Trans-metatarsal amputation: Amputee Case Study

Title

Trans-metatarsal amputation: Amputee Case Study

Abstract

This case presentation demonstrates the difficulties associated with achieving a satisfactory functional outcome with a trans-metatarsal amputation. These procedures are associated with a high rate of revision and failure. A coordinated approach from planning surgical procedure through post operative care and rehabilitation is required. Though a number of types of orthotic and prosthetic options are available, there is little evidence supporting one over the other, making achieving desired outcomes challenging.

Key Words

partial foot amputation, trans-metatarsal amputation, insensate, equino-varus

Client Characteristics

The patient is a 66-year-old female who acts as a carer for her intellectually disabled adult son, and provides part time care for a grandchild. She has Type II diabetes for 6 years with retinopathy and peripheral neuropathy. Patient has a proximal trans-metatarsal amputation of the right foot secondary to osteomyelitis. 2 revisions and 1 skin graft required to reach definitive length. Non-healing ulcer of the plantar disto-lateral aspect of the stump persisted for 15 months after final procedure. Despite the presence of peripheral neuropathy, there was significant pain associated with the ulcer. Ambulation was limited by both pain, and the need to offload the wound site to facilitate healing.

Examination Findings

Patient's diabetes was controlled, vascular supply intact. Both lower limbs were insensate to mid-tibia. Wound exhibited classic characteristics of plantar neuropathic ulcer - localized, 'punched-out' appearance with development of callous at peri-wound margins, requiring regular debridement.

Physical examination notes generalized limited range of motion (ROM) with equinus deformity of the ankle, at 15 degrees plantarflexion. There was a marked equino-varus deformity of the stump. It was noted by both the patient and the treating team that this position had become more exaggerated since the amputation was performed. The tibialis anterior tendon had become increasingly tight and prominent in the absence of resistance from extensor and lateral muscle groups resected at the time of the procedure. No tendon transfer or lengthening procedures were done at the time. The resulting position of the foot focused pressure onto the wound site.

Gait was apropulsive, with shortened stride length and a pronounced limp (secondary to both pain and increased functional length on the affected side due to equinus). A zimmer frame was used for ambulation. Balance was poor, as was patient confidence. Pain was also a significant limiting factor. The goals for both the patient and the healthcare team were long term wound healing and restoring mobility.

Clinical Hypothesis

Patient's longstanding ulceration and physical limitations are secondary to diabetes, peripheral neuropathy and altered mechanics. Improvement of residual limb mechanics by the use of appropriate physical therapy and orthosis/prosthesis should improve mobility and facilitate wound healing.

Intervention

  • Local wound care.

  • Review by medical teams. Some concern that there was irregularity at end of 5th metatarsal (on X-ray) corresponding to ulcer site. No intervention planned. Revision of the stump would run high risk of proximal amputation.

  • Walking style footwear with a deep opening to accommodate the width of the stump with insole and toe filler. Also provided protection and accommodation to the contra-lateral foot. Carbon foot plate was added, to improve the length of the lever for propulsion. This promoted earlier heel lift, reducing stability and increasing shear at the ulcer site. A traditional ankle foot orthosis (AFO) also failed.

  • Prosthetist suggested alternative AFO. Anterior strut provided resistance to the leg as it progressed forward during stance, controls heel lift, and facilitates propulsion with a rigid foot plate. The addition of foot orthosis accommodated deformity and controls shear. Immediate improvement in balance and stride, reduced limp (less pain) and greater confidence. No walking aids were needed. The wound healed, with episodes of recurrence. There was an issue with fitting as the anterior strut passed across the ankle. The 'bowstring' prominence of the tibialis anterior tendon rubbed against the strut causing trauma and affecting fit.

  • Physiotherapy released tension in the tibialis anterior and mobilised midtarsal, subtalar and ankle joints. This resolved remaining issues. An ongoing home regimen was provided. Improved ROM was evident.

Outcome

  • Definitive wound healing.

  • Clinical improvement and maintenance of range of motion in ankle joint and rear foot of affected limb. Equinus deformity still exists, though presently measured at approximately 5 degrees. Ongoing maintenance program is required to maintain current level of function.

  • Release of tibialis anterior tendon reducing varus position of stump and improving function.

  • Alleviation of local pain and its impact on gait
  • Improved mobility, both of the affected foot and ankle complex, and the patient's gross mobility.

  • 'Normalised' gait. Return to high-level 2-limb balance, increased stride length, increased muscle strength and mobility, improved stamina and aerobic fitness, increased activity (level and range) with concurrent improvement in psychological wellbeing.

  • Desired clinical outcomes were achieved 39 months amputation procedure. After 6 months the wound site remains healed and local skin condition is excellent, with patient using emollient to both healed wound and amputation scar sites. The patient's level of activity has increased and now includes a return to bi-weekly exercise classes for general fitness. The patient continues with her own physiotherapy-guided home exercise regimen to maintain joint mobility, and attends 2-4 weekly physiotherapy sessions for re-evaluation and maintenance.

Discussion

Partial foot amputation (PFA) affects about 2 per 1000 people in industrialised countries, but is associated with a high failure rate and many complications[1]. 
In PFA the patient is left with a smaller weight-bearing surface subject to greater mechanical stress. Ulceration easily occurs in the insensate foot.

Retaining a balanced metatarsal parabola and avoiding uneven bone spurs is critical in avoiding failure[2]. Muscle imbalance occurs with most PFA. Resection of muscle/tendon results in functional instability. Equino-varus deformity often results from unopposed action of gastrocnemius, tibialis anterior, and tibialis posterior, coupled with loss of extensor tendons[3]. Ankle equinus results if Achilles tenotomy or transfer is not performed[2].

Initially flexible and reducible instability will eventually become fixed, and distal stump breakdown is inevitable.
There is evidence that once the metatarsal heads have been amputated, power generation across the ankle is negligible, and the assumption that PFA is less energy expensive than trans-tibial amputation is incorrect[3]. Despite a range of below and above ankle prosthetic interventions available, there is little evidence to support the effectiveness of any combination of devices, thus informed decisions about treatment options is difficult. The fact remains, that orthotic/prosthetic management is paramount in the insensate foot after amputation

References

  1. Dillon MP 2010 'Partial Foot Amputation: Aetiology, Incidence, Complications, Prosthetic Intervention and a Characterisation of Gait' In: JH Stone, M Blouin, editors. International Encyclopaedia of Rehabilitation http://cirrie.buffalo.edu/encyclopaedia/en/article/154/
  2. 2.0 2.1 Sullivan JP 2005 'Complications of Pedal Amputations' Clinics in Podiatric Medicine and Surgery Vol 22, pp 469-484 doi:10.1016/j.cpm.2005.03.004
  3. 3.0 3.1 Nather A & Wong KL 2013 'Distal amputations for the diabetic foot' Diabetic Foot & Ankle Vol 4: 21288 http://dx.doi.org/10.3402/dfa.v4i0.21288