European Journal of Cardiovascular Medicine

The foot is a bodily structure that functions as a dynamic sensory-motor interface between the ground and the body. Although it has a small surface area, it consists of 26 bones and 29 muscles, aligning to form joints and arches, with neurovascular bundles packed in between them.[1] These structures primarily function to transmit and disperse force, as well as to manage the movements of the human body upon surface contact. Foot paincan arise from various etiologies including illfitting foot wear, excessive use or repetitive strain as in athletes, dancers all of them leading to compression of plantar nerves resulting in compression neuropathy of foot. [2]

Unlike other regions, the foot contains four intermuscular layers. The first, third, and fourth layers consist of the abductor hallucis, flexor muscles, and interosseous muscles, respectively, all of which originate and terminate within the foot. However, the second layer includes the flexor hallucis longus (FHL) and the flexor digitorum longus (FDL) muscles, which travel all the way from the back of the leg, pass along the inner side of the foot, and reach the digits [3] in between the superficial first & second layer of the foot lie the medial & lateral plantar nerves & vessels (neurovascular structures) that supply the foot with blood and innervation [2,3]. Hence being crucial for the foot's function and sensation.

Symptoms of medial and lateral plantar nerve entrapment include almost constant pain, whether walking or sitting. Just standing is often difficult. The pain is often chronic, difficult to treat, and aggravated by high-impact activities such as running. Burning, numbness, and tingling, which often occur when nerves are compressed, usually do not occur in medial and lateral plantar nerve entrapment.  it is important to carefully assess the site of entrapment as proximal treatment will not address distal pathology.[4] Lateral plantar nerve entrapment, also known as Baxter's nerve entrapment, is a condition where the lateral plantar nerve, a branch of the posterior tibial nerve, is compressed or pinched, causing pain and sometimes numbness on the inner part of the heel and sole of the foot. This entrapment can occur at various points along the nerve's path, including near the heel bone, and can mimic plantar fasciitis.[5] 

The first branch of the lateral plantar nerve, also known as the inferior calcaneal nerve or Baxter's nerve, is a common site of entrapment. It supplies sensation to the heel and inner sole of the foot and is sometimes implicated in chronic heel pain. 

The lateral plantar nerve is responsible for sensation and movement in the bottom of the foot, particularly the sole and toes. Entrapment occurs when this nerve is compressed, usually by fascia, ligaments, or bone, leading to pain and sometimes numbness. Common symptoms include pain on the inner part of the heel, which may radiate to the sole of the foot and arch. Pain may be worse with weight-bearing, after prolonged rest, or in the morning. Some individuals may experience burning sensations, tingling, or numbness.[6] 

The medial plantar nerve is a major nerve in the foot, a branch of the tibial nerve, responsible for sensation and motor function in the medial part of the foot. It carries signals from the skin and muscles of the medial sole, as well as providing motor innervation to certain muscles of the foot, including the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and lumbricals. [5,6]

Several factors can contribute to medial plantar nerve entrapment, including:Pressure on the nerve due to foot problems like flat feet or high arches. Activities that place extra stress on the foot, such as running or dancing. 

Certain types of shoes, especially those with minimal cushioning. 

Underlying medical conditions like diabetes. India has second highest number of people living with diabetes (101.3 million) in the world next to China (140.9 million). Diabetic foot-related problems is one of the most common problems in people with diabetes. India also faces the increasing burden of foot-related problems among people with diabetes. [7]

Diagnosis is often made based on a physical exam, where tenderness is found at the site of entrapment (usually around the abductor hallucis muscle). Injections of local anesthetics can help confirm the diagnosis by providing temporary relief of pain. 

Treatment options vary depending on the severity and duration ranging from Initial: Rest and activity modification. to Anti-inflammatory medications. Stretching exercises. Local steroid injections. Orthotic devices to support the arch and finally resorting to. Surgical release of the nerve [6,8]. Pressure on the nerve due to foot problems like flat feet or high arches poses a substantial burden on patients, who can experience impaired gait and loss of balance, predisposing them to falls and fractures, and neuropathic pain, which is frequently difficult to treat and impairs quality of life [8]. Hence it was our objective to study the location & morphometrics of knot of henry with respect to the nerves of the foot that could serve as a critical point during hind foot, midfoot surgeries & also help in effective management of foot neuropathy.

42 feet of formalin-fixed adult cadavers of Indian population were which were donated for research purposes to Department of Anatomy, Dr B.R. Ambedkar Medical College, Bangalore. There were no indications of previous surgery or any other deformity around the foot.

To ensure accurate measurement, the foot was secured in a neutral anatomic position. To expose the Knot of Henry, the skin, superficial fascia, plantar aponeurosis, flexor digitorum brevis, and abductor hallucis muscles were sequentially resected. Dissection then proceeded along the tendons of the Flexor Digitorum Longus and Flexor Hallucis Longus to locate their intersection - the Knot of Henry. The Medial and lateral plantar nerves were identified and were subsequently delineated, and their distance to the Knot of Henry was precisely recorded using a digital caliper. Additionally, the distance of Knot of Henry from medial tubercle of calcaneum and head of first metatarsal was measured.

The medial plantar nerve presented as a single trunk near the knot in 96.9% of cases, and as an already bifurcated structure in 6.25% (2 out of ). The mean distance between the Medial Plantar Nerve and Knot of Henry measured 6mm± SD4.8 mm (right foot) and 5mm±SD 3.2mm (left foot), with 60% specimens falling within the range of 1.2-10.8 mm, 26.7% were closer, and 13.3% were farther than that. the specific ranges along with sides have been demonstrated in the following pie  chart. Additionally, we observed the lateral plantar was on average 24.6±4mm from the knot of henry,

The mean distance between the medial tubercle of calcaneus and Knot of Henry measured 4.2cm±SD0.8cm (right foot) and 3.8cm±SD0.9 cm (left foot) with 60% falling within the mean range, 23.3% were more proximal, and 16.6% were more distal. On the other hand, the mean distance between head of first metatarsal and knot of henry was 17.6 cm± SD 1.9 cm (left foot) and 17.2 cm ± SD1.7 cm (right foot) with 78% specimens falling within the mean range. The knot was closer to medial tubercle of calcaneum than the head of first metatarsal in 100% of cases.

Knot of Henry  or master knot of Henry or chiasma tendineu plantare was identified and reported by Arnold Kirkpatrick Henry in 1945[9]. It was described as the superficial oblique crossing over of the tendon of FDL over FHL as they move from back of leg to the medial side  side of the foot for insertion  to the phalanges of the toes thus allowing flexion of toes during the Walking stride.  Previous studies[10]considered  the distance of proximal and distal points of slips and MKH to medialmalleolus, navicular tuberosity and first interphalangeal joint were recorded   A review of existing literature reveals mpn is often overlooked or misdiagnosed. Herbst, Murphy,khwaja et al  in their separate studies reported patients with persistent medial foot pain following Surgical tendon transfer  & managem Ent of joggers foot only to find persisting  MPN involvement later on neuropathy of foot  initially manifests  as painful activities that place extra stress on the foot, such as running or dancing. Certain types of shoes, especially those with minimal cushioning. Underlying medical conditions like diabetes. Common symptoms include pain on the inner part of the heel, which may radiate to the sole of the foot and arch. Pain may be worse with weight-bearing, after prolonged rest, or in the morning. Some individuals may experience burning sensations, tingling, or numbness.[11] 

The foot complex plantar anatomy with interconnected fascial muscular layers and intricate neurovascular bundle. Knot of henry being located in midfoot  is prone for mid-foot tendon disorders &  Other underlying causes being trauma, infection (usually diabetes related), benign/malignant soft-tissue or bone-related pathologies. However we  conducted the location of knot of henry from medial tubercle of calcaneum to head of first metatarsal  as it reduces the margin of error  in contrast to medial malleolus, compared to navicular tuberosity  it is more prominent, more proximal to tarsal tunnel providing a direct approach to neurovascular  structures .

Importance of knot of Henry - intersection syndrome. It is one   of the most frequent site of plantar foot pain. Tensosynovitis of FDL is  often seen in ballet dancers and soccer players due to overuse and repetitive movements leading to pain, swelling and difficulty in movement. interconnections between  FDL and FHL are usually used for tendon transfer in cases of for tibialis posterior dysfunction and neglected achillestendon rupture, which is frequently seen in runners and athletes leading to flat foot. Furthermore it is needed  for reconstructive foot and ankle surgeries. This knowledge is helpful in reducing functional loss post-tendon transfer procedures.[11,12] The knot is often overlooked because of its small anatomical space and  there is need for surgeons and radiologists to identify and appreciate of surgeries releasing tendons, sheaths, and tensile synovitis of FHL. unlike previous studies[13,14], our current  study  considered Navicular  tuberosity  plus  head of first metatarsal as the landmarks, the mean distance between head of first metatarsal and knot of henry was 17.6 cm± SD 1.9 cm (left foot) and 17.2 cm ± SD1.7 cm (right foot) & The mean distance between the medial tubercle of calcaneus and Knot of Henry measured 4.2cm±SD0.8cm (right foot) and 3.8cm±SD0.9 cm (left foot0)  hence implying that knot of henry was more closer to medial tubercle of calcaneum compared to head of first metatarsal . and thus during  surgeries involving   hindfoot biomechanics  or in certain in certain surgical procedures for conditions like flatfoot and hindfoot deformities the closer location of knot of henry should serve as a critical area.[15,16]

Location of knot of henry

Mao et al., proposed that narrow space between knot of henry & division of FDL located distal to knot of Henry should be termed as  the triangle of henry and described relations of lateral plantar nerve close to location of knot of henry [17], while our study showed a statistically significant relation of mpn with knot of henry than with lateral plantar nervebecause of numerous tendinous intersections. O berger  described  attachments of flexor accessorium to flexor hallucis longus also, however in  our current study didnot show attachment of accesorius to hallucis and in fact  its attachment to digitorum was proximal to knot of henry.

Tom Muller in his cadaveric  study on 24 foot specimens used incision proximal & distal to medial malleolus for harvesting flexor hallucis longus tendon which resulted in nerve lesions in 33 of all foot specimens. He concluded that mpn & lpn are at risk of injury when fhl harvesting is done distal to knot of henry [18.19]. Mao et al  in his 68 embalmed feet study concluded that mpn & lpn injuries did not occur more frequently during harvest of fhl tendon  due to large  distance between  the fhl tendon & mpn  & lpn  in contrast to our study which showed significant relation of mpn at level of  knot of henry.

The findings, drawn from meticulous dissection and morphometric analysis, highlight the close proximity of medial plantar nerve to the Knot OF HENRY  AND THE FARTHER LOCATION OF LATERAL PLANTAR NERVE  FROM KNOT OF HENRY  in the majority of specimens, point out to its potential vulnerability during surgical procedures.  By using fixed bony landmarks—the medial tubercle of the calcaneum and the head of the first metatarsal— we found out it's relative proximity to medial tubercle of calcaneum and offered a practical reference for locating the Knot of Henry. KNOWLEDGE OF THIS STUDY MIGHT CONTRIBUTE DURING  surgical interventions for tendon transfers, chronic foot pain, or neuropathies  MAKING THEIR become more refined, & EFFECTIVE.

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