A Randomized and Clinical Effectiveness Trial Comparing Two Pharmacogenetic Algorithms and Standard Care for Individualizing Warfarin Dosing (CoumaGen-II)

Background—

Warfarin is characterized by marked variations in individual dose requirements and a narrow therapeutic window. Pharmacogenetics (PG) could improve dosing efficiency and safety, but clinical trials evidence is meager.

Methods and Results—

A Randomized and Clinical Effectiveness Trial Comparing Two Pharmacogenetic Algorithms and Standard Care for Individualizing Warfarin Dosing (CoumaGen-II) comprised 2 comparisons: (1) a blinded, randomized comparison of a modified 1-step (PG-1) with a 3-step algorithm (PG-2) (N=504), and (2) a clinical effectiveness comparison of PG guidance with use of either algorithm with standard dosing in a parallel control group (N=1866). A rapid method provided same-day CYP2C9 and VKORC1 genotyping. Primary outcomes were percentage of out-of-range international normalized ratios at 1 and 3 months and percentage of time in therapeutic range. Primary analysis was modified intention to treat. In the randomized comparison, PG-2 was noninferior but not superior to PG-1 for percentage of out-of-range international normalized ratios at 1 month and 3 months and for percentage of time in therapeutic range at 3 months. However, the combined PG cohort was superior to the parallel controls (percentage of out-of-range international normalized ratios 31% versus 42% at 1 month; 30% versus 42% at 3 months; percentage of time in therapeutic range 69% versus 58%, 71% versus 59%, respectively, all P <0.001). Differences persisted after adjustment for age, sex, and clinical indication. There were fewer percentage international normalized ratios ≥4 and ≤1.5 and serious adverse events at 3 months (4.5% versus 9.4% of patients, P <0.001) with PG guidance.

Conclusions—

These findings suggest that PG dosing should be considered for broader clinical application, a proposal that is being tested further in 3 major randomized trials. The simpler 1-step PG algorithm provided equivalent results and may be preferable for clinical application.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00927862.

The knee in full flexion: an anatomical study

There has been only one limited report dating from 1941 using dissection which has described the tibiofemoral joint between 120 degrees and 160 degrees of flexion despite the relevance of this arc to total knee replacement. We now provide a full description having examined one living and eight cadaver knees using MRI, dissection and previously published cryosections in one knee. In the range of flexion from 120 degrees to 160 degrees the flexion facet centre of the medial femoral condyle moves back 5 mm and rises up on to the posterior horn of the medial meniscus. At 160 degrees the posterior horn is compressed in a synovial recess between the femoral cortex and the tibia. This limits flexion. The lateral femoral condyle also rolls back with the posterior horn of the lateral meniscus moving with the condyle. Both move down over the posterior tibia at 160 degrees of flexion. Neither the events between 120 degrees and 160 degrees nor the anatomy at 160 degrees could result from a continuation of the kinematics up to 120 degrees . Therefore hyperflexion is a separate arc. The anatomical and functional features of this arc suggest that it would be difficult to design an implant for total knee replacement giving physiological movement from 0 degrees to 160 degrees .

Randomized Trial of Genotype-Guided Versus Standard Warfarin Dosing in Patients Initiating Oral Anticoagulation

Background— Pharmacogenetic-guided dosing of warfarin is a promising application of “personalized medicine” but has not been adequately tested in randomized trials.

Methods and Results— Consenting patients (n=206) being initiated on warfarin were randomized to pharmacogenetic-guided or standard dosing. Buccal swab DNA was genotyped for CYP2C9 *2 and CYP2C9 * 3 and VKORC1 C1173T with a rapid assay. Standard dosing followed an empirical protocol, whereas pharmacogenetic-guided dosing followed a regression equation including the 3 genetic variants and age, sex, and weight. Prothrombin time international normalized ratio (INR) was measured routinely on days 0, 3, 5, 8, 21, 60, and 90. A research pharmacist unblinded to treatment strategy managed dose adjustments. Patients were followed up for up to 3 months. Pharmacogenetic-guided predicted doses more accurately approximated stable doses ( P <0.001), resulting in smaller ( P =0.002) and fewer ( P =0.03) dosing changes and INRs ( P =0.06). However, percent out-of-range INRs (pharmacogenetic=30.7%, standard=33.1%), the primary end point, did not differ significantly between arms. Despite this, when restricted to wild-type patients (who required larger doses; P =0.001) and multiple variant carriers (who required smaller doses; P <0.001) in exploratory analyses, results (pharmacogenetic=29%, standard=39%) achieved nominal significance ( P =0.03). Multiple variant allele carriers were at increased risk of an INR of ≥4 ( P =0.03).

Conclusions— An algorithm guided by pharmacogenetic and clinical factors improved the accuracy and efficiency of warfarin dose initiation. Despite this, the primary end point of a reduction in out-of-range INRs was not achieved. In subset analyses, pharmacogenetic guidance showed promise for wild-type and multiple variant genotypes.

Acetabular revision with the Burch-Schnieder antiprotrusio cage and cancellous allograft bone

A retrospective review of 25 patients who underwent 28 acetabular revisions with the Burch-Schnieder antiprotrusio cage (Protek, Berne, Switzerland) and cancellous allograft bone was performed. Follow-up periods averaged 33 months. Patients had averaged 2.1 prior operations per hip. Twenty-two hips had American Academy of Orthopaedic Surgeons type III (combined segmental and cavitary bone loss) acetabular deficiency. Five hips had type II (cavitary bone loss) and one hip had type I (segmental bone loss) acetabular deficiency. After surgery, 80% of the patients had mild or no pain and 80% functioned as at least a community ambulator. Radiographic analysis included a detailed study of implant migration and the degree to which the hip center and bone stock were restored. Significant component migration was documented in 14% of the acetabular reconstructions. The hip center was improved from a preoperative side-to-side difference of 12.5 mm to 4.9 mm at final evaluation (P = .01). Average medial wall bone stock was improved from 1.9 mm before surgery to 10.1 mm postrevision (P < .01). No patients required revision of the antiprotrusio cage for problems related to the acetabular reconstruction. For failed acetabular components associated with moderate to massive bone loss, the antiprotrusio cage reliably reconstituted the hip joint center and acetabular bone stock. The short-term incidence of mechanical loosening parallels that of previously reported acetabular reconstruction techniques.

The patellofemoral joint in total knee prostheses. Design considerations

Some desirable design features of the patellofemoral joint in a total knee arthroplasty condylar prosthesis are proposed. These are that the femoral element should be grooved, have a high anterior flange, and be circular as viewed from the side. The groove should be about 5 mm deep and have relatively vertical walls. The patellar component should have a saddle-shaped articular surface matching the femur and should be countersunk into the patella. The components should be placed so as to position the joint automatically. Results with such a design are reported; loosening, wear, dislocation, and fracture have been rare. Osteolysis of the patella has not been seen after 9 years, so that the cementless press-fit fixation of an H.D.P. patellar prosthesis to date seems safe and efficacious.

Homograft bone in revision acetabular arthroplasty. A clinical and radiographic study

Thirty-seven patients with extensive acetabular defects due to loose implants had revisions with uncemented components, the acetabulum being augmented with homograft bone. In six of these, a histological study of graft incorporation was made. At a mean follow-up of 1.5 years 34 patients were free of pain and 35 could walk for 30 minutes or longer. No graft had obviously sequestrated. Two components had radiological evidence of migration but remain asymptomatic. We conclude that cementless revision surgery with homograft supplementation of the acetabulum is clinically successful in the short-term. The long-term outcome is unknown.

Bone grafting and noncemented revision arthroplasty of the knee

Revision of failed cemented total knee arthroplasties with cementless stemmed components and allogeneic bone grafts was performed on 22 patients, with clinical results comparable to those in primary arthroplasty. On roentgenograms, most of the allogeneic grafts appeared to be incorporated in the host bone. Various bone reactions not fitting any particular pattern, occurred around the stems.

Knee arthroplasty at the London Hospital. 1975-1984

In the past ten years, three related prostheses (Freeman-Swanson, ICLH, Freeman-Samuelson) have been used at the London Hospital. The new findings reported in this article are the result of cementless fixation of the ICLH prosthesis has not deteriorated with time; the patellofemoral complications and postoperative limitation of movement seen with the ICLH prosthesis has been resolved by the Freeman-Samuelson design; and cementless press-fit fixation of all three components of the Freeman-Samuelson design resulted in a 1.6% (tibial) revision rate in the first four years.

Stemmed revision arthroplasty for aseptic loosening of total knee replacement

Fifty-three failed knee replacements were revised using minimally constrained implants with smooth uncemented intramedullary stems and metal-backed tibial components. Polymethylmethacrylate was used only to replace lost bone near the surface of the implant. Excluding four knees which had serious postoperative complications, 91% had successful relief of pain, 84% had over 90 degrees of movement and 80% could walk for more than 30 minutes. Review of the radiographs showed that there were no progressive lucencies at the interface between bone and cement, and no subsidence of components or changes in alignment. At the uncemented stem-to-bone interface, thin white lines developed near the metal, and their significance is discussed. This revision technique is an effective treatment for aseptic failure of primary total knee arthroplasty.

Freeman-Samuelson total arthroplasty of the knee

Experience with cementless fixation over the last six years indicates that the technique offers greater opportunities for bone conservation. Thus, when cement is used, and especially if it is forced into the skeleton under pressure, the amount of bone incorporated into the implant is considerable. Conversely, if no cement is used, grafting techniques to fill defects are becoming increasingly routine, so that today no bone may be removed from the replaced knee or hip--all fragments that are excised are repositioned as grafts in defects. Thus, cementless fixation meets the fundamental orthopedic maxim of the conservation of bone stock. Given that an implant can be fixed with satisfactory clinical results without cement and without bone ingrowth, it becomes difficult to demonstrate a clinical advantage for the latter. Nevertheless, bone ingrowth is possible both experimentally and (with less confidence) in man. Thus, it is clearly a technique that should be evaluated. However, it is not, in the senior author's view, a technique that should as yet be generally used. Hopefully, investigations of this problem will take place in a restrained scientific way rather than by the current method, which is in response to the dictates of fashion and commerce.

Implant arthroplasty in the adult hindfoot

In patients with mild to moderate valgus deformity and localized pain due to lateral impingement, the subtalar implant has been effective in controlling position and relieving localized pain. When used in conjunction with a talonavicular resurfacing prosthesis in the absence of talonavicular subluxation, the implant has been effective in relieving pain and maintaining the foot in a normal or nearly normal position. In feet with valgus deformity and talonavicular subluxation, both the subtalar implant and the talonavicular prosthesis with a built-in stop must be used. Use of these implants requires that the foot be supple and correctable to at least neutral position at surgery. The valgus hindfoot with a subluxated but otherwise normal talonavicular joint presents a greater problem. In this condition correction can be maintained only if the subtalar implant is used in conjunction with the modified talonavicular joint with a built-in stop. External supports in the shoe have not been routinely used in all patients after operation for a variety of reasons (mostly nonmedical). It may be advisable in patients who have had correction of a deformity to continue to use some sort of support in the shoe for most ambulation. Arthroplasty early in the disease course, before severe deformities develop, may prevent progression of the disorder, but more experience is necessary to validate clinical impressions.

Development and evolution of the ICLH ankle replacement

In 1972 the original ICLH ankle was first used clinically, and since then the authors have implanted 75 ICLH ankles. The overall percentage of acceptable results in this series is about 70%. The most frequent complication seen was delayed wound healing. Talomalleolar contact with resultant pain was a significant problem early in the series. Partial collapse of the talus has occurred in five ankles. Our experience has shown that it is possible to replace the ankle and initially achieve a functioning, pain-free arthroplasty. There are many factors that may adversely influence the ultimate outcome; and thus, the procedure should be approached with caution.

Talonavicular joint surface anatomy and prototype resurfacing prostheses

The curvature and extent of a joint surface largely determine the type and range of motion possible. The talonavicular surface anatomy of 10 human foot specimens has been determined quantitatively, and the data have been compared with the design parameters for a prototype prosthetic joint. It was found that, in general, the natural talus as compared with the navicular was slightly larger in surface area and in mean arc length, but slightly smaller in mean radius of curvature. The arc length of the joint was found to be generally slightly longer along an axis positioned from slightly medial of dorsal to slightly lateral of ventral. In contrast, no general orientation of the radius of curvature was observed. Also, it was found that the congruency between the talus and navicular surfaces, as indicated by corresponding radii of curvature, varied widely. In comparison to the human specimens, a previously designed prototype talonavicular prosthesis proved somewhat smaller in radius, arc length, and surface area. Experimental studies related to other prosthesis design parameters, besides type and range of motion, are in progress.

Investigation of lateral ankle ligament reconstruction

The problem of chronic instability of lateral ankle ligaments has been approached with both conservative and surgical measures. Many operative procedures have been devised to correct this problem, and of these the Watson-Jones, modified Elmslie and Evans procedures are the most commonly used in our community. This paper was designed to: 1) compare the results of the three procedures; 2) investigate subtalar motion in a population of uninjured ankles; and 3) compare these results to subtalar motion in ankles after lateral ligament reconstruction. We found that each of the three procedures had a surprisingly high incidence of postoperative pain. All procedures had a high rate of return to preinjury activity level, and the majority of the patients were satisfied with the results of the operation. Postoperatively, the Watson-Jones repair exhibited the highest percentage of subjective instability. Twenty-four per cent of the Watson-Jones repairs had a postoperative talar tilt greater than 5 degrees. It was determined that subtalar motion was affected by the type of reconstructive procedure, and although this fact had been theorized in the literature, it had not been documented by objective data.

A roentgenographic technique to evaluate and document hindfoot position

The position of the posterior portion of the foot is difficult to evaluate and document on the basis of clinical examination. Conventional roentgenographic techniques also do not allow objective determination of hindfoot position. A new roentgenographic technique utilizing a double-exposure has been developed to allow accurate documentation of the position of the calcaneus relative to the ankle. Normal adult values for this technique have been determined from 60 normal feet.

Localized nodular synovitis of the knee: a case report

A 25-year-old man with chronic swelling of the right knee had a mass that was eventually palpated in the suprapatellar pouch. Arthrotomy and biopsy revealed localized nodular synovitis. Since surgical excision of the mass the patient has been asymptomatic. While localized nodular synovitis generally appears as an internal derangement of the joint, this patient had signs and symptoms of chronic monoarthritis.

Pes cavovarus. Review of a surgical approach using selective soft-tissue procedures

This study reviews the surgical treatment of twenty-seven patients (thirty-nine feet) with cavovarus foot deformity. The patients' ages ranged from six months to fifteen years. Only those patients who had at least a two-year follow-up were selected for statistical analysis. This group comprised twenty patients (twenty-seven feet). A standardized treatment program was used, based on the flexibility of the deformity. A radical plantar or plantar medial release was employed as indicated, in combination with tendon transfers or osteotomy of the fore part of the foot, or both. All patients were available for follow-up examination and special roentgenograms of the hind part of the foot. Follow-up appraisal of the patients with more than two years' follow-up revealed more than 85 per cent acceptable results with no major complications.

Analysis of foot position in ankle arthrodesis and its influence on gait

This study was carried out on 24 patients who underwent 25 ankle fusions. Twenty-four of 25 ankles operated upon by eight different surgeons achieved a solid fusion. A review showed that when the ankle was fused in a neutral position, the patient would, on the average, have 10 degrees of plantar flexion occurring in the midfoot. This motion allowed him to wear most normal foot gear. In gait, the plantar flexion in the foot approximated the plantar flexion in the normal ankle, giving little difficulty. In contrast, those individuals whose ankle was fused in 10 degrees of plantar flexion who also had 10 degrees of plantar motion in the midfoot and no dorsiflexion motion in the midfoot were, in effect, in 10 degrees of equinus. These patients showed a vaulting pattern while ambulating barefoot, but were usually able to accommodate this position while wearing shoes. The patient with a neutral position of the foot and ankle showed a very satisfactory gait in shoes and a much improved barefoot gait. It is concluded that fusion in a neutral position is indicated and that midtarsal motion occurs in the plantar direction but that no dorsiflexion is present in the midtarsal area.

Ligament injuries in the knees of children

Injuries of the medial collateral ligament in children are rarely reported. We are describing six tears of the medial collateral ligament in which an operative repair was done. The patients' ages were six to eleven years. Five were boys and one, a girl. The follow-up (seven months to thirteen years) showed normal results in three; good, in two; and fair, in one. Three patients also had had an injury to the anterior cruciate ligament or an avulsion injury to the anterior tibial spine.

Nontraumatic myositis ossificans in healthy individuals

Myositis ossificans has been subclassified into three categories: traumatic, progressive, or those cases associated with neuromuscular and chronic disease. Four cases of myositis ossificans occurred in otherwise healthy individuals without any history of trauma. These four patients illustrate a fourth and distinct subclassification of the disease.