Hallux Rigidus- Moberg procedure

A subtle dorsal cheilus which is a common finding with milder first metatarso-phalangeal (MTP) arthritis.
The joint is normally aligned with no element of Hallux valgus. This should be looked for and questioned as to whether symptomatic in all cases as a Moberg procedure will not reduce medial eminence symptoms (but could be combined with a first metatarsal osteotomy).

Dorsiflexion is restricted here to perhaps 60 degrees on-table. Immediate pre and post-operative ranges should be recorded. Pre-operative movement in absolute terms (and also relative to the potentially uneffected other side ) should of course be noted. As with all MTP arthritis it is worth also assessing the inter-phalangeal (I-P) joint. A pre-exisiting tendancy to hyper-extension at the I-P joint will prove beneficial to the post-operative range of dorsi-flexion displayed by the Hallux.
A key point about the Moberg operation is that plantar-flexion from the MTP joint is being transferred to dorsi-flexion. The more plantar flexion that exists then in theory the greater the dorsal wedge of bone that can be excised , resulting in more MTP dorsiflexion. As with most things it is all about being proportionate. Too much of a wedge will defunction the joint so it is important that this is assessed carefully intra-operatively.

A medial midline skin incision is used.
In this case the MTP joint debridement is being carried out with an open technique and so the exposure needs to include the MTP joint. The exposure therefore extends just proximal to the metatarsal neck .
The debridement can of course alternatively be carried out with a minimally invasive technique as detailed elsewhere in which case a more distal and shorter incision is used to access the base of the phalanx only.
Blunt dissection through the fat layer with fine tenotomy scissors is used to avoid the dorsomedial cutaneous nerve of the Hallux which sits in a fairly well defined thin fascial layer and can be reflected and avoided. Injury to it produces a variable patch of medial Hallux cutaneous numbness (and only rarely a painful neuroma).

The dorsomedial cutaneous nerve(1)dissected away from the underlying capsule(2).

Once the capsule is opened with a horizontal capsulotomy further freeing of it off the underlying bone is facilitated by placing it under tension with a McDonalds retractor(1).The metatarsal head (2) and base of proximal phalanx (3) are seen.

The capsular attachments to the base of the proximal phalanx (3) should be left intact.The proximal phalanx(1) should be exposed by sharp dissection and blunt periosteal elevation (2) to allow visualisation of its dorsal and plantar aspects.
Dorsally the Extensor Hallucis Longus tendon is at risk and plantarwards the Flexor Hallucis Longus tendon.

Adequate exposure of the plantar aspect of the proximal phalanx(1) means that the immediate under-surface of the bone has the flexor tendon easily held away (and protected during the osteotomy) as seen here.
The plantar-medial soft tissue attachments to the metatarsal head (which deliver vascular supply to the distal metatarsal) are left intact

Adequate exposure of the metatarsal head(1) requires sharp dissection across to the lateral aspect of the joint(4), reflecting capsular attachments. A chondral ulcer(2) is not an uncommon finding.The articular surface of the proximal phalanx (3) also needs to be inspected and potentially treated .
By placing a Homans’ retractor dorso-laterally as here (4) and another dorso-medially close against the Metatarsal head (not shown) it is possible to “deliver” the metatarsal head anteriorly for complete inspection , including its plantar aspect.
The sesamoids should also be visible (using a degree of distraction on the toe to aid access). Discreet sesamoid located symptoms are unusual but if prominent osteophytes are present these can be debrided with bone nibblers.

The full extent of the ulcer is now revealed. Any lose chondral edges are debrided back to stable. Areas devoid of cartilage can be microfractured with a 1mm diameter k wire or so.

With a larger chondral ulcer a number of microfracture points are likely to be required.

After micro fracture the dorsal cheilus should be removed. The classical description is removing the dorsal 1/3 rd of the metatarsal head. That amount or resection in my experience is rarely required in particular in milder cases of arthritis.
The articular surface of the proximal phalanx should also be inspected and micro-fractured if required.
On occasion a dorsal cheilus also effects the base of the proximal phalanx and this should also be dealt with.

This joint is fairly well preserved with only a small cheilus and moderate sized chondral ulcer. It requires only a a small cheilectomy. After removal of the cheilus any sharp cut bone dorsal edges should be smoothed and not left proud.

Returning to the Moberg part of the operation with the proximal phalanx adequately exposed an appropriate sized staple is chosen before the osteotomy is performed(3).
This is both to ensure the more appropriate size is used as well as to ensure that the bone cut is placed with adequate room for placement of fixation .The MTP joint is fairly concave and close to the proximal entry point of the staple. One should aim not to breach the joint obviously. Two Homans retractors (2) are used to guard the tendons dorsally and plantar during the osteotomy cut.
A blade (3) should be chosen that produces a thin bone cut with little bone removal and a saw that results in a narrow (and accurate) arc of travel of the saw blade should be used.
The varisation staples (1, here held in the introducer ) come usually as 8 or 10mm implants and are trialled against the phalanx

The completed first cut of the osteotomy(1), at the junction of metaphyseal flare and diaphysis. One should aim to leave a hinge of plantar cortex intact to aid stability of the osteotomy.
Note the Homans retractors elevating/protecting the deeper soft tissues.

A second cut(2) , distal to the first (1) removes the dorsally based wedge of bone.
It is not possible to be proscriptive about the size of the dorsal wedge.
Start with a relatively small wedge and judge its effect in terms of the resting position of the phalanx.

The osteotomy closed , showing good apposition of base of phalanx(1) and shaft(2). If the cut surfaces do not come together then open the osteotomy manually and ensure the cut surfaces are both flat. Ensure in particular that the plantar aspect has had enough bone removed to allow both limbs of the osteotomy to oppose.
Once the bone sits well hold it reduced and assess the range now evident through the MTP joint. In particular that the tip of the distal phalanx still makes contact with a flat plantar applied surface (to simulate weight-bearing) with the heel and MTP joint also in contact with the same surface. As long as this is respected more dorsi-flexion may be obtainable by a further dorsal wedge of bone being removed.

The first varisation staple being inserted using the Introducer. This step is as easily done using a heavy needle holder. It should be angled away slightly from the joint surface of the proximal phalanx. It is helpful to pre-drill the holes with a 1mm K-wire. The osteotomy needs to be held reduced as the staple is hammered in .A second pair of hands usually required.

2 staples are best used , though adequate stability can sometimes be achieved with a single one. Post-operatively it is important to push early joint mobilisation if the on-table achieved range is going to be maintained. For this the osteotomy needs to be as immediately stable as it can be.

The impactor(1) being used to seat down the varisation staple as far as possible . A few well aimed blows with a small hammer are required.