Hip joint

The hip joint is the articulation between the head of the femur and the acetabulum. In standing, the femoral head is not completely covered by the acetabulum. This occurs in a position which mimics a quadruped stance, hip flexion to 90°, abduction to 5°, and lateral rotation to 10°. Hip flexion is free, being limited by soft tissue contact, but extension is usually limited to about 20–30°, depending on the amount of anterior pelvic tilt which occurs. Common values for abduction and adduction are 45° each, given a total range of rotation of 90°.

In single leg standing, vertical compression forces of 1.8–3.0 times bodyweight have been recorded at the hip, while in the stance phase of walking, forces between 3.3 and 5.5 times bodyweight have been measured. In running, the forces are higher still. Although the major force on the hip is vertical, anteroposterior forces (AP or ‘shearing’) are still present. At heel-strike and toe off, the AP forces acting on the hip actually exceed bodyweight (Palastanga, Field and Soames, 1998).

The hip passes through one flexion/extension movement during the running cycle. The limit of flexion occurs within the middle of the swing phase, and the limit of extension just before the end of the stance phase.

Knee joint

The knee joint articulation is between the condyles of the femur and tibia. The posterior surface of the patella and the patellar surface of the femur is usually considered in the knee complex. The neutral position of the knee is full extension. From this position, approximately 140° of flexion is possible in the average subject. In full extension, no transverse plane motion is possible, but as the knee flexes rotation can occur.

During the last 15° of extension, the femur medially rotates on a fixed tibia, or if the tibia is free it will laterally rotate to bring the bones into close pack formation and lock the knee (the screw home mechanism). Flexion progresses as a combination of rolling and gliding movements of the femoral condyles. At the beginning of flexion, rolling occurs alone, and as flexion increases the amount of gliding increases, until at the end of range, gliding is the only movement present.

The medial condyle only rolls for the first 10–15° of flexion, while the lateral condyle continues until 20° flexion, and at the same time the two menisci deform. This range of motion is the amount required during normal gait, and means that the knee is more stable (no gliding movement) during this functional range. Beyond 20° flexion, the knee becomes looser as the part of the femoral condyles now involved in the articulation is smaller. As a result the knee ligaments relax, and a wider range of rotation is available.

During walking, forces between two and four times bodyweight are taken by the knee. Peak forces correspond to hamstring, quadriceps and gastrocnemius contraction, and occur at heel strike and during propulsion. In jumping, forces may approach 24 times bodyweight on the knee (tibiofemoral) joint and 20 times bodyweight on the patellofemoral joint (Palastanga, Field and Soames, 1998). When walking down stairs, the intense eccentric activity in the quadriceps results in joint forces on the patellofemoral joint which are up to six times greater than those seen when walking on a flat surface.

The knee flexes and extends twice during running. At initial contact the knee is extended, and it flexes during mid-stance to absorb shock. As toe-off is reached, the knee extends again to provide propulsion and flexes as part of the swing phase.

Ankle joint

The ankle or talocrural joint consists of the trochlear surface of the talus and the distal ends of the tibia and fibula. The talar trochlea is wider anteriorly, and so plantarflexion is more free than dorsiflexion, average values being 30–50° and 20–30°, respectively. Marked variations occur both between individuals and following injury, and normal foot function can be achieved with as little as 20° of plantarflexion and 10° of dorsiflexion (McPoil and Brocato, 1990).

The ankle is essentially a hinge, externally rotated to between 20 and 25° with the malleoli (Fig. 7.1). In the neutral position, with the foot perpendicular to the lower leg, there is very little frontal or transverse plane motion. With dorsiflexion, abduction of the foot is possible, and during plantarflexion, adduction can occur. In dorsiflexion the broad anterior part of the talus is forced into the narrower mortice between the tibia and fibula. The interosseous and transverse tibiofibular ligaments are stressed, as the bones part slightly, and the joint moves into close pack position.

Figure 7.1 Relationship between the ankle, knee and hip joint axes.

From Palastanga, Field and Soames (1998) with permission.

Plantarflexion sees the narrow posterior part of the trochlear surface of the talus moving into the broader tibiofibular mortice. Recoil of the above ligaments causes the malleoli to approximate and maintain contact with the talus.

During running, the ankle is dorsiflexed at heel strike, and plantarflexes to bring the forefoot to the ground. Plantarflexion occurs again at push-off, and the foot dorsiflexes throughout the swing phase. As the speed of gait increases, the total range of motion at the ankle decreases, the range reducing by 10% when changing from a cadence of 40 strides/min to one of 60 strides/min. Joint forces at the ankle (Palastanga, Field and Soames, 1998) at heel strike are three times bodyweight for compression and 80% bodyweight for AP shear. At heel lift, muscle force creating the plantarflexion force to lift the body increase compression at the ankle to five times bodyweight (Fig. 7.2). Patients with ankle pain modify their gait pattern to reduce these forces, but in so doing stress other areas of the kinetic chain.

Figure 7.2 Forces acting on the ankle joint during the stance phase of walking.

Adapted from Stauffer, R.N., Chao, E.Y.S. and Brewster, R.C. (1977) Force and motion analysis of the normal diseased, and prosthetic ankle joint. Clinical Orthopaedics and Related Research, 127, 189–196.

Subtalar joint

The subtalar joint (STJ) lies between the concave undersurface of the talus and the convex posterior portion of the upper surface of the calcaneum. The STJ is said to be in neutral position when the posterior aspect of the heel lies vertical to the supporting surface of the foot, and parallel to the lower one-third of the leg (Subotnick, 1989).

Biomechanics of the STJ

An essential feature of the STJ is its ability to perform triplane motion. This occurs when movement of one joint is in all three body planes, because the joint axis is oblique.

Pronation of the foot is a triplane movement of the calcaneum and foot consisting of calcaneal eversion (frontal plane), abduction (transverse plane) and dorsiflexion (sagittal plane). Supination is an opposing movement of calcaneal inversion, adduction and plantarflexion in the same planes. These are both open chain movements in their pure forms. Functionally, the movements occur in closed chain formation with the foot on the ground. Abduction and adduction cannot occur owing to friction with the floor, and dorsiflexion and plantarflexion will not occur in their pure form as they are no longer free to move. Instead, the talus takes over these movements with supination consisting of calcaneal inversion with abduction and dorsiflexion of the talus, while pronation combines calcaneal eversion with adduction and plantarflexion of the talus (Fig. 7.3).

Figure 7.3 Weight-bearing motion of the sub-taloid joint. (A) Supination. (B) Neutral position. (C) Pronation.

From Gould (1990) with permission.

Definition

In the weight-bearing foot, supination (high arched foot) consists of calcaneal inversion with abduction and dorsiflexion of the talus, while pronation (flattened foot) combines calcaneal eversion with adduction and plantarflexion of the talus.

The foot has two important functions during the gait cycle. The first is to act as a mobile adaptor, adjusting to alterations in the ground surface and reducing the shock travelling up to the other lower limb joints. Second, the foot must efficiently transmit force from the muscles of the lower leg to provide propulsion to push off. For this, the foot must change into a rigid lever. These two diametrically opposed functions of mobile adaptor and rigid lever are achieved by changing the bony alignment of the foot joints, and ‘locking’ or ‘unlocking’ the foot.

Related posts:

The ankle The elbow The cervical spine The thorax and thoracic spine The shin The shoulder

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