The biomechanics of the patellofemoral joint

Physical therapy for patella malalignment differs from therapy for other knee conditions. In fact, accepted forms of knee therapy can be counterproductive when one is dealing with patella malalignment. This article reviews some of the biomechanical foundations of patella-specific therapy and addresses common controversies. We emphasize the concept of articular cartilage stress over that of joint reaction force. The rationale for strengthening the vastus medialis obliquus and for avoiding certain forms of open chain strengthening are discussed, and we outline some of the exciting work being done in our laboratory concerning patellofemoral tracking, contact area, and cartilage properties.     

Kinematic CT of the patellofemoral joint

The relationship between time structure and procrastination was investigated among 115 Irish undergraduate students. Significant negative zero-order correlations were found among scores for all five subscales of time structure and procrastination. A follow-up stepwise multiple regression indicated a significant multiple correlation (R = .61) between all five time structure subscale scores and procrastination. Significant predictors of procrastination were scores on the Time Structure subscales of Effective Organization followed by Sense of Purpose. These results suggest that strategies focusing on time management in conjunction with existential approaches of psychotherapy may be an effective intervention for reducing procrastination.     

Differential diagnosis in patients with disorders of the patellofemoral joint

Anterior knee complaints are difficult diagnostic problems. It cannot be overstated that the most important information available is to be found in the patient's history. Onset, quality, and quantity of symptoms must be assessed. This information is then synthesized to determine the specific functional disabilities resulting from the patient's anterior knee disorder. Once a history is obtained, a consistent, methodical physical examination can be performed to narrow the differential diagnosis. Radiographic evaluation is used to further hone the differential or to confirm the most likely diagnosis. Ultimately, a specific working diagnosis is selected and treatment is tailored to changing the underlying structural or biomechanical abnormalities that led to the patient's complaints.     

Effect of patellar meniscus on patellofemoral contact stress in total knee arthroplasty

A wide variety of surgical procedures and implant materials have been used to satisfy the growing demand of patients for lip augmentation. The authors describe our experience with Alloderm (LifeCell Corp, The Woodlands, TX). It has proven to be a safe and effective means of offering mild to moderate augmentation of the lips.     

The effect of intersegmental knee moments on patellofemoral contact mechanics in cycling

The aim of this study was to evaluate the effect of bicycle pedal design on the mechanics of the patellofemoral joint. Previous research determined that for certain riders the non-driving varus and internal knee moments could be reduced by switching from fixed to free floating pedals (Ruby and Hull, 1993). It was postulated that the presence of varus and internal knee moments during fixed pedal cycling may adversely affect patellofemoral joint contact mechanics which could lead to the development of anterior knee pain. To investigate the effect of pedal design the hypothesis that varus and internal intersegmental knee moments significantly increase patellofemoral contact pressure, contact area and contact force was tested. To test this hypothesis cycling loads were simulated in vitro using a six-degree-of-freedom load application system (LAS). Using the LAS, varus moments ranging from 0-20 Nm and internal knee moments ranging from 0-10 Nm were applied simultaneously with quadriceps force at knee flexion angles of 60 and 90 degrees. Patellofemoral contact patterns were measured using pressure sensitive film. An applied 10 Nm internal moment significantly increased both contact area by 16% and contact force by 22% at 90 of flexion. The application of a 20 Nm varus moment modestly yet significantly increased contact area by 6% and contact force by 5%. When applied in combination, varus and internal knee moments increased contact area and force by as much as 29% and 28% respectively. The mean contact pressure was not significantly increased by either of the two moments. The results suggest that non-driving intersegmental knee moments subject the patellofemoral joint to loads and contact patterns which may accelerate the development of chondromalacia.     

Experimental feline panleucopenia in the conventional cat

Coventional kittens, 12-27 weeks old, were inoculated with cell-cultured feline panleucopenia virus and killed sequentially between day 3 and day 24 after inoculation. All developed a non-fatal mild disease between days 2 and 9, characterized by lymphopenia, neutropenia, listlessness, depression and the development of neutralizing antibodies to the virus. Small intestinal bacterial counts were reduced during the period of maximal clinical disease, presumably a result of decreased food intake. There was involution of the thymus with marked depletion of lymphocytes between days 3 and 12. Depletion of lymphocytes also characterized the lesions in the lymph nodes between days 3 and 8. At the same time crypt lesions with spotty distribution were in the small intestinal and colonic mucosa. The changes were loss of crypt epithelial cells with compensatory attenuation of the remaining epithelium. Electron microscopically, the number and size of microvilli and secretory granules were reduced but there was no change indicating lethal cell injury. There were no virus particles. The findings point to an early and transient cellular damage by the virus. Intestinal alkaline phosphatase activity disappeared from the luminal surface of the attenuated crypt epithelial cells. Otherwise, intestinal alkaline and acid phosphatase activity were not altered in inoculated cats.     

Tibiofemoral contact pressures in degenerative joint disease

Using tibiofemoral joints from older (age, 53-80 years) human cadavers with articular cartilage degeneration, contact pressures and contact areas were measured in the extended knee in four conditions: (1) neutral alignment; (2) 5 degrees varus (simulating single limb stance of gait); (3) 5 degrees valgus; and (4) after a 5 degrees proximal tibial closing wedge valgus osteotomy. In degenerated cartilage, contact pressures were reduced at the lesion sites and were high on the borders of the lesions. No statistically significant changes occurred in contact pressures and areas when values from neutral loading were compared with values during loading in each of the other three conditions. Lateral average and maximum contact pressures were less in varus loading than in valgus loading. Equal medial and lateral contact pressures during varus loading, in contrast to lower medial than lateral contact pressures in the other three loading, supports the theory that the varus moment imposed on the knee in single limb stance could be a mechanism causing medial tibiofemoral osteoarthritis. The 5 degrees valgus osteotomy resulted in contact pressures similar to those in neutral loading. These experiments do not support the value of the 5 degrees valgus osteotomy in reducing contact pressures on the medial tibial plateau.     

Patellofemoral joint compressive forces in forward and backward running

The use of backward running is becoming more common in the rehabilitation setting. In particular, backward running has been suggested as a treatment modality in patients experiencing patellofemoral pain syndrome. To date, no study has examined the loads at the patellofemoral joint during backward running. The purpose of this study was to compare patellofemoral joint compressive forces during forward and backward running. Ground reaction force and kinematic data were collected on five male joggers during free speed forward and backward running. A floor reaction force vector model was used to calculate the stance phase knee extension moments. The distance used for the extensor muscle lever arm was 4.9 cm. Patellar mechanism angle was calculated based on knee joint angle. There was a reduction in the peak patellofemoral joint compressive forces in backward compared with forward running (2277 +/- 192N vs. 4253 +/- 1292N; p < 0.05) at self-selected speeds. Peak patellofemoral joint compressive force occurred significantly later (p < 0.05) in the stance phase of backward running (52 +/- 4%) than in forward running (35 +/- 3%). The peak patellofemoral joint compressive force normalized to subject body weight was 5.6 +/- 1.3 body weight in forward running and 3.0 +/- 0.6 body weight in backward running. The results suggest that backward running at a self-selected speed may reduce patellofemoral joint compressive forces and, coupled with the quadriceps strengthening that has previously been reported, may be beneficial in the rehabilitation of patellofemoral pain syndrome in runners. However, constant speed comparisons or other models may yield different results.     

Experimental osteoarthritis in the rabbit knee joint

The development of arthrotic-like changes following the resection of the cruciate ligaments in the knee joint of rabbits has been studied at intervals from 2 weeks to 10 months in 35 animals. Signs of cartilage degeneration were followed by changes in the subchondral bone, where formation of osteophytes and condensation took place. An increased vascular supply was demonstrated by microangiographic and scintigraphic investigations. The uptake of 18F and 99mTc-polyphosphate reached a maximal value about 2 months after the operation and then diminished despite further development of arthrotic changes.     

A theoretical evaluation of crack closure

Premature crack closure has been considered an important factor affecting the applied driving force under cyclic load. Among several factors that induce crack closure, plasticity and oxidation or corrosion have been recognized as the most significant. An analytical estimation of both is made using dislocation theory. The analysis indicates that (a) plasticity originating from crack tip does not induce crack closure and (b) closure arising from asperity ridges due to oxides, corrosion products or surface roughness is small and insignificant unless crack is completely packed with asperities.     

The vastus medialis oblique muscle and its relationship to patellofemoral joint deterioration in human cadavers

Patellofemoral joint deterioration (PFJD) is frequently seen in physical therapy clinics and represents a significant problem for both patients and rehabilitation clinicians. The vastus medialis oblique (VMO) muscle is reported to be the primary stabilizer of the patella during knee extension. Most studies and treatment protocols emphasize strengthening of the VMO as the nonsurgical treatment of choice for patients with PFJD. The purpose of this study was to determine whether any relationship exists between the morphology of the VMO and the presence and severity of PFJD in human cadavers. Dissection of 374 vastus medialis (VM) muscles and patellofemoral joints was performed on 229 human cadaver lower limbs to determine what relationships exist between gender, VMO features, and PFJD. Patellofemoral joint deterioration was determined by direct visual observation and assigned a score based on severity of joint deterioration present. Two-way chi-square tests were performed to determine the relationships between cadaver gender, the presence of VMO features, and the presence and severity of PFJD. Linear regression was performed to determine whether any correlation existed between the VMO fiber angle and the severity of PFJD. A one-way analysis of variance was performed to determine whether any differences existed between the VMO fiber angle and the PFJD groups. No statistically significant relationships, correlation, or differences existed in any of the tests performed between cadaver gender, VMO features, and presence or severity of PFJD. The presence or severity of PFJD in human cadavers is not related to either gender or VMO morphologic features. The results of this study do not support the premise that a more distal insertion of the VMO onto the patella of the VMO will have any effect on the presence or severity of PFJD.     

Material and functional properties of articular cartilage and patellofemoral contact mechanics in an experimental model of osteoarthritis

The purposes of this study were to determine the in situ functional and material properties of articular cartilage in an experimental model of joint injury, and to quantify the corresponding in situ joint contact mechanics. Experiments were performed in the anterior cruciate ligament (ACL) transected knee of the cat and the corresponding, intact contralateral knee, 16 weeks following intervention. Cartilage thickness, stiffness, effective Young's modulus, and permeability were measured and derived from six locations of the knee. The total contact area and peak pressures in the patellofemoral joint were obtained in situ using Fuji Pressensor film, and comparisons between experimental and contralateral joint were made for corresponding loading conditions. Total joint contact area and peak pressure were increased and decreased significantly (alpha=0.01), respectively, in the experimental compared to the contralateral joint. Articular cartilage thickness and stiffness were increased and decreased significantly (alpha=0.01), respectively, in the experimental compared to the contralateral joint in the four femoral and patellar test locations. Articular cartilage material properties (effective Young's modulus and permeability) were the same in the ACL-transected and intact joints. These results demonstrate for the first time the effect of changes in articular cartilage properties on the load transmission across a joint. They further demonstrate a substantial change in the joint contact mechanics within 16 weeks of ACL transection. The results were corroborated by theoretical analysis of the contact mechanics in the intact and ACL-transected knee using biphasic contact analysis and direct input of cartilage properties and joint surface geometry from the experimental animals. We conclude that the joint contact mechanics in the ACL-transected cat change within 16 weeks of experimental intervention.     

Experimental and theoretical study of the phase equilibria in the fe-ni-w system

Experimental data on the Fe-Ni-W phase diagram have been obtained at 1273, 1373, 1473, 1573, and 1673 K by means of the diffusion-couple technique and electron microprobe analysis. These data were combined with selected literature information on the liquidus surface and the complete Fe-Ni-W phase diagram was evaluated. The evaluation was performed by analyzing the experimental data in terms of thermodynamic models for the Gibbs energy of the various phases and by computer-optimizing the model parameters involved. The optimized phase diagram satisfactorily describes the available data.     

Functional evaluation of 6-hydroxydopamine-induced sympathectomy in the liver of the cat

Intraportal injection of 6-hydroxydopamine (25 mg/kg) results in nearly complete functional sympathectomy in the cat liver 1 week after the injection. Functional sympathectomy was verified by comparing the changes in liver blood volume (measured in vivo in a plethysmograph) resulting from direct stimulation of the hepatic nerves in control and pretreated animals. Pretreatment prevented the large reductions in hepatic blood volume normally seen with nerve stimulation while the response to infused noradrenaline was not reduced. Lack of morphological changes in right atrial nerve endings and an unaltered pressor response to bilateral carotid arterial occlusion indicate that sympathectomy at sites other than the liver did not occur.     

Control of torque direction by spinal pathways at the cat ankle joint

To study the biomechanics of the calcaneal tendon's complex insertion onto the calcaneus, we measured torque-time trajectories exerted by the triceps surae and tibialis anterior muscles in eight unanesthetized decerebrate cats using a multi-axis force-moment sensor placed at the ankle joint. The ankle was constrained to an angle of 110 degrees plantarflexion. Muscles were activated using crossed-extension (XER), flexion (FWR), and caudal cutaneous sural nerve (SNR) reflexes. Torque contributions of other muscles activated by these reflexes were eliminated by denervation or tenotomy. In two animals, miniature pressure transducers were implanted among tendon fibers from the lateral gastrocnemius (LG) muscle that insert straight into the calcaneus or among tendon fibers from the medial gastrocnemius (MG) that cross over and insert on the lateral aspect of calcaneus. Reflexively evoked torques had the following directions: FWR, dorsiflexion and adduction; SNR, plantarflexion and abduction; and XER, plantarflexion and modest abduction or adduction. The proportion of abduction torque to plantarflexion torque was always greater for SNR than XER; this difference was about 50% of the magnitude of abduction torque generated by tetanic stimulation of the peronei. During SNR, pressures were higher in regions of the calcaneal tendon originating from MG than regions originating from LG. Similarly, pressures within the MG portion of the calcaneal tendon were higher during SNR than during XER, although these two reflexes produced matched ankle plantarflexion forces. Selective tenotomies and electromyographic recordings further demonstrated that MG generated most of the torque in response to SNR, while soleus, LG, and MG all generated torques in response to XER.(ABSTRACT TRUNCATED AT 250 WORDS)     

工作辊交叉式轧机辊系轴向力的实验研究

本文介绍了工作辊交叉式轧机辊系轴向力的测试方法和测试结果，分析了测试过程中所遇到的种种现象和所存在的问题，以供同行参考