In vivo blood metal ion levels in patients after total shoulder arthroplasty.

BACKGROUND: Products from metal wear have been identified as a potential cause of adverse local tissue reactions and implant failure in total hip arthroplasty. However, the role of metal ion exposure in patients after total shoulder replacement is unclear. The objective of the present study was to determine in vivo blood metal ion levels of cobalt, chromium, and titanium in patients after anatomic total shoulder arthroplasty (TSA) or reverse TSA. METHODS: A consecutive series of patients after anatomic TSA or reverse TSA was evaluated retrospectively. After exclusion of patients with additional metal implants, 40 patients with unilateral anatomic TSA (n = 20) or reverse TSA (n = 20) were available for whole-blood metal ion analysis at a mean follow-up of 28 ± 9.6 months. Twenty-three healthy individuals without metal implants served as a control group. RESULTS: Mean cobalt ion concentrations were 0.18 µg/L (range, 0.1-0.66 µg/L), 0.15 µg/L (range, 0.03-0.48 µg/L), and 0.11 µg/L (range, 0.03-0.19 µg/L), mean chromium ion levels were 0.48 µg/L (range, 0.17-2.41 µg/L), 0.31 µg/L (range, 0.09-1.26 µg/L), and 0.14 µg/L (range, 0.04-0.99 µg/L), and mean titanium ion concentrations were 1.31 µg/L (range, 0.75-4.52 µg/L), 0.84 µg/L (range, 0.1-1.64 µg/L), and 0.62 µg/L (range, 0.32-2.14 µg/L) in the reverse TSA group, the anatomic TSA group, and the control group, respectively. CONCLUSIONS: TSA resulted in elevated metal ion levels compared with healthy controls, although overall metal ion concentrations measured in this study were relatively low. The role of local metal ion exposure in patients with total shoulder replacements should be further investigated.

Fixation pattern of conical and cylindrical modular revision hip stems in different size bone defects.

PURPOSE: Femoral defects often make it difficult to achieve sufficient fixation of the stem during revision surgery. No clinical studies comparing modular stems are available and differentiated recommendations are rare. The aim of this study was to compare the fixation of different revision stems in an experimental and standardised manner. METHODS: Segmental AAOS type I and III defects were reproduced in four femur pairs and two modular stems of different shape (cylindrical and conical) were implanted. Interfacial stem-bone movements were measured under axial torque application to analyze the stem fixation depending on defect extension. RESULTS: Both stems showed adequate fixation in AAOS type I defect. The defect extension significantly reduced the fixation of both implants. The fixation pattern changed significantly for the cylindrical-shaped stem but was maintained for the conical-shaped stem. CONCLUSIONS: Shape as well as the extension of femoral defect have an impact on primary fixation. A type I defect seems to be bridgeable for both stems albeit in a different way. In contrast, stem-demanding activities during the healing phase have to be avoided for the conical-shaped stem in a type III defect, whereas the cylindrical-shaped stem has already ceased to be sufficiently stable in this case.

Do short-stemmed-prostheses induce periprosthetic fractures earlier than standard hip stems? A biomechanical ex-vivo study of two different stem designs.

INTRODUCTION: The causes of periprosthetic fractures of the femur due to the design of the prosthesis and the individual parameters of the patient are unexplored. By different anchorage techniques in cementless total hip arthroplasties, it is assumed that there are various load limits of the implant's bearing femur. MATERIALS AND METHODS: In the present study, we compared a standard hip stem (cementless Spotorno) and a short-stemmed design (Mayo) by an artificial reproduction of periprosthetic fractures in 20 femur specimens. RESULTS: The measured fracture loads showed an extensive range, with higher maximum loads in the standard stem group. The bone mineral density and the subsiding pattern of the standard stems showed a significant correlation to the incidence of the periprosthetic fractures. In the experimental setup, a slightly lower fracture resistance was shown for the short-stemmed prosthesis. Additionally, it was shown that donors with a higher body mass index had a significantly increased fracture risk. CONCLUSIONS: Short-stemmed prostheses, especially the Mayo hip, do not constitute a higher fracture risk. In general, an increased body mass index among patients with a cementless hip stem is associated with an increased fracture risk, particularly at high load values, i.e., resulting from a step during stumbling. Taking into account the ascertained results, the danger of provoking a femoral periprosthetic fracture can be reduced.

Primary rotational stability of cylindrical and conical revision hip stems as a function of femoral bone defects: an in vitro comparison.

Bone stock losses in cementless femoral stem revisions compromise a stable fixation. The surgeon has to rely on his wealth of experience in deciding which stem shape to use. The aim of our study was to compare the primary rotational stability of cylindrical and conical revision hip stems subjected to femoral defects. Four current prostheses (two cylindrical, two conical) were implanted into four synthetic femora. Micro-motion was measured under torque application and femoral neck osteotomy and segmental AAOS Type I and III defects were simulated. The relative movements of all prostheses were significantly influenced by the extent of bone loss (p<0.01). Major differences were seen in fixation behavior (p<0.01). The main fixation area of conical stems is within the distal femoral isthmus, whereas cylindrical implants are dependent on proximal bone stock. In our study, cylindrical stems are advantageous for minor defects because they provide a proximal fixation. In cases of extensive substance loss, the conical implants showed lesser relative movements. These findings should be taken into account for clinical decisions.

Fracture load for periprosthetic femoral fractures in cemented versus uncemented hip stems: an experimental in vitro study.

This cadaveric study examined fracture loads in cemented and uncemented hip stems. Additionally, individual data and bone quality were analyzed and correlated to fracture patterns and fracture load. Cemented or uncemented hip stems were implanted in a randomized fashion in 10 matched paired fresh-frozen femora (donor median age, 78 years, and donor median weight, 74.2 kg). Bone density was measured before the femurs were fractured under load (maximum load of 10,000 N), and fracture patterns were analyzed according to the Vancouver and Johansson classification systems. In the uncemented group, all of the femurs fractured with a median load of 2625 N (range, 1725-7647 N). In the cemented group, 5 femurs fractured with a median maximum load of 9127 N (range, 2845-10,000 N) and 5 femurs did not fracture with a maximum load of 10,000 N. Fracture load corresponded to 4 times and 8.8 times body weight in the uncemented and cemented groups, respectively. Fracture patterns corresponded to Vancouver type A fractures in uncemented stems and Vancouver type C fractures in cemented hip stems. Analysis showed a significant correlation between fracture load and bone density in the uncemented group, whereas there was no correlation in the cemented group. Patients with poor bone quality treated with an uncemented hip stem are at higher risk for periprosthetic fractures; therefore, we recommend cemented stems in this group of patients. Cementation appears to protect against periprosthetic fractures, probably from internal stiffening of the femoral cavity.

Tibial revision knee arthroplasty: influence of modular stems on implant fixation and bone flexibility in AORI Type T2a defects.

BACKGROUND: Due to the varying bone defects presented to surgeons during revision total knee arthroplasty, modular implant systems are preferred over standard implant designs. However, every implant combination (sleeves, stems and augments) can affect the fixation in different ways and thus influence the long-term outcome. We therefore aimed to analyze the effect of large metaphyseal sleeves with and without short modular stems on implant fixation and bone flexibility of a modular tibial revision knee system. METHODS: A new tibial revision implant (Attune RP Revision; DePuy Synthes) with a sleeve was compared to a sleeve/stem combination implanted in synthetic bones with Anderson Orthopaedic Research Institute (AORI) Type T2a defects and also compared to an intact bone. Implant-bone-interface micromotions and bone deformations during standardized load application were measured using a digital image correlation system. RESULTS: The lowest relative micromotions were measured more distally for stemmed implants, and more proximally for the stemless group. When compared to an intact bone, there is increased proximal bone deformation in the stemless group. CONCLUSIONS: Using a short stem in addition to a tibial revision implant with a metaphyseal sleeve in a moderate bone defect provides for more natural bone deformation. Although the main fixation area was shifted distally, relative micromotions were reduced. Based on this biomechanical study, the use of diaphyseal short stems with metaphyseal sleeves seems to be beneficial in terms of the initial implant fixation and for its flexibility, which is similar to that of intact bones in the case of AORI T2a defects.