Effects of lateral retinacular release on the lateral stability of the patella

The objective of this cadaveric study was to evaluate quantitatively the effects of lateral retinacular release on the lateral stability of the patella. A materials testing machine was used to displace the patella of seven cadaveric specimens 10 mm laterally while measuring the required force, with 175 N quadriceps tension. The patella was connected via a ball-bearing patellar mounting 10 mm deep to the anterior surface to allow rotations. Patellar force--displacement behaviour was tested from 0° to 60° knee flexion. At 0°, 10° and 20° flexion the mean force required to displace the patella 10 mm laterally was reduced significantly due to lateral retinacular release, by 16–19%. The average force required to displace the patella was also reduced for larger flexion angles, although this was not statistically significant. These findings suggest that lateral retinacular release may not be appropriate in treatment of patellar lateral instability.     

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.     

Dynamic lateral patellar tilt in the anterior cruciate ligament-deficient knee. A magnetic resonance imaging analysis

An open-configuration magnetic resonance imaging scanner was used to document patellar tracking abnormalities in 11 anterior cruciate ligament-injured knees. The contralateral normal knees were used as controls. Images were obtained with the quadriceps muscles at rest (knee flexion at 40 degrees, 25 degrees, and 10 degrees) and with the quadriceps muscles contracted (knee flexion at 40 degrees and 25 degrees). When the quadriceps muscles were at rest there were no differences in patellar alignment between the anterior cruciate ligament-injured knees and the contralateral normal knees. When the quadriceps muscles were maximally contracted at 40 degrees of flexion, the patellae of the anterior cruciate ligament-injured knees tilted laterally 3.6 degrees relative to the resting state. When the quadriceps muscles were contracted at 25 degrees of flexion, the patellae of the anterior cruciate ligament-injured knees tilted laterally approximately 4 degrees relative to the resting state. Quadriceps-active lateral patellar tilt at 25 degrees of flexion was greater in the anterior cruciate ligament-injured knees than in the contralateral normal knees, and it correlated with instrumented measurements of anterior tibial translation. Dynamic lateral patellar tilt during open kinetic chain exercises and during other activities that produce anterior tibial translation may contribute to extensor mechanism dysfunction in the anterior cruciate ligament-injured knee.     

The effect of femoral attachment location on anterior cruciate ligament reconstruction: graft tension patterns and restoration of normal anterior–posterior laxity patterns

The issue of the best place to attach an anterior cruciate ligament graft to the femur is controversial, and different anatomic or isometric points have been recommended. It was hypothesised that one attachment site could be identified that would be best for restoring normal anterior–posterior laxity throughout the range of knee flexion. It was also hypothesised that these different attachment sites would cause different graft tension patterns during knee flexion. Using six cadaver knees, an isometric point was found 3 mm distal to the posterior edge of Blumensaats line, at the 10:30–11:00 oclock position in right knees, at the antero-proximal edge of the anatomic ACL attachment. Anterior–posterior laxity was measured at ±150 N draw force at 20–120° flexion with the knee intact and after anterior cruciate ligament transection. The graft was placed at the isometric point, and AP laxity was restored to normal at 20° flexion, then measured at other angles. Graft tension was measured throughout, and also during passive flexion–extension. This was repeated for four other graft positions around the isometric point in every knee. Laxity was restored best by grafts tensioned to a mean of 9±14 N, positioned isometrically and 3 mm posterior to the isometric point. Their tension remained low until terminal extension. Grafts 3 mm anterior to the isometric point caused significant overconstraint, and had higher tension beyond 80° knee flexion. Small changes in attachment site had large effects on laxity and tension patterns. These results support an isometric/posterior anatomic femoral graft attachment, which restored knee laxity to normal from 20 to 120° flexion and did not induce high graft tension as the knee flexed. Grafts attached to the roof of the intercondylar notch caused overconstraint and higher tension in the flexed knee.     

Computed tomography of the normal patellofemoral joint

Radiographic assessment of the patellofemoral joint (PFJ) is problematic because conventional views are cumbersome, difficult to standardize, and not reliable for displaying this joint with flexion of the knee less than about 30 degrees. We used computed tomography (CT) to obtain conveniently a direct transaxial view of the PFJ in ten normal human volunteers at different 0 degree, 20 degrees, and 45 degrees of knee flexion and during both contraction and relaxation of the quadriceps muscle. From the CT images we measured femoral trochlear angle, patellar centralization, femoral trochlear depth, and patella tilt angle. In full extension, with the quadriceps muscle relaxed, 19 of 20 knees showed the patella well centered in the femoral trochlear groove. The tilt and centralization of the patella were largely unchanged at 20 and 45 degrees of knee flexion with quadriceps contraction. CT appears to be an optimal method of studying the PFJ. The normal relationships described in this report can be the basis for evaluating patients with known or suspicious history of recurrent subluxation or dislocation of the patella.     

Effect of an UHMWPE patellar component on stress fields in the patella: a finite element analysis

An increased stress in the patella due to the implantation of a patellar button may also be another potential source of pain in total knee arthroplasty patients. This study assessed the location inside the patella having largest stress change after implantation of an ultra high molecular polyethylene patella button. Finite elements models of the patellae before and after implantation of patellar button were created. Experimentally determined spring constants of muscles and ligaments, and patellofemoral contacting loads were applied to the models at 30 degrees , 60 degrees , and 90 degrees of knee flexion. The Von Mises stress of the intact patella decreased with increased knee flexion, while that of implanted patella increased. Also, the stress range in the implanted patella was 3~9 times higher than in the intact one. The highly stressed region of the intact patella moved proximally with higher knee flexion angles, while that of the implanted model stayed near the central anterior patella. At 90 degrees of knee flexion, the stress in the anterodistal patella increased considerably after implantation of a patella button so that the anterodistal patella may be susceptible to be painful source after the total knee replacement.     

A lower leg surrogate study to investigate the effect of quadriceps–hamstrings activation ratio on ACL tensile force

ObjectivesMany studies have investigated the relationship between muscle activation and tensile force of the anterior cruciate ligament. These studies lacked a holistic representation of the muscle status. For instance, they were limited with respect to the peak muscle forces, number of muscles, and possible muscle activation patterns.DesignThis study used a knee surrogate including ten muscles with motor-controlled muscle force activation crossing the knee joint, thus providing a fully muscle-supported knee joint. Methods: Anterior cruciate ligament tensile force is measured in different knee flexion and extension movements to evaluate ratios of quadriceps/hamstring muscle activations in low hip angle setups.ResultsIncreasing the extension of the leg increased anterior cruciate ligament tension forces. Different quadriceps/hamstring ratios had different effects on anterior cruciate ligament tension forces during unrestricted flexion and extension movements. This was dependent on the direction of movement. Sole hamstring activation increased the anterior cruciate ligament tensile forces in extension movements compared with flexion movements. Sole quadriceps activation provoked greater anterior cruciate ligament tensile forces in flexion than in extension. This was not prominent in the test in which the other muscle groups counteracted the dominant muscle group.ConclusionsThe findings from the present study demonstrate that active hamstring activation can reduce the load on the anterior cruciate ligament, and the dominant quadriceps increase anterior cruciate ligament loads for knee flexions of less than 40°. Moreover, the anterior cruciate ligament is loaded differently in flexion or extension movements with flexion movements, resulting in higher anterior cruciate ligament loads.     

Quantitative evaluation of knee instability and muscle strength after anterior cruciate ligament reconstruction using patellar and quadriceps tendon.

Anterior cruciate ligament reconstruction using an autologous graft harvested from the central one-third of the patellar and quadriceps tendon was performed in 65 knees of 65 patients who were followed from 3 to 7 years. Mean anterior laxity of both knees was measured before and after surgery in each patient using the Styker Knee Laxity Tester. At 30 degrees of knee flexion, 58 patients (89%) had differences of less than 2.5 mm between the operated and unoperated knees. Quadriceps strength was measured with the Cybex II and was less than 50% of the uninjured knee at 3 months after surgery. In men, quadriceps strength returned to 78% of normal at 1 year and 85% at final followup. These values were equal to the preoperative level. In women, the quadriceps strength at final followup was 70%, significantly lower than preoperative strength. Hamstring strength recovered to equal the normal strength. Although anterior cruciate ligament reconstruction using one-third of the patellar and quadriceps tendon achieves stability, postoperative quadriceps weakness is a disadvantage. This weakness may be caused by impairment of the knee extensor mechanism resulting from harvesting the graft. We do not currently recommend this technique for anterior cruciate ligament reconstruction.     

Is impingement the cause of jumper's knee? Dynamic and static magnetic resonance imaging of patellar tendinitis in an open-configuration system

BACKGROUND: Chronic overload is considered the main cause of patellar tendinitis, but it has been postulated that impingement of the inferior patellar pole against the patellar tendon during knee flexion could be responsible. HYPOTHESIS: The role of the patellar pole in patellar tendinitis can be determined by dynamic magnetic resonance imaging. STUDY DESIGN: Case-control study. METHODS: We compared 19 knees with patellar tendinitis and 32 asymptomatic knees of age-matched subjects using an open-configuration magnetic resonance imaging system. Dynamic sagittal images were obtained from full extension to 100 degrees of flexion with and without activation of the quadriceps muscle. The following measurements were made from the images: tendon-patella angle, anteroposterior diameter of the tendon, signal difference-to-noise ratio, the shape of the inferior patellar pole, and the location of the patellar tendon insertion. RESULTS: The tendon-patella angle was not significantly different between groups at any flexion angle, with or without quadriceps muscle activation. The insertion site of the patellar tendon differed significantly but not the shape of the inferior pole of the patella. The volume and the signal difference-to-noise ratio of zones of increased intratendinous signal as well as the anteroposterior diameter of the proximal patellar tendon were increased in symptomatic knees. CONCLUSIONS: The relationship between the patella and the patellar tendon was identical in both groups; therefore, chronic overload seems to be a major cause of patellar tendinitis.     

Active patellar tracking measurement: a novel device using ultrasound

BACKGROUND: Many patients suffer patellar instability that may relate to transient patellar tracking abnormalities. OBJECTIVE: To develop and test a technique to measure dynamic patellar tracking. STUDY DESIGN: Controlled laboratory and in vivo study. METHOD: A functional knee brace was modified to allow an ultrasound transducer to be mounted laterally to the femur, following the path of the patella during knee movement. An ultrasound system was used to measure patellar mediolateral position parallel to the femoral transepicondylar axis. Ten subjects with no patellar instability were studied to obtain patellar tracking and accuracy data. RESULTS: The interobserver and intraobserver reproducibility ranged from 0.2 +/- 0.1 mm to 1.0 +/- 0.5 mm. The accuracy of the ultrasound measurement was checked against magnetic resonance imaging and was 0.6 +/- 1.9 mm. The patella moved medially then laterally from extension to flexion when sitting. Squatting and stepping produced a more lateral path, without the initial medial translation. The patella was more lateral during knee extension than during flexion. CONCLUSIONS: This novel method for measurement of dynamic patellar mediolateral tracking was found to have good intraobserver and interobserver reproducibility, and the measurements matched closely with those obtained from magnetic resonance imaging reconstructions of static patellar positions. Some preliminary data for tracking in 3 activities were obtained from 10 normal knees.     

In vivo and noninvasive three-dimensional patellar tracking induced by individual heads of quadriceps

PURPOSE: Unbalanced actions of the quadriceps components are closely linked to patellar mal-tracking and patellofemoral pain syndrome. However, it is not clear how individual quadriceps components pull and rotate the patella three dimensionally. The purpose of this study was to investigate in vivo and noninvasively patellar tracking induced by individual quadriceps components. METHODS: Individual quadriceps component was activated selectively through electrical stimulation at the muscle motor point, and the resulting patellar tracking was measured in vivo and noninvasively in 18 knees of 12 subjects. The in vivo and noninvasively patellar tracking was corroborated with in vivo fluoroscopy and in vitro cadaver measurements. RESULTS: Vastus medialis (VM) mainly pulled the patella first in the medial and second in the proximal directions and vastus lateralis (VL) pulled first in the proximal and second in the lateral directions. The oblique portion (VMO) of the VM pulled the patella mainly medially and the longus portion (VML) more proximally. Medial tilt was the major patellar rotation induced by VMO contraction at full knee extension. With the knee at the more flexed positions, the amplitude of patellar movement induced by comparable quadriceps contractions was reduced significantly compared to that at full knee extension, and VMO changed its main action from extending to flexing the patella. CONCLUSIONS: The medial and lateral quadriceps components moved the patella in rather different directions, and rotated the patella differently about the mediolateral tilt and mediolateral rotation axes but similarly in extension. The approach can be used to investigate patellar tracking in vivo and noninvasively in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.     

Patello-femoral tracking in the weight-bearing knee: a study of asymptomatic volunteers utilising dynamic magnetic resonance imaging: a preliminary report

Normal patello-femoral tracking is not well defined, and conventional radiological techniques do not allow imaging in the physiological, weight-bearing stance. A vertical-access open configuration magnetic resonance scanner allows imaging of patello-femoral tracking during weight-bearing and through a wide range of knee flexion. We imaged 40 asymptomatic knees in this way, producing axial scans which were analysed qualitatively and quantitatively using sulcus angle, congruence angle, lateral patello-femoral angle and patellar centralisation, to assess patellar tilt and displacement. Mild lateral tilting in hyperextension with the quadriceps relaxed was seen, but quantitative assessment of this was impeded by internal rotation of the femur in extension. One-half of the knees were slightly laterally displaced in hyper-extension, becoming central during the first 30 degrees of knee flexion. During passive flexion of the knee in a seated position, fewer knees were laterally tilted or displaced, and no consistent change was seen during flexion. These results indicate that mild lateral tilting and displacement can be normal phenomena in the weight-bearing knee in early flexion and should not necessarily be taken as evidence of abnormal tracking in symptomatic patients. Lateral to medial movement of the patella occurs during normal knee flexion. In addition, imaging in the weight-bearing knee can provide valuable information not gained by imaging during passive knee flexion.     

Strain patterns in the patellar tendon and the implications for patellar tendinopathy

This study investigated the strain pattern in human patellar tendon in an area of the tendon where changes commonly associated with patellar tendinitis are found. Eight fresh frozen human knees were instrumented with strain gauges on both the anterior and posterior side of the proximal patellar tendon. Both static and dynamic measurements were carried out in a range from 0 degrees to 60 degrees of flexion. We found uniform tensile strain in the tendon with the knee in full extension. However, as the knee was brought into flexion, the tensile strain increased on the anterior side but decreased on the posterior side in the central, proximal location of the tendon. The posterior side of the proximal patellar tendon is most commonly affected in patellar tendinopathy. This study indicates that this area of the tendon may not subjected to the highest tensile loads in the functional flexion range. It is possible that stress shielding is more important etiological factor in insertional tendinopathy as opposed to repetitive tensile loads.     

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.     

Aggressive quadriceps loading can induce noncontact anterior cruciate ligament injury

BACKGROUND: The force responsible for noncontact anterior cruciate ligament (ACL) injuries remains controversial. The patella tendon to tibial shaft angle causes an anterior tibial shear force with quadriceps activation. HYPOTHESIS: An aggressive quadriceps contraction can injure the ACL. METHODS: The authors characterized noncontact ACL injury and kinematics with aggressive quadriceps loading. Thirteen fresh-frozen knees were potted in a jig held in 20 degrees of flexion while a 4500 N quadriceps contraction was simulated. Knee kinematics were recorded. A KT-1000 arthrometer and a simulated active quadriceps test assessed anterior displacement. Statistics were performed using paired t tests and 1-way analysis of variance. RESULTS: Kinematics revealed the following mean values: anterior displacement, 19.5 mm; valgus, 2.3 degrees; and internal rotation, 5.5 degrees. Mean KT-1000 and active quadriceps test differences were 4.0 mm and 2.7 mm, respectively (statistically significant P =.002 and P =.002). Six knees showed gross ACL injury at the femoral insertion. Based on ACL injury, KT-1000 differences were statistically significant (P =.029). CONCLUSIONS: Aggressive quadriceps loading, with the knee in slight flexion, produces significant anterior tibial translation and ACL injury. This suggests that the quadriceps is the intrinsic force in noncontact ACL injuries, producing a model for further investigation.     

Intraarticular anterior cruciate ligament graft placement on the average most isometric line on the femur. Does it reproducibly restore knee kinematics?

In the past, there has been a plausible hypothesis that anterior cruciate ligament graft placement at isometric sites, such that the tibial and femoral attachment sites remain equidistant from each other throughout knee range of motion, would increase the likelihood of a satisfactory outcome. For a given tibial placement we wanted to determine whether placing the graft on the average of the most isometric femoral line, a fixed distance from the outlet of the intercondylar notch, would return normal laxity to all knees. The three-dimensional kinematics of seven cadaveric knees were measured for angles from full extension to 90 degrees of flexion at 15 degrees increments. Physiologic levels of quadriceps muscle forces were applied to the intact knee, after transection of the anterior cruciate ligament, and after ligament reconstruction with a patellar tendon graft. On average, the reconstruction was found to return anterior-posterior translation, internal-external rotation, and varus-valgus rotation to levels not significantly different from those of the intact knee. However, the ranges of the translation and rotations were large. Placing the graft on the average most isometric femoral line did not restore knee laxity to normal in all knees. This supports the need to customize graft placement in each knee at the time of surgery.     

The anterior cruciate ligament does play a role in controlling axial rotation in the knee

This study deals with the influence of peroperative ligament tension on total tibial rotation at different knee flexion angles. Fourteen human cadaver knees with a mean age of 56 years (range 42–84 years) were examined. The cadaver knees were subjected to internal/external (i/e) rotational torque of 6 Nm, at 10, 30, 50, 70 and 90 deg of knee flexion. The mean total i/e rotation with the anterior cruciate ligament (ACL) intact at 10 deg of knee flexion was 30.4 deg and after removing the ACL, 33.1 deg. At 10 and 30 deg of knee flexion, the increase in i/e rotation was significant, while there was no significant difference in mean values at greater knee flexion. Ligament reconstruction with a tension of 5 N at 30 deg of knee flexion using either the over the top or through the femoral condyle reconstructive procedure restored normal tibial rotation. With increased graft tension the knee motion was increasingly restricted at low angles of knee flexion. Our results indicate that the ACL does play a role in limiting axial rotation, and even minor tensioning forces introduced in any of the two ACL reconstructions used produced restricted knee motion.     

Effect of patellar brace on patellofemoral relationships

The effect of patellar brace on patellofemoral relationships was analyzed using magnetic resonance imaging in 17 knees with patellar subluxation or dislocation. Images were produced in 0° and 20° knee flexions without the patellar brace, with patellar brace and with patellar brace after 1 h of walking. In knee extension, the patellar brace had an unfavorable effect on lateral patellar tilt, but decreased the tilt in 20° knee flexion. The excessive lateral patellar displacement was alleviated in both knee flexion angles. The corrected position was still apparent after physical exercise. Isometric quadriceps muscle contraction increased the displacement. These results suggest a positive stabilizing effect of the brace in patients with patellar instability.     

Anterior-posterior and rotational displacement of the tibia elicited by quadriceps contraction.

The anterior-posterior displacement and rotation of the tibia elicited by isolated loading of the quadriceps muscle was determined as a function of joint angle and muscle load using a computerized radiographic technique. Data collected from 12 fresh-frozen cadaveric knees demonstrated that quadriceps contraction can result in significant (less than 7 mm) anterior displacement of the tibia in the range of 0 degrees to 80 degrees of flexion, and a mild (less than 2 mm) posterior displacement in the range of 80 degrees to 120 degrees of flexion. Peak anterior displacement of 6.3 mm was observed at 30 degrees of flexion under a 12 kg load in the quadriceps, while a constant 1.5 mm posterior displacement was observed throughout flexion angles exceeding 80 degrees. It was further shown that the magnitude of the anterior displacement increased nonlinearly as the quadriceps force increased. Loading of the quadriceps also resulted in internal rotation of the tibia in the range of 0 degrees to 90 degrees of flexion, and in external rotation of the tibia in the range of 90 degrees to 120 degrees. Peak internal rotation of 7 degrees was observed at 15 degrees of flexion and a peak external rotation of 1 degrees was detected at 120 degrees of flexion. Larger quadriceps load resulted in larger rotation. We concluded that quadriceps contraction during knee extension has direct impact on anterior displacement and rotation of the tibia and therefore on anterior cruciate ligament stress, increasing it as the muscle's force is increased during knee extension.(ABSTRACT TRUNCATED AT 250 WORDS)     

Retropatellar forces after rupture of the PCL and patello-tibial transfixation: An in vitro study

Compared to injuries of the other knee ligaments, a rupture of the posterior cruciate ligament (PCL) is relatively rare. Treatment may be conservative or operative. A rupture that has been operated on temporarily can be stabilised using a Grammont patello-tibial transfixation (olecranisation). Flexion and extension between 30° and 60° are allowed. The advantage of this method is that it avoids complete immobilisation of the joint and also the reduction of pull on the PCL. However, patients treated with this method show long-term osteoarthritis of the retropatellar joint area. Our study aimed to show the distribution of forces at the dorsal patellar surface in the following: (1) knee with intact ligament; (2) knee with PCL rupture; (3) knee with PCL rupture plus olecranisation. Fourteen fresh knee specimens were investigated in a Plitz/Wirth knee kinemator. The femur was fixed while the tibia was flexed between 5° and 120°. Pull was placed on the patella and on the dorsal side of the tibia with weights over the tendons of the quadriceps and the roots of the ischio-crural muscles. With the aid of a special measurement device in the patella, the medially laterally, proximally and distally acting forces in a movement cycle could be measured as well as the total retropatellar force in the above experimental setups. We found that, dependent on load and flexion angle in each preparation, (1) the total retropatellar force and some of the force components were greater when the PCL was ruptured than in the intact specimen. (2) with olecranisation the total force and the medial and lateral components were less than in the unrestricted patella with ruptured PCL, (3) the proximal area of the patella with olecranisation was less loaded than in the knee with either intact or defective PCL, and (4) the distal area of the patella with olecranisation was more loaded than in the knee joint with either intact or defective PCL.Conclusions To avoid destruction caused by overloading, especially in the distal area of the patella, the duration of patello-tibial transfixation should be carefully considered. Patients should be kept moving, at the same time being warned about excessive loading.