Musculoskeletal clinical case of the month – SPECT

Imaging in Musculoskeletal medicine

Good musculoskeletal patient care starts with a thorough clinical assessment. Sometimes it may be appropriate to request further investigation. Imaging modalities are becoming more readily available for patients to access. On one hand this allows for more in-depth investigation. On the other, as with any aspect of clinical medicine, it is vital the clinician understands the strengths and limitations of the investigation they are requesting.

Ultrasound, MRI and CT scanning are commonly used imaging techniques in healthcare. A newer technique, SPECT, is becoming more available and is providing to be extremely useful clinically. This case study highlights the key points around the use of SPECT scanning.

Single-photon emission computed tomography (SPECT):

Traditional computed tomography (CT) scanning is initially obtained while the patient is lying on a bed that moves into a ring- or ‘donut’-shaped X-ray machine. The X-ray machine rotates over a 360-degree arc around the patient, allowing for images to be reconstructed in three dimensions.

SPECT is a specialised type of bone scan, where images are taken after an injection of a nuclear medicine radiopharmaceutical (e.g. technitium-99m). The injected tracer ‘sticks’ to specific areas in the body where there is higher metabolic activity, and emits gamma rays, which in turn are detected by gamma cameras. The cameras rotate over a 360-degree arc around the patient, allowing for images to be reconstructed in three dimensions.

The increased areas of tracer uptake are then demonstrated as ‘hotspots’, which indicate underlying pathology. The sensitivity for detecting bone disease is high, but the specificity is extremely low (i.e unable to differentiate between pathologies). It is then imperative that the clinical history and background of the patient is carefully correlated to understand the nature of any hotspots.

Clinical Presentation

  • 17 year old male school rugby player
  • Pain developing over base of first metatarsal over past 2 years
  • No previous acute injury to area
  • Pain increased in intensity to eventually caused pain on walking and cessation of all physical activity
  • Patient self presented to A+E where x-rays were taken, with no abnormal findings. Foot and ankle sprain advice given.
  • GP referred to physio who initiated calf strengthening and ankle/foot mobility exercises with only mild improvement in symptoms
  • DH – Nil else
  • PMH – Nil of note
  • FH – Nil of note
  • Patient referred to orthopaedics by GP as not making any real improvement with physio.
  • MRI conducted which showed no significant bone or ligament abnormality. Discharged from orthopaedics.
  • Presented to LBSM 14 months after first onset of pain.
  • Examination at consultation:
  • Anatalgic gait, unable to weight bear without significant pain from midstance to toe off
  • Very tender and stiff over the base of first and second metatarsal and tarsometatarsal joints
  • Deconditioned lower limb on effected side
  • Patient asked to offload in Aircast boot
  • Referred for SPECT scan

Imaging

  • Top left – X-ray left foot. No bone abnormality detected
  • Top right – MRI left foot. No bone oedema in midfoot, no ligamentous damage (e.g. Lisfranc complex intact)
  • Bottom left and right – SPECT-CT. Hot spot and increased bone activity at 1st and 2nd tarsometarsal junction
Musculoskeletal clinical case of the month Musculoskeletal clinical case of the month - SPECT

Management

Podiatry review;

  • Patient sent for gait analysis, kinematic and force place assessment;
  • Custom made orthotics for daily activity aiming to;
  • protect against tarsometatarsal compression and stress during normal gait
  • improving medial column alignment and stability, optimising 1st ray
  • Further orthotics made for sport specific purposes

Rehabilitation;

  • Gradually weaned out of boot until able to walk around house pain free
  • Midfoot and forefoot mobilisations, actively and passively
  • Generalised lower limb strengthening programme
  • Foot intrinsic and calf strengthening programme
  • Progressive proprioceptive and pylometric rehabilitation
  • Graded return to running, including Anti-gravity treadmill

Patient made a full return to Rugby within 3 months of rehabilitation at LBSM. A repeat scan was not required as patient remained asymptomatic.

Use of SPECT in musculoskeletal and sports medicine

SPECT and radionuclide imaging is already well grounded in musculoskeletal and orthopaedic practice. Examples include the detection of;

  • Malignant disease in the axial skeleton
  • vertebral column and pelvis are the most frequent sites of metastatic bone disease because of their high red marrow content
  • radionuclide imaging may be the only modality to demonstrate pathology before it becomes evident on anatomical imaging
  • Osteomyelitis or other bone infection
  • Joint prosthesis infection and loosening
  • Paget’s disease

In sports medicine, as this case demonstrates, the use of SPECT can be very informative, giving deeper insight to biomechanical loading patterns and stressors that may potential act as injury risk factors. Some examples may include the detection of;

  • Fractures that are absent radiographically, e.g. stress or insufficiency fractures
  • Biomechanical overloading in the skeletal system:
  • pars overload in patients with repeated spine flexion/extension cycles e.g. cricket, tennis players
  • foot and ankle overload, e.g. runners or contact sports
  • Impingement syndromes
  • SPECT has shown to be sensitive to detecting hip impingement when MRI is normal
  • Ankle impingement, posterior and anterior

Practical considerations with SPECT

As with any intervention/investigation, the risks and benefits need to be fully considered and clearly articulated to the patient.

As a radioactive tracer is used, the radiation exposure with SPECT is around 5 mSv, equivalent to approximately 2 years worth of natural background radiation (for comparison, a single x-ray emits 0.1 mSv, equivalent to 10 days natural background radiation). This exposure, however, is limited because the agent typically have short half-lives (technitium-99m half life is 6 hours).

Other risks include an allergic reaction to the tracer or contrast agent. Women who are pregnant or nursing should also not undergo a SPECT scan.

The risks associated with SPECT may be more ethical to take when carrying out medical assessment for potential serious disease, over routine biomechanical assessment. Previous exposure to medical and non-medical radiation must also be considered.

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