The effect of harvesting the central one-third of the patellar tendon on patellofemoral contact pressure.

This study assessed whether removing the central one-third of the patellar tendon, with or without side-to-side repair of the patellar tendon defect, would alter patellofemoral pressure. Patellofemoral pressure was assessed by testing five stable knees from five different cadaveric donors on a specially designed hydraulic knee machine. Patellofemoral joint pressures were measured by placing pressure-sensitive film into the patellofemoral articulation. The joint was loaded in a static fashion, with quadriceps forces consistent with walking (647 N) and stair climbing (1923 N), at 30 degrees, 60 degrees, and 90 degrees of knee flexion. Using the same knees, the central one-third of the patellar tendon was then sectioned, and patellofemoral joint pressure measurements were repeated at identical knee flexion angles and quadriceps-forces. Side-to-side repair of the patellar tendon defect was performed and patellofemoral joint pressure measurements were repeated. There were no statistically significant differences between the control and sectioned values or between the control and repaired defect values. These results suggest that harvesting the central one-third of the patellar tendon--with or without side-to-side repair of the patellar tendon defect--does not alter patellofemoral pressures.     

The effect of bracing on patella alignment and patellofemoral joint contact area

PURPOSE: To examine the influence of two patellofemoral braces on pain response, patellar alignment, and patellofemoral joint contact area in persons with patellofemoral pain. METHODS: Fifteen women between the ages of 18 and 45 yr with a diagnosis of patellofemoral pain participated. After the assessment of pain response using a visual analog scale, subjects underwent axial plane magnetic resonance imaging of patellofemoral joint at 0 degrees, 20 degrees, 40 degrees, and 60 degrees of knee flexion. Imaging was done with the knee extensors contracted (25% body weight) under three conditions: 1) no brace, 2) On-Track brace, and 3) Patellar Tracking Orthosis (PTO). Measures of mediolateral patellar displacement and tilt and medial and lateral facet contact area were obtained from the magnetic resonance images. RESULTS: On average, the On-Track brace reduced symptoms by 50%, whereas the PTO reduced pain by 44%. When averaged across all knee flexion angles, the PTO and the On-Track brace significantly increased total patellofemoral joint contact area by 52.0 mm (21%) and 59.3 mm (24%), respectively, when compared with the no-brace condition. Bracing had no influence on lateral patellar tilt; however, small but significant changes in lateral patellar displacement were observed. CONCLUSION: Large changes in pain and contact area occurred without sizable changes in patellar alignment. The results of this study suggest that changes in patellar alignment by itself may not be responsible for pain alleviation after patellar bracing.     

The effects of removal and reconstruction of the anterior cruciate ligament on the contact characteristics of the patellofemoral joint.

Seven cadaveric knees were used to investigate the effects of removal and reconstruction of the anterior cruciate ligament with a bone-patellar tendon-bone graft on contact characteristics of the patellofemoral joint during physiologic levels of quadriceps muscle loads at 30 degrees, 60 degrees, and 90 degrees of knee flexion. Loads were applied to the quadriceps tendon to equilibrate externally applied flexion moments equivalent to one-third of values for maximum isometric extension moments. Patellofemoral contact areas and pressures were measured using pressure-sensitive film. Excision of the anterior cruciate ligament resulted in significant decreases in the total patellofemoral contact area by as much as 94 mm2 (68%), the medial facet contact area by as much as 55 mm2 (93%), the combined average contact pressure by 0.7 MPa (21%), the medial facet average contact pressure by 2.3 MPa (70%), the combined peak contact pressure by 3.0 MPa (38%), and the medial facet peak contact pressure by 5.4 MPa (76%), all at 30 degrees of knee flexion. Excision of the anterior cruciate ligament also resulted in significant decreases in total, medial facet, and lateral facet patellofemoral contact areas at 60 degrees and 90 degrees of knee flexion. Intraarticular reconstruction returned these to levels not significantly different from those of the intact knee.     

髌骨倾斜导致髌股关节接触压力与面积改变

我们采用压敏片测量技术对髌骨倾斜状态下髌股关节的生物力学变化特点进行了研究。７例新鲜人尸体标本采用手术方法将髌外侧支持带紧缩造成髌骨外侧倾斜状态，超低压型压敏片置于髌股关节之间，等长加载２００Ｎ，分别在正常状态及髌骨倾斜状态下于屈膝３０°、６０°、９０°、１２０°时测量髌股关节接触压力与面积。结果表明：髌骨倾斜后使髌股关节原正常的“哑铃型”接触压迹转变为“彗星尾状”，外侧面孤立接触，内侧面接触区减少或失接触，接触压力改变表现为髌内侧软骨面接触压力减少或消失，外侧面接触压力集中且明显增高上述改变均以屈膝３０°时最明显。实验结果提示：各种纠正髌骨倾斜状态及治疗髌骨软骨软化症的手术方法，必须以恢复髌骨内外侧关节面压力平衡为标准，特别是屈膝３０°时病理力学的改善最为重要     

Effect of bracing on patellar kinematics in patients with patellofemoral joint pain

PURPOSE: Bracing is commonly used to correct patellar malalignment syndromes. However, there are little objective data documenting the effect of such supports on patellofemoral joint relationships. The purpose of this study was to assess the effectiveness of an elastic patellofemoral sleeve brace in altering patellar tracking in subjects with patellofemoral pain. METHODS: Ten female subjects (12 patellofemoral joints) between the ages of 17 and 46 participated in this study. All subjects had a diagnosis of patellofemoral pain and demonstrated lateral patellar tracking based on magnetic resonance imaging (MRI) assessment. Each subject underwent kinematic MRI of the patellofemoral joint through a range of 45 to 0 degrees of knee flexion against a resistance of 15% body weight. Imaging was performed with and without a patellofemoral joint brace (Bauerfeind Genutrain P3 brace, Atlanta, GA). Measurement of medial/lateral patellar displacement, medial/lateral patellar tilt, and the depth of the trochlear groove (sulcus angle) were obtained with midpatellar image sections at 45, 36, 27, 18, 9 and 0 degrees of knee flexion. RESULTS: No statistically significant differences in medial/lateral patellar displacement or tilt were found between braced and unbraced trials across all knee flexion angles (P < 0.05). A small but statistically significant increase in sulcus angle was found across all knee flexion angles with the braced trials (P > 0.05). CONCLUSIONS: These results do not support the hypothesis that the brace used in this study corrects patellar tracking patterns in subjects with patellofemoral pain. However, the increased sulcus angle indicates a change in patella position within the trochlea. It is possible that the clinical improvements seen with bracing may be the result of subtle differences in joint mechanics and not gross changes in alignment.     

Reducing the lateral force acting on the patella does not consistently decrease patellofemoral pressures

BACKGROUND: Extensor mechanism procedures that decrease the lateral component of the patellar tendon or quadriceps force acting on the patella do not consistently reduce pain. HYPOTHESIS: Patellofemoral treatments do not consistently decrease patellofemoral pressures because of variations in the moments acting on the patella. STUDY DESIGN: Computer simulation study. METHODS: Computational models of 4 knees were constructed to characterize the patellofemoral pressure distribution during simulated squatting from 40 degrees to 90 degrees. The knees were given an initial Q angle of 25 degrees. Patellofemoral treatments were simulated by increasing the percentage of the quadriceps force applied by the vastus medialis by 50% and by medializing the tibial tuberosity to decrease the Q angle to 15 degrees. RESULTS: Decreasing the Q angle caused a larger decrease in the lateral component of the force applied by the quadriceps and patellar tendon than did increasing the force applied by the vastus medialis and, therefore, was more effective at decreasing patellofemoral pressures and the force needed to resist lateral subluxation. Both treatments also decreased the moments acting to rotate the distal patella laterally and tilt the patella laterally during flexion. Variations in these moments increased patellofemoral pressures for some knees. CONCLUSIONS: Treatments that reduce patellofemoral subluxation can have an unexpected influence on patellofemoral pressures because of the moments acting on the patella. CLINICAL RELEVANCE: Extensor mechanism procedures that restore patellofemoral stability may not provide pain relief.     

Biomechanical and kinematic influences of a total infrapatellar fat pad resection on the knee

BACKGROUND: This biomechanical study was performed to evaluate the consequences of total infrapatellar fat pad resection on knee kinematics and patellar contact pressure. HYPOTHESIS: Resection of the infrapatellar fat pad produces significant changes in knee kinematics and patellar contact pressure. STUDY DESIGN: Biomechanical cadaveric study. METHODS: Isokinetic knee extension was simulated on 10 human knee cadaveric specimens (6 men, 4 women; mean age at death, 44 years). Joint kinematics were evaluated by an ultrasound-based 3D motion analysis system, and retro-patellar contact pressure was measured using an electronic pressure-sensitive film. All data were taken before and after resection of the infrapatellar fat pad and statistically analyzed. RESULTS: A total resection of the infrapatellar fat pad resulted in a significant decrease of the tibial external rotation relative to the femur between 63 degrees of flexion and full knee extension (maximum: 3 degrees rotation difference at 0 degrees knee flexion, P = .011), combined with a significant medial translation of the patella between 29 degrees and 69 degrees of knee flexion (range, 0.9-1.3 mm, P = .017-.028). Retro-patellar contact pressure was significantly reduced (from 20% to 25%, P = .008-.021) at all flexion angles. CONCLUSION: A resection of the infrapatellar fat influences patellar biomechanics and knee kinematics. CLINICAL RELEVANCE: The infrapatellar fat pad may have a biomechanical function and may play a role in anterior knee pain syndrome.     

股骨髁髌股、胫股关节运动重叠接触区域及其生物力学测定

目的 :明确膝关节运动时胫骨、髌骨与股骨髁接触的重叠区域 ,测量并比较分析重叠区域内髌股、胫股关节各自接触压大小及分布特点 ,探讨髌股关节置换术中股骨滑车假体长度的设计。方法 :收集 8具新鲜膝关节尸体标本 ,在Instron 85 0 1生物力学测试仪上构建实验平台 ,模拟生理状态下膝关节站立到下蹲屈膝的过程 ,采用染色法描记重叠区域、压敏法测量髌股、胫股关节在该区域接触压。结果 :股骨髁关节面存在髌股、胫股关节运动重叠接触区域 ,范围大致相当股骨髁髌股关节接触区域内、始于屈膝 75°髌股接触部的后部分区域 ;重叠区域内髌股、胫股关节各自接触压测定显示 ,前者的接触压明显高于后者。结论 :股骨滑车假体的有效长度应涵盖髌股关节在股骨髁所有接触区域。     

Increased patellofemoral pressure after TKA: an in vitro study

Purpose

Considering the discrepant results of the recent biomechanical studies, the purpose of this study was to simulate dynamic muscle-loaded knee flexion with a large number of specimens and to analyse the influence of total knee arthroplasty (TKA) without and with patellar resurfacing on the patellofemoral pressure distribution.

Methods

In 22 cadaver knee specimens, dynamic muscle-loaded knee flexion (15°–90°) was simulated with a specially developed knee simulator applying variable muscle forces on the quadriceps muscles to maintain a constant ankle force. Patellofemoral pressures were measured with flexible, pressure-sensitive sensor foils (TEKSCAN) and patellofemoral offset with an ultrasound motion-tracking system (ZEBRIS). Measurements were taken on the native knee, after total knee arthroplasty and after patellar resurfacing. Correct positioning of the patellar implant was examined radiologically.

Results

The maximal patellofemoral peak pressure partly increased from the native knee to the knee with TKA with intact patella (35°–90°, p < 0.012) and highly increased (twofold to threefold) after patellar resurfacing (20°–90°, p < 0.001). Concurrently, the patellofemoral contact area decreased and changed from a wide area distribution in the native knee, to a punctate area after TKA with intact patella and a line-shaped area after patellar resurfacing. Patellar resurfacing led to no increase in patellar thickness and patellofemoral offset.

Conclusions

Despite correct implantation of the patellar implants and largely unchanged patellofemoral offset, a highly significant increase in pressure after patellar resurfacing was measured. Therefore, from a biomechanical point of view, the preservation of the native patella seems reasonable if there is no higher grade patellar cartilage damage.     

Trochlear contact pressures after anteromedialization of the tibial tubercle

BACKGROUND: Anteromedialization is recommended for cartilage restoration of patellofemoral defects, with the presumption that it decreases contact pressures across the trochlea. No study has evaluated pressures on the trochlear side of the patellofemoral joint after anteromedialization of the tibial tubercle. HYPOTHESIS: Anteromedialization of the tibial tubercle decreases contact pressure across the trochlea. STUDY DESIGN: Controlled laboratory study. METHODS: Ten cadaveric knees were tested by placing an electroresistive pressure sensor on the femoral side of the patellofemoral joint. A validated model of nonweightbearing resisted extension was simulated by loading the extensor mechanism at 89.1 N and 178.2 N. Knees were tested 3 times per load at 30 degrees , 60 degrees , 90 degrees , and 105 degrees . The center of force and pressure across the patellofemoral articulation were compared before and after a reproducible and consistent anteromedialization. RESULTS: The mean center of force shifted medially after anteromedialization at 89.1 N and 178.2 N. At 89.1 N, the mean total contact pressure decreased significantly (P < .05) at all angles, and at 178.2 N, it decreased significantly at 30 degrees , 60 degrees , and 90 degrees of knee flexion. The mean lateral trochlear contact pressure decreased significantly (P < .05) at all flexion angles at both 89.1 N and 178.2 N. The mean central trochlear contact pressure decreased significantly (P < .05) at 30 degrees with the 89.1-N and 178.2-N loads but increased significantly (P < .05) at 90 degrees with the 89.1-N load. The mean medial trochlear contact pressure increased significantly (P < .05) at all flexion angles at 89.1 N and 178.2 N. CONCLUSION: Anteromedialization shifts the contact force to the medial trochlea and decreases the mean total contact pressure. CLINICAL RELEVANCE: Anteromedialization decreases the mean total contact pressure while shifting contact pressure toward the medial trochlea. This study suggests that anteromedialization is appropriate for unloading the lateral trochlea. However, this procedure appears to have minimal benefit on central chondral defects, and it may actually increase the load in patients with medial defects.     

Patellofemoral problems after anterior cruciate ligament reconstruction

Between 1982 and 1986, 126 patients who had undergone ACL reconstruction were followed in a prospective manner. One year follow-up statistics were reviewed for the presence of 13 different complications. The most prevalent complications were quadriceps weakness, flexion contracture, and patellofemoral pain. Quadriceps weakness (strength less than 80% of the normal side) was present in 65% of patients and correlated positively with flexion contracture, patellar irritabibilty, and ACL reconstructions using patellar tendon grafts. Flexion contracture of 5 degrees or more was present in 24% of patients and correlated positively with increased age and patellar irritability. Patellofemoral pain was present in 19% of patients and correlated positively with flexion contracture. Clinical relevance: The three most common complications of knee ligament surgery are shown to be strongly interrelated. It is likely that a causal relationship is present in which flexion contracture causes patellofemoral irritability, and that both of these factors, alone or in combination, result in quadriceps weakness. If this theory is correct, then it is crucial that postoperative rehabilitation programs place a major emphasis on the avoidance of flexion contracture.     

Dynamic measurement of patellofemoral kinematics and contact pressure after lateral retinacular release: an in vitro study

The purpose of this study was to investigate the influence of lateral retinacular release and medial and lateral retinacular deficiency on patellofemoral position and retropatellar contact pressure. Human knee specimens (n = 8, mean age = 65 SD 7 years, all male) were tested in a kinematic knee-simulating machine. During simulation of an isokinetic knee extension cycle from 120° to full extension, a hydraulic cylinder applied sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm. The position of the patella was measured using an ultrasound based motion analysis system (CMS 100^®, Zebris). The amount of patellofemoral contact pressure and its pressure distribution was measured using a pressure sensitive film (Tekscan^®, Boston). Patellar position and contact pressure were first investigated in intact knee conditions, after a lateral retinacular release and a release of the medial and lateral retinaculum. After lateral retinacular release the patella continuously moved from a significant medialised position at flexion (P = 0.01) to a lateralised position (P = 0.02) at full knee extension compared to intact conditions, the centre of patellofemoral contact pressure was significantly medialised (0.04) between 120° and 60° knee flexion. Patellofemoral contact pressure did not change significantly. In the deficient knee conditions the patella moved on a significant lateralised track (P = 0.04) through the entire extension cycle with a lateralised centre of patellofemoral pressure (P = 0.04) with a trend (P = 0.08) towards increased patellofemoral pressure. The results suggest that lateral retinacular release did not inevitably stabilise or medialise patellar tracking through the entire knee extension cycle, but could decrease pressure on the lateral patellar facet in knee flexion. Therefore lateral retinacular release should be considered carefully in cases of patellar instability.     

The tendon defect after anterior cruciate ligament reconstruction using the midthird patellar tendon—a problem for the patellofemoral joint?

Retrospective clinical and radiographic evaluation was performed on 41 patients seen at the Salzburg General Hospital Department of Traumatology on average 2 years following ACL reconstruction. In 26 patients (61%) clinical examination revealed pain trigger points over the donor site of the midthird patellar tendon and in the patellofemoral joint. Functional pain during kneeling activities was observed in 19 patients (46%). Objective measurement of the length of the patellar tendon in bilateral radiographs demonstrated exactly equal patellar tendon length in both knees in 11 patients (27%). The radiographs showed tendon shortening following harvesting of the midthird patellar tendon by 1–3 mm in 7 patients (17%), by 4–6 mm in 16 (39%), and by 6–9 mm in 7 (17%). Average length change in the patellar tendon on the donor side was –3 mm, representing a patellar tendon shortening of 9.8%. On the basis of the OAK score, however, good and very good results were recorded in 33 patients (80%). On the whole, these good overall results were compromised only by patellar tendon defect morbidity. In addition to the local scarring problems at the donor site, shortening of the patellar tendon was observed with changes to patella position and interference with the mechanics of the patellofemoral joint. Tendon shortening can be explained on the basis of cicatricial contraction in the process of autorepair to the tendon defect. The problems affecting the patellofemoral joint are inherent in the therapy and must be treated as a negative factor. In the case of patients whose work requires mainly a kneeling position and those who make significant functional demands of the extension system of the knee, a critical assessment is required of the use of the midthird patellar tendon for anterior cruciate ligament reconstruction.     

Magnetic resonance imaging of patellofemoral relationships

Patellofemoral relationships were analyzed in 11 patients (13 knees) with patellar dislocation and 15 asymptomatic subjects (15 knees) at 0° and 20° of flexion. The measurements were made from five consecutive axial images through the patellofemoral joint. The six indices measured were lateral patellar tilt (LPT), lateral patellofemoral angle (LPA), lateral patellar displacement (LPD), patella-lateral condyle index (L/PW), congruence angle (CA), and sulcus angle (SA). The reproducibility of the method was evaluated. The difference between the two study groups was more evident at 0° than at 20° of knee flexion. Significant differences were noted between measurements made at different levels of the joint, particularly in the controls. Isometric contraction of the quadriceps muscle lateralized and tilted the patella slightly in both groups. L/PW with and without quadriceps muscle contraction, and LPA with reference to the anterior condyles differentiated between the two study groups most clearly. LPT and LPA with reference to the anterior condyles differentiated the study groups better than LPT and LPA with reference to the posterior condyles. The reproducibility was good except for inter-observer comparison of CA and SA. The use of an imaging plane selected at the midpoint of the patellar articular cartilage increases the sensitivity of the measurements, since it takes into account both the height of the patella and the tendency towards lateralization. These results indicate that patellar tilt is best measured with the LPA index and patellar lateralization with the L/PW index at 0° knee flexion. This study should always include isometric contraction of the quadriceps muscle.     

The influence of patellar bracing on patellar and knee load-distribution and kinematics: an experimental cadaver study

The aim of this study was to analyze the biomechanical consequences of patella bracing in order to evaluate possible mechanisms supporting its clinical application. The hypothesis is that the patellar bracing reduces patellofemoral pressure by influencing patellar and knee kinematics, and load distribution. Physiologic isokinetic knee extension motions were simulated on ten human knee cadaver specimens using a knee kinematic simulator. Joint kinematics were evaluated using an ultrasound-based motion analysis system and patellofemoral contact pressure was measured using a thin-film piezoresistive pressure measuring system. Infrapatellar tissue pressure was analyzed using a closed sensor-cell. Three different patella braces were fitted to the knee cadavers and their influence on the kinematic and kinetic biomechanical parameters were evaluated and compared to the physiologic situation. Patellar bracing resulted in a significant (p = 0.05) proximalization of the patella up to 3 mm. Depending on the type of brace used, a decrease in the infrapatellar fat pad pressure was found and the patellofemoral contact area was decreased significantly (p = 0.05) between 60° of knee flexion and full extension (maximum 22%). Patella bracing significantly (p = 0.05) reduced the patellofemoral contact pressure an average of 10%, as well as the peak contact pressure which occurred. Patellar bracing significantly influences patella biomechanics in a reduction of the patellofemoral contact area and contact pressure as well as a decrease in the infrapatellar tissue pressure. The application of infrapatellar straps is suggested for the treatment and prevention of anterior knee pain, especially in high level sports.     

Kinematic MRI assessment of McConnell taping before and after exercise

BACKGROUND: The authors assessed the effectiveness of McConnell medial glide taping after exercise using an MRI extremity scanner. HYPOTHESIS: McConnell taping would not be effective in maintaining medial glide of the patella after exercise. METHODS: Eighteen healthy women (mean age 22.28 +/- 2.02 years) participated in the study. The patellofemoral joint was imaged at 4 knee flexion angles (0 degrees, 12 degrees, 24 degrees, and 36 degrees ) in 3 conditions (no tape, with McConnell taping-medial glide, and with tape after exercise). Effectiveness was determined by measuring lateral patellar displacement. ANOVA and post hoc paired t tests were used to test for changes in lateral patellar displacement at each knee angle and condition. RESULTS: Statistical analysis revealed significant differences in lateral patellar displacement at all test angles, between the tape and no tape and between tape and tape after exercise conditions. CONCLUSIONS: McConnell medial glide taping resulted in significant medial glide of the patellofemoral joint at all 4 knee angles before but not after exercise. However, McConnell medial glide taping may be effective under controlled rehabilitation conditions in which exercise is less intense. Clinical Relevance: Beneficial effects of McConnell medial glide taping may be related to factors other than altered patellar alignment.     

The effects of medialization and anteromedialization of the tibial tubercle on patellofemoral mechanics and kinematics

BACKGROUND: Medialization and anteromedialization of the tibial tubercle are used to correct patellar subluxation in adults. PURPOSE: To compare the effects of the 2 osteotomies on patellofemoral joint contact pressures and kinematics. STUDY DESIGN: Controlled laboratory study. METHODS: Tibial tubercle osteotomies were performed on 10 cadaveric human knees. The knees were tested between 0 degrees and 90 degrees of flexion while dynamic patellofemoral joint contact pressure and kinematic data were simultaneously obtained. Four conditions were tested: normal knee alignment, simulated increased Q angle, postmedialization of the tibial tubercle, and postanteromedialization of the tubercle. RESULTS: An increased Q angle laterally translated the patella, shifted force to the lateral facet, and increased patella contact pressures. Both medialization and anteromedialization partially corrected the abnormal contact pressures. Medialization partially corrected the shift of force to the lateral facet induced by an increased Q angle, whereas the anteromedialization could not. Both medialization and anteromedialization corrected the patella maltracking. CONCLUSION: Medialization and anteromedialization are equivalent in their ability to correct abnormal patellar mechanics and kinematics.     

Patellofemoral stresses during open and closed kinetic chain exercises. An analysis using computer simulation

Rehabilitation of the symptomatic patellofemoral joint aims to strengthen the quadriceps muscles while limiting stresses on the articular cartilage. Some investigators have advocated closed kinetic chain exercises, such as squats, because open kinetic chain exercises, such as leg extensions, have been suspected of placing supraphysiologic stresses on patellofemoral cartilage. We performed computer simulations on geometric data from five cadaveric knees to compare three types of open kinetic chain leg extension exercises (no external load on the ankle, 25-N ankle load, and 100-N ankle load) with closed kinetic chain knee-bend exercises in the range of 20 degrees to 90 degrees of flexion. The exercises were compared in terms of the quadriceps muscle forces, patellofemoral joint contact forces and stresses, and "benefit indices" (the ratio of the quadriceps muscle force to the contact stress). The study revealed that, throughout the entire flexion range, the open kinetic chain stresses were not supraphysiologic nor significantly higher than the closed kinetic chain exercise stresses. These findings are important for patients who have undergone an operation and may feel too unstable on their feet to do closed chain kinetic chain exercises. Open kinetic chain exercises at low flexion angles are also recommended for patients whose proximal patellar lesions preclude loading the patellofemoral joint in deeper flexion.     

胫骨结构抬高术治疗髌股软骨病机理的研究

为客观评价胫骨结节抬高术治疗髌股软骨病的机理,采用Ｆｕｉｊ压敏片测压力和染色法测面积相结合,共测试８具新鲜离体膝关节标本,比较胫骨结节抬高术前后的髌股接触部位、面积和应力分布。发现胫骨结节抬高术后,髌骨的习惯性接触区位置向近端移行,这种现象有助于避开对软骨病灶区的挤压和应力集中,对缓解和消除髌股疼痛症状可能有利。因此,提出了“应力集中传导至软骨损伤区导致髌股疼痛”的设想。胫骨结节抬高术后,小屈膝角度（３０°－６０°）有一定的髌股减压作用,但随屈膝角度增加,髌股接触面积减小并出现压力分布不均或局部高压现象。胫骨结节抬高术后,“腱股接触”现象提早（６０°）出现,对髌股关节生物力学行为可能造成影响。     

Patella-tibial transfixation for posterior cruciate ligament repair and reconstruction: a biomechanical analysis

The posterior cruciate ligament (PCL) restricts posterior translation of the tibia on the femur. Because flexion of the knee increases tension on the PCL, the knee is usually immobilized in extension after PCL repair or reconstruction. Patella-tibial transfixation (olecranization), however, has been proposed to reduce the tension on the PCL without requiring immobilization of the knee. The objective of this study was: (1) to evaluate the distribution of strain in the anterolateral and posterior oblique fiber bundles of the PCLs in eight cadaveric knees before and after olecranization and (2) to measure the patellofemoral contact pressures at various degrees of knee flexion. Olecranization significantly (P < 0.05) reduced the strain on the anterolateral fiber bundles of the PCL at 15°–45° of flexion. No significant strain reduction was observed in the posterior oblique fiber bundles. Patellofemoral contact pressures measured from digitized Fuji sensitive film indicated significantly increased contact pressures (P < 0.05) following olecranization from 0°–60° of knee flexion. Increased parapatellar soft tissue tightness limited knee flexion to 90° and patella lift-off occurred at 75°. Although olecranization of the patella does reduce strain on the intact PCL within a selected range of motion, the beneficial effect of allowing early motion may be negated by the potentially harmful effects imposed upon the patellofemoral articular cartilage by increased contact pressures. Received: 20 December 1996 Accepted: 24 June 1997