The knee joint is the joint where the center of gravity transfers the most complex load during the walking action and is the joint of the movement system that is most exposed to forces from different directions. In the distal of the femur, articulation of the condylar structure with the plateau structure in the proximal of the tibia creates a composite joint structure with cartilage and ligament structures that provide congurency and stability. It should be well known that the knee joint is more than a simple hinge-like biomechanics, as it is thought, but a complex joint system that manages opposing vectors to create motion by changing its axis with rotation during flexion. Surgical procedures or conservative orthotic treatments performed by ignoring knee biomechanics; When combined with misdiagnosis, it causes injury to healthy structures by being under more load, progressing of the disease and decreasing patient satisfaction.


Osteologically, it consists of the femur, patella, and tibia. The femur provides the hip joint connection and the tibia provides the ankle-foot connection. In gait mechanics, knee loads and the position of the knee, femur/tibia axes, mechanical axis relationship and alignment disorders change the loading forces in the knee joint. There is a 5-7 degree varus angulation between the femoral axis and the mechanical axis. Our mechanical axis is transferred to the ground by two axes of force thought to pass through both hips. This axis continues along the tibial axis just in front of the anterior cruciate ligament attachment in the anteromedial of the knee, passes through the middle of the talus from the ankle and is transferred to the ground at the calcaneus, first and fifth metatarsal heads via the plantar arch.

With the increase in the angle of the femur axis with the mechanical axis, the approach of the femurdistal to the midline leads to the “varus deformity” genu varum. The mechanical axis shifts laterally, and excessive tension of the medial structures due to balancing in knee joint mechanics causes the external rupture to be under severe axial loads. The decrease in the angle of the femoral axis and its outward angulation causes the mechanical axis to remain medial to the knee, this is a valgus deformity, called “genu valgum”.

The knee joint is of the sino-arthroidal joint type. Rotation, abduction and adduction movements are restricted in its structure designed for movement in the flexion-extension direction. It consists of three compartments and two joints. The patella femoral joint is between the femoral groove and patella facets in the axial direction, it forms the patellafemoral compartment, its movement is up and down (Figure-4). The tibiofemoral joint consists of two compartments; participates in the medial and lateral femoral condyles, meniscal structures and cruciate ligaments involved in flexion, extension and restricted rotation movements.

During the hinge movement, the knee axis rotates internally and completes its movement with a multi-axis rotational movement. The range of motion is 120-140 degrees of flexion, 0-5 degrees of extension, and 5-15 degrees of internal rotation during flexion. During flexion, the tibia balances internal rotation with translation.

The relationship of the patella femoral joint with the mechanical axis is defined by the Q angle (figure-5). The 12-15 degree angulation between the patellar tendon and the mechanical axis is a very important feature that provides the mechanical stability of the vastus joint tendon-femoral groove and patellar facet and provides knee-hip compensation in gait mechanics. Dynamic-varus-valgus movements provide abduction-adduction-type sitting and range of motion that allows twist movement during squatting and rising.

The normal alignment of the knee is 2-3 degrees varus from the mechanical axis. The kinematic axis, on the other hand, is different in flexion and extension and may have individual characteristics depending on the femur/tibia location. With gait analysis or robotic system tests, the external rotation rate of the femur and the relationship of the tibia can be determined.

The ligamentous structure of the knee forms the intra-articular ligaments and lateral ligaments and the popliteus complex posterolaterally. Crosslinks resist translational forces as well as rotational stability. The posterolateral complex is strong enough to serve as a pivot as the strongest fulcrum of the knee, which includes the popliteus, lateral meniscus, and the head of the fibula. The structures that stabilize the knee during loading are the collateral ligaments associated with the capsule, the pes anserunus adductor complex in the media, and the iliotibial band structures in the lateral.

Looking at the structures that balance the internal and external vectors on the knee joint of an athlete in the squat position, it will be understood that the knee joint has an extremely complex load distribution. The extensor structures and the hamstring muscles that meet it provide the stability of the knee.

In lower extremity alignment disorders, varus-valgus in the anterior background, recurvatum and flexion deformities in the sagittal plane
Genu varum, also known as “That leg” deformity, is mostly based on disorders such as rickets. However, the result of knee osteoarthritis accompanying rotational alignment disorders can also develop in advanced ages. The body center of gravity has been displaced medially and the knee motion axis has lost its parallelism to the ground plane, causing wear. Inner wedge shoes and medial supported knee pads can regulate the patient’s gait even though they do not change the alignment. It should be known that the medial support cannot meet the forces if the continuous use of knee brace causes the lateral supporting muscle groups to atrophy. The alignment can be surgically corrected with tibial osteotomy, which is elevated according to its severity, and femoral osteotomy in advanced mechanical axis impairment.

In the genu valgum or “X-crooked leg” deformity, the center of gravity has shifted laterally in the tibia valgus. As the medial structures try to meet the weight vectors, a tendency to excessive wear occurs in the lateral. The leg is in internal rotation. The lateral load is tried to be transferred to the medial with outer wedge shoes, but it is difficult to provide stability with the knee brace as in the genu varum and often requires surgical treatment.


The stability of the knee depends on the geometric structure, the weight distribution with the alignment, and the strength of the capsule, ligament, and muscle structures corresponding to it. We can divide these open stabilizers into two:
Static: Capsular, capsular ligaments and extracapsular ligaments
Dynamic stabilizers: Musculotendinous units (pes anserinus, iliotibial band, patella tendon, hamstrigs, politeus complex, gastrocnemius)

In this respect, we can classically examine knee instability in 3 main groups:
Unidirectional instabilities;
Medial, Lateral Posterior and anterior

rotational instabilities;
Anteromedial, Anterolateral (flexion and extension type)
Posteromendial and posterolateral

Combined or Complex instabilities
Patellafemoral instabilities


Orthotic treatments are used in cases where surgery is not required and to support the healing of tissues repaired after surgery. In this respect, bands and supports and knee pads are designed to resist the vectors encountered by the ligament structures. Choosing the right knee brace is essential in both surgical and conservative treatments. While the treatment is being organized, knee pads that are rigid enough to cause muscle atrophy will usually be used in the first weeks and will be replaced by soft knee pads that feel the impact effect. Likewise, after surgical treatment, the physician may prefer different knee brace options during the rehabilitation phase of the treatment. In this respect, working in harmony with the physician will increase the success of the treatment.


Amputations of the knee joint can be done at three different levels; above the knee, disarticulation, below the knee.

Since the knee joint is preserved and adductor and lateral stabilization can be achieved in below-knee amputations, prosthesis application is extremely successful. It is easy for the patient to adapt without training. Since the knee joint is completely lost in above-knee amputations, a certain period of training may be required, although compliance with dynamic prostheses with special joints can be achieved very well to ensure weight transfer in the thigh and lower extremity on the prosthesis. Preparing the patient to walk requires more strength.

Disarticulation can be performed to allow extremity elongation, which is especially preferred in children of growing age. Requires fairly good stump closure experience. A good surgeon can create a soft tissue-muscle balance that will provide a weight distribution as successful as below-knee amputation. The adaptation process of the patients can be accelerated with education.


If the prosthesis application after amputation is not a new generation prosthesis augmented to the bone, we can schedule it in two ways:
Immediate during surgery
After the postoperative wound has healed

Immediate prosthesis application is done with a specially designed foot placed on the plaster with stump care every three days. The orthotic team must be present during the surgery for this prosthesis application, which enables the patient to be mobilized early and considerably reduces the postoperative orbit. In follow-up wound care, the plaster is reapplied each time. Excellent results have been reported in terms of stump development and compliance.
A good amputation surgery, appropriate stump flaps, osteomyoplasty and adequate soft tissue support will facilitate prosthesis application. If the nerves are sufficiently deep during amputation so as not to form a neuroma, the success of the practitioner will increase with painless manipulations.

The knee is always open to problems in terms of the load it carries as a large and complex joint. When problem-oriented personal data (alignment, joint and bone compatibility, footprint, gait analysis) are collected well in knee diseases, the source of the problem can be reached and patient satisfaction can be maximized. In this respect, it is very valuable for orthopedic and prosthetic orthotics laboratories to work in harmony in this direction.