Upload a hip X-ray, get the patient's CPAH femoral morphotype, and a ranked, evidence-based femoral stem shortlist across 224 stems from 73 manufacturers — in under a minute.
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Request a stem/implant integration or ask a question: admin@stemfit.ai
Research / educational tool — not a medical device. Do not upload identifiable patient data. · Privacy Policy
StemFit is a web-based clinical decision-support and educational platform for hip arthroplasty surgeons, fellows, and residents. It turns a single calibrated hip radiograph into a structured, evidence-based plan for femoral stem selection — bringing consistency to a decision usually made by eye and varying widely between surgeons.
The workflow is fast and guided. A surgeon uploads an AP hip X-ray, places a few points to calibrate and mark landmarks, and StemFit automatically computes the neck-shaft angle, cortical index, femoral offset, and offset ratio. From these it assigns the femur to one of nine Coronal Plane Alignment of the Hip (CPAH) morphotypes — a peer-reviewed classification (Ettinger, Stauss, Seyler) combining bone quality (Dorr type) with coronal geometry.
For that morphotype, StemFit produces a ranked shortlist of femoral stems from a curated database of 224 implants across 73 manufacturers, each classified by the Radaelli geometry system. It indicates whether cemented or cementless fixation is favored, runs a built-in osteoporosis screen from the cortical thickness index, and lets each surgeon build their hospital's stem "formulary" so recommendations reflect what's on the shelf.
Powered by the CPAH classification, StemFit is designed for individualized, personalized THA planning and for teaching femoral morphology, Dorr typing, and stem geometry. Importantly, it is an educational and decision-support tool — not a diagnostic medical device — and every measurement and recommendation must be independently verified by the operating surgeon.
StemFit does not template or size femoral stems. It classifies femoral morphology and recommends stem designs matched to that morphotype; it does not perform digital templating, predict implant size, or determine the specific size, length, or offset of any implant. Component sizing remains the responsibility of the operating surgeon using appropriate templating and intraoperative judgement.
Questions or a request to integrate a specific stem/implant design? Email admin@stemfit.ai.
Do not save if the radiograph contains any patient identifiers.
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Full access — CPAH morphotyping, evidence-based stem recommendations, the 224-stem database, cemented/cementless & bone-quality guidance, PDF case reports, and your saved cases & formularies.
Personalized THA · the right stem for every femur — Ettinger · Stauss · Seyler
Your saved classifications, most recent first — each recorded with its date, CPAH morphotype, key measurements and recommended stems. Radiographs you save are stored privately to your account — view the X-ray or regenerate the PDF report anytime.
| Date | Side | Patient | CPAH | Fixation focus | NSA | CI | FOR | Top recommendations | Radiograph | Report | Notes |
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Pick a site (＋ Site for multiple hospitals) and tick Stock for the stems it carries — changes save automatically to that site and persist across logins. Recommendations can then be filtered to the active site's formulary.
| Stock | ★ | Stem | Manufacturer | Fixation | Geometry | Length | Modularity | Collar | Surface | Use | Code | Src |
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The Coronal Plane Alignment of the Hip (CPAH) classification defines nine femoral morphotypes by combining an intramedullary parameter (Dorr canal shape) with an extramedullary one (neck–shaft angle), each further split by the femoral offset ratio.
CI = (Z − X) / Z, measured 10 cm distal to the mid-lesser-trochanter line, where Z = femoral diaphyseal (outer) diameter and X = intramedullary canal diameter. Dorr A > 0.60 · B 0.50–0.60 · C < 0.50.FOR = FO / Z — scale-independent. Normal < 1.60 · high ≥ 1.60.Image quality matters: use a low-centred AP pelvis with 15° internal rotation and a neutral pelvis, and always include a calibration marker — plain radiographs magnify/underestimate offset by ~3–5 mm without one.
The cortical thickness index doubles as an osteoporosis screen. Sah et al. found CTI correlates with DXA T-score: CTI (AP) ≤ 0.50 (specificity 0.84) or CTI (lateral) ≤ 0.40 (sensitivity 0.85, specificity 0.79, LR+ 4.0) flags likely osteoporosis and should prompt a DXA referral. Dorr C also tracks lower T-scores; the canal-to-calcar ratio did not correlate with BMD. Enter a lateral CTI under “Enter values manually” for the stronger threshold.
The tool suggests a fixation mode from canal shape and bone quality: Dorr A / adequate cortical thickness favours cementless press-fit; a low cortical thickness index (osteoporotic bone, Sah et al.) or a Dorr C ‘stovepipe’ canal leans toward cemented fixation given the higher periprosthetic-fracture and loosening risk of cementless stems in poor bone. The recommended fixation now also re-ranks the stem shortlist — cemented designs rise when the indices favour cement, and vice-versa — and every stem is tagged Cemented or Cementless. This is decision support only — age, activity, comorbidity and surgeon experience remain decisive.
With renewed interest in cemented femoral fixation, Hegde & Khanuja proposed an alphanumeric classification that StemFit applies to every cemented stem in the database. Load transfer through the cement mantle divides designs into two philosophies:
Surface finish Ra: polished 0–5, satin 15–40, roughened >40 µin — a polished surface is essential to a taper-slip design; roughening raises interface shear (lower fracture, higher loosening). Collars pressurise cement and limit subsidence (Type II / line-to-line). The “French paradox” line-to-line technique fills the canal with a thin (<2 mm) mantle to minimise micromotion — most typical of Type I stems. Modern cemented stems are Co-Cr or stainless steel; cemented titanium has fallen out of favour.
CPAH indices drive the fixation decision first, then the cemented sub-type:
A flat taper · B1/B2/B3 rectangular / quadrangular / short-quadrangular tapers · C1/C2/C3 fit-and-fill / anatomic / short fit-and-fill · D conical · E cylindrical · F calcar-guided ultra-short — with length, modularity (I–IV), collar and surface modifiers.
Stauss R, Savov P, Biestmann F, Brueggemann M, Mont MA, Seyler TM, Ettinger M. Definition of Femoral Morphotypes Based on the Coronal Plane Alignment of the Hip Classification. The Journal of Arthroplasty 2026 (in press). — the CPAH classification this app implements.
Femoral stem classification & fixation
Femoral morphotype & anteversion
Bone quality & the Dorr classification
Femoral offset
⚠️ Not a medical device. StemFit (powered by the CPAH classification) is an educational and research decision-support tool. It is not FDA/CE cleared or registered and is not intended to diagnose, treat, or make or confirm any clinical or surgical decision. All measurements, classifications, bone-quality flags, fixation guidance and stem recommendations are approximations dependent on radiograph quality, positioning and calibration, and must be independently verified by the operating surgeon, who remains solely responsible for all clinical decisions. The software and its data (including inferred/possibly outdated stem classifications) are provided “AS IS” without warranty of any kind; verify stem specifications against the manufacturer’s current instructions for use. To the maximum extent permitted by law, the authors and developers accept no liability for any damages arising from use of or reliance on this tool. Do not upload patient-identifying data; you are responsible for de-identification and for compliance with HIPAA, GDPR and your institution’s policies. Figures © the CPAH study group, used with permission. Use constitutes acceptance of these terms.
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| Morphotype | Cases | Female / Male | Mean age | Mean BMI | % cemented focus | Top race/ethnicity |
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| Name | Institution | Affiliation | Approach | Fellowship | Age | Sex | Location | Sub | Collab | Joined | Reg IP |
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Radiographs are stored with each saved case (research use only when the surgeon consented). IP, timezone and timestamp are recorded.
| When (UTC) | User | CPAH | Side | Patient | Fixation | Top recommendations | X-ray | TZ |
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