Oligodactyly

The three signalling axes

Upper limb development occurs between approximately the fourth and eighth weeks of gestation, from the limb bud, and is organised along three axes, each with its own signalling centre. The OMT classification is built directly on this scheme.

• The AER and the ZPA maintain each other through an FGF-SHH feedback loop. Disturbance of the AER interrupts outgrowth along the proximal-distal axis and is the accepted developmental basis of transverse deficiency and symbrachydactyly.
• Interdigital apoptosis, mediated by bone morphogenetic proteins, sculpts the separate digits from the hand plate. Failure of apoptosis produces syndactyly; excessive or aberrant apoptosis contributes to the digital loss seen in symbrachydactyly.

The subclavian artery supply disruption sequence

An influential vascular hypothesis proposes that interruption of the early embryonic blood supply in the subclavian arteries, the vertebral arteries or their branches — occurring during or around the sixth week — produces a spectrum of defects depending on the site of occlusion. Bavinck and Weaver grouped Poland, Klippel-Feil and Möbius anomalies, isolated absence of pectoralis major with breast hypoplasia, isolated terminal transverse limb defects and the Sprengel anomaly under the term subclavian artery supply disruption sequence (SASDS). It explains the characteristic unilaterality and sporadic occurrence of symbrachydactyly, and the association with Poland syndrome, better than any genetic model.

Symbrachydactyly

• Sporadic, essentially always. Unilateral in the great majority of cases.
• No consistent single-gene cause identified. Familial recurrence is very rare, and this is central to parental counselling.
• Associated with Poland syndrome in a proportion of cases.

True transverse deficiency

• Also sporadic and unilateral in most cases, most commonly at the proximal third of the forearm.
• Distinguish carefully from amelia (complete absence of the limb) and from phocomelia (an intercalary deficiency, in which the hand is attached to a shortened or absent intervening segment) — phocomelia is classically associated with thalidomide embryopathy and with Roberts syndrome.

Longitudinal deficiency

• Radial longitudinal deficiency: strongly associated with syndromes; the syndromic burden is the dominant clinical issue.
• Ulnar longitudinal deficiency: far less often syndromic; associated instead with musculoskeletal anomalies — proximal femoral focal deficiency, fibular deficiency, scoliosis — and with a high rate of associated hand anomalies including syndactyly and absent digits.
• Central (cleft hand) deficiency: typical cleft hand is sporadic, bilateral and often familial with variable penetrance; atypical cleft hand overlaps with symbrachydactyly. Ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome is the key association, with TP63 mutations and the 10q24 locus implicated in split hand-foot malformation.

Constriction ring sequence

• A deformation, not a malformation. Amniotic bands or an intrinsic disruption process constrict a normally formed part.
• Sporadic, non-genetic, no recurrence risk. Associated with prematurity and oligohydramnios in some series.
• Look for the four components described by Patterson: simple constriction rings, rings with distal deformity and lymphoedema, rings with acrosyndactyly, and intrauterine amputation.

Teratogens and maternal factors

• Thalidomide (historical, phocomelia), valproate, misoprostol, maternal diabetes, and chorionic villus sampling before 10 weeks have all been associated with limb reduction defects.
• In the overwhelming majority of cases no cause is identifiable, and this must be said clearly and early to parents.

The Oberg-Manske-Tonkin (OMT) classification

Proposed in 2010 and subsequently approved by the IFSSH Scientific Committee for Congenital Conditions as a replacement for the Swanson classification. It is organised on developmental biology and dysmorphology terminology rather than on morphology alone, placing each condition in one of three main groups — malformations, deformations and dysplasias — with recognised syndromes catalogued alongside.

Where oligodactyly sits

• Most commonly: OMT I.A, failure of formation along the proximal-distal axis — symbrachydactyly or transverse deficiency.
• Also: OMT I.A radial-ulnar — radial or ulnar longitudinal deficiency with absent digits.
• Also: OMT I.B — cleft hand (central deficiency) affecting the hand plate only.
• Also: OMT II — constriction ring sequence with intrauterine amputation.

The examination point: oligodactyly is not a category in OMT. Name the process, then place it.

Blauth and Gekeler classification of symbrachydactyly

A morphological classification along a spectrum of increasing severity, and the one to know:

The nubbin sign — the single most useful physical finding

Ectodermal remnants — small skin nubbins, rudimentary nails, tiny nail folds — at the end of a deficient ray indicate that soft tissue formed but skeleton did not. That is symbrachydactyly.

A true transverse arrest has a clean, smooth, well-padded, conical stump with no nubbins and no nail remnants.

Why it changes the plan: a symbrachydactylous digit has a soft tissue sleeve waiting for a skeleton. Insert a non-vascularised toe phalanx into that sleeve and you have a digit. A transverse arrest has neither skeleton nor sleeve, so there is nothing to graft into.

Poland syndrome

• Symbrachydactyly plus ipsilateral absence or hypoplasia of the sternocostal head of pectoralis major.
• May include hypoplasia of the breast and nipple, absence of costal cartilages, rib deficiency, and hypoplasia of latissimus dorsi and serratus anterior.
• Almost always unilateral, more often right-sided in most series, sporadic.
• Examine the chest wall of every child with symbrachydactyly. It is easy to miss under a vest and it changes the discussion — chest wall reconstruction may be considered in adolescence, and it flags the vascular disruption hypothesis to the family.

Transverse deficiency — by level

Named by the level at which the limb terminates: shoulder, upper arm (transhumeral), elbow, forearm (transradial — the commonest), wrist (carpal), metacarpal, phalangeal.

• Transradial at the proximal third of the forearm is the classic and commonest true transverse deficiency.

Radial longitudinal deficiency — Bayne and Klug, with the Goldfarb modification

• Type 0: deficient carpus only, normal radius.
• Type N: deficient thumb only (added in the modification).
• Type I: short distal radius.
• Type II: hypoplastic radius, abnormal proximal and distal physes.
• Type III: partial absence of the radius.
• Type IV: total absence of the radius — the commonest type.

Thumb hypoplasia — modified Blauth (Manske and McCarroll)

Runs alongside radial deficiency and is graded separately:

• I: minor hypoplasia. No treatment.
• II: thenar hypoplasia, narrow first web, ulnar collateral ligament laxity, stable basal joint. Reconstruct.
• IIIA: as II plus extrinsic tendon and skeletal deficiency, stable trapeziometacarpal joint. Reconstruct.
• IIIB: unstable or absent trapeziometacarpal joint. Pollicise.
• IV: floating thumb (pouce flottant). Pollicise.
• V: complete absence. Pollicise.

The pivotal finding is trapeziometacarpal joint stability, separating IIIA from IIIB and therefore reconstruction from pollicisation.

Ulnar longitudinal deficiency — Bayne

• Type I: hypoplastic ulna, both physes present.
• Type II: partial ulnar aplasia, distal physis absent, with a fibrocartilaginous ulnar anlage.
• Type III: total ulnar aplasia.
• Type IV: radiohumeral synostosis.

Key point: in ulnar deficiency the hand is the problem, not the forearm. Absent ulnar digits, syndactyly, first web deficiency and thumb anomalies dominate function, and hand reconstruction takes priority over any forearm procedure.

Cleft hand — Manske and Halikis, by first web space

• Type I: normal first web.
• Type IIA: mildly narrowed web. Type IIB: severely narrowed.
• Type III: syndactylised first web.
• Type IV: merged first web, index ray suppressed.
• Type V: absent first web, thumb elements absent.

The first web, not the cleft, determines function and therefore the operation.

Non-vascularised toe phalanx transfer (NVTPT)

The critical technical points

Expected outcome

• Series performing transfer before 18 months report continued growth of the transferred phalanx in the great majority of cases, with growth rates approaching, though generally below, those of the native phalanx.
• Transfer after 18-24 months is associated with markedly reduced growth and a significant rate of resorption.
• The transferred digit is stiff — it provides length and a stable post, not motion. Counsel the family that this is a post, not a finger.

Donor morbidity

• Shortening of the donor toe and a tendency to deviation or floppiness. Syndactylising the donor toe to its neighbour mitigates this.
• Foot function is generally unaffected; gait and footwear are not usually a problem. Long-term donor foot outcomes are good in reported series, but parents deserve to see photographs of a donor foot before consenting.

Microvascular toe-to-hand transfer

Principle: transfer of a vascularised, innervated, growing toe with its joint, tendons and nail to the hand. Unlike a non-vascularised phalanx transfer, this creates a digit that grows, moves and feels.

Donor selection

Timing

• Usual window: 2 to 4 years. Vessel calibre is adequate from around 18 months to 2 years in experienced hands, but many centres wait until 2-4 years to balance technical feasibility against the benefit of establishing grasp before school entry and while cortical plasticity is high.
• Earlier is better for cortical integration; later is easier technically. The compromise is the reason the window exists.

Prerequisites — the checklist that decides feasibility

1. Adequate recipient vessels. Symbrachydactyly hands frequently have an abnormal or absent superficial palmar arch. Angiography is mandatory.
2. Recipient nerves. Without sensation the transferred toe will not be incorporated into use.
3. Motors. Extrinsic flexor and extensor tendons must be present or reconstructable, and the child must have a functioning forearm. In severe symbrachydactyly the intrinsic muscles are absent, so the transferred toe will have limited independent motion regardless of technique — counsel accordingly.
4. A stable base. A carpometacarpal or metacarpal platform on which to mount the toe.
5. An opposing post. A single mobile digit with nothing to pinch against achieves little; plan the pair.
6. A family who understand a multi-stage, multi-year plan with a real risk of failure.

Outcomes

• Flap survival exceeds 90-95% in experienced centres, and toe transfer in children has survival comparable with adults.
• The transferred toe grows, with reported growth broadly tracking the child's own growth, because the physis is transferred vascularised.
• Sensation recovers well in children, typically better than in adults, with useful two-point discrimination in most reported paediatric series.
• Motion is the limiting factor, particularly in symbrachydactyly where intrinsic musculature is absent.
• Cortical integration in young children is excellent — this is the strongest argument for early transfer.
• Donor foot morbidity after second toe harvest is well tolerated; great toe harvest has a measurable effect on push-off and should be reserved for thumb reconstruction.

Web space deepening

• The single highest-value operation in many oligodactylous hands. Deepening the web between two short digits functionally lengthens both and dramatically improves grasp span, without adding any tissue.
• Techniques: four-flap Z-plasty, dorsal transposition (Bauer) flap, or a dorsal rectangular flap with full-thickness grafting of the secondary defects.
• Do this before considering anything more complex. It is low risk, single stage, and often makes further surgery unnecessary.

Distraction lengthening

• Callotasis of a metacarpal or phalanx using a small external fixator, typically at a rate of 0.5-1 mm per day after a latency period, achieving lengthening of the order of 30-50% of the original bone length.
• Best in older children with an adequate soft tissue envelope and a bone segment of reasonable length to distract.
• Complications are frequent: pin site infection, premature consolidation, non-union of the regenerate (often needing bone grafting), joint stiffness and soft tissue contracture.
• A useful adjunct after a toe phalanx transfer that has produced a stable but short digit.

On-top plasty (digital transposition)

• Transposition of a functioning distal digital segment, on its neurovascular pedicle, onto a better-positioned proximal stump.
• Useful where the hand has a well-formed digit in the wrong place — for example, transposing a functioning ray onto a better metacarpal base to create opposition.

Pollicisation

• Transposition of the index finger on its neurovascular pedicle to the thumb position, with shortening, rotation and reassignment of the intrinsics.
• Indicated in Blauth IIIB, IV and V thumb hypoplasia and in radial longitudinal deficiency with an absent thumb.
• Technical targets: position the new metacarpal in approximately 120-140 degrees of pronation and around 40 degrees of palmar abduction, shorten by resecting the metacarpal shaft and fusing the metacarpal head (which becomes the new trapezium) to the base, and reassign the intrinsics — the first dorsal interosseous becomes the new abductor pollicis brevis and the first palmar interosseous the new adductor.
• Usually performed at around 1 to 2 years of age.

Nubbin excision

• Simple excision of ectodermal remnants for appearance. Not urgent, and never at the cost of a soft tissue sleeve that might later receive a toe phalanx. Discuss the reconstructive plan before excising nubbins.

Constriction ring release

• Circumferential rings with distal lymphoedema or vascular compromise need urgent release in the neonate.
• Technique: staged or single-stage excision of the constricting band with multiple Z-plasties to break up the circumferential scar. Single-stage circumferential release is now widely practised and safe in experienced hands.
• Acrosyndactyly with proximal fenestrations is released separately, treating the digits as conjoined rather than as a simple syndactyly.