Hamstrings--an anterior cruciate ligament protagonist. An in vitro study.

A cadaveric model that incorporated quadriceps and hamstrings muscle loads was developed to simulate the squat exercise. The addition of hamstrings load affected knee kinematics in two ways. First, anterior tibial translation during flexion ("femoral roll-back") was significantly reduced (P = 0.003) and second, internal tibial rotation during flexion was reduced (P = 0.008). However, quadriceps force was unaffected by the addition of hamstrings load. Thus, it seems likely that hamstrings muscle activity that has been observed in vivo during a squat probably functions synergistically with the anterior cruciate ligament to provide anterior knee stability. After the ACL was sectioned, anterior tibial translation was significantly increased during the squat (P = 0.04). The anterior cruciate ligament was then reconstructed using a graft instrumented with a load cell. During passive motion, maximal graft tension was at full extension. During simulated squat exercise, the addition of hamstrings caused a significant decrease in graft load (P = 0.006). During the squat, maximal graft tension was at full extension, and was equal to the graft tension at full passive extension. Thus, the squat exercise may be useful in the early stages of anterior cruciate ligament rehabilitation.

Acetabular reconstruction with a threaded prosthesis for failed total hip arthroplasty.

The MEC-Ring threaded acetabular component was used in 35 patients for revision of failed cemented hip arthroplasties, and 32 have been observed for two to four years (mean, 2.5 years). With only a short-term follow-up period, 44% of patients have already required revision for failure of the MEC-Ring acetabular component. Patients with especially poor acetabular bone stock that had had structural bone graft had a significantly higher rate of failure. The authors developed a technique of supine oblique roentgenograms that allowed better visualization of the component-bone interface. Eighty-six percent of patients had radiolucencies, and 67% of these were progressive. The presence of progressive radiolucencies, component migration, or both was associated with a higher failure rate. Progressive radiolucencies were also associated with a worse pain score in patients whose arthroplasties have not failed. The MEC-Ring threaded component is not recommended for revision hip arthroplasty, especially in cases with poor acetabular bone stock.

The effects of two nonsteroidal antiinflammatory drugs on limb swelling, joint stiffness, and bone torsional strength following fracture in a rabbit model.

Using a rabbit distal tibia fracture model treated by immobilization for three weeks, the effects of two nonsteroidal antiinflammatory drugs on postfracture limb swelling, joint stiffness, and torsional bone strength were examined. Limb swelling in rabbits treated with low-dose piroxicam was reduced by 39%, and high-dose piroxicam reduced limb swelling by 86%. Flunixin, tested at one dose, reduced swelling by 53%. Neither piroxicam nor flunixin affected ankle stiffness or tibia torsional strength.

The anthropometric total hip femoral prosthesis. Preliminary clinical and roentgenographic findings of exact-fit cementless application.

Total hip arthroplasty in the young patient remains a considerable challenge. Cemented arthroplasty has an unacceptably high failure rate. Porous ingrowth designs are one alternative, but bone ingrowth is unpredictable, thigh pain is a frequent clinical finding, stress shielding is often observed, revision is more complicated, and microporous components are mechanically weaker. A new anthropometric femoral component has been designed with a goal of long-term stability through osseointegration. The prosthesis is optimized for canal fill in the distal metaphysis and proximal diaphysis. The components are manufactured in 16 sizes, with cutting broaches precisely machined to the same dimensions to provide an exact fit to the femur. The high-strength TiAl6V4 alloy stem is combined with heads of either CoCr alloy or alumina (Al2O3) for reduced polyethylene wear. The 135 degrees neck-shaft angle and modular design allow for restoration of the abductor lever arm. Because the prosthesis is not porous coated, it is also suitable for use with cement. In cemented application, the prosthesis shape provides an optimal cement mantle. Seventy-one total hip arthroplasties have been performed using the Anthropometric Total Hip (ATH) prosthesis: 31 with exact-fit cementless fixation and 40 with cement. Of those using cementless fixation, 21 have been followed for more than one year (mean, 20 months; range, 12-48 months). The early clinical findings are as good as, or superior to, other cementless designs used at the authors' institution. Stress remodeling of the proximal femur occurs early and stabilizes by one year. The observed changes appear to improve the stability of the prosthesis. Clinical and roentgenographic findings suggest the osseointegration of the ATH femoral component.

Measurement of stability of the knee and ligament force after implantation of a synthetic anterior cruciate ligament. In vitro measurement.

A Gore-Tex prosthetic ligament was inserted, with an over-the-top femoral placement, into thirteen fresh-frozen cadaver knees as a substitute for the anterior cruciate ligament. The femoral eyelet was screwed into bone and the tibial eyelet was attached to a force-transducer, which was positioned and locked on a tibial slider track to record forces in the ligament as the tibia was externally loaded. A reference position was established for the tibial eyelet so that, after the Gore-Tex ligament was implanted, the total anterior-posterior laxity of the knee (at 200 newtons of applied tibial force) matched that of the intact knee (that is, before the anterior cruciate ligament had been cut) at 20 degrees of flexion. With both ends of the ligament secured in the knee, repeated 200-newton anterior-posterior load cycles produced an increase of five to seven millimeters in the total laxity. This apparent stretch-out of the ligament could be worked out of the knee by manually flexing and extending the knee thirty times between zero and 90 degrees of flexion while a constant 200-newton force was applied to the tibial eyelet. After implantation of the Gore-Tex ligament, the laxity of the knee matched that of the intact specimen at 20 degrees of flexion and matched it within one millimeter at zero, 5, and 10 degrees of flexion. For each millimeter that the tibial eyelet was moved distally, the total anterior-posterior laxity decreased by the same amount. The anterior stiffness of the knee after implantation of the Gore-Tex ligament was always less than that of the intact specimen. With an applied extension moment of ten newton-meters, section of the anterior cruciate ligament increased hyperextension of the knee by 2.3 degrees; implantation of the Gore-Tex ligament did not restore full extension, even when the ligament was over-tightened by using a distal location for the tibial eyelet. When the eyelet was in the reference position, the ligament forces ranged from three to 319 newtons when the knee was in full extension, they rose dramatically as the knee was hyperextended, and they decreased to zero in most specimens as the knee was flexed more than 15 degrees. The pull of the quadriceps tendon against fixed resistance always increased the ligament forces. The application of tibiofemoral contact force reduced the ligament forces that were generated during a straight anterior tibial pull.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of dimethyl sulfoxide on posttraumatic limb swelling and joint stiffness. A review and an experimental study in rabbits.

Dimethyl sulfoxide (DMSO) is an inorganic compound with many interesting in vitro properties, including the ability to scavenge oxygen-free radicals. DMSO has been used to treat a variety of clinical conditions, especially musculoskeletal trauma, but valid data regarding its effectiveness are lacking. This paper reviews the pharmacology of DMSO and reports on its effectiveness in reducing posttraumatic limb swelling and ankle joint stiffness in a rabbit hind limb model. The left and right hind limbs of the test and control animals were instrumented and fractured identically. DMSO was applied daily to the skin of only one limb in the test animals. DMSO reduced postinjury ankle stiffness in both ankles of the test rabbits by 41% but had no effect on limb swelling compared to control rabbits. Postulated mechanisms of decreased joint stiffness include oxygen-free radical scavenging and inhibition of fibroblast proliferation.

Cortical evoked potential monitoring during spinal surgery: sensitivity, specificity, reliability, and criteria for alarm.

Cortical somatosensory evoked potentials (EP) were used for intraoperative monitoring of spinal cord integrity during 158 consecutive cases involving surgical correction of spinal deformities. Using a monitoring technique designed to optimize recording, 88% of patients had stable EP results at the time of spinal manipulation. However, five of six patients with preexistent neurological deficits did not have stable EPs. A persistent EP amplitude attenuation of greater than or equal to 40% was a sensitive and specific criterion for alarm. Seven patients had transient attenuations of greater than or equal to 40% after distraction that recovered, so that the distraction instrumentation could be left in place. Overall, this particular cortical somatosensory EP recording technique appears to be appropriate for clinical monitoring. Other recording techniques may be necessary for patients with preexisting neurological deficits.

Anterior-posterior stiffness and laxity of the knee after major ligament reconstruction.

We recorded anterior-posterior force-versus-displacement curves at 20 and 90 degrees of flexion preoperatively and three years after major ligament reconstruction in patients with documented absence of the anterior cruciate ligament. Patients who had an extracapsular stabilization procedure alone showed no significant changes in laxity or stiffness of the injured knee in either position of flexion. Those who underwent reconstruction of the absent anterior cruciate ligament utilizing the middle or medial one-third of the patellar ligament in addition to the extracapsular procedure showed a significant decrease in anterior laxity and increase in anterior stiffness of the injured knee at 20 degrees of flexion. These changes in stability were not observed at 90 degrees of flexion. Six patients with a cruciate substitution had improved laxity and stiffness values at one year postoperatively which were unchanged at three years. At three-year follow-up the increases in activity scores, decreased feelings of giving-way and pain, and elimination of the pivot shift were comparable in both groups of patients.