NMR observation of exchangeable protons of pyridoxal phosphate and histidine residues in cytosolic aspartate aminotransferase

Observation of the 93-kDa cytosolic aspartate aminotransferase by 500-MHz 1H NMR spectroscopy in H2O has revealed a series of resonances in the 10-18 ppm range arising from exchangeable protons. One of these (peak A) has been assigned to the proton bound to the ring nitrogen of the coenzyme pyridoxal 5'-phosphate. A second (peak B) is assigned to H143 which participates in a chain of hydrogen bonds that includes also the coenzyme-bound proton. There is a mutual nuclear Overhauser effect between these two resonances. Peaks A and B respond to changes in pH and to interaction of the enzyme with coenzyme derivatives and inhibitors. Peak A moves from 15.4 to 17.4 ppm as the pH is lowered, while peak B moves in the opposite direction from 14.7 to 13.7 ppm, both with an apparent pKa of 6.15. This pKa is associated with deprotonation of the imine nitrogen at the Schiff base linkage of the coenzyme with K258 of the enzyme. In spectra of enzyme containing pyridoxamine 5'-phosphate, peak A is observed at 16.5 ppm and peak B is at 13.9 ppm over a broad pH range. Peaks A and B are found at 17.8 and 14.0 ppm, respectively, for the enzyme complex with glutarate. When alpha-methylaspartate is added to the enzyme several new resonances appear in the spectrum, which are attributed to formation of the external aldimine. The position of peak A in spectra of various forms of the enzyme is interpreted to reflect the electronic distribution in the coenzyme ring. Several other peaks in this region of the spectrum also are sensitive to changes in pH or the addition of inhibitors. Some possible assignments of these resonances are discussed.

Radiographic detection of metal-induced synovitis as a complication of arthroplasty of the knee

Radiographs of eighteen patients who had had a diagnosis of metal-induced synovitis subsequent to a knee-replacement arthroplasty were retrospectively reviewed. The presence of a dense line outlining a portion of the capsule or articular surface of the knee joint (the so-called metal-line sign) was noted in association with wear in eleven patients. In the nine patients who had a positive sign and also had specimens available for histological examination, there was dense deposition of metal particles, whereas in the six patients who did not have a metal-line sign and had specimens available for histological examination, five had only a slight amount of metal in the synovial tissue and one, a moderate amount. The presence of the metal-line sign was associated with metal-induced synovitis in eleven of the eighteen patients. The sign should be useful in helping to make this diagnosis preoperatively in many patients.

NMR spectra of exchangeable protons of pyridoxal phosphate-dependent enzymes

We have recorded 1H NMR spectra in H2O for exchangeable protons of four pyridoxal phosphate-dependent enzymes: D-serine dehydratase, aspartate aminotransferase, tryptophan: indole-lyase and glutamate decarboxylase. The molecular masses range from 48-250 kDa. In every case there are downfield peaks which are lost when the apoenzyme is formed. In most cases some peaks shift in response to interactions with substrates and inhibitors and with changes in pH. We associate one downfield resonance with the proton on the ring nitrogen of the coenzyme and others with imidazole groups that interact with coenzyme or substrates. The chemical shift for the coenzyme-bound proton differs for free enzyme, substrate Schiff base or quinonoid forms.

Capsular impingement as a source of pain following bipolar hip arthroplasty

Concerns regarding the extent and predictability of pain relief with bipolar hemiarthroplasty have been raised. Inconsistent clinical results have been reported, with persistent postoperative groin pain noted in some patients. A diverse number of bipolar operative techniques have been reported, but discussion of the surgical treatment of capsular tissue has usually been omitted. Although the source of postoperative pain is difficult to determine, the authors report the relief of groin pain after a capsulectomy in a patient with a preexisting bipolar hemiarthroplasty, thus offering one possible etiology.

The accuracy of tibial intramedullary alignment devices in total knee arthroplasty

The accuracy of a tibial medullary alignment device is assessed radiographically in 30 varus and 30 valgus knees undergoing total knee arthroplasty. The results suggest that although the device is reliable and accurate for varus knees, it may lead to malalignment of up to 5 degrees in valgus knees. Overall neutral alignment was achieved in 83% of the varus knees and 37% of the valgus knees. Tibial bowing was the main source of error and was present in 66% of the valgus knees, with mean of 3 degrees. Preoperative long films or cross-checking with external alignment devices is recommended to assure neutral alignment in genu valgus deformity.

Total shoulder arthroplasty versus hemiarthroplasty. Indications for glenoid resurfacing

The results of total shoulder arthroplasty and hemiarthroplasty in a similar patient population were compared in an effort to define more clearly the indications for resurfacing the glenoid. The results of 64 Neer hemiarthroplasties in 59 patients were compared with 146 Neer total shoulder arthroplasties in 134 patients in a retrospective review of the period between 1974 and 1986. The average follow-up period was 44 months (range, 24-124 months). Hemiarthroplasty and total shoulder arthroplasty produced similar results in terms of functional improvement. Pain relief, range of motion, and patient satisfaction were better with total shoulder arthroplasty than hemiarthroplasty in the rheumatoid population. Progressive glenoid loosening was found in 12% of total should arthroplasties but no correlation with pain relief or range of motion was noted. Total shoulder arthroplasty is recommended for patients with inflammatory arthropathies, and hemiarthroplasty is recommended for patients with osteoarthritis, avascular necrosis, and four-part fractures with preservation of glenoid congruity and absent synovitis.

Two- to four-year results of posterior cruciate-sparing condylar total knee arthroplasty with an uncemented femoral component

One hundred fourteen hybrid Press-Fit Condylar total knee arthroplasties (TKAs) were reviewed an average of 2.8 years after surgery to determine if this method of implantation provided satisfactory results compared with conventional cemented TKAs. Ninety-three percent of the knees had good or excellent results, and 94% of the knees had at most only mild or occasional pain. One knee with a metal-backed patella was revised for mechanical failure of the patellar button. Roentgenographic analysis of the femoral component interface showed that 30% of knees had a radiolucent line in at least one zone. However, none of the lines was wider than 1 mm, and none was about the central stem. There were no signs of loosening about any of the components. It was concluded that hybrid TKA provides a good and predictable result that is comparable to cemented TKA.

Bone loss in the distal anterior femur after total knee arthroplasty

Bone loss in the distal anterior femur in asymptomatic total knee arthroplasty (TKA) patients has been noted roentgenographically and during revision surgery. A retrospective roentgenographic review of 147 TKA cases was carried out to document bone loss. The influence that the mode of fixation (porous coated and cemented) and the implant design have on bone loss was examined. The time of onset and the progression of bone loss were studied. Bone loss occurred in the distal anterior femur in the majority of cases reviewed (68%). The prevalence of bone loss was independent of the mode of fixation and the implant design. By qualitative observation, roentgenographically detectable bone loss occurred within the first postoperative year and did not progress further. Previously three-dimensional finite element analysis demonstrated that the replacement of the bearing surface of the femur with a stiff metallic implant reduces the stress in the distal anterior femur by at least one order of magnitude. It is therefore speculated that the observed bone loss results from stress shielding. The apparent lack of progression may reflect the development of a new remodeling equilibrium under the altered stress conditions. The bone loss in the distal anterior femur described has not been implicated as a source of failure. However, since the bone strength in the femoral region is compromised as it becomes osteopenic, bone failure may occur with longer periods of cyclic loading. Furthermore, as a result of bone loss, revision arthroplasty may be more difficult.

Total hip and knee arthroplasty in juvenile rheumatoid arthritis

Total hip or knee arthroplasty is indicated in patients with juvenile rheumatoid arthritis when there is marked functional impairment and/or severe disabling pain from advanced structural hip or knee joint involvement. Relief of pain and dramatic improvement in function can be achieved in most patients. When both the hip and knee are involved, hip arthroplasty should probably be done first. Regional anesthesia is preferable. Careful preoperative planning is essential because custom prostheses are often required. Small bone size, osteoporosis, and soft-tissue contractures make the surgery technically demanding. Skeletal immaturity is not an absolute contraindication to surgery. Component loosening is the most frequent late complication in hip arthroplasty. It is less common in condylar metal-to-plastic knee arthroplasty in which patellar complications predominate. Cementless arthroplasty has an evolving role in the patient with juvenile rheumatoid arthritis and, to date, is more often used in the hip than in the knee.

Reconstruction of the deficient acetabulum using the bipolar socket

Although originally conceived as part of a two-stage procedure for the reconstruction of the deficient acetabulum, the use of a bipolar/grafting technique in selected patients can provide acceptable results as a definitive procedure. Critical technical considerations include proper preparation and grafting of the acetabular bed and careful sizing of the outer bipolar shell. Acceptable levels of pain relief and functional gain were obtained in 47 cases, with a follow-up mean Harris hip score of 86. Despite some initial socket migration in all hips, roentgenographic stability was gained after the first year. One acetabular failure was related to graft placement in the superolateral position. Bipolar reconstruction is indicated for contained acetabular defects only. In addition, the surgeon must have access to a complete inventory of socket sizes to ensure a proper fit and a bone bank to obtain adequate amounts of allogeneic bone.

Tibial tray augmentation with modular metal wedges for tibial bone stock deficiency

Peripheral defects in the proximal tibia can be difficult to treat during total knee arthroplasty. Attempts can be made to solve the problem with cement, cement with screws, bone grafts, metal wedges, and custom components. In vitro testing has shown that a custom-augmented prosthesis with a built-up metal wedge is mechanically superior in resisting deflections when loaded. Using modular metal wedges, the tibial tray can be customized at the time of surgery. In vitro testing has also shown the wedge to be superior to the use of cement alone or cement reinforced by screws. The authors report on modular metal wedges to augment tibial bone stock deficiency. Twenty-two knees (20 patients) were followed for a minimum of two years with an average follow-up time of 37 months. The average age of the patients at the time of surgery was 70 years. There have been no failures of this technique and no loosening of tibial components. The incidence of nonprogressive radiolucent lines was 27%. All but one patient was pain-free, and this patient's discomfort was not related to the tibial component fixation. No patient has had subsequent revision surgery. This technique should be considered in the treatment of severe peripheral tibial deficiencies in the elderly, low-demand patient.

Unicompartmental total knee arthroplasty

This article traces the evolution of unicondylar design and examines its indications, common aspects of surgical technique independent of design, results, and complications. The dichotomy of opinion concerning unicompartmental knee arthroplasty may reflect differences in patient selection, prosthesis selection, and surgical technique.

Blood supply to the patella. Significance in total knee arthroplasty

Patellofemoral problems occur in approximately 5% of total knee arthroplasties and account for 50% of complications of total knee arthroplasty. Surgical disruption of the blood supply to the patella may cause an increase in the incidence of osteonecrosis, stress fracture, and loosening. The authors discuss patellar blood supply and surgical considerations in total knee arthroplasty and review the clinical experience with avascular patellae.

Unicompartmental knee arthroplasty. A 4.5-6-year follow-up study with a metal-backed tibial component

The results in the first 50 patients to receive an improved-design unicompartmental knee prosthesis were reviewed after an average follow-up period of 5.5 years. The prosthesis is composed of a metal-backed polyethylene tibial component and a wide femoral surface replacement that are fixed to bone with acrylic cement. Forty-five patients with 55 unicompartmental knee arthroplasties were available for clinical study. Ninety-two percent of the knees were rated as having a good or excellent result, and 94% had lasting relief of pain. There have been no failures requiring revision. A radiographic review demonstrated that no tibial component was bordered by a complete radiolucent line. There was no subsidence or loosening of either the tibial or femoral components, and there was no instance of local osteolysis. These results, coupled with a 14-year follow-up experience with the original-design unicondylar prosthesis, encourages the authors to remain advocates of this procedure in selected patients with unicompartmental osteoarthritis.

Press-fit condylar total knee replacement

In 1984 the press-fit condylar knee was first introduced and was intended to provide a condylar knee system primarily for posterior cruciate retention that addressed refinements in metallurgy, prosthetic geometry and sizing, cementless fixation, inventory management, and instrumentation. This article addresses the results observed in the use of this prosthesis.

Surgical treatment of unicompartmental degenerative arthritis of the knee

The number of patients with unicompartmental osteoarthritis is increasing with the average age of our population. Good surgical techniques are available to improve pain and increase motion in the knee with degenerative disease. It is important to make early accurate diagnoses in arthritic patients so that the least surgically ablative procedure can be performed that will maximally benefit each patient. Total knee replacement is an extremely effective operation for relieving pain, but its major drawback is the large amount of bone stock that must be sacrificed during the procedure. Unicondylar knee replacement has proven itself to be an excellent alternative to total knee replacement in more limited arthritic disease. High tibial osteotomy still plays a major role as treatment for unicompartmental arthritis in younger and more active patients. McKeever interpositional hemiarthroplasty is an alternative in young patients when osteotomy is contraindicated. Arthroscopy is playing an increasing role in both diagnosis and treatment of unicompartmental osteoarthritis. The decision to perform unicompartmental arthroplasty, osteotomy, or total knee replacement is made on an individual basis. The extent of cartilage degeneration in the knee as well as the age, weight, and activity demands of the patient help to guide that decision.

Further observations on metal-backed patellar component failure

The clinical data, failure pattern, symptoms, roentgenographic findings, and failure mechanism of a series of 25 metal-backed patellar component failures are summarized. Diagnosis of implant failure was unknown prior to arthrotomy in seven of 25 cases (28%). Clinical findings and history were not helpful in making the diagnosis. Roentgenographic findings led to the diagnosis in 17 of 18 and were by far the most useful data. Metal-backed patellar component failure is a new complication of total knee arthroplasty and will be seen in increasing numbers. Caution is urged in implanting metal-backed designs until further design research is done.

Failure of the metal-backed patellar component after total knee replacement

Twenty-five patients had failure of a metal-backed patellar component after total knee replacement. Five manufacturers and seven designs were involved. There was no apparent correlation between failure of the component and the age or sex of the patient, the diagnosis, the use of cement, the femorotibial alignment, or the use of lateral release. The patients in whom the patellar implant failed were relatively heavy, and the diagnosis in most of them was osteoarthritis. The failure was due to one of two mechanisms: wear or fracture, or both, of the polyethylene over the edge of the metal backing (eighteen components), or dissociation of the polyethylene or the base-plate, or both, from the anchoring pegs (seven components). In many of the patients, failure of the component was not suspected before arthrotomy. The failure led to considerable wear of the femoral component in eleven patients and to metal-induced synovitis in twenty-three. We concluded that metal backing may predispose the patellar component to a small but important likelihood of failure, and we urge caution in choosing a metal-backed patellar implant. Additional research is necessary to improve designs for the patellar component, especially if metal backing is to be used.

The patellofemoral component of total knee arthroplasty

Patellofemoral complications continue to form a large proportion (up to 50%) of total knee arthroplasty (TKA) complications. If adequate attention is paid intraoperatively to patellar tracking and component position, the incidence of subluxation, component loosening, and fracture should decrease. When treating patellar subluxation and dislocation, tibial tubercle transfer should be avoided because there is an unacceptably high incidence of complications. Care should be taken to treat the underlying cause of dislocation with either a soft tissue procedure or component revision. Fracture of the patella may be treated nonoperatively in 50% and 80% of patients. Cysts, if large, may be bone-grafted to avoid the potential complications of stress fracture and component loosening. Loosening of the patellar component is likely to be symptomatic and to require surgery in up to 75% of cases. A displaced patellar component may cause attritional wear of the quadriceps tendon or patellar ligament. All rheumatoid patellae should be resurfaced. The present trend in the osteoarthritic patella is toward resurfacing more often. With improved implant design and a predicted decrease in complications, resurfacing in the osteoarthritic patella may become routine. Osteoarthritic patellae that maintain good cartilage, normal anatomic shape, and congruent tracking need not be resurfaced.

Diffuse contralateral pulmonary metastases in malignant mesothelioma. An unusual radiographic presentation

We describe a patient with malignant pleural mesothelioma involving the lung parenchyma bilaterally in a diffuse nodular fashion. This pattern of metastasis is seldom reported for this tumor.

Revision total knee arthroplasty

Revision total knee arthroplasty can be very successful if careful preoperative planning has been carried out and the surgeon is equipped to handle potential problems encountered with restoration of static alignment, stability, and deficient bone stock. Special femoral and tibial component extractors are indispensable tools. A high-speed burr is helpful. Posterior cruciate ligament-preserving prostheses often can be used, but prostheses with extra degrees of constraint must be available. Long-stemmed components for both the femoral and tibial sides should be available. Access to a bone bank to obtain allogeneic bone for grafting is essential. The surgeon must be familiar with techniques other than bone grafting for restoration of deficient stock, such as the use of bone screws and cement, custom-augmented components, and metal wedge spacers.