Failure of bipolar hemiarthroplasty: a retrospective review of 31 consecutive bipolar prostheses converted to total hip arthroplasty.

Bipolar hemiarthroplasty has been widely used for the treatment of femoral neck fractures in elderly patients. Outcome studies show excellent results with near preoperative ambulation and lasting, painless hip function. However, what has only recently been considered is that, in some cases, failure of bipolar hemiarthroplasty may be due to wear of the thin, ultra-high-molecular weight polyethylene (UHMWPE) insert between the inner and outer bearings of the prosthesis with subsequent generation of particulate debris, periprosthetic osteolysis, and stem loos ening. We reviewed 31 consecutive bipolar hemiarthroplasties converted to total hip arthroplasties by a single surgeon between 1986 and 1994. The average time to failure was 38 months. Fifty-six percent of the cases showed radiographic evidence of osteolysis around the stem. Radiographic migration of the bipolar head of more than 1 mm into the pelvis, suggestive of cartilage wear, occurred in 67% of the cases. Among the patients with radiographic osteolysis and a loose stem at the time of revision, 92% showed a characteristic histiocytic and giant cell reaction to polyethylene particles in tissue obtained during surgery. The UHMWPE liners from the retrieved outer shells showed an average wear rate of 0.7 mm per year. Recent studies comparing bipolar to unipolar hemiarthroplasty show little difference between the two with regard to morbidity, mortality, or functional outcome. In light of our findings, it might be prudent to reconsider the design and indications for bipolar hemiarthroplasty.

The HIV-1 Nef protein as a target for antiretroviral therapy.

HIV-1 Nef is a peripheral membrane protein that affects both signal transduction and membrane trafficking in infected cells. Alterations in these cellular processes enhance the efficiency of viral replication and the pathogenesis of AIDS in vivo. The precise mechanisms by which Nef functions are not fully elucidated. Nef is not an enzyme but appears to act as a linker molecule, mediating a variety of protein-protein interactions. Structural, biochemical and mutational data have allowed tentative identification of the key interactive surfaces on Nef, their cellular partners and their roles in Nef activity. Nef contains an SH3-binding surface through which it can interact with cellular Src-family tyrosine kinases and/or activator molecules for small GTPases involved in signal transduction. This SH3-binding surface is important for the ability of Nef to facilitate the activation of host T-lymphocytes, a process which renders the cells more permissive for viral replication. Nef also contains two relatively unstructured, solvent-exposed loops, through which it interacts with the cellular proteins that coat vesicles involved in membrane trafficking. These surfaces are important for Nef-mediated alterations in the subcellular distribution of transmembrane proteins, a process which causes diverse effects, including the assembly of maximally infectious viral particles and viral evasion of the host immune system. These data provide precise molecular targets within the Nef protein. Molecules that bind these interactive surfaces are predicted to inhibit Nef activity and provide the basis for novel chemotherapeutic agents for the treatment of HIV-infection.

Treatment of isolated articular cartilage lesions of the medial femoral condyle. A clinical nad MR comparison of autologous chondrocyte implantation vs. microfracture.

Microfracture (MFX) and Autologous Chondrocyte Implantation (ACI) have been utilized in an effort to promote the regeneration of articular cartilage in the knee. The purpose of this study is first, to determine which of these two treatments yields the best clinical results and, second, to determine whether the MR appearance of treated cartilage lesions correlates with clinical outcome. Thirty-five patients with isolated articular cartilage lesions of the medial femoral condyle (MFC) were treated either with ACI (17 patients) or with MFX (18 patients, 19 knees). Patients were evaluated clinically using the modified Cincinnati Knee Questionnaire and with a physical exam. MRs were graded using eight different criteria: an MR score of 100% represents normal cartilage. The average follow-up was 2,6 years for the ACI group and 2,8 years for the MFX group. The average size of the lesion was 472 mm2 for the ACI group and 326mm2 for the MFX group. The Cincinnati scores improves an average of 22% for the ACI patients and 42% for the MFX patients from preoperatively to postoperatively. The average MR score was 66% for the ACI group and 44% for the MFX group. Fifty-nine percent of the ACI patients required at least one additional procedure. This is the first clinical and MR comparison of ACI and MFX to treat full thickness cartilage lesions of the MFC. Clinical improvement was 2 times greater for the MFX patients compared to the ACI patients. The MR scores did not correlate with clinical outcome using our grading system.

Ribosome assembly in three strains of Escherichia coli with mutations in the rpmB,G operon.

The rpmB,G operon of Escherichia coli codes for the synthesis of ribosomal proteins L28 and L33. In one mutant strain (TP28), these two proteins are made at about half their normal rates, ribosome assembly is greatly perturbed and precursor particles accumulate. The mutation in strain TP28 is in a Shine-Dalgarno sequence in the leader region of the rpmB,G messenger RNA. Another mutant, strain AM108, makes neither protein because it has the mobile element IS1 inserted into the rpmB coding sequence. Surprisingly, ribosome assembly in this strain is virtually normal with respect to growth rate. Strain AM90, which fails to make protein L33, has the element IS3 inserted into rpmG and also shows no major defects in ribosome assembly.