Effects of removal of the acetabular labrum in a sheep hip model.

OBJECTIVE: The aim of this study was to learn whether partial resection of the acetabular labrum would lead to degenerative arthritis in an ovine model. METHODS: A 2 cm segment of labrum was removed from one hip in 18 mature Swiss Alpine sheep and a sham procedure was performed on the opposite side. Animals were permitted ad lib activity until sacrifice at 6, 12 or 24 weeks. The hip joint was removed en bloc, and loaded with a force of one body weight, using a custom device designed to recreate a physiologic joint reaction force. While under load, the joint was plunge frozen, and then fixed by freeze substitution using aldehydes in methanol/acetone solvents. The entire joint was embedded in methacrylate and sectioned in a standardized frontal plane following the reaction force and including the femoral neck and the acetabular fossa. The sections were evaluated for concentricity and evidence of arthrosis. Six hip joints of three sheep with no surgical procedure were loaded with high or low loads and served as non-surgical controls. RESULTS: Degenerative changes were present in all surgical hips, but the changes were symmetrical and mild. In 16 of 18 hips, the labrum regenerated to the extent that dense fibrous scar extending from the surgically denuded origin filled the defect. CONCLUSION: Resection of the labrum does not cause rapid degeneration or altered stability of the sheep hip.

Deformation of chondrocytes in articular cartilage under compressive load: a morphological study.

The main function of articular cartilage is to transmit load. The objective of this study was to describe the deformation of chondrocytes under static loading and its relation to collagen matrix deformation. Whole intact rabbit knee joints were loaded statically with either high or low magnitude and long or short duration. Specimens were cryopreserved while under load and prepared for morphological evaluation by field emission scanning electron microscopy. With this method an immediate preservation of the chondrocyte in its loaded state was possible. Static compression of articular cartilage produced a zone-specific deformation of chondrocyte shape, depending on the magnitude and duration of load. Under high-force and long-duration loading, the chondrocytes showed considerable deformation concomitant with the highly deformed collagen fibres. Chondrocyte deformation occurred mostly in the transitional and upper radial zones and less in the lower layers. There was no significant change of the chondrocyte shape in the tangential zone under high- or low-force short-duration loading. These results show that the chondrocytes undergo significant changes in shape ex vivo and that they are sensitive to differences in the magnitude and duration of loads being applied. Chondrocyte deformation is strongly linked to the deformation of the surrounding cartilage collagen matrix.

[Treatment of acute slips and clinical results in slipped capital femoral epiphysis]. / Therapie der akuten Epiphysenlösung des Hüftkopfes und klinische Behandlungsergebnisse.

In looking at the pathoanatomy of slipped capital epiphysis, it is important to appreciate that the articular cartilage ruptures at the level of the physis as the articular cartilage also covers part of the femoral neck metaphysis. As a consequence, smoothness is lost and already with mild slips the irregularities may injure the acetabular cartilage structures and may cause tears of the labrum. Principally therefore an open revision and restoration of the anatomy as perfectly as possible is needed. The technique for open reduction was developed by Dunn in 1964 and then refined by Ganz in 1997 applying new anatomical vascular studies. However, the long-term data on the "conservative" approach of only using transfixation to avoid further slipping show relatively good results and long-term studies of a more aggressive open approach will be needed to show evidence of further improvement. For the more severe cases, restoration of the correct anatomy by open reduction or improved axial relationships by more distant osteotomies have already been proven to give better results. Besides the extent of the slip, it is important to consider whether the slip is acute or chronic or acute and chronic. So far there are no data showing that the surgical treatment of slipped capital femoral epiphysis must be made on an emergency basis. However, prevention of further slips, e.g., by supine transport, is to be considered an emergency.

The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement.

Impingement by prominence at the femoral head-neck junction on the anterior acetabular rim may cause early osteoarthritis. Our aim was to develop a simple method to describe concavity at this junction, and then to test it by its ability to distinguish quantitatively a group of patients with clinical evidence of impingement from asymptomatic individuals who had normal hips on examination. MR scans of 39 patients with groin pain, decreased internal rotation and a positive impingement test were compared with those of 35 asymptomatic control subjects. The waist of the femoral head-neck junction was identified on tilted axial MR scans passing through the centre of the head. The anterior margin of the waist of the femoral neck was defined and measured by an angle (alpha). In addition, the width of the femoral head-neck junction was measured at two sites. Repeated measurements showed good reproducibility among four observers. The angle alpha averaged 74.0 degrees for the patients and 42.0 degrees for the control group (p < 0.001). Significant differences were also found between the patient and control groups for the scaled width of the femoral neck at both sites. Using standardised MRI, the symptomatic hips of patients who have impingement have significantly less concavity at the femoral head-neck junction than do normal hips. This test may be of value in patients with loss of internal rotation for which a cause is not found.

Perfusion of the femoral head during surgical dislocation of the hip. Monitoring by laser Doppler flowmetry.

We used laser Doppler flowmetry (LDF) with a high energy (20 mW) laser to measure perfusion of the femoral head intraoperatively in 32 hips. The surgical procedure was joint debridement requiring dislocation or subluxation of the hip. The laser probe was placed within the anterosuperior quadrant of the femoral head. Blood flow was monitored in specific positions of the hip before and after dislocation or subluxation. With the femoral head reduced, external rotation, both in extension and flexion, caused a reduction of blood flow. During subluxation or dislocation, it was impaired when the posterosuperior femoral neck was allowed to rest on the posterior acetabular rim. A pulsatile signal returned when the hip was reduced, or was taken out of extreme positions when dislocated. After the final reduction, the signal amplitudes were first slightly lower (12%) compared with the initial value but tended to be restored to the initial levels within 30 minutes. Most of the changes in the signal can be explained by compromise of the extraosseous branches of the medial femoral circumflex artery and are reversible. Our study shows that LDF provides proof for the clinical observation that perfusion of the femoral head is maintained after dislocation if specific surgical precautions are followed.

[The relationship between fovea capitis femoris and weight bearing area in the normal and dysplastic hip in adults: a radiologic study]. / Die radiologische Beziehung der Fovea capitis femoris zur azetabulären Belastungszone bei der normalen und dysplastischen Hüfte des Erwachsenen.

AIM: In residual hip dysplasia the fovea capitis femoris lays often more cranial than in the normal hip morphology, the ligamentum capitis femoris thereby articulating with the weight-bearing area of the acetabular cartilage. The aim of this study was to quantitate this aspect with regard to its potential negative effect for the degeneration of the dysplastic acetabulum. METHOD: The relation between the fovea capitis femoris and the weight-bearing area were studied using the a.p.-pelvis view in normal and dysplastic hips. The measurements were made by digital image analysis. RESULTS: The hypothesis that the "fovea alta" is characteristic for the dysplastic hip was confirmed. In dysplastic hips the typically wider fovea lays on average 30 degrees more cranial, touching the weight-bearing area over 11 degrees. The fovea in normal hips has on average a distance of 26 degrees to the acetabular roof. In dysplastic hips the steeper roof, the tendency for decentering of the femoral head as well as a higher CCD angle explain this phenomenon to a certain degree. In a theoretical model to correct the acetabular position over the femoral head alone one quarter of the foveae would still touch the weight-bearing area. Nevertheless, in our series after periacetabular osteotomy this was never the case due to better centering. CONCLUSION: lt is our hypothesis that a "fovea alta", which further reduces the already smaller loaded cartilage surface, is one part leading to the early degeneration of the dysplastic hip. Therefore, it should be considered in biomechanical models and in the planning of corrective procedures.

The acute structural changes of loaded articular cartilage following meniscectomy or ACL-transection.

OBJECTIVE: Meniscectomy and anterior cruciate ligament (ACL) rupture have been identified as precursors of osteoarthrosis (OA) in clinical reviews and animal experiments. In this study, the acute effects of these injuries on articular cartilage matrix deformation, preserved in a loaded state using a cryopreservation technique, were studied by scanning electron microscopy (SEM). METHOD: Whole knee joints from adult White New Zealand rabbits (N=87) were loaded ex vivo, using a simulated quadriceps pull under static and cyclic loading conditions, following medial meniscectomy or transection of the ACL. Specimens were plunge-frozen while under load, or following a recovery period, and prepared for SEM by cryofixation. Using SEM and photographic images, the medial tibial plateau cartilage was assessed both qualitatively and quantitatively. RESULTS: After meniscectomy, significantly increased bending and crimping of radial collagen fibers occurred with static loading. Compared to intact knees, the area of tibial cartilage showing an indentation was increased by 80% (P< 0.05), the articular cartilage thickness was significantly more reduced when under load (for high force long duration static loading, intact joints had 53%+/-3 reduction in cartilage thickness compared to 39%+/-4 after meniscectomy, P< 0.05), and it took nearly twice as long for the cartilage thickness to recover following loading. These post-meniscectomy differences were either not present or were minimal when the joint was allowed to extend when loaded. ACL-transection slightly increased collagen deformation in the deeper zones, but only with cyclic loading. CONCLUSION: The findings indicate that, with static loading, significantly increased deformation of articular cartilage collagen structure can occur following meniscectomy, but is minimized by joint motion. This increased deformation may be relevant to the etiology and progression of joint degeneration.

Treatment of tibial plateau fractures with small fragment internal fixation: a preliminary report.

OBJECTIVE: To evaluate the use of small fragment implants for fractures of the proximal tibia. DESIGN: Retrospective. SETTING: Level I trauma center. PATIENTS/PARTICIPANTS: Seventeen patients with AO Classification Type B and C fractures of the proximal tibia. Two patients were lost to follow-up. INTERVENTION: After atraumatic dissection and open reduction, fracture stabilization was accomplished with the use of the AO/ASIF small T-plate (3.5-millimeter system). In two patients a medial uniplanar external fixator was applied as additional fixation. In six patients a cancellous autograft was performed. MAIN OUTCOME MEASUREMENTS: At an average follow-up of forty-two months (range, 24 to 75 months), all patients were evaluated radiographically and functionally. The incidence of local complications was specifically recorded. RESULTS: Postoperatively, the radiographs showed 86.7 percent anatomic or near anatomic reduction with respect to the articular joint surface. In three separate patients condylar widening, condylar narrowing or varus deformity was evident. In one patient, a minimal secondary displacement of less than two millimeters was observed before bony healing. All fractures healed within twelve weeks. At the latest follow-up, there were 53.3 percent excellent, 33.3 percent good, and 13.3 percent fair results. There were no infection or soft tissue complications. CONCLUSIONS: The use of small fragment implants combined with atraumatic soft tissue dissection potentially offers good results for the treatment of fractures of the proximal tibia. These initial results suggest that this technique may have the advantage of anatomic reduction while comparing favorably with less invasive methods regarding radiologic and functional outcome as well as incidence of complications.

Effect of mechanical load on articular cartilage collagen structure: a scanning electron-microscopic study.

Little is known about the morphological effect of a mechanical load upon articular cartilage. The objective of this study was to describe and quantify the deformation of the articular cartilage collagen structure of the tibial plateau under static loading. Whole intact rabbit knee joints were loaded in vitro by simulating a quadriceps force of 3x, 1x or 0.5x body weight (high, medium, low) over durations of 30 or 5 min (long, short). Specimens were cryopreserved while under load and prepared for morphological evaluation by field emission scanning electron microscopy. Under high force and long duration loading the collagen fibers exhibited high deformation with an increased thickness of the layer of collagen fibers oriented almost parallel to the surface and a cartilage thickness reduced to 54%. Collagen fiber deformation occurred mostly in the transitional and upper radial zone. The area of tibial indentation and the cartilage thickness reduction increased with magnitude and duration of load. The collagen matrix did show a bulging edge at the border of the meniscus and exhibited remarkable deformation under the meniscus.

The surface contour of articular cartilage in an intact, loaded joint.

The friction coefficients measured in diarthrodial joints are small. Theories of joint lubrication attribute this efficiency to entrapment or movement of synovial fluid, yet anatomical models of the surface are based on studies of isolated fragments of cartilage, not functional joints. To investigate the functional interrelationship of joint surfaces and synovial fluid, the ultrastructure of loaded joints was examined. Twenty-four New Zealand white rabbit knee joints were loaded either statically or moved ex vivo using simulated muscle forces and then plunge-frozen under load. After fixation in the frozen/loaded state by freeze-substitution fixation, the medial joint compartments were embedded in epoxy resin while still articulated. Bone was trimmed away from the articular surfaces, permitting the cartilage to be sectioned for light and electron microscopy. These joint surfaces were then compared with controls which were not loaded, not moved or had been disarticulated prior to embedding. Articular surfaces of loaded joints were smooth at magnifications from x 35 to x 7500, whereas the tibial surfaces of nonloaded joints were irregular. Small pools of joint fluid were observed at the meniscal edge and beneath the anterior horn of the meniscus. At magnifications of x 40000, the joint surfaces were separated by a uniform 100 nm space containing fluid. An amorphous, electron dense articular surface lamina was present but, when loaded, was thicker and flatter than previously reported. No surface pits or bumps were visible in embedded, loaded joints. This is the first ultrastructural study of intact loaded joints. The findings suggest that fluid film lubrication is present in diarthrodial joints, but the fluid sequestration postulated in several models is not apparent.

Collagen fibre arrangement in the tibial plateau articular cartilage of man and other mammalian species.

Experimental animal models are frequently used to study articular cartilage, but the relevance to man remains problematic. In this study animal models were compared by examination of the collagen fibre arrangement in the medial tibial plateau of human, cow, pig, dog, sheep, rabbit and rat specimens. 24 cartilage samples from each species were prepared and maximum cartilage thickness in the central tibial plateau measured. Samples were fixed, dehydrated, freeze-fractured and imaged by scanning electron microscopy (SEM). At low magnification, 2 different arrangements of collagen fibres were observed: leaf-like (human, pig, dog) and columnar (cow, sheep, rabbit, rat). The porcine collagen structure was the most similar to that of man. This arrangement was consistent from the radial to the upper zones. Under higher magnification at the surface of the leaves, the collagen was more randomly oriented, whereas the columns consisted of parallel collagen fibrils. The maximum thickness of cartilage did not correlate with the type of collagen arrangement but was correlated with the body weight of the species (r = 0.785). When using animal models for investigating human articular cartilage function or pathology, the differences in arrangement of collagen fibres in tibial plateau cartilage between laboratory animals should be considered especially if morphological evaluation is planned.

Deformation of articular cartilage collagen structure under static and cyclic loading.

Relatively little is known about the morphology of articular cartilage under conditions of normal use, yet a more profound knowledge is both critical to the understanding of cartilage function and helpful for the validation of tissue-engineered cartilage. In this study, the deformation of the articular cartilage of the tibial plateau under compressive static and cyclic loading is characterized. Whole knee joints of rabbits were loaded ex vivo while the knee was held statically or allowed to move against resistance. Load magnitudes of quadriceps were maintained at either three (high) or one (low) times body weight for 30 minutes. For cyclic loading, the tibia was flexed between 70 and 150 degrees relative to the femur at 1 Hz with either a cyclic or constant force. The recovery of cartilage after unloading was examined for each loading condition. At the end of the loading, specimens were cryofixed while under load, freeze-substituted, and prepared for scanning electron microscopy. Morphological examination demonstrated significantly higher deformation of the collagen structure throughout all cartilage zones under static loading conditions compared with cyclic loading conditions in which deformation was limited to the superficial regions. The minimum thickness of the cartilage that remained after loading was dependent on the magnitude of load and was significantly smaller with static loads (54% of the thickness of the unloaded controls) than after cyclic loading or constant-force cyclic loading (78 or 66% of the thickness of the unloaded controls, p < 0.05). Acute bending of the collagen fibers was observed under both loading conditions: in the superficial half of the articular cartilage after static loading and in the superficial quarter after cyclic loading. Complete recovery of all deformation occurred within 30 minutes but was significantly faster after cyclic loading. These data suggest that the structure of the collagen of articular cartilage exhibits a zone-specific deformation that is dependent on the magnitude and type of load.

[Treatment concept in complex fractures of the head of the tibia]. / Behandlungskonzept bei komplexen Tibiakopffrakturen.

Complex tibial condylar fractures are intraarticular fractures with associated lesions of capsule and ligaments, menisci, soft tissue envelope and neurovascular structures. They are in general produced by a high-energy trauma and are usually part of a polytraumatized patient. The frequency for the associated lesions are up 50% for the collateral ligaments, and up to 40% for the cruciate ligaments and the menisci, respectively. The paper presents the crucial steps of clinical and radiological assessment and outlines a concept of treatment, documented by two illustrative cases.

Open-reduction and intertrochanteric osteotomy for osteonecrosis and extrusion of the femoral head in adolescents.

Extrusion of the femoral head during late childhood and adolescence can be caused by tissue interposition following traumatic hip dislocation, inflammatory joint disease, or avascular necrosis with flattening of the femoral head. We report our experience of treatment by reorientation of the extruded femoral head with combined open-reduction and intertrochanteric osteotomy in seven young patients with Ficat stage III or IV avascular necrosis. Six of the seven patients showed improvement of pain and limp. They also had radiographic improvement of joint space and congruency, which suggests that the degenerative process and further surgery may be delayed.

Laser Doppler flowmetry for bone blood flow measurements: helium-neon laser light attenuation and depth of perfusion assessment.

Laser Doppler flowmetry (LDF) has been successfully used in clinical and experimental settings to evaluate bone perfusion but unanswered questions regarding its capabilities and limitations still remain. This study was undertaken to determine absorption of He-Ne laser light (632.8 nm) and maximum depth for flow assessment (threshold thickness) under optimal conditions in bone. Light transmittance in bovine bone samples of femora and tibia was measured after each step of grinding and depth of penetration calculated. The threshold thickness was obtained by placing the same samples in a flow chamber where a solution of 2% latex circulated beneath; flow was detected by a laser Doppler probe resting on top of the sample. The results showed a significantly higher depth of penetration for trabecular than for cortical bone. A regression analysis showed a high correlation between the inorganic fraction of the bone and the depth of penetration. The maximum depth at which the laser Doppler probe can evaluate flow in bone conditions was found to be 2.9 +/- 0.2 mm in cortical bone, 3.5 +/- 0.3 mm in bone covered by 1 mm cartilage and 3.5 +/- 0.2 mm in trabecular bone. The study showed the limitations of LDF in bone and their correlations to various bone properties.