A Guide To Digital Amputations In Patients With Diabetes
- Volume 24 - Issue 9 - September 2011
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Pertinent Insights On Performing A Hallux Amputation
The hallux plays an important role in stabilizing the medial aspect of the foot and the extensor hallucis longus (EHL) is one of the most important extrinsic muscles of the foot during the swing phase of gait. Therefore, amputation of the hallux frequently leads to an apropulsive gait.4 The degree of biomechanical dysfunction depends on the level of amputation.
The anatomy of the hallux is different from the lesser toes and deserves a quick review. The base of the proximal phalanx has the insertion of the flexor hallucis brevis, sesamoid complex and plantar fascia, which make up the windlass mechanism. The windlass mechanism provides stability and rigidity to the medial side of the foot, preventing arch collapse and allowing for a propulsive gait.
Accordingly, surgeons should not approach a hallux amputation lightly and should exercise caution, precision and careful incision planning. Total hallux amputation will inevitably lead to extensor tendon contracture with development or exacerbation of lesser hammertoe deformities. The retrograde pressure from the lesser digits leads to prominent metatarsal heads and distal fat pad migration. The transfer of weightbearing becomes very obvious and will frequently lead to adjacent metatarsal head ulcerations.
A study by Mann and colleagues shows the effect of hallux amputation in patients who underwent re-implantation of the hallux in place of a lost thumb. The authors found that the plantar pressure moved from the second metatarsal head to the third.5 This was due to the loss of the flexor hallucis brevis and windlass mechanism causing the load to transfer laterally.
When approaching a hallux amputation, one should make an effort to salvage as much of the base of the proximal phalanx as possible. An ideal situation would be to leave the base of the proximal phalanx intact in order to keep the windlass mechanism intact. Doing so would save the MPJ. Hakim-Zargar and colleagues reported that one should retain 10 mm of the hallux proximal phalangeal base during amputation to preserve the integrity of the flexor hallucis brevis insertion to a physiologic load.6 Resecting the insertion results in decreased flexion strength, retraction of the sesamoids and transfer metatarsalgia. In our experience, one can perform the majority of hallux amputations without resecting the base of the proximal phalanx.
Keys To Ensuring Adequate Vascular Supply
Arterial perfusion is often one of the most important predictors of healing and is also an important factor in planning the level of amputation. Non-invasive arterial studies are the mainstay recommendations prior to any amputation.7 In the senior author’s opinion, predicting the level of amputation and the level of healing depends on several factors.
First, the surgeon must understand that there is no specific pressure or value that is 100 percent predictive of healing. Generally speaking, the toe pressure of >40 mmHg is considered to be consistent with healing. The higher the pressure is above 40 mmHg, the higher the likelihood of healing.8
So does this mean that patients with pressures of 40 mmHg and below will not be able to heal? The simple answer is that some patients will be able to heal and some patients will not. It is our recommendation that anyone with toe pressures of less than 40 mmHg should undergo a vascular workup for a possible revascularization. However, we all see patients who are too frail or too old, and are not candidates for revascularization. It is these patients — whose toe pressures are less than 40 mmHg and who are not candidates for revascularization — whom we need to assess and figure out whether their digital amputation will heal.