The hip joint is a ball and socket synovial joint, formed by an articulation between the pelvic acetabulum and the head of the femur.
It forms a connection from the lower limb to the pelvic girdle, and thus is designed for stability and weight-bearing – rather than a large range of movement.
In this article, we shall look at the anatomy of the hip joint – its articulating surfaces, ligaments and neurovascular supply.
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Learn MoreThe hip joint consists of an articulation between the head of femur and acetabulum of the pelvis.
The acetabulum is a cup-like depression located on the inferolateral aspect of the pelvis. Its cavity is deepened by the presence of a fibrocartilaginous collar – the acetabular labrum. The head of femur is hemispherical, and fits completely into the concavity of the acetabulum.
Both the acetabulum and head of femur are covered in articular cartilage, which is thicker at the places of weight bearing.
The capsule of the hip joint attaches to the edge of the acetabulum proximally. Distally, it attaches to the intertrochanteric line anteriorly and the femoral neck posteriorly.
The ligaments of the hip joint act to increase stability. They can be divided into two groups – intracapsular and extracapsular:
Intracapsular
The only intracapsular ligament is the ligament of head of femur. It is a relatively small structure, which runs from the acetabular fossa to the fovea of the femur.
It encloses a branch of the obturator artery (artery to head of femur), a minor source of arterial supply to the hip joint.
Extracapsular
There are three main extracapsular ligaments, continuous with the outer surface of the hip joint capsule:
The arterial supply to the hip joint is largely via the medial and lateral circumflex femoral arteries – branches of the profunda femoris artery (deep femoral artery). They anastomose at the base of the femoral neck to form a ring, from which smaller arteries arise to supply the hip joint itself.
The medial circumflex femoral artery is responsible for the majority of the arterial supply (the lateral circumflex femoral artery has to penetrate through the thick iliofemoral ligament). Damage to the medial circumflex femoral artery can result in avascular necrosis of the femoral head.
The artery to head of femur and the superior/inferior gluteal arteries provide some additional supply.
The hip joint is innervated primarily by the sciatic, femoral and obturator nerves. These same nerves innervate the knee, which explains why pain can be referred to the knee from the hip and vice versa.
The primary function of the hip joint is to weight-bear. There are a number of factors that act to increase stability of the joint.
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The first structure is the acetabulum. It is deep, and encompasses nearly all of the head of the femur. This decreases the probability of the head slipping out of the acetabulum (dislocation).
There is a horseshoe shaped fibrocartilaginous ring around the acetabulum which increases its depth, known as the acetabular labrum. The increase in depth provides a larger articular surface, further improving the stability of the joint.
The iliofemoral, pubofemoral and ischiofemoral ligaments are very strong, and along with the thickened joint capsule, provide a large degree of stability. These ligaments have a unique spiral orientation; this causes them to become tighter when the joint is extended.
In addition, the muscles and ligaments work in a reciprocal fashion at the hip joint:
The movements that can be carried out at the hip joint are listed below, along with the principle muscles responsible for each action:
The degree to which flexion at the hip can occur depends on whether the knee is flexed – this relaxes the hamstring muscles, and increases the range of flexion.
Extension at the hip joint is limited by the joint capsule and the iliofemoral ligament. These structures become taut during extension to limit further movement.
Congenital hip dislocation occurs as a result of developmental dysplasia of the hip (DDH). It occurs when the Acetabulum is shallow as a result of failure to develop properly in utero
Common clinical features include:
DDH is usually treated with a Pavlik harness. This holds the femoral head in the acetabular fossa and promotes normal development of the hip joint. Surgery is indicated in cases that do not respond to harness treatment.
Acquired dislocations of the hip joint are relatively uncommon, owing to the strength and stability of the joint. They usually occur as a result of trauma, but it can occur as a complication following Total Hip Replacement or hemiarthroplasty.
There are two main types of acquired hip dislocation; posterior and anterior:
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Learn MoreIn patients with a hip disarticulation amputation, does a polycentric hydraulic hip joint improve gait biomechanics and functional capabilities compared to a single axis, constant friction hip joint?
People with hip disarticulation amputations often have limitations in activities of daily living associated with walking, climbing stairs, and sitting down.1 In addition, published literature shows that the higher the amputation level, the lower the acceptance rate of using a prosthesis.2 Less than 50% of people with a hip disarticulation amputation use a prosthesis in everyday life.3 Lower user acceptance rates are caused by prosthetic limitations like poor gait pattern, socket discomfort, high energy consumption, and more walking aids required.2-4 For the last several decades, hip disarticulation prostheses have been made with a forward tilted monocentric hip joint, which moves in one plane, allowing only flexion and extension. This motion limitation often leads to body compensations such as increased lumbar involvement or posterior pelvic tilt during prosthetic swing phase.5-6 Polycentric hydraulic hip joints have a four-bar linkage hip joint with a hydraulic unit that provides controlled resistance to motion during both stance and swing phase.4 Due to the added motion of this style of hip joint, it has the potential to reduce some of the gait abnormalities commonly associated with hip disarticulation prostheses.
Search Terms: (hip disarticulation OR hemipelvectomy) AND (gait) AND (outcome OR rehabilitation) AND (helix OR hip joint) AND (comparison OR evaluation OR analysis OR efficiency OR case report) NOT (infection OR cancer). The included articles are a representative sample.
Inclusion/Exclusion Criteria: English, peer-reviewed and published, to present
Literature shows that gait using a hip disarticulation prosthesis with a monocentric hip joint has significant asymmetry compared to the intact side.4 However, significant enhancements with regards to the gait patterns of hip disarticulation amputees are shown when walking with a polycentric hydraulic hip joint compared to the monocentric joint.3,4 Enhancements included improved hip extension control, more moderate hip flexion velocity during swing phase, and increased stance flexion in the prosthetic knee, which leads to improved gait kinematics and increased stability.3 Using a polycentric hydraulic hip joint “provided a gait pattern more similar to that of able-bodied persons.”3 In addition to biomechanical gait analysis, outcome measures showed reduced TUG times and increased walking velocity using a polycentric hydraulic hip joint.2 For qualitative data, patient scores from the Locomotor Capabilities Index (LCI) showed increased advanced ambulation skills and activities considered difficult for hip disarticulation amputees when fit with a polycentric hydraulic hip joint, resulting in increased independence. Overall outcomes of participants fit with a polycentric hydraulic hip were statistically improved.2 However, for some patients, the continued discomfort of wearing a prosthesis or the increased motion of a polycentric hydraulic hip joint ultimately led to rejection.4 Due to the low incidence of hip disarticulation amputations and complexity of their prostheses, there has not been considerable research done on this patient population. Some limitations to these studies include the small subject populations, the lack of comparative polycentric hip designs, and inconsistencies in prosthetic adjustment periods that can greatly effect outcome measure results as well as overall component selection and socket fit.
Use of a polycentric hydraulic hip joint is likely to improve the gait biomechanics of hip disarticulation prosthetic wearers. Existing evidence has low subject populations with varying results, but qualitative and quantitative outcome measures with a polycentric hydraulic hip joint show higher patient-reported functional level of activities of daily living and self-selected walking speeds compared to the monocentric constant friction standard of care. The patient still must overcome the obstacles associated with prosthetic use at the hip disarticulation level, but the use of a polycentric hydraulic hip joint may prove to provide a more biomechanically effective alternative compared to monocentric options for these prosthetic users.
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