1. General Principles & Basic Science MCQs

DISCUSSION: The area indicated by the arrow represents gadolinium contrast extending into a separation between the lateral labrum and its acetabular attachment. This can be a traumatic detachment, but occasionally a cleft may be present as a normal variant of the labral morphology. The capsular attachment of the iliofemoral ligament is peripheral to the labrum. The pulvinar is the common name applied to the fat and overlying synovium contained within the acetabular fossa above the ligamentum teres. The zona orbicularis is a circumferential thickening of the capsule around the femoral neck, and the retinacular vessels travel within the capsular synovium up the femoral neck to supply the femoral head. REFERENCES: Petersilge CA, Haque MA, Petersilge WJ, Lewin JS, Lieberman JM, Buly R: Acetabular labral tears: Evaluation with MR arthrography. Radiology 1996;200:231-235. Czerny C, Hofmann S, Neuhold A, et al: Lesions of the acetabular labrum: Accuracy of MR imaging and MR arthrography in detection and staging. Radiology 1996;200:225-230. Byrd JWT: Indications and contraindications, in Byrd JWT (ed): Operative Hip Arthroscopy. New York, NY, Thieme, 1998, pp 7-24.

Figures A-C shows atrophy of teres minor and deltoid due to compression of the axillary nerve. The correct pathway of the axillary nerve within the brachial plexus is, C5-C6 nerve roots; upper trunk, posterior division, posterior cord.Quadrilateral space syndrome is a condition defined by axillary nerve, +/- posterior humeral circumflex artery compression in the quadrilateral space. It most commonly affects the dominant shoulder in overhead movement athletes (e.g. basketball players) or other throwing athletes. Physical examination may reveal weakness with the arm positioned in abduction and external rotation. In situations of long-standing compression, there may also be atrophy of the teres minor and deltoid muscle.Chafik et al. dissected thirty-one cadaveric human shoulders to describe the neuromuscular anatomy of teres minor. They showed that the primary nerve branch to teres minor travelled in a fascial sling 44 mm medial to the muscular insertion. Thisarea may be the potential site of greatest compression and tethering of this nerve in patients with isolated teres minor atrophy.Friend et al. performed a cadaveric dissection of nine shoulder specimens to look at the anatomical variability in course, length and branching pattern of both the teres minor nerve and the axillary nerve. These were compared to a case-based study of these two male patients with isolated atrophy of teres minor. They concluded that there is no good anatomical predictor of nerve compression outside the quadrilateral space as there is considerable anatomical variation in its origin and course, as well as potential site of compression.Figure A-C are MRI images that show atrophy of the teres minor muscle and possibly deltoid muscle. The rotator cuff muscles are labeled in Illustration A. The teres minor muscle is labeled in Illustration B. Illustration C shows a diagram of the brachial plexus.Incorrect1:Thisdescribesthemusculocutaneousnerve.3:Thisdescribesthesuprascapularnerve.4:Thisdescribesthelong thoracicnerve.

BMPs signal through the activation of a transmembrane serine/threonine kinase receptor that leads to the activation of intracellular signaling molecules called SMADs. There are currently eight known SMADs, and the activation of different SMADs within a cell leads to different cellular responses. The other mediators are not believed to be directly involved with BMP signaling.

DISCUSSION: The patient is presenting with radial nerve palsy secondary to his humerus fracture. Motor recovery proceeds in a proximal to distal direction. Abrams et al detailed the order of innervation of the radial nerve and found the following order (proximal to distal): brachioradialis, extensor carpi radialis longus, supinator, extensor carpi radialis brevis, extensor digitorum communis, extensor carpi ulnaris, extensor digiti quinti, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and extensor indicis proprius. Branovacki et al found a slightly different pattern: brachioradialis, extensor carpi radialis longus, superficial sensory, extensor carpi radialis brevis, supinator, extensor digitorum/extensor carpi ulnaris, extensor digiti minimi, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus and extensor indicis proprius. While both extensor digitorum and extensor indicis proprius extend the index finger MCP joint, only extensor indicis proprius hyperextends the index finger past neutral.

DISCUSSION: The most common cause of myositis ossificans is contusion. Certain regions, including the quadriceps and brachialis, are more commonly affected. The mechanisms of development have not been clearly established. REFERENCES: Beiner JM, Jokl P: Muscle contusion injuries: Current treatment options. J Am Acad Orthop Surg 2001;9:227-237. Jarvinen TA, Jarvinen TL, Kaariainen M, et al: Muscle injuries: Biology and treatment. Am J Sports Med 2005;33:745-764.

DISCUSSION: The lumbosacral plexus is formed from the lumbar and sacral roots that are redistributed into the obturator, femoral, and sciatic nerves. The obturator nerve is composed of the L1, L2, and L3 roots. The femoral nerve has contributions from the L3 and L4 roots. The sciatic nerve contains the L4, L5, S1, and lower sacral roots. Therefore, only the L4 root contributes to the femoral and sciatic (via the lumbosacral trunk) nerves, which allows it to innervate the quadriceps and the anterior tibialis muscles.

A positive straight leg raising sign causes pain radiating distal to the knee when the nerve is under tension. This increased tension generally occurs between 30 degrees and 70 degrees of passive elevation.

DISCUSSION: The basic diagnostic test for hepatitis C (HCV) is detection of an antibody to epitopes on an enzyme-linked immunosorbent anti-HCV assay (ELISA). The currently used ELISA has high sensitivity (92%) and specificity (95%). False positives, however, still occur. The currently used supplemental test for HCV is strip immunoblot assay, which is based on detection of several HCV epitopes on nitrocellulose paper by antibody-capture techniques. Molecular amplification by PCR technology is very sensitive, but difficult to standardize and susceptible to contamination. Microarray and proteomics are relatively recent molecular techniques used for analysis of genes or proteins, respectively. A Northern blot is used to detect mRNA levels of specific genes but is not used in this situation. REFERENCES: de Medina M, Schiff ER: Hepatitis C: Diagnostic assays. Semin Liver Dis 1995;15:33-40. McGrory BJ, Kilby AE: Hepatitis C virus infection: Review and implications for the orthopedic surgeon. Am J Orthop 2000;29:261-266.

The L5 nerve root is located on the anterior sacrum and is indicated by the arrow. The position of this neural structure must be considered whether the surgeon is stabilizing the sacroiliac (SI) joint with percutaneous iliosacral screws or with anterior SI plating through the lateral window of the ilioinguinal approach. The posterior position of the sciatic nerve in relation to the acetabulum and the lateral peroneal division makes the peroneal division of the sciatic nerve the portion of the nerve that is most likely to be injured in a posterior traumatic hip dislocation.

Discussion: In this patient, the radial nerve is most likely injured at the level of the radial neck. The radial nerve emerges from the posterior cord of the brachial plexus and travels along the spiral groove of the humerus. At the level of the lateral humeral condyle, the radial nerve branches into the posterior interosseous nerve after giving off two cutaneous branches, the superficial radial and the posterior cutaneous. The posterior interosseous nerve travels through the supinator muscle and winds around the radial neck. At this level, the posterior interosseous nerve is vulnerable to injury, particularly following fracture or penetrating trauma.

Many factors influence the outcome of lower extremity amputations with worse outcomes noted in patients with lower socioeconomic status, preexisting medical conditions, and low self-efficacy. Patients with amputations performed in a zone of injury, especially if this was a through-the-knee amputation, have a significantly poorer outcome than those with either above-the-knee or below-the-knee amputations. Patients with above-the-knee amputations have similar outcomes to those with below-the-knee amputations, although those with below-the-knee amputations have faster self-selected walking speeds. Gender and sophistication of the prosthesis have no bearing on outcome. The type of muscle anchoring technique used also plays no role in outcome.

Prolia, or denosumab, is a newly approved drug used to treat osteoporosis and has a mechanism of action similar to osteoprotegerin (inhibits binding of RANKL to RANK).RANKL (Receptor activator of nuclear factor kappa-B ligand) is a key molecule for osteoclast differentiation and activation. Inhibition of RANKL activity with anti-RANKL antibody reduces osteoclastogenesis, resulting in inhibition of bone resorption.Capozzi et al. author a review article on denosumab. They state the medication confers improved bone mineral density and prevents new fragility fractures similar to alendronate. However, denosumab presents less risk of atypical femoral fractures andosteonecrosis of the jaw.Yasuda et al. present a review that details the creation of three elegant animal models to mimic metabolic bone disease and how the animal models can create a template to help cure human metabolic bone disease. These enable modeling of osteoporosis, hypercalcemia, and osteopetrosis by treating normal mice with soluble RANKL (sRANKL), adenovirus expressing sRANKL, and anti-mouse RANKL neutralizing antibody, respectively. They report that these animal models can be established in about 14 days using normal mice.Illustration A demonstrates the mechanism of action of bisphosphonates and denosumab.Incorrect Answers:1: Romosozumab is the first humanized anti-sclerostin monoclonal antibody that has been demonstrated to increase bone formation. 2: Zoledronic acid (Reclast) is a nitrogen containing bisphosphonates that inhibits osteoclast resorption by inhibiting the enzyme farnesyl diphosphate synthase. 4: Teriparatide (Forteo) comprises the first 34 amino acids of the 84 amino acid parathyroid hormone (PTH) and can reproduce the primary effects of PTH by activating adenyl cyclase. 5: Blosozumab is an investigational monoclonal anti-sclerostin antibody showing osteoanabolic properties with the potential to improve clinical outcomes in patients with osteoporosis.

Although a recent push for prospective, randomized trials has been advocated by multiple orthopaedic journals, many studies published continue to be of Level 4 evidence (retrospective case series). Case series represented 64% of all studies reviewed by Freedman and associates in 2001 from the British and American volumes of Journal of Bone and Joint Surgery and from Clinical Orthopaedics and Related Research. Obremskey and associates published that 58.1% of all studies from nine orthopaedic journals were Level 4 evidence. Further investigation of more current trends is likely warranted with the current emphasis on publishing higher level-of-evidence studies in orthopaedic journals.

The complication rate with halo vest treatment in children is reported to be as high as 68% in contrast to a 36% complication rate in adults. These complications include not only pin tract infections, but also skull penetration. Multiple pins allow for the early removal of pins without fixation consequences should pin site infections begin to develop. Moreover, there is significant variability in the insertional torque applied by a variety halo pin torque wrenches, including those from the same manufacturer. Consequently, the use of a large number of pins (8 to 12) placed a very low insertional torque (1 to 5 in-lb) in children is recommended. A CT scan of the head should also be considered to assess for the thickest areas of the skull suitable for pin application.

The extensor carpi radialis brevis, supinator muscle, arcade of Frohse, and leash of Henry are potential sites of compression for the posterior interosseous nerve. The most common location of spontaneous entrapment is the arcade of Frohse. The lateral intermuscular septum is a site of compression for the radial nerve.

One of the most difficult aspects of posterior cruciate ligament reconstruction is placement of the tibial tunnel and passing of the graft through this tunnel. The tibial inlay technique requires a posteromedial approach to the tibia whereby the graft is directly fixed to the posterior aspect of the tibia. This obviates the need for a tibial tunnel. This technique has never been shown to be less invasive, more cosmetic, or require decreased surgical time. It has also never been shown in a published level I study to have superior clinical results. However, it does eliminate the need for the 90-degree critical "killer" turn and passing of the tibial graft through the tibial tunnel which may lead to graft failure.

The type of study design in which a series of cases is presented with outcomes (without a control population or comparison group) is known as a case series. This type of study design, although frequently seen in orthopaedic literature, provides the lowest level of evidence. There is no control group and the population is usually poorly defined. This type of study can be helpful as a starting point for further analysis. A randomized trial provides the highest level of evidence in medical research, featuring a comparison group and randomized (and usually blinded) placement of subjects into study groups. In case-control studies, cases are compared to a control group. The control group has not been randomized, but may be a naturally occurring group of subjects who have not had the same exposure or intervention as the case group. A cohort study can be retrospective or prospective and usually looks at a large group of people over time to assess exposures and incidence of disease.

The fundamental structure of normal adult articular cartilage is divided into four different zones: superficial, transitional, deep, and calcified. These layers vary in chondrocyte morphology, size and orientation of collagen bundles, and water and proteoglycan content. The deep zone has the highest concentration of proteoglycans and the lowest concentration of water. The tidemark is a boundary between the calcified and uncalcified layers of articular cartilage.

A muscle that lengthens as it is activated is an eccentric contraction. Isometric contraction involves no change in length. Concentric contraction occurs while the muscle is shortening. In isotonic contraction, the force remains constant through the contraction range. Isokinetic muscle contraction occurs at a constant rate of angular change of the involved joint.