Arie M. Rijke

Magnetic resonance imaging of injury to the lateral ankle ligaments

To establish the value of magnetic resonance imaging in determining which patients with ankle sprains will benefit from surgical treatment, 1 uninjured volunteer and 15 patients with acute, subacute, and chronic injuries of the lateral ankle ligaments were imaged at 1.0 tesla using a fast imaging with steady-state preci sion three-dimensional technique and 1.5-mm slice thickness. A dedicated knee coil was used to hold the foot in a neutral or plantar-flexed position. In cases of acute, low-grade injuries, fraying of the anterior talofib ular ligaments with intact calcaneofibular ligaments was observed in the presence of edema and hemorrhagic fluid. In cases of acute, high-grade sprains, the calca neofibular ligament appeared wavy or was visualized only partially or not at all. Subacute injuries showed ligament disruption; chronic lesions, on occasion, showed atrophy of the calcaneofibular ligament but no edema or hemorrhagic fluid. These findings showed a good qualitative correlation with the results of graded stress radiography. Magnetic resonance imaging can definitely determine the ligaments involved in lateral ankle sprains and pro vide useful anatomic information in cases in which acute or reconstructive surgery is contemplated. However, the magnetic resonance imaging findings do not directly correlate with degree of instability and do not replace those of physical examination or routine radiographic studies.

Instrumented Arthrometry for Diagnosing Partial Versus Complete Anterior Cruciate Ligament Tears

Nineteen patients with the clinical diagnosis of anterior cruciate ligament injury were examined by KT-1000 ar thrometry before arthroscopy in an effort to differentiate partial from complete tears. To this end, the KT-1000 arthrometer was equipped with a strain gauge and pro cessor that permitted the required force to increase the anterior displacement by 1-mm increments, to be read on a light-emitting diode. The measured force has been plotted against anterior displacement expressed in non linear increments along the x-axis to allow for the vis coelastic nature of the ligament. The results show that stress-strain diagrams of partially torn and completely torn ligaments are similar to those obtained by graded stress radiography. Using arthroscopy as the standard of measurement, partial tears can be differentiated from complete tears with a sensitivity of 80% and a specificity of 100%. The figures for complete tears versus partial tears are 100% and 80%, respectively. Graded arthrom etry with x-y recording of the force-displacement rela tionship that allows for the viscoelastic qualities of liga ment further extends the capabilities of instrumented arthrometry.

Stress examination of traumatized lateral ligaments of the ankle.

In the diagnostic analysis of acute injury to the lateral ankle ligaments, ankle arthrography and plain film stress examination play an important role. Inasmuch as the treatment of choice, whether conservative or surgery, and insofar as the therapeutic results may be determined by the extent of injury, it is important to have access to quantitative information on the functional properties of the involved ligaments at the time of the initial diagnostic studies. This can be obtained by measuring the strain on the anterior talofibular (tf) and calcaneofibular (cf) ligaments as a function of pressure applied to the distal tibia. Any device that ensures that the externally applied pressure is proportionally carried through to the ligaments can be used for this purpose. The results of 25 quantitative stress examinations using a Telos stress device are compared with arthrography findings and findings at surgery. Stress examination correlates well with both arthrographic and operative findings. The method is also useful for the evaluation of chronic ankle instability, follow-up examinations, and for the detection of vestiges of previous trauma of the contralateral ankle. The procedure is straightforward and noninvasive and can be performed within 15 minutes.

Injury to the lateral ankle ligaments of athletes A posttraumatic followup

Twenty of 26 original athletes with injuries to the lateral ligaments of the ankle were reexamined 2 to 5 years following treatment. The functional quality of their an terior talofibular (TF) and calcaneofibular (CF) ligaments was tested by stress examination, using a commercially available stress device, and was compared with the results of stress examination, arthrography, and sur gery at the time of injury. Surgically treated patients showed a 70% to 100% recovery of the functional properties of the lateral ankle ligaments on comparison with the contralateral, unin jured ankle. Of the six patients treated conservatively With elastic bandages and rest, only one had regained normal function, whereas the others showed minimal or no improvement. Isolated lesions of the anterior TF ligaments, when treated conservatively, may have only a slightly better prognosis than a combined lesion of both anterior TF and CF ligaments in the athletic pop ulation.

PLUMAGE WETTABILITY OF THE AFRICAN DARTER ANHINGA MELANOGASTER COMPARED WITH THE DOUBLE-CRESTED CORMORANT PHALACROCORAX AURITUS

Summary Rijke, A. M., Jesser, W. A. & Mahoney, S. A. 1989. Plumage wettability of the African Darter Anhinga melanogaster compared with the Double-crested Cormorant Phalacrocarax auritus. Ostrich 60:128-132. Darters emerge from water “dripping wet” but are able to become airborne without delay. Their plumage is, on the whole, three times more wettable than that of cormorants. We investigated the microscopic structure and resistance to water penetration of the body, wing and tail feathers of the African Darter, Anhinga melanogaster. The results show values of the structural parameter (r + d)/r for body feathers in the range of 9 to 12, whereas for rectrices, primaries, secondaries and tertiaries, a range of 2 to 3 was observed, with barbules measuring 2 to 3. Penetration pressures measure zero to 1 cm water head for the body feathers and 6 to 15 cm for the wing and tail feathers. These findings suggest that on submersion, the body feathers wet out entirely but wing and tail feathers resist becoming waterlo...

Water repellency and feather structure of the Blue Swallow Hirundo atrocaerulea

Rijke, A.M., Jesser, W.A., Evans, S.W & Bouwman, H. 2000. Water repellency and feather structure of the Blue Swallow Hirundo atrocaerulea. Ostrich 71 (1 & 2): 143–145. The Blue Swallow is an endangered species in southern Africa and is probably the most endangered passerine. It is restricted to escarpments with grasslands above 1 000 m where mists are frequent. It appears to forage on the wing even in thick mist raising the question of feather wettability in relation to its adaptation. Extensive physical and behaviourial adaptations are known to occur in a wide variety of birds to deal with the problem of shedding water continuously. To study the water repellency and resistance to water penetration of Blue Swallow feathers, we have examined the microscopic structure of head, back, throat, breast and abdominal feathers as well as remiges and tail feathers by transmission light microscopy. The width (2R) and separation (2D) of rami and barbules have been measured and were used to calculate the parameter (R + D)/R that serves as an indicator ofwater shedding potential. For the remiges and tail feathers the values of the (R+D)/R range from 5 to 10 which is comparable to values for other terrestrial birds. However, for body feathers the range is from 10 (head) and 35 (abdomen)-higher than previously observed for any other bird including Swifts, Apodidae. Blue Swallow feathers are thus the most effective feather yet discovered at repelling water drops. The water repellency is highest in those feathers that are relatively shielded From the direct impact of small water drops (throat, breast, abdomen, back). By contrast, the flight feathers must possess a relatively large resistance to water penetration to avoid becoming waterlogged and this is coupled to low (R+D)/R values. Values for the barbules lay between 2 and 6—the same as found for other bird families—supporting an earlier conclusion that they have little direct effect in repelling water.

GRADED STRESS RADIOGRAPHY OF INJURED ANTERIOR CRUCIATE LIGAMENTS

Fifty-five patients with clinical suspicion of injury to their anterior cruciate ligament (ACL) were examined by graded stress radiography before arthroscopic verification in an effort to determine the loss of ACL function as a result of ligament tearing. Using a commercially available stress device capable of applying varying pressures to the mid-calf, anterior drawers were measured from lateral radiographs at 0-, 7-, 14-, and 21-kiloPascal pressures and used to calculate the equivalent elastic modulus of the remaining ACL fibers. According to viscoelastic theory, this modulus is proportional to the number of elastically active fibers in the ligament. To verify the validity of this concept, the stress-strain relationship of a freshly excised ACL ligament was examined in a tensile testing machine, and the procedure was repeated after the ligament had been partially transsected with a scalpel. Comparison with the elastic modulus of the (intact) ACL of the opposite knee permits an estimate of the percentage of rupture in cases of partial tears. Overstretched ligaments show essentially normal viscoelastic properties once the slack in the ligament has been taken up. Complete tears, on the other hand, show a complete breakdown in the viscoelastic properties of the ACL. The results show that partial tears can be diagnosed by graded stress radiography with a sensitivity of 20% and specificity of 90%. Diagnosis of overstretched ligaments had sensitivity of 50% and specificity of 94%. Complete tears were detected with sensitivity of 88% and specificity of 75% as diagnosed against all other ACL lesions and including normals.(ABSTRACT TRUNCATED AT 250 WORDS)

The Feather Structure of Dippers: Water Repellency and Resistance to Water Penetration

Abstract Dippers (Cinclidae) are the only passerines that find their prey almost exclusively under water. We examined the breast feathers of the five species of dippers for barb diameter and spacing. These results were compared with those measured for other bird families, both aquatic and terrestrial, to detect the presence of any adaptation in the structure of their plumage to their aquatic lifestyle. Barb diameters (2r) were about the same for all dipper species at ∼25 µm, but spacing (2d) varied from ∼150 to 215 µm. Dipper feathers exhibited large values for (r + d)/r, the structural requirement for excellent water repellency, comparable to that of many other terrestrial birds including starlings (Sturnidae), swifts (Apodidae), and nightjars (Caprimulgidae). A slightly improved resistance to water penetration, indicated by a smaller value for (r + d)/r, was observed for White-throated Dipper (Cinclus cinclus), whereas increased water repellency was found for both American (C. mexicanus) and Brown dippers (C. pallasii). Each of these three species is known to dive. No adaptations were observed for White-capped (C. leucocephalus) and Rufous-throated (C. schulzi) dippers, neither of which dive. The breast feathers of dippers have evolved excellent water repellency, but diving dippers show further adaptations for improved resistance to water penetration and water repellency to allow under-water foraging.

A comparison of magnetic resonance imaging to bone scintigraphy in early traumatic ischemia of the femoral head

In adult rabbits, a unilateral subcapital osteotomy of the femoral neck was performed to induce avascularity. One half of the osteotomy sites were fixed with a magnetic resonance imaging (MRI) compatible absorbable pin and the other osteotomies had no fixation. The femoral heads were studied at three, five, and 12 days with roentgenographs, bone scintigraphy, and MRI, and MRI only at four weeks and six weeks after osteotomy. Histologic studies were performed after imaging to evaluate the viability of the femoral heads. At three, five, and 12 days after osteotomy, bone scintigraphy showed a decrease in uptake of radioisotope in the region of the femoral head on the operated side relative to the acetabulum and greater trochanter in 17 of 18 rabbits. A comparison of the surgically treated hip to the normal hip in fixed and unfixed osteotomies showed no change in the signal behavior of T1− or T2-weighted images in all rabbits Days 3, 5, and 12 (n = 18) after operation. The rabbit femoral heads with fixation of the osteotomy 28 days after operation showed a decrease in signal intensity in the subcapital region of the femoral head. Six weeks after operation, the fixed femoral head shows a loss of signal in a portion of the femoral head near the osteotomy. The MRI signal intensity appears to increase in the unfixed femoral heads six weeks after operation. At three, five, and 12 days after operation, there was a change in the staining characteristics of the hematopoietic elements with a distinct absence of india ink in the vessel lumens (an indication of the avascularity of the femoral head), but preservation of the fat cells. In the fixed femoral head 28 days after operation, india ink was visualized in vessel lumens, and fibrous tissue with an abundance of fat cells was noted closer to the subchondral region of the femoral head. The unfixed femoral heads 43 days after operation show poor basophilic staining of the hematopoietic cells, but preservation of fat cells. Bone scintigraphy was better than MRI in determining the viability of the rabbit femoral heads up to 12 days after avascularity was induced. Once the reparative process replaces nonviable fatty marrow, MRI was a sensitive method for detecting avascular necrosis.

Tibiofemoral Joint Positioning for the Valgus Stress Test

CONTEXT Recommendations on the positioning of the tibiofemoral joint during a valgus stress test to optimize isolation of the medial collateral ligament (MCL) from other medial joint structures vary in the literature. If a specific amount of flexion could be identified as optimally isolating the MCL, teaching and using the technique would be more consistent in clinical application. OBJECTIVE To determine the angle of tibiofemoral joint flexion between 0 degrees and 20 degrees that causes a difference in the slope of the force-strain line when measuring the resistance to a valgus force applied to the joint. DESIGN Cross-sectional study. SETTING University research laboratory. PATIENTS OR OTHER PARTICIPANTS Twelve healthy volunteers (6 men, 6 women: age = 26.4 +/- 5.6 years, height = 170.9 +/- 8.4 cm, mass = 75.01 +/- 14.6 kg). INTERVENTION(S) Using an arthrometer, we applied a valgus force, over a range of 60 N, to the tibiofemoral joint in 0 degrees , 5 degrees , 10 degrees , 15 degrees , and 20 degrees of flexion. MAIN OUTCOME MEASURE(S) Force-strain measurements were obtained for 5 positions of tibiofemoral joint flexion. RESULTS As knee flexion angle increased, slope values decreased (F(4,44) = 17.6, P < .001). The slope at full extension was not different from that at 5 degrees of flexion, but it was different from the slopes at angles greater than 10 degrees of flexion. Similarly, the slope at 5 degrees of flexion was not different from that at 10 degrees of flexion, but it was different from the slopes at 15 degrees and 20 degrees of flexion. Further, the slope at 10 degrees of flexion was not different from that at 15 degrees or 20 degrees of flexion. Finally, the slope at 15 degrees of flexion was not different from that at 20 degrees of flexion. CONCLUSIONS When performing the manual valgus stress test, the clinician should fully extend the tibiofemoral joint or flex it to 5 degrees to assess all resisting medial tibiofemoral joint structures and again at 15 degrees to 20 degrees of joint flexion to further assess the MCL.