Floating Joints — Floating Knee, Floating Elbow & Floating Shoulder

A `floating joint` describes a clinical and radiological pattern in which a joint is `freed` from the axial skeleton or the distal limb segment by fractures on BOTH sides of it — a proximal fracture and a distal fracture — resulting in the joint being suspended between two unstable bony segments with no direct skeletal continuity above or below. The joint itself is typically not dislocated, but its mechanical connections to the rest of the limb are lost, making the entire joint and its attached limb segment mechanically unsupported. The concept applies to three major joints in orthopaedic surgery: the KNEE (floating knee — ipsilateral femur and tibia fractures), the ELBOW (floating elbow — ipsilateral distal humerus and forearm fractures, predominantly in children), and the SHOULDER (floating shoulder — ipsilateral clavicle and scapular neck fractures disrupting the superior shoulder suspensory complex). All three patterns share common features: high-energy mechanisms, high rates of associated injuries, complex surgical management, and significant morbidity. Understanding the specific anatomy of each pattern, the classification systems, and the indications for operative versus non-operative management is essential for orthopaedic examinations and clinical practice.

• Shared principles across all floating joint injuries: (1) HIGH ENERGY mechanism — all three patterns result from high-energy trauma (road traffic accidents, falls from height, industrial injuries) and carry a high rate of associated injuries (polytrauma, vascular injury, nerve injury, thoracic injury); (2) ASSESSMENT priority — neurovascular assessment of the limb distal to the floating joint is MANDATORY and must be performed and documented before and after any manipulation or reduction; (3) SURGICAL tendency — the mechanical instability of floating joint injuries almost always favours surgical stabilisation of at least one of the two fractures to restore limb stability and allow functional rehabilitation; (4) COMPLEX decision-making — the choice of which fracture(s) to fix, the order of fixation, and the implant selection are influenced by the specific fracture patterns, the patient`s overall condition, and associated injuries

Definition & Epidemiology

The floating knee describes the combination of an ipsilateral FEMUR FRACTURE and TIBIA FRACTURE on the same side, resulting in the knee joint being `floating` between two unsupported bony segments. First described by Blake and McBryde in 1975, and formally classified by Fraser in 1992. It is a high-energy injury, occurring most commonly in road traffic accidents (the dashboard injury mechanism — the knee strikes the dashboard, transmitting force simultaneously up to the femur and down through the tibial shaft) and high-velocity falls. The floating knee constitutes approximately 2–5% of long bone fractures and carries a mortality of approximately 5–10% due to associated injuries (thoracic trauma, abdominal injury, head injury). It is a classic polytrauma injury pattern.

• Mechanism: the most common mechanism is the `dashboard injury` in road traffic accidents — the knee strikes the dashboard during a frontal collision; the impact force is transmitted both proximally through the femur and distally through the tibia, fracturing both bones simultaneously; a direct lateral impact to the knee may produce a similar pattern; high-energy falls from height (construction workers, jumpers) also produce ipsilateral femur and tibia fractures from axial loading; associated injuries are present in up to 60–70% of patients: vascular injury (popliteal artery — the most feared associated injury; up to 5%); ligamentous injury of the knee joint (up to 40–50%); ipsilateral hip dislocation or fracture-dislocation; compartment syndrome (the distal leg); head injury; thoracic injury

Fraser Classification of Floating Knee

Management of the Floating Knee

• Vascular assessment — the critical priority: the popliteal artery runs in close proximity to the posterior capsule of the knee and is tethered at the level of the adductor hiatus (proximally) and at the bifurcation into the anterior and posterior tibial arteries (distally); ipsilateral femur and tibia fractures can trap, stretch, or lacerate the popliteal artery; all floating knee patients require a formal vascular assessment of the distal limb: palpation of dorsalis pedis and posterior tibial pulses; ankle-brachial pressure index (ABPI) — an ABPI <0.9 in a trauma patient should prompt formal vascular imaging (CT angiography); hard signs of vascular injury (absent pulse, expanding haematoma, bruit, pallor, paraesthesia, paralysis) mandate immediate vascular surgery referral; the limb-threatening complication of an unrecognised popliteal artery injury is well documented in floating knee injuries
• General management principle — fix both fractures: the overwhelming evidence supports stabilisation of BOTH fractures in floating knee injuries to restore mechanical stability, allow nursing care, reduce pain, prevent fat embolism, and facilitate early mobilisation; non-operative management of BOTH fractures is associated with significantly worse outcomes (prolonged bed rest, higher malunion and non-union rates, worse functional outcomes); the choice of implant for each fracture follows the same principles as for isolated fractures of that bone
• Surgical approach for Fraser Type I (both extra-articular): FEMUR — antegrade IM nail (preferred for shaft fractures) or retrograde IM nail (preferred for distal femoral metaphyseal fractures); TIBIA — IM nail (the standard for tibial shaft fractures); both nails can be placed in the same anaesthetic; the femur is typically nailed first to restore limb length and alignment, then the tibia; intraoperative fluoroscopy throughout
• Ligamentous injury of the knee: MRI assessment of the knee ligaments (ACL, PCL, collateral ligaments, posterolateral corner) should be performed after fracture stabilisation; ligamentous injuries are present in 40–50% of floating knees; acute repair of ligamentous injuries at the time of fracture fixation is technically demanding and not always possible; many surgeons prefer staged management — fracture fixation first, ligament assessment and repair/reconstruction after fractures have healed; the knee is splinted in extension during the fracture healing phase to protect unstable ligaments
• Outcomes and complications: non-union rates for floating knee fractures are higher than for isolated femur or tibia fractures, reflecting the severity of initial injury; malunion (especially of the tibia) is common; knee stiffness (from prolonged immobilisation, intra-articular haematoma, and ligamentous injury) is a significant problem in intra-articular types; compartment syndrome of the lower leg occurs in up to 10%; fat embolism syndrome is a recognised complication of bilateral or floating long bone fractures; deep infection rates are higher than for isolated fractures

Definition & Epidemiology

The floating elbow describes an ipsilateral DISTAL HUMERUS FRACTURE combined with a FOREARM FRACTURE (fracture of the radius, ulna, or both) on the same limb, resulting in the elbow joint being `floating` between two unstable segments. It is predominantly a PAEDIATRIC injury — the most common form is a supracondylar humerus fracture combined with an ipsilateral forearm fracture (distal radius, radial shaft, or both-bone forearm fracture). In adults, the combination of a distal humerus fracture (intercondylar or supracondylar) with a forearm fracture is less common but carries significant morbidity. The reported incidence of ipsilateral forearm fracture in paediatric supracondylar humerus fractures is 2–13%. The combination significantly increases surgical complexity, complication rates (particularly neurovascular injury), and rehabilitation requirements compared to either fracture in isolation.

• Mechanism in children: the most common mechanism is a fall onto an outstretched hand (FOOSH) from a height (playground equipment, bicycle); the impact force is transmitted through the extended wrist and forearm to the elbow, fracturing the distal radius and/or forearm AND the supracondylar region simultaneously; the combination pattern has been termed the `floating elbow` because the elbow joint is suspended between an unstable distal humerus and unstable forearm; the forearm fracture is typically at the level of the distal radius (most common), distal radial metaphysis, or proximal forearm
• Neurovascular injury risk — greatly increased: the neurovascular injury rate in paediatric floating elbow is substantially higher than for supracondylar fractures alone; reported rates of anterior interosseous nerve (AIN) injury in floating elbow: up to 18–25% (compared to 5–10% for isolated supracondylar fractures); brachial artery injury rate is also higher; the increased risk is explained by the greater overall energy of the injury and the compound displacement of the distal humeral fragment which stretches the neurovascular structures over a greater arc; ALWAYS perform a thorough neurovascular examination before any manipulation in floating elbow injuries — document radial pulse, capillary refill, and individual motor testing of AIN (FPL, FDP index finger), median nerve (intrinsics, thenar), radial nerve (wrist extension), and ulnar nerve (intrinsics)

Classification of Floating Elbow

Management of the Floating Elbow

• The `supracondylar first` rule in children: the supracondylar humerus fracture is ALWAYS addressed and stabilised BEFORE the forearm fracture in paediatric floating elbow; the rationale: (1) the supracondylar fracture poses the greatest vascular risk (brachial artery tethered at the fracture, compressed by the proximal fragment); stabilising the supracondylar fracture restores the normal anatomical relationship of the brachial artery to the humerus, reducing vascular compromise; (2) the supracondylar fracture is the proximal injury — restoring humeral alignment first provides a stable platform for addressing the forearm; (3) forearm fractures in children have a greater capacity to remodel than supracondylar fractures — a suboptimal forearm reduction may be acceptable; a poor supracondylar reduction is not
• Anaesthesia considerations: floating elbow injuries almost always require general anaesthesia in children; tourniquet use is at the surgeon`s discretion but must be applied PROXIMAL to both fractures (upper arm tourniquet); patient positioning must provide access to both fractures simultaneously; a sterile field for both the elbow and forearm must be prepared; image intensifier (C-arm) access to the entire upper limb is required
• The `pink pulseless hand` in floating elbow: if the hand is pink (adequate perfusion through collateral vessels) but the radial pulse is absent, this represents a potentially compromised but not yet ischaemic hand; the management decision is controversial but the standard approach is: urgent closed reduction and K-wire fixation of the supracondylar fracture; reassess the hand after fixation (pulse may return after fracture reduction decompresses the brachial artery); if the hand remains pulseless but pink after anatomical reduction → Doppler ultrasound; consider vascular exploration vs close monitoring; a white cold hand (true ischaemia) requires IMMEDIATE vascular surgical intervention without delay for fracture fixation
• Compartment syndrome risk: is substantially elevated in floating elbow injuries; multiple forearm compartments are at risk; the combination of swelling from the supracondylar fracture AND the forearm fracture creates additive swelling in the enclosed forearm compartments; maintain high clinical suspicion; perform compartment pressure measurements if any clinical doubt; four-compartment forearm fasciotomy if pressure criteria are met; a cast that is too tight post-operatively is a common avoidable cause of compartment syndrome in floating elbow — all post-operative immobilisation must be applied as a posterior backslab (not circumferential cast) with the elbow at 90°
• Outcomes: functional outcomes for floating elbow are generally good in children when the supracondylar fracture is anatomically stabilised and the forearm fracture is appropriately treated; the rate of Volkmann`s ischaemic contracture (from unrecognised or delayed compartment syndrome) is the most feared long-term complication; stiffness is more common than in isolated fractures; pin tract infection from K-wires is managed as standard; nerve injuries (AIN most common) typically recover spontaneously over 3–6 months; surgical exploration is indicated if there is no evidence of recovery by 3 months

Definition & The Superior Shoulder Suspensory Complex (SSSC)

The floating shoulder describes an injury pattern in which the glenohumeral joint (the shoulder joint proper) is `disconnected` from the axial skeleton by fractures or disruptions at TWO points in the `superior shoulder suspensory complex` (SSSC) — the ring of bony and ligamentous structures that normally maintain the shoulder`s attachment to the thorax. The most common pattern is an ipsilateral CLAVICLE FRACTURE combined with a SCAPULAR NECK FRACTURE, resulting in the glenoid and its attached glenohumeral joint being suspended free with no stable skeletal connection to the thorax — a `double disruption of the SSSC.` The concept was described and formalised by Goss in 1993.

• The Superior Shoulder Suspensory Complex (SSSC — Goss 1993): the SSSC is a bony and ligamentous ring that maintains the mechanical relationship between the shoulder girdle and the axial skeleton; the ring consists of: (1) the GLENOID PROCESS of the scapula; (2) the CORACOID PROCESS; (3) the CORACOCLAVICULAR LIGAMENTS (conoid and trapezoid — the primary ligamentous link between the coracoid and the clavicle); (4) the DISTAL CLAVICLE (the link between the SSSC and the rest of the clavicle); (5) the ACROMIOCLAVICULAR JOINT; (6) the ACROMION PROCESS; two `struts` attach this ring to the axial skeleton: the CLAVICLE (connecting the ring to the sternum via the sternoclavicular joint) and the SCAPULAR BODY (connecting the ring to the thorax via the scapulothoracic articulation); a SINGLE disruption of the SSSC (e.g. isolated clavicle fracture alone, or isolated scapular neck fracture alone) is generally stable — the other structures maintain the ring`s integrity; a DOUBLE disruption of the SSSC (disruption at TWO points — e.g. clavicle fracture + scapular neck fracture) renders the glenoid and the entire shoulder girdle FREE-FLOATING — no stable connection to the axial skeleton remains
• Epidemiology: floating shoulder accounts for approximately 0.1% of all fractures and 1–5% of scapular fractures; high-energy mechanism (road traffic accidents in 60–80%; motorcycle accidents; industrial crush injuries; falls from height); predominantly young adult males; associated injuries are present in 80–90% of patients (rib fractures and pneumothorax are the most common; brachial plexus injury in 10–20%; subclavian or axillary artery injury; head and abdominal injuries); the high rate of associated injuries means that the shoulder injury is frequently not the primary management priority in the acute setting

Components of the Floating Shoulder — Common Combinations

Assessment of Floating Shoulder — Glenopolar Angle

• Glenopolar angle (GPA): the key radiological measurement for quantifying displacement of the glenoid fragment in floating shoulder injuries; measured on the AP shoulder X-ray — the angle between: (1) a line connecting the most superior and inferior points of the glenoid articular surface; and (2) a line from the superior pole of the glenoid to the inferior angle of the scapula body; normal GPA = 30–45°; a REDUCED GPA (less than 22–30°) indicates significant medial (inferior) displacement of the glenoid fragment — the glenoid has rotated medially and inferiorly relative to the scapular body; a GPA <22° is associated with significantly worse functional outcomes if managed non-operatively; a GPA <22° is a widely cited threshold for surgical intervention in floating shoulder injuries
• Indications for surgery in floating shoulder: the management of floating shoulder remains controversial — some series report acceptable outcomes with non-operative management even for doubly disrupted SSSC injuries; however, the weight of current evidence supports surgical intervention for: GPA <22°; medial displacement of the glenoid fragment >2 cm; significant clavicle shortening (>2 cm); a completely unstable construct where the glenoid is visibly dropped on clinical examination; associated brachial plexus injury requiring early exploration; most authors agree that FIXATION OF THE CLAVICLE alone (restoring the clavicular strut) is sufficient to indirectly restore glenoid stability in most cases — direct fixation of the scapular neck is rarely required

Management of Floating Shoulder

• Non-operative management: a simple sling for 6 weeks, followed by graduated physiotherapy; appropriate for: minimally displaced clavicle fracture with minimally displaced scapular neck (GPA >22°, glenoid displacement <1 cm); elderly low-demand patients; patients with significant comorbidities or associated injuries that preclude early surgery; the rationale for non-operative management is that even displaced floating shoulder injuries often unite with acceptable functional outcomes — particularly in lower-demand patients; however, young active patients and manual workers with significantly displaced glenoids have markedly impaired shoulder function if managed non-operatively
• Operative management — clavicle ORIF as the primary intervention: ORIF of the clavicle fracture (with a superior or antero-inferior locking plate) is the primary surgical intervention for most floating shoulder injuries requiring surgery; the rationale: restoring the clavicular strut length and alignment re-tensions the coracoclavicular ligaments and indirectly reduces and stabilises the glenoid fragment (by pulling the entire SSSC ring back into alignment through the re-tensioned CC ligaments); in most cases, clavicle ORIF alone is sufficient to restore glenoid stability and a satisfactory GPA without the need for direct scapular neck fixation
• Direct scapular neck ORIF: direct fixation of the glenoid neck fracture is technically demanding (posterior approach to the scapula — the Judet approach); reserved for cases where: the glenoid remains significantly displaced after clavicle fixation; the scapular neck fracture pattern is not amenable to indirect reduction through clavicle fixation; isolated scapular neck fractures with significant displacement in a high-demand patient; direct fixation requires posterior dissection between infraspinatus (above) and teres minor (below) to expose the posterior scapula and the glenoid neck
• Brachial plexus injury in floating shoulder: up to 10–20% of floating shoulder injuries are associated with a brachial plexus injury; the traction force that produces the double SSSC disruption also stretches the brachial plexus; the plexus injury is typically a traction injury (upper trunk most common — C5/C6 — producing the `Erb`s palsy` pattern: loss of shoulder abduction, external rotation, and elbow flexion); lower trunk injuries are less common but associated with hand intrinsic weakness; brachial plexus injuries require formal neurological assessment (including EMG/NCS at 3–6 weeks) and specialist neurological follow-up; the presence of brachial plexus injury influences the urgency of shoulder fixation (early stability facilitates nerve recovery)
• Outcomes: outcomes for floating shoulder are closely correlated with the degree of glenoid displacement and the presence of brachial plexus injury; appropriately managed floating shoulders with good reduction achieve 80–90% satisfactory functional outcomes; brachial plexus injuries worsen the prognosis significantly; post-traumatic shoulder arthritis is uncommon (the glenohumeral joint itself is typically preserved); shoulder stiffness and reduced range of abduction are the most common long-term functional impairments

• Fraser classification for floating knee: Type I (both extra-articular — best prognosis; IM nail both); IIA (intra-articular femur — ORIF distal femur + nail tibia); IIB (intra-articular tibia — ORIF tibial plateau + nail femur); IIC (both intra-articular — worst prognosis; staged external fixator then ORIF both)
• Floating knee — popliteal artery: always assess; ABPI <0.9 → CT angiogram; hard signs (absent pulse, expanding haematoma, pallor, paralysis) → immediate vascular surgery; popliteal artery is tethered at adductor hiatus above and at trifurcation below — both tether points make it vulnerable in combined femur/tibia fractures
• Floating elbow — supracondylar FIRST rule: always stabilise the supracondylar humerus fracture before the forearm fracture in children; brachial artery decompression is the priority; AIN is the most commonly injured nerve (18–25% in floating elbow vs 5–10% in isolated SCH); Volkmann`s ischaemic contracture is the most feared long-term complication
• Floating elbow — pink pulseless hand: reduce and fix the supracondylar fracture first; reassess pulse after reduction; if remains pulseless but hand is pink → monitor with Doppler; if hand becomes white/cold (ischaemia) → immediate vascular exploration; never accept a white ischaemic hand without vascular assessment
• SSSC (Goss): the bony-ligamentous ring — glenoid process, coracoid, CC ligaments, distal clavicle, AC joint, acromion — with two struts (clavicle and scapular body); single disruption = stable (other structures maintain ring); double disruption = FLOATING SHOULDER — unstable; the glenoid droops inferiorly and medially
• GPA (glenopolar angle): normal 30–45°; GPA <22° = significant glenoid displacement = indication for surgery; ORIF of the CLAVICLE alone is usually sufficient (indirect reduction of glenoid via CC ligament re-tensioning); direct scapular neck ORIF (Judet approach) is rarely required
• Floating shoulder — brachial plexus injury in 10–20%: upper trunk (C5/C6) most common — Erb`s palsy pattern (loss of abduction, external rotation, elbow flexion); EMG/NCS at 3–6 weeks to assess severity; presence of plexus injury worsens prognosis regardless of fracture management
• Associated injuries in ALL floating joint patterns: all are high-energy injuries with polytrauma; primary survey (ATLS) takes precedence over orthopaedic management; damage control orthopaedics (DCO) principles apply to unstable patients — stabilise with external fixators acutely, definitive fixation once patient is stable