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Biomedical subjects

P T Simonian

Publications and source records attributed to P T Simonian.

At least 19 recordsLinked to original sources
PubMed2001

Development of the popliteomeniscal fasciculi in the fetal human knee joint.

PURPOSE: The purpose of this study is to better understand the function of the popliteomeniscal fasciculi and their relationship to the popliteus tendon and the lateral meniscus by describing these structures during embryonic development. TYPE OF STUDY: Anatomic dissection and histologic evaluation. METHODS: Twelve fresh-frozen lower extremity specimens (6 paired limbs) from second and third trimester human fetuses were obtained from spontaneous abortions. Each specimen was fixed in formalin and decalcified in 9.0% nitric oxide. The specimens were prepared by removal of all skin and most of the soft tissues before dissection of the lateral meniscus, parts of the posterolateral joint capsule, and the popliteus tendon and muscle. The right-side specimens were sectioned in the transverse plane, and the left-side specimens in the coronal plane. Histologic sections were prepared with H&E and Masson's trichrome stains. Light microscopy was used to evaluate the lateral meniscal attachment, with detailed attention to the popliteomeniscal fasciculi. RESULTS: The close interrelationship of lateral meniscus and popliteus tendon, especially during embryologic development, does give a better understanding how the fasciculi stabilize the lateral meniscus and allow the popliteus tendon to function as a retractor of the lateral meniscus. The fasciculi consist of 3 layers including a dense collagen layer, a vascular layer, and a synovial or capsular layer. CONCLUSIONS: During embryologic development, the fasciculi appeared to provide a vascular supply to the lateral meniscus adjacent to the popliteal hiatus where the meniscus is devoid of capsular attachments.

Collagen↗
PubMed2001

Patella fracture after anterior cruciate ligament reconstruction with the patellar tendon: a comparison between different shaped bone block excisions.

Tensile failure of a patella after anterior cruciate ligament (ACL) reconstruction with autogenous patellar tendon graft is an uncommon but serious complication. One factor that may affect post-harvest patella strength is the shape of the bony defect. The effect of patella defect shape on ultimate tensile strength and mode of failure of the extensor mechanism has not been studied using physiologic moments. Twelve matched pair knee specimens were randomly distributed within three groups comparing rectangular versus triangular, rectangular versus circular, and circular versus triangular shaped patella defects. Specimens were loaded in tension to failure using physiologic moments. Patella fracture occurred in 21 of 24 specimens. Mean ultimate strength for all patellae with a circular defect was 2540 N (+/-651), rectangular defect was 3267 N (+/-920), and triangular defect was 3009 N (+/-1057). There was no significant difference in mean ultimate tensile strength between defect shapes or between matched pairs within the groups. Mode of failure also was similar in all three groups. No defect shape was found to be superior in this investigation comparing ultimate tensile strength or mode of failure between different shaped patella defects.

Aged↗
PubMed2001

Biodegradable interference screw augmentation reduces tunnel expansion after ACL reconstruction.

This study assessed 40 patients who underwent anterior cruciate ligament reconstruction with hamstring autografts using our standard technique. Twenty patients underwent tibial fixation augmentation with a biodegradable interference screw, and the remaining 20 patients did not. Patient groups were compared using radiographic evaluation of bone tunnel diameter, physical examination, and arthrometer measurements. The two groups differed in only one way: the placement of the tibial biodegradable interference screw. Biodegradable interference screw augmentation resulted in decreased distal tibial and some femoral tunnel diameters at both 3- and 12-month follow-up. There was no significant difference in the Lachman and arthrometer testing in either group of patients at the termination of this study. These results indicate that although distal tibia tunnel diameter reduction is significant, it does not appear to have any clinical significance in the first year.

Absorbable Implants↗
PubMed2000

Irreducible posterolateral dislocation of the knee.

Traumatic knee dislocations are relatively rare, often associated with neurovascular injury, and almost always amenable to closed reduction. However, over the years, several authors have recognized that the rare knee dislocation not reducible by closed manipulation usually involves posterolateral dislocation of the tibia and button-holing of the medial femoral condyle through the medial retinaculum. These cases present with a dimple sign, a characteristic invagination of tissues at the medial joint line. Open reduction entails extraction of the soft-tissue collar that becomes incarcerated in the trochlea and intercondylar notch. We present an interesting case of irreducible posterolateral knee dislocation and review many of the salient points associated with this entity. Additionally, we include intraoperative video footage available on the Journal Web site to promote a better appreciation of the dramatic visual presentation and physical examination of this unusual injury.

Follow-Up Studies↗
PubMed2000

Tunnel expansion after hamstring anterior cruciate ligament reconstruction with 1-incision EndoButton femoral fixation.

In this study, we compared a study group of 20 patients who underwent anterior cruciate ligament (ACL) reconstruction with hamstring autografts using a 1-incision endoscopic technique verses a control group of 20 patients using a 2-incision technique. The patient groups were compared based on increase of bone tunnel diameter seen radiographically, physical examination, and arthrometer measurements. The 1-incision technique differed from the 2-incision technique in 2 ways: an EndoButton femoral fixation system and drilling of the femoral tunnel through the tibial tunnel (transtibial). This study shows that the majority of tunnel diameter measurements for the 1-incision ACL reconstruction technique were greater than those of the 2-incision ACL reconstruction technique using autologous hamstring tendons, at both 3 and 12 months of follow-up. Between 3 and 12 months follow-up, there was no statistical differences in tunnel enlargement between the 2 groups of patients. The measured tunnel enlargement, therefore, would have occurred before the 3-month follow-up. There was no significant difference in the Lachman or arthrometer testing in either group of patients at the termination of this study. This indicates that, although tunnel expansion is significant, the increased expansion is not related to increased knee laxity in the first year.

Adolescent↗
PubMed2000

Simple anterior pelvic external fixation.

BACKGROUND: Unstable pelvic ring disruptions are often associated with significant morbidity and mortality, especially in patients with multiple injuries. Early pelvic fixation provides stability and should diminish ongoing hemorrhage. A simple anterior single-pin pelvic external fixator can be applied rapidly and accurately to stabilize pelvic ring injuries as a part of the initial patient resuscitation of such patients. Simple anterior pelvic external fixation (SAPEF) frames can be used as either temporary, definitive, or supplementary fixation depending on the pelvic injury pattern. METHODS: Over a 32-month period, 41 patients with unstable pelvic ring disruptions were stabilized using a simple anterior pelvic external fixator. Eight patients had open pelvic ring injuries and 13 others had genitourinary system disruptions. Fluoroscopic imaging was used to insert all of the fixation pins into the iliac crest between the iliac cortical tables to a depth of at least 5 cm. Each patient had closed manipulative reduction of the pelvic ring using external methods before SAPEF application. RESULTS: One patient died less than 24 hours after injury because of torrential hemorrhage. Clinical evaluations and serial radiographs, including postoperative computed tomographic scans, were available for the other 40 patients postoperatively. Seventy-five of the 80 (94%) pins were completely contained between the iliac cortical tables, according to the computed tomographic scans. The initial pelvic closed reductions were maintained until the fixators were removed in 37 of 40 patients (93%). Only one deep pin track infection developed, mandating early frame removal and intravenous antibiotic therapy. CONCLUSION: Simple anterior pelvic external fixation can be applied rapidly using fluoroscopic guidance to direct accurate pin insertion and closed manipulative reduction of the pelvis. Depending on the specific pelvic ring injury pattern and clinical scenario, SAPEF can serve as a resuscitative temporary fixation device, as definitive pelvic treatment, or as a supplement for pelvic internal fixation implants.

Adolescent↗
PubMed2000

Response of hamstring and patellar tendon grafts for anterior cruciate ligament reconstruction during cyclic tensile loading.

The efficacy of anterior cruciate ligament (ACL) reconstruction in the knee using hamstring tendon or patellar tendon grafts is thought to depend on the relative amounts of graft elongation, or creep, following postoperative rehabilitation. In this study, the creep responses of the tendinous portions of these two graft types were compared during 1 hour of cyclic loading to 200 N at 1 Hz. In the hamstring tendon grafts, strains were measured in both the tissue and in the length-augmentation tape to identify the relative contribution of this particular graft fixation to overall creep. Differences in tissue strain between graft types during cyclic loading were not statistically significant. For both types of grafts, overall graft length significantly increased after 3600 cycles while tissue creep was not significant. The greatest creep in the hamstring tendon grafts occurred at the tissue-tape interface, indicating a potential disadvantage of this composite graft construct.

Aged↗
PubMed1999

Anterior cruciate ligament injuries in the skeletally immature patient.

Injuries of the anterior cruciate ligament (ACL) in children are more frequent than once thought. Special factors must be taken into consideration when treating ACL injuries in the skeletally immature patient. Risks of surgery must be weighed against potential damage to the knee caused by repeated injury. The authors prefer the use of both tibial and femoral centrally placed drill holes, hamstring tendon autografts, fixation distant from the physis, and avoidance of dissection near the physis. This technique will minimize damage to the physis and should not hinder normal growth.

Adolescent↗
PubMed1998

Angulated screw placement in the lateral condylar buttress plate for supracondylar femoral fractures.

Certain supracondylar femoral fractures are not amenable to internal fixation with fixed angle devices. In these instances, the condylar buttress plate is the recommended alternative; however, this is a less rigid device. Because of the decreased rigidity and strength of this device, there is a tendency toward varus angulation and malunion. In six fresh-frozen human knee specimens, segmental osteotomies were created to mimic supracondylar femoral fractures. The medial cortex was completely removed to make the fracture unstable to varus deformity. The fracture was fixed with a lateral condylar buttress plate using 4.5 mm screws. Each specimen was tested once with all the screws installed perpendicular to the plate, and again with the middle screw, just proximal to the fracture, angled 45 degrees diagonally across the fracture into the subchondral bone of the medial femoral condyle. For the construct with all screws placed perpendicular to the buttress plate, the initial stiffness was 410 N/mm, and after 1000 cycles it was 230 N/mm. With a screw placed diagonally across the fracture site, stiffness increased to 833 N/mm on the first cycle, and 796 N/mm after 1000 cycles. In all specimens with the screws placed perpendicular to the plate, the distal fragment had a permanent varus deformity after 1000 cycles, under no load, of 0.91 mm. For the diagonal screw condition, the average magnitude for all six specimens was 0.42 mm. This simple means of screw angulation in the plate strengthened the overall construct to resist the tendency toward varus deformity. The attractive features include the ease of application, and the use of an existing construct.

Aged↗
PubMed1998

Pretibial cyst formation after anterior cruciate ligament surgery with soft tissue autografts.

Four cases of subcutaneous pretibial ganglion, with direct communication to the tibial tunnel after autologous reconstruction of the anterior cruciate ligament (ACL) with hamstrings or iliotibial band, are reported. Tibial graft fixation was with a staple in three cases, and with a screw and soft tissue washer in one. The average time to ganglion development was 44 months, and all occurred more than 2 years after ACL surgery. At the time of cyst development, no patient had subjective or objective knee instability. No patient had evidence of tibial tunnel enlargement. All ganglion communicated with the tibial tunnel. This communication was shown with magnetic resonance imaging in two cases, which showed the origin at the joint. Three patients elected to have the ganglion removed; in each of these there was a direct communication with the tibial tunnel. Additionally, hardware was removed in all cases, and local autologous bone grafting of the tibial tunnel aperture was done in two. Minimum follow-up after surgical excision was 2 years, without evidence of recurrence.

Adult↗
PubMed1998

Hamstring and patellar tendon graft response to cyclical loading.

This study evaluates the effect of submaximal cyclical loads on the tendinous portion of the central 10 mm of the patellar tendon compared with doubled semitendinosus and gracilis tendons. Six fresh-frozen cadaveric knee specimens were used for the study. There was no significant difference between the cross-sectional areas of a 10-mm patellar tendon and four strands of hamstring tendon (looped semitendinosus and gracilis) from the same specimen. The mean cross-sectional area was 44.4 mm2 for the patellar tendon and 47.5 mm2 for the four strands of hamstring. The specimens were cyclically loaded for 1000 cycles from 0 to 300 N at a rate of 1 Hz; the materials testing machine was set on load control. There were no significant differences in the strain, stress, or modulus between the 10-mm patellar tendon and four strands of hamstring tendon after 1000 cycles of loading to 300 N. These data substantiate the excellent clinical results obtained with either graft source and support the use of either graft source for ACL reconstruction.

Aged↗
PubMed1998

The skeletally fixed knee hinge for the grossly unstable knee.

This study examined whether a skeletally fixed prefabricated knee hinge can provide the intact or unstable knee with normal motion through a specific arc of motion. Eight cadaveric knee specimens were used. The amount of motion mismatch between knee and hinge motion was evaluated at six different knee flexion angles. With all knee ligaments intact, addition of the hinge resulted in increasing amounts of joint compression with knee flexion. When all knee ligaments were cut, there was some degree of distraction with 0 degrees of knee flexion, which seemed to gradually decrease and become compressive at 80 degrees of flexion. These values were not statistically significant. In contrast, the mismatch between anterior and posterior tibial translation mismatch was statistically significant. With the ligaments intact, the addition of the hinge resulted in increased amounts of posterior tibial translation, which became significant at 80 degrees of flexion. Similarly, when the ligaments were cut with the hinge intact, there was an increasing amount of posterior tibial translation, which became significant at 60 degrees of flexion. There was also a significant amount of anterior tibial translation at 0 degrees in this group. These results indicate that the hinge allows only a limited range of motion that does not significantly alter tibial translation or joint compression or distraction. Whether this amount of motion is enough to improve the outcome of the grossly unstable knee is unknown. The use of a more sophisticated hinge system might accomplish a greater range of anatomic motion before significant mismatch occurs between hinge and knee motion.

Aged↗
PubMed1997

Scanning electron microscopy of "fibrillated" and "malacic" human articular cartilage: technical considerations.

Specimens of articular cartilage from human knees with gross evidence of malacia (dull appearance and/or softness) or fibrillation (exposed fibrous strands and/or staining with India ink) were prepared for scanning electron microscopy (SEM) and compared to cartilage from apparently intact regions. Vertical cryofractures were made through the center of each specimen, so the matrix collagen structure and its relationship to surface features could be examined. Soft, dull, malacic cartilage was characterized by the presence of numerous clefts among the collagen fibers within the most superficial region of the cartilage. In one form of this condition, these clefts did not extend through the articular surface. In a second form, usually observed where the tangential zone was normally thin or absent, the free ends of radial collagen fibers were exposed, but the deeper layers were intact. Two forms of fibrillation were also identified. The first is created by separation of the superficial lamellae which curl up from the tangential layer and form frondlike projections above the normal plane of the joint surface. In the second, deep radial fibers are exposed by vertical fissures. This second form is associated with advanced damage to the joint. The early stages of cartilage failure are characterized by debonding among the major collagen fiber tracts. This process may initiate in the deep tangential zone where the radial fibers cross into the surface. The patterns of the degenerative changes are dictated by the original architecture of the collagen matrix. The microscopic findings do not correlate adequately with conventional gross grading. SEM provides useful information about injured articular cartilage.

Adolescent↗
PubMed1997

The unstable iliac fracture: a biomechanical evaluation of internal fixation.

Neither plating nor lag screw fixation of a displaced iliac wing fracture as part of an unstable pelvic ring disruption has been studied biomechanically. The purpose of this study was to compare the stability of various combinations of fixation, specifically contrasting lag screws placed between the tables of the ilium with plating in different locations across the fracture line. Various combinations of these fixation implants were evaluated for an unstable iliac fracture. A longitudinal iliac fracture was created in each of six hemi-pelvic specimens prior to testing. Compressive force, up to 500 N or to the magnitude necessary to displace the fracture 2 mm, was applied to the fracture line through the hemi-pelvis for each of the plate and lag screw combinations tested. There was no statistical difference between any of the implants or combinations tested. A single 3.5-mm reconstruction (cephalad) plate placed along the cephalad internal aspect of the iliac crest provided the least stability allowing 2 mm of displacement with a mean load of 80 N. The two combinations of fixation that required the greatest loads for 2 mm of displacement were a single 3.5-mm lag (cephalad) screw inserted into the iliac crest between the tables of the ilium coupled with either a 3.5-mm reconstruction (brim) plate placed along the internal aspect of the inferior iliac fossa at the pelvic brim (239 N) or a 4.5-mm lag (brim) screw between the inner and outer tables at the inferior aspect of the fracture just above the greater sciatic notch (225 N).

Aged↗