The anatomy and function of a bilateral accessory flexor digitorum superficialis muscle: A case report and review of literature.

Anatomical variations of the flexor digitorum superficialis (FDS) include variations of the muscle belly and/or tendon. We present a case of a bilateral accessory FDS muscle and tendon. Dissection was performed in a male specimen (56 years), where an unusual variation was found: a bilateral accessory FDS muscle and tendon. The accessory FDS muscle belly originated at the medial epicondyle, between the tendinous portions of the FDS and flexor carpi radialis, with average dimensions of 70mm in length and 23mm in width. The accessory FDS muscle belly was innervated by the median nerve. After developing a strong tendon, with a length of 51mm (right) and 85mm (left) and width of approximately 9.5mm, the accessory FDS inserted into the dorsal muscle belly of the main FDS. To further analyze the variation, the left accessory FDS muscle and tendon were separated from the adjacent tissues at the elbow and kept attached at the wrist. On a custom jig, 10N were applied sequentially to the main and accessory FDS separately and then together to access their function. Loading of the main FDS muscle resulted in flexion of the fingers with accentuation of the ulnar rays. Loading of the accessory FDS caused flexion of all four long fingers. We described a rare case of an accessory flexor digitorum superficialis, which may assist surgeons with clinical decisions. Surgeons should be aware of variability in forearm anatomy.

The effect of pin location on the rigidity of the halo pin-bone interface.

Optimal insertion of halo fixation pins to maximize the rigidity of the interface between the halo pins and the outer table of the skull is important in reducing the incidence of pin loosening. An in vitro biomechanical study was performed using cadaver skulls to investigate the effects of pin location on the rigidity of this pin-bone interface. Halo pins were inserted at nine positions within a recommended "safe zone" for pin insertion. It was found that the rigidity of the pin-bone interface progressively decreased as pins were inserted more superiorly on the calvaria. The rigidity of the interface did not change significantly when the location of the pins was varied in the horizontal axis. This reduction in interface rigidity associated with inserting pins more superiorly on the skull may be related to an increase in the angle of insertion of the pins with respect to the surface of the calvaria. Based on this study, a change in the technique of halo pin insertion is recommended. Pins should be placed as inferiorly as possible, close to the supraorbital ridge, to achieve the most perpendicular angle of insertion and thus the most rigid fixation. The improved rigidity obtained with perpendicular pin insertion may minimize the rate of pin loosening and other complications associated with use of the halo orthosis.

The effects of ulnar axial malalignment on supination and pronation.

BACKGROUND: Forearm fractures are common injuries in both adults and children. Despite efforts to obtain anatomical alignment, axial rotational malunions occur, resulting in a decreased range of motion and a poor appearance. The objective of this study was to quantify loss of forearm rotation after simulation of ulnar malunions in supination and pronation. METHODS: Six fresh-frozen cadaveric upper extremities (mean age at the time of death, 79.4+/-2.8 years) were used to quantify loss of forearm rotation after simulation of axial rotational malunions of the ulna. First, maximum forearm rotation in supination and pronation was measured at torques of 6.8, 13.6, and 20.4 kilograms-centimeter applied with use of a custom jig. Following a midshaft ulnar osteotomy, a custom adjustable internal fixation plate was used to simulate axial rotational malunions of the ulna of 0, 15, 30, and 45 degrees in both directions. Measurements in supination and pronation were then repeated at the prespecified torques. Analysis of variance, with a p value of 0.05, was used for statistical analysis. RESULTS: In all instances, a decrease in forearm rotation after simulation of the ulnar rotational malunion was accompanied by an increase in rotation in the opposite direction. Supination and pronation were significantly influenced, whereas the total arc of rotation was not affected by ulnar rotational malunion. At a torque of 20.4 kilograms-centimeter, pronation malunions of 15, 30, and 45 degrees resulted in a mean loss of supination (and standard error of the mean) of 5+/-1, 11+/-1, and 20+/-1 degrees, respectively, and supination malunions of 15, 30, and 45 degrees resulted in a mean loss of pronation of 4+/-1, 10+/-2, and 18+/-4 degrees, respectively. The ratio of the simulated rotational malunion to the loss of motion was larger than one. CONCLUSIONS: Ulnar rotational malunions do not lead to a significant change in the total arc of forearm rotation. Instead, loss of motion in one direction is accompanied by increased motion in the opposite direction. Even with a 45-degree ulnar rotational malunion, forearm rotation decreases no more than 20 degrees.

The effect of angled insertion on halo pin fixation.

This study evaluated the effect of angled insertion of halo pins on the biomechanical characteristics of the halo pin-calvarium complex. Halo pins were inserted into isolated calvarium sections at 90 degrees, 75 degrees, and 60 degrees to the surface of the bone at an insertional torque of 0.68 N-m (6 inch-pounds). Initial rigidity, load at failure, and deformation at failure of the pin-bone complex were assessed during transverse shear loading. The structural properties of the pin-bone complex were maximized at loads approaching failure when pins were inserted perpendicular (90 degrees) to the bony surface and significantly decreased at more acute angles of insertion. Perpendicular insertion of halo pins maximizes the structural properties of the complex formed by the halo pin and the calvarium. This improved structural behavior may minimize the incidence of pin loosening clinically, and may reduce the frequency of other complications currently associated with the use of the halo orthosis.

Structural behavior of the halo orthosis pin-bone interface: biomechanical evaluation of standard and newly designed stainless steel halo fixation pins.

The structural response of the halo orthosis pin-bone interface to transverse loading was evaluated on an Instron testing machine using fresh cadaver calvarium sections. Commercially available stainless steel (control) pins and newly designed stainless steel experimental pins were evaluated. Cyclic loading tests and load-to-failure tests were performed. Of the many designs tested, one pin demonstrated an improvement in structural properties at the pin-bone interface compared with the control pin. Furthermore, the new pin design was more resistant to insertional torque reduction when subjected to cyclic loading after insertions at 4 and 6 in-lb. Both the control and experimental pins exhibited improved structural behavior at 8 in-lb of insertional torque compared to the currently recommended 6 in-lb.

Meniscal repair supplemented with exogenous fibrin clot and autogenous cultured marrow cells in the goat model.

This study was undertaken to evaluate the placement of fibrin clot and cultured autologous marrow cells in surgically created, full-thickness, meniscal lesions in the avascular zone in 32 female Spanish goats. The menisci were repaired with two vertically oriented sutures (N = 8), exogenous fibrin clot was placed into the meniscal defect before placement of the two sutures (N = 8), fibrin clot plus cultured adherent bone marrow cells were placed in the defect (N = 8), or the meniscal lesions were left unrepaired (N = 8). On gross and manual inspection, meniscal lesions showed some degree of healing in all animals except for the eight unrepaired lesions. All the experimental specimens had decreased tensile strength compared with the contralateral control medial menisci. Ultimate load to failure, energy absorbed to failure, and stiffness were less than 40% of the controls for all groups. Histologic sections demonstrated focal cellular areas consisting of giant cells and macrophages in the repair sites. Our observations failed to demonstrate a statistically significant enhancement of healing with the use of exogenous fibrin clot compared with vertically oriented sutures alone. The addition of cultured adherent autologous bone marrow-derived cells in conjunction with the fibrin clot did not enhance the meniscal healing.

Glenohumeral joint translation after arthroscopic, nonablative, thermal capsuloplasty with a laser.

The purpose of this study was to determine whether there are changes in anterior and posterior glenohumeral translation after arthroscopic, nonablative, thermal capsuloplasty with a laser. Two anteriorly and two posteriorly directed loads were sequentially applied to the humerus of nine cadaveric glenohumeral joints, and anterior and posterior translation of the humerus on the glenoid was measured. The glenoid was rigidly fixed, and the glenohumeral joint was positioned simulating 90 degrees of shoulder abduction and 90 degrees of external rotation. Using the holmium:yttrium-aluminum-garnet laser, thermal energy was then applied to the anterior capsuloligamentous structures and anterior and posterior translation measurements were then repeated. The results showed a significant reduction in anterior and posterior translation after laser anterior capsuloplasty. Anterior translation decreased from 10.9 +/- 2.0 mm (mean +/- SEM) to 6.4 +/- 1.5 mm with the 15-N load; and from 13.4 +/- 2.1 mm to 8.9 +/- 1.8 mm with the 20-N load. Posterior translation decreased from 7.2 +/- 1.2 mm to 4.4 +/- 0.6 mm with the 15-N load and from 10.4 +/- 1.4 mm to 6.5 +/- 0.9 mm with the 20-N load. These results indicate that the holmium:yttrium-aluminum-garnet laser can be used to decrease glenohumeral joint translation and may be an effective treatment for glenohumeral joint instability.

Effects of simulated scapular protraction on anterior glenohumeral stability.

We evaluated the effect of simulated scapular protraction on anterior glenohumeral translation and in situ inferior glenohumeral ligament strain. Five fresh-frozen cadaveric glenohumeral joints were tested in the position of apprehension while simulating scapular protraction using a custom translation testing device and a differential variable reluctance transducer. The results showed a statistically significant decrease in anterior glenohumeral translation as the scapula was increasingly rotated to simulate 20 degrees of scapular protraction. With 15 N of thorax-based, anteriorly directed load, the mean anterior translation was 6.3 +/- 1.6 mm (mean +/- SEM). With 10 degrees of simulated scapular protraction, translation decreased to 4.1 +/- 1.0 mm; with 20 degrees of simulated scapular protraction, it decreased further to 2.5 +/- 0.5 mm. For each of the other anteriorly directed loads, translations also decreased when 20 degrees of scapular protraction was simulated. Concurrently for each of the anteriorly directed loads, there was increased in situ strain of the anterior band of the inferior glenohumeral ligament with increased simulated scapular protraction. These results suggest that repetitive or chronic protraction of the scapula may result in excessive strain and, ultimately, insufficiency in the anterior band of the inferior glenohumeral ligament.

The anterior band of the inferior glenohumeral ligament. Assessment of its permanent deformation and the anatomy of its glenoid attachment.

Surgical treatment for traumatic, anterior glenohumeral instability requires repair of the anterior band of the inferior glenohumeral ligament, usually at the site of glenoid insertion, often combined with capsuloligamentous plication. In this study, we determined the mechanical properties of this ligament and the precise anatomy of its insertion into the glenoid in fresh-frozen glenohumeral joints of cadavers. Strength was measured by tensile testing of the glenoid-soft-tissue-humerus (G-ST-H) complex. Two other specimens of the complex were frozen in the position of apprehension, serially sectioned perpendicular to the plane containing the anterior and posterior rims of the glenoid, and stained with Toluidine Blue. On tensile testing, eight G-ST-H complexes failed at the site of the glenoid insertion, representing a Bankart lesion, two at the insertion into the humerus, and two at the midsubstance. For those which failed at the glenoid attachment the mean yield load was 491.0 N and the mean ultimate load, 585.0 N. At the glenoid region, stress at yield was 7.8 +/- 1.3 MPa and stress at failure, 9.2 +/- 1.5 MPa. The permanent deformation, defined as the difference between yield and ultimate deformation, was only 2.3 +/- 0.8 mm. The strain at yield was 13.0 +/- 0.7% and at failure, 15.4 +/- 1.2%; therefore permanent strain was only 2.4 +/- 1.1%. Histological examination showed that there were two attachments of the anterior band of the inferior glenohumeral ligament at the site of the glenoid insertion. In one, poorly organised collagen fibres inserted into the labrum. In the other, dense collagen fibres were attached to the front of the neck of the glenoid.

The healing effects on the biomechanical properties of joint capsular tissue treated with Ho:YAG laser: An in vivo rabbit study.

PURPOSE: The objective of this study was to evaluate the healing response, after thermal treatment with a Ho:YAG laser, on the biomechanical properties of capsular soft tissue. TYPE OF STUDY: Before and after trial. METHODS: Forty-five New Zealand white rabbits were used in this study. A medial peripatellar retinacular thermal capsuloplasty using a Ho:YAG laser and a lateral peripatellar retinacular release was performed on 1 knee of each rabbit. The contralateral knee served as a control and had a lateral release of the retinaculum only. The temperature of the medial retinaculum was maintained at 55 degrees C +/- 5 degrees C during treatment. The medial peripatellar retinaculum was evaluated at 0, 6, and 12 weeks postoperatively. Tensile testing of the medial retinaculum and a biomechanical assessment evaluating the structural and material properties were performed. RESULTS: The ultimate load (force) of the medial retinaculum was 70%, 56%, and 84% of control at 0, 6, and 12 weeks, respectively, after the procedure. The stiffness (force/deformation) of the medial retinaculum was 83% of control at 0 weeks, 54% at 6 weeks, and 85% at 12 weeks. The ultimate stress (force/area) of the medial retinaculum also showed a significant reduction at 0 and 6 weeks postoperatively, 63% and 62% of control, respectively. By 12 weeks, the ultimate stress was 83% of control. CONCLUSIONS: Thermal treatment of the medial retinaculum with a Ho:YAG laser results in soft tissue with significantly diminished biomechanical properties after treatment. The results of this study suggest that a 12-week period of minimal stress on the capsular tissues should follow a thermal capsuloplasty procedure.

Arthroscopic suture tying: A comparison of knot types and suture materials.

PURPOSE: The purpose of this study was to determine the structural properties of 3 arthroscopically tied knots using 2 different suture materials: the French knot, the Duncan loop knot, and the original Revo knot. TYPE OF STUDY: Cohort analytic study. METHODS: The sutures used were No. 1 PDS II, an absorbent monofilament, and No. 1 Ethibond (Ethicon, Somerville, NJ), a braided nonabsorbent material. The resulting 6 suture-knot combinations were individually tested to failure in both open- and closed-loop configurations. RESULTS: The French knot showed the greatest strength compared with the Duncan loop and the Revo knot with both No. 1 Ethibond and No. 1 PDS II sutures (P <.05). The No. 1 Ethibond exhibited higher initial stiffness than the No. 1 PDS II for all 3 knot types (P <.05). Results were similar for both open and closed-loop configurations. Also, the French knot failed predominantly by suture breakage instead of knot slippage for both suture materials. CONCLUSIONS: The results of this study suggest that, among the suture and knot combinations investigated in this study, the arthroscopic repair of musculoskeletal injuries should be performed using the French knot and No. 1 Ethibond suture.

Effects of screw types in cementless fixation of tibial tray implants: stability and strength assessment.

OBJECTIVE: To test the stability and strength of tibial trays fixed with cortical screws and tibial trays fixed with cancellous screws under axial and anterior-posterior shear loading conditions. DESIGN: Five matched human fresh frozen cadaver knees without prior pathology were used as paired specimens for comparison of cortical to cancellous screw fixation of tibial trays. BACKGROUND: Current cementless fixation of tibial trays in total knee arthroplasty is obtained by using a combination of stems, keels, posts, pegs, and screws. To date there has been no study comparing isolated cortical and cancellous screw fixation in cementless arthroplasty. METHODS: An Instron machine and a video digitizing system were used to examine tibial tray lift-off, subsidence, and anterior-posterior load to failure at the bone-implant interface in five matched pairs of knees and compare the difference between cancellous and cortical screw fixation. RESULTS: Non-destructive cyclic testing showed a significant difference between the two types of screws for tibial tray subsidence with cancellous fixation greater than cortical (P < 0.05), but not for lift-off (P > 0.05). Load to failure testing in anterior-posterior direction did not result in a significant difference between the two types of screws for initial stiffness and ultimate load (P > 0.05), but did result in a significant difference of energy absorbed to failure (P < 0.01). CONCLUSIONS: The difference in amount of subsidence between cortical and cancellous fixation could possibly be due to microfractures of the underlying trabecular bone with cancellous fixation. Neither screw type was able to completely fix the tibial tray to bone and prevent micromotion. Although the load at failure for anterior-posterior shear was similar for the two screw types, the energy absorbed was greater for the cortical screws which may be a result of additional strength provided by the cortical bone surrounding the screw.

Age related biomechanical properties of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex.

OBJECTIVE: To quantify the biomechanical properties of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex for the two age groups. DESIGN: In vitro human cadaver study evaluating the biomechanical properties of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex for a younger group (n=5, mean age 38.5, SD 0.5 years) and an older group (n=7, mean age 74.8, SD 5.3 years). BACKGROUND: Glenohumeral instability is more of a problem in younger than in older individuals, primarily because recurrence is much more common at a young age. METHODS: Tensile testing was performed on the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex in the shoulder apprehension position using a custom jig, Instron machine and a video digitizing system. RESULTS: In the younger individuals disruption of the complex most often occurred at the glenoid-labrum region of the glenoid insertion site. In the older individual, disruption most often occurred at the midsubstance region. The load and the stress at failure of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex showed that the older group was only 61% and 46% of the younger group, respectively. CONCLUSIONS: The structural properties of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex and the material characteristics of the anterior band of the inferior glenohumeral ligament for the younger group were significantly superior than the older group. RELEVANCE: A stronger and more extensive repair, such as the traditional open technique, may be necessary for younger individuals with glenohumeral instability whereas in older individuals, a different repair technique, such as an arthroscopic technique, may be sufficient.

Biomechanical properties of human tibias in long-term spinal cord injury.

Long-term spinal cord injury (SCI) profoundly alters skeletal structure and function. In this study, the biomechanical properties of tibias from persons with SCI and from individuals closely matched in age and size but without SCI were quantified at both the structural and material levels. Nondestructive torsion tests were performed to determine apparent shear moduli for the tibia. The cortical thicknesses and polar moment of inertia were determined numerically. Four-point bending tests were performed to determine flexural modulus of elasticity on cortical bone specimens of the tibia. The apparent shear moduli of the SCI tibias were found to be lower than the non-SCI tibias (p < 0.05). The cortical thicknesses of the SCI tibias were significantly thinner than the control tibias (p < 0.05), while the polar moment of inertia showed no significant differences between control and SCI tibial cross sections (p > 0.05). The flexural modulus of elasticity of the cortical bone specimens were lower in the SCI tibias than the controls (p < 0.05). These differences suggest that tibias may undergo micro-structural changes as well as structural adaptation following SCI, which alter their mechanical properties.

Potential application of photoplethysmography technique in evaluating microcirculatory status of STAMP patients: preliminary report.

Diabetes mellitus and peripheral vascular disease often lead to infections that result in lower extremity amputations. Transcutaneous oxygen pressure (TcPO2) has been shown by many investigators to be a highly reliable means of assessing cutaneous blood supply and, thus, predicting healing potential. However, TcPO2 measurements are time-consuming and subject to technical difficulties. For this reason, a potential application of photoplethysmography (PPG) as a method for assessing the level of cutaneous circulation was investigated by comparing PPG peak-to-peak voltages with corresponding TcPO2 measurements. The comparisons were made at 37 locations in 20 patients with an age range of from 20 to 81 years (mean = 64.4 years). Although the two methods are intrinsically different and measure two different physiological parameters, the peak-to-peak voltages from PPG were compared with TcPO2 measurements since TcPO2 was reported to be the best single adjunct in determining healing potential after amputation. Linear regression analysis correlating output peak-to-peak voltages from PPG with TcPO2 yielded a correlation coefficient of 0.60. The anatomic locations did not affect the PPG or the TcPO2 measurement. The results of this study encourage further investigation of this technique and instrumentation as a method of assessing the level of cutaneous circulation and ultimately aid in determination of optimal amputation levels.

The effects of tibial rotation on the patellofemoral joint: assessment of the changes in in situ strain in the peripatellar retinaculum and the patellofemoral contact pressures and areas.

The objective of this study was to determine the effects of tibial rotation on in situ strain in the peripatellar retinaculum and patellofemoral contact pressures and areas. Patellofemoral joint biomechanics demonstrate a strong correlation with the etiology of patellofemoral disorders, such as chondromalacia, and are significantly influenced by tibial rotation. Six human cadaveric knees were used along with a patellofemoral joint testing jig that permits physiological loading of the knee extensor muscles. Patellofemoral contact pressures and areas were measured with a Fuji pressure-sensitive film, and the changes in in situ strain in the peripatellar retinaculum were measured with four differential variable reluctance transducers. Tibial rotation had a significant effect on patellofemoral joint biomechanics. The data showed an inverse relationship between increasing knee flexion angles and the change in patellofemoral contact pressures and in situ strain with tibial rotation. At higher knee flexion angles, the patella is well-seated in the trochlear groove and the function of the peripatellar retinaculum is minimized and less affected by tibial rotations.

A proximal femoral implant preserves physiological bone deformation: a biomechanical investigation in cadaveric bones.

The aim of this study was to compare the perturbances in bone deformation patterns of the proximal femur due to a conventional cemented femoral stem and a novel uncemented implant designed on the principles of osseointegration. Five matched pairs of fresh frozen human femora were mechanically tested. Bone deformation patterns, measured with a video digitizing system under 1.5 kN joint force, showed that the cemented Spectron femoral implant caused significant alterations to the proximal femoral deformation pattern, whereas the Gothenburg osseointegrated titanium femoral implant did not significantly alter the bone behaviour (p < 0.05). Vertical micromotions measured under 1 kN after 1000 cycles were within the threshold of movement tolerable for bone ingrowth (21 microm for the Gothenburg system and 26 microm for the cemented implant).

Initial stability comparison of modular hip implants in synthetic femurs.

Synthetic femurs were used to assess the initial bone-implant interface stability of three total hip systems: Wright Medical Technology's Infinity smooth trochanteric module (S-TM), Infinity porous-coated trochanteric module (PC-TM), and Johnson and Johnson S-ROM with a porous surface. The hips were implanted into synthetic femurs, rigidly fixed, and subjected to internal rotation and cyclic, axial compressive loads. The results showed that all three implants achieved good initial implant stability and would be expected to permit bone ingrowth. The porous-coated implants showed greater initial implant stability with less axial micromotion compared with the smooth implants. This finding suggests that surface texture plays a role in initial stability of uncemented prostheses if the bone behaves similar to the material used in this study.

The proximal and distal position of the radius relative to the ulna through a full range of elbow flexion and forearm rotation.

The purpose of this study was to measure the position of the radius relative to the ulna through a complete range of elbow flexion and forearm rotation. Twenty cadaveric upper extremities were mounted on a testing jig that allowed simultaneous control of elbow flexion and forearm rotation. The longitudinal position of the radius relative to the ulna was measured using a three-dimensional digitizer at full pronation, mid-pronation (45°), neutral (0°), mid-supination (45°) and full supination at 10°, 30°, 60°, 90° and 120° of elbow flexion. Our results showed that the radius is located distally when in supination and is located more proximally as it is rotated into pronation. The longitudinal position of the radius changes over 9 mm when moving through a complete arc of forearm rotation. The angle of elbow flexion had a secondary effect on the longitudinal position of the radius, causing changes of less than 0.8 mm.

A new method for determining cross-sectional shape and area of soft tissues.

Assessment of the mechanical properties of soft tissues requires accurate measurement of the cross-sectional area. To date, techniques for determining cross-sectional areas of ligaments and tendons have been less than ideal due to the tissues' complex geometries and the fact that they deform easily under an applied external load. A new procedure has been developed for determining the cross-sectional area by means of an image reconstruction technique based on measurements from collimated laser beams. Using this procedure, the actual shape of the specimen cross-section can also be determined. The results are demonstrated to be highly accurate, and this methodology does not require mechanical contact with the specimen.