Anatomy and Biomechanics of Hip Joint: The hip is a classical ball-and-socket joint. It meets the four characteristics of a synovial or diarthrodial joint: it has a joint cavity; joint surfaces are covered with articular cartilage; it has a synovial membrane producing synovial fluid, and; it is surrounded by a ligamentous capsule (Byrd J., 2004). The cup-shaped acetabulum is formed by the innominate bone with contributions from the ilium (approximately 40 percent of the acetabulum), ischium (40 percent) and the pubis (20 percent) (Schuenke M, Schulte E, 2006). In the skeletally immature these three bones are separated by the triradiate cartilage – fusion of this starts to occur around the age of 14 – 16 years and is complete usually by the age of 23 ( Moore, 1992). The actual articular surface appears a lunate shaped when viewed looking into the acetabulum. Within the lunate, or horseshoe shaped articular cartilage is a central area – the central inferior acetabular fossa. This fat filled space houses a synovial covered fat pad and also contains the acetabular attachment of the ligamentum teres. Inferior to this, the socket of the hip is completed by the inferior transverse ligament. Attached to the rim of the acetabulum is the fibrocartilaginous labrum. The labrum has been closely studied as tears of the labrum are the most common indication for hip arthroscopy(Byrd 2005) . Although it makes less of a contribution to joint stability than the glenoid labrum in the shoulder it does serve its purpose. It plays a role in normal joint development and in distribution of forces around the joint(Kim YH, 1987; Tanabe H, 1991). It has also been suggested it plays a role in restricting movement of synovial fluid to the peripheral compartment of the hip, thus helping exert a negative pressure effect within the hip joint(Ferguson SJ, Bryant JT, Ganz R 2003). The labrum is a fibrocartilagenous ring surrounding the acetabulum in the hip. It is triangular in cross-section, approximately 4.7 mm wide at the bony attachment by approximately 5.5 mm tall (Seldes et al., 2001). The labrum is primarily composed of circumferential Type I collagen fibers (Petersen et al., 2003). The labrum functions to stabilize the joint, rather than to decrease cartilage contact stresses, during activities of daily living ( Henak CR et al., 2011) . Labral tears are often diagnosed in a clinical setting, suggesting that the labrum can be subjected to substantial loads in vivo (Blankenbaker et al., 2007; Burnett et al., 2006)
The femoral head is covered with a corresponding articular cartilage beyond the reaches of the acetabular brim to accommodate the full range of motion. The covered region forms approximately 60 to 70% of a sphere. There is an uncovered area on the central area of the femoral head –the fovea capitis – for the femoral insertion of the ligamentum teres. The ligamentum teres, while containing a blood supply does not contribute to the stability of the joint. It is covered in synovium, so while it is intra-articular it is actually extra-synovial. The head of the femur is attached to the femoral shaft by the femoral neck, which varies in length depending on body size. The neck-shaft angle is usually 125±5 degrees in the normal adult, with coxa valga being the condition when this value exceeds 130 degrees and coxa vara when the inclination is less than 120 degree. The importance of this feature is that the femoral shaft is laterally displaced from the pelvis, thus facilitating freedom for joint motion. If there is significant deviation in angle outside this typical range, the lever arms used to produce motion by the abductor muscles will either be too small or too large. The neck-shaft angle steadily decreases from 150 degrees after birth to 125 degrees in the adult due to remodelling of bone in response to changing stress patterns. The femoral neck in the average person is also rotated slightly anterior to the coronal plane. This medial rotation is referred to as femoral anteversion. The angle of anteversion is measured as the angle between a mediolateral line through the knee and a line through the femoral head and shaft. The average range for femoral anteversion is from 15 to 20 degrees .
The joint capsule is strong. While the ball and deep socket configuration naturally gives the hip great stability the ligamentous capsule undoubtedly contributes significantly. The iliofemoral ligament can be seen anterior to the hip in the form of an inverted ‘Y’ or a modified ‘∆’. It is the strongest ligament in the body with a tensile strength greater than 350N. It spans, in a spiralling fashion, from its proximal attachment to the ilium to insert along the intertrochanteric line. It is taut in extension and relaxed in flexion keeping the pelvis from tilting posteriorly in upright stance and limiting adduction of the extended lower limb. While the ligamentous capsule is very strong, two weak points can be noted - the first anteriorly between the iliofemoral and pubofemoral ligaments, and the second posteriorly between the iliofemoral and ischiofemoral ligaments. Although dislocation is rare in the native hip, with extreme external trauma the hip can dislocate through either of these weak points (Schuenke et al. 2006). There are two further ligaments at the hip joint. One, the ligamentum teres has been mentioned above – it contributes little in the way of stability to the hip and can be torn in traumatic dislocations. Some propose that it plays a role in joint nutrition(Gray AJ, Villar RN; 1997). Its potential for degeneration is better appreciated with the increasing utilisation of hip arthroscopy. The second is the zona orbicularis or angular ligament. This encircles the femoral neck like a button hole and again plays little role in stability.
The musculature of the hip and thigh is invested in a fibrous layer the fascia lata. This is a continuous fibrous sheath surrounding the thigh. Proximally it is attached to the inguinal ligament, lip of the iliac crest, posterior aspect of the sacrum, the ischial tuberosity, the body of the pubis and the pubic tubercle. Its inelasticity functions to limit bulging of the thigh muscles thus improving the efficiency of their contractions The major flexor of the hip joint is iliopsoas. This comprises psoas major and minor, and iliacus. Psoas major arises from T12-L5 vertebral bodies and insets into the lesser trochanter. It is joined at the level of the inguinal ligament to form the iliopsoas(Schuenke M. et al. 2006; Moore K. 1992). Iliopsoas is the most powerful hip flexor but it is also aided by sartorius, rectus femoris and tensor fascia latae (TFL) The principal abductors include gluteus medius and minimus. Lying beneath the fascia lata, the proximal insertion of gluteus medius into the iliac crest is almost continuous with it. From its broad based proximal attachment it appears like an upside-down triangle inserting into a relatively narrow base on the lateral aspect of the greater trochanter. Gluteus minimus is deep again to gluteus medius arsing proximally from the gluteal surface of the ilium and inserting deep to the gluteus medius on the anterolateral aspect of the greater trochanter.
Pathomechanics of Hip Joint: The human hip, the weight-bearing diarthrodial joint containing the acetabulum and the femoral head, is a highly congruent joint built for stability. The femoral head is contained in the acetabulum and articulates with a “horse shoe” shaped acetabular cartilage. The acetabulum provides approximately 165 degrees of circumferential bony coverage around the femoral head in the sagittal plane. In addition to its inherent stability, the human hip is also highly mobile with six degrees of freedom( Hughes et al.2002). The estimation of forces across the hip joint may provide insight into the etiology of hip pain. Abnormal or excessive loading of the hip has recently been recognized as a potential cause of anterior hip pain and subtle hip instability (Shindle et al., 2006). Hip instability and excessive hip forces may cause a tear of the acetabular labrum even in the absence of a traumatic event (Mason, 2001; McCarthy et al., 2001; Shindle et al., 2006). Understanding these joint forces may improve rehabilitation outcomes (Heller et al., 2001). Decreased force contribution from the gluteal and iliopsoas muscles and hip hyperextension may contribute to anterior hip forces. Increased anterior gliding of the femoral head is proposed to result from weakness or decreased utilization of the gluteal muscles during hip extension and the iliopsoas muscles during hip flexion (Sahrmann, 2002). Increased anteriorly directed hip force is the likely cause for the increased anterior glide. Distance runners may be particularly at risk for increased anterior gliding due to the exaggerated hip extension position inherent in running (Sahrmann, 2002). This subtle instability along with repeated hip extension position may also lead to a tear of the acetabular labrum (Guanche and Sikka, 2005).
People with hip instability, anterior hip pain or acetabular labral tear report pain with certain hip movements. Hip extension with external rotation produces pain in patients with anterior hip pain and subtle instability (Philippon, 2001). Pain with resisted supine hip flexion with the knee maintained in extension (straight leg raising) is a common finding in patients with anterior hip pain and an anterior labral tear (Binningsley, 2003; McCarthy et al., 2001). Lewis and Sahrmann et al.(2007) theorized that the anterior hip joint force is affected by both the balance of muscles contributing force to the movement and the hip position, and that increases in this force may lead to subtle hip instability, hip pain and acetabular labral tears.
Important Clinical Tests of Hip Joint
1) ACTUAL LEG LENGTH TEST
Procedure: The patient is in supine position. The clinician measures the distance between the anterior superior iliac supine and the medial malleolus on each leg. The measurement is compared.
Clinical Significance: Any difference in the measurement on one side as compared with the other indicates a true leg length discrepancy. If the difference in length between the two legs is greater than one-quarter inch, it is considered an impairment.
2) APPARENT LEG LENGTH TEST
Procedure: The patient is in supine position. The clinician measures the distance between the umbilicus and the medial malleolus of both sides.
Clinical Significance: Any discrepancy in leg length is significant; the shorter side is the affected one.
3) ANVIL TEST
Procedure: The patient is in supine position. The clinician slightly raises the leg on the side being tested and deliver a forceful blow to the heel.
Rationale: The force of the blow is delivered into the hip joint. This is an attempt to jam the femur head into the joint, which will exacerbate pain in presence of a hip lesion.
Clinical Significance: Reproduction of pain within the hip joint is positive for hip joint lesion.
4) FABERE- PATRICK’S TEST
Procedure: The patient is supine. The patient’s hip and knee are flexed on tested side , hip is taken for abduction and external rotation component so that outer malleolus rests on the opposite knee. Stress this side further by pressing downward on the flexed knee.
Rationale: This test places maximum stress on the hip because it is flexed, abducted, and externally rotated. Adding downward pressure will exacerbates pain in the hip joint with a suspected lesion.
Clinical Significance: Pain within the hip joint, especially at the hip flexor attachment, is a positive test.
5) LAGUERRE TEST
Procedure: The patient is supine. First, flex the hip 90 degrees and then flex the knee 90 degrees. Next, rotate the thigh outward and force the patient’s heel up while pressing downward on the knee.
Rationale: This maneuver forces the head of the femur into the acetabulum, stressing the anterior joint capsule, but not the lumbosacral or lumbar spinal area.
Classical Significance: Pain within the hip joint from pressure of the head of the femur being pushed into the acetabulum is a positive test.
6) TRENDELENBURG TEST
Procedure: The patient is standing. Ask the patient to raise one knee toward the chest, balancing on the supporting limb. The patient should be supported by a table or a nearby wall if unable to balance on one leg. Observe the gluteal fold of the supporting leg.
Rationale: If the patient is able to support the weight of the body on one leg, the gluteal muscles responsible for abduction and extension are intact. A weakness within these muscles will cause the patient to shift the weight as the extremity buckles.
Classical Significance: The gluteal fold will drop below the level of the contralateral side if the gluteal muscles are weak.
Clinical Significance: In the absence of glutealness, the inability to perform this test may be associated with an unrelated disequilibrium syndrome, which requires further investigation.
MANUAL THERAPY TECHNIQUES OF HIP JOINT
The following manual therapy techniques are very useful for the treatment of hip joint mechanical dysfunctions.
1) CEPHALIC GLIDE
Subject’s position: Subject is in supine lying position.
Clinician’s position: The clinician stands at the side of the couch (lateral to the concerned side).
Procedure: The clinician palpates for the greater trochanter of femur. To locate the greater trochanter (G.T) the clinician places entire palm at the upper lateral aspect of the thigh and supports the knee joint with the other hand, the hip is then taken into adduction and abduction to locate the G.T. Clinician places the hip in loose back position (i. e 30 degree flexion, 30 degree abduction and slight lateral rotation).From the anterior and mid part of the patella the clinician applies the glide along the long axis of femur in cephalic direction.
Significance: This technique is useful to decrease the pain associated with hip adduction and to increase the adduction range of motion.
2) CAUDAL GLIDE
Subject’s position: Subject is in supine lying position.
Clinician’s position: The clinician stands at the side of the couch (lateral to the concerned side).
Procedure: The clinician palpates for the greater trochanter with one hand and keeps the other hand at distal posterior aspect of femur slightly above the popliteal fossa.The clinician applies glides by pulling the hip caudally.
Significance: This technique is useful to increase the abduction range of motion and to decrease the pain associated with abduction
3) ANTERO- POSTERIOR GLIDE
Subject’s position: Subject is in supine lying position.
Clinician’s position: The clinician stands at the side of the couch.
Procedure: Clinician places the hip in loose pack position (30 degree flexion, 30 degree abduction and slight external rotation).Clinician places the heel of the palm at antero-medial aspect of greater trochanter. The clinician applies the glide in antero-posterior direction.
Significance: This technique is useful to increase the range of flexion and medial rotation; also used to decrease the pain associated with flexion and medial rotation.
4) LATERAL GLIDE
Subject’s position: Subject is in supine lying position.
Clinician’s position: The clinician stands at the side of the couch (lateral to the concerned side).
Procedure: The clinician places the hip joint in the loose pack position.Clinician interlocks the fingers and places at the upper medial aspect of the thigh.The lateral aspect of the knee joint is kept in contact with the shoulder of the clinician.The clinician applies the lateral glide. The proximal and distal aspect should move as a single unit so that there is distraction at the hip joint.
Significance: This technique is useful to decrease the irritation at the hip joint instantly by the joint space enhancement.
5) MEDIAL GLIDE
Subject’s position: Subject is in side lying position.
Clinician’s position: The clinician stands at the back of the subject
Procedure: Clinician places the hip in loose pack position (flexion, abduction and external rotation) Clinician places the heel of the palm on the lateral aspect of G.T The glide is applied with grading from lateral aspect medially.
Significance: The medial glide is applied to increase the abduction range of motion and also to decrease pain associated with abduction.
6) POSTERO – ANTERIOR GLIDE
Subject’s position: Subject is in prone lying position.
Clinician’s position: The clinician stands at the side of the couch.
Procedure: Clinician takes the hip for abduction, flexion and slight lateral rotation.Clinician keeps the heel of the palm in the postero – medial aspect of the greater trochanter. Clinician applies the glide anteriorly with grades.
Significance: The postero-anterior glide is applied to increase the extension range of motion and also to decrease pain associated with extension.
7) FLEXION ADDUCTION MOBILISATION OF THE HIP JOINT
Subject’s position: The subject is in supine lying position.
Clinician’s position: Clinician stands at the side of the couch in walk stand position.
Procedure: The clinician flexes the hip joint, the knee joint is flexed to 90 degree and supported on the shoulder of clinician.Clinician interlocks the fingers and keeps on the upper aspect of the thigh.Clinician applies the superior to inferior translation while taking the hip for horizontal adduction.Then the clinician applies the axial compression and the hip joint is taken for internal rotation with grades.
Significance: This technique is very useful to identify the osteoarthritis of the hip joint and also to treat the same.
Conclusion: The manual therapy techniques mentioned in this article are very useful for the treatment of mechanical dysfunctions of the hip joint. However a thorough subjective examination, clinical reasoning and physical examination must be performed to identify the mechanical dysfunction of hip joint.