Sanders CT Classification — Calcaneus

Overview — Calcaneal Fractures & CT Classification

The Sanders classification is the universally accepted CT-based classification system for intra-articular calcaneal fractures, specifically those involving the posterior facet of the subtalar joint. Developed by Roy Sanders and colleagues in 1992–1993, it was the first practical CT-based system that could reliably guide surgical decision-making, predict outcomes, and communicate fracture complexity between surgeons. Prior plain radiograph-based systems (Essex-Lopresti, Rowe) were unable to adequately characterise the three-dimensional nature of calcaneal fractures — particularly the critical posterior facet — making CT an essential prerequisite for applying the Sanders classification.

CT technique for Sanders classification: a semi-coronal CT scan through the posterior facet of the subtalar joint at 30° to the long axis of the tibia; the critical image is the coronal slice at the WIDEST POINT of the posterior facet of the subtalar joint; this slice shows the full width of the posterior facet and allows identification and counting of the fracture lines within the posterior facet; 3D CT reconstruction is increasingly used as an adjunct for surgical planning but the classification is based on the 2D coronal slice
The three columns of the posterior facet (A, B, C): the widest coronal CT slice of the posterior facet is divided into THREE equal parts by two imaginary lines — these create the three columns: Column A (the lateral third of the posterior facet — closest to the fibula); Column B (the middle third); Column C (the medial third — closest to the sustentaculum tali); the Sanders classification counts the number of fracture lines within the posterior facet and their position within these three columns

Sanders Classification

Sanders Type	Number of Posterior Facet Fragments	CT Description	Prognosis	Treatment Recommendation
Type I — Undisplaced	Any number of fracture lines but ALL undisplaced (<2 mm step-off in the posterior facet)	The fracture lines may be visible within the posterior facet on CT but the articular congruency is maintained; there may be associated fractures of the anterior process, sustentaculum, or tuberosity but the posterior facet remains reduced; Böhler`s angle may be minimally reduced	EXCELLENT — minimal articular disruption; low risk of post-traumatic subtalar arthritis; Böhler`s angle restoration is good	Non-operative — immobilisation in a cast or CAM boot; protected weight-bearing for 6–8 weeks; serial X-rays to confirm no late displacement; physiotherapy; good functional outcomes expected without surgery
Type II — Two fragments (one fracture line)	Two fragments in the posterior facet (ONE fracture line divides it into 2 pieces)	A single fracture line divides the posterior facet into two displaced fragments; sub-classified by the position of the fracture line: Type IIA (fracture line between A and B columns — lateral fracture line); Type IIB (fracture line between B and C columns — middle fracture line); Type IIC (fracture line through C column only — medial, through the sustentaculum region); the fragment position and size determine the surgical approach (sinus tarsi vs extensile lateral)	GOOD — two-fragment fractures are the most amenable to anatomical reduction and internal fixation; the best outcomes among displaced fractures; Sanders reported ~73% good/excellent results with ORIF for Type II; post-traumatic subtalar arthritis risk is lower than Type III/IV	ORIF — open reduction and internal fixation via extensile lateral approach or sinus tarsi approach; elevation of the displaced posterior facet fragment to restore articular congruency; lag screw fixation of the posterior facet + lateral wall reconstruction with plate; sinus tarsi approach increasingly used for Type II fractures (equivalent outcomes with significantly lower wound complication rates)
Type III — Three fragments (two fracture lines)	Three fragments in the posterior facet (TWO fracture lines dividing it into 3 pieces)	Two fracture lines create three articular fragments; sub-classified: Type IIIAB (fracture lines through columns A-B and B-C — the central fragment is characteristically depressed into the calcaneal body creating a `central depression fragment`); Type IIIAC (fracture lines through A-B and C — lateral + medial involvement); Type IIIBC (fracture lines through B-C and C — both involving the medial column); the CENTRAL DEPRESSION FRAGMENT in IIIAB is the most challenging intraoperatively — it must be elevated and supported with bone graft or substitute	MODERATE to POOR — significant articular comminution; outcomes are inferior to Type II; approximately 44% good/excellent results with ORIF in Sanders` original series; post-traumatic subtalar arthritis develops in 20–40% of Type III even with anatomical reduction	ORIF if technically feasible and patient is medically appropriate; the central depression fragment must be elevated and supported (often requires bone graft substitute — calcium sulphate or calcium phosphate — or iliac crest autograft to prevent re-depression after screw fixation); extensile lateral approach for most IIIAB (direct visualisation needed for the central fragment); primary subtalar arthrodesis is an alternative for very elderly or comorbid patients with Type III injuries (avoids ORIF complications while restoring hindfoot alignment)
Type IV — Four or more fragments (three or more fracture lines)	Four or more fragments (>3 fracture lines — highly comminuted posterior facet)	The posterior facet is shattered into four or more pieces; all three columns are involved with multiple fracture lines; the articular cartilage is fragmented beyond reliable reconstruction; Böhler`s angle is severely reduced or negative; the calcaneal height and width are dramatically altered; the fibular-calcaneal impingement space is lost	POOR — the articular surface cannot be reliably reconstructed; high rates of post-traumatic subtalar arthritis regardless of management; Sanders reported only ~9% good/excellent results with ORIF for Type IV; the joint is effectively destroyed	Primary subtalar arthrodesis (in situ fusion or with calcaneal realignment osteotomy) — avoids the complications of ORIF while restoring calcaneal morphology (calcaneal body height and width) and performing definitive subtalar fusion; non-operative management for medically unfit patients; ORIF is rarely indicated for Type IV (outcome not improved over non-operative or primary fusion)

The `Wrinkle Sign` & Operative Timing

The wrinkle sign: the most important clinical sign for timing of ORIF of calcaneal fractures; when the acute swelling of the calcaneal fracture has sufficiently subsided, wrinkles appear over the lateral heel skin as the skin returns to its resting state; the appearance of wrinkles over the lateral heel (when the foot is slightly dorsiflexed) = the `wrinkle sign` = the soft tissues are ready for the extensile lateral approach; performing surgery before the wrinkle sign (in the acute swollen phase) dramatically increases the risk of wound dehiscence, skin edge necrosis, and deep infection; typical waiting time = 7–14 days from injury; the wrinkle sign is the clinical indicator of soft tissue readiness
Risk factors for wound complications: smoking (the single most important modifiable risk factor — cessation for at least 4 weeks is recommended before elective fixation); diabetes; peripheral vascular disease; obesity; immunosuppression; severe initial swelling (degree 4 blistering); open injuries; operating before the wrinkle sign; these risk factors significantly increase wound complication rates with the extensile lateral approach

Sinus Tarsi Approach vs Extensile Lateral Approach

Feature	Extensile Lateral Approach	Sinus Tarsi Approach
Incision	Large L-shaped incision over the lateral heel; full-thickness flap elevated off the lateral calcaneal wall from the Achilles tendon to the calcaneocuboid joint; peroneal tendons and sural nerve are elevated within the flap	Small oblique incision over the sinus tarsi (between the fibular tip and the base of the 4th metatarsal); limited dissection; the posterior facet is accessed through this `window`
Visualisation	Excellent direct visualisation of the entire posterior facet and lateral calcaneal wall; best for complex Type III and IV fractures	Limited direct visualisation; relies on C-arm fluoroscopy and arthroscopy (in some cases); adequate for Type I, II, and selected Type III fractures
Wound complication rate	Higher — ~5–25% wound dehiscence/deep infection in high-risk patients; the large full-thickness flap is vulnerable to vascular compromise, particularly in the corner of the L-shaped incision	Significantly LOWER — ~2–5%; the small incision has much less wound edge ischaemia risk; recommended for smokers, diabetics, and high-risk patients
Evidence base	Long established; gold standard for complex fractures; best for achieving anatomical reduction of Type IIIB	Multiple RCTs (STARR trial, others) demonstrate equivalent functional outcomes to extensile lateral for Type II and III fractures with significantly lower wound complications; increasingly adopted as the preferred approach at high-volume centres

Exam Pearls

Sanders classification: based on CORONAL CT through widest point of posterior facet; Type I (undisplaced — non-op); Type II (2 fragments, 1 line — ORIF, best prognosis); Type III (3 fragments, 2 lines — ORIF or primary subtalar fusion); Type IV (≥4 fragments — primary subtalar fusion or non-op)
Three columns A, B, C: A = lateral third; B = middle third; C = medial third (sustentaculum side); fracture line position determines subtype (IIA/IIB/IIC; IIIAB/IIIAC/IIIBC)
Central depression fragment (Type IIIAB): the middle column B fragment is depressed into the calcaneal body; requires elevation and support with bone graft; the most technically challenging aspect of Type III calcaneal ORIF; without support, it re-depresses after screw fixation
Wrinkle sign: wrinkles appear over the lateral heel skin when acute swelling subsides (7–14 days post-injury); indicates soft tissue readiness for extensile lateral ORIF; operating before the wrinkle sign = dramatically increased wound complication rate
Sinus tarsi approach: small incision over sinus tarsi; equivalent outcomes to extensile lateral for Type II/III; significantly lower wound complications; preferred for high-risk patients (smokers, diabetics); increasingly adopted as the primary approach
Böhler`s angle: normal 20–40°; reduced/negative = significant posterior facet depression; restoration to >15° correlates with better functional outcomes; measured on the lateral plain X-ray (line from highest point of tuberosity to highest point of posterior facet to highest point of anterior process)
Primary subtalar fusion for Type IV: restores calcaneal morphology (height/width/alignment) AND definitively fuses the destroyed subtalar joint; avoids the complexity of ORIF reconstruction; combined calcaneal osteotomy (to restore shape) + fusion; appropriate for elderly/comorbid patients and younger patients with severe Type IV

Sanders CT Classification — Calcaneus

References

Share Wiki