MRI of intermittent meniscal dislocation in the knee

Anterior Mobility of the Posterior Horn of the Lateral Meniscus Is Associated With Abnormal Magnetic Resonance Imaging Findings of Anteroinferior Popliteomeniscal Fascicle and Posterosuperior Popliteomeniscal Fascicle as Well as a Clinical History of Catching or Locking Symptoms

Purpose

To identify predictors of anterior mobility of the posterior horn of the lateral meniscus (PHLM) among patient demographics (age, sex), clinical characteristics (a history of catching or locking symptoms [CLS], body mass index, alignment of limb), and magnetic resonance imaging (MRI) findings of 4 restraints: anteroinferior popliteomeniscal fascicle (aiPMF), posterosuperior popliteomeniscal fascicle (psPMF), posteroinferior popliteomeniscal fascicle (piPMF), and meniscofibular ligament (MFibL).

Methods

Between October 2010 and December 2014, patients who underwent arthroscopic measurement of mobility of the PHLM were identified. The Sakai classification was used to classify aiPMF and psPMF on MRI into the following 3 types: type A, the fascicle was depicted with obvious continuity and with a low-intensity band; type B, depicted with continuity but with an ambiguous intensity structure; and type C, depicted with discontinuity or not visible. Magnetic resonance images of the piPMF and MFibL were evaluated as presence or absence. The mobility of the PHLM was measured arthroscopically at traction forces of 10 and 20 N.

Results

A total of 73 patients (47 men, mean age 41.8 ± 19.3 years) were included. Multivariate regression analyses revealed aiPMF type C and psPMF types B and C to be independent factors associated with mobility at both traction forces, and CLS was an independent factor at a traction force of 20 N. Compared with that of type A, the increased mobility of aiPMF type C was 5.0 mm (P = .019) and 5.6 mm (P = .011) at 10 and 20 N, respectively; the increased mobility of psPMF type B was 2.5 mm (P = .007) and 3.5 mm (P = .0003), respectively; and the increased mobility of psPMF type C was 3.3 mm (P = .021) and 3.6 mm (P = .014), respectively. The increased mobility associated with CLS was 3.5 mm at 20 N (P = .022).

Conclusions

Anterior displacement of the PHLM induced by an external traction force at 90° of flexion of the knee joint was associated with abnormal MRI findings of the anteroinferior popliteomeniscal fascicle and posterosuperior popliteomeniscal fascicle, as well as a history of catching or locking symptoms.

Clinical Relevance

Understanding signs and symptoms and associated pathology in patients with symptomatic anterior mobility of the posterior horn of the lateral meniscus may help guide best treatment.

Does discoid lateral meniscus have inborn peripheral rim instability? Comparison between intact discoid lateral meniscus and normal lateral meniscus

INTRODUCTION

Little is known about peripheral rim instability (PRI) of adult discoid lateral meniscus (DLM). We compared PRI of the intact DLM (iDLM) to those of intact normal lateral meniscus (LM) in adult patients and also investigated whether there was any association between PRI and DLM tears.

MATERIALS AND METHODS

We investigated PRI in 17 DLMs and 60 normal LMs without tears during arthroscopic surgery for medial compartmental pathologies between June 2012 and October 2015. We also investigate PRI of torn DLM (tDLM) excluding peripheral tear to compare the PRI between intact and torn DLM. Stability parameters were measured using a probing hook and arthroscopic ruler at the anterior, middle, and posterior parts of the peripheral rim of the menisci: translating the anterior horn (AH) and mid-body (MB) and lifting the posterior horn (PH).

RESULTS

AH and PH instabilities were greater in the iDLM group than in the iLM group (2.2 ± 1.4 vs. 0.9 ± 1.4 mm, p = 0.006 and 3.4 ± 1.7 vs. 1.7 ± 1.2 mm, p = 0.004, respectively). However, there was no significant difference in MB instability between two groups. In addition, no significant difference was observed in all the parameters between the iDLM and tDLM groups.

CONCLUSION

Both iDLM and tDLM had greater PRI of the AH and PH than the iLM in adult patients. Thus, the DLM is prone to tear and careful inspection is needed not to overlook PRI of a DLM even if the peripheral attachment is intact.

LEVEL OF EVIDENCE

Level 3, comparative study of anatomical instability of living subjects.

MRI of popliteo-meniscal fasciculi of the knee: a pictorial review

The popliteomeniscal fascicules (PMFs) provide the attachment of the lateral meniscus to the popliteus musculotendinous region, forming the floor and the roof the popliteal hiatus. In the second half of 1900's, some anatomic studies claim the important function of the PMF as stabilizers of the lateral meniscus; these anatomical structures work in conjunction with the popliteus musculotendinous unit to prevent excessive lateral meniscal movement and possible meniscus subluxation. A correct diagnosis of the PMFs pathology is crucial to establish the suitable surgical treatment for each patient. MRI is a well-established imaging technique in the musculoskeletal system and the frequency of recognition of normal PMF in the normal knees is high in almost all MRI studies. At day, the gold standard for diagnosis is the arthroscopic evaluation that allows the direct visualization of the popliteo-meniscal ligaments at popliteal hiatus and evaluation of lateral meniscal movements. For this reason if unstable condition of meniscus was suspected, arthroscopic observation with probing into the popliteo-meniscal fascicle area is essential for the identification of the fascicle tears. Despite many treatments have being proposed in literature since now there is high recurrence of knee locking after repair and it is fundamental to develop new surgical techniques in order to achieve better outcome.

Reconstruction of the Popliteomeniscal Fascicles for Treatment of Recurrent Subluxation of the Lateral Meniscus

Recurrent subluxation of the lateral meniscus is characterized by episodes of mechanical locking of the knee joint. To completely preclude the posterior segment of the lateral meniscus from undergoing anterior dislocation during deep knee flexion, the structures to which it is attached need to be relatively taut. The posterosuperior popliteomeniscal fascicle retains its tension during deep knee flexion; therefore, reconstruction of the posterosuperior and anteroinferior popliteomeniscal fascicles was performed with an autograft harvested from the iliotibial band. This technique provides stabilization of the posterior segment of the lateral meniscus during deep knee flexion without interfering with the normal movement of the lateral meniscus throughout the range of motion of the knee joint.

Displacing lateral meniscus masquerading as patella dislocation

PURPOSE

To alert the treating clinician to an uncommon knee meniscal condition that often masquerades as a more common patella condition.

METHODS

Retrospective chart review of a series of cases was undertaken. A series of 12 knees in 11 patients were referred to an orthopaedic surgeon with a diagnosis of recurrent lateral patella dislocation. Three knees had undergone patella realignment surgery with continuance of symptoms. Eight patients had prior magnetic resonance images read as no meniscal pathology and no acute patella/patella retinacular injury. All patients presented for a consult with a similar history.

RESULTS

Under anaesthesia, all knees had a stable patella as judged by physical examination. At the time of surgery, six patients had a frank tear in the lateral meniscus, all of which were readily displaceable. Six knees showed a displaceable lateral meniscus with attenuation but not a visible frank tear. Ten menisci were treated with repair, and two knees underwent partial lateral meniscectomies. Patient follow-up of minimally 18 months revealed no further episodes of "knee-cap dislocation" or symptoms of catching and locking.

CONCLUSIONS

The clinician treating a patient with a history of a knee locking in flexion should have a high index of suspicion for a lateral meniscus tear or an unstable hypermobile lateral meniscus, despite patient report of perceived patella movement. History of symptoms occurring in knee flexion and attention to patella physical examination should be key factors in this diagnostic conundrum.

LEVEL OF EVIDENCE

Retrospective chart review, Level IV.

Magnetic resonance imaging and arthroscopic findings of the popliteomeniscal fascicles with and without recurrent subluxation of the lateral meniscus

PURPOSE

The aim of this study was to examine the posterosuperior popliteomeniscal fascicle (sPMF) and anteroinferior popliteomeniscal fascicle (iPMF) by use of magnetic resonance imaging in control knee joints and joints with recurrent subluxation of the lateral meniscus (RSLM) to determine the incidence of abnormal popliteomeniscal fascicles (PMFs) in these groups.

METHODS

Knee joints were diagnosed with RSLM when there was a history of mechanical locking episodes and when subluxation of the lateral meniscus was recognized on arthroscopy. In this study 238 knee joints were evaluated. The joints were classified into a control group (215 joints), RSLM group (16 joints), and contralateral RSLM group (7 joints). Classification of the sPMF (iPMF) on magnetic resonance imaging was as follows: type I, a tense, low-intensity band ran from the superior (inferior) border of the lateral meniscus to the popliteus tendon; type II, an unclear band ran from the superior (inferior) border of the lateral meniscus; and type III, no band was observed. Types II and III were thought to exhibit abnormal PMFs. The distribution of knee joints among the 3 groups and PMF types was examined.

RESULTS

Percentages of abnormal sPMFs and iPMFs were 40% and 26%, respectively, in the control group; 100% and 29%, respectively, in the contralateral RSLM group; and 100% and 100%, respectively, in the RSLM group. A significant difference in the distribution of knee joints by classification of sPMFs was recognized between the control and contralateral RSLM groups (P < .0001). A significant difference in iPMFs was also recognized between the contralateral RSLM and RSLM groups (P = .0005).

CONCLUSIONS

A significantly high incidence of abnormal sPMFs was found in RSLM and contralateral knees. Thus abnormal sPMFs existed in both knee joints before patients had locking symptoms, suggesting that abnormal sPMFs may be required for locking symptoms. A significantly high incidence of abnormal iPMFs was found only in the knee joints with RSLM. An abnormal iPMF is thus the essential lesion to allow the at-risk lateral meniscus to become unstable beyond the rate of control knees.

LEVEL OF EVIDENCE

Level III, case-control study.

Association of internal rotation of the knee joint with recurrent subluxation of the lateral meniscus

PURPOSE

To compare the arc of rotation of the knee joint at 90° of flexion in control knee joints and those affected by recurrent subluxation of the lateral meniscus (RSLM), in determining whether rotatory instability of the knee joint is a risk factor for RSLM.

METHODS

Knee joints were diagnosed with RSLM when there was a history of mechanical locking episodes and when subluxation of the lateral meniscus with the peripheral margin of the posterior segment moving anteriorly beyond the lateral femoral condyle was recognized on arthroscopy. In this study 288 knee joints in 270 subjects were evaluated. The joints were classified into a control group (252 joints), an RSLM group (24 joints), and a contralateral RSLM group (12 joints). The arcs of external and internal rotation at 90° of flexion of the knee joint induced by 7 Nm of torque under non-weight-bearing conditions were measured with a Biodex System 3 (Biodex Medical Systems, Shirley, NY).

RESULTS

There were no significant differences in mean values of external rotation among the 3 groups. The mean values of internal rotation of both the RSLM and contralateral RSLM groups were significantly larger than that of the control group, by about 15° (P < .0001). The mean value of internal rotation was slightly higher than that of external rotation in the RSLM and contralateral RSLM groups, although the mean value of internal rotation was smaller than that of external rotation by 10.1° in the control group.

CONCLUSIONS

RSLM was found to be strongly related to bilateral increase in the arc of internal rotation at 90° of flexion of the knee joint, suggesting that internal rotatory instability of the flexed knee joint can be considered one of the risk factors for and diagnostic parameters of RSLM.

LEVEL OF EVIDENCE

Level III, diagnostic study of nonconsecutive patients.