Biomedical subjects

N A Sharkey

Publications and source records attributed to N A Sharkey.

At least 37 records · Page 2Linked to original sources

PubMed1997

Displacement and strain of the median nerve at the wrist.

Median nerve displacement and strain in the carpal tunnel region were measured as functions of wrist position and carpal tunnel pressure in 5 cadaver forearms during simulated active finger flexion. The positions of spherical stainless-steel markers embedded within the median nerve and flexor digitorum superficialis of the long finger were measured in 3 dimensions by a radiographic direct linear transformation technique. Each limb was tested in 3 wrist positions (60 degrees extension, neutral, and 60 degrees flexion) and 4 carpal tunnel pressures (0, 30, 60, and 90 mmHg). Carpal tunnel pressure was controlled with a balloon angiocatheter inserted deep to the flexor digitorum profundus. The ratio of median nerve to flexor tendon excursion was linear and was affected by wrist position but not carpal tunnel pressure. Patterns of strain in the median nerve proximal to the flexor retinaculum were different from those of strain within the carpal tunnel. Nerve strains were affected by wrist position, but carpal tunnel pressure had no effect. The hydrostatic pressure effect associated with carpal tunnel syndrome does not appear to influence median nerve kinetics or kinematics for the wrist positions studied.

Biomechanical Phenomena↗

PubMed1997

Modified transverse locking nail fixation of proximal femoral fractures.

It was hypothesized that transverse locking screws of intramedullary nails, seated above the lesser trochanter, provide equal strength to that of reconstruction nails, and that screws placed through the medial cortex of the femoral neck do not have adverse biomechanical effects during physiologic loading. Synthetic femurs (n = 10) and paired anatomic specimen femurs (n = 14) were tested intact and with an intramedullary device in place. Intact specimens were loaded nondestructively, then a segmental subtrochanteric defect was created and either a high seated transverse locking nail or a reconstruction nail was inserted and statistically locked. Axial and torsional stiffness were determined followed by axial failure testing. Mechanical parameters evaluated were stiffness, displacement, and energy. The implanted specimens did not show any statistically significant difference between transverse or reconstruction screw constructs with any of the measured parameters (stiffness, displacement, and energy). Failure tests in implanted specimens also did not show any statistically significant difference in yield load, yield displacement, or energy to failure between implant constructs. All anatomic specimens failed, with fractures of the proximal fragment involving medial and lateral cortices. Synthetic specimens did not fracture but showed failure with implant deformation at the level of the skeletal defect. The use of high seated transverse locking nails for complex proximal femoral fractures is a viable option and has comparable in vitro mechanical performance with reconstruction nails. Although not shown to be a problem in the present study, clinical evaluation of screws through the medial femoral neck cortex is required.

Bone Nails↗

PubMed1996

Immune response to nonspecific and altered tissue antigens in soft tissue allografts.

Soft tissue allografts have many uses in orthopaedic surgery, including knee ligament reconstruction, hand tendon surgery, shoulder instability, and rotator cuff reconstruction. The predictable biologic incorporation of soft tissue allografts without rejection or fear of disease transmission continues to be a goal of basic science researchers. A review of the current knowledge if the immune system response to donor specific, nonspecific, and altered tissue antigens in soft tissue or tendon allografts is presented. An in vitro study was done in an attempt to decrease immunogenicity of a frozen bone-ligament graft by adding irrigation with Betadine scrub solution and hydrogen peroxide to the conventional storage process of freezing. Although the irrigation with cytotoxic agents would undoubtedly further decrease immunogenicity, it also decreased stiffness and maximum load by 15%. Whether this decreased strength and stiffness would compromise the incorporation and long term success of soft tissue allografts would need to be studied by in vitro experiments.

Anti-Infective Agents, Local↗

PubMed1996

Immune response inhibition by irrigating subchondral bone with cytotoxic agents.

Attempts have been made (in the recent past) to inhibit the immune response to fresh osteoarticular (shell) allografts because the occurrence and the magnitude of this response is considerably greater and more harmful than that seen after frozen bone and soft tissue allografts. To decrease in immunogenicity of these fresh grafts, the subchondral bone of rat distal femur allografts was irrigated with Betadine scrub solution (n = 10) or Triton-X (n = 11) before transplantation (Study 1). The Triton-X significantly reduced the immunogenicity of the grafts, but the Betadine scrub solution had no effect. A similar experiment with Triton-X was done in sheep where trochlear knee autografts (n = 3) were compared with unirrigated allografts (n = 3) and allografts receiving irrigation with Triton-X (n = 3) (Study 2). All 3 Triton-X irrigated allografts had no immune response, and showed much improved grafts compared with the control allografts (where an immune response developed in 2 of 3). Neither of the 2 allograft groups were as good as the autografts. These techniques may prove useful for inhibiting the recipient immune responses to fresh osteoarticular allografts in humans requiring partial joint reconstruction.

Animals↗

PubMed1996

The effect of variable size posterior wall acetabular fractures on contact characteristics of the hip joint.

The indications for open reduction and internal fixation of posterior wall acetabular fractures associated with a clinically stable hip joint are unclear. In previous work a large posterior wall defect (27% articular surface area) resulted in significant alteration of load transmission across the hip; specifically, there was a transition from evenly distributed loading along the acetabular articular surface to loading concentrated mainly in the superior portion of the articular surface during simulated single leg stance. However, the majority of posterior wall fractures involve a smaller amount of the articular surface. Posterior wall acetabular fractures not associated with instability of the hip are commonly treated nonoperatively. This practice does not account for the size of the posterior wall fracture. To study the biomechanical consequences of variably sized articular defects, a laboratory experiment was conducted evaluating three progressively larger posterior wall defects of the acetabulum during simulated single leg stance using superlow Fuji prescale film (Itochu International, New York): (a) 1/3 articular surface width through a 50 degrees arc along the posterior wall of the acetabulum, (b) 2/3, and (c) 3/3 articular width defects through the same 50 degrees arc along the posterior wall of the acetabulum. In the intact acetabulum, 48% of the total articular contact was located in the superior acetabulum. Twenty-eight percent of articular contact was in the anterior wall region of the acetabulum and 24% in the posterior wall region. After the 1/3 width posterior wall defect, 64% of the articular contact was located in the superior acetabulum (p = 0.0011). The 2/3 width posterior wall defect resulted in 71% of articular contact area being located in the superior acetabulum (p = 0.0006). After the 3/3 width posterior wall defect, 77% of articular contact was located in the superior acetabulum, significantly greater than the intact condition (p < 0.0001) and 1/3 width defect (p = 0.0222). The total absolute contact areas for all defect conditions were significantly less than the intact conditions. The results of this study reconfirm the observation that posterior wall fractures of the acetabulum significantly alter the articular contact characteristics in the hip during single leg stance. The relationship between defect size and changes in joint contact showed that the smallest defect resulted in the greatest alteration in joint contact areas, whereas larger defects resulted in minor increments of change in contact area. This finding is of concern because the clinical practice of managing acetabular fractures nonoperatively if the hip joint is stable is based on the supposition that the joint retains enough integrity to function without undue risk of late posttraumatic osteoarthritis. A better understanding of the natural history of stable posterior wall acetabular fractures is needed to ascertain whether some of these fractures merit operative repair.

Acetabulum↗

PubMed1995

Freeze clamping musculo-tendinous junctions for in vitro simulation of joint mechanics.

Incorporation of physiologic muscle tensions to simulate normal in vivo joint loading in cadaveric biomechanical studies has been a challenging problem, especially about the knee, foot, and shoulder. Simulation of muscle contraction requires attachment of tension producing devices to musculotendinous units. To this end, we modified the 'cryo-jaw' device, first described by Riemersma and Schamhardt (1982, J. Biomechanics 15, 619-620) to couple linear actuators to fresh cadaver tendons. These clamps were used in the simulation of 11 different muscles in laboratory investigations of shoulder, elbow, knee, and foot function. The clamps were able to transmit repetitively 3500 N of quadriceps force in eight knees and 2000 N of Achilles force in 11 feet. Overall success rate was 95%.

Ankle Joint↗

PubMed1995

Influence of extrinsic plantar flexors on forefoot loading during heel rise.

This investigation studied the effects of simulated plantar flexor muscle activity on forefoot loading using a static cadaver model. Nine cadaver feet were mounted in an apparatus in the heel rise position. Using computer-controlled and pneumatic actuators, forces were simultaneously applied to the tendons of the triceps surae, flexor hallucis longus, flexor digitorum longus, peroneus brevis and longus, and tibialis posterior until 750 N of ground reaction force was achieved, at which time forefoot plantar pressure patterns were captured immediately with a pedobarograph. Second metatarsal bending moments were calculated from strain gauge data collected concurrently. Consecutive loading cycles were performed with sequential elimination of simulated muscle force from each tendon except the Achilles. Loss of simulated flexor hallucis longus activity significantly decreased great toe contact forces and significantly increased forces under the forefoot. Simulated loss of both the flexor hallucis longus and flexor digitorum longus caused significant decreases in contact area, pressure, and force beneath the toes and significant increases in contact area and force under the forefoot. Bending moments in the second metatarsal were shown to vary directly with peak pressure under the second metatarsal head (r = 0.801). These findings demonstrate the load distributing function of the extrinsic plantar flexors during heel rise.

Adult↗

PubMed1995

Strain and loading of the second metatarsal during heel-lift.

Metatarsal stress fractures occur in military recruits after long marches and in athletes after episodes of overtraining involving running or jumping. It has been demonstrated that contraction of the plantar flexors of the toes helps to counteract the moments placed on the metatarsals by body weight. It is possible that physiological fatigue due to strenuous or repetitive exercise reduces the rate and force of contraction of the plantar flexors, thereby increasing metatarsal strain per cycle, and that this mechanism is the primary cause of stress fractures of these bones. To test the hypothesis that fatigue of the plantar flexors causes increased metatarsal loading, thereby predisposing these bones to stress fracture, we measured metatarsal strains in nine fresh cadaveric feet with use of an apparatus that simulated physiological loading due to body weight as well as contraction of the plantar flexors. Each foot was loaded to 750 newtons of ground-reaction force by simulated contraction of the triceps surae, and strains were recorded in the mid-part of the shaft of the second metatarsal. Tests were repeated with use of simulated activity of different combinations of the flexor digitorum longus, flexor hallucis longus, peroneus brevis, peroneus longus, and tibialis posterior muscles. In situ bending moments and axial loads subsequently were derived for each configuration. Dorsal strain was significantly reduced by simulated contraction of the flexor hallucis longus. Plantar-dorsal bending was significantly reduced by simulated contraction of the flexor digitorum longus.

Achilles Tendon↗

PubMed1995

Biomechanical consequences of fracture and repair of the posterior wall of the acetabulum.

We measured the distribution of contact area and pressure between the acetabulum and the femoral head of cadaveric pelves in three different conditions: intact, with an operatively created fracture of the posterior wall, and after anatomical reduction and fixation of the fracture with a buttress plate and interfragmentary screws. The study involved eight cadaveric hip joints from five pelves loaded to 2000 newtons in simulated single-limb stance. Measurements were made with pressure-sensitive film. The acetabulum was divided into three areas--the anterior wall, the superior aspect, and the posterior wall--for the analysis of the data. Creation of a fracture of the posterior wall was followed by an increase in contact area, maximum pressure, and contact force in the superior aspect of the acetabulum. A concomitant decrease in these parameters was observed in the anterior and posterior walls. Anatomical reduction and fixation of the fracture with a plate and screws did not restore the pattern of loading to pre-injury levels.

Acetabulum↗

PubMed1995

Lumbar pedicle screw salvage: pullout testing of three different pedicle screw designs.

Although research has determined pedicle screw pullout strengths for normal and osteoporotic bone, this study provides the first biomechanical analysis of pedicle screw salvage. Ten fresh frozen human lumbar spines were separated into individual vertebrae; 6.0 x 40 mm pedicle screws were placed in each pedicle; and an axial pullout test was performed to establish control values. Ultimate load, initial stiffness, work, and displacement data were calculated. Each vertebra was reinstrumented with one 7.0 x 40 mm variable screw placement (VSP) screw side by side with either a 7.0 mm Cotrel Dubousset sacral screw (CD) or a 7.0 mm Compact Cotrel Dubousset pedicle screw (CCD). Pullout tests were repeated and compared to control data for individual screws and for each VSP/CD or VSP/CCD pair. Vertebrae were then reinstrumented with 8.0 mm VSP and CD screws and paired pullouts repeated. Statistical analysis was carried out using a paired T test. Analysis of intravertebral and intergroup variation of controls was carried out using a Paired Two Sample T test. The 7.0 mm CCD screws restored pullout strength to 62% of control pullouts; 7.0 mm CD screws, to 85%; 7.0 mm VSP screws, to 99%; 8.0 mm CD screws, to 109%; and 8.0 mm VSP screws, to 148% of control pullouts. The 7.0 mm VSP salvage screws exceeded CD screws in ultimate load by 22.5% (p < .03) and CCD screws by 33.5% (p < .05). The 8.0 mm salvage screws significantly increased pullout relative to both controls and all 7.0 mm salvage screws, with 8.0 mm VSP exceeding 8.0 mm CD by 34% (p < .03). Initial stiffness was also significantly greater in VSP than CD screws. Although applied in a smaller number of vertebrae, 8.0 mm screws sufficiently outperformed smaller screws to provide statistically significant differences. The 7.0 mm VSP salvage screws restored pullout to control levels, roughly equivalent to outcomes previously obtained with unpressurized polymethylmethacrylate (PMMA).

Aged↗

PubMed1994

The entire rotator cuff contributes to elevation of the arm.

The function of the infraspinatus, teres minor, and subscapularis during elevation of the arm remains poorly defined. These muscles may generate moments that contribute to abduction of the arm, although they frequently are classified as humeral depressors. The purposes of this study were to measure the contributions to abduction made by the more inferiorly positioned rotator cuff muscles relative to the contributions of the supraspinatus and to determine the range of motion at which the muscles are most effective. Five fresh cadaveric shoulder girdles were mounted in an apparatus designed to simulate contraction of the deltoid and rotator cuff while maintaining the normal relationship between glenohumeral and scapulothoracic motions. The deltoid force required for elevation was measured without simulated contraction of the rotator cuff and with simulated contraction of the entire rotator cuff, of the supraspinatus only, and of the infraspinatus-teres minor and subscapularis only. A significant reduction in deltoid force when other muscle activity was added indicated that the additions contributed significantly to abduction. The deltoid force required with concurrent contraction of the entire rotator cuff averaged 41% less than with the deltoid alone but was not significantly different than with the deltoid and supraspinatus or with the deltoid, infraspinatus-teres minor, and subscapularis. Concurrent application of forces to the supraspinatus or the infraspinatus-teres minor and subscapularis significantly reduced the required deltoid force over the range of motion studied by an average of 28 and 36%, respectively. The contributions of the rotator cuff muscles to abduction of the arm were greatest at low abduction angles (30 and 60 degrees) and were insignificant by 120 degrees. The infraspinatus-teres minor and subscapularis contribute significantly to abduction: their contribution was equal to that of the supraspinatus and, like the supraspinatus, they are most effective during the first 90 degrees of abduction.

Aged↗

PubMed1994

Biomechanics of the thumb flexor pulley system.

The purpose of this study was to quantify the contributions of the thumb flexor pulleys on the mechanical efficiency and angular joint displacement of the human thumb. Fourteen human (below elbow) cadaveric specimens were divided into two study groups. Four experimental trials were performed with each thumb. Group 1 was tested with an intact pulley system, as well as after sequential sectioning of the oblique, A1, and A2 pulleys. Group 2 was tested with all pulleys intact and following the sequential sectioning of the (A1), oblique, and (A2) pulleys. Each forearm was mounted to a dynamic testing apparatus, and an 815 g load was applied at the thumb tip. The flexor pollicus longus tendon was attached to a force transducer and computer-driven stepper motor, and tension was recorded through full range of motion of the interphalangeal and metacarpophalangeal joints. The initial sectioning of either the A1 or oblique pulley did not significantly alter the thumb efficiency or its interphalangeal or metacarpophalangeal joint angular displacement. When both the A1 and oblique pulleys were cut, significant bowstringing was observed, as well as decreased interphalangeal flexion and increased metacarpophalangeal flexion; total angular motion remained unchanged. The tension required to achieve a given displacement also decreased following the sectioning of both the A1 and oblique pulleys. There was no statistical difference between an isolated, intact A2 pulley and no intact pulleys. These findings indicate that repair or reconstruction of either the A1 or oblique pulley after injury will restore normal thumb kinematics.

Biomechanical Phenomena↗

PubMed1994

Median nerve displacement through the carpal canal.

We determined the direct relationships between wrist position and displacement of the median nerve during active contraction of the flexor tendons at the wrist with an intact, transected transverse carpal ligament (TCL). Nine fresh cadavers were mounted in an apparatus to allow variable wrist position. Excursions of the tendons and displacement of the median nerve were measured by tracking markers with a video camera. Each limb was tested at 0 degree, 30 degrees, and 60 degrees of wrist extension before and after release of the TCL. Excursion of the flexor tendons required for full finger flexion ranged from 2.3 to 3.1 cm (mean, 3 cm). Median nerve displacement ranged from 0.9 to 1.4 cm (mean, 1 cm). The relationship between median nerve and flexor tendon excursion was consistently linear. Finger motion alone allows for median nerve displacement after surgery in the carpal tunnel.

Analysis of Variance↗

PubMed1993

Iliac crest bone graft. Osteotome versus saw.

The strength of saw-harvested vs. osteotome-harvested Smith-Robinson iliac crest grafts from five fresh frozen cadavers was compared. Matched pairs of grafts were harvested, one with a saw and the other with an osteotome from equivalent locations on the two iliac crests of each pelvis. Grafts were tested to failure in axial compression, and load-displacement curves were recorded for each test. Yield load and displacement, ultimate load, and stiffness were calculated, and statistical analysis was performed with the Student t test and three-way analysis of variance. Evaluation of the 66 pairs of grafts revealed that saw-harvested grafts were consistently stronger than were matched grafts harvested with an osteotome. The middle third of the iliac crest produced significantly stronger grafts, and those harvested from younger donors were significantly stronger than those obtained from older donors. Of even greater clinical relevance, saw-harvested grafts were stiffer than osteotome-harvested grafts. Based on these findings, it is recommended that iliac crest grafts harvested for spine fusion be obtained with an oscillating saw rather than with an osteotome.

Adult↗

PubMed1993

Response of peripheral nerve to cyclic compression in a laboratory rat model.

Repetitive cyclic loading of a nerve has been proposed as a pathogenic factor in the development of occupational compression neuropathies. Little is known about the basic response of peripheral nerve to cyclic compression. We investigated the hypothesis that cyclic compression is more detrimental to nerve function than constant compression. We measured the amplitudes and velocities of distally evoked action potentials in the presence of constant or cyclic compression of the tibial nerve in rats. Seven groups were subjected to constant or cyclic compression for 6 h by a computer controlled, hydraulically activated compression chamber. Nerves were compressed with 0 (control group), 30, 60, or 90 mm Hg of constant pressure or 0-30, 20-50, or 30-60 mm Hg of cyclic compression for approximately 20,000 compression cycles. Action potentials were recorded every 15 min. The effects of cyclic compression on nerve conduction were equivalent to the effects of constant compression at the average applied pressure. Cyclic loading itself does not appear to be an important pathogenic factor in the development of nerve conduction block.

Action Potentials↗

PubMed1993

Bone ingrowth and mechanical properties of coralline hydroxyapatite 1 yr after implantation.

A previous study of coralline hydroxyapatite as a bone-graft substitute was extended from 4 to 12 months to determine better the relationships between implantation time, bone ingrowth and mechanical properties. The model consisted of a 10 x 30 mm window defect in the shaft of the canine radius (a cortical site), and a 10 mm diameter cylindrical defect in the head of the humerus (a cancellous site). In the new study, these two defects were made bilaterally in eight dogs, and filled with block-form coralline hydroxyapatite. The radius defects were supported by a metal fixation plate which was removed after 9 months. After 12 months, the dogs were killed and the left-side implants were analyzed histomorphometrically and mechanically. The right-side radius and humerus were reserved for structural analysis. The results were combined with those previously measured after 4, 8, 12 and 16 wk of implantation. In the cortical site, bone ingrowth increased from 52% at 16 wk to 74% at 1 yr. In the cancellous site, bone ingrowth was 38% after 4 wk, then fell monotonically, reaching 17% at 1 yr. Bending and compressive strength and stiffness of the radius implants increased throughout the post-implantation year, but compressive strength and stiffness of the humerus implants did not change after the first 2-4 months. Mechanical properties were strongly correlated to bone ingrowth in the cortical, but not the cancellous, site. The volume fraction of the coralline hydroxyapatite material diminished significantly with time in the cortical, but not the cancellous, site.

Animals↗

PubMed1993

Effects of partial patellectomy and reattachment of the patellar tendon on patellofemoral contact areas and pressures.

We used a previously reported experimental method to measure patellofemoral contact areas and pressures in four pairs of human cadaveric knees before and after a partial patellectomy. The knee joints were loaded by application of a flexion moment, which was resisted by the extension moment of the quadriceps mechanism. Patellofemoral contact was measured with the use of pressure-sensitive film, at 30, 60, and 90 degrees of flexion of the knee. Partial patellectomy decreased the patellofemoral contact area and increased pressure. We observed alterations in the patterns of contact, including a proximal shift in patellofemoral contact, after partial patellectomy. An anterior reattachment of the patellar tendon significantly minimized the effects of 20 and 40 per cent patellectomies (p < 0.05). After a 60 per cent patellectomy, patellofemoral contact was altered markedly, with the contact area reduced to less than 50 per cent of the control values regardless of the position of the patellar tendon reattachment.

Adult↗

PubMed1991

Coupled suturing: a new technique for microvascular anastomosis.

The left carotid artery of 12 Sprague-Dawley rats was sectioned and anastomoses immediately performed utilizing a new technique termed coupled suturing. Patency and constriction were assessed immediately postoperatively and at 1, 2, and 3 weeks. Specimens were also evaluated by light microscopy and scanning electron microscopy. Vessels healed well with excellent patency and edge eversion. With the development of a specialized needle, coupled suture could prove to be a reasonable alternative to current methods of anastomosis. Its main advantage is better intimal eversion, which decreases the risk of thrombosis.

Anastomosis, Surgical↗