Analysis of failed Van Straten LPM proximal interphalangeal prostheses

Failure of an ACCIS metal-on-metal hip resurfacing prosthesis: A case report

The introduction of coatings on joint replacements was intended to reduce wear volumes, prevent corrosion and reduce metal ion release. However, retrieval analysis to confirm their in vivo performance has been limited. The aim of study was to examine the coating on a retrieved hip prosthesis to determine whether substantial damage or wear had occurred. A single advanced ceramic-coated implant systems titanium niobium nitride-coated hip resurfacing prosthesis was retrieved for examination. Wear volumes and surface roughness were measured to quantify the damage to the articulating surfaces. The coating had been completely removed from substantial parts of both the femoral head and the acetabular cup, corresponding to areas of wear as measured by a coordinate measuring machine. The total wear rate (61 mm³/year) was high and corresponded with the high metal ion levels recorded pre-operatively (83 ppb chromium and 110 ppb cobalt). Roughness data indicated that the coating has a lower roughness than the substrate and substantially lower than the boundary between the coating and the substrate. The wear rate is very high and it is likely that damage to the coating resulted in accelerated wear of the prosthesis. No sudden change between the boundary of the substrate and the coating was observed that would indicate delamination or failure of the coating substrate interface layer. While coatings may offer some theoretical benefits, they may also result in catastrophic failure of the prosthesis.

Robert Mathys Finger prosthesis of the proximal interphalangeal joint: a retrospective case series of 19 joints in 17 patients

INTRODUCTION

The Robert Mathys (RM) Finger is a hinged type of arthroplasty for the metacarpophalangeal and proximal interphalangeal (PIP) joint that compensates ligament instability. The aim of this study is to evaluate the outcomes and complications of RM Finger arthroplasty of the PIP joint.

MATERIALS AND METHODS

A retrospective case series of 19 RM Finger arthroplasties of the PIP joint in 17 patients was performed with a median follow-up of 36 months. The active range of motion (AROM) was measured pre-operatively, at the 6-week follow-up, at the termination of hand therapy, and at the final follow-up. Complications were recorded, as well as pain on a visual analog scale (VAS), stability, deformity, pinch strength, the Michigan Hand Outcomes Questionnaire (MHQ), and the Patient Global Index of Improvement Questionnaire.

RESULTS

One implant fracture occurred. Another patient had an amputation due to stiffness. For the remaining joints, AROM was 61°. One joint mobilization under local anesthesia, one arthrolysis and two extensor tendon reconstructions were also necessary. Pain at the follow-up was 1.2 on the VAS. Relative pinch strength was 69%. Joint stability was restored in all fingers, although one joint had an ulnar deviation of 15°. Eight fingers developed a snapping phenomenon, of which five had a swan neck deformity. One finger had an extension lag with a Boutonnière deformity. MHQ scores were less compared to the unaffected hand. Fifteen patients rated their outcome as improved compared to their pre-operative condition.

CONCLUSIONS

RM Finger arthroplasty of the PIP joint restores joint stability with AROM improvement, and with low pain, although it has a high rate of complications.

LEVEL OF EVIDENCE

IV.

Chrome nitride coating reduces wear of small, spherical CrCoMo metal-on-metal articulations in a joint simulator

Metal-on-metal articulations have fallen out of favour in larger joint replacements, but are still used in smaller joints. Coating the articulation has been suggested as one way of reducing wear. We compared a standard 6 mm CrCoMo articulation designed for the carpometacarpal joint of the thumb with a chromium nitride-coated version after 512,000 cycles in a joint simulator. A total of 6 articulations in each group were tested with a unidirectional load of 5 kg in Ringer's solution. We found a statistically significant reduction in weight loss, amount of metallic wear produced and volumetric wear for the chromium nitride-coated articulation. Our findings support the use of chromium nitride coating in order to minimize the amount of metallic wear produced.

The design and development of a finger joint simulator

Artificial finger joints lack the long-term clinical success seen with hip and knee prostheses. In part, this can be explained by the challenges of rheumatoid arthritis, a progressive disease which attacks surrounding tissues as well as the joint itself. Therefore, the natural finger joints’ biomechanics are adversely affected, and consequently, this imbalance due to subluxing forces further challenges any prosthesis. Many different designs of finger prosthesis have been offered over a period of greater than 50 years. Most of these designs have failed, and it is likely that many of these failures could have been identified had the prostheses been appropriately tested prior to implantation into patients. While finger joint simulators have been designed, arguably only those from a single centre have been able to reproduce clinical-type failures of the finger prostheses tested in them. This article describes the design and development of a finger simulator at Durham University, UK. It explains and justifies the engineering decisions made and thus the evolution of the finger simulator. In vitro results and their linkage to clinical-type failures are outlined to help to show the effectiveness of the simulator. Failures of finger implants in vivo continue to occur, and the need for appropriate in vitro testing of finger prostheses remains strong.