David G. Murray

Ipsilateral supracondylar femur fractures following knee arthroplasty.

A retrospective study was performed to evaluate the treatment of five patients with prosthetic knee arthroplasty who sustained a supracondylar femoral fracture of the ipsilateral side. Four of the patients were initially treated by plaster immobilization or traction. Two of the four showed no signs of healing at three months postfracture and had to have open reduction and internal fixation. The fifth patient had primary open reduction and internal fixation. The three patients who were treated surgically regained their prefracture knee rating score. The two who were treated nonoperatively for their fracture had a significant loss in limb function and failed to regain their prefracture knee rating score. Open reduction and internal fixation of these fractures achieves the best results despite the complicating factors of in situ prosthetic components.

Complications of Variable Axis total knee arthroplasty.

Three hundred seventy-six patients were treated by a Variable Axis total knee arthroplasty between 1974 and 1980 and were reviewed for mechanical and orthopedic complications of their surgery. Sixty-five patients had significant complications. Twenty-eight (7.4%) patients developed significant problems with their patellae, 13 (3.4%) patients required reoperation for patellar realignment, and four (1.0%) patients had a patellar resurfacing for retropatellar pain. Two (0.5%) cases of aseptic loosening of the femoral component required revision surgery. There was no aseptic loosening of the tibial component. Other complications included a ligamentous instability (2.9%), postoperative joint stiffness (1.6%), peroneal nerve palsy (1.3%), supracondylar fractures (1.0%), and postoperative joint infection (1.8%).

Posterior stabilization of pelvic fractures by use of threaded compression rods. Case reports and mechanical testing.

Threaded compression rods were placed between the posterior-superior spines as a means of posterior stabilization of pelvic fractures. To document the increase in sacroiliac stability afforded by this technique, biomechanical testing was performed. Malgaigne-type fractures with sacroiliac disruptions were created in four cadaver pelvises. The fractures were stabilized with anterior frames of the Slatis or Pittsburgh type and subjected to longitudinal and torsional loading patterns on an Instron machine. The anterior fixation was then augmented with threaded compression rods placed between the posterior-superior spines to compress the disrupted sacroiliac joints, and repeat testing was conducted. Anterior frames alone were found to provide little stabilization of the disrupted sacroiliac joints with either longitudinal or torsional loading. Markedly improved stabilization in both loading modes was achieved with posterior augmentation. Two typical cases are presented to demonstrate that posterior stabilization is as efficacious in clinical practice as in the biomechanics laboratory.

Some investigations of the accuracy of knee joint kinematics

Abstract A previous paper on the kinematics of the human knee established the loci of points which were the intersections of the instantaneous axis of rotation and sagittal planes. This paper is a study of the effects and magnitudes of three possible errors in examining those kinematics. The sources of error are: 1. (1) the influence of the preservative on the tissue, 2. (2) the effect of error in locating the points from photographic data, 3. (3) the effect of mechanical data reduction techniques. In order to remove the influence of the preservatives, a fresh cadaver joint was used in this study, eliminating error of the first type. Care was taken to minimize error of the second type. A computer program was written to replace the mechanical construction technique, thereby eliminating the possibility of error of the third type. This program, used as a sub-routine, facilitated analysis of the magnitude of errors of the second type. As a final step another computer program was used to evaluate the construction technique used in the previous paper.

Fracture separation of the coracoid process associated with acromioclavicular dislocation: conservative treatment--a case report and review of the literature.

Complete acromioclavicular dislocation associated with fracture separation of the base of the coracoid process is uncommon. This is a report of a 51-year-old man with severe emphysema and limited physical demands in whom the acromioclavicular dislocation and coracoid process fracture were treated conservatively with sling immobilization and early motion and exercises. Good power and full, painless range of motion with minimal symptoms was observed at 6 months follow-up. The strong coracoclavicular ligaments, rather than rupture, may avulse the coracoid process near its base and with disruption of the acromioclavicular joint may allow complete dislocation of the clavicle. A satisfactory result may be obtained without operative reduction of either the acromioclavicular joint or the coracoid process.

Knee extensor mechanics after subtotal excision of the patella.

Two sets of six fresh frozen autopsy specimens were used to test the quadriceps force requirements for knee extension after sequential distal-to-proximal and proximal-to-distal excisions of the patella. The quadriceps force as a function of knee flexion angle was recorded for varying amounts of excision and compared with the results for total patellectomy. Excision of the proximal one half or less resulted in lower force requirements when compared with total patellectomy. The effects of removal of the proximal three-fourths length of patella were inconsistent and actually increased the force requirements in three knees. The effects of distal to proximal excisions indicate a biomechanical advantage to maintaining a fragment equal to at least three fourths the length of the proximal patella. Retaining a fragment of adequate size preserves at least some of the mechanical advantage provided by the intact patella.

Bone tolerance to poly (2-hydroxyethyl methacrylate). A self-locking implant.

Abstract A methacrylic hydrogel with the properties of variable flexibility and swelling to a predictable volume in a fluid medium has been tested in rabbits. As an implant it is capable of locking itself in bone through swelling as it absorbs fluid. The hydrogel is well tolerated by the tissues and over a 5-month period in this experiment produced no observable bone necrosis or significant inflammation in adjacent fibrous tissue. The potential of this material as an implant in orthopedic surgery is discussed.

Experience with the variable axis knee prosthesis.

In an evaluation of 245 variable axis total knee arthroplasties, no significant deterioration of results were found five to nine years after implantation. The patellar problems originally reported diminished with the use of a patellar button, widening of the flange on the femoral component and the increased use of lateral retinacular release. The local complications were: severe patellar problems, 6.9%; ligamentous laxity, 2.9%; aseptic loosening, 1.2%; deep infections, 2.0%; supracondylar fractures, 1.2%; peroneal nerve palsy, 1.6%.

Surface interaction between hydrophilic gels and articular cartilage

One of the important factors to be considered in the development of new implants for use in orthopedic surgery is the effect of the artificial material on opposing natural surfaces. In the case of materials which are intended for use as joint surface replacements, it is necessary to assess the effect of the material on the cartilage surfaces with which it will articulate in the joint. Rigid or abrasive materials tend to cause irreversible damage to opposing cartilage, whereas those which are too soft and pliable have a tendency to be eroded by the opposing natural surface. An ideal material for cartilage replacement would be resilient enough to avoid damaging the opposing cartilage and yet sufficiently strong to resist wear. It is also necessary that such a material be of a form that could be easily implanted in bone and, once implanted, would remain fixed in place for long periods of time. Compounds for potential implantation which seem to fulfill some of these requirements are the hydrophilic methacrylates. This group is one of a number of methacrylate polymers which has been shown to have a relatively high degree of biocompatibility with mammalian tissue [l]. Among the hydrophilic gels with desirable characteristics are two specific polymers named poly-(2hydroxyethyl methacrylate) or polyHEMA and Hydron N. These polymers have the capacity to expand in a fluid medium as a result of the absorption of water and dissolved solutes. As a result of this expansion they change from hard, brittle substances