Iyengar-Botchu (IB) confluence of the medial knee- anatomy and clinico-radiological review

Abstract

The Iyengar-Botchu confluence is a quadrilateral space on the medial side of the knee. Due to the presence of unique anatomical structures, this region is prone to injuries. The aim of this pictorial review is to illustrate an anatomical description of the structures, which form the IB complex confluence. Clinico-pathological correlation of common conditions associated with these structures will increase awareness of injuries in this area. A complementary imaging guidance will support clinical diagnosis and appropriate patient management.

1. Introduction

The medial side of the knee has distinct anatomical structures, which are associated with common injuries and a region associated with other pathologies such as degenerative tears, sprains, benign soft tissue or osseous/bone-related pathologies.^{1, 2, 3, 4, 5}

The Iyengar-Botchu (IB) confluence refers to a quadrangular space with unequal sides formed by 4 corners, 3 of which are bony prominences on the medial side of the femur and the fourth formed by the femoral attachment of the medial patellofemoral ligament (MPFL).

The present article will review the normal anatomical structures associated with the IB confluence and illustrate the findings of complementary imaging undertaken to assess the various common pathologies in this region.^{6, 7, 8}

A comprehensive understanding of the clinical anatomy of the IB confluence and radiological correlation will help diagnose and formulate an appropriate management plan for the patient.

1.1. Anatomy of the IB confluence

The knee is a compound synovial joint, incorporating a saddle joint between patella and the femur, and two condylar joints between the condyles of femur and tibia. The large, convex surface of the medial femoral condyle forms the floor of the quadrilateral space of IB confluence. LaPrade et al. in their cadaveric study have undertaken extensive quantitative description of the anatomy of the medial side of the knee.¹ We highlight the anatomy of this area with clinico-radiological association of these structures in the IB confluence.

The quadrilateral space of the IB confluence is defined by following landmarks (Table 1).

Table 1.

Components of IB confluence.

Superior/Proximal corner	Adductor tubercle (AT) and its attachments
Inferior/Distal corner	Medial epicondyle (ME) and its attachments
Anterior	Femoral attachment of the medial patellofemoral ligament (MPFL).
Posterior	Gastrocnemius tubercle (GT) supporting origin of the medial head of Gastrocnemius
Floor	shallow, formed by the osseous medial femoral condyle.
Roof	covered by the skin and subcutaneous tissue.
Contents	no major neurovascular structures traverse this space.

The 3 osseous landmarks include [i] Medial epicondyle (ME), [ii] Adductor tubercle (AT) and the [iii] Gastrocnemius tubercle (GT). (Fig. 1).

Fig. 1.

Schematic diagram showing components of the Iyengar-Botchu (IB) Confluence: MPFL (Medial Patellofemoral Ligament), AT(adductor magnus tendon), POL(Posterior oblique ligament), sMCL(superficial component of Medial Collateral Ligament) attachment at Medial epicondyle, Gastrocnemius tubercle (GT) and origin of the medical head of Gastrocnemius.

The 3 medial ligaments consist of the [i] Medial collateral ligament (femoral attachment of superficial component), [ii] Femoral attachment of medial patellofemoral ligament (MPFL), [iii] Posterior oblique ligament (POL). (Fig. 2, Fig. 3).

Fig. 2.

Schematic showing tubercles and attachments of MPFL, AT (adductor magnus tendon), POL(Posterior oblique ligament), sMCL(superficial component of MCL), medial Gastroc(gastconemius).

Fig. 3.

Axial schematic showing the sMCL, dMCL, POL and SM (semimembranosus).

The 4 connected medial muscle units are formed by [i] Adductor magnus (AM), [ii] medial head of Gastrocnemius and [iii] Semimembranosus.

1.2. Stability of the medial side of the knee

The stability of the medial side of the knee and patella has been enhanced by a multi-layered system of ligaments and tendinous attachments. Warren and Marshall have described a three-layered system on the medial side of the knee and represents the medial retinaculum.^{9, 10, 11}

• 1.Layer 1 is the superficial fascial covering with little role in stability
• 2.Layer 2 is composed of the superficial medial collateral ligament (sMCL) and the medial patellofemoral ligament (MPFL).
• 3.Layer 3 is made up of the deep part of medial collateral ligament (dMCL), medial meniscus and the medial capsule.

Familiarity with the outcomes of nonoperative and operative treatment of isolated and combined grade I, II, and III injuries is essential for managing these injuries.

2. Medial epicondyle (ME) and medial collateral ligament (MCL)

2.1. Medial epicondyle (ME)

The ME is the key osseous pillar of the IB confluence. It is the most anterior and distal bony prominence on the medial side of the knee (Fig. 1, Fig. 2). The MCL is a broad, band like structure, superiorly attached to the ME and divides inferiorly into the Superficial MCL (s-MCL) and Deep MCL (d-MCL). MCL injuries are common and are often associated with concomitant ligamentous, meniscus, and cartilage injuries. The superficial MCL(s-MCL) has a single point of femoral attachment and 2 distal attachments on the tibia. Dimensionally it measures approximately 10 cm in length with a breadth of 1.25 cm. The femoral attachment is few millimetres proximal and posterior to the ME in an oval shape. It fans distally into a shorter proximal and an extensive distal deeper insertion anterior to the poster-medial crest of the proximal tibia. It is the main stabilizer against valgus stress to the knee in all degrees of knee flexion. Deep MCL (d-MCL): The d-MCL runs parallel to the s-MCL, close to medial joint capsule and consists of two distinct components: the meniscofemoral and the meniscotibial ligaments. These fascicles contribute to the valgus stability of medial side of the knee especially in 30–60° of flexion. The d-MCL also helps in holding the medial meniscus firmly attached to the femoral condyle.¹²

2.2. Posterior oblique ligament (POL)

The POL is anatomically distinct from the s-MCL and essentially a distal fibrous expansion of the semimembranosus tendon (Fig. 3). The femoral attachment is distal and posterior to the AT whilst distal and anterior to the osseous prominence of: Gastrocnemius tubercle (GT). The POL provides a secondary restraint to valgus deformity between 0 and 30° of knee flexion and reinforces the medial capsule.

The commonest mechanism of injury to the MCL is a valgus directed force to the outer aspect of the knee in a slight flexion. This is usually secondary to a ‘tackle’ playing sport such as football. Patients usually present with medial knee pain. This may be associated with or without swelling and sometimes with a feeling of instability. Medial tenderness may be coupled with knee effusion. Isolated MCL injuries are graded into grade I (no valgus laxity), grade II (valgus laxity at 30° flexion), and grade III (valgus laxity at 0° and 30°) injuries.¹³ The femoral component of the sMCL is the commonest site of injury of MCL. Radiologically these can be seen as thickened MCL with edema and disruption of fibres (grade 1- III sprain) (Fig. 4). Bone avulsion can be seen on plain radiographs are rare. MCL injuries are commonly associated with tears of medial meniscus, POL and Anterior Cruciate Ligament (ACL)(Fig. 5). Grade I and II sprains are treated conservatively with early rehabilitation to allow return of function. Isolated grade III injuries especially with valgus instability or with bony avulsion usually need acute, primary repair. Augmentation of repair or reconstruction is indicated to correct chronic valgus instability.^14,15

Fig. 4.

PDFS coronal showing full thickness rupture of the femoral attachment of the superficial MCL (arrow) as well the meniscofemoral ligament.

Fig. 5.

PDFS axial (a) and sag(b) showing thickened edematous POL(arrow).

3. Adductor tubercle (AT) and adductor magnus (AM)

The adductor tubercle is the second prominent osseous tubercle on the medial side of the knee. This is located proximal and posterior to the medial epicondyle. The AT and its main attachment, the Adductor magnus (AM) tendon insertion forms the proximal and superior corner of the IB confluence. (Fig. 1, Fig. 2). The AM is the largest and the deepest muscle of the medial compartment of the thigh. The insertion of this fan-shaped muscle occurs over a large surface extending over Linea aspera, medial supracondylar line with the distal most part forming a tendinous structure attaching itself to the AT. Because of the nature of the distal expansion of the AM muscle, avulsion injuries at the distal adductor magnus are noted infrequently with more commoner findings of muscle sprain³. As AM and its tendon injuries are uncommon, the mechanism of the injury and clinical presentation may suggest a commoner associated injury to the medial side of the knee; e.g. MCL injury Patients with AM tendon injuries present with medial knee pain usually sustained during contact sports or sporting endeavours such as skiing. Clinically, these injuries will reveal features of tender swelling at the IB confluence. A high index of suspicion is necessary to clinically diagnose this uncommon entity with radiological correlation.³ Plain radiographs may reveal a bony avulsion suggestive of AT avulsion. Magnetic Resonance Imaging (MRI) usually delineates the pathology associated with the adductor magnus tendon in the form of sprain or an avulsion of the tendon. MRI is also helpful is delineating in the size extent and the location of the tear in the adductor magnus tendon (Fig. 6). Additionally, is also helpful in elucidating the other commoner injuries in this IB confluence such as MCL rupture or ACL tear. AM tendon injuries are usually managed conservatively with rest, ice, compression and principles of soft tissue knee injury management with the gradual introduction of isometric and rehabilitation exercises.¹⁶

Fig. 6.

PDFS axial (a) and sag (b) showing edema in relation to the insertion of the adductor magnus(arrow) in keeping with a strain.

4. Medial patellofemoral ligament (MPFL)

The medial patellofemoral ligament (MPFL) is a broad structure located on the medial side of the knee joint. It forms the third corner of the IB confluence. It has 2 attachments. It originates between the medial epicondyle of the femur and the adductor tubercle, superior to the superficial medial collateral ligament origin (Fig. 1, Fig. 2). The MPFL passes deep to the VMO to attach to the medial border of the patella at variable level anatomically. MPFL has been indicated as the primary stabilizer of the patella and reported to show 50–80% of restraint in preventing lateral patellar instability.^5,11 Apart from this main function of providing dynamic patellar stability, it helps to guide the patella into the trochlear groove during active flexion. MPFL injuries are usually secondary to acute lateral patella dislocations (2–3% of all knee injuries) commonly seen in the young athletes and teenage people. Tall, young adolescent females and overweight males appear to be at a higher risk of lateral patellar instability.^17,18 The initiating event usually tends to be a traumatic event or a sports injury. Though there is a debate in literature, the MPFL ruptures predominantly from its patellar attachment with Krebs et al. suggesting the femoral attachment rupture being more common.^5,18

Classically patients present with medial knee pain and history suggestive of lateral patellar dislocation. Patients with MPFL injuries have tenderness on the medial border of the patella, medial retinaculum and may have an associated hemarthrosis of the knee. Awareness of the anatomical structures in the IB confluence is necessary to allow clinico-radiological correlation of other common injuries in the region such as that of MCL and medial meniscus. MPFL injuries have been classified into four categories based on location either at the level of the MPFL patellar insertion, within the mid-substance of the ligament, at the femoral origin, or in more than one location.¹⁹ (Fig. 7). Patellar insertion MPFL injuries can be further subdivided into three categories: type P0 with purely ligamentous disruption, type P1 with a bony avulsion fragment and type P2 with bony avulsion involving the articular surface from the medial facet of the patella.²⁰ The location of the ligament's origin can be identified radiographically at “Schottle's point found anterior to the intersection of the posterior femoral cortical line and the posterior margin of the medial femoral condyle.⁵

Fig. 7.

PDFS axial showing full thickness rupture of the femoral attachment of MPFL(arrow) with haematoma(arrow head). Not osseous edema of the medial part of the patella and lateral femoral condyle in keeping with a reduced patellar dislocation.

Obvious lateral subluxation of the patella in the lateral gutter of the knee leads to the suspicion of the rupture of MPFL and sometimes may be associated with an osseous avulsion, which may be noted on the plain radiographs. MRI provides an excellent visualization of the MPFL injury and shown to be more accurate than arthroscopy, especially in identifying femoral disruption of the MPFL.⁸

Management of MPFL depends on the site (patellar or femoral attachment) with a spectrum of surgical techniques described including those of open and arthroscopic techniques.²¹

5. Gastrocnemius tubercle (GT) and origin of the medial head of gastrocnemius

The gastrocnemius tubercle (GT) along with the origin of the medial head of gastrocnemius tendon form the fourth corner of the IB confluence. The GT forms an integral part of structures on the medical aspect of the knee, however abnormalities including injuries involving the proximal attachment of the medial head are rare. The GT tubercle is found distal and posterior to the adductor tubercle (AT). It gives attachment to the medial gastrocnemius tendon which itself has a thick fascial attachment along its lateral aspect to the adductor magnus (AM) tendon.^1,22 The medical gastrocnemius muscle tendon unit contributes to the formation of Achilles tendon and thus is responsible for plantar flexion of the ankle. Along with this the gastrocnemius muscle provided flexion of the non-weight bearing knee and acts as an agonist for the PCL.

Abnormalities involving the proximal medial gastrocnemius tendon could involve partial or full thickness tears usually on the background of chronic overuse tendinopathy or associated underlying posteromedial knee joint instability (Fig. 8). Case reports in literature describe features of interstitial or partial-thickness tears which may cause symptoms resembling commoner injuries associated with the medial aspect of the knee such as MCL sprains or medial meniscal tears.^23,24 Patients usually notice gradual onset of pain in the region of the IB confluence. Examination will reveal tenderness at the GT tubercle with swelling at the posteromedial corner of the knee. There may be some weakness and pain on plantar flexion of the ipsilateral ankle. The treatment for symptomatic medial gastrocnemius proximal tendinosis or partial tears is usually conservative, with rest and anti-inflammatory medications. Physiotherapy rehabilitation is indicated to regain knee joint function and return to sporting activities.

Fig. 8.

a, Sagittal PDFS showing edema of the medial gastrocnemius close to its origin in keeping with grade 1 strain. b, Sagittal PDFS showing marked edema of the medial gastrocnemius close to its origin with moderate osseous edema in keeping with grade 2 strain.

6. Conclusion

The IB confluence represents an unique anatomical space on the medial side of the knee with structures which play a crucial role in the medial stability of the knee joint. The Medial Collateral Ligament complex is the comment structure injured followed by injuries to the MPFL. Injuries to attachments of AM tendon and Medial head of gastrocnemius are rare. Awareness of the structures in the IB confluence helps in clinico-radiological diagnosis of patients presenting with medial sided knee joint pain following injuries or occasionally following gradual onset pain due to chronic, overuse tendinopathies.