A new automated way to measure polyethylene wear in THA using a high resolution CT scanner: method and analysis

Prosthetic liner wear in total hip replacement: a longitudinal 13-year study with computed tomography

This case report follows a woman who had a total hip replacement in 1992 when she was 45 years old. Six serial computed tomography (CT) examinations over a period of 13 years provided information that allowed her revision surgery to be limited to liner replacement as opposed to replacement of the entire prosthesis. Additionally, they provided data that ruled out the presence of osteolysis and indeed none was found at surgery. In 2004, when the first CT was performed, the 3D distance the femoral head had penetrated into the cup was determined to be 2.6 mm. By 2017, femoral head penetration had progressed to 5.0 mm. The extracted liner showed wear at the thinnest part to be 5.5 mm, as measured with a micrometer. The use of modern CT techniques can identify problems, while still correctable without major surgery. Furthermore, the ability of CT to assess the direction of wear revealed that the liner wear changed from the cranial to dorsal direction.

The effect of a low radiation CT protocol on accuracy of CT guided implant migration measurement: A cadaver study

The current study compared the impact of low radiation CT protocols on the accuracy, repeatability, and inter- and intra-observer variability of implant migration studies in total hip arthroplasty. Two total hip replacements were performed in two human cadavers and six tantalum beads were inserted into the femur similar to radiostereometric analysis. Six different 28 mm heads (-3 mm, 0 mm, 2.5 mm, 5.0 mm, 7.5 mm, and 10 mm) were added to simulate five reproducible translations (maximum total point migration) of the center of the head. Three CT scans with varying levels of radiation were performed for each head position. The effective dose (mSv) was 3.8 mSv for Protocol A (standard protocol), 0.7 mSv for Protocol B and 1.6 mSv for Protocol C. Implant migration was measured in a 3-D analysis software (Geomagic Studio 7). The accuracy was 0.16 mm for CT Protocol A, 0.13 mm for Protocol B and 0.14 mm for Protocol C; The repeatability was 0.22 mm for CT Protocol A, 0.18 mm for Protocol B and 0.20 mm for Protocol C; ICC for inter observer reliability was 0.89, intra observer reliability was 0.95. The difference in accuracy between standard protocol A and the two low radiation protocols (B, C) was less than 0.05 mm. The accuracy, inter- and intra-observer reliability of all three CT protocols is comparable to radiostereometric analysis. Reducing the CT radiation exposure to numbers similar to an AP Pelvis radiograph (0.7 mSv protocol B) does not affect the accuracy of implant migration measurements.

A CT method for following patients with both prosthetic replacement and implanted tantalum beads: preliminary analysis with a pelvic model and in seven patients

BACKGROUND

Radiostereometric analysis (RSA) is often used for evaluating implanted devices over time. Following patients who have had tantalum beads implanted as markers in conjunction with joint replacements is important for longitudinal evaluation of these patients and for those with similar implants. As doing traditional RSA imaging is exacting and limited to specialized centers, it is important to consider alternative techniques for this ongoing evaluation. This paper studies the use of computed tomography (CT) to evaluate over time tantalum beads which have been implanted as markers.

METHODS

The project uses both a hip model implanted with tantalum beads, acquired in several orientations, at two different CT energy levels, and a cohort of seven patients. The model was evaluated twice by the same observer with a 1-week interval. All CT volumes were analyzed using a semi-automated 3D volume fusion (spatial registration) tool which provides landmark-based fusion of two volumes, registering a target volume with a reference volume using a rigid body 3D algorithm. The mean registration errors as well as the accuracy and repeatability of the method were evaluated.

RESULTS

The mean registration error, maximum value of repeatability, and accuracy for the relative movement in the model were 0.16 mm, 0.02° and 0.1 mm, and 0.36° and 0.13 mm for 120 kVp and 0.21 mm, 0.04° and 0.01 mm, and 0.39° and 0.12 mm for 100 kVp. For the patients, the mean registration errors per patient ranged from 0.08 to 0.35 mm. These results are comparable to those in typical clinical RSA trials. This technique successfully evaluated two patients who would have been lost from the cohort if only RSA were used.

CONCLUSIONS

The proposed technique can be used to evaluate patients with tantalum beads over time without the need for stereoradiographs. Further, the effective dose associated with CT is decreasing.

Is the use of thin, highly cross-linked polyethylene liners safe in total hip arthroplasty?

PURPOSE

Due to the high number of total hip arthroplasties (THA) revised due to instability, the use of large femoral heads to reduce instability is justifiable. It is critical to determine whether or not large femoral heads used in conjunction with thin polyethylene liners lead to increased wear rates, which can lead to osteolysis. Therefore, by using validated wear-analysis software, we evaluated linear wear rates in a consecutive cohort of patients who underwent primary THA with thin polyethylene liners.

METHODS

All patients were selected from a consecutive, prospectively collected database of 241 THAs performed at a single institution by two fellowship-trained joint-reconstruction surgeons between July 2007 and June 2011. These patients were 1:1 matched to a cohort of patients who had conventional-thickness polyethylene liners.

RESULTS

No significant differences were observed between linear wear rates of thin or conventional-thickness liners. The Kaplan-Meier survivorship for both cohorts was 100 %, and no cases of polyethylene fracture were observed in either cohort.

CONCLUSIONS

Our results suggest that according to a mean follow-up of 4 years, the use of thin liners in THA is promising. Longer follow-up is required to assess whether these outcomes are observed later.