CHT Exam Study Guide: Linking Anatomy to Splint Decisions

Study for the CHT exam by pairing every anatomical fact with the clinical decision it supports. When you review a structure, immediately state what changes in evaluation or splinting if that structure is injured, tight, or overstretched. Concepts worth drilling: intrinsic versus extrinsic tightness and the Bunnel-Littler test, boutonnière versus swan neck versus mallet deformities, flexor and extensor tendon zones, the flexor pulleys, tendon gliding positions, and the antideformity (safe) position. Work through the scenarios and the self-observation exercise, then use the readiness checks to judge whether your reasoning holds without notes.

Intrinsic versus Extrinsic Tightness: One Test, Two Different Splints

Intrinsic tightness limits PIP flexion when the MCP is extended and improves when the MCP flexes; extrinsic flexor tightness improves with wrist flexion. The test conditions, not the posture alone, classify the restriction.

The intrinsics (lumbricals and interossei) cross the MCP joints and insert into the extensor mechanism, so they slacken when the MCP flexes. In the Bunnel-Littler test you hold the MCP in extension and measure PIP flexion; if PIP flexion improves once the MCP is passively flexed, the restriction was intrinsic muscle tightness rather than a joint problem. That matters because the intervention target shifts from the PIP joint itself to positioning and mobilizing the intrinsics across the MCPs.

The extrinsic flexors, FDS and FDP, cross the wrist as well as the fingers, so wrist position changes their length. If PIP flexion is limited with the wrist extended but improves with the wrist flexed, the restriction sits in the extrinsic flexors, and stretching them across the wrist becomes the priority. A tempting shortcut is labeling any limited PIP flexion a joint capsule problem; in a stem, read the wrist and MCP positions first, because those positions are the test conditions that classify the restriction.

Worked scenario: a stem reports markedly limited PIP flexion with the MCP held extended, but nearly full flexion when the examiner passively flexes the MCP first. The plausible mistake is prescribing PIP joint mobilization for a 'PIP contracture.' The better decision is reading the improvement as intrinsic tightness: MCP flexion slackened the intrinsics, so the restriction was never the joint, and a joint-focused plan targets the wrong tissue.

• MCP extended → PIP limited; MCP flexed → PIP improves: intrinsic tightness.
• Wrist extended → PIP limited; wrist flexed → improves: extrinsic flexor tightness.
• PIP limited regardless of MCP or wrist position: consider a PIP joint restriction and assess end-feel.

Boutonnière, Swan Neck, and Mallet: Same Joints, Opposite Mechanics

These deformities differ by which structure failed and which joint is pulled where. Boutonnière is central slip loss with PIP flexion and DIP extension; swan neck is PIP hyperextension; mallet is DIP extension loss.

In boutonnière deformity, the central slip of the extensor mechanism at the PIP fails and the lateral bands slip volarly, becoming flexors of the PIP and extensors of the DIP: PIP flexion with DIP hyperextension. Because the missing structure is a PIP extensor, the splint answer holds the PIP in full extension while permitting DIP motion. In mallet deformity, the terminal tendon at the DIP fails, producing a DIP extension lag; splinting isolates the DIP in extension and allows PIP motion. Both are extensor injuries, yet the affected joint inverts, and the splint target follows the joint.

Swan neck deformity shows the opposite PIP posture: hyperextension, often with DIP flexion, arising from imbalance such as volar plate laxity or a mallet injury whose DIP lag redirects extensor force to the PIP. The splint goal is blocking PIP hyperextension while preserving flexion, for example a figure-of-eight or ring-style PIP design. A tempting misread is seeing a DIP extension lag and answering swan neck, or splinting the DIP when the PIP is the involved joint; anchor each deformity to its failed structure first, then let the splint follow the structure.

Worked scenario: after a fingertip-level extensor injury, a patient develops a DIP extension lag and, over following weeks, a drifting PIP hyperextension. The plausible mistake is splinting only the PIP against hyperextension and treating it as the primary problem. The better decision is recognizing a mallet-type origin: splint the DIP in extension and support the PIP secondarily, because the PIP drift is downstream of the DIP extension loss. Controlling the secondary posture without addressing the originating joint leaves the imbalance in place.

• Boutonnière: central slip injury → PIP flexion, DIP hyperextension → splint the PIP in extension.
• Mallet: terminal tendon injury → DIP extension lag → splint the DIP in extension.
• Swan neck: PIP hyperextension → block hyperextension, preserve PIP flexion.

Extensor and Flexor Zones: Why the Injury Level Changes the Goal

Tendon zones identify which joint the injured tendon crosses, so the zone predicts the deformity pattern and the motion rehabilitation must balance. Learn zones as joint maps, not numbering trivia.

For the extensors, the commonly taught odd-numbered zones sit over joints (DIP, PIP, MCP, wrist) and the even-numbered zones over bone between them. That mapping explains the deformities in the previous section: a zone over the PIP concerns the central slip, and a zone over the DIP concerns the terminal tendon. For the flexors, zones progress from the fingertips toward the palm and carpal region, discussed alongside the pulleys, especially A2 and A4, which hold the tendon close to bone.

The exam-ready habit is to locate the injured level and immediately predict posture and goal: an injury where a tendon crosses a joint threatens that joint's balance, and a repair near a pulley region changes the flexion mechanics being protected. A tempting answer pattern is a generic wrist-and-fingers splint that never names which joint the protection plan controls. Practice by writing, for any zone you name, one sentence stating which joint it governs and what motion restriction that implies.

Worked scenario: a stem describes an injury near the proximal phalanx where the finger bows away from the bone during attempted flexion. The plausible mistake is attributing the weakness purely to tendon laceration and planning tendon-gliding drills alone. The better decision is recognizing pulley failure: without A2 or A4 support the tendon bows (bowstringing), requiring greater excursion to flex, so the protection plan must account for altered flexion mechanics, not only for tendon healing.

• Extensors: joint-level zones map to the joint whose extension is at risk.
• Flexors: finger zones progress from tip toward the palm and carpal region.
• A2/A4 pulley failure: tendon bows from bone in flexion, reducing flexion efficiency.

The Safe Position and Clawing: Positioning That Comes From Force Imbalance

The antideformity (safe) position places the wrist in modest extension with MCPs flexed and IPs extended, countering likely deforming forces. Clawing shows the reverse imbalance: MCP hyperextension with IP flexion.

The safe position exists because immobilized collateral ligaments shorten most when a joint rests in their slackened position, and the MCP collaterals are held at length in flexion while the IP collaterals are stretched in extension. With slight wrist extension, MCPs flexed, and IP joints extended, the ligaments and the extensor mechanism stay at useful length. An exam stem describing positioning during immobilization expects you to recognize this intrinsic-plus arrangement, not a flexed, fist-like posture.

Clawing demonstrates the same force logic in reverse: with intrinsic muscle loss, the long extensors hyperextend the MCPs while the extrinsic flexors flex the IPs, producing the intrinsic-minus posture. The positional answer supports the MCPs in flexion to restore balance, the same MCP direction as the safe position, which makes a useful consistency check. A tempting error is splinting the IPs first in a claw pattern; the force imbalance originates at the MCPs, so positioning starts there.

Check yourself: derive the safe position from collateral ligament reasoning aloud, then explain why the intrinsic-plus posture can serve as a splint template but is not itself the deformity being treated. If you can only recite the position without the reasoning, rebuild it by drawing which joints the intrinsics and extrinsics cross and letting the force balance produce the posture.

• Safe position: wrist extension, MCP flexion, IP extension, thumb positioned away from the palm.
• Rationale: maintains collateral ligament length and extensor balance during immobilization.
• Claw pattern: intrinsic weakness lets extrinsics win at the MCPs; restore MCP flexion first.

Tendon Gliding and Tenodesis: An Exercise You Can Verify on Yourself

Tendon gliding exercises move the FDP, FDS, and combined flexors through distinct fist positions, and tenodesis passively couples wrist motion to finger motion. Both are observable on your own hand, making them ideal self-check drills.

The standard gliding series uses four positions: a straight (tabletop) fist, a hook fist, a full fist, and a position combining MCP flexion with PIP and DIP extension. The reasoning is excursion differences: the FDP travels farthest, to the distal phalanx; the FDS to the middle phalanx; and the combined positions separate their glides. Run the series on your own hand and watch which joints move least in each position. In the hook fist your MCPs stay extended while PIPs and DIPs flex; in the full fist everything flexes together. That kinesthetic observation is the kinesiology made visible.

Tenodesis is the passive coupling produced by the multiarticular extrinsics: as the wrist flexes, the fingers tend to extend, and as the wrist extends, the fingers tend to curl. Trace this on your own wrist: relax your fingers and move only the wrist, noting the coupling is passive and structural, not driven by extra muscles. This chain explains why the safe position includes wrist extension and why wrist position is a test condition when assessing extrinsic tightness. A tempting error is assuming finger and wrist motion require independent muscle sets; the coupling shows otherwise.

Self-check rubric: for each of the four positions, name which joints move and which tendon glide the position emphasizes; for tenodesis, state in one sentence why wrist extension belongs in the safe position. A clean second pass after a short delay, reproducing all positions and the coupling explanation without notes, is your learning signal that the drill has taken hold.

• Gliding positions: straight fist, hook fist, full fist, MCP-flexed/IP-extended position.
• Recall ranking: FDP travels farthest (to the DIP); FDS to the PIP; positions isolate combined versus separate glides.
• Self-check: hook fist keeps MCPs extended while PIPs and DIPs flex; full fist flexes everything together.

Two Worked Scenarios: Where a Reasonable Answer Is the Wrong Answer

Work these on paper before reading the resolutions. Each stem contains a condition that could plausibly be misread; the better decision comes from testing the structure rather than pattern-matching the posture.

Scenario A: limited PIP flexion is noted, markedly worse with the MCP held extended but nearly full when the MCP is passively flexed before measuring. Plausible mistake: choosing PIP joint mobilization for a 'PIP contracture.' Better decision: recognize the Bunnel-Littler result as intrinsic tightness, because MCP flexion slackens the intrinsics and restores PIP flexion. It matters because the intervention target changes from the joint to the muscle group, and a joint-focused plan spends effort on tissue that was never the restriction.

Scenario B: a DIP extension lag follows a fingertip extensor injury, and the PIP drifts toward hyperextension over time. Plausible mistake: splinting only the PIP against hyperextension. Better decision: identify the mallet-type terminal tendon injury as the origin, splint the DIP in extension, and support the PIP secondarily, because the PIP drift is downstream of the DIP extension loss. It matters because the originating imbalance remains if only the secondary posture is controlled. Then re-solve both scenarios with one condition reversed: extrinsic tightness in A (result improves with wrist flexion instead) and a primary swan neck in B, writing the new correct answers.

• Scenario rubric: did you name the test before the diagnosis, state which structure failed, and point the splint at that structure?
• Re-test by swapping one condition in each stem and re-solving rather than rereading the resolution.

A Preparation Sequence and Readiness Checks for CHT Study

Sequence your study as anatomy-to-decision chains: kinesiology, then deformity mechanics, then differentiation tests, then splint logic, then integrated cases. Judge readiness by whether you can justify decisions aloud without notes.

An adaptable sequence: first, map the extrinsic and intrinsic muscles by which joints they cross, and derive the safe position and tenodesis from that map rather than from a list. Second, reproduce the deformity table (boutonnière, swan neck, mallet, clawing) from memory, including failed structure and splint target. Third, drill the differentiation tests with all conditions: Bunnel-Littler under both MCP and wrist changes, plus end-feel reasoning for joint versus soft tissue restriction. Fourth, work zones and pulleys as joint control and protection implications. Fifth, solve integrated paper cases end to end: predict the posture, name the test, identify the structure, defend the splint. Reorder so your weakest chain comes first, and repeat the chains that produced wrong decisions rather than rereading correct ones.

Readiness checks, attempted without notes: state the four gliding positions and which tendon glide each isolates; derive the safe position from collateral ligament reasoning; explain why MCP flexion changes the Bunnel-Littler result and what it would mean instead if wrist flexion changed the result; and solve both worked scenarios including the reversed variants, naming the test, the failed structure, and the splint. Treat a clean second pass after a delay as the learning signal; this is a study milestone, not a prediction of your exam result. For administrative matters such as eligibility, application, and current exam administration, check the Hand Therapy Certification Commission directly at htcc.org, since this guide covers study content only. Pair these chains with the free practice questions and the broader study guides on this site, which support the same decision-based review across the credential's knowledge areas.

• Chain 1: muscle-to-joint map → derive the safe position and tenodesis yourself.
• Chain 2: deformity table reproduced from memory with splint targets.
• Chain 3: differentiation tests run under every test condition.
• Chain 4: zones and pulleys stated as joint control and protection implications.
• Chain 5: integrated cases solved end to end: posture → test → structure → splint.

References and further reading

Use these references to explore the concepts and check the latest information from the relevant organizations.

• htcc.org
• htcc.org

Continue your preparation

• Hand Therapy Certification Commission Certified Hand Therapist Cht
• Study Guides