Loosening of Tibial Prosthesis

Clinical History

A female patient underwent arthrodesis of the right ankle joint and right talo-calcaneal joint in April 2005 secondary to a bone fracture. The patient presented with persistent pain and was referred for a SPECT•CT scan to assess the location of the pain, and whether the discomfort was being caused by pseudoarthrosis.

Imaging Findings
Examination Protocol*
SPECT:

3 Phase bone scan after injection of 740 MBq (20 mCi) 99mTc DPD
Immediate acquisition of dynamic images during the perfusion phase (anterior view)
2 minutes post injection blood pool phase (anterior and lateral view)
3 - 4 hours post injection delayed images (planar as well as SPECT images)

CT:

Low dose spiral CT
Slice thickness 1 mm, pitch 2, reconstruction increment 1 mm
Symbia T2

Imaging Findings

SPECT:

During the perfusion phase there was a mild hyperaemia in the region of the right ankle.
In the blood pool phase there was slightly increased tracer retention in the lower third of the shaft of the right tibia in the
region of the proximal end of the nail used in the arthrodesis, as well as several smaller areas of blood pool activity in the
lower lateral and medial ankle.

Delayed Images and SPECT•CT of right foot:

The CT images showed the intact nail with screws (VersaNail™) extending from the lower edge of anterior calcaneus through the body of the talus and into the lower third of the shaft of the tibia. The tibia showed the old impacted fracture across the shaft with fusion in anteversion and with medial displacement of the lower fragment (Fig. 1).

Gross cortical sclerosis was also visualized secondary to the fracture malunion and as a reactive change to the nail implantation.

The SPECT•CT images showed increased focal uptake of tracer at the upper end of the lower third of the tibial shaft, which corresponded to the tip of the nail implanted into the tibial shaft (Fig 2).

There was no abnormal increase in tracer uptake to the screws in the upper part of the nail within the tibia. The lower end of the tibia and the adjacent ankle joint and upper articular surface of the talus (trochlea) were completely distorted, secondary to the healing of the old fracture with associated nailing. The joint space was replaced with sclerotic new bone with total obliteration of the normal articular cavity (Fig. 3).

The distal fibula was also fused to the lower end of the tibia and talus with a screw passing through the nail and showed complete obliteration of the lower tibio-fibular joint space with sclerotic bone.

The SPECT•CT images revealed focal areas of increased uptake at the region of the distal screw passing laterally through the calcaneum and the lower end of the nail. The second screw, passing through the distal fibula, body of the talus and the lateral malleolus of the tibia also showed focal increased tracer uptake in the region medial, lateral and posterior to its attachment to the nail (Fig. 4).

There was also intense focal increased uptake in the bone lateral to the distal end of the nail, impacted through the articular surface and anterior end of the calcaneum, which may be related to shearing stress due to abnormal bony fusion and loosening of the nail.

A small area of hyperdensity on the CT scan resembling a small metal remnant (arrows Fig. 6c and Fig. 6d) was located in the region of the head of the talus with associated bone loss but without signs of increased bone metabolism and was probably a screw fragment related to a previous surgery.

There were distinct cystic changes in the head, neck and body of the talus related to bone loss, disuse and shearing stress. The talonavicular joint showed localized contour irregularities without increased metabolic activity. The remaining foot joints showed normal bone metabolism.

Delayed Images and SPECT•CT of left foot (images not displayed) There was moderate activity in the second tarso-metatarsal joint in connection with a slightly reduced joint cavity and a lowgrade activity in the lateral portion in the first tarso-metatarsal joint. The remaining foot joints did not show significantly increased pathological bone metabolism.

Diagnosis

Right foot:

A patient with a history of right lower tibial shaft fracture in April 2005 was treated with arthrodesis of the ankle and talocalcaneal joint using VersaNail™ in April 2005. The fracture malunited with anteversion and medial lateral shift of the lower tibial fragment.

The scan showed almost total replacement of the joint space between the tibia and talus, in the talo-calcaneal joint and tibiofibular articular surface with sclerotic bone, secondary to the arthrodesis with nail and screws. The talus and calcaneus and adjacent small tarsal bones showed cystic changes due to bone loss and irregular sclerosis.

The study showed focal increased pathological bone metabolic activity at the proximal tip of the nail and the two distal attachment screws as well as in the lateral compartment of the lower ankle joint, and was probably due to loosening.

Left foot:

Arthritis of the left tarso-metatarsal joints.

Impact on Treatment

The SPECT•CT scan allowed the exact localization of the areas of increased bone metabolism and correlated the abnormal activity in the upper nail tip and around the lower screws to loosening, which had major therapeutic implications. The distortion of the bone and joint space as visualized on the CT images was critical in proper planning and the SPECT•CT findings directed the decision for the subsequent surgical removal of the loosened prosthesis.

The value of hybrid imaging in this case was the exact correlation of the areas of increased tracer uptake to the anatomical structures and the different parts of the implant. Additionally, it provided important information about the bone structure and pathological changes such as bone loss and cystic bony changes as well as information about the complete or partial fusion of the joint.

With just one exam, all areas of abnormal bone metabolism could be correlated to the morphology and the surgeon was provided with important information regarding the level of ossification as well as the integrity of the different joint cavities and the remaining bony structures.

Data courtesy of:
Prof. Müller-Brand, Dr. Rasch,
University Hospital, Basel, Switzerland
* Any of the protocols presented herein are for informational purposes and are not meant to substitute for any clinicians' judgment in how best to use any medical devices. It is the clinician that makes all diagnostic determinations based upon education, learning and experience.