NPTAE

Expect the exam to test musculoskeletal knowledge through the lens of PTA scope. You will be asked to choose the correct goniometer alignment, recognize which muscle is weak from a gait or posture finding, identify a post-operative complication, and decide when a finding is outside what the PTA can manage alone. The PTA collects data and reports it; the physical therapist (PT) interprets examination findings, sets the diagnosis and prognosis, and changes the plan of care (POC). Keep that division in mind on every item.

This chapter reviews the bones, joints and key muscles the exam expects you to know, then the mechanical rules that explain how joints move: arthrokinematics, the convex-concave rule, kinematic chains, levers, contraction types and the length-tension relationship. These ideas drive both data collection (where to place a goniometer, what a weak muscle looks like) and intervention choices in Section 2.

Synovial joints are the focus of the exam. Each has a joint capsule, synovial membrane and fluid, articular (hyaline) cartilage, and supporting ligaments. They are classified by shape: hinge (elbow humeroulnar, interphalangeal joints), pivot (proximal radioulnar, atlantoaxial), condyloid (radiocarpal, metacarpophalangeal), saddle (first carpometacarpal of the thumb), plane (intercarpal, acromioclavicular) and ball-and-socket (glenohumeral, hip). Fibrous joints (skull sutures, distal tibiofibular syndesmosis) and cartilaginous joints (pubic symphysis, intervertebral discs) allow little or no motion.

The shoulder complex is four joints working together: glenohumeral, acromioclavicular, sternoclavicular and the scapulothoracic articulation. Scapulohumeral rhythm is about 2 deg of glenohumeral motion for every 1 deg of scapular upward rotation, so full 180 deg of elevation needs about 120 deg at the glenohumeral joint and 60 deg of scapular rotation. Weak scapular stabilizers or a stiff glenohumeral joint disturb this rhythm and produce the shoulder shrug sign.

The exam rarely asks for an isolated origin or insertion. It asks which muscle is weak given a functional finding, which nerve is involved, or which muscle a precaution protects. Learn the muscles in the following table well enough to reason from function.

The rotator cuff (supraspinatus, infraspinatus, teres minor, subscapularis; memory aid SITS) compresses and centers the humeral head in the glenoid so the deltoid can elevate the arm without the head riding up into the acromion. When the cuff is weak or torn, the deltoid pulls the humeral head superiorly and the patient shrugs to lift the arm.

Clinical links you should be able to make quickly: weak gluteus medius produces a Trendelenburg sign (the opposite pelvis drops in single-limb stance on the weak side); weak gluteus maximus produces a backward trunk lean at initial contact; weak quadriceps produces a forward trunk lean or knee hyperextension in loading response; weak dorsiflexors produce foot slap (mild) or steppage gait (foot drop).

Osteokinematics describes the motion of the bone through space (flexion, abduction). Arthrokinematics describes what the joint surfaces do: roll (new points meet new points), glide or slide (one point slides across new points) and spin (rotation around a fixed axis). Normal motion combines roll and glide so the joint surfaces stay congruent.

The convex-concave rule tells you which way the glide goes. When a convex surface moves on a fixed concave surface, roll and glide occur in opposite directions. When a concave surface moves on a fixed convex surface, roll and glide occur in the same direction.

In an open kinetic chain (OKC) exercise the distal segment moves freely in space: seated knee extension, biceps curl, straight-leg raise. In a closed kinetic chain (CKC) exercise the distal segment is fixed against a surface and the proximal segments move: squat, leg press, step-up, wall push-up, quadruped weight shifting.

CKC exercise produces co-contraction of muscles around the joint, adds joint compression that improves stability, loads proprioceptors, and is more functional for weight-bearing tasks. OKC exercise isolates a muscle, which is useful when weight bearing is restricted or a single muscle needs targeted strengthening. After ACL reconstruction, OKC knee extension in the last 30-40 deg increases anterior tibial shear and graft strain, which is why protocols restrict it early (details in Topic 2.3).

First-class levers have the axis between force and resistance (head nodding on the atlas, like a seesaw). Second-class levers have the resistance between axis and force (rising onto the toes, with the axis at the metatarsal heads, often taught as the second-class example); they favor force. Third-class levers have the force between axis and resistance (biceps at the elbow); they favor speed and range and are the most common in the body.

The practical point is the moment arm. Resistance placed farther from the joint creates more torque. Moving a cuff weight from the knee to the ankle during a straight-leg raise makes the exercise harder without changing the weight; moving a manual resistance closer to the joint makes it easier. The same rule explains why holding a load close to the body during lifting reduces stress on the lumbar spine.

Isometric contraction produces tension without joint motion. Concentric contraction shortens the muscle while producing tension (lifting). Eccentric contraction lengthens the muscle under tension (lowering) and produces the most force with the least energy cost, but causes the most delayed-onset muscle soreness. Isokinetic exercise holds velocity constant through a machine and is uncommon in PTA practice.

The length-tension relationship states that a muscle produces maximum tension near its resting length, where actin and myosin overlap best. Active insufficiency occurs when a two-joint muscle cannot shorten enough over both joints to produce full force (a tight fist is weaker with the wrist fully flexed because the finger flexors are shortened over both joints). Passive insufficiency occurs when a two-joint muscle cannot lengthen enough to allow full motion at both joints (hip flexion is limited with the knee straight because the hamstrings are taut). Tenodesis uses passive insufficiency of the finger flexors on purpose: extending the wrist pulls the fingers into a functional grasp, a skill people with C6 spinal cord injury rely on.

In ideal standing posture viewed from the side, the plumb line passes through the earlobe, the acromion, the bodies of the lumbar vertebrae, the greater trochanter, slightly anterior to the knee joint axis and slightly anterior to the lateral malleolus. Common faulty patterns include forward head with rounded shoulders (tight pectorals and upper trapezius, weak deep neck flexors and lower and middle trapezius), excessive lumbar lordosis with anterior pelvic tilt (tight hip flexors and lumbar extensors, weak abdominals and gluteals), and flat back (posterior pelvic tilt, tight hamstrings). This pattern-recognition is sometimes called upper and lower crossed syndrome.

• The rotator cuff centers the humeral head; the deltoid elevates the arm; weak cuff means superior migration and a shrug.
• Convex moving on concave: roll and glide opposite. Concave moving on convex: same direction.
• CKC exercise adds compression, co-contraction and function; OKC exercise isolates muscles and is useful when weight bearing is limited.
• Moving resistance farther from the joint increases torque and difficulty.
• Eccentric contractions generate the most force and the most soreness; muscles are strongest near resting length.
• Gait and posture faults point to specific weak muscles: gluteus medius for Trendelenburg, gluteus maximus for backward lean, quadriceps for forward lean or recurvatum.