Robert G. Volz

The mechanical stability of various noncemented tibial components.

Four different porous-coated tibial prosthetic implants were tested for their mechanical stability following implantation into paired cadaver tibias: Porous Coated Anatomic (PCA), Miller-Galante, Whiteside, and Anatomic Modular Knee (AMK). Following implantation the test sample was loaded eccentrically over the medial tibial plateau at 40 cycles per minute for 300,000 cycles, using an MTS machine. This represents the number of steps taken by the average person in a six- to 12-month period. Load varied sinusoidally from 5 to 115 kg. Subsidence and lift-off of the tibial plate from its bony bed was recorded for each implant, using linear variable differential transformers. The greatest degree of mechanical stability was observed with the AMK design, which is secured to the bone bed using four peripherally placed 6.5-mm cancellous screws. No motion in excess of 100 micron was observed. The central-stemmed Whiteside design and the cortical screw fixated Miller-Galante designs provided slightly less stability, each demonstrating approximately 200 micron of lift-off on the unweighted side. The PCA design exhibited the greatest amount of micromotion with subsidence and lift-off displacements of 500 micron (0.5 mm).

Comparison of the subvastus and paramedian surgical approaches in bilateral knee arthroplasty

A prospective randomized study was performed on 20 patients undergoing one-stage bilateral knee arthroplasty. One knee was exposed using a standard median parapatellar arthrotomy and the other knee with a subvastus arthrotomy. All patients underwent quantitative strength testing before surgery and at 1 week, 1 month, and 3 months after surgery. The knees were also evaluated for range of motion, and patients, who were blinded as to the approach used, completed questionnaires at each evaluation period as to their preference, if any, regarding knee pain and level of function. There was no difference in the range of motion between knees exposed with the paramedian or subvastus arthrotomy at any time period. The subvastus knees demonstrated significantly greater strength at the 1-week and 1-month intervals, but there was no strength difference at the 3-month interval. There were more lateral releases performed in the paramedium knees, and three minor complications were related to the subvastus approach. Patients who expressed a preference chose the subvastus knee 4:1 over the paramedian knee. The subvastus approach offers a reasonable alternative to the paramedian arthrotomy and preserves greater quadriceps strength in the early postoperative period.

Biomechanics of the wrist.

The wrist joint is a complex linkage between forearm and hand which is capable of an impressive arc of motion yet retaining a remarkable degree of stability. Carpal stability is derived from numerous intra-and intercarpal ligaments in addition to closely approximated wrist flexors and extensors. Motion occurring at the carpus is predominantly biplane--radial ulnar deviation and palmar flexion and extension. The center of motion for these planes of movement is located within the proximal and palmar pole of the capitate. When painful conditions arise at the wrist, a loss of wrist motion usually follows. Occasionally a loss of volitional control over wrist extensors is noted with the abnormal recruitment of wrist flexors with finger flexor activity. When instability and pain co-exist at the wrist, deformity can arise as a result of the inherent motor imbalance noted between the 6 wrist motors. Vector force analyses disclose that the flexor carpi ulnaris is the dominant wrist motor with the least significant force being supplied by the extensor carpi radialis longus. Although wrist motion is not essential for most activities of daily living, the preservation of wrist motion is for some individuals essential for the performance of specific occupational or recreational activities.

The development of a total wrist arthroplasty.

For many individuals the preservation of wrist motion is essential for augmentation of fine motor control of the hand and fingers. When significant functional disability exists at the wrist, currently available surgical treatment includes soft tissue arthroplasty, carpectomy, or arthrodesis. A total wrist joint arthroplasty offers the patient the potential of a pain-free, stable, and mobile wrist. Based upon the principles of total joint replacement as applied to the hip and knee, the prosthesis is secured to the carpus and radius with methylmethacrylate cement, following removal of the navicular, lunate, and head of the capitate. The design of the prosthesis provides for the two planes of motion normally seen at the wrist; 90 degrees of flexion and extension and 50 degrees of radial ulnar deviation are permitted by the design. Candidates for total wrist arthroplasty are patients who exhibit far-advanced disease at the wrist and who might be considered as candidates for arthrodesis, but in whom the permanent loss of motion would represent a significant handicap. To date 17 arthroplasties have been performed in 14 patients. The longest follow-up is 14 months. All but 2 patients have gained a useful range of motion. All patients have noted dramatic relief of pain and deformity, permitting them to perform tasks which were preoperatively impossible.

The role of fixation and bone quality on the mechanical stability of tibial knee components

Tibial component loosening remains one of the major causes of failure of cemented and noncemented total knee arthroplasties. In this study, the authors identified the role of implant design, method of fixation, and bone density as it related to implant stability. The physical properties of “good” and “bad” bone were simulated using a “good” and “bad” foam model of the proximal tibia, fabricated in the laboratory from DARO RF-100 foam. A generic tibial component permitting various fixation designs was implanted into “good” and “bad” variable density foam tibial models in both cemented and noncemented modes. The mechanical stability of the implants was determined using a Materials Testing Machine by the application of an eccentrically applied cyclic load. The micromotion (subsidence and lift-off) of the tibial implants was recorded using two Linear Variable Differential Transformers. Statistically significant differences in implant stability were recorded as a function of fixation method. The most rigid implant fixation was achieved using four peripherally placed, 6.5-mm cancellous screws. The addition of a central stem added stability only in the case of “poor” quality foam. The mechanical stability of noncemented implants related directly to the density of the foam. Implant stability was greatly enhanced in “poor” quality foam by the use of cement. The method of implant fixation and bone density are critical determinants to tibial implant stability.

Bilateral total knee replacement under one anesthetic.

The postoperative results and complications among 41 patients undergoing bilateral total knee arthroplasty were compared with 40 patients who underwent unilateral total knee replacement. Among the bilateral group, the most common diagnosis was rheumatoid arthritis (68%), while degenerative arthritis prevailed in the unilateral group (50%). Preoperatively, patients in the bilateral group exhibited generally a greater degree of physical disability and limitation of activity due to multiple joint involvement. Postoperatively, no change in the arc of motion was noted in either group, although flexion contractures were significantly diminished in both. The degree of postoperative pain relief was identical in both groups as was the decreased need for walking devices. The most commonly observed complication among the unilateral group was prosthetic loosening (12.%). This was felt explainable on the basis of the increased postoperative activity level of patients with degenerative arthritis and single joint disease. Patients in the bilateral group showed a higher incidence of wound problems, presumably secondary to the long-term use of steroids. The infection rate was identical in each group, but the bilateral group displayed a higher incidence of pulmonary emboli (9.7 vs. 2.5%). The postoperative need for rehabilitation services and the duration of time before dependent walking was achieved was not prolonged in the bilateral group. Hospitalization of the bilateral group was increased only 20%. No deaths were reported in either group. When the need for total knee replacement exists bilaterally, bilateral replacement with a single anesthetic would appear reasonable, provided careful patient selection and technical guidelines are followed.

Efficacy of a topical antibiotic irrigant in decreasing or eliminating bacterial contamination in surgical wounds.

Using a simple in vitro system, the authors showed that colony counts of Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas species can be reduced by 12%–56% with saline irrigation; the reduction of colony numbers, however, especially for S. aureus, was not always statistically significant. However, even if it were statistically significant, the amount of reduction would not be clinically significant. A topical antibiotic irrigant containing bacitracin/neomycin was effective against S. aureus, S. epidermidis-, and E. coli-treated agar plates. Except for a single plate containing Pseudomonas organisms, the growth of Pseudomonas colonies was also prevented by antibiotic irrigation. Tissue samples of muscle, fat, and bone obtained during operations showed antibiotic levels comparable with, and in most cases greater than, those found in the blood agar plates. These data may be clinically significant and suggest that bacitracin/neomycin irrigation can be safely used to reduce the incidence of postoperative infection.

Total elbow arthroplasty: a clinical review of 30 cases employing the Mayo and AHSC prostheses.

Chronic synovitis of the elbow in rheumatoid arthritics that has not responded to four to six months of optimal nonoperative management should be treated by synovectomy even in the absence of significant intra-articular X-ray changes. When intra-articular damage is significant, an arthroplasty will not only relieve the pain, but may also provide a satisfactory range of motion. It is necessary to consider all the possible complications and the fact that technically, total elbow arthroplasty is a difficult operation to perform. Because of the potential for loosening, one might consider using an unconstrained device in the patient with adequate bone structure, reserving the semiconstrained devices for elbows with disintegrated bone tissues. The constrained prostheses should be used only for the most severely disorganized and unstable elbows.

Traumatic laceration of the radial nerve following supracondylar fracture of the elbow. A case report.

Traumatic laceration of the median, ulnar, or radial nerve is an extremely rare complication of supracondylar fracture of the humerus in children. A recent review of the literature disclosed only two reported cases of a laceration involving the radial nerve; a third such injury in an 8-year-old boy is reported in the present paper. Traumatic neuropraxia of one or more of the three adjacent peripheral nerves is a more common complication of supracondylar fracture, with the great majority of these lesions responding to conservative treatment. Vascular compromise secondary to traumatic laceration of the brachial artery is a more frequently observed injury, with an incidence in some series as high as 10%. Clinical findings that suggest vascular injury, therefore, warrant a more aggressive approach, either by arteriography or surgical exploration.

The Use of Methylmethacrylate as a Temporary Spacer Following en Bloc Resection of the Distal Femur: A Case Report

The current state of the art of prosthetic joint replacement permits sizeable segments of the appendicular skeleton to be resected and replaced with prosthetic components which are secured with methylmethacrylate cement. Occasionally it is necessary to resect a rather sizeable area of pathologic bone and to provide for some type of temporary fixation until a specially fabricated prosthetic component can be made available. Under such circumstances it is necessary to maintain length of the involved extremity, and provide for skeletal stability to the area of resection. Although external fixation offers a reasonable option, the employment of an internal type of fixation in the form of titanium mesh reinforced with methylmethacrylate cement seems more desirable. With this technique, the potential problem of pin track infection is avoided while space suitable to the dimensions of the prosthetic implant can be preserved.