Musculoskeletal System - Anatomy

The posterior cruciate ligament (PCL) is a large ligament located in the center of the knee behind the anterior cruciate ligament. The primary role of the PCL is to provide stability and prevent posterior deviation of the tibia relative to the femur. A posterior drawer test or tibial sag test can be used to assess PCL injury or damage.

In contrast, the anterior cruciate ligament (ACL) prevent anterior deviation of the tibia relative to the femur. Damage to the ACL can be assessed with an anterior drawer test.

It is likely that the compartment syndrome is compromising the femoral nerve, which would result in an inability to extend the knee. We need to know that the femoral nerve runs close to the femur in the anterior compartment of the thigh. The high compartment pressures have cut off blood supply and compromised the femoral nerve, as evidenced by sensory deficits in the anterior thigh.

The femoral nerve arises from L2-L4 in the lumbar plexus and innervates the quadriceps muscles, which serve to extend the knee.

Flexion of the knee is accomplished by the hamstring muscles, which are supplied by common peroneal and tibial nerves. Eversion of the foot is a function of the peroneus longus and brevis, innervated by the superficial peroneal nerve. Plantar flexion is accomplished by the tibialis anterior, supplied by the deep peroneal nerve. Dorsiflexion is by the tibialis posterior, supplied by the tibial nerve.

The axilla is an important area housing a large region of the brachial plexus. It is located between the rib cage, scapula, and humerus. More specifically, it is bounded by:

• The pectoralis major muscle anteriorly
• The latissimus dorsi, teres major, and subscapularis muscles posteriorly
• The shaft of the humerus laterally
• The serratus anterior and rib cage medially

The clavicle, supraspinatus, deltoid, and biceps brachii all lie outside of the axilla region.

Although it's function has only recently been described, surgical literature suggests that the anterolateral ligament functions to provide additional rotary stability to the knee. Because of this, some patients who have had an ACL reconstruction, but not an ALL reconstruction, will demonstrate a positive pivot-shift sign, a sign of knee rotational instability upon flexion of the tibia at the knee during medial rotation.

The anterior slide and crank tests are tests for tears of the glenoid labrum. The following are common tests, with varying diagnostic value, for the other pathologies listed: O'Brien's test (acromioclavicular ligament injury), horn blower's sign (teres minor tear), lift off sign (subscapularis tear), and olecranon-manubrium-percussion test (clavicle fracture).

The origin of the sartorius Anterior superior iliac spine (ASIS). Accordingly, if the sartorius avulsed from its origin, we would suspect damage to this bony prominence.

The "Terry Thomas/David Letterman" sign is specific to the articulations of the wrist, and involves injury to the scapholunate ligament. When this ligament is damaged, the scaphoid and lunate drift apart, creating a gap on x-rays reminiscent of the gap in Terry Thomas'/David Letterman's front teeth.

Lachman's test has good diagnostic value for ACL tears. The McMurray's and Thessaly tests have mixed diagnostic value, and test for meniscus injuries, the valgus stress tests is a test for tibial collateral ligament injury, and the sag sign tests for posterior cruciate ligament (PCL) injury.

A Lachman's test requires the clinician to apply an anterior force on the tibia, looking for an end-feel (or resistance created by the ACL). Godfrey's (90-90), posterior drawer and quadriceps active test all test for a rupture, or sprain of the posterior cruciate ligament (PCL). McMurray's tests for meniscal tear.

The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are both affected with hyperflexion of the knee, as these two ligaments are located deep inside the knee capsule, and prevent anterior and posterior sheering forces. If this action occurred with enough force, these structures would be injured. The sedial collateral ligament (MCL) and lateral collateral ligament (LCL) would be injured with a valgus or varus force, both with occur in the coronal plane. The iliotibial band (ITB) and and medial collateral ligament (MCL) would require multiplaner forces in order to be injured.

Oxidative phosphorylation generates roughly 6.3 high energy phosphates (ATP) per unit of oxygen (O2).

It is also important to note that ATP generation occurs anaerobically via lactic acid production, with the ratio being 1.5 high energy phosphates (ATP) per unit of lactate. But this is not the correct answer in this context.

Although it is a very new test, the available literature suggests that the lever sign has superior diagnostic value to the Lachman, pivot-shit, and anterior drawer tests, to detect anterior cruciate ligament (ACL) injuries. Additionally, the preliminary evidence suggests that the lever sign has high diagnostic value for both acute and chronic ACL injuries.

Golfer's elbow, or medial epicondylitis, is due to inflammation of the medial epicondyle of the elbow. The tendons of several muscles involved in flexing the forearm, wrist, and fingers originate at the medial epicondyle of the humerus at the elbow and this insertion point can become inflamed in response to injury.

Lateral epicondylitis is sometimes associated with tennis elbow.

The boy is suffering from Duchenne Muscular Dystrophy (DMD). This condition is a genetic disorder caused by a mutation resulting in absence of the dystrophin protein.

DMD is an X-linked recessive disease that caused muscle wasting and death. Mutations in the dystrophin gene on the X-chromosome cause absence of the protein dystrophin and instability in muscle cell membranes. Proximal muscles are affected first with noticeable atrophy of the legs and pelvis. This spreads to the arms, neck, and other parts of the body. Patients have pseudohypertrophy of the calves and deltoids and have poor endurance. Patients often show Gower’s sign, pushing on their thighs with their arms to help them stand up. A diagnosis is made with DNA testing or muscle biopsy showing absence of dystrophin. Becker’s muscular dystrophy is a less severe form of DMD in which mutated dystrophin is produced. Signs and symptoms are similar, but less severe.

Frataxin is a mitochondrial protein that is deficient in patients with Freidrich's ataxia, an autosomal recessive trinucleotide repeat disorder. It is the most common hereditary ataxia involving the posterior column, lateral corticospinal tracts, and spinocerebellar tracts of the spinal cord. This is a result of progressive atrophy and sclerosis of the dorsal root ganglia and dorsal roots. This condition is characterized by staggering gait, frequent falling, nystagmus, pes cavus, kyphoscoliosis, and hypertrophic cardiomyopathy.

Actin is a protein found in eukaryotes with multiple functions, including muscle contraction, vesicle and organelle transport, and cell signaling.

Troponin is a regulatory protein in muscle contraction. In skeletal muscle, troponin is bound to tropomyosin, a protein that covers actin binding sites, prohibiting muscle contraction. Binding of calcium to troponin causes a conformational change in troponin, which shifts tropomyosin to expose actin binding sites.

Huntingtin is a protein that, when mutated, causes Huntington's disease, a genetic disorder that progressively damages brain cells to result in chorea (jerky, uncontrollable movements) as well as changes in personality and dementia.

When the nucleus propulsus inside an intervertebral disk protrudes through a weakened area of the annulus fibrosus, the ability of that disk to respond to torsion forces is severely compromised. Further, the protruding nucleus itself puts pressure on the vertebrae, resulting in a "compressed" or herniated disk. This can impact nearby nerves, resulting in radiating pain, weakness, and numbness or tingling.

Injury to the lateral thigh area could result in injury to the lateral cutaneous nerve of the thigh, which is associated with L2-L3.

L1 is associated with the ilio-inguinal nerve, located in the genital region. Both the obturator and femoral nerves are associated with L2-L4.

The annular ligament of the radius stabilizes the radial head against the capitellum of the humerus. If this ligament is lax or damaged, the head of the radius can dislocate, leading to "nursemaid's elbow". This injury is most common in young children. The sternoclavicular and coracoclavicular ligaments do not articulate with the elbow, rather they are superior to the elbow, at the shoulder. The collateral ligaments of the elbow stabilize the joint but are not subject to the subluxation indicated in nursemaid's elbow.

The serratus anterior holds the scapula tight to the posterior wall of the chest. Damage to it, and especially to the thoracic nerve (descending from the axilla) causes this muscle to become paralyzed. Because of this, the scapula can project posteriorly from the back when actions such as pushing against a wall are performed.

The obturator nerve can be damaged in car accidents, abdominal surgeries. It descends thru the pelvis to innervate the medial side of the thigh and adductor muscles of the thigh (external obturator, adductors longus, brevis, magnus and gracilis muscles). Adduction is movement of an extremity closer to the midline of the body. Abduction is the reverse of adduction.

An indirect inguinal hernia is a congenital processes, where the bowel and peritoneum move through a patent processus vaginalis into the scrotum. In an indirect inguinal hernia the protrusion passes through the inguinal ring lateral to the inferior epigastric vessels. Males are significantly more likely than females to develop indirect inguinal hernias.

Direct inguinal hernias are loops of gut that enter through a weak point in the abdominal wall fascia. In direct inguinal hernias the defect is medial to the inferior epigastric vessels. Males are also significantly more likely to develop direct inguinal hernias.