plain radiographs by 5 observers.

Results

The protocol almost completely eliminated metal artifacts in the CT images and allowed accurate assessment of periprosthetic lucency of the glenoid fixation. Positioning of the patient within the CT scanner as described was possible for all 11 patients. A radiolucent line was identified in 54 of the 55 observed CT scans and osteolysis was identified in 25 observations. The average radiolucent line Molé score was 3.4 (SD 2.7) points with plain radiographs and 9.5 (SD 0.8) points with CT scans(p = 0.001). The mean intra-observer variance was lower in the CT scan group than in the plain radiograph group (p = 0.001).

Interpretation

The CT scan protocol we used is of clinical value in routine assessment of glenoid periprosthetic lucency after TSA. The technique improves the ability to detect and monitor radiolucent lines and, therefore, possibly implant loosening also.Glenoid loosening is the main complication of total shoulder arthroplasty (TSA). In a recent analysis that included 33 clinical studies and 2,540 shoulder arthroplasties from 1996 to 2005, the rate of aseptic loosening was reported to be 39%; of these, 83% involved the glenoid component (Bohsali et al. 2006).In current practice, patient evaluation after TSA is based on successive clinical and radiographic assessments with plain and profile radiographs. Radiolucent lines are often seen around the glenoid implant on plain radiographs, and they are thought to be linked to glenoid loosening. The mean rate of radiolucent lines has been reported to be 80% (Bohsali et al. 2006) in a series with more than 10 years of follow-up, which indicates the scale of the loosening problem. The reported occurrence of radiolucent lines also varies greatly between published studies (from 0% to 100%) (Cofield 1984, Barrett et al. 1987, Torchia et al. 1997, Boileau 2000, Mileti et al. 2004, Desmukh et al. 2005, Martin et al. 2005, Szabo et al. 2005). Thus, it appears that the radiolucent lines seen on plain radiographs have only a tenuous link with loosening. One possible reason for this is that radiolucent lines are not always seen, even when the implant really is loose. Yian et al. (2005) used computed tomography (CT) to identify and assess radiolucencies in the glenoid fixation for the purpose of evaluating component loosening. However, they concluded that major artifacts (caused by the metallic humeral head) severely blurred the images, preventing reliable analysis of the implant fixation.We describe a simple and reproducible patient-positioning protocol that moves the metallic humeral head out of the CT scan acquisition plane, reducing metal artifacts and thereby providing clear images for analysis and monitoring of radiolucent lines adjacent to the glenoid fixation.We quantitatively assessed the usefulness of the protocol for evaluation of glenoid component periprosthetic radiolucency and compared it to that of standard methodology using plain-film radiographs to assess loosening. A secondary aim was to assess radiolucent lines in 11 patients to demonstrate the feasibility and the usefulness of the method.     

High incidence of loosening at 5-year follow-up of a cemented metal-on-metal acetabular component in THR

Introduction

High rates of polyethylene wear in metal-on-polyethylene-bearing surfaces correlate with peri-prosthetic osteolysis and early loosening. Hard-bearing surfaces have been used as they may decrease the production of debris and improve survival of the prosthesis. The aim of this study is to ascertain the rate of early loosening of a polyethylene cemented acetabular component with a metal-on-metal (MOM) insert.

Methods

Between 1997 and 1999, 121 total hip replacements in 114 patients were performed at a single centre by two senior surgeons, using the same prosthesis with a MOM hard-bearing surface of 28 mm diameter. At the mean follow-up of 5 years and 6 months (range 5–7 years), nine patients had died and three were lost to follow-up. We reviewed 107 hips (101 patients). The radiographs and case notes of deceased patients were examined. Follow-up was thus 117 out of 121 hips (96%). Results were evaluated clinically with the Merle d’Aubigne classification, and radiographically with analysis of implant migration and radiolucent lines in the Delee and Charnley areas. The survival rate was calculated.

Results

Six patients (5.6%) had revision surgery for aseptic loosening of the cup: one 2 years after the primary operation, two after 4 years, two after 5 years and one after 6 years. The clinical results according to Postel-Merle d’Aubigne gave 85 excellent results (80%), 10 good results (9.4%) and 6 bad results (5.6%). At the latest follow-up, there were no signs of migration, osteolysis or radiolucent lines involving the femoral component. In the acetabular component, there were five cases of radiolucent lines smaller than 1 mm, which were not progressive. In 24 cases, the radiolucent lines progressed over time and there was a probable failure in 18 cases. The survival rate at 5 years is 94.8% taking revision for any cause as the endpoint and 86.9% taking revision or impending failure (as ascertained by radiographic review) of the cup as the endpoint. Numbers of revisions and radiographic failures were significantly higher with the smaller cups (<48 mm diameter) than the larger (p < 0.05).

Conclusions

This series reports a higher rate of failure with a cemented polyethylene cup with a MOM insert than that reported in the scientific literature for metal-on-polyethylene-bearing surface or MOM uncemented cups. Other similar studies found in the literature are discussed. The authors do not recommend use of this cemented polyethylene-Metasul^® acetabular component.     

Are There Long-term Benefits to Cementing the Metaphyseal Stem in Hip Resurfacing?

Background

Cementing the metaphyseal stem during hip resurfacing surgery improves the initial fixation of the femoral component. However, there may be long-term detrimental effects such as stress shielding or an increased risk of thermal necrosis associated with this technique.

Questions/purposes

We compared (1) long-term survivorship free from radiographic femoral failure, (2) validated pain scores, and (3) radiographic evidence of component fixation between hips resurfaced with a cemented metaphyseal stem and hips resurfaced with the metaphyseal stem left uncemented.

Methods

We retrospectively selected all the patients who had undergone bilateral hip resurfacing with an uncemented metaphyseal stem on one side, a cemented metaphyseal stem on the other side, and had both surgeries performed between July 1998 and February 2005. Forty-three patients matched these inclusion criteria. During that period, the indications for cementing the stem evolved in the practice of the senior author (HCA), passing through four phases; initially, only hips with large femoral defects had a cemented stem, then all stems were cemented, then all stems were left uncemented. Finally, stems were cemented for patients receiving small femoral components (< 48 mm) or having large femoral defects (or both). Of the 43 cemented stems, two, 13, 0, and 28 came from each of those four periods. All 43 patients had complete followup at a minimum of 9 years (mean, 143 ± 21 months for the uncemented stems; and 135 ± 22 months for the cemented stems; p = 0.088). Survivorship analyses were performed with Kaplan-Meier and Cox proportional hazards ratios using radiographic failure of the femoral component as the endpoint. Pain was assessed with University of California Los Angeles (UCLA) pain scores, and radiographic femoral failure was defined as complete radiolucency around the metaphyseal stem or gross migration of the femoral component.

Results

There were four failures of the femoral component in the press-fit stem group while the cemented stem group had no femoral failures (p = 0.0471). With the numbers available, we found no differences between the two groups regarding pain relief or radiographic appearance other than in patients whose components developed loosening.

Conclusions

Cementing the metaphyseal stem improves long-term implant survival and does not alter long-term pain relief or the radiographic appearance of the proximal femur as had been a concern based on the results of finite element studies. We believe that patients with small component sizes and large femoral head defects have more to gain from the use of this technique which adds surface area for fixation, and there is no clinical downside to cementing the stem in patients with large component sizes.

Level of Evidence

Level III, therapeutic study     

10 years results of an uncemented metaphyseal fit modular stem in elderly patients

Background:

There are concerns with regard to the femoral fixation in cementless total hip arthroplasty in elderly patients. We report a retrospective analysis of clinical and radiological results of uncemented metaphyseal fit modular stem in elderly patients irrespective of anatomic characterstics of proximal femur.

Materials and Methods:

This study reviews the outcomes of 60 primary hip replacements using a metaphyseal fit modular stem (third-generation Omniflex stem) conducted in 54 patients, of age 75 years or older. After a mean follow-up of 10,4 years, complete clinical and radiographic records were available for 52 hips of 48 patients. The patients were evaluated by Harris Hip Score (HHS).

Results:

There was a significantly improved pain score and Harris Hip Score (41,6 to 83,2). Six stems (11.53%) were revised: four because of periprosthetic fracture; one stem was well fixed, but presented a large osteolytic lesion in the metaphyseal area and the last stem was revised because of aseptic loosening. Stem survival taking aseptic loosening as the end-point was 98%. Bone atrophy in the proximal femur caused by stress shielding was observed in 39 stems (75%), but there was no case of subtrochanteric stress shielding. Moreover, atrophy appeared within two years postoperatively, with no extension thereafter.

Conclusions:

We achieved good clinical and radiographic results by uncemented metaphyseal fit femoral stem regardless of patient''s age and femoral canal type.     

Development and validation of a quantitative method to assess pedicle screw loosening in posterior spine instrumentation on plain radiographs

Purpose

Currently, the diagnosis of pedicle screw (PS) loosening is based on a subjectively assessed halo sign, that is, a radiolucent line around the implant wider than 1 mm in plain radiographs. We aimed at development and validation of a quantitative method to diagnose PS loosening on radiographs.

Methods

Between 11/2004 and 1/2010 36 consecutive patients treated with thoraco-lumbar spine fusion with PS instrumentation without PS loosening were compared with 37 other patients who developed a clinically manifesting PS loosening. Three different angles were measured and compared regarding their capability to discriminate the loosened PS over the postoperative course. The inter-observer invariance was tested and a receiver operating characteristics curve analysis was performed.

Results

The angle measured between the PS axis and the cranial endplate was significantly different between the early and all later postoperative images. The Spearman correlation coefficient for the measurements of two observers at each postoperative time point ranged between 0.89 at 2 weeks to 0.94 at 2 months and 1 year postoperative. The angle change of 1.9° between immediate postoperative and 6-month postoperative was 75 % sensitive and 89 % specific for the identification of loosened screws (AUC = 0.82).

Discussion

The angle between the PS axis and the cranial endplate showed good ability to change in PS loosening. A change of this angle of at least 2° had a relatively high sensitivity and specificity to diagnose screw loosening.     

Minimum ten-year results of a 28-mm metal-on-metal bearing in cementless total hip arthroplasty in patients fifty years of age and younger

Purpose

Concerns have been raised in relation to metal-on-metal (MoM) articulations with catastrophic soft-tissue reactions due to metal debris. We reviewed how small head MoM articulations perform in primary uncemented total hip arthroplasty (THA) in young patients at a minimum of ten years.

Methods

We retrospectively evaluated the clinical and radiographic results of the first 100 consecutive primary cementless THAs using the 28-mm Metasul MoM articulation in 91 patients younger than 50 years of age at the time of surgery.

Results

After 13 years, survival for the endpoint revision due to any reason was 90.9 % and 98.9 % for revision due to aseptic implant loosening. The cumulative incidence of MoM related revisions was 1.2 %. Small proximal femoral osteolysis was found in 18 % of hips. No acetabular osteolysis or loosening was detected. Two hips showed signs of femoral neck impingement with severe damage to the neck.

Conclusions

Early in the second decade, MoM-associated complications were rare using the 28-mm Metasul articulation, and aseptic loosening was not a major mode of failure in this cohort of young patients.

Level of evidence

Therapeutic Level IV.     

Reconstruction of the rotation center of the hip after oblong cups in revision total hip arthroplasty

Background

The preoperative bone defect and the reconstruction of the center of rotation of the hip are critical in acetabular revision surgery. Uncemented oblong cups are employed in order to manage these issues. We analyzed the clinical results and rates of revision of two different uncemented oblong cups, the reconstruction of the center of rotation of the hip, as well as the rate of radiological loosening and possible risk factors.

Materials and methods

Forty-five patients (46 hips) underwent acetabular revision surgery using two different uncemented oblong cups. We assessed the clinical results and the survival rate for revision and aseptic loosening. Intraoperative bone loss was classified according to Paprosky, and acetabular reconstruction was assessed according to Ranawat. The mean follow-up was 7.2 years (range 4–11 years).

Results

There were four re-revisions (three due to aseptic loosening); the survival rate for re-revision due to aseptic loosening was 60.1 % at seven years. The mean distance between the center of the femoral head prosthesis and the approximate center of the femoral head improved from 21.5 to 10.2 mm. Thirteen cups showed radiological loosening; the survival rate for radiological loosening at seven years was 40.54 %. A smaller postoperative horizontal distance was correlated with cup loosening.

Conclusions

Although optimal acetabular reconstruction can be achieved by using oblong uncemented cups in revision hip surgery, the clinical and radiological results are not encouraging. Excessive medialization of the cup may increase the rate of loosening.