Pipkin Classification — Femoral Head

Overview — Femoral Head Fractures

Femoral head fractures are rare injuries, occurring almost exclusively in association with hip dislocations — most commonly posterior hip dislocation (approximately 6–16% of posterior hip dislocations are associated with a femoral head fracture). They result from the femoral head impacting the posterior acetabular rim as it dislocates, shearing off a fragment from the inferior aspect of the femoral head (Pipkin I and II) or from the femoral head being driven through the acetabulum (Pipkin III and IV). The Pipkin classification (1957), developed by Frederic Pipkin, is the universal system for describing these fractures and directly guides management — ranging from non-operative for small undisplaced fragments to complex ORIF or arthroplasty for high-grade patterns.

Epidemiology: femoral head fractures account for approximately 1–2% of all hip injuries; they occur predominantly in young adults from high-energy trauma (road traffic accidents — the `dashboard injury`, where the knee strikes the dashboard driving the femoral head posteriorly out of the acetabulum); the mechanism and the degree of hip flexion/adduction at the time of impact determine whether a femoral head fracture occurs and where the fracture is located
Vascular anatomy — AVN risk: the femoral head blood supply enters from the retinacular vessels (medial femoral circumflex artery, MFCA) running along the posterior femoral neck under the capsule; posterior hip dislocation stretches or tears these retinacular vessels at the time of dislocation; the longer the hip remains dislocated, the greater the ischaemic insult; the primary determinant of AVN risk is TIME TO REDUCTION — reduction within 6 hours significantly reduces AVN risk; reduction within 12 hours is associated with higher AVN rates; beyond 24 hours, AVN is common; reduction should be performed URGENTLY under sedation/anaesthesia as soon as the patient is stabilised

Pipkin Classification

Pipkin Type	Description	Fragment Location	Clinical Significance	Treatment
Type I — Below fovea	A fracture of the femoral head BELOW (caudal to) the fovea capitis (the central non-articular pit where the ligamentum teres inserts); the fracture fragment is from the INFERIOR femoral head — the non-weight-bearing portion; the superior (weight-bearing) femoral head articular surface is intact; this is the MOST COMMON Pipkin type	INFERIOR femoral head — the non-weight-bearing zone; the fragment is below the central pit of the femoral head; the superior dome (the weight-bearing contact area in standing) is intact	The most favourable prognosis — the fragment is from the non-weight-bearing portion; if the fragment reduces concentrically after hip reduction, the weight-bearing articular surface is restored; the detached fragment may or may not be avascular (the ligamentum teres provides some vascular supply to the inferior femoral head)	Urgent closed reduction of the dislocation; post-reduction CT to assess fragment position and size; if fragment is REDUCED concentrically (≤2 mm step-off) AND the fragment is small (non-weight-bearing location) → non-operative (protected weight-bearing for 4–6 weeks); if fragment is DISPLACED or INTERPOSED in the joint → surgical excision of the small fragment (if <one-third of the head surface) via posterior approach (Smith-Petersen anterior approach for large fragments requiring fixation)
Type II — Above fovea	A fracture of the femoral head ABOVE (cranial to) the fovea capitis — the fragment is from the SUPERIOR femoral head; the weight-bearing articular dome is directly involved; the superior dome is the area in contact with the acetabulum in the standing and weight-bearing position; this is the most clinically important Pipkin type for long-term functional outcome	SUPERIOR femoral head — the WEIGHT-BEARING zone; the fragment involves the dome area that is in contact with the acetabular cartilage during normal loading; disruption of this area directly affects joint congruency and load distribution	Significantly worse prognosis than Type I because the weight-bearing surface is disrupted; articular incongruency at the dome leads to early post-traumatic arthritis; anatomical reduction of the dome fragment is critical; AVN rate is similar to Type I but post-traumatic arthritis is more likely from articular damage	Urgent hip reduction; post-reduction CT assessment; if concentrically reduced (≤2 mm) → non-operative (but careful CT follow-up); if displaced (>2 mm) → ORIF of the femoral head fragment (Herbert screws or headless compression screws placed below the articular surface — the screws must be countersunk below the cartilage); approach: posterior approach (for most posterior dislocations) or anterior (Smith-Petersen) for anterior access to large superior dome fragments; primary THA in elderly patients with poor bone quality or severely comminuted fragments
Type III — Type I or II + femoral neck fracture	A Pipkin Type I or II femoral head fracture COMBINED WITH a femoral neck fracture on the same side; two distinct fractures co-exist: (1) the femoral head fragment (above or below the fovea) AND (2) a separate femoral neck fracture; the femoral neck fracture may be intracapsular (anatomical neck, subcapital, or transcervical)	Both the femoral head AND the femoral neck are fractured; the combination represents a `two-level` injury of the proximal femur on the same side	The WORST PROGNOSIS of all Pipkin types; AVN rate is very high (the femoral neck fracture disrupts the remaining retinacular blood supply to the femoral head that has already been compromised by the dislocation); non-union of the femoral neck is also a concern; this combination essentially ensures a high risk of femoral head AVN and femoral neck non-union	MOST COMPLEX management; young patients: attempt ORIF of both the neck fracture (screw or sliding hip screw) and the head fragment (headless screws) — preserving the femoral head despite the high AVN risk (nothing to lose in a young patient by attempting head preservation); elderly patients: primary total hip arthroplasty (THA) — the combination of femoral neck fracture + femoral head fracture in an elderly patient with likely AVN = primary THA is the most reliable management
Type IV — Type I, II, or III + acetabular fracture	A Pipkin Type I, II, or III femoral head fracture COMBINED WITH a fracture of the ACETABULUM (the acetabular fracture may involve the posterior wall, posterior column, or any acetabular element); the hip dislocation has caused BOTH a femoral head fracture AND an acetabular fracture	Both the femoral head AND the acetabulum are fractured; the combination is equivalent to a femoral head fracture + acetabular fracture in the context of a posterior hip dislocation	Very poor prognosis — dual articular injury (femoral head + acetabulum); post-traumatic arthritis is almost certain from combined articular disruption on both sides of the joint; the acetabular fracture must be assessed by CT (Judet-Letournel classification) to determine whether operative fixation of the acetabulum is required (if the posterior wall fragment is >50% of the posterior wall → ORIF of the posterior wall); the femoral head fragment is managed as per its Pipkin type	MOST COMPLEX combination; management addresses both injuries: (1) acetabular fracture fixation if indicated (posterior wall ORIF via Kocher-Langenbeck approach); (2) femoral head fragment management (excision if small non-weight-bearing; ORIF if large weight-bearing); (3) primary THA in elderly patients with combined femoral head + acetabular fracture who are unlikely to benefit from head-preserving surgery; timing: the hip is reduced immediately; definitive acetabular ORIF at 3–10 days; the femoral head fragment is addressed simultaneously or at staged ORIF

Emergency Management of Hip Dislocation

Closed reduction of posterior hip dislocation — MUST be performed within 6 hours: the most time-critical aspect of management; AVN risk rises dramatically with time; techniques: (1) Allis manoeuvre — the patient is supine; the operator kneels on the stretcher or stands above the patient; traction is applied in the line of the deformity (hip flexed to ~90°, slight adduction); an assistant stabilises the pelvis; traction is applied to the femur, then internal rotation + extension to reduce the femoral head into the acetabulum; a `clunk` is felt when the head reduces; (2) Stimson technique — the patient is prone, the hip flexed 90°, the lower leg hanging over the edge of the table; downward pressure on the proximal tibia applies traction to reduce the hip; (3) Captain Morgan technique — the operator`s knee is placed under the patient`s flexed knee and used as a fulcrum to lever the femoral head into the acetabulum
Reduction assessment: post-reduction AP pelvis + AP/lateral hip X-ray confirms reduction; CT is mandatory after reduction to: (1) confirm concentric reduction (ensure no fragment or meniscoid tissue is interposed); (2) characterise any femoral head or acetabular fracture; (3) identify intra-articular loose bodies; a hip that is reduced on plain X-ray but has a persistently widened joint space on CT = an intra-articular fragment must be excluded

Complications

Avascular necrosis (AVN): the most feared complication; directly related to time to reduction; reduction within 6 hours = low risk; reduction at 6–24 hours = moderate risk; >24 hours = high risk; AVN presents 2–3 years after injury with progressive hip pain and X-ray changes (sclerosis → subchondral fracture → femoral head collapse); MRI is the most sensitive early investigation; treatment: core decompression (early); vascularised bone graft (established); THA (late collapse)
Post-traumatic osteoarthritis: the second most common late complication; directly proportional to the degree of articular damage and the quality of articular restoration; even with anatomical reduction, articular cartilage damage from the impact may lead to progressive arthritis; Pipkin II and IV carry the highest arthritis risk; THA is the eventual salvage
Sciatic nerve injury: present in approximately 10–20% of posterior hip dislocations with femoral head fractures; the nerve is tethered at the greater sciatic notch and is stretched by the posteriorly displaced femoral head; clinical: foot drop (peroneal division most vulnerable), posterior thigh/leg sensory loss; mostly neuropraxia — the majority recover with hip reduction; residual foot drop at 3–4 months → EMG and surgical exploration

Exam Pearls

Pipkin: I (below fovea — non-weight-bearing fragment — best prognosis); II (above fovea — weight-bearing dome — ORIF with headless screws); III (+ femoral neck fracture — worst prognosis, high AVN + non-union risk); IV (+ acetabular fracture — dual articular injury — most complex)
Urgent reduction within 6 hours: the single most important prognostic intervention; every hour of dislocation increases AVN risk; reduce under sedation/GA as soon as patient is stabilised; Allis or Stimson manoeuvre
Post-reduction CT is MANDATORY: confirms concentric reduction; identifies interposed fragments; characterises femoral head and acetabular fractures; identifies intra-articular loose bodies; a hip that looks reduced on X-ray but has a widened joint space = interposed fragment until proven otherwise
Fovea capitis: the central non-articular pit of the femoral head; ligamentum teres inserts here; Pipkin I (below = inferior = non-WB zone); Pipkin II (above = superior = WB dome zone); the fovea divides the weight-bearing from the non-weight-bearing femoral head surface
ORIF of Pipkin II: headless compression screws (Herbert or Acutrak) countersunk below the articular cartilage surface; placed through a posterior or anterior approach depending on fragment location; anatomical reduction of the dome fragment is mandatory (<2 mm step-off)
Pipkin III management dilemma: young patient = attempt ORIF of BOTH the neck fracture and the head fragment (head preservation despite high AVN risk); elderly = primary THA; the femoral neck fracture adds vascular insult to the already compromised femoral head
Sciatic nerve: peroneal division most vulnerable (runs most superficially over the posterior hip joint); foot drop from the peroneal division; most recover after hip reduction (neuropraxia); electromyography at 3 months if no recovery; sciatic nerve palsy is associated with higher-grade Pipkin patterns (III and IV)

Pipkin Classification — Femoral Head

References

Share Wiki