Case Report

An eleven-year-old boy was referred by his general practitioner with an insidious onset of a limp and swelling on dorsum of his left foot of two-month duration. The patient himself did not recall any penetrating injury to his foot. On close enquiry patient gave a history of playing in the woods a few months back. Clinical examination revealed a large, tender swelling overlying the base of 1 ^st metatarsal with no local signs of inflammation.

Laboratory investigations revealed a WBC of 6.55X10 ³ /ml & ESR of 4mm/hour. Radiographs of the foot revealed an osteolytic lesion with a sclerotic rim in the metaphysis of the 1 ^st metatarsal. (Fig 1).

Figure 1

Figure 1: Plain X Ray showing a lytic lesion at the base of 1 st Metatarsal

There was increased uptake in all three phases of Bone scan . The patient was treated with intravenous flucloxacilline and benzyl penicillin for 10 days with a presumptive diagnosis of osteomyelitis, but failed to show any response. An MRI scan showed diffusely altered soft tissue signal with a sinus tract formation centering on medial aspect of proximal 1 ^st metatarsal with bone erosion and reactive marrow edema (fig 2 and 3).

Figure 2

Figure 2: Altered soft tissue signal on T 2 image

Figure 3

Figure 3: Tract formation centering on medial aspect of 1 st metastarsal

Surgical exploration through 1 ^st web space revealed a 1.5 cm black thorn embedded in granulation tissue in the base of the 1 ^st metatarsal bone. The wound was curetted, washed and closed.

Discussion

Penetrating injury to the hand and foot by foreign body are common. Immediate removal cause little morbidity. Many of these are caused by thorns or splinters of wood that are retained in the hand or foot creating a foreign body grannuloma [₁]. Embedded thorns have been reported to cause bone lesions resembling those of osteomylitis [₂]. Organic material when present in or near a bone can produce a pathological reaction, either osteolytic, osteoblastic or combination of both, the radiological appearance of which may resemble a soft tissue tumour. Symptomatic lesions may appear years after initial injury and patient may not recall a specific traumatic event [₃]. Various manifestations of the black thorn (Pranus spinosa) penetrating the skin have been reported [₄]. Because of exposure, hands are the most common site for thorns or splinters. The second common site is the foot, of which 5 metatarsal cases [₅,₆], one cuneiform [₇], one cuboids [₈] and one phalangeal lesion [₉] have been reported in the literature. Thorns have been shown to cause foreign body cysts, bursitis, tenosynovitis, synovitis & also bony reaction. Case reports in the literature reveal a consistent feature of patient's delay in seeking medical advice and clinician's delay in reaching correct diagnosis. In thirty-one reported cases, nineteen had osteolysis, five had periosteal reaction without osteolysis and seven cases had a combination of both. The mean time at presentation in different case reports in the literature was 4 months [₁₀]. In recent years with the use of Ultrasound, C.T scan and MRI scan any suspected foreign body detection has been increased [₁₁,₁₂,₁₃]. But it has been also reported that splinters that have been there for less than three days are not detected reliably by any of the imaging method [12].

It was also found in different cases that foreign body was hypointensive on T1 weighted images and most important factor for identification by MRI is the presence of a surrounding rim of fluid rich granulation tissue or fluid filled cyst [₁₄,₁₅].

Conclusion

The presence of a thorn in or adjacent to a bone induces a foreign body reaction, osteolysis and/or periosteal reaction of the bone. One should be aware of the characteristic clinical and radiological presentation in the differential diagnosis of hand and foot tumors. MRI scan was found to be a sensitive diagnostic tool. Treatment should be aimed at operative exploration, debridement with appropriate antibiotics.

Correspondence to

Nabeel Dastgir Specialist Registrar Trauma & Orthopaedics 76 Culcranagh Dooradoyle Limerick. Ireland. Tel: 00353-61-228285 E-mail: nabeel@esatclear.ie