BACKGROUND
Body weight from above is transmitted downward through the lower extremity in the upright position, and this force is greatly multiplied in locomotion. A priority in examining disorders of the lower extremity is to determine whether the primary lesion is local. While it is true that nerve contusions or entrapment syndromes will produce pain, weakness, paresthesias, and other neurologic symptoms locally, such symptoms can also mean a vascular disturbance or a neurologic lesion in the brain or spinal cord. It is also well to note that, at times, pelvic or retroperitoneal disease will mimic a nerve root impingement syndrome manifesting solely in one or both lower extremities.
Hip Pain
The common causes of hip pain are shown in Table 1.
Table 1. Common Causes of Hip Pain
|
Chronic Hip Pain |
Acute Hip Pain |
|
Avascular necrosis |
Arthritis |
|
Congenital fault (eg, coxa vera) |
Bursitis |
|
Contractures/other fixations |
Contusion and bone bruises |
|
Degenerative joint disease |
Dislocation |
|
Fugal infection |
Epiphyseal slip |
|
Gout (rare) |
Fracture |
|
Meralgia paresthetica |
Psoas abscess |
|
Otto pelvis (protrusio acetabuli) |
Referred pain |
|
Referred pain |
Sprain/strain |
|
Rheumatoid arthritis |
Subluxation |
|
Subluxation |
Synovitis |
|
Transient synovitis |
Tendinitis |
|
Tuberculosis |
|
Soderberg points out that, regardless of etiology, pain is a symptom common of most hip diseases.
"In such a circumstance, patients assume postures that diminish the force through the hip joint. During normal standing, the magnitude of the forces is low and usually tolerable.
However, single limb stance during gait significantly increases
the joint force due to the abductor muscle force required to
keep the pelvis from dropping on the opposite side."
Thus, overstressed fatigued muscles from an adductor lurch are a common cause of hip pain, and it should be recognized that this soft-tissue stress and the pain associated are almost always a secondary condition.
Another initial concern during physical examination when hip pain is the primary complaint is to determine if joint motion is restricted and if certain passive motions conducted in a nonweight-bearing position aggravate or initiate the pain. Early evaluation should include internal and external rotation, abduction and adduction, and flexion and extension. Branch reports that the loss of normal internal rotation is the most sensitive sign of hip disease.
Hip joint dysfunctions often refer pain more distally in the ipsilateral lower extremity, and while the lumbosacral region may refer pain to the area of the hip, rarely does a diseased hip joint refer pain to the lower back. Sciatic pain and tenderness clearly confined to the distribution of the sciatic nerve can usually be traced to lumbar or sacroiliac subluxation, strain, or looseness; spondylitis; and neuritis. Some pathologies that often refer to the hip area are prostatitis, prostatic abscess or neoplasm, and pelvic tumors or abscesses, including psoas abscess.
Thigh Trauma
Sports injuries and related disorders of the thigh include contusions, abrasions, strains, contractures, vascular abnormalities, and infrequent femoral fractures. Pain can be referred from above (eg, lumbar spine, pelvis, hip) or from below (eg, knee, ankle, foot). Minor mat, court, or turf abrasions of the thigh are seen in sports that do not require protection. These are usually easily managed if precaution is taken against secondary infection. Lacerations are rarely seen excepting vehicular and cycle sports, but muscle contusions and strains are common.
SCREENING TESTS FOR THE LOWER EXTREMITY
Gillet found that when extra-vertebral articulations are fixated, they have a tendency to produce and reproduce spinal subluxations. Thus, the analysis and elimination of articular causes must consider every segment in the kinematic chain from foot to occiput.
Background
Most primary injuries involving the lower extremities are of a musculotendinous unit. For accurate physical diagnosis, inspection, thorough palpation of bone and soft tissues, comprehensive evaluation of joint motion, and testing reflexes and active muscle action against resistance will usually point out the effects. Chronic weakness or shortening of muscles and ligaments often underlies a sprain or strain initiated by abrupt trauma or prolonged overstress.
Pioneer chiropractors considered most subluxations the effect of trauma. We now realize that this is not the case and that many subluxations can be the effect of intrinsic stresses (eg, mechanical, chemical, emotional). In general, it is believed that these subluxations will continually recur if the reasons for their existence are not also eliminated. In general, any fixated subluxation that has been effectively mobilized yet tends to recur should be considered as secondary to another cause.
During the evaluation of lower-extremity neuromusculoskeletal disorders, it is well to initially seek signs of atrophy, hypertrophy, fibrillation, and abnormal movements such as tremors, myoclonus, chorea, athetosis, tics, etc. Gross postural defects, structural attitude, and deformities should also be noted. The range of joint motion at each area can be measured with a goniometer during the orthopedic part of the examination. Then voluntary power of each group of muscles can be tested against resistance and compared bilaterally. Abnormal muscle tone and texture can be determined by palpation during passive movements.
Paralysis
True paralysis is usually pathologic rather than the effect of local malfunction (eg, transient circulatory insufficiency), and common clues aid the gross differentiation of paralyses. For example, in spastic paraplegia of any type, the legs are stiff, the reflexes are increased, but sensation and the sphincters are normal. There is no atrophy. Hysteria, however, is not uncommon in youth. It may take on almost any type of paralysis and deceive even the experienced examiner. As a rule, other evidence of hysteria will guide the diagnosis.
PHYSICAL SIGNS OF HIP LESIONS
Following are some clinical tests designed to bring out a hip lesion or pathology affecting the hip. Although the originators of these tests often claimed the procedures to be specific and diagnostic, analysis of the biomechanics involved during the maneuvers usually disprove inflated claims. They are all helpful, however, when used as one tool in the diagnostician's kit that must be thoroughly substantiated.
Remark's Sign. This sign results when for any reason the conducting pathways of the spinal cord are interrupted. When the upper third of the anterior surface of the thigh is mildly stimulated by stroking, the reflex consists of extension of the knee with plantar flexion of the first three toes in which the foot may also participate plantarly.
Patrick's F-AB-ER-E Test. This general test helps to confirm a suspicion of hip joint pathology. The patient lies supine, and the examiner grasps the ankle and the flexed knee. The thigh is flexed (F), abducted (AB), externally rotated (ER), and extended (E). Hip pain during the maneuvers, particularly on abduction and external rotation, is said to be a sign of a hip lesion.
Hibb's Test. The patient is placed in the prone position, and the examiner stands next to the patient on the side of involvement. The examiner stabilizes the patient's contralateral uninvolved hip, flexes the patient's knee on the involved side toward the buttock, and then slowly adducts the leg, which externally rotates the femur. Pain initiated in the hip joint indicates a hip lesion; pain rising in the sacroiliac joint, but not the hip, points to a sacroiliac lesion.
Lasegue's Differential Sign. This test is used to rule out hip disease, but it is not reliable without further confirmation. A patient with sciatic symptoms is placed supine. If pain is elicited on flexing the thigh on the trunk with the knee extended but not produced when the thigh is flexed on the trunk with the knee relaxed (flexed), coxa pathology can be ruled out.
Trendelenburg's Hip Test. If the hip and its muscles are normal, the iliac crest and sacral dimple will be slightly low on the weight-bearing side and high on the leg-elevated side when one leg is lifted. In testing, have the patient with suspected hip involvement stand on one foot on the side of involvement and raise the other foot and leg in hip and knee flexion. If there is hip joint involvement with muscle weakness, the iliac crest and sacral dimple will be markedly high on the standing side and low on the side the leg is elevated. A positive sign suggests the gluteus medius and minimus muscles on the supported side are weak. The gait exhibits a characteristic lurch to counteract the imbalance caused by the descended hip. This sign is also commonly positive in epiphyseal separation, pathology of the superior gluteal nerve, coxa ankylosis, hip dislocation, fracture, or chronic subluxations of L4--S1. Pathology to rule out includes Perthe's disease, poliomyelitis, muscular dystrophy, coxa vara, and Otto's pelvis.
Gauvain's Sign. With the patient in the sidelying position, the examiner stabilizes the patient's uppermost iliac crest with the heel of the hand and the fingerpads are fixed against the patient's lower abdomen. With the patient's uppermost knee extended, the examiner grasps the patient's upper ankle with the other hand, moderately abducts the limb, and firmly rotates it internally and externally. With the patient's knee locked in extension, these rotary maneuvers will affect the entire limb, as far superiorly as the head of the femur. A positive sign is seen when a strong abdominal contraction occurs, indicating a somatosomatic reflex spasm that is usually traced to hip disease.
Hip Adduction Deformity Sign. When a patient with hip disease walks or stands, it may be noted that the iliac crest is elevated on the affected side, the heel is elevated, and the patient walks on the toes of affected side. The sign is positive if measurement from umbilicus to each medial malleolus shows one leg short but measurements from the right ASIS to the right medial malleolus and from the left ASIS to the left medial malleolus shows limbs to be the same length. This is significant of adduction deformity of the hip of the apparently short limb and suspicious of tuberculosis. This stage often precedes the actual shortening of the involved limb by destruction of the femur head or joint cup.
Meralgia Paresthetica. This is the presence of a patch of anesthesia, paresthesia, or hyperesthesia, with or without pain, on the anterior and upper surface of one or both thighs (the area of the external cutaneous nerve).
Radiologic Signs of Hip Disease
Epiphysitis. Epiphysitis is more common in youth than any other serious lesion of the thigh except fracture. The diagnosis of acute cases depends chiefly on roentgenographic evidence, WBC count, and excluding arthritis of any type. Solicitous examination with testing of joint motions will usually demonstrate that the pain and tenderness are in the bone and not in the joint. Monarticular arthritis, the only variety likely to be considered in such a diagnosis, is rare in youth, when most cases of acute epiphysitis occur. Whether a disease starts in the shaft of the bone or in the epiphysis is determined by the seat of pain, tenderness, and x-ray findings.
Necrosis of the Femoral Head. The examiner should recognize the possibility of post-ischemic changes in the head of the femur during roentgenography of a hip or pelvic fracture. Subchondral collapse, related sclerosis, and irregularity on the weight-bearing anterolateral and superior aspect of the femoral head are characteristic of ischemic necrosis. Signs are best shown in the "frog-leg" abduction, lateral, and partially flexed-hip A-P views. It is an important consideration in traumatology because it often is an effect of cortisone therapy, so often used by allopathic team physicians and trainers to subdue inflammation. Aseptic necrosis may also result from hip dislocation without fracture. The examiner should take special care not to confuse a radiodense femoral head with that of necrosis. After bone or vascular injury, bone ischemia may exist without film evidence. Most of the density noted on film following bony ischemia is attributed to the reparative sclerosis of new bone laid on necrotic trabeculae (ie, creeping substitution). The relative increased density can also be contributed by osteoporosis in the nonischemic zone or by minute trabeculae collapse attenuating the x-ray beam.
Abscesses. Psoas abscess or hip-joint abscess may burrow downward to the lateral thigh. Psoas abscess presents the ordinary signs of infection and is commonly associated with vertebral tuberculosis (dorsal or lumbar). It would be embarrassing to treat an acute hip disorder for several visits and then see an MD withdraw a cup of pus from just below the patient's hip.
POSTURAL PATTERNS INVOLVING THE HIP
Underlying most all physical activity is the maintenance of upright posture, which is essentially a continuous challenge between the individual and gravity. In opposing gravity to achieve and maintain posture, approximately 40% of total energy is consumed in the physically fit. If only a slight neuromuscular problem exists, even more energy is used just to maintain balance. When many sports events are won or lost by a fraction of a second, the importance of alert chiropractic care in athletics is underscored.
Plumb-Line Analysis
During good postural balance when viewed from the side, the gravity line passes slightly anterior to the S2 segment, behind the axis of the hip joint, slightly anterior to the transverse axis of rotation of the knee (slightly posterior to the patella), crosses anterior to the lateral malleolus, and through the cuboid-calcaneal junction to pass between the heel and metatarsal heads. When viewed from the back, the lateral line of gravity passes through the spinous of L5 and the coccyx and bisects the knees and ankles. When viewed from the front, a line dropped from the anterior-superior iliac spine (ASIS) should bisect the patella and the web space between the 1st and 2nd toes.
Adaptation to Hip Abductor Weakness
When one foot is removed from the floor (eg, in walking), the center of mass of above body weight plus the weight of the lifted limb sits on the supporting hip medial to the femoral head. This force, which tends to force the pelvis downward on the unsupported side, is counteracted by contraction of the hip abductors on the supported side so that the pelvis is relatively stabilized in the frontal plane. These two forces are opposed by the force of the femoral head acting upward. However, if the hip abductors are weak, the patient must laterally abduct the trunk from the supporting side so that the gravity line falls laterally over the supporting femoral head to stabilize the hip in the frontal plane. This gross shifting moves the center of mass of the supported weight closer to the femoral fulcrum to reduce the moment of superimposed weight on the supporting hip and thus reduce the need for abductor stabilization. The resulting limp is often attributed to gluteus medius weakness, but the gluteus minimus, upper gluteus maximus, and tensor fascia lata are also important considerations.
Pelvic Muscle Effects on the Hip
Attention to hip biomechanics is important to achieve maximum performance. Secondary spinal curves depend to a large extent on the inclination of the pelvis below, and this plane relies greatly on the posture of the hip joints. Thus, hip muscles are strategically involved in determining pelvic inclination.
In the upright position, the thighs are fixed points from which these muscles act. Contraction or shortening of the extensors (glutei, hamstrings) decreases pelvic inclination, and contractions or shortening of the flexors (iliopsoas, rectus femoris) increases inclination. Weakness of antagonists has the same effect. Thus, rehabilitation is directed to relax muscles shortened by spasm or contracture (eg, abnormal reflex patterns) and strengthen counterparts weakened by inactivity, a nerve lesion, or constitutional factors. Restoration of agonist/antagonist integrity need not be a dual activity as a muscle relaxes as its antagonist contracts against resistance.
Weak Agonist or Spastic Antagonist?
Chiropractic studies of bilateral muscle checking during posture analysis suggest that the overwhelming majority of patients presenting chronic postural defects have relative muscle weakness rather than primary muscle spasm. It appears to be this weakness that causes contralateral muscles to contract into an apparent spasm. Therefore, the weakness is said to be primary by applied kinesiologists and the spasm is secondary and thought to be the result of the prime-mover/antagonist reciprocal relationship. For example, an elevated iliac crest on the right relative to the left may be due to weakness on the right of the psoas, gluteals, and tensor fascia lata or weakness on the left of the adductors, quadratus lumborum, rectus or transverse abdominis, or the sacrospinalis muscles.
Direction of Muscle Therapy in Postural Hip Distortions
During the correction of almost all postural distortions, certain muscles must be strengthened and certain muscles will require stretching. The hip is no exception to this rule. The common muscles to be strengthened in postural distortions of the hip are the lateral and medial hip rotators, hip adductors, knee extensors and flexors, foot invertors, metatarsophalangeal flexors, and the abductors, flexors, and extensors of the toes. The common muscles to be stretched in lower extremity postural distortions are the flexors, medial rotators, and adductors of the thigh; the ankle plantar flexors; and the foot evertors and invertors. Specific muscle dysfunction in individual patients varies somewhat from those listed above depending on occupation, age, gender, trauma history, and other variables, but those described should be given priority consideration.
RULING OUT HIP AND FEMUR FRACTURES
Hip pain directs physical and roentgenographic evaluation of the soft tissues on the lateral and medial aspects of the hip. A hip dislocation with or without fracture should be considered a major injury and referred immediately without attempts of reduction. Radiographs will never indicate all soft-tissue damage present. Severe pain on mild motion is typical in both hip dislocations and fractures, but this may be subdued initially by shock and the patient's fear (denial).
The possibility of nonunion and of absorption of the femur neck must be kept in mind when forming a prognosis in hip fracture. The vitality of the femur head can be inferred from its density; ie, a viable head becomes decalcified to the same degree as surrounding bone. If it is dead, density will be equal to or greater than that of healthy bone.
Adult diaphyseal fractures require more severe trauma than that usually seen in sports, excepting vehicular or parachuting accidents. Extensive connective tissue, vascular, and possibly nerve damages are associated. Fat embolism is always a danger, and severe shock is typical. Diagnosis is usually not difficult, and immediate orthopedic care is required. Incidence of isolated shaft fracture is high in children and the elderly and usually oblique from rotational stress. If fracture is suspected, special care must be made to avoid soft-tissue damage during movement and transportation.
Clinical Tests for the Hip
Following are a number of clinical tests that have shown to be helpful in screening for possible fracture. A positive sign in any one or two of the below tests is rarely conclusive in itself, however. Some are often found to be positive in functional disorders. Their importance is in their relationship with the patient's history, complaints, and physical, roentgenographic, and laboratory findings.
Allis' Hip Sign. This sign features relaxation of the fascia between the crest of the ilium and the greater trochanter. It suggests a fracture of the neck of the femur.
Allis' Knee Sign. With the patient supine, knees flexed, and soles of feet flat on the table, the examiner observes the heights of knees superiorly from the foot of the table. If the top of one knee is lower than the other, it points to a unilateral hip dislocation, a severe coxa disorder, or a short femur.
Langoria's Sign. Relaxation of the extensor muscles of the thigh is an indication of intracapsular fracture of the femur.
Hannequin's Sign. The patient is placed supine with the knees extended. A positive sign is found if deep palpation just inferior to Poupart's ligament and lateral to the large inguinal vessels produces deep tenderness, pain, and crepitation --features of femoral neck fracture.
Anvil Test. If an uncomplicated fracture of the leg or femur is suspected, the patient is placed supine and the examiner holds the ankle of the involved side in one hand and mildly strikes the patient's heel with the fist of the other hand, sending a shock wave up the extremity. The result may be localized pain that will help forecast the site of fracture or pathologic focus.
Roentgenographic Signs
The most common hip injuries viewed on film are dislocations and fractures, both of which may lead to avascular necrosis of the femoral head. Femur fractures occurring above the intertrochanteric line are within the joint capsule. They heal, as a rule, without the formation of visible callus.
Shenton's line is frequently disturbed in hip fracture. A gracefully arching line is drawn connecting the inferior margin of the superior pubic ramus with the medial margin of the neck of the femur. With minimal hip displacement, normal landmarks will be altered unilaterally.
Impactions. Following an impaction injury, it is often difficult to locate a fracture of the margin of the head of the femur. It is shown by slight contour changes and unusual densities. Comparative views, oblique and stereoscopic, tomography, or arthrography are frequently necessary to identify small fracture fragments.
Avulsions. The trochanteric areas should be checked for possible injury of the gluteal insertion at the greater trochanter or avulsion of the iliopsoas insertion at the lesser trochanter. Any type of hip pain encourages evaluation of the soft-tissue structures in the area of the obturator internus.
Epiphyseal Slippage. It is common for athletes in later years to exhibit degenerative disease of the hip suggesting evidence of an old slipped capital femoral epiphysis. Even in minimal slip of this epiphysis, a chronic "tilt deformity" may result that shows the femoral head sitting eccentrically on the neck in a drooped or tipped position. When swelling and ecchymosis appear at the base of Scarpa's triangle and the patient is unable to raise the thigh while in the sitting position, traumatic separation at the epiphysis of the lesser trochanter is indicated (Ludloff's sign).
Evidence is clear that there is an association of certain forms of degenerative hip disease, often with osteophytic flanges on the femoral head, secondary to a rearranged femoral-acetabular articulation. Thus, recognition during the early years is most helpful. Slips of the femoral capital epiphysis often occur 1 or 2 years earlier in females because the most rapid growth in that area comes earlier.
Fractures of the Proximal Femur
Femoral neck fractures are rare in the young; usually a degree of osteoporosis is predisposing. However, in contact athletics, a stress fracture of the femoral neck may become a complete fracture following later torsional stress. Repetitive trauma may result in comminuted femoral head fractures.
HIP DISLOCATIONS
Posterior Dislocations. The most common luxation is posterior dislocation of the femoral head, exhibiting thigh adduction and internal rotation at the hip and leg shortening on the affected side. When dislocation occurs, the head of the femur is driven into the posterior or central acetabulum creating comminuted acetabular fragments. The inferior aspect of the head may fracture. But posterior displacement may also be seen without fracture, with a single major posterior acetabular fragment, or with femoral head fracture. The cause is usually a force against the flexed knee with the hip in flexion and slight adduction. Complications include sciatic nerve stretching causing foot drop and numbness of the lateral calf.
Central Dislocations. These may be seen with displacement toward the inner wall only, with partial dome fractures or with central displacement with comminution of the dome. This type of dislocation-fracture commonly results from a severe force to the lateral trochanter and pelvis directed through the femoral head (eg, baseball slide). Occasionally, they are produced by a force on the long axis of the femur when the hip is abducted.
Anterior Dislocations. Anterior dislocation is relatively rare because Bigelow's ligament offers considerable protection. The limb will be externally rotated, abducted, without leg shortening. Obturator, iliac, and pubic displacements may be seen, as well as those associated with femoral head fractures. A shear fracture of the superior aspect of the femoral head is usually associated. The limb will usually be externally rotated without leg shortening. Anterior dislocations usually occur from a blow to the back while squatting, a fall where forced abduction occurs (eg, vaulting), or forced abduction of the extended hip.
Gait Clues
When observing the stance phase of the patient's gait, the dynamics of heel strike, foot flat, midstance, and toe push-off of each extremity should be noted. Failure of the knee to extend during heel strike is a sign of weak quadriceps or a flexion fusion of the knee. Weak quadriceps will display themselves in excessive flexion and poor knee stability during midstance. A midstance forward lurch of the hip is a typical sign of a weak gluteus medius, while a midstance backward lurch suggests a weak gluteus maximus.
During the swing phase, note acceleration, midswing, and deceleration of each extremity. If the patient must rotate the pelvis severely anterior to provide a thrust for the leg, the cause is likely weak quadriceps. A harsh heel strike, usually associated with knee hyperextension, is a common sign of weak hamstrings.
Leg-Length Discrepancy Observations
Bilateral differences because of anatomical discrepancies can arise from growth irregularities, effects of severe fractures, or pathology causing bone loss. Apparent discrepancies are usually due to unilateral rotatory misalignment of an ilium on the sacrum, adductor spasm causing pelvic tilt, knee distortion, or a fallen arch. Anatomical (true) leg lengths are bilaterally measured from the ASIS to a point on the medial malleolus of the respective tibia. It is usually preferred that the patient be in the nonweight-bearing supine position. In contrast, functional (apparent) leg lengths are measured bilaterally from the umbilicus to the respective medial malleolus when the patient is in the standing position.
A pelvic sag sideward (short-leg syndrome) when viewed from the front or back can be caused by several abnormalities. The most common are muscle shortening or weakness, a unilateral lower extremity deficiency, sacroiliac dysfunction, and hip or lower extremity alignment problems. Muscle fixation from lack of stretch is a common cause, second only to the common unilateral leg-length deficiency.
An anatomical or functional short leg, or both, will show that:
1. On fully extending the legs of a supine patient with a leg deficiency, the extremity on the side of involvement will be shorter than its mate on the opposite side because posterior innominate rotation causes the acetabulum to be carried superiorly and anteriorly: the superior position producing the retraction of the limb. However, on bringing the extremities upward to a position of right angles to the body, the short leg will appear to be the longest because the acetabulum of the posterior innominate has been carried superiorly and anteriorly, and the anterior position now produces the added length.
2. If a standing patient with a short leg seeks to rest his back by shifting from one foot to the other, he will come to rest by bearing most weight on the side on which the leg is short, the sacrum has gravitated anteriorly and inferiorly, and the low iliac crest has rotated posteriorly and inferiorly. Using dual weight scales, the patient habitually carries most weight on the side of the short leg. When posterior iliac rotation, sacral inferiority, or weight dominance is on the side of the long leg, a biomechanical or antalgic complication is likely.
3. Two other basic points must be considered: (a) The pelvis normally tends to rotate as a whole anteriorly on the low side during stance. (b) With the patient flexed in the Adams position, the pelvis slants anteriorly and inferiorly on the side of extremity deficiency. The lumbar spine gravitates into scoliotic deviation to the low sacral side, which establishes a state of reverse rotation between L5 and the sacrum. If the pelvis rotates horizontally backward on the low side during stance or the lumbar curve is toward the high extremity in the Adams position, a biomechanical complication is involved. A common exception to this is an acutely inflamed sacroiliac lesion on the low side where the patient attempts to maintain weight on the high side to relieve pain. This would cause the lumbar scoliosis to straighten or possibly reverse to the high side. If the lower lumbar region is fixated, adaptation will not occur until the first freely movable segment is reached (eg, T12) and then the shift will be made sharply.
ARTHROKINEMATICS
Stableness of the Hip
Stability of the hip joint is provided by its structural design and ligaments. The shaft of the femur attaches to the pelvis near a 130° angle by way of its superomedially-slanted neck. The neck ends in the large globe-like head of the femur, which articulates within the deep acetabulum, while the shaft proper ends cephally in the greater trochanter.
The articulating surface of the head of the femur is more than half a sphere, and a fibrocartilaginous labrum surrounds the acetabulum to further deepen the articular cavity. The femoral shaft bows inferiorly and twists obliquely anteriorly and medially to bring the knee joint in plumb with the hip joint. This spiral of the shaft of the femur gives it increased resistance to bending forces and shear stress.
Hip Ligaments
The capsule of the hip, unlike the shoulder, is quite strong and closely associated with four ligaments: the iliofemoral, ischiofemoral, pubofemoral, and interarticular. The strong triangular iliofemoral ligament covers the front of the joint capsule and connects with the ilium below the AIIS. It attaches to the femur at two insertions (the inverted Y ligament of Bigelow) on the anterior aspects of the greater and lesser trochanters, and thus is able to restrict excessive extension of the joint imposed by body weight in the erect posture.
The ischiofemoral ligament covers the posterior aspect of the capsule. It spans relatively horizontal between the ischial rim of the acetabulum and the greater trochanter. The spiral design of its fibers gives extra stability to the joint during extension.
The pubofemoral ligament spans from the pubic aspect of the acetabulum to the medial aspect of the femoral neck, thus covering the medial aspect of the capsule. This position allows the pubofemoral ligament to strap excessive abduction of the femur and helps to check severe extension.
These three ligaments described above tend to tighten on internal rotation and relax on external rotation and flexion. This forces the hip muscles to provide stability during external rotation and flexion.
The flat interarticular band of the hip is frequently referred to as the ligament of the femur head, ligamentum teres, or the round ligament of the hip. It courses from the pit of the femur head, through the capsule, to the nonarticular surface of the acetabulum.
Hip Joint Motion
The prime movers and accessory muscles involved in hip motion are shown in Table 2.
Table 2. Hip Motion
