Pain related to the great toe sesamoids is uncommon in a general foot and ankle practice, but may be commoner where there is a large sports medicine component to the practice.
The hallux MTP sesamoids are embedded in the tendons of flexor hallucis brevis. They are subjected to the stresses of muscle contraction and MTP joint movement, and also to ground reaction force.
Figures for the prevalence of symptomatic and asymptomatic multipartite sesamoids vary widely, from 3-33%. Prieskorn et al found bipartite sesamoids in 13.5% of 200 feet, bilateral in 34% of these. The tibial sesamoid was bipartite ten times more often than the fibular.
Sesamoid problems are commoner in athletes of any age. The tibial sesamoid is the commoner source of pain.
The main pathologies include:
- Stress fracture – probably the main cause of sesamoid pain. Several series also describe “avascular necrosis” and “sesamoiditis” but histological studies suggest these are actually stress fractures
- Symptomatic multipartite sesamoid, usually after a forced dorsiflexion injury (“turf toe”)
- Osteoarthritis – the sesamoid-MT joint may be a significant cause of pain in an osteoarthritic 1st MTP joint
- Overload – there may be a separate syndrome of overload, especially in a plantar flexed first ray, without stress fracture
- Neuropathic ulceration, usually in diabetics, may involve one or both sesamoids
Patients usually complain of pain under the 1st MTP joint and can often localise it, usually to the tibial sesamoid, with a finger. However, the problem may be referred with a much more vague label, such as “bunion”, “arthritis” or “metatarsalgia” because the referring clinician is not aware of the entity of sesamoid pain.
There is often a history of dorsiflexion or local impact trauma or a change in activity leading to greater forefoot loading. However, some patients have a spontaneous onset of pain. It is also important to ask about systemic arthropathy and neurological disease including peripheral neuropathy.
Examination may show a plantarflexed first ray, with or without an overall cavus deformity. If so, a neurological examination should be carried out. Sesamoid problems may be commoner in patients with hallux valgus. There may be evidence of degenerative change throughout the MTP joint (hallux rigidus). A callus is often present under the MT head.
There is usually point tenderness over the affected sesamoid which may be exacerbated by compression or friction against the metatarsal head. Allen et al (2001) described an axial compression test to reproduce symptoms. The sensitivity and specificity of this test have not been measured.
Generalised arthropathy may require appropriate investigation. Otherwise, imaging techniques are the main investigations.
Standing AP and lateral forefoot films show bipartite sesamoids and OA, but a better view is usually obtained with an axial skyline view of the sesamoids with the MTPJ in dorsiflexion. An isotope bone scan will usually show a stress fracture and may be more accurate than an MR, although there is no real comparative data. MR will show articular problems in the MTP joint and any soft tissue element to the problem, but this is often not relevant.
A few patients may need only explanation and simple advice about shoes and analgesia. Most respond well to an insole with a cut-out or pad (Axe and Ray 1988), or a modified rocker shoe (Rosenfield and Trepman 2000). An injection of local anaesthetic and depot steroid into the sesamoid-metatarsal joint may also be useful.
Only a few patients will have continuing problems after orthotic treatment, and surgery may be offered to these patients. Surgical options include:
- Sesamoidectomy – usually through a medial approach for the tibial sesamoid and a plantar or first interspace incision for the fibular sesamoid. Care must be taken not to injure the medial plantar digital nerve which runs just below the abductor hallucis tendon. As most of the blood supply to the sesamoid enters proximally, exposure medially or laterally is least likely to interfere with vascularity (Sobel et al1992, Chamberland et al 1993). An arthroscopic technique has been described (Perez Carro et al 1999). Removal of the distal part of either sesamoid or the whole tibial sesamoid has little effect on FHB moment arm, but resection of both bones reduces the moment arm by 1/3 in dorsiflexion (Aper et al 1994). FHL moment arm is reduced by complete resection of either bone (Aper et al 1996). Hallux valgus may follow tibial sesamoid resection, hallux varus fibular resection and cock-up deformity resection of either or both sesamoids. Post-operatively the patient is usually protected from weightbearing for 3-6 weeks with splintage. However, Saxena (2003) encouraged NWB exercise after 3 weeks in athletes and managed to return them to sporting participation in a mean of 7.5 weeks.
- Sesamoid shaving – Mann and Wapner (1992) shaved the superficial half of the tibial sesamoid through a medial incision in 16 feet. They felt this was a less invasive operation than sesamoidectomy. Only one patient had significant residual symptomas at a mean of 4 years follow-up, although reporting of outcome was superficial.
- Bone grafting for non-united fractures – Anderson et al (1997) treated sesamoid non-unions proven on isotope bone scan by curettage and grafting (from the first metatarsal). Immobilisation was in a plaster boot for 8 weeks. 19/21 fractures united with complete relief of pain, and 17 returned to their previous sports.
- Internal fixation of non-unions – Blundell et al (2002) described percutaneous fixation with a Barouk screw, achieveing union in all of 9 pateints and return to previous activities within 3 months, although the mean AOFAS hallux score was only 80.7.