Biomechanical consequences of a posterior root tear of the lateral meniscus: stabilizing effect of the meniscofemoral ligament

Purpose

The purpose of this study was to evaluate the effects of different types of lateral meniscus root tears in terms of tibiofemoral contact stress.

Methods

Ten porcine knees each underwent five different testing conditions with the menisci intact, a simulated lateral posterior root tear with and without cutting the meniscofemoral ligament and with an artificial tear of the posterior root of the medial meniscus. Biomechanical testing was performed at 30° of flexion with an axial load of 100 N. A pressure sensor (st Sensor Type S2042, Novel, Munich) was used to measure the tibiofemoral contact area and the tibiofemoral contact pressure. Data were analyzed to assess the differences in contact area and tibiofemoral peak contact pressure among the five meniscal conditions.

Results

There was no significant difference in mean contact pressure between the state with the menisci intact and an isolated posterior root tear of the lateral meniscus. In case of a root tear and a tear of the meniscofemoral ligament, the contact area decreased in comparison with the intact state of the menisci. After additional cutting of the meniscofemoral ligament, the tibiofemoral contact pressure was significantly higher in comparison with the intact state and the avulsion injury. In the medial compartment, joint compression forces were significantly increased in comparison with the intact state after cutting the posterior root of the medial meniscus (P < 0.05).

Conclusions

The consequence of a medial meniscus root tear is well known and was verified by this analysis. The results of the present study show that the biomechanical consequences of a lateral meniscus root tear depend on the state of the meniscofemoral ligament. An increase in tibiofemoral contact pressure is only to be expected in combined injuries of the meniscus root and the meniscofemoral ligaments.

Clinical relevance

Posterior lateral meniscus root tear might have a better prognosis in terms of the development of osteoarthritis when the meniscofemoral ligament is intact.     

Common pitfalls in magnetic resonance imaging of the knee

Magnetic resonance examinations of 200 knees were studied retrospectively to determine the frequency with which normal ligamentous and tendinous structures mimicked pathological changes in the meniscus or elsewhere in the knee. Although the course of the transverse geniculate ligament simulated a tear of the anterior horn of the lateral meniscus on forty-four (22 per cent) of the sagittal magnetic-resonance scans, no tear of the lateral meniscus was found in the nine patients in this group who had an arthroscopic examination. The normal anatomy of the meniscofemoral ligament varies greatly. The ligament of Humphry, the anterior branch of the meniscofemoral ligament, was visualized on sixty-six (33 per cent) of the magnetic resonance scans. The ligament of Wrisberg, the posterior branch of the meniscofemoral ligament, was identified on sixty-five (32.5 per cent) of the scans. On sagittal images, these ligamentous branches can be mistaken for osteochondral or meniscal fragments. However, a loose body was found in only one of the thirty-two patients who had an arthroscopic examination after the ligament of Humphry or of Wrisberg was seen on the magnetic resonance image. The bursa of the popliteus tendon simulated a tear of the posterior horn of the lateral meniscus in fifty-five (27.5 per cent) of the studies, although an actual tear of the posterior horn was found in only two of the eleven patients who had an arthroscopic examination.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of meniscofemoral contact pressure after repair of bucket-handle tears with biodegradable implants

Introduction Biodegradable implants are frequently used for meniscus repair. Articular cartilage damage has been reported recently after meniscus repair with biodegradable implants. The aim of the study was to investigate the meniscofemoral contact pressure at the posterior horn of the medial and lateral meniscus after repair of bucket-handle lacerations.Materials and methods Specimens were mounted in a materials testing machine (Bionix 858, MTS) which was equipped with a load cell. The quadriceps tendon was attached to a hydraulic cylinder, and knee motion was controlled via tension of the quadriceps tendon. A piezo-resistive system (Tekscan, Boston, MA, USA) measured the meniscofemoral contact pressure. Five different types of biodegradable implants (Arrow, Dart, Fastener, Stinger and Meniscal Screw) and horizontal suture (no. 2 Ethibond) were tested. The knee was extended from 90° of flexion to 0° under a constant load of 350 N due to adjustment of the tension force of the quadriceps tendon. The femorotibial pressure and contact area were recorded at 0°, 30°, 60° and 90° of flexion.Results The meniscofemoral pressure did not increase after meniscus repair with biodegradable implants or sutures. The meniscofemoral peak pressure at the posterior horn was 1.46±1.54 MPa in the medial compartment and 1.08±1.17 MPa in the lateral compartment at full knee extension. The meniscofemoral pressure increased significantly in both compartments with knee flexion from 0° to 90°.Conclusion Biodegradable implants for meniscus repair do not affect the meniscofemoral pressure. However, there remains a risk of damage to the cartilage when barbed implants are used. If the implant is not entirely advanced into the meniscus, the sharp head or some of the barbs at the column of the implant may come into direct contact with the articular cartilage of the femoral condyle or tibial plateau. The authors presume that incorrect positioning of the implant seems to be the major reason for cartilage damage.     

Medial collateral ligament avulsion from both tibial and femoral attachments: a case report

The medial collateral ligament (MCL) is the most commonly injured ligament of the knee joint. Proximal MCL tears occur more frequently than do distal ones. We report a 28-year-old man with a valgus injury of his left knee joint after a fall from a motorcycle. Magnetic resonance imaging of the affected knee joint revealed complete avulsion of the superficial MCL from both its femoral and tibial insertions. The meniscofemoral portion of the deep part of the MCL was also torn and the medial meniscus was subluxated. Such a pattern, an MCL tear with subluxation of the medial meniscus, is rare.     

膝关节内外侧半月板后根部撕裂的MRI诊断价值

目的:探讨MRI对膝关节内外侧半月板后根部撕裂的诊断价值。方法:回顾性分析2012年1月至2016年1月,关节镜下证实为半月板后根部撕裂的患者43例。其中男25例,女18例;年龄27~69(42.5±8.3)岁;右侧27例,左侧16例。由2名医师采用双盲法独立回顾性分析经关节镜证实的43例半月板后根部撕裂患者的MRI表现,计算MRI对半月板后根部撕裂的诊断敏感性、特异性和准确性,并计算膝关节韧带损伤及半月板脱位等伴随情况。结果:143例中,关节镜手术证实43例半月板后根部撕裂,包括内侧撕裂24例,外侧撕裂19例。医师A诊断内侧半月板后根部撕裂的敏感性、特异性、准确性分别为91.67%、86.6%、83.9%,伴内侧半月板突出19例,伴前交叉韧带撕裂2例;外侧半月板后跟部撕裂的敏感性、特异性、准确性分别为73.7%、79.9%、79%,伴外侧半月板突出4例,伴前交叉韧带撕裂16例。医师B诊断内侧半月板后根部撕裂的敏感性、特异性、准确性分别为87.5%、87.4%、87.4%,伴内侧半月板突出19例,伴前交叉韧带撕裂2例;外侧半月板后跟部撕裂的敏感性、特异性、准确性分别为78.9%、82.3%、82.5%,伴外侧半月板突出4例,伴前交叉韧带撕裂16例。2名医师采用MRI诊断内、外侧半月板后根部撕裂的一致性均好,Kappa值分别为0.81和0.67。结论 :膝关节MRI诊断内外侧半月板后跟部撕裂及其伴随征象具有较大价值,为临床医生术前诊断提供依据,值得临床推广应用。     

Arthroscopic Pullout Repair of a Complete Radial Tear of the Tibial Attachment Site of the Medial Meniscus Posterior Horn

We developed an effective arthroscopic pullout technique for repairing complete radial tears of the tibial attachment site of the medial meniscus posterior horn (MMPH). In our technique, the torn meniscus is reattached to the tibial plateau immediately medial or anteromedial to the posterior cruciate ligament (PCL) using two No. 2 Ethibond sutures (Ethicon, Somerville, NJ). After a complete radial tear of the tibial attachment site of the MMPH and its reparability were confirmed, using a Caspari suture loaded with a suture shuttle, one No. 2 Ethibond suture is placed through the meniscus, through the red-red zone, 3 to 5 mm medial to the torn edge of the MMPH, and the other is passed through the meniscocapsular junction 3 to 5 mm medial to the torn edge of the meniscus. Then, a tibial tunnel, 5-mm in diameter, is made from the anteromedial aspect of the proximal tibia to the previously prepared tibial plateau, immediately medial or anteromedial to the PCL, and the two No. 2 Ethibond sutures are pulled out through the tibial tunnel and then fixed to the proximal tibia using a 3.5-mm cortical screw and washer. Firm reattachment of the torn meniscus was confirmed arthroscopically.     

Impact of Partial and complete rupture of anterior cruciate ligament on medial meniscus: A cadavaric study

Background:

The clinical relationship between medial meniscus tear and anterior cruciate ligament (ACL) rupture has been well documented. However, the mechanism of this clinical phenomenon is not exactly explained. Our aim is to investigate the biomechanical impact of partial and complete ACL rupture on different parts of medial meniscus.

Materials and Methods:

Twelve fresh human cadaveric knee specimens were divided into four groups: ACL intact (ACL-I), anteromedial bundle transection (AMB-T), posterolateral bundle transection (PLB-T), and ACL complete transection (ACL-T) group. Strain on the anterior horn, body part, and posterior horn of medial meniscus were measured under 200 N axial compressive tibial load at 0°, 30°, 60°, and 90° of knee flexion, respectively.

Results:

Compared with the control group (ACL-I), the ACL-T group had a higher strain on whole medial meniscus at 0°, 60°, and 90° of flexion. But at 30°, it had a higher strain on posterior horn of meniscus only. As to PLB-T group, strain on whole meniscus increased at full extension, while strain increased on posterior horn at 30° and on body of meniscus at 60°. However, AMB-T only brought about higher strain at 60° of flexion on body and posterior horn of meniscus.

Conclusions:

Similar to complete rupture, partial rupture of ACL can also trigger strain concentration on medial meniscus, especially posterior horn, which may be a more critical reason for meniscus injury associated with chronic ACL deficiency.     

Posterior root tear fixation of the lateral meniscus combined with arthroscopic ACL double-bundle reconstruction: technical note of a transosseous fixation using the tibial PL tunnel

According to our observation in ACL reconstruction, we find root tears of the posterior horn of the lateral meniscus as a common concomitant injury in ACL-deficient knees. This might be a consequence of initial trauma or of the increased anterior–posterior translation of the tibia and an overload impact on the posterior meniscus root in ACL-deficient knees. A tear of the posterior horn of the medial meniscus causes a 25% increase in peak pressure in the medial compartment compared with that found in the intact condition. The repair restores the peak contact pressure to normal (Allaire et al. in J Bone Joint Surg Am 90(9):1922–1931, [2008]). A tear of the posterior horn of the lateral meniscus might have similar consequences. We hypothesize the surgical anatomical reattachment of the root at the tibia helping to restore knee joint kinematics and helping to advance ACL-graft function. This article presents an arthroscopical technique to reattach the posterior meniscus root in combination with ACL double-bundle reconstruction. The procedure uses the tibial PL tunnel to fix the meniscus suture.     

Combined Injury to the ACL and Lateral Meniscus Alters the Geometry of Articular Cartilage and Meniscus Soon After Initial Trauma

Combined injury to the anterior cruciate ligament (ACL) and meniscus is associated with earlier onset and increased rates of post-traumatic osteoarthritis compared with isolated ACL injury. However, little is known about the initial changes in joint structure associated with these different types of trauma. We hypothesized that trauma to the ACL and lateral meniscus has an immediate effect on morphometry of the articular cartilage and meniscus about the entire tibial plateau that is more pronounced than an ACL tear without meniscus injury. Subjects underwent magnetic resonance imaging scanning soon after injury and prior to surgery. Those that suffered injury to the ACL and lateral meniscus underwent changes in the lateral compartment (increases in the posterior–inferior directed slopes of the articular cartilage surface, and the wedge angle of the posterior horn of the meniscus) and medial compartment (the cartilage-to-bone height decreased in the region located under the posterior horn of the meniscus, and the thickness of cartilage increased and decreased in the mid and posterior regions of the plateau, respectively). Subjects that suffered an isolated ACL tear did not undergo the same magnitude of change to these articular structures. A majority of the changes in morphometry occurred in the lateral compartment of the knee; however, change in the medial compartment of the knee with a normal appearing meniscus also occurred. Statement of clinical significance: Knee injuries that involve combined trauma to the ACL and meniscus directly affect both compartments of the knee, even if the meniscus and articular cartilage appears normal upon arthroscopic examination. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:759-767, 2020     

The role of the meniscus in the anterior-posterior stability of the loaded anterior cruciate-deficient knee. Effects of partial versus total excision

The effects of progressive removal of the menisci on the anterior-posterior force-versus-displacement response of the anterior cruciate-deficient knee were studied in fresh cadaver specimens at 20 degrees of flexion without and with tibial-femoral contact force (joint load). In the absence of joint load, removal of the medial meniscus increased total anterior-posterior laxity measured at 200 newtons of applied tibial force by 10 per cent, and subsequent lateral meniscectomy produced an additional 10 per cent increase. When a bucket-handle tear of the medial meniscus was removed, the application of joint load caused the tibia to displace (subluxate) forward on the femur, thereby changing the balance condition of the knee. Subsequent removal of the remainder of the medial meniscus and complete lateral meniscectomy both produced additional smaller anterior tibial subluxations. Changes in total anterior-posterior laxity due to progressive meniscectomy in the loaded knee were dependent on both the amount of applied anterior-posterior force and the level of compressive force. At 200 newtons of anterior-posterior tibial force, increases in laxity in the loaded knee due to progressive meniscal removal were not significantly different than those recorded in the unloaded condition. At applied forces of fifty newtons or less, the laxities for loaded specimens were always significantly less than those for unloaded specimens at comparable stages of meniscal removal. Bilateral meniscectomy had no significant effect on the posterior response curve, as posterior tibial translation was effectively checked by the intact posterior cruciate ligament.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biomechanical analysis of the centralization procedure for extruded lateral menisci with posterior root deficiency in a porcine model

PurposeThe purpose of this study was to investigate the biomechanical properties of load distribution following a centralization procedure for extruded lateral menisci with posterior root deficiency in a porcine model.MethodsSix porcine knee joints were analyzed in a universal tester, as follows: 1) Intact; 2) Extrusion (meniscus extrusion was created by resecting the posterior root of the lateral meniscus, as well as the posterior synovial capsule); and 3) Centralization (two anchors were inserted at the lateral tibial plateau, and the meniscus was sutured to secure it close to the original position). Meniscus extrusion was evaluated using two markers put on the posterior cruciate ligament and the lateral meniscus, and the load distribution were assessed using a pressure mapping sensor system after applying a loading force of 200 N to the knee joint.ResultsDistance between two markers (mm, Average; 95% CI) was larger in the extrusion group (21.9; 17.8, 25.6) than in the intact (18.1; 15.1, 22.7) or the centralization (15.3; 12.9, 18.0) groups. The contact area (mm²) in the middle of the meniscus was significantly smaller in the extrusion group (45.8; 18.5, 73.2) than in the intact (85.7; 72.1, 99.2) or the centralization (98.3; 88.8, 107.8) groups. The maximum contact pressure (MPa) in the tibial plateau was significantly higher in the extrusion group (0.37; 0.35, 0.40) than in the intact (0.29; 0.21, 0.37) or the centralization (0.29; 0.22, 0.36) groups.ConclusionsThe centralization procedure enabled a reduction of the meniscus extrusion in the lateral meniscus with posterior root deficiency and restored the maximum load and contact pressure to values close to those of the normal knee joint.     

Editorial Commentary: Determinants of Outcome After Repair of Knee Medial Meniscus Posterior Root Tear Are Multifactorial

Medial meniscus posterior root tears alter tibiofemoral contact, leading to medial knee osteoarthritis. Repair can restore kinematics and biomechanics. Female sex, age, obesity, high posterior tibial slope, varus malalignment >5°, and Outerbridge grade ≥3 chondral lesions in the medial compartment are associated with risk for medial meniscus posterior root tears and poor healing after repair. Extrusion, degeneration, and tear gap may increase tension across the repair site, resulting in poor outcome.     

Editorial Commentary: Medial and Lateral Meniscus Root Injuries Are Distinct,and Indications for Repair May Differ: Get Down to the Root of the Problem!

Medial and lateral root injuries are different clinical entities. Medial root injuries are of a degenerative nature and frequently are associated with obesity and varus deformity. Lateral root injuries, however, are more often of traumatic origin and usually associated with injuries to the anterior cruciate ligament. There is also a biomechanical difference between the 2 injuries. In the case of medial root injuries, the loss of circular hoop tension leads to an increase in peak contact pressure. In the case of lateral root lesions, the loss of hoop stress can be compensated for by an intact meniscofemoral ligament. Nevertheless, a repair also seems to make sense on the lateral meniscus, as the posterior root also has a stabilizing effect on the knee. The most suitable technique for lateral root repair depends on the type of lesion. A transtibial pull out repair is suitable for frequent avulsion injuries (type 1). In the case of type 2 injuries, which are also common, a side-to-side suture is an option.     

Postoperative change in medial meniscal length in concurrent all-inside meniscus repair with anterior cruciate ligament reconstruction

Purpose

Meniscus repair can restore meniscal function that transfers the axial compressive force to circumferential tensile strain. However, few reports have investigated the relationship between concurrent meniscus repair with acute anterior cruciate ligament (ACL) reconstruction and postoperative meniscal position. This study aimed to evaluate medial meniscal size and clinical results in patients who underwent ACL reconstruction and concomitant all-inside medial meniscus repair.

Methods

Twenty patients underwent ACL reconstruction and concurrent medial meniscus repair of a peripheral longitudinal tear using the FasT-Fix meniscal repair device. Medial tibial plateau length (MTPL) and width (MTPW) were determined by radiographic images. We evaluated the Lysholm score, anteroposterior instability, meniscal healing and magnetic resonance imaging (MRI)-based medial meniscal length (MML) and width (MMW). Correlations between MRI-based meniscal size, radiographic measurement and height were investigated.

Results

All patients showed complete healing of the repaired meniscus in arthroscopic evaluation. However, one patient needed a subsequent meniscus repair during the follow-up period. Lysholm score and anteroposterior instability improved significantly. A better correlation was observed between MMW and MTPW than between MML and MTPL. Concurrent all-inside medial meniscus repair with ACL reconstruction significantly increased MML percentage (%MML) (100 MML/MTPL) but did not affect MMW percentage (%MMW) (100 MMW/MTPW).

Conclusions

Concurrent all-inside medial meniscus repair with ACL reconstruction had satisfactory clinical results. %MML was increased by concurrent medial meniscus repair without affecting %MMW. Our results suggest that medial meniscus repair associated with ACL reconstruction may restore meniscal function by adjusting the anteroposterior length of the torn medial meniscus.     

Usefulness of knee arthroscopy for diagnosis of knee pain in pediatric patients: comparison with preoperative clinical diagnosis

Purpose

To investigate the knee arthroscopic findings of pediatric patients with knee pain.

Subjects

Ninety-five knees of 94 patients (46 males and 48 females) aged 15 years or younger who underwent knee arthroscopy during a 4-year period from January 2007 were studied. The mean age at surgery was 13.5 (7–15) years. The mean interval from symptom onset to arthroscopic examination was 6.8 months (5 days to 2 years 10 months).

Results

The most common cause of knee pain was sports-related activities (64 knees). Other causes included falling from a moving bicycle (5 knees), while knee pain appeared with no defined reason in 14 knees. The most frequent final diagnosis based on knee arthroscopic findings was anterior cruciate ligament (ACL) injury (35 knees), followed by discoid lateral meniscus (16 knees), lateral meniscal tear (11 knees), and medial plica syndrome (9 knees), while no arthroscopic abnormality was observed in 8 of 95 knees. Among the 95 knees, the diagnosis based on preoperative physical tests and imaging findings was different from the arthroscopic diagnosis in 16 knees, 8 of which were diagnosed preoperatively as medial meniscal tear.

Conclusion

ACL injury and discoid lateral meniscus were the predominant conditions in pediatric patients who underwent knee arthroscopic surgery for knee pain. Knee arthroscopy is useful to provide a definitive diagnosis for knee pain in pediatric patients. Preoperative evaluations had a diagnostic accuracy of only 83.2 % and failed to diagnose conditions such as medial plica syndrome and chondral injury. Therefore, diagnosis before knee arthroscopy has to be interpreted with caution.     

Delayed Reduction of Irreducible Chronic Posterolateral Dislocation of the Knee with Buttonholing of the Medial Femoral Condyle

Abstract Traumatic knee dislocations are relatively rare and almost always respond to closed reduction; however, a small percentage of knee dislocations are irreducible and in these cases open reduction is frequently required. A 65-year-old man with an unreduced posterolateral knee dislocation with laterally dislocated patella was seen 3 weeks after a motor vehicle accident. Medial femoral condyle was found buttonholed through the medial capsule together with the medial collateral ligament and lying in the medial joint space that allowed posterior rotary dislocation of the joint. Both cruciate ligaments and medial meniscus were torn. There was no evidence of any vascular or nerve injury. Reduction was accomplished by removal of the capsuloligamentous structures which were incarcerated in the trochlea and intercondylar notch and by excision of meniscal tear. Following posterior cruciate ligament reconstruction with patellar tendon autograft, lateral patellar release, vastus medialis advancement, and gracilis transfer were done.     

膝关节半月板撕裂的磁共振表现

目的进一步认识膝关节半月板撕裂的磁共振成像(MRI)表现。方法回顾分析50例膝关节半月板撕裂的MRI资料,所有病例均经关节镜手术证实。采用永磁型MRI机,场强0.2T。结果50例半月板撕裂中,按照部位分类,半月板撕裂位于内侧半月板前角2例,内侧后角37例,外侧半月板前角5例,外侧后角3例,同时累及半月板前角、体部和后角者内侧2例,外侧1例。按照半月板撕裂的形式分为:水平撕裂8例;垂直撕裂4例;斜形撕裂26例;纵形撕裂3例;放射状撕裂4例;桶柄状撕裂2例;复杂撕裂3例。结论MRI能够清楚显示膝关节半月板撕裂的部位和形式,为临床治疗提供可靠的依据,是目前诊断半月板撕裂的最好的影像学检查方法。     

Radial tears associated with cleavage tears of the medial meniscus in athletes

Purpose: To evaluate the significance of a small radial tear in the root of the posterior horn of the medial meniscus in an otherwise normal-looking meniscus in individuals who play vigorous sports. Type of Study: Retrospective review. Methods: Arthroscopy was performed in 1,270 patients; 11 patients (0.86%) had a small radial tear in the root of the medial meniscus. Trimming of the tear revealed a large horizontal cleavage tear of the posterior horn and body of the meniscus. The average age of the affected patients was 29.6 years (range, 21 to 45 years), and all were active in sports. Magnetic resonance imaging was of dubious diagnostic value. Three patients had undergone previous arthroscopy at which time the small radial root tear had been noted but was not thought to warrant treatment. Results: All 11 patients returned to their former levels of activity after adequate surgery. Conclusions: When a radial root tear in the medial meniscus is found in an athletic patient, the edges of the tear should be trimmed, the root of the medial meniscus examined, and any additional torn cartilage resected.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 3 (March), 2002: pp 254–256     

Simultaneous avulsion fracture of the posterior medial and posterior lateral meniscus root: a case report and review of the literature

Injuries of the meniscus roots are increasingly recognized as a serious knee joint pathology. An avulsion fracture of the meniscus root is a rare variant of this injury pattern. In this article, a case of a traumatic simultaneous avulsion fracture of both the posterior medial and posterior lateral meniscus root associated with a tear of the anterior cruciate ligament is presented. Both avulsion fractures were treated by indirect arthroscopic transtibial pullout fixation of the bony fragment. Based on the findings of our literature review, root avulsion fractures seem to be more common in young male patients after an acute trauma to the knee joint.     

Meniscofemoral ligaments revisited. Anatomical study,age correlation and clinical implications

The meniscofemoral ligaments were studied in 84 fresh-frozen knees from 49 cadavers. Combined anterior and posterior approaches were used to identify the ligaments. In total, 78 specimens (93%) contained at least one meniscofemoral ligament. The anterior meniscofemoral ligament (aMFL) was present in 62 specimens (74%), and the posterior meniscofemoral ligament (pMFL) in 58 (69%). The 42 specimens (50%) in which both ligaments were present were from a significantly younger population than that with one MFL or none (p < 0.05). Several anatomical variations were identified, including oblique fibres of the posterior cruciate ligament (PCL), which were seen in 16 specimens (19%). These were termed the 'false pMFL'. The high incidence of MFLs and their anatomical variations should be borne in mind during arthroscopic and radiological examination of the PCL. It is important to recognise the oblique fibres of the PCL on MRI in order to avoid wrongly identifying them as either a pMFL or a tear of the lateral meniscus. The increased incidence of MFLs in younger donors suggests that they degenerate with age.