How to Prepare for ABOS Part I (Written)

The American Board of Orthopaedic Surgery (ABOS) Part I examination is the written half of US board certification. You sit it once, in the July after you finish residency, and a pass makes you board eligible for the Part II oral. It is a single-day, 328-question computer-based test weighted heavily towards the limbs. This article covers the format, the official blueprint and a revision plan built around them. For eligibility, the KSB Program, Part II and recertification, see our ABOS board certification guide.

What is the ABOS Part I format?

The ABOS Part I page (opens in a new tab) and standard timing sheet (opens in a new tab) set out the structure:

Unscheduled breaks are allowed but the examination clock keeps running. That works out at about 87 seconds per question in the long blocks, so pace matters as much as knowledge.

Eligibility. You must be in PGY-5 of, or have completed, an ACGME-accredited orthopaedic residency, with the last 24 months in a single programme. Residency and the ABOS KSB participation requirement (opens in a new tab) must both be complete by 30 June of the examination year. For the 2027 sitting, first-time candidates need at least 160 surgical skills assessments, 12 professional behaviour assessments and one completed OITE logged in KSB.

Key dates for 2027 (Part I calendar (opens in a new tab)): applications open 30 September 2026 and close at 4 pm ET on 1 December 2026, with a late deadline of 15 December. Scheduling opens on 1 April 2027. An alternate date on 18 August 2027 is available only for candidates whose life events make July impossible and who have approval from the Credentials Committee. The fee is $1,240, plus$750 if you apply late.

What does the ABOS Part I blueprint cover?

The ABOS builds each paper from its Part I blueprint (opens in a new tab). The 2025 version weights the content like this:

The ABOS also publishes a subspecialty version (opens in a new tab) of the same content. It is more useful for planning revision by rotation: adult trauma 13.5%, general principles 13%, surgery of the hand 10.5%, foot and ankle 10%, sports medicine 9.5%, spine 9%, adult reconstruction 8%, shoulder and elbow 7.5%, paediatrics 12% and oncology 7%.

Two points follow. First, basic science is not a quarter of the paper, as older revision advice often claims. Basic science principles are 4%, and the whole general principles domain is 16%. Second, the knee alone is worth more than the whole of adult spine. Weight your time accordingly.

How should you use the OITE?

The OITE is the knowledge strand of the KSB Program and shares a blueprint with Part I. The ABOS and AAOS also run a linking study (opens in a new tab) using items common to both papers. The 2025 study estimated that the minimum Part I pass corresponded to 182 items (69%) on the 2024 OITE. Earlier estimates ranged from 63% to 69%. You can see your own linked score on the ABOS Resident Dashboard.

Treat this as a rough benchmark, as the ABOS does. Use each OITE score report to find the domains where you are weakest, and plan your PGY-5 revision around those domains, scaled by their blueprint weight.

A phased revision plan

PGY-1 to PGY-4: build the base

• Read around the cases you see. An evening on ankle fractures after a day of ankle fractures sticks better than a chapter read cold.
• Learn surgical approaches as internervous planes and structures at risk; anatomy and approaches are 4% of the paper on their own and underpin many clinical questions.
• Sit every OITE seriously and review it. It is a required KSB assessment and your best regular measure against the blueprint.

January to March of PGY-5: structure

• Take a timed baseline block of fresh questions to find weak domains.
• Choose two or three main resources and stick with them; switching between many banks fragments revision.
• Build a weekly calendar weighted by the blueprint table above, with your weakest high-weight domain first.

April to July: volume and timing

• Work through 50 to 100 questions a day, and read the explanation for every question, including those you answered correctly.
• Do full 52-question blocks in 75 minutes to train pace, and at least two full-length timed mocks to build stamina for a 9-hour day.
• In the final two weeks, revise the facts that fade fastest: tumour translocations and age/location patterns, ossification centres, nerve root levels, material properties and statistics formulas.

Which resources should you use?

According to AAOS (opens in a new tab), ResStudy contains nearly 3,500 questions drawn from AAOS self-assessment examinations, selected Orthopaedic Knowledge Update self-assessments, special interest examinations and OITEs. It does not contain ABOS Part I questions, but the OITE shares its blueprint with Part I, which makes past OITE questions useful practice. Use Miller's as a reference: when you miss a question, read the surrounding section to fix the context. OrthoVellum's ABOS track organises questions against the Part I blueprint.

High-yield content by domain

These are the areas candidates most often need to tighten, grouped by blueprint domain.

General principles (16%)

• Biomechanics and materials: the stress–strain curve (elastic and plastic regions, yield and failure points); stiffness is the slope of the elastic region and toughness the area under the curve. Know galvanic corrosion, fretting and creep, and the relative moduli of cortical bone, titanium and stainless steel.
• Bone biology: primary versus secondary healing; osteoclasts come from the haematopoietic (monocyte–macrophage) lineage and osteoblasts from mesenchymal stem cells. Know the Hueter-Volkmann law and Wolff's law. See bone healing.
• Statistics: calculate sensitivity, specificity, PPV and NPV from a 2×2 table (diagnostic test statistics), know the levels of evidence, and choose a t-test for comparing two means and chi-square for categorical data.
• Antibiotics: vancomycin inhibits cell wall synthesis; fluoroquinolones inhibit DNA gyrase. Understand biofilm.

Lower extremities (32%)

• Periprosthetic joint infection: the major criteria are a sinus tract communicating with the joint or two positive cultures of the same organism; a synovial WBC over 3,000 cells/µL with more than 80% neutrophils supports chronic infection. DAIR suits acute infection with symptoms under 3 weeks and well-fixed implants; chronic infection usually needs staged revision. See periprosthetic joint infection.
• THA approaches: the direct anterior approach uses the sartorius–tensor fasciae latae interval superficially and rectus femoris–gluteus medius deep, with the lateral femoral cutaneous nerve at risk; the posterior approach puts the sciatic nerve at risk.
• ACL reconstruction: the trade-offs between bone–patellar tendon–bone autograft (anterior knee pain), hamstring autograft and allograft (higher failure in young athletes), and the phases of graft healing from necrosis to ligamentisation. See ACL injuries.
• Compartment syndrome: a delta pressure (diastolic minus compartment pressure) under 30 mmHg; the four leg compartments and their nerves; pain out of proportion and pain on passive stretch as early signs. See compartment syndrome.

Upper extremities (25%)

• Shoulder instability: Bankart and Hill-Sachs lesions, and the glenoid bone loss threshold, commonly quoted at about 20%, at which arthroscopic Bankart repair gives way to Latarjet. See anterior shoulder instability.
• Hand: flexor tendon zones (zone II is the classic problem zone) and early active motion protocols (flexor tendon lacerations); median and ulnar nerve compression signs, including Froment's and Wartenberg's signs.

Paediatrics (12%)

• The limping child by age: septic arthritis, transient synovitis and toddler's fracture in the youngest; Perthes disease in mid-childhood; slipped capital femoral epiphysis in adolescence. Know the Kocher criteria.
• Genetics: achondroplasia (FGFR3, autosomal dominant), Marfan syndrome (fibrillin-1), osteogenesis imperfecta (type I collagen, COL1A1/COL1A2).
• Physeal injuries: Salter-Harris types III and IV cross the physis into the joint and need anatomical reduction. See physeal injuries.

Spine (8%) and neoplasms (7%)

• Spine trauma: the TLICS score; central cord (arms worse than legs, older patients with hyperextension), Brown-Séquard (ipsilateral motor, contralateral pain and temperature loss) and anterior cord (worst prognosis) syndromes.
• Tumours: learn each lesion by age, location, radiographic appearance and histology or genetics. Osteosarcoma is a metaphyseal tumour of adolescents with sunburst periosteal reaction and Codman's triangle (osteosarcoma); chondroblastoma is epiphyseal with chicken-wire calcification; Ewing sarcoma is diaphyseal with onion-skin periosteal reaction, small round blue cells and t(11;22) (Ewing sarcoma); synovial sarcoma carries t(X;18).

Test-day tactics

1. Pace each block. At 75 minutes for 52 questions, flag anything you cannot narrow to two options within about a minute and come back to it.
2. Read the question stem first. Long vignettes often contain detail that does not bear on what is asked; read the final sentence, then scan the stem for the clues it needs.
3. Change answers only for a reason. Change an answer if you find you misread the question (a missed NOT or EXCEPT) or recall a specific fact, not on a vague second thought.
4. Plan your 40 minutes of break. You can split it however you like across seven blocks. Do the tutorial at home to bank an extra 20 minutes, and leave the room when you do take a break.
5. Eat and drink steadily. Bring food you know you tolerate; a long day of reading suits regular snacks better than one heavy lunch.

After the exam

Results appear on your ABOS Dashboard in early September. Once you pass, the five-year board-eligibility clock for Part II starts, and fellowship time does not count against it. The next step is building a practice that meets the Part II 17-month rule and collecting your six-month case list, both covered in the ABOS board certification guide. For managing nerves in the final weeks, see managing exam performance anxiety.

Checklist before you sit

• Application submitted by 1 December and KSB numbers on track for 30 June
• Exam scheduled at a Pearson centre once scheduling opens in April
• Each blueprint domain revised in proportion to its weight
• Questions completed with every explanation read, and weak OITE domains revisited
• Tumour, genetics, statistics and material-property facts reviewed in the final fortnight
• At least two full-length timed mocks completed
• Route, identification and food for the day sorted