Comment on the Definition and Labeling of pK50

We propose a more rigorous definition for the recently introduced concept of pK50. The value of pK50 should be associated not with a "functional group", as originally postulated, but instead with an atom. The proposed clarification is meant to improve the interpretation and labeling of pK50.

Epik: pKa and Protonation State Prediction through Machine Learning

Epik version 7 is a software program that uses machine learning for predicting the pK_a values and protonation state distribution of complex, druglike molecules. Using an ensemble of atomic graph convolutional neural networks (GCNNs) trained on over 42,000 pK_a values across broad chemical space from both experimental and computed origins, the model predicts pK_a values with 0.42 and 0.72 pK_a unit median absolute and root mean square errors, respectively, across seven test sets. Epik version 7 also generates protonation states and recovers 95% of the most populated protonation states compared to previous versions. Requiring on average only 47 ms per ligand, Epik version 7 is rapid and accurate enough to evaluate protonation states for crucial molecules and prepare ultra-large libraries of compounds to explore vast regions of chemical space. The simplicity and time required for the training allow for the generation of highly accurate models customized to a program's specific chemistry.

Mechanistic Investigation of Dimethylmercury Formation Mediated by a Sulfide Mineral Surface

Mercury (Hg) pollution is a global environmental problem. The abiotic formation of dimethylmercury (DMeHg) from monomethylmercury (MMeHg) may account for a large portion of DMeHg in oceans. Previous experimental work has shown that abiotic formation of DMeHg from MMeHg can be facilitated by reduced sulfur groups on sulfide mineral surfaces. In that work, a mechanism was proposed in which neighboring MMeHg moieties bound to sulfide sites on a mineral surface react through an S_N2-type mechanism to form DMeHg and incorporate the remaining Hg atoms into the mineral surface. Here, we perform density functional theory calculations to explore the mechanisms of DMeHg formation on the 110 surface of a CdS(s) (hawleyite) nanoparticle. We show that coordination of MMeHg substituents to adjacent reduced sulfur groups protruding from the surface indeed facilitates DMeHg formation and that the reaction proceeds through direct transmethylation from one MMeHg substituent to another. Coordination of Hg by multiple S atoms provides a transition-state stabilization and activates a C-Hg bond for methyl transfer. In addition, solvation effects play an important role in the surface reconstruction of the nanoparticle and in decreasing the energetic barrier for DMeHg formation relative to the corresponding reaction in vacuo.

Synthesis of spirocyclic orthoesters by 'anomalous' rhodium(ii)-catalysed intramolecular C-H insertions

A tetrahydropyranyl acetal bearing a proximal phenyl diazoketone substituent underwent Rh(ii)-catalysed C-H insertion via an 'anomalous' C-O bond-forming, rather than C-C bond-forming, transformation, giving spirocyclic orthoesters. Density functional theory calculations with M06 show that the formation of these anomalous products involves hydride transfer to the rhodium carbene, giving an intermediate zwitterion which undergoes C-O bond formation in preference to C-C bond formation.

Catalytic Enantioselective [2,3]-Rearrangements of Allylic Ammonium Ylides: A Mechanistic and Computational Study

A mechanistic study of the isothiourea-catalyzed enantioselective [2,3]-rearrangement of allylic ammonium ylides is described. Reaction kinetic analyses using ¹⁹F NMR and density functional theory computations have elucidated a reaction profile and allowed identification of the catalyst resting state and turnover-rate limiting step. A catalytically relevant catalyst-substrate adduct has been observed, and its constitution elucidated unambiguously by ¹³C and ¹⁵N isotopic labeling. Isotopic entrainment has shown the observed catalyst-substrate adduct to be a genuine intermediate on the productive cycle toward catalysis. The influence of HOBt as an additive upon the reaction, catalyst resting state, and turnover-rate limiting step has been examined. Crossover experiments have probed the reversibility of each of the proposed steps of the catalytic cycle. Computations were also used to elucidate the origins of stereocontrol, with a 1,5-S···O interaction and the catalyst stereodirecting group providing transition structure rigidification and enantioselectivity, while preference for cation-π interactions over C-H···π is responsible for diastereoselectivity.

Toward Quantitatively Accurate Calculation of the Redox-Associated Acid-Base and Ligand Binding Equilibria of Aquacobalamin

Redox processes in complex transition metal-containing species are often intimately associated with changes in ligand protonation states and metal coordination number. A major challenge is therefore to develop consistent computational approaches for computing pH-dependent redox and ligand dissociation properties of organometallic species. Reduction of the Co center in the vitamin B12 derivative aquacobalamin can be accompanied by ligand dissociation, protonation, or both, making these properties difficult to compute accurately. We examine this challenge here by using density functional theory and continuum solvation to compute Co-ligand binding equilibrium constants (Kon/off), pKas, and reduction potentials for models of aquacobalamin in aqueous solution. We consider two models for cobalamin ligand coordination: the first follows the hexa, penta, tetra coordination scheme for Co(III), Co(II), and Co(I) species, respectively, and the second model features saturation of each vacant axial coordination site on Co(II) and Co(I) species with a single, explicit water molecule to maintain six directly interacting ligands or water molecules in each oxidation state. Comparing these two coordination schemes in combination with five dispersion-corrected density functionals, we find that the accuracy of the computed properties is largely independent of the scheme used, but including only a continuum representation of the solvent yields marginally better results than saturating the first solvation shell around Co throughout. PBE performs best, displaying balanced accuracy and superior performance overall, with RMS errors of 80 mV for seven reduction potentials, 2.0 log units for five pKas and 2.3 log units for two log Kon/off values for the aquacobalamin system. Furthermore, we find that the BP86 functional commonly used in corrinoid studies suffers from erratic behavior and inaccurate descriptions of Co-axial ligand binding, leading to substantial errors in predicted pKas and Kon/off values. These findings demonstrate the effectiveness of the present approach for computing electrochemical and thermodynamic properties of a complex transition metal-containing cofactor.

Computational Insights into the Central Role of Nonbonding Interactions in Modern Covalent Organocatalysis

The flexibility, complexity, and size of contemporary organocatalytic transformations pose interesting and powerful opportunities to computational and experimental chemists alike. In this Account, we disclose our recent computational investigations of three branches of organocatalysis in which nonbonding interactions, such as C-H···O/N interactions, play a crucial role in the organization of transition states, catalysis, and selectivity. We begin with two examples of N-heterocyclic carbene (NHC) catalysis, both collaborations with the Scheidt laboratory at Northwestern. In the first example, we discuss the discovery of an unusual diverging mechanism in a catalytic kinetic resolution of a dynamic racemate that depends on the stereochemistry of the product being formed. Specifically, the major product is formed through a concerted asynchronous [2 + 2] aldol-lactonization, while the minor products come from a stepwise spiro-lactonization pathway. Stereoselectivity and catalysis are the results of electrophilic activation from C-H···O interactions between the catalyst and the substrate and conjugative stabilization of the electrophile. In the second example, we show how knowledge and understanding of the computed transition states led to the development of a more enantioselective NHC catalyst for the butyrolactonization of acyl phosphonates. The identification of mutually exclusive C-H···O interactions in the computed major and minor TSs directly resulted in structural hypotheses that would lead to targeted destabilization of the minor TS, leading to enhanced stereoinduction. Synthesis and evaluation of the newly designed NHC catalyst validated our hypotheses. Next, we discuss two works related to Lewis base catalysis involving 4-dimethylaminopyridine (DMAP) and its derivatives. In the first, we discuss our collaboration with the Smith laboratory at St Andrews, in which we discovered the origins of the regioselectivity in carboxyl transfer reactions. We disclose how different Lewis base catalysts (NHC or DMAP) can lead to different regiomeric products as a result of differing magnitudes of aromatic and C-H···O interactions present in the respective transition states. In the second example, we discuss the mechanism and origins of the stereoselectivity of a reaction catalyzed by a planar-chiral 4-(pyrrolidino)pyridine derivative, namely, the coupling of ketenes with cyanopyrrole. We discovered that the chiral base mechanism is operative, in contrast to the originally proposed Brønsted acid mechanism. The selectivity is determined by the ease with which the major and minor TSs can realize strong stabilizing C-H···N interactions between the pyrrole cyano group and the catalyst. These interactions induce increased catalyst distortion in the minor TS, thereby leading to enantioselectivity. Finally, we discuss our computations related to amine-based organocatalysis in collaboration with the Carter laboratory at Oregon State. We probed the mechanism and stereoselectivity of a bifunctional amine thiourea-catalyzed Michael reaction. Our computations led to the design of an improved catalyst. However, synthesis and tests revealed that this catalyst was prone to degradation to side products that also catalyze the reaction, ultimately reducing the observed enantioselectivity. Lastly, we discuss our study of the mechanism and stereoselectivity of a proline sulfonamide-catalyzed Robinson annulation, in which we discovered that the enantioselectivity is controlled by the first Michael step but the diastereoselectivity is controlled by the following Mannich step.

Construction of Stereogenic α,α-Disubstituted Cycloalkanones via 1° Amine Thiourea Dual Catalysis: Experimental Scope and Computational Analyses

The mechanistic exploration and an expanded experimental discussion of the organocatalyzed, asymmetric Pfau-d'Angelo reaction by exploiting a bifunctional 1° amine thiourea catalyst system is disclosed. Notable breadth in substrate scope has been demonstrated on both the cyclic ketone moiety and the α,β-unsaturated electrophile. Exploration into the matched and mismatched selectivity of this process with a ketone containing pre-existing stereocenters has been demonstrated. Computational analyses of the reaction mechanism are reported. In concert with kinetic isotope effect (KIE) experiments, these computational results provide a detailed understanding of the likely mechanism, including the aspects of the organocatalyst scaffold that are critical for stereoselectivity.

Biosynthetic insights provided by unusual sesterterpenes from the medicinal herb Aletris farinosa

A series of novel sesterterpenes (2-6) have been isolated from the roots of Aletris farinosa and structurally characterized by MS, NMR, and X-ray crystallography in conjunction with computational modeling. Their structures provide new insights into the mechanisms of sesterterpene biosynthesis. Specifically, we propose with support from density functional theory computations that the configuration at a single stereocenter determines the fate of a key tetracyclic carbocationic intermediate, derived from an oxidogeranylfarnesol precursor. Whereas one epimer of the carbocation undergoes H⁺ elimination to give 6, the other undergoes a spectacular cascade of seven 1,2-methyl and hydride migrations leading to the previously unreported carbon skeleton of 5. Theoretical calculations suggest that the cascade is triggered by substrate preorganization in the enzyme active site.

A comparative study on the impact of two artemisinin derivatives, artemether and artesunate, on the female reproductive system of Fasciola hepatica

An in vivo study in the laboratory rat model has been carried out to monitor changes to the female reproductive system in adult Fasciola hepatica following treatment with the artemisinins, artemether and artesunate. Rats infected with the triclabendazole (TCBZ)-resistant Sligo isolate were dosed orally with artemether at a concentration of 200mg/kg and flukes recovered at 24, 48 and 72 h post-treatment (pt). Rats infected with the TCBZ-resistant Oberon isolate were dosed orally with artesunate at a concentration of 200mg/kg and flukes recovered 24, 48, 72 and 96 h pt. The flukes were processed for histological and transmission electron microscope (TEM) examination of the uterus, Mehlis' gland, ovary and vitellaria. After treatment with artemether, egg production had become abnormal by 72 h pt, with free vitelline cells and masses of shell protein material within the uterus; spermatozoa were absent. The Mehlis' gland and ovary retained a normal morphology over the 3-day period. A change in the cell population in the vitelline follicles was seen at 48 h pt, with a decline in the number of immature cells. This became more marked by 72 h and the follicles became progressively vacuolated over the 3-day period. At the TEM level, there were changes in the immature vitelline cells at 24h pt, as evidenced by a decrease in shell protein production and the presence of lipid droplets and abnormal mitochondria. Spaces in the follicles separated the cells from each other. The changes became progressively more severe with time, so that, by 72 h pt, the follicles were very disrupted, containing cells in the advanced stages of apoptotic breakdown. In extreme cases, the follicles were scarcely recognisable and had become filled with cellular debris. Fine structural changes to the vitelline cells induced by artesunate treatment were similar to those described for artemether, but generally occurred more quickly and were greater; this was particularly true of the swelling of the ger cisternae. Overall, the results have shown that artemisinin treatment has a severe impact on egg production by TCBZ-resistant flukes, an effect that is mediated by disruption of the vitelline cells.

AlCl₃-Catalyzed Ring Expansion Cascades of Bicyclic Cyclobutenamides Involving Highly Strained Cis,Trans-Cycloheptadienone Intermediates

We report the first experimental evidence for the generation of highly strained cis,trans-cycloheptadienones by electrocyclic ring opening of 4,5-fused cyclobutenamides. In the presence of AlCl3, the cyclobutenamides rearrange to [2.2.1]-bicyclic ketones; DFT calculations provide evidence for a mechanism involving torquoselective 4π-electrocyclic ring opening to a cis,trans-cycloheptadienone followed by a Nazarov-like recyclization and a 1,2-alkyl shift. Similarly, 4,6-fused cyclobutenamides undergo AlCl3-catalyzed rearrangements to [3.2.1]-bicyclic ketones through cis,trans-cyclooctadienone intermediates. The products can be further elaborated via facile cascade reactions to give complex tri- and tetracyclic molecules.

Functionalized cyclopentenes through a tandem NHC-catalyzed dynamic kinetic resolution and ambient temperature decarboxylation: mechanistic insight and synthetic application

An unusual room temperature β-lactone decarboxylation facilitated a five-step enantioselective formal synthesis of the cyclopentane core of an estrogen receptor β-agonist. A computational study probed the underlying factors facilitating unprecedented, rapid decarboxylation. Aryl substitution promotes faster reaction in the retro-[2+2] as a result of conjugative stabilization with the forming olefin. Additionally, the configuration of the α-ester in these fused β-lactones leads to differential decarboxylation rates.

Novel heterozygous ABCB4 gene mutation causing recurrent first-trimester intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy (ICP) typically presents in the late second or third trimester and carries an increased risk of fetal demise and neonatal morbidity and mortality. First trimester onset is rare and should alert the physician to explore a possible genetic basis for the disease. We present a 26-year-old Hispanic gravida 3, para 0202 with recurrent first-trimester onset ICP. Given her atypical history and presentation, a genetic cause was considered. She was found to have a novel heterozygous missense mutation in the ABCB4 canalicular membrane transport gene. First or early second trimester presentation of ICP should prompt investigation into genetic causes of the disease. Individualized family counseling and neonatal evaluation should be addressed if a disease-causing genetic mutation is diagnosed.

Torquoselective ring opening of fused cyclobutenamides: evidence for a cis,trans-cyclooctadienone intermediate

Electrocyclic ring opening of 4,6-fused cyclobutenamides 1 under thermal conditions leads to cis,trans-cyclooctadienones 2-E,E as transient intermediates, en route to 5,5-bicyclic products 3. Theoretical calculations predict that 4,5-fused cyclobutenamides should likewise undergo thermal ring opening, giving cis,trans-cycloheptadienones, but in this case conversion to 5,4-bicyclic products is thermodynamically disfavored, and these cyclobutenamides instead rearrange to vinyl cyclopentenones.

Catalytic Kinetic Resolution of a Dynamic Racemate: Highly Stereoselective β-Lactone Formation by N-Heterocyclic Carbene Catalysis

This study describes the combined experimental and computational elucidation of the mechanism and origins of stereoselectivities in the NHC-catalyzed dynamic kinetic resolution (DKR) of α-substituted-β-ketoesters. Density functional theory computations reveal that the NHC-catalyzed DKR proceeds by two mechanisms, depending on the stereochemistry around the forming bond: 1) a concerted, asynchronous formal (2+2) aldol-lactonization process, or 2) a stepwise spiro-lactonization mechanism where the alkoxide is trapped by the NHC-catalyst. These mechanisms contrast significantly from mechanisms found and postulated in other related transformations. Conjugative stabilization of the electrophile and non-classical hydrogen bonds are key in controlling the stereoselectivity. This reaction constitutes an interesting class of DKRs in which the catalyst is responsible for the kinetic resolution to selectively and irreversibly capture an enantiomer of a substrate undergoing rapid racemization with the help of an exogenous base.

Asymmetric homoenolate additions to acyl phosphonates through rational design of a tailored N-heterocyclic carbene catalyst

A highly selective NHC-catalyzed synthesis of γ-butyrolactones from the fusion of enals and α-ketophosphonates has been developed. Computational modeling of competing transition states guided a rational design strategy to achieve enhanced levels of enantioselectivity with a new tailored C1-symmetric biaryl-saturated imidazolium-derived NHC catalyst.

Synthesis and computational analysis of densely functionalized triazoles using o-nitrophenylalkynes

Dipolar cylcoadditions with azides using a series of o-nitrophenylethynes and disubstituted alkynes were studied experimentally and computationally. Density functional theory computations reveal the steric and electronic parameters that control the regioselectivity of these cycloadditions. Several new substrates were predicted that would either give enhanced regiocontrol or invert the regiochemical preference. Experimentally, the alkynes were screened in the [3 + 2] cycloaddition with benzyl azide. Of the 11 alkynes screened experimentally, the acetylenes containing halogen substitution directly on the alkyne provided the highest levels of regioselectivity. These haloalkynes were also shown to tolerate variation of the azide moiety with continued good levels of regioselectivity in most cases. Diverse functional groups can be incorporated through the cycloaddition process and their subsequent orthogonal modification was demonstrated.

Total hip arthroplasty with cement and without acetabular bone graft for severe hip dysplasia. A concise follow-up, at a minimum of twenty years, of a previous report

We previously evaluated a cohort of fifty-three patients with severe hip dysplasia (Crowe Type-II, III, or IV subluxation) who underwent a total of sixty-six Charnley total hip arthroplasties. The acetabular component was placed at the anatomic hip center, the superolateral defect was filled with cement, and no bone-grafting was used to supplement the acetabular wall. All but one patient, who was lost to follow-up, were followed until death or for a minimum of twenty years. Radiographic and functional follow-up data were collected prospectively. This retrospective review included twenty-four patients (thirty-four hips) who were alive at a minimum of twenty years following the surgery. Fourteen (22%) of the sixty-five hips underwent revision of a component, with eleven of the revisions performed because of aseptic loosening. Eight of those eleven hips underwent revision because of acetabular loosening alone; two, because of femoral loosening alone; and one, because of loosening of both components. The combined prevalence of revision because of aseptic loosening of the acetabular component and radiographic evidence of failure of the acetabular component was 28% (eighteen hips). With the numbers available, the need for acetabular revision was not associated with the percentage of cement coverage (p = 0.362) or the Crowe classification (p = 0.159). At a minimum of twenty years postoperatively, the survivorship of the acetabular component was 86% +/- 8% with revision because of aseptic loosening as the end point and 82% +/- 10% with revision because of aseptic loosening or radiographic evidence of loosening as the end point. The results that we evaluated at a minimum of twenty years after use of this technique can be compared with the results of other techniques in studies with similar long-term follow-up periods.

Comparison of femoral head penetration rates between cementless acetabular components with 22-mm and 28-mm heads

Between April 1993 and July 1994, the senior author (R.C.J.) performed 151 consecutive primary total hip arthroplasties using a Harris-Galante II acetabular component and a polished Iowa femoral component. In 105 hips, 22-mm head components were used, and in 46 hips, 28-mm head components were used. Femoral head penetration into the acetabular shell was measured using digital edge detection techniques. The group average penetration for the initial 2-year bedding-in period was 0.35 mm/y for the 22-mm and 0.31 mm/y for the 28-mm head components. The long-term rate of penetration into the shell was 0.11 mm/y for the 22-mm heads and 0.17 mm/y for the 28-mm heads, a significant difference (P=.029). The dislocation rate was significantly higher, however, with the 22-mm heads (P=.001). The 22-mm components showed significantly less wear but at the expense of an increase in the prevalence of dislocation.

Prevention of dislocation after hip arthroplasty: lessons from long-term followup

Regarding dislocation after total hip arthroplasty, prevention is worth an ounce of cure. The current authors evaluated dislocation after total hip arthroplasty during the 26-year practice of one surgeon to identify potential variables that can contribute to the prevention of dislocation. Between 1970 and 1996, dislocation after total hip replacement occurred after 7.2% of primary hip arthroplasty procedures (298 of 4164 primary hip replacements) and 11.2% of revision hip arthroplasty procedures (90 of 803 revision hip replacements). Significant findings included an increase in dislocation when 22-mm modular femoral heads were used and a decrease in dislocation after revision for dislocation when constrained liners were used. An additional finding was that 26% of first time dislocations occurred more than 2 years after surgery. Concerning prevention of dislocation, small head modular femoral components should be used cautiously, and constrained liners should be considered in complex revision cases. Patients should be counseled concerning the potential for dislocation many years after their arthroplasty.

Impaction allografting with cement for extensive femoral bone loss in revision hip surgery: a 4- to 8-year follow-up study

The current study evaluates the 4- to 8-year results of 26 cemented femoral revisions with impaction allografting using a collared femoral component in cases of extensive femoral bone loss. Patients were followed prospectively and were evaluated at an average of 6.0 years after the allograft revision procedure. The average age at the time of surgery was 69.3 years. At final follow-up, 20 patients (20 hips) were living, and 6 patients (6 hips) were deceased. No femoral component rerevisions were performed for any reason in any patient, and none were radiographically loose at final follow-up. There was 1 subsided femoral component of <5 mm, 3 postoperative periprosthetic femoral fractures, and a greater trochanter nonunion rate of 32%. At the current follow-up interval, these cemented femoral revisions with impaction allografting have performed well with excellent clinical and radiographic durability in this difficult patient population. The prevalence of periprosthetic fracture is a significant concern. This study shows durable results using the impaction allografting technique in cases of severe bone loss.

Charnley total hip arthroplasty with use of improved cementing techniques: a minimum twenty-year follow-up study

BACKGROUND

In total hip arthroplasty, techniques for cementing the femoral component have changed over time. The purpose of the present study was to determine whether a cementing technique that includes use of a distal cement plug and retrograde filling of the femoral canal affects the fixation of the femoral component at a minimum of twenty years after the operation.

METHODS

Between 1976 and 1978, the senior one of us (R.C.J.) performed 357 total hip arthroplasties with use of a Charnley flatback polished femoral stem and a contemporary cementing technique (insertion of a distal cement plug and retrograde filling of the femoral canal with cement) in 320 patients. The results after a minimum follow-up of twenty years were compared with those after 330 total hip arthroplasties performed, between 1970 and 1972, with the same femoral stem by the same surgeon with use of a hand-packing technique of cementing in 262 patients. The clinical and radiographic evaluation as well as the duration of follow-up were identical in the two groups.

RESULTS

In the group managed with the contemporary cementing technique, six (1.8%) of the 336 hips that had not been lost to follow-up or revised because of infection or dislocation were revised because of aseptic loosening of the femoral component. Of the ninety-one hips in the eighty-two patients who were alive at a minimum of twenty years, five (5%) had a revision because of aseptic loosening of the femoral component. Only one hip was revised during the fifteen-to-twenty-year follow-up interval. (The revision was performed because of a fracture of the femoral component.) The rate of failure when radiographic signs of loosening were included was 4.8% (sixteen of 336 femoral components that had not been revised because of infection or dislocation) for the group managed with the contemporary cementing technique compared with 6.3% (twenty of 319 hips) in the group managed with the hand-packing technique; the difference was not significant (p = 0.40). Adequate filling of the femoral canal with cement was found to be associated with improved survival of the femoral component (p = 0.03).

CONCLUSIONS

While no significant difference between the two cementing techniques could be identified, the ability to deliver adequate cement around the femoral component was more predictable with the contemporary cementing technique. In addition, the prevalence of loosening of the femoral component was low with use of either technique, a tribute to the Charnley flatback polished femoral component design.

Revision of a cemented acetabular component to a cementless acetabular component. A ten to fourteen-year follow-up study

BACKGROUND

Although cementless acetabular components are routinely used in revision hip surgery, few investigators have evaluated the retention and efficacy of these components in the long term. In the current study, the clinical and radiographic outcomes of a series of arthroplasties performed by one surgeon with a cementless acetabular component were assessed at a minimum of ten years.

METHODS

From 1986 through 1988, sixty-one consecutive revision total hip arthroplasties were performed in fifty-five patients because of aseptic failure of one or both components of a prosthesis in which both components had been cemented. Twenty-eight patients (thirty-two hips) were alive at a mean of 12.9 years (range, 11.5 to 14.3 years) after the operation. In all of the patients, the acetabular component was revised to a porous-coated Harris-Galante component inserted without cement, and the femoral component was revised to an Iowa component affixed with contemporary cementing techniques. The hips were evaluated clinically and radiographically at a minimum of ten years subsequent to the index revision. No hips were lost to follow-up.

RESULTS

None of the acetabular components required revision because of aseptic loosening. Two hips (3%) demonstrated radiographic evidence of aseptic loosening of the acetabular component. The polyethylene liner was exchanged during the follow-up period in eight hips.

CONCLUSION

After a minimum of ten years of follow-up, cementless acetabular fixation in revision hip arthroplasty had produced durable results that were markedly better than those reported for acetabular fixation with cement.

Experimental and computational simulation of total hip arthroplasty dislocation

Other than fatal pulmonary embolism and deep infection, dislocation following total hip replacement remains probably the most vexing complication to patient and surgeon. Subluxation and dislocation are complex, poorly understood phenomena. Many important questions in this area unfortunately do not lend themselves well to clinical or registry study. Appropriate realistic laboratory models have been lacking. This article synthesizes new work undertaken independently by two groups of biomechanical investigators using very different, but complimentary, methodologies to study the mechanisms of dislocation, and especially the influence of specific design and surgical variables.

Dislocation after total hip arthroplasty: a single surgeon's experience

The purpose of this article is to evaluate the dislocations that occurred in a single surgeon practice over a 26 year period. After extensive research, the authors concluded that dislocation continues to occur long after the initial arthroplasty procedure. Patients should be aware that more than a quarter of dislocations occur 2 years following surgery. Use of modular 22 millimeter components were associated with the highest dislocation rate. These components should be used very cautiously. Constrained liners have helped decrease the dislocation rate following revision for dislocation.

Cemented rotating-platform total knee replacement. A nine to twelve-year follow-up study

BACKGROUND

Although the LCS (low contact stress) rotating-platform mobile-bearing knee replacement has been used extensively, there have been few intermediate or long-term clinical and radiographic follow-up studies evaluating the device. The purpose of this study was to report the nine to twelve-year results of a consecutive series of patients who had a primary total knee replacement performed with this device.

METHODS

Between November 1985 and November 1988, the senior author (R. C. J.) performed 119 consecutive total knee arthroplasties in eighty-six patients with LCS rotating-platform femoral and tibial components and a Townley all-polyethylene dome patellar component. All components were fixed with cement. The average age of the patients at the time of the operation was seventy years (range, thirty-seven to eighty-eight years). Fifty-two patients (seventy-six knees) were female, and thirty-four patients (forty-three knees) were male. The patients were evaluated with clinical knee ratings and radiographic analysis nine to twelve years following the knee replacement.

RESULTS

At the time of the nine to twelve-year follow-up, sixty-four patients (eighty-six knees) were alive, eighteen patients (twenty-eight knees) had died, and four patients (five knees) had been lost to follow-up. Of the 114 knees in the eighty-two patients for whom the final outcome was known, none required a reoperation and none had a dislocation of the mobile-bearing prosthesis. For the forty-five patients (sixty-six knees) who returned for final clinical and radiographic follow-up examinations at nine to twelve years, the average clinical and functional Knee Society ratings were 30 points (range, 2 to 70 points) and 44 points (range, 0 to 80 points) preoperatively and 90 points (range, 63 to 102 points) and 75 points (range, 30 to 100 points) at the final follow-up evaluation. The average Hospital for Special Surgery knee rating was 57 points (range, 28 to 80 points) preoperatively and 84 points (range, 59 to 97 points) at the final follow-up evaluation. The average active range of knee flexion was from 0 degrees (range, 0 to 10 degrees) to 102 degrees (range, 15 to 120 degrees) at the final follow-up evaluation. Seven of the sixty-six knees were painful anteriorly. There was no periprosthetic osteolysis and no evidence of loosening on follow-up radiographs.

CONCLUSIONS

After nine to twelve years of follow-up, the cemented LCS rotating-platform knee replacement was found to be performing well, with durable clinical and radiographic results.

Charnley total hip arthroplasty with cement. Minimum twenty-five-year follow-up

BACKGROUND

This report presents the results of the senior author's initial twenty-five-year experience with the use of Charnley total hip arthroplasty with cement. The purpose of this paper was to evaluate the long-term results of total hip arthroplasty.

METHODS

Between July 1970 and April 1972, the senior author (R. C. J.) performed 330 Charnley total hip replacements with cement using a hand-packing cement technique in 262 patients. Fifty-one patients (sixty-two hips) who were alive at least twenty-five years post-operatively were evaluated from a clinical standpoint with use of a standard-terminology questionnaire. The average age of this group at the time of surgery was fifty-six years (range, thirty-five to seventy-one years) compared with sixty-five years (range, twenty-one to eighty-nine years) for the entire group. All patients were evaluated for radiographic changes at the time of their most recent follow-up. Of the fifty-one patients (sixty-two hips) who were alive at least twenty-five years postoperatively, thirty-one (thirty-six hips) had a follow-up radiograph made at a minimum of twenty-five years after the surgery. The average duration of radiographic follow-up for the fifty-one patients was 22.7 years (range, two to twenty-seven years).

RESULTS

Of the sixty-two hips in the fifty-one patients who were alive at least twenty-five years postoperatively, fourteen (23 percent) had been revised. Three (5 percent) had the revision because of loosening with infection; eleven (18 percent), because of aseptic loosening; and none, because of dislocation. The prevalence of revision due to aseptic loosening of the acetabular component in all 316 hips (excluding those that were lost to follow-up or that were revised for infection or dislocation) was 6 percent (eighteen hips), whereas the prevalence in the fifty-nine hips (excluding the three revised for infection) in the patients who were alive at least twenty-five years after the arthroplasty was 15 percent (nine hips). The prevalence of revision because of aseptic loosening of the femoral component in all 316 hips was 3 percent (nine hips), and the prevalence in the fifty-nine hips in the living patients was 7 percent (four hips). In the group of living patients, osteolysis occurred in Gruen zone 1 or 7 in thirty-three hips and in Gruen zones 2 through 6 in two hips. Ballooning acetabular osteolysis occurred in five hips. Of the 327 hips for which the outcome was known after a minimum of twenty-five years, 295 (90 percent) had retained the original implants until the patient died or until the most recent follow-up examination. Of the sixty-two hips in patients who lived for at least twenty-five years after the surgery, forty-eight (77 percent) had retained the original prosthesis.

CONCLUSIONS

Our follow-up study at twenty-five years following Charnley total hip arthroplasty with cement demonstrates the durability of the results of the procedure. These results should provide a means for comparison with the results of newer cementing techniques as well as those associated with newer cemented and cementless hip designs.

MAD3 encodes a novel component of the spindle checkpoint which interacts with Bub3p, Cdc20p, and Mad2p

We show that MAD3 encodes a novel 58-kD nuclear protein which is not essential for viability, but is an integral component of the spindle checkpoint in budding yeast. Sequence analysis reveals two regions of Mad3p that are 46 and 47% identical to sequences in the NH(2)-terminal region of the budding yeast Bub1 protein kinase. Bub1p is known to bind Bub3p (Roberts et al. 1994) and we use two-hybrid assays and coimmunoprecipitation experiments to show that Mad3p can also bind to Bub3p. In addition, we find that Mad3p interacts with Mad2p and the cell cycle regulator Cdc20p. We show that the two regions of homology between Mad3p and Bub1p are crucial for these interactions and identify loss of function mutations within each domain of Mad3p. We discuss roles for Mad3p and its interactions with other spindle checkpoint proteins and with Cdc20p, the target of the checkpoint.

The John Charnley Award. Practice surveillance: a practical method to assess outcome and to perform clinical research

The senior author systematically began collecting preoperative and postoperative data on all the total hip arthroplasties he performed starting in July 1970. The data collected represent a 26-year experience using practice surveillance (preoperative and regular interval postoperative collection and analysis of outcomes) as a method to document the outcome of the total hip arthroplasty procedure and as a method to evaluate the need for changes in the procedure. As the senior author made few selected changes in the operative procedure during the followup period, the primary author has been able to evaluate the change in outcome based on these changes. The six studies reported in the current study show the durability of the long-term results of cemented total hip arthroplasty, the improvement in radiographic reproducibility obtained on the femoral side of the construct with improved cementing techniques, the deleterious effects of using cable to reattach the greater trochanter, the deleterious effects of changing femoral component design that included a change in surface finish, the improvement in acetabular fixation using cementless fixation, and the optimization of bearing surface wear using smaller diameter femoral heads. All of these findings have been incorporated into the primary surgeon's practice based on this practice surveillance. As shown, practice surveillance also has provided a tool for performing clinical research. Although practice surveillance of controlled cohorts never will supplant prospective randomized clinical trials in evidence based medicine, it should help each surgeon with his or her own practice and can be used as an important research tool to study the optimization of outcomes of a surgical procedure.

One-stage revision surgery of the infected hip. A minimum 10-year followup study

Between 1977 and 1983, 24 one-stage revision surgeries were performed for septic failure of a total hip arthroplasty in 24 patients by one surgeon. Twelve patients died and none were lost to followup at a minimum of 10 years after the procedure. Infection reoccurred around two hips (8.3%). If the selected criteria (patients without draining sinuses, without immunocompromise, and with adequate bone quality after debridement) and the standard approach (meticulous debridement, use of antibiotic-impregnated cement, and use of 3 to 6 months postoperative oral antibiotic therapy) used in this study are implemented, direct exchange of an infected total hip arthroplasty construct is a reasonable and cost-effective alternative for some patients with infection after total hip arthroplasty.

Unicompartmental knee replacement. A minimum 15 year followup study

One hundred forty Marmor cemented unicompartmental knee replacements were inserted in 103 patients between 1975 and 1982. Fifty-two patients were women and 51 were men. One hundred twenty-five were medial compartment knee replacements and 15 were lateral knee replacements. At minimum 15 year followup 34 patients with 48 knee replacements were living; only four patients with four knee replacements were lost to followup. Average preoperative and final followup Hospital for Special Surgery knee scores were 57 and 82 points, respectively for the knees of living patients. Average preoperative and final followup Knee Society clinical and Knee Society functional scores were 31 and 42, and 85 and 71 points, respectively. For all knees, 10.2% (14 knees) were revised [4.4% (six knees) for tibial loosening, 5.1% (seven knees) for disease progression, and .7% (one knee) for pain]. For patients living 15 years, 12.5% (six knees) were revised [2.1% (one knee) for tibial loosening, and 10.4% (five knees) for disease progression]. Revision for failure of fixation of these unicompartmental replacements was comparable with that reported for fixed bearing total knee replacement. Disease progression (46%; 62 of 136 knees) and tibial subsidence with wear (10.4%; 15 of 136 knees, five of which required revision) were the major long term problems in this group of patients.

The effects of surface roughness and polymethylmethacrylate precoating on the radiographic and clinical results of the Iowa hip prosthesis. A study of patients less than fifty years old

BACKGROUND

The purpose of the present study was to compare the results associated with two different surface finishes (bead-blasted and grit-blasted) for Iowa femoral components used in total hip arthroplasties performed between January 1979 and June 1991 in patients who were less than fifty years old.

METHODS

Between January 1979 and December 1985, thirty-six primary total hip replacements were performed in twenty-five patients with insertion of a bead-blasted Iowa femoral component (average surface roughness, 0.8 micrometer) with cement and insertion of a titanium-backed acetabular component (thirty-five hips) or non-metal-backed acetabular component (one hip) with cement. Between January 1986 and June 1991, forty-five primary total hip replacements were performed in thirty-seven patients with use of a precoated grit-blasted Iowa femoral component (average surface roughness, 2.1 micrometers) and a Harris-Galante-I porous ingrowth acetabular component (forty-one hips) or an Osteonics component (four hips). The only change in the design of the femoral component (other than the surface finish) between the two consecutive series was the addition of polymethylmethacrylate precoating to the proximal third of all forty-five grit-blasted stems and modularity of the femoral head of the last eight grit-blasted stems.

RESULTS

No hip was lost to follow-up. The duration of radiographic follow-up of the hips treated with the bead-blasted component averaged 11.3 years (range, ten to sixteen years) postoperatively, whereas that of the hips treated with the precoated grit-blasted component averaged 8.2 years (range, five to eleven years). Two (6 percent) of the bead-blasted femoral components were revised because of aseptic loosening compared with eight (18 percent) of the precoated grit-blasted components. Four bead-blasted components (11 percent) were either radiographically loose or were revised because of loosening compared with eleven precoated grit-blasted components (24 percent). Kaplan-Meier survivorship curves evaluated with log-rank analysis revealed that the bead-blasted Iowa femoral components were revised because of aseptic loosening (p = 0.0184) and were radiographically loose (p = 0.0068) less often than the precoated grit-blasted Iowa femoral components.

CONCLUSIONS

The findings of the present study have led the senior ones of us to resume using femoral components with a polished surface and fixed with cement.

Total hip arthroplasty with cement in patients who have rheumatoid arthritis. A minimum ten-year follow-up study

One hundred and six consecutive total hip arthroplasties with cement were performed by one surgeon, at least ten years before the time of the present clinical and radiographic review, in seventy-five patients who had adult-onset rheumatoid arthritis. Two patients (three hips) were lost to follow-up. Seven (7 per cent) of the remaining 103 hips were revised. The revisions were performed because of infection (three hips), dislocation (two hips), or aseptic loosening (two hips). Of the ninety-eight hips that were not lost to follow-up or revised because of infection or dislocation, eight (8 per cent) had radiographic loosening of the acetabular component and two (2 per cent) had radiographic loosening of the femoral component. Although the prevalence of radiographic loosening of the acetabular component was four times greater than the prevalence of radiographic loosening of the femoral component, the prevalence of revision because of aseptic loosening of the acetabular component was identical to that for the femoral component (one component each). These results compared favorably with those of total hip arthroplasty with cement, performed by the same surgeon, for the treatment of other diagnoses. Loosening of the acetabular component was significantly associated with a younger age at the time of the index operation (p = 0.03) and with acetabular osteolysis (p = 0.0006). Of forty-eight hips in thirty-two patients who survived for at least ten years, 96 per cent (forty-six hips) were considered by the patients to have a satisfactory result. At the time of the latest follow-up, twenty-four (75 per cent) of the patients had no pain in the hip. Although eighteen patients (56 per cent) could walk without support at a minimum of ten years after the operation, we found that the functional results for patients who had rheumatoid arthritis were inferior to those observed for patients who had had a total hip arthroplasty with cement, performed by the same surgeon, for the treatment of other diagnoses.

Salvage of total hip instability with a constrained acetabular component

Between April 1988 and February 1993, 101 constraining acetabular components were implanted into 98 patients. One patient was lost to followup at 8 months. Otherwise, all patients were observed until death or for at least 2 years minimum followup. The average clinical followup for the living patients was 61 months (range, 24-97 months). Indications for the use of the constrained acetabular components were recurrent dislocation (an average of six dislocations, range 2-20) in 56 cases, intraoperative instability in 38 cases, and neurologic impairment in seven cases. For the entire group there were four cases of recurrent dislocation or failure of the component (4%). For the cases where this component was used for recurrent dislocation, 96% (54 of 56 cases) had no additional dislocations. Radiographically, at this short term followup, there was no evidence of an increased incidence of femoral or acetabular component loosening. The authors recommend judicious use of this component as a salvage measure for desperate cases of hip instability during or after total hip arthroplasty.

Hybrid total hip arthroplasty in patients under the age of fifty: a five- to ten-year follow-up

In 37 patients, 45 total hip replacements were performed using contemporary cementing techniques, an uncemented Harris-Galante I acetabular component and a cemented precoated Iowa femoral component in patients under the age of 50 at the time of their surgery; 36 patients with 43 hybrid hips were living, 1 patient with 2 hybrid hips was decreased. No patients were lost to follow-up. At 5- to 10-year follow-up, eight hips were revised for aseptic loosening. No acetabular components, and eight femoral components (18%) were revised for aseptic loosening. When looking at radiographic results, including revision as well as those components that were probably or definitely loose on radiographs, 0 acetabular components and 11 femoral components (24%) were radiographically loose. These results demonstrate the excellent durability of the uncemented Harris-Galante acetabular component in the younger patient. However, the Iowa grit-blasted methyl methacrylate precoated femoral component had a magnitude increase in the prevalence of revision for aseptic femoral loosening when compared to the senior author's long-term Charnley results in this age group. The authors attribute the failure to the rough surface finish applied to the femoral component. However, the polymethyl methacrylate proximal precoating and the femoral component design may also contribute to the femoral failures.

Charnley total hip arthroplasty in patients less than fifty years old. A twenty to twenty-five-year follow-up note

We evaluated the results twenty to twenty-five years after ninety-three consecutive, nonselected Charnley total hip arthroplasties performed with cement by the senior one of us in sixty-nine patients who were less than fifty years old at the time of the procedure. Seventy of the seventy-two hips in the living patients were followed radiographically for at least twenty years. Twenty-seven hips (29 per cent) had a revision or a resection of the prosthesis during the follow-up period. The revision or the resection was performed because of aseptic loosening in twenty-one hips (23 per cent), infection in four (4 per cent), dislocation in one (1 per cent), and fracture of the femur in one. Eighteen acetabular components (19 per cent) and five femoral components (5 per cent) were revised because of aseptic loosening, and an additional fourteen acetabular components (15 per cent) and seven femoral components (8 per cent) demonstrated definite or probable radiographic loosening. The present study demonstrates the long-term durability of total hip arthroplasty performed with cement in an active population of patients. The fixation of the femoral component was found to perform better than that of the acetabular component at twenty to twenty-five years after the procedure.

Salvage of a recurrently dislocating total hip prosthesis with use of a constrained acetabular component. A retrospective analysis of fifty-six cases

Fifty-six constrained acetabular components were placed, between April 1988 and February 1993, in fifty-five patients who had had recurrent dislocations (average, six dislocations; range, two to twenty dislocations) of the femoral component after a previous total hip arthroplasty. All patients had additional factors contributing to the instability of the implant, including absence or disruption of the abductor mechanism, poor health, mental retardation, confusion, and Alzheimer disease. One patient was lost to follow-up. The remaining patients were followed clinically for a minimum of three years (average, sixty-four months; range, thirty-seven to ninety-seven months) or until the time of death. During the follow-up interval, only two (4 per cent) of the fifty-five patients had a subsequent dislocation. The use of this type of component should be considered for patients who have recurrent dislocation if other treatment modalities are unlikely to be effective.

The Frank Stinchfield Award. Contribution of cable debris generation to accelerated polyethylene wear

The decision of the senior author of a large total hip replacement practice to switch from wire to braided cable for reattachment of the greater trochanter provided the opportunity to evaluate the long term effects (on acetabular component wear, osteolysis, and component loosening) caused by the introduction of metallic debris (generated by cable fretting and breakage) into the total hip arthroplasty construct. Seven hundred and nine consecutive primary total hip arthroplasties were performed during a 5-year period and followed up for a minimum of 10 years. Wire and cable reattachment of the greater trochanter was used sequentially. At minimum 10-year followup the cable group had significantly more wear, osteolysis, and acetabular radiographic evidence of loosening. Those involved in the design and use of total hip arthroplasty devices must minimize potential sources of metallic debris and other potential sources for third body wear in the total hip arthroplasty construct to help ensure longevity of the arthroplasty.

Total hip arthroplasty in the young adult

The durability of cemented and hybrid total hip arthroplasty in the young adult was evaluated. A consecutive series of primary cemented total hip arthroplasties performed between 1970 and 1976, and a consecutive series of primary hybrid total hip arthroplasties performed between 1986 and 1991, were evaluated for revision and radiographic loosening of the components. All patients were younger than 50 years of age at the time of surgery and all surgery was performed by one surgeon. At minimum 20 years followup of the cemented group (93 hips in 69 patients) 22% of hips (21 hips) were revised for aseptic loosening (5% of femoral components, five hips, and 19% of acetabular components, 18 hips). At 5- to 10-year followup of the hybrid group (45 hips in 37 patients) 18% of hips (eight hips) were revised for aseptic loosening (18% of femoral components, eight hips, and 0% of acetabular components, 0 hips). Although the cemented femoral component used in the hybrid series showed a marked increase in revision and loosening compared with the cemented series, the excellent fixation obtained with uncemented acetabular components has encouraged the authors to continue the use of hybrid fixation in the young adult. However, the femoral component has been modified to incorporate a polished surface finish and a stem geometry similar to the Charnley flat back prosthesis used in the cemented series.

Long-term results of revision total hip arthroplasty with improved cementing technique

We performed 83 consecutive cemented revision total hip arthroplasties in 77 patients between 1977 and 1983 using improved cementing techniques. One patient (two hips) was lost to follow-up. The remaining 76 patients (81 hips) had an average age at revision of 63.7 years (23 to 89). At the final follow-up 18 hips (22%) had had a reoperation, two (2.5%) for sepsis, three (4%) for dislocation and 13 (16%) for aseptic loosening. The incidence of rerevision for aseptic femoral loosening was 5.4% and for aseptic acetabular loosening 16%. These results confirm that cemented femoral revision is a durable option in revision hip surgery when improved cementing techniques are used, but that cemented acetabular revision is unsatisfactory.